SIMULATION OF BEHAVIOR OF FUNCTIONALLY - HETEROGENEOUS MATERIALS UNDER TEMPERATURE LOADS

The paper considers the issue of nonlinear mathematical modeling of functionally inhomogeneous materials at temperature loads. The proposed model makes it possible to describe the thermo-pseudo-plastic behavior  of the material at the point. The diagram of pseudo-elastic material consisting of three curvilinear sections is used. This approach leads to an unstable stress-strain diagram, and to describe the thermo-mechanical behavior of samples of different shapes, it is necessary to have a solution of the boundary value problem taking into account the development of the deformation front of the phase transformation. This takes into account not only the ambient temperature, but also the heat released at the point during the phase transition. A numerical procedure for calculating a material diagram has been developed, which is a curve enveloping a family of material diagrams constructed for certain laws of change in the velocity of the deformation rupture front. An integrated diagram of the material under the influence of a complex load is constructed.Keywords: phenomenological model, nonlinear material model, materials with shape memory, thermo-pseudo-plasticity, numerical procedure for calculating the diagram

PHENOMENOLOGICAL MODELING OF VOLUME NANOMATERIALS WITH FORM MEMORY

The paper presents a phenomenological approach to modeling bulk memory nanomaterials form. A phenomenological model has been proposed that can be applied to model the behavior of nanomaterials with shape memory properties. The study of shape memory alloys as functionally inhomogeneous materials with the properties of pseudo-elastic-plasticity is presented. The phenomenological model is confirmed by experimental data. Tables of diagrams for different temperatures of alloys with shape memory are given.Key words: modeling, functionally inhomogeneous materials, nanomaterials, phenomenological approach, large deformation

The structure of helix 89 of 23S rRNA is important for peptidyl transferase function of Escherichia coli ribosome

AbstractHelix 89 of the 23S rRNA connects ribosomal peptidyltransferase center and elongation factor binding site. Secondary structure of helix 89 determined by X-ray structural analysis involves less base pairs then could be drawn for the helix of the same primary structure. It can be that alternative secondary structure might be realized at some stage of translation. Here by means of site-directed mutagenesis we stabilized either the “X-ray” structure or the structure with largest number of paired nucleotides. Mutation UU2492-3C which aimed to provide maximal pairing of the helix 89 of the 23S rRNA was lethal. Mutant ribosomes were unable to catalyze peptide transfer independently either with aminoacyl-tRNA or puromycin

Role of integrin receptors in cytotoxic lymphocyte function

Natural killer cells (NK cells) are an essential tool of the immune cell defense against aberrant cells, especially tumors. NK cells can kill tumor target cells upon activation through one of the germ-line coded activating receptors, CD16 in particular. CD16 recognizes Fc fragments of IgG antibody molecules bound to antigens on the surface of the target cell and mediates target cell lysis in the process called ADCC (antibody dependent cellular cytotoxicity). The killing of the target cell is mediated by the release of soluble molecules contained within membrane bound vesicles, lytic granules. The granules are released directionally from the NK cell to the target cell through highly organized contact interface called the immunological synapse (IS) as a result of a complex series of signaling events. In the current work we examine the range of integrin employed by NK cells and address the contribution of integrin outside in signaling to effective CD16-mediated NK cytotoxicity. We found that for their activation NK cells utilize a wide range of integrin molecules, both containing and not containing beta2 subunit. We also found that integrin engagement supports sustained proximal signaling and extended adhesion area formation. Furthermore, we show that integrin-mediated signaling and not the amount of available CD16 ligands is primarily responsible for size, mobility and persistence of CD16 microclusters. The finding described herein uncover novel mechanisms used by NK cells to mediate efficient cytotoxic response under wide range of conditions and demonstrate the crucial importance of integrin involvement in NK cell signal transduction. These findings have important implications for the development of personalized anti-tumor therapies in the future

РАзрАботкА методА повышенноЙ точностИ решениЯ задаЧ теорИИ термо-псевдоупруго-пластИчностИ

Сложное поведение тел из псевдоупругих и псевдоупругопластических материалов требует развития специальных алгоритмов расчета напряженно-деформированного состояния. В настоящей работе разработан численный метод повышенной точности для решения многомерных нестационарных задач теории термо-упруго-пластичности для тел из псевдоупругих и псевдоупругопластических материалов. Это метод покомпонентного расщепления, который основан на применении нового выражения для двумерных сплайн-функций позволил повысить на два порядка точность вычислений. При условии соблюдения одинаковой точности вычислений с классическим конечно-разностным методом данный метод позволяет быстрее получать результаты в силу выбора более крупных шагов интегрирования по координатам. Это приводит к уменьшению на два порядка количество используемых узлов пространственной сетки, что представляется важным и полезным с практической точки зрения.Записаны основные уравнения. Это уравнение теплопроводности, уравнения движения, геометрические соотношения. При построении физических соотношений предполагалось, что деформация в точке представляется в виде суммы упругой составляющей, скачка деформации при фазовом переходе, пластической деформации и деформации, вызванной температурными изменениями. В общем виде сформулированы граничные и начальные условия.Проведено экспериментальное обоснование варианта феноменологической модели поведения материала с памятью формы. В этой модели заложена возможность количественной оценки сложных взаимодействий между напряжениями, температурой, деформацией и скоростью нагружения материала, которые пригодны и для моделирования континуального уровня. На основании этого решен качественно новый класс двумерных нестационарных задач для материалов с памятью формы, когда неизвестные величины разыскиваются в виде двухмерных напряженных сплайно

Mutations at the accommodation gate of the ribosome impair RF2-dependent translation termination

During protein synthesis, aminoacyl-tRNA (aa-tRNA) and release factors 1 and 2 (RF1 and RF2) have to bind at the catalytic center of the ribosome on the 50S subunit where they take part in peptide bond formation or peptidyl-tRNA hydrolysis, respectively. Computer simulations of aa-tRNA movement into the catalytic site (accommodation) suggested that three nucleotides of 23S rRNA, U2492, C2556, and C2573, form a “gate” at which aa-tRNA movement into the A site is retarded. Here we examined the role of nucleotides C2573 of 23S rRNA, a part of the putative accommodation gate, and of the neighboring A2572 for aa-tRNA binding followed by peptide bond formation and for the RF2-dependent peptide release. Mutations at the two positions did not affect aa-tRNA accommodation, peptide bond formation, or the fidelity of aa-tRNA selection, but impaired RF2-catalyzed peptide release. The data suggest that the ribosome is a robust machine that allows rapid aa-tRNA accommodation despite the defects at the accommodation gate. In comparison, peptide release by RF2 appears more sensitive to these mutations, due to slower accommodation of the factor or effects on RF2 positioning in the A site