974 resultados para 240200 Theoretical and Condensed Matter Physics


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There are vast changes in the work environment, and the traditional rules and management methods might not be suitable for today’s employees anymore. The meaning of work is also changing due to the younger and higher educated generations entering the markets. Old customs need to be re-validated and new approaches should be taken into use. This paper strongly emphasizes the importance of happiness research and happiness at work. The values towards the meaning of work are changing; people demand happiness and quality from all aspects of their lives. The aim of this study is to define happiness - especially at work - and to explain how it can be measured and what kind of results achieved. I also want to find out how the contents of work and the working environment might enhance happiness. The correlation between education and happiness is discussed and examined. I am aware that the findings and theories are concentrating mainly on Western Countries and highlighting the values and work-environments of those societies. The main aim of the empirical study is to find out if there are connections between happiness and work in data collected by World Value Survey in 2005, and if the profession has effects on happiness. Other factors such as the correlation of age, sex, education and income are examined too. I also want to find out what kind of values people have towards work and how these affect the happiness levels. The focus is on two nations: Finland (N=1014) and Italy (N=1012). I have also taken the global comparison within, that is all 54 countries (N=66,566) included in the 5th wave (during the years 2005 -2008) of the World Value Survey. The results suggest that people are generally happy around the world; happiness decreasing with the age, the educated being happier than the uneducated and the employed happier than the unemployed. People working in neat “white collar” jobs are more likely happier than those working in factories or outdoors. Money makes us happier, until certain level is reached. Work is important to people and the importance of work adds happiness. Work is also highly appreciated, but there are more happy people among those who do not appreciate work that highly. Safety matters the most when looking for a job, and there are more happy people among those who have selected the importance of work as the first choice when looking for a job, than among those to whom an income is the most important aspect. People are more likely happy when the quality of work is high, that is when their job consists of creative and cognitive tasks and when they have a feeling of independence.

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In Part I, theoretical derivations for Variational Monte Carlo calculations are compared with results from a numerical calculation of He; both indicate that minimization of the ratio estimate of Evar , denoted EMC ' provides different optimal variational parameters than does minimization of the variance of E MC • Similar derivations for Diffusion Monte Carlo calculations provide a theoretical justification for empirical observations made by other workers. In Part II, Importance sampling in prolate spheroidal coordinates allows Monte Carlo calculations to be made of E for the vdW molecule var He2' using a simplifying partitioning of the Hamiltonian and both an HF-SCF and an explicitly correlated wavefunction. Improvements are suggested which would permit the extension of the computational precision to the point where an estimate of the interaction energy could be made~

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Copper arsenite CuAs2O4 and Copper antimonite CuSb2O4 are S=1/2 (Cu2+ 3d9 electronic configuration) quasi-one-dimensional quantum spin-chain compounds. Both compounds crystallize with tetragonal structures containing edge sharing CuO6 octahedra chains which experience Jahn-Teller distortions. The basal planes of the octahedra link together to form CuO2 ribbon-chains which harbor Cu2+ spin-chains. These compounds are magnetically frustrated with competing nearest-neighbour and next-nearest-neighbour intrachain spin-exchange interactions. Despite the similarities between CuAs2O4 and CuSb2O4, they exhibit very different magnetic properties. In this thesis work, the physical properties of CuAs2O4 and CuSb2O4 are investigated using a variety of experimental techniques which include x-ray diffraction, magnetic susceptibility measurements, heat capacity measurements, Raman spectroscopy, electron paramagnetic resonance, neutron diffraction, and dielectric capacitance measurements. CuAs2O4 exhibits dominant ferromagnetic nearest-neighbour and weaker antiferromagnetic next-nearest-neighbour intrachain spin-exchange interactions. The ratio of the intrachain interactions amounts to Jnn/Jnnn = -4.1. CuAs2O4 was found to order with a ferromagnetic groundstate below TC = 7.4 K. An extensive physical characterization of the magnetic and structural properties of CuAs2O4 was carried out. Under the effect of hydrostatic pressure, CuAs2O4 was found to undergo a structural phase transition at 9 GPa to a new spin-chain structure. The structural phase transition is accompanied by a severe alteration of the magnetic properties. The high-pressure phase exhibits dominant ferromagnetic next-nearest-neighbour spin-exchange interactions and weaker ferromagnetic nearest-neighbour interactions. The ratio of the intrachain interactions in the high-pressure phase was found to be Jnn/Jnnn = 0.3. Structural and magnetic characterizations under hydrostatic pressure are reported and a relationship between the structural and magnetic properties was established. CuSb2O4 orders antiferromagnetically below TN = 1.8 K with an incommensurate helicoidal magnetic structure. CuSb2O4 is characterized by ferromagnetic nearest-neighbour and antiferromagnetic next-nearest-neighbour spin-exchange interactions with Jnn/Jnnn = -1.8. A (H, T) magnetic phase diagram was constructed using low-temperature magnetization and heat capacity measurements. The resulting phase diagram contains multiple phases as a consequence of the strong intrachain magnetic frustration. Indications of ferroelectricity were observed in the incommensurate antiferromagnetic phase.

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Differentes études ont montré que la sensibilité au Ca2+ du canal KCa3.1, un canal potassique indépendant du voltage, était conférée par la protéine calmoduline (CaM) liée de façon constitutive au canal. Cette liaison impliquerait la région C-lobe de la CaM et un domaine de $\ikca$ directement relié au segment transmembranaire S6 du canal. La CaM pourrait égalment se lier au canal de façon Ca2+ dépendante via une interaction entre un domaine de KCa3.1 du C-terminal (CaMBD2) et la région N-lobe de la CaM. Une étude fut entreprise afin de déterminer la nature des résidus responsables de la liaison entre le domaine CaMBD2 de KCa3.1 et la région N-lobe de la CaM et leur rôle dans le processus d'ouverture du canal par le Ca2+. Une structure 3D du complexe KCa3.1/CaM a d'abord été générée par modélisation par homologie avec le logiciel MODELLER en utilisant comme référence la structure cristalline du complexe SK2.2/CaM (PDB: 1G4Y). Le modèle ainsi obtenu de KCa3.1 plus CaM prévoit que le segment L361-S372 dans KCa3.1 devrait être responsable de la liaison dépendante du Ca2+ du canal avec la région N-lobe de la CaM via les résidus L361 et Q364 de KCa3.1 et E45, E47 et D50 de la CaM. Pour tester ce modèle, les résidus dans le segment L361-S372 ont été mutés en Cys et l'action du MTSET+ (chargé positivement) et MTSACE (neutre) a été mesurée sur l'activité du canal. Des enregistrements en patch clamp en configuration ``inside-out`` ont montré que la liaison du réactif chargé MTSET+ au le mutant Q364C entraîne une forte augmentation du courant, un effet non observé avec le MTSACE. De plus les mutations E45A et E47A dans la CaM, ont empêché l'augmentation du courant initié par MTSET+ sur le mutant Q364C. Une analyse en canal unitaire a confirmé que la liaison MTSET+ à Q364C cause une augmentation de la probabilité d'ouverture de KCa3.1 par une déstabilisation de l'état fermé du canal. Nous concluons que nos résultats sont compatibles avec la formation de liaisons ioniques entre les complexes chargés positivement Cys-MTSET+ à la position 364 de KCa3.1 et les résidus chargés négativement E45 et E47 dans la CaM. Ces données confirment qu'une stabilisation électrostatique des interactions CaM/KCa3.1 peut conduire à une augmentation de la probabilité d'ouverture du canal en conditions de concentrations saturantes de Ca2+.

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Dans ce travail, j’étudierai principalement un modèle abélien de Higgs en 2+1 dimensions, dans lequel un champ scalaire interagit avec un champ de jauge. Des défauts topologiques, nommés vortex, sont créés lorsque le potentiel possède un minimum brisant spontanément la symétrie U(1). En 3+1 dimensions, ces vortex deviennent des défauts à une dimension. Ils ap- paraissent par exemple en matière condensée dans les supraconducteurs de type II comme des lignes de flux magnétique. J’analyserai comment l’énergie des solutions statiques dépend des paramètres du modèle et en particulier du nombre d’enroulement du vortex. Pour le choix habituel de potentiel (un poly- nôme quartique dit « BPS »), la relation entre les masses des deux champs mène à deux types de comportements : type I si la masse du champ de jauge est plus grande que celle du champ sca- laire et type II inversement. Selon le cas, la dépendance de l’énergie au nombre d’enroulement, n, indiquera si les vortex auront tendance à s’attirer ou à se repousser, respectivement. Lorsque le flux emprisonné est grand, les vortex présentent un profil où la paroi est mince, permettant certaines simplifications dans l’analyse. Le potentiel, un polynôme d’ordre six (« non-BPS »), est choisi tel que le centre du vortex se trouve dans le vrai vide (minimum absolu du potentiel) alors qu’à l’infini le champ scalaire se retrouve dans le faux vide (minimum relatif du potentiel). Le taux de désintégration a déjà été estimé par une approximation semi-classique pour montrer l’impact des défauts topologiques sur la stabilité du faux vide. Le projet consiste d’abord à établir l’existence de vortex classi- quement stables de façon numérique. Puis, ma contribution fut une analyse des paramètres du modèle révélant le comportement énergétique de ceux-ci en fonction du nombre d’enroulement. Ce comportement s’avèrera être différent du cas « BPS » : le ratio des masses ne réussit pas à décrire le comportement observé numériquement.

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La prise de décision est un processus computationnel fondamental dans de nombreux aspects du comportement animal. Le modèle le plus souvent rencontré dans les études portant sur la prise de décision est appelé modèle de diffusion. Depuis longtemps, il explique une grande variété de données comportementales et neurophysiologiques dans ce domaine. Cependant, un autre modèle, le modèle d’urgence, explique tout aussi bien ces mêmes données et ce de façon parcimonieuse et davantage encrée sur la théorie. Dans ce travail, nous aborderons tout d’abord les origines et le développement du modèle de diffusion et nous verrons comment il a été établi en tant que cadre de travail pour l’interprétation de la plupart des données expérimentales liées à la prise de décision. Ce faisant, nous relèveront ses points forts afin de le comparer ensuite de manière objective et rigoureuse à des modèles alternatifs. Nous réexaminerons un nombre d’assomptions implicites et explicites faites par ce modèle et nous mettrons alors l’accent sur certains de ses défauts. Cette analyse servira de cadre à notre introduction et notre discussion du modèle d’urgence. Enfin, nous présenterons une expérience dont la méthodologie permet de dissocier les deux modèles, et dont les résultats illustrent les limites empiriques et théoriques du modèle de diffusion et démontrent en revanche clairement la validité du modèle d'urgence. Nous terminerons en discutant l'apport potentiel du modèle d'urgence pour l'étude de certaines pathologies cérébrales, en mettant l'accent sur de nouvelles perspectives de recherche.

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The electrical properties of polymers make up an inherently interdisciplinary topic, being closely associated, on the one hand, with the mechanical properties of polymers polarization and relaxation) and, on the other hand, with the semi conductive properties (conduction and break down). In addition, unlike conventional technologies, which use these properties in its various applications like antistatic coatings, rechargeable batteries, sensors, electrochromic devices, electrochemical devices etc, microwave technology extract the microwave absorbing ability of electrically conducting polymers. The conducting polymers are widely used in its potential applications like electro magnetic interference shielding, satellite communication links, beam steering radars, frequency selective surfaces etc. Considering the relevance of microwave applications of conducting polymers, the study of microwave properties of conducting polymers stands poised to become a compelling choice for synthetic chemists and condensed - matter physicists, physical chemists and material scientists, electrochemists and polymer scientists. The main aim of the present work is to study the microwave and low frequency properties of various conducting polymers, conducting semi-interpenetrating networks, conducting copolymers and to characterise it. Also this thesis collated the microwave properties of these conducting systems and exposes the various technologically important applications in the industrial, scientific, communication and defence applications.

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The antikaon optical potential in hot and dense nuclear matter is studied within the framework of a coupled-channel self-consistent calculation taking, as bare meson-baryon interaction, the meson-exchange potential of the Jlich group. Typical conditions found in heavy-ion collisions at GSI are explored. As in the case of zero temperature, the angular momentum components larger than L=0 contribute significantly to the finite temperature antikaon optical potential at finite momentum. It is found that the particular treatment of the medium effects has a strong influence on the behavior of the antikaon potential with temperature. Our self-consistent model, in which antikaons and pions are dressed in the medium, gives a moderately temperature dependent antikaon potential which remains attractive at GSI temperatures, contrary to what one finds if only nuclear Pauli blocking effects are included.

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The present work emphasizes the use of chirality as an efficient tool to synthesize new types of second order nonlinear materials. Second harmonic generation efficiency (SHG) is used as a measure of second order nonlinear response. Nonlinear optical properties of polymers have been studied theoretically and experimentally. Polymers were designed theoretically by ab initio and semiempirical calculations. All the polymeric systems have been synthesized by condensation polymerization. Second harmonic generation efficiency of the synthesized systems has been measured experimentally by Kurtz and Perry powder method

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In this thesis, a dual mode tunable gas sensor based on intracavity laser absorption spectroscopy (ICLAS) principle is investigated, both, numerically and experimentally. In order to minimize the cost and size of the gas sensor, relative intensity noise (RIN) is implemented as a detection parameter. Investigation is performed to determine the effect of injection current, operating temperature, mode spacing, and cavity length on RIN. It has been found that it is best to operate the gas sensor at smaller mode spacing and near the threshold current or at larger mode spacing and far above the threshold current for the use of RIN as the readout parameter.

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We extend a previous model of the Neolithic transition in Europe [J. Fort and V. Méndez, Phys. Rev. Lett. 82, 867 (1999)] by taking two effects into account: (i) we do not use the diffusion approximation (which corresponds to second-order Taylor expansions), and (ii) we take proper care of the fact that parents do not migrate away from their children (we refer to this as a time-order effect, in the sense that it implies that children grow up with their parents, before they become adults and can survive and migrate). We also derive a time-ordered, second-order equation, which we call the sequential reaction-diffusion equation, and use it to show that effect (ii) is the most important one, and that both of them should in general be taken into account to derive accurate results. As an example, we consider the Neolithic transition: the model predictions agree with the observed front speed, and the corrections relative to previous models are important (up to 70%)

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This paper develops some theoretical and methodological considerations for the development of a critical competence model (CCM). The model is defined as a set of skills and knowledge functionally organized allowing measurable results with positive consequences for the strategic business objectives. The theoretical approaches of classical model of competences, the contemporary model of competencies and human competencies model were revised for the proposal development. implementation of the model includes 5 steps: 1) conducting a job analysis considering which dimensions or facets are subject to revision, 2) identify people with the opposite performance (the higher performance and lower performance); 3) identify critical incidents most relevant to the job position, 4) develop behavioral expectation scales (bes) and 5) validate BES obtained for experts in the field. As a final consideration, is determined that the competence models require accurate measurement. Approaches considering excessive theoreticism may cause the issue of competence become a fashion business with low or minimal impact, affecting its validity, reliability and deployment in organizations.