Doorway States and Billiards

Whenever a distinct state is immersed in a sea of complicated and dense states, the strength of the distinct state, which we refer to as a doorway, is distributed in their neighboring states. We analyze this mechanism for 2-D billiards with different geometries. One of them is symmetric and integrable, another is symmetric but chaotic, and the third has a capricious form. The fact that the doorway-state mechanism is valid for such highly diverse cases, proves that it is robust.Comment: 7 pages, 6 figures, Accepted in Proceedings of "Symmetries in Nature", Symposium in Memoriam Marcos Moshinsk

A q-deformed Aufbau Prinzip

A building principle working for both atoms and monoatomic ions is proposed in this Letter. This principle relies on the q-deformed chain SO(4) > G where G = SO(3)_q

Monte Carlo Analysis of a New Interatomic Potential for He

By means of a Quadratic Diffusion Monte Carlo method we have performed a comparative analysis between the Aziz potential and a revised version of it. The results demonstrate that the new potential produces a better description of the equation of state for liquid $^4$He. In spite of the improvement in the description of derivative magnitudes of the energy, as the pressure or the compressibility, the energy per particle which comes from this new potential is lower than the experimental one. The inclusion of three-body interactions, which give a repulsive contribution to the potential energy, makes it feasible that the calculated energy comes close to the experimental result.Comment: 36 pages, LaTex, 11 PostScript figures include

Modulation of calcification of vascular smooth muscle cells in culture by calcium antagonists, statins, and their combination

Background Vascular calcification is an organized process in which vascular smooth muscle cells (VSMCs) are implicated primarily. The purpose of the present study was to assess the effects of calcium antagonists and statins on VSMC calcification in vitro. Methods VSMC calcification was stimulated by incubation in growth medium supplemented with 10 mmol/l β-glycerophosphate, 8 mmol/l CaCl2, 10 mmol/l sodium pyruvate, 1 μmol/l insulin, 50 μg/ml ascorbic acid, and 100 nmol/l dexamethasone (calcification medium). Calcification, proliferation, and apoptosis of VSMCs were quantified. Results Calcium deposition was stimulated dose-dependently by β-glycerophosphate, CaCl2, and ascorbic acid (all P < 0.01). Addition of amlodipine (0.01–1 μmol/l) to the calcification medium did not affect VSMC calcification. However, atorvastatin (2–50 μmol/l) stimulated calcium deposition dose-dependently. Combining treatments stimulated calcification to a degree similar to that observed with atorvastatin alone. Both atorvastatin and amlodipine inhibited VSMC proliferation at the highest concentration used. Only atorvastatin (50 μmol/l) induced considerable apoptosis of VSMCs. Conclusion In vitro calcification of VSMCs is not affected by amlodipine, but is stimulated by atorvastatin at concentrations ≥10 μmol/l, which could contribute to the plaque-stabilizing effect reported for statins

β1-integrins signaling and mammary tumor progression in transgenic mouse models: implications for human breast cancer

Consistent with their essential role in cell adhesion to the extracellular matrix, integrins and their associated signaling pathways have been shown to be involved in cell proliferation, migration, invasion and survival, processes required in both tumorigenesis and metastasis. β1-integrins represent the predominantly expressed integrins in mammary epithelial cells and have been proven crucial for mammary gland development and differentiation. Here we provide an overview of the studies that have used transgenic mouse models of mammary tumorigenesis to establish β1-integrin as a critical mediator of breast cancer progression and thereby as a potential therapeutic target for the development of new anticancer strategies

The Presidency and the Executive Branch in Latin America: What We Know and What We Need to Know

The presidential politics literature depicts presidents either as all- powerful actors or figureheads and seeks to explain outcomes accordingly. Th e president and the executive branch are nonetheless usually treated as black boxes, particularly i n developing countries, even though the presidency has evolved into an extremely complex branch of government. While these developments have been studied in the U nited States, far less i s known in other countries, particularly in Latin America, where presi dential systems have been considered the source of all goods and evils. To help close the knowledge gap and explore differences in policymaking characteristics not only between Latin America and the US but also across Latin American countries, this paper s ummarizes the vast literature on the organization and resources of the Executive Branch in the Americas and sets a research agenda for the study of Latin American presidencies.Fil: Bonvecchi, Alejandro. Universidad Torcuato Di Tella. Departamento de Ciencia Política y Estudios Internacionales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scartascini, Juan Carlos. Banco Interamericano de Desarrollo; Estados Unido

Un point de vue théorique sur la catalyse

Les calculs mécanoquantiques en général, et en particulier ceux qui se font au niveau strictement ab initio, dirigés pour l'étude des processus catalytiques, deviennent de plus en plus courants. Dans ce travail nous présentons une révision de quelques-uns de ces efforts ; spécialement ceux qui veulent éclairer la liaison métal-oléfine, la chimisorption sur des surfaces métalliques et les mécanismes des réactions catalytiques avec des complexes organométalliques. Nous mettons en relief surtout les aspects qui montrent le plus nettement la possibilité d’une collaboration fructueuse entre l’expérimentateur et le théoricien dans le problème complexe de la catalyse

THE PSEUDO-ATOM : A SOLUBLE MANY BODY PROBLEM

Si on néglige tous les effets relativistes, un atome ou plus généralement un ion de charge Z, est un système de n fermions de spin 1/2 qui sont dans un potentiel coulombien attractif et interagissent par l'intermédiaire d'une force de Coulomb répulsive. Comme ce problème n'a pas de solution exacte pour n > 1, un grand nombre de techniques d'approximation ont été employées dans son étude et, dans beaucoup de cas, sans qu'il soit fait une analyse critique suffisante. Dans cet article on remplace le potentiel coulombien commun par un oscillateur harmonique attractif et la force d'interaction par un oscillateur harmonique répulsif. Le modèle qui en résulte, que nous appelons pseudo-atome, peut être résolu exactement pour n'importe quelle valeur de n. On applique alors à ce problème des procédés d'approximation basés sur les méthodes de perturbation, de variation, de Hartree-Fock, de la variance, de la matrice densité, etc... On discute, dans toutes ces méthodes, la convergence vers les valeurs exactes de l'énergie et de la fonction d'onde, tout d'abord pour n = 2 électrons, ensuite pour des pseudo-atomes à couches complètes, et ceci jusqu'à 112 électrons.If we disregard any relativistic effects, an atom, or more generally an ion of charge Z, is a system of n fermions of spin 1/2 which are in an attractive Coulomb potential and interact through a repulsive Coulomb force. As this problem is not exactly soluble for any n > 1, a large number of approximation techniques have been used in its discussion in many cases without sufficient critical analysis. In the present paper we replace the Coulomb common potential by an attractive harmonic oscillator and the interacting force by a repulsive harmonic oscillator. The resulting model which we call a pseudo-atom can be solved exactly for any n. We then proceed to apply to this problem approximation procedures such as those based on perturbation, variation, Hartree-Fock, variance, density matrix, etc. methods. We discuss the convergence of all these methods to the exact energy and wave function, first for n = 2 electrons and then for closed shell pseudo-atoms that go up to 112 electrons

Theoretical study of the CuRu+H-2 molecular interaction

The results of Hartree-Fock (with relativistic effective core potentials) followed by variational and second-order multireference perturbational configuration interaction (CIPSI) calculations are reported for the nine lowest-lying electronic states of the CuRu molecule and the eight low-lying states of the CuRuH2 molecule belonging to the C-2v symmetry group which evolve from the H-2 side-on interaction with the ruthenium atom. The effect of the copper atom on the ability of the ruthenium atom toward the capture and dissociation of the H-2 molecule is analyzed through comparison with the results previously reported for the simpler systems RuH2 and RuH2+. For all the reaction channels investigated here, the copper atom depresses the ability of ruthenium to dissociate the H-2 molecule. (C) 2001 Published by Elsevier Science B.V