Biblioteca Digital

Barium stars are optimal sites for studying the correlations between the neutron-capture elements and other species that may be depleted or enhanced, because they act as neutron seeds or poisons during the operation of the s-process. These data are necessary to help constrain the modeling of the neutron-capture paths and explain the s-process abundance curve of the solar system. Chemical abundances for a large number of barium stars with different degrees of s-process excesses, masses, metallicities, and evolutionary states are a crucial step towards this goal. We present abundances of Mn, Cu, Zn, and various light and heavy elements for a sample of barium and normal giant stars, and present correlations between abundances contributed to different degrees by the weak-s, mains, and r-processes of neutron capture, between Fe-peak elements and heavy elements. Data from the literature are also considered in order to better study the abundance pattern of peculiar stars. The stellar spectra were observed with FEROS/ESO. The stellar atmospheric parameters of the eight barium giant stars and six normal giants that we analyzed lie in the range 4300 < T(eff)/K < 5300, -0.7 < [Fe/H] <= 0.12 and 1.5 <= log g < 2.9. Carbon and nitrogen abundances were derived by spectral synthesis of the molecular bands of C(2)...

O efeito Raman ressonante do complexo (NH4)4Mo2Cl8.NH4Cl.H2O, contendo o íon Mo2Cl84-, foi estudado tanto na temperatura ambiente como na de nitrogênio líquido. Com base nos resultados obtidos mostra-se que a explicação previamente oferecida por outros autores para o aparecimento de ressonância com excitação em 568,2 nm não é correta. É sugerida uma explicação diferente para este comportamento baseada nos espectros Raman e de absorção. A transferência de elétron fotoestimulada no íon complexo (NH3)5RuII-pz-CuII foi comprovada através do estudo do efeito Raman ressonante. Com base nos espectros Raman obtidos em condições de ressonância e também nas medidas de polarização, o estado eletrônico excitado envolvido foi caraterizado. Os perfis de excitação para v1 e 2vl do íon RuO42- em solução aquosa foram obtidos usando diversas radiações excitantes. Os perfis mostraram uma desintensificação das intensidades Raman pré-ressonantes na região da transição interna do íon. O efeito foi interpretado usando o tratamento proposto por Stein e col. para o efeito Raman anti-ressonante.; The Raman resonance effect of the complex (NH4)4Mo2Cl8.NH4Cl.H2O, containing the Mo2Cl84- ion, was investigated at both room and liquid nitrogen temperatures. On basis of the obtained results it is shown that the previous explanation given by others authors for the resonance observed with 568.2 nm excitation is not a correct one. A different explanation for this behaviour is suggested...

We employ finite elements methods for the approximation of solutions of the Ginzburg-Landau equations describing the deconfinement transition in quantum chromodynamics. These methods seem appropriate for situations where the deconfining transition occurs over a finite volume as in relativistic heavy ion collisions. where in addition expansion of the system and flow of matter are important. Simulation results employing finite elements are presented for a Ginzburg-Landau equation based on a model free energy describing the deconfining transition in pure gauge SU(2) theory. Results for finite and infinite system are compared. (C) 2009 Elsevier B.V. All rights reserved.

Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s¹ and s0 configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations.

Transfer of membrane between endoplasmic reticulum and Golgi apparatus in situ is considered to occur via 60-nm transition vesicles derived from part-rough, part-smooth transition elements of the endoplasmic reticulum. A procedure is described for the isolation of a fraction enriched in these transition elements from rat liver. The isolated fraction generates small vesicles morphologically resembling transition vesicles when incubated with nucleoside triphosphate at 37 degrees C. In the cell-free system consisting of a donor fraction enriched in transition elements and an acceptor fraction consisting of intact Golgi apparatus immobilized on nitrocellulose strips, transfer in vitro of radiolabeled membranes was demonstrated. Nucleoside triphosphates were required for transfer, and transfer was facilitated by a cytosol fraction of Mr greater than 10,000. In the presence of both nucleoside triphosphate and cytosol, radiolabeled proteins were transferred in a manner dependent upon both time and temperature. Transfer appeared to be both vectorial and specific in that, with Golgi apparatus (or endoplasmic reticulum) as both donor and acceptor, only negligible time and temperature-dependent transfer was observed. The test system described is expected to facilitate further investigation of the transfer process and to provide a convenient assay to guide transition vesicle isolation and characterization.

Selon des thèses développées au cours des années 1990 et 2000, le développement économique constitue à la fois la source et la solution aux problèmes environnementaux. Au sujet des forêts, les transitions forestières (c’est-à-dire le passage de la déforestation à la reforestation) documentées dans certains pays développés seraient causées par des dynamiques universelles intrinsèques au développement et à la modernisation des sociétés. Nos travaux ont porté sur l’application de cette vision optimiste et controversée à l’évolution des superficies forestières en Thaïlande. S’appuyant sur une recension de la littérature, sur des données secondaires ainsi que nos travaux de terrain dans la région de Phetchabun, la thèse offre les apports suivants. Elle démontre que contrairement à l’idée répandue en Thaïlande, le ralentissement de la déforestation a été suivi par une expansion forestière substantielle entre environ 1995 et 2005. Ce regain forestier est lié à la disparition presque complète de l’expansion agricole, à l’établissement de plantations sylvicoles et, surtout, à l’abandon de terres agricoles. Cet abandon agricole découle d’abord et avant tout de la faible et incertaine rentabilité de l’agriculture dans certaines zones non irriguées. Ce phénomène s’explique...

Cette thèse propose une analyse des transformations postcommunistes en Roumanie à partir d’une étude de la structuration de trajectoires familiales. La réflexion sur les itinéraires très variés de ces trajectoires familiales met en valeur les pratiques développées par les familles dans la construction de leur mode de vie quotidienne après la chute du communisme. L’approche utilisée privilégie deux axes d’analyse. Le premier vise les aspects socio-structurels concernant les cadres de la vie incluant les aspects matériels, alors que le deuxième, l’axe socio-symbolique, concerne les aspects subjectifs liés au vécu des acteurs en corrélation avec le contexte social en mutation. L’analyse est fondée sur des éléments issus de la théorie de la structuration qui ont contribué à la construction du cadre conceptuel. Elle s’appuie aussi sur la méthodologie qualitative qui comprend des récits de vie obtenus à partir des entretiens semi-dirigés réalisés avec les membres de 11 familles. Les thématiques retenues après l’analyse du corpus de données nous ont permis d’identifier des stratégies que les familles ont mises en place et les projets familiaux qui ont orienté leur parcours de vie durant la période de transition postcommuniste. Ces deux concepts révèlent des éléments liés à l’ordre général permettant ainsi la mise en évidence des tendances structurelles de la société postcommuniste.; This thesis presents an analysis of the process of post-communist transformation in Romania...

Malgré tous les efforts déployés sur les unités de soins intensifs (USI) pour maintenir en vie les patients admis, plusieurs statistiques rapportent un nombre important de décès chaque année sur ces unités. Comme il arrive que le décès ne soit pas soudain, les traitements de soutien pour la vie doivent donc se transformer en soins de fin de vie. Les pratiques et expertises n’étant pas les mêmes sur une unité de soins palliatifs que sur une USI, tout comme les besoins des patients et des membres de sa famille sont différents, c’est ainsi que, lorsque vient le temps d’envisager et d’offrir des soins de fin de vie sur une USI, il est nécessaire de procéder à des ajustements dans les pratiques de soins afin de bien accompagner ces personnes devant leur nouvelle réalité. L’objectif de ce travail sera donc de proposer un modèle d’accompagnement des patients et des membres de leur famille lors de la transition vers les soins de fin de vie sur les USI. Pour se faire, une recension des écrits, pratiquée à l’aide de la méthode intégrative de Whittmore et Knafl (2005), a permis d’identifier différentes théories, approches et modèles proposés par différents chercheurs et auteurs. Le cadre de référence choisi aux fins de ce travail sera la théorie de la transition de Meleis. Après un examen attentif des écrits...

The mass spectra and fragmentation of a variety of fluoroaromatic compounds of Group V and some selected transition elements are discussed in some detail, aided by data from metastable defocussed experiments. Results of ,studies on the coupling reaction using unstable organotitanium chloride intermediate species are reported. The preparation of some 5-substituted octafluorodibenzophospho1es is also discussed. Rearrangements under electron bombardment resulting in the loss of heteroatom-fluoride fragments are discussed in the light of presently accepted mechanisms for these processes as are rearrangements observed in compounds involving thionophosphoryl bonds ( p=s ).

Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T. New phase diagrams created for Hf, Ti and Zr from experimental data. P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled). All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature). Complete thermodynamic data for selected elements from standard to extreme conditions. The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software...

Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents:^ • An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K).^ • An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T.^ • New phase diagrams created for Hf, Ti and Zr from experimental data.^ • P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope.^ • New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams.^ • First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled); All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature); Complete thermodynamic data for selected elements from standard to extreme conditions.^ The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software...

Density functional calculations were performed to determine equilibrium geometrical structures, transition states and relative energies for M(3) clusters (M = Nb, Mo, Tc, Ru, Rh, Pd, Ag) reacting with CO, leading to proposed reaction pathways. For the Nb(3), Mo(3), and Tc(3) clusters, the lowest energy structure correlates to dissociated CO, with the C and O atoms bound on opposite sides of the metal triangle. For all other trimers, the lowest energy structures maintain the CO moiety. In the case of Pd(3) and Ag(3) the dissociated geometries lie higher in energy than the sum of the separated reactants. In most cases, several multiplicities were found to be similar in energy and for Mo(3)CO and Pd(3)CO singlet-triplet minimum energy crossing points were identified. In the case of Rh(3)CO, minimum energy crossing points for the doublet, quartet, and sextet reaction pathways were determined and compared. The electron densities of pertinent M(3)CO species were investigated using Natural Bond Order calculations. It was found that the effect of the metal trimer on the energy of the pure p-type pi* antibonding orbital of carbon monoxide directly correlates with the occurrence of CO dissociation.; Matthew A. Addicoat, Mark A. Buntine, Brian Yates...

The influence of substitutional alloying elements (Al, Nb and W) on the mechanical properties of MoSi₂ with both C11b and C40 structures was explored by first principles calculations. Using the shear modulus/bulk modulus ratio (G/B), Poisson’s ratio and Peierls stress, the change in the mechanical properties of the C40 and C11b structured MoSi₂ due to the addition of the solute atom has been investigated. The results showed that the ductility of C11b MoSi₂ was increased by alloying with the elements (Al and Nb) that form a C40 structured disilicide but decreased by alloying with the elements (W) that form a C11b structured disilicide. In contrast, the effect of alloying elements on the ductility of C40 MoSi₂ showed a reverse trend to that of C11b MoSi₂.; J. Xu, J. D. Wu, D. H. Lai, Z. H. Xie and P. Munroe

1. Distribution of trace elements between biotite and hydrous granitic melt. The synthetic system haplogranite-anorthite-biotite-H2O, doped with a suite of trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Sr, Ba, Mo, W, Nb, Ta, REE, Pb and Zr) was experimentally investigated over the temperature interval of 700-800°C at 200 MPa (H2O) to study the distribution of trace elements between biotite and coexisting hydrous melt. The starting materials were a series of volatile-free synthetic glasses obtained by heating a mixture of appropriate reagent grade chemicals (oxides, carbonates or hydroxides) corresponding to ~76 wt% haplogranite (35 wt% SiO2, 40 wt% NaAlSi3O8 and 25 wt% KAlSi3O8), ~8 wt% anorthite, ~15 wt% biotite (with a 1:1 molar ratio of Mg/Fe) and ~1 wt% total trace elements, so selected as to avoid peak interference during microprobe analysis. Experiments were carried out under water-saturated conditions in cold-seal autoclaves with run durations of between 35 and 45 days. The oxygen fugacity was close to the Ni-NiO buffer. Run products were analysed by electron microprobe. Besides biotite, run products contained other phases including amphibole (hornblende), clino-pyroxene, plagioclase, magnetite, allanite and glass. Measured partition coefficients indicate that most alkalis...

ABSTRACT: To what extent what is known as “literature of the self” is a useful historical source? In what way does it allow to know about the historical reality? What benefits can a historian derive from its use? In this essay we try to find answers to all these questions. For this purpose, we will use the “Spanish Transition” case, one of the most important events in our recent history and, at the same time, the most recalled by this genre. Firstly, we will carry out a theoretical and methodological review of the problematic and the history of the “ literatura of the self ”. Secondly we will analyze the different autobiographies and political memoirs of the Spanish Transition main protagonists. We will approach them from the perspective of “confessional reading”, watching the self-constructions made by the authors and their aim by doing so. We will also study the different constructions of “collective self” built by generational, political or regional shared visions, which are really important elements to convey the feeling of a time period. Finally, we will scrutinize them from the perspective of “documentary reading”, by analyzing the information that they provide and how it can be used. This will be done in order to understand their author's diverse conceptions of the Transition to democracy as a specific historical time...

The linear global instability and resulting transition to turbulence induced by an isolated cylindrical roughness element of height h and diameter d immersed within an incompressible boundary layer flow along a flat plate is investigated using the joint application of direct numerical simulations and fully three-dimensional global stability analyses. For the range of parameters investigated, base flow computations show that the roughness element induces a wake composed of a central low-speed region surrounded by a three-dimensional shear layer and a pair of low- and high-speed streaks on each of its sides. Results from the global stability analyses highlight the unstable nature of the central low-speed region and its crucial importance in the laminar–turbulent transition process. It is able to sustain two different global instabilities: a sinuous and a varicose one. Each of these globally unstable modes is related to a different physical mechanism. While the varicose mode has its root in the instability of the whole three-dimensional shear layer surrounding the central low-speed region, the sinuous instability turns out to be similar to the von Kármán instability in the two-dimensional cylinder wake and has its root in the lateral shear layers of the separated zone. The aspect ratio of the roughness element plays a key role on the selection of the dominant instability: whereas the flow over thin cylindrical roughness elements transitions due to a sinuous instability of the near-wake region...

We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, Mn with the sp elements N, P, As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends of half-metallicity, present the calculated equilibrium lattice constants, and examine the half-metallic behavior of their transition element terminated (001) surfaces.; Comment: 2nd Version: lattice constants calculations added, text revised

For a given crystal structure, say body-centred-cubic, the many-body Hamiltonian in which nuclear and electron motions are to be treated from the outset on the same footing, has parameters, for the elements, which can be classified as (i) atomic mass M, (ii) atomic number Z, characterizing the external potential in which electrons move, and (iii) bcc lattice spacing, or equivalently one can utilize atomic volume, Omega. Since the thermodynamic quantities can be determined from H, we conclude that Tc, the superconducting transition temperature, when it is non-zero, may be formally expressed as Tc = Tc^(M) (Z, Omega). One piece of evidence in support is that, in an atomic number vs atomic volume graph, the superconducting elements lie in a well defined region. Two other relevant points are that (a) Tc is related by BCS theory, though not simply, to the Debye temperature, which in turn is calculable from the elastic constants C_{11}, C_{12}, and C_{44}, the atomic weight and the atomic volume, and (b) Tc for five bcc transition metals is linear in the Cauchy deviation C* = (C_{12} - C_{44})/(C_{12} + C_{44}). Finally, via elastic constants, mass density and atomic volume, a correlation between C* and the Debye temperature is established for the five bcc transition elements.; Comment: EPJB...

In quadricovalent complexes of transition elements (Ni^(II), Pd^(II), Pt^(II), Au^(III), Ag^(II), Cu^(II)) the central atom uses four s or d orbitals of its outer shell for unshared electron pairs and two s or d and two p orbitals for bond formation. The problem here is to find the strongest possible four hybrid bond orbitals obtained by combining the two s—d and the two p orbitals available for bond formation. The strongest bond orbitals thus obtained are directed from the middle towards the four corners of a square, as it is expected from experimental evidence; they are composed of 4/9 s, 14/9 d, and two p orbitals, the strength being 2.943. These strongest possible orbitals are presumably used in complex of Ni^(II), Pt^(II), Au^(III), and Cu^(II), but probably not in complexes of Pd^(II) and Ag^(II); in the latter two cases there must be assumed square bond orbitals of composition s^nd^(2−n)p^2 with n somewhere between 1 and 4/9, i.e., orbitals of character between that of the strongest square bond orbitals of composition s^(4/9)d^(14/9)p^2 mentioned above and that of sdp^2 square orbitals discovered by Pauling.

Fracture toughness characterization of ferritic steels in the ductile to brittle transition region is problematic due to the observed scatter. This scatter makes not possible to obtain a single toughness value, although some statistical methods presented in the literature allow to manage it and indeed to have a lower bound value. The ability of some of these proposals to give a technological lower bound value from experimental sets of data was studied. Data from literature and our research were used for this purpose. One hundred random combinations of reduced number of elements from each data set were taken, repeating this procedure for different number of elements. The lower bound value dependence on sample size and the minimum number of specimens needed for a technological lower bound value determination were studied. The SPRÖDZON Method seems to give the best estimation of a technological lower bound LB.