Nikitin I.S. Models of multiaxial fatigue and life time estimation of structures \\ Mechanics of Solids

Abstract-We study criteria and models of multiaxial fracture under the conditions of low-cycle fatigue (L.CF). The model parameters are determined by using the data of uniaxial fatigue tests for different coefficients of the cycle asymmetry. A procedure for calculating the stress state of the compressor disk in a gas turbine engine (GTE) in the flight cycle of loading is outlined. The calculated stress state and models of multiaxial fatigue fracture are used to estimate the service life of the compressor disk. The results are compared with the observational data collected during the operation

The structures of Hausdorff metric in non-Archimedean spaces

For non-Archimedean spaces $X$ and $Y,$ let $\mathcal{M}_{\flat } (X), \mathfrak{M}(V \rightarrow W)$ and $\mathfrak{D}_{\flat }(X, Y)$ be the ballean of $X$ (the family of the balls in $X$), the space of mappings from $X$ to $Y,$ and the space of mappings from the ballen of $X$ to $Y,$ respectively. By studying explicitly the Hausdorff metric structures related to these spaces, we construct several families of new metric structures (e.g., $\widehat{\rho } _{u}, \widehat{\beta }_{X, Y}^{\lambda }, \widehat{\beta }_{X, Y}^{\ast \lambda }$) on the corresponding spaces, and study their convergence, structural relation, law of variation in the variable $\lambda,$ including some normed algebra structure. To some extent, the class $\widehat{\beta }_{X, Y}^{\lambda }$ is a counterpart of the usual Levy-Prohorov metric in the probability measure spaces, but it behaves very differently, and is interesting in itself. Moreover, when $X$ is compact and $Y = K$ is a complete non-Archimedean field, we construct and study a Dudly type metric of the space of $K-$valued measures on $X.$Comment: 43 pages; this is the final version. Thanks to the anonymous referee's helpful comments, the original Theorem 2.10 is removed, Proposition 2.10 is stated now in a stronger form, the abstact is rewritten, the Monna-Springer is used in Section 5, and Theorem 5.2 is written in a more general for

Hyperbolic Geometry of Complex Networks

We develop a geometric framework to study the structure and function of complex networks. We assume that hyperbolic geometry underlies these networks, and we show that with this assumption, heterogeneous degree distributions and strong clustering in complex networks emerge naturally as simple reflections of the negative curvature and metric property of the underlying hyperbolic geometry. Conversely, we show that if a network has some metric structure, and if the network degree distribution is heterogeneous, then the network has an effective hyperbolic geometry underneath. We then establish a mapping between our geometric framework and statistical mechanics of complex networks. This mapping interprets edges in a network as non-interacting fermions whose energies are hyperbolic distances between nodes, while the auxiliary fields coupled to edges are linear functions of these energies or distances. The geometric network ensemble subsumes the standard configuration model and classical random graphs as two limiting cases with degenerate geometric structures. Finally, we show that targeted transport processes without global topology knowledge, made possible by our geometric framework, are maximally efficient, according to all efficiency measures, in networks with strongest heterogeneity and clustering, and that this efficiency is remarkably robust with respect to even catastrophic disturbances and damages to the network structure

Closed geodesics in Alexandrov spaces of curvature bounded from above

In this paper, we show a local energy convexity of $W^{1,2}$ maps into $CAT(K)$ spaces. This energy convexity allows us to extend Colding and Minicozzi's width-sweepout construction to produce closed geodesics in any closed Alexandrov space of curvature bounded from above, which also provides a generalized version of the Birkhoff-Lyusternik theorem on the existence of non-trivial closed geodesics in the Alexandrov setting.Comment: Final version, 22 pages, 2 figures, to appear in the Journal of Geometric Analysi

Essential self-adjointness of magnetic Schr\"odinger operators on locally finite graphs

We give sufficient conditions for essential self-adjointness of magnetic Schr\"odinger operators on locally finite graphs. Two of the main theorems of the present paper generalize recent results of Torki-Hamza.Comment: 14 pages; The present version differs from the original version as follows: the ordering of presentation has been modified in several places, more details have been provided in several places, some notations have been changed, two examples have been added, and several new references have been inserted. The final version of this preprint will appear in Integral Equations and Operator Theor

Orientation and symmetries of Alexandrov spaces with applications in positive curvature

We develop two new tools for use in Alexandrov geometry: a theory of ramified orientable double covers and a particularly useful version of the Slice Theorem for actions of compact Lie groups. These tools are applied to the classification of compact, positively curved Alexandrov spaces with maximal symmetry rank.Comment: 34 pages. Simplified proofs throughout and a new proof of the Slice Theorem, correcting omissions in the previous versio

Локальный воспалительный ответ на использование шовного материала в хирургической практике: экспериментальные данные

Objective: to study the effect of various types of suture materials, potentially suitable for cardiovascular surgery, on experimental surgical outcomes. Materials and methods. Polypropylene sutures (Prolene 6/0), titanium nickelide (TiNi) sutures (6/0) and absorbable polydioxanone sutures (Monoplus 6/0) were used in the study. Male Wistar rats were used for in vivo studies. The effect of suture materials on abdominal adhesions was studied. In vivo calcification process was examined, and response of blood components in contact with suture materials was also assessed in vitro. Results. There is a negative inflammatory response to suture materials. The severity of this response depended on the type of material used. Polypropylene sutures demonstrated the most severe inflammatory response provoking massive adhesion formation. In addition, large calcium deposits were found both in the suture area and in the thickness of the biomaterial, stitched with prolene and implanted subcutaneously in the rats. Titanium nickelide sutures showed high hemocompatibility and biocompatibility. The Monoplus sutures caused minimal inflammatory response and provoked calcification of the biomaterial to a lesser degree. Conclusion. The suture material could have significant effects on surgical outcomes and could cause postoperative complications.Цель. Изучить влияние различных видов шовного материала, потенциально пригодных для сердечно-сосудистой хирургии, на результаты оперативного вмешательства в эксперименте. Материалы и методы. В работе использовали нить на основе полипропилена «Prolene» 6/0, нити из никелида титана (TiNi) (6/0) и рассасывающийся шовный материал «Monoplus» 6/0 (полидиоксанон). Исследования in vivo проводили на крысах-самцах субпопуляции «Wistar». Изучали влияние шовного материала на развитие спаечного процесса в брюшной полости, процесс кальцификации in vivo, а также оценивали реакцию компонентов крови при контакте с шовным материалом in vitro. Результаты. Реакция на шовный материал является негативной, а степень ее выраженности зависит от вида используемого материала. Шовный материал на основе полипропилена вызывает максимальную воспалительную реакцию, что провоцирует массивное спайкообразование. Помимо этого, при подкожной имплантации крысам образцов биоматериала, прошитых нитью «Prolene», были выявлены крупные кальциевые депозиты, как в области шовного материала, так и в толще биоматериала. Шовный материал на основе никелида титана TiNi продемонстрировал высокие гемо- и биосовместимые свойства. Нить «Monoplus» вызывала минимальную воспалительную реакцию и в меньшей степени провоцировала кальцификацию биоматериала. Заключение. Полученные результаты доказывают, что шовный материал может оказывать существенное влияние на результаты хирургического вмешательства и может быть одной из причин послеоперационных осложнений

СКОРОСТЬ РЕЗОРБЦИИ ТРАНСПЛАНТАТА НА ОСНОВЕ ПОЛИГИДРОКСИАЛКАНОАТОВ И МУЛЬТИПОТЕНТНЫХ МЕЗЕНХИМАЛЬНЫХ СТРОМАЛЬНЫХ КЛЕТОК

The article presents the findings of histological analysis of local tissue response to subcutaneous implantation of polyhydroxyalkanoatebased scaffolds and scaffolds with multipotent mesenchymal stromal cells. There were no rejection and acute inflammatory response of the implanted biopolymeric materials. The connective tissue capsule has formed around the implanted materials. Active cell infiltration of the implanted material and its vascularization have been observed. The implanted scaffolds undergo slow biodegradation. The presence of multipotent mesenchymal stromal cells on the scaffold surface slows down the resorption rate of the polymer.В статье представлены результаты гистологического исследования местной реакции тканей при подкожной имплантации биополимерных матриксов на основе полиоксиалканоатов и мультипотентных мезенхимальных стромальных клеток. Показано, что имплантированный материал не вызывает отторжения и острой воспалительной реакции. Вокруг имплантированных материалов формируется соединительнотканная капсула. Наблюдается активная инфильтрация имплантированного материала клетками и васкуляризация. Имплантированные матриксы подвергаются медленной биодеструкции. Наличие мультипотентных мезенхимальных стромальных клеток на поверхности матриксов замедляет скорость резорбции полимера

ТКАНЕИНЖЕНЕРНЫЙ МАТРИКС, МОДИФИЦИРОВАННЫЙ БИОЛОГИЧЕСКИ АКТИВНЫМИ МОЛЕКУЛАМИ ДЛЯ НАПРАВЛЕННОЙ РЕГЕНЕРАЦИИ ТКАНЕЙ

Search of an ideal polymer for the preparation of the artificial scaffolds is an important goal of vascular tissue engineering. Biofunctionalization of the scaffolds may assist in creation of the bioactive environment at the site of implantation. Combination of biodegradable polymers and growth factors may be an appropriate approach for the directed regeneration of the vascular tissues.Purpose. To assess tissue reaction to nonwoven scaffolds prepared from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/polycaprolactone (PCL) with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and stromal-derived growth factor-1α (SDF -1α) implanted into the rat pericardial sac.Materials and methods. Nonwoven PHBV/PCL scaffolds with and without VEGF, bFGF, and SDF -1α were prepared using electrospinning and implanted into the rat pericardial sac for 2 weeks, 1, 2, and 3 months with the further histological examination.Results. Implantation of the scaffolds did not cause any inflammatory reaction. We detected an active neoangiogenesis in both PHBV/PCL/VEGF and PHBV/PCL/SDF -1α scaffolds and adjacent tissues at all the time points. Moreover, we observed a considerable cell infiltration and production of extracellular matrix in PHBV/PCL/SDF -1α scaffolds. PHBV/PCL/bFGF scaffolds were colonized by fibroblasts and were surrounded by a connective tissue capsule. Therefore, growth factors retained their bioactivity in the tissues during the whole time of the experiment.Conclusions. Incorporation of the growth factors into biodegradable polymers is an appropriate approach for the creation of thetissue engineered scaffolds for directed tissue regeneration. VEGF, bFGF, and SDF -1α may be used for the creation of biodegradable vascular graft promoting de novo formation of the vascular tissue after the implantation.Важной задачей тканевой инженерии кровеносных сосудов является поиск материалов для изготовления искусственного матрикса, применяемого в качестве основы для восстановления тканей. Особый интерес представляет модификация матриксов для создания биологически активной среды в месте имплантации. Возможным решением данной проблемы может стать комбинирование биодеградируемых полимеров, ростовых факторов и хемоаттрактантных молекул.Цель. Оценить реакцию окружающих тканей на нетканные матриксы из полигидроксибутирата/валерата (ПГБВ) и поликапролактона (ПКЛ) с VEGF, bFGF и SDF -1α, имплантированные на переднюю поверхность сердца крыс.Материалы и методы. Нетканные матриксы ПГБВ/ПКЛ, немодифицированные и модифицированные сосудистым эндотелиальным фактором роста (VEGF), основным фактором роста фибробластов (bFGF) или хемоаттрактантной молекулой SDF -1α, изготавливали методом двухфазного электроспиннинга и имплантировали на переднюю поверхность сердца крыс сроком на 2 недели, 1, 2 и 3 месяца. По истечении срока наблюдения матриксы эксплантировали с прилежащими тканями и проводили гистологическое исследование.Результаты. Имплантация пустых и биофункционализированных ПГБВ/ПКЛ-матриксов не вызывала местной воспалительной реакции. В матриксах с VEGF и прилежащих к ним тканях отмечали активный ангиогенез на протяжении 3 месяцев. Образцы этой группы отличались умеренной клеточной инфильтрацией. ПГБВ/ПКЛ+bFGF-матриксы были значительно заселены фибробластами и окружены наиболее выраженной соединительнотканной капсулой. В матриксах с инкорпорированным SDF -1α наблюдали активную инфильтрацию клетками, синтезирующими внеклеточный матрикс, и неоангиогенез с образованием более крупных кровеносных сосудов относительно всех исследуемых образцов. Таким образом, инкорпорированные молекулы после высвобождения из матрикса проявляли биологическую активность в окружающих тканях в течение всего эксперимента.Заключение. Введение ростовых факторов и хемоаттрактантных молекул в биодеградируемые полимеры позволяет создавать тканеинженерные матриксы, обладающие бионаправленностью своего действия. Данный подход с использованием VEGF, bFGF и SDF -1α может быть использован в разработке функционально активного биодеградируемого сосудистого графта, способствующего формированию in situ ткани de novo после имплантации

Collective consciousness and its pathologies: Understanding the failure of AIDS control and treatment in the United States

We address themes of distributed cognition by extending recent formal developments in the theory of individual consciousness. While single minds appear biologically limited to one dynamic structure of linked cognitive submodules instantiating consciousness, organizations, by contrast, can support several, sometimes many, such constructs simultaneously, although these usually operate relatively slowly. System behavior remains, however, constrained not only by culture, but by a developmental path dependence generated by organizational history, in the context of market selection pressures. Such highly parallel multitasking – essentially an institutional collective consciousness – while capable of reducing inattentional blindness and the consequences of failures within individual workspaces, does not eliminate them, and introduces new characteristic malfunctions involving the distortion of information sent between workspaces and the possibility of pathological resilience – dysfunctional institutional lock-in. Consequently, organizations remain subject to canonical and idiosyncratic failures analogous to, but more complicated than, those afflicting individuals. Remediation is made difficult by the manner in which pathological externalities can write images of themselves onto both institutional function and corrective intervention. The perspective is applied to the failure of AIDS control and treatment in the United States