The cone of curves of Fano varieties of coindex four

We classify the cones of curves of Fano varieties of dimension greater or equal than five and (pseudo)index dim X -3, describing the number and type of their extremal rays.Comment: 27 pages; changed the numbering of Theorems, Definitions, Propositions, etc. in accordance with the published version to avoid incorrect reference

Métodos de avaliação da segurança de pontes existentes

O presente trabalho pretende descrever, de uma forma acessível, os métodos de análise de fiabilidade e a metodologia de verificação da segurança por etapas, que podem ser úteis na avaliação da segurança de pontes existentes. A metodologia apresentada sugere o recurso a uma análise mais avançada sempre que a ponte não cumpra os requisitos estabelecidos no nível de avaliação anterior, culminando no método de avaliação que combina a análise não-linear com a análise probabilística.The present work aims to describe, in an accessible way, the methods of reliability analysis and the step-level assessment methodology, which might be useful in the safety evaluation of existent bridges. The presented methodology suggest to use a more advanced analysis when the bridge doesn’t fulfill the requirements established in the previous safety evaluation level, culminating in the method of evaluation that combines the non-linear and probabilistic analysis.Comissão Europeia - VI Programa Quadro "Sustainable Bridges” FP6-PLT-0165

Сomparative study of arc-to-glow transition efficiency when use multilayer condensed materials in electric contacts

The paper presents and discusses results of the study of arc to glow transformation at breaking of DC inductive load of a low power (less than 10 J) and low voltage (about 250 V). The ratio in duration of arcing and glowing is investigated in dependence on circuit parameters, gas quenching medium and its pressure and in particular on contact material. The transition, to complete the study, was analyzed also by means of fast photography and radiation spectra measurements. On the basis of the results the conclusions on possibility of control of the arc to glow transformation, for practical use in low power contact switching devices, are formulated.Представлено і обговорено результати дослідження дуги, що горить, при відключенні постійного струму з індуктивним навантаженням малої потужності (менше 10 Дж) і низької напруги (біля 250 В). Відношення тривалості горіння дуги і жевріючого розряду досліджується в залежності від параметрів ланцюга, виду гасильного газу та його тиску і, головним чином, від контактного матеріалу. Для повноти дослідження змінення типу розряду аналізували також за допомогою швидкісної зйомки і вимірювання спектрів випромінювання. На основі одержаних результатів сформульовано висновки про можливість практичного застосування контролю переходу дуги в жевріючий розряд в малопотужних контактах комутуючих пристроїв.Представлены и обсуждены результаты исследования дуги, горящей при отключении постоянного тока с индуктивной нагрузкой малой мощности (менее 10 Дж) и низкого напряжения (около 250 В). Отношение продолжительности горения дуги и тлеющего разряда исследовано в зависимости от параметров цепи, вида гасящего газа и его давления и, главным образом, от контактного материала. Для полноты исследования смену типа разряда анализировали также с помощью скоростной съемки и измерения спектров излучения. На основании полученных результатов сформулированы выводы о возможности практического использования контроля перехода дуги в тлеющий разряд в маломощных контактах коммутирующих устройств

CO 2 - reinforced nanoporous carbon potential energy field during CO 2 /CH 4 mixture adsorption. A comprehensive volumetric, in-situ IR, and thermodynamic insight

CO2/CH4 mixture adsorption is very important in different fields like, for example, a biogas purification. Using a comprehensive experimental approach based on volumetric and in-situ FTIR measurements the new results of CO2/CH4 mixture separation on a carbon film are reported. The application of this experimental approach makes it possible to elaborate the effect of enhanced CH4 adsorption at low CO2 concentrations in the adsorbed phase. The presence of this effect is proved experimentally for the first time. This effect is responsible for the deviation of Ideal Adsorption Solution model from the experimental data. To discuss separation mechanism the activity coefficients at constant spreading pressure values are calculated. At low spreading pressure, CO2 activity coefficient is strongly disturbed by the presence of CH4 molecules in the surface mixture. In contrast, the CH4 activity coefficients are remarkably influenced by adsorbed CO2 only at higher CO2 surface concentrations. The obtained activity coefficients are successfully described by a new modification of the Redlich-Kister equation. This modification takes into account the interaction between binary mixture components and an adsorbent. Finally we show that the studied carbon possesses very good CO2/CH4 mixture separation properties, comparable to those reported for other adsorbents

Strong magnetic pair breaking in Mn substituted MgB_2 single crystals

Magnetic ions (Mn) were substituted in MgB_2 single crystals resulting in a strong pair-breaking effect. The superconducting transition temperature, T_c, in Mg_{1-x}Mn_xB_2 has been found to be rapidly suppressed at an initial rate of 10 K/%Mn, leading to a complete suppression of superconductivity at about 2% Mn substitution. This reflects the strong coupling between the conduction electrons and the 3d local moments, predominantly of magnetic character, since the nonmagnetic ion substitutions, e.g. with Al or C, suppress T_c much less effectively (e.g. 0.5 K/%Al). The magnitude of the magnetic moment, derived from normal state susceptibility measurements, uniquely identifies the Mn ions to be divalent, and to be in the low-spin state (S = 1/2). This has been found also in X-ray absorption spectroscopy measurements. Isovalent Mn^{2+} substitution for Mg^{2+} mainly affects superconductivity through spin-flip scattering reducing T_c rapidly and lowering the upper critical field anisotropy H_{c2}^{ab}/H_{c2}^c at T = 0 from 6 to 3.3 (x = 0.88% Mn), while leaving the initial slope dH_{c2}/dT near T_c unchanged for both field orientations.Comment: 9 pages, 9 figure

Morphologically disordered pore model for characterization of micro-mesoporous carbons

We present a new morphologically disordered slit-shaped pore (MDSP) model for simulating gas adsorption in micro-mesoporous carbonaceous materials. The MDSP model qualitatively accounts for the inherent roughness of carbon pore walls in accord with the atomistic structural model of LMA10 reference carbon material. The MDSP model is applied to pore size distribution (PSD) calculations from nitrogen adsorption isotherms measured at 77.4 K in the range of pore widths from 0.72 to 40 nm. The MDSP model improves significantly the nitrogen adsorption porosimetry and, being fully atomistic, it is transferable to study various adsorbate-adsorbent systems. Computations of PSD functions for a series of carbonaceous materials, including activated carbon fiber, granular activated carbons, synthetic activated carbons showed that MDSP generates smooth Gaussian-type PSD functions with a well-defined average pore size. Furthermore, PSD functions computed from the MDSP model are free from the artificial gaps in the region of narrow micropores (∼1 nm and ∼2 nm) predicted from the standard slit-shaped pore models with ideal graphite-like walls. MDSP is not only a complementary model to existing approaches, such as quench-solid density functional theory method, but it paves the way to efficient atomistic simulations of various compounds within morphologically disordered carbon nanopores

Super-sieving effect in phenol adsorption from aqueous solutions on nanoporous carbon beads

Removal of aromatic contaminants, like phenol, from water can be efficiently achieved by preferential adsorption on porous carbons which exhibit molecular sieving properties. Here, we present nanoporous carbon beads exhibiting an outstanding sieving effect in phenol adsorption from aqueous solution at neutral pH, which is evidenced experimentally and theoretically. The molecular sieving with pure phenol adsorbed phase is achieved by tuning the pore size and surface chemistry of the adsorbent. This study elucidates the essential role of hydrophobic interactions in narrow carbon micropores in removal and clean-up of water from organic pollutants. Furthermore, we suggest a new theoretical approach for evaluation of phenol adsorption capacity that is based on the Monte Carlo simulation of phenol adsorption with the relevance to the pore size distribution function determined by the density functional theory method from low temperature nitrogen adsorption

Einstein black holes, free scalars and AdS/CFT correspondence

We investigate AdS/CFT correspondence for two families of Einstein black holes in d > 3 dimensions, modelling the boundary CFT by a free conformal scalar field and evaluating the boundary two-point function in the bulk geodesic approximation. For the d > 3 counterpart of the nonrotating BTZ hole and for its Z_2 quotient, the boundary state is thermal in the expected sense, and its stress-energy reflects the properties of the bulk geometry and suggests a novel definition for the mass of the hole. For the generalised Schwarzschild-AdS hole with a flat horizon of topology R^{d-2}, the boundary stress-energy has a thermal form with energy density proportional to the hole ADM mass, but stress-energy corrections from compactified horizon dimensions cannot be consistently included at least for d=5.Comment: 32 pages. LaTeX with amsfonts, amsmath, amssymb. (v2: References added. v3: Geodesic horizon-crossing clarified in section 2; comparison with quasilocal energy-momentum included in section 4.