Some Magnetized Bulk Viscous String Cosmological Models in Cylindrically Symmetric Inhomogeneous Universe with Variable ∧-Term

Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion （θ） in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field.     

Elastic moduli of η‐Ta2N3, a tough self‐healing material,via laser ultrasonics

The elastic moduli of the dense polycrystalline oxygen‐bearing η‐Ta₂N₃, a novel hard and tough high‐pressure (HP) material, were measured using the laser ultrasonic technique. The bulk modulus was determined to be B₀ = 281(15) GPa which is only ～11% below that from HP compression measurements. Our value of the shear modulus G₀ = 123(2) GPa is below those ones predicted theoretically for model structures. The discrepancies in G₀ could be due to a substitution of an‐ ions and the formation of cation vacancies in η‐Ta₂N₃. Self‐healing behaviour of η‐Ta₂N₃ by mechanical polishing was observed and confirmed by two independent experimental methods. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relationship between positron bulk lifetime and lattice constants-research on NaCl-type crystals

The positron lifetimes of some compounds with NaCl-type crystal structure are calculated with the method of atomic superposition approximation (ATSUP) based on the theories of local-density-approximation (LDA) and generalgradient-approximation (GGA).The systematical results are fitted to a curve as a function of lattice constants.The positron bulk lifetimes of some other compounds with NaCl-type crystal structure,which are deduced from the systematical results,are in agreement with the experimental results given in other literature.     

Extreme compression behaviour of equations of state

The extreme compression (P→∞) behaviour of various equations of state with K′_∞>0 yields (P/K)_∞=1/K′_∞, an algebraic identity found by Stacey. Here P is the pressure, K the bulk modulus, K^′=dK/dP, and K′_∞, the value of K^′ at P→∞. We use this result to demonstrate further that there exists an algebraic identity also between the higher pressure derivatives of bulk modulus which is satisfied at extreme compression by different types of equations of state such as the Birch–Murnaghan equation, Poirier–Tarantola logarithmic equation, generalized Rydberg equation, Keane's equation and the Stacey reciprocal K-primed equation. The identity has been used to find a relationship between λ_∞, the third-order Grüneisen parameter at P→∞, and pressure derivatives of bulk modulus with the help of the free-volume formulation without assuming any specific form of equation of state.     

Mechanical stability and thermodynamic properties of OsC from first-principles calculations

The elastic and thermodynamic characteristics of OsC crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Compared with WC-type OsC, NaCl-type OsC is not only energy unfavorable but also mechanics unstable. The five independent elastic constants (C_ij), bulk modulus (B₀), the dependence of bulk modulus on temperature and pressure as well as the thermal expansion coefficient (α_V) at various temperatures for WC-type OsC are discussed. According to our calculations, WC-type OsC should be an ultra-incompressible material with high bulk modulus about 381 GPa. In addition, the bulk modulus will increase with increasing pressure while decrease with increasing temperature. The researches on the thermal expansion coefficient indicate that there will be a knee point during the process of thermal expansion coefficient variation versus increasing temperature. Our results may provide useful information for theoretical and experimental investigation of OsC.     

Numerical calculation of trapped magnetic field for square multiple bulk superconductors

In this work, the trapped magnetic field was calculated for square bulk superconductors using the sand-pile model and Biot–Savart law. The numerical simulation of the trapped magnetic field was performed varying the sample dimensions, distance between the sample surface and observation point. In addition the magnetic field characteristics of superconducting bulk arrangement in an array was determined. The trapped magnetic field was found to be depending on the sample dimensions and distance between the sample and observation point. It is observed that, when the distance from the surface is larger, the value of the trapped magnetic field decreases, but the variation of the trapped magnetic field becomes small due to averaging the distribution of the trapped magnetic field.     

Bulk工艺气体微网探测器的研究

In this paper, we present a study of a micromegas detector prototype built with bulk technology. Following a short discussion of the micromegas detector＇s structure and working mechanism, the bulk fabrication process is described, and some testing results of the prototype are presented.     

Surface Acoustic Wave Characterization of Equivalent Young's Moduli for Patterned Films北大核心CSCD

Based on the equivalent elasticity theory for layered materials, the micro-mechanics equivalent models for single and dual damascene structures were established. The equivalent elastic constant of the patterned structure was introduced, to establish the propagation model for the surface acoustic waves propagating in the layered structure of the patterned film/ substrate, and the theoretical dispersion curves of the surface acoustic waves were calculated with Green’s function and the matrix method. The finite element method was used to calculate 24 numerical examples of damascene structures with different volume ratios, and the results were compared with those of the strain energy method. The results show that, the average relative errors of the equivalent Young’s moduli of the 300 nm-thick dual damascene film and the 100 nm-thick single damascene film are 2.06% and 2.27%, respectively. The research verifies the correctness of the equivalent patterned structure model and the feasibility of the surface acoustic wave method to characterize the mechanical properties of patterned films, and provides a reference for the development of suitable chemico-mechanical polishing technologies for patterned films under low pressure. © 2023 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.     

线性互补问题基于模同步块多重分裂方法的收敛性

通过利用不动点迭代来研究线性互补问题,根据基模同步多重分裂迭代方法将其线性互补问题的系数矩阵是点的形式推广到块H+的形式,并且分析了当系数矩阵是块矩阵时线性互补问题解的收敛情况。     

Colour symmetry double point groups

Thirty four distinct composition series arising out of the 32 crystallographic double point groups are employed to re-derive in a simple and elegant fashion all the 169 distinct colour symmetry groups generated by the 32 double point groups, exploiting the idea of colour generators. The advantage of the method employed and some possible applications of these colour groups are discussed. The resulting colour groups are tabulated.