Dissertations / Theses on the topic 'Reacting experiments'
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Heitor, Manuel Frederico Tojal de Valsassina. "Experiments in turbulent reacting flows." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/12044.
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Montello, Aaron David. "An Experimental Investigation of Water Droplet Growth, Deformation Dynamics and Detachment in a Non-Reacting PEM Fuel Cell via Fluorescence Photometry." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228248650.
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Keller, Tobias [Verfasser]. "Reactive Distillation for Multiple-reaction Systems: Experimental Investigation, Modelling and Optimisation / Tobias Keller." München : Verlag Dr. Hut, 2013. http://d-nb.info/103728948X/34.
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Brown, Richard J. "Experimental investigation of a turbulent reacting plume." Thesis, The University of Sydney, 1996. https://eprints.qut.edu.au/32127/1/Richard_Brown_Thesis.pdf.
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An experimental investigation has been made of a round, non-buoyant plume of nitric oxide, NO, in a turbulent grid flow of ozone, 03, using the Turbulent Smog Chamber at the University of Sydney. The measurements have been made at a resolution not previously reported in the literature. The reaction is conducted at non-equilibrium so there is significant interaction between turbulent mixing and chemical reaction. The plume has been characterized by a set of constant initial reactant concentration measurements consisting of radial profiles at various axial locations. Whole plume behaviour can thus be characterized and parameters are selected for a second set of fixed physical location measurements where the effects of varying the initial reactant concentrations are investigated. Careful experiment design and specially developed chemilurninescent analysers, which measure fluctuating concentrations of reactive scalars, ensure that spatial and temporal resolutions are adequate to measure the quantities of interest. Conserved scalar theory is used to define a conserved scalar from the measured reactive scalars and to define frozen, equilibrium and reaction dominated cases for the reactive scalars. Reactive scalar means and the mean reaction rate are bounded by frozen and equilibrium limits but this is not always the case for the reactant variances and covariances. The plume reactant statistics are closer to the equilibrium limit than those for the ambient reactant. The covariance term in the mean reaction rate is found to be negative and significant for all measurements made. The Toor closure was found to overestimate the mean reaction rate by 15 to 65%. Gradient model turbulent diffusivities had significant scatter and were not observed to be affected by reaction. The ratio of turbulent diffusivities for the conserved scalar mean and that for the r.m.s. was found to be approximately 1. Estimates of the ratio of the dissipation timescales of around 2 were found downstream. Estimates of the correlation coefficient between the conserved scalar and its dissipation (parallel to the mean flow) were found to be between 0.25 and the significant value of 0.5. Scalar dissipations for non-reactive and reactive scalars were found to be significantly different. Conditional statistics are found to be a useful way of investigating the reactive behaviour of the plume, effectively decoupling the interaction of chemical reaction and turbulent mixing. It is found that conditional reactive scalar means lack significant transverse dependence as has previously been found theoretically by Klimenko (1995). It is also found that conditional variance around the conditional reactive scalar means is relatively small, simplifying the closure for the conditional reaction rate. These properties are important for the Conditional Moment Closure (CMC) model for turbulent reacting flows recently proposed by Klimenko (1990) and Bilger (1993). Preliminary CMC model calculations are carried out for this flow using a simple model for the conditional scalar dissipation. Model predictions and measured conditional reactive scalar means compare favorably. The reaction dominated limit is found to indicate the maximum reactedness of a reactive scalar and is a limiting case of the CMC model. Conventional (unconditional) reactive scalar means obtained from the preliminary CMC predictions using the conserved scalar p.d.f. compare favorably with those found from experiment except where measuring position is relatively far upstream of the stoichiometric distance. Recommendations include applying a full CMC model to the flow and investigations both of the less significant terms in the conditional mean species equation and the small variation of the conditional mean with radius. Forms for the p.d.f.s, in addition to those found from experiments, could be useful for extending the CMC model to reactive flows in the atmosphere.
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O'Neal, Stephen Vernon. "A kinetic study of the chromium (VI) - arsenic (III) reaction in pyridine-pyridinium buffer solutions containing oxalate." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/104524.
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Jerez, Briones Jorge Antonio. "Aluminosilicate-coated silica sand for reactive transport experiments." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Spring2005/J-J%5FBriones%5F050305.pdf.
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Prat, Resina Xavier. "Study of the reaction mechanism in Mandelate racemase enzyme: reaction path and dynamical sampling approaches." Doctoral thesis, Universitat Autònoma de Barcelona, 2004. http://hdl.handle.net/10803/3175.
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En aquesta tesi s'ha dissenyat i aplicat diferents eines teòriques i computacionals per a l'estudi de la reactivitat de l'enzim Mandelat Racemasa.L'enzim Mandelat Racemasa catalitza la interconversió dels dos enantiòmers (S) i (R) de l'àcid mandèlic a una velocitat semblant. El mecanisme de reacció que es postula experimentalment passa per l'abstracció d'un protó molt poc àcid. Aquesta reacció molt poc favorable en medi aquós l'enzim la catalitza a una velocitat sorprenentment alta.
Fent un estudi Mecànica Quàntica / Mecànica Molecular (QM/MM) de la reactivitat de l'enzim s'han trobat els intermedis i les barreres de reacció que permeten deduir tres mecanismes a través dels quals el substracte natural mandelat i altres dos substractes anàlegs poden racemitzar. Expliquem de quina manera l'enzim pot fer la catàlisi tant efectiva i equivalent per als dos enantiòmers.
Partint de la necessitat de millorar l'estudi QM/MM anterior, sobretot pel què fa a l'acurada localització dels estats de transició (barreres reacció), s'ha dissenyat un mètode d'optimització d'estructures per ser aplicat a sistemes de milers d'àtoms com ho és el nostre enzim.
El mètode anomenat micro-iteratiu es basa en una cerca segons les equacions Rational Function Optimization (RFO) en una zona reduida mentre es minimitza l'entorn amb un mètode computacionalment barat com el LBFGS. Aquest mètode micro-iteratiu ha estat formulat, implementat i testejat en sistemes moleculars grans i petits. Se n'ha estudiat les diferents opcions donant una recepta pràctica per al seu ús en altres reaccions. També se n'ha justificat el seu desenvolupament posant de relleu les millores obtingudes amb aquest nou mètode quan es comparen els nous resultats amb els obtinguts en l'estudi QM/MM inicial.
Finalment, l'energia lliure de la reacció enzimàtica s'ha calculat amb tècniques de la dinàmica molecular i de l'Umbrella Sampling. Per aquest tipus de càlcul és imprescindible escollir a priori una coordenada de reacció que permeti anar de reactius a productes, en altres paraules, és necessari saber com té lloc la reacció. Gràcies a la prèvia localització d'estats de transició amb el mètode micro-iteratiu podem conèixer el mecanisme de reacció. I per tant podem emprar una coordenada de reacció adequada que ens permet calcular l'energia lliure de reacció de forma efectiva.
In this thesis several theoretical techniques to study the Mandelate Racemase enzyme reactivity are designed and used.
The Mandelate Racemase enzyme catalyses the interconversion of both enantiomers (S) and (R) of mandelic acid at apparently the same rate. Experimental results suggest that the reaction mechanism takes place through the abstraction of a non-acid hydrogen. This reaction is very low in aqueous media but the enzyme catalyzes it at an extremely fast rate.
We carry out a QM/MM study of the enzyme reativity. We have found the intermediate structures and the energy barriers corresponding to three proposed mechanisms that the natural substrate mandelate and two other substrate analogues may undergo. We are able to explain how the the efficient catalysis is performed for the two enantiomers.
Due to the lack in the previous QM/MM study of an efficient method to locate transition state structures (energy barriers) we have designed an structure optimization method to be applied to systems constituted by thousands of atoms such as our enzyme.
The so-called micro-iterative method consists in a search based on the Rational Function Optimization (RFO) equations applied in a core zone while the environment is minimized through a computationally affordable method such as LBFGS. The micro-iterative method has been formulated, implemented and tested for small and big molecular systems. We have studied several possible options giving as a result a practical guide for its usage in other reactions. Comparing the results coming from the initial QM/MM study with the ones found by this micro-iterative method we show an improvement that justifies the development.
Finally, the free energy corresponding to the enzymatic reaction is calculated by means of Molecular Dynamics and Umbrella Sampling techniques. The free energy computation requires the a priori election of a reaction coordinate that allows the system to go from reactants to products. In other words, it is essential to know how the reaction takes place. Thanks to the accurate search of transition states performed previously by the micro-iterative we can find the reaction mechanism. In this sense we can use an adequate reaction coordinate that permits us an efficient calculation of the reaction free energy.
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Terremoto, Luis Antonio Albiac. "Experimento de coincidência 26Mg (e,e\'c)." Universidade de São Paulo, 1993. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-11032014-165807/.
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O objetivo deste trabalho consiste em estudar as ressonâncias gigantes no \'ANTPOT. 26 MG\' por intermédio de reações nucleares de eletrodesintegração em que o elétron espalhado inelasticamente e a partícula carregada c emitida (onde c designa um próton ou uma partícula alfa) são medidos em coincidência. Durante o experimento foi utilizado o feixe contínuo de elétrons do acelerador Microtron-A2, instalado no Instituto de Física Nuclear da Universidade de Mainz (Alemanha). Os elétrons espalhados foram medidos nos ângulos de \'22 GRAUS\' e \'35 GRAUS\', correspondentes a momentos transferidos de 0,35 e 0,54 \'fm POT. -1\', respectivamente, uma vez que a energia cinética dos elétrons incidentes era de 183,5 MeV. O experimento abrangeu uma faixa de energia de excitação do núcleo-alvo compreendida entre 10,6 MeV 31,8 MeV e tornou possível a investigação do decaimento das ressonâncias gigantes em um estado final definido dos núcleos-produto. Os elétrons espalhados inelasticarnente foram detectados por um espectrômetro magnético de \'180 GRAUS\' bifocal e as partículas carregadas c por um sistema compostos por detectores de barreira de superfície, ambos conectados por uma eletrônica de coincidência. O processo de redução e análise dos dados experimentais constitui a ênfase deste trabalho, uma vez que não houve participação direta na realização do experimento. Foram obtidas as seções de choque e distribuições angulares para as reações \'ANTPOT. 26 MG\'(e, e\' \'alfa IND. 0\') \'ANTPOT. 22 NE\', \'ANTPOT. 26 MG\'(e, e\' \'alfa IND. 1\') \'ANTPOT. 22 NE\', \'ANTPOT. 26 MG\'(e, e\' \'p IND. 01\') \'ANTPOT. 25 NA\' e \'ANTPOT. 25 MG\'(e, e\' \'p IND. 2\') \'ANTPOT. 25 NA\'. No caso específico do decaimento \'alfa IND. 0\' , foi efetuada uma separação independente de modelo das componentes multipolares da seção de choque. Um estudo da influência de efeitos de isospin e deformação nuclear nas ressonâncias gigantes do \'ANTPOT. 26 MG\' foi realizado com base em comparações com resultados de outros experimentos que abrangem a faixa de energia de excitação localizada entre 10 Me V e 40 MeV.Measurements of the ANTPOT 26 MG\'(e, e\' c) reaction (c standing for p or alfa) have been performed at electron energy of 183.5 Me V and scattering angles of \'22 GRAUS\' and \'35 GRAUS\' (momentum transfer of 0.35 and 0.54 \'fm POT. -1\', respectively). Excitation energy of the target nucleus ranged from 10.6 MeV to 31.8 MeV and cross sections and angular distributions were determined for the following decay channels: \'alfa IND. 0\', \'alfa IND. 1\', \'p IND. 01\' and \'p IND. 2\'. The multi polar composition of the \'alfa IND. 0 channel was determined by means of a model independent analysis. A simple model based on effects of isospin, nuclear deformation and configurational splitting was used to explain the observed behaviour of the strength distribution of the giant resonances as a function of energy.
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Rallabhandi, Aniketh S. "Experimental Investigation of the Reacting Flowfield of a Radial-Radial Swirler." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin154409847287965.
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Geipel, Philipp. "Experimental research on turbulent reacting flows using gaseous and liquid fuels." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5544.
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An investigation into turbulent reacting flows in an opposed jet geometry and a sudden expansion duct has been performed. For the opposed jet geometry, measurements of the velocity and reaction progress variable were obtained in lean premixed flames. Both velocity and scalar measurements were taken using PIV (Particle Image Velocimetry). Three gaseous fuels (methane, propane and ethylene) and three liquid fuels (JP-10, cyclopentane and cyclopentene) were considered for a range of equivalence ratios. The broad range of fuels enabled an investigation of the effect of different fuel reactivities on the velocity field and flame location and also allowed the effect of the Lewis number on flame extinction to be investigated. Preliminary work included isothermal measurements of the flow between and inside the nozzles. The use of fractal grids inside the nozzle increased turbulence intensities at the nozzle exit by 100% and turbulent Reynolds numbers between 50 - 220 were achieved. Velocity and normal stress components were measured with attention focused on the inlet boundary, along the burner centreline and the stagnation plane. A circular duct, incorporating a sudden expansion step, was also used to investigate the effect of swirl on pressure oscillations within the duct, the lean flammability limits and the NOx emissions. Measurements were performed for stratified flow conditions using methane as a fuel. The results show that excessive swirl leads to an increase in local strain in the vicinity of the expansion step and makes the flame more prone to local extinction. Moderate swirl was found to lower the amplitudes of the pressure oscillations close to global extinction and also to decrease the lean extinction limit of the stratified flow conditions. However, it did not decrease the overall equivalence ratio of flows with a richer core and a leaner annulus. Flows with only air in the core flow led to an overall equivalence ratio as lean as 0.3 for methane compared with 0.6 for the uniform flow. Stratification with a fuel rich core flow and a leaner annular flow led to an increase in NOx emissions due to locally increased temperatures. The addition of moderate swirl enhanced mixing of the annular and the core flows, which resulted in a more uniform fuel distribution close to the step and a reduction in NOx-levels up to 50%.
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Griselli, Massimo. "C-reactive protein and experimental myocardial infarction." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408605.
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Beyer, Keith D. (Keith Donald). "Laboratory experiments of chemical reactions on polar stratospheric cloud particles." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12269.
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Wyrwas, Richard Ben Jr. "Vanadium Oxide Anions Clusters: Their Abundances, Structures and Reactions with SO₂." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4908.
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Early transition metal oxide clusters have been a focus of study for several years. The production of vanadium oxide cluster anions in a pulsed helium flow reactor provides a relatively precise way of introducing defect sites and controlling the oxidation state of the vanadium atoms. The composition of the clusters can be changed from the V2O5 stoichiometry, where the vanadium atom is in a +5 oxidation state, to more reduced stoichiometries yielding a mixture of oxidation states containing atoms in the +2 oxidation state. The subsequent addition of reactant gases such as H2O and SO2 yields very intense adsorption reactions as well as a demonstration of the robustness of particular defect free clusters. For example, the cluster has been identified as a defect free cluster where all vanadium atoms are in the +5 oxidation state and all oxygen atoms are predicted to be in the 2- state. The cluster has been shown to not adsorb SO2- while clusters in a reduced oxidation state, such as and readily adsorb one or more SO2 molecules. The adsorption process has been shown to be size dependent, with the smallest monovanadium oxide anions being the most reactive.
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García, Melchor Maximiliano. "Theoretical Study on Pd-catalyzed Cross-Coupling Reactions." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96827.
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D’ençà el seu descobriment, fa ja prop de tres dècades, les reaccions d’acoblament creuat C-C catalitzades per Pd han esdevingut una de les transformacions més poderoses dins la química organometàl·lica. De fet, tres dels desenvolupadors de les reaccions d’acoblament més emprades (reaccions de Heck, Suzuki i Negishi) van ésser guardonats l'any 2010 amb el premi Nobel de Química. El mecanisme general de les reaccions d'acoblament creuat C-C consisteix en tres etapes: addició oxidant, transmetal·lació, i eliminació reductiva. La millora d’una reacció comporta el coneixement profund del seu mecanisme de reacció, o el que és el mateix, la comprenssió del seu funcionament a nivell molecular. Així doncs, aquesta tesi doctoral s'ha centrat en l’estudi del mecanisme de reacció de diferents reaccions d’acoblament creuat C-C catalitzades per Pd: la reacció de Negishi, la reacció de Sonogashira en la seva variant sense coure, i una versió enantioselectiva de la reacció de Suzuki-Miyaura. Tots aquests estudis s'han dut a terme mitjançant càlculs mecano-quàntics i en estreta col·laboració amb grups experimentals de prestigi mundial.
En el cas de la reacció de Negishi, s'ha investigat el procés de transmetal·lació amb ZnMeCl i ZnMe2 amb l'objectiu de proporcionar una visió detallada dels respectius mecanismes de reacció. Concretament, per a la transmetal·lació amb ZnMeCl, els càlculs teòrics han mostrat les elevades probabilitats que existeixen de generar-se nous intermedis que donarien lloc a productes d'homo-acoblament no desitjats. Per altra banda, per a la transmetal·lació amb ZnMe2, els resultats teòrics han demostrat l'existència d'intermedis catiònics a priori inesperats. A més, s'han identificat altres mecanismes de transmetal·lació competitius que fins ara no s'havien proposat mai. En resum, en aquest estudi s'ha obtingut una visió detallada dels mecanismes de reacció involucrats en aquestes reaccions.
Per a la reacció de Sonogashira sense coure, s'han investigat els dos mecanismes de reacció proposats en la literatura. Els resultats teòrics han permès descartar un d'aquests mecanismes (carbopal·ladació) i han demostrat que l'altre (desprotonació) és factible. A més, l'anàlisi dels mecanístic ha portat a la proposta d'un nou mecanisme de reacció (iònic). Aquest mecanisme consisteix en la desprotonació de l'alquí i la posterior reacció d'aquesta espècie amb el catalitzador de Pd. L'efecte dels substituents en l'alquí en aquests mecanismes de reacció també s'ha analitzat. En termes generals, aquest estudi mecanistic ha revelat que, de la mateixa manera que en altres reaccions d'acoblament, hi ha varis mecanismes competitius i que el canvi de les condicions de reacció (solvent, lligands, substrat, base) pot afavorir un o altre.
Finalment, s'ha investigat el mecanisme de reacció per un acoblament assimètric de Suzuki-Miyaura catalitzat per un complex de Pd bis-hidrazona. Els resultats derivats d'aquest estudi han revelat que el mecanisme de transmetal·lació difereix del camí general proposat a la literatura: en aquest cas dos etapes addicionals són necessàries. Aquesta modificació es pot atribuir a la capacitat del lligand bis-hidrazona de dissociar un dels àtoms de N directament coordinat al catalitzador de Pd (comportament hemilàbil). Pel que fa referència a l'estereoquímica de la reacció, els càlculs realitzats fins ara no han pogut donar una explicació clara de les enantioselectivitats observades experimentalment.
En resum, els resultsats teòrics obtinguts en aquesta tesi han demostrat que els càculs teòrics són una eina de gran ajut per a l’elucidació i/o proposta de mecanismes de reacció d'aquest tipus de processos.Since its discovery, nearly three decades ago, the Pd-catalyzed cross-coupling reactions have become one of the most powerful transformations in organometallic chemistry. In fact, three of the developers of the most widely used cross-coupling reactions were awarded in 2010 with the Nobel Prize in Chemistry. The general reaction mechanism for C-C cross-coupling consists in three main steps: oxidative addition, transmetalation, and reductive elimination. The reaction improvement entails a deep knowledge of their complete mechanism, or what is the same thing, how they work at the molecular level. Thus, this thesis has been focused on studying the reaction mechanism for different Pd-catalyzed cross-coupling reactions: the Negishi reaction, the copper-free Sonogashira reaction, and an enantioselective version of the Suzuki-Miyaura reaction. All these studies have been carried out by means of quantum-mechanics calculations and in close collaboration with top experimental groups worldwide. In the case of the Negishi reaction, the transmetalation process with ZnMeCl and ZnMe2 reagents has been investigated in order to provide a detailed picture of their reaction mechanisms. In particular, for the transmetalation with ZnMeCl, calculations have pointed out the many chances for the generation of new intermediates that would eventually give rise to homocoupling side products. On the other hand, for the transmetalation with ZnMe2, the theoretical results have proved the existence of previously unexpected cationic intermediates. Moreover, additional competitive transmetalation pathways for this reaction, some of which had not been invoked before, have been also identified. Overall, in this study a general picture of the reaction mechanisms involved in these reactions has been obtained. For the copper-free Sonogashira reaction, the two reaction mechanisms proposed in the literature have been evaluated. Theoretical results, have been able to discard one of those mechanisms (carbopalladation), whereas the other one (deprotonation) has been found to be feasible. Furthermore, the mechanistic analysis have conducted to the proposal of a new reaction mechanism (ionic). This mechanism involves the deprotonation of the alkyne and the subsequent reaction of this species with the Pd catalyst. The effect of the alkyne's substituents on these reaction mechanisms has been also analyzed. Overall, the mechanistic study reported in this thesis has revealed that, just like in other cross-coupling reaction, there are several competing reaction pathways and a change on the reaction conditions (e.g. solvent, ligands, substrate, base) might favor one over the other ones. Finally, the theoretical investigation on the reaction mechanism for an asymmetric Suzuki-Miyaura coupling catalyzed by a bis-hydrazone Pd catalyst has been carried out. The results derived from this study have revealed that the transmetalation mechanism differs from the common reaction pathway proposed in the literature: the transmetalation process requires two additional steps. This modification can be attributed to the relative ability of the bis-hydrazone ligand, which can easily dissociate one of the N atoms directly coordinated to Pd catalyst (hemilabile behavior). As far as the stereochemistry of the reaction is concerned, calculations so far do not provide a clear explanation for the high enantioselectivities observed in the experiments. In summary, the theoretical results derived from this thesis have demonstrated that theoretical calculations are a very useful tool for elucidating and/or proposing reaction mechanisms for these type of processes.
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Amar, Yehia. "Accelerating process development of complex chemical reactions." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288220.
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Process development of new complex reactions in the pharmaceutical and fine chemicals industries is challenging, and expensive. The field is beginning to see a bridging between fundamental first-principles investigations, and utilisation of data-driven statistical methods, such as machine learning. Nonetheless, process development and optimisation in these industries is mostly driven by trial-and-error, and experience. Approaches that move beyond these are limited to the well-developed optimisation of continuous variables, and often do not yield physical insights. This thesis describes several new methods developed to address research questions related to this challenge. First, we investigated whether utilising physical knowledge could aid statistics-guided self-optimisation of a C-H activation reaction, in which the optimisation variables were continuous. We then considered algorithmic treatment of the more challenging discrete variables, focussing on solvents. We parametrised a library of 459 solvents with physically meaningful molecular descriptors. Our case study was a homogeneous Rh-catalysed asymmetric hydrogenation to produce a chiral γ-lactam, with conversion and diastereoselectivity as objectives. We adapted a state-of-the-art multi-objective machine learning algorithm, based on Gaussian processes, to utilise the descriptors as inputs, and to create a surrogate model for each objective. The aim of the algorithm was to determine a set of Pareto solutions with a minimum experimental budget, whilst simultaneously addressing model uncertainty. We found that descriptors are a valuable tool for Design of Experiments, and can produce predictive and interpretable surrogate models. Subsequently, a physical investigation of this reaction led to the discovery of an efficient catalyst-ligand system, which we studied by operando NMR, and identified a parametrised kinetic model. Turning the focus then to ligands for asymmetric hydrogenation, we calculated versatile empirical descriptors based on the similarity of atomic environments, for 102 chiral ligands, to predict diastereoselectivity. Whilst the model fit was good, it failed to accurately predict the performance of an unseen ligand family, due to analogue bias. Physical knowledge has then guided the selection of symmetrised physico-chemical descriptors. This produced more accurate predictive models for diastereoselectivity, including for an unseen ligand family. The contribution of this thesis is a development of novel and effective workflows and methodologies for process development. These open the door for process chemists to save time and resources, freeing them up from routine work, to focus instead on creatively designing new chemistry for future real-world applications.
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Lindwall, Greta. "Multicomponent diffusional reactions in tool steels : Experiment and Theory." Doctoral thesis, KTH, Termodynamisk modellering, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103328.
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Many phenomena determining the microstructure of a tool steel and consequently the properties of the material, are governed by multicomponent diffusion. The diffusion driven reactions that take place during, for example, tempering of a hot-work tool steel or when the microstructure develops during hot isostatic pressing of cold-work tool steel, are dependent on the types and amounts of alloying elements. In order for computational methods to be usable, these alloying effects need to be understood and incorporated in the models. In this work the influence of some typical tool steel alloying elements on the coarsening behavior of precipitates is investigated. Experimental coarsening studies are performed and the impact of the diffusion mobility descriptions and the thermodynamic descriptions are investigated by means of DICTRA coarsening calculations. The kinetic descriptions for diffusion in the body centered-cubic phase in the case of the chromium-iron-vanadium system and the chromium-iron-molybdenum system are improved by assessments of diffusion mobility parameters, and are shown to have a large impact on the calculated coarsening rate for vanadium-rich and molybdenum-rich precipitates. The effect of cobalt is examined by a coarsening experiment for vanandiumrich carbides and by a diffusion couple experiment for the investigation of the vanadium interdiffusion. The presence of cobalt is experimentally shown to have retarding effect on the coarsening rate of the carbides, but not on the vanadium diffusion. The coarsening rate of nitrogen-rich precipitates is compared to the coarsening rate of carbon-rich precipitates, and a lower coarsening rate for nitrides compared to carbides can be confirmed. Correlation between coarsening calculations and experiments is obtained suggesting that the thermodynamic description of the two systems is the underlaying reason for the different coarsening rates. Further, calculations utilizing the DICTRA software are combined with experimental investigations in order to study the possibility to apply computational methods for compound material development and explore application areas for high nitrogen alloyed tool steels produced by powder metallurgy.QC 20121011
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Nascimento, Márcia Cristina. "Contribuições das atividades experimentais com gerenciamento dos compostos gerados para a aprendizagem das reações químicas." Universidade Tecnológica Federal do Paraná, 2013. http://repositorio.utfpr.edu.br/jspui/handle/1/730.
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Acompanha: Sugestão de roteiro de atividades experimentais com gerenciamento dos compostos gerados para o conteúdo de reações químicas, p. 53.O conhecimento químico é de suma importância para o desenvolvimento sustentável, para melhores formas de alimentação e energia. Neste sentido, a aprendizagem acerca desta área de estudo deve ocorrer pelo uso de metodologias favoráveis ao desenvolvimento sustentável e com caráter motivador. Uma possibilidade é através da contextualização e experimentação. A contextualização da questão ambiental é citada nos Parâmetros Curriculares Nacionais como elemento de promoção de aprendizagem, e a experimentação é descrita como o fazer com as mãos, sentir e manipular, analisar criteriosamente e articular a prática à teoria. Este trabalho foi desenvolvido para o 1º ano do Ensino Médio sobre o conteúdo de reações químicas, contemplando a realização de atividades experimentais com gerenciamento das substâncias produzidas. Para isso, foram realizados: (i) elaboração e aplicação de uma Proposta de Experimentos; (ii) seleção de turmas para sua aplicação; (iii) verificação dos conhecimentos de reações químicas e gerenciamento de resíduos, antes a após a aplicação da mesma. As respostas fornecidas pelos estudantes, nos pré-teste e pós-teste realizados, permitiram comparar o efeito da aplicação da Proposta de Experimentos ao qual foi executada em 18 horas-aula. As mudanças conceituais sobre reações químicas foram registradas e permitiram verificar novas formas de interpretação da transformação, que passou da simples observação macroscópica dos aspectos físicos, para o nível teórico, incluindo os conhecimentos submicroscópicos, onde se encontram as interações entre substâncias e formação de novos compostos. O enfoque nas questões ambientais, com o gerenciamento dos compostos produzidos em aula pelos alunos evidenciou uma maior conscientização entre a maioria dos participantes sobre a problemática do descarte indevido de substâncias e da necessidade de avaliar as implicações do despejo de materiais tóxicos no meio ambiente.
The chemical knowledge is of paramount importance for the sustainable development for better forms of feeding and energy. In this sense, the learning about this study area should occur with the use of methodologies in sustainable development and motivating character. One possibility is through contextualization and experimentation. The contextualization of environmental issues is mentioned in the National Curricular Parameters and element to promote learning, and experimentation is described as “do with hands”, feel and manipulate, analyze critically and articulate practice to theory. This paper was developed for the first year of high school about the content of chemical reactions, contemplating the conducting experimental activities, with management of substances produced. For this, was performed: (i) Preparation and implementation of a proposed experiments. (ii) Selection of classes for its application. (iii) Verification of knowledge of chemical reactions and waste management before and after the application of the same. The answer provided by students, in pretest and posttest, was possible to compare the effect of application of proposed experiments, which was performed is eighteen weeks. The conceptual changes about chemical reactions were registered and allowed to verify new ways of the interpretation and of the transformation, from simple macroscopic observation of the physical aspects to the theoretical level, including knowledge microscopic, where the interactions are found between substances and formation of new compounds. The focus on environmental issues with management of compounds in class by students showed a greater awareness among the majority of participants on the problem of improper disposal of substances and of to assess the implication of dump toxic materials into the environment.
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Smith, Sean Campbell. "Experimental and theoretical studies of ion-molecule reactions." Thesis, University of Canterbury. Chemistry, 1989. http://hdl.handle.net/10092/7814.
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The present work deals with the development of a coherent and accurate means of modelling unimolecular decomposition, association and chemical activation reactions, particularly those involving ions, by the use of RRKM theory in conjunction with solution of the master equation.
A new solution of the chemical activation master equation (which includes association as a special case) is derived which reveals a very simple relationship between the non-equilibrium rate coefficient for association and that for the reverse unimolecular dissociation. It is shown that the non-equilibrium association rate coefficient is related to the reverse non-equilibrium unimolecular dissociation rate coefficient by the equilibrium constant and a non-equilibrium factor that is calculated from solution of the unimolecular master equation. Hence separate solution of the chemical activation or association master equations to obtain the stabilisation rate coefficient is not necessary: both solutions are implicit in the solution of the single or multichannel unimolecular master equation.
Solutions to the two-dimensional unimolecular master equation are developed which allow full incorporation of the constraint of angular momentum conservation into single and multi-channel unimolecular master equation calculations at any pressure for the first time. In conjunction with the solution to the chemical activation and association master equations, this allows ion/molecule association and chemical activation reactions, predictions for which are very sensitive to the effects of angular momentum conservation, to be modelled by accurate master equation calculations for the first time.
Two extensions to RRKM theory, necessary for the accurate prediction of microscopic rate coefficients k(ɛ,J) in ion/molecule reactions, are identified. (1) Correct incorporation of the hindrance to dipole rotation, produced by the non-central ion/dipole potential, into the determination of the density of states in the loose transition state. An exact semiclassical means of incorporating this effect is derived and implemented. (2) Adiabatic effects, i.e., the absence of coupling of many degrees of freedom with the reaction coordinate at large separation of an ion/dipole pair, are shown to significantly reduce the predicted capture rate from that obtained by normal microcanonical variational implementation of RRKM theory. A variant of the normal RRKM expression for k(ɛ,J) is derived which enables exact accounting for this non-coupling.
The theory is applied to three well-studied ion/molecule reactions: (1) the association of CH₃⁺and HCN in a helium bath gas, (2) the chemical activation reaction between CH/ and NH₃ in helium, and (3) the chemical activation reaction between CH₃⁺ and CH₃CN in both helium and CH₃CN bath gases. In the case of the reaction between CH₃⁺and HCN, RRKM parameters are sufficiently well known to allow the average downward transfer of internal and (external) rotational energies in collisions to be estimated as 150cm⁻¹ ± 50%. The results of modelling of the other reactions are consistent with similar sized average energy transfer parameters. Illustrative calculations for two neutral reactions, the recombination of methyl radicals and the two-channel dissociation of 1-iodopropane, are also presented.
An experimental study involving unimolecular dissociation of the CH₃CH₂OH² ⁺ ion, induced in the drift field of a Variable-Temperature, Selected-Ion-Flow-Drift Tube, is presented. The theoretical interpretation of this experiment is discussed. It is found that (1) the induction time for approach to steady state of the vibrational and rotational degrees of freedom of the CH₃CH₂OH₂⁺ ion in the helium carrier gas is negligible on the experimental timescale for motion of the ions through the drift region, and (2) the unimolecular dissociation rate coefficients do not correspond directly to thermal data at an elevated temperature with mean energy equal to the ion centre-of-mass energy. This implies that the steady-state ion translational-energy distribution is not sufficiently close to a Maxwellian distribution to enable simple interpretation of the results as pseudo-thermal data. The form of interpolation to zero field required to obtain thermal data is not yet clear. A simple extension to the Langevin capture model is derived which allows an improved estimate of the total non-reactive ion/induced-dipole collision frequency (necessary for master equation modelling of ion/molecule reactions) by including steric effects due to the finite size of the species involved.
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Wilson, Paul Francis. "Experimental studies of gas-phase ion-molecule reactions." Thesis, University of Canterbury. Department of Science, 1994. http://hdl.handle.net/10092/8318.
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Development on both selected ion flow tube (SIFT) and ion cyclotron resonance (ICR) instruments is described.
Modifications to the SIFT described here include; a new, off-axis ion source, and new hardware and programs to measure the neutral flow and the ion count using a personal computer.
Mechanical, electrical, electronic, and programming modifications to the ICR instrument are described. Several well known ion-molecule reactions are used to calibrate, and monitor the performance of the ICR instrument.
The reactions of t-C₄H₉Cl with a number of protonated bases, BH⁺, are reported. The reactions were studied using both the SIFT and the ICR. The branching ratio of the product channels is reported for each reaction. For some bases, the process,
BH⁺ + t-C₄H₉Cl →’ t- C₄H₉⁺ + B + HCl
appears to be fast, although it is significantly endothermic. The thermochemistry of the system is discussed, and it is suggested that either the tabulated thermochemical values are significantly wrong, or the reaction proceeds via formation of weakly bound complexes which dissociate on focussing in the down stream region of the SIFT.
The chemistry of several srtuctural isomers of protonated ethyl cyanide, C₃H₆N⁺ is examined. Two reactions thought to be routes to interstellar synthesis of ethyl cyanide are shown to be unlikely to yield that ion upon dissociative recombination. The association of HCNH⁺ with C₂H₄ is shown to lead to the protonated ethyl isocyanide isomer. The association of CH₃#x207A; with CH₃CN is reasoned to lead to formation of the CH₃CNCH₃#x207A; structure.
The isomerism observed is rationalised in terms of the potential surface for the system derived from both experimental observation, and several previous ab initio studies.
The reactivity of the methoxymethyl cation with several oxygen and nitrogen bases is reported. The exothermic proton transfer channel is not observed, but competing methyl cation and CH⁺ transfer dominate.
The reactivity in both the SIFT and the ICR is explained in terms of several factors. An activation barrier to proton transfer proceeds from ring closure to form the neutral product, oxirane. The SN2 methyl cation transfer process is sterically hindered and results proceeds via a tight transition state, whereas the alkyl transfer process has a greater density of states at the transition state. Where there is a labile hydrogen on the base, the alkyl transfer process dominates because of its' looser transition state.
The association reactions of acrylonitrile are reported in both the ICR and SIFT instruments. The reaction of CH₂CHCN⁺ shows competition between proton transfer and association. Proton transfer dominates in the ICR and association dominates in the SIFT. The termolecular rate of formation of the proton bound dimer of acrylonitrile is measured at 1.2 x 10⁻²³cm¶ s⁻±.
An RRKM study of the association of CH₃⁺and acetonitrile is reported. The collisional parameters of both helium and acetonitrile bath gases are estimated. The average downward energy transferred per collision, ‹ΔΕdown›, for helium is estimated as 300 cm-⁻±, and for acetonitrile as 950 cm-⁻±. The fall off of the association reaction with pressure is shown in comparison with experimental results.
The ion-molecule reactions of acetylene have been studied, and the results confirm earlier work. The ions C₆H₅⁺, and C₆H₄⁺ are shown to exist as a mixture of two or more isomers of differing reactivity. One isomer reacts with unsaturated hydrocarbons at the collision rate while the other is unreactive. C₆H₄⁺ exists as a mixture of isomers when formed from sequential ion-molecule reactions of acetylene or electron impact or chemical ionisation on halobenzenes. C₆H₄⁺ exists as a mixture of two isomers when formed from sequential ion-molecule reactions of acetylene.
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Baz̆bauers, Gatis. "Experimental investigation of low Damkohler number turbulent reaction." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36074.
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Tubb, Catherine Pollard. "Experimental and computational investigations into stereoselective epoxidation reactions." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613119.
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Jiang, Julong. "Experimental & theoretical investigation of palladium catalyzed reactions." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/4997/.
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Krükow, Artjom [Verfasser]. "Three-body reaction dynamics in cold atom-ion experiments / Artjom Krükow." Ulm : Universität Ulm, 2017. http://d-nb.info/1133171419/34.
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Kendrick, Donald William Zukoski E. E. "An experimental and numerical investigation into reacting vortex structures associated with unstable combustion /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10122007-131523.
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Laird, Darin Wiley. "Theoretical and experimental investigations of norbornyne and cyclohexyne /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008374.
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He, Liu. "Development of reagent-less processes for water decontamination. Tuning of temperature and redox parameters to remove toxic oxyanions." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/326753.
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Los estudios que se han llevado a cabo en esta tesis se basan en el desarrollo de métodos para la eliminación de contaminantes en aguas mediante procesos en lo que no se utilizan reactivos, lo que proporcionan un valor añadido al tratamiento del agua contaminada. En nuestro caso, los métodos utilizados se centrar en la eliminación de oxoaniones de arsénico y selenio en disoluciones acuosas mediante procesos de adsorción-desorción. Estos procesos caracterizados por la no utilización de reactivos se desarrollaron mediante el estudio de parámetros termodinámicos, como por ejemplo, la temperatura y/o el potencial redox de las disoluciones de estudio. Por tanto, estos métodos no solo nos proporcionarán un ahorro de reactivos en la recuperación del adsorbente, sino que permitirán el reciclado de dicho adsorbente y su reutilización.
La capacidad de adsorción del arsenito/arsenato en la esponja cargada con nanoparticulas de óxido de hierro superparamagneticas (SPION) está influenciada por el pH, el tiempo de contacto, la concentración inicial, cantidad de adsorbente, la temperatura y por el potencial redox. La adsorción máxima para el arsenato en el sistema esponja-SPION se ha obtenido en medio ácido (pH 3.6) tras 1 hora a 20ºC, mientras que el equilibrio de desorción se alcanzó a las 2h a 70ºC. Las constantes del equilibrio de adsorcion se determinaron como logK20=4,198 y logK70=1.023 a 20°C y 70°C respectivamente. La disminución de estos valores se relacionan un valor de ∆G negativo, lo que indica un aumento de la adsorción de As(V) cuando la temperatura disminuye. Los valores de ∆H y ∆S calculados son -122,150 kJ mol-1 y 337 J mol-1 K-1 respectivamente, lo que indica que el proceso de adsorción es exotérmico. La oxidación de As(III) a As(V) y el proceso de reducción correspondiente fueron caracterizados para probar el concepto de potencial redox como parámetro clave en estos procesos. La oxidación de As(III) a As(V) mediante dicromato de potasio (tasa de conversión>91%) y la reducción de As(V) a As(III) mediante zinc en polvo o estaño laminado (tasa de conversión>90%) en presencia del adsorbente han mostrado el efecto que tiene el potencial redox en el proceso de adsorción.
Por otro lado, también se han estudiado las características del proceso de adsorción/desorción de los aniones selenito/selenato utilizando como adsorbente nanoesferas de γ-Al2O3 y esponja cargada con SPION. La máxima adsorción que presentan selenato y selenito sobre γ-Al2O3 se alcanzó a las 6 horas en un medio ácido (pH 2) a 20ºC y a las 14h a 70ºC, respectivamente. Los estudios cinéticos y termodinámicos muestran que los datos se ajustan a una cinética de pseudo-segundo orden y a una isoterma de Frendlich. El valor de ∆H obtenido para Se(IV) y Se(VI) entre 20ºC y 70ºC fue de 13,955 KJ mol-1 y -3,927 KJ mol-1 respectivamente. Por tanto, el sistema esponja-SPION tiene una mayor capacidad de adsorción para arsenato y selenato que para arsenito y selenito. La máxima adsorción para selenato en el sistema esponja-SPION se alcanzó tras 1h en medio ácido (pH 3,6) a 20ºC y tras 6h a 70ºC respectivamente, mientras que el tiempo necesario para alcanzar el equilibrio en el caso del selenito fue de 14h a 20ºC y 24h a 70ºC.
En conclusión, se han estudiado el efecto que tiene sobre el proceso de adsorción-desorcion la combinación de los aspectos que depende de la temperatura con el potencial redox. El modo en columna utilizado para el tratamiento de aguas residuales, que contienen arsenato/arsenito o selenato/selenito, confirma que estos oxoaniones tóxicos se pueden eliminar con estos adsorbentes, que además pueden ser regenerados y reutilizados controlando combinando la temperatura y el uso de un agente reductor.The studies that have been carried out in the present PhD thesis project are based on the development of methods to remove water pollutants by using reagent-less processes and to provide and added value to the contaminated water treatment. In our case, the methods are related to arsenic or selenium oxyanions removal in aqueous solution. Methods are based on sorption-desorption processes for the indicated oxyanions. Nanostructured materials have been implemented as adsorption substances, being either iron or aluminum oxides the nanoparticles active constituents. Reagent-less processes were developed by using intensive thermodynamic parameters, e.g, temperature and/or redox potential of the target solution. Appropriate tuning of these parameters will allow both process selectivity and regeneration of the adsorption material. Synergic interaction of thermo-tuning with redox variation will provide such results. Thus, this reagentless method could not only provide reagent savings for recovering the adsorbent, but also the adsorbent recycling to be reused will contribute to a-cost efficient process. The results show as follows: The adsorption capacity of arsenate/arsenite on sponge loaded with superparamagnetic iron oxide nanoparticles (SPION) is influenced by pH, contact time, initial concentration, adsorbent dosage, temperature as well as redox potential. The maximum adsorption for arsenate on sponge-SPION was obtained in an acid media (pH 3.6) in 1 hour contact time under 20ºC while desorption equilibrium was achieved with 2 hours under 70ºC. Equilibrium adsorption constants were determined as log K20=4.198 and log K70=1.023 under 20ºC and 70ºC respectively. These values correlate with the decrease of related negative ∆G° values, indicating the adsorption increase of As(V) when temperature decreases. ΔH° and ΔS° were found to be -122.150 kJ mol-1 and 337 J mol-1 K-1 respectively, indicating the adsorption reaction to be exothermic. The oxidation of As (III) to As(V) and the respective reduction processes were characterized to prove the concept of using redox potential as key parameter for a reagent-less process. Oxidation of As(III) to As(V) by potassium dichromate (conversion rate>91%) and reduction As(V) to As(III) by Zn powder or Sn foil (conversion rate>90%) in presence of the adsorbent, have shown the effect on the adsorption when tuning the solution redox potential, being As(V) of higher adsorption capacity than As(III). In addition, aqueous selenate/ selenite adsorption/desorption characteristics by γ-Al2O3 nanospheres or SPION loaded sponge were also investigated. The maximum adsorption for selenate and selenite on γ-Al2O3 nanospheres was achieved at pH 2 in 6 hours under 20ºC and 14 hours under 70ºC, respectively. The kinetic and thermodynamic studies show that they are fitted very well to the pseudo-second order and Frendlich isotherm model. The ∆H value of Se (IV) and Se (VI) between 20ºC and 70ºC were -13.955 KJ mol-1and -3.927 KJ mol-1,respectively. It shows that lower temperature favor removal of aqueous selenium. The results represent very similar adsorption phenomenon of selenate/selenite on sponge- SPION as that of arsenate/arsenite on sponge-SPION, thus, sponge-SPION has much higher adsorption capacity for arsenate or selenate than that of arsenite or selenite. The maximum adsorption for selenate and selenite on sponge loaded with SPION was achieved at pH 3.6 in 1 hour under 20ºC and 6 hours under 70ºC, respectively, while time for obtaining equilibrium of selenite needs 14 hours under 20ºC and 24 hours under 70ºC. More importantly, the temperature dependence aspects combined with the redox potential effect for controlling the adsorption-desorption process have been studied. The column mode for treating the waste water, which contains the arsenate/ arsenite or selenate/selenite systems, confirms that toxic oxyanions could be removed by the related adsorbent, which could be regenerated and reused by controlling the temperature combined with the tuning of the reducing reagent.
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Specht, Paul Elliott. "Shock compression response of aluminum-based intermetallic-forming reactive systems." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47559.
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Heterogeneities at the meso-scale strongly influence the shock compression response of composite materials. These heterogeneities arise from both structural variations and differing physical/mechanical properties between constituents. In mixtures of reactive materials, such as Ni and Al, the meso-scale heterogeneities greatly affect component mixing and activation, which, in turn, can induce a chemical reaction. Cold-rolled multilayered composites of Ni and Al provide a unique system for studying the effects of material heterogeneities on a propagating shock wave, due to their full density, periodic layering, and intimate particle contacts. Computational analysis of the shock compression response of fully dense Ni/Al multilayered composites is performed with real, heterogeneous microstructures, obtained from optical microscopy, using the Eulerian hydrocode CTH. Changes in the orientation, density, structure, and strength of the material interfaces, as well as the strength of the constituents, are used to understand the influence microstructure plays on the multilayered composite response at high strain rates. The results show a marked difference in the dissipation and dispersion of the shock wave as the underlying microstructure varies. These variations can be attributed to the development of two-dimensional effects and the nature of the wave reflections and interactions. Validation of the computational results is then obtained through time-resolved measurements (VISAR, PDV, and PVDF stress gauges) performed during uniaxial strain plate-on-plate impact experiments. The experimental results prove that the computational method accurately represents the multilayered composites, thereby justifying the conclusions and trends extracted from the simulations. The reaction response of cold-rolled multilayer composites is also investigated and characterized using uniaxial stress rod-on-anvil impact experiments through post-mortem microscopy and x-ray diffraction. This extensive understanding of the shock compression response of the multilayers systems is contrasted with other composites of Ni and Al, including shock consolidated and pressed (porous) powder compacts. A comprehensive design space is then developed to assist in the understanding and design of Ni/Al composites under conditions of high pressure shock compression. Research funded by ONR/MURI grant No. N00014-07-1-0740.
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Falardo, Sara Figueiredo Caeiro. "Children emotional reactions toward advertising and brands: A drawing experiment." Master's thesis, NSBE - UNL, 2011. http://hdl.handle.net/10362/10071.
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Liljeström, Simon. "Emotional Reactions to Music : Prevalence and Contributing Factors." Doctoral thesis, Uppsala universitet, Institutionen för psykologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-151605.
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People value music mainly for its abilities to induce emotions. Yet little is known about these experiences. The aim of this thesis was thus to investigate the nature and prevalence of emotional reactions to music, and what factors in the listener, the music, and the situation might contribute to such reactions. Study I explored the prevalence of musical emotions and possible factors influencing such experiences through the use of a questionnaire sent out to a random and nationally representative sample. The results indicated that a majority of the responders frequently reacted emotionally to music, and that their reactions included both basic and complex emotions. Prevalence correlated with personality, gender, age, and music education. Study II was designed to obtain a representative sample of situations where music induced emotions in listeners. The results showed that emotional reactions to music occurred in 24% of all episodes, and that the prevalence of specific emotions varied depending on the situation (e.g., other people present). However, causal inferences could not be drawn from Study I and II, so it was considered important to test predictions in a more controlled setting. Study III showed in an experiment that listeners experienced more intense emotions (a) to self-chosen music than to randomly selected music and (b) when listening with a close friend or partner than when listening alone. Moreover, Openness to experience correlated with emotion intensity. All three factors were linked to positive emotions. Overall, the thesis shows that (a) musical emotions are relatively common, (b) music can induce a variety of emotions, and (c) there are several features in the listener, the music, and the situation that may influence emotional reactions to music.
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Managlia, Maria Vittoria. "Study of 18O+12,13C fusion-evaporation reactions with the GARFIELD array." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23932/.
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Non statistical effects in the emission of light charged particles from fusion-evaporation nuclear reactions are known for light and medium mass nuclei. Cases previously reported by the NUCL-EX collaboration show discrepancies between experimental data and statistical calculations in decay channels with even residues, possibly due to alpha clusterization. This thesis is focused on the analysis of an experimental campaign carried out at the Legnaro National Laboratories with the GARFIELD+RCo setup to further investigate these topics. The studied systems are: 18O+13C at 112.5 MeV and 18O+12C at 122 and 300 MeV. This thesis work covers the various steps of a typical nuclear experiment conducted with the GARFIELD array. After data taking, preliminary experimental data have been reconstructed through data cleaning, calibration and particle identification. Being the experimental data reconstruction still ongoing, no final experimental reconstructed data have been reported. Nonetheless, simulated data by Monte Carlo statistical decay code have been analysed to investigate the evolution of fusion-evaporation processes from a statistical point of view. The analysis has been focused on the study of global observables like total charge and multiplicity and on single-particle observables like energy spectra and angular distributions. GEMINI++ statistical decay code simulating the fragment emission from a hot source has been considered in the study of the 122 MeV reaction and for a direct comparison of the three reactions. Finally, the HFl statistical code conceived by the collaboration for the light nuclei decay and containing the details of the known excited levels has been compared with GEMINI++. This thesis work paves the way for further studies on the reconstructed data to highlight possible agreements with theoretical models.
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Honkanen, A. (Anna). "Insect optomotor experiments in the dark using virtual reality." Doctoral thesis, University of Oulu, 2014. http://urn.fi/urn:isbn:9789526207025.
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Abstract
Vision is capable of providing an animal with a wealth of information very fast. Visually guided behaviours are numerous, ranging from foraging to navigation. Vision can be quite reliable in bright light, but the signals produced by the photoreceptors become progressively more unreliable with falling light intensities.
In this thesis the usefulness of a novel virtual reality-based environment for insect vision research is reviewed, and the low-light vision of the American cockroach, Periplaneta americana, is assessed using the optomotor behavioural paradigm and intracellular photoreceptor recordings. The optomotor reaction is visual behaviour where an animal responds to a rotation of its environment by following the movement of its surroundings with its eyes or - like insects - by rotating its body in the direction of the movement. Placing the cockroach on a trackball in the middle of the virtual reality apparatus and projecting a rotating pattern of vertical stripes around it invariably causes an optomotor reaction if the cockroach is able to see the moving pattern. Presenting the cockroaches with the stimulus pattern at different low light levels and observing their abilities to follow the movement reveal the lowest light intensity at which they are able to use vision in guiding their behaviour. The compound eye photoreceptor signals at this behavioural threshold consist of singlephoton absorption events called ‘bumps’ at the extremely low rate of one bump every ten seconds.
Furthermore, the role of the simple eyes or ocelli in the low-light vision of the cockroach is studied in the virtual reality by covering the compound eyes, the ocelli, or both. The ocelli seem to measure the light intensity and communicate this information to the compound eyes, and also have a direct effect on the general activity level of the cockroach.
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Garabedian, Stephen P. "Large-scale dispersive transport in aquifers : field experiments and reactive transport theory." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14645.
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Alam, Md Mahbub. "Bioreduction of hexavalent chromium flow-through column experiments and reactive transport modeling /." Online access for everyone, 2004. http://www.dissertations.wsu.edu/Dissertations/Summer2004/m%5Falam%5F072804.pdf.
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Ha, Heon Phil. "An experimental and theoretical study of the peritectic reaction." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298262.
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Coombes, Neil Edwin. "The reactive tabu search for efficient correlated experimental designs." Thesis, Liverpool John Moores University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275932.
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Caginalp, Paul Aydin. "Mean square displacements as an alternative to simulating fluorescence correlation spectroscopy experiments." Diss., Online access via UMI:, 2006.
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Mikocki, Stanislaw. "Inclusive resonance production in single-vee events in [pi]- nucleon interactions at 200 GeV." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/52310.
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We present results from Fermilab MPS experiment E580 on the reactions π⁻N->V°X where V° is K°S, A or A̅ and X are charged particles. Transverse and longitudinal momentum distributions for the V° and for K*±(892), Σ±(1385), Ξ⁻(1321) and Ξ⁺(1321) are presented. A comparison is made with the prediction of QCD quark counting rules. Evidence for A⁺C; is presented.Ph. D.
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Levy, S. A. "Experimental and computational studies of radical scavenging and polymerisation inhibition." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234863.
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Couce, Ríos Almudena. "Mechanistic insights into metal-catalyzed hydroamination reactions." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/403762.
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El tema de esta tesis es el estudio DFT del mecanismo de hidroaminaciones intermoleculares catalizadas por catalizadores de rodio y oro.
Los compuestos que contienen nitrógeno son muy valiosos y tienen muchos usos que van desde productos farmacéuticos hasta productos químicos. La reacción de hidroaminación es la vía más económica para sintetizar aminas sustituidas. Los catalizadores metálicos que han sido desarrollados para la hidroaminación directa incluyen tanto lantánidos como metales de transición tempranos y tardíos. Los catalizadores más versátiles para la hidroaminación intermolecular se basan en metales de transición tardíos. Hay muchos estudios publicados en los últimos años acerca de esta reacción, pero a pesar del esfuerzo algunas preguntas permanecen abiertas.
Los principales retos de las reacciones de hidroaminación son el uso de aminas simples y sustratos inactivados, la versión intermolecular, el control de la regioselectividad (especialmente la versión anti-Markovnikov) y la versión asimétrica. En esta tesis nos hemos centrado principalmente en el estudio del control de la regioselectividad en la versión intermolecular de esta reacción y en un proceso asimétrico.
El primer y segundo capítulo son una introducción al tema y una explicación teórica de todos los temas utilizados en esta tesis. En el tercer capítulo se recogen los puntos que este trabajo pretende lograr, en el cuarto capítulo se estudió una reacción de hidroaminación anti-Markovnikov de alquenos catalizada por un catalizador de rodio desarrollado por Hartwig et al. El quinto capítulo trata de la reacción de hidroaminación enantioselectiva de alenos catalizados por un catalizador de rodio. El sistema desarrollado por Breit y compañeros ha sido elegido para nuestro estudio. El sexto capítulo está dedicado a la reacción de hidroaminación de alquinos, alquenos y alenos con hidracina catalizada por tres catalizadores catiónicos de oro diferentes desarrollados por los grupos de Bertrand y Hasmi. En el séptimo capítulo estudiamos una reacción de hidroaminación anti-Markovnikov catalizada por oro. El sistema de Widenhoefer ha sido seleccionado ya que es el único ejemplo presente en la literatura. El último capítulo de esta tesis incluye una breve conclusión y un resumen del resultado del trabajo realizado.The topic of this thesis is the DFT study of the mechanism of intermolecular hydroaminations catalyzed by rhodium and gold catalyst. The nitrogen-containing compounds are very valuable and have a lot of uses ranging from pharmaceutical to chemical. The hydroamination reaction is the most economical pathway to synthesize substituted amines. Metal catalysts developed for direct hydroamination includes lanthanides, as well as early and late transition metals. The most versatile catalysts for the intermolecular hydroamination are based on late transition metals. There are a lot of studies published in recent years about this reaction, but despite the effort some questions remain open. The main challenges of hydroamination reactions are the use of simple amines and unactivated substrates, the intermolecular version, the control of regioselectivity (especially the anti-Markovnikov version) and the asymmetrical version. In this thesis we mainly focused on the study of the control of regioselectivity in the intermolecular version of this reaction and an asymmetric process. The first and second chapters are an introduction to the subject and a theoretical explanation of all the topics used in this thesis. In the third chapter are collected the points this work pretends to achieve, in the fourth chapter we studied an anti-Markovnikov hydroamination of alkenes catalyzed by a rhodium catalyst developed by Hartwig et al. The fifth chapter deals with the enantioselective hydroamination of allenes catalyzed by a rhodium catalyst. The system developed by Breit and coworkers has been chosen for our study. The sixth chapter is devoted to the hydroamination reaction of alkynes, alkenes and allenes with hydrazine catalyzed by three different cationic gold catalysts developed by Bertrand and Hasmi’s groups. In the seventh chapter we studied an Au-catalyzed anti-Markovnikov hydroamination. The Widenhoefer system has been selected since is the only example in the literature. The last chapter of this thesis includes a brief conclusion and summary of the outcome of the work carried out.
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Karakowski, Jonathan J. "Can the neutron polarizabilities be determined from a deuteron Compton scattering experiment? /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9809.
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Chen, Gang. "Experiments and modeling of the Belousov-Zhabotinsky reaction with 1,4-cyclohexanedione and ferroin." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/282877.
Full textAbstract:
We describe some observations during the induction period (IP) of a Belousov-Zhabotinsky (BZ) system with 1,4-cyclohexanedione (CHD) and ferroin in batch reactor. There are three stages during the whole course of the reaction: transitional period, the IP, and the post-IP. Two bifurcations are observed in this unique system: It starts with monostability (orange reduced steady-state) during the transitional period, switches to bistability (both blue oxidized and orange reduced steady-states) during the IP, and then eventually bifurcates to monostability (orange reduced steady-state) during the end of the IP. The stable orange steady-state is always excitable during the whole course of the reaction. The stable blue steady-state is not excitable during the blue IP: pulses cannot propagate and pacemakers cannot survive during this interval. As the medium ages, waves decrease their propagation speed except for the reduction step that speeds up during the end of the IP. We also investigate the change of ferroin and ferriin concentrations and photosensitivity during the IP. We find no analog to the situation suggested in the bromate-MA-ruthenium system, in that the oxidized state is experimentally excluded as the photosensitive species in this bromate-CHD-ferroin system. We construct here an Oregonator-like model that interprets the unique reduction step propagation before the second bifurcation. Based on the FKN mechanism with, we consider three reverse reactions, a breakdown of skeletal process C in the FKN model into three reactions with the addition of the hydrolysis of BrCHD. The model thus constructed endows bistability in some region of its parameter plane. We give a tentative interpretation of the differentiated speed between the reduction step propagation and that of the pulses, but rigorous mathematical mechanism awaits further investigation.
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Lee, Dongwoo. "Nanocalorimetry Experiments and First-Principles Theoretical Studies of Solid-State Reactions in Nanolaminates." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493483.
Full textAbstract:
The extraordinary sensitivity and extremely small thermal mass of chip-based nanocalorimetry sensors allow the study of reactions in thin films over a broad range of heating rates, from isothermal to 10^5 K/s. First-principles calculations provide insight in the phase transformation and diffusion behavior of a material at the atomistic scale. Combination of nanocalorimetry and first-principles, therefore, is highly efficient and reliable to determine the atomistic-to-macroscopic response of materials. This thesis explores, through use of this combined approach, reactions in reactive multilayers to synthesize ultra-high temperature ceramic coatings.
We employ scanning AC and DC calorimetry techniques to investigate the synthesis of ZrB2 and carbon-doped ZrB2 using Zr/B and Zr/B4C multilayered reactive nanolaminates (MRNL). The solid-state reactions in these multilayers are shown to proceed in two distinct steps: an interdiffusion/amorphization step followed by a crystallization step. Measurements performed at heating rates ranging from 1,000 to 55,000 K/s allows determination of the kinetic parameters of the multilayer reactions, such as the activation energies of interdiffusion and crystallization. Low activation energies in the interdiffusion processes in the Zr/B MRNLs are found and amorphization is shown to facilitate fast transport of B atoms into Zr lattice. It has also been shown that C impurity atoms in the Zr/B4C MRNLs further reduce activation energies of interdiffusion and crystallization.
First-principles theoretical modeling provides insight in the amorphization processes in the Zr/B MRNLs and confirms the relatively low activation energies associated with the processes. The simulations further elucidate the effects of concentration (ZrBx, 0
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Mallon, P. T. "The modulation of experimental colitis by reactive oxygen species scavengers." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484983.
Full textAbstract:
Inflammatory bowel disease is a common condition causing debilitating symptoms. Existing treatments are successful in many cases but there are a significant proportion of patients in whom conventional therapy fails or results in significant side effects. Alternative treatments are therefore being sought. Reactive oxygen species have been implicated in the pathogenesis of human IBO and experimental colitis. Edaravone and mesna are drugs which have been licenced for use in clinical practice for conditions other than IBO. Edaravone is a potent scavenger of reactive oxygen species such as the hydroxyl ion. It has been shown to reduce long term disability in patients with acute cerebral infarction. It is known that free radicals play an important role in the pathogenesis of secondary brain injury following cerebral infarction. Mesna is licenced for use in the prevention of haemorrhagic cystitis induced by cyclophosphamide chemotherapy protocols. Mesna has been shown to be a scavenger of hydroxyl and hypochlorus free radicals. Mesna, when administered topically has reduced the severity of experimental colitis in TNBS rats. The aim of the experiments in this thesis was to determine the effectiveness of edaravone and mesna at suppressing experimental colitis This thesis had demonstrated that edaravone is effective at suppressing experimental colitis when administered prophylactically. It has a partial benefit in established colitis. Mesna however, when administered orally appears to have no impact on experimental colitis. Edaravone may have a role to playas an alternative therapy for lBO, further trials are however needed to prove its efficacy in patients with IBD.
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Hildebrand, Bengt E. "Neurobiological basis of the nicotine withdrawal reaction : an experimental analysis /." Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-3874-1/.
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Hadden, Rory. "Smouldering and self-sustaining reactions in solids : an experimental approach." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5587.
Full textAbstract:
Smouldering combustion governs the burning of many materials in the built and natural environments. Smouldering is flameless, heterogeneous combustion which occurs when oxygen reacts with the surface of a solid fuel. Understanding the conditions which will result in the ignition and smouldering of a porous fuel is important and the phenomena involved are complex and coupled, involving heat and mass transfer, and chemical kinetics. This thesis reports experimental studies of the ignition, spread, suppression and emissions from reactions in porous media. Similar experimental techniques are shown in this thesis to be applicable when studying a wide range of solids which undergo self-sustaining reactions. This thesis is presented in a manuscript style. Each chapter takes the form of an independent paper which has been prepared for journal publication and as such, each chapter can stand on its own as a piece of research. A final chapter summarizes the findings and conclusions and suggests further areas of research. Chapter 1 presents a study of self-sustaining decomposition of ammonium nitrate containing inorganic fertilizer. This is of importance to the shipping industry which transports these materials in large quantities. Upon exposure to a heat source, ammonium nitrate may undergo exothermic decomposition which can propagate through the material, posing safety and economic threats. This reaction does not involve oxygenbased chemistry, but has many similarities to the propagation of a smoulder front in a porous material. Small-scale experiments to investigate the self-sustaining decomposition (SSD) behaviour of NPK (nitrogen, potassium, phosphorous) 16.16.16 fertilizer were undertaken. Experiments showed that this material will undergo self-sustaining decomposition and are used to formulate a reaction framework. Findings were applied to the events that occurred aboard the Ostedijk in 2007. Chapter 2 is a study of smoulder in polyurethane foam to study the relationship between sample size, critical heat flux and spread rate. Smouldering fires are the leading cause of residential fire deaths in developed countries and polyurethane foam is ubiquitous in the modern world. The critical heat flux for ignition was found to decrease with increasing sample size and the spread rate was found to be a function of the sample size, smoulder propagation depth and the applied heat flux. This is the first time that results on the effect of sample size on smouldering have been reported in the literature and these can be used to aid the extrapolation of small-scale flammability testing results to large scale scenarios. Chapter 3 presents an experimental investigation into the ignition of porous fuels by hot particles. This is related to the problem of spotting ember ignition in wildland fires which is a major, but poorly understood, spread mechanism. The process of spotting occurs in wildland fires when fire-lofted embers or hot particles land downwind, leading to ignition of new, discrete fires. The work studies the ignition of a fuel as a function of ember size and temperature. Metal particles are used as a proxy for burning embers and powdered cellulose to represent the forest fuel. Relationships between the size and temperature of the particle required for flaming and smouldering ignitions are found. These results are used to assess the ability of hot-spot ignition theory to determine the particle size–temperature relationship required for ignition of a cellulose fuel bed. Chapter 4 is an investigation into the suppression of smouldering coal. Subsurface coal fires are a significant global problem with fires in China alone estimated to consume up to 200 million tons of coal per year. As global demand for coal increases, accidental fires are a waste of a useful energy resource as well as a source of pollution and greenhouse gases. The results are the first attempt reported in the literature to study the suppression of these fires under controlled laboratory conditions. The ignition, spread and suppression of subsurface coal fires were studied using small-scale laboratory experiments. Time to ignition was seen to depend on particle size with small and large particles resulting in long times to ignition, while medium sized particles resulted in the shortest time to ignition. The maximum temperature, spread rate and mass lost were found to be independent of particle size above a critical particle size. The effectiveness of three systems for delivery of a suppression agent were assessed – direct injection, shower and spray. The effect of particle size on the water required for extinguishing using a spray was found to be weak. Chapter 5 presents an experimental investigation of the smouldering behaviour of peat. This is of particular interest in understanding the impact of smouldering fires on the earth system. The longer burn durations and different combustion dynamics of smouldering compared to flaming means that they have been shown to consume large amounts of biomass in, and contribute significantly to the emissions from, natural fires occurring in peatlands. The dynamics of smouldering peat in shallow, strong fronts was studied in the Fire Propagation Apparatus and a smoulder reaction framework with two burning regimes is presented. The first regime is peat smouldering and was found to be controlled by the applied heat flux and the second regime corresponded to char smouldering and was more sensitive to the flow of oxidizer. Chapter 6 complements Chapter 5 with an analysis of the CO and CO2 emissions for smouldering and flaming peat. This data can be used with large-scale measurement techniques to improve emission estimates. The emissions are found to be dependent of the burning regime and the type of combustion with flaming resulting in higher fluxes of CO2 and lower fluxes of CO compared to peat smouldering. Char smouldering resulted in the highest yields of CO and CO2. The large majority of emissions (85% of CO2 and 97% of CO) are released during the smoulder phase of the reaction. This highlights the differences in the chemical processes occurring under these two modes of combustion. Chapter 7 summarizes the research undertaken in this thesis and presents possible further work.
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Scott, Graham Bruce Ian. "Experimental studies of astrochemical ion-atom and ion-molecule reactions." Thesis, University of Canterbury. Chemistry, 1997. http://hdl.handle.net/10092/7813.
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Data is presented for a number of ion-molecule and ion-atom reactions of likely relevance to the chemistry of interstellar clouds and planetary atmospheres. The measurements were made using a Selected Ion Flow Tube, (SIFT), operating at ambient temperatures, (300 ± 5 K), and at pressures between 0.30 - 0.35 Torr.
The reactivity of two C₃H₃0+ isomers, namely protonated propynal, (HC=C-CHOH⁺), and the association product of C₂H₃⁺ with CO, (C₂H₃.CO), were characterised in laboratory experiments. These measurements bracket the proton affinity of propynal between 759 and 736 kJ mol⁻¹. The proton affinity of propadienone is similarly constrained between 896 and 868 kJ mol⁻¹. In a complementary investigation, the C₃H₃0⁺ potential surface was mapped using ab-initio calculations at the G2 level of theory. This combined experimental/theoretical study demonstrates that the condensation product between C₂H₃⁺ and CO is C₂-protonated propadienone, (H₂C=CH-C=O). Consequently, this finding indicates that propynal is not synthesised in the interstellar medium via the reaction of C2H3 + with carbon monoxide.
The reactions between twenty-eight cations and molecular and atomic hydrogen were examined in a series of laboratory experiments. Most hydrocarbon cations react with H atoms by termolecular association or, alternatively, H atom transfer routes. In contrast, only unsaturated hydrocarbon cations tend to react with H₂ via H atom abstraction processes. There are fewer clear trends evident in the reactions between non-hydrocarbon ions and H atoms. If exothermic, H atom abstraction is almost always observed during reactions between non-hydrocarbon cations and H₂. Molecular and atomic hydrogen are both extremely plentiful in dense and diffuse interstellar clouds and these processes are therefore particularly relevant to the chemistry occurring within these objects.
Results are presented for the reaction of approximately thirty cations with molecular and atomic nitrogen. Most ions are unreactive with N₂, however atomic nitrogen is a more reactive neutral species. Small hydrocarbon cations react with N atoms by forming C-N bonds and eliminating H or H₂, while larger CmHn⁺ species react with this neutral by forming HCN and a fragment hydrocarbon ion. In general there are no obvious patterns to the reactivity of non-hydrocarbon cations with atomic nitrogen. These processes are pertinent both to interstellar chemistry and the aeronomy of nitrogenous planetary atmospheres.
The crucial reaction between H3 + and N has been measured for the first time in the laboratory and found to be rapid, (k= 4.5 x 10⁻¹⁰cm³). This result offers an alternative, (and possibly more facile), synthetic route to ammonia in interstellar clouds.
Data is reported for the reaction of nineteen cations with O atoms, O₂ and NO. Small and medium sized hydrocarbon cations react with O atoms forming CmHnO⁺ ions and an H or H₂ fragment, whilst larger CmHn⁺ ions often react by C atom transfer forming CO and a smaller hydrocarbon ion. Most non-hydrocarbon cations examined were unreactive with atomic oxygen. Molecular oxygen is relatively unreactive with most ionic species, however many ions react with NO by charge transfer and/or termolecular association pathways. Nitric oxide, O₂ and O atoms are all present to varying degrees in interstellar clouds, hence the measurements presented here are applicable to the chemistry of these objects.
A number of preliminary experiments between ions and atomic carbon are detailed. The techniques for generating C atoms are described.
The research described in this thesis is pertinent to the many environments in which plasmas occur.
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Greaves, Stuart Jeffrey. "Theoretical and experimental studies of molecular motions and reaction mechanisms." Thesis, Durham University, 2005. http://etheses.dur.ac.uk/2621/.
Full textAbstract:
The time-delayed forwards scattering mechanism recently observed by Althorpe et al. [1] for the H + D2 (v=O, j=O) --? HD(v'=3, j'=O) + D reaction was analysed using the quasi-classical trajectory (QCT) methodology. QCT's were found to reasonably match the quantum snapshots of Althorpe, without the quantum effects. Trajectories were analysed on the fly to investigate the motions of the atoms during the reaction. The dominant reaction mechanism progresses from hard collinear impacts, leading to direct recoil, to glancing impacts. The increased time required for forward scattered trajectories is due to the rotation of the HDD complex. Forwards scattered trajectories display symmetric stretch vibrations of the HDD complex, indicating the presence of a resonance or a quantum bottleneck state. Reactive scattering in the HD(v'=O, j'=O) product channel was found to be governed by two unexpected and dominant new mechanisms, and not by direct recoil as is generally assumed. The new mechanisms involve strong interaction with the conical intersection, an area of the potential energy surface not previously thought to have much effect upon reactive scattering. Initial investigations indicate up to 56% of reactive scattering could be the result of these mechanisms.UV Cavity Ring-Down Spectroscopy of 1, 4-bis(phenylethynyl}benzene The torsional motion of 1, 4 bis(phenylethynyl)benzene (BPEB), a prototype molecular wire, is important for switching in molecular electronics. Cavity ring-down spectroscopy was used to record the torsional spectra of BPEB and 1, 4-bis(phenylethynyl) 2,3,5,6-tetradeuterobenzene in the gas phase. The spectra were modelled using a simple cosine potential. The experimental torsional barrier is very similar to the two ring system, Tolane. It was found that DFT calculations completely overestimate the torsional barrier.IV
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Allison, Mark. "An experimental and computational investigation of transition metal-free reactions." Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=30916.
Full textAbstract:
Over recent decades transition metal-catalysed cross-coupling has been developed significantly, opening up new areas of reactivity in both an academic and industrial environment. However, over recent years transition metal-free coupling reactions of haloarenes to arenes, proceeding by the Base-promoted Homolytic Aromatic Substitution (BHAS) mechanism have been widely reported in the literature. These reactions work well when initiated by organic electron donors that are formed in situ from organic additives of various types. The work in this thesis builds on previous work carried out within the Murphy group and other groups working in this field. Scheme 1 - BHAS mechanism proposed by Studer and Curran as responsible for transition metal-free cross coupling reactions. The work in this thesis looks at transition metal-free reactions in two forms; firstly looking at new additives that could form electron donors to initiate the BHAS mechanism and secondly, looking at where coupling reactions are occurring when there is no electron donor present. The final aspect of this thesis looks at exploring observations seen in experiments with haloarenes and potassium hydride. The first set of work was looking at a series of additives that were designed to form electron-rich alkenes, a common feature of electron donors, under basic conditions. These were studied both computationally and experimentally and this work showed these can work together effectively in studying electron donors. Scheme 2 - Additives used in Chapter 4 produced high yields of coupled products. While these reactions proceed in good yield when there is an electron donor present in the reaction, when there is no electron donor a measurable amount of cross coupling still occurs. A plausible mechanism, shown in scheme 3, has been proposed for the initiation of the BHAS pathway. This thesis shows that biradicals, generated in Bergman cyclisations and hexadehydro-Diels-Alder reactions, can indeed act as a source of initiation for this pathway. This thesis now shows that additives that afford arenediyls, provide independent initiation of the coupling reactions for this substrate in the absence of electron donors, supporting a similar capability for benzyne generated by base-dependent means. Scheme 3 - Proposed benzyne initiation of the BHAS cycle. In reactions performed by other members of the Murphy group involving haloarenes and KH, some interesting reaction products were observed. In this thesis these have been rationalised using computational studies. Scheme 4 - This thesis proposes formation of 7.7 proceeds via the four-memberedtransition state calculated.
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Cruz, João Duarte Neves. "Experimental study of proton induced nuclear reactions in 6,7 Li." Doctoral thesis, FCT - UNL, 2006. http://hdl.handle.net/10362/1139.
Full textAbstract:
This work presents the results of the experimental study of proton induced nuclear reactions
in lithium, namely the 7Li(p,α)
4He, 6Li(p,α)
3He and 7Li(p,p)7Li reactions.
The amount of 7Li and 6Li identified as primordial and observed in very old stars of the
Milky Way galactic halo strongly deviates from the predictions of primordial nucleosynthesis
and stellar evolution models which depend, among other factors, on the cross sections of reactions
like
7Li(p,α)
4He and 6Li(p,α)
3He. These discrepancies have triggered a large amount
of research in the fields of stellar evolution, cosmology, pre-galactic evolution and low energy
nuclear reactions.
Focusing on nuclear reactions, this work has measured the 7Li(p,α)
4He and 6Li(p,α)
3He reactions
cross sections (expressed in terms of the astrophysical S -factor) with higher accuracy,
and the electron screening effects in these reactions for different environments (insulators and
metallic targets). The 7Li(p,α)
4He angular distributions were also measured. These measurementstook
place in two laboratory facilities, in the framework of the LUNA (Laboratory for Undergroud
Nuclear Astrophysics) international collaboration, namely the Laboratorio ´ de Feixe de
Ioes ˜ in ITN (Instituto Tecnologico ´ e Nuclear) Sacavem, ´ Portugal, and the Dynamitron-TandemLaboratorium
in Ruhr-Universitat¨ Bochum, Germany. The ITN target chamber was modified
to measure these nuclear reactions, with the design and construction of new components, the
addition of one turbomolecular pump and a cold finger. The 7Li(p,α)
4He and 6Li(p,α)
3He reactions
were measured concurrently with seven and four targets, respectively. These targets were
produced in order to obtain adequate and stable lithium depth profiles.
In metallic environments, the measured electron screening potential energies are much
higher than the predictions of atomic-physics models. The Debye screening model applied
to the metallic conduction electrons is able to explain these high values. It is a simple model,
but also very robust. Concerning primordial nucleosynthesis and stellar evolution models, these results are very important as they show that laboratory measurements are well controlled, and
the model inputs from these cross sections are therefore correct.
In this work the 7Li(p,p)7Li differential cross section was also measured, which is useful to
describe the 7Li(p,α)
4He entrance channel.
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Bryant, Will, Timothy J. Bartkoski, John P. Meriac, and C. Allen Gorman. "User Reactions to Frame-of-Reference Scales. An Experimental Study." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/2616.
Full textAbstract:
Raters have been shown to react differently to performance evaluation formats. However, reactions to a new and promising format, frame-of-reference scales (FORS), remains untested. This experiment found that FORS users reacted more positively compared to standard scale users overall, and results were attributable to perceived accuracy and fairness.