Influence of composition on the structure, electric and magnetic properties of Pd-Mn-P and Pd-Co-P amorphous alloys

The influence of composition on the structure and on the electric and magnetic properties of amorphous Pd-Mn-P and Pd-Co-P prepared by rapid quenching techniques were investigated in terms of (1) the 3d band filling of the first transition metal group, (2) the phosphorus concentration effect which acts as an electron donor and (3) the transition metal concentration.

The structure is essentially characterized by a set of polyhedra subunits essentially inverse to the packing of hard spheres in real space. Examination of computer generated distribution functions using Monte Carlo random statistical distribution of these polyhedra entities demonstrated tile reproducibility of the experimentally calculated atomic distribution function. As a result, several possible "structural parameters" are proposed such as: the number of nearest neighbors, the metal-to-metal distance, the degree of short-range order and the affinity between metal-metal and metal-metalloid. It is shown that the degree of disorder increases from Ni to Mn. Similar behavior is observed with increase in the phosphorus concentration.

The magnetic properties of Pd-Co-P alloys show that they are ferromagnetic with a Curie temperature between 272 and 399°K as the cobalt concentration increases from 15 to 50 at.%. Below 20 at.% Co the short-range exchange interactions which produce the ferromagnetism are unable to establish a long-range magnetic order and a peak in the magnetization shows up at the lowest temperature range . The electric resistivity measurements were performed from liquid helium temperatures up to the vicinity of the melting point (900°K). The thermomagnetic analysis was carried out under an applied field of 6.0 kOe. The electrical resistivity of Pd-Co-P shows the coexistence of a Kondo-like minimum with ferromagnetism. The minimum becomes less important as the transition metal concentration increases and the coefficients of ℓn T and T^2 become smaller and strongly temperature dependent. The negative magnetoresistivity is a strong indication of the existence of localized moment.

The temperature coefficient of resistivity which is positive for Pd- Fe-P, Pd-Ni-P, and Pd-Co-P becomes negative for Pd-Mn-P. It is possible to account for the negative temperature dependence by the localized spin fluctuation model and the high density of states at the Fermi energy which becomes maximum between Mn and Cr. The magnetization curves for Pd-Mn-P are typical of those resulting from the interplay of different exchange forces. The established relationship between susceptibility and resistivity confirms the localized spin fluctuation model. The magnetoresistivity of Pd-Mn-P could be interpreted in tenns of a short-range magnetic ordering that could arise from the Rudennan-Kittel type interactions.

Radiation from a short electric dipole antenna in a hot uniaxial plasma

The effects of electron temperature on the radiation fields and the resistance of a short dipole antenna embedded in a uniaxial plasma have been studied. It is found that for ω < ω_p the antenna excites two waves, a slow wave and a fast wave. These waves propagate only within a cone whose axis is parallel to the biasing magnetostatic field B_o and whose semicone angle is slightly less than sin ^(-1) (ω/ω_p). In the case of ω > ω_p the antenna excites two separate modes of radiation. One of the modes is the electromagnetic mode, while the other mode is of hot plasma origin. A characteristic interference structure is noted in the angular distribution of the field. The far fields are evaluated by asymptotic methods, while the near fields are calculated numerically. The effects of antenna length ℓ, electron thermal speed, collisional and Landau damping on the near field patterns have been studied.

The input and the radiation resistances are calculated and are shown to remain finite for nonzero electron thermal velocities. The effect of Landau damping and the antenna length on the input and radiation resistances has been considered.

The radiation condition for solving Maxwell's equations is discussed and the phase and group velocities for propagation given. It is found that for ω < ω_p in the radial direction (cylindrical coordinates) the power flow is in the opposite direction to that of the phase propagation. For ω > ω_p the hot plasma mode has similar characteristics.

Optimization of nonvolatile holographic recording by application of an external electric field

The dependences of the recording properties of LiNbO3:Fe:Mn crystals on an external electric field (applied in the recording or fixing phase of the nonvolatile holographic recording process) are numerically investigated and the optimal conditions for applying an external electric field in this two-step process of nonvolatile holographic recording are discussed in detail. Significant improvement of the photorefractive performance has been found and experimental verifications using a small external electric field are described. Moreover, direct measures relating to the dominant photovoltaic mechanism in the doubly doped LiNbO3 crystals and the unconventional grating-enhanced fixing are revealed by applying an external electric field in the recording and the fixing phases, respectively.

Improvement in refractive-index change in LiNbO3 : Ce : Cu by applying an external electric field

By jointly solving two-centre material equations with a nonzero external electric field and coupled-wave equations, we have numerically studied the dependence of the non-volatile holographic recording in LiNbO3:Ce:Cu crystals on the external electric field. The dominative photovoltaic effect of the non-volatile holographic recording in doubly doped LiNbO3 crystals is directly verified. And an external electric field that is applied in the positive direction along the c-axis (or a large one in the negative direction of the c-axis) in the recording phase and another one that is applied in the negative direction of the c-axis in the fixing phase are both proved to benefit strong photorefractive performances. Experimental verifications are given with a small electric field applied externally.

Modelización acústica del interior de un Tren de Alta Velocidad

[ES]El presente Trabajo de Fin de Grado, titulado ‘Modelización Acústica del Interior de un Tren de Alta Velocidad’, tiene como objetivo el análisis acústico a bajas frecuencias del habitáculo de un coche de un tren de alta velocidad. La temática ha sido elegida debido a la creciente presencia de trenes de alta velocidad en nuestro entorno, en los cuales el Control Acústico o de Ruidos es un aspecto muy importante para el confort del medio de transporte. Dentro de los ruidos por los que se ve afectado el tren, los de baja frecuencia son los más difíciles de tratar y controlar, y es por ello que van a constituir la línea de trabajo de este proyecto. La estructura de lo que se va a tratar en este proyecto es la siguiente: En primer lugar, se analizará el contexto en que se encuadra este proyecto y las razones que han llevado a su realización. Posteriormente, se explicarán los fundamentos teóricos que hay detrás de los análisis que se van a realizar. Más adelante se pasará al análisis del caso práctico que se ha elegido para ilustrar el proyecto: el habitáculo de un coche del tren Serie 120 de Renfe, construido por CAF [1, 2, 3]. Se realizarán tanto análisis modales como de respuesta forzada. Dicho ejemplo servirá de base para asentar las conclusiones y proponer la aplicación que se les puede dar a éstas, así como las líneas de investigación para las cuales este proyecto puede ser un punto de partida.

Part I. Electric birefringence studies of deoxyribonucleic acids. Part II. Selective dissociation of nucleohistone complexes

Part I

The electric birefringence of dilute DNA solutions has been studied in considerable detail and on a large number of samples, but no new and reliable information was discovered concerning the tertiary structure of DNA. The large number of variables which effect the birefringence results is discussed and suggestions are made for further work on the subject.

The DNA molecules have been aligned in a rapidly alternating (10 to 20 kc/sec) square wave field confirming that the orientation mechanism is that of counterion polarization. A simple empirical relation between the steady state birefringence, Δn_st, and the square of the electric field, E, has been found: Δn_st = E²/(a E² + b), where a = 1/Δn_s and b = (E²/Δn_st)_E→o. Δn_s is the birefringence extrapolated to infinite field strength.

The molecules show a distribution of relaxation times from 10^-4 to 0.2 sec, which is consistent with expectations for flexible coil molecules. The birefringence and the relaxation times decrease with increasing salt concentrations. They also depend on the field strength and pulse duration in a rather non-reproducible manner, which may be due in part to changes in the composition of the solution or in the molecular structure of the DNA (other than denaturation). Further progress depends on the development of some control over these effects.

Part II

The specificity of the dissociation of reconstituted and native deoxyribonucleohistones (DNH) by monovalent salt solutions has been investigated. A novel zone ultracentrifugation method is used in which the DNH is sedimented as a zone through a preformed salt gradient, superimposed on a stabilizing D₂O (sucrose) density gradient. The results, obtained by scanning the quartz sedimentation tubes in a spectrophotometer, were verified by the conventional, preparative sedimentation technique. Procedures are discussed for the detection of microgram quantities of histones, since low concentrations must be used to prevent excessive aggregation of the DNH.

The data show that major histone fractions are selectively dissociated from DNH by increasing salt concentrations: Lysine rich histone (H I) dissociates gradually between 0.1 and 0.3 F, slightly lysine rich histone (H II) dissociates as a narrow band between 0.35 and 0.5 F, and arginine rich histone (H III, H IV) dissociates gradually above 0.5 F NaClO₄.

The activity of the partially dissociated, native DNH in sustaining RNA synthesis, their mobility and their unusual heat denaturation and renaturation behavior are described. The two-step melting behavior of the material indicates that the histones are non-randomly distributed along the DNA, but the implications are that the uncovered regions are not of gene-size length.

Anomalous electric dipole internal conversion

Electric dipole internal conversion has been experimentally studied for several nuclei in the rare earth region. Anomalies in the conversion process have been interpreted in terms of nuclear structure effects. It was found that all the experimental results could be interpreted in terms of the j ∙ r type of penetration matrix element; the j ∙ ∇ type of penetration matrix element was not important. The ratio λ of the El j ∙ r penetration matrix element to the El gamma-ray matrix element was determined from the experiments to be:

Lu¹⁷⁵,396 keV, λ = - 1000 ± 100;

282 keV, λ = 500 ± 100;

144 keV, λ = 500 ± 250;

Hf¹⁷⁷, 321 keV λ = - 1400 ± 200;

208 keV λ = - 90 ± 40;

72 keV |λ| ≤ 650;

Gd¹⁵⁵, 86 keV λ = - 150 ± 100;

Tm¹⁶⁹, 63 keV λ = - 100 ± 100;

W¹⁸², 152 keV, λ = - 160 ±80;

67 keV, λ = - 100 ± 100.

Predictions for λ are made using the unified nuclear model.

I. Electronic processes in α-sulfur. II. Polaron motion in a D.C. electric field

Part I: The mobilities of photo-generated electrons and holes in orthorhombic sulfur are determined by drift mobility techniques. At room temperature electron mobilities between 0.4 cm²/V-sec and 4.8 cm²/V-sec and hole mobilities of about 5.0 cm²/V-sec are reported. The temperature dependence of the electron mobility is attributed to a level of traps whose effective depth is about 0.12 eV. This value is further supported by both the voltage dependence of the space-charge-limited, D.C. photocurrents and the photocurrent versus photon energy measurements.

As the field is increased from 10 kV/cm to 30 kV/cm a second mechanism for electron transport becomes appreciable and eventually dominates. Evidence that this is due to impurity band conduction at an appreciably lower mobility (4.10^-4 cm²/V-sec) is presented. No low mobility hole current could be detected. When fields exceeding 30 kV/cm for electron transport and 35 kV/cm for hole transport are applied, avalanche phenomena are observed. The results obtained are consistent with recent energy gap studies in sulfur.

The theory of the transport of photo-generated carriers is modified to include the case of appreciable thermos-regeneration from the traps in one transit time.

Part II: An explicit formula for the electric field E necessary to accelerate an electron to a steady-state velocity v in a polarizable crystal at arbitrary temperature is determined via two methods utilizing Feynman Path Integrals. No approximation is made regarding the magnitude of the velocity or the strength of the field. However, the actual electron-lattice Coulombic interaction is approximated by a distribution of harmonic oscillator potentials. One may be able to find the “best possible” distribution of oscillators using a variational principle, but we have not been able to find the expected criterion. However, our result is relatively insensitive to the actual distribution of oscillators used, and our E-v relationship exhibits the physical behavior expected for the polaron. Threshold fields for ejecting the electron for the polaron state are calculated for several substances using numerical results for a simple oscillator distribution.

1. Ultrasonic studies of binary liquid structure in the critical region. Theory and experiment for the 2,6-lutidine/water system. 2. Hartree-Fock calculations of electric polarizabilities of some simple atoms and molecules, and their practicality. 3. Calculation of vibrational transition probabilities in collinear atom-diatom and diatom-diatom collisions with Lennard-Jones interaction

Part 1. Many interesting visual and mechanical phenomena occur in the critical region of fluids, both for the gas-liquid and liquid-liquid transitions. The precise thermodynamic and transport behavior here has some broad consequences for the molecular theory of liquids. Previous studies in this laboratory on a liquid-liquid critical mixture via ultrasonics supported a basically classical analysis of fluid behavior by M. Fixman (e. g., the free energy is assumed analytic in intensive variables in the thermodynamics)--at least when the fluid is not too close to critical. A breakdown in classical concepts is evidenced close to critical, in some well-defined ways. We have studied herein a liquid-liquid critical system of complementary nature (possessing a lower critical mixing or consolute temperature) to all previous mixtures, to look for new qualitative critical behavior. We did not find such new behavior in the ultrasonic absorption ascribable to the critical fluctuations, but we did find extra absorption due to chemical processes (yet these are related to the mixing behavior generating the lower consolute point). We rederived, corrected, and extended Fixman's analysis to interpret our experimental results in these more complex circumstances. The entire account of theory and experiment is prefaced by an extensive introduction recounting the general status of liquid state theory. The introduction provides a context for our present work, and also points out problems deserving attention. Interest in these problems was stimulated by this work but also by work in Part 3.

Part 2. Among variational theories of electronic structure, the Hartree-Fock theory has proved particularly valuable for a practical understanding of such properties as chemical binding, electric multipole moments, and X-ray scattering intensity. It also provides the most tractable method of calculating first-order properties under external or internal one-electron perturbations, either developed explicitly in orders of perturbation theory or in the fully self-consistent method. The accuracy and consistency of first-order properties are poorer than those of zero-order properties, but this is most often due to the use of explicit approximations in solving the perturbed equations, or to inadequacy of the variational basis in size or composition. We have calculated the electric polarizabilities of H₂, He, Li, Be, LiH, and N₂ by Hartree-Fock theory, using exact perturbation theory or the fully self-consistent method, as dictated by convenience. By careful studies on total basis set composition, we obtained good approximations to limiting Hartree-Fock values of polarizabilities with bases of reasonable size. The values for all species, and for each direction in the molecular cases, are within 8% of experiment, or of best theoretical values in the absence of the former. Our results support the use of unadorned Hartree-Pock theory for static polarizabilities needed in interpreting electron-molecule scattering data, collision-induced light scattering experiments, and other phenomena involving experimentally inaccessible polarizabilities.

Part 3. Numerical integration of the close-coupled scattering equations has been carried out to obtain vibrational transition probabilities for some models of the electronically adiabatic H₂-H₂ collision. All the models use a Lennard-Jones interaction potential between nearest atoms in the collision partners. We have analyzed the results for some insight into the vibrational excitation process in its dependence on the energy of collision, the nature of the vibrational binding potential, and other factors. We conclude also that replacement of earlier, simpler models of the interaction potential by the Lennard-Jones form adds very little realism for all the complication it introduces. A brief introduction precedes the presentation of our work and places it in the context of attempts to understand the collisional activation process in chemical reactions as well as some other chemical dynamics.

Nos braços da lei: o uso daviolência negociada no interior das prisões

O presente estudo objetiva, a partir da narrativa do trabalhador prisional da SEAP-RJ, abordar em que situações e com base em quais justificativas esse profissional recorre ao uso da força física em seu cotidiano prisional. A rotina de trabalho dos agentes penitenciários é apresentada a partir de um estudo de caso realizado no Instituto Presídio Hélio Gomes. Nele, os relatos dos integrantes das turmas de guardas se constituíram em nossa principal fonte de informações. Em outra fase da pesquisa, o processo de formação profissional dos servidores prisionais admitidos em 2004, pela SEAP-RJ, foi acompanhado através das aulas ministradas na Escola de Gestão Penitenciária. Em ambos os casos, a observação participante foi o instrumento metodológico que me permitiu a coleta de dados e a interação com o grupo estudado. A narrativa está centrada no processo de socialização por que passam os servidores prisionais para se integrarem a (s) moralidade (s) vigente nas prisões. Sugere-se que a integração plena do operador da lei ao universo prisional, implique em sua socialização no mundo do crime. A possibilidade de uso da violência física como mecanismo de controle, em sua modalidade violência negociada, mostrou-se uma hipótese viável. Porém, ainda necessita de maiores comprovações empíricas, em especial junto aos internos penitenciários, para que possa ser formalmente validada.

Modelization and analysis of the electric arc in low voltage circuit breakers

246 p.

Electric and magnetic losses and gains in determining the sign of refractive index

Within the framework of classic electromagnetic theories, we have studied the sign of refractive index of optical medias with the emphases on the roles of the electric and magnetic losses and gains. Starting from the Maxwell equations for an isotropic and homogeneous media, we have derived the general form of the complex refractive index and its relation with the complex electric permittivity and magnetic permeability, i.e. n = root epsilon mu, in which the intrinsic electric and magnetic losses and gains are included as the imaginary parts of the complex permittivity and permeability, respectively, as epsilon = epsilon(r) + i(epsilon i) and mu = mu(r) + i mu(i). The electric and magnetic losses are present in all passive materials, which correspond, respectively, to the positive imaginary permittivity and permeability epsilon(i) > 0 and mu(i) > 0. The electric and magnetic gains are present in materials where external pumping sources enable the light to be amplified instead of attenuated, which correspond, respectively, to the negative imaginary permittivity and permeability epsilon(i) < 0 and mu(i) < 0. We have analyzed and determined uniquely the sign of the refractive index, for all possible combinations of the four parameters epsilon(r), mu(r), epsilon(i), and mu(i), in light of the relativistic causality. A causal solution requires that the wave impedance be positive Re {Z} > 0. We illustrate the results for all cases in tables of the sign of refractive index. One of the most important messages from the sign tables is that, apart from the well-known case where simultaneously epsilon < 0 and mu < 0, there are other possibilities for the refractive index to be negative n < 0, for example, for epsilon(r) < 0, mu(r) > 0, epsilon(i) > 0, and mu(i) > 0, the refractive index is negative n < 0 provided mu(i)/epsilon(i) > mu(r)/vertical bar epsilon(r)vertical bar. (c) 2006 Elsevier B.V. All rights reserved.

Modelización acústica del interior de un tren de alta velocidad.

[ES]El presente Trabajo de Fin de Grado titulado 'Modelización Acústica del Interior de un Tren de Alta Velocidad' tiene como tarea la realización de diversos análisis acústicos de un habitáculo de un coche ferroviario. El principal objetivo va a ser ofrecer una guía detallada a modo de manual de usuario para llevar a cabo dichos análisis sin necesitar información adicional. Las herramientas de ayuda a utilizar van a ser un programa CAD de diseño como Solid Edge ST6 o Catia V5 y un software de elementos finitos como Ansys.

Medidas radioeléctricas en el interior de edificios.

[ES]En este Trabajo de Fin de Grado se ha realizado una campaña de medidas basada en el cálculo de las pérdidas de propagación en interiores, para la frecuencia de 2 GHz, usada en sistemas móviles. Se han estudiado enlaces de 1 a 80 metros, realizando medidas a lo largo de la planta 4 del edificio B de la Escuela desde diferentes puntos. También se realiza un modelo de propagación completando el trabajo con la medida de las pérdidas de inserción introducidas por materiales y elementos usados en el interior de la Universidad. Para observar adecuadamente el trabajo se realiza una representación gráfica de los resultados obtenidos. Por último utilizando un software se modela el entorno físico de la planta y se comparan los resultados teóricos obtenidos con el caso práctico realizado.