Дисертації з теми "Homogeneous and heterogeneous sets"
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1
Yang, Dan-Hui. "Homogeneous and heterogeneous sonochemistry." Doctoral thesis, Universite Libre de Bruxelles, 1992. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212940.
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2
Yolov, Nikola. "Homogeneous sets in graphs and hypergraphs." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:23a05b21-773b-4bf9-8776-1bd4b10c3c34.
Повний текст джерелаАнотація:
A set of vertices in a graph or a hypergraph is called homogeneous if it is independent, that is it does not contain any edge, or if it is complete, that is it contains all possible pairs or subsets of it as edges. We investigate the properties of graphs and hypergraphs in two cases of imposed restrictions on the structure of their homogeneous sets. First we study the asymptotic structure of random perfect graphs. We give a generation model which yields such graphs almost uniformly, with an additive error of e-Ω(n) in the total variation distance. We use this model to determine a number of properties of random perfect graphs, including the distribution of the stability and the clique number, the probability of containing a fixed induced subgraph, Hamiltonicity, clique-colourability, connectivity, edge colouring, and the limit of a uniformly drawn sequence of perfect graphs. In the second part, we give a hypergraph parameter μ(H), called minor- matching number, with the property that hypergraphs H with bounded rank and minor-matching number contain a polynomially-bounded number of maximal independent sets. In the other direction, every hypergraph H contains at least 2μ(H) maximal independent sets. A number of hard hypergraph problems, including maximum-sized independent set, k-colouring and hypergraph homomorphism can be solved in polynomial time if a list with all maximal independent sets of the hypergraph is given as part of the input, and hence a family of instances with bounded minor-matching number of the input hypergraph form a new polynomial class for the problems above. The class can further be generalised by considering the maximum minor matching number of a bag in a tree decomposition as a new treewidth measure. We explain how to use this measure, defined as minor-matching treewidth, to solve hard problems and how to algorithmically construct a tree decomposition with approximate minimal width.
3
Shaikh, Muhammad. "Homogeneous to heterogeneous Face Recognition." Thesis, Northumbria University, 2015. http://nrl.northumbria.ac.uk/32283/.
Повний текст джерелаАнотація:
Face Recognition, a very challenging research area, is being studied for almost more than a decade to solve variety of problems associated with it e.g. PIE (pose, expression and illumination), occlusion, gesture, aging etc. Most of the time, these problems are considered in situations when images are captured from same sensors/cameras/modalities. The methods in this domain are termed as homogeneous face recognition. In reality face images are being captured from alternate modalities also e.g. near infrared (NIR), thermal, sketch, digital (high resolution), web-cam (low resolution) which further alleviates face recognition problem. So, matching faces from different modalities are categorized as heterogeneous face recognition (HFR). This dissertation has major contributions in heterogeneous face recognition as well as its homogeneous counterpart. The first contribution is related to multi-scale LBP, Sequential forward search and KCRC-RLS method. Multi scale approaches results in high dimensional feature vectors that increases computational cost of the proposed approach and overtraining problem. Sequential forward approach is adopted to analyze the effect of multi-scale. This study brings an interesting facts about the merging of features of individual scale that it results in significant reduction of the variance of recognition rates among individual scales. In second contribution, I extend the efficacy of PLDA to heterogeneous face recognition. Due to its probabilistic nature, information from different modalities can easily be combined and priors can be applied over the possible matching. To the best of author’s knowledge, this is first study that aims to apply PLDA for intermodality face recognition. The third contribution is about solving small sample size problem in HFR scenarios by using intensity based features. Bagging based TFA method is proposed to exhaustively test face databases in cross validation environment with leave one out strategy to report fair and comparable results. The fourth contribution is about the module which can identify the modality types is missing in face recognition pipeline. The identification of the modalities in heterogeneous face recognition is required to assist automation in HFR methods. The fifth contribution is an extension of PLDA used in my second contribuiton. Bagging based probabilistic linear discriminant analysis is proposed to tackle problem of biased results as it uses overlapping train and test sets. Histogram of gradient descriptors (HOG) are applied and recognition rates using this method outperform all the state-of-the-art methods with only HOG features.
4
Bosquain, Sylvain S. "Homogeneous and heterogeneous oxidations of alkylbenzenes." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288594.
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Bloomberg, Deborah M. "Pedophilia a heterogeneous or homogeneous phenomenon?" Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/4562.
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Roberts, Virginia Marie. "Homogeneous and heterogeneous catalyzed hydrolysis of lignin." kostenfrei, 2008. http://mediatum2.ub.tum.de/doc/652904/652904.pdf.
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7
Snider, Graydon. "Homogeneous and heterogeneous oxidation of gaseous elemental mercury." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107726.
Повний текст джерелаАнотація:
Mercury is an atmospheric global pollutant with complex cycling behavior. Two-thirds of the mercury present in our atmosphere is anthropogenic in origin. Chemical oxidation of gaseous elemental mercury governs the deposition rate of mercury over most lakes, land, and oceans. A major uncertainty comes from the effect of atmospheric surfaces such as aerosols. Much research is devoted to mercury capture technologies to be used in coal fire power plants, which are the major source of anthropogenic emissions.This thesis is a report on oxidation kinetics and mechanistic studies relevant to mercury-scavenging reactions. It provides an overview of the mechanisms of mercury oxidation by ozone, nitrogen dioxide, and titanium dioxide (exposed to ultra-violet light). The role of surfaces was quantified, as appropriate for each system. Crossover effects between gaseous co-pollutants (e.g. CO, SO2) and surfaces (SiO2, TiO2) are discussed. Rate constants were measured for each process and product studies were performed and compared with the available literature. The effects of different surfaces and gases on the oxidation of mercury by ozone were measured. This reaction was confirmed to be a surface-enhanced gas phase initiated reaction with a second-order rate constant for pure gas-phase (kgas = (5.40 +/- 0.56) x 10-19 cm3 molec-1 s-1) and an enhanced surface component (ksur = (2.91 +/- 0.12) x 10-15 cm7 molec-1 s-1), or knet = (6.1 +/- 1.1) x 10-19 cm3 molec-1 s-1. Water vapor had no effect on the rate but liquid water and gaseous carbon monoxide both rapidly accelerated the reaction. Mechanisms were placed in context with atmospheric oxidative scavenging processes. Future work may combine aerosols (soot, acid, silica) in ozone oxidation reactions and/or addition of SO2 gas. The feasibility of removing mercury from a coal flue gas via titanium dioxide and ultra violet light was investigated. Discussed are some of the possible surface chemistry models of oxidation. The uptake rates of mercury over photosensitized titanium dioxide films was described by the Langmuir-Hinshelwood rate equation, where KHg = (5.1 +/- 2.4) x 10-14 cm3 molec-1 and k = (7.4 +/- 2.5) x 1014 molec cm-2 min-1. Effects of sulfur dioxide and water were evaluated but neither was found to impede the reaction. By contrast low oxygen level strongly impeded oxidation rates. Deposits of HgO on titania surfaces were widely dispersed in concentrated clusters. Currently there is no explanation to this pattern. Future experiments may use light emitting diodes to capture Hg0(g) over TiO2The oxidation of mercury by nitrogen dioxide was found to be a pure gas phase reaction, second order with respect to NO2, where k = (3.5 +/- 0.5) x 10-35 cm6 molec-2 s-1. The mechanism was conjectured to be a two-step addition of NO2 to Hg0; at higher NO2 concentrations the reaction may be first order with respect to NO2 but further experiments would be required for validation. The rate constant was also found in agreement with a previous study. Rates were unaffected by changes in pressure, available surfaces, presence of SO2, and water. It was discovered that TiO2 surfaces saturated in HgO deposits, when exposed to NO2 were 'revived' in Hg uptake activity. It is suspected the reaction between HgO and NO2 re-disperses the deposits.Le mercure est un polluant atmosphérique globale avec le comportement les cyclismes complexes. Deux tiers du mercure présent dans notre atmosphère est d'origine anthropique. L'oxydation chimique de mercure élémentaire gazeux régit la vitesse des dépôts de mercure sur la plupart des lacs, des terres et des océans. Une incertitude majeure provient de l'effet des surfaces atmosphériques tels que les aérosols. Beaucoup de recherches sont consacrées aux technologies de captage du mercure pour être utilisés dans les centrales au charbon de puissance de feu, qui sont la principale source d'émissions anthropiques.Cette thèse est un rapport sur la cinétique d'oxydation et d'études mécanistiques relatives au mercure-balayage réactions. Il donne un aperçu des mécanismes d'oxydation du mercure par l'ozone, le dioxyde d'azote et dioxyde de titane (exposé à la lumière ultraviolette). Le rôle des surfaces ont été quantifiés, comme il convient pour chaque système. Effets de coupure entre gazeux co-polluants (par exemple CO, SO2) et les surfaces (SiO2, TiO2) sont discutées. Les constantes de vitesse ont été mesurées pour chaque processus et études de produits ont été effectués et comparés avec la littérature disponible.Les effets de différentes surfaces et de gaz sur l'oxydation du mercure par l'ozone ont été mesurés. Cette réaction a été confirmé à une phase gazeuse augmenter a la surface réaction initiée avec un taux de second ordre constant de pures en phase gazeuse (kgaz = (5,40 +/- 0,56) x 10-19 cm3 moléc-1 s-1) et une surface améliorée composant (ksur = (2,91 +/- 0,12) x 10-15 cm7 moléc-1 s-1), ou knet = (6,1 +/- 1,1) x 10-19 cm3 molec-1 s-1. La vapeur d'eau n'a eu aucun effet sur la vitesse, mais l'eau liquide et de monoxyde de carbone gazeux, à la fois rapidement accéléré la réaction. Des mécanismes ont été mis en contexte avec l'atmosphère oxydant processus de balayage. Les travaux futurs peuvent combiner les aérosols (suie, de l'acide, de la silice) dans les réactions d'oxydation de l'ozone et / ou ajout de SO2.La faisabilité de l'élimination du mercure des gaz de combustion de charbon par du dioxyde de titane et de lumière ultra-violette a été étudiée. Discuté sont quelques-uns des modèles possibles chimie de surface de l'oxydation. La vitesse d'absorption de mercure au cours photosensibilisées films de dioxyde de titane a été décrit par l'équation du taux de Langmuir-Hinshelwood, où KHg = (5,1 +/- 2,4) x 10-14 cm3 moléc-1 et k = (7,4 +/- 2,5) x 1014 cm-2 moléc-1 min-1. Effets du dioxyde de soufre et de l'eau ont été évalués, mais ni a été trouvée pour empêcher la réaction. Par niveau d'oxygène à faible contraste fortement entravé les taux d'oxydation. Dépôts sur des surfaces de HgO oxyde de titane ont été largement dispersés dans les amas concentré. Actuellement, il n'existe pas d'explication à ce modèle. Les expériences futures peuvent utiliser des diodes électroluminescentes à saisir Hg0 (g) sur TiO2. L'oxydation du mercure par le dioxyde d'azote a été trouvé à une réaction gaz pur phase du second ordre par rapport au NO2, où k = (3,5 +/- 0,5) x 10-35 cm6 molec-2 s-1. Le mécanisme a été conjecturé être un ajout en deux étapes de NO2 à Hg0(g); à des concentrations élevées de NO2 la réaction peut être de premier ordre à l'égard de NO2, mais d'autres expériences seraient nécessaires pour la validation. La constante de vitesse a également été trouvé en accord avec une étude précédente. Les vitesses ont été affectées par les changements de pression, les surfaces disponibles, la présence de SO2, et l'eau. On a découvert que le TiO2 surfaces saturées dans les dépôts HgO(s), lorsqu'ils sont exposés à de NO2 ont été 'relancé' dans l'activité d'absorption de mercure. Il est soupçonné de la réaction entre HgO(s) et NO2 disperse les dépôts.
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Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst." University of Sydney. Chemistry, 2005. http://hdl.handle.net/2123/622.
Повний текст джерелаАнотація:
Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
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Hales, Jason Alexander. "COMPARING THE PERFORMANCE OF HETEROGENEOUS AND HOMOGENEOUS SWARMS." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11082007-132337/.
Повний текст джерелаАнотація:
This thesis compares the performance of heterogeneous and homogenous swarms. Swarms are defined as particles or agents which react to their environment and fellow particles or agents according to social rules. The weights of three attributes of an individual agent were varied for these experiments: Collision Avoidance with individual agents in the swarm, Center of Mass of the swarm and the parameter that controls Velocity Matching in the swarm. In homogenous swarms, all individuals had the same attribute weights while in heterogeneous swarms weights for one attribute were taken from a normal distribution for the population. These swarms were then given goals on a map to pursue. The maps were two-dimensional grid-surfaces with terrains of open, mountain and swamps. Performance was defined as the number of steps it took for 90% of the swarm to reach its final goal. The results show that heterogeneous swarms outperformed homogenous swarms if the weights for the Center of Mass Weight attribute were heterogeneous in the population. The Collision Avoidance and Matched Velocity attributes showed little performance difference for heterogeneous and homogenous swarms for the parameter weights tested. However, swarms heterogeneous in the Matched Velocity parameter showed substantial performance improvements for the most difficult map.
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Souza, Jeckson Dellagostin. "A reconfigurable heterogeneous multicore system with homogeneous ISA." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/140321.
Повний текст джерелаАнотація:
Dada a grande diversidade de aplicações embarcadas presentes nos atuais dispositivos portáveis, ambos os paralelismos em nível de threads e de instruções devem ser explorados para obter ganhos de desempenho e energia. Enquanto MPSoCs (sistemas em chip de múltiplos núcleos) são amplamente usados para esse propósito, estes falham quando consideramos produtividade de software, já que eles são compostos de chips com diferentes arquiteturas que precisam ser programados separadamente. Por outro lado, processadores multi núcleos de propósito geral implementam a mesma arquitetura, mas são compostos de núcleos homogêneos de processadores superescalares que consomem muita potência. Nesta dissertação, propõe-se um novo sistema, que tira proveito de circuitos reconfiguráveis para criar diferentes organizações que implementam a mesma arquitetura, capazes de apresentar alto desempenho com baixo custo energético. Para garantir a compatibilidade binária, usa-se um mecanismo de tradução binária que transforma o código a ser executado no circuito reconfigurável durante a execução. Usando aplicações representativas, mostra-se que uma versão do sistema heterogêneo pode ganhar da sua versão homogênea em média de 59% em desempenho e 10% em energia, com melhoras em EDP (Energy-Delay Product – Produto da energia pelo tempo de execução) em quase todos os cenários. Além disso, este trabalho também propõe e avalia seis escalonadores para este sistema heterogêneo: dois algoritmos estáticos, os quais alocam as threads no primeiro núcleo livre, onde elas permanecerão durante toda a execução; um escalonador direcionado por contagem de instruções, o qual realoca as threads durante pontos de sincronização de acordo com a sua contagem de instruções; um escalonador de Feedback, que usa dados de dentro da unidade reconfigurável para realocar threads; o PC-Feedback, que adiciona um mecanismo de reuso de dados ao último escalonador; e um escalonador Oráculo, que é capaz de decidir a melhor alocação de threads possível. Mostra-se que o algoritmo estático pode ter alto desempenho em aplicações com alto paralelismo, contudo para um desempenho mais uniforme em todas as aplicações os algoritmos de Feedback e PC-Feedback são mais indicados.Given the large diversity of embedded applications one can find in current portable devices, for energy and performance reasons one must exploit both Thread- and Instruction Level Parallelism. While MPSoCs (Multiprocessor system-on-chip) are largely used for this purpose, they fail when one considers software productivity, since it comprises different ISAs (Instruction Set Architecture) that must be programmed separately. On the other hand, general purpose multicores implement the same ISA, but are composed of a homogeneous set of very power consuming superscalar processors. In this dissertation, we show how one can effectively use a reconfigurable unit to provide a number of different possible heterogeneous configurations while still sustaining the same ISA, capable of reaching high performance with low energy cost. To ensure ISA compatibility, we use a binary translation mechanism that transforms code to be executed on the fabric at run-time. Using representative benchmarks, we show that one version of the heterogeneous system can outperform its homogenous counterpart in average by 59% in performance and 10% in energy, with EDP (Energy-Delay Product) improvements in almost every scenario. Furthermore, this work also proposes and evaluates six schedulers for the heterogeneous system: two static algorithms, which allocate the threads on the first free core, where they will run during the entire execution; an Instruction Count (IC) Driven scheduler, which reallocates threads during synchronization points accordingly to their instruction count; a Feedback scheduler, which uses data from inside the reconfigurable unit to reallocate threads; the PCFeedback scheduler, that adds a reuse mechanism to the last one; and an Oracle scheduler, which is capable of deciding the best thread allocation possible. We show that the static algorithm can reach high performance in applications with high parallelism, however for uniform performance in all applications, the Feedback and PC-Feedback algorithms are better designated.
11
Oh, Seokjoon. "Graphite-conjugated catalysts : bridging heterogeneous and homogeneous catalysts." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122714.
Повний текст джерелаАнотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis. Page 156 blank.
Includes bibliographical references.
This interconversion occurs via complex multistep, multielectron reactions, which can be carried out by either metallic heterogeneous or molecular homogeneous electrocatalysts. Metallic heterogeneous catalysts have a continuum of electronic states that distribute the redox burden of multielectron reactions, allowing for efficient catalysis. However, heterogeneous catalysts display a variety of active sites and local electronic structures, and are difficult to fine-tune at a molecular level. On the other hand, homogeneous catalysts allow a great degree of synthetic control over the catalytic active site. Moreover, the relative ease in spectroscopic characterization allows a mechanistic understanding of molecular catalysis at a level that is unattainable for heterogeneous catalysis. To bridge the advantages of both types of catalysts, we have developed a surface functionalization strategy for conjugating molecularly well-defined active sites to graphitic carbon surfaces.
First, I will discuss the preparation and characterization of two new types of conjugating N-heterocyclic linkages to graphitic carbon surfaces. This work presents a general method for characterizing modified carbon surfaces with molecular-level structural detail. Then, I will present the electrocatalytic carbon dioxide reduction activity of a graphite-conjugated rhenium catalyst, and compare its catalytic behavior to that of a molecular analog. Electrochemical and spectroscopic data show that graphite-conjugated catalysts do not behave identically to their molecular analogs, but rather show properties similar to that of metallic heterogeneous catalysts, providing a unique bridge between the worlds of heterogeneous and homogeneous catalysis.
Finally, in the appendix, I will present a chapter on the stability of graphite-conjugated linkages under electrochemical polarization, followed by a chapter on catalyzing the reduction of molecular pyridinium species using a graphite-conjugated rhodium catalyst.
by Seokjoon Oh.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
12
Pare, Diane. "Grouping Students by Ability| Homogeneous versus Heterogeneous Classrooms." Thesis, Minot State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10618052.
Повний текст джерелаАнотація:
The primary purpose of this examination was to determine attitude s regarding homogeneously grouped students from a focus group of teachers. Do they think that students benefit sufficiently from a homogenously grouped educational setting? Homogeneous grouping assembles students with similar abilities together, wh ereas heterogeneous grouping assembles a mixture of student ability levels within the same classroom. Proponents of both grouping styles confirm the benefits of their preferred style; however each has its own limitations. Those in fa vor of homogeneous grou ping suggest it creates an atmosphere where students feel comfortable with like-minded students, allowing the teacher to reach the student better and students to achieve more success. Those who favor heterogeneous grouping suggest a mixed setting of studen ts creates an environment in which students are pushed to perform to the best of th eir capability. This study delve d into the experiences, opinions, and attitudes of teachers who instruct in homogeneous classrooms as well as examining the field research of other scholars, showing that homogeneous grouping s broken into smaller heterogeneous groups favor ed the most.
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Fritsche, Maria. "Homogeneous and heterogeneous ability grouping in the EFL classroom : A study of teachers' experience and views regarding homogeneous and heterogeneous ability groups." Thesis, Karlstads universitet, Institutionen för språk, litteratur och interkultur (from 2013), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-84943.
Повний текст джерелаАнотація:
In this qualitative case-study, EFL teachers’ experience and views regarding homogeneous and heterogeneous ability groups are investigated. Four EFL teachers working in the Introduction program in upper secondary school were interviewed through semi-structured questions. The interviews were held individually and conducted by the researcher. The questions focused on a teacher perspective as well as a student perspective and the teachers were also asked whether they preferred any of the two ability groups and possible reasons for this. The answers were quite similar and the teachers mentioned some common factors, such as time and efficiency, assignments, lectures, student interaction and learning progression. It was clear that the teachers found homogeneous ability groups easier to manage and this was also the group that three of them preferred working with. Additional reasons for this choice was the experience that this type of group was more beneficial for students and the teachers also felt more successful in their roles as teachers. Although one teacher mostly agreed with the others she was more in favour of heterogeneous ability groups, or a mix of both groups, because it allowed students to develop in their own pace and from their individual preferences and she also experienced more satisfaction in finding the right structure and strategies for each student.I den här kvalitativa fallstudien undersöks engelsklärares erfarenheter och perspektiv angående homogena och heterogena nivågrupper. Fyra engelsklärare som arbetar på introduktionsprogrammen inom gymnasieskolan intervjuades genom semistrukturerade frågor. Intervjuerna genomfördes individuellt och av forskaren. Frågorna fokuserade på ett lärarperspektiv likväl som ett elevperspektiv och lärarna fick också svara på frågan om de föredrog någon av de två nivågrupperingarna och ange möjliga orsaker till detta. Svaren var någorlunda lika och samtliga lärare lyfte några gemensamma nämnare så som tid och effektivitet, uppgifter, genomgångar, elevinteraktion samt inlärningsprogression. Det var tydligt att lärarna ansåg det enklare att hantera homogena nivågrupper och det var även den typ av grupp som tre av dem föredrog att arbeta med. Ytterligare orsaker till detta var upplevelsen att denna typ av grupp var mer gynnsam för elever och lärarna kände sig även mer framgångsrika i rollen som lärare. Även om en lärare ofta höll med övriga så föredrog hon heterogena nivågrupper, alternativt en blandning av båda grupper, då detta lät elever utvecklas i sin egen takt och utifrån sina individuella förutsättningar. Hon upplevde också mer tillfredsställelse av att hitta rätt struktur och strategier för varje elev.
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Tong, Wing Chiu. "Ectopic pacemaking in homogeneous and heterogeneous cardiac virtual tissues." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485750.
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Dean, Suzanne Lee. "Heterogeneous versus Homogeneous Measures:A Meta-Analysis of Predictive Efficacy." Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1452866556.
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Wei, Jinzhu Jinzhu Wei. "Stereospecific polymerization of propylene with heterogeneous and homogeneous catalytic systems /." [S.l.] : [s.n.], 1988. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8734.
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Ni, Zhihong. "Glacial isostatic adjustment of laterally homogeneous vs. heterogeneous earth models." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0009/NQ31057.pdf.
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Al-Kuwari, Saif. "Forensic tracking and surveillance : algorithms for homogeneous and heterogeneous setting." Thesis, Royal Holloway, University of London, 2011. http://repository.royalholloway.ac.uk/items/d4b37ec3-d1ea-39f3-5caf-3b263d830381/10/.
Повний текст джерелаАнотація:
Digital forensics is an emerging field that has uniquely brought together academics, practitioners and law enforcement. Research in this area was inspired by the numerous challenges posed by the increased sophistication of criminal tools. Traditionally, digital forensics has been confined to the extraction of digital evidence from electronic devices. This direct extraction of digital evidence, however, no longer suffices. Indeed, extracting completely raw data without further processing and/or filtering is, in some cases, useless. These problems can be tackled by the so-called "computational forensics" where the reconstructs evidence are undertaken further processing. One important application of computational forensics is criminal tracking, which we collectively call "forensic tracking" and is the main subject of this thesis. This thesis adopts an algorithmic approach to investigate the feasibility of conducting forensic tracking in various environments and settings. Unlike conventional tracking, forensic tracking has to be passive such that the target (who is usually a suspect) should not be aware of the tracking process. We begin by adopting pedestrian setting and propose several online (real-time) forensic tracking algorithms to track a single or multiple targets passively. Beside the core tracking algorithms, we also propose other auxiliary algorithms to improve the robustness and resilience of tracking. We then extend the scope and consider vehicular forensic tracking, where we investigate both online and offline tracking. In online vehicular tracking, we also propose algorithms for motion prediction to estimate the near future movement of target vehicles. Offline vehicular tracking, on the other hand, entails the post-hoc extraction and probabilistic reconstruction of vehicular traces, which we adopt Bayesian approach for. Finally, the contributions of the thesis concludes with building an algorithmic solution for multi-modal tracking, which is a mixed environment combining both pedestrian and vehicular settings.
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Lo, Kwok Cheong Michael Carleton University Dissertation Computer Science. "Performance of load sharing policies in homogeneous and heterogeneous systems." Ottawa, 1996.
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Furman, Olha. "Reactivity of oxygen species in homogeneous and heterogeneous aqueous environments." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Summer2009/o_furman_072109.pdf.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Washington State University, August 2009.Title from PDF title page (viewed on Sept. 1, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references..
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Vaquer, Malia Lydia. "Mononuclear Ruthenium Complexes and their Application in Homogeneous and Heterogeneous Catalysis." Doctoral thesis, Universitat Autònoma de Barcelona, 2011. http://hdl.handle.net/10803/42304.
Повний текст джерелаАнотація:
La tesis presentada es un estudio basado en la síntesis, caracterización espectrocópica y electroquímica y aplicaciones en catálisis de nuevos complejos mononucleares de rutenio con una amplia variedad de ligandos polipiridílicos. La influencia de las propiedades electrónicas de los ligandos coordinados al centro metálico sobre las propiedades redox de los complejos resultantes y su comportamiento en catálisis de oxidación ha sido estudiada y racionalizada. De la familia de complejos Ru-OH2 sintetizados y estudiados, unos pocos fueron seleccionados para desarrollar sistemas más complejos y poder ser utilizados para (a) catálisis heterogénea (obteniendo sistemas catalíticos fácilmente reciclables) y (b) catálisis supramolecular (para poder llevar a cabo oxidaciones regioselectivas de sustratos orgánicos). Para el desarrollo de catálisis heterogénea, nanopartículas magnéticas (NPs) de óxidos de hierro fueron seleccionadas como soporte y los sistemas resultantes NP-Ru presentaron una buena dispersión en disolventes orgánicos y pudieron ser fácilmente separados y reutilizados, obteniendo así un sistema casi-homogéneo, en el que las ventajas de ambos procesos homogéneo y heterogéneo fueron combinados. Como último capítulo de la tesis, se presenta la introducción de quiralidad en el sistema catalítico mediante la utilización de un nuevo ligando tipo pineno tridentado quiral.The PhD thesis presented deals with the synthesis, thorough spectroscopic and electrochemical characterization and catalytic application of new mononuclear RuII-OH2 complexes containing a wide set of N- and O-donor ligands. The key influence of the electronic properties of the surrounding ligands on the redox chemistry of the resulting complexes and in the final output of catalytic oxidation reactions has been studied and rationalized. From the wide set of exhaustively studied Ru-OH2 catalysts a few were selected in order to develop more complex systems to be used in (a) heterogeneous catalysis (gathering easily recyclable catalytic systems) and (b) supramolecular catalysis (in order to pursue the regio-selective oxidation of complex organic substrates). For the development of heterogeneous catalysis magnetic nanoparticles (NPs) were chosen as support and the resulting Ru-NP systems presented good dispersion in organic solvents and could be easily removed and recycled, reaching a quasi-homogeneous system in which the advantages of both homogeneous and heterogeneous processes were combined. Furthermore, the introduction of chirality into the catalytic systems was also performed in the last chapter through a new chiral pineno-fused tridentate ligand.
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Krause, Jens Olaf. "Development of new ruthenium catalysts for homogeneous and heterogeneous olefin metathesis." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972590218.
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Kilic, Bahattin. "Peridynamic Theory for Progressive Failure Prediction in Homogeneous and Heterogeneous Materials." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/193658.
Повний текст джерелаАнотація:
The classical continuum theory is not capable of predicting failure without an external crack growth criteria and treats the interface having zero thickness. Alternatively, a nonlocal continuum theory referred to as peridynamic theory eliminates these shortcomings by utilizing formulation that uses displacements, rather than derivatives of displacements, and including material failure in its constitutive relations through the response functions. This study presents a new response function as part of the peridynamic theory to include thermal loading. Furthermore, an efficient numerical algorithm is presented for solution of peridynamic equations. Solution method relies on the discretization of peridynamic equations at collocation points resulting in a set of ordinary differential equations with respect to time. These differential equations are then integrated using explicit methods. In order to improve numerical efficiency of the computations, spatial partitioning is introduced through uniform grids as arrays of linked lists. Furthermore, the domain of interest is divided into subunits each of which is assigned to a specific processor to utilize parallel processing using OpenMP. In order to obtain the static solutions, the adaptive dynamic relaxation method is developed for the solution of peridynamic equations. Furthermore, an approach to couple peridynamic theory and finite element analysis is introduced to take advantage of their salient features. The regions in which failure is expected are modeled using peridynamics while the remaining regions are modeled utilizing finite element method. Finally, the present solution method is utilized for damage prediction of many problems subjected to mechanical, thermal and buckling loads.
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Sorrell, Brian R. "Homogeneous and heterogeneous metalloporphyrins catalysts for alkene epoxidation with hydrogen peroxide." Thesis, University of York, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245969.
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Kua, Jeremy Goddard William A. "Computational studies of heterogeneous and homogeneous catalysis by late transition metals." Diss., Pasadena, Calif. : California Institute of Technology, 2001. http://resolver.caltech.edu/CaltechTHESIS:11192009-085252318.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--California Institute of Technology, 2001. PQ #3018752.Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/09/10. Includes bibliographical references.
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Warratz, Svenja. "Homogeneous and Heterogeneous Chelation-Assisted Ruthenium(II)-Catalyzed C–H Functionalizations." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-002B-7CF4-0.
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Souleymanou, Myriam. "Pyrene-tagged Ligands as a Bridge between Homogeneous and Heterogeneous Catalysis." Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/668974.
Повний текст джерелаАнотація:
La present tesi tracta sobre el desenvolupament de catalitzadors homogenis que contenen fragments poliaromàtics
per facilitar el seu ancoratge en suports sòlids per aconseguir la fàcil separació i reciclatge del catalitzador. Es van
triar els grups pirè, ja que és conegut que promouen interaccions aromàtiques fortes pi-pi per apilament en
superfícies de carboni. En conseqüència, el treball s'ha centrat en els suports de carboni (nanotubs de carboni, òxid
de grafè reduït i perles de carboni) com a suports sòlids per a aquesta estratègia d'ancoratge no covalent en suports
sòlids. A més, s'ha explorat un sistema catalític bifàsic com una altra estratègia per al reciclatge i la reutilització de
catalitzadors homogenis. Aquest sistema catalític bifàsic, que consisteix en líquids iònics (IL) i diòxid de carboni
supercrític (scCO2), s'usa en la reacció de telomerització de 1,3-butadiè amb diòxid de carboni per produir ä-lactona
en un flux continu.La presente tesis trata sobre el desarrollo de catalizadores homogéneos que contienen fragmentos poliaromáticos que se han introducido con el objetivo de facilitar el anclaje en soportes sólidos para conseguir la fácil separación y el reciclaje del catalizador. Se eligieron grupos pireno, ya que es conocido que promueve interacciones aromáticas fuertes pi-pi por apilamiento en superficies de carbono. En consecuencia, el trabajo se ha centrado en los soportes de carbono (nanotubos de carbono, óxido de grafeno reducido y perlas de carbono) como materiales para esta estrategia de anclaje no covalente en soportes sólidos. Además, se ha explorado un sistema catalítico bifásico como otra estrategia para el reciclaje y la reutilización de catalizadores homogéneos. Este sistema catalítico bifásico, que consiste en líquidos iónicos (IL) y dióxido de carbono supercrítico (scCO2), se usa en la reacción de telomerización de 1,3-bytadieno con dióxido de carbono para producir ä-lactona en un flujo continuo.
The present thesis deals with the development of established homogeneous catalysts bearing polyaromatic fragments that would facilitate catalyst separation and recycling. Pyrene tags were chosen as it is a well-known antenna that promotes strong aromatic pi-pi stacking interactions onto carbon surfaces. Consequently, we focused our attention on carbon supports (carbon nanotubes, reduced graphene oxide and carbon beads) as solid supports for this noncovalent anchoring strategy on solid supports. In addition, a biphasic catalytic system as another strategy for the recycling and reuse of homogeneous catalysts is explored. This biphasic catalytic system consisting of ionic liquids (ILs) and supercritical carbon dioxide (scCO2) was used in the Pd-catalyzed telomerization reaction of 1,3-butadiene with carbon dioxide to yield ä-lactone in a continuous flow-manner.
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Cooper, Christine J. "Catalysts for stereoselective transformations." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548099.
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Мазурок, Наталия Степановна. "Физико-статистический метод определения надежности изделий твердотельной электроники". Doctoral thesis, Киев, 2013. https://ela.kpi.ua/handle/123456789/6457.
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Valls, Aïda. "CLUSDM: a multiple criteria decision making method for heterogeneous data sets." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6638.
Повний текст джерелаАнотація:
Aquesta tesi presenta una nova metodologia per resoldre problemes de presa de decisions. Hemestudiat els casos en què cal considerar més d'un criteri. Aquests tipus de mètodes de decisió es
coneixen com MCDM (Multiple Criteria Decision Making), o també MCDA (Multiple Criteria
Decision Aid). La diferència entre simplement "prendre decisions" o "ajudar a prendre
decisions" recau en si el mètode es dissenya per recomanar la decisió a prendre o si també
inclou elements que permeten entendre com es prenen les decisions en un cert context. La nostra
proposta inclou elements dels dos plantejaments. D'una banda, hem intentat que la persona que
ha d'usar el mètode no necessiti aprendre tècniques complexes abans de poder-lo aplicar a casos
reals. D'altra banda, el mètode no és una caixa negra, sinó que l'usuari rep informació sobre
característiques de les dades que ha de tenir en compte abans de fer la decisió final.
ClusDM és un mètode de presa de decisions pensat per resoldre dos tipus concrets de
problemes: (i) ordenar un conjunt d'alternatives de la millor a la pitjor, (ii) seleccionar les
millors alternatives del conjunt. La dificultat d'aquest procés recau en que cal maximitzar
diversos criteris parcials (i normalment no correlacionats) al mateix temps. A la tesi es pot
trobar un resum de les diferents aproximacions a aquest tipus de problemes de decisió. Només
destacar que el nostre mètode segueix les bases de la Teoria de la Utilitat.
Els mètodes clàssics consideren només criteris numèrics. Diferents extensions a aquests models
s'han anat desenvolupant durant els últims anys. En aquesta tesis ens hem plantejat la
possibilitat de tenir criteris que utilitzin diferents tipus de valors. A més, hem afegit dues fases a
la metodologia habitual (que té una fase d'agregació i una d'ordenació), que són: l'explicació
del resultat i l'avaluació de la qualitat.
La "Fase d'explicació" està dedicada a assignar un terme lingüístic per descriure cada
alternativa segons la seva posició en el ranking. L'ús de vocabularis qualitatius facilita la
comprensió del resultat. El significat dels diferents termes usats ve donat per una funció de
negació. Aquesta representació es basa en contrastar el significat d'un terme amb el dels termes
oposats (els seus antònims).
La "Fase d'Avaluació de la Qualitat" analitza a fons els resultats intermedis obtinguts en els
diferents passos del procés i intenta mesurar l'error acumulat. ClusDM proporciona diverses
mesures de qualitat parcial per cada fase del procés, de manera que l'usuari tingui constància de
la confiança que pot donar al resultat final que doni el sistema.
This thesis presents a new methodology for decision making. In particular, we have studied the
problems that consider more than one criterion, which is known as Multiple Criteria Decision
Making (MDCM) or Multiple Criteria Decision Aid (MCDA). The difference relies on the fact
of imitating the behaviour of the decision maker (i.e. develop a method that makes decisions) or
giving to the decision maker some additional information that allows him to understand the
mechanism of solving decisions (i.e. the decision maker can learn from the use of the method).
Our proposal fits better in the MCDA approach, but has also similarities with the MCDM
perspective. On one hand, the method we have designed is independent enough to not require a
deep understanding of the process by the decision maker. On the other hand, we have carefully
studied the process and the method is able to extract knowledge about the decision problem,
which is given to the user to let him know any special characteristics of the data analysed.
ClusDM is a new method to solve multicriteria decision problems. It is able to find a ranking of
alternatives or to select the best ones. This process is not easy since usually it is not possible to
maximise all the partial profits (i.e.criteria) at the same time. In the thesis we present an
overview of the large amount of methods developed to solve this problem. We follow the utility
theory approach.
Classical methods consider only numerical criteria. Some extensions allow the consideration of
other scales, such as, fuzzy or ordinal values, but usually they are required to have a common
scale for all criteria. This thesis faces the problem of managing different types of criteria at the
same time. Methods following the utility approach consider two steps to sort a decision
problem out: the aggregation and the ranking. We have included some additional steps in order
to improve the process: (i) the explanation phase and (ii) the quality measurement phase.
In the "Explanation Phase", special attention is devoted to give an appropriate linguistic
description of the ranking. The necessity to give a qualitatively described result has been argued
by different authors. The rationale behind this belief is that human decision makers understand
better a linguistic statement characterising the selected alternative (or ranking of alternatives)
than a numerical result or even a membership function. In this context, a new negation-based
semantics has been studied. The key idea is that we can infer the meaning of a term knowing the
terms that express an opposite value. The use of this new semantics representation seems
appropriate to obtain a result that can be easily understood by the decision maker.
In the "Quality Measurement Phase", different quality measures for each stage of the process
are calculated. With these measures we can give an overall value of the trustworthiness of the
final result. This kind of information is very useful for the decision maker in order to pay more
or less attention to the recommendations of the system.
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Messele, Selamawit Ashagre. "Homogeneous and heterogeneous aqueous phase oxidation of phenol with fenton-like processes." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/283319.
Повний текст джерелаАнотація:
A les passades dècades, s’han desenvolupat diverses tècniques basades en l’oxidació química a fi de superar els inconvenients associats al tractament d’aigües residuals industrials. Els processos d’oxidació avançada (AOPs) són efectius en la degradació de contaminants no biodegradables presents en aigües residuals i freqüentment permeten una quasi total degradació sota condicions raonables de pressió i temperatura. Entre elles, el procés Fenton és àmpliament utilitzat malgrat els seus molts inconvenients, com sensibilitat al pH, formació de fangs i pèrdua de les espècies actives. Aquest treball dissenya diferents alternatives de millora d’aquests inconvenients usant processos basats en Fenton per a l’oxidació homogènia i heterogènia de fenol. Així, l’addició d’agents quelants permet ampliar el rang efectiu de pH. Així mateix, l’ús de nanoferro zero valent suportat sobre materials carbonosos millora la capacitat d’eliminació i suprimeix la requerida separació del fang d’hidròxid de ferro.En las pasadas décadas, se desarrollaron diversas técnicas basadas en la oxidación química para superar los inconvenientes asociados al tratamiento de aguas residuales industriales. Los procesos de oxidación avanzada (AOPs) son efectivos en la degradación de contaminantes no biodegradables presentes en aguas residuales y frecuentemente permiten una casi total degradación bajo condiciones razonables de presión y temperatura. Entre ellas, el proceso Fenton es ampliamente utilizado pese a sus muchos inconvenientes, como sensibilidad al pH, formación de fangos y pérdida de las especies activas. Este trabajo diseña diferentes alternativas de mejora de estos inconvenientes usando procesos basados en Fenton para la oxidación homogénea y heterogénea de fenol. Así, la adición de agentes quelantes permite ampliar el rango efectivo de pH. Igualment, el uso de nanohierro cero valente soportado sobre materiales carbonosos mejora la capacidad de eliminación y suprime la requerida separación del fango de hidróxido de hierro.
In the last decades, various chemical oxidation techniques have been developed to overcome the inconveniences associated to conventional treatment of industrial wastewaters. Advanced oxidation processes (AOPs) have been reported to be effective for the degradation of soluble organic contaminants from wastewaters containing non-biodegradable organic pollutants, because they can often provide an almost total degradation, under reasonably mild conditions of temperature and pressure. Among them, Fenton process is widely implemented, although it has many drawbacks such as pH sensitivity, formation of sludge and loss of active species. Therefore, this work is specially focused on different alternatives to overcome the above drawbacks using Fenton-like processes for homogeneous and heterogeneous oxidation of phenol. Thus, the addition of chelating agents allowed broading the pH range of efficient operation. In turn, the use of nano zero valent iron supported on carbon materials enhances the removal performance and eliminates the subsequent separation of iron hydroxide sludge.
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Charland, Paule. "Characterization of small high energy photon beams in homogeneous and heterogeneous media." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0034/NQ38865.pdf.
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Magg, Sven. "Self-organised task differentiation in homogeneous and heterogeneous groups of autonomous agents." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9038.
Повний текст джерелаАнотація:
The field of swarm robotics has been growing fast over the last few years. Using a swarm of simple and cheap robots has advantages in various tasks. Apart from performance gains on tasks that allow for parallel execution, simple robots can also be smaller, enabling them to reach areas that can not be accessed by a larger, more complex robot. Their ability to cooperate means they can execute complex tasks while offering self-organised adaptation to changing environments and robustness due to redundancy. In order to keep individual robots simple, a control algorithm has to keep expensive communication to a minimum and has to be able to act on little information to keep the amount of sensors down. The number of sensors and actuators can be reduced even more when necessary capabilities are spread out over different agents that then combine them by cooperating. Self-organised differentiation within these heterogeneous groups has to take the individual abilities of agents into account to improve group performance. In this thesis it is shown that a homogeneous group of versatile agents can not be easily replaced by a heterogeneous group, by separating the abilities of the versatile agents into several specialists. It is shown that no composition of those specialists produces the same outcome as a homogeneous group on a clustering task. In the second part of this work, an adaptation mechanism for a group of foragers introduced by Labella et al. (2004) is analysed in more detail. It does not require communication and needs only the information on individual success or failure. The algorithm leads to self-organised regulation of group activity depending on object availability in the environment by adjusting resting times in a base. A possible variation of this algorithm is introduced which replaces the probabilistic mechanism with which agents determine to leave the base. It is demonstrated that a direct calculation of the resting times does not lead to differences in terms of differentiation and speed of adaptation. After investigating effects of different parameters on the system, it is shown that there is no efficiency increase in static environments with constant object density when using a homogeneous group of agents. Efficiency gains can nevertheless be achieved in dynamic environments. The algorithm was also reported to lead to higher activity of agents which have higher performance. It is shown that this leads to efficiency gains in heterogeneous groups in static and dynamic environments.
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Kunst, Rafael. "A QoS-aware resources sharing architecture for homogeneous and heterogeneous wireless networks." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/169287.
Повний текст джерелаАнотація:
O atual modelo de alocação espectral implementado pelas autoridades governamentais somado à crescente demanda por recursos imposta pela implementação de modernas aplicações e serviços de rede irá resultar em um problema relacionado à escassez de recursos em um futuro próximo. Lidar com este problema demanda esforços no sentido de melhorar a alocação de recursos. Uma das maneiras de atingir este tipo de melhoria é permitir o compartilhamento de recursos entre operadores em redes homogêneas e heterogêneas que podem implementar diferentes tecnologias, como a utilização coletiva do espectro e de recursos licenciados. Diversos trabalhos relacionados à esta pesquisa foram propostos. Entretanto, estes trabalhos geralmente identificam a necessidade de obter recursos adicionais, porém buscam por esses recursos sem levar em conta os requisitos de qualidade de serviço e o custo envolvido no compartilhamento desses recursos. Considerando esse contexto, nesta tese, uma nova arquitetura é proposta para permitir a implementação do compartilhamento de recursos e para encorajar operadores a alugarem recursos sobressalentes levando em conta o custo e a qualidade de serviço oferecida. Esta abordagem permite que operadores tenha ganhos com o aluguel dos recursos, ao mesmo tempo em que o cliente recebe serviços com maior qualidade. As principais contribuições da arquitetura proposta incluem o projeto de um controlador de recursos para coordenar o processo de compartilhamento. Esse controlador busca estabelecer contratos de serviço dinâmicos levando em conta a qualidade de serviço requerida. Para tanto, é necessária a troca de informações que, no caso da arquitetura proposta, é mantida baixa para evitar que a rede seja sobrecarregada e acabe interferindo com o tráfego de dados. Além disso, a solução proposta é capaz de tomar decisões rápidas sobre a alocação de recursos, o que permite o redirecionamento do tráfego sem que ocorram interferências com os demais usuários. A arquitetura proposta é modela analiticamente e simulada com o auxílio da ferramenta Matlab. O desempenho da proposta é medido em três diferentes cenários, considerando tanto redes homogêneas, quanto heterogêneas. A sobrecarga gerada pela troca de informações de controle corresponde a menos de 1% do tráfego total da rede, o que é desprezível do ponto de vista da interferência com o tráfego de dados. As decisões rápidas tomadas pela arquitetura são baseadas na previsão acurada do tráfego futuro da rede e permitem o redirecionamento do tráfego para outras redes em um tempo até 46% abaixo do limite máximo especificado na literatura para este tipo de redirecionamento. Os resultados mostram ainda que as métricas de atraso e variação do atraso também são mantidas abaixo dos limites especificados, o que indica que a qualidade de serviço é garantida nos cenários avaliados.The static model currently applied by governmental authorities for allocating the spectrum of frequencies and the increasing demand for network resources imposed by modern applications and services may lead to a resources scarcity problem in the near future. Dealing with this problem demands improvements on resources allocation. One of the ways of providing such improvements is by allowing resources sharing among network operators in both homogeneous and heterogeneous network scenarios. These network operators may implement different technologies, such as collective use of spectrum and licensed shared access to the spectrum of frequencies. Many related works have been proposed in the same context of the presented research, however these related works generally identify the need for additional resources and search for available resources without taking into account the QoS requirements of the resources renter and the costs involved in the resources sharing initiative. Therefore, in this thesis, a novel architecture is proposed to facilitate the implementation of resources sharing and consequently encourage network operators to lease their underutilized resources taking into account both the cost and the QoS requirements. This approach allows the network operator which is serving the resources to improve its profits at the same time that allows quality of service improvements to the resources renter. The main contributions of the proposed architecture include but are not limited to the design of a multilevel resources broker to control the resources sharing process. This broker is concerned on dynamically establishing a service level agreement that takes into account the quality of service requirements of resources renter. This process focuses on exchanging a small amount of control information to prevent the overhead from interfering with the legitimate traffic of the network operators. Another important contribution of the proposed approach is to improve the resources allocation in comparison with related work. Furthermore, the proposed solution is capable of taking fast decisions regarding resources allocation, what leads to the implementation of fast handover, allowing the traffic steering without interfering with incumbent users. The proposed architecture is modeled analytically and simulated using Matlab to evaluate its behavior in three different scenarios, considering both homogeneous and heterogeneous networks. The overhead in practical operation scenarios is kept under 1% of the total network traffic, what is considered not to interfere with the transmissions of the network operators. The fast decisions taken by the resources sharing architecture are based on accurate traffic load forecasting, what leads to fast handover, attaining times up to 46% lower than the maximum allowed handover duration. Results also show that both delay and jitter metrics are controlled to be maintained below their specific thresholds of the analyzed applications and therefore, the QoS is guaranteed for the resources renter, considering the coexistence of up to 500 devices.
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Schwartz, Cindy Rochelle. "Ability and Performance Comparisons of Gifted Students in Homogeneous and Heterogeneous Settings." ScholarWorks, 2016. https://scholarworks.waldenu.edu/dissertations/2233.
Повний текст джерелаАнотація:
To meet the educational needs and acceleration of talented and gifted (TAG) students, it is important to determine the best learning environment to afford optimal academic success during their educational experience. A study at a Bartow County school district in Georgia has been conducted in order to establish this best learning environment. This study investigated if Lexile scores (ability) and academic averages (performance) differ for 6th grade TAG students in homogeneous classes compared to TAG students in heterogeneous settings. Vygotsky's theory of social constructivism, which proposes that students need to feel socially and cognitively supported by their environment, was the theoretical foundation of this study. Using a time series, quasi-experimental, between-group comparison, and a 2-group, nonequivalent control group design, this study analyzed archival data for reading, language arts, and social studies from sixth grade middle school TAG students (n = 43) who were enrolled in both homogenous and heterogeneous settings depending on the scheduling of the courses. The results revealed no significant differences in either the reading or language arts classes but did reveal a significant difference (p = .03) in the level of academic performance for social studies in homogeneous classes compared to students in heterogeneous classes. The findings may contribute to positive social change by informing educators about the utility of specific curricular content for TAG students in a particular setting.
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Busireddy, Bhargavi. "Study of Mercury Transformation with Chlorinated Species under Homogeneous and Heterogeneous Conditions." University of Dayton / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1299087195.
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Bozeman, Alan Kyle. "Weakly Dense Subsets of Homogeneous Complete Boolean Algebras." Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc330803/.
Повний текст джерелаАнотація:
The primary result from this dissertation is following inequality: d(B) ≤ min(2^< wd(B),sup{λ^c(B): λ < wd(B)}) in ZFC, where B is a homogeneous complete Boolean algebra, d(B) is the density, wd(B) is the weak density, and c(B) is the cellularity of B.
Chapter II of this dissertation is a general overview of homogeneous complete Boolean algebras. Assuming the existence of a weakly inaccessible cardinal, we give an example of a homogeneous complete Boolean algebra which does not attain its cellularity.
In chapter III, we prove that for any integer n > 1, wd_2(B) = wd_n(B). Also in this chapter, we show that if X⊂B is κ—weakly dense for 1 < κ < sat(B), then sup{wd_κ(B):κ < sat(B)} = d(B).
In chapter IV, we address the following question: If X is weakly dense in a homogeneous complete Boolean algebra B, does there necessarily exist b € B\{0} such that {x∗b: x ∈ X} is dense in B|b = {c € B: c ≤ b}? We show that the answer is no for collapsing algebras.
In chapter V, we give new proofs to some well known results concerning supporting antichains. A direct consequence of these results is the relation c(B) < wd(B), i.e., the weak density of a homogeneous complete Boolean algebra B is at least as big as the cellularity. Also in this chapter, we introduce discernible sets. We prove that a discernible set of cardinality no greater than c(B) cannot be weakly dense.
In chapter VI, we prove the main result of this dissertation, i.e., d(B) ≤ min(2^< wd(B),sup{λ^c(B): λ < wd(B)}). In chapter VII, we list some unsolved problems concerning this dissertation.
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Mugume, Edwin. "Green heterogeneous cellular networks." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/green-heterogeneous-cellular-networks(e7976a91-c891-4174-abaf-18820ff1736d).html.
Повний текст джерелаАнотація:
Data traffic demand has been increasing exponentially and this trend will continue over theforeseeable future. This has forced operators to upgrade and densify their mobile networks toenhance their capacity. Future networks will be characterized by a dense deployment of different kinds of base stations (BSs) in a hierarchical cellular structure. However network densification requires extensive capital and operational investment which limits operator revenues and raises ecological concerns over greenhouse gas emissions. Although networks are planned to support peak traffic, traffic demand is actually highly variable in both space and time which makes it necessary to adapt network energy consumption to inevitable variations in traffic demand. In this thesis, stochastic geometry tools are used to perform simple and tractable analysis of thecoverage, rate and energy performance of homogeneous networks and heterogeneous networks(HetNets). BSs in each tier are located according to independent Poisson Point Processes(PPPs) to generate irregular topologies that fairly resemble practical deployment topologies. The homogeneous network is optimized to determine the optimal BS density and transmit power configuration that minimizes its area power consumption (APC) subject to both coverage and average rate constraints. Results show that optimal transmit power only depends on the BSpower consumption parameters and can be predetermined. Furthermore, various sleep modemechanisms are applied to the homogeneous network to adapt its APC to changes in userdensity. A centralized strategic scheme which prioritize BSs with the least number of usersenhances energy efficiency (EE) of the network. Due to the complexity of such a centralizedscheme, a distributed scheme which implements the strategic algorithm within clusters of BSsis proposed and its performance closely matches that of its centralized counterpart. It is more challenging to model the optimal deployment configuration per tier in a multi-tier HetNet. Appropriate assumptions are used to determine tight approximations of these deployment configurations that minimize the APC of biased and unbiased HetNets subject tocoverage and rate constraints. The optimization is performed for three different user associationschemes. Similar to the homogeneous network, optimal transmit power per tier also depends onBS power consumption parameters only and can also be predetermined. Analysis of the effect of biasing on HetNet performance shows appropriate biasing can further reduce the deploymentconfiguration (and consequently the APC) compared to an unbiased HetNet. In addition, biasing can be used to offload traffic from congesting and high-power macro BSs to low-power small BSs. If idle BSs are put into sleep mode, more energy is saved and HetNet EE improves. Moreover, appropriate biasing also enhances the EE of the HetNet.
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Mirza, Amin Ruhul. "Developments in supported aqueous-phase catalysis." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311179.
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Maleki, Hamed [Verfasser]. "Numerical study of homogeneous and heterogeneous crystal nucleation in colloidal systems / Hamed Maleki." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1022116878/34.
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Aslam, Ahmad Moeed. "Energy Efficient Analysis for WCDMA/ 3G Homogeneous and Heterogeneous Deployments in Indoor Environment." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-90809.
Повний текст джерелаАнотація:
In near future, the cellular traffic will increase rapidly with majority of the increase coming from Indoor traffic. To cope up with the ever increasing demand, more Base Stations are being deployed in limited areas, which can increase the capacity but will also be responsible for increased energy consumption. Since power is a valuable commodity today both economical and environmental wise, energy efficient deployment along with capacity improvement is crucial for both incumbent and new telecom operators. The objective of this Thesis is to evaluate Power consumption and Capacity for Indoor users, both in Homogeneous and Heterogeneous infra structure cases for the 3G WCDMA/UMTS technology. The comparison is done for Uniform and Non-Uniform Traffic Distributions. In homogeneous case, results indicate that there is a tradeoff between Area Power Consumption, APC and Area Spectral Efficiency, ASE. Large Macro Base Stations covering a limited Indoor Area use less APC but provides low ASE. Small Micro Base Stations which cover the same Indoor Area consumes little more APC then Macro BS but increases the ASE manifold. In Heterogeneous case results suggest that Heterogeneous Networks (HETNET) cases enhance the Area Throughput significantly with a small increase in Area Power Consumption. MACRO+10WLAN 1is the best HETNET case in both Uniform and Non-Uniform Traffic with up to 40% Energy savings and higher data/user compared to MACRO Only deployment. The traffic patterns, number of active users in a cell and Inter Site Distances between Base Stations strongly influence the energy saving and capacity enhancements.
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Petel, Oren E. "A study of the failure mechanism of detonations in homogeneous and heterogeneous explosives /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99530.
Повний текст джерелаАнотація:
The present study measured the critical diameter and critical thickness of a variety of explosives. The explosives tested included two "unstable" homogeneous explosives (nitromethane and a nitromethane/nitroethane blend); a model heterogeneous explosive consisting of a packed bed of glass beads (Φ ~ 80 μm) saturated with the homogeneous nitromethane/nitroethane blend; and a commercial heterogeneous explosive, Apex Elite(TM). The comparison of the critical diameter and thickness of an explosive is used to identify the dominant propagation and failure mechanisms of the various explosives. The ratio of critical diameter to critical thickness for nitromethane, the nitromethane/nitroethane blend, the beaded heterogeneous explosive, and Apex Elite(TM) were found to be 3.2 +/- 0.6, 3.6 +/- 0.4, 2.3 +/- 0.1, and 3.5 +/- 1.2 respectively. According to accepted detonation failure theories, the energy losses associated with detonation front curvature are responsible for detonation failure. The curvature model, which is elaborated upon in the present work, leads to a predicted critical diameter to critical thickness ratio of exactly 2. The present study has shown that the only explosive which follows the behaviour predicted by curvature failure models is the beaded heterogeneous explosive, which exhibits fine scale heterogeneities. This seems to indicate that unstable liquid explosives and heterogeneous explosives with large scale heterogeneities do not fail simply due to the wave front curvature, but rather by a local mechanism of failure and reinitiation which dominates the detonation propagation.
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Schätz, Alexander. "Immobilization of homogeneous catalysts on nanoparticles and their application in semi-heterogeneous catalysis." kostenfrei, 2009. http://www.opus-bayern.de/uni-regensburg/volltexte/2009/1239/.
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Ever, Enver. "Performability modelling of homogeneous and heterogeneous multi-server systems with breakdowns and repairs." Thesis, Middlesex University, 2007. http://eprints.mdx.ac.uk/13516/.
Повний текст джерелаАнотація:
This thesis presents analytical modelling of homogeneous multi-server systems with reconfiguration and rebooting delays, heterogeneous multi-server systems with one main and several identical servers, and farm paradigm multi-server systems. This thesis also includes a number of other research works such as, fast performability evaluation models of open networks of nodes with repairs and finite queuing capacities, multi-server systems with deferred repairs, and two stage tandem networks with failures, repairs and multiple servers at the second stage. Applications of these for the popular Beowulf cluster systems and memory servers are also accomplished. Existing techniques used in performance evaluation of multi-server systems are investigated and analysed in detail. Pure performance modelling techniques, pure availability models, and performability models are also considered. First, the existing approaches for pure performance modelling are critically analysed with the discussions on merits and demerits. Then relevant terminology is defined and explained. Since the pure performance models tend to be too optimistic and pure availability models are too conservative, performability models are used for the evaluation of multi-server systems. Fault-tolerant multi-server systems can continue service in case of certain failures. If failure does not occur at a critical point (such as breakdown of the head processor of a farm paradigm system) the system continues serving in a degraded mode of operation. In such systems, reconfiguration and/or rebooting delays are expected while a processor is being mapped out from the system. These delay stages are also taken into account in addition to failures and repairs, in the exact performability models that are developed. Two dimensional Markov state space representations of the systems are used for performability modelling. Following the critical analysis of the existing solution techniques, the Spectral Expansion method is chosen for the solution of the models developed. In this work, open queuing networks are also considered. To evaluate their performability, existing modelling approaches are expanded and validated by simulations, for performability analysis of multistage open networks with finite queuing capacities. The performances of two extended modelling approaches are compared in terms of accuracy for open networks with various queuing capacities. Deferred repair strategies are becoming popular because of the cost reductions they can provide. Effects of using deferred repairs are analysed and performability models are provided for homogeneous multi-server systems and highly available farm paradigm multi-server systems. Since one of the random variables is used to represent the number of jobs in one of the queues, analytical models for performance evaluation of two stage tandem networks suffer because of numerical cumbersomeness. Existing approaches for modelling these systems are actually pure performance models since breakdowns and repairs cannot be considered. One way of modelling these systems can be to divide one of the random variables to present both the operative and non-operative states of the server in one dimension. However, this will give rise to state explosion problem severely limiting the maximum queue capacity that can be handled. In order to overcome this problem a new approach is presented for modelling two stage tandem networks in three dimensions. An approximate solution is presented to solve such a system. This approach manifests itself as a novel contribution for alleviating the state space explosion problem for large and/or complex systems. When two state tandem networks with feedback are modelled using this approach, the operative states can be handled independently and this makes it possible to consider multiple operative states at the second stage. The analytical models presented can be used with various parameters and they are extendible to consider systems with similar architectures. The developed three dimensional approach is capable to handle two stage tandem networks with various characteristics for performability measures. All the approaches presented give accurate results. Numerical solutions are presented for all models developed. In case the solution presented is not exact, simulations are performed to validate the accuracy of the results obtained.
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Armstrong, Nancy A. "The effects of cooperative learning on gifted students in heterogeneous and homogeneous groups." Virtual Press, 1993. http://liblink.bsu.edu/uhtbin/catkey/861387.
Повний текст джерелаАнотація:
The purpose of this study was to investigate whether gifted students scored higher on reading achievement and self-esteem ratings when they worked in mixed ability (heterogeneous) groups or similar ability (homogeneous) groups while participating in cooperative learning activities. The participants were 47 fourth grade students from six intact classrooms in four elementary schools in small midwestern school districts.The Gates-MacGinitie Reading Tests were used to obtain pre- and posttest scores in the area of reading ability. The test consisted of 93 items, including 45 vocabulary and 48 comprehension questions. The Coopersmith Self-Esteem Inventory was also given to the students as a pre- and posttest measure of self-esteem. A treatment of cooperative learning activities was then completed with each class by the researcher to determine if there was a difference between the two groups.The following hypotheses were tested at the.05 level of significance:Hypothesis 1: There is no significant difference between the reading achievement of gifted students who participate in cooperative learning with heterogeneous groups of students and gifted students who participate in cooperative learning with homogeneous groups of students.Hypothesis ll: There is no significant difference in the self-esteem ratings of gifted students who participate in cooperative learning with heterogeneous groups of students and gifted students who participate in cooperative learning with homogeneous groups of students.To test the hypotheses an analysis of variance (ANOVA) was used. For each hypothesis, the obtained F-ratio exceeded the F-value for significance at the .05 level. Therefore, the tests failed to reject the null hypotheses. The findings of this study indicate that students achieve equally well in reading achievement and self-esteem regardless of the grouping strategy used.Department of Elementary Education
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Betham, Michael. "A comparative study of homogeneous and heterogeneous phosphine and carbene based palladium catalysts." Thesis, University of Newcastle Upon Tyne, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407617.
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Rodrigues, Anne Kerolaine de Oliveira. "Lactic acid production from hydrothermal conversion of glycerol using homogeneous and heterogeneous catalysis." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=16779.
Повний текст джерелаАнотація:
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel SuperiorThe use of alternative energy sources is a of the major current priorities, that appears to circumvent the serious problems caused by technological development. Accordingly, biodiesel arises as an alternative fuel to petroleum. However, high biodiesel production generates a large quantity of glycerin (10 wt%) which is considered an unwanted byproduct. To increase the market values of the biodiesel byproduct, it is necessary to convert glycerin into other chemicals, such as in lactic acid, which is becoming increasingly important due to their promising polymers applications - eg.: poly(lactic acid) (PLA) - as an alternative to replace petrochemical plastics. In the present study the hydrothermal process was used for lactic acid production, replacing the fermentation process that is currently used to obtain this product. For hydrothermal conversion of glycerol into lactic acid by homogeneous catalysis, NaOH and KOH catalysts were used. And for hydrothermal glycerol lactic acid by heterogeneous catalysis, Cu/SiO2 catalyst was used. Initial glycerol concentration (0.51-17.1 M), temperature (160-280 ÂC), pressure (2-43 bar), water/glycerol volumetric ratio (0.8 to 31), catalyst/glycerol molar ratio (0.01 to 1.02) and total reaction time (3-4 hours) were the variables studied with temperature and water/glycerol volumetric ratio having the major influence. In addition, a first-order kinetic model for glycerol concentration versus time was developed and verified experimentally under conditions with different temperatures. Comparing the results obtained from hydrothermal conversion by homogeneous and heterogeneous catalysis, it was observed that KOH was catalyst with the best performance. The highest yield obtained was 87.5% at 220 ÂC and 28.8 bar, after 3 h, from a solution water/glycerol volumetric ratio equal to 0.8 and KOH/glycerol molar ratio equal to 0.03. From this result, hydrothermal process can be seen as a promising method to add value to glycerol.
A utilizaÃÃo de fontes alternativas de energia à uma das grandes prioridades atuais, que surge para contornar os graves problemas ocasionados pelo desenvolvimento tecnolÃgico. Neste sentido, o biodiesel surge como um combustÃvel alternativo ao petrÃleo. No entanto, a elevada produÃÃo de biodiesel gera uma grande quantidade de glicerina (10% em massa) que à considerada um coproduto. Para aumentar o valor de mercado da glicerina, faz-se necessÃrio convertÃ-la em outros produtos quÃmicos, como por exemplo, em Ãcido lÃtico, que està se tornando cada vez mais importante, devido a aplicaÃÃes promissoras de seus polÃmeros â ex.: poli(Ãcido lÃtico) (PLA) â como uma alternativa para substituir os plÃsticos petroquÃmicos. O presente estudo teve como objetivo utilizar o processo hidrotÃrmico para a produÃÃo de Ãcido lÃtico, em substituiÃÃo ao processo fermentativo que Ã, atualmente, utilizado para a obtenÃÃo deste produto. Para conversÃo hidrotÃrmica do glicerol em Ãcido lÃtico, via catÃlise homogÃnea, NaOH e KOH foram os catalisadores utilizados. E para a conversÃo hidrotÃrmica do glicerol em Ãcido lÃtico, via catÃlise heterogÃnea, Cu/SiO2 foi o catalisador usado. ConcentraÃÃo inicial de glicerol (0,51-17,1 M), temperatura (160-280 ÂC), pressÃo (2-43 bar), razÃo volumÃtrica de Ãgua/glicerol (0,8-31), razÃo molar catalisador/glicerol (0,01-1,02) e tempo total de reaÃÃo (3-4 horas) foram as variÃveis estudadas. A temperatura e a razÃo volumÃtrica de Ãgua/glicerol foram as variÃveis de maior influÃncia. AlÃm disso, um modelo cinÃtico de primeira ordem para determinaÃÃo da concentraÃÃo de glicerol em funÃÃo do tempo foi desenvolvido e verificado experimentalmente em diferentes temperaturas. Comparando os resultados obtidos a partir das conversÃes hidrotÃrmicas, via catÃlise homogÃnea e heterogÃnea, foi possÃvel observar que o KOH foi o catalisador com o melhor desempenho. O maior rendimento obtido foi de 87,5%, a 220 ÂC e a 28,8 bar, em um tempo total de reaÃÃo de 3 h, a partir de uma soluÃÃo de razÃo volumÃtrica Ãgua/glicerina igual a 0,8 e razÃo molar KOH/glicerol igual a 0,03. A partir deste resultado, processo hidrotÃrmico pode ser visto como sendo um processo promissor para agregar valor ao glicerol.
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Carreiro, Elisabete da Palma. "Homogeneous and heterogeneous asymmetric catalysis with Bis (Oxazoline), Mono (Oxazoline) and diphosphine ligands." Doctoral thesis, Universidade de Évora, 2010. http://hdl.handle.net/10174/22414.
Повний текст джерелаАнотація:
Neste projecto de doutoramento teve-se como objectivo estudar ligandos monooxazolinas, bis-oxazolinas e difofinas em reacções catalíticas assimétricas nas fases homogéneas e heterogéneas. Uma pequena biblioteca de sete mono-oxazolinas foi sintetizada e usada em ciclopropanações catalíticas assimétricas (CPCA) combinatórias. Os homo- e heterocomplexos formados com estes ligandos e cobre (I) foram alvo de estudos cinéticos, espectroscópia de RMN e computacionais, os quais indicaram que o heterocomplexo di-coordenado é o mais estável. Arylid-BOXs com orto substituintes foram sintetizadas e usadas em CPCA usando Cu(I) e Ru(II) como pré-catalisadores e realizadas com solventes orgânicos e sistemas bifásicos. Estudos computacionais dos metalocarbenos das Arylid-BOX reforçaram o mecanismo concertado na CPCA. Os catalisadores Cu(I)-Arylid-BOX foram imobilizados em montmorilonite K10 e silica através ligações não-covalentes e testados em CPCA, os resultados revelaram bastante líxiviação do metal. Um ligando derivado da Arylid-BOX foi ligado a uma resina polimérica, e usado em CPCA com Cu(I) e Cu(II). Os resultados revelaram-se semelhantes as CPCA na fase homogénea. Por fim, o ligando PYRPHOS foi imobilizado no polímero polivinilalcool (PVA), e usado em hidroformilações catalíticas assimétricas catalisadas por Rh. ____ ABSTRACT: The aim of this work was the study of mono(oxazolines), bis(oxazolines) and diphosphines in metal-catalyzed asymmetric reactions in the both homo- and heterogeneous phase. A small library of seven mono(oxazoline) ligands, was synthesized and evaluated in a combinatorial homogeneous catalytic asymmetric cyclopropanation reaction (CACP). The kinetics, NMR spectroscopic and computational studies of the homo- and heterocomplexes revealed that the most stable in solution was the di-coordinated heterocomplex. The synthesis of two ortho-substituted-Arylid-BOX ligands is described, which were evaluated in the CACP using Cu(I) and Ru(II) in organic solvents and biphasic media. The electrophilicity of the Arylid-BOX metallocarbenes was calculated using the Fukui Function. The Arylid-BOXs were immobilized on Montmorillonite K10 and on silica via non-covalent bonding and tested in the same reaction. The synthesis of a polymer supported Arylid-BOX-derivative, and its application in the CACP with copper (I). Good yields, enantioselectivities and diastereoselectivities were obtained. Moreover, the polymer-bound catalyst could be easily and efficiently recycled. Finally, the synthesis of supported PYRPHOS ligand on polyvinlyalcohol (PVA) and it's use in the catalytic asymmetric hydroformylation was studied.
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Sheng, Meili. "Heterogeneous and Homogeneous Nickel-Based Electrocatalysts for Oxygen Evolution and Carbon Dioxide Reduction." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/5151.
Повний текст джерелаАнотація:
Electrolysis of water to form H2 and O2 and electrocatalytic reduction of CO2 to CO have attracted increasing attention these years. To realize a large-scale production of H2 and CO, it is critical to develop efficient and earth-abundant catalysts that could overcome the slow kinetics of the O2 evolution reaction in water splitting and selectively reduce CO2 over the competing H2 evolution reaction. This thesis describes the synthesis, characterization, and evaluation of nickel-based heterogeneous and homogeneous (molecular) electrocatalysts for water oxidation and CO2 reduction, respectively. The first project describes the Fe incorporated ultrathin Ni(OH)2 nanosheets which exhibit dramatically enhanced performance in electrocatalytic O2 evolution. The second project focus on a molecular Ni complex with a pyridyl biscarbene ligand for electrocatalytic CO2 reduction. Compared to those typical Ni complexes with cyclam-derivatized and/or -analogous tetradentate ligands, our Ni complex showed high selectivity for CO2 reduction over the competing H2 evolution reaction.
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Shi, Jianyou. "Conservative and reactive mass transport in homogeneous and heterogeneous ground-water flow systems /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488194825667624.
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