Updated Nucleosynthesis Constraints on Unstable Relic Particles

We revisit the upper limits on the abundance of unstable massive relic particles provided by the success of Big-Bang Nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, he3, he4, li6 and li7. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of he4 and li6 exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh ~100 GeV, their primordial abundance should have been below about 10^{-13} of the total entropy. This would imply an upper limit on the reheating temperature of a few times 10^7 GeV, which could be a potential difficulty for some models of inflation. We discuss possible ways of evading this problem.Comment: 40 pages LaTeX, 18 eps figure

DESARROLLO DE UN INDICADOR DE PERCEPCIÓN EMPRESARIAL DEL RIESGO DEL ENTORNO POLÍTICO

El objetivo del estudio es el de desarrollar un indicador de percepción empresarial del riesgo del entorno político, que aborde en profundidad las dimensiones que conforman el riesgo político en Latinoamérica. El estudio se realiza en cuatro fases: primero revisión bibliográfica, segundo desarrollo del concepto “Percepción empresarial del riesgo político”, tercero el instrumento para medir el “Índice de percepción empresarial de riesgo político” y cuarto la aplicación del instrumento. Este último arrojó un importante nivel de riesgo político percibido. El desarrollo de esta investigación permitirá optimizar las herramientas de la teoría de la administración para abordar la problemática de detectar las oportunidades y amenazas de su entorno político.AbstractDevelopment a business indicator of risk perception of political environmentThe purpose of this study is to develop an Indicator of Business Risk Perception of Political Environment, to address in depth the dimensions that  build up the political risk in Latin America. The result is presented in four stages: first bibliography review, second the development of the concept "Business Perceptions of Political Risk", third the instrument for measuring the "Index of Political Risk Perception Enterprise", and fourth application of the instrument. The latter showed a significant level of perceived political risk. The development of this research allows to optimize the tools of management theory to identify key opportunities and threats to their political environment

Desarrollo de un indicador de percepción empresarial del riesgo del entorno político

El objetivo del estudio es el de desarrollar un indicador de percepción empresarial del riesgo del entorno político, que aborde en profundidad las dimensiones que conforman el riesgo político en Latinoamérica. El estudio se realiza en cuatro fases: primero revisión bibliográfica, segundo desarrollo del concepto ¿Percepción empresarial del riesgo político¿, tercero el instrumento para medir el Índice de percepción empresarial de riesgo político y cuarto la aplicación del instrumento. Este último arrojó un importante nivel de riesgo político percibido. El desarrollo de esta investigación permitirá optimizar las herramientas de la teoría de la administración para abordar la problemática de detectar las oportunidades y amenazas de su entorno político

TRANSITION-METAL COMPLEXES OF THE NOVEL TRIDENTATE DI-2-PYRIDYLMETHANAMINE (DIPA)

The first row transition metal complexes [M(dipa)2]n+ (dipa = di-2-pyridylmethanamine, M = Fe(III), Fe(II), Co(III), Ni(II) and Cu(II)) have been synthesized in generally high yields. Stability constants for the labile Co(II), Ni(II), and Cu(II) complexes have been determined by potentiometric titrations and are as follows (log K1, log K2): 7.63 (1), 6.57 (1); 8.55 (1), 8.25 (1); and 8.89 (1), 7.94 (1). A rather large degree of steric strain within the complexes is evident from the X-ray crystal structures of rac-[Fe(dipa)2](ClO4)2.2H2O (monoclinic, P2(1)/n, a = 9.392 (3) angstrom, b = 16.749 (3) angstrom, c = 17.131 (14) angstrom, beta = 96.62 (5)-degrees, Z = 4) rac-[Co(dipa)2](ClO4)3 (orthorhombic, Pcca, a = 17.574 (5) angstrom, b = 8.568 (2) angstrom, c = 19.159 (3) angstrom, Z = 4), meso-[Ni(dipa)2](S2O6).4H2O (triclinic, P1BAR, a = 7.903 (3) angstrom, b = 9.810 (3) angstrom c = 10.900 (2) angstrom, alpha = 113.10 (3)-degrees, beta = 106.01 (3)-degrees, gamma = 96.93 (4)-degrees, Z = 1), and meso- [Cu(dipa)2] (ClO4)2 (monoclinic, P2(1)/n, a = 7.964 (3) angstrom, b = 10.1 54 (2) angstrom, c = 16.842 (4) angstrom, beta = 100.12 (4)-degrees, Z = 2). Molecular mechanics calculations indicate that the formation of rac-[Co(dipa)2]3+ in preference to the meso isomer is dominant, and this is in agreement with experimental results based on NMR spectra of equilibrated solutions. In the case of Cu(II), formation of the meso isomer is not selective, and this was confirmed by the successful Cu(II)-directed template condensation of the rac isomer with formaldehyde and nitroethane. Calculations also indicate that the rac isomer of the Ni(II) complex is more stable than the crystallized meso isomer