Physics of Solid and Liquid Alkali Halide Surfaces Near the Melting Point

This paper presents a broad theoretical and simulation study of the high temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface by the melt. Simulations are conducted using two-body rigid ion BMHFT potentials, with full treatment of long-range Coulomb forces. After a preliminary check of the description of bulk NaCl provided by these potentials, which seems generally good even at the melting point, we carry out a new investigation of solid and liquid surfaces. Solid NaCl(100) is found in this model to be very anharmonic and yet exceptionally stable when hot. It is predicted by a thermodynamic integration calculation of the surface free energy that NaCl(100) should be a well ordered, non-melting surface, metastable even well above the melting point. By contrast, the simulated liquid NaCl surface is found to exhibit large thermal fluctuations and no layering order. In spite of that, it is shown to possess a relatively large surface free energy. The latter is traced to a surface entropy deficit, reflecting some kind of surface short range order. Finally, the solid-liquid interface free energy is derived through Young's equation from direct simulation of partial wetting of NaCl(100) by a liquid droplet. It is concluded that three elements, namely the exceptional anharmonic stability of the solid (100) surface, the molecular short range order at the liquid surface, and the costly solid liquid interface, all conspire to cause the anomalously poor wetting of the (100) surface by its own melt in the BMHFT model of NaCl -- and most likely also in real alkali halide surfaces.Comment: modified version of JCP 123, 164701 15 pages, 25 figure

Melting and nonmelting of solid surfaces and nanosystems

We present an extensive but concise review of our present understanding, largely based on theory and simulation work from our group, on the equilibrium behavior of solid surfaces and nanosystems close to the bulk melting point. In the first part we define phenomena, in particular surface melting and nonmelting, and review some related theoretical approaches, from heuristic theories to computer simulation. In the second part we describe the surface melting/nonmelting behavior of several different classes of solids, ranging from van der Waals crystals, to valence semiconductors, to ionic crystals and metals. In the third part, we address special cases such as strained solids, the defreezing of glass surfaces, and rotational surface melting. Next, we digress briefly to surface layering of a liquid metal, possibly leading to solid-like or hexatic two dimensional phases floating on the liquid. In the final part, the relationship of surface melting to the premelting of nanoclusters and nanowires is reviewed.Comment: 54 pages, 26 figure

The problem of injuries in volleyball

The article deals with the characteristics and description of volleyball, its impact on athletes and the problems associated with injuries when practicing this sport, you will find recommendations on preventing different kind of injuries while playing volleyballВ статье рассмотрена характеристика и описание волейбола, его влияние на спортсменов и проблемы, связанные с травматизмом при занятиях этим видом спорта, приведены рекомендации по пре-дотвращению различного рода травм во время игры в волейбо

Modern methods of Ta₂O₅ coatings deposition for biomedical applications

The study of e-beam evaporated Ta₂O₅ film structure and properties effect on cell/material response was performed. The surface properties and structure of e-beam evaporated Ta₂O₅ films were investigated by means of XPS and XRD methods. The cytotoxicity and cytocompatibility were estimated by in vitro tests. Films of Ta₂O₅ are bio- and chemically inert, which allows their use in various medical applications, e.g., in diagnostic and treatment techniques employing short-range quasi-static electric fields for stimulation of positive biological processes in live organisms.Дослідження структури та властивостей покриттiв Ta₂O₅, які нанесено методом електронно-променевого випарювання, було зроблено методами рентгеноструктурного аналізу та фотоелектронної спектроскопії. Цитотоксичнiсть i цiтосумiснiсть були визначені in vitro. Плiвки Ta₂O₅ мають бiо- та хімічно- інертні властивості, що сприятиме їх застосуванню з метою діагностики та лікування з використанням близькодіючих квазiстацiонарних електричних полів, якi стимулюють позитивні біологічні процеси.Исследования структуры и свойств покрытий Ta₂O₅, нанесенных методом электронно-лучевого испарения, были проведены методами рентгеноструктурного анализа и фотоэлектронной спектроскопии. Цитотоксичность и цитосовместимость были определены in vitro. Пленки Ta₂O₅ являются био- и химически- инертными, возможно их применение для диагностики и лечения с использованием близкодействующих квазистационарных электрических полей, стимулирующих позитивные биологические процессы

Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?

Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted by their own melt at the triple point. We present extensive simulations for NaCl, followed by calculations of the solid-vapor, solid-liquid, and liquid-vapor free energies showing that solid NaCl(100) is a nonmelting surface, and that its full behavior can quantitatively be accounted for within a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting is traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface. The latter is pursued in detail, and it is shown that surface short-range charge order acts to raise the surface tension because incipient NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl much below that of solid NaCl(100).Comment: 4 pages, 3 figure

Tuberous sclerosis syndrome: a typical case of a rare disease

The article is devoted to a rare hereditary disease from the group of phak omatoses with an autosomal dominant type of inheritance — Pringle — Burnevill disease. The questions of the prevalence of the disease, the variability of the clinical picture, the timeliness of the clinical diagnosis are considered. Particular attention is paid to skin manifestations and their differential diagnosis. A clinical case of this disease is described

Features of Physical Training Student Engineers

Вопрос профессиональной физической подготовки актуален в наше время, особенно в процессе обучения будущих инженеров. Представленные опыт и идейные позиции студентов и преподавателей Технического университета УГМК связанные с особенностями физической подготовки студентов-инженеров, а также разработанные на основе анализа деятельности специалистов в данной сфере деятельности индивидуальные комплексы физических упражнений позволили повысить уровень теоретических знаний и физической подготовленности обучающихся Технического университета УГМК направлений подготовки Горное дело, Технологические машины и оборудование, Электроэнергетика и электротехника, Металлургия и Автоматизация технологических процессов и производств