Electroluminescence and photoluminescence of Ge-implanted Si/SiO_2/Si structures

Electroluminescent devices were fabricated in SiO_2 films containing Ge nanocrystals formed by ion implantation and precipitation during annealing at 900 °C, and the visible room‐temperature electroluminescence and photoluminescence spectra were found to be broadly similar. The electroluminescent devices have an onset for emission in reverse bias of approximately −10 V, suggesting that the mechanism for carrier excitation may be an avalanche breakdown caused by injection of hot carriers into the oxide. The electroluminescent emission was stable for periods exceeding 6 h

The role of quantum-confined excitons vs defects in the visible luminescence of SiO2 films containing Ge nanocrystals

Synthesis of Ge nanocrystals in SiO2 films is carried out by precipitation from a supersaturated solid solution of Ge in SiO2 made by Ge ion implantation. The films exhibit strong room-temperature visible photoluminescence. The measured photoluminescence peak energy and lifetimes show poor correlations with nanocrystal size compared to calculations involving radiative recombination of quantum-confined excitons in Ge quantum dots. In addition, the photoluminescence spectra and lifetime measurements show only a weak temperature dependence. These observations strongly suggest that the observed visible luminescence in our samples is not due to the radiative recombination of quantum-confined excitons in Ge nanocrystals. Instead, observations of similar luminescence in Xe+ -implanted samples and reversible PL quenching by hydrogen or deuterium suggest that radiative defect centers in the SiO2 matrix are responsible for the observed luminescence

Defect-related versus excitonic visible light emission from ion beam synthesized Si nanocrystals in SiO2

Two sources of room temperature visible luminescence are identified from SiO2 films containing ion beam synthesized Si nanocrystals. From a comparison of luminescence spectra and photoluminescence decay lifetime measurements between Xe + -implanted SiO2 films and SiO2 films containing Si nanocrystals, a luminescence feature attributable to defects in the SiO2 matrix is unambiguously identified. Hydrogen passivation of the films selectively quenches the matrix defect luminescence, after which luminescence attributable to Si nanocrystals is evident, with a lifetime on the order of milliseconds. The peak energy of the remaining luminescence attributable to Si nanocrystals ``redshifts'' as a function of different processing parameters that might lead to increased nanocrystal size and the intensity is directly correlated to the formation of Si nanocrystals. Upon further annealing hydrogen-passivated samples at low temperatures (< 500 °C), the intensity of nanocrystal luminescence increases by more than a factor of 10

Efficient semi-analytical integration of vortex sheet influence in 3D vortex method

The original numerical scheme is developed for vortex sheet intensity computation for 3D incompressible flow simulation using meshless Lagrangian vortex methods. It is based on tangential components of the velocity boundary condition satisfaction on the body surface instead of widespread condition for normal components. For the body triangulated surface the corresponding integral equation is approximated by the system of linear algebraic equations, which dimension is doubled number of triangular panels. Vortex layer intensity on the panels assumed to be piecewise-constant. The coefficients of the matrix are expressed through double integrals over the influ- ence and control panels. When these panels have common edge or common vertex these integrals become improper. In order to compute them it is necessary to exclude the sin- gularities, i.e., to split the integrals into regular and singular parts. Regular parts are expressed by smooth functions, so they can be integrated numerically with high precision by using Gaussian quadrature formulae. For singular parts exact analytical integration formulae are derived. The developed approach allows to raise significantly the accuracy of vortex layer in- tensity computation in vortex method for flow simulation around arbitrary 3D bodies. The test problem of flow simulation around the sphere is considered. The exact analyt- ical solution is known for it, and the developed numerical scheme provides more accurate results in comparison with ‘classical’ 3D vortex method, especially when non-uniform un- structured triangular meshes are used for bodies surface representation. It allows to use arbitrary triangular mesh on body surface and to refine mesh near sharp edges, what is especially important for flow simulation around bodies with complicated geometry

Lagrangian vortex loops method for hydrodynamic loads computation in 3D incompressible flows

A new approach is developed for incompressible 3D flow simulation around bodies by Lagrangian vortex method. Closed vortex loops are considered as vortex elements, which are generated on all the body surface and provide the satisfaction of the no-slip boundary condition. The procedure of double layer potential density reconstruc- tion is considered, which consists of two steps. Firstly, the integral equation with respect to vortex sheet intensity is solved, which expresses the equality between the tangential components of flow velocity limit value and the body surface velocity. It is solved by using Galerkin approach. Secondly, the least-squares procedure is implemented, which permits to find nodal values of the double layer potential density. It is shown that the developed algorithm makes it possible to improve significantly the quality of solution for the bodies with very complicated geometry and low-quality surface meshes. The combination of this approach with vortex wake modelling with vortex loops, permits to simulate unsteady flows with higher resolution with acceptable numerical complexity. It can be useful for CFD applications and visual effects reproducing in computer graphics

ABSTRACT MODELS FOR SYSTEM VIRTUALIZATION

The paper is dedicated to issues of system objects securing (system files and user system or application configuration files) against unauthorized access including denial of service attacks. We have suggested the method and developed abstract system virtualization models, which are used toresearch attack scenarios for different virtualization modes. Estimation for system tools virtualization technology effectiveness is given. Suggested technology is based on redirection of access requests to system objects shared among access subjects. Whole and partial system virtualization modes have been modeled. The difference between them is the following: in the whole virtualization mode all copies of access system objects are created whereon subjects’ requests are redirected including corresponding application objects;in the partial virtualization mode corresponding copies are created only for part of a system, for example, only system objects for applications. Alternative solutions effectiveness is valued relating to different attack scenarios. We consider proprietary and approved technical solution which implements system virtualization method for Microsoft Windows OS family. Administrative simplicity and capabilities of correspondingly designed system objects security tools are illustrated on this example. Practical significance of the suggested security method has been confirmed

Two-Fluid RANS-RSTM-PDF Model for Turbulent Particulate Flows

A novel three-dimensional (3D) model based on Reynolds turbulence stress model (RSTM) closure of equations of carrier and particulate phases was elaborated for channel turbulent flows. The essence of the model is the direct calculation of normal and shear components of the Reynolds stresses for the particulate phase similar to the carrier fluid. The model is based on the Eulerian approach, which is applied for the 3D RANS modeling of the carrier flow and the particulate phase and the statistical probability dense function (PDF) approach focusing on the mathematical description of the second moments of the particulate phase

Organizational and Technical Support for Remote Work of Employees in the Conditions of Industrial Production Diversification

The article is devoted to the analysis of a very relevant topic at present: the process of transferring employees (employees) of an organization (company, firm, Department etc.) to a remote (remote) mode of operation, and thus creating a so-called virtual office. For the most part, the translation algorithm and organizational and technical support of the virtual office creation process are typical (universal). However, there is certain specificity in the organization and implementation of this process in relation to engineering organizations and high-tech industrial enterprises, due to the peculiarities of their activities in modern conditions of diversification of industrial production at the enterprises of the defense-industrial complex

Аминирование эпоксидов как удобный способ синтеза липофильных полиаминов

Objectives. Alkylated derivatives of polyamines are able to block the growth of cancer cells due to their embedding into the polyamine biosynthesis mechanisms. The study aimed to synthesize lipophilic derivatives of norspermine or triethylenetetramine based on the formation of a C–N bond during the opening of the oxirane ring by primary amines to expand a number of synthetic polyamine derivatives with antitumor activity.Methods. The starting compounds—glycidol alcoholate or epichlorohydrin—were reacted with hexadecyl bromide or sodium hexadecanolate to give glycidyl hexadecyl ether. The key reaction for the preparation of lipophilic polyamines was the amination of lipophilic epoxides with polyamines in the presence of calcium triflate. Acylation of the hydroxyl group formed during the opening of oxirane was carried out by the action of 4-dimethylaminopyridine and acetic anhydride. The introduction of an alkyl substituent in the presence of sodium hydride led to intramolecular cyclization with the formation of an oxoazolidine cycle. The regioselectivity of the oxirane ring opening reaction at the C(1) position of glycerol was confirmed by two-dimensional heteronuclear {1H,13C} nuclear magnetic resonance spectroscopy.Results. An approach to the synthesis of novel lipophilic polyamines based on the catalytic amination of epoxides was developed and tested. Compounds based on norspermine and triethylentetramine containing a hydroxyl group at the C(2) atom of the glycerin backbone were obtained. For norspermine derivatives, the hydroxyl group was modified: an acetyl substituent was introduced and a derivative containing an oxoazolidine cycle was obtained.Conclusions. The obtained lipophilic polyamines can be considered as potential antitumor agents, for which cytotoxicity against various cancer cells will be evaluated in the future.Цели. Алкилированные производные полиаминов способны блокировать рост раковых клеток за счет встраивания в механизмы биосинтеза полиаминов. Цель исследования – синтезировать новые липофильные производные норспермина или триэтилентетрамина, основанные на формировании связи C–N при раскрытии оксиранового кольца первичными аминами, для расширения ряда синтетических производных полиаминов, обладающих противоопухолевой активностью.Методы. Исходные соединения – алкоголят глицидола или эпихлоргидрин – вводили во взаимодействие с гексадецилбромидом или гексадецилатом натрия, получая гексадецилглицидиловый эфир. Ключевой реакцией получения липофильных полиаминов являлось аминирование липофильных эпоксидов полиаминами в присутствии трифлата кальция. Ацилирование гидроксильной группы, образовавшейся в ходе раскрытия оксирана, проводили действием 4-диметиламинопиридина и уксусного ангидрида. Введение алкилильного заместителя в присутствии гидрида натрия приводило к внутримолекулярной циклизации с образованием оксоазолидинового цикла. Региоселективность реакции раскрытия оксиранового цикла по C(1) положению глицерина подтверждали двумерной гетероядерной {1H,13C} спектроскопией ядерного магнитного резонанса.Результаты. Разработан и апробирован подход к синтезу новых липофильных полиаминов, основанный на каталитическом аминирование эпоксидов. Получены соединения на основе норспермина и триэтилентетрамина, содержащие гидроксильную группу при С(2) атоме глицеринового остова. Для производных норспермина проведена модификация гидроксильной группы: введен ацетильный заместитель и получено производное, содержащее оксоазолидиновый цикл.Выводы. Полученные липофильные полиамины можно рассматривать как потенциальные противоопухолевые агенты, для которых в дальнейшем будет проведена оценка цитотоксичности против различных раковых клеток

Algorithm for selecting predictors and prognosis of atrial fibrillation in patients with coronary artery disease after coronary artery bypass grafting

Aim. To develop an algorithm for selecting predictors and prognosis of atrial fibrillation (AF) in patients with coronary artery disease (CAD) after coronary artery bypass grafting (CABG).Material and methods. This retrospective study included 886 case histories of patients with CAD aged 35 to 81 years (median age, 63 years; 95% confidence interval [63; 64]), who underwent isolated CABG under cardiopulmonary bypass. Eighty-five patients with prior AF were excluded from the study. Two groups of persons were identified, the first of which consisted of 153 (19,1%) patients with newly recorded AF episodes, the second — 648 (80,9%) patients without cardiac arrhythmias. Preoperative clinical and functional status was assessed using 100 factors. Chi-squared, Fisher, and Mann-Whitney tests, as well as univariate logistic regression (LR) were used for data processing and analysis. Multivariate LR and artificial neural networks (ANN) were used to develop predictive models. The boundaries of significant ranges of potential predictors were determined by stepwise assessment of the odds ratio and p-value. The model accuracy was assessed using 4 metrics: area under the ROC-curve (AUC), sensitivity, specificity, and accuracy.Results. A comprehensive analysis of preoperative status of patients made it possible to identify 11 factors with the highest predictive potential, linearly and nonlinearly associated with postoperative AF (PAF). These included age (55-74 years for men and 60-78 years for women), anteroposterior and superior-inferior left atrial dimensions, transverse and longitudinal right atrial dimensions, tricuspid valve regurgitation, left ventricular end systolic dimension &gt;49 mm, RR length of 1000-1100 ms, PQ length of 170-210 ms, QRS length of 50-80 ms, QT &gt;420 ms for men and &gt;440 ms for women, and heart failure with ejection fraction of 4560%. The metrics of the best predictive ANN model were as follows: AUC — 0,75, specificity — 0,73, sensitivity — 0,74, and accuracy — 0,73. These values in best model based on multivariate LR were lower (0,75; 0,7; 0,68 and 0,7, respectively).Conclusion. The developed algorithm for selecting predictors made it possible to verify significant predictive ranges and weight coefficients characterizing their influence on PAF development. The predictive model based on ANN has a higher accuracy than multivariate HR