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1
Johansson, Emil. "Synthesis and Characterisation of Potential Hydrogen Storage Materials." Doctoral thesis, Uppsala universitet, Fysik III, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4509.
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The dissociative and non-dissociative hydrogen uptake in carbon nanostructures and metallic films were investigated by measurements and analysis of solubility isotherms. The total, non-dissociative, uptake for multi-walled nano-barrels and amorphous nanoporous carbon was determined to be 6.2 and 4.2 wt. % respectively at 77 K and the adsorption energies (at lowest coverage) -7.2 and -4.2 kJ/mol. At 298 K the H-uptake was negligible. At low concentrations the H-uptake of Nb-films is strongly affected by the film thickness. For thicknesses less then about 31 nm, the absorption energy was found to be temperature dependent. Such changes have not been observed in Nb films before. The presence of multiple absorption energies was shown to limit the possibility to obtain relevant absorption and interaction energies by traditional Sievert's and van 't Hoff analysis. The Mg1-xNix system (0<0.43) was investigated with respect to the hydrogen uptake. For Mg2Ni the hydrogen uptake, at an external hydrogen pressure of 1 bar, is close to 1.33 H/M (Mg2NiH4). The enthalpy of formation is smaller in the film as compared to bulk material. The changes in the absorption energy are caused by the adhesion to the substrate as well as the nanocrystallinity of the absorbing layers. The optical band gap of Mg2NiH4 was determined to be 2.4 eV. In Mg1-xYx (0<0.17) it was found that the Y-concentration limits the hydrogen uptake at 1 bar. However, the kinetics of the uptake improves substantially with a minimum of 7 at.% of Y. For Mg-Y the optical band gap (3.6 eV) is independent of Y concentration within the concentration range investigated, while the transmittance decreases with increasing Y content.
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Verstraete, Dries. "The Potential of Liquid Hydrogen for long range aircraft propulsion." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4089.
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The growth of aviation needed to cater for the needs of society might be undermined by
restrictions resulting from the environmental implications of air traffic. Hydrogen could
provide an excellent alternative to ensure a sustainable future for aviation. Several challenges
remain to be addressed though before its adoption can become reality. The liquid
hydrogen tanks are one of the areas where considerable research is needed. Further insight
into unusual restrictions on aircraft classes that would be thought of as ideal candidates
for hydrogen is also required. Hydrogen fueled very large long range transport
aircraft for instance suffer from the 80 m airport box constraint which leads to a strong
decrease in performance compared to other aircraft classes.
In this work 3 main tools are developed to look into some of these issues. An aircraft
conceptual design tool has been set up to allow a comparison between kerosene and hydrogen
on a common and hence fair basis. An engine performance assessment routine is
also developed to allow the coupling of the design of engine and aircraft as one integrated
system. As the link between both subsystems is the liquid hydrogen tank, a detailed design
method for the tanks has also been created.
With these tools it has been shown that the gravimetric efficiency for large transport aircraft
varies by only a few percent for a wide range of fuel masses and aircraft diameters
with values in the order of 76to 80%. The performance of the long range transport aircraft
itself however varies strongly from one class to another. For aircraft with a passenger load
around 400 passengers, takeoff weight reductions around 25% can be obtained for similar
operating empty weights and fuel weights of about 30% of the equivalent kerosene fuel
weight. For 550 passenger aircraft however, the takeoff weight reduction reduces strongly
due to the need for a triple deck fuselage and the resulting increase in fuselage mass.
Whereas for the first category of aircraft, a 3 to 6 times higher fuel price per energy content
can be afforded for similar direct operating costs, this cost advantage is reduced by
about a third for the 550 passenger aircraft. A twin fuselage configuration alleviates the
geometrical restrictions and restores the potential for an aircraft family but does not yield
strong weight reductions.
In a subsequent study, the implications of unconventional engine cycles as well as drag
reduction resulting from natural laminar flow through surface cooling should be assessed
using the developed set of tools as this will reveal the full potential of hydrogen as an
aviation fuel.
3
Billet, Beau. "Lightweight Intermetallics with Laves Structures as Potential Hydrogen Storage Materials." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357330819.
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MacSween, Jeffrey Vanek. "Investigating the microwave-hydrogen peroxide treatment process for potential commercialization." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55365.
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Two pilot-scale, dielectric heaters, that utilize different frequencies of electromagnetic radiation (EMR), were modified to treat organic slurries with the aid of hydrogen peroxide (H₂O₂). Organic slurries investigated include: waste activated sludge (WAS), liquid dairy manure (DM), and palm oil mill effluent (POME). Treatment efficacy was evaluated in terms of changes in the substrate’s digestibility, available nutrients, and physical properties. The first heating system operated at a microwave frequency of 915MHz (MW-H₂O₂) and was modified to attain treatment temperatures above 100°C. Results showed that such high temperatures permitted the effective use of larger oxidant dosages, which was found to be beneficial for treating DM and useful for treating WAS, in select circumstances. However, the additional equipment costs and difficulties encountered in operating a pressurized high temperature dialectic heating system may prove inhibiting at larger scales. The second heating system used radiofrequency EMR at 27MHz (RF-H₂O₂) and was modified from its original batch configuration for continuous operation. The continuous RF-H₂O₂ process, the first of its kind, was demonstrated to be a viable treatment technology that achieved comparable results to the better studied MW-H₂O₂ system for DM and WAS substrates. A controlled comparison of the two dielectric heaters showed that their treatment efficacy was similar, but suggested that heating at 27MHz offers advantages with respect to its operation and the degradation of organics. The effect of higher heating rates and a 60°C treatment regime on WAS were also investigated, revealing that the treatment efficacy of the MW/RF-H₂O₂ process was suppressed in both cases, particularly in regards to the release of nutrients. Using original experimental results and information from the literature, a full-scale, RF-H₂O₂ process is presented for treating thickened WAS from one million people. The proposed system recommends three 900kW 27MHz dielectric heaters, a final treatment temperature of 95°C, a H₂O₂ dosage of 0.35%(v/v) per percent of dry solids, a heat exchanger to preheat the substrate, and an optional holding tank to enhance the release of orthophosphates.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Mcdermott, Morgan Marie. "The Remineralization Potential of Nano-Hydroxyapatite in Hydrogen Peroxide Whitening Mouthwash." Walsh University Honors Theses / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=walshhonors1461323620.
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Long, Tyler Richard. "Synthesis of polymers with the potential to release H2S: polydicyclopentadiene nanoporous membranes." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/4682.
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This thesis discuses two very different projects. In the first project, synthesizing a polymer with the potential to release H2S. This was accomplished through the copolymerization of L-lactide and lactide monomers that has been functionalized with 4-hydroxythiobenzamide which is known to release H2S in vivo. The synthesis of the functionalized monomer required the development of a new method to attach functional groups to a derivative of L-lactide, which involved the addition of a thiol to an alpha- beta-unsaturated lactide using catalytic I2. After polymerization, the molecular weight of the copolymers ranged from 8 to 88 kg mol-1 with PDIs below 1.50. These polymers have the ability to be loaded with different amounts of thiobenzamide by controlling the ratio of the functionalized monomer with L-lactide during polymerization. The copolymers were fabricated into two sizes of microparticles with average diameters of 0.52 and 12 µm. The degradation of the smaller microparticles was studied in a PBS buffered solution at pH 7.4 which showed the slow release of the thiobenzamide over a 4 week period. These microparticles are the first to show potential to deliver H2S over a period of weeks. This research addresses a critical need in the field of H2S in medicine where no method exists to release H2S in vivo at times over a few hours.
In the second project dicyclopentadiene was polymerized with Grubbs first generation catalyst and fabricated into highly cross-linked membranes with a thickness of 100 µm. The flux of twenty-one molecules with varying polarities and molecular weights ranging from 101 to 583 g mol-1 were studied. Molecules that permeated these membranes had flux rates of 10-5 to 10-6 mol cm-2 h-1 but molecules that did not permeate these membranes had flux rates 104 to 105 times slower. The large difference in flux did not have a strong correlation to molecular weight or solubility in the membrane. However, there was a strong correlation to the cross-sectional areas of the molecules. Cross-sectional area is the smallest two-dimensional rectangle determined by molecular modeling. The cross-sectional area cut-off of the membranes was determined to be between 0.38 and 0.50 nm2. This property gives these membranes the selectivity to successfully separate constitutional isomers, such as tributylamine and triisobutylamine. The membranes have also been used to separate organic products from expensive catalyst and ligands as well as different fatty acids from each other as their respective amine salts.
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Olson, Jared K. "Ab Initio Search for Novel BxHy Building Blocks with Potential for Hydrogen Storage." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/844.
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On-board hydrogen storage presents a challenging barrier to the use of hydrogen as an energy source because the performance of current storage materials falls short of platform requirements. Because boron is one of the lightest chemical elements that can form strong covalent bonds with hydrogen, it provides an excellent opportunity to design new lightweight materials on the basis of novel boron hydride building blocks. Realizing this potential requires an understanding of the electronic structure, chemical bonding, and stability of neutral and anionic BxHy clusters with variable stoichiometry. While a large number of boron hydride compounds are known, there are still entire classes of yet unknown neutral and anionic BxHy clusters and molecules with various new x/y ratios which may be good candidates for hydrogen storage or as intermediates of borane de-hydrogenation. The primary aim of this dissertation was to search for neutral and anionic BxHy clusters that are thermochemically stable towards hydrogen release and to understand the chemical bonding in these novel clusters. These goals were accomplished by performing an unbiased search for neutral and anionic global minimum BxHy clusters using ab initio methods. In addition to finding a rich variety of new neutral and anionic BxHy (x = 3 – 6 and y = 4 – 7) clusters that could be building blocks for novel hydrogen-boron materials during the course of conducting this research, optical isomerism was discovered in select neutral and anionic boron-hydride clusters. Furthermore, the transition from planar to 3- dimensional geometries in global minimum B6Hx - clusters was discovered using ab initio techniques during this study. Chemical bonding analysis using the AdNDP method was performed for all global minimum structures and low-lying isomers. The chemical bonding pattern recovered by the AdNDP method in all cases is consistent with the geometric structure. The theoretical vertical detachment energies presented in this dissertation may help interpret future photoelectron spectroscopic studies of the anions presented here.
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Hoy, Jason Michael. "Syntheses of Aluminum Amidotrihydroborate Compounds and Ammonia Triborane as Potential Hydrogen Storage Materials." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1260474478.
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Zhurakovskyi, Oleksandr. "NOVEL DUAL LEWIS ACID - LEWIS BASE BINDERS AS POTENTIAL HYDROGEN AND CARBONYL ACTIVATORS." Thesis, The University of Arizona, 2010. http://hdl.handle.net/10150/193458.
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A series of new “frustrated Lewis pairs” (FLPs), including chiral versions, with a predefined spatial relationship between the basic and acidic centers is proposed. Several synthetic protocols toward the targets were investigated: through an aryllithium-haloborane coupling; using organotin reagents and a chiral diazaborolidine; and through organoboranes RBH₂ as the boron component. Further development of the project is discussed in light of the discovered data. The intermolecular system consisting of 8-bromo-2-methylquinoline and (C₆F₅)₃B was shown to exist in the form of an FLP. This FLP is not capable of heterolytic H-H bond cleavage with formation of an isolable adduct either at 1 atm or at 4 atm of H₂.
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Sorbie, Natalie. "Synthesis and structure of group I and II nitrides as potential hydrogen stores." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/3284/.
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This thesis describes the synthesis and characterisation of group I and group II nitride materials as potential hydrogen stores. New synthetic routes as well as the development of conventional methods were employed to synthesise binary and ternary nitrides. Ball milling of single phase α-Li3N and of commercial Li3N was performed to induce a phase transformation in order to synthesise β-Li3N which adopts a hexagonal crystal structure (space group P63/mmc). The beta polymorph was initially characterised by PXD and subsequently by a variable temperature PND experiment, which demonstrated that the phase transformation to α-Li3N began at 600 K. Due to the fact that β-Li3N exhibits the same magnitude of Li+ conductivity as α-Li3N and that lithium ion diffusion is thought to be an important factor in the hydrogen storage potential of the solid, a further PND investigation to study the interaction of D2 gas with β-Li3N was performed. At lower temperatures, negative thermal expansion can be observed; this expands following similar trends known for α-Li3N and commercial Li3N. In agreement with the behaviour of Li3N reported in the literature, Li3N reacts with D2 at higher temperatures resulting in the formation of LiND2 and LiD. The phase behaviour in the complex Li-N-H system is still being debated despite significant research in this area. This work has focussed on lithium nitride hydride, which has been reported as a minority phase during the hydrogenation of Li3N. Li4ND was prepared by both conventional means and by a novel synthesis using microwaves; the product was characterised by PXD and PND. During both conventional and microwave syntheses, tetragonal Li4ND (space group I-4) and a new high temperature cubic polymorph formed (space group Fm-3m) where N3-, D- and (ND)2- are disordered across the anti-fluorite anion sites. With regard to providing further evidence for the proposition of a new reaction pathway upon hydrogenation of Li3N, Li4ND and Li2ND were reacted in-situ during a PND investigation forming a solid solution and resulting in synthesis of a cubic ‘quasi-imide’ phase. The ‘quasi-imide’ phase was refined against a modified cubic Li2ND starting model. The presence of D+ and D- ensured that charge balance was maintained. As the stoichiometry increases, the anion distribution changes; the occupancy of N3- and N from (ND)2- on the 4a site increases as does the occupancy of protonic D from (ND)2- on the 192l site. A ternary nitride, LiCaN (space group Pnma), was prepared by both conventional and novel (via microwaves) means. Optimization of the reaction parameters was the initial focus of the investigation in order to synthesise single phase LiCaN. Firstly, a PND study was performed in order to ascertain accurate Li positions and ensure the material was perfectly stoichiometric as made. In order to compare the Li-Ca-N system with reports on the Li-Mg-N system in which both Mg-rich and Li-rich phases as well as stoichiometric LiMgN have been synthesised, attempts were made to synthesise nonstoichiometric Li-Ca-N compounds. This system was investigated by PND.
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Bloss, Elaine. "Diffusion of solid molecular hydrogen and chemical potential changes in submonolayer helium flow." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324134.
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Ishibashi, Jacob Shotaro Afaga. "BN Isosteres of Acenes for Potential Applications in Optoelectronic Devices." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107613.
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Thesis advisor: Shih-Yuan LiuThis dissertation describes progress in the field of polycyclic boron- nitrogen-containing systems, especially for potential application in organic-based optoelectronic devices and hydrogen storage materials. The replacement of a BN unit for a CC unit organic compounds (BN/CC isosterism) can have a profound effect on the electronic structure and even function of a given molecular topology without changing its physical structure very much. Direct comparison between a BN-containing molecule and its direct all-carbon analogue is crucial to establishing the origin of these differences. The synthesis and optoelectronic characterization of boron- nitrogen-containing analogues of naphthalene, anthracene, and tetracene are disclosed. Also examined herein is the aromatic Claisen rearrangement applied to an azaboryl allyl ether. Finally, the chemistry of saturated BN heterocycles, including an iridium-catalyzed transfer dehydrogenation method for synthesizing BN-fused azaborines. Also disclosed is the actual application of these cyclic amine-boranes in supplying hydrogen for a proton exchange membrane (PEM) fuel cell
Thesis (PhD) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Wannerberg, Karin. "Evaluation of Odomin and potential factors reducing the hydrogen sulphide levels in sewage systems." Thesis, KTH, Maskinkonstruktion (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175675.
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Xylem Inc. develops pumps and integrated solutions for sewages systems. A new concept has been designed to reduce the levels of hydrogen sulphide, H2S, in wastewater. H2S is a toxic, stinking gas that smells at levels above 0.002-0.2 ppm. Recommended exposure level is 15 ppm for 15 minutes. The gas is soluble in water and arises with both increasing temperatures and long retention times. Levels of H2S normally differ between 0-1000 ppm, depending on the time of year. The new concept, a pre-chamber installed upstream a pump station, is called Odomin. Inside Odomin H2S is oxidized to sulphuric acid, H2SO4, on moist surfaces. A plate is used to splash thewastewater onto the moist surfaces surrounding the plate. This master thesis aims to find the reduction rate, in terms of H2S, between Odomin 65 and the pump sump and to evaluate three factors that have possibility to improve the performance of Odomin 65. The investigated factors are 1) a sacrificial anode made from carbon steel 2) a reduced area of the inlet which increases the splash effect and 3) an increased inner area to increase themoist surfaces inside Odomin. The evaluation is made with 23 factorial design. The analysis indicates that no factor affect the daily mean value with a significance at 5%. The sacrificial anode is the one factor showing a reduction by the levels of H2S in the pump sump for both mean and extreme values. The general reduction rate is 5.33 and this can be increased with 55% by using the splash. The tests were affected by several influences that impact the trustworthiness of the results. Therefore this analysis needs additional investigations in order to be verified.Xylem Inc. utvecklar pumpar och lösningar för avloppssystem. De har utvecklat ett nytt koncept för att reducera halten av svavelväte, H2S, i avloppsvattnet. H2S är en giftig, illaluktande gas med kännbar lukt vid 0.002-0.2 ppm. Rekommenderat är att utsättas för högst 15 ppm under 15 minuter. Gasen är löslig i vatten och nivåerna ökar med både höga temperaturer och långa uppehållstider i ledningarna. Normalt sätt kan nivåerna av H2S variera mellan 0-1000 ppm, beroende på årstid. Det nya konceptet som kallas Odomin är en för-kammare som installeras uppströms till en pumpstation. I Odomin oxideras H2S till svavelsyra, H2SO4, på våta ytor. Genom att avloppsvattnet kaskaderar på en platta kan gasen komma i kontakt med våta ytor kring plattan. Examensarbetet syftar till att hitta reduktionstalet mellan Odomin 65 och pumpsumpen samt utvärdera 3 faktorer som kan förbättra effekten av Odomin. De undersökta faktorerna är 1) en offeranod av kolstål 2) en minskad inloppsarea för att öka kaskadet och 3) en ökad inre area, för att öka andelen våta ytor, i Odomin. De 3 faktorerna utvärderas med faktorförsök (factorial design). Utvärderingen ger indikationen att ingen av de tre faktorerna påverkar det dagliga medelvärdet på en 5 % signifikansnivå. Offeranoden är den faktor som tenderar minska både medelvärdet och extremvärdet i pump sumpen. Reduktionen av H2S mellan Odomin 65 och pump sumpen är 5.33 och analysen visar att en ökad kaskadeffekt kan öka reduktionen med 55 %. Testerna influeras av flera yttre faktorer vilket påverkar resultatens trovärdighet. Denna analys bör därför repeteras för att resultaten ska kunna verifieras.
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Orondo, Peter Omondi. "A theoretical analysis of interstitial hydrogen : pressure-composition-temperature, chemical potential, enthalpy and entropy." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78547.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 371-373).
We provide a first principles analysis of the physics and thermodynamics of interstitial hydrogen in metal. By utilizing recent advances in Density Functional Theory (DFT) to get state energies of the metal-hydrogen system, we are able to model the absorption process fairly accurately. A connection to experiment is made via Pressure-Composition-Temperature (PCT) isotherms, and thermodynamic molar quantities. In the model, we understand the excess entropy of absorbed hydrogen in terms of the change in its accessible microstates. A connection is also made between the entropy and electronic states of interstitial hydrogen. However, our model indicates that this connection is too small to account for experimental results. Therefore, a conclusion is made that the entropy of absorbed hydrogen is mostly (non-ideal) configurational in nature. To model the latter in a manner consistent with experiment, we have explored a new model that posits a weak binding between clusters of hydrogen atoms at neighboring sites. We have developed a formulation and fitted the results to experimental data. We find a least squares fitting of the model to the entropy and enthalpy results in model parameters which seem physically reasonable. The resulting model appears to provide a natural physical explanation for the dependence of the excess entropy on loading.
by Peter Omondi Orondo.
Ph.D.
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Svensson, Fredrik. "Potential of reducng the environmental impact of civil subsonic aviation by using liquid hydrogen." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/10726.
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Svensson, Fredrik. "Potential of reducing the environmental impact of civil subsonic aviation by using liquid hydrogen." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/10726.
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Mainly owing to the dwindling fossil oil resources and the environmental concerns of discharging greenhouse gases into the atmosphere, it is essential to find an alternative to kerosene for civil aviation. The overall objective of this thesis is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. Mainly due to the complex interactions among a number of different fields affected by the introduction of hydrogen in aviation and due to the nature of the research question, the chosen scientific approach for this thesis is to carry out a broad study covering a number of selected fields. Engine and combustion chamber design are studied in detail, along with the cruise altitude for minimum environmental impact. Airport implications, and available and envisioned methods for hydrogen production, are discussed. From a technical point of view, it seems to be feasible to use hydrogen for aero gas turbines. In terms of pollutant emissions, hydrogen use offers the possibility of a significantly reduced number of emission species, resulting in only H₂0 and small quantities of NOₓ emissions. For minimum environmental impact, the results suggest that cryoplanes should cruise at an altitude of about 2-3 km below where conventional aircraft cruise today. If the priority is to lower the mission fuel consumption, the results indicate that an engine employing increased combustor outlet temperature, overall pressure ratio and by-pass ratio, seems to be the most attractive choice. The mission NOₓ emissions, on the other hand, seem to be reduced by using engines with a weak core and lowered by-pass ratio. Ignoring the cost implications, from an airport infrastructure point of view, it seems feasible to change to hydrogen use. With respect to the availability of energy, it would be reasonable to change from kerosene to liquid hydrogen as fuel for all civil aviation refuelling in Sweden.
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Nadeem, Muhammad. "Synthesis and characterization of biopolymer nanoapatite composite electrospun bioactive scaffold: A potential application for guided tissue/bone regeneration." University of the Western Cape, 2019. http://hdl.handle.net/11394/7040.
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Philosophiae Doctor - PhDSearch for an ideal scaffold for guided tissue/bone (GTR/GBR) regeneration continues as till now none of the commercially available GTR/GBR membrane fulfils the desired criteria. Currently, a variety of new materials and techniques have been investigated all over the world to improve the properties of GTR/GBR membranes. In the recent past three dimensional bioactive scaffolds composed of natural polymers have gained enormous popularity as potential future GTR/GBR devices. Electrospinning has emerged as one of the relatively simple, cost effective and efficient technique to fabricate three dimensional nanofibrous scaffolds in the field of tissue engineering. The rationale of this project is to investigate the natural polymers based bioactive nanofibrous scaffolds for GTR/GBR applications in the field of Periodontology.
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Pritchard, Rachel Elizabeth. "CATALASE ACTIVITY, POTENTIAL VIRULENCE FACTORS, AND THEIR RESPONSE TO OXYGEN IN MYCOPLASMA IOWAE." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1413553221.
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Bürchner, Mara [Verfasser], and Ingo [Akademischer Betreuer] Krossing. "Boron ionic liquids as potential hydrogen storage materials = Bor-ionische Flüssigkeiten als potentielle Wasserstoffspeicher-Materialien." Freiburg : Universität, 2014. http://d-nb.info/1123480079/34.
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Eklund, Melissa. "The potential benefits to balance power shortage in future mobility houses with hydrogen energy storages." Thesis, Uppsala universitet, Elektricitetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388494.
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This master thesis investigated how a hydrogen energy storage could be used anddimensioned to reduce the problem of power shortage in the local distributiongrid in Uppsala, Sweden. By implementing such a storage system in mobilityhouses, which are parking garages with integrated charging stations for electric vehicles and smart renewable energy solutions for power generation, the problem with power shortage could be decreased. The results showed that by integrating a hydrogen storage together with battery packs, it was possible to reduce power peaks in mobility houses. Further, it was clear that more power peaks facilitated the dimensioning of these type of systems. It was also shown that due to today's initial cost of hydrogen storages, the total savings related to a limited purchase of electricity from the grid were insignificant. It was therefore found that this type of hydrogen storage would not reduce costs in the short term for the mobility houses considered in this study. However, implementing a smaller kW storage could generate and improve knowledge in the hydrogen/hybrid field, which could facilitate the implementation of larger systems in the future. Furthermore, the results showed that it could be interesting to implement hydrogen storages on a bigger scale for municipalities or actors, who would want to reduce the power shortage in the local distribution grid.
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Evans, Ian Christopher. "Metallated derivatives of ammonia borane with a view to their potential as hydrogen storage materials." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1702/.
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Ammonia borane has attracted significant interest in the field of hydrogen storage due to its high gravimetric hydrogen content. In this study the reaction of NH\(_3\)BH\(_3\) with various metal hydrides was investigated. The reactions with hydrides of lithium and sodium required a molar ratio of 1:2 in favour of NH\(_3\)BH\(_3\) and the reaction products were characterised as [Li(NH\(_3\))]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\) and [Na]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\), respectively, through solid state \(^1\)\(^1\)B and \(^2\)\(^3\)Na MAS NMR and Raman spectroscopy. The reaction of CaH\(_2\) with NH\(_3\)BH\(_3\) required a reaction stoichiometry of 1:4 and this reaction proceeded through a different reaction mechanism, forming Ca(BH\(_4\))\(_2\)•2NH\(_3\). The crystal structures of Ca(BH\(_4\))\(_2\)•2NH\(_3\) and Ca(BH\(_4\))\(_2\)•NH\(_3\) were determined by powder diffraction methods and the reaction pathway investigated through solid state \(^1\)\(^1\)B MAS NMR spectroscopy. The thermal desorption properties of these hydrogen rich materials were investigated and hydrogen was released from all the materials. However, under certain conditions ammonia was the major gaseous desorption product from Ca(BH\(_4\))\(_2\)•2NH\(_3\) and was observed as a minor product from the decomposition of [Li(NH\(_3\))]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\). Ammonia was also released during the synthesis of [Na]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\), but the decomposition of this material was free from ammonia release. Ramped thermal desorption studies of [Na]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\) and [Li(NH\(_3\))]\(^+\)[BH\(_3\)NH\(_2\)BH\(_3\)]\(^−\) to 350°C resulted in weight losses due to hydrogen desorption of 7.5 wt% and 12.5 wt%, respectively. Heating Ca(BH\(_4\))\(_2\)•2NH\(_3\) to 350°C resulted in a total weight loss of 27.5 wt%, which was predominantly due to NH\(_3\) desorption. Powder XRD and solid state \(^1\)\(^1\)B MAS NMR spectroscopy were employed to identify the solid decomposition products and decomposition pathways were proposed. Metal borohydrides were identified in all cases as well as polymeric products possessing B–N chains.
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Yu, Katayama. "Towards the realization of anion-exchange membrane fuel cell technology: potential of hydrogen-carrier utilization." Kyoto University, 2017. http://hdl.handle.net/2433/227631.
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Gier, Megan Loran. "The potential neuroprotective effects of two South African plant extracts in hydrogen peroxide-induced neuronal toxicity." University of the Western Cape, 2018. http://hdl.handle.net/11394/6553.
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Magister Scientiae (Medical Bioscience) - MSc(MBS)Background: Oxidative stress induced by reactive oxygen species has been strongly associated with many neurodegenerative diseases (NDDs) and many medicinal plant-derived products have been reported to exert potent antioxidant properties. Sutherlandia frutescens (SF) and Carpobrotus edulis (CE) are two indigenous South African plants with known anti-inflammatory, anti-bacterial, antioxidant and anti-cancer properties. However, the neuroprotective effects of SF and CE have not been extensively studied. Aims: This study was done to investigate the neuroprotective potentials of S. frutescens and C. edulis aqueous extracts on hydrogen peroxide (H2O2)-induced toxicity in an SH-SY5Y neuroblastoma cellular model of oxidative stress injury. Methods: The maximum non-toxic dose (MNTD) of SF and CE against SH-SY5Y cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Thereafter, the cells were exposed to 250 μM H2O2 for 3 hours before treatment with the determined MNTDs of SF and CE extracts respectively and the effects of the treatments on caspase-9 protease activity, intracellular ROS levels, mitochondrial membrane permeability (MMP), nitric oxide (NO) activity, intracellular calcium activity and endogenous antioxidant activity in SH-SY5Y cells was evalaluated using caspase activity kits, DCFH-DA assay, rhodamine 123 fluorescent dye, Griess reagent, Fluo-4 direct calcium reagent, Hoechst staining dye, Superoxide dismutase (SOD) colorimetric and Catalase (CAT) assays, respectively.
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Crisp, Michael G. "Organoplatinum(II) complexes with hydrogen-bonding functionality and their potential use as molecular receptors for adenine : a thesis submitted for the degree of Master of Science." Title page, abstract and contents only, 2002. http://web4.library.adelaide.edu.au/theses/09SM/09smc932.pdf.
Full textAbstract:
Errata pasted onto front end-paper. Includes bibliographical references (leaves 82-86). Describes the preparation and characterisation of a novel series of organoplatinum(II) complexes with hydrogen-bonding functionality.
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Esswein, Stefan Theo. "Probing protein-ligand interactions via solution phase hydrogen exchange mass spectrometry." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4638.
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Mass spectrometry is a versatile, sensitive and fast technique with which to probe biophysical properties in biological systems and one of the most important analytical tools in the multidisciplinary field of proteomics. The study of nativestate proteins and their complexes in the gas-phase is well established and direct infusion electrospray ionisation mass spectrometry (DI-ESI-MS) techniques are becoming increasingly popular as a tool for screening and determining quantitative information on protein-protein and protein-ligand interactions. However, complexes retained by ESI-MS are not always representative of those in solution and care must be taken in interpreting purely gas-phase results. This thesis details modification and advancement of solution phase techniques devised by Gross et al. utilising ESI-MS and Fitzgerald et al. applying matrix assisted laser desorption ionisation (MALDI)-MS termed PLIMSTEX (protein-ligand interactions by mass spectrometry, titration and hydrogen-deuterium-exchange)[1] and SUPREX (Stability of unpurified proteins from rates of H/D exchange)[2] to quantify these interactions with regards to high throughput analysis. The first part of this thesis describes the different developmental stages of the devised HPLC-front ends and their optimisation with myoglobin and insulin. The successfully developed HPLC-front end in conjunction with PLIMSTEX and SUPREX and ESI-MS then gets tested with self expressed and purified cyclophilin A(CypA)- cyclosporin A (CsA) system, followed by a test screen with potential CypA binding ligands. Dissociation constants (Kd’s) within one order of magnitude to reported values are determined. In the third part of this thesis the application of the devised ESI-SUPREX methodology has been applied to anterior gradient 2 (AGr2) and the factor H complement control proteins module 19-20 (fH19-20) exhibiting binding potential to a taggedhexapeptide and a synthetic pentasaccharide, respectively, resulting in thermodynamical data for these protein-ligand interactions. For the AGr2 system another dimension of investigation has been added by temperature controlling the devised ESI-SUPREX approach, revealing a phase transition in the protein at higher temperatures. The final part of this thesis describes the application of the ESI-SUPREX methodology to probe folding properties of CypA in the presence of the self expressed and purified E. coli chaperonin groEL. Thereby the denaturing properties of groEL have been emphasised along with the stabilisation of a denatured CypA species.
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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.
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Arrage, Andrew Anthony. "Characterization of DNA-repair potential in deep subsurface bacteria challenged by UV light, hydrogen peroxide, and gamma radiation." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08182009-040256/.
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Chiuta, Steven. "The potential utilization of nuclear hydrogen for synthetic fuels production at a coal–to–liquid facility / Steven Chiuta." Thesis, North-West University, 2010. http://hdl.handle.net/10394/4840.
Full textAbstract:
The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed
to global warming due to the huge CO2 emissions of the process. This corresponds to
inefficient carbon conversion, a problem growing in importance particularly given the limited
lifespan of coal reserves. These simultaneous challenges of environmental sustainability and
energy security associated with CTL facilities have been defined in earlier studies. To reduce
the environmental impact and improve the carbon conversion of existing CTL facilities, this
paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS)
plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to
produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL
plant. A synthesis gas (syngas) plant mass–analysis model described in this paper
demonstrates that the water–gas shift (WGS) and combustion reactions occurring in
hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The
nuclear–assisted CTL plant concept that we have developed is entirely based on the
elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of
plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the
oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75%
reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification
plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas
output. In addition, we have developed a financial model for use as a strategic decision
analysis (SDA) tool that compares the relative syngas manufacturing costs for conventional
and nuclear–assisted syngas plants. Our model predicts that syngas manufactured in the
nuclear–assisted CTL plant would cost 21% more than that produced in the conventional
CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model
also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the
costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen
production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic
advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2.
However, the cost of CO2 avoided in our model works out to below this threshold for the
range of critical assumptions considered in the sensitivity analyses. Consequently, this paper
demonstrates the practicality, feasibility and economic attractiveness of the nuclear–assisted
CTL plant.Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.
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Zhou, Xu. "Synthesis and characterization of rigid nanoporous hypercrosslinked copolymers for high surface area materials with potential hydrogen storage capabilities." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/78048.
Full textAbstract:
Hydrogen storage remains a major technological barrier to the widespread adoption of hydrogen as an energy source. Organic polymers offer one potential route to useful hydrogen storage materials. Recently, Frechet and his coworkers described a series of hypercrosslinked polymers with high surface area and studied their surface properties and hydrogen storage capacities. McKeown and his coworkers studied a class of materials termed Polymers of Intrinsic Microporosity (PIMs) which are also based on a "hypercrosslinked" concept. We enchained N-substituted maleimide and functionalized stilbene alternating copolymers into a "hypercrosslinked system" to achieve high rigidity, high surface areas, high aromatic content and good thermal stability.
Hypercrosslinked copolymers of N-(3-methylphenyl)maleimide (3MPMI), 4-methyl stilbene (4MSTBB), vinylbenzyl chloride (VBC) and divinyl benzene (DVB) were synthesized. Scanning electron micrographs (SEM) show the copolymers are porous and some examples have shown surface areas over 1200 m²/g. We have also found the incorporation of 3MPMI and 4MSTBB improves the thermal stability and raises the glass transition temperature of the copolymer. However, the incorporation of 3MPMI and 4MSTBB decreases the hypercrosslinking density and therefore causes a decrease in the copolymer surface area. The systematic study of styrene (STR) – vinylbenzyl chloride (VBC) – divinyl benzene (DVB) networks indicates that a low density of chloromethyl groups leads to a decrease in surface area. Therefore, we are continuing to investigate other monomers, such as N-substituted maleimide and functionalized stilbene containing chloromethyl groups, in order to enhance thermal stability while maintaining surface area.
In order to increase the enthalpy of hydrogen adsorption and thus raise the temperature of hydrogen storage, the monomer N,N-dimethyl-N',N'-diethyl-4,4'-diaminostilbene (4,4'DASTB-3MPMI) which contains electron donating groups was incorporated into hypercrosslinked polymer particles. Hypercrosslinked polymer (4,4'DASTB-3MPMI)1.0(VBC)98.5(DVB).50 exhibits a surface area of 3257 m²/g.Master of Science
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Janke, Svenja Maria. "Theoretical Description of Hydrogen Atom Scattering off Noble Metals." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-87A3-4.
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DelloStritto, Daniel Justin. "TRPing up the Balance of Oxidative Stress - Transient Receptor Potential Vanilloid 1’s Role in Diabetic Microvascular Disease." NEOMED Integrated Pharmaceutical Medicine / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ne2mh1469567446.
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Linnane, Cathal David. "Investigation of high temperature enhanced hydrogen formation in mineral amended sediment slurries, as a potential novel deep biosphere energy source." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54810/.
Full textAbstract:
The deep biosphere has been estimated to be the largest prokaryotic habitat on Earth. However, what energy sources sustain these prokaryotes at depth and over geological timescales, remote from photosynthetic energy supply, is unclear. Hydrogen generation from basalt weathering has been controversially suggested as a potential deep terrestrial energy source, although other minerals were thought to be unimportant, as they did not generate H2 under abiotic conditions. In this study these experiments were repeated but in the presence of sedimentary prokaryotes using a range of minerals, with differing iron concentrations at a range of temperatures (4-105 C) and under anoxic conditions. Results showed that at certain temperatures high levels of H2 were produced from several minerals (600-1650 umol l"1). This was associated with high levels of acetate formation (-5000-1000 umol l"1). Substantial CH4 (100-600 umol f1) was also produced. Sulphate reduction proceeded between 50-85 C, which no removal at higher temperatures, similar to hot oil reservoirs. The amounts of these compounds produced varied depending on mineral composition. The presence of iron in minerals was found not to be necessary to facilitate the production of H2 as previously thought. Under sterile conditions little H2 or other products were formed. This shows that H2 generation from minerals was a microbially mediated process and was consistent with the presence of considerable prokaryotic cell numbers (range 4.3 x 107 to 5.1 x 108 cells ml"1) in these experiments. Prokaryotic cell numbers decrease with increases in temperature, similar to the predicted decrease in numbers with depth in the sub seafloor biosphere (e.g. 99 C 6.67 x 105 cells ml"1). Sequential ramping experiments to 155 C, demonstrated that prokaryotic activity in the biotic zone <120 C, increased the formation of products such as H2 (x34) and low weight molecular acids (acetate x2.3) in the abiotic zone >120 C. This has implications for hydrous pyrolysis experiments, which are used to simulate high temperature diagenesis. This increases the sources of potential energy, which may migrate upward to feed the base of the deep biosphere. The prokaryotic community present was assessed using 16S rRNA gene analysis (PCR-DGGE). Communities varied with mineral type and included thermophilic methanogens and acetate oxidisers, iron-reducers and Deltaproteobacteria, Thermoplasmatales, as well as uncultured bacterial and archaeal sequences. Clone libraries indicate that the archaeal community is similar to proposed HyperSliMe communities, dominated by Thermococcales related species at high temperature 80- 95 C. Fresh grinding of minerals enhanced activity, which has implications for the rate of energy supply in the subsurface. A mechanochemical process based on the interaction of Si radicals, which is enhanced by the presence of prokaryotes, perhaps through microbial weathering, is hypothesised to be involved in H2 generation. But the interaction of other mineral constituents such as Fe, Al and Ti may also play a role. We found minerals stimulated prokaryotic activity up to at least 100 days. Interestingly, the carbon isotope values for the CH4 produced covered a wide range of values (-42 to -78‰), including depleted values that could be misinterpreted as being indicative of an abiotic origin. These results extend the range of minerals that could be potential "dark energy" sources in the subsurface and provide details of the prokaryotes and processes that such energy sources could stimulate.
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Ye, Xuemin. "The effect of water pH on swimming performance, blood pH, red cell pH, ion concentrations and catecholamine concentrations in plasma, and gill potential in rainbow trout (Salmo gairdneri)." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26676.
Full textAbstract:
The effect of transferring fish from water at pH 7.0 to either more acid or more alkaline conditions was to reduce the maximum critical velocity of the fish. In water of pH 4.0, 5.0, and 10.0, the maximum critical velocity was only 54.5%, 66.5%, and 61% respectively of that recorded for fish in the water of pH 7.0. Thus, both acid and alkaline conditions in the water reduce the aerobic swimming capacity of trout.
Exposure to acid conditions increased mucus secretion and this was associated with an increase in coughing and breathing frequency in resting fish. Coughing rate increased from 41/hr to 592/hr; and respiration frequency increased from 81/min to 104/min when fish were transferred from water at pH 7.0 to water at pH 4.0.
In comparing fish exposed to acid and alkaline waters, the results indicates that fish have a greater capacity to regulate blood pH in acid than in alkaline conditions.
The gill potential was strongly dependent on water pH, being negative in neutral water, but positive in acid water and more negative in alkaline solution. Catecholamine levels increased significantly during acid exposure, but were not altered during alkaline exposure. The increasing catecholamine levels appeared at different time periods in different fish during acid exposure and seemed to be associated with the death of the fish.
Na⁺ and C1⁻ ion concentrations in plasma decreased significantly after 24hrs of acid exposure, but did not change significantly in alkaline water. This may indicate that ionoregulatory disturbance in plasma is one of the reasons for the decrease in the maximum critical velocity in acid water, but not in alkaline water.Science, Faculty of
Zoology, Department of
Graduate
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Foster, Rory 1982. "False optimism for the hydrogen economy and the potential of biofuels and advanced energy storage to reduce domestic greenhouse gas emissions." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32818.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (leaves 52-53).
Discussion of the general domestic energy situation addresses the motivations which underlie the push for an hydrogen energy economy. The validity of claims about such a hydrogen economy and the official DOE position regarding such are evaluated, and then discarded as overly optimistic given the inherent physics of the required production and transportation processes. Biomass is then introduced as a potential source of greenhouse gas reduction in both stationary and mobile applications for the near term future (10-25 years). Combined renewable power (mainly solar and wind power) and attached energy storage to buffer the inherently fluctuating supply is also discussed, and recommended as potential zero-emission power generation technology for the long-term depending on the advances in photovoltaics, wind power and pumped liquid electrolyte battery technology.
by Rory Foster.
S.B.
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Chen, Szu-Lin. "An empirical potential for hydrogen bond energies determination of the orientation of anthracene molecules in the unit cell by means of a refractivity method: some ab initio calculations involving acetonitrile exchange reaction." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76509.
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Topic I
An empirical potential for calculating hydrogen bonding energies is developed for systems of the type A-H--B, where A and/or B is oxygen or nitrogen. Point charge and van der Waals interaction are included in the potential. The parameters of the potential were optimized by means of a simplex algorithm within a range of A-B distances from 2.8 A through 5.0 A. The root mean square deviation between the empirical potential and the ab initio results of 216 configurations of (H₂O)₂, (NH₃)₂ and NH₃•H₂O is 0.9 kcal/mol and 0.5 kcal/mol for 61 configurations of methanol dimers. Applications of the potential to water dimers, ammonia dimers, their mixed dimers, water oligomers and ice-h as well as the β form of the methanol crystal show that the potential yields reasonable results compared to those computed by "ab initio" methods using 6-31G* basis sets. The potential is compatible with MM2 program. It is simpler than earlier potentials in that neither dipoles nor Morse potentials are involved. It should be superior to the empirical potentials developed by Jorgensen that used STO-3G ab initio calculated results as the standards. The potential might be useful for estimation of hydrogen bond energies in a local part of a large molecule to avoid the prohibitive expense of ab initio calculation.
Topic II
The monoclinic anthracene crystal is used as an example to demonstrate the feasibility of optimizing the orientation of molecules in the unit cell by matching calculated and experimental refractivity ellipsoids using a simplex algorithm. The calculated refractivity ellipsoid is determined by use of an empirical formula using bond directional polarizabilities. Optimization of the molecular orientations to provide the best fit to the experimental ellipsoid starting from several assumed orientations results in fits for which the maximum deviation from the experimental molecular orientation was no more than 10 degrees. The method can be applied to other monoclinic molecular crystals directly and could be extended to other crystal systems with anisotropic optical properties.
Topic III
Three mechanisms (Walden inversion, addition-rearrangement-elimination and proton 1,3 shift mechanisms) of the following reaction were suggested by Jay et al. and Andrade et al. respectively.
CH₃CN + C⃰N- = CH₃C⃰N + CN-.
The mechanism of Walden inversion was determined to be the least likely one based on Andrade's MNDO results. Our calculations, based on 3-21G and 4-31G results, show the contrary result that the Walden inversion is the most likely mechanism among the three considered. However, solvation effects were neglected in the calculations and these effects could play a major role in the choice of mechanisms. Simple calculations based on Boltzmann distribution of precursor concentrations and the Arrhenius law show that Walden inversion predominates over Jay's addition-elimination-rearrangement mechanism even when MNDO energy levels were used. Estimated orders of magnitude for the rate ratios were determined.Ph. D.
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Rose, Philipp [Verfasser], and M. [Akademischer Betreuer] Wietschel. "Modeling a potential hydrogen refueling station network for fuel cell heavy-duty vehicles in Germany in 2050 / Philipp Rose ; Betreuer: M. Wietschel." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/121100628X/34.
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Khalil, R. M. A. "Ab initio studies of the structural, dynamical and thermodynamical properties of graphitic and hydrogenated graphitic materials and their potential for hydrogen storage." Thesis, University of Salford, 2014. http://usir.salford.ac.uk/32059/.
Full textAbstract:
The study presented in this PhD thesis is related to exploration of the properties of graphitic materials within the frame-work of ab initio methods. Structural and dynamical properties of graphitic materials are evaluated using the ab initio pseudopotential method. In graphitic materials, properties are obtained by incorporating Van der Waals interactions together with the generalized gradient approximation to density functional theory. These Van der Waals interactions improve the structural and dynamics of graphitic systems. In order to study the dynamical properties, the finite displacement method has been used to construct the dynamical matrix and force constant matrix. Phonon dispersions are investigated by the direct force constant matrix method in supercells. In this approach, force constants are assumed to be zero beyond a certain limit. Phonon frequencies are calculated from the force constant matrix. The dispersion relations and the Brillouin zone integrated density of states are also investigated. The significance of phonon dispersion has been studied to in various regions. Results are compared with dispersion corrected scheme and without dispersion corrected schemes to understand the importance of dispersion correction. Conclusions are also drawn on the applicability of theoretical approximations used. Further, ab initio results are also compared with the available data from experimental studies. The binding energies and electronic band gaps of exo-hydrogenated carbon nanotubes are determined to investigate the stability and band gap opening using density functional theory. The vibrational density of states for hydrogenated carbon nanotubes has been calculated to confirm the C-H stretching mode due to sp3 hybridization. The thermodynamical stability of hydrogenated carbon nanotubes has been explored in the chemisorption limit. Statistical physics and density functional theory calculations have been used to predict hydrogen release temperatures at standard pressure in zigzag and armchair carbon nanotubes.
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Цейтлин, Мусий Абрамович, and Валентина Федоровна Райко. "Математическое моделирование равновесного состава системы BaS–Ba(HS)₂–H₂S–H₂O." Thesis, Національний технічний університет України "Київський політехнічний інститут імені Ігоря Сікорського", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/41241.
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Разработана математическая модель, описывающая равновесный состав системы BaS–Ba(HS)₂–H₂S–H₂О, позволяющая, в частности, рассчитывать рН раствора. Модель использована для расчета движущей силы десорбции сероводорода в процессе получения карбоната бария.A mathematical model describing the equilibrium composition of the BaS–Ba(HS)₂–H₂S–H₂О system is developed. Model allows, in particular, to calculate the pH of the solution, and was used to calculate the driving force for desorption of hydrogen sulfide in the process of obtaining barium carbonate.
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Horbatenko, Yevhen. "Structure and hydrogen dynamic behavior in proton sponge cations and organometallic complexes." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/128511.
Full textAbstract:
This thesis focuses on the study of hydrogen dynamic behavior in a series of proton sponge cations as well as in bis(silyl)hydride organometallic complexes. To understand the dynamic behavior, a new tool, i.e. the three-dimensional vibrational Schrödinger equation has been derived and solved. Three different vibrational patterns for hydrogen motion have been revealed. The classification of proton sponges and bis(silyl)hydride complexes into those with localized and delocalized hydrogen behavior has been proposed. For the organometallic complexes the influence of the vibrational motion of the hydrogen on J(Si−H) spin−spin coupling constants has been studied. Also this thesis presents a study of [Cp*Co(SiR3)2(H)2] cobalt complexes and their iridium analogues to detect possible Si···H interactions. Based on molecular geometries, Wiberg bond indices, and J(Si–H) spin-spin coupling constants, at least two residual Si···H interactions have been detected in cobalt complexes while there are only rudimentary Si···H interactions in the case of iridium complexesAquesta tesi es centra en l'estudi del comportament dinàmic d'hidrogen en una sèrie de cations d'esponges de protó, així com en bis(silil)hidrur complexos organometàl•lics. Per entendre el comportament dinàmic, una nova eina com l'equació de Schrödinger vibracional tridimensional s'ha derivat i resolt. S'han trobat tres patrons diferents pel moviment vibracional d'hidrogen. S'ha proposat la classificació d'esponges de protó i bis(silil)hidrur complexos amb el comportament d'hidrogen localitzat i deslocalitzat. Per als complexos organometàl·lics s'ha estudiat la influència del moviment vibracional d'hidrogen en J(Si–H) constants d'acoblament de espín-espín. Una altra part d'aquesta tesi presenta un estudi de [Cp*Co(SiR3)2(H)2] complexos de cobalt i els seus anàlegs d'iridi per detectar possibles interaccions Si···H. Basat en geometries moleculars, en els índexs d'enllaç de Wiberg i constants d'acoblament d'espín-espín J(Si-H), s'han detectat almenys dues interaccions residuals Si···H en els complexos de cobalt, mentre que hi ha interaccions rudimentàries Si···H en el cas dels complexos d'iridi
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Topriska, Evangelia Vasiliki. "Experimental and computational study of a solar powered hydrogen production system for domestic cooking applications in developing economies." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/12824.
Full textAbstract:
In many developing economies, a high percentage of domestic energy demand is for cooking based on fossil and biomass fuels. Their use has serious health consequences affecting almost 3 billion people. Cleaner cooking systems have been promoted in these countries such as solar cooking and smokeless stoves with varying degrees of success. In parallel, solar electrolytic hydrogen systems have been developed and increasingly used during the last 25 years for electricity, heat and automobile fueling applications. This study has developed and tested experimentally in the laboratory a solar hydrogen plant numerical model suitable for small communities, to generate and store cooking fuel. The numerical model was developed in TRNSYS and consists of PV panels supplying a PEM electrolyser of 63.6% measured stack efficiency and hydrogen storage in metal hydride cylinders for household distribution. The model includes novel components for the operation of the PEM electrolyser, its controls and the metal hydride storage, developed based on data of hydrogen generation, stack temperature and energy use from a purpose constructed small-scale experimental rig. The model was validated by a second set of experiments that confirmed the accurate prediction of hydrogen generation and storage rates under direct power supply from PV panels. Based on the validated model, large-scale case studies for communities of 20 houses were developed. The system was sized to generate enough hydrogen to provide for typical domestic cooking demand for three case-studies; Jamaica, Ghana and Indonesia. The daily cooking demands were calculated to be 2.5kWh/day for Ghana, 1.98kWh/day for Jamaica and 2kWh/day for Indonesia using data mining and a specific quantitative survey for Ghana. The suitability of weather data used in the model was evaluated through Finkelstein Schafer statistics based on composite and recent weather data and by comparing simulation results. A difference of 0.9% indicated that the composite data can be confidently used. Simulations results indicate that a direct connection system to the PV plant rather than using a battery is the optimal design option based on increased efficiency and associated costs. They also show that on average 10tonnes of CO2/year/household can be saved by replacing biomass fuel with hydrogen. The potential of total savings in the three case-study countries is shown in the form of novel solar hydrogen potential maps. The results of this study are a contribution towards better understanding the use of hydrogen systems and enhancing their role in renewable energy policy.
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Grant, Paul Allan Anthony. "A study of the neurotoxic effects of hydrogen peroxide and of the potential neuroprotective effects of carbachol in SK-N-SH human neuroblastoma cells." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322307.
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LIRA, Renato Pereira de. "Qualidade pós-colheita da abóbora brasileirinha (curcubita moshata) em diferentes épocas de colheita e tempos de armazenamento." Universidade Federal de Campina Grande, 2017. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/757.
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A abóbora ‘Brasileirinha’ é uma cultivar que produz frutos bicolores (verde e amarelo) com excelente potencial nutricional. No entanto, a época de colheita e o tempo de armazenamento podem ser considerados fatores que interferem diretamente na qualidade do fruto. Assim, objetivou-se avaliar a qualidade pós–colheita da abóbora brasileirinha em diferentes épocas de colheita e tempo de armazenamento. Os frutos foram colhidos em uma área de cultivo, localizado no município de Teixeira – PB a 103 km de Pombal – PB. A pesquisa foi realizada entre março e maio de 2016, no Laboratório de Química, Bioquímica e Análises de Alimentos do Centro de Ciências e Tecnologia Agroalimentar da Universidade Federal de Campina Grande, Pombal - PB. Utilizou-se o delineamento inteiramente casualizado, em esquema fatorial 3 x 6, três épocas de colheita da abóbora (70, 90 e 110 dias após o plantio) e seis tempos de armazenamento (0, 7, 14, 21, 28 e 35 dias), contendo 5 repetições, com 1 fruto por repetição. As características físicas avaliadas foram: perda de massa fresca, comprimento longitudinal, diâmetros superior e inferior, cavidade interna, espessura da polpa, espessura da polpa do pescoço e firmeza. As características químicas avaliadas foram: potencial hidrogeniônico (pH), vitamina C, sólidos solúveis (SS), acidez titulável (AT), razão (SS/AT), carotenóides total, compostos fenólicos, flavonoides, antocianinas, açucares solúveis totais e açucares redutores. As características físicas avaliadas, não apresentaram diferença significativa nas três épocas de colheita, com exceção da firmeza que variou de 136 a 158 N. Os frutos oriundos da terceira época de colheita aos (110 dias) foram os que apresentaram os maiores teores de sólidos solúveis, vitmina C e carotenóides durante os 35 dias de armazenamento. A razão SS/AT foi maior na primeira época de colheita aos (70 dias). Os frutos oriundos da terceira época de colheita aos (110 dias) foram os que resultaram melhor qualidade para as características físicas e químicas estudadas, sendo recomendado a melhor época de colheita para o consumo da abóbora brasileirinha.
A 'Brasileirinha' pumpkin is a cultivar that produces bicolour fruits (green and yellow) with excellent nutritional potential. However, a harvesting time and storage time can be considered factors that interfere in the quality of the fruit. The objective of this study was to evaluate a post-harvest quality of the Brazilian pumpkin at different harvesting times and storage time. The fruits were harvested in a growing area, located in the municipality of Teixeira - PB, 103 km from Pombal - PB. The research was carried out between March and May of 2016, not Laboratory of Chemistry, Biochemistry and Food Analysis of the Center of Sciences and Technology Agrifood of the Federal University of Campina Grande, Pombal - PB. A completely randomized design was used in a 3 x 6 factorial design, three pumpkin harvest times (70, 90 and 110 days after the plan) and six storage times (0, 7, 14, 21, 28 and 35 days ), containing 5 replicates, with 1 fruit per replicate. The physical characteristics evaluated were: loss of fresh mass, longitudinal length, upper and lower diameters, internal cavity, pulp thickness, neck pulp thickness and firmness. The chemical characteristics evaluated were: hydrogenation potential (pH), vitamin C, soluble solids (SS), titratable acidity (AT), ratio (SS / AT), total carotenoids, phenolic compounds, flavonoids, anthocyanins, total soluble sugars and sugars. . The physical characteristics evaluated did not present the difference in the three harvest periods, with the exception of the company that ranged from 136 to 158 N. The fruits from the third harvest season at (110 days) were those that presented the highest solids soluble Vitmina C and carotenoids during the 35 days of storage. The SS / AT ratio was higher in the first harvest season at (70 days). The fruits from the third harvest season at (110 days) were the ones that resulted in better quality for the physical and chemical characteristics studied, being recommended the best harvest season for the Brazilian pumpkin consumption.
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Haurais, Florian. "Evaluate the contribution of the fuel cladding oxidation process on the hydrogen production from the reflooding during a potential severe accident in a nuclear reactor." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS375/document.
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En centrales nucléaires, un accident grave est une séquence très peu probable d’événements durant laquelle des composants du réacteur sont significativement endommagés, par interactions chimiques et/ou fusion, à cause de très hautes températures. Cela peut mener à des rejets radiotoxiques dans l’enceinte et à une entrée d’air dans le réacteur. Dans ce contexte, ce travail de thèse mené chez EDF R&D visait à modéliser la détérioration du gainage combustible, en alliages de zirconium, en conditions accidentelles : haute température et soit vapeur soit mélange air-vapeur. L’objectif final était d’améliorer la simulation par le code MAAP de l’oxydation du gainage et de la production d’hydrogène, en particulier pendant un renoyage avec de l’eau. Dû à l’épaississement progressif d’une couche de ZrO2 dense et protectrice, la cinétique d’oxydation du Zr en vapeur à hautes températures est généralement (sous-)parabolique. Cependant, à certaines températures, cette couche d’oxyde peut se fissurer, devenant poreuse et non protectrice. Par ce processus de « breakaway », la cinétique d’oxydation devient plus linéaire. De plus, l’augmentation de température peut mener les matériaux du réacteur à fondre et à se relocaliser dans le fond de cuve dont la rupture peut induire une entrée d’air dans le réacteur. Dans ce cas, l’oxygène et l’azote réagissent avec les gaines pré-oxydées, successivement par oxydation du Zr (épaississant la couche de ZrO2), nitruration du Zr (formant des particules de ZrN) et oxydation du ZrN (créant de l’oxyde et relâchant de l’azote). Ces réactions auto-entretenues relancent la fissuration du gainage et de sa couche de ZrO2, induisant une hausse de sa porosité ouverte. Afin de quantifier cette porosité du gainage, un protocole expérimental innovant en deux étapes a été défini et appliqué : il consistait à soumettre des échantillons de gainage en ZIRLO® à diverses conditions accidentelles pendant plusieurs durées puis à des mesures de la porosité ouverte par porosimétrie par intrusion de mercure. Les conditions de corrosion comprenaient plusieurs températures allant de 1100 à 1500 K ainsi que de la vapeur et un mélange air-vapeur 50-50 mol%. Pour les échantillons de ZIRLO® oxydés en vapeur, sauf à 1200 et 1250 K, les transitions de cinétique n’ont pas lieu et la porosité ouverte reste négligeable au cours de l’oxydation. Cependant, pour les autres échantillons, corrodés en air-vapeur ou oxydés en vapeur à 1200 ou 1250 K, des transitions « breakaway » sont observées et les résultats de porosimétrie montrent que la porosité ouverte augmente au cours de la corrosion, proportionnellement au gain en masse. De plus, il a été mis en évidence que la distribution de tailles de pores des échantillons de ZIRLO® s’étend significativement pendant la corrosion, en particulier après « breakaway ». En effet, ces tailles vont de 60 μm à environ : 2 μm avant la transition, 50 nm juste après et 2 nm plus longtemps après. Enfin, un modèle numérique en deux étapes a été développé dans le code MAAP pour améliorer sa simulation de l’oxydation du gainage. D’abord, grâce à la proportionnalité entre porosité ouverte et gain en masse des échantillons, des corrélations de porosité ont été implémentées pour chaque condition de corrosion. Ensuite, les valeurs de porosité calculées sont utilisées pour augmenter proportionnellement la vitesse d’oxydation du gainage. Ce modèle amélioré simule ainsi non seulement les réactions chimiques des gaines en Zr (oxydation et nitruration) mais aussi leur dégradation mécanique et son impact sur leur vitesse d’oxydation. Ceci a été validé en simulant des essais QUENCH (-06, -08, -10 et -16), conduits au KIT pour étudier le comportement de gaines dans des conditions accidentelles avec un renoyage final. Ces simulations montrent un meilleur comportement thermique du gainage et une production d’hydrogène significativement plus haute et donc plus proche des valeurs expérimentales, en particulier pendant le renoyageIn nuclear power plants, a severe accident is a very unlikely sequence of events during which components of the reactor core get significantly damaged, through chemical interactions and/or melting, because of very high temperatures. This may potentially lead to radiotoxic releases in the containment building and to air ingress in the reactor core. In that context, this thesis work led at EDF R&D aimed at modeling the deterioration of the nuclear fuel cladding, made of zirconium alloys, in accidental conditions: high temperature and either pure steam or air-steam mixture. The final objective was to improve the simulation by the MAAP code of the cladding oxidation and of the hydrogen production, in particular during a core reflooding with water. Due to the progressive thickening of a dense and protective ZrO2 layer, the oxidation kinetics of Zr in steam at high temperatures is generally (sub-)parabolic. However, at certain temperatures, this oxide layer may crack, becoming porous and not protective anymore. By this “breakaway” process, the oxidation kinetics becomes rather linear. Additionally, the temperature increase can lead core materials to melt and to relocate down to the vessel lower head whose failure may induce air ingress into the reactor core. In this event, oxygen and nitrogen both react with the pre-oxidized claddings, successively through oxidation of Zr (thickening the ZrO2 layer), nitriding of Zr (forming ZrN particles) and oxidation of ZrN (creating oxide and releasing nitrogen). These self-sustained reactions enhance the cracking of the cladding and of its ZrO2 layer, inducing a rise of its open porosity.In order to quantify this cladding porosity, an innovative two-step experimental protocol was defined and applied: it consisted in submitting ZIRLO® cladding samples first to various accidental conditions during several time periods and then to measurements of the open porosity through porosimetry by mercury intrusion. The tested corrosion conditions included numerous temperatures ranging from 1100 up to 1500 K as well as both pure steam and a 50-50 mol% air-steam mixture. For the ZIRLO® samples oxidized in pure steam, except at 1200 and 1250 K, the “breakaway” kinetic transitions do not occur and the open porosity remains negligible along the oxidation process. However, for all other samples, corroded in air-steam or oxidized in pure steam at 1200 or 1250 K, “breakaway” transitions are observed and the porosimetry results show that the open porosity increases along the corrosion process, proportionally to the mass gain. Moreover, it was evidenced that the pore size distribution of ZIRLO® samples significantly extends during corrosion, especially after “breakaway” transitions. Indeed, the detected pore sizes ranged from 60 μm down to around: 2 μm before the transition, 50 nm just after and 2 nm longer after. Finally, a two-step numerical model was developed in the MAAP code to improve its simulation of the cladding oxidation. First, thanks to the proportionality between open porosity and mass gain of cladding samples, porosity correlations were implemented for each tested corrosion condition. Second, the calculated porosity values are used to proportionally enhance the cladding oxidation rate. This improved model thus simulates not only chemical reactions of Zr-based claddings (oxidation and nitriding) but also their mechanical degradation and its impact on their oxidation rate. It was validated by simulating QUENCH tests (-06, -08, -10 and -16), conducted at KIT to study the behavior of claddings in accidental conditions with a final reflooding. These simulations show a better cladding thermal behavior and a hydrogen production significantly higher and so closer to experimental values, in particular during the reflooding
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Guimarães, João de Jesus. "Comportamento agronômico do lúpulo (Humulus lupulus L.) em cultivo protegido submetido a irrigações com diferentes faixas de pH da água na região de Botucatu-SP /." Botucatu, 2020. http://hdl.handle.net/11449/192238.
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Orientador: Rodrigo Máximo Sánchez-RománResumo: O cultivo de lúpulo (Humulus Lupulus L) exige um adequado fornecimento de água, principalmente na fase de desenvolvimento, o qual envolve a formação e crescimento dos ramos laterais, florescimento, formação das inflorescências e maturação dos cones. Sabendo da importância do fornecimento de água na fase de desenvolvimento, a irrigação passou a ser utilizada nas áreas de cultivo desde o século XIX. No contexto da irrigação, a qualidade da água é um fator importante e que, quando não se dá a devida atenção, pode causar efeitos deletérios no sistema de irrigação, solo e na planta. O potencial hidrogeniônico (pH) é um dos parâmetros que caracteriza a qualidade de água para irrigação podendo influenciar na microbiologia do solo e no processo de intercâmbio de cátions (solo para a solução e vice-versa). Em virtude da importância da irrigação e dos poucos estudos relacionados ao pH da água da irrigação da cultura do lúpulo, este trabalho teve como objetivo avaliar o efeito da irrigação com diferentes faixas de pH da água sob o desenvolvimento agronômico do lúpulo, variedade Cascade, cultivado em ambiente protegido. A pesquisa foi conduzida em casa de vegetação no Departamento de Bioprocessos e Biotecnologia – DBB da Faculdade de Ciências Agronômicas – FCA/UNESP, Campus de Botucatu. O delineamento estatístico utilizado foi o inteiramente casualizados (DIC) com três tratamentos e dez repetições. Os tratamentos foram constituídos por três faixas de pH da água, sendo: T1 – pH 6 a 6,5, T... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Hop cultivation (Humulus Lupulus L) requires a adequate supply of water, especially at the developmental stage, or as involved in lateral branch formation and growth, flowering, inflorescence formation and cone maturation. Knowing the importance of water supply in the development phase, irrigation has been used in cultivated areas since the 19th century. In the context of irrigation, water quality for irrigation is an important factor which, when not given due attention, can have deleterious effects on the irrigation system, soil and the plant. The hydrogen potential (pH) of water is one of the parameters that characterizes the quality of water for irrigation and can influence soil microbiology and the cation exchange process (soil for solution and vice versa). Due to the importance of irrigation and the few studies related to the water pH of the irrigation of the hop culture, this work had as objective evaluate the effect of irrigation with different water pH ranges on the agronomic development of hops, Cascade variety cultivated in protected environment. The research was conducted in a greenhouse at the Department of Bioprocesses and Biotechnology – DBB of the Faculty of Agronomic Sciences - FCA/UNESP, Botucatu Campus. The statistical design used was the completely randomized design (CRD) with three treatments and ten replications. The treatments consisted of three water pH ranges: T1 - pH 6 to 6.5, T2 - pH 6.5 to 7 and T3 - 7 to 7.5. To obtain the treatments, 0,1 mol L-1 s... (Complete abstract click electronic access below)
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Polischuk, Vladimir. "Etude et réalisation de structure à base de silicium poreux en vue de la détection de gaz." Ecully, Ecole centrale de Lyon, 1999. http://www.theses.fr/1999ECDL0016.
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Ce travail de thèse visait à étudier les potentialités du silicium poreux comme support d'un élément sensible pour les capteurs de gaz. Afin de comprendre les mécanismes de formation du silicium poreux nous avons eu recours à l'électrochimie fondamentale de silicium. Ainsi, les mesures I-V de l'interface silicium/solution d'acide fluorhydrique ont mis en évidence deux mécanismes compétitifs : la formation électrochimique de l'oxyde de silicium et sa dissolution par HF. De même, la nature de l'oxyde de silicium est discutée dans le cadre des diagrammes d'équilibres tension-ph du système silicium-eau. Dans le but de développer de nouveaux capteurs de gaz, nous avons élaboré des couches de silicium poreux modifiées ultérieurement par un métal catalytique. Dans le cas des structures de type diode (Pd/Sp/Si), l'épaisseur de la couche de silicium poreux contrôle les processus de transport de courant. La quantité du palladium déposée influe beaucoup sur la sensibilité des structures sous gaz. Ainsi, ce sont les structures avec une couche ultramince de palladium qui présentent les meilleures réponses à l'hydrogène. En s'appuyant sur le modelé d'une hétérojonction métal/silicium poreux/si ayant une couche mince de silicium poreux, nous avons relie ce phénomène a la variation des porteurs libres de la zone de charge d'espace du silicium. La mesure de la différence de potentiel de contact nous a permis d'étudier l'effet de l'adsorption d'hydrogène sur la surface de palladium supporte sur du silicium poreux. Malgré nos attentes, les structures a base du silicium poreux ont montré une faible amélioration de la sensibilité par rapport aux structures traditionnelles Pd/SiO2/Si. Par contre, elles étaient plus performantes en ce qui concerne la cinétique, donc le temps de réponse deux fois plus rapide.
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Pinto, Marcelo Mendes. ""Influência do pH de armazenamento no crescimento subcrítico de trincas de porcelanas odontológicas com diferentes microestruturas"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/23/23140/tde-28082006-200019/.
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O objetivo do trabalho foi determinar o efeito do pH de armazenamento (pH 3,5; 7,0 e 10,0) nos parâmetros de crescimento subcrítico (n e ? f0) de duas porcelanas odontológicas com diferentes microestruturas (com e sem leucita). A hipótese testada foi a de que o pH do meio afeta os parâmetros de crescimento subcrítico dos dois materiais. Duas porcelanas feldspáticas foram avaliadas: 1) Ultropaline Dentina (UD), JenDental/Ucrânia; 2) Veneer Material 7 (VM7), Vita/Alemanha. A porcelana UD é composta de matriz vítrea com dispersão de partículas de segunda fase de leucita, enquanto a porcelana VM7 apresenta exclusivamente fase vítrea. Espécimes em forma de disco com características específicas (diâmetro e espessura) foram sinterizados com os dois materiais seguindo o ciclo proposto pelos fabricantes. Os espécimes foram armazenados em diferentes soluções com pH específico (3,5; 7,0 e 10,0) por 10 dias antes de serem testados. Os parâmetros de fadiga foram obtidos pelo método de fadiga dinâmica utilizando o ensaio de resistência à flexão biaxial (piston on three balls) com cinco taxas constantes de carregamento (0,01; 0,1; 1; 10 e 100 MPa/s). A tenacidade à fratura e a dureza foram avaliadas pelo método da fratura por indentação (IF). A microestrutura dos materiais foi analisada por meio de microscopia eletrônica de varredura, difração de raios X e análise química por fluorescência de raios X. O efeito do pH no coeficiente de susceptibilidade ao crescimento subcrítico (n) foi diferente para os dois materiais estudados. Os resultados mostraram que, para a porcelana vítrea (VM7), o valor de n não variou significativamente em função do pH. Para a porcelana com leucita (UD), houve uma diminuição do valor de n quando a armazenagem foi feita em pH 3,5. O efeito do pH no parâmetro escalar (? f0) também foi diferente para os dois materiais. Para a porcelana VM7, tanto o pH ácido como o básico resultaram em menores valores de resistência em relação ao pH neutro. Para a porcelana UD, somente a armazenagem em pH básico resultou em queda do valor de ? f0. Os valores de dureza dos dois materiais diminuíram conforme o pH foi aumentado, porém, somente a diferença entre o grupo armazenado a seco e o grupo armazenado em pH 10 foi estatisticamente significativa para as duas porcelanas. Com relação à tenacidade, o pH não influenciou significativamente nas médias obtidas para os dois materiais. Com base nos resultados foi possível concluir que o efeito pH do meio de armazenamento no crescimento subcrítico de porcelanas dontológicas varia de acordo com a microestrutura do material.The objective of the study was to determine the effect of the pH of the storage medium (pH 3,5; 7,0 e 10,0) on the fatigue parameters (n and ? f0) of two dental porcelains with different microstructures (with and without leucite). The hypothesis tested was that the pH affects the fatigue parameters of both materials. The dental porcelains tested were: 1) Ultropaline Dentin (UD), JenDental/Ucraine; 2) Veneer Material 7 (VM7), Vita/Germany. UD contains leucite and VM7 is only vitreous. Disc specimens were produced with both materials following manufacturers firing cycles. The specimens were stored in water solutions with different pHs (3,5; 7,0 e 10,0) for 10 days and after that the fatigue parameters were obtained by means of the dynamic fatigue test. Hardness and fracture toughness were determined by means of the indentation fracture technique. Microstructural analysis of the materials was also carried out. The effect of the pH in the fatigue parameters was different for the two materials tested. The results showed that, for VM7, the n value did not vary as a function of the pH. For porcelain UD, the n value was lower when the specimens where stored in pH 3,5. The parameter ? f0 was also affected by the pH. For both materials, the storage in basic pH resulted in a decrease in the ? f0 value. The hardness of both materials decreased with the increase in the pH of the storage media, and fracture toughness was not affect by the pH. Based on the results, it was possible to conclude that the effect of the pH (of the storage media) on the fatigue parameters of the dental porcelains studied varied according to the porcelains microstructure.
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Nylén, Linda. "Influence of the electrolyte on the electrode reactions in the chlorate process." Doctoral thesis, KTH, Tillämpad elektrokemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4681.
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The chlorate process is very energy intensive and a major part of the production costs are for electrical energy. Since the electricity prices are constantly increasing and may also vary periodically, the chlorate plants may be forced to adjust their production rate to the price at each moment in order to minimise their costs. Variation of current load requires increased knowledge regarding the electrode behaviour in a wide current range. In this thesis, the aim was to study the impact of the electrolyte on the electrode reactions in order to reduce the energy consumption. The work has mainly been experimental and additionally mathematical modelling has been carried out. A wide current range has been investigated in order to increase the understanding of the phenomena and to obtain results useful for low-load operation during the periods of high electricity cost. To operate the anode as energy efficiently as possible, the anode potential should not exceed the critical potential (Ecr), where the slope of the anodic polarisation curve increases, most likely due to ruthenium(VIII)-formation, and where the side reaction of oxygen evolution increases. In this work, the influence of different electrolyte parameters on Ecr has been studied. It was shown that a higher chloride concentration and an increased temperature lowered Ecr, which was expected to increase the risk of exceeding Ecr. However, this was not observed due to a simultaneous favouring of the chloride oxidation. Hence it was concluded that the electrolyte parameters should be optimised so that the lowest possible anode potential is obtained, which would enable higher current densities without exceeding Ecr. A further conclusion is that the increased slope of the polarisation curve at Ecr was possibly related to the lower activity for chloride oxidation on ruthenium oxidised to ruthenium(VIII). At full-load operation, the cathode potential was shown to be rather independent of the electrolyte composition despite a large variation of electrolyte parameters. The cathode composition appears to be more critical than the electrolyte composition when aiming at reducing the energy consumption. A strategy to increase the cathode activity could be to in situ apply a catalytic film onto the electrode surface. Therefore, Y(III) was added to a chloride electrolyte in order to form a yttrium hydroxide film on the alkaline cathode surface during hydrogen evolution. The yttrium-hydroxide film activated reduction of water (hydrogen evolution) and hindered hypochlorite reduction, proton reduction and nitrate reduction. The inhibiting properties are important for the prevention of side reactions, which currently are avoided by reducing Cr(VI) of the electrolyte on the cathode, producing an inhibiting chromium-hydroxide film. The studies on Y(III) increase the expectations for finding alternatives to the toxic Cr(VI). The addition of chromate to the chlorate electrolyte gives a high cathodic current efficiency and chromate has buffering properties in the electrolyte. The role of the buffer has been investigated for the oxygen evolution from water (one possible anodic side reaction), as well as cathodic hydrogen evolution. Models have been developed for these systems to increase the understanding of the interaction between buffer, electrode reactions and mass transport; the results have been verified experimentally. The chromate buffer increased the limiting current significantly for the cathodic H+ reduction and the cathodic overpotential was reduced drastically at currents lower than the limited current. A too low overpotential could result in the cathodic protection being lost. The presence of chromate buffer increased the limiting current for the oxygen evolution from OH-. The modelling of these systems revealed that the homogeneous reactions connected to the electrode reactions were not in equilibrium at the electrode surface. Further, a good resolution of the interface at the electrode surface was crucial since the, for the electrode reactions, important buffering takes place in an nm-thick reaction layer.Framställning av klorat är mycket energiintensiv och kräver stora mängder elenergi. Stigande elpriser, som dessutom ofta varierar under dygnet eller säsongsvis, gör att man vill reducera onödiga förluster samt ibland försöka anpassa produktionen så att man när elpriset är högt minskar den, för att sedan öka produktionen igen då elpriset sjunker. Denna flexibla drift kräver ny kunskap om hur elektroderna beter sig i ett större strömintervall än vad som tidigare varit av intresse. Målet med detta arbete var att, med fokus på elektrolytens betydelse, identifiera möjliga förbättringar för kloratprocessen och därmed minska energiförbrukningen. Studierna har i huvudsak varit experimentella men även matematisk modellering har använts. Ett brett strömintervall har undersökts för att bättre förstå fenomenen och för att även kunna använda resultaten då höga elpriser gör att man vill köra processen vid lägre laster än normalt. För att driften av anoden ska vara så energieffektiv som möjligt bör anodpotentialen inte överskrida den kritiska potentialen (Ecr), där den anodiska polarisationskurvan får en högre lutning (troligtvis pga Ru(VIII)-bildning) och bireaktionen syrgasutveckling ökar. I detta arbete har påverkan av olika elektrolytparametrar på Ecr undersökts. Det visade sig att en ökad kloridkoncentration och ökad temperatur sänkte Ecr. Trots att detta borde göra att Ecr lättare överskrids, blev inte detta fallet eftersom kloridoxidationen samtidigt gynnades. Slutsatsen blir därför att elektrolytparametrarna bör optimeras så att lägsta möjliga anodpotential uppnås, vilket då även gör att strömtätheten kan ökas utan att Ecr överskrids. Slutsatsen är vidare att polarisationskurvans högre lutning vid Ecr kan ha att göra med att rutenium oxiderat till rutenium(VIII) har lägre aktivitet för kloridoxidation. Vid full last visade sig katodens potential vara relativt oberoende av elektrolytsammansättningen trots att denna varierades kraftigt. Katodens sammansättning verkar vara viktigare att ta hänsyn till än elektrolytens för kunna åstadkomma en större energibesparing. Ett alternativ till att öka katodens aktivitet skulle vara att in-situ belägga elektrodytan med en katalytisk film. Försök gjordes att sätta till Y(III) till kloridelektrolyt för att under vätgasutveckling fälla ut en yttriumhydroxidfilm på den alkaliska katodytan. Yttriumhydroxidfilmen aktiverade vattenreduktion (vätgasutveckling) och inhiberade hypokloritreduktion, protonreduktion och nitratreduktion. De inhiberande egenskaperna är viktiga för att förhindra bireaktioner, vilka idag hindras av att Cr(VI) i elektrolyten reduceras på katoden och bildar en hindrande kromhydroxidfilm. Försöken med Y(III) visar att det finns goda möjligheter att hitta alternativ till det miljöfarliga Cr(VI). Kromattillsatsen i kloratelektrolyt ger förutom ett högt katodiskt strömutbyte även en buffrande effekt till elektrolyten. Effekten av buffert har undersökts för en av de anodiska bireaktionerna, syrgasutveckling ur vatten, samt för vätgasutvecklingen på katoden. Dessa system har modellerats för att bättre förstå samspelet mellan buffert, elektrodreaktioner och materietransport och resultaten har verifierats experimentellt. Kromatbufferten ökade gränsströmmen för katodisk H+-reduktion betydligt och katodöverpotentialen sjönk kraftigt vid lägre strömmar än gränsströmmen. Detta kan vara ett problem om överpotentialen sjunker så lågt att elektroden inte är katodiskt skyddad. För syrgasutvecklingen ökade närvaron av kromatbuffert gränsströmmen för syrgasutveckling ur OH-. Modellering av dessa system visar att de homogena reaktioner som var kopplade till elektrodreaktionerna inte var i jämvikt vid elektrodytan. Vidare visade det sig vara mycket viktigt med en bra upplösning av gränsskiktet vid elektrodytan, då den buffring som är viktig för elektrodreaktionerna sker i ett mycket tunt reaktionsskikt (nanometertjockt).
QC 20100901
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Abdel, Latif Marwa K. "Electrochemical oxidation of aliphatic carboxylates: Kinetics, thermodynamics, and evidence for a shift from a concerted to a stepwise mechanism in the presence of water." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82522.
Full textAbstract:
The mechanism and the oxidation potential of the dissociative single electron transfer for tetra-n-butylammonium acetate has been investigated via conventional (cyclic voltammetry) and convolution voltammetry. The oxidation potential for tetra-n-butylammonium acetate was determined to be 0.60 ± 0.10 (vs. Ag/ (0.1 M) AgNO3) in anhydrous acetonitrile. The results also indicated the mechanism of oxidation was concerted dissociative electron transfer (cDET), rather than stepwise as was previously reported.
To further investigate the mechanism, a series of aliphatic and aromatic tetra-n
butylammonium carboxylates were synthesized and investigated via convolution and conventional methods under anhydrous conditions (propionate, pivalate, phenyl acetate, and benzoate). The reported results showed high reproducibility and consistency with a concerted dissociative electron transfer for aliphatic carboxylates with a systematic shift in the oxidation potentials (0.60 ± 0.09 V for acetate, 0.47 ± 0.05 V for propionate, and 0.40 ± 0.05 V for pivalate) within the series which is expected trend based on radical stabilization energies of the alkyl groups on the aliphatic carboxylates.
Hydrogen bonding was investigated as a possible source for the discrepancy between our results and the reported mechanism of the dissociative electron transfer. Because of the extreme hygroscopic nature of carboxylate salts, it was hypothesized that the presence of small amounts of water might alter the reaction mechanism. Deionized water and deuterium oxide additions to anhydrous acetonitrile were performed to test this hypothesis. The mechanism was noted to shift towards a stepwise mechanism as water was added. In addition, the derived oxidation potentials became more positive with increasing concentrations of water. Several explanations are presented with regards to water effects on the shift in the electron transfer mechanism.
Indirect electrolysis (homogeneous redox catalysis) was also employed as an alternative
and independent approach to quantify the oxidation potentials of carboxylates. A series of substituted ferrocenes were investigated as mediators for the oxidation of tetra-n-butylammonium acetate. Preliminary data showed redox catalysis was feasible for these systems. Further analyses of the electrochemical results suggested a follow-up chemical step (addition to mediator) that competes with the redox catalysis mechanism. As predicted from theoretical working curves, a plateau region in the ip/ipd plots (where no meaningful kinetic information could be obtained) was observed. Products mixture analyses verified the consumption of the mediator upon electrolysis, but no further information with regards to the nature of the mechanism was deduced.
In a related study the effects of hydrogen bonding and ions on the reactivity of neutral free radicals were examined by laser flash photolysis. The rate of the β-scission of the cumyloxyl radical is influenced by cations (Li+ > Mg2+ ≈ Na+ > nBu4N+) due to stabilizing ion-dipole interactions in the transition state of the developing carbonyl group. Experimental findings are in a good agreement with theoretical work suggesting metal ion complexation can cause radical clocks to run fast with a more significant effect if there is an increase in dipole moment going from the reactant to the transition state.Ph. D.
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Bataillon, Christian. "Application de l'analyse spectrale du bruit electrochimique a l'etude de la corrosion par piqures des alliages d'aluminium." Paris 6, 1987. http://www.theses.fr/1987PA066251.
Full textAbstract:
Application de l'analyse du bruit en potentiel genere par la piquration des alliages d'aluminium a la caracterisation de leur resistance a cette forme de corrosion. Presentation de quelques considerations phenomenologiques concernant les fluctuations de potentiel. Presentation d'un mecanisme de la propagation des piqures sur les alliages d'aluminium
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PEREIRA, Francinaldo de Freitas. "Desenvolvimento e avaliação de um sistema de aquecimento utilizando hidrogênio eletrolítico como combustível." Universidade Federal de Campina Grande, 2005. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/2009.
Full textAbstract:
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O objetivo deste trabalho é estudar o desempenho de um forno tipo mufla adaptado para utilizar hidrogénio eletrolítico como combustível. O sistema de aquecimento poderá ser aplicado em fornos de produção de tijolos, telhas, materiais cerâmicos, e produtos derivados do trigo. Neste sentido o hidrogénio eletrolítico substituiria os combustíveis de origem orgânica, que são os grandes vetores da poluição atmosférica, o hidrogénio poderá ser produzido usando-se energias renováveis como painéis fotovoltaicos e/ou turbinas eólicas. O hidrogénio foi produzido a partir da eletrolise da água em um reator bipolar usando hidróxido de potássio como eletrólito. O consumo de energia e a produção de hidrogénio foram estimados para diferentes níveis temperaturas de 300°C, 900°C e, 1100°C.
The objective of this work is the study of an oven adapted to use electrolytic hydrogen as fuel. The possible applications are the cooking of clay used in the production of ceramic materiais, bricks and tiles; as well as the production of derived products of the wheat. The electrolytic hydrogen, used as a fuel in replacement of carbonaceous fuels which contribute to the atmospheric pollution, can be produced using renewable energies like photovoltaic solar paneis and/or aeolian turbine power generators. The hydrogen production is done by electrolysis of water which occurs in a bipolar reactor using potassium hydroxide as electrolyte. The energy consumption and the hydrogen production are calculated for different temperatures of 300°C, 900°C and 1100°C range. They are respectively, 0,9 kWh and 0,131 m3, 2,1 kWh and 0,311 m3 and 3,2 kWh and 0,498 m3.