Subgroup separability in integral group rings

We give a list of finite groups containing all finite groups $G$ such that the group of units $\Z G^*$ of the integral group ring $\Z G$ is subgroup separable. There are only two types of these groups $G$ for which we cannot decide wether $ZG^*$ is subgroup separable, namely the central product $Q_8 Y D_8$ and $Q_8\times C_p{with} p \text{prime and} p\equiv -1 \mod (8)$.Comment: 9 page

High-perveance charged particles source for implementation of e-beam technology

Presented a number of electron-beam technologies, it is possible to implement by high-perveanced plasma source of charged particles. A discharge structure of high-perveance source that can form electron and ion beams, with parameters satisfying presented technologies

High-perveance charged particles source for implementation of e-beam technology

Presented a number of electron-beam technologies, it is possible to implement by high-perveanced plasma source of charged particles. A discharge structure of high-perveance source that can form electron and ion beams, with parameters satisfying presented technologies

Multibit structure for the formation of combined or alternating electron-ion beams

Currently, sources of ion and electron beams make it possible to implement a wide range of effective technologies for processing materials and surface modifications. In some cases, a significant increase in the effectiveness of such technologies is achieved with simultaneous exposure to electron and ion beams through the use of two types of separate (electron and ion) sources. At the same time, experience in the development and use of plasma sources of charged particles shows the possibility of creating a combined electron-ion flow in one direction and in a single discharge system. In this work, we propose an experimental electrode structure of a plasma electron-ion source for the formation of a combined electron-ion or separate electron and ion beams. A number of its characteristics and the prospects for further development of an electron-ion source for industrial use on its basis are shown

Remarks on singular Cayley graphs and vanishing elements of simple groups

Let Γ be a finite graph and let A(Γ) be its adjacency matrix. Then Γ is singular if A(Γ) is singular. The singularity of graphs is of certain interest in graph theory and algebraic combinatorics. Here we investigate this problem for Cayley graphs Cay(G,H) when G is a finite group and when the connecting set H is a union of conjugacy classes of G. In this situation, the singularity problem reduces to finding an irreducible character χ of G for which ∑h∈Hχ(h)=0. At this stage, we focus on the case when H is a single conjugacy class hG of G; in this case, the above equality is equivalent to χ(h)=0 . Much is known in this situation, with essential information coming from the block theory of representations of finite groups. An element h∈G is called vanishing if χ(h)=0 for some irreducible character χ of G. We study vanishing elements mainly in finite simple groups and in alternating groups in particular. We suggest some approaches for constructing singular Cayley graphs

Плазменный источник заряженных частиц для формирования совмещенных ионно-электронных пучков

One of the ways to increase the efficiency of the implementation of ion-plasma technologies of exposure to the surfaces of various materials is partial or full compensation of the positive charge of ions in the stream or on the treated surface, for which additional emitting systems are used that create compensating electron flows in the discharge space, accelerating gap or on the processed surface. It was previously shown that for the implementation of such a compensating effect, it is possible to use plasma sources of charged particles, capable of forming beams of both signs when the polarity of the accelerating voltage is changed. The main problem in this case is the difficulty in achieving simultaneously high emission efficiency of ions and electrons, since the conditions for their emission from plasma are significantly different. This article proposes a concept and a design developed on its basis for a prototype of a multi-discharge plasma electron-ion source for the joint or alternating formation of electron and ion beams. It is shown that the proposed design realizes the possibility of increasing the perveance by compensating for the space charge by particles of the opposite sign. A number of characteristics of the developed model of a plasma electron-ion source (current-voltage characteristics of the extraction of electrons and ions) are presented and its prospects for further development of an electron-ion source for industrial use on its basis are shown. Combined or alternating ion-electron beams formed in the presented source can be used to implement the technology of applying thin-film layers of metals, semiconductors, and dielectrics to maintain ionization processes and ensure stable discharge burning, compensation of both the space charge in the beam and the surface charge on the formed film.Одним из способов повышения эффективности реализации ионно-плазменных технологий воздействия на поверхности различных материалов является частичная или полная компенсация положительного заряда ионов в потоке или на обрабатываемой поверхности, для чего используются дополнительные эмитирующие системы, которые создают компенсирующие электронные потоки в разрядное пространство, ускоряющий промежуток или на обрабатываемую поверхность. Для реализации такого компенсирующего воздействия возможно применение плазменных источников заряженных частиц, способных при изменении полярности ускоряющего напряжения формировать пучки обоих знаков. Основная проблема при этом заключается в сложности достижения одновременно высокой эффективности эмиссии ионов и электронов, поскольку условия их эмиссии из плазмы существенно различаются. В данной статье предложена концепция и разработанная на ее основе конструкция макета мультиразрядного плазменного электронно-ионного источника для совместного или попеременного формирования электронных и ионных пучков. Показано, что в предложенной конструкции реализуется возможность повышения первеанса за счет компенсации объемного заряда частицами противоположного знака. Приведен ряд характеристик разработанного макета плазменного электронно-ионного источника (вольтамперные характеристики извлечения электронов и ионов) и показана его перспективность для дальнейшей разработки на его основе электронно-ионного источника для промышленного применения. Совмещенные или попеременные ионно-электронные пучки, формируемые в представленном источнике, могут быть использованы при реализации технологий нанесения тонкопленочных слоев металлов, полупроводников и диэлектриков для поддержания процессов ионизации и обеспечения устойчивого горения разряда, компенсации как объемного заряда в пучке, так и поверхностного на формируемой пленке

Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry

In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO3. It is generally accepted that the main reason of the ferroelectric distortion in BiFeO3 is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic beta-phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity - its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO3 in the range from 945 C down to 25 C and found the couplings, which undergo the antiferromagnetic-ferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table

Системы плазменной эмиссии для электронно-ионно-лучевых технологий

Designs and basic characteristics of plasma sources of charged particles allowing one to realize a wide spectrum of electron- and ion-beam technologies are presented. Some applications of the developed structures of charged particles sources are considered. Sketches of promising designs of gas-discharge structures capable of forming combined electron and ion beams are proposed