Friction behavior of silicon in contact with titanium, nickel, silver and copper

Sliding friction experiments are conducted with the semiconductor silicon in contact with the metals titanium, nickel, copper, and silver. Sliding is on the (111) plane of single-crystal silicon in the 112 crystallographic direction both in dry and lubricated (mineral oil) sliding. The friction coefficient in dry sliding is controlled by adhesion and the surface chemical activity of the metal. The more active the metal the stronger the adhesion and the higher the friction. In lubricated sliding the lubricant absorbs to the surfaces and reduces the importance of metal chemical effects. In lubricated sliding, silicon ceases to behave in a brittle manner and undergoes plastic deformation under load

Effect of barrier height on friction behavior of the semiconductors silicon and gallium arsenide in contact with pure metals

Friction experiments were conducted for the semiconductors silicon and gallium arsenide in contact with pure metals. Polycrystalline titanium, tantalum, nickel, palladium, and platinum were made to contact a single crystal silicon (111) surface. Indium, nickel, copper, and silver were made to contact a single crystal gallium arsenide (100) surface. Sliding was conducted both in room air and in a vacuum of 10 to the minus 9th power torr. The friction of semiconductors in contact with metals depended on a Schottky barrier height formed at the metal semiconductor interface. Metals with a higher barrier height on semiconductors gave lower friction. The effect of the barrier height on friction behavior for argon sputtered cleaned surfaces in vacuum was more specific than that for the surfaces containing films in room air. With a silicon surface sliding on titanium, many silicon particles back transferred. In contrast, a large quantity of indium transferred to the gallium arsenide surface

Снегозадерживающие лесные насаждения в мировой практике

In winter, in the countries with snow covered regions, one of the main tasks of road maintenance is to combat snow deposits, snowpacks and snowdrifts on the roadway. Living snow fences consisting of tree and shrub plantings are among known world practices to protect roads against effects of snow deposits. They are environmentally friendly, durable and have great snow retention capacity. However, there are several constraints regarding application of those practices.The analysis of the design, spacing and planting schemes refers to Russian and foreign living snow fences used to protect highways, considers the features, advantages, and disadvantages of living fences in different countries. Japanese and American designs are reviewed as international experience. The influence of the state of trees on the efficiency of their snow-retaining function has been determined. As a result, the need for monitoring and proper maintenance of existing living snow fences throughout their life cycle was confirmed using the examples of surveys of forest plantations in Kazakhstan and in Volgograd region of the Russian Federation.The author presents promising directions for improving the structures and planting schemes of snow storage living fences, namely, an integrated approach to their design as of a protection not only against snowdrifts, but also against pollutants. Such solutions include the design of protective living fences using only tall shrubs, providing the best blowing of roadside areas and dispersion of contaminants. Another solution is to complement the species planted within living fences with willow and corn. Besides, referring to global climate changes, an important task for modern science has been identified, that is to update the current standards for the design of living fences under the current meteorological conditions.Recommendations on the use of mathematical modelling with the help of computer software are suggested regarding development of new configurations of living fences, assessment of their effectiveness, as well as on the adoption of modern technologies such as video cameras and drones during field tests. В зимний период одной из основных задач содержания автомобильных дорог в странах со снежным покровом является борьба со снежными отложениями на проезжей части. С целью защиты автомобильных дорог от снега в мировой практике прибегают к посадке снегозадерживающих лесных насаждений. Они экологичны, долговечны и обладают большой снегозадерживающей способностью. Однако, есть ряд ограничений в их использовании.Приведён анализ конструкций и схем посадки отечественных и зарубежных снегозадерживающих лесных насаждений, применяемых на автомобильных дорогах, рассмотрены особенности, преимущества и недостатки лесных насаждений в разных странах. В качестве зарубежного опыта рассмотрены японские и американские конструкции. Определено влияние состояния деревьев на эффективность их работы. Как следствие, подтверждена необходимость мониторинга и надлежащего ухода за существующими лесопосадками на протяжении их жизненного цикла на примере обследований лесных насаждений в Казахстане и в Волгоградской области Российской Федерации.Автором приведены перспективные направления по усовершенствованию конструкций и схем посадки снегозадерживающих лесополос, а именно комплексный подход к проектированию данных средств защиты не только от снега, но и от загрязняющих веществ. К таким решениям относится конструкция защитных лесополос с применением только высокорослых кустарников, обеспечивающая наилучшее продувание придорожных территорий и рассеивание контаминантов. Другим решением является включение в состав лесопосадок дополнительно таких растений, как ива и кукуруза. Кроме этого, в связи с глобальными изменениями климата определена важная для современной науки задача обновления действующих норм проектирования лесополос в актуальных на сегодняшний день метеорологических условиях.Даны рекомендации по применению математического моделирования при помощи компьютерных программ при разработке новых конфигураций лесных посадок и оценке эффективности их работы, а также по внедрению современных технологий, таких как видеокамеры и дроны, при натурных испытаниях.

Electromagnetically induced transparency in inhomogeneously broadened Lambda-transition with multiple excited levels

Electromagnetically induced transparency (EIT) has mainly been modelled for three-level systems. In particular, a considerable interest has been dedicated to the Lambda-configuration, with two ground states and one excited state. However, in the alkali-metal atoms, which are commonly used, hyperfine interaction in the excited state introduces several levels which simultaneously participate in the scattering process. When the Doppler broadening is comparable with the hyperfine splitting in the upper state, the three-level Lambda model does not reproduce the experimental results. Here we theoretically investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that it can be strongly reduced due to the presence of multiple excited levels. Given this model, we also show that a well-designed optical pumping enables to significantly recover the transparency

Estabilidad y funcionalidad de sellantes dentales en altas temperaturas ambientales

Los sellantes dentales son materiales que se emplean en estomatología para sellar las fosas y fisuras oclusales de los dientes y evitar la adherencia del estreptococus mutans agente que produce la caries dental. Estos materiales se suministran en dos partes que al mezclarse producen el endurecimiento de la resina. Sin embargo, estos productos presentan dificultades para su comercialización en los países tropicales, debido a que las altas temperaturas ambientales traen problemas en su manipulación y almacenamiento en lugares sin control de clima. En Cuba se desarrolló un sellante dental, CUBRIDEM, el cual cumple con las normativas internacionales y mantiene su estabilidad como mínimo por un año, entre 2 y 8 °C . El objetivo de este trabajo ha sido obtener una variante de CUBRIDEM más estable a mayores temperaturas y con tiempos de trabajo (TT) y de fraguado (TF) adecuados, cuando el producto se manipula en ambientes no climatizados. Se realizaron diseños experimentales factoriales 23 donde se estudió la influencia de la concentración de los componentes minoritarios: peróxido de benzoílo (PBO), N,N-dimetil p-toluidina (DMPT) y éter monometílico de la hidroquinona (MHQ), manteniendo invariable la composición de la mezcla monomérica Bis-GMA/Dimetacrilato de tetraetilenglicol: 1/1. El sellante, compuesto por un Diluyente que contiene 0.8 % de PBO y 0.05 % de MHQ y una Base con 0.8 % DMPT, manipulado a 30±2°C después de un almacenamiento por dos meses a la misma temperatura, permite obtener valores de TT y TF cercanos a los deseados. Por otra parte, el almacenamiento a 16±2°C y un contenido de 0,6 % de DMPT en la Base permiten lograr tiempos similares para almacenamientos más prolongados. Los resultados de las regresiones lineales sugieren que, para un almacenamiento a 16±2°C, contenidos de 0.7 %, tanto de PBO en Diluyente como de DMPT en Base, posibilitan alcanzar tiempos satisfactorios: TT=44 s y TF=113 s.Peer Reviewe

Surgical management of ovarian dermoid cysts in children and adolescents

Department of Obstetrics and Gynecology, Medical University “N. Testemitsanu”, Kishinev, MoldovaIntroduction: The ovarian dermoid cysts are one of the most common neoplastic ovarian injuries found both in children and teenagers. For the girls with small ovarian diseases organ preserving operation it's extremely important for a proper functioning of puberty and future fertility. Purpose and Objectives: The aim of study was to present the reasons for making these surgeries in all the cases of ovarian dermoid cysts in order to ensure fertility and menstruation every month. Methods and materials: A prospective and retrospective analysis of all the ovarian cysts both in children and teenagers aged between 8 and 18, from the year 2000 through 2012 admitted in the Institute of Mother and Child Care, the department of operative gynecology was performed. Results: The ovarian dermoid cysts were localized mostly in the right side having a percentage of 64.7 vs. 35.3 for the left side. Cysts outermost dimension were 79.6±7.2 mm (95% CI:64.30-94.82) and minimum were - 65.1±6.5 mm (95% C l:51.21 -79.04), from 56 to 156 mm. Laparatomy was the surgery that was mostly used - 14/17 (82.4%), and laparoscopy was done only in 3/17 (17.6% ) cases. All of the organ preserving operations were statistically more common (p<0.001) over ovariectomy and were 14/17 (82.4%) vs. 3/17 (17.6%). Conclusions: It is vital to have a proper surgical approach for all the children and teenagers with ovarian cysts for maintaining a good sexual growth and fertility in the near future. These surgeries are the best method for this group of patient

Ferroelectric Nanotubes

We report the independent invention of ferroelectric nanotubes from groups in several countries. Devices have been made with three different materials: lead zirconate-titanate PbZr1-xTixO3 (PZT); barium titanate BaTiO3; and strontium bismuth tantalate SrBi2Ta2O9 (SBT). Several different deposition techniques have been used successfully, including misted CSD (chemical solution deposition) and pore wetting. Ferroelectric hysteresis and high optical nonlinearity have been demonstrated. The structures are analyzed via SEM, TEM, XRD, AFM (piezo-mode), and SHG. Applications to trenching in Si dynamic random access memories, ink-jet printers, and photonic devices are discussed. Ferroelectric filled pores as small as 20 nm in diameter have been studied