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Mynatt, Trenton T. "Splitting Maul." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2176.
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Kuo, Yenting. "Photocatalytic water splitting." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/12141.
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Doctor of PhilosophyDepartment of Chemistry
Kenneth J. Klabunde
New photocatalystic materials Ti-In oxy(nitride) and nanosized Ru-loaded strontium titanate doped with Rh (Ru/SrTiO3:Rh) have been synthesized. The textural and surface characteristic properties were studied by nitrogen BET analysis, diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy and powder XRD. The photocatalytic properties were enhanced by the binary metal oxides of titanium dioxide and indium oxide. The XRD patterns confirmed the oxygen exchange between two metal oxides during the synthesis. Moreover, the presence of titanium dioxide can help the stabilization of InN during hot NH3(g) treatment. On the other hand, the particle sizes of aerogel prepared Ru/SrTiO3:Rh varied from 12 to 25 nm depended on different Rh doping. A mixture of ethanol and toluene was found to be the best binary solvent for supercritical drying, which yielded a SrTiO3 sample with a surface area of 130 m2 Enhanced photocatalytic hydrogen production under UV-vis light irradiation was achieved by ammonolysis of intimately mixed titanium dioxide and indium oxide at high temperatures. Gas chromatography monitored steadily the formation of hydrogen when sacrificial (methanol or ethanol) were present. XRD patterns confirmed that the photocatalysts maintain crystalline integrity before and after water splitting experiments. Moreover, the presence of InN may be crucial for the increase of hydrogen production activities. /g and an average crystallite size of 6 nm. These Ru/SrTiO3:Rh photocatalysts have been studied for photocatalytic hydrogen production under visible light. The band gap of the bulk SrTiO3 (3.2 eV) does not allow response to visible light. However, after doping with rhodium and loaded with ruthenium, the modified strontium titanates can utilize light above 400 nm due to the formation of valence band or electron donor levels inside of the band gap. Moreover, the surface areas of these photocatalysts are much larger than conventional solid-state synthesized samples (1-2 m 2/g), which yielded more Ru loading and reaction sites. The areogel and hydrothermal synthesized samples required basic (alkaline) conditions for hydrogen generation facilitation compared with acidic conditions for conventional solid-state samples.
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Khosh, Khooee Saba. "Routes Splitting Urban Areas." Thesis, KTH, Urbana och regionala studier, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-47855.
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Since automobiles are detachable elements of contemporary urban life, studying the interactions imposed by them to urban forms is helpful to develop urban areas. The isolated neighborhoods locating along highways are the common picture that easily can be found in most of developed cities. The more advanced traffic networks a city possesses the more detached neighborhoods can be detected in it. The main question trying to be answered in this study is how to reattach these separated areas together and how to create a peaceful coexistence between highways and their neighborhoods. In order to find an answer, a municipality named Upplands Väsby (in the north of Stockholm) has been studied and analyzed. This real sample with internal connectivity problems was supposed to provide a ground to analyze the outcome of proposed interventions. This process resulted in obtaining a general policy in approaching this issue and some flexible interventions proper for this specific site of study. Finally, the study implies on the possibility of reattaching isolated area over high-speed roads. It also brought up some suggestions for improvement of mobile passenger’s perception of the road and surrounding areas while facilitating the pedestrian’s movement through the site.
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Mashayekhi, Mohammadsadegh. "Splitting a Bose condensate." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12647.
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The primary goal of this thesis is to find the distribution function of number of particles imbalance for ultra cold bosons trapped in a double well potential elongated in one direction for different strength of interaction between particles. This distribution function has been found to be Gaussian distribution function in two different limits. The first limit is weak interaction limit, where we only consider one energy level per well that is called "two mode approximation" regime. The second limit is when the interaction energy is in the same order as gap between energy levels where in this case, we consider finite number of levels per well. The standard deviation of number of particles distribution also has been found in both limits to be proportional to the square root of the total number of particles. In addition, some numerical work is done to find these distribution functions and the results are in agreement with analytical results.
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Davis, Samuel M. "Electrochemical Splitting of Sodium Sulfate." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11505.
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Five cation exchange membranes and four anion exchange membranes were tested in a three-compartment, two-membrane, electrolysis salt-splitting cell for the recycle of sodium sulfate into sodium hydroxide and sulfuric acid. The cell is further examined using DuPont Nafion 324 cation exchange membrane and Sybron Ionac MA-7500 anion exchange membrane to determine the maximum concentration of sodium hydroxide that can be produced by electrolysis salt-splitting as well as to determine the chief source of inefficiency. The discussion includes recommendations for future electrolysis salt-splitting cells and a mathematical model of the cell is created to determine optimum operating conditions.
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Svengren, Henrik. "Water splitting by heterogeneous catalysis." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148181.
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A sustainable solution for meeting the energy demands at our planet is by utilizing wind-, solar-, wave-, thermal-, biomass- and hydroelectric power. These renewable and CO2 emission-free energy sources are highly variable in terms of spatial and temporal availability over the Earth, introducing the need for an appropriate method of storing and carrying energy. Hydrogen has gained significant attention as an energy storage- and carrier media because of the high energy density that is exploited within the ‘power-to-gas’ process chain. A robust way of producing sustainable hydrogen is via electrochemical water splitting. In this work the search for new heterogeneous catalyst materials with the aim of increasing energy efficiency in water splitting has involved methods of both electrochemical water splitting and chemical water oxidation. Some 21 compounds including metal- oxides, oxofluorides, oxochlorides, hydroxide and metals have been evaluated as catalysts. Two of these were synthesized directly onto conductive backbones by hydrothermal methods. Dedicated electrochemical cells were constructed for appropriate analysis of reactions, with one cell simulating an upscale unit accounting for realistic large scale applications; in this cell gaseous products are quantified by use of mass spectrometry. Parameters such as real time faradaic efficiency, production of H2 and O2 in relation to power input or overpotentials, Tafel slopes, exchange current density and electrochemical active surface area as well as turnover numbers and turnover frequencies have been evaluated. Solubility, possible side reactions, the role of the oxidation state of catalytically active elements and the nature of the outermost active surface layer of the catalyst are discussed. It was concluded that metal oxides are less efficient than metal based catalysts, both in terms of energy efficiency and in terms of electrode preparation methods intended for long time operation. The most efficient material was Ni-Fe hydroxide electrodeposited onto Ni metal foam as conductive backbone. Among the other catalysts, Co3Sb4O6F6 was of particular interest because the compound incorporate a metalloid (Sb) and redox inert F and yet show pronounced catalytic performance. In addition, performance of materials in water splitting catalysis has been discussed on the basis of results from electron microscopy, solubility experiments and X-ray diffraction data.
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Tang, Wei-pai. "Schwarz splitting and template operators." Stanford, CA : Dept. of Computer Science, Stanford University, 1987. http://doi.library.cmu.edu/10.1184/OCLC/19643650.
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Thesis (Ph. D.)--Stanford University, 1987."June 1987." "Also numbered Classic-87-03"--Cover. "This research was supported by NASA Ames Consortium Agreement NASA NCA2-150 and Office of Naval Research Contracts N00014-86-K-0565, N00014-82-K-0335, N00014-75-C-1132"--P. vi. Includes bibliographical references (p. 125-129).
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Ayala, P. Silvana, Shelby Vorndran, Yuechen Wu, Benjamin Chrysler, and Raymond K. Kostuk. "Segmented holographic spectrum splitting concentrator." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622711.
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This paper presents a segmented parabolic concentrator employing holographic spectral filters that provide focusing and spectral bandwidth separation capability to the system. Strips of low band gap silicon photovoltaic (PV) cells are formed into a parabolic surface as shown by Holman et. al. [1]. The surface of the PV segments is covered with holographic elements formed in dichromated gelatin. The holographic elements are designed to transmit longer wavelengths to silicon cells, and to reflect short wavelength light towards a secondary collector where high-bandgap PV cells are mounted. The system can be optimized for different combinations of diffuse and direct solar illumination conditions for particular geographical locations by controlling the concentration ratio and filtering properties of the holographic elements. In addition, the reflectivity of the back contact of the silicon cells is used to increase the optical path length and light trapping. This potentially allows the use of thin film silicon for the low bandgap PV cell material. The optical design combines the focusing properties of the parabolic concentrator and the holographic element to control the concentration ratio and uniformity of the spectral distribution at the high bandgap cell location. The presentation concludes with a comparison of different spectrum splitting holographic filter materials for this application.
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Jackson, Jack Lee. "Splitting in finite metacyclic groups." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289018.
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It is well known that all finite metacyclic groups have a presentation of the form G = ‹a,x,aᵐ = 1,xˢaᵗ = 1,aˣ = aʳ›. The primary question that occupies this dissertation is determining under what conditions a group with such a presentation splits over the given normal subgroup ‹a›. Necessary and sufficient conditions are given for splitting, and techniques for finding complements are given in the cases where G splits over ‹a›. Several representative examples are examined in detail, and the splitting theorem is applied to give alternate proofs of theorems of Dedekind and Blackburn.
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Roger, Barba Isolda. "Investigations into electrochemical water splitting." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8228/.
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The work detailed in this thesis is organized in the following manner: In Chapter 1 we discuss electrochemical and photoelectrochemical catalysts in the context of their application for solar-to-hydrogen devices. During this introduction we will give an overview of the current state of the field, discussing the different kinds of materials that are being investigated before giving a brief description of some actual solar-to-hydrogen devices and finishing with a discussion of the current and future challenges in the field. Chapter 2 is a description of the different techniques used throughout this thesis. Once having set the bases, we shall start with the actual research, which corresponds to Chapters 3 to 5. Chapter 3 and 4 deal with the effect of trace metal impurities in electrochemical water splitting. In Chapter 3 we show that adventitious nickel at trace levels can act as a water oxidation catalyst in mildly basic aqueous solutions at overpotentials comparable to many recently-reported water oxidation catalysts, therefore serving to raise the burden of proof required of new materials in this field. Chapter 4 shows how silver ions leaking from Ag/AgCl reference electrodes in aqueous buffers at low pH can deposit on the working electrode as Ag(0) and catalyze the hydrogen evolution reaction, calling into question the validity of any reports using these electrodes that cannot demonstrate significantly superior activity to the baseline we set in this chapter. In Chapter 5 we describe a direct hydrothermal deposition method to prepare Cobalt-doped MoS2 thin films onto transparent Fluorine-doped SnO2 substrate and demonstrate that the obtained films display good activity for the hydrogen evolution reaction from acid solution.
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Creus, Casanovas Jordi. "Electrocatalytic water splitting with ruthenium nanoparticles." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664045.
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L’estudi de sistemes basats en nanopartícules per a la catàlisi de les reaccions de reducció de protons a hidrogen (HER) i oxidació d’aigua a oxigen (OER) permet el disseny i desenvolupament de noves espècies catalítiques de manera racional, les quals poden millorar l’eficiència de la reacció de dissociació de l’aigua o “water splitting” (WS) per l’obtenció de H2, fent d’aquest procés una alternativa viable als combustibles fòssils. D’entre els metalls més utilitzats, el Pt i l’Ir són els que han donat millors resultats d’activitat i estabilitat per la HER i l’OER, respectivament. En aquest sentit, bona part d’investigació en el camp és dedicada a estudiar i entendre les interaccions que tenen part entre les diferents espècies durant la catàlisi, per poder transferir aquest coneixement a altres espècies basades en metalls més barats. El Ruteni podria ser una alternativa als metalls Pt/Ir, tenint en compte la seva versatilitat i la possibilitat que ofereix a ser estudiat mitjançant un ampli ventall de tècniques analítiques com a resultat de les seves propietats.
L’objectiu d’aquesta tesis doctoral és el de desenvolupar nano-materials basats en Ru com a catalitzadors per a les reaccions de HER i OER, i estudiar-ne les característiques que indueixen una certa activitat catalítica. L’ús del mètode organometàl·lic com a procediment de síntesis de nanopartícules permet l’obtenció d’aquestes amb un control en les propietats que les defineixen com ara el diàmetre, l’entorn superficial o la dispersió. El mètode organometàl·lic permet l’addició d’agents coordinants a la mescla de reacció, els quals aturen la nucleació termodinàmica per formar un material “bulk” i estabilitzen la formació de partícules de mida nanomètrica. Aquestes espècies poden influenciar no només en la síntesi dels materials, sinó també a la reactivitat de les NPs, un efecte molt important pels processos catalítics en què poden estar involucrades. A més a més de la formació de partícules col·loïdals, una altra possibilitat que ofereix l’aproximació organometàl·lica és la síntesis de NPs a la superfície d’un suport com ara nanotubs de carboni, fibres, òxids metàl·lics, MOFs, etc. Aquest mètode va ser desenvolupat per primera vegada en el grup de recerca de la Dr. Philippot tres dècades enrere i actualment és àmpliament utilitzat per un número de grups d’investigació elevat.
En resum, en aquesta memòria es descriu la síntesi de RuNPs per la seva avaluació com a catalitzadors per la HER i l’OER, amb l’objectiu d’entendre quines propietats de les NPs afecten els diferents passos catalítics i així ser capaços de dissenyar nous catalitzadors amb un millor rendiment catalític per la producció d’H2 a partir de l’aigua.The study of nanoparticulated systems for the hydrogen evolution (HER) and oxygen evolution (OER) reactions allows to rationally design new catalysts that enhance the water splitting process for obtaining H2, and thus making it a suitable alternative to fossil fuels as energy carriers. Nowadays Pt and Ir are the leading metals in HE and OE catalysts, respectively, but a huge effort is being devoted to understand the mechanistic pathways that rule both semi-reactions in order to transfer the knowledge to other metals which can be more abundant and thus cheaper. Ru appears as a feasible alternative to deeply explore the reaction steps involved in the process, because it is a highly-versatile metal which shows similar activities than Pt/Ir and which can be studied by a wide range of analytical techniques as a result of its properties. In addition, Ru is four times cheaper than the state-of-the-art Pt. This PhD work aims to develop Ru-based nanocatalysts for both HER and OER, and study the characteristics that induce a specific catalytic response. The use of the organometallic approach as synthetic methodology allows to finely control the properties of the NPs, e.g. size, surface environment, dispersion, etc. In this synthetic procedure, organic ligands can be added as stabilizing agents to halt the nucleation of metal atoms leading to the formation of the nanosized systems. These ligands can alter the chemical properties of the surface of the nanoparticles, a key feature in the catalytic processes. This methodology allows as well the preparation of metal nanoparticles onto the surface of solid supports, e.g. carbon nano-tubes, fibers, metal oxides, MOFs, etc. The organometallic approach was first developed in our group around three decades ago, and today its wide use by the global scientific community has brought a large knowledge on different nanometric systems. The development of precisely controlled nanocatalysts for their application in challenging catalysis like the production of H2 by water-splitting lies among our research interests. To sum up, the synthesis of Ru-NPs and their evaluation as catalysts for the HER and OER are described, aiming to understand the factors ruling the catalytic steps on the surface of the particles, to be able to rationally design new catalysts that make the water splitting process efficient enough to replace fossil fuels by H2.
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Jerdonek, Christopher John. "The girth of a Heegaard splitting /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Roberts, Jacob Thomas. "Splitting techniques in vertical pneumatic conveying." Thesis, University of Nottingham, 2007. http://eprints.nottingham.ac.uk/13593/.
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The following work details an investigation into improving efficiency in pulverised-fuel- fired power stations. The particular area of focus is the splitter box; this is located in the pneumatic conveying pipeline within the power station. The conveying pipelines take the pulverised fuel from the mill to the burner face, at some point the air/fuel mixture has to be split to feed the individual burners. It is at these points that the splitter boxes occur, dividing the pipe into multiple legs. It is common for some of these splits to produce poor fuel balance between legs, leading to excess air being required for their combustion at the burner wall. The increased supply of air increases the chance of the formation of NOx gases as well as reducing the overall efficiency of the plant. The poor fuel balance is caused by a particle rope, a dense area of particle stratification that creates an area of high fuel density that is not easily divided by the splitter boxes. The objective of this work is to develop devices to improve the fuel balance at splitter boxes. The work involves an investigation into existing devices and station geometries to see why existing devices have not become commonplace in coal-fired power stations. It also involves conceptual design of devices and then their testing, both computationally and experimentally. Finally, the devices are assessed for their suitability for full-scale power station implementation. This thesis used both experimental and computational techniques to develop devices to overcome the problems at splitter boxes and successfully produced several devices that could be developed and deployed in full scale testing.
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吳潔貞 and Kit-ching Betty Ng. "Correlation effects in crystal field splitting." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31230714.
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Smith, David W. "Spin-orbit splitting of surface states." Thesis, University of Bath, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426149.
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Roller, Martin Albrecht. "Splitting theroms for Poincare duality groups." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257295.
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Burch, Henry Arthur. "Nanostructured electrodes for photoelectrochemical water splitting." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6903/.
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Nanostructured MoS\(_2\) and ZnFe\(_2\)O\(_4\) were synthesised and tested as catalytic water splitting photoelectrodes. MoS\(_2\) was nanopatterned from a bulk crystal using a combination of nanosphere lithography and plasma etching. Three morphologies were produced: nanospheres deposited with interstices between them produced nanopillars, nanospheres squashed into hexagons imprinted a nanowell pattern, and linked nanopillars resulted from parts of each. The MoS\(_2\) was tested as a photocathode and morphologies with linkages between features had improved catalysis than those without. This was attributed to the layered structure of MoS\(_2\). These samples degraded in air to MoSxO(\(_2\)\(_-\)\(_x\)), and an electrochemical technique utilising Na\(_2\)S\(_2\)O\(_3\) was used to re-sulfidate the MoSxO(\(_2\)\(_-\)\(_x\)). The technique decreased the onset potential from -0.27 V SHE to -0.17 V SHE, and the Tafel slope from 282 mV dec\(^{-1}\) to 87 mV dec\(^{-1}\). ZnFe\(_2\)O\(_4\) electrodes were deposited by AACVD from a precursor molecule. The deposition solvent composition was systematically altered between methanol and ethanol to examine its effect on the nanostructure. ZnFe\(_2\)O\(_4\) electrodes deposited from predominantely methanol solvent had compact morphologies due to heterogenous nucleation, while the electrodes deposited from predominantly ethanol solvent had high surface area structures due to homogeneous nucleation. The more exothermic enthalpy of combustion of ethanol was deemed responsible.
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Piotter, Jason Matthew. "Longitudinal Slab Splitting in Composite Girders." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31765.
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Longitudinal slab splitting in composite hot rolled girders and joist girders was investigated. Two different type of framing configurations were studied with two tests conducted per configuration. The framing configurations were designated as either flush-framed or haunched, which describes the framing of the joists into the joist girders or H-shape. Each floor system consisted of at least one exterior or spandrel joist girder, one interior joist girder, and in three of the four tests, an exterior or spandrel H-shape. The nominal lengths of the girders were 30 ft 4 in. with a centerline spacing of 7 ft for the flush-framed tests and 6 ft 9 in. for the haunch tests. Varying amounts of transverse reinforcement were used in the slab over each girder. Shear connectors were all 0.75 in. diameter headed shear studs of varying lengths. The results of these tests were used to determine the minimum amount of transverse reinforcement required to prevent longitudinal splitting from controlling the strength of the section. A comparative analytical study was performed to generate a design procedure for determining the appropriate amount of transverse reinforcement. This consisted of adapting existing procedures in reinforced concrete for similar shear problems and generating alternative procedures based on existing research for composite construction. Results from these methods were then calibrated against experimental data obtained in this study.Master of Science
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Sellama, Hocine. "Difference equations and splitting of separatrices." Université Louis Pasteur (Strasbourg) (1971-2008), 2007. http://www.theses.fr/2007STR13162.
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Nous avons étudié l'influence de la discrétisation d'une équation différentielle sur les variétés stables et instables dans deux exemples concrets : l'équation logistique et l'équation du pendule. L'équation logistique est équivalente à un système qui admet deux points selles A et B. Il est connu que la variété stable en A coïncide avec la variété instable en B. En améliorant des résultats antérieures de A. Fruchard et R. Schäfke, nous montrons que les deux variétés ne coïncident plus pour l'équation discrétisée. La démonstration est basée sur une modification d'une approche développée par R. Schäfke et H. Volkmer. La deuxième partie est consacrée à une étude analogue concernant l'équation du pendule et de sa discrétisation. Des résultats similaires ont été obtenus par Lazutkin et al. , mais la preuve que nous avons utilisée est complètement différenteThe purpose of this dissertation is to study how the discretization of a differential equation affects, the stable and unstable manifolds in two concrete examples: the logistic equation and the pendulumequation. The logistic equation is equivalent to a system with two fixed points A and B. It is known that the stable manifolds at A coincides with the unstable manifold at B. By improving some results of A. Fruchard and R. Schäfke, we show that the two manifolds do not coincide any more in the discretezed equation. The proof is a modification of an approach introduced by R. Schäfke and H. Volkmer. The second part of the thesis is dedicated to an analogous study regarding the pendulum equation and its discretization (Standard mapping). Similar results were obtained by Lazutkin et al. , but our proof is completely different
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Höjer, Pontus. "Photoelectrochemical Water-Splitting using 3C-SiC." Thesis, Linköpings universitet, Halvledarmaterial, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-139761.
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In 1972 Fujishima and Honda conceptualised a photoelectrochemical cell for hydrogen generation via PEC water splitting. Hydrogen as a clean energy carrier provides environmentally friendly energy storage solutions or can fuel certain applications. This idea has since then been further built upon with new materials and combinations with the aim of improving efficiency. In this project n-type cubic silicon carbide thick layers were grown by a sublimation method and characterised for water splitting performance. A generated photo-current density of 0.45 mA/cm2 was measured with no bias between the working and counter electrodes.
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Ng, Kit-ching Betty. "Correlation effects in crystal field splitting /." [Hong Kong : University of Hong Kong], 1986. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12323342.
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Sultana, Ummul Khair. "Electrochemical synthesis of water splitting nanomaterials." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/126972/1/Ummul%20Khair_Sultana_Thesis.pdf.
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This project was a step forward in electrochemically synthesizing nanomaterials for the water splitting reaction which directly produces hydrogen and oxygen. The thesis investigated the performances of newly developed nanomaterials for the energetically demanding water splitting reaction. In order to understand the reaction mechanism, thorough materials characterization was carried out to identify structure-activity relationships. This study also answers some fundamental questions such as "bifunctionality" in the field of water electrolysis. It also presents the modification of a readily available and cheap material, stainless steel, into an efficient water splitting catalyst that operates under industrial conditions.
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Dal, Compare Laura <1998>. "Two dimensional nanoplateletes for water splitting." Master's Degree Thesis, Università Ca' Foscari Venezia, 2021. http://hdl.handle.net/10579/19920.
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The subject of this research work is the synthesis and characterization of 2 dimensional (2D) materials (graphitic carbon nitride, g-C3N4, and layered double hydroxides, LDHs) for applications in energy conversion. g-C3N4 system was synthesised through a simple pyrolysis method with different precursors (thiourea and urea) and temperatures (400, 440, 500, 550, 600 °C). The delamination of the as-synthesised photocatalyst into 2D nanosheets was performed using an ultrasonic treatment to enhance the photocatalytic activity. NiCo-LDH system was also obtained using a co-precipitation method at 90 °C (NiCo LDH). In order to further enhance the catalytic performance of the as-synthesised 2D systems, single atom catalysis was also performed on them. In particular, selected metals (Ni, Co, Cu in the case of g-C3N4 and Ru and Pt for NiCo LDH) were deposited on them with a loading of 0.5 wt%. The crystalline structure of the as-synthesized 2D systems was investigated with X-ray diffraction (XRD) while their morphology was studied through field emission-scanning electron microscopy (FE-SEM). g-C3N4-based samples underwent diffuse reflectance UV-vis spectroscopy to investigate their optical properties. The structure of LDH samples was further assessed through Raman spectroscopy. Finally, the samples were tested for electrochemical and photoelectrochemical water splitting to investigate their catalytic applicability.
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Yang, Yeongmee. "On a stable Splitting of Stiefel Manifolds." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150810.
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Romero, Alejandro Antonio. "Phase-splitting prediction in isothermal flash calculations." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27996.
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The development of processes that operate at conditions where multiple fluid-phase equilibria may occur demands fast and reliable simulation algorithms. The success of these algorithms depends on the correct prediction of the number and compositions of the phases present at a given temperature, pressure and overall fluid composition. The most commonly used routine for this purpose is the isothermal (single-stage) flash calculation.
A robust and efficient method to predict phase-splitting previous to performing an isothermal flash is implemented in this work. It is based on the thermodynamic stability analysis of the source phase using a Gibbs energy tangent-plane criterion. Depending on the outcome of the phase-split tests, the system may be declared stable as a single phase and thus no further calculations are needed, or unstable in which case a potential two- or three-phase solution can be obtained. Only in this last instance would the corresponding flash calculation follow, depending on the nature and quantity of the phases found: a vapour-liquid (VL) or a liquid- liquid (LL) flash if two phases are predicted, or a multiphase flash (VLL) when three phases are expected.
In addition to readily recognizing the number and type of phases present, the stability tests provide excellent initial composition estimates for the flash which assure fast convergence to the stable solution. Even though the algorithms developed can be used with any suitable model to calculate equilibrium properties, cubic equations of state are used throughout in this work as a single model to describe all fluid phases.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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Zebarjad, Seyyed Mohammad. "Positronium hyperfine splitting corrections using nonrelativistic QED." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ44643.pdf.
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Voltaire, Joakim. "Ink Film Splitting Acoustics in Offset Printing." Doctoral thesis, Stockholm : Chemical Science and Engineering, KTH, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3869.
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Hendrich, Christopher. "Proximal Splitting Methods in Nonsmooth Convex Optimization." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-149548.
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This thesis is concerned with the development of novel numerical methods for solving nondifferentiable convex optimization problems in real Hilbert spaces and with the investigation of their asymptotic behavior. To this end, we are also making use of monotone operator theory as some of the provided algorithms are originally designed to solve monotone inclusion problems.
After introducing basic notations and preliminary results in convex analysis, we derive two numerical methods based on different smoothing strategies for solving nondifferentiable convex optimization problems. The first approach, known as the double smoothing technique, solves the optimization problem with some given a priori accuracy by applying two regularizations to its conjugate dual problem. A special fast gradient method then solves the regularized dual problem such that an approximate primal solution can be reconstructed from it. The second approach affects the primal optimization problem directly by applying a single regularization to it and is capable of using variable smoothing parameters which lead to a more accurate approximation of the original problem as the iteration counter increases. We then derive and investigate different primal-dual methods in real Hilbert spaces. In general, one considerable advantage of primal-dual algorithms is that they are providing a complete splitting philosophy in that the resolvents, which arise in the iterative process, are only taken separately from each maximally monotone operator occurring in the problem description. We firstly analyze the forward-backward-forward algorithm of Combettes and Pesquet in terms of its convergence rate for the objective of a nondifferentiable convex optimization problem. Additionally, we propose accelerations of this method under the additional assumption that certain monotone operators occurring in the problem formulation are strongly monotone. Subsequently, we derive two Douglas–Rachford type primal-dual methods for solving monotone inclusion problems involving finite sums of linearly composed parallel sum type monotone operators. To prove their asymptotic convergence, we use a common product Hilbert space strategy by reformulating the corresponding inclusion problem reasonably such that the Douglas–Rachford algorithm can be applied to it. Finally, we propose two primal-dual algorithms relying on forward-backward and forward-backward-forward approaches for solving monotone inclusion problems involving parallel sums of linearly composed monotone operators.
The last part of this thesis deals with different numerical experiments where we intend to compare our methods against algorithms from the literature. The problems which arise in this part are manifold and they reflect the importance of this field of research as convex optimization problems appear in lots of applications of interest.
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Sheng, Qin. "Solving partial differential equations by exponential splitting." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317937.
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Cosh, Benjamin Colin. "Vertex splitting and connectivity augmentation in hypergraphs." Thesis, Goldsmiths College (University of London), 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272126.
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We consider problems of splitting and connectivity augmentation in hypergraphs. In a hypergraph G = (V +s, E), to split two edges su, sv, is to replace them with a single edge uv. We are interested in doing this in such a way as to preserve a defined level of connectivity in V . The splitting technique is often used as a way of adding new edges into a graph or hypergraph, so as to augment the connectivity to some prescribed level. We begin by providing a short history of work done in this area. Then several preliminary results are given in a general form so that they may be used to tackle several problems. We then analyse the hypergraphs G = (V + s, E) for which there is no split preserving the local-edge-connectivity present in V. We provide two structural theorems, one of which implies a slight extension to Mader’s classical splitting theorem. We also provide a characterisation of the hypergraphs for which there is no such “good” split and a splitting result concerned with a specialisation of the local-connectivity function. We then use our splitting results to provide an upper bound on the smallest number of size-two edges we must add to any given hypergraph to ensure that in the resulting hypergraph we have λ(x, y) ≥ r(x, y) for all x, y in V, where r is an integer valued, symmetric requirement function on V*V. This is the so called “local-edge-connectivity augmentation problem” for hypergraphs. We also provide an extension to a Theorem of Szigeti, about augmenting to satisfy a requirement r, but using hyperedges. Next, in a result born of collaborative work with Zoltán Király from Budapest, we show that the local-connectivity augmentation problem is NP-complete for hypergraphs. Lastly we concern ourselves with an augmentation problem that includes a locational constraint. The premise is that we are given a hypergraph H = (V,E) with a bipartition P = {P1, P2} of V and asked to augment it with size-two edges, so that the result is k-edge-connected, and has no new edge contained in some P(i). We consider the splitting technique and describe the obstacles that prevent us forming “good” splits. From this we deduce results about which hypergraphs have a complete Pk-split. This leads to a minimax result on the optimal number of edges required and a polynomial algorithm to provide an optimal augmentation.
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BECERRA, MELISA YVONE ZAMBRANO. "FILM - SPLITTING FLOWS OF VISCOELASTIC LIQUIDS VISUALIZATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7356@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO processo de deposição de uma fina camada de líquido sobre um substrato em movimento é conhecido como processo de revestimento. Um das técnicas mais utilizadas é o Revestimento por Rotação Direta, devido a sua simplicidade e baixo custo de instalação e operação. A baixas velocidades, o escoamento na região de aplicação do líquido é bi- dimensional e permanente. Porem quando a velocidade é elevada o escoamento bi- dimensional torna-se instável, levando a um escoamento tri-dimensional, com variação da espessura do filme de líquido depositado ao longo da largura do substrato. Este tipo de instabilidade é comunmente denominado Ribbing, e limita a velocidade do processo dependendo dos requisitos de uniformidade de espessura. Geralmente, os líquidos utilizados neste processo são soluções poliméricas, os que apresentam um comportamento não Newtoniano. Foi demonstrado, para líquidos Newtonianos, que o gradiente da pressão perto do menisco destabiliza o escoamento. O parâmetro crítico para o aparecimento da instabilidade é o número de capilaridade. Para líquidos viscoelásticos o comportamento do escoamento muda dramaticamente, o inicio das instabilidades ocorre a bem menores números de capilaridade quando é comparado ao caso Newtoniano. O mecanismo pelo qual a elasticidade desestabiliza o escoamento perto da superfície livre ainda não é completamente entendido. Predições recentes mostraram que a zona de recirculação perto do menisco presente para líquidos Newtonianos, diminui e desaparece posteriormente a medida que o escoamento torna-se mais viscoelástico (aumento do Número de Weissenberg). O objetivo deste trabalho é verificar experimentalmente este fenômeno e determinar o efeito das propriedades viscoelásticas do líquido no processo. Para isso, o escoamento entre uma placa estacionaria e o cilindro girante é analisado experimentalmente visualizando a região perto da superfície livre e medindo o campo de velocidade usando a técnica de Velocimetria por Imagem de Partículas (PIV).Diferentes soluções de baixo peso molecular polietileno glicol (PEG), e alto peso molecular oxido de polietileno (PEO), característica elástica, em agua foram usados para avaliar o efeito da viscoelasticidade no comportamento do escoamento. Com este analises experimental se quer confirmar la prediçao teórica de Zevallos(2003) sobre o efeito da viscoelasticidade nas linhas de corrente e na estabilidade da superfície livre com respeito às perturbaçoes tri-dimensionais.
Roll coating is a common method in the manufacture of a wide variety of products. It is used to apply a thin liquid layer to a continuous flexible substrate. At low speeds, the flow is two-dimensional and steady; as the roll speed is raised, the two-dimensional flow is unstable and is replaced by a steady three-dimensional flow, which results in more or less regular stripes in the machine direction. This type of the instability is commonly called ribbing, it can limit the speed of the process if a smooth film is required as a final product. The liquids used in this process generaly are polimeric solutions, which present Non-Newtonian behavior. It was demonstrated, for Newtonian liquids, that the gradient of the pressure close to the meniscus destabilizes the flow, whereas the surface tension has a stabilizing effect. The critical parameter for the flow stability is the capillary number. For viscoelastic liquids can drastically change the nature of the flow near the free surfaces of the coating bead. The onset of the instabilities occurs at much lower capillary numbers than Newtonian flow case, which falls with the growth of the elasticity. Accurate theoretical predictions of the onset of ribbing when viscoelastic liquids are used is still not available. The mechanisms by which the liquid elasticity makes the flow unstable at Capillary numbers much lower than in the Newtonian case is not completely understood. Recent theoretical predictions have shown that at high Weissenberg number, the recirculation zone, present in the Newtonian flow completely disappears. In this work, film splitting flows between a stationary plate and rotating roll are analyzed experimentally by visualizing the free surface configuration and measuring the velocity field using the Particle Image Velocimetry (PIV) technique. Various solutions of low molecular weight polyethylene glycol (PEG) and high molecular weight polyethylene oxide (PEO) in water were used in order to evaluate the effect of mildly viscoelastic behavior on the flow. The goal was to confirm the theoretical predictions of Zevallos et al. (2004) on the effect of the liquid viscoelasticity on the streamline pattern and on the stability of the free surface with respect to three-dimensional disturbances.
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Swinbank, Richard. "Virtual forced splitting in multidimensional access methods." Thesis, University of Birmingham, 2008. http://etheses.bham.ac.uk//id/eprint/213/.
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External, tree-based, multidimensional access methods typically attempt to provide B+ tree like behaviour and performance in the organisation of large collections of multidimensional data. The B+ tree’s efficiency comes directly from the fact that it organises data occupying a single dimension, which can be linearly ordered, and partitioned at arbitrary points in that order. Using a multiway tree to partition a multidimensional space becomes increasingly difficult with increasing dimensionality, often leading to the loss of desirable properties like high fanout and low internode overlap. The K-D-B tree is an example of a structure in which one property, that of zero internode overlap, is provided at the expense of another, high fanout. Its approach to doing this, by forced splitting, is shared by a collection of other structures, and in 1995 Freeston suggested a novel approach to mitigate the effects of forced splits, by executing them virtually. This approach has not been taken up widely, but we believe it shows a great deal of promise. In the thesis, we examine the virtual forced splitting approach in depth. We identify a number of problems presented by the approach, and propose solutions to them, allowing us to characterise a general class of virtual forced splitting structures that we call VFS-trees. The efficacy of our approach is demonstrated by our implementation of a new VFS structure, and by what we believe to be the first implementation of a BV-tree, together with new algorithms for region and K Nearest Neighbour search. We further report experimental results on construction, exact-match search and K-NN search of BV-trees, and show how they compare, very favourably, with the corresponding operations on the currently most popular multidimensional file access method, the R*-tree.
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Kularathna, Shyamini. "Splitting solution scheme for material point method." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274140.
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Material point method (MPM) is a numerical tool which was originally used for modelling large deformations of solid mechanics problems. Due to the particle based spatial discretiza- tion, MPM is naturally capable of handling large mass movements together with topological changes. Further, the Lagrangian particles in MPM allow an easy implementation of history dependent materials. So far, however, research on MPM has been mostly restricted to explicit dynamic formu- lations with linear approximation functions. This is because of the simplicity and the low computational cost of such explicit algorithms. Particularly in MPM analysis of geomechan- ics problems, a considerable attention is given to the standard explicit formulation to model dynamic large deformations of geomaterials. Nonetheless, several limitations exist. In the limit of incompressibility, a significantly small time step is required to ensure the stability of the explicit formulation. Time step size restriction is also present in low permeability cases in porous media analysis. Spurious pressure oscillations are another numerical instability present in nearly incompressible flow behaviours. This research considers an implicit treatment of the pressure in MPM algorithm to simu- late material incompressibility. The coupled velocity (v)-pressure (p) governing equations are solved by applying Chorin’s projection method which exhibits an inherent pressure stability. Hence, linear finite elements can be used in the MPM solver. The main purpose of this new MPM formulation is to mitigate artificial pressure oscillations and time step restrictions present in the explicit MPM approach. First, a single phase MPM solver is applied to free surface incompressible fluid flow problems. Numerical results show a better approximation of the pressure field compared to the results obtained from the explicit MPM. The proposed formulation is then extended to model fully saturated porous materials with incompress- ible constituents. A solid velocity(v S )-fluid velocity (v F )-pore pressure (p) formulation is presented within the framework of mixture theory. Comparing the numerical results for the one-dimensional consolidation problem shows that the proposed incompressible MPM algorithm provides a stable and accurate pore pressure field even without implementing damping in the solver. Finally, the coupled MPM is used to solve a two-dimensional wave propagation problem and a plain strain consolidation problem. One of the important features of the proposed hydro mechanical coupled MPM formulation is that the time step size is not dependent on the incompressibility and the permeability of the porous medium.
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Batson, Joshua. "Obstructions to slicing knots and splitting links." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90178.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mathematics, 2014.49
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 65-68).
In this thesis, we use invariants inspired by quantum field theory to study the smooth topology of links in space and surfaces in space-time. In the first half, we use Khovanov homology to the study the relationship between links in R3 and their components. We construct a new spectral sequence beginning at the Khovanov homology of a link and converging to the Khovanov homology of the split union of its components. The page at which the sequence collapses gives a lower bound on the splitting number of the link, the minimum number of times its components must be passed through one another in order to completely separate them. In addition, we build on work of Kronheimer- Mrowka and Hedden-Ni to show that Khovanov homology detects the unlink. In the second half, we consider knots as potential cross-sections of surfaces in R4. We use Heegaard Floer homology to show that certain knots never occur as cross-sections of surfaces with small first Betti number. (It was previously thought possible that every knot was a cross-section of a connect sum of three Klein bottles.) In particular, we show that any smooth surface in R 4 with cross-section the (2k, 2k - 1) torus knot has first Betti number at least 2k - 2.
by Joshua Batson.
Ph. D.
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Quintana, Michael Steven. "Two phase flow splitting in piping branches." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50127.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (leaf 36).
The objectives of this research are to evaluate the performance of a flow-splitting tripod, discover the factors which most affect the flow distribution; and quantify the effects of geometry, quality and flow rate on the distribution. Knowing all this allows one to predict the distribution for given conditions. An R-22 test apparatus was constructed for carrying out the experiments. The factors examined were tripod orientation, Froude number, void fraction, and swirl induced by helical grooves in the tube supplying the two-phase flow to the tripod. The flow regime of concern is primarily annular. Experiments were run and data was collected and analyzed. The two piece tripods were generally found to have manufacturing defects which made their performance unpredictable. The hole through which the flow was provided was often off center. This defect greatly affected the distribution and masked other geometric factors. To eliminate this variable a number of tripods were tested, using an air-water rig, to find a tripod that was not defective. Tests using R-22 were then run on this tripod and it was found that inlet swirl had little or no affect on the flow distribution. The factors that had the greatest effect on the flow distribution were the tripod's orientation, the Froude number of the flow, and the void fraction. An empirical correlation for flow splitting was derived including these factors.
by Michael Steven Quintana.
S.M.
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Thorne, James E. "Understanding the Limitations of Photoelectrochemical Water Splitting." Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:108257.
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Thesis advisor: Dunwei WangArtificial photosynthesis is achieved by placing a semiconductor in water, where photoexcited charges generate a photovoltage at the surface of the semiconductor. However, solar to fuel efficiencies of earth abundant metal oxides and metal nitrides remain limited by their low photovoltages. Many different treatments have been used to improve the photovoltages of semiconductors, such as photocharging, surface regrowths, or the addition of heterogeneous catalysts. However, in these treatments, it remains unclear whether the enhanced photovoltage arises from improved kinetics or energetics. In many of the following studies, the surface kinetics of different semiconductors are measured in order to quantify how surface kinetics are related to the photovoltage of these materials. Different spectroscopic measurements are made along with detailed analysis of the Fermi level and quasi Fermi level in order to corroborate the kinetic data with energetic data. Together, this dissertation explores a multitude of methods and procedures that demonstrate how the photovoltage of semiconductors can be understood and manipulated for photoelectrochemial artificial photosynthesis
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Brookman, Jeremy. "Splitting homotopy equivalences along codimension 1 submanifolds." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/12802.
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Peacock, Sheila. "Shear-wave splitting in the Earth's crust." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/15614.
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Li, Xinxin. "Some operator splitting methods for convex optimization." HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/43.
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Many applications arising in various areas can be well modeled as convex optimization models with separable objective functions and linear coupling constraints. Such areas include signal processing, image processing, statistical learning, wireless networks, etc. If these well-structured convex models are treated as generic models and their separable structures are ignored in algorithmic design, then it is hard to effectively exploit the favorable properties that the objective functions possibly have. Therefore, some operator splitting methods have regained much attention from different areas for solving convex optimization models with separable structures in different contexts. In this thesis, some new operator splitting methods are proposed for convex optimiza- tion models with separable structures. We first propose combining the alternating direction method of multiplier with the logarithmic-quadratic proximal regulariza- tion for a separable monotone variational inequality with positive orthant constraints and propose a new operator splitting method. Then, we propose a proximal version of the strictly contractive Peaceman-Rachford splitting method, which was recently proposed for the convex minimization model with linear constraints and an objective function in form of the sum of two functions without coupled variables. After that, an operator splitting method suitable for parallel computation is proposed for a convex model whose objective function is the sum of three functions. For the new algorithms, we establish their convergence and estimate their convergence rates measured by the iteration complexity. We also apply the new algorithms to solve some applications arising in the image processing area; and report some preliminary numerical results. Last, we will discuss a particular video processing application and propose a series of new models for background extraction in different scenarios; to which some of the new methods are applicable. Keywords: Convex optimization, Operator splitting method, Alternating direction method of multipliers, Peaceman-Rachford splitting method, Image processing
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Kitaguchi, Masaaki. "Cold-neutron interferometry using beam splitting etalons." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/64951.
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Wang, Shi. "Barycentric Straightening, Splitting Rank and Bounded Cohomology." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1466552761.
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Judd, John David. "Stream splitting in support of intrusion detection." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FJudd.pdf.
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Comitti, Victor Schmidt. "Splitting longitudinal-transversal em uma microcavidade semicondutora." Universidade Federal de Minas Gerais, 2013. http://hdl.handle.net/1843/BUOS-97WH78.
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In this work we investigate a splitting of aproximately 0,19 meV in the luminescense spectrum of the Lower Polariton (LP) in a semiconductor microcavity of thickness with a GaAs quantum well embedded. There are some possible causes for this energy splitting in the LP mode. Along this dissertation we mention the main ones and then follow to demonstrate, by a process of hypothesis elimination based in photoluminescense experiments, that the phenom observed is a splitting between excitons with longitudinal and transversal dipole momentos in relation to the exciton wave vector in the plane of the quantum well due to the exchanche interactions.Neste trabalho investigamos um desdobramento de aproximadamente 0,19 meV no espectro de luminescência do Lower Polariton (LP) em uma microcavidade semicondutora de espessura com um poço quântico de GaAs imerso. Existem algumas causas possíveis para o desdobramento em energia do LP em uma microcavidade. Ao longo da dissertação citamos as principais e, em seguida, tentamos demonstrar por um método de eliminação de hipóteses, baseado em medidas de fotoluminescência, que o fenômeno observado é o splitting entre éxcitons com momento de dipolo Longitudinal e Transversal em relação ao vetor de onda do éxciton no plano do poço quântico decorrente das interações de troca.
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YANG, BING. "Source and field reconstruction with field splitting." Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2503165.
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The research activity has concerned diagnostics for antennas and other intentional or un-intentional radiating structures (e.g. for EMI considerations).
The diagnostics effort is based on measured field, and on information on the device under test (DUT) wrapping volume; the latter is used to reconstruct equivalent currents that radiate the same field as measured.
Current reconstruction is based on a previous work.
The activity has involved testing of the existing approach -not reported in this thesis document-, and its extension.
The main emphasis has been on relating the polarization of the radiated field to the (equivalent) currents on the DUT, especially to allow the designer a clear view of what the origin could be of possible deviations from expected or desired performance. In this sense, the geometry of the current reconstruction surface plays a key role: one would like to do this reconstruction on a closely wrapping surface to maximize the information content.
The basic idea is to split the measured field into two polarization components (co- and cross-polarization), and then observe the corresponding equivalent currents; for example, the sources of cross-polarization could be directly tracked this way.
However, this approach cannot be applied in a straightforward manner for two different reasons.
In the first place, it is well known that polarization (co-polarized and cross-polarized orthogonal components of the radiated field) is not defined uniquely, and the definition of co- and cross-polarization depends on utility for the specific use. This problem can be handled in a conventional way, but requires attention, and in view of the subsequent use, and in particular for the definition of the cross-polarized field.
Second, and more important for the present purpose, there is no guarantee that a purely polarized field could be radiated by a set of currents having spatial support on the wrapping surface of the DUT (e.g., a purely polarized field might require a larger antenna). Also, one is normally interested in co- and cross-polarizations levels only in the main radiation lobe, or a portion thereof. This has prompted the definition of an “improved” field. This “improved” field has a given polarization purity only in a portion of the main beam, via a windowing process that sets the level of cross-polarization and the extent of the (angular) region where the improvement is enforced.
The improvement is in any case a perturbation of the actual measured fields, that potentially worsens the current reconstruction process; therefore, trade-offs have been studied in several cases between the information conveyed by the current reconstruction via improved field, and the accuracy in reproducing the measured field.
The concept is more general, though, and can indeed be used to “improve” a prototype DUT whose measured performances are below the level of expectation, e.g. by lowering the side lobes. This can be recognized as a linear synthesis (“field synthesis”) procedure, whose results is a useful indication for the designer on what parts of the DUT have to be modified and on how to get a better performance. Issues about the extent of the “improvement” (distance from actually measured pattern) and physical realizability in the volume occupied by the DUT are still to be considered.
Conversely, and to some extent counter-intuitively, the polarization splitting is simpler when two polarizations are specified at the source level; this is what commonly happens for dual-polarized antennas. In this case it can be seen that the field splitting in polarization leads to a stable reconstructions of the related currents.
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Blot, Adeline. "Design of Heterostructured Photoelectrodes for Water-Splitting." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS458.
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La photo-électrolyse de l’eau est une solution innovante pour la production durable de dihydrogène. Pour créer une cellule photoélectrochimique autosuffisante capable de réaliser l'électrolyse de l'eau sans nécessiter d'apport d'énergie externe, le développement de matériaux photo-actifs efficaces au sein d'un unique électrolyte est nécessaire. Dans ce contexte, nous avons étudié le vanadate de bismuth (BiVO4) comme photoanode pour l'oxydation de l'eau dans des conditions acides où l’optimum d’efficacité des photocathodes est atteint. A ce jour, peu de travaux ont porté sur l’efficacité et la durabilité de ces électrodes en conditions acides. Dans cette étude, nous avons exploré deux approches de synthèse de la photoanode par trempage-retrait : i la chimie sol-gel et ii le dépôt d’une suspension colloïdale. Pour améliorer le photo-courant et la stabilité de l’électrode, nous avons exploré deux stratégies : modifier la structure de BiVO4 en dopant avec du molybdène pour influencer le transport de charge à l'intérieur du matériau, améliorer la réactivité de surface en ajoutant un co-catalyseur cobalt-phosphate. Dans cette dernière approche, nous avons étudié la cinétique de transfert de charge en ajoutant un co-catalyseur à la surface de BiVO4 et la passivation de la surface grâce à une couche ultramince de TiO2. Enfin, nous avons synthétisé une hétérojonction BiVO4-V2O5 en s’inspirant d’une approche de type "brique-mortier", dans laquelle la taille et la structure des particules de BiVO4 sont contrôléesPhotoelectrochemical water-splitting is an innovative solution for sustainable dihydrogen production. To create a self-sustaining photoelectrochemical cell capable of performing water electrolysis without the need for external energy input, the development of efficient photoactive materials within a single electrolyte is essential. In this context we have studied bismuth vanadate (BiVO4) semiconductor as promising photoanode for water oxidation in acidic conditions where photocathodes are efficient. However, little research has been carried out into its effectiveness and durability in an acid environment. In this thesis, we studied the performance of this electrode in an acidic environment by developing two approaches to the manufacture of photoanodes based on dip-coating: i sol-gel chemistry and ii colloidal suspension. To enhance photocurrents and electrode stability, we explored two strategies: modifying the electrode composition by doping it with molybdenum to influence charge transport within the material, and improving surface reactivity by adding a cobalt-phosphate co-catalyst. For the latter, we analysed the charge transfer kinetics with the addition of a co-catalyst and the passivation of the surface with an ultrathin TiO2 layer, obtained by the sol-gel or ALD process. Finally, we synthesized a BiVO4- V2O5 heterojunction based on a ‘brick and mortar’ approach, in which the size and structure of BiVO4 particles are controlled
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Kunkle, Daren. "Splitting of power series spaces of (PLS) - type." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964131331.
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Duan, Lele. "Artificial Water Splitting: Ruthenium Complexes for Water Oxidation." Doctoral thesis, KTH, Organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-40848.
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This thesis concerns the development and study of Ru-based water oxidation catalysts (WOCs) which are the essential components for solar energy conversion to fuels. The first chapter gives a general introduction about the field of homogenous water oxidation catalysis, including the catalytic mechanisms and the catalytic activities of some selected WOCs as well as the concerns of catalyst design. The second chapter describes a family of mononuclear Ru complexes [Ru(pdc)L3] (H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) towards water oxidation. The negatively charged pdc2− dramatically lowers the oxidation potentials of Ru complexes, accelerates the ligand exchange process and enhances the catalytic activity towards water oxidation. A Ru aqua species [Ru(pdc)L2(OH2)] was proposed as the real catalyst. The third chapter describes the analogues of [Ru(terpy)L3]2+ (terpy = 2,2′:6′,2′′-terpyridine). Through the structural tailor, the ligand effect on the electrochemical and catalytic properties of these Ru complexes was studied. Mechanistic studies suggested that these Ru-N6 complexes were pre-catalysts and the Ru-aqua species were the real WOCs. The forth chapter describes a family of fast WOCs [Ru(bda)L2] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Catalytic mechanisms were thoroughly investigated by electrochemical, kinetic and theoretical studies. The main contributions of this work to the field of water oxidation are (i) the recorded high reaction rate of 469 s−1; (ii) the involvement of seven-coordinate Ru species in the catalytic cycles; (iii) the O-O bond formation pathway via direct coupling of two Ru=O units and (iv) non-covalent effects boosting up the reaction rate. The fifth chapter is about visible light-driven water oxidation using a three component system including a WOC, a photosensitizer and a sacrificial electron acceptor. Light-driven water oxidation was successfully demonstrated using our Ru-based catalysts.QC 20110922
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Alshehri, Salimah. "Step by Step Water Splitting: Heterogeneous Photocatalysis Studies." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37541.
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Due to the environmental problems caused by the steadily increasing usage of fossil fuels, the interest for renewable sources of energy has amplified significantly. Among the several possibilities, hydrogen gas is considered to be one of the most promising fuels forof the future. IfOnce formed from water via photocatalysis it is a desirable, convenient and green improvement in the field of energy. During this work, we have tried to contribute to this important field.
4wt.% Au/TiO2 synthesized by deposition-precipitation with urea was the main photocatalysts used in this project. Other noble metal-loaded (Pt and Ag) titanium dioxide materials were synthesized by deposition precipitation with urea and other methods such as sol gel and sol immobilization. These catalytic systems were studied and their activity compared for hydrogen production from water/methanol mixtures. Sets of monometallic Au, Ag, Pt and bimetallic Au-Pt and Au-Ag supported titanium dioxide were synthesized and tested.
Au/TiO2 photocatalysts synthesized by deposition precipitation with urea was were the best in terms of hydrogen production compared to other photocatalysts. In the evaluation of possible sacrificial molecules, isopropanol was less efficient than methanol. Through the formation of bi-metallic Ag-Au/TiO2 and Pt-Au/TiO2 catalysts, the hydrogen production could be further improved.
Finally, Ir supported Al2O3 was investigated for the first time as a heterogeneous catalyst for hydrogen production by photocatalytic dehydrogenation of aqueous p-formaldehyde and photoreduction of carbon dioxide.
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au, A. Bremner@murdoch edu, and Alexandra Bremner. "Localised splitting criteria for classification and regression trees." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040606.142949.
Full textAbstract:
This thesis presents a modification of existing entropy-based splitting criteria for classification and regression trees. Trees are typically grown using splitting criteria that choose optimal splits without taking future splits into account. This thesis examines localised splitting criteria that are based on local averaging in regression trees or local proportions in classification trees. The use of a localised criterion is motivated by the fact that future splits result in leaves that contain local observations, and hence local deviances provide a better approximation of the deviance of the fully grown tree. While most recent research has focussed on tree-averaging techniques that are aimed at taking a moderately successful splitting criterion and improving its predictive power, this thesis concentrates on improving the splitting criterion.
Use of a localised splitting criterion captures local structures and enables later splits to capitalise on the placement of earlier splits when growing a tree. Using the localised splitting criterion results in much simpler trees for pure interaction data (data with no main effects) and can produce trees with fewer errors and lower residual mean deviances than those produced using a global splitting criterion when applied to real data sets with strong interaction effects.
The superiority of the localised splitting criterion can persist when multiple trees are grown and averaged using simple methods. Although a single tree grown using the localised splitting criterion can outperform tree averaging using the global criterion, generally improvements in predictive performance are achieved by utilising the localised splitting criterion's property of detecting local discontinuities and averaging over sets of trees grown by placing splits where the deviance is locally minimal. Predictive performance improves further when the degree of localisation of the splitting criterion is randomly selected and weighted randomisation is used with locally minimal deviances to produce sets of trees to average over. Although state of the art methods quickly average very large numbers of trees, thus making the performance of the splitting criterion less critical, predictive performance when the localised criterion is used in bagging indicates that different splitting methods warrant investigation.
The localised splitting criterion is most useful for growing one tree or a small number of trees to examine structure in the data. Structurally different trees can be obtained by simply splitting the data where the localised splitting criterion is locally optimal.
50
Bremner, Alexandra. "Localised splitting criteria for classification and regression trees." Bremner, Alexandra (2004) Localised splitting criteria for classification and regression trees. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/440/.
Full textAbstract:
This thesis presents a modification of existing entropy-based splitting criteria for classification and regression trees. Trees are typically grown using splitting criteria that choose optimal splits without taking future splits into account. This thesis examines localised splitting criteria that are based on local averaging in regression trees or local proportions in classification trees. The use of a localised criterion is motivated by the fact that future splits result in leaves that contain local observations, and hence local deviances provide a better approximation of the deviance of the fully grown tree. While most recent research has focussed on tree-averaging techniques that are aimed at taking a moderately successful splitting criterion and improving its predictive power, this thesis concentrates on improving the splitting criterion.
Use of a localised splitting criterion captures local structures and enables later splits to capitalise on the placement of earlier splits when growing a tree. Using the localised splitting criterion results in much simpler trees for pure interaction data (data with no main effects) and can produce trees with fewer errors and lower residual mean deviances than those produced using a global splitting criterion when applied to real data sets with strong interaction effects.
The superiority of the localised splitting criterion can persist when multiple trees are grown and averaged using simple methods. Although a single tree grown using the localised splitting criterion can outperform tree averaging using the global criterion, generally improvements in predictive performance are achieved by utilising the localised splitting criterion's property of detecting local discontinuities and averaging over sets of trees grown by placing splits where the deviance is locally minimal. Predictive performance improves further when the degree of localisation of the splitting criterion is randomly selected and weighted randomisation is used with locally minimal deviances to produce sets of trees to average over. Although state of the art methods quickly average very large numbers of trees, thus making the performance of the splitting criterion less critical, predictive performance when the localised criterion is used in bagging indicates that different splitting methods warrant investigation.
The localised splitting criterion is most useful for growing one tree or a small number of trees to examine structure in the data. Structurally different trees can be obtained by simply splitting the data where the localised splitting criterion is locally optimal.