镁热还原气相法白炭黑制备纳米硅及其电化学性能

以气相法白炭黑(FS)为Si前驱体,通过镁热还原工艺和对获得的NPs-Si进行SiOx和C复合包覆,制备出NPs-Si@SiOx@C纳米复合结构,将其用作锂电池负极进行电化学性能测试。研究结果表明:镁热还原过程分两步进行,即SiO_2与Mg先生成Mg2Si中间相,Mg2Si继续与SiO_2反应生成Si的反应路径;根据此规律镁热还原气相法白炭黑的Si转化率达87.9%。电化学性能测试中NPs-Si@SiOx@C负极在2.0 A·g-1的电流密度下有1 300 mAh·g-1的容量平台,1 000次循环后的放电比容量为964.2mAh·g-1,容量保持率达75%。     

Three-dimensional fermionic determinants,Chern-Simons and nonlinear field redefinitions

The three-dimensional abelian fermionic determinant of a two component massive spinor in flat euclidean space-time is reset to a pure Chern-Simons action through a nonlinear redefinition of the gauge field.     

Multiobjective symmetric duality with cone constraints

We formulate a pair of multiobjective symmetric dual programs for pseudo-invex functions and arbitrary cones. Our model is unifying the Wolfe vector symmetric dual and the Mond-Weir vector symmetric dual models. We establish the weak, strong, converse and self duality theorems for our pair of dual models. Nanda and Das' results (Optimization 28 (1994) 267; Eur. J. Oper. Res. 88 (1996) 572) are obtained as special cases.     

Ternary phase equilibria for the sodium chloride–sodium sulfate–water system at 200 and 250 bar up to 400°C

Phase equilibria in the NaCl–Na₂SO₄–H₂O system were investigated at 200 and 250 bar for total salt concentrations ranging from 5 to 20 wt.% total salt over temperatures ranging from 320 to 400°C. In addition to providing data for this ternary system, the experiments also added information on the phase behavior of the two binary systems: NaCl–H₂O and Na₂SO₄–H₂O. For salt mixture compositions which were rich in sodium sulfate, a solid phase was observed to nucleate from the homogeneous liquid phase. Salt mixture compositions which had a high fraction of sodium chloride exhibited a vapor separation from a homogeneous liquid phase. By fitting curves to the solid–liquid and vapor–liquid separation temperatures, the temperature and composition of a constrained invariant point where liquid, solid salt and vapor are in equilibrium were estimated. These estimates were performed at discrete compositions of 5, 10, 15 and 20 wt.% total salt at pressures of 200 and 250 bar. The temperature and composition of the invariant point increased with increasing pressure following a simple thermodynamic model for boiling point elevation in a nearly ideal solution.     

An (s,S) random lifetime inventory model with a positive lead time

Positive lead times substantially complicate the modeling and analysis of inventory systems with finite shelf lifetimes and they have not been sufficiently addressed in the existing literature. In this paper, we analyze an (s, S) continuous review model with a positive lead time. We assume an exponential lifetime and an exponential lead time. Matrix-geometric solutions can be obtained for the steady state probability distribution of the inventory level. We then derive the total expected cost function. We carry out numerical studies and gain insights to the selection of system parameters. The findings on the impact of a positive lead time on the optimal reorder point and reorder batch size will be useful in developing strategies in handling inventory problems with finite lifetimes and positive lead times.     

Development and assessment of algorithms for DEM-LES simulations of fluidized bed

The use of high-fidelity Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD) for particle-scale simulations demands extensive simulation times and restricts application to small particulate systems. DEM-CFD simulations require good performance and satisfactory scalability on high-performance computing platforms. A reliable parallel computing strategy must be developed to calculate the collision forces, since collisions can occur between particles that are not on the same processor, or even across processors whose domains are disjoint. The present paper describes a parallelization technique and a numerical verification study based on a number of tests that allow for the assessment of the numerical performance of DEM used in conjunction with Large-Eddy Simulation (LES) to model dense flows in fluidized beds. The fluid phase is computed through solving the volume-averaged four-way coupling Navier-Stokes equations, in which the Smagorinsky sub-grid scale tensor model is used. Furthermore, the performance of Sub-Grid Scale (SGS) turbulence models applied to Fluidized Bed Reactor (FBR) configurations has been assessed and compared. The developed numerical solver represents an interesting combination of techniques that work well for the present purpose of studying particle formation in fluidized beds.     

Particulate modification of lithium-ion battery anode materials and electrolytes

Lithium-ion batteries (LIBs) are considered a rechargeable and commercial energy storage device for electronic equipment such as smartphone and electric vehicles. Despite the prospective future of LIBs, unsatisfied electrochemical properties like reversible capacity, cycle ability and coulombic efficiency still hinder their development. High volume expansion rate, uncontrolled Li dendrite growth and unsatisfied solid electrolyte interphase also occur when LIBs are applied in long-time usage. Numerous modification methods such as exploring high-capacity anode/cathode materials, constructing artificial solid electrolyte interphase and improved conductive binders can be adopted to enhance the performances. Among them, particulate modification for LIBs anode and electrolytes is receiving tremendous attraction in the recent work. The method is composed of changing the morphology and particle size of the active materials, also introduce nano-size additives to the main structure. This review emphasizes on introducing and discussing the modification in following aspects: particulate modification on carbon group IVA element anodes, introduction of additives like transition metal oxide nanoparticles into anode and electrolyte materials, dissipate the influence of Li dendrite growth and ameliorate the performances of solid electrolyte interface. This review hopes to be denoted for the future development of LIBs with the comprehensive understanding on the particulate modification.     

Liquid-liquid extraction of iron(III) and gallium(III) with macrocyclic Schiff bases containing bisphenol A subunits

The quantitative extraction of iron(III) and gallium(III) was investigated with the recently synthesized macrocyclic Schiff base containing bisphenol A subunits. The phenol groups in the Schiff base moiety led to a large increase in the percent extraction of trivalent metal ions. The substitution of methoxy groups for phenolic OH ligands resulted in a marked decrease in the extractability of metal ions, and no iron(III) was extracted. The corresponding acyclic Schiff base was found to have a reasonable reactivity toward metal ions and a better solubility in organic solvents. The iron(III) and gallium(III) complexes with macrocyclic and acyclic Schiff bases were quantitatively extracted into nitrobenzene without the presence of bulky counter anions. A single extraction gave a good separation of iron(III) from iron(II) in the mole ratios 4:1 to 1:3. The red iron(III) complexes can be used for the extraction-spectrophotometric determination of iron(III). The apparent molar absorptivity at 518 nm is 5.43 × 10³lmol⁻¹ cm⁻¹.     

A superconducting solenoid system which cancels fluctuations in the ambient magnetic field

An extra superconducting coil added to a standard, high-field solenoid results in a self-shielding solenoid system which utilizes flux conservation to passively shield an interior volume from changes in the ambient field, such as those from elevators or subways. For this first experimental demonstration, a highly homogeneous 6 T solenoid and an added coil were arranged in one of the geometries predicted to produce effective shielding. The fluctuations in the shielded high-field region are observed to be smaller than the fluctuations in the spatially uniform ambient magnetic field by a large factor of 156, confirming the general shielding principles presented earlier. This shielding is crucial for ongoing antiproton cyclotron resonance experiments and should be useful for nuclear magnetic resonance experiments and ion cyclotron resonance experiments and for other applications where high field and high stability are required simultaneously.     

Low frequency vibrational spectra of crystalline and glassy metaborates Ba2MII(B3O6)2 (MII  Mg,Ca, Ni,Co, Cd)

The low frequency vibrational spectra (Raman and IR) of crystalline metaborates Ba₂M^II(B₃O₆)₂ (M^II  Mg, Ca, Ni, Co, Cd) are interpreted on the basis of a factor group analysis and with the help of ²⁴Mg²⁶Mg and ⁴⁰Ca⁴⁴Ca isotopic shifts. The far-IR spectra of the glasses appear as the envelope of the spectra of the corresponding crystalline compounds for M^II  Mg, Ca and Cd, but they exhibit an additional broad absorption centred near 400 cm⁻¹ for M^II  Co, Ni and Zn. This absorption is assigned to a fourfold coordination of part of the M^II cations, the remaining being in sixfold coordination (as in the crystal) and responsible for a broad absorption in the 300-200 cm⁻¹ region. The possible existence of correlations between coordination and vibrational frequencies is discussed for either alkali and alkaline-earth cations, or transition elements.