A DISCRETE ELEMENT FORMALISM FOR MODELLING WEAR PARTICLE FORMATION IN CONTACT BETWEEN SLIDING METALS

The paper describes an advanced discrete-element based mechanical model, which allows modelling contact interaction of ductile materials with taking into account fracture and surface adhesion by the cold welding mechanism. The model describes these competitive processes from a unified standpoint and uses plastic work of deformation as a criterion of both local fracture and chemical bonding of surfaces in contact spots. Using this model, we carried out a preliminary study of the formation of wear particles and wedges during the friction of rough metal surfaces and the influence of the type of forming third body (interfacial) elements on the dynamics of the friction coefficient. The qualitative difference of friction dynamics in the areas of the contact zone characterized by different degrees of mechanical confinement is shown

Delirium in Children after Cardiac Surgery: Brain Resuscitation

This chapter presents the current data on delirium in children in the postoperative period with the correction of congenital heart defects. The analysis of the causes of delirium, according to the literature data, pathophysiology, clinical signs, and methods of diagnosis of postoperative delirium, is shown. In addition, methods for the prevention of delirium in children during cardiac surgery are presented

Chiral criticality in doped Mn1−y_{1-y}Fey_ySi compounds

The critical spin fluctuations in doped compounds Mn$_{1-y}$Fe$_y$Si have been studied by means of ac-susceptibility measurements, polarized neutron small angle scattering and spin echo spectroscopy. It is shown that these compounds undergo the transition from the paramagnetic to helimagnetic phase through continuous, yet well distinguishable crossovers: (i) from paramagnetic to partially chiral, (ii) from partially chiral to highly chiral fluctuating state. The crossover points are identified on the basis of combined analysis of the temperature dependence of ac-susceptibility and polarized SANS data. The whole transition is marked by two inflection point of the temperature dependence of ac-susceptibility: the upper one corresponds to the crossover to partially chiral state at $T^*$, where the inverse correlation length $\kappa \approx 2 k$, the lower one corresponds to the transition to the spin helix structure. The intermediate crossover to the highly chiral phase is observed at the inflection point $T_k$ of the first derivative of ac-susceptibility, where $\kappa \approx k$. The temperature crossovers to the highly chiral fluctuating state is associated with the enhancing influence of the Dzyaloshinskii-Moria interaction close to $T_c$.Comment: 5 pages, 5 figures, 1 table, 13 cite

Development of a formalism of discrete element method to study mechanical response of geological materials and media at different scales

A general approach to realization of models of elasticity, plasticity and fracture of heterogeneous materials within the framework of particle-based discrete element method is proposed in the paper. The approach is based on constructing many-body forces of particle interaction, which provide response of particle ensemble correctly conforming to the response (including elastic-plastic behavior and fracture) of simulated solids. For correct modeling of inelastic deformation and failure of geological materials and media at "high" structural scales (relative to the scale of grains) an implementation of dilatational Nikolaevsky's model of plasticity of rocks within the framework of mathematical formalism of discrete element method is proposed. Perspectives of multiscale modeling of geological materials from grainrelated scale up to macroscopic scale within the same numerical technique (DEM) are discussed

Trigonal-bipyramidal Anion [Ph2Cl3Sn]- in the Structure of N-[(Diethylphosphoryl)methyl] piperidinium Diphenyltrichlorostannate(IV)

Crystal structure of N-(diethylphosphoryl)methyl-piperidinium diphenyltrichlorostannate(IV), C10H23NO3P+ C12H10Cl3Sn- has been determined, a = 11.416(2), b = 11.582(2), c = 12.491(2) Å, α = 69.82(2), β = 81.22(2), γ = 60.73(2)°, space group P1̅, 4493 reflections, R(F) = 0.0271, wR(F2) = 0.0712. The structure consists of isolated trigonal-bipyramidal anions and hydrogen-bonded dimers formed by cations. The impact of secondary Sn⋅⋅⋅Cl interactions on the geometry of complex anions is discussed

РОЛЬ ГИПОТЕРМИИ ДЛЯ ЦЕРЕБРОПРОТЕКЦИИ ПРИ ХИРУРГИЧЕСКОЙ КОРРЕКЦИИ ВРОЖДЕННЫХ ПОРОКОВ СЕРДЦА

HighlightsThis article is devoted to a review of studies on the mechanisms of cerebral protection and the effects of hypothermia on the patient. AbstractA large number of surgical corrections of congenital heart defects are performed around the world annually, most of them using cardiopulmonary bypass. This kind of surgery can be a pathological factor for the brain. In some patients, the kind of surgery involves the use of hypothermia. Supposedly, hypothermia should have a neuroprotective effect, however, as recent studies show, this is not always the case. This review is devoted to the mechanisms of the effect of hypothermia on the patient’s body, including not only a decrease in brain metabolism, but also a number of others. Moreover, a review of current works on the use of hypothermia in clinical practice in surgeries that do not require circulatory arrest is presented, along with an analysis of the intra- and postoperative period.Основные положенияПредставлен обзор исследований о механизмах церебропротекции и влиянии гипотермии на пациента. РезюмеЕжегодно в мире проводят большое количество хирургических коррекций врожденных пороков сердца, большую часть из них – с использованием искусственного кровообращения. Любая такая операция имеет набор патологических для головного мозга факторов, в некоторых хирургическая стратегия предполагает применение гипотермии. В частности, гипотермия должна обладать нейропротективным эффектом, однако, как показывают последние исследования, это не всегда так. Обзор посвящен механизмам влияния гипотермии на организм пациента, среди которых не только снижение метаболизма мозга, но и ряд других. Представлены актуальные работы о применении гипотермии при операциях, не требующих циркуляторного ареста, с анализом интра- и послеоперационного периода

Влияние трансфузии и гипоксии на клетки модели нейроваскулярной единицы in vitro

Up to 57% of patients develop postoperative delirium after surgery for congenital heart defects (CHD). To reduce cerebral damage in pediatric patients during CHD surgery it is important to find out what inflicts the worse damage: would it be a systemic inflammatory response (SIR) triggered by transfusion, or hypoxia developed in non-transfused patients? In vitro evaluation of hypoxia and SIR effects on the neurovascular unit (NVU) cells might contribute to finding the answer.The aim of the study was to compare the effect of varying severity hypoxia and SIR on the functional activity of NUV cells in vitro.Materials and methods. An in vitro NVU model was designed including neurons, astrocytes and endotheliocytes. The effect of hypoxia on NVU was evaluated in the control (C) and 4 study groups (H 1-4), formed based on O2 content in the medium. The C group NVU were cultivated in standard conditions: N2-75%, O2-20%, CO2-5%; H1: N2-99%, O2-1%; H2: N2- 98%, O2-2%; H3: N2-97%, O2-3 %; H4: N2-96%, O2-4%. The significance of the differences was 0.0125. The effect of interleukin-6 (IL-6) content on NVU was measured by adding to culture medium pediatric patients’ serum with known minimal or maximal SIRS-response. The assessment was made in the Control - an intact NVU model, and 2 study groups – “Minimum” and “Maximum”, i.e. samples with minimum or maximum IL-6 content in culture, respectively. The significance of the differences was 0.017. The cells were incubated at a normothermia regimen for 30 minutes. Then, the functional activity of NVU cells was evaluated by measuring transendothelial resistance (TER) for 24 hours and Lucifer Yellow (LY) permeability test at 60 and 90 minutes after the start of the experiment.Results. After incubation under hypoxic conditions, TER changes occurred in all studied groups. However, they were statistically significant only in the group with 1% oxygen content in the medium. TER decrease in this group was observed after 2, 4 and 24 hours. LY permeability also changed at 60 and 90 minutes, similarly - in NVU cultivated with 1% oxygen in the medium. Minimal TER values were documented at 4 hours after patients’ serum was added to NVU cells culture medium, and TER increased at 24 hours in both study groups. Cellular permeability to LY changed significantly after 1 hour exposure in both groups - with minimum and maximum IL-6 content in the medium. Although at 90 minutes, there was no difference between the 3 groups in LY permeability tests.Conclusion: Intensive SIR demonstrated short-term but more deleterious than hypoxia, effect on cells in the NVU model. Hypoxia disrupted functional activity of NUV cells only at 1% O 2 concentration in the medium.Частота развития послеоперационного делирия при коррекции врожденных пороков сердца (ВПС) достигает 57%. В поиске путей профилактики церебрального повреждения при коррекции ВПС у детей важным является вопрос - что опаснее: гипоксия при отказе от трансфузии или действие повышенного системного воспалительного ответа (СВО) при ее применении. Исследование действия гипоксии и СВО на клетки нейроваскулярной единицы (НВЕ) in vitro способствует решению данного вопроса.Цель исследования: сравнить влияние гипоксии различной выраженности и системного воспалительного ответа на функциональную активность клеток нейроваскулярной единицы.Материалы и методы. Сформировали in vitro модель НВЕ, состоящую из нейронов, астроцитов и эндотелиоцитов. Влияние гипоксии на НВЕ оценивали в контрольной (К) и 4 исследуемых (Г1-4) группах. Группы сформировали по содержанию О2 в среде: К – стандартные условия культивирования: N2-75%, O2-20%, CO2-5%; Г1: N2-99 %, O2-1 %; Г2: N2-98 %, O2-2 %; Г3: N2-97 %, O2-3 %; Г4: N2-96 %, O2-4 %. Значимость различий составила 0,0125. Влияние содержания интерлейкина-6 (ИЛ-6) на НВЕ определяли при культивировании клеток с добавлением сыворотки крови пациентов детского возраста с минимальным, либо максимальным напряжением СВО. Оценку провели в контрольной и 2 исследуемых группах: «Контроль» – интактная модель НВЕ; группы «Минимум» и «Максимум» - образцы с минимальным либо максимальным содержанием ИЛ-6 в культуре соответственно. Значимость различий составила 0,017. Инкубацию клеток проводили в режиме нормотермии в течение 30 минут. Затем оценивали функциональную активность клеток НВЕ методом измерения трансэндотелиального сопротивления (ТЭС) в течение 24 часов и измерения проницаемости для красителя Lucifer Yellow (LY) через 60 и 90 минут от начала эксперимента.Результаты. После инкубации в условиях гипоксии изменения ТЭС наступили во всех исследуемых группах клеток. Однако, только в группе с 1% содержанием кислорода в среде они были статистически значимы. Снижения ТЭС в данной группе наблюдали через 2, 4 и 24 часа. Проницаемость клеток для красителя LY изменилась через 60 и 90 минут также только в условиях их инкубации в среде с 1 % кислородом. При культивировании клеток НВЕ с сывороткой крови пациентов выявили минимальные значения ТЭС через 4 часа и их дальнейшее повышение через 24 часа для обеих исследуемых групп НВЕ. Проницаемость клеток для LY значительно изменилась к 60-й минуте как в группе с минимальным, так и с максимальным содержанием ИЛ-6 в среде. При этом к 90-й минуте различий этого показателя в исследуемых группах и в контрольной группе уже не наблюдали.Заключение. Напряженный СВО оказал более выраженное, но кратковременное действие на модель НВЕ, чем гипоксия. Гипоксия нарушила функциональную активность НВЕ только при концентрации кислорода в среде - 1 %

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

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