Проблемы нуклеосинтеза. Куда исчез литий?

В данной статье рассматриваются проблемы нуклеосинтеза во Вселенной - процесса образованияядер химических элементов тяжелее водорода в ходе реакции ядерного синтеза. В статье анализируютсяактуальные научные работы, выдвигающие или опровергающие различные гипотезы, объясняющиевозможные причины дисбаланса лития во Вселенной. Проведенный анализ и составленный обзор научныхработ позволили сделать общий вывод о современном состоянии и перспективах исследований по проблеметеории большого взрыва.Im vorliegenden Artikel werden die Probleme der Nucleosynthese im Weltall - der Entstehung vonAtomkernen kurz nach dem Urknall - betrachtet. Im Artikel werden auch die neuesten wissenschaftlichen Arbeitenzum Thema "Abgleichfehler von Lithium im Universum", die verschiedene Hypothesen vom angegebenen Probleminterpretieren, analysiert. Aufgrund der durchgefuhrten Analyse wird die allgemeine Schlussfolgerung uber dasProblem von der Urknall-Theorie und die Perspektiven ihrer weiteren Erforschung gemacht

Risks and controls in the implementation of ERP systems

The implementation of ERP systems has been problematic for many organizations. Given the many reports of substantial failures, the implementation of packaged ERP software and associated changes in business processes has proved not to be an easy task. As many organizations have discovered, the implementation of ERP systems can be a monumental disaster unless the process is handled carefully. The aim of this study is to identify the risks and controls used in ERP implementations, with the objective to understand the ways in which organizations can minimize the business risks involved. By controlling and minimizing the major business risks in the first instance, the scene can be set for the successful implementation of an ERP system. The study was motivated by the significance, for both the research and practice communities, of understanding the risks and controls critical for the successful implementation of ERP systems. Following the development of a model of risks and controls, a field study of an ERP system implementation project in an organization was conducted to provide a limited test of the model. The results from the field study provided support for risks and controls identified in the literature. The results also identified several controls not mentioned in the reviewed literature. The study lays the foundation for further research into the risk/control framework so important for the success of the implementations of ERP systems.La implementación de los sistemas ERP ha sido problemática para muchas organizaciones. Dada la cantidad de informes sobre fallos considerables, la implementación de los paquetes de software ERP y los cambios asociados en los procesos de negocios han demostrado no ser tarea fácil. Como muchas organizaciones ya han descubierto, la implementación de los sistemas ERP pueden ser un desastre monumental a no ser que el proceso se lleve a cabo cuidadosamente. El objetivo de este estudio es identificar los riesgos y controles usados en las implementaciones de ERP, con el propósito de comprender la forma en que las organizaciones pueden minimizar los riesgos implicados en los negocios. Mediante el control y disminución de los riesgos en primer lugar, se puede preparar el escenario para una implementación exitosa de un sistema de ERP. El estudio fue motivado por la importancia de comprender y controlar los riesgos críticos (tanto para las comunidades de investigación como las que los practican), para la implementación exitosa de los sistemas ERP. Siguiendo el desarrollo de un modelo de riesgos y control, un estudio de campo de un proyecto de implementación de un sistema ERP se llevó a cabo en una organización para proporcionar una pequeña prueba del modelo. Los resultados de este estudio proporcionaron apoyo para los riesgos y controles identificados en la literatura. El estudio pavimenta las bases para ahondar en las investigaciones sobre el ámbito del riesgo/control que es tan importante para una implementación exitosa de los sistemas ERP

Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution

A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the ball milling using different technological modes. Cold and hot pressing at different conditions and also SPS process were used for consolidation of the powder into a bulk nanostructure and nanocomposites. The main factors allowing slowing-down of the growth of nanograins as a result of recrystallization are the reduction of the temperature and of the duration of the pressing, the increase of the pressure, as well as addition of small value additives (like MoS2, thermally expanded graphite or fullerenes). It was reached the thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of the thermoelectric efficiency in bulk nanocrystalline semiconductors based on BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead to improvement of the thermoelectric figure of merit. The theoretical dependence of the electric and heat conductivities and the thermoelectric power as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference

Effect of boron doping on grain boundary cohesion in technically pure molybdenum investigated via meso-scale three-point-bending tests

Molybdenum has numerous advantageous functional and high-temperature properties. However, plastic deformation as well as structural applications are limited due to a propensity for brittle, intercrystalline failure, especially at low temperatures. It is well known that oxygen segregations have a detrimental effect, whereas it is assessed that carbon and/or boron have a beneficial effect on grain boundary cohesion. An advanced approach for the improvement of these interfaces is segregation engineering, e.g. the addition of cohesion enhancing elements segregating to the grain boundaries. To investigate early stages of crack formation, three-point bending tests on recrystallized commercially pure and boron micro-doped molybdenum were conducted between −28 \ub0C and room temperature. The tensile-loaded top surface of the specimens was examined post-mortem close to the final fracture area via scanning electron microscopy. The occurring separations of grains are investigated for distinct features and the chemical composition of the interface is complementary measured by atom probe tomography

Role of mitochondria in the pheromone- and amiodarone-induced programmed death of yeast

Although programmed cell death (PCD) is extensively studied in multicellular organisms, in recent years it has been shown that a unicellular organism, yeast Saccharomyces cerevisiae, also possesses death program(s). In particular, we have found that a high doses of yeast pheromone is a natural stimulus inducing PCD. Here, we show that the death cascades triggered by pheromone and by a drug amiodarone are very similar. We focused on the role of mitochondria during the pheromone/amiodarone-induced PCD. For the first time, a functional chain of the mitochondria-related events required for a particular case of yeast PCD has been revealed: an enhancement of mitochondrial respiration and of its energy coupling, a strong increase of mitochondrial membrane potential, both events triggered by the rise of cytoplasmic [Ca2+], a burst in generation of reactive oxygen species in center o of the respiratory chain complex III, mitochondrial thread-grain transition, and cytochrome c release from mitochondria. A novel mitochondrial protein required for thread-grain transition is identified

Evolution of nano-pores during annealing of technically pure molybdenum sheet produced from different sintered formats

Molybdenum is a refractory metal with no phase transformation in the solid state and a high melting point. It is therefore an excellent structural material for various high temperature applications. Especially in this field of operation, significant creep resistance is essential. To achieve this, a microstructure with grains in the range of millimeters is desired. However, as demonstrated in the present study, the onset temperature for secondary recrystallization, which would lead to a beneficial grain size, is among other things dependent on the initial dimensions of the sintered part. One possible reason for the different microstructural evolutions is the influence of residual pores in sub-micrometer size. Sheets were thus fabricated via three different production routes employing the same initial Mo powder to exclude chemical variation as an influencing factor. The samples were investigated by in-situ small-angle X-ray scattering at a synchrotron radiation source with two different heating rates. Additionally, selected annealed samples were studied ex-situ with high energy X-rays. The apparent volume fraction of pores is compared to a volatilization model for the vaporization of typical accompanying elements and the induced thermal expansion

Nonequilibrium functional RG with frequency dependent vertex function: A study of the single impurity Anderson model

We investigate nonequilibrium properties of the single impurity Anderson model by means of the functional renormalization group (fRG) within Keldysh formalism. We present how the level broadening Gamma/2 can be used as flow parameter for the fRG. This choice preserves important aspects of the Fermi liquid behaviour that the model exhibits in case of particle-hole symmetry. An approximation scheme for the Keldysh fRG is developed which accounts for the frequency dependence of the two-particle vertex in a way similar but not equivalent to a recently published approximation to the equilibrium Matsubara fRG. Our method turns out to be a flexible tool for the study of weak to intermediate on-site interactions U <= 3 Gamma. In equilibrium we find excellent agreement with NRG results for the linear conductance at finite gate voltage, magnetic field, and temperature. In nonequilibrium, our results for the current agree well with TD-DMRG. For the nonlinear conductance as function of the bias voltage, we propose reliable results at finite magnetic field and finite temperature. Furthermore, we demonstrate the exponentially small scale of the Kondo temperature to appear in the second order derivative of the self-energy. We show that the approximation is, however, not able to reproduce the scaling of the effective mass at large interactions.Comment: [v2] - minor changes throughout the text; added new Fig. 3; corrected pert.-theory data in Figs. 10, 11; published versio