With the rapid development of cellular communication techniques, many recent studies have focused on improving the quality of service (QoS) in cellular networks. One characteristic of the systems in cellular networks, which can have direct impact on the system QoS, is the fluctuation of the system capacity. In this thesis, the QoS of systems with capacity fluctuations is studied from two perspectives: (1) priority queueing systems with preemption, and (2) the M/M/~C/~C system. In the first part, we propose two models with controlled preemption and analyze their performance in the context of a single reference cell that supports two kinds of traffic (new calls and handoff calls). The formulae for calculating the performance measures of interest (i.e., handoff call blocking probability, new call blocking and dropping probabilities) are developed, and the procedures for solving optimization problems for the optimal number of channels required for each proposed model are established. The proposed controlled preemption models are then compared to existing non-preemption and full preemption models from the following three perspectives: (i) channel utilization, (ii) low priority call (i.e., new calls) performance, and (iii) flexibility to meet various constraints. The results showed that the proposed controlled preemption models are the best models overall. In the second part, the loss system with stochastic capacity, denoted by M/M/~C/~C, is analyzed using the Markov regenerative process (MRGP) method. Three different distributions of capacity interchange times (exponential, gamma, and Pareto) and three different capacity variation patterns (skip-free, distance-based, and uniform-based) are considered. Analytic expressions are derived to calculate call blocking and dropping probabilities and are verified by call level simulations. Finally, numerical examples are provided to determine the impact of different distributions of capacity interchange times and different capacity variation patterns on system performance.

The 2,2'-disubstituated 1,1'-binaphthyls (BINOLs) are important ligands in enantioselective synthesis . The major approach for their preparation is based on transition-metal-mediated oxidative C-C coupling of 2-substituted naphtalenes. This diploma thesis examined the mechanism of the coupling reaction in the gas phase using mass spectrometry with electrospray ionization. The aim of this thesis was to compare the selectivity of the copper(II)- catalyzed coupling reaction of 2-naphthol and its derivative with an electron-withdrawing group, to detect possible reaction intermediates, and to determine the origin of the preference of the cross-coupling. The electron-withdrawing group of naphthol slows down the coupling reaction which enabled us to detect the reaction intermediates. The intermediates in the reaction of 2-naphthol were not observed, because the coupling reaction proceeds too quickly. Hence, we have observed only complexes of the coupling products. The preferential cross coupling was explaned on the basis of an interplay between the probability of the formation of binuclear copper complexes and the reactivity of such complexes.

William C. C. Claiborne found himself a stranger in a strange land. Almost more a colonial governor of a European power rather than an American statesman, Claiborne grappled with maintaining a militia force for the Territory of Orleans, now the present day state of Louisiana. He built upon the volunteer companies he found within the city of New Orleans, but had little success molding the entire militia into an effective, efficient military force. Claiborne, hoping to use the fear generated by the January 1811 slave revolt to spur militia reform, maintained an active correspondence with the state's legislators, the area's military commanders, the members of the Louisiana congressional delegation, and even the President of the United States for assistance with militia matters. Ultimately, Claiborne failed and the British attack on New Orleans in 1814/1815 made the matter of reform academic.

The non-sustainable nature of fossil fuels as feedstocks for valuable chemicals, combined with the environmental damage caused by their extraction and combustion, increases the need for the development of a bio-based economy. While industry and public opinion are slowly shifting towards acceptance of this change, efficient technologies for the depolymerization and subsequent separation of lignocellulosic biomass fall short of the ever-increasing demand. In particular, there are currently no efficient, sustainable mass scale methods to convert lignin, the most abundant source of aromatic molecules on Earth. The use of oxovanadium(V) catalyst complexes to aerobically cleave C‒C bonds has been demonstrated previously and remains an attractive option for incorporation into a sustainable bio-based economy. Two new triphenoxyamine oxovanadium(V) catalysts with reduced steric bulk and electron density at the metal center (vs. previously reported complexes) have been synthesized for aerobic oxidative diol C‒C bond cleavage. These complexes were found to cleave less activated and more complex substrates than previous generations, including cyclic diols and polyalcohols. Several insights into the reaction pathways of this class of complex were elucidated through a series of kinetic studies. Experimentally, the rate of C‒C bond cleavage of both pinacol and hydrobenzoin was determined to be unaffected by substitution of the O‒H bonds with deuterium, suggesting that currently proposed mechanisms need to be revised. Multiple catalytic regimes were observed during anaerobic reaction, which were not altered significantly by the brief addition of O2. A series of density functional theory calculations revealed a plausible mechanism for the trialkoxy complex that did not involve a proton transfer in the rate determining step, instead suggesting that ligand-arm dissociation-reassociation play a significant role in the reaction. In a second project, new bisphenoxyamine-N-appended base ligand with less steric hindrance and electron density at the metal center, has been synthesized utilizing similar design principles gained from work with triphenoxyamine catalysts. When reacting with lignin model compound 1,2-diphenyl-2-methoxyethanol, this new complex displays a higher selectivity towards aldehydes and esters (relative to previous bisphenoxyamine-N-appended ligands), leading to a higher rate of C‒C bond cleavage. Investigations into the mechanism of bisphenoxy complexes, as well as the role of the N-appended base in reactivity, were performed using substrate pre-complexed bisphenoxy compounds. Thermolysis at 60 and 100 °C produced almost exclusively oxidative C‒H bond cleavage product benzyl methyl ether, with evidence for overoxidation product benzoic acid observed. Thermolysis of labelled substrate pre-complexed revealed that N-appended base may impede C‒C cleavage of 1,2-diphenyl-2-methoxyethanol by forcing the methyl ether away from the oxovanadium(V) center. Through the use of these multidentate phenoxyamine ligands, advances have been made towards sustainable oxovanadium catalysis in the pursuit of efficient and selective lignocellulosic disassembly for a sustainable bio-based economy.

No description available.

Depuis ces vingt dernières années, les nanotechnologies représentent une aire de recherche en plein développement. En particulier, les nanoparticules métalliques ont suscité un intérêt croissant en catalyse de part leurs propriétés intermédiaires entre les catalyseurs homogènes et hétérogènes classiques. Ainsi, leur réactivité de surface peut entrainer de nouvelles sélectivités lors des synthèses de molécules d'intérêt médical, pharmaceutique ou agrochimique. Au cours de cette thèse, une nouvelle famille de ligands chiraux polyfonctionnels dérivés du 9,10-dihydroanthracène, pour la stabilisation de nanoparticules de palladium, a été synthétisée. Les colloïdes ont été obtenus par décomposition de précurseurs organométalliques en présence de ces nouveaux ligands. Les particules de taille, de forme et de composition chimique contrôlées ont été utilisées en réaction de couplage C-C de Suzuki. Ces réactions ont été réalisées en milieux organique et liquide ionique. Aussi, la réactivité de surface a été étudiée dans l'hydrogénation et la dismutation du 1,4-cyclohexadiène. Dans l'objectif d'étudier la chimie de coordination des ligands, des complexes de palladium ont été synthétisés et complètement caractérisés. L'induction asymétrique apportée par ces ligands optiquement purs a été estimée dans des réactions asymétriques d'alkylation allylique et de couplage C-C de Suzuki.

This thesis describes the development and mechanistic studies of carbocyclization reactions of allene-substituted olefins and 1,3-dienes, catalyzed by palladium(0) and palladium(II). These reactions results in the formation of [n,3,0] bicyclic systems (n = 3-5) with high stereoselectivity and in good to excellent yields. The first carbocyclization presented is a novel palladium(0)-catalyzed cyclo- isomerization of allene-substituted olefins. Secondly an efficient aerobic biomimetic system has been developed for a Pd(II)-catalyzed allylic oxidative carbocyclization of allene-substituted olefins. Additionally, during the studies of palladium-catalyzed carbocyclizations of allene-substituted olefins, it was found that in the absence of palladium a mild thermal ene-reaction occurs. In this manner stereodefined, functionalized bicyclic compounds are obtained with good regioselectivity and in high yields. The third and fourth carbocyclization developed are a palladium(II)-catalyzed oxidation and a palladium(0)-catalyzed intramolecular telomerization of allene-substituted 1,3-dienes. A mechanistic study of the palladium(II)-catalyzed oxidation of allene-substituted 1,3-dienes was made, and reaction intermediates could be isolated. The stereochemistry of the reaction intermediates was assigned, and this made it possible to suggest a mechanism for the reaction. The presented mechanism is a trans carbopalladation of the 1,3-diene, where the allene act as the carbon nucleophile. Due to different stereochemical outcomes of the stoichiometric and catalytic reactions, this mechanism could only explain the stoichiometric reaction. Another mechanism for the catalytic reaction was suggested, which rationalizes both the regio- and stereochemistry of the products.

Tridentate "pincer" ligands provide a unique balance of stability and reactivity in organometallic chemistry. The development of diarylamido-based PNP pincer ligands has led to many applications in catalysis, including the potential to facilitate unique chemical transformations at transition metal centers. The main objective of this thesis was to explore transition metal chemistry supported by the PNP pincer framework for both early and late transition metals. In Chapter I, the history behind the design and synthesis of pincer complexes is described. The advantages and disadvantages of various pincer ligands are reviewed to show the reasoning behind the synthesis of the PNP pincer framework. Chapter II discusses the synthesis of novel Hf and Ta complexes involving the PNP ligand. Reactions of (PNP)HfCl3 with large alkyl Grignards led to double alkylation and triple alkylation was achieved with methyl Grignard. (PNP)HfMe3 and (PNP)Hf(CH2SiMe3)2Cl displayed remarkably irregular coordination environments about hafnium, in contrast to the approximately octahedral structure of (PNP)HfCl3. (PNP)HfMe3 was found to be thermally stable at 75 degrees C, whereas thermolysis of (PNP)Hf(CH2SiMe3)2Cl under similar conditions led to a mixture of products. The major decomposition product is believed to be a Hf alkylidene complex on the basis of in situ NMR spectroscopic observations (e.g., delta 248.2 ppm in the 13C{1H} NMR spectrum). The reaction of (PNP)TaF4 with an excess of ethyl Grignard led primarily to the double alkylation product, (PNP)Ta(CH2CH3)2F2. Repeating this reaction in the presence of excess ethyl Grignard and dioxane resulted in the formation of an ethylene complex, (PNP)Ta(=CHCH3)(C2H4). In Chapter III, a C-C reductive elimination study is described comparing two pincer ligand scaffolds: Me(PNP) ligand and TH(PNP) ligand. The tied ligand has previously been found to be more sterically demanding than the untied ligand, which has allowed for faster N-C cleavage, faster oxidative addition and a more selective alkyne dimerization catalyst. This study reveals that the tied ligand complex, TH(PNP)Rh(C6H4CF3)(Ph), undergoes slower reductive elimination of p-Ph-C6H4CF3 (< 4% after 7 h at 38 degrees C; t1/2 = 7.7 h at 64 degrees C; t1/2 = 2.13 h at 75 degrees C) than Me(PNP)Rh(C6H4CF3)(Ph) (t1/2 = 15.6 min at 38 degrees C).

Els sistemes objecte d'estudi en aquest treball són aliatges metàl·lics d'estructura reticular b.c.c. els quals, a baixes temperatures, experimenten una transició de fase estructural de tipus martensític (bàsicament descrita per una deformació de cisallament). Particularment interessants, entre d'altres, són els aliatges: Cu-Zn, Cu-Zn-Al, Ag-Zn, Cu-AI-Ni, ... , a causa de les propietats termomecàniques que posen de manifest i que els fan de gran utilitat en aplicacions tecnològiques (robòtica, aplicacions mèdiques... ) [1]: efecte de memòria de forma i pseudoelasticitat.Aquestes propietats tenen el seu origen en la pròpia transformació martensítica (TM) termoelàstica que experimenten aquests aliatges per sota de la temperatura M(s). A més a més, aquests sistemes (aliatges amb efecte de memòria de forma) experimenten una transició ordre-desordre a una temperatura (Tc) normalment molt més alta que M(s). Per sota de Tc presenten estructures d'ordenació B(2), D0(3) o Heusler.Partint de l'evidència experimental que posa de manifest la forta influència que l'estat d'ordre atòmic de la fase d'alta temperatura [(T)Ms, o fase-beta] té sobre les característiques de la TM [2,3], en aquest treball ens proposem desenvolupar els models pertinents quc permetin de quantificar aquest problema. així com l'associat als efectes d'envelliment observats i que es relacionen amb canvis d'ordre.En el desenvolupament del treball, primerament es fa una revisió de les característiques generals bàsiques de les TM, així com dels principals models utilitzats en l'estudi de transicions de fase i que són emprats al llarg del treball.A fi de dur a terme la quantificació esmentada, es fa indispensable una caractcrització prèvia de l'estat d'ordenació atòmic de la fase-beta. Per fer-ho hem desenvolupat un model termodinàmic en l'aproximació de Bragg-Williams per al cas d'aliatges ternaris que presenten estructures d'ordenació DO(3) (a baixes temperatures) i B(2) (a temperatures intermitges). La seva aplicació al sistema Cu-Zn-Al ens permet avaluar les energies d'ordenació tant per a parelles de primers com de segons veïns.A continuació introduïm un model termodinàmic per a l'estudi concret del nostre problema que ens permet tractar sistemes que experimenten transicions de fase de primer i de segon ordre, amb interacció entre les corresponents formes d'ordenació. Aquesta interacció s'ha introduït a través d'un terme d'acoblament biquadràtic entre els paràmetres d'ordre que descriuen respectivamente les dues transicions de fase. Quan l'apliquem a l'estudi de l'efecte del grau d'ordre atòmic en sistemes que experimenten TM termoelàstiques (aliatges amb efecte de memòria de forma) i transicions ordre-desordre, el model prediu una variació lineal de la constant elàstica C' =(C(11) - C(12))/2 (rellevant del nostre problema) de la fase-beta i el quadrat del paràmetre d'ordre de llarg abast del sistema. Aquest canvi en C' determina els canvis en les característiques termodinàmiques de la TM (T(0), - Delta - H(B->H)). Aquest comportament ha estat justificat comparant els resultats teòrics amb les dades experimentals disponibles per a l'aliatge Cu-Zn-Al.Posteriorment, hem generalitzat el model anterior per poder tractar sistemes no homogenis i s'ha estudiat, a partir d'un formalisme de Fokker-Planck, com evoluciona, a temperatura constant Tf en fase-beta, la constant elàstica C' durant un procés d'ordenació atòmic que segueix un refredament ràpid des de Ti < Tc. Dins de l'aproximació lineal, el resultat és coherent amb les dades experimentals [4].Atès el caràcter fenomenològic de l'aproximació utilitzada, que no permet d'extreure una conclusió definitiva en termes físics, pensem que fóra interessant de dur a terme un estudi a nivell microscòpic per assegurar la validesa de la funcionalitat proposada. Per fer-ho s'ha posat a punt un programa de simulació numèrica pel mètode de Monte CarIo per calcular constants elàstiques en sistemes binaris AB que presenten una estructura reticular de tipus b.c.c. Els paràmetres del potencial per a les diferentes interaccions que s'han de considerar AA, BB i AB s'han obtingut mitjançant ajustos a T =OK, de dades conegudes de la constant elàstica C' a T =T(amb) en funció de la composició [5]. No obstant, posteriorment comprovem que aquest comportament es conserva a temperatura finita, quan C' es calcula numèricament pel mètode de Monte Carlo. Finalment, hem calculat a Tf= OK, C' en sistemes parcials o totalment desordenats (després d'un refredament ràpid des de Ti a Tf = OK). Les configuracions corresponents a diferents graus d'ordenació s'han obtingut per la simulació numèrica d'un model d'lsing utilitzant el mètode de Monte Cario. Els resultats que obtenim justifiquen en forma molt satisfactòria la funcionalitat lineal entre C' i el quadrat del paràmetre d'ordre de llarg abast [6] proposada en el marc d'una aproximación de camp mig [7].REFERÈNCIES1. L. Delaey, R. V. Krishnam, H. Tas i H. Warlimont, J. Mater. Sci. 9 (1974) 1521.2. R. Rapacioli i M. Ahlers, Acta Met. 27 (1979) 777.3. A. Planes, J.L. Macqueron, M. Morin i G. Guénin, Mater. Sci. Engng. 50 (1981) 53.4. T. Castan i A. Planes, Phil. Mag. A (en premsa).5. T. Castan i A. Planes, enviat a J. Phys. F.6. T. Castan i A. Planes, Phase Transformations-87, TheInstitut of Metals (1987). En premsa.7. A. Planes, J. Viñals i V. Torra, Phil. Mag. A48 (1983) 501.

La primera parte de la tesis se dedica al estudio del mecanismo de una reacción de activación C-H por un complejo de niobio. Se racionalizó el mecanismo de activación de enlaces C-H del benceno por el complejo TpMe2NbCH3(c-C3H5)(MeCCMe). El intermedio clave es un complejo inusual de 2-ciclopropeno. Conseguimos también racionalizar las selectividades obtenidas para la activación de varios alquilaromáticos por el complejo de niobio 2-ciclopropeno. También se investigó el papel del ligando alquino en estos complejos y su posible papel en procesos de migración de ligandos. En la segunda parte de la tesis, se investigaron las reacciones de acoplamiento cruzado con reactivos basados en silicio. Los resultados sugieren que la transmetalación es más fácil después de la disociación de la fosfina, o cuando un ligando bromuro está coordinado al paladio. El efecto beneficioso de la dibencilidenoacetona en el acoplamiento también fue aclarado. / The first part of the thesis is mainly devoted to the mechanism of a C-H activation reaction by a niobium complex. The mechanism of C-H bond activation of benzene by the TpMe2NbCH3-(c-C3H5)-(MeCCMe) complex was rationalized. The key intermediate is an unusual 2-cyclopropene complex. We rationalized the selectivities obtained for the activation of several alkylaromatics by the 2-cyclopropene niobium complex. The intriguing role of the alkyne ligand of the same complex, and its possible role in the migration processes, was investigated. In the second part of the thesis, we focused on the silicon based cross-coupling. The results suggest than the transmetalation is easier after phosphine dissociation, and in presence of the bromide ligand on the palladium. The beneficial effect of dibenzylideneacetone on the coupling was clarified.