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1
Booman, Richard Albert 1957. "DETERMINATION OF LOSS MECHANISMS IN LONG RANGE SURFACE PLASMON MODES". Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/275490.
Testo completo
2
Wright, Samantha C. "Understanding the mechanisms behind surface elevation loss in ditched marshes". Thesis, Boston University, 2012. https://hdl.handle.net/2144/12682.
Testo completoAbstract (sommario):
Thesis (M.A.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Loss of surface elevation makes salt marshes more susceptible to impacts from accelerated sea level rise, such as vegetation drowning, die-off, and conversion of marsh to open water. The ultimate degradation of the salt marsh system is disastrous with ramifications ranging from loss of critical habitat to loss of an important buffer for coastal communities from storm surges. Effectively, a more comprehensive understanding of the mechanisms driving surface elevation loss in anthropogenically altered and degraded marshes is key to engineering successful marsh restoration projects, in an effort to reverse this trend. This study aims to achieve that goal in an area of a northern Massachusetts salt marsh with high man-made ditch density, through comparison of the hydrologic, sedimentary, and vegetative conditions to a non-ditched, reference portion of salt marsh. It was hypothesized that a decrease in subsurface hydroperiod through increased drainage, characteristic of areas of high ditch density, would allow for increased oxygen diffusion into the subsurface causing belowground decomposition rates to increase. This ultimately would lead to a reduction in organic matter, and without compensation from an inorganic sediment supply, marsh subsidence would occur. Water table levels, belowground biomass, bulk density data, and percent organic content data all supported this hypothesis, but direct analysis of the belowground litterbag component of this study did not demonstrate significant differences in decomposition rates between the ditched and non-ditched sites. Further study of belowground conditions, resulted in a live root turnover rate about twenty percent slower in the ditched marsh than in the non-ditched marsh. This suggests that turnover rates, not decomposition rates, may ultimately be the mechanism behind surface elevation loss in ditched marshes.
3
Nicoletti, Olivia. "Mapping surface plasmons of metal nanoparticles with electron energy-loss spectroscopy". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608025.
Testo completo
4
Oliver, Trevor N. "Surface acoustic wave devices with low loss and high frequency operation". Thesis, Aston University, 1989. http://publications.aston.ac.uk/8083/.
Testo completoAbstract (sommario):
This thesis describes an industrial research project carried out in collaboration with STC Components, Harlow, Essex. Technical and market trends in the use of surface acoustic wave (SAW) devices are reviewed. As a result, three areas not previously addressed by STC were identified: lower insertion loss designs, higher operating frequencies and improved temperature dependent stability. A review of the temperature performance of alternative lower insertion loss designs,shows that greater use could be made of the on-site quartz growing plant. Data is presented for quartz cuts in the ST-AT range. This data is used to modify the temperature performance of a SAW filter. Several recently identified quartz orientations have been tested. These are SST, LST and X33. Problems associated with each cut are described and devices demonstrated. LST quartz, although sensitive to accuracy of cut, is shown to have an improved temperature coefficient over the normal ST orientation. Results show that its use is restricted due to insertion loss variations with temperature. Effects associated with split-finger transducers on LST-quartz are described. Two low-loss options are studied, coupled resonator filters for very narrow bandwidth applications and single phase unidirectional transducers (SPUDT) for fractional bandwidths up to about 1%. Both designs can be implemented with one quarter wavelength transducer geometries at operating frequencies up to 1GHz. The SPUDT design utilised an existing impulse response model to provide analysis of ladder or rung transducers. A coupled resonator filter at 400MHz is demonstrated with a matched insertion loss of less than 3.5dB and bandwidth of 0.05%. A SPUDT device is designed as a re-timing filter for timing extraction in a long haul PCM transmission system. Filters operating at 565MHz are demonstrated with insertion losses of less than 6dB. This basic SPUDT design is extended to a maximally distributed version and demonstrated at 450MHz with 9.8dB insertion loss.
5
Oh, Tchang-hun. "Control of lateral diffraction loss in vertical-cavity surface-emitting lasers /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Testo completo
6
Gu, Xiaoxiong. "Modeling effects of random rough surface on conductor loss at microwave frequencies /". Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/5831.
Testo completo
7
Beasley, Jeffrey S. "Nitrogen Regime Influence on Nutrient and Sediment Surface Runoff During Vegetative Establishment of Bermudagrass". Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/31900.
Testo completoAbstract (sommario):
Bermudagrass (Cynodon dactylon (L.) Pers.) is a popular turfgrass used throughout the Southeast. Bermudagrass is established primarily as sprigs on large acreage sites. Currently, the industry standard practice (ISP) of fertilization during
bermudagrass sprig establishment is 48.8 kg N ha-1 wk-1. This fertilizer rate can be excessive on morphologically immature sprigs in the initial weeks of establishment, thus making the possibility of offsite surface runoff N events more likely. Two experiments were conducted in 2000 and 2001 where sprigs were established at 2, 4, 6, 8, and 10 weeks prior to applying simulated rainfall (WPRS) following N fertilization rates of the ISP or a lower initial N (LIN) rate of 12.2 kg N ha-1 wk-1 the first four weeks and then
48.8 kg N ha-1 wk-1 until full establishment. At the tenth week all treatments were subjected to rainfall simulation at 63.5 mm hr-1. Once surface runoff was induced, rainfall continued for thirty minutes during which time runoff samples were taken every five minutes and analyzed for sediment losses, N concentrations in the nitrate and ammonium forms, and phosphorus losses as dissolved reactive P (DRP). Experimental results indicate an ability to curb N losses through surface runoff during the initial weeks of sprig establishment following the LIN with only modest delays in sprig establishment.
Sprigs established for the same time period, under the ISP or LIN, were very similar in
growth, release of surface runoff, and sediment losses during runoff events.Master of Science
8
Dienes, Susanna. "Beneath the Surface". ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/1058.
Testo completoAbstract (sommario):
Beneath the Surface is a collection of seven individual literary nonfiction essays. Five of the essays are personal essays, and three come from the author's contribution to UNO's Katrina Narrative Project. The collection represents the author's cumulative body of work upon completion of her MFA in Creative Nonfiction Writing at UNO. Titles include: "Beneath the Surface, " "Hello, Harry, " "My One-Summer Bike, " "Just Like Jazzfest, " In Defense of Sodom, " "'Every Year It's Something, '" and "Revising my Approach. The essays explore themes such as sibling bereavement, Latin American travel, the incomprehensibility of death, experiencing new cultures, online teaching, and hurricane evacuation.
9
Prior, Mark Kevan. "Low frequency sound propagation in sea surface mixed layers in the presence of internal waves". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243119.
Testo completo
10
Finke, Manuela. "Studying food-related demineralisation of teeth with atomic force microscopy (AFM) and nanoindentation". Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/8d6de76b-d940-47ad-b0f6-095f56ddf54e.
Testo completo
11
Meneses, Bruno Miguel do Carmo Santana. "Influência de um fogo florestal na qualidade da água da Ribeira de São Domingos localizada na Região Oeste de Portugal". Master's thesis, ISA, 2013. http://hdl.handle.net/10400.5/6489.
Testo completoAbstract (sommario):
Mestrado em Engenharia do Ambiente - Instituto Superior de AgronomiaForest fires are responsible for several environmental problems, especially for polluting watercourses. In this dissertation we intend to evaluate the changes occurring in the physical and chemical constitution of water of São Domingos stream (crossing the municipalities of Lourinhã and Peniche, Portugal), in particular pH and nutrient content variation, related to surface runoff from the burnt area of the Cezaredas plateau, where a forest fire occurred at July 19th, 2012. Thus, water samples were collected in three points strategically chosen along this stream (one upstream of the burnt area and two downstream, one of the last being located immediately after the burnt area) from which the pH, the electrical conductivity and the concentrations of N, P, K, Na, Ca and Mg were assessed. The data obtained in the analysis of the samples collected downstream of the burnt area show an input of nutrients in the stream water and an evidence that nutrient transportation occurs in a higher degree during the first episodes of rainfall which are also responsible for generating surface runoff. This is due to the greater availability of nutrients in these areas and the reduced soil protection, a factor that facilitates surface runoff.
12
Davies, P. R. "Reactions of molecules at surfaces studied by photoelectron and electron energy loss spectroscopies". Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305213.
Testo completo
13
Young, Michael Howard 1961. "Monitoring near-surface soil water loss with time domain reflectometry and weighing lysimeters". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/191191.
Testo completoAbstract (sommario):
Three goals of this research were: 1) to develop a field-scale research facility that could be used for conducting a variety of soil water experiments in both deep (greater than 2 meters) and near-surface soils where the soil water balance could be accurately determined; 2) to develop a transient experimental technique for calibrating time domain reflectometry (TDR) probes; and 3) to study the use of vertically-installed TDR probes for measuring near-surface soil water movement in a field setting, and to compare these measurements with those made by the weighing lysimeter. The weighing lysimeter facility consists of two lysimeter tanks, 4.0 m deep and 2.5 m in diameter, which rest atop a scale with a resolution of ±200 g, equivalent to ±0.04 mm of water on the surface. Data collection is completely automated with a data logger and personal computer. Both lysimeters are instrumented with TDR probes, tensiometers, and pore water solution samplers; thermocouples are installed in one lysimeter for measuring temperature. The TDR probes were calibrated using a transient method known as upward infiltration. The method is rapid, allows the soil to remain unchanged during the experiment, and provides many data points. The upward infiltration method was tested using two different length probes in soils of three textures. Results show that the upward infiltration method is stable, repeatable, and provides accurate dielectric constants and calibration curves. Four, vertically-installed TDR probes of different lengths (200, 400, 600, and 800 mm) were placed in the lysimeter at ground surface to measure water added and water lost during a one-month period in the presence of daily irrigated turfgrass. The purpose of this study was to compare changes in soil water storage as measured by the TDR system, against measurements made using the weighing lysimeter. The TDR probes detected diurnal changes in water content due to irrigation and evapotranspiration, even when these amounts changed slightly from day to day. The TDR probes underestimated the measurements of both water added and water loss, as confirmed using measurements from the weighing lysimeter. The presence of a 47-mm thick biomass above the TDR waveguides retained water that otherwise would have percolated the soil surface into the measurement domain of the probes. Addition and loss of water in the biomass were recorded by the lysimeter, but not by the TDR probes, thus explaining the underestimation. Modeling of near-surface water movement with the HYDRUS model showed very similar water movement behavior as measured by the TDR probes. This confirms our hypothesis that TDR would a useful tool for measuring diurnal changes in water content for irrigation scheduling.
14
Flack, Paul E. 1960. "A method for establishing base-line soil loss rates on surface mine sites". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276985.
Testo completoAbstract (sommario):
Surface mining operations require a comparison of post-mining erosion rates with pre-mining soil loss to ascertain if remedial measures are needed. In this study the Universal Soil-Loss Equation (USLE) was modified to reflect conditions of western rangelands to develop a procedure for estimating pre-mining soil loss rates. The modification used back-calculation for the C-Factor and an adjusted R-Factor based on storm size. Soil loss simulation based on stochastic precipitation patterns is appropriate to the site--the La Plata mine area in northern New Mexico--and increases the flexibility of the USLE as a soil loss predictor for western rangelands.
15
Chaudhury, Kreteeka. "An Experimental Investigation of the Impact of Engineered Surface Processes on Efficiency of Spur Gears". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556553897979376.
Testo completo
16
Tarkalson, David Dale. "PHOSPHORUS LOSS IN SURFACE RUNOFF FROM PIEDMONT SOILS RECEIVING ANIMAL MANURE AND FERTILIZER ADDITIONS". NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010926-002603.
Testo completoAbstract (sommario):
The purpose of this research was to measure P losses in runoff from agricultural land in the Piedmont region of the southeastern U.S. with varying soil P levels and receiving broiler litter and inorganic P fertilizers. The experimental results will be helpful for the development of the P Loss Assessment Tool in North Carolina and other P Index approaches in states with similar soil characteristics and crop management practices. A net influx of P into many areas due to high animal populations has resulted in increased potential P losses to sensitive surface waters. A typical North Carolina broiler farm and dairy farm were found to have annual P surpluses of 65 kg P/ha and 20 kg P/ha respectively. The use of low phytic acid corn varieties and phytase enzyme has the potential to reduce the P surplus on broiler farms by 25 to 58%. Phosphorus losses in runoff from Piedmont conventional till (CT) and no-till (NT) soils with varying soil P concentrations and from soils currently receiving broiler litter and fertilizer P applications were assessed. In these studies, rainfall simulation at rates of 6 and 7.6 cm/hr were utilized to collect runoff samples from crop land with a range of initial P concentrations and from plots with varying fertilizer P and broiler litter application rates, both incorporated and broadcast. Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive P (RP), algal-available (AAP), and total P (TP). Concentration of RP in runoff from CT and NT plots was positively correlated with Mehlich-3 extractable P (r2 = 0.61 and 0.7 respectively) and oxalate extractable degree of P saturation (DPS) (r2 = 0.6 and 0.61 respectively). However, only TP mass loss (kg TP/ha) in runoff from CT was correlated with DPS (r2 = 0.57). A Mehlich 3 extractable P concentration of 350 mg P/kg and a DPS of 84% corresponded to 1 mg RP/L in runoff. Incorporation of broiler litter and inorganic P fertilizer into the soil at all P application rates virtually eliminated P runoff loses and had similar P losses in runoff as the unfertilized control. Surface application of broiler litter resulted in runoff containing between 2.9 and 24.5 mg RP/L for application rates of 8 to 82 kg P/ha respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P/ha over the same application rates. There was no significant relationship between surface applied inorganic P application rate and RP concentrations or TP mass losses in runoff. However, there was a trend for increased RP concentrations and TP mass losses in runoff with increasing application rate. Concentration of RP and mass loss of TP in runoff from surface applied inorganic P averaged 4.9 mg RP/L and 1.1 kg P/ha over all application rates. There was no significant difference between P losses in runoff from plots receiving surface applied conventional broiler litter and broiler litter derived from birds fed a low phytic acid corn (High Available P corn).
17
Holman, David. "Surface loss of heteromeric AMPA receptor complexes in response to transient NMDA receptor activation". Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420888.
Testo completo
18
Ryan, Jonathan. "UAV investigation of surface and tidewater mass loss processes across the Greenland Ice Sheet". Thesis, Aberystwyth University, 2018. http://hdl.handle.net/2160/018cf7b7-fc9b-4327-a80e-6ec866193d5f.
Testo completoAbstract (sommario):
Accurately forecasting the contribution of the Greenland Ice Sheet to global sea-level requires precise observations to constrain present-day processes and incorporate them into models. However, the spatial and temporal resolution of satellite imagery and representativeness of in situ measurements often precludes or obscures our understanding of mass loss processes. This thesis investigates whether imagery from unmanned aerial vehicles (UAVs) have the potential to 1) bridge the scale gap between in situ and satellite observations and, 2) resolve processes of mass loss which are beyond the resolution of satellite imagery. It is found that the footprints of ground-based pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Point-to-pixel albedo comparisons are therefore often invalid, meaning that satellite-derived albedo measurements may be more accurate than previously thought. A 25 km transect intersecting the dark zone reveals that distributed impurities, not cryoconite nor surface water, govern spatial albedo patterns and may have implications for the future expansion of the dark zone. Repeat surveys over Store Glacier show that UAVs can be used to quantify calving rates and surface velocities of tidewater glaciers. The surveys indicate that large calving events cause short-term terminus velocity accelerations and can explain the seasonal pattern of acceleration and retreat. Any process which accelerates calving, such as removal of the ice m ́elange, therefore has important implications for the glaciers future behaviour.
19
Sindi, Khalid Hussain F. "In vitro and in vivo feasibility study of ultrasound for monitoring tooth surface loss". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/6296/.
Testo completoAbstract (sommario):
This work attempted to appraise the usefulness of ultrasound as a diagnostic tool for use in dentistry. A number of possibilities were modelled and the most promising, at this time, was monitoring tooth surface loss (TSL). TSL is a serious dental condition affecting patients worldwide. Current methods used to monitor TSL in the dental surgery are subjective and unreliable. Laboratory-based monitoring methods are time consuming and costly. Ultrasound is a non-invasive, non-destructive method that is mainly used in the medical field. Its use in dentistry started in the 1950s but is still limited to therapeutics (e.g. periodontics and endodontics) and head and neck imaging. There are several modes of ultrasound imaging. Of particular note are amplitude mode (A-mode) and brightness mode (B-mode) ultrasound. In A-mode, a single beam is sent to an object, and its reflected echo is captured. This mode does not produce an image but is rather displayed as a waveform in time and amplitude domains. B-mode ultrasound has two spatial axes and therefore is used as a cross-sectional imaging tool. To date, there are no in vivo studies investigating the use of ultrasound to directly monitor TSL in the dental surgery. The aim of this thesis was to assess the feasibility and optimisation of ultrasound as a potential clinical dental tool in monitoring erosive TSL in vivo. This thesis investigated the coupling efficiency of various dental and other materials and their suitability as couplants. The results showed that Perspex was a suitable ultrasonic couplant for the purpose of enamel thickness measurements and the tightness of the coupling at an interface was of importance for efficient transmission of ultrasound energy into an object. However, a purpose-built apparatus was required for this as the ultrasound echoes were angle dependent. It further investigates the angle dependency of echoes arising from premolars compared to synthetic maxillary central incisors, as natural incisors were not available. The results demonstrated that the more planar incisors reflected ultrasound more readily and were less angle dependent than premolars (p-value < 0.001). B-mode ultrasound imaging was then investigated to measure intact enamel in human teeth and validated with μ-computed tomography (μ-CT). Two systems were evaluated for this purpose; the first was an in-house ultrasound apparatus and the second was a commercial ultrasound scanner, with the data obtained validated with μ-CT. The results showed that the commercial ultrasound scanner was more accurate than the in-house scanner with Bland-Altman 95% limits of agreement of -0.48 to 0.47 mm and -1.21 to 0.87 mm respectively. However, the B-mode images produced were not of sufficient clarity and consequently the accuracy of the enamel thickness measurements was not suitable for monitoring progressive enamel loss. Therefore, the simpler A-mode ultrasound approach was investigated for enamel thickness measurements and validated with histological sections of the same teeth. A study of speed of sound (SOS) variations in enamel was also performed. It was found that A-mode ultrasound was able to measure enamel thickness in vitro with an accuracy of 10% compared to histology and the mean SOS in enamel was 6191 ±199 ms-1. Finally, A-mode ultrasound was assessed in vivo (n = 30) to determine if it could monitor enamel thickness reliably and reproducibly on the labial surface of maxillary central incisors. The results showed that ultrasound was a highly reproducible and reliable technique for monitoring enamel thickness with 95% limits of agreement of -0.04 to 0.05 mm. The results demonstrated for the first time in vivo that A-mode ultrasound had sufficient precision (0.05 mm) to allow it to be used as a direct method for serial assessment of erosive TSL. The preferable site for making ultrasonic measurements was the cervical site (site 1) followed by the mid-buccal site (site 2). Therefore ultrasound is a promising and simple method to monitor early erosive changes in thickness of the enamel layer, especially in vulnerable patients with frequent acidic intake or in patients with gastro-oesophageal reflux disease (GORD).
20
Acharya, Ananta R. "Indium Nitride Surface Structure, Desorption Kinetics and Thermal Stability". Digital Archive @ GSU, 2013. http://digitalarchive.gsu.edu/phy_astr_diss/62.
Testo completoAbstract (sommario):
Unique physical properties such as small effective mass, high electron drift velocities, high electron mobility and small band gap energy make InN a candidate for applications in high-speed microelectronic and optoelectronic devices. The aim of this research is to understand the surface properties, desorption kinetics and thermal stability of InN epilayers that affect the growth processes and determine film quality as well as device performance and life time. We have investigated the structural properties, the surface desorption kinetics, and the thermal stability using Auger electron spectroscopy (AES), x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). Investigations on high pressure chemical vapor deposition (HPCVD)-grown InN samples revealed the presence of tilted crystallites, which were attributed to high group V/III flux ratio and lattice mismatch. A study of the thermal stability of HPCVD-grown InN epilayers revealed that the activation energy for nitrogen desorption was 1.6±0.2 eV, independent of the group V/III flux ratio. Initial investigations on the ternary alloy In0.96Ga0.04N showed single-phase, N-polar epilayers using XRD and HREELS, while a thermal desorption study revealed an activation energy for nitrogen desorption of 1.14 ± 0.06 eV.
HREELS investigations of atomic layer epitaxy (ALE)-grown InN revealed vibrational modes assigned to N-N vibrations. The atomic hydrogen cleaned InN surface also exhibited modes assigned to surface N-H without showing In-H species, which indicated N-polar InN. Complete desorption of hydrogen from the InN surface was best described by the first-order desorption kinetics with an activation energy of 0.88 ± 0.06 eV and pre-exponential factor of (1.5 ± 0.5) ×105 s-1.
Overall, we have used a number of techniques to characterize the structure, surface bonding configuration, thermal stability and hydrogen desorption kinetics of InN and In0.96Ga0.04N epilayers grown by HPCVD and ALE. High group V/III precursors ratio and lattice mismatch have a crucial influence on the film orientation. The effects of hydrogen on the decomposition add to the wide variation in the activation energy of nitrogen desorption. Presence of surface defects lowers the activation energy for hydrogen desorption from the surface.
21
Blomdahl, Klara. "Changes in the Cold Surface Layer on a Polythermal Glacier during Substantial Ice Mass Loss". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-251362.
Testo completoAbstract (sommario):
Climate change in the Arctic and sub-Arctic has induced substantial changes in the inland cryosphere. The warming climate is causing a reduction in glacier size and extent and the average net mass balance for Arctic glaciers have been negative over the past 40 years. Relatively few studies have been conducted concerning the development of the thermal distribution in glaciers during extensive volume changes. There is a possible diversity in how the thermal structure might change with a changing climate. Storglaciären is losing the cold surface layer in the ablation area and progressively becomes more temperate, while Kårsaglaciären is losing the zone of temperate ice in the ablation area and consequently becoming colder. The overall objective of this study has been to improve the understanding of the thermal response of polythermal glaciers to climate change. The results from Pårteglaciären, northern Sweden, indicate a decrease in volume by 18% in the last 15 years with an expected decrease of 35% of its present size during the coming century. As a consequence of the prevailing climate and volume decrease Pårteglaciären is experiencing a thinning of the cold surface layer at an average rate of 1.13 m a-1. The volumetric and cold surface layer changes are in the same magnitude, which may indicate that the CTS adapts relatively rapidly to the present changes. Assuming a climatic effect similar to what has been observed on Storglaciären, it can be concluded that the thinning has influenced the thermal regime. But in contrast to Kårsaglaciären, the thermal distribution on Pårteglaciären has become more temperate as a result of the substantial mass loss.Klimatförändringar i Arktis och subarktis har orsakat stora förändringar i kryosfären. Ett varmare klimat orsakar en minskning av glaciärers storlek och omfattning och nettomassbalansen för Arktiska glaciärer har varit negativ under de senaste 40 åren. Relativt få studier har genomförts angående utvecklingen av den termiska fördelningen i glaciärer under omfattande volymförändringar. Det finns en möjlig diversitet i hur den termiska strukturen kan ändras med ett förändrat klimat. Storglaciären förlorar det kalla ytskiktet i ablationsområdet och blir successivt mer tempererad, medan Kårsaglaciären förlorar zonen med tempererad is i ablationsområdet och blir därmed kallare. Syftet med den här studien har varit att öka förståelsen för den termiska reaktionen hos polytermala glaciärer till ett förändrat klimat. Resultaten från Pårteglaciären i norra Sverige visar en volymreducering med 18% under de senaste 15 åren med en förväntad minskning på 35% av den nuvarande storleken under det kommande århundradet. Som en följd av det rådande klimatet och den reducerade volymen genomgår det kalla ytskiktet på Pårteglaciären en förtunning med en genomsnittlig hastighet av 1.13 m a-1. Volymförändringarna och förändringarna i kalla ytskiktet är i samma storleksordning, vilket tyder på att CTS anpassas relativt snabbt till de nuvarande förändringarna. Förutsatt en klimatisk effekt liknande den som observerats på Storglaciären, kan slutsatsen dras att förtunningen har påverkat den termiska regimen. Men i motsats till Kårsaglaciären har den termiska fördelningen på Pårteglaciären blivit mer tempererad som ett resultat av den omfattande massförlusten.
22
Villegas, Juan Camilo, Darin J. Law, Scott C. Stark, David M. Minor, David D. Breshears, Scott R. Saleska, Abigail L. S. Swann et al. "Prototype campaign assessment of disturbance-induced tree loss effects on surface properties for atmospheric modeling". WILEY, 2017. http://hdl.handle.net/10150/623209.
Testo completoAbstract (sommario):
Changes in large-scale vegetation structure triggered by processes such as deforestation, wildfires, and tree die-off alter surface structure, energy balance, and associated albedo-all critical for land surface models. Characterizing these properties usually requires long-term data, precluding characterization of rapid vegetation changes such as those increasingly occurring in the Anthropocene. Consequently, the characterization of rapid events is limited and only possible in a few specific areas. We use a campaign approach to characterize surface properties associated with vegetation structure. In our approach, a profiling LiDAR and hemispherical image analyses quantify vegetation structure and a portable mast instrumented with a net radiometer, wind-humidity-temperature stations in a vertical profile, and soil temperature-heat flux characterize surface properties. We illustrate the application of our approach in two forest types (boreal and semiarid) with disturbance-induced tree loss. Our prototype characterizes major structural changes associated with tree loss, changes in vertical wind profiles, surface roughness energy balance partitioning, a proxy for NDVI (Normalized Differential Vegetation Index), and albedo. Multi-day albedo estimates, which differed between control and disturbed areas, were similar to tower-based multiyear characterizations, highlighting the utility and potential of the campaign approach. Our prototype provides general characterization of surface and boundary-layer properties relevant for land surface models, strategically enabling preliminary characterization of rapid vegetation disturbance events.
23
Hillborg, Henrik. "Loss and recovery of hydrophobicity of polydimethylsiloxane after exposure to electrical discharges". Doctoral thesis, KTH, Polymer Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3082.
Testo completoAbstract (sommario):
Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions.
Keywords:silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.
24
Rabias, J. "Power loss in amorphous ribbon materials : The effect of surface roughness on the power loss and harmonic content of flux density of amorphous ribbon materials". Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375618.
Testo completo
25
WANG, AIHUA. "EFFECTS OF FREE SURFACE HEAT TRANSFER AND SHAPE ON THERMOCAPILLARY FLOW OF HIGH PANDTL NUMBER FLUIDS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1094682055.
Testo completo
26
Bhasin, Amit. "Development of methods to quantify bitumen-aggregate adhesion and loss of adhesion due to water". Texas A&M University, 2003. http://hdl.handle.net/1969.1/5934.
Testo completoAbstract (sommario):
Moisture induced damage of hot mix asphalt pavements has a significant
economic impact in terms of excessive maintenance and rehabilitation costs. The
moisture sensitivity of an asphalt mix depends on the combined effects of material
properties, mixture design parameters, loading conditions and environmental factors.
Traditional methods to assess moisture sensitivity of asphalt mixes rely on mechanical
tests that evaluate the mix as a whole. These methods do not measure material properties
and their role in moisture sensitivity of the mix independently. This information is very
important to select materials resistant to moisture induced damage, or to modify locally
available materials to improve their resistance to moisture damage for economic reasons.
The objective of this research is to develop experimental and analytical tools to
characterize important material properties that influence the moisture sensitivity of
asphalt mixes.
Quality of adhesion between the aggregate and bitumen binder in wet and dry
conditions plays an important role on the moisture sensitivity of the asphalt mix. A part
of this research work was to develop the Wilhelmy plate method and the Universal
Sorption Device to measure the surface free energy components of the bitumen and
aggregate with adequate precision and accuracy, respectively. Surface energy of these
materials was used to identify parameters based on thermodynamics that can quantify
their interfacial adhesion and propensity to debond in the presence of water. The
thermodynamic parameters were shown to correlate well with the moisture sensitivity of
asphalt mixes determined from laboratory tests. Specific surface areas of the aggregates
were also used to account for the influence of mechanical interlocking at the micro scale.
In some mixes, chemical bonding also contributes to the adhesion between bitumen and aggregate. The use of a micro calorimeter was introduced in this research as a versatile
and fast tool to quantify the combined effects of physical and chemical adhesion between
these materials.
27
Hashim, Nur Zatil Ismah. "Au-compensated high resistivity silicon for low loss microwave devices : suppression of parasitic surface conduction effect". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/387343/.
Testo completoAbstract (sommario):
Deep-level doping compensation process using elemental gold is used to create high resistivity silicon substrate for microwave application. Gold atoms are introduced into low resistivity Czochralski silicon substrates through an ion-implantation process and activated via high-temperature annealings. The highest substrate resistivity recorded for optimised substrates is 60 k-cm. A constant attenuation value of 0.19 dB/mm is measured at 20 GHz for a bias voltage range of -6 V to +6 V, for coplanar waveguides fabricated on this type of substrate, indicating full suppression of parasitic surface conduction effect at microwave frequencies. The attenuation results are supported by the capacitance-voltage characteristics, where the substrate is seen to be insensitive towards bias voltage. Based on a finite element analysis, this effect is caused by the reduced number of free carriers in the substrate and the increased interface trap densities at the oxide-silicon interface. Optimisation of substrate-processing stages are presented in this work. It is shown that the combination of slow-cooling and quenching for activation annealing provide a higher resistivity enhancement and a lower attenuation compared to single annealing. The removal of the near surface gold to increase substrate's resistivity is found to be unnecessary as it does not provide reduced attenuation. It can therefore be avoided to reduce process complexity. The influence of oxide type is studied, and thermal oxidation is seen to be unsuitable for oxide passivation. Bias-dependent attenuation characteristics suggest gold out-diffusion during the high-temperature treatment. Reactively sputtered oxides do, however, give excellent performance. In addition to coplanar waveguides attenuation responses, quality factor performance of meander inductors fabricated on gold-compensated high resistivity silicon substrate is evaluated. A higher quality factor is recorded for all inductance values for Au-compensated high resistivity silicon compared to Float-zone silicon. The highest quality factor value of 14 is measured for 0.7-nH inductors.
28
Zielke, Dimitri [Verfasser]. "Supressing loss channels in the bulk and at the surface of crystalline silicon solar cells / Dimitri Zielke". Hannover : Technische Informationsbibliothek (TIB), 2017. http://d-nb.info/1136297995/34.
Testo completo
29
Ali, Fowziya M. "Investigations of the potential effects of different preventive products on treatment and prevention of enamel surface loss". Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/20567/.
Testo completoAbstract (sommario):
Maintaining strong healthy teeth for life is important; therefore the present study was concerned with the recognition of the significance of exploring some of the preventive and therapeutic products on the surface loss of enamel slabs subjected to acidic erosion and tooth brushing abrasion challenges using in vitro and in situ experiments. Study 1 In vitro assessment of the effect of fluoridated toothpastes on bovine and human enamel subjected to acidic erosion and tooth brushing abrasion. Aims: To assess the anti-erosive potential of toothpastes containing different delivery fluoride systems using bovine dental enamel (Part Ι) and human enamel (Part ІΙ) subjected to both acidic erosion and tooth brushing abrasion. Part Ι: Methods: Fifty bovine enamel slabs were mounted in acrylic blocks, ground flat, tested for flatness by scanning profilometry (Proscan 2000, Scantron, UK), standardised for hardness using a Knoop hardness tester (under 100 g load for 15 s) and divided into five experimental groups (E1-E5) including 10 specimens per group. The tested toothpastes were : E1 Meridol® group, (AmF/SnF2; 0.14%), E2 Elmex® anti-caries group (AmF; 0.14%F), E3 Pronamel®, (NaF, 1450 ppm F), E4 Elmex® sensitive plus (AmF; 0.14%F), and E5 Aronal® 0 ppm F. De/remineralisation cycling procedures were achieved with immersion of the slabs under static conditions in aliquots of citric acid (0.3%, pH 3.6) for 2 mins followed by soaking for 1hr in artificial saliva between the erosive challenges. The erosive challenges procedures were repeated 5 times daily for 28 days. All groups were subjected twice a day to brushing abrasion during application of a slurry of toothpaste/saliva (1: 3) with 15 tooth brushing strokes using a 300 g load and incubated overnight at 37 ̊C in night time saliva at the end of the last brushing of the enamel slabs. Erosion and abrasion depths (μm) were quantified using profilometry scanning (Proscan 2000, Scantron, UK) at 7, 14, 21 and 28 days. Part ΙΙ: Similar erosive / abrasive experimental procedures were used on human enamel specimens. Results: After 28 days of erosion cycling with tooth brushing abrasion, all groups showed different enamel surface loss (μm). One-way ANOVA, demonstrated that E1 showed similar trends with E5, whereas (E2, E3, E4 showed significantly less surface loss (p < 0.05) compared to E1 and E2. Conclusions: The effect of dental erosion and tooth brushing abrasion combined can be decreased by toothpastes containing amine fluoride and sodium fluoride, whereas no protection was observed with the stannous and amine fluoride paste. Similar result trends were observed for both bovine and human enamel specimens under this erosive/abrasive model. Study 2 The effect of therapeutic products in combination on prevention of tooth surface loss. Aims: To study combined topical fluoridated measures on erosive and abrasive enamel wear in vitro. Methods: Sixty bovine enamel specimens were divided into four groups containing (15 samples per group) were subjected to cyclic de/remineralisation procedures. Demineralisation was performed with 0.3% citric acid (pH 3.6) 2 min / five times per day. The enamel slabs were immersed in day artificial saliva between each erosive challenge for 1 hour and incubated overnight in night saliva at 37 oC. Two times daily fluoride application with toothpaste and artificial saliva slurry (1:3 ratio) plus a tested mouthrinse with automated tooth brushing (15 strokes, 300 g load) for (2x2 min/day) during the experimental process. The test product treatments were: group 1 Elmex® sensitive plus toothpaste (AmF, 1400 ppm F) Plus Elmex® erosion mouthrinse containing (500 ppm F as AmF/NaF and 800 ppm Sn as SnCl2) stannous chloride rinse (Elmex TP plus MR) 2 times/day; group 2 Pronamel® toothpaste (NaF, 1450 ppm F+ 5%KNO3) + Pronamel® (NaF) mouthrinse (Pronamel® TP plus MR) 2 mins x2 times/day; group 3 Pronamel® toothpaste (NaF, 1450 ppm F) 2/day plus GC tooth mousseTM once/ a day for 5 mins (Pronamel® TP plus TM) after the last brushing; group 4 (0 ppm F toothpaste) as a control. Enamel loss was determined by scanning profilometry after the last experimental days at 7, 14, 21, and 28 days. Results: after 28 days significantly less enamel surface loss (μm) was observed with group1: (Elmex TP plus MR) (0.40±0.23) and group 2: (Pronamel TP plus MR) (0.60±0.28)(Pronamel TP plus TM) had (2.65±1.79) (p < 0.01) compared to 0 ppm F control (1.84±1.85). Conclusions: The topical applications of preventive therapeutic measures in the form of AmF, 1400 ppm F toothpaste plus Elmex® erosion dental rinse (500 ppm F + 800 ppm Sn) or applications of NaF/5% KNO3 toothpaste plus NaF mouthrinse significantly decreased the effect of erosion and tooth brushing abrasion compared to combinations containing remineralising agent or fluoride-free toothpaste. Study 3: Investigations of therapeutic products on prevention of enamel surface loss under erosive and abrasive challenges in situ Aims: To investigate the effect of fluoridated toothpaste alone or in combination with mouth rinse on the prevention of tooth surface loss under acidic erosion and tooth brushing abrasion in situ. Methods: Seventeen healthy participants wore a small upper removable mouth appliance holding two sterilised bovine enamel slabs that were randomly assigned to investigate one of the five test products for 14 days entered a prospective controlled, double-blind, crossover with five phases trial. All participants that signed informed consents and fulfilled the inclusion criteria were enrolled in the study. The five treatment groups were: group A (Elmex® erosion protection toothpaste (1400 ppm F as AmF/NaF and 3500 Sn2); group B (non-fluoride® toothpaste as a control); group C (Sensodyne Pronamel® 1450 ppm F as NaF/5%KNO3 toothpaste); group D (.Sensodyne Pronamel® 1450 ppm F as NaF toothpaste plus Pronamel® mouth wash as 450 ppm F NaF) and group E (Elmex® erosion protection toothpaste (1400 ppm F as AmF/NaF and 3500 Sn2) with Elmex® erosion protection dental rinse as AmF and NaF 500 ppm F plus stannous chloride 800 stannous (Sn2). The enamel slabs were dipped extra-orally in 0.3% citric acid solution at predetermined times for 2 minutes/ five times daily. In addition the enamel slabs were brushed for 1min extra-orally then 1 min intra-orally using the standard toothpaste/natural saliva slurry and 10 ml mouthrinse was used for 60s twice per day (10 ml x2). Enamel loss was determined by surface profilometry (Proscan 2000, Scantron, UK). Results: Treatment with therapeutic products Elmex® erosion protection toothpaste, Sensodyne Pronamel® toothpaste, Sensodyne Pronamel® toothpaste plus Sensodyne Pronamel® mouthrinse and Elmex® protection erosion toothpaste and Elmex® erosion protection rinse demonstrated a highly statistically significant difference in reducing the erosive and abrasive enamel surface loss (p ≤ 0.001) compared to the control group (0 ppm F). Conclusion: Elmex® erosion protection (1400 ppm F) toothpaste combined with Elmex® erosion protection mouthrinse gave the greatest outstanding benefit. Furthermore, using combined anti-erosive therapeutic products in the form of Sensodyne Pronamel® 1450 ppm F NaF toothpaste plus Pronamel® mouth wash 450 ppm F NaF; Elmex® erosion protection toothpaste (1400 ppm F as AmF).and Sensodyne Pronamel® 1450 ppm F as NaF toothpaste significantly reduced the daily effect of erosive/abrasive tooth wear and provided better enamel surface loss reduction compared to the non-fluoride® toothpaste.
30
Sharma, Sumana. "Genome-scale identification of cellular pathways required for cell surface recognition". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271825.
Testo completoAbstract (sommario):
A range of biochemically diverse molecules located in the plasma membrane— such as proteins, glycans, and lipids—mediate cellular recognition events, initiation of signalling pathways, and the regulation of processes important for the normal development and function of multicellular organisms. Interactions mediated by cell surface receptors can be challenging to detect in biochemical assays, because they are often highly transient, and membrane-embedded receptors are difficult to solubilise in their native conformation. The biochemical features of low-affinity extracellular protein interactions have therefore necessitated the development of bespoke methods to detect them. Here, I develop a genome-scale cell-based genetic screening approach using CRISPR-Cas9 knockout technology that reveals cellular pathways required for specific cell surface recognition events. Using a panel of high-affinity monoclonal antibodies, I first establish a method from which I identify not only the direct receptor but also other required gene products, such as co-receptors, post-translational modi cations, and transcription factors contributing to antigen expression and subsequent antibody-antigen recognition on the surface of cells. I next adapt this method to identify cellular factors required for receptor interactions for a panel of recombinant proteins corresponding to the ectodomains of cell surface proteins to the endogenous surface receptors present on a range of cell lines. In addition to finding general cellular features recognised by many ectodomains, I also identify direct interaction partners of recombinant protein probes on cell surfaces together with intracellular genes required for such associations. Using this method, I identify IGF2R as a binding partner for the R2 subunit of GABAB receptors, providing a mechanism for the internalisation and regulation of GABAB receptor signalling. The results here demonstrate that this single approach can identify the molecular nature and cell biology of surface receptors without the need to make any prior assumptions regarding their biochemical properties.
31
Davis, Daniel E. "A Technique for Evaluating the Uncertainties in Path Loss Predictions Caused by Sparsely Sampled Terrain Data". Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23314.
Testo completoAbstract (sommario):
Radio propagation models provide an estimate of the power loss in a communication link caused by the surface of the ground, atmospheric refraction, foliage, and other environmental factors. Many of the models rely on digital topographic databases to provide information about the terrain, and generally the databases are sparsely sampled relative to the electromagnetic wavelengths used for communication systems. This work primarily develops a technique to evaluate the effects of that sparsity on the uncertainty of propagation models.That is accomplished by accurately solving the electromagnetic fields over many randomly rough surfaces which pass through the sparse topographic data points, many possible communication links, all of which fit the underlying data, are represented. The power variation
caused by the different surface realizations is that due to the sparse sampling. Additionally, to verify that this solution technique is a good model, experimental propagation measurements were taken, and compared to the computations.
Master of Science
32
Monkman, James. "Identification and functional characterisation of TGFB-regulated and cell surface candidates in pancreatic cancer". Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/213218/1/James_Monkman_Thesis.pdf.
Testo completoAbstract (sommario):
This thesis is an investigation into the role of novel proteins that may influence pancreatic cancer cell migration and thereby tumour progression. Multiple approaches were used to select 41 candidate proteins for in-vitro loss-of-function experiments and several lead candidates were generated including GPRC5A and CRLF1. Further investigation is warranted to better define their cellular roles in pancreatic cancer.
33
Chapman, Antony Shaun. "Particulate phosphorus loss from agricultural land via sub-surface drainage in the UK : tracing, modelling and risk assessment". Thesis, Coventry University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365249.
Testo completo
34
Liu, Chung-Ni. "Laboratory investigation of the effect of the dampening solution on the loss of surface strength of coated paper /". Online version of thesis, 1993. http://hdl.handle.net/1850/11983.
Testo completo
35
Vimercati, Bianca Mataveli. "Influência da aplicação de selantes de superfície na perda de massa e alteração da rugosidade superficial de um compósito após aplicação tópica de flúor fosfato acidulado e ensaio de escovação". Universidade do Estado do Rio de Janeiro, 2007. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=1818.
Testo completoAbstract (sommario):
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorEste estudo teve por objetivo avaliar a degradação de um compósito após ciclos de escovação simulada, com ou sem a aplicação de selantes de superfície e com ou sem a aplicação tópica de flúor fosfato acidulado (FFA). A avaliação foi feita através da análise alteração da massa e da rugosidade superficial. Foram confeccionados 80 corpos-de-prova (CP) com o compósito Z250 (3M) (8mm x 3mm) e divididos em 4 grupos. Todos os grupos tiveram as superfícies regularizadas com lixa dágua 1.200. O grupo A (controle) não recebeu selamento, o grupo B recebeu aplicação do selante de superfície Fortify (Bisco), o grupo C, BisCover (Bisco) e o grupo D, Fill Glaze (Vigodent). Após isso, os CP foram armazenados em água destilada por 7 dias, em temperatura ambiente e, posteriormente, pesados em balança analítica para obtenção da massa inicial e submetidos à análise da rugosidade superficial inicial, utilizando rugosímetro Surftest SJ 201 P Mitutoyo. Os grupos A, B, C e D foram subdivididos em 2 grupos cada (n:10) e um subgrupo da cada grupo inicial (A2, B2, C2 e D2) foi submetido à aplicação de FFA (4 min), antes da escovação. Os grupos A1, B1, C1 e D1 permaneceram em água destilada. Após a remoção do FFA, todos os grupos foram armazenados em saliva artificial por 1 hora, em temperatura ambiente. Posteriormente foram submetidos a 30.000 ciclos de escovação, representando 6 meses de escovação diária. Foi utilizada escova dental macia (Ultra) e uma solução de creme dental (Colgate Máxima Proteção Anticáries) e água destilada na proporção de 1:2. Ao fim do ensaio, os CP foram lavados em água corrente por 5 minutos, secos com papel absorvente, pesados novamente para obtenção da massa final e submetidos à análise da rugosidade superficial final. O desgaste de cada CP foi avaliado através da perda de massa, que foi calculada pela diferença das pesagens antes e após a escovação e a alteração da rugosidade superficial foi calculada pela diferença entre os valores das médias de rugosidade superficial inicial e final. Algumas amostras foram analisadas em microscópio de força atômica com finalidade ilustrativa. Os dados obtidos foram tratados estatisticamente. Na análise da alteração de massa, quando comparado os grupos isoladamente, somente o grupo D1(FIL) não sofreu alteração de massa significativa. As comparações entre as médias de alteração de massa dos grupos que receberam e que não receberam FFA revelaram não existir diferenças significativas entre todas as comparações. Com relação aos grupos que não receberam FFA, houve diferença significativa somente nas comparações: A1(CONT)xB1(FFY) e B1(FFY)xD1(FIL). Para os grupos que receberam FFA, não houve diferença significativa entre as médias de alteração de massa. Na análise da alteração de rugosidade superficial, quando comparado os grupos isoladamente, houve aumento significativo de rugosidade superficial nos grupos A2(FFA), B2(FFY+FFA), C1(BIS) e C2(BIS+FFA). As comparações entre as médias de alteração de rugosidade superficial dos grupos que receberam e que não receberam FFA revelaram não existir diferenças significativas entre todas as comparações. Com relação aos grupos que não receberam FFA, houve diferença significativa apenas na comparação: C1(BIS)xD1(FIL). Para os grupos que receberam FFA, as comparações A2(FFA)xD2(FIL+FFA); B2(FFY+FFA)xD2(FIL+FFA); C2(BIS+FFA)xD2(FIL+FFA) mostraram diferenças significativas. Não foi observada correlação estatisticamente significante entre a alteração de massa e rugosidade superficial entre os grupos analisados. Com base nos resultados obtidos e na análise estatística realizada, pôde-se concluir que a aplicação de FFA e a aplicação de selantes de superfície não tiveram influência na alteração de massa e na rugosidade superficial dos materiais testados. O selante de superfície Fortify não protegeu o compósito após escovação, apresentando uma maior perda de massa no grupo B1 (Fortify) em comparação com o grupo A1 (controle). Os demais selantes testados protegeram o compósito. Não existiu correlação significativa entre perda de massa e alteração da rugosidade.
The aim of this study was to assess the degradation of a composite after simulated toothbrushing cycles, with or no applying surface sealants and with or no topical application of acidulated phosphate fluoride (APF). The assessment was made by analysis of change of weight and of surface roughness. Eighty specimens were made with the Z250 composite (3M) (8 mm x 3 mm) and divided in 4 groups. All the groups have their surfaces regularized with sandpapers 1.200 under water. The group A (control) have not seal, in the group B was applied the surface sealant Fortify (Bisco), in the group C the BisCover (Bisco), and in the group D the Fill Glaze (Vigodent). Following, the specimens were stored in distilled water for 7 days at room temperature and, subsequently, they were weighted in analytical scales for obtaining initial weight and subjected to analysis of initial surface roughness using the Surftest SJ 2001 P Mitutoyo profilometer of surface roughness. The groups A, B, C and D were subdivided in 2 groups each (n = 10) and a subgroup of every initial group (A2, B2, C2, D2) was subjected to application of APF (for 4 minutes) before the toothbrushing. The groups A1, B1, C1 and D1 remained in distillated water. After the removal of the APF, all the groups were stored in artificial saliva for 1 hour at room temperature. Subsequently they were subjected to 30000 cycles toothbrushing, representing 6 months of daily toothbrushing. The soft toothbrush (Ultra) and a toothpaste (ColgateCavity Protection) and distillated water in ratio 1:2 were used. At final of assay, the specimens were washed in running water for 5 minutes, dried with absorbent paper, measured again in order to obtain the final weight, and they were subjected to analysis of final surface roughness. The wear of each specimen was assessed by weight loss, which was calculated by difference of measuring before and after toothbrushing, and the change of surface roughness was calculated by difference between the values of initial and final surface roughness. Some samples were analysed in atomic force microscope with illustrative purpose. The data were treated statistically. In the analysis of weight change, when compared to groups separately, only the group D1 (FIL) have no significant weight change. The comparisons between the means of weight change of groups with or no APF showed there are no significant differences between all the comparisons: A1 (CONT) X B1 (FFY) and B1 (FFY) x D1 (FIL). For the groups with APF, there are no significant differences between the means of weight change. In the analysis of surface roughness change, when compared to groups separately, there was a significant increase of surface roughness in groups A2 (APF), B2 (FFY + APF), C1 (BIS) and C2 (BIS + APF). The comparisons between the means of surface roughness change of the groups with and no APF revealed there no differences significant between all of comparisons. For the groups with no APF, there was significant difference only in comparison C1 (BIS) x D1 (FIL). For the groups with APF, the comparisons A2 (APF) x D2 (FIL + APF), B2 (FFY + APF) x D2 (FIL + APF), C2 (BIS + APF) x D2 (FIL + APF) showed significant differences. It wasnt noted correlation significant statistically between weight change and surface roughness between the groups analyzed. With basis on findings obtained and in the statistical analysis accomplished, it could to conclude that the application of APF and the use of surface sealants have not influence on the weight change and surface roughness of composite tested. The surface sealant Fortfy have not protected the composite after toothbrushing, showing the higher weight loss in the group B1 (Fortfy) when compared to group A1 (control). The remainder sealants tested has protected the composite. There wasnt significant correlation between weight loss and roughness change.
36
Gautreau, Thierry. "Estimation des pertes fer dans les machines électriques : modèles d'hysteresis Loss Surface et application aux machines synchrones à aimants". Grenoble INPG, 2005. http://www.theses.fr/2005INPG0167.
Testo completoAbstract (sommario):
Suite aux directives européennes incitant les constructeurs de moteurs électriques à supprimer de leur offre, les moteurs à faible rendement, une politique de conception de moteurs à haut rendement est engagée. Toutefois, l'évaluation préalable, en simulation, de ce paramètre, et notamment des pertes fer de la machine reste aujourd'hui un problème difficile. Dans cette optique, depuis quelques années, un modèle, nommé " Loss Surface ", de calcul a posteriori des pertes fer sous le logiciel éléments finis Flux2DTM a été développé. Au cours de ce travail, plusieurs améliorations sont apportées à ce modèle LS. Un nouveau banc de caractérisation à partir d'un onduleur de tension performant a permis de prolonger en fréquence la surface dynamique LS. Une nouvelle formulation de l'identification de la contribution dynamique, plus simple, a également été réalisée. Au final, les gains apportés sont conséquents. Deux machines synchrones à aimants aux caractéristiques très différentes ont ensuite été utilisées pour évaluer les améliorations sur des structures complexes. La première machine, nous a permis de tester l'impact du niveau d'induction sur l'évolution des pertes fer, et la seconde machine, l'influence de la fréquence. Deux phénomènes physiques importants ont également été étudiés afin de connaître leurs contributions aux pertes d'origine magnétique : les pertes par courants induits dans un matériau massif tel qu'un aimant, et l'effet sur les propriétés magnétiques des contraintes mécaniques induites par le poinçonnage du circuit magnétiqueFollowing European directives inciting electrical motors manufacturers to replace engines with poor efficiency in the near future, a high efficiency motor design policy was committed. However, the preliminary evaluation, in Finite Element Method (FEM) simulation, of the efficiency, and in particular the iron losses in the machine remains a difficult problem nowadays. An iron losses a posteriori calculation module, named " Loss Surface ", for the finite element software Flux2DTM has been developed since several years. This work proposes several improvements of LS dynamical model. A new magnetic characterization by perform inverter has permitted to increase the frequency data for the dynamical surface LS. A new formulation of dynamic contribution identification has also been achieved. Finally, the gains are consistent. Two different synchronous permanent magnet motors have been tested to evaluate the LS improvements on complex structures. The first machine is used to test the effect of induction level on iron losses evolution and the second, the frequency impact. Two physical phenomenon are as weil as studied in order to know theirs contributions on magnetic losses : the eddy-current distribution in the magnet bulk, and the influence of punching stress on magnetic mate rial proprieties
37
Karlsson, Linda. "Transmission Electron Microscopy of 2D Materials : Structure and Surface Properties". Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-127526.
Testo completoAbstract (sommario):
During recent years, new types of materials have been discovered with unique properties. One family of such materials are two-dimensional materials, which include graphene and MXene. These materials are stronger, more flexible, and have higher conductivity than other materials. As such they are highly interesting for new applications, e.g. specialized in vivo drug delivery systems, hydrogen storage, or as replacements of common materials in e.g. batteries, bulletproof clothing, and sensors. The list of potential applications is long for these new materials. As these materials are almost entirely made up of surfaces, their properties are strongly influenced by interaction between their surfaces, as well as with molecules or adatoms attached to the surfaces (surface groups). This interaction can change the materials and their properties, and it is therefore imperative to understand the underlying mechanisms. Surface groups on two-dimensional materials can be studied by Transmission Electron Microscopy (TEM), where high energy electrons are transmitted through a sample and the resulting image is recorded. However, the high energy needed to get enough resolution to observe single atoms damages the sample and limits the type of materials which can be analyzed. Lowering the electron energy decreases the damage, but the image resolution at such conditions is severely limited by inherent imperfections (aberrations) in the TEM. During the last years, new TEM models have been developed which employ a low acceleration voltage together with aberration correction, enabling imaging at the atomic scale without damaging the samples. These aberration-corrected TEMs are important tools in understanding the structure and chemistry of two-dimensional materials. In this thesis the two-dimensional materials graphene and Ti3C2Tx MXene have been investigated by low-voltage, aberration-corrected (scanning) TEM. High temperature annealing of graphene covered by residues from the synthesis is studied, as well as the structure and surface groups on single and double Ti3C2Tx MXene. These results are important contributions to the understanding of this class of materials and how their properties can be controlled.
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Abdelhameed, Elbana Maha. "Comparison between surface and subsurface drip irrigation systems using effluents". Doctoral thesis, Universitat de Lleida, 2011. http://hdl.handle.net/10803/51585.
Testo completoAbstract (sommario):
Els sistemes de reg per degoteig es consideren com un mètode apropiat per a la reutilització d’aigües regenerades, ja que disminueixen els riscos sanitaris. No obstant això, el problema més important en l’aplicació dels efluents en els sistemes de reg localitzat és l’obturació dels filtres i degoters, el que disminueix la uniformitat de distribució del aigua. L’objectiu principal d’aquesta tesi doctoral va ser comparar el comportament hidràulic d’un sistema de reg per degoteig superficial (DI) i un d’enterrat (SDI) aplicant un efluent terciari amb tres freqüències de rentat dels laterals (sense rentat, un rentat al final de cada temporada de reg i un rentat mensual) amb dos tipus d’emissors (autocompensant i no autocompensant). Altres objectius han estat investigar la influència de la qualitat de l’efluent en el procés de filtració i calcular la pèrdua de càrrega i la durada dels cicles de filtració en el filtre de sorra mitjançant l’anàlisi dimensional. Els resultats van demostrar que la durada del cicle de filtració va dependre principalment de la qualitat de l’efluent aplicat i del diàmetre efectiu de la sorra utilitzada. També es va constatar que l’eficàcia del procés de filtració va ser deguda al diàmetre efectiu de la sorra del filtre i que quan menor va ser el diàmetre efectiu de la sorra utilitzada, més eficaç va ser la filtració. L’anàlisi dimensional va ajudar a desenvolupar un model matemàtic per a descriure la pèrdua de càrrega en el filtre amb un alt coeficient de determinació ajustat i una bona distribució del residus. A més, es va trobar que el cabal del lateral va dependre significativament del tipus de degoter, sistema de reg, la temporada de reg i la freqüència de neteja. En el sistema de DI, el cabal de l’emissor no autocompensant es va incrementar significativament durant l’experiment a causa d’un desgast de l’emissor i es va disminuir significativament en el sistema de SDI degut a l’obturació del degoters. El cabal del degoter autocompensant va augmentar durant l’experiment en els sistemes de DI i SDI. També es va observar que la causa principal de l’obturació de l’emissor en el sistema de DI va ser el desenvolupament de biofilm, mentre que en el SDI es va correspondre a una combinació de factors biològics i físics. Finalment, es va trobar que rentar els laterals una sola vegada al final de cada temporada de reg va ser la millor opció de maneig per assolir la major eficiència de distribució de l’aigua després de 1620 h de reg, tant en DI com SDI.Los sistemas de riego por goteo se consideran como un método apropiado para la reutilización de aguas regeneradas, ya que disminuyen los riesgos sanitarios. Sin embargo, el problema más importante en la aplicación de los efluentes en sistemas de riego localizado es la obturación tanto de filtros como de goteros, lo que disminuye la uniformidad de distribución del agua. El objetivo principal de esta tesis doctoral es comparar el comportamiento de un sistema de riego por goteo superficial (DI) y otro enterrado (SDI) aplicando un efluente terciario con tres frecuencias de lavado de los laterales (sin lavado, un lavado al final de cada temporada de riego y otro mensual) con dos tipos de emisores (autocompensante y no autocompensante). Otros objetivos fueron investigar la influencia de la calidad del efluente en el proceso de filtración y calcular la pérdida de carga y la duración de los ciclos de filtración en filtro de arena mediante el análisis dimensional. Los resultados demostraron que la duración del ciclo de filtración dependió principalmente de la calidad del efluente aplicado y del diámetro efectivo de la arena utilizada. También se constató que la eficacia del proceso de filtración fue debida al diámetro efectivo de la arena del filtro, pues cuanto menor era el diámetro efectivo de la arena utilizada, más eficaz fue la filtración. El análisis dimensional ayudó a desarrollar un modelo matemático para describir la pérdida de carga en el filtro con un alto coeficiente de determinación ajustado y una buena distribución de los residuos. Además, se encontró que el caudal del lateral dependió significativamente del tipo del gotero, sistema de riego, temporada de riego y la frecuencia del lavado. En el sistema de DI, el caudal del emisor no autocompensante se incrementó significativamente durante el experimento debido a un deterioro del gotero y se disminuyó significativamente por culpa de la elevada porcentaje de los emisores obturados. El caudal del gotero autocompensante aumentó durante el experimento en los sistemas de DI y SDI. También se observó que la causa principal de la obturación del emisor en el sistema de DI fue el desarrollo de un biofilm, mientras que el de SDI se correspondió a una combinación de factores biológicos y físicos. Sin embargo, se encontró que lavar los laterales una sola vez al final de cada temporada de riego fue la mejor opción de manejo para lograr la mayor eficiencia de distribución del agua después de 1620 h de riego tanto en el sistema de riego por goteo superficial como en el enterrado.
Microirrigation is considered as an appropriate method for reclaimed wastewater reuse because it diminishes the health risks. However, the most important problem when applying reclaimed effluents in microirrigation systems is emitter and filter clogging, which lead to low system distribution uniformity. The main target of this PhD dissertation is to compare the performance of a surface (DI) and a subsurface (SDI) drip irrigation systems when applying a tertiary treated effluent under three flushing frequency (no flushing, seasonal flushing and monthly flushing) using two emitter types (pressure and non-pressure compensating). In addition, the study aimed to investigate the influence of effluent quality on the sand filtration process. Another purpose was to compute head loss across the sand media filter and time between backwashing in a sand filter media through dimensional analysis. The results revealed that sand filtration cycle duration depended mainly on the applied effluent quality and sand filter effective diameter. It was also found that the effectiveness of filtration process was significantly due to sand effective diameter, being the smaller the effective diameter the more effective the filtration process. The dimensional analysis helped to develop a mathematical model to calculate head loss across sand filter with a high adjusted coefficient of determination and a good distribution of residuals. Besides, it was found that lateral flow rates depended significantly on emitter type, irrigation system, irrigation season and flushing frequency. In DI system, lateral flow of the non-pressure compensating emitter was significantly increased throughout the experimental time due to emitter failure and significantly decreased in SDI one due to the elevated percentage of clogged emitters. The pressure compensating emitter lateral flow was increased during the experiment for DI and SDI systems. The study, as well, showed that emitter clogging in DI system was primarily due to biological factors and in the SDI one was due to a combination of biological and physical factors. However, it was found that the seasonal flushing frequency was the best management practice for achieving the highest system distribution uniformity after 1620 h of irrigation for both DI and SDI systems.
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Andrews, Aaron A. "Phosphorus loss with surface runoff as affected by bioenergy-based residue and nutrient management systems for an Iowa loam soil". [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1475914.
Testo completo
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Mikula, Léopold. "Contribution à la Modélisation des pertes dans les matériaux magnétiques de dispositifs électromécaniques : Extension vectorielle du Modèle LS et intégration en résolution éléments finis". Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALT052.
Testo completoAbstract (sommario):
Afin de parvenir a augmenter les performances des machines tournantes, les logiciels de conception doivent être affinés pour fournir de meilleurs estimations des pertes générées. L'objectif dans cette étude est donc l'amélioration des modèles de matériaux magnétiques doux en 2D . Des approches dites 'a priori' et 'a posteriori' (Preisach, loss surface) seront évaluées et comparées en s'appuyant sur l'expérimentation et la simulation. Le modèle Loss surface a été vectorisé afin de permettre la prise en des phénomène dit d'hystérésis dynamique en résolution élément finisIn order to increase the performance of rotating machines, design software must be refined to provide better estimates of the losses generated. The aim of this study is therefore to improve 2D soft magnetic material models. So-called 'a priori' and 'a posteriori' approaches (Preisach, loss surface) will be evaluated and compared, based on experimentation and simulation. The loss surface model has been vectorized to take into account dynamic hysteresis phenomena in finite element resolution
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Rauthan, Kanishk. "Investigation of surface textures on thermal and pressure drop performance of plate-fin heat exchangers". Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2022. https://ro.ecu.edu.au/theses/2597.
Testo completoAbstract (sommario):
Firstly, I would like to show my sincere gratitude to my supervisors Dr. Ferdinando Guzzomi and Dr. Ana Vafadar for their immeasurable guidance and support throughout the duration of the project. Dr. Guzzomi and Dr. Vafadar have always had an open-door policy for me which helped me accomplish my goals on or before the deadlines.
I highly appreciate Dr. Ferdinando Guzzomi for listening to and putting up with my ridiculous ideas and vision towards the project and pointing me in the right course of direction. I would like to thank Dr. Guzzomi for giving me the creative freedom and putting his trust on me with the project, allowing me to think outside the box and making my ideas a reality.
I would also like to show my heartfelt appreciation towards Dr. Ana Vafadar for listening to my confusion every week and to draw meaning out of my words. Your feedback along with the constructive criticism has been highly valuable throughout this journey and has kept me in check. Your constant support and faith in me have allowed me to finish the project on time and with significant contributions to the area of my research.
Dr. Kevin Hayward has also played a key role in the completion of this project. His feedback and suggestions towards my manuscripts and reports and numerous data analysis techniques have been critical in making this work presentable.
From the bottom of my heart, I would like to say a big thank you to Mr. Adrian Davis, Dr. Michael Stein and Joshua Bolton for their technical and literacy support throughout my bachelors and master’s project. Without your guidance and wisdom, none of this would have been possible.
A special thanks goes to my fellow researchers Aakash Shaun Hurry and Prashan Perera for all the cake and coffee I’ve had in the past 2 years and for the lovely discussions we had regarding our projects. I highly appreciate their immense support through times of doubt and uncertainty. I would also like to thank the ECU-Motorsports team specially Adam Honeycombe and Mario Leone for allowing me to use the facilities within the motorsports workshop and to be a part of the team and experience the Aus-West competition. I will cherish these memories and friendships forever.
Last but not the least, my biggest gratitude goes towards my uncle and aunt for their unconditional love and support throughout my bachelors and masters. I would not be where I am without their constant support. I would also like to thank my family and friends back in India who have helped me through this journey and allowed me to accomplish my goals.
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Pourrahimi, Amir Masoud. "The synthesis, surface modification and use of metal-oxide nanoparticles in polyethylene for ultra-low transmission-loss HVDC cable insulation materials". Doctoral thesis, KTH, Polymera material, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-190808.
Testo completoAbstract (sommario):
Polyethylene composites which contain low concentrations of metal-oxide nanoparticles e.g. ZnO and MgO are emerging materials for the use in insulations of extruded high-voltage direct-current (HVDC) cables. The challenge in the development of the composites with ultra-low electrical conductivity is to synthesize uniform and high-purity metal-oxide nanoparticles, which are functionalized with hydrophobic groups in order to make them compatible with polyethylene. The thesis reports different approaches to prepare this new generation of insulation materials. Different reaction parameters/conditions – zinc salt precursor, precursor concentrations and reaction temperature – were varied in order to tailor the size and morphology of the ZnO nanoparticles. It was shown that different particle sizes and particle morphologies could be obtained by using different zinc salt precursors (acetate, nitrate, chloride or sulphate). It was shown that 60 °C was a suitable reaction temperature in order to yield particles with different morphologies ranging from nano-prisms to flower-shaped superstructures. For removal of reaction residuals from the particles surfaces, a novel cleaning method based on ultrasonication was developed, which was more efficient than traditional water-replacement cleaning. After cleaning, the presence of one atomic layer of zinc-hydroxy-salt complex (ZHS) on the nanoparticle surfaces was suggested by thermogravimetry and infrared spectroscopy. A method involving three steps – silane coating, heat treatment and silica layer etching – was used to remove the last trace of the ZHS species from the nanoparticle surface while preserving its clean and active hydroxylated surface. The surface chemistry of these nanoparticles was further tailored from hydroxyl groups to hydrophobic alkyl groups with different lengths by reactions involving methyltrimethoxysilane (C1), octyltriethoxysilane (C8) and octadecyltrimethoxysilane (C18). MgO nanoparticles were prepared by aqueous precipitation of Mg(OH)2 followed by a partial transformation to MgO nanoparticles via heat treatment at 400 °C. The surface regions of the MgO nanoparticles convert into a hydroxide phase in humid media. A novel method to obtain large surface area MgO nanoparticles with a remarkable inertness to humidity was also presented. The method involved three steps: (a) thermal decomposition of Mg(OH)2 at 400 °C; (b) silicone oxide coating of the nanoparticles to prevent inter-particle sintering and (c) a high temperature heat treatment at 1000 °C. These MgO nanoparticles showed essentially no sign of formed hydroxide phase even after extended exposure to humid air. The functionalized metal-oxide nanoparticles showed only a minor adsorption of phenolic antioxidant, which is important in order to obtain nanocomposites with an adequate long-term stability. Tensile testing and scanning electron microscopy revealed that the surface-modified metal-oxide nanoparticles showed improved dispersion and interfacial adhesion in the polyethylene matrix with reference to that of unmodified metal-oxide nanoparticles. The highly “efficient” interfacial surface area induced by these modified nanoparticles created the traps for charge carriers at the polymer/particle interface thus reducing the DC conductivity by more than 1 order of magnitude than that of the pristine polyethylene.Polyetenkompositer med mycket låga halter av ZnO och MgO metalloxid nanopartiklar är en växande kategori material för användning som isolering av extruderade kablar avsedda för likriktad högspänning. En utmaning i utvecklingen av dessa material kan relateras till den praktiska kompositframställningen, vilken innefattar framställning av högrena metalloxid nanopartiklar som ytmodifieras med hydrofoba molekylstrukturer för att möjliggöra blandning med den hydrofoba polyetenplasten. Denna avhandling behandlar olika metoder för att framställa denna generation av isoleringsmaterial. Vid syntesen av de rena nanopartiklarna krävdes optimering av ett antal olika reaktionsparametrar för att uppnå tillfredställande slutresultat i form av partikelstorlekar och partikelmorfologier. Dessa inkluderade val av zinksalt, zinksaltkoncentration vid utfällning, samt reaktionstemperatur vid framställningen. Experimenten avslöjade att olika partikelstorlekar och partikelmorfologier kunde framställas som endast korrelerat mot källan av zinkjonerna, och berodde av vilka motjoner som zinkatomerna haft i zinksaltet (acetat, nitrat, klorid eller sulfat). Optimering av reaktionstemperaturen visade att ca 60 °C utgjorde en lämplig start för utvärdering av synteserna, som resulterade i olika partikelmorfologier i form av pyramidformade nanopartiklar till blomformationer. Utöver de specifika reaktionsparametrarna utvecklades även en ny ultrasonikeringsmetod för att rena ytorna hos partiklarna från motjoner relaterade till de valda specifika salterna. Metodiken som visade sig avsevärt mer effektiv än sedvanlig rening att utfällda nanopartiklar via repetitivt vattenutbyte, och skapade förutsättningar etablering av kolloidal stabilitet och fragmentering av aggregat i vattensuspensionerna. Efter ultrasonikeringsreningen beräknades de kvarvarande zinkhydroxidsalterna (ZHS) utgöra endast ett atomlager ZHS utifrån termogravimetriska data kompletterade med infraröd spektroskopi. En metod att eliminera de kvarvarande ZHS-komplexen från ytan av partiklarna tillämpades/utvecklades, inkluderade ytbeläggning av partiklarna med silan, följt av värmebehandling samt etsning av den resulterande kiseloxidytan, för att uppnå en ren hydroxylyta på partiklarna. Ytkemin hos dessa partiklar modifierades från att bestå av hydroxylgrupper till att utgöras av hydrofoba alkylgrupper med olika längder relaterade metyltrimetoxysilan (C1), oktyltrietoxysilan (C8), eller oktadekyltrimetoxysilan (C18). Även MgO nanopartiklar framställdes via vattenutfällning av Mg(OH)2 partiklar, vilka omvandlades till MgO nanopartiklar via en lågtemperatur värmebehandling vid 400°C. Ytan av dessa partiklar omvandlades dock till hydroxid i fuktig miljö. En ny metod att bibehålla den stora ytarean av MgO nanopartiklarna med anmärkningsvärd motståndskraft mot att omvandlas till hydroxid utvecklades således. Metoden består av (a) en låg temperatur omvandling av Mg(OH)2, (b) en kiseloxidytbehandling av nanopartiklarna för att undvika partikelsintring vid högre temperaturer och (c) en hög temperaturbehandling vid 1000 °C. De framställda partiklarna uppvisade ingen anmärkningsvärd känslighet mot luftfuktighet och bibehöll MgO sammansättningen efter exponering mot fukt. De modifierade metalloxid nanopartiklarna visade mycket liten adsorption av fenoliska antioxidanter, vilket medförde en långtidsstabilitet hos polyeten nanokompositerna. De ytmodifierade metalloxidpartiklarna visade även förbättrade möjligheter för dispergering och yt-kompatibilitet med/i polyetenmatrisen i jämförelse med omodifierade metalloxidpartiklar, utifrån mätningar baserade på dragprovning och svepelektronmikroskopi. Slutligen, de utvecklade ytorna på de modifierade nanopartiklarna skapade ett polymer/nanopartikel gränssnitt som kunder fungera som laddningsansamlingsområden i nanokompositerna, vilket resulterade i en storleksordning minskad ledningsförmåga hos kompositerna jämfört med den rena polyetenen.
QC 20160829
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Bhatta, Rudra Prasad. "Electron Spectroscopic Study of Indium Nitride Layers". Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/23.
Testo completoAbstract (sommario):
Surface structure, chemical composition, bonding configuration, film polarity, and electronic properties of InN layers grown by high pressure chemical vapor deposition (HPCVD) have been investigated. Sputtering at an angle of 50-70 degrees followed by atomic hydrogen cleaning (AHC) was successful in removing the carbon contaminants. AHC is found to be the most effective cleaning process to remove oxygen contaminants from InN layers in an ultrahigh vacuum (UHV) system and produced a well ordered surface. Auger electron spectroscopy (AES) confirmed the cleanliness of the surface, and low energy electron diffraction (LEED) yielded a 1×1 hexagonal pattern demonstrating a well-ordered surface. High resolution electron energy loss spectra (HREELS) taken from the InN layers exhibited loss features at 550 cm-1, 870 cm-1 and 3260 cm-1 which were assigned to Fuchs-Kliewer phonon, N-H bending, and N-H stretching vibrations, respectively. Assignments were confirmed by observation of isotopic shifts following atomic deuterium dosing. No In-H species were observed indicating N-termination of the surface and N-polarity of the film. Broad conduction band plasmon excitations were observed centered at 3100 cm-1 to 4200 cm-1 in HREEL spectra acquired with 25 eV electrons, for a variety of samples grown with different conditions. Infrared reflectance data shows a consistent result with HREELS for the bulk plasma frequency. The plasmon excitations are shifted about 300 cm-1 higher in HREEL spectra acquired using 7 eV electrons due to the higher plasma frequency and carrier concentration at the surface than in the bulk, demonstrating a surface electron accumulation. Hydrogen completely desorbed from the InN surface upon annealing for 900 s at 425 ºC or upon annealing for 30 s at 500 ºC. Fitting the coverage versus temperature for anneals of either 30 or 900 s indicated that the desorption was best described by second order desorption kinetics with an activation energy and pre-exponential factor of 1.3±0.2 eV and 10-7.3±1.0 cm2/s, respectively. Vibrational spectra acquired from HREEL can be utilized to explain the surface composition, chemical bonding and surface termination, and film polarity of InN layers. The explanation of evidence of surface electron accumulation and extraction of hydrogen desorption kinetic parameters can be performed by utilizing HREEL spectra.
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Kammler, Marvin. "MD simulations of atomic hydrogen scattering from zero band-gap materials". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0003-C17A-A.
Testo completo
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Cariou, Arnaud. "Contribution à la caractérisation et la modélisation des matériaux magnétiques doux pour les machines électriques en associant les modèles Play et Loss Surface (LS)". Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALT002.
Testo completoAbstract (sommario):
Cette thèse vise à développer un modèle de pertes fer valide pour des fréquences allant du continu à 2kHz pour des formes d'onde d'induction complexes en une dimension puis de l'étendre sur deux dimensions. Une étude sur l'influence de la température sur l'hystérésis magnétique sera menéeThis thesis aims to develop a valid iron loss model for frequency from DC to 2kHz for complex flux density waveforms in one dimension, then extending it in two dimensions. A study about the impact of temperature over the magnetic hysteresis will be conducted
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Chernos, Matthew. "The relative importance of calving and surface ablation at a lacustrine terminating glacier : a detailed assessment of ice loss at Bridge Glacier, British Columbia". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50182.
Testo completoAbstract (sommario):
Bridge Glacier is a lacustrine calving glacier located in the southern Coast Mountains and terminates in a 6.2 km² proglacial lake. The glacier has retreated more than 3.55 km up-valley since 1984, the majority of the retreat having occurred since 2003. While surface melt may have contributed to the retreat, calving allowed for an additional annual volume of ice loss. The relative contributions from surface melt and calving to the total volume of ice loss is examined for the 2013 melt season. Surface melt is quantified using on-glacier meteorological data to drive a distributed energy balance model. The calving flux is quantified using field measurements of lake bathymetry, terminus area change, and ice thickness. Calving flux estimates are completed by daily measurements of terminus surface velocity derived from manual feature tracking using oblique time lapse camera imagery. Calving accounts for 23% of the total ice loss in the 2013 melt season, suggesting that surface melt is the main driver of mass loss at Bridge Glacier.
Data from the 2013 field season is used to inform historical calving flux and surface melt estimates from 1984 to 2013. The calving flux is minor until 1991, at which point the glacier terminus achieves flotation, and begins to discharge large tabular icebergs. Calving was characterized by large, multi-annual retreats, alternating with periods of relative stability. The calving flux peaked from 2005 to 2010, when it was roughly equal to the mass loss due to surface melt. Calving was a much smaller contributor of mass loss from Bridge Glacier, except for a transient high-calving period in the late 2000s. Looking forward, Bridge Glacier will retreat into shallower water where the terminus will no longer float, and calving losses should decrease substantially. Although calving losses will become an increasingly minor portion of the mass balance, future retreat is expected at Bridge Glacier due to a legacy of dynamic thinning brought about by its transient calving phase.Arts, Faculty of
Geography, Department of
Graduate
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Bobe, Bedadi Woreka. "Evaluation of soil erosion in the Harerge region of Ethiopia using soil loss models, rainfall simulation and field trials". Thesis, University of Pretoria, 2004. http://hdl.handle.net/2263/26929.
Testo completoAbstract (sommario):
Accelerated soil erosion is one of the major threats to agricultural production in Ethiopia and the Harerge region is not exceptional. It is estimated that about 1.5 billion tones of soil is being eroded every year in Ethiopia. In the extreme cases, especially for the highlands, the rate of soil loss is estimated to reach up to 300 t ha-1yr-1 with an average of about 70 t ha -1yr-1 which is beyond any tolerable level. The government have made different attempts to avert the situation since 1975 through initiation of a massive program of soil conservation and rehabilitation of severely degraded lands. Despite considerable efforts, the achievements were far bellow expectations. This study was aimed at assessing the effect of some soil properties, rainfall intensity and slope gradients on surface sealing, soil erodibility, runoff and soil loss from selected sites in the Harerge region, eastern Ethiopia, using simulated rainfall. Soil loss was also estimated for the sites using Soil Loss Estimation Model for Southern Africa (SLEMSA) and the Universal soil Loss Equation (USLE). Moreover, the effectiveness of various rates and patterns of wheat residue mulching in controlling soil loss was also evaluated for one of the study sites, (i.e. Regosol of Alemaya University), under both rainfall simulation and field natural rainfall conditions. For most of the erosion parameters, the interaction among soil texture, slope gradient and rainfall intensity was significant. In general however, high rainfall intensity induced high runoff, sediment yield and splash. The effect of slope gradients on most of the erosion parameters was not significant as the slope length was too small to bring about a concentrated flow. The effect of soils dominated by any one of the three soil separates on the erosion parameters was largely dependent on rainfall intensity and slope gradient. The soils form the 15 different sites in Harerge showed different degrees of vulnerability to surface sealing, runoff and sediment yield. These differences were associated with various soil properties. Correlation of soil properties to the erosion parameters revealed that aggregate stability was the main factor that determined the susceptibility of soils to sealing, runoff and soil loss. This was in turn affected by organic carbon content, percent clay and exchangeable sodium percentage (ESP). Soils with relatively high ESP such as those at Babile (13.85) and Gelemso (7.18) were among the lowest in their aggregate stability (percent water stable aggregates of 0.25 –2.0mm diameter); and have highest runoff and sediment yield as compared to other soils in the study. Similarly, most of those soils with relatively low ESP, high organic carbon content (OC%) and high water stable aggregates such as Hamaressa, AU (Alemaya University) vertisol and AU regosol were among the least susceptible to sealing and interrill erosion. Nevertheless, some exceptions include soils like those of Hirna where high runoff was recorded whilst having relatively high OC%, low ESP and high water stable aggregates. Both the SLEMSA and USLE models were able to identify the erosion hazards for the study sites. Despite the differences in the procedures of the two models, significant correlation (r = 0.87) was observed between the values estimated by the two methods. Both models estimated higher soil loss for Gelemso, Babile, Karamara and Hamaressa. Soil loss was lower for Diredawa, AU-vertisol and AU-Alluvial all of which occur on a relatively low slope gradients. The high soil loss for Babile and Gelemso conforms with the relative soil erodibility values obtained under rainfall simulation suggesting that soil erodibility, among others, is the main factor contributing to high soil loss for these soils. The difference in the estimated soil losses for the different sites was a function of the interaction of the various factors involved. Though the laboratory soil erodibility values were low to medium for Hamaressa and Karamara, the estimated soil loss was higher owing to the field topographic situations such as high slope gradient. SLEMSA and USLE showed different degrees of sensitivities to their input variables for the conditions of the study sites. SLEMSA was highly sensitive to changes in rainfall kinetic energy (E) and soil erodibility (F) and less sensitive to the cover and slope length factors. The sensitivity of SLEMSA to changes in the cover factor was higher for areas having initially smaller percentage rainfall interception values. On the other hand, USLE was highly sensitive to slope gradient and less so to slope length as compared to the other input factors. The study on the various rates and application patterns of wheat residue on runoff and soil loss both in the laboratory rainfall simulation and under field natural rainfall conditions revealed that surface application of crop residue is more effective in reducing soil loss and runoff than incorporating the same amount of the residue into the soil. Likewise, for a particular residue application method, runoff and soil loss decreased with increasing application rate of the mulch. However, the difference was not significant between 4 Mg ha-1 and 8 Mg ha-1 wheat straw rates suggesting that the former can effectively control soil loss and can be used in areas where there is limitation of crop residues provided that other conditions are similar to that of the study site (AU Regosols). The effectiveness of lower rates of straw (i.e. less than 4 Mg ha-1 ) should also be studied. It should however be noted that the effectiveness of mulching in controlling soils loss and runoff could be different under various slope gradients, rainfall characteristics and cover types that were not covered in this study. Integrated soil and water conservation research is required to develop a comprehensive database for modelling various soil erosion parameters. Further research is therefore required on the effect of soil properties (with special emphasis to aggregate stability, clay mineralogy, exchangeable cations, soil texture and organic matter), types and rates of crop residues, cropping and tillage systems, mechanical and biological soil conservation measures on soil erosion and its conservation for a better estimation of the actual soil loss in the study sites. Copyright 2004, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bobe, BW 2004, Evaluation of soil erosion in the Harerge region of Ethiopia using soil loss models, rainfall simulation and field trials, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-08022004-141533 / >Thesis (PhD (Soil Science))--University of Pretoria, 2004.
Plant Production and Soil Science
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Andersson, Martin. "Churning losses and efficiency in gearboxes". Licentiate thesis, KTH, Tribologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-152914.
Testo completoAbstract (sommario):
Efficient transmissions systems are key to producing competitive motor vehicles that have a smaller environmental impact. Gears are the main components in vehicle transmissions and although they are already highly efficient, there is still room for improvement. In this study, the focus falls on the lubricant used to create separating films between gears and todissipate heat. When driving, the gears churn this lubricant, giving rise to power losses that are related to the amount and properties of the lubricant. However, any attempt to reduce these losses must not compromise the required lubrication and heat dissipation. Paper A reports on the use of an FZG gear test rig to investigate power losses and heat generation for different gear immersion depths, surface roughness and coatings. The results show that lower gear roughness reduces gear mesh losses and heat generation. A polishing affect was obtained when a non-coated gear ran against a coated gear.The aim of the research reported in paper B was to increase the accuracy of efficiency testing. It investigated how and whether repeated disassembly and re-assembly of the same test equipment, as well as test performance and rig conditions, affect the measured torque loss in an FZG gear test rig. It was shown that the measured torque loss changes between one assembly and another. Repeatability between tests is crucial for accurate conclusions.The aim of the research reported in paper C was to study whether gear efficiency could be increased by a running-in procedure, which would reduce the need for a coolant. A back-to-back gear test rig was used to test two running-in loads. Higher gear mesh efficiency was seen when a higher running-in load was used.QC 20141006
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Padilla, Scott T. "Novel Transducer Calibration and Simulation Verification of Polydimethylsiloxane (PDMS) Channels on Acoustic Microfluidic Devices". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6922.
Testo completoAbstract (sommario):
The work and results presented in this dissertation concern two complimentary studies that are rooted in surface acoustic waves and transducer study.
Surface acoustic wave devices are utilized in a variety of fields that span biomedical applications to radio wave transmitters and receivers. Of interest in this dissertation is the study of surface acoustic wave interaction with polydimethylsiloxane. This material, commonly known as PDMS, is widely used in the microfluidic field applications in order to create channels for fluid flow on the surface of a piezoelectric substrate. The size, and type of PDMS that is created and ultimately etched on the surface of the substrate, plays a significant role in its operation, chiefly in the insertion loss levels experienced. Here, through finite element analysis, via ANSYS® 15 Finite Element Modeling software, the insertion loss levels of varying PDMS sidewall channel dimensions, from two to eight millimeters is investigated. The simulation is modeled after previously published experimental data, and the results demonstrate a clear increase in insertion loss levels with an increase in channel sidewall dimensions. Analysis of the results further show that due to the viscoelastic nature of PDMS, there is a non -linear increase of insertion loss as the sidewall dimensions thicken. There is a calculated variation of 8.31 decibels between the insertion loss created in a microfluidic device with a PDMS channel sidewall thickness of eight millimeters verse a thickness of two millimeters. Finally, examination of the results show that insertion loss levels in a device are optimized when the PDMS sidewall channels are between two and four millimeters.
The second portion of this dissertation concerns the calibration of an ultrasonic transducer. This work is inspired by the need to properly quantify the signal generated by an ultrasonic transducer, placed under a static loading condition, that will be used in measuring ultrasonic bone conducted frequency perception of human subjects. Ultrasonic perception, classified as perception beyond the typical hearing limit of approximately 20 kHz, is a subject of great interest in audiology. Among other reasons, ultrasonic signal perception in humans is of interest because the mechanism by which either the brain or the ear interprets these signals is not entirely understood. Previous studies have utilized ultrasonic transducers in order to study this ultrasonic perception; however, the calibration methods taken, were either incomplete or did not properly account for the operation conditions of the transducers. A novel transducer calibration method is detailed in this dissertation that resolves this issue and provides a reliable means by which the signal that is being created can be compared to the perception of human subjects.
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Blauth, David. "Streifende Streuung schneller Atome an Oberflächen von Metalloxid-Kristallen und ultradünnen Filmen". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16106.
Testo completoAbstract (sommario):
Im Rahmen dieser Dissertation wurden Experimente zur Wechselwirkung von schnellen Atomen mit Oberflächen von Oxidkristallen, Metallkristallen und ultradünnen Oxidfilmen auf Metalloberflächen durchgeführt und modellhaft beschreiben. Die Experimente wurden im Regime der streifenden Streuung für Energien im keV-Bereich durchgeführt. Diese Streugeometrie bietet den Vorteil einer außerordentlich hohen Oberflächensensitivität und somit die Möglichkeit, die kristallographischen Eigenschaften der obersten Atomlage zu untersuchen. Darüber hinaus wurden Experimente zur Bestimmung des Energieverlustes der an den verschiedenen Oberflächen gestreuten Projektile und zur, durch diese Projektile induzierten, Elektronenemission durchgeführt. Die Anregungsenergie für die Elektronenemission und Exzitonen wurde an der Alumina/NiAl(110)- und der SiO2/Mo(112)- Oberfläche für die Streuung von He bestimmt. Durch die Bestimmung der Anzahl von emittierten Elektronen in Abhängigkeit des azimutalen Winkels konnten die Strukturen von obersten Lagen von Adsorbaten mit der Methode der Ionenstrahltriangulation bestimmt werden.In the framework of the present dissertation the interactions of fast atoms with surfaces of bulk oxides, metals and thin films on metals were studied. The experiments were performed in the regime of grazing incidence of atoms with energies of some keV. The advantage of this scattering geometry is the high surface sensibility and thus the possibility to determine the crystallographic and electronic characteristics of the topmost surface layer. In addition to these experiments, the energy loss and the electron emission induced by scattered projectiles was investigated. The energy for electron emission and exciton excitation on Alumina/NiAl(110) and SiO2/Mo(112) are determined. By detection of the number of projectile induced emitted electrons as function of azimuthal angle for the rotation of the target surface, the geometrical structure of atoms forming the topmost layer of different adsorbate films on metal surfaces where determined via ion beam triangulation.