Dissertations / Theses on the topic 'Aggregati stabili'
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1
Jia, Zichen. "Stability, aggregation kinetics and aggregates thermal restructuring of polymer colloids /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16913.
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Johnsson, Markus. "Sterically stabilised liposomes and related lipid aggregates : fundamental studies on aggregate structure and stability /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5027-X/.
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Hammond, Christian B. "Real Time Investigations of Aggregation of Sulfur-Rich Asphaltene." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1587405713284981.
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Lang, Lisa. "SOD1 Aggregation : Relevance of thermodynamic stability." Doctoral thesis, Stockholms universitet, Institutionen för biokemi och biofysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-139943.
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Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the upper and lower motor neurons causing muscle atrophy and paralysis followed by death. Aggregates containing superoxide dismutase (SOD1) are found as pathological hallmark in diseased ALS patients. Consequently ALS is regarded as a protein misfolding disorder like Alzheimer’s disease and Parkinson’s disease. So far, little is known about the cause and mechanism behind SOD1 aggregation but the inherent property of all polypeptide chains to form stable aggregated structures indicates that the protein misfolding diseases share a common mechanism. Our results show that SOD1 aggregation starts from the globally unfolded state, since fibrillation is fastest at full occupancy of denatured protein induced either by chemical denaturation or mutation. Even so, the fibrillation rate shows a surprisingly weak dependence on the concentration of globally unfolded SOD1 indicating fibril fragmentation as the dominant mechanism for aggregate formation. This is further supported by the observation that the SOD1 sample has to be mechanically agitated for fibrillation to occur. Interestingly, we observe a similar SOD1 aggregation behaviour in vivo, where the survival times of ALS transgenic mice correlates with mutant stability, and aggregate growth depends weekly on the concentration of unfolded monomer. Additionally, in-cell NMR measurements reveal that in live cells the thermodynamic equilibrium is shifted towards the unfolded state of SOD1, which is also more fully extended than in vitro. This suggests that the globally unfolded aggregation competent protein is more abundant in the crowded environment in vivo than dilute in vitro conditions. Finally, antibody analysis of aggregates from ALS transgenic mice reveals the existence of aggregate strains involving different parts of the protein depending on mutation, which may offer an explanation for the various disease phenotypes observed in ALS. Altogether these findings provide important clues for understanding SOD1 aggregation with implications for ALS, as well as other protein misfolding diseases.
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Applewhite, James Kenneth. "Aggregate stability, infiltration, and glomalin in eroded and compacted soils on Fort Hood Military Reservation." Texas A&M University, 2008. http://hdl.handle.net/1969.1/86062.
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Fort Hood Military Reservation is a 900 km2 military installation located between Killeen, Copperas Cove, and Gatesville in central Texas. It supports two full armored divisions which require year-round, live-fire maneuvers and training (Ft. Hood, 2003). As a result of the constant foot traffic and use of heavy equipment, the soils on the training ranges have become increasingly compacted, eroded, and stripped of vegetation. This study evaluated the impact that selected soil amendments would have on soil aggregation, infiltration, and levels of glomalin. A field study was done on plots located inside Fort Hood on a Nuff silty clay (fine-silty, carbonatic, thermic Udic Calciustoll). The plots were amended with composted dairy manure, inorganic fertilizers, and native grass seed. Aggregate stability was determined using a wet sieving procedure and total glomalin values were quantified using a Bradford assay. Field measurements of infiltration rates were taken using a drip-type rainfall simulator.
Aggregate stability exhibited decreased values over time for all treatments but two (Site Prep / No Seed and Site Prep / Compost / Seed). In addition, three treatments changed significantly over time (from before treatment application to after treatment application). These treatments were the Site Prep / Compost / No Seed, No Prep / No Seed, and No Prep / Seed treatments. Levels of glomalin increased significantly over time for all treatments (p-value <0.001). Glomalin was correlated to aggregate stability after treatments were applied (p-value <0.01) but not before (p-value 0.89). In addition, infiltration rates were not related to glomalin (p-value 0.9) or aggregate stability (p-value 0.09). Additional sampling of Fort Hood beyond the plot study demonstrates significant differences in aggregate stability, infiltration rates, and levels of glomalin. Measurements taken from ten sites showed no correlations between aggregate stability, infiltration rates, or glomalin. Organic C was correlated to percent water stable aggregates (%WSA) and levels of glomalin. These results illustrate the relationship between organic C and aggregate stability as well as glomalin levels in maintaining infiltration rates and reducing soil loss by erosion.
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Koch, Tyree J. "Aggregation Propensity: Characterization of Monoclonal Antibody Stability." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:24078351.
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The study of aggregation propensity of a monoclonal antibody (mAb) and its sensitivity to applied stresses is believed to correlate with the overall stability of the mAb. As such, the aggregation propensity under various stresses can be used to develop a unique aggregation metric to rank order a panel of mAbs based on their stability. Often in a drug discovery campaign, multiple mAbs may imbue the desired in vivo efficacy, at which point identification of the most developable mAb becomes an important factor to decide on a single candidate for further development. This study focuses on the assessment of the stability of a panel of mAbs, by defining their propensity for aggregation along the native and non-native aggregation pathways. Kosmotrope based solubility evaluates a mAb’s colloidal stability, or propensity for native aggregation, while differential scanning fluorescence reports conformational stability, or propensity for non-native aggregation. By combining the conformational and colloidal stability metrics, an overall aggregation propensity profile can be generated for a mAb. To parse out further information on stability, the mAb panel was exposed to a series of stresses, which mimic stresses a mAb based drug would be exposed to during manufacturing and storage. After exposure to stress, the mAb panel was then monitored for change in apparent colloidal and conformational stability. There was no variation in the stability metrics measured, as a function of stress. However, observed precipitation denoted differential sensitivity to the stresses. Combining observational data with the stability metrics measured, allowed for rank ordering of aggregation propensity, and overall stability.
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Tucker, E. Shannon. "Instability within stability: Conflicting trends beneath Canada's aggregate incarceration rate." Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28196.
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Contrary to the significant increases of incarceration rates in the United States and England, Canada has maintained relatively stable incarceration rates for the years 1978 2004. However, this overall stability conceals not only bifurcated trends of increasing and decreasing incarceration rates but also significant variation within these trends at the federal, provincial, and territorial sub-levels. As such, this thesis reveals -- on a theoretical level -- that Canada has not entirely resisted the shift towards increasing punitiveness. From a policy perspective, it is suggested that the competing trends must be monitored to avoid exacerbation to the point in which justice is brought into disrepute. This work also raises a methodological question of whether punitiveness is best measured in terms of admissions or counts data.
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Sluzky, Victoria. "Insulin stability and aggregation in agitated aqueous solutions." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/36923.
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Molope, Mishack Bochankge. "Some effects of biological and physical processess on soil aggregate stability." Thesis, University of Stirling, 1985. http://hdl.handle.net/1893/2595.
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The effects of biological and physical processes on the aggregate stability of some weakly structured arable and pasture soils were investigated. Preliminary investigations showed significant correlations between soil organic matter and both wet sieving and turbidimetric methods of aggregate stability; the latter method was chosen on grounds of convenience. Scanning electron microscope pictures showed the presence of both fungi and bacteria when soils were incubated. Growth of fungi, estimated by ergosterol measurement, correspond to temporary stability increases, which could be explained by retention of soil particles within the reticulum of fungal hyphae. The effect disappeared as the fungi were destroyed and replaced by bacteria and actinomycetes. Effects caused by fungi were examined separately, using vancomycin to inhibit bacterial growth, and bacterial effects by using cycloheximide to eliminate fungi. Bacterial growth had little direct effect in stabilising soil aggregates; periodate oxidation showed that polysaccharides produced by bacteria are mainly responsible. To examine the contribution of physical processes to increased stability in remoulded soils biological processes were eliminated by sterilisation. Thixotropic changes made a contribution to age hardening in remoulded aggregates similar in magnitude to biological processes. Thixotropic changes were reversible and accompanied by soil strength and metric water potential changes. Polysaccharides did not contribute to thixotropic aging processes. Remoulded soils were subjected to wetting/drying and freezing/thawing cycles. After 3 to 6 cycles the stability of both sterilised and unsteriliserd soils recovered to that of natural aggregates, suggesting a contribution by thixotropy. Repeated weathering cycles decreased the stability of unsterilised, and more so sterilised, field aggregates suggesting that in the former, bond reformation due to biological activity counteracted the destruction caused by wetting/drying and freezing/thawing.
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Miyashita, Satoru, Yukio Saito, and Makio Uwaha. "Fractal Aggregation Growth and the Surrounding Diffusion Field." Elsevier, 2005. http://hdl.handle.net/2237/7318.
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Blackman, Jonathan David. "Variation and change in the aggregate stability and erodibility of downland soils." Thesis, University of Sussex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580147.
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Lamagna, Sarah Frances. "Development of health indicators for rough fescue grasslands in the southern interior of British Columbia." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/4129.
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Grasslands throughout the world including those in British Columbia have been severely
reduced and altered by agricultural production and inappropriate livestock grazing practices.
Ongoing degradation of rangelands is a worldwide problem, currently affecting about 680
million hectares of rangelands.
Studies on development and application of criteria and indicators for forests and
grasslands are often lacking, or have been done on a limited number of sites with relatively
narrow ranges of climate and soil type. This study aims to (i) quantify the relationships among
soil/vegetation properties known to be affected by grazing to easily-assessed indicators, used in
the existing health assessment systems, that do not require laboratory analyses or time
consuming measurement, and (ii) to evaluate impacts of grazing on soil aggregate stability on the
rough fescue grasslands of the southern interior of British Columbia. During the growing
seasons of 2006 and 2007, soil and vegetation properties were measured on nine open grassland
sites with a potential natural plant community dominated by rough fescue (Festuca campestris
Rydb.) in the southern interior of British Columbia. Each site had at least one area excluded
from grazing and all units were classified into different seral stages according to the amount of
rough fescue present on the land.
Rough fescue cover was found to be a useful indicator of the presence of functioning
recovery mechanisms. Percent exposed mineral soil was found to be a sensitive indicator of the
degree of soil stability and watershed function, as well as an indicator of the integrity of nutrient
cycles and energy flows in rough fescue grasslands. Percent Junegrass cover was not as sensitive
an indicator as percent exposed mineral soil, but has general overall strength with many health
measures.. Only the 1-2 mm aggregate size class was closely related to most soil and vegetation
properties, showing that it is more sensitive than the other aggregate stability parameters to soil
and vegetation properties.
The results from this study can help rangeland managers and ranchers in determining the
rangeland health in their area as well as help researchers understand that only a certain number of
parameters need to be assessed.
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Castillo, Cano Virginia. "Using Small Globular Proteins to Study Folding Stability and Aggregation." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/107824.
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El propòsit d’aquesta tesis que porta com a títol “Estudi de l’estabilitat de plegament i l’agregació mitjançant l’ús de proteïnes globulars petites” és el de contribuir al coneixement de com les proteïnes globulars adquireixen la seva estructura nativa i funcional o, alternativament, despleguen i agreguen donant lloc a assemblatges tòxics.
Les malalties conformacionals inclouen un número important de desordres humans com la malaltia del Parkinson i Alzheimer, les quals estan relacionades amb canvis conformacionals d’espècies solubles no tòxiques a agregats tòxics. A més, la sobrexpressió de proteïnes recombinants normalment promou l’acumulació d’agregats proteics, essent un gran blocatge en diversos processos biotecnològics. D’aquesta manera, el desenvolupament d’estratègies per reduir o evitar aquestes reaccions aberrants s’ha convertit en un problema molt important tant a la indústria biomèdica com biotecnològica.
En la present tesis hem utilitzat una bateria de tècniques biofísiques i computacionals per analitzar el plegament, l’estabilitat conformacional i la tendència a agregar de diverses proteïnes globulars. La combinació d’aproximacions experimentals (in vivo i in vitro) i bioinformàtiques ha proveït nous coneixements sobre les propietats intrínseques i estructurals, incloent la presència de ponts disulfurs i d’estructura quaternària, que modulen aquests processos sota condicions fisiològiques.
En general, aquests resultats demostren com l’establiment de contactes natius que promouen la formació d’intermediaris de plegament, estructures natives o interfases proteiques amb estabilitat termodinàmica significativa és un procés crucial tant en la conducció del plegament proteic com de l’agregació.The purpose of the thesis entitled “Using small globular proteins to study folding stability and aggregation” is to contribute to understand how globular proteins fold into their native, functional structures or, alternatively, misfold and aggregate into toxic assemblies. Protein misfolding diseases include an important number of human disorders such as Parkinson’s and Alzheimer’s disease, which are related to conformational changes from soluble non‐toxic to aggregated toxic species. Moreover, the over‐expression of recombinant proteins usually leads to the accumulation of protein aggregates, being a major bottleneck in several biotechnological processes. Hence, the development of strategies to diminish or avoid these aberrant reactions has become an important issue in both biomedical and biotechnological industries. In the present thesis we have used a battery of biophysical and computational techniques to analyze the folding, conformational stability and aggregation propensity of several globular proteins. The combination of experimental (in vivo and in vitro) and bioinformatic approaches has provided insights into the intrinsic and structural properties, including the presence of disulfide bonds and the quaternary structure, that modulate these processes under physiological conditions. Overall, the data illustrates how the establishment of native‐like contacts providing folding intermediates, native structures or protein interfaces with significant thermodynamic stability is a crucial process both to drive protein folding and to compete toxic aggregation.
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Liang, Yun [Verfasser]. "Emerging threats to the stability of soil aggregates / Yun Liang." Berlin : Freie Universität Berlin, 2021. http://d-nb.info/1234451573/34.
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Rushton, Andrew G. "The effect of flow conditions on the stability of flocs." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/27194.
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An investigation into aggregate breakage has been carried out using suspensions of uniform polystyrene spheres destabilised by addition of salt or polymer. A controlled flow apparatus was used to expose the suspended aggregates to turbulent pipe flow of variable intensity and duration. Analysis of aggregate size distribution was carried out using the HIAC light obscuration technique.
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Rogers, Stephen Lloyd. "The effect of phototrophic microbial inoculants on soil aggregate stability and soil fertility." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305060.
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Drahos, Karen Elizabeth. "Sulfatides mediate Disabled-2 membrane localization and stability during platelet aggregation." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/31626.
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Thrombosis, the major cause of heart attack and strokes,1 is triggered by localized clotting of the blood as the result of deregulated platelet aggregation. During the repair of vascular injury, clotting usually occurs when platelets adhere to each other at the site of vascular injury in order to stop bleeding.2 Distinct protein receptors and adhesive ligands together with the blood flow conditions govern this process. One of the negative regulators in platelet aggregation is Disabled-2 (Dab2), a modular protein that is released upon platelet activation to the extracellular platelet surface.3 Dab2 inhibits platelet aggregation through its phosphotyrosine-binding (PTB) domain by competing with fibrinogen for ï ¡IIï ¢3 integrin binding on the activated platelet surface.3 Sulfatides are also found on the platelet surface,4 interacting with adhesive and coagulation proteins5-7 and, thus, they are thought to play a major role in haemostasis and thrombogenesis.
Here, we show that the Dab2 PTB domain specifically interacts with sulfatides through two conserved basic motifs. The sulfatide-binding site overlaps with that of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2) in the PTB domain. Whereas sulfatides recruit the Dab2 PTB domain to the platelet surface, thus sequestering the protein from thrombin-mediated platelet aggregation, the phosphoinositide mediates its internalization. Experimental data support the hypothesis that two pools of Dab2 co-exist at the platelet surface and that the balance between them controls the extent of the clotting response.Master of Science
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Abu-Sen, Laila. "Environmental stability studies of an organic semiconductor." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/environmental-stability-studies-of-an-organic-semiconductor(283b640d-b373-4c2d-bfeb-68d7bcae21d4).html.
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The formulation induced photooxidative stability of substituted 6, 13 trialkylsilylethynylpentacene derivatives is report for the first time. It is known that 6,13 trialkylsilylethynylpentacene derivatives undergo rapid oxidation through singlet oxidation and is believed to be primarily to the 6,13 endoperoxide. The effect of solvent, organic semiconductor concentration and the presence of polymeric binder on the rate of photooxidative degradation in oxygen saturated solutions on degradation kinetics have been investigated. The photochemical stability of 6,13 trialkysilylethynylpentacene has been studied in toluene, THF, dichloromethane, chloroform, decane and dodecane at concentrations ranging from 2.5×10-6 M to 5×10-2 M by measurement of the half-life by UV-visible spectroscopy. The predominant degradation products of TIPS-Pentacene are the same regardless of solvent and concentration, being predominantly an endo-peroxide resulting from O2 addition across the 6, 13 position of the pentacene. At low concentration (< 1×10 -3 M), the half- life of TIPS-Pentacene is observed to vary with solvent and the amount of dissolved oxygen, with half-life showing a strong, positive correlation between the product of the Hansen Solubility Parameter (HSP) and the mole-fraction oxygen solubility. In this range, the half-life is observed to increase markedly with increasing solution concentration, showing a linear correlation with mean intermolecular distance within the solution. From intermediate to high concentration, the half-life increase more rapidly with increasing concentration, which is attributed to aggregation. In most solvents, this behaviour shows a specific onset point, suggesting a cooperative rather than isodesmic aggregation mechanism. Photooxidative half-lives of TMTES-pentacene and fluorinated soluble pentacene derivatives were determined from 2.5 × 10-6 M to 5.0 × 10-3 M solutions in THF, toluene, chloroform and CH2Cl2. Independent of solvent and at constant concentration the relative ordering of photo-oxidative resistance was: α-di-FTIPS-pentacene > β-di-FTIPS-pentacene, α-mono -FTIPS-pentacene, β-mono-FTIPS-pentacene > TIPS-pentacene ≥ TMTES-pentacene. The same rank order for a particular derivative was generally maintained over the concentration range 2.5 x 10-6 M to 5 x 10-3 M the stability to photooxidation for all derivative increased with increasing concentration. All derivatives showed a mixture of endooxidation products as shown by APCI mass spectrometry, and 1H NMR.Added polystyrene and isotactic polystyrene were found to accelerate photooxidative degradation whist isotactic polymethylmethacrylate (i-PMMA) and poly (triaylamine) (PTAA) had no effect adding weight to the argument that anything which can act as an acceptor to the solution slows down the degradation and anything which impairs pair-wise energy transfer speeds up the degradation. Understanding of these phenomena is therefore essential for the further application of solution processing of organic materials.
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Geeves, Guy William, and not available. "Aggregate Breakdown and Soil Surface Sealing under Rainfall." The Australian National University, 1997. http://thesis.anu.edu.au./public/adt-ANU20010702.142014.
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Aggregate breakdown is an important process controlling the availability of fine soil material necessary for structural sealing of soil surfaces under rainfall. It may be caused by slaking resulting from rapid soil wetting and by physical dispersion resulting from direct and indirect energetic raindrop impacts. Relationships have been proposed by others predicting steady infiltration rate and saturated hydraulic conductivity from final aggregate size following high energy rainfall on initially dry, uncovered soil surfaces. Under these extreme conditions, both rapid wetting and energetic raindrop impact result in maximum aggregate breakdown and surface sealing. Knowledge of the relative importance of these two agents under less severe conditions and knowledge of how increased aggregate stability due to conservative soil management may ameliorate them should improve prediction and management of aggregate breakdown and surface sealing.
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This study has isolated and quantified effects of rapid soil wetting and energetic raindrop impact on aggregate breakdown and surface sealing. Simulated rainfall was applied to re-packed soils from differing tillage treatments on light textured soils from near Cowra and Condobolin in New South Wales, Australia. Aggregate breakdown was assessed using aggregate size distribution, determined by wet sieving and summarised by a range of statistics. The degree of breakdown was assessed after 66 mm of simulated rainfall whilst the rate of change in aggregate size distribution was assessed by sampling after 5, 10, 15, 30 and 60 mm. The degree of surface sealing was assessed using final surface hydraulic conductivity after 66 mm rainfall calculated from inferred infiltration and measured sub-seal soil water potential. The rate of surface sealing was assessed prior to ponding using cumulative rainfall volume at ponding and throughout the post-ponding phase by decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. Two levels of raindrop kinetic energy flux and three wetting treatments were used to isolate effects of these agents of aggregate breakdown and surface sealing.
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Significant surface aggregate breakdown was observed when either rapid soil wetting or highly energetic raindrop impact were allowed to occur. The majority of the data suggest a negative interaction between the two agents. When soil was initially dry rapid soil wetting was the dominant agent causing rapid aggregate breakdown, generally within the first 5 mm of rainfall. When rapid soil wetting was prevented by tension pre-wetting, energetic raindrop impact was the dominant agent and was able to cause aggregate breakdown of an almost equivalent degree. This breakdown occurred over a period lasting for up to 30 mm of rainfall. In contrast, the rate and degree of surface sealing were influenced primarily by raindrop kinetic energy with highly energetic impact leading to significant surface sealing, irrespective of soil wetting. For the soils studied, it was concluded that structural sealing of surface soil, could be significantly reduced by protecting the soil surface from energetic raindrop impact but that prevention of surface aggregate breakdown required amelioration of both processes.
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In addition to the negative interaction referred to above, a positive interaction was observed whereby energetic raindrop impact occurring concurrently with rapid soil wetting caused a greater degree of aggregate breakdown and a greater degree of surface sealing than energetic raindrop impact occurring subsequent to rapid soil wetting. The effect on surface sealing may be explained by the effect of lower sub-seal water potential that necessarily results from initially dry soil condition required for concurrent rapid wetting. However, the effect on aggregate breakdown remains unexplained.
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Notwithstanding the above, permeability was reduced under high kinetic energy rainfall even when soil wetting was reduced to very slow rates by tension pre-wetting. Likewise, surface sealing did occur under low kinetic energy rainfall for the least stable soil following rapid soil wetting. It was concluded that threshold soil wetting rates and threshold rainfall energy levels, proposed by others, are either not applicable to these soils or are negligible.
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The rate and degree of aggregate breakdown was also dependent on the soil with the Cowra soil being more stable than the Condobolin soil. Greater aggregate stability brought about by conservative tillage treatments at both soil locations retarded and reduced surface sealing. Unvalidated simulation modelling was used to illustrate possible effects for the soil water balance. In contrast to the conclusions of Loch (1994b), that were based on soils throughout eastern Queensland, the soil water balance simulations predicted that the residual benefits in ameliorating surface sealing resulting from improved aggregate stability could significantly reduce point runoff under the lower intensity winter rainfalls experienced in southern New South Wales.
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Limited testing with Condobolin soil following tension pre-wetting showed that rainfall intensity, varying over the range from 16.5 to 66 mm h-1, had little effect on the decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. This contrasts with greater seal permeability under higher rainfall intensities observed by Romkens et al. (1985) and others. It is proposed that an alternative explanation exists for the observations of Romkens et al. based on reduction in seal permeability due to lower sub-seal water potential under lower intensity rainfall.
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Post-ponding reduction in K[subscript sat] under high kinetic energy rainfall exhibited exponential decline as a function of cumulative raindrop kinetic energy as proposed by Moore (1981b). However, inferred rates of decline prior to ponding were more rapid than measured post-ponding rates suggesting that infiltration models using only a single exponential rate of surface K[subscript sat] decline based on post-ponding measurements may be in error. Potential for error is greatest at early times for loose soil that is highly susceptible to sealing.
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Pre-ponding decline in surface aggregation was also relatively more rapid than post-ponding decline. This discrepancy was evident irrespective of soil pre-wetting. From this it was concluded that the more rapid initial aggregate breakdown and surface sealing was due, at least in part, to processes other than aggregate slaking due to rapid soil wetting. An explanation has been proposed as follows. Raindrops initially fall on aggregates that have not been subjected to rainfall and therefore each drop has the capacity to cause greater aggregate breakdown than subsequent raindrops that fall on aggregates or soil fragments that have been strong enough to survive preceding rainfall impacts. Such a mechanism could provide an alternative explanation of the findings of Baumhardt et al. (1991) who found that less cumulative raindrop kinetic energy was necessary to achieve a given reduction in surface conductance when the cumulative energy was supplied through lower energy drops.
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Relationships predicting rates of surface sealing using aggregate breakdown under rainfall and aggregate stability were evaluated. Post-ponding infiltration rate and surface K[subscript sat] were related to aggregate size by exponential functions. The proportion of surface aggregates less than 0.125 mm in diameter provided slightly more consistent relationships. Parameters of fitted relationships differed among wetting pre-treatments suggesting that the influence of sub-seal water potential on surface K[subscript sat] must be considered whenever such relationships are developed or applied. Aggregate stability determined by wet sieving was related to rainfall volume required for ponding, final K[subscript sat] and final aggregate size but only for initially dry soil suggesting that such relationships may be unique to the rainfall, soils and flow conditions used to develop them.
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This study has established the relative importance of rapid soil wetting and energetic raindrop impact in both aggregate breakdown and surface sealing over a range of antecedent soil water and rainfall conditions. It has quantified the effectiveness of culturally induced aggregate stability in ameliorating effects of these two important agents and illustrated the potentially significant consequences for the soil water balance. It has quantified temporal patterns of surface sealing and aggregate breakdown and proposed an alternative mechanism explaining more rapid aggregate breakdown during the initial stages of rainfall. It has identified possible explanations for effects of rainfall intensity on surface sealing observed in other studies. It has also partially evaluated a mechanism proposed to explain important effects of subseal water potential on seal permeability found in this and other studies. These significant findings have been used with the findings of other studies to amend the conceptual model proposed by Le Bissonnias (1990). The amended model gives a more complete description of the relationships between parameters and processes determining aggregate breakdown and structural surface sealing under rainfall.
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Tilligkeit, Jacqueline Elizabeth. "The Spatial Distribution of K-Factor Values Across a Toposequence and a Soil Survey Map Unit." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/826.
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Rivers and streams are adversely affected by an increase in sedimentation in their waters from eroding land. High sediment loads in streams can bury fish eggs and prevent hatching, increasing nutrients in the water causing algae blooms, or even contaminating the water with heavy metals carried in or on the aggregates. The erodibility of soil is valuable knowledge to all land users so that we may predict soil loss and its potential to pollute streams. This is done by using the Revised Universal Soil Loss Equation (RUSLE). By predicting soil loss from a given landscape, land managers can take mitigation measures. The precision of the current scale available for soil erodibility (K-factor) by the US Department of Agriculture is not useful to small landowners or on a site-by-site basis. In California’s Central Coast, a grassland hillslope toposequence was investigated in a Los Osos-Diablo soil series complex. Geographic information systems software was used for spatial analysis of variation in the K-factor as well as interpolating areas that were not sampled. Analysis of soils’ particle size, infiltration rate, organic matter content, and structure across the toposequence allowed calculation of the soils’ K-factor values. K-factor values for the footslope, backslope, and shoulder were found to be statistically different from one another. All slope position’s average K-factor values were statistically different than the published Los Osos and Diablo series’ K-factor with the exception of the backslope which was not significantly different than Diablo’s K-factor value. The average of all K-factors was found not to be statistically different than the Los Osos’ K-factor but it was statistically different from the Diablo’s soil series K-factor. The USDA K-factors overestimated the predicted soil loss for the study site.
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Kittner, Madeleine. "Folding and aggregation of amyloid peptides." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5357/.
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Aggregation of the Amyloid β (Aβ) peptide to amyloid fibrils is associated with the outbreak of Alzheimer’s disease. Early aggregation intermediates in form of soluble oligomers are of special interest as they are believed to be the major toxic components in the process. These oligomers are of disordered and transient nature. Therefore, their detailed molecular structure is difficult to access experimentally and often remains unknown. In the present work extensive, fully atomistic replica exchange molecular dynamics simulations were performed to study the preaggregated, monomer states and early aggregation intermediates (dimers, trimers) of Aβ(25-35) and Aβ(10-35)-NH2 in aqueous solution.
The folding and aggregation of Aβ(25-35) were studied at neutral pH and 293 K. Aβ(25-35) monomers mainly adopt β-hairpin conformations characterized by a β-turn formed by residues G29 and A30, and a β-sheet between residues N27–K28 and I31–I32 in equilibrium with coiled conformations. The β-hairpin conformations served as initial configurations to model spontaneous aggregation of Aβ(25-35).
As expected, within the Aβ(25-35) dimer and trimer ensembles many different poorly populated conformations appear. Nevertheless, we were able to distinguish between disordered and fibril-like oligomers. Whereas disordered oligomers are rather compact with few intermolecular hydrogen bonds (HBs), fibril-like oligomers are characterized by the formation of large intermolecular β-sheets. In most of the fibril-like dimers and trimers individual peptides are fully extended forming in- or out-of-register antiparallel β-sheets. A small amount of fibril-like trimers contained V-shaped peptides forming parallel β-sheets. The dimensions of extended and V-shaped oligomers correspond well to the diameters of two distinct morphologies found for Aβ(25-35) fibrils.
The transition from disordered to fibril-like Aβ(25-35) dimers is unfavorable but driven by energy. The lower energy of fibril-like dimers arises from favorable intermolecular HBs and other electrostatic interactions which compete with a loss in entropy. Approximately 25 % of the entropic cost correspond to configurational entropy. The rest relates to solvent entropy, presumably caused by hydrophobic and electrostatic effects.
In contrast to the transition towards fibril-like dimers the first step of aggregation is driven by entropy. Here, we compared structural and thermodynamic properties of the individual monomer, dimer and trimer ensembles to gain qualitative information about the aggregation process. The β-hairpin conformation observed for monomers is successively dissolved in dimer and trimer ensembles while instead intermolecular β-sheets are formed. As expected upon aggregation the configurational entropy decreases. Additionally, the solvent accessible surface area (SASA), especially the hydrophobic SASA, decreases yielding a favorable solvation free energy which overcompensates the loss in configurational entropy. In summary, the hydrophobic effect, possibly combined with electrostatic effects, yields an increase in solvent entropy which is believed to be one major driving force towards aggregation.
Spontaneous folding of the Aβ(10-35)-NH2 monomer was modeled using two force fields, GROMOS96 43a1 and OPLS/AA, and compared to primary NMR data collected at pH 5.6 and 283 K taken from the literature. Unexpectedly, the two force fields yielded significantly different main conformations. Comparison between experimental and calculated nuclear Overhauser effect (NOE) distances is not sufficient to distinguish between the different force fields. Additionally, the comparison with scalar coupling constants suggest that the chosen protonation in both simulations corresponds to a pH lower than in the experiment. Based on this analysis we were unable to determine which force field yields a better description of this system.
Dimerization of Aβ(10-35)-NH2 was studied at neutral pH and 300 K. Dimer conformations arrange in many distinct, poorly populated and rather complex alignments or interlocking patterns which are rather stabilized by side chain interactions than by specific intermolecular hydrogen bonds. Similar to Aβ(25-35) dimers, transition towards β-sheet-rich, fibril-like Aβ(10-35) dimers is driven by energy competing with a loss in entropy. Here, transition is mediated by favorable peptide-solvent and solvent-solvent interactions mainly arising from electrostatic interactions.Die Aggregation des Amyloid β (Aβ) Peptids zu Amyloidfibrillen wird mit dem Ausbruch der Alzheimer Krankheit in Verbindung gebracht. Die toxische Wirkung auf Zellen wird vor allem den zeitigen Intermediaten in Form von löslichen Oligomeren zugeschrieben. Aufgrund deren ungeordneter und flüchtiger Natur kann die molekulare Struktur solcher zeitigen Oligomere oft experimentell nicht aufgelöst werden. In der vorliegenden Arbeit wurden aufwendige atomistische Replica-Exchange-Molekulardynamik-Simulationen durchgeführt, um die molekulare Struktur von Monomeren und Oligomeren der Fragmente Aβ(25-35) und Aβ(10-35)-NH2 in Wasser zu untersuchen. Die Faltung und Aggregation von Aβ(25-35) wurde bei neutralem pH und 293 K untersucht. Monomere dieses Fragments bilden hauptsächlich β-Haarnadelkonformationen im Gleichgewicht mit Knäulstrukturen. Innerhalb der β-Haarnadelkonformationen bilden die Residuen G29 und A30 einen β-turn, während N27–K28 and I31–I32 ein β-Faltblatt bilden. Diese β-Haarnadelkonformationen bildeten den Ausgangspunkt zur Modellierung spontaner Aggregation. Wie zu erwarten, bilden sich eine Vielzahl verschiedener, gering besetzter Dimer- und Trimerkonformationen. Mit Hilfe einer gröberen Einteilung können diese in ungeordnete und fibrillähnliche Oligomere unterteilt werden. Ungeordnete Oligomere bilden kompakte Strukturen, die nur durch wenige intermolekulare Wasserstoffbrückenbindungen (HBB) stabilisiert sind. Typisch für fibrillähnliche Oligomere ist hingegen die Ausbildung großer intermolekularer β-Faltblätter. In vielen dieser Oligomere finden wir antiparallele, in- oder out-of-register β-Faltblätter gebildet durch vollständig ausgestreckte Peptide. Ein kleiner Teil der fibrillähnlichen Trimere bildet parallele, V-förmige β-Faltblätter. Die Ausdehnungen ausgestreckter und V-förmiger Oligomere entspricht in etwa den Durchmessern von zwei verschiedenen, experimentell gefundenen Fibrillmorphologien für Aβ(25-35). Die Umwandlung von ungeordneten zu fibrillähnlichen Aβ(25-35) Dimeren ist energetisch begünstigt, läuft aber nicht freiwillig ab. Fibrillähnliche Dimere haben eine geringere Energie aufgrund günstiger Peptidwechselwirkungen (HBB, Salzbrücken), welche durch den Verlust an Entropie kompensiert wird. Etwa 25 % entsprechen dem Verlust an Konfigurationsentropie. Der restliche Anteil wird einem Verlust an Lösungsmittelentropie aufgrund von hydrophoben und elektrostatischen Effekten zugesprochen. Im Gegensatz zur Umwandlung in fibrillähnliche Dimere, ist die Assoziation von Monomeren oder Oligomeren entropisch begünstigt. Beim Vergleich thermodynamischer Eigenschaften der Monomer-, Dimer- und Trimersysteme zeigt sich im Verlauf der Aggregation, wie erwartet, eine Abnahme der Konfigurationsentropie. Zusätzlich nimmt die dem Lösungsmittel zugängliche Oberfläche (SASA), insbesondere die hydrophobe SASA, ab. In Verbindung damit beobachten wir eine Abnahme der freien Solvatisierungsenergie, welche den Verlust an Konfigurationsentropie kompensiert. Mit anderen Worten, der hydrophobe Effekt in Kombination mit elektrostatischen Wechselwirkungen führt zu einem Ansteigen der Lösungsmittelentropie und begünstigt damit die Aggegation. Die spontane Faltung des Aβ(10-35)-NH2 Monomers wurde für zwei verschiedene Proteinkraftfelder, GROMOS96 43a1 und OPLS/AA, untersucht und mit primären NMR-Daten aus der Literatur, gemessen bei pH 5.6 und 283 K, verglichen. Beide Kraftfelder generieren unterschiedliche Hauptkonformationen. Der Vergleich zwischen experimentellen und berechneten Kern-Overhauser-Effekt (NOE) Abständen ist nicht ausreichend, um zwischen beiden Kraftfeldern zu unterscheiden. Der Vergleich mit Kopplungskonstanten aus Experiment und Simulation zeigt, dass beide Simulationen einem pH-Wert geringer als 5.6 ensprechen. Basierend auf den bisherigen Ergebnissen können wir nicht entscheiden, welches Kraftfeld eine bessere Beschreibung für dieses System liefert. Die Dimerisierung von Aβ(10-35)-NH2 wurde bei neutralem pH und 300 K untersucht. Wir finden eine Vielzahl verschiedener, gering besetzter Dimerstrukturen, welche eher durch Seitenkettenkontakte als durch spezifische HBB stabilisiert sind. Wie bei den Aβ(25-35) Dimeren, ist die Umwandlung zu β-Faltblattreichen, fibrillähnlichen Aβ(10-35) Dimeren energetisch begünstigt, konkurriert aber mit einem Entropieverlust. Die Umwandlung wird in diesem Fall durch elektrostatische Wechselwirkungen zwischen Peptid und Lösungsmittel und innerhalb des Lösungsmittels bestimmt.
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Dorji, Tshering. "Soil organic carbon variability under montane ecosystems: assessing the influence of landscape attributes." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14811.
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Soil organic carbon (SOC) is integral to soil functioning and serves as a common indicator for soil security, water security, food security, energy security, climate change abatement, biodiversity protection, and ecosystem service. Since SOC varies in space and time, its quantification is essential to better understand the carbon (C) dynamics at various scales. As a gamut of montane ecosystems, the Himalayan region serves as one of the major C storage pools in the world due to its rich biodiversity and good forest cover. However, much of the Himalayan region is environmentally vulnerable because of rapid socio-economic development taking place, unsustainable land management, and land degradation. As a result, C emissions are steadily increasing in the region and, thus, contributing to global climate change. Despite this, there are still substantial gaps in terms of data and knowledge on SOC in the Himalayas, as in many other part of the globe. Therefore, this thesis was aimed to: (i) investigate the spatial distribution of SOC stock and its variation under different land use and land cover (LULC) types; (ii) examine the vertical distribution of SOC density in relations to LULC types, altitudinal zones, and aspect directions; (iii) determine the complex interrelationships of SOC fractions with LULC types and landform attributes; and (iv) assess the impacts of LULC type on aggregate stability, and hence aggregate size distribution and aggregate-associated organic carbon (AAOC). This study focused on a sub-catchment of Bhutan in the eastern Himalayas. First the SOC stock and its spatial distribution under different LULC types was determined using digital soil mapping technique of regression kriging (RK). Among the several environmental covariates used in RK are altitude, LULC type, slope gradient, and aspect directions. The results show that the mean top one meter SOC stock (mapped to 90 × 90 m grid resolution) decreased in the order of fir > mixed conifer > shrubland > grassland > broadleaf > blue pine > dry land (rain-fed agriculture) > orchard > paddy land. The overall SOC stock for the study area was estimated at 27.1 Mt (average 24.9 kg m-2), which is very high given the relatively small spatial extent of the study area. This indicates that the Himalayan region is characterized by high SOC storage capacity, which needs to be protected to remain as one of the major C sinks in the world. Second, in order to gauge the profile homogeneity of SOC density, its vertical profiles were each fitted with a smooth spline function followed by the estimation of the proportions of SOC density in top 0.20 m relative to the total density in the top one meter. The SOC density homogeneity values under different LULC types, altitudinal zones, and aspect directions were then compared. It revealed that the homogeneity under agricultural land was estimated at 34% compared to 38% for forest, 43% for shrubland, and 59% under grassland. In the case of influence of altitudinal zones on the SOC density, the latter was more uniformly distributed in the 3500-4000 m zone with homogeneity of about 35%, significantly less than 41% estimated for each of the 1769-2500 m and 2500-3000 m zones, and even lesser than 43% for the 3000-3500 m zone. Conversely, the homogeneity of SOC density estimated for different aspect directions indicated that the northern aspect exhibited higher vertical homogeneity compared to other aspect directions whose homogeneity values were indeterminate. These results suggest that vegetation and soil moisture, as influenced by LULC type, altitude, and aspect direction, are the main factors controlling the vertical distribution of SOC density. These outcomes have contributed significantly to our understanding of the conditions favorable to most vigorous vegetative growth and litter production leading to deeper incorporation of organic matter into the soil. The third component of this study was focused on explaining the complex interrelationships of SOC pools with environmental controlling factors of climate, landscape, and anthropogenic. It was hypothesized that the various SOC fractions/pools would respond differently to the environmental factors controlling the physical, chemical, and biological processes. Therefore, the multivariate statistical techniques of canonical correspondence analysis (CCA) was applied to reveal the subtle interrelationships of both the particulate organic carbon (POC) and humic organic carbon (HOC) with the different LULC types and landform attributes as the environmental covariates. It revealed that POC exhibited higher variation than HOC under different LULC types and landform attributes probably due to faster turnover rates of POC compared with that of HOC. Unlike HOC, the POC was largely concentrated in the upper depths of the soil profiles and hence more susceptible to soil erosion and rapid mineralization. The POC and HOC ratio became larger with depth suggesting that SOC becomes more stable with depth. This study also revealed that the influence of the natural LULC types on POC and HOC was higher than was the impacts due to agriculture. The findings have contributed to better understanding of POC and HOC in relation to various environmental factors in maintaining an optimum level of POC and HOC for enhancing sustainable agriculture, environmental quality, and ecosystem services. Lastly, the thesis explored how the vulnerability of the Himalayan region to land degradation can potentially be addressed by studying the impacts of LULC types on aggregate size distribution and stability as influenced by aggregate-associated organic carbon (AAOC). This is aimed to inform appropriate future soil and water conservation measures to combat land degradation. The results of aggregate size distribution show that the large macroaggregates (> 2 mm) accounted for 86-93% of the total aggregates under all LULC types except under dry land (64%) and paddy land (35%). The aggregate stability under different LULC types decreased in the order of fir > shrubland > grassland > orchard > blue pine > broadleaf > mixed conifer > dry land > paddy land. As expected, the AAOC in all aggregate fractions was much higher in the non-agricultural soils than under different agricultural lands. The AAOC in the large macroaggregates constituted more than 76% of the total AAOC across all LULC types except under dry land (65%) and paddy land (38%). Furthermore, the AAOC of the large macroaggregates depicted a similar trend with aggregate stability under different LULC types indicating its significant role in aggregate stability compared to AAOC of other aggregate fractions. The quadratic correlation between aggregate stability and AAOC of the large macroaggregates suggests an upper threshold for SOC to further improve soil aggregation and aggregate stability. In conclusion, this thesis has revealed the spatial/vertical distribution of SOC stocks as impacted by the different controlling factors. The thesis examined the complex interrelations of SOC fractions with LULC and landform attributes to help maintain an optimum level of all functional SOC fractions to improve soil quality. Furthermore, it investigated the microscopic/macroscopic aspects of soil aggregate stability in relation to the AAOC and how this can impact on potential soil degradation in the study region. This is the first systematic study on SOC undertaken in Bhutan which is envisaged to provide the springboard for further investigations across the Himalaya region. The findings of this research are anticipated to contribute in formulating appropriate sustainable land management and C sequestration strategies (e.g. conservation agriculture, agro-forestry, change in land use policy to safeguard and conserve the current forest cover) to combat C emission, soil erosion, and other forms of land degradation, specifically in Bhutan and generally in the Himalayan region. In addition, it is expected to contribute towards land use policy reform agenda to conserve the natural vegetation to ensure continued ecosystem service delivery in the region.
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SALA, BENEDETTA MARIA. "DISSECTING STRUCTURAL ASPECTS OF PROTEIN STABILITY." Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/570253.
Full textAbstract:
The contribution of a single residue in the structural stability of a whole protein can seem small if its position in the structure is not considered. Indeed, the stability of a protein is determined by the contribution of many forces among amino acids: hydrophobicity, hydrogen-bonding network and van der Waals interactions, salt bridges. Three independent projects were carried out during my PhD studies addressing mutations that affect protein fold stability.
I
β2-Microglobulin (β2m), the light chain of the Major Histocompatibility Class I complex (MHC-I), can assemble into amyloid fibrils and deposit in joints and bones of patients receiving long term haemodialysis, leading to dialysis-related amyloidosis (DRA).
β2m has been object of many mutational studies to investigate the molecular bases of its aggregation propensity. Among other residues, these analyses have pointed out that Trp60 plays a crucial role for β2m stability, in particular, W60G β2m, has an increased conformational stability and a reduced amyloidogenicity compared to the wild type protein.
To identify the key-residues that prompt the amyloidogenicity of β2m, the native state dynamics of WT β2m and W60G β2m have been compared, combining solution NMR spectroscopy and molecular dynamics (MD) simulations. As a result, three β2m variants were designed and characterized: W60G-Y63W, W60G-N83V and V85E. All mutants have displayed the expected structure, stability and aggregation propensity, giving insights into structural determinants of aggregation propensity of WT β2m.
II
To date, only a single natural β2m variant at residue Asp76, D76N β2m, has been reported. This mutation destabilizes the protein making it more prone to aggregation and has been related to a systemic and hereditary amyloid disorder.
To study the fundamental properties of protein dynamics and stability in solution and in crystal, D76N, WT and W60G β2m variants were chosen. These proteins display significant different stabilities and aggregation propensities, although conserving well comparable structures, with the same crystal symmetry and number of molecules in the asymmetric unit. These properties make them suitable as model system to obtain results free of spurious effects, reflecting the changes on protein dynamics related to the mutation.
Thus, these three variants were used to investigate the correlation between protein stability in solution and in crystalline form by Fourier transform infrared spectroscopy (FT-IR).
FT-IR spectra indicate that each β2m variant displays an increased structural order in the crystals compared to the protein in solution; temperature ramps show that increased melting temperatures for crystals compared to protein in solution. Nevertheless, the differences in protein stability between the three variants are well detectable in crystalline form and they well correlate with the trend observed in solution.
III
MHC-I complexes are hetero-trimers composed by the polymorphic heavy chain, the light chain β2m and an antigenic peptide.
The overall structural stability of the complex together with peptide-complex affinity, is fundamental for an effective presentation of the antigen: a strong peptide/MHC-I (pMHC) interaction and a time-extended peptide presentation trigger the best immunogenic CD8+ T-cell response.
Accordingly, aim of the work is the exploration of the impact on protein fold stability of complex-stabilizing point mutations on the tumour antigenic peptide NY–ESO157-165 (SLLMWITQC). This peptide is expressed by a broad range of tumour types, but not in healthy adult somatic tissue, making it an ideal cancer vaccine candidate.
The in vitro stability of eight complexes has been monitored following the thermal unfolding. All complexes bearing the mutated peptides displayed an increase in stability compared to that of the complex with the NY–ESO157-165 WT.
The structural contributions to the stability of the complexes have been investigated through X-ray crystallography. Thanks to the structural studies it has been possible to deepen the molecular characteristics determining peptide binding to MHC- I molecules and rationalize the optimization of the MHC- I anchor residues in tumour epitopes to enhance binding of the peptide to the complex.
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Rebodos, Robert Louie Fermo. "Implications of Oxidation on the Colloidal Stability of Magnetite Nanoparticles and Cluster." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77117.
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Synthetic nanomagnetite has been suggested as a potential reactant for the in-situ treatment of contaminated groundwater. Although the application of nanomagnetite for environmental remediation is promising, a full understanding of its reactivity has been deterred by the propensity of the nanoparticles to aggregate and form clusters. To characterize the factors responsible for this aggregation behavior, we determined the magnetic properties of magnetite using a superconducting quantum interference device (SQuID). Importantly, because magnetite readily reacts with O2 to produce maghemite, we analyzed the effect of oxidation on its magnetic properties. We observed that oxidation caused a decrease in the saturation magnetization and the anisotrophic barrier of magnetite resulting in less significant magnetic interactions between particles. Consequently, a decrease in the aggregation of magnetite clusters and a potential increase in stability are expected after oxidation. To support these findings, an extended series of experiments to measure the aggregation and the sedimentation of clusters of unoxidized and oxidized magnetite nanoparticles were conducted. Although the individual particle diameter remained constant after oxidation, the cluster size and the aggregation and sedimentation kinetics of magnetite were determined to be different. Oxidized samples of magnetite tended to have lower aggregation rates and were more resistant to sedimentation. These findings can be used to have a better understanding of the overall fate, transport, and reactivity of nanomagnetite, and to gain new insights on its role as a remediation agent in the subsurface environment.Ph. D.
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DeLong, George T. (George Thomas). "Solution Studies of the Structures and Stability of Mixed Lithium Alkoxide/Alkvllithium Aggregates." Thesis, University of North Texas, 1992. https://digital.library.unt.edu/ark:/67531/metadc279031/.
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New one- and two-dimensional NMR techniques were used to elucidate the solution structures of these complex mixtures. The system, lithium tert-butoxide/tert-butyllithium, was studied as a model system with O/Li ratios varying from 0/1 to 1/1. It was found that at low O/Li ratios, a single mixed tetrameric aggregate was formed. At higher O/Li ratios, mixed hexameric species were formed. Two other systems, lithium isopropoxide/iso-propyllithium and lithium n-propoxide/n-propyllithium were also studied at low O/Li ratios.
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Sifniotis, Vicki. "Towards The Development of Biobetter Therapeutic Whole Antibodies." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20829.
Full textAbstract:
The development of therapeutic antibodies has been revolutionary in the pharmaceutical industry due to the specificity of antibodies to a biological target and their ability to elicit a response that engages the immunological destruction of the target. As with all biologic pharmaceuticals, active antibody is lost in downstream production processes and long term storage due to intrinsic instability causing degradation and aggregation. Pharmaceutical formulations currently adopt an approach to reduce loss in aggregation through lyophilised product to be reconstituted only when in use, to large volumes appropriate for intravenous, or in some instances sub-cutaneous administration. This project explores avenues of identifying regions in the peptide structure of a model antibody (Trastuzumab) from which to improve intrinsic stability and improve affinity to its target. As many therapeutic antibody peptide structures have homologous constant regions, Adalimumab was used to show transferability and proof of concept with the modifications specific to improving antibody stability. Sites for modification were derived through in silico analysis of the crystal structures of antibody fragments. Trastuzumab and Adalimumab genes were cloned into suitable vectors to produce an optimised laboratory scale expression system. The modifications derived from in silico analysis were translated to Trastuzumab and Adalimumab through site directed mutagenesis. The mutant libraries were expressed for testing in vitro for stability and binding kinetics against their biological targets HER-2/TNF-a and Fcγ receptors. Our findings show that several of our rationally designed peptide modifications showed improvement in their targeted effect, and that can be translated to improving production and formulation strategies, as well as better treatment outcomes.
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Adams, Kimberly Ellen. "Influence of Vineyard Floor Management Practices on Soil Aggregate Stability, Total Soil Carbon and Grapevine Yield." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/612.
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Soil aggregates provide pore spaces of various sizes supplying water, gases and nutrients to plant roots and microorganisms, and facilitate moisture retention and availability. Soil aggregate stability is indicative of soil biological and structural health, and is increased by soil carbon derived from plant roots and the soil microbial biomass. Aggregate stability and soil carbon can be enhanced by increasing organic matter through compost additions or by planting cover crops. Additionally, aggregate stability is enhanced by arbuscular mycorrhizal fungi (AMF) that form a symbiotic association with plant roots, and consolidate soil particles into aggregates through hyphal networks and through the production of glomalin, binding soil particles together. The use of herbicides decreases soil carbon as it removes vegetation and the microorganisms associated with it. Soils having poor aggregate stability slake and disperse into primary soil particles becoming dense and subject to erosion when exposed to heavy rains. The use of herbicides amplifies this risk as it removes vegetation, leaving the soil bare, with nothing to absorb rainfall impact.
The effect of vineyard floor management practices on aggregate stability, soil carbon and grapevine fruit yield was studied at two vineyard sites located within the Estrella district of Paso Robles, CA. In late fall of 2008, treatments were applied to the vine line including an herbicide, an herbicide plus compost, a cover crop, a cover crop plus compost and a cover crop plus a fungal inoculant treatment. The control had no herbicides, compost, cover crop, or fungal inoculant applied to it. The cover crop treatments were applied at 30 lbs/ac consisting of a mixture of 20 % blando brome (Bromus hordeaceus), 20 % Zorro fescue (Vulpia myuros), 30 % crimson clover (Trifolium incarnatum) and 30 % subterranean clover (Trifolium subterraneum). Commercially available compost was applied at a rate of five tons per acre. The fungal inoculant was applied at eight pounds per acre, consisting of the AMF: Glomus intraradices, G. mosseae, G. aggregatum and G. etunicatum each at 32 propagules/ cc. Samples were collected in the spring of 2009 and the winter of 2010.
Percent carbon was significantly higher in the areas where compost applications were received (P=0.014). Cover crops did not significantly increase the level of carbon in the soil (P=0.253). Compost and cover crops significantly increased the amount of > 4.0 mm soil aggregates (P=0.004 for compost and P=0.027 for cover crops). Herbicide treatments significantly reduced the amount of > 4.0 mm aggregates (P=0.028). Fungal inoculants had no effect on > 4.0 mm aggregate stability (P=0.361). Compost significantly increased mean fruit weight (P=0.041). These results suggest that the addition of compost and cover crops are an effective way of increasing > 4.0 mm aggregates and compost alone is an effective way to increase soil carbon and fruit yield.
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Chevallier, Marie. "Stabilisation des émulsions laitières aux cours des traitements technologiques : action combinée des agrégats de protéines de lactosérum et des caséines." Thesis, Rennes, Agrocampus Ouest, 2017. http://www.theses.fr/2017NSARB294/document.
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Les émulsions laitières sont des systèmes thermodynamiquement instables qui doivent résister aux contraintes technologiques (chauffage, congélation) appliquées lors de leur fabrication ou usage. Les émulsions riches en protéines de lactosérum sont particulièrement sensibles et l’emploi d’additifs alimentaires est un moyen de ralentir leur déstabilisation. Dans l’objectif d’offrir des produits 100 % lait aux consommateurs, concevoir des émulsions, riches en protéines de lactosérum, sans additifs alimentaires et stables aux traitements technologiques, constitue un réel challenge. La stratégie employée dans ce projet de thèse a été de combiner les propriétés des agrégats de protéines de lactosérum et des caséines pour stabiliser des émulsions aux cours des traitements technologiques sur une large gamme de concentration.Des émulsions ont été préparées avec des agrégats de protéines de lactosérum de structure différente et avec différents ratios agrégats/caséines. Quelle que soit leur structure, la présence d’agrégats à la surface des globules gras déstabilise l’émulsion (gélification /séparation de phase) alors que dans la phase dispersante ceux-ci sont stables aux traitements technologiques. A l’inverse, les émulsions dont la surface des globules gras est recouverte de caséines sont très stables aux traitements technologiques. Ainsi, il est possible de moduler la stabilité des émulsions riches en protéines de lactosérum aux cours des traitements technologiques en exploitant les propriétés des agrégats et des caséines et en contrôlant leur répartition entre la surface des gloDairy emulsions are thermodynamically unstable systems, which have to be resistant to the technological treatments (heating, freezing/thawing) applied during their manufacture or use. Whey protein-rich emulsions are particularly sensitive to technological treatments and instabilities are currently tackled by the use of non-dairy additives. With aim to offer products that are more natural to consumers (additive-free), the preparation of whey protein-rich emulsions without additive and stable during technological treatments constitutes a major challenge for dairy companies. The strategy adopted during this thesis was to combine the properties of the whey proteins aggregates and caseins in order to stabilize emulsion during technological treatments in a large range of protein concentrationsEmulsions were prepared with various whey protein aggregates and various whey protein aggregates/caseins ratio. Whatever the whey protein aggregates, their presence at the fat droplet surface destabilize the emulsions (gelation/phase separation) whereas they are stable in the continuous phase of the emulsions during technological treatments. In contrast, emulsions are extremely stable during technological treatments when caseins fully cover the fat droplet surface. The results obtained highlighted the possibility of modulating the stability during technological treatments of whey protein-rich emulsions by combining the properties of the whey protein aggregates and the caseins and by controlling their repartition between the fat droplet surface and the continuous phase of the emulsion
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Johnsson, Markus. "Sterically stabilised liposomes and related lipid aggregates : Fundamental studies on aggragate structure and stability." Doctoral thesis, Uppsala University, Department of Physical Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-663.
Full textAbstract:
Various aspects of and approaches towards the steric stabilisation of liposomes have been investigated, mainly by use of fluorescence techniques and cryo-transmission electron microscopy (cryo-TEM). It is shown that PEG(2000)-lipids can be incorporated in the liposome membrane up to a critical concentration of 8-10 mol% without any observable structural perturbations. Above 10 mol%, a breakdown of the liposome structure into flat lamellar discs was observed. The sterically stabilised liposomes displayed similar, or even reduced, membrane permeability as compared with conventional liposomes. The presence of PEG-lipids in the EPC membrane was shown to affect the liposome-to-micelle transition in mixtures containing OG. Little or no effects of the PEG-lipids were found on the transition in mixtures containing C12E8.
The interactions between a number of PEO-PPO-PEO triblock copolymers and PC or PC/Chol liposomes have been investigated. It is shown that these polymers adsorb rapidly onto the liposome surface and induce a substantial increase in membrane permeability as well as structural perturbations. No evidence of an effective steric stabilisation due to the presence of the polymers at the membrane surface was found. This was shown, by the use of a QCM-technique, to be a consequence of the weak interaction between the polymers and the lipid membrane.
Dispersions of reversed lipid phases in mixtures of DOPE and PEG-lipids were characterised using cryo-TEM. Dispersions displaying reasonable colloidal stability were obtained and particles exhibiting a periodic dense inner structure were observed.
PEG-lipid micelles were characterised mainly using light scattering techniques. Micelle aggregation numbers and hydrodynamic radii were determined as a function of temperature. It is shown that the inter-micellar interactions are dominated by the steric repulsion.
PEG-lipid stabilised liposomes loaded with boronated drugs intended for BNCT have been characterised. The drugs were efficiently encapsulated into the liposomes, resulting in a drug precipitation in the water core of the liposomes.
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Pothier, Laura J. "Effects of amino acid substitutions on the conformation and stability of A[beta]₁₆₋₂₂ aggregates /." Connect to online version, 2007. http://ada.mtholyoke.edu/setr/websrc/pdfs/www/2007/213.pdf.
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Peduzzo, Alessia [Verfasser]. "Mechanistic insights into α-synuclein aggregation: from fibril stability to surface nucleation / Alessia Peduzzo." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2019. http://d-nb.info/1201881978/34.
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Herman, David Joel. "Stabilization of weakly charged microparticles using highly charged nanoparticles." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/34345.
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An experimental investigation was conducted to evaluate the possible use of highly-charged spherical nanoparticles to stabilize an aqueous dispersion of weakly-charged microspheres. At low pH values, the surface of silica is weakly charged, which leads to flocculation of colloidal suspensions of silica microspheres. Binary solutions of weakly charged silica microspheres and highly charged polystyrene latex nanoparticles result in adsorption of the nanoparticles onto the surface of the silica microspheres. This effectively â rechargesâ the silica spheres, with effective zeta potentials increased to the range that is unfavorable for flocculation of microspheres in a silica-only solution. However, this does not guarantee stability, and comparisons between positively charged amidine latex nanoparticles and negatively charged sulfate latex nanoparticles indicate that the degree of coverage plays an important role in the restabilization. The sulfate latex nanoparticles do not cover the surface sufficiently, and though they seemingly provide sufficient charge, the weakly charged patches of the exposed silica substrate can lead to flocculation. The amidine latex nanoparticles, on the other hand, cover the surface more completely, and effectively prevent flocculation of the silica microspheres. The mechanisms responsible for this different adsorption and stabilizing behavior are not entirely understood, as both the amidine and sulfate latex nanoparticles are of similar size and the magnitude of the zeta potentials of the different particle types are comparable.Master of Science
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Flaugh, Shannon L. "Folding, stability and aggregation of the long-lived eye lens protein human gamma D crystallin." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34572.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2006.Vita.
Includes bibliographical references (p. 179-194).
Human [gamma]D crystallin (H[gamma]D-Crys) is a monomeric, two domain, primarily P-sheet protein found in high concentrations in the human eye lens. H[gamma]D-Crys and other crystallins are found in insoluble protein inclusions associated with the eye disease cataract. H[gamma]D-Crys is expressed in utero and does not regenerate during life, thus necessitating high stability and solubility. Covalent damage, including glutamine deamidation, of the lens crystallins increases with age and as a result of exposure to environmental insults. Such covalent damage may cause partial-unfolding into aggregation-prone confomations that cause cataract. The in vitro stability of H[gamma]D-Crys was analyzed in the denaturant guanidine h[gamma]Drochloride at pH 7.0 and 370C. An off-pathway aggregation reaction that competed with refolding was previously reported when H[gamma]D-Crys was refolded to less than 1 M GuHC1. Equilibrium transitions of H[gamma]D-Crys were best fit to a three-state model suggesting the presence of a partially-folded intermediate that likely had a structured C-terminal domain (C-td) and unstructured N-terminal domain (N-td). Similarly, previous analyses revealed a sequential domain refolding pathway where the C-td refolds first followed by the N-td.
(cont.) These findings suggest that the inter-domain interface of H[gamma]D-Crys is important in both folding and stability. The domain interface of H[gamma]D-Crys contains a central h[gamma]Drophobic cluster of six residues and two pairs of peripheral interacting residues. To test this importance of these residues in folding and stability, site-directed alanine mutants were constructed at all ten positions and properties of the mutant proteins were analyzed. Single mutations of h[gamma]Drophobic domain interface residues caused a decrease in stability of the N-td, but did not affect stability of the C-td. Similarly, stability of the N-td but not the C-td was reduced as a result of single and double mutations of peripheral interface residues. Minimal to no interaction energy was observed for the peripheral residues suggesting they contribute to stability indirectly, perhaps by shielding the central h[gamma]Drophobic cluster from solvent. Both the h[gamma]Drophobic and peripheral domain interface alanine mutants also had reduced rates of productive refolding for the N-td while refolding rates for the C-td were unchanged. These results suggest a productive folding pathway where the C-td refolds first and domain interface residues of the structured C-td act as a nucleating center for refolding of the N-td.
(cont.) Effects on N-td refolding rates were most prominent for the h[gamma]Drophobic residues indicating the importance of proper h[gamma]Drophobic burial during refolding. The peripheral domain interface residues of H[gamma]D-Crys include a pair of two glutamines that are targets for covalent damage during aging. Deamidation mimics at these sites were constructed by site directed mutagenesis of glutamine to glutamate. Properties of the mutants were analyzed to assess the affects of deamidation on stability and folding. Similar to the alanine mutants at these sites, the deamidation mutants had a destabilized N-td but not C-td at pH 7.0. In contrast, stabilities of the mutants were indistinguishable from wild type at pH 3.0. The N-td of the deamidation mutants also unfolded faster than that of wild type during kinetic unfolding. These results indicate that deamidation of domain interface glutamines destabilizes H[gamma]D-Crys and lowers the kinetic barrier to unfolding. A reduction in the thermodynamic and kinetic stability as a result of domain interface deamidation could result in the population of partially-unfolded conformations in the lens that may aggregate through mechanisms such as domain swapping or loop-sheet insertion.
by Shannon L. Flaugh.
Ph.D.
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Mills-Henry, Ishara Amenti Rakem. "Stability, unfolding, and aggregation of the gamma D and gamma S human eye lens crystallins." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38627.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2007.Includes bibliographical references (v. 2, leaves 189-208).
The transparency of the human eye lens depends on the properties of the a- crystallin and py-crystallin families of proteins, which accumulate to very high concentrations in mature lens fiber cells. The 0- and y-crystallins are thought to be primarily structural proteins while a-crystallin possess an additional chaperone activity. Aggregation of partially unfolded or covalently damaged forms of these proteins results in cataract, which is the leading cause of blindness in the world. The biochemical basis of the very high crystallin stability, and the nature of the misfolded, modified, or aggregated states, are thus of considerable importance in understanding the etiology of loss of lens transparency. All vertebrate P- and y-crystallins are homologous and contain two highly symmetrical domains with a hydrophobic interface connected by an interdomain linker. The overall sequences, fold topology, and domain interfaces of vertebrate py-crystallins are highly conserved. The two domain 0- and y-crystallins are believed to have evolved by gene duplication and fusion from an ancestral single domain py-crystallin. This thesis is focused on stability and aggregation properties of human yD crystallin (yDwT) and human yS crystallin (ySwT), two of the most abundant proteins in the human lens.
(cont.) Terminally differentiated fiber cells in the central nucleus of the lens are enucleated and devoid of organelles. The yD crystallins synthesized in utero must remain stable and soluble throughout life. The yS protein is more prevalent in the cortical regions of the lens, where protein degradation and synthesis do occur. Given the importance of long-term solubility for the crystallins, it seems likely that selection for the two-domain form is related to the need for very long-term stability. Comparison of the stabilities of the isolated domains and the intact protein indicated that the domain interface contributes a AGH20 of~ 4.2 kcal*mol-l to the stability of the complete yDwT two-domain protein. The differential stability observed for the yD isolated domains was not as distinct for the yS isolated domains. These results support the idea that selection for increased thermal stability was one of the factors leading to the evolution of two domain crystallins. A distinct hysteresis occurs during equilibrium unfolding and refolding, due to a kinetic barrier in the unfolding pathway. By extrapolating kinetic unfolding results from denaturing GuHCl concentrations to buffer, I show that the ti2 for the initial unfolding step is -19 years. The value extrapolated for the YSwT is not as long, though still significant. This supports the earlier conclusion that the domain interface is an important source of stability.
(cont.) Previous studies had shown that upon dilution from denaturant partially folded intermediates of yD crystallin formed highly ordered fibrous aggregates that were not amyloid in nature. This aggregation reaction of yDwT polypeptide chains competing with productive refolding provided a model for cataractogenesis in vitro. The structurally homologous ySwT crystallin did not exhibit an off-pathway aggregation under the same conditions as yDwT. This suggested that the pathway of aggregation involved specific amino acids or sequences essential for association and was not a general feature of the y- crystallins. To investigate this disparity between two structurally similar crystallins, chimera proteins were created in an attempt to narrow down regions of the protein that promoted aggregation in DwTr or regions in ySwT that inhibited aggregation. The aggregation behavior upon refolding was analyzed for the chimeras and isolated single domains. Partitioning of refolding chains into the aggregation pathway was strongest for the full-length proteins that retained the yD interface. This result is consistent with a domain swapping mechanism for the off-pathway aggregation of the crystallins. This aggregation reaction may be coupled to the increased stability of the yD-protein, as a kind of evolutionary cost of the extremely stable and long-lived native state conformation.
by Ishara Amenti Rakem Mills-Henry.
Ph.D.
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Krchnák, Martin. "Sestava ocelových zásobníků kameniva." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240079.
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This diploma thesis describes the design and assessment of steel structural design of the steel aggregate bins including roofing. The construction has a ground plan of about 33 x 9 m and it is divided into 8 cells bins. Main material is steel, grade S355 and S235. There is developed a static analysis of the main load-bearing parts of the structure, including joints and selected details.
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Ghiafeh, Davoodi Majid. "Long term stability of concrete made from red sand in a marine environment." Thesis, Curtin University, 2008. http://hdl.handle.net/20.500.11937/1108.
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The desire of the minerals industry to be more sustainable has led towards the increasing development of by-products. One such industry is the production of Alumina. The Alumina industry in Australia is the major producer of alumina in the western world with over 25 million tonnes of Bauxite Residue per annum. Alcoa World Alumina (Alcoa) has three refineries in Western Australia producing approximately 20,000 tonnes of Mud and a similar level of Red Sand each day. These as yet unutilised potential resources are being stockpiled, occupying a significant footprint. It is widely recognised within industry that there would be economic, environment and social benefits if a sustainable use for these materials were found. One such potential by-product is the production of coarse bauxite residue (Red Sand), neutralised and washed low in salt. The main purpose of this research was to establish a potential market for this material, through scientific evaluation of Red Sand as a replacement of natural fine aggregate (Natural Yellow Sand) in concrete mixes. For this research, the mixed stream of Bauxite Residue (fine and coarse) obtained in the Bayer process was neutralized by a process of carbonation then washed using cyclones and counter current wash towers to a value added byproduct. The coarse particles (Washed and Carbonated Sand-WCS) of the stream were separated by Wet High Intensity Magnetic Separation technique (WHIMS) so that different segments such as High Iron Sand (HIS) and Low Iron Sand (LIS) were formed. Physical, chemical and mineralogical properties of these materials have been tested and compared with that of natural sand. Several mixes of concrete were then designed using Red Sand as a fine aggregate in order to verify their effects on strength and durability indicators of concrete.The comparative analysis between normal mix proportions and the mix proportions utilizing Red Sand was also achieved. In addition, the impact of marine environment on concrete mix design and properties of manufactured concrete were evaluated with a series of standard laboratory tests. The findings were promising in terms of both mechanical properties and durability and suggested that Red Sand, in particular Low Iron Sand is likely to be effective in place of fine aggregates and can be used within marine grade concrete with no major differences when compared to normal concrete. From the results obtained, it can be deduced that this material can be used in a wide range of concrete applications in Civil Engineering and Construction.
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Larišová, Lucie. "Vliv vodní eroze na vybrané fyzikální vlastnosti půdy." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-392276.
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The aim of the dissertation thesis is the assessment of the degradation of selected soil properties due to water erosion, including the temporal dynamics of these properties and the assessment of how this change affects the cumulative infiltration of the soil in watershed. Between 2012 and 2015, undisturbed and disturbed soil samples were collected on three experimental areas and the cumulative infiltration of the soil was measured. Experimental areas were selected on sloping, erosion-endangered blocks of arable land, in three cadastral territories of the Czech Republic, and this in the cadastral areas of Větřkovice, Čejkovice and Hustopeče. The cumulative infiltration was measured in three landscapes positions of the slope and soil samples were collected in three landscapes positions of the slope, at soil crust, topsoil and subsoil. In the Pedological Laboratory at the Institute of Landscape Water Management, Brno University of Technology, the particle density, bulk density, porosity, soil texture and water stable aggregates were determined from the samples taken. The cumulative infiltration of the soil was measured using the Double Ring Infiltrometer, the Mini Disc Infiltrometer and the mobile rainfall simulator. Using one-way analysis of variance to analyze the differences among soil samples and infiltration test. In addition, the dependence of soil crust formation, its physical properties and its influence on the cumulative infiltration of the soil were monitored on the areas.
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Metzman, Jonathan Seth. "Nanoparticle Encapsulation and Aggregation Control in Anti-reflection Coatings and Organic Photovoltaics." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85580.
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Nanoparticles present a myriad of physical, optical, electrical, and chemical properties that provide valuable functionality to thin-film technologies. In order to successfully exploit these aspects of nanoparticles, appropriate dispersion and stability measures must be implemented. In this dissertation, different types of nanoparticles are coated with polymer and metallic layers to enable their effectiveness in both anti-reflection coatings (ARCs) and organic photovoltaics (OPVs).
Ionic self-assembled multilayers (ISAMs) fabrication of poly(allylamine hydrochloride) (PAH) and silica nanoparticles (SiO2 NPs) results in highly-transparent, porous ARCs. However, the ionic bonding and low contact area between the film constituents lack sufficient mechanical and chemical stability necessary for commercial application. Chemical stability was established in the film by the encapsulation of SiO2 NPs by a photo-crosslinkable polyelectrolyte, diazo-resin (DAR) to make modified silica nanoparticles (MSNPs). UV-irradiation induced decomposition of the diazonium group and the development of covalent bonds with polyanions. Crosslinked MSNP/poly(styrene sulfonate) (PSS) ISAMs exhibited excellent anti-reflectivity (transmittance >98%, reflectance <0.2% in the visible range) and chemical stability against dissolution in a ternary solvent. Mechanical stability was also achieved by the incorporation of two additional PAH and poly(acrylic acid) (PAA) layers to create PAH/PAA/PAH/SiO2 NP interlayer ISAM ARCs. Thermal crosslinking of PAH and PAA facilitates the formation of covalent amide bonds between the two polyelectrolytes, as confirmed by FTIR. Since PAH and PAA are both weak polyelectrolytes, adjustment of the solution pH causes significant variations in the polymer chain charge densities. At low PAA pH, the decreased chain charge densities caused large SiO2 NP encapsulation thicknesses in the film with great mechanical stability, but poor anti-reflection (≤97% transmittance). At high PAA pH, the high chain charge densities induced thin encapsulation layers, insufficient mechanical stability, but excellent anti-reflection. At trade-off between the two extremes was founded at a PAA pH of 5.2 with excellent anti-reflection (less than 99% transmittance) and sufficient mechanical stability. The normal force required for scratch initiation was increased by a factor of seven for films made from a pH of 5.2 compared to those made from a pH of 6.0.
Organic photovoltaics (OPVs) are an attractive area of solar cell research due to their inexpensive nature, ease of large-scale fabrication, flexibility, and low-weight. The introduction of the bulk heterojunction greatly improved charge transport and OPV performance by the blending of the active layer electron donor and acceptor materials, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), into an interpenetrating network with high interfacial area between adjacent nanodomains. However, constrained active layer thicknesses restrict the total optical absorption and device performance. The localized surface plasmon resonance (LSPR) of plasmonic nanoparticles, such as anisotropic silver nanoplates (AgNPs), provides large local field enhancements and in coupling with the active layer, substantial optical absorption improvements can be realized. AgNPs were first integrated into the hole-transport layer (PEDOT:PSS) by ISAM deposition. Here, PEDOT:PSS was used as a negatively-charged ISAM layer. Encapsulation of the AgNPs by PAH (ENPs) provided a positive surface charge and allowed for the creation of ENP/PEDOT:PSS ISAMs. Stability against acidic etching by PEDOT:PSS was imparted to the AgNPs by coating the edges with gold (AuAgNPs). The AuAgNP ISAMs substantially improved the optical absorption, but were ineffective at increasing the device performance. The dispersion effects of functionalized polymer coatings on AgNPs were also deeply investigated. Functionalized AgNPs were dispersed in methanol and spin-coated onto the active layer. When the AgNPs possessed hydrophilic properties, such as unfunctionalized or functionalized by poly(ethylene glycol) methyl ether thiol (PEG-SH), they formed large aggregates due to unfavorable interactions with the hydrophobic P3HT:PCBM layer. However, the hydrophobic functionalization of AgNPs with thiol-terminated polystyrene (PS-SH) (PS-AgNPs) resulted in excellent dispersion, optical absorption enhancements, and device performance improvements. At a PS-AgNP concentration of 0.57 nM, the device efficiency was increased by 32% over the reference devices.Ph. D.
Investigations are presented on the quality of distribution or dispersion of functional inorganic (composed of silicon dioxide or silver) particles that have dimensions of less than 100 nanometers, called nanoparticles. The nanoparticle surfaces were covered with polymer layers, where polymers are organic materials with repeating molecular structures. The study of these nanoparticle distribution effects were first examined in anti-reflection coatings (ARCs). ARCs induce transparency of windows or glasses through a reduction in the reflection of light. Here, the ARCs were fabricated as self-assembled thin-films (films with thicknesses ranging from 1 to 2000 nanometers). The self-assembly process here was carried out by immersing a charged substrate (microscope slide) into a solution with an oppositely-charged material. The attraction of the material to the substrate leads to thin-film growth. The process can continue by sequentially immersing the thin-film into oppositely-charged solutions for a desired number of thin-film layers. This technique is called ionic self-assembled multilayers (ISAMs). ARCs created by ISAM with charged polymers (polyelectrolytes) and silicon dioxide nanoparticles (SiO2 NPs) can lead to highly-transparent films, but unfortunately, they lack the stability and scratch-resistance necessary for commercial applications. In this dissertation, we address the lack of stability in the ISAM ARCs by adding additional polyelectrolyte layers that can develop strong, covalent bonds, while also examining nanoparticle dispersive properties. First, SiO2 NP surfaces were coated in solution with a polyelectrolyte called diazo-resin, which can form covalent bonds by UV-light exposure of the film. After tuning the concentration for the added diazo-resin, the coated SiO2 NPs were used to make ARCs ISAM films. The ARCs had excellent nanoparticle dispersion, high levels of transparency, and chemical stability. Chemically stability entails that the integrity of the film was unaffected by exposure to polar organic solvents or strong polyelectrolytes. In a second method, two additional v polyelectrolyte layers were added into the original polyelectrolyte/SiO2 NP design. Here, heating of the film to 200 oC temperatures induced strong covalent bonding between the polyelectrolytes. Variation of the solution pH dramatically changed the polyelectrolyte thickness, the nanoparticle dispersion, the scratch-resistance, and the anti-reflection. An optimum trade-off was discovered at a pH of 5.2, where the anti-reflection was excellent (amount of transmitted light over 99%), along with a substantially improved scratch-resistance. A change of pH from 6.0 (highest tested pH) to 5.2 (optimal) caused a difference in the scratch-resistance by a factor of seven. In these findings, we introduce stability enhancing properties from films composed purely of polyelectrolytes into nanoparticle-containing ISAM films. We also show that a simple adjustment of solution parameters, such as the pH value, can cause substantial differences in the film properties. Nanoparticle dispersion properties were next investigated in organic photovoltaics (OPVs) OPVs use semiconducting polymers to convert sunlight into usable electricity. They have many advantages over traditional solar cells, including their simple processing, low-cost, flexibility, and lightweight. However, OPVs are limited by their total optical absorption or the amount of light that can potentially be converted to electricity. The addition of plasmonic nanoparticles into an OPV device is a suitable way to increase optical absorption without changing the other device properties. Plasmonic nanoparticles, which are composed of noble metals (such as silver or gold), act as “light antennas” that concentrate incoming light and radiate it around the particle. In this dissertation, we investigate the dispersion and stability effects of polymer or metallic layers on silver nanoplates (AgNPs). The stability of the AgNPs was found to be greatly enhanced by coating the nanoparticle edges with a thin gold layer (AuAgNPs). AuAgNPs could then be introduced into a conductive, acidic layer of the OPVs (PEDOT:PSS) to increase the overall light absorption, which otherwise would be impossible with uncoated AgNPs. Next, the AgNPs were distributed on top of the photoactive layer or the layer that is responsible for absorbing light. Coating the AgNPs with a polystyrene polymer layer (PS-AgNPs) allowed for excellent dispersion on this layer and contrastingly, dispersion of the uncoated AgNPs was poor. An increased amount PS-AgNPs added on top of the photoactive layer progressively increased the optical absorption of the OPV devices. However, trends were quite different for the power conversion efficiency or the ratio of electricity power to sunlight power in the OPV device. The greatest PCE enhancements (27 – 32%) were found at a relatively low coverage level (using a solution concentration of 0.29 to 0.57 nM) of the PS-AgNPs on the photoactive layer.
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Vahidnia, Arash. "Wide area control through aggregation of power systems." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/61186/1/Arash_Vahidnia_Thesis.pdf.
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This thesis was a step forward in improving the stability of power systems by applying new control and modelling techniques. The developed methods use the data obtained from voltage angle measurement devices which are synchronized with GPS signals to stabilize the system and avoid system-wide blackouts in the event of severe faults.
New approaches were developed in this research for identifying and estimating reduced dynamic system models using phasor measurement units. The main goal of this research is achieved by integrating the developed methods to obtain a feasible wide-area control system for stabilizing the power systems.
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Joshi, Gyawali Ayush. "A fresh soil health perspective: Soil health dynamics and improved measurement techniques." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/89949.
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Encouraging greater implementation of conservation agriculture practices such as reduced tillage and cover crops may require better understanding of the effect of these practices on soil health. The overall objective of this study was to quantify soil health dynamics due to conservation agriculture practices and address methodological gaps in terms of measuring soil health parameters. We developed five sites across the state of Virginia; each site had replicated plots with combinations of reduced tillage versus disk tillage and wintertime cover crops versus no cover crops as experimental treatments. Soil and plant samples were collected 1-2 times per year for 3 years, and were analyzed for 30 soil health parameters. The parameters were first evaluated to determine if any consistently detected treatment differences. We then quantified the temporal dynamics of the eight most responsive soil health parameters, while considering influences of soil water content at time of tillage, cover crop biomass, and previous land management history.
Of the analyzed parameters, only 2-4 mm aggregate stability and magnesium showed high responsiveness and consistency in identifying tillage and cover crop effects. None of the parameters detected treatment differences in all sites or at all times, yet samples collected after high biomass cover crops or after tillage in wet conditions tended to show significant treatment differences for multiple indicators. The previous history of management in each site may have affected trends in aggregate stability, but did not appear to influence other indicators.
As soil aggregate stability was found to be the most important soil health parameter, our third study developed an improved method for measuring soil aggregate stability. This new method, Integrated Aggregate Stability (IAS), interprets aggregate stability using a laser diffraction machine. Overall, IAS showed higher correlation with the wet sieving method (R2 = 0.49 to 0.59) than widely used median aggregate size (d50) (R2 = 0.09 to 0.27). IAS can also quantify stability of macro- and micro-sized aggregates, which d50 cannot. When comparing between IAS and wet sieving, IAS requires considerably less time and sample amounts.
Our fourth study focused on creating an inexpensive yet accurate tool for measuring soil respiration, as microbial assessments based on respiration rates have great potential for detecting rapid changes in soil health. Using an Arduino-based infrared gas analyzer (IRGA) sensor, we developed the Soil Microbial Activity Assessment Contraption (SMAAC) for less than $150. Our results show that SMAAC provided consistent readings with a commercial IRGA unit when tested using three different configurations.
Altogether, the research presented in this dissertation identifies important soil health parameters and quantifies their temporal and between-site dynamics. Using this narrower set of indicators can help producers and practitioners save resources when conducting measurements to assess soil health effects of agricultural practices. Further, this work also provides improved measurement techniques for useful soil health parameters like aggregate stability and soil respiration. These findings and innovations should help to encourage greater adoption of agricultural management practices that build and preserve soil health.Doctor of Philosophy
If we want to make sure that ample and safe food is available to future generations, then it is time that we produce food without damaging the soil. Many widely used soil management techniques like tillage and leaving the field bare can harm the soil and decrease productivity in the long run. One potential technique to produce food while protecting the soil and environment is conservation agriculture, which can include reduced tillage and cover cropping. Reduced tillage is a technique in which we grow food without majorly disturbing the soil, while cover crops are planted when cash crops are not in the field in order to improve or sustain the soil. Understanding the soil-related benefits of conservation agriculture practices is important to encourage farmers to adopt these practices. In this study we tested the effects on soils of reduced tillage and cover crop practices versus conventional tillage and bare soil practices, using five locations across Virginia. We also developed improved methods for measuring two informative soil parameters. We found that, when looking at all of our five sites, the stability of soil aggregates, the rate at which water enters soil, and the nutrients in surface soils were all affected by the type of management that the soils were subjected to. Reduced tillage increased stability of soil aggregates when compared with conventional till. This increased stability of aggregates indicators lower potential for surface water runoff, erosion, and flooding when we practice reduced tillage. Cover cropping also increased stability of soil aggregates, especially when the cover crops attained substantial above-ground mass. Soil nutrients (which are essential for plants to grow) were also overall higher in the surface soil layers under no-till. Since the stability of soil aggregates was found to be an important benefit of CA practices, we also perceived a need for a better method for measuring stability of these aggregates. In response, we developed a new index called Integrated Aggregate Stability (IAS). IAS was found to give similar results as established methods, but the time required to get IAS result is about 10 minutes, whereas the time required for established methods like wet sieving is around 2 days. IAS measurements are therefore both accurate and quick to perform. We also focused on developing an inexpensive tool for measuring soil respiration. Soil respiration-based measurements help us to understand the activity of microbes in the soil. These microbes are very important for soils to function. Our tool, Soil Microbial Activity Assessment Contraption (SMAAC), was very consistent with a currently used tool and shows high potential for future use. Altogether, we found that no-tillage and cover cropping can increase stability of soil aggregates even within 1-3 years of starting those practices. No-till can also increase nutrient concentrations in the top soil layer. The tools and innovations developed in this study have the potential to increase the ability of farmers to assess soil health and also encourage greater adoption of conservation agriculture practices.
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Pokhrel, Lok R. "Evaluation of Colloidal Stability and Ecotoxicity of Metal-based Nanoparticles in the Aquatic and Terrestrial Systems." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etd/1132.
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Intrinsic to the many nano-enabled products are atomic-size multifunctional engineered nanomaterials, which upon release contaminate the environments, raising considerable health and safety concerns. This Ph.D. dissertation is designed to investigate (i) whether metals or oxide nanoparticles are more toxic than ions, and if MetPLATETM bioassay is applicable as a rapid nanotoxicity screening tool; (ii) how variable water chemistry (dissolved organic carbon (DOC), pH, and hardness) and organic compounds (cysteine, humic acid, and trolox) modulate colloidal stability, ion release, and aquatic toxicity of silver nanoparticles (AgNP); and (iii) the developmental responses of crop plants exposed to Ag- or ZnO- (zinc oxide) nanoparticles.
Results suggest that the MetPLATEcan be considered a high-throughput screening tool for rapid nanotoxicity evaluation. Detectable changes in the colloidal diameter, surface charge, and plasmonic resonance revealed modulating effects of variable water chemistry and organic ligands on the particle stability, dissolution, and toxicity of AgNPs against Escherichia coli or Daphnia magna. Silver dissolution increased as a function of DOC concentrations but decreased with increasing hardness, pH, cysteine, or trolox levels. Notably, the dissociated Ag+ was inadequate to explain AgNP toxicity, and that the combined effect of AgNPs and dissolved Ag+ under each ligand treatment was lower than of AgNO3. Significant attenuation by trolox signifies an oxidative stress-mediated AgNP toxicity; its inability to attenuate AgNO3 toxicity, however, negates oxidative stress as Ag+ toxicity mechanism, and that cysteine could effectively quench free Ag+ to alleviate AgNO3 toxicity in D. magna. Surprisingly, DOC-AgNPs complex that apparently formed at higher DOC levels might have led daphnids filter-feed on aggregates, potentially elevating internal dose, and thus higher mortality. Maize root anatomy showed differential alterations upon exposure to AgNPs, ZnONPs, or their ions.
Overall, various metal-based nanoparticles revealed lower toxicity than their ions against multiple organisms. This study showed that particle size, surface properties, and ion release kinetics of AgNPs modify following release into aquatic environment, suggesting potential implications to ecosystem health and functions, and that caution be applied when extending one species toxicity results to another because obvious differences in organism biology—supporting species sensitivity paradigm—can significantly alter nanoparticle or ionic toxicity.
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Forero-Laverde, Germán. "The Impossible Trinity and Financial Stability. The Incidence of Trilemma Regimes on the (In)stability of Stock Markets and Credit Aggregates (1922-2013)." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663993.
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This dissertation discusses the accumulation and unwinding of financial imbalances in stock markets and credit aggregates in advanced economies since the interwar years until the present. The project is framed within the literature that arose with the Great Financial Crisis (2007-09) and that, against the mainstream consensus at the time, posits the existence of a financial cycle best characterised by the joint evolution of asset prices and credit. As a theoretical framework, we build on the open macroeconomy trilemma which indicates that policymakers can choose two out of three desirable and competing goals: fixed exchange rates, free capital flows, and autonomous monetary policy. We construct exchange rate and capital control regimes, for twelve advanced economies, from several sources to identify whether the behaviour of the boom-bust cycle in asset prices and credit growth and the drivers of financial instability are contingent on changing institutional conditions. Additionally, we test for the existence of a global financial cycle, proxied by the United States, which may be driving the evolution of both dependent variables.
In the first part of the dissertation which covers the literature review (chapter 1) and the data and methodology (chapter 2), we tackle the issue of measuring financial imbalances. To shift from the usual framework of financial crises towards the study of financial stability, we develop a new indicator for expansions and contractions in financial time series: the Local Bull Bear Indicator (LBBI). This technique, which constitutes the main methodological contribution of the dissertation, identifies above or below trend risk-adjusted returns, expressed as standard deviations. It allows for the identification of expansions and contractions to different time horizons, according to the persistence of shocks. As a data contribution, we offer a dating and characterisation of boom and bust phases in stock markets and credit aggregates, to different time horizons, for all the countries in the database.
Regarding the empirical findings, the second part of the dissertation presents panel data evidence using a panel corrected standard errors model (PCSE) for stocks (chapter 3) and credit (chapter 4). First, regarding the literature on global financial integration, we find evidence of a global financial cycle proxied by the US stock market and credit aggregates. Secondly, we find that the relationship between the dependent variables and a selection of control variables and trilemma-associated covariates is contingent on the way in which countries resolve the macroeconomic trilemma at different times. Finally, regarding financial stability, we find that beyond price stability, the variables that drive LBBIs are contingent on the way countries resolve the macroeconomic trilemma at different moments in history.
The third part of the dissertation presents time-series evidence for two case studies on the United Kingdom. Chapter 5 discusses whether the evolution of the stock market is contingent on domestic policy or trilemma regimes and finds that the usual story of global financial integration following a U-shape with peaks during the gold standard and the present-day inflation targeting regime requires nuance. The long-run co-movement between the stock market in the UK and the global cycle seems to peak in periods of heightened systemic risk such as the Second World War and the two oil shocks (1973, 1978). Finally, Chapter 6 finds that there is a financial cycle in the UK and that the causal relationship between stocks and credit for the UK is both time-varying and contingent on the regulatory framework in place. As the financial system becomes unregulated, credit growth seems to drive the behaviour in asset prices, allowing us to conclude, preliminarily, that while price stability is important, policymakers should include the evolution of credit aggregates in their policymaking function.
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Zhang, Li. "The study of phase separation in the miscibility gap and ion specific effects on the aggregation of soft matter system." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS106/document.
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Le procédé de séparation de phase est importante car elle détermine la structure des matériaux finaux. Il existe de nombreux systèmes qui ont plus d'une phase tels que des mousses et des gels. Les mousses sont des dispersions aqueuses de bulles de gaz dans une phase aqueuse et gels apparaissent lorsque certains microscopique unité de base commence à se rassembler formant un grand réseau solide qui enjambe l'espace macroscopique. Ils ont de nombreuses applications dans l'industrie et la vie quotidienne. Dans cette thèse, tout d'abord, je me concentre sur l'étude de différents types de séparation de phase. Deuxièmement, je étudié les effets spécifiques d'ions sur l'agrégation des particules colloïdales et tensioactif, le but est de faire des mousses stables. Dans la lacune de miscibilité il existe deux types de séparation de phase: la croissance nucléation et la décomposition spinodale, ils ont différents mécanismes et de la cinétique de croissance. Par conséquent, mon premier projet est d'étudier le processus d'évolution d'eux et de leurs effets sur la structure finale du matériau. Les gels peuvent être préparés par l'ajout de sel à la dispersion de particules colloïdales, ils ont un grand nombre d'applications telles que dans les aliments et la science des matériaux. Dans cette thèse, nous utilisons différents types de sels de comparer les propriétés de gel à partir de deux aspects macroscopiques et microscopiques. Obtenir des mousses stables est significatif dans la vue de leur beaucoup d'applications, mais les moyens de les faire sont pour la plupart compliqué. Dans cette thèse, nous pouvons obtenir des mousses stables par l'intermédiaire de deux façons. On est tout simplement en ajoutant des sels de solutions de tensioactifs, à travers lequel nous pouvons faire la mousse ultra-stable. Une autre façon est d'utiliser la phase de gel, nous avons étudié en tant que phase continue dans les mousses à arrêter le vieillissement de la moussePhase separation process is important as it determines the structure of the final materials. There are many systems that have more than one phase such as foams and gels. Aqueous foams are dispersions of gas bubbles in a water phase and gels appear when some basic microscopic unit starts to aggregate forming a large solid network that spans macroscopic space. They have many applications in industry and daily life. In the present thesis, firstly, I focus on studying different types of phase separation. Secondly, I studied the ion specific effects on the aggregation of colloidal particles and surfactant, the purpose is to make stable foams. In the miscibility gap there are two types of phase separation: Nucleation growth and spinodal decomposition, they have different growth mechanisms and kinetics. Therefore, my first p project is to investigate the evolution process of them and their effects to the final structure of material. Gels can be made by adding salt to the dispersion of colloidal particles, they have a large number of applications such as in food and material science. In this dissertation, we use different types of salts to compare gel properties from both macroscopic and microscopic aspects. Obtaining stable foams is significant in the view of their plenty of applications, but the ways to make them are mostly complicated. In this thesis, we can obtain stable foams via two ways. One is simply by adding salts to surfactant solutions, through which we can make ultrastable foam. Another way is using the gel phase we have studied as the continuous phase in foams to arrest the foam aging
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Bauer, Horst Hermann. "Physical stability of peptide pharmaceuticals : aggregation and conformational changes of human calcitonin (hCT) in aqueous solution /." [S.l.] : [s.n.], 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10989.
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Molina, Diogenes. "Intelligent control and system aggregation techniques for improving rotor-angle stability of large-scale power systems." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50291.
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A variety of factors such as increasing electrical energy demand, slow expansion of transmission infrastructures, and electric energy market deregulation, are forcing utilities and system operators to operate power systems closer to their design limits. Operating under stressed regimes can have a detrimental effect on the rotor-angle stability of the system. This stability reduction is often reflected by the emergence or worsening of poorly damped low-frequency electromechanical oscillations. Without appropriate measures these can lead to costly blackouts. To guarantee system security, operators are sometimes forced to limit power transfers that are economically beneficial but that can result in poorly damped oscillations. Controllers that damp these oscillations can improve system reliability by preventing blackouts and provide long term economic gains by enabling more extensive utilization of the transmission infrastructure.
Previous research in the use of artificial neural network-based intelligent controllers for power system damping control has shown promise when tested in small power system models. However, these controllers do not scale-up well enough to be deployed in realistically-sized power systems. The work in this dissertation focuses on improving the scalability of intelligent power system stabilizing controls so that they can significantly improve the rotor-angle stability of large-scale power systems.
A framework for designing effective and robust intelligent controllers capable of scaling-up to large scale power systems is proposed. Extensive simulation results on a large-scale power system simulation model demonstrate the rotor-angle stability improvements attained by controllers designed using this framework.
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Quadling, Amanda Gail. "The role of aggregates in the thermal stability of Mg-PSZ refractories for vacuum induction melting." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/28684.
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Mg-PSZ refractories used as vacuum induction melting crucibles are particle-reinforced composites with aggregate and matrix phases comprising fused zirconia. Three commercial varieties were cycled eight times to service temperatures and their microstructural and thermomechanical evolution investigated, with focus placed on the aggregate populations. Two refractories, with large aggregates of similar size, were found to retain stiffness after cycling but in the refractory containing aggregates with high stabiliser levels, reaction between the stabiliser and Al and Si impurities produced secondary phases. Volume changes accompanying formation of these phases, and subsequent thermal expansion mismatches, led to aggregate break-up with consequent reductions in refractory toughness and strength. Secondary phases developed only rarely in the aggregates (with lower levels of stabiliser) of the second refractory. These aggregates remained intact and the refractory retained its toughness and strength. A third refractory contained small, unstabilised aggregates in a stabilised matrix and the strain mismatches that ensued during polymorphic transformation damaged microstructural interfaces. Refractory stiffness halved within eight cycles and toughness and strength were lost. All three refractories displayed R-curve behaviour and quasi-stable fracture curves were observed during bend tests. The study shows that when using fused zirconia aggregates to design refractories, engineers need to i) limit stabiliser concentrations - a difference of just ± 1 wt% Mg (in the presence of impurity elements) may determine whether secondary phase formation occurs and ii) eliminate alumina and silica impurities when possible through substitution of zircon sand with baddeleyite as the source for fused zirconia.
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Nciizah, Adornis Dakarai. "Aggregate stability, crust formation, steady state infiltration and mode of seedling emergence in soils with various texture and mineralogy." Thesis, University of Fort Hare, 2014. http://hdl.handle.net/10353/d1015539.
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The general objective of this study was to quantify the interactive effects of soil texture and mineralogy on soil crusting, infiltration and erosion and the subsequent effects on maize seedling emergence and early development using soils collected from 14 ecotopes in the Eastern Cape Province. The specific objectives were to determine; i) particulate organic matter, soil texture and mineralogy relations, ii) aggregate stability and breakdown mechanisms as affected by soil texture and organic matter, iii) crust formation and steady state infiltration, iv) rainfall pattern effects on crusting, infiltration and erodibility and v) rainfall intensity effects on crusting and mode of seedling emergence. Particulate organic matter (POM) was fractionated into litter POM, coarse POM and fine POM. Both total soil organic matter (SOM) and the POM in each fraction were determined using the weight loss on ignition procedure. Most ecotopes were either sandy loam or sandy clay loam and primary minerals especially quartz dominated the soil mineralogy. The clay content was significantly related to the total SOM (r = 0.78), hematite (r = 0.83) and quartz (r = -0.74). Aggregate stability was determined following methods described by Le Bissonnais (1996) i.e. fast wetting (FW), slow wetting (SW) and wet stirring (WSt). Aggregate breakdown followed the order; slaking < mechanical breakdown < micro-cracking for most ecotopes except Lujiko Leeufontein and Amatola Jozini where SW and WSt resulted in the least MWD respectively. Aggregate stability was significantly correlated to POM only for FW and SW and only positive but not significant for WSt. To study crust formation, aggregate sizes <2, 2 to 3, 3 to 5 mm were exposed to 60 mm hr-1 simulated rainfall. Sieving structural crusts, ~0.2 to ~0.8 mm thick with a surface layer of loose grains overlying a thin plasmic layer, formed in all ecotopes. Crusts with strengths between 0.25 and 3.42 10-4 kg m-2 developed on the <2 mm compared to <2.23 10-4 kg m-2 in the >2 mm aggregates. The reverse occurred in Alice Jozini, which had relatively low clay content of 120 g kg-1. Two significantly different groups of the SSIR were observed. The SSIR was between 1.24 and 3.60 mm hr-1 in the group of ecotopes dominated by primary minerals and relatively lower clay content. In the second group, consisting one ecotope dominated by kaolinite and relatively higher clay content, the SSIR was 15.23 mm hr-1. Rainfall pattern i.e. rainfall applied either as an eight minute single rainstorm (SR) or four-two minute intermittent rainstorms (IR) separated by a 48 h drying period significantly (p < 0.05) affected crust strength, SSIR and erosion. The IR resulted in higher crust strength and SSIR than SR. The effect of rainfall pattern on SSIR was mostly influenced by the primary minerals namely, quartz. Three maize seeds of equal size were planted in plastic pots, pre-wetted by capillary action and then subjected to simulated rainfall at three intensities for 5 min. Rainfall intensity (30, 45 and 60 mm h-1) significantly (P < 0.05) affected crust strength and mean emergence day (MED) but not emergence percentage (EMP) and shoot length (P > 0.05). The 60 mm h-1 rainfall intensity resulted in the highest crust strength and MED.
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Cousen, S. M. L. "The assessment of soil aggregate stability to raindrop impact for some tropical soils material, with particular reference to iron." Thesis, University of Portsmouth, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375487.
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Soil aggregate stability to raindrop impact is df fundamental importance to many aspects of the soil system, in particular rainsplash erosion. This stability has been measured by use of single drop rainfall simulators, the characteristics and operation of which have, in the past, shown considerable variation. The drop sizes, impact frequency, drop fall height, chemistry of drop-forming liquid, aggregate pretreatment, and definition of breakdown affect the way in which the the apparatus can be used to define stability. In this thesis an apparatus is developed that is believed to give results with increased consistency and replicability. An index of stability (F) is evolved from data collected using the raindrop simulator which is then used to characterise a set of iron rich, tropical soils from Kenya and Mo~ambique. Information about the iron, textural, chemical and magnetic status of each soil sample is also collected and used to try to predict the stability index through a process of statistical modelling. Models for highly stable and poorly stable soils are developed and finally a definitive model that can be used for all the soils. The last section of this investigation attempts to try and explain the results in terms of the processes that might be operating in the soil. Specific reference is made to the iron content of the soils because of its natural abundance in the samples considered. The possible contributions of total iron, crystalline iron, amorphous iron and organic iron to aggregate stability are discussed.
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Lee, Sung Mun. "Role of aggregation conditions and presence of small heat shock proteins on abeta structure, stability and toxicity." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/3905.
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AlzheimerÂs disease (AD) is a neurodegenerative disorder that is one of such diseases associated with protein aggregation. Aβ is the main protein component of senile plaques in AD, and is neurotoxic when aggregated. In particular, soluble oligomeric forms of Aβ are closely related to neurotoxicity. In this dissertation, we examine the differences in Aβ aggregation intermediates, and final structures formed when only a simple modification in Aβ aggregation conditions is made, the presence or absence of mixing during aggregation. We show that intermediates in the aggregation pathway show significantly different structural rearrangements. The protein stabilities of Αβ species show that spherical aggregates corresponding to the most toxic Αβ species change their structure the most rapidly in denaturant, and that in general, increased toxicity correlated with decreased aggregate stability. In AlzheimerÂs disease, even delaying Aβ aggregation onset or slowing its progression might be therapeutically useful, as disease onset is late in life. Small heat shock proteins (sHsps) may be useful for prevention of Αβ aggregation, since sHsps can interact with partly folded intermediate states of proteins to prevent incorrect folding and aggregation. In this research, several small heat shock proteins (sHsps) are tested to prevent Aβ aggregation and toxicity. sHsps used in this research are Hsp17.7, Hsp27, and Hsp20. All types of Hsp20, Hsp20-MBP, His-Hsp20 and His-Hsp20 without 11 residues in C-terminus, can prevent Aβ1-40 aggregation. Hsp20 also prevents Aβ toxicity in the same concentration ranges of it aggregation prevention activity. Hsp17.7 and Hsp27, however, can inhibit Αβ1-40 aggregation but not toxicity. A number of experiments to examine the mechanism of Hsp20 suggest that multivalent binding of sHsp to Aβ is necessary for the toxicity prevention activity. Conclusively, different Aβ incubation conditions in vitro can affect the rate of Aβ fibril formation, the morphology, the toxicity and the conformation of intermediates in the aggregation pathway. Hsp20 rather than other sHsps may be a useful molecular model for the drug design of the next generation of Aβ aggregation inhibitors to be used in the treatment of AD.
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Ghiafeh, Davoodi Majid. "Long term stability of concrete made from red sand in a marine environment." Curtin University of Technology, School of Engineering, Department of Civil Engineering, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=115095.
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The desire of the minerals industry to be more sustainable has led towards the increasing development of by-products. One such industry is the production of Alumina. The Alumina industry in Australia is the major producer of alumina in the western world with over 25 million tonnes of Bauxite Residue per annum. Alcoa World Alumina (Alcoa) has three refineries in Western Australia producing approximately 20,000 tonnes of Mud and a similar level of Red Sand each day. These as yet unutilised potential resources are being stockpiled, occupying a significant footprint. It is widely recognised within industry that there would be economic, environment and social benefits if a sustainable use for these materials were found. One such potential by-product is the production of coarse bauxite residue (Red Sand), neutralised and washed low in salt. The main purpose of this research was to establish a potential market for this material, through scientific evaluation of Red Sand as a replacement of natural fine aggregate (Natural Yellow Sand) in concrete mixes. For this research, the mixed stream of Bauxite Residue (fine and coarse) obtained in the Bayer process was neutralized by a process of carbonation then washed using cyclones and counter current wash towers to a value added byproduct. The coarse particles (Washed and Carbonated Sand-WCS) of the stream were separated by Wet High Intensity Magnetic Separation technique (WHIMS) so that different segments such as High Iron Sand (HIS) and Low Iron Sand (LIS) were formed. Physical, chemical and mineralogical properties of these materials have been tested and compared with that of natural sand. Several mixes of concrete were then designed using Red Sand as a fine aggregate in order to verify their effects on strength and durability indicators of concrete.The comparative analysis between normal mix proportions and the mix proportions utilizing Red Sand was also achieved. In addition, the impact of marine environment on concrete mix design and properties of manufactured concrete were evaluated with a series of standard laboratory tests. The findings were promising in terms of both mechanical properties and durability and suggested that Red Sand, in particular Low Iron Sand is likely to be effective in place of fine aggregates and can be used within marine grade concrete with no major differences when compared to normal concrete. From the results obtained, it can be deduced that this material can be used in a wide range of concrete applications in Civil Engineering and Construction.