Special features of thermal evaporation of rare-earth metals

The process of thermal evaporation of rare-earth metals (Ce-Yb) with an incomplete 4f-shell is discussed in terms of electronic structure of their surface. Evaluation of the surface density of neutral intrinsic atoms determining the evaporation process is made. The fact of detachment of Sm atoms in the lowest excited 4f⁵5d6s²-state from the surface is experimentally demonstrated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 43–47, June, 2006.     

Influence of indentation-forming conditions on the estimation of the photomechanical effect

The anisotropy, spectral dependence, and time dependence of relaxation of the dimensions of microhardness indentations in silicon are investigated. It is shown that the time and spectral dependences correlate with the density of excited carriers in the (defective and elastically deformed) region in which they are excited, and the anisotropy is determined by various types of deformations of the chemical bonds for different positions of the indenter. Fiz. Tverd. Tela (St. Petersburg) 40, 503–504 (March 1998)     

Revêtements modérés et groupe fondamenttal de graphe de groupes

Let R be a discrete complete valuation ring, with algebraically closedresidue field. Let X be a semi-stable R-curve, with smooth generic fibre. In this paper we study tame coverings of X.     

Calculations on the mechanism of ion polymerization in the formaldehyde crystal

A number of possible crystal structures of formaldehyde are calculated using an atom—atom scheme in order to explain some phenomena observed in the low-temperature solid-state polymerization of this and related systems. The structures whose molecular packing favours the polymerization are shown to represent local energy minima. Studies of various molecular motions in so calculated crystals support the hypothesis that polymer chains move spontaneously at the propagation stage. Main peculiarities of the solid-state polymerization mechanism are formulated on the basis of the present and previous calculations.     

Experimental studies of passive correlation tomography of incoherent acoustic sources in the megahertz frequency band

Correlation properties of thermal acoustic radiation in the megahertz frequency band are studied experimentally. The amplitudes of correlation peaks measured at the sum of the delays that correspond to the direct signal propagation between the piezoelectric transducers are found to depend on the relative transducer positions. This effect is explained by a possible difference between the receive patterns of the transducers and the patterns of their intrinsic thermal radiation. The correlation of signals received from a spatial region heated above the ambient medium is measured. The correlation between the received signals is found to depend on the time of heating of the emitter’s working medium. Numerical calculation of temperature distributions and the allowance for the decorrelation effect due to the spatial extent of the source provide a quantitative agreement between the theoretical and experimental results. Estimates of the spatial resolution achievable with the given experimental configuration show that it is close to the coherence length of the received radiation.     

The influence of grain shape,friction and cohesion on granular compaction dynamics

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the influence of the grain shape, the friction and the cohesion between the grains. Two dimensionnal and three dimensionnal systems are analysed. And the role of dimensionality will be emphasized. Theoretical and numerical investigations provide additional informations about that phenomenon. Indeed numerical models permit us to study the influence of some parameters not easily accessible experimentally. Our results show that the above mentioned parameters have a deep impact on the compaction dynamics. Anisotropic grains lead to two different compaction regimes separated by a “burst" of the packing fraction. Friction is observed to modify how the grains are arranged in the pile. This is confirmed by numerical simulations. Cohesive forces between particles inhibit compaction and lead to extremely low values of the packing fraction.     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

Mössbauer spectroscopic study of high-temperature proton-conducting Ba<Subscript>2</Subscript>SnY<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>6 − δ</Subscript> oxides

High-temperature proton-conducting Ba₂SnY_{1 ? x} Fe _x O_{6 ? δ} oxides are studied by Mössbauer spectroscopy on ¹¹⁹Sn and ⁵⁷Fe isotopes. For the perovskite structure, the possible states of anionic vacancies are discussed as a function of the nature of the nearest small cations. It is concluded that the energy of formation of a cation-vacancy-cation defect depends on the overall concentration of vacancies in the compound. As the result, with the increase in the water content in the Ba₂SnYO_{6 ? δ} compound, the equilibrium shifts to the tin-vacancy-tin state.     

甘肃岷县不同生长年限当归药材的红外光谱分析

采用傅里叶变换红外光谱(FTIR)及其二阶导数谱对不同生长年限当归药材进行分析研究.结果表明,不同生长年限当归药材的红外图谱较为相似,仅从一维谱图上无法反映出不同生长年限当归药材的红外特征谱明显的异同,但通过二阶导数图谱中1771、1747、1712、1559、1514、1466、766、711cm-1和668cm-1处的峰型差异可发现不同生长年限当归药材之间的一些成分存在较明显的差异.由于生长时间不同,导致它们的化学成分存在差异,所以体现了各自的红外特征谱,其中第三年当归药材与第一年和第二年当归药材间差异较大.