No abstract available

[en] Hall coefficient and electrical resistivity values are reported for Pb-In solid solutions thin films (≅ 170 nm). It is found that R_H varies from the small positive value of Pb to negative values, reaching its maximum value (negative) at a concentration of about 80 at. % In. The change from positive to negative occurs at a concentration of about 16 at. % In. The superconducting transition temperature as a function of concentration was also measured for Pb rich samples. (Author)

[en] The problem of bringing experimental electron-scattering cross sections to the absolute scale using the so-called Lassettre theorem is addressed. Experimental data that have been measured by electron-scattering experiments for different incident energies (in the range of 100 to 600 eV) and have been normalized on the basis of this theorem are compared with absolute cross sections that have been calculated within the first Born approximation by means of the complex-scaling method. The agreement is not found to be satisfactory even for the smallest values of momentum transfer. This, however, is a contradiction to Lassettre's theorem. A new normalization procedure for the experimental data is suggested that has yielded good agreement between the present calculated and the measured data even for a comparatively large range of momentum transfer. This indicates an extended range of validity of the first Born approximation. (Author)

[en] A theoretical approach was developed that allows for a full numerical description of a pair of ultracold atoms trapped in a three-dimensional optical lattice. This approach includes the possible coupling between centre-of-mass and relative motion coordinates in a configuration-interaction type formulation. The atoms are allowed to interact by their full interaction potential that is, presently, only limited to be central. With the aid of the newly developed method deviations from the harmonic approximation are discussed for the heteronuclear ⁸⁷Rb-⁴⁰K pair

[en] Consider a fast nonrelativistic, positively charged particle (ion) traversing a crystal, assumed to be simple cubic and monatomic for simplicity. Let the Cartesian coordinates X₁,X₂,X₃ be parallel to the crystal axes, and η_i be the initial value of the component of the particle's momentum vector along X_i. If vertical bar η₃ vertical bar is sufficiently large compared to vertical bar η₁ vertical bar, vertical barη₂ vertical bar, then (under mild technical assumptions) the ion's motion is well approximated for a long time by a solution of the equations of motion (EOM) of the axial-continuum Hamiltonian H, obtained from the ion's nonrelativistic Hamiltonian H by replacing the potential V(X₁,X₂,X₃), describing its interaction with the atoms of the crystal, by its average V(X₁,X₂) over X₃. Furthermore, if vertical bar η₂ vertical bar, vertical bar η₃ vertical bar are sufficiently large compared with vertical bar η₁ vertical bar, vertical bar η₂ vertical bar, respectively, then to a good approximation its motion is given, again for a long time, by a solution of the EOM of the planar continuum Hamiltonian H, obtained from H by replacing V(X₁,X₂) by its average V(X₁) over X₂. We define motions of the first (respectively, second) type as axial (respectively, planar) channeling. In this paper, the transition from the first to the second kind of motion, occurring when the crystal is suitably rotated, is discussed in a mathematically rigorous way by using an improved version of first-order single-phase averaging theory

[en] The probability distribution of electronic excitations of HeT⁺ following the β decay of the T₂ molecule has been calculated for the first time in the beyond sudden impulse approximation, removing the uncertainty related to the reliability of this approximation in connection with the neutrino mass experiments. Final state interactions are introduced to infinite order with respect to the decaying nucleus, and to first order with respect to all other particles, within the relativistic framework. The presented distribution features, in addition, corrections due to the nuclear motion, resonant structure, and long tail (up to 800eV) in the ionization continuum of HeT⁺. copyright 1996 The American Physical Society

[en] Activating mutations in the RET gene leads to medullary thyroid carcinoma (MTC). Guidelines encourage performing RET analysis in subjects with hereditary and sporadic disease. Materials and Methods. Design. Observational, case series report study. Patients. Subjects diagnosed with MTC, with a thyroidectomy performed in a single center in Costa Rica between the years 2006 and 2015. Diagnosis and Follow-Up. Pre- and postoperative calcitonin, RET mutation, and neck ultrasound and tomography were obtained. Results. 21 subjects with histological diagnosis of MTC were followed up. The average age at diagnosis was 52.0 ± 15.7 years. The preoperative mean value of calcitonin was 1340 ± 665 pg/mL. Evidence of RET mutation was found in 26.3% of the patients, with only 2 of them grouped in the same kindred. We found statistically significant differences in mean ages between mutated (38.4 ± 20.2 y) versus non mutated RET gene (54.6 ± 11.8 y (P=0.04). There were no significant differences regarding tumor size, metastases, and surgical reintervention. Conclusions. We report the results of RET mutation analysis in subjects with MTC in a single center of Costa Rica. The availability of this tool increases the probability of identifying familial MTC, with the benefit of detecting affected subjects and their relatives at an earlier age.

[en] The final-state distribution of HeT⁺ resulting from the β decay of molecular tritium has been investigated with particular emphasis on its reliability in connection with the interpretation of the tritium neutrino-mass experiments. This investigation concentrates on two aspects. First, the reliability within the sudden approximation is examined. This includes the extension of previously calculated final-state distributions to a larger range of energy transfer, i.e., to an excitation energy of 800 eV, the investigation of the effect of nuclear motion on the continuous electronic spectrum, and the use of improved basis sets. Second, the molecular transition-probability spectrum (including electronic bound and continuous states) has been calculated for the first time in a beyond sudden-impulse approximation. It is concluded that the concomitant corrections are too small to explain the problems of recent experiments difficulties to extract the neutrino mass out of the β spectrum of T₂. copyright 1997 The American Physical Society

[en] In this work the β decay of a nucleus hosted in an atomic or a molecular system is considered. A formalism is derived that allows the calculation of the changes in the β spectrum that are caused by the Coulombic final-state interaction of the β electron (or positron) with all molecular electrons as well as nuclei. Explicit formulas are derived for the matrix elements occurring in a perturbational treatment up to the pure first-order correction term, and different approximations are discussed. The result obtained in this work is especially applicable to cases where the decaying nucleus is part of a molecular system. In contrast to previous works a complete partial-wave analysis of the interaction operator has been performed, and for the first time explicit results are derived for all partial waves. The total symmetric contribution agrees (for atoms) with previous results and confirms the early work of Rose. However, the nonspherical contributions are of the same order of magnitude as the total symmetric contribution and have therefore to be taken into account, if the Rose correction is applied. This can be done in a very simple way, since the correction turns out to be (approximately) proportional to the number of electrons but otherwise completely independent of the atomic or molecular system under consideration. In the case of molecular systems also the contribution of the spectator nuclei has to be considered, since this contribution is again of the same order of magnitude as the correction term given by Rose. It is shown that the interaction with the decaying nucleus (that leads to the occurrence of the Fermi function) is very well approximated within the present perturbational approach, where it is treated in the same way as the interaction with the other particles. copyright 1997 The American Physical Society

[en] Thin films (of the order of nm) of Al-Cr alloys were prepared by successive depositions by an electron gun in a vacuum chamber. Three Al and two Cr layers, of thicknesses as to yield the final composition, were deposited on both hot (350 C and 440 C) and cold (70 C and 108 C) substrates and the phases formed were characterized in each case by X-ray diffraction and TEM observations, both in bright and in dark field conditions. The results show that on the hot substrates, Bragg peaks that do not correspond to any reported crystalline or quasi-crystalline phase appear. Both the samples on cold substrates and those heated afterwards showed an amorphous structure by X-ray diffractometry but TEM demonstrated the presence of tiny faulted crystallites, with the same Bragg reflections than those deposited on hot substrates. The results show that, for the composition range studied, a new phase not reported before appears and the substrate temperature only produces crystallite growth, not the formation of new phases. (orig.)