Charge density of Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sb

Charge density calculations and electronic band structures for Ga _x Al_{1 − x} Sb with x = 1.0, 0.5 and 0.0 are presented in this work. The calculations are performed using the empirical pseudopotential method. The charge density is computed for a number of planes, i.e. z = 0.0, 0.125 and 0.25 A ₀ by generating the potential through a number of potential parameters available in the literature. The virtual crystal approximation was applied for the semiconducting alloy. The characteristics of the band structure and charge density are observed to be affected by the potential parameters. Calculated band gaps and the nature of gaps are in good agreement with the experimental data reported. The ionicity is also reasonably in good agreement with other scales proposed in the literature; however the formulation needs to be improved. The present work also demands indirect experimental band gap for the alloy.      

Hard magnetic properties in Pr2Fe14B/α-Fe nanocomposite magnets with a combined addition of V and C

Nanostructured Pr₈Fe_86−xV_xB_6−yC_y (x=0, 1; y=0, 1) ribbons composed of Pr₂Fe₁₄B and α-Fe phases with a high coercivity are fabricated by direct melt spinning. The effects of a single addition of V and a combined addition of V and C on the structures and magnetic properties of melt-spun Pr₈Fe₈₆VB_6−xC_x (x=0 and 1) ribbons have been investigated. Compared with addition-free ribbons, 1 at% V addition is found to reduce the grain sizes of the samples and improve their magnetic properties due to a strong exchange coupling between the hard and the soft phase. A remanence ratio of 0.82, a coercive field of 6.2 kOe and a maximum energy product of 23.4 MGOe in melt-spun Pr₈Fe₈₅VB₆ ribbons are obtained at room temperature. The combined addition of V and C is found to lead to the formation of an intermediate phase of VC at grain boundaries, which appears as a pinning barrier during magnetization and results in an increase of the coercivity value to 6.9 kOe for melt-spun Pr₈Fe₈₅VB₅C ribbons.     

Li3V2(PO4)3/C正极材料在不同电压区间的电化学行为及容量衰减原因

采用溶胶-凝胶法制备锂离子电池正极材料Li₃V₂(PO₄)₃/C. 通过恒电流充放电测试、循环伏安(CV)、电化学阻抗谱(EIS)等方法, 研究了Li₃V₂(PO₄)₃/C 在不同电压区间的电化学行为(3.0-4.5 V和3.0-4.8 V). 结果表明, 3.0-4.8 V电压区间的循环性能和倍率性能均不及3.0-4.5 V电压区间的. 3.0-4.5 V区间0.1C (1C=150mA·g^-1)倍率首次放电比容量为127.0 mAh·g^-1, 循环50次后容量保持率为99.5%, 而3.0-4.8 V区间的分别为168.2 mAh·g^-1和78.5%. 经过高倍率测试后再回到0.1C倍率充放电, 3.0-4.5 V和3.0-4.8 V的放电比容量分别为初始0.1C倍率的99.0%和80.7%. 经过3.0-4.8 V电压区间测试后, 少部分第三个锂离子能够在低于4.5V的电压脱出, 使3.0-4.5 V电压区间的放电比容量提升了7.4%. CV结果表明3.0-4.8 V区间的容量损失主要表现为第一个锂离子的不可逆损失. 极片的X射线衍射(XRD)和X射线光电子能谱(XPS)分析测试结果表明经过3.0-4.8 V测试后, Li₃V₂(PO₄)₃的结构发生了轻微的改变. 电感耦合等离子体(ICP)测试结果表明循环后的电解液中含有少量的V. 结构变形和V溶解可能是Li₃V₂(PO₄)₃在3.0-4.8 V区间容量衰减的主要原因.     

Design of a reentrant double staggered ladder circuit for V-band coupled-cavity traveling-wave tube

The reentrant double staggered ladder slow-wave structure is employed in a high-power V-band coupled-cavity traveling-wave tube. This structure has a wide bandwidth, a moderate interaction impedance, and excellent thermal dissipation properties, besides the easy fabrication. A well-matched waveguide coupler is proposed for the structure. Combining the design of attenuators, a full-scale three-dimensional circuit model for the V-band coupled-cavity traveling-wave tube is constructed. The electromagnetic characteristics and the beam--wave interaction of this structure are investigated. The beam current is set to be 100 mA, and the cathode voltage is tuned from 16.8 kV to 15.8 kV. The calculation results show that this tube can produce a saturated average output power over 100 W with an instantaneous bandwidth greater than 1.25 GHz in the frequency ranging from 58 GHz to 62 GHz. The corresponding gain and electronic efficiency can reach over 32 dB and 6.5%, respectively.     

Synthesis, characterization and crystal structures of tri- and tetraphenylantimony(V) compounds containing arylcarbonyloxy moiety

A series of tri- and tetraphenylantimony(V) compounds containing arylcarbonyloxy moiety have been synthesized and characterized by elemental analysis, IR, and NMR spectroscopy. Attempts to grow crystals led to colorless blocks identified by X-ray diffraction as (ArCOO)₂SbPh₃ or (ArCOO)SbPh₄.     

ESCA-studies of the structure and composition of the passive film formed on stainless steels by various immersion times in 0.1 M NaCl solution

This report deals with the structure of the passive film formed on stainless steels during immersion in a 0.1 M NaCl solution for various immersion times. The film was examined using ion etching and Electron Spectroscopy for Chemical Analysis (ESCA).Through the chemical-composition profiles a three-factor model was developed to describe the structure of the passive films: a hydrated layer in contact with the solution, an oxide layer consisting of iron and chromium oxides having maxima at depths of 3 and 10 Å, respectively, and a metallic layer enriched in nickel. There is a smooth transition between the layers, with the thickness of the outer two layers being about 15 A. The maximum concentration of iron in the oxidized state decreases with increasing immersion time concomitant with an increase in both the maximum concentration of chromium in the oxidized state and the maximum concentration of nickel in the metallic state.It is found that air-formed films have similar structures to films formed by exposure to the solution. Longer air exposure thickens the air-formed film, with the maximum of both oxidized iron and chromium nearly equal in magnitude in comparison with the solution formed films. Films formed by short-time exposure only to the solution are somewhat thinner indicating that the total history is important in determining the structure of these passive films, whereas passive films formed by exposures of 15 h to the solution are no longer strongly dependent on prior air exposure.     

Silyl Modification of Biologically Active Compounds. 7. Synthesis, Structure, Physicochemical and Biological Properties of Some Silicon-containing “3+1” Oxorhenium(V) Complexes

With the aim of studying the structure-physicochemical properties-biological activity relation, we have synthesized a series of organosilicon neutral oxorhenium(V) complexes with mixed ligands and we have determined their lipophilicity. X-ray diffraction has been used to establish the molecular structure of (3-triphenylsiloxypropanethiolato)(3-thiapentane-1,5-dithiolato)oxorhenium(V), (2-trimethylsiloxy- and 2-hydroxyethanethiolato)[3-(N-methyl)azapentane-1,5-dithiolato]oxorhenium(V). We have studied the neurotropic properties and acute toxicity of the synthesized complexes in vivo and their dependence on the nature of the monodentate and tridentate ligands. We have established that all the studied compounds have pronounced sedative action (they prolong the life of mice under hypoxia conditions, they are phenamine antagonists, they exhibit anticonvulsive action and prevent retrograde amnesia).     

Rigidity in CR geometry: The Schoen-Webster theorem

The Schoen-Webster theorem asserts that a strictly pseudoconvex CR manifold whose automorphism group acts nonproperly is either the standard sphere or the Heisenberg group. The purpose of this paper is to survey successive works around this result and then provide a short geometric proof in the compact case.     

Fatigue Loading and Life Prediction in Three Fretting Fatigue Fixtures

Three fixtures for conducting laboratory fretting fatigue tests are described and their respective testing methods and the results of the analysis are compared. Each of these fixtures has been used to investigate the effects of various parameters of interest in fretting fatigue. These fixtures include a unique apparatus in which all load applied to the specimen is transferred to the fretting pads, an apparatus similar to many found in the literature where partial load transfer occurs across the pads, and a simplified dovetail fixture in which the clamping load, P, and the shear load, Q, are varied in phase. Select test conditions from prior experiments performed on identical material and resulting in similar lives ranging from one to ten million cycles from these fixtures are identified. The various testing conditions were used to compute the unique stress field for each case. The resulting contact stresses were used to calculate crack initiation based criteria, and to calculate stress intensity factors. The three fixtures were shown to be able to accommodate a range of loads, fretting pad contours, and specimen geometries that produced a variety of stress fields. A crack-initiation-based criterion was shown to predict the failure lives of thinner specimens accurately. The stress intensity factor calculations showed the possibility of a crack arresting for a stress field that decays rapidly and the possibility of a local minimum for K as a function of depth. The fixtures are shown to be complementary in generating data for development of robust fretting fatigue models that use these criteria.