Calculation of the ��-material for Bulk MgB2 Superconductor

Vickers microindentation tests were carried out on a bulk MgB₂ superconductor with loads ranging from 300 to 1500 mN at room temperature. The load-penetration depth curves were analyzed by a power law of the form P=Ch ^m . The ??-material for bulk MgB₂ is determined.     

Preparation and Characterization of Mg1−x B2 Bulk Samples and Cu/Nb Sheathed Wires with Low Grade Amorphous Boron Powder

MgB₂ bulk and wire samples were prepared using cheap, low grade amorphous boron powders. Based on chemical analysis performed on the starting reagents, three nominal stoichiometries were studied. It was found that the structural and superconducting properties of the bulk samples were not affected by the composition, but that residual Mg was left in the wires for the nominal MgB₂ composition. In contrast, slightly Mg-deficient compositions were free from residual Mg and exhibited higher critical current densities. The MgB₂ phase formation kinetics was not influenced by the variations in the nominal powder composition.     

A New Type of Carbon Resistance Thermometer with Excellent Thermal Contact at Millikelvin Temperatures

Using a new brand of commercially available carbon resistor we built a cryogenic thermometer with an extremely good thermal contact to its thermal environment. Because of its superior thermal contact the thermometer is insensitive to low levels of spurious radio frequency heating. We calibrated our thermometer down to 5 mK using a quartz tuning fork He-3 viscometer and measured its thermal resistance and thermal response time.     

Molecular Dynamics Simulations of Li x Mn2O4 Spinel Solid Solutions with Simple Potential Models

Molecular dynamics simulations of Li _x Mn₂O₄ (0 < x 1) spinel solid solutions were carried out with the use of simple pair potentials available in the literature. The results demonstrate that computer simulations using the existing potentials with an exponential repulsion term fail to adequately reproduce appreciable Li⁺ mobility in a stable (near-zero mobility of the manganese and oxygen ions) crystalline phase. Lennard-Jones potentials make it possible to simulate such a phase at high temperatures (on the order of 1000 K).     

Possible Mechanism of a New Type of Three-Dimensional Quantized Hall Effect in Layered Semiconductors Bi2−xSnxTe3

We have found a new type of three-dimensional quantized Hall effect (QHE) in layered semiconductors Bi₂–xSn_xTe₃ (x0.0125) single crystals. The Hall resistivity is not expressed in a universal relation applicable for a conventional QHE and depends appreciably on the doped Sn concentration x. The flat Hall plateaus are visible at higher Landau levels but are rather suppressed at lower regions. The calculated Landau levels of the upper valence band (UVB) with the best-fit band parameters are in excellent agreement with the experiments, including spin splitting. For Bi₂–xSn_xTe₃, the Sn-originated impurity band (IB) has resonant nature and enhances the density of states at the Fermi level of UVB. The charge transfer occurs between the quantized UVB and the resonant IB or the lower valence band (LVB) for Bi₂–xSn_xTe₃ or Bi₂Te₃, respectively, and the Landau levels are enhanced appreciably. We have revealed that the quasi-localized states are formed in quantized three-dimensional density of state spectra. We have proposed a possible model for the present QHE, which is a modification of Mani's model, where the quasi-localized state is formed at the disorder-originated tail of each Landau level. In the quasi-localized regime, the IB or LVB are responsible for the carrier reservoir to regulate the Hall resistivity.     

New family of binary sequences of period 4(2 n − 1) with low correlation

A new family of binary sequences of period 4(2 ⁿ −1) with low correlation is constructed for integer n = em. Especially, we obtain a new family with family size 2 ⁿ and maximum nontrivial correlation magnitude for odd m and e = 1. Each sequence in the family is constructed by the interleaving of four GKW-like sequences and a perfect sequence. The correlation distribution and linear spans of the sequences are also determined for odd m. This study was supported by the National Natural Science Foundation of China (NSFC) under Grants 60573053, 60603012, 60773134 and 60772086, and by the Chenguang plan of Wuhan City under Grant 200850731340.     

Thermodynamics of the System MgCl2–NaCl–H2O to 573 K: New Measurements of Heat of Mixing and Heat of Dilution

Heats of mixing of NaCl(aq) with MgCl₂(aq) at 373.15, 423.15, 473.15, 523.15, and 573.15 K for ionic strengths of 0.5 to 3.8 mol·kg^–1, and heats of dilution of MgCl₂(aq) at 523.15 and 573.15 K for ionic strengths of 0.3 to 4.6 mol·kg^–1, have been measured at 20.5 MPa. These experimental data are combined with published heat of mixing data at 298 and 373 K to provide a comprehensive Pitzer ion-interaction treatment for the thermodynamic properties of the system to 573 K. The treatment includes a general equation valid to 523 K, incorporating the published equations for NaCl(aq) and MgCl₂(aq), and equations for MgCl₂(aq) and the mixed system valid at 573 K.     

Large Eddy Simulation of a Turbulent Flow in a Differentially Heated Cavity with Rayleigh Numbers up to 1011： Part I,Numerical Methods

Large Eddy Simulations of the anisothermal turbulent flows has been used in the context of interaction problems thermal fluid, structure. In this context, the aim of this work lies not only in identifying the various elements that may underestimate the temperature fluctuations at the interface fluid-solid but also the introduction of the models capable of reproducing the physical setting Thurs. At first, the choice of convection scheme 〈optimizing〉 the scalar transport has led to the adoption of an upwind scheme of theorem 2 order. The use of models with conventional walls showed weaknesses in the estimation of temperature fluctuations bet stalls in the case of boundary layers attached. This work presents a numerical validation of LES-WALE model using the results of the K-epsilon model, this study is based on 3D numerical simulation using FLUENT code calculates to determine the longitudinal velocity, the thermal fields for the configuration the and speed vectors （U, V, W） for configuration in the plane of the recirculation zones for the case of different values of flow Rayleigh. Therefore, the results have good agreement with those of k-epsilon model, as they show the difference between the cases of flows.     

Band gap tuning and nonlinear optical characterization of TiO2–SiO2 nanocomposites with respect to composition and phase

We report on the linear and nonlinear optical studies on TiO₂–SiO₂ nanocomposites with varying percentage ratio. It is found that optical band gap of the material varies with respect to the amount of the SiO₂ in the composite. Nonlinear optical characterization of these samples was studied by using open as well as closed aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). The nanocomposites showed enhanced nonlinear optical properties than pure TiO₂ and this can be attributed to the surface states and weak dielectric confinement of TiO₂ nanoparticles by SiO₂ matrix. The nanocomposites were thermally treated and similar studies were performed. The anatase form of TiO₂ in the nanocomposites showed superior properties relative to the amorphous and rutile phase of the composite. The involved mechanism is explained by taking into account the dominant role played by the excitons in the TiO₂ nanoparticles.     

A Nonclassical Model of a Type 2 Mixture with Vapor–Liquid, Liquid–Liquid, and Three-Phase Equilibria

A model with nonclassical exponents is developed for phase equilibria of a Type 2 mixture with vapor–liquid equilibrium (VLE) and liquid–liquid equilibrium (LLE). Starting with a Leung–Griffiths model for a Type 1 mixture with only VLE, the model adds a Schofield parametric construction to describe LLE and a three-phase locus. Care is taken to suppress a spurious and artificial phase boundary. The model is applied to VLE data of carbon dioxide+methane. It is conjectured that this mixture upon cooling would undergo liquid–liquid separation, but it freezes before such virtual LLE can be observed. Experimental bubble curves and the LLE structure from a classical equation of state are accurately modeled.     

<Emphasis Type="Italic">PVT</Emphasis> Relationships of Binary Mixtures of Indole with 2-Methylnaphthalene and Biphenyl at 333.15 K and Pressures up to 270 MPa

PVT relationships of two binary mixtures of indole with 2-methylnaphthalene and with biphenyl have been measured at 333.15 K and at pressures up to 270 MPa or up to near the freezing pressure of each mixture. The compositions in mole fraction of indole were set to be 0.2500, 0.5000, and 0.7500 for both systems. PVT relationships of indole (at 343.15 K and 353.15 K), 2-methylnaphthane (at 333.15 K and 343.15 K), and biphenyl (at 353.15 K and 363.15 K) under pressure and those for the binary mixtures at 0.1 MPa in the temperature range from 293.15 K to 363.15 K were also measured. PVT data were analyzed with the use of the Tait equation and Carnahan–Starling–van der Waals (CS–vdW) equation. It was found that both the equations can be used to represent the experimental PVT relationships for the pure compounds and the binary mixtures with an average absolute deviations of 0.04% for the Tait equation and 0.29% for the CS–vdW equation. As for mixture density calculations with the CS–vdW equation, the effect of mixing rules was investigated.     

Densities and Volumetric Properties of Binary Mixtures of Aniline with 1-Propanol, 2-Propanol, 2-Methyl-1-Propanol,and 2-Methyl-2-Propanol at Temperatures from 293.15 to 318.15 K

The densities of binary mixtures of aniline with 1-propanol, 2-propanol, 2-methyl-1-propanol, and 2-methyl-2-propanol were measured over the entire composition range, along with the pure components, at temperatures of 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K and atmospheric pressure. Using the experimental data, the excess molar volumes, , and the temperature coefficients of the excess molar volume, for the binary mixtures were calculated. The variations of these parameters with composition and temperature of the mixtures have been discussed in terms of molecular interactions in these mixtures. The values were found negative for all the mixtures at each temperature studied, indicating the presence of specific interactions between aniline and alkanol molecules. The extent of negative deviations in values follows the order: 1-propanol < 2-propanol < 2-methyl-1-propanol < 2-methyl-2-propanol. It is observed that the values depend upon the positions of hydroxyl and methyl groups in these alkanol molecules.     

Electronic Structure of HgBa<Subscript>2</Subscript>CuO<Subscript>4+<Emphasis Type="Italic">δ</Emphasis></Subscript> with Self-organized Interstitial Oxygen Wires in the Hg Spacer Planes

While recent experiments have found that at optimum doping for the highest critical temperature in HgBa₂CuO_{4 + y} (Hg1201) the oxygen interstitials (O-i) are not homogeneously distributed but form one-dimensional atomic wires, there are no available information of its electronic structure considering self-organized O-i atomic wires. Here we report the calculated electronic structure of HgBa₂CuO_{4 + y} where oxygen interstitials form atomic wires along (1,0,0) crystal direction in the Hg layer. We find that at optimum doping for superconductivity the chemical potential is tuned near an electronic topological Lifshitz transition for the appearing of a second quasi 1D Fermi surface. A first large Fermi surface coexists with a second incipient quasi one-dimensional (1D) Fermi surface related with atomic wires of oxygen interstitials. Increasing oxygen doping the chemical potential is driven to the band edge of the second 1D-band giving a peak in the density-of-states. The new 1D electronic states are confined near the oxygen interstitial wires with a small spread only on nearby sites. Spin-polarized calculations show that the magnetic response is confined in the oxygen-poor domains free of oxygen interstitials wires and it is quite insensitive to the density of O-i wires.     

On the CVD of MoSi2: an experimental study from the MoCl4–SiCl4–H2–Ar precursor with a view to the preparation of C/MoSi2/SiC and SiC/MoSi2/SiC microcomposites

The chemical vapour deposition of MoSi2 on plane substrates (graphite or sintered-SiC) and ceramic fibres has been studied from MoCl4–SiCl4–H2–Ar gas mixtures at 900相似文献   

Dynamics of optical solitons,multipliers and conservation laws to the nonlinear schrödinger equation in (2+1)-dimensions with non-Kerr law nonlinearity

This work studies the (2 + 1)-dimensional nonlinear Schrödinger equation which arises in optical fibre. Grey and black optical solitons of the model are reported using a suitable complex envelope ansatz solution. The integration lead to some certain conditions which must be satisfied for the solitons to exist. On applying the Chupin Liu's theorem to the grey and black optical solitons, we construct new sets of combined optical soliton solutions of the model. Moreover, classification of conservation laws (Cls) of the model is implemented using the multipliers approach. This is achieved by constructing a set of first-order multipliers of a system of nonlinear partial differential equations acquired by transforming the model into real and imaginary components are derived, which are subsequently used to construct the Cls.