Model reconstructions for the Si(337) orientation

Although unstable, the Si(337) orientation has been known to appear in diverse experimental situations such as the nanoscale faceting of Si(112), or in the case of miscutting a Si(113) surface. Various models for Si(337) have been proposed over time, which motivates a comprehensive study of the structure of this orientation. Such a study is undertaken in this article, where we report the results of a genetic algorithm optimization of the Si(337)-$(2\times 1)$ surface. The algorithm is coupled with a highly optimized empirical potential for silicon, which is used as an efficient way to build a set of possible Si(337) models; these structures are subsequently relaxed at the level of ab initio density functional methods. Using this procedure, we retrieve most of the (337) reconstructions proposed in previous works, as well as a number of novel ones.Comment: 5 figures (low res.); to appear in J. Appl. Phy

Ground states of a mixture of two species of spin-1 Bose gases with interspecies spin exchange in a magnetic field

We consider a mixture of two species of spin-1 atoms with both interspecies and intraspecies spin exchanges in a weak magnetic field. Under the usual single mode approximation, it can be reduced to a model of coupled giant spins. We find most of its ground states. This is a complicated problem of energy minimization, with three quantum variables under constraints, i.e. the total spin of each species and the total spin of the whole mixture, as well as four parameters, including intraspecies and interspecies spin coupling strengths and the magnetic field. The quantum phase diagram is very rich. Compared with the case without a magnetic field, the ground states are modified by a magnetic field, which also modifies the ground state boundaries or introduces new crossover regimes on the phase diagram. Without interspecies spin coupling, the quantum phase transitions existing in absence of a magnetic field disappear when a magnetic field is applied, which leads to crossover regimes in the phase diagram. Under ferromagnetic interspecies spin coupling, the ground states remain disentangled no matter whether there is a magnetic field. For antiferromagnetic interspecies spin coupling, a magnetic field entangles the ground states in some parameter regimes. When the intraspecies spin couplings are both ferromagnetic, the quantum phase transition between antiferromagnetic and zero interspecies spin couplings survives the magnetic field. When the intraspecies spin couplings are both antiferromagnetic, a magnetic field induces new quantum phase transitions between antiferromagnetic and zero interspecies spin couplings.Comment: 17 pages, initially submitted to Phys. Rev. A on September 15 2010, to appear in Int. J. Mod. Phys.

Elastic constants of beta-eucryptite: A density functional theory study

The five independent elastic constants of hexagonal $\beta$-eucryptite have been determined using density functional theory (DFT) total energy calculations. The calculated values agree well, to within 15%, with the experimental data. Using the calculated elastic constants, the linear compressibility of $\beta$-eucryptite parallel to the c-axis, $\chi_c$, and perpendicular to it, $\chi_a$, have been evaluated. These values are in close agreement to those obtained from experimentally known elastic constants, but are in contradiction to the direct measurements based on a three-terminal technique. The calculated compressibility parallel to the c-axis was found to positive as opposed to the negative value obtained by direct measurements. We have demonstrated that $\chi_c$ must be positive and discussed the implications of a positive $\chi_c$ in the context of explaining the negative bulk thermal expansion of $\beta$-eucryptite.Comment: 3 eps figures, submitted for publicatio

Surface Science Letters Structure and stability of the Si(1 0 5) surface

Abstract Recent experimental studies have shown that well-annealed, unstrained Si(1 0 5) surfaces appear disordered and atomically rough when imaged using scanning tunnelling microscopy. We construct new models for the Si(1 0 5) surface that are based on single-and double-height steps separated by Si(0 0 1) terraces, and propose that the observed surface disorder of Si(1 0 5) originates from the presence of several structural models with different atomic-scale features but similar energies. This degeneracy can be removed by applying compressive strains, a result that is consistent with recent observations of the structure of the Ge/Si While the structure of Ge/Si(1 0 5) surface has been recently elucidated, the Si(1 0 5) surface shows intriguing features that are not well understood. Experimental work by Tomitori et al. [8], Fujikawa et al. [5] and Zhao et al

Prototype tests for the ALICE TRD

A Transition Radiation Detector (TRD) has been designed to improve the electron identification and trigger capability of the ALICE experiment at the Large Hadron Collider (LHC) at CERN. We present results from tests of a prototype of the TRD concerning pion rejection for different methods of analysis over a momentum range from 0.7 to 2 GeV/c. We investigate the performance of different radiator types, composed of foils, fibres and foams.Comment: Presented at the IEEE Nuclear Science Symposium and Medical Imaging Conference, Lyon, October 15-20, 2000 (accepted for publication in IEEE TNS), Latex (IEEEtran.cls), 7 pages, 11 eps figure

Влияние озонотерапии на показатели гуморального и клеточного иммунитета у больных с дуоденальной язвой

Catedra Medicină internă nr. 6, USMF “Nicolae Testemiţanu”, Universitatea „Lucian Blaga”, Sibiu, România, Spitalul Clinic al Ministerului Sănătăţii, Chişinău, Conferinţa Ştiinţifico-Practică „Medicina modernă, actualităţi şi perspective”, consacrată aniversării de 40 de ani ai Spitalului Clinic al Ministerului Sănătăţii, 27-28 mai, 2010, Chişinău, Republica MoldovaThe study included 180 patients with chronic duodenal ulcer H. pylori associated in exacerbation. The patients underwent: physical examination, laboratory diagnosis fibrogastroscopy and laboratory exams for H. pylori. Under the influence of ozonotherapy both cellular and humoral components of the immune status were stimulated. Sometimes the effects of ozonotherapy occured 6 weeks after the treatment. It was established that the inclusion of ozonotherapy with the standard treatment contributed to the increase of H. pylori eradication. В исследование были включены 180 больных хронической язвой двенадцатиперстной кишки в стадии обострения и положительной H. pylori. Изучено влияние озонотерапии на клеточные и гуморальные звенья иммунитета. При исследовании иммунного статуса наблюдалась активация T- и B-клеточного ответа. Эффективность озонотерапии наблюдалась через 6 недель после окончания лечения. Было установлено, что включение озонотерапии в базисное лечение способствовало увеличению эрадикации H. pylori

Position Reconstruction in Drift Chambers operated with Xe, CO2 (15%)

We present measurements of position and angular resolution of drift chambers operated with a Xe,CO$_2$(15%) mixture. The results are compared to Monte Carlo simulations and important systematic effects, in particular the dispersive nature of the absorption of transition radiation and non-linearities, are discussed. The measurements were carried out with prototype drift chambers of the ALICE Transition Radiation Detector, but our findings can be generalized to other drift chambers with similar geometry, where the electron drift is perpendicular to the wire planes.Comment: 30 pages, 18 figure

Transition Radiation Spectroscopy with Prototypes of the ALICE TRD

We present measurements of the transition radiation (TR) spectrum produced in an irregular radiator at different electron momenta. The data are compared to simulations of TR from a regular radiator.Comment: 4 pages, 5 Figures, Proceedings for "TRDs for the 3rd millennium" (Sept. 4-7, 2003, Bari, Italy