Reconstruction of group-IV semiconductor surfaces: origin, energetics and consequences

This work presents extensive first-principles studies of the energetics and the reconstructions of the clean low-index (111), (110), (100) and high-index (113) surfaces of the three group- IV semiconductors diamond, silicon, and germanium. The calculations have been performed within density-functional-theory (DFT) using the local-density-approximation (LDA) and the repeated-slab approximation. Different reconstructions including the largest ones observed experimentally such as Si(111)7?7 and Si(110)16?2 have been investigated. The atomic geometries have been optimized in order to find the minimum of the total energy. For these atomic structures the electronic band structures have also been calculated. For the most interesting surface reconstructions scanning-tunneling-microscopy (STM) images have been simulated in order to make a comparison with experimentally observed surface images. Presented results highlight the physical origins of the reconstruction behavior in dependence on surface orientation and size of the group-IV atoms. Clear evidence for an opposite reconstruction behavior of diamond and Si or Ge surfaces is shown. Adatoms, interstitials, and symmetry-breaking distortions are unlikely for diamond as a consequence of the short interatomic distances and strong bonds. However, such elements of the surface reconstruction occur on Si and Ge surfaces. The complicated interplay of bonding, resulting atomic geometry, and accompanying electronic structure has been derived and used to discuss driving forces for the surface reconstruction. A rather complete data base of absolute surface energies of group-IV semiconductors is presented. For all the elements, there is a strong tendency to reduce substantially surface energies by taking into account surface reconstructions. The absolute surface energies have been used to discuss the equilibrium shapes of diamond, silicon and germanium

A case of domestic goat parasitism by Neotrombicula heptneri (Acariformes: Trombiculidae) in Turkey

International audienceA chigger mite Neotrombicula heptneri Kudryashova, 1973, which was originally described from three gerbillid species in Iran, is for the first time recorded in Turkey and on the domestic goat Capra hircus L. It is the second chigger species found infesting livestock in Turke

Incorporation of glycine-2-C-14 in acid-insoluble proteins of rat bones and teeth during hypokinesia and administration of thyrocalcitonine

A forced limitation of the motor activity in rats (from 5 to 60 days) results in reduced incorporation of glycine 2-C14 in the total acid insoluble proteins of limb bones and its increase in the teeth and mandibular-maxillary bones. Daily administration of five micrograms of thyrocalcitonine together with polyvinylpyrrolidone normalizes the protein metabolism in the bone tissues during the 40 days of experimentation

A case of domestic goat parasitism by Neotrombicula heptneri (Acariformes: Trombiculidae) in Turkey

A chigger mite Neotrombicula heptneri Kudryashova, 1973, which was originally described from three gerbillid species in Iran, is for the first time recorded in Turkey and on the domestic goat Capra hircus L. It is the second chigger species found infesting livestock in Turkey.Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR) [13-04-00028-a]The authors wish to express their appreciation to Dr Naina I. Kudryashova (ZMMU), who gave them an opportunity to study the type material of N. heptneri. They are also grateful to two anonymous reviewers for useful comments. This research was supported by a grant from the Russian Foundation for Basic Research No. 13-04-00028-a (to A.A. Stekolnikov)

Effects of solar magnetic field on cosmic rays

Aspects of the problem of galactic cosmic ray propagation, including inversion of the solar total magnetic field and an analysis of data related to the heliomagnetic cycle are discussed. It is noted that the global structure of the solar magnetic field results in an additional flux of galactic cosmic rays generated by curvature and gradient drifts. An analysis of heliomagnetic cycle data shows that the latitudinal gradient results in a N-S asymmetry, with the amplitude of the effect growing with depth in the atmosphere. The inversion of the solar total magnetic field, drift effects, and other space distributions are found to contribute to a 22-year cycle of solar activity

Simulation of formation of an intensive electron beam in bipolar electron-optical system with the plasma anode

The algorithm of numerical simulation of electrons sources in base of the high-voltage glow discharge with the anode plasma, taking into account change of the form and the location of a surface of anode plasma, that renders essential influence on formation of an ion stream, which at hit on the cold cathode as a result of secondary ion - electronic emission forms an electron beam, is offered. As against other algorithms the offered physics-mathematical model takes into account influence on distribution of potential not only an ion space charge, but also a space charge of beam electrons, distribution of potential in turn defines as a trajectory the beam electrons and a stream of ions, and position of plasma edge which movement is considered during formation of a beam according to Stefan's condition

Efficient and reliable method for the simulation of scanning tunneling images and spectra with local basis sets

Based on Bardeen's perturbative approach to tunneling, we have found an expression for the current between tip and sample, which can be efficiently coded in order to perform fast ab initio simulations of STM images. Under the observation that the potential between the electrodes should be nearly flat at typical tunnel gaps, we have addressed the difficulty in the computation of the tunneling matrix elements by considering a vacuum region of constant potential delimited by two surfaces (each of them close to tip and sample respectively), then propagating tip and sample wave functions by means of the vacuum Green's function, to finally obtain a closed form in terms of convolutions. The current is then computed for every tip-sample relative position and for every bias voltage in one shot. The electronic structure of tip and sample is calculated at the same footing, within density functional theory, and independently. This allows us to carry out multiple simulations for a given surface with a database of different tips. We have applied this method to the Si(111)-(7x7) and Ge(111)-c(2x8) surfaces. Topographies and spectroscopic data, showing a very good agreement with experiments, are presented.Comment: 10 pages, 11 figure

Геопространственное распределение госпитальных ресурсов в региональных травматологических системах (обзор зарубежной литературы)

The review presents the results of foreign studies related to geospatial analysis and modeling of the distribution of trauma centers and helicopter emergency medical services in developed regional trauma systems. The optimal number and geographical location of the trauma centers in the region is determined taking into account the timing of the delivery of victims to the trauma centers of a high level, population density, hospitalization of patients with severe trauma, and the frequency of inter-hospital transfers. The distribution of hospital resources of the trauma system should be based on the needs of the population, and vary depending on the geographical and social characteristics of the region. В обзоре представлены результаты зарубежных исследований, касающихся геопространственного анализа и моделирования распределения травмоцентров и вертолетных баз скорой медицинской помощи в развитых региональных травматологических системах. Оптимальное количество и географическое расположение травмоцентров в регионе определяется с учетом сроков доставки пострадавших в травмоцентры высокого уровня, плотности населения, объема госпитализаций пациентов с тяжелой травмой, частоты межбольничных переводов. Распределение госпитальных ресурсов травматологической системы должно основываться на потребностях населения, варьировать в зависимости от географических и социальных особенностей региона.

Hexagon versus Trimer Formation in In Nanowires on Si(111): Energetics and Quantum Conductance

Article on hexagon versus trimer formation in In nanowires on Si(111)