An improvement for multidimensional characteristic‐based scheme by using different selected waves

In this study, an improved multidimensional characteristic‐based (MCB) scheme, used for calculation of incompressible flows via artificial compressibility method, is presented. The new idea uses four different waves instead of traditional waves, which were used in the original MCB scheme corresponding to coordinate axes. In the new selection of waves, the number of compatibility relations is increased to eight, and therefore, more information reaches to each face in order to estimate convective fluxes. Numerical tests show that the new improved MCB scheme is faster in terms of convergence and demonstrates the same accuracy by the older one. Also, it needs less CPU time in comparison with traditional MCB scheme for running the computer code at the same conditions. The new scheme is able to use higher CFL numbers compared with the old MCB scheme. Results obtained by the new proposed method are in good agreement with the benchmark solutions at the wide range of Reynolds numbers. Copyright © 2014 John Wiley & Sons, Ltd.     

Complex phase behavior and state of miscibility in Poly(ethylene glycol)/Poly(l‐lactide‐co‐ε‐caprolactone) Blends

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T_g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T_m = 64 °C) and only a small one in crystallinity fraction (X_c = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true T_g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T_g's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121     

The fundamental theorem for singular surfaces with limiting tangent planes

In this paper, we prove a similar result to the fundamental theorem of regular surfaces in classical differential geometry, which extends the classical theorem to the entire class of singular surfaces in Euclidean 3-space known as frontals. Also, we characterize in a simple way these singular surfaces and its fundamental forms with local properties in the differential of its parametrization and decompositions in the matrices associated to the fundamental forms. In particular, we introduce new types of curvatures that can be used to characterize wave fronts. The only restriction on the parametrizations that is assumed in several occasions is that the singular set has empty interior.     

Great enhancement of efficiency of intumescent flame retardants by titanate coupling agent and polysiloxane

Modified intumescent flame retardants (MIFRs) and polysiloxane (APID) have been used in combination to enhance the flame retardancy of polypropylene (PP). The IFR system was composed of melamine (MEL), ammonium polyphosphate (APP) and pentaerythritol (PER). Aimed to improve the thermal stability of the IFR and its dispersivity in PP, titanate coupling agent NDZ‐201 was used to modify the IFRs via ball milling. MIFRs and APID have a cooperative effect on the flame retardant properties of PP. With 25 wt.% of MIFR and APID, the flame retardant sample (PPMA) was rated V0 for UL‐94, the LOI value was 34.3%, and the peak heat release rate (PHRR) was reduced by 80% in cone calorimeter test. In addition, APID could improve the compatibility of MIFR with the PP matrix, thereby increasing the mechanical properties of PP blends. The flame retardant effect of APID and MIFR in PP was presented in the condensed phase resulting in a rigid, thermally stable and expanded carbon layer due to different char structures.     

生物高分子-氧化石墨烯三维多功能复合凝胶的制备及其血液净化性能

以生物高分子(壳聚糖、白蛋白、脱氧核糖核酸)为交联剂与氧化石墨烯片层进行三维自组装,冻干后得到生物高分子-氧化石墨烯复合凝胶。通过扫描电镜、原子力显微镜、纳米粒度分析仪等分析其物化性能。结果表明:生物高分子成功组装到氧化石墨烯片层上,并形成三维多孔结构,制备的凝胶显示出极好的血液相容性,有效抑制了红细胞的溶血现象,对阳离子毒性分子及重金属离子有较高的吸附量。     

晶态Li_4Ti_5O_(12)负极材料的制备及其与电解液的兼容性研究

本文以醋酸锂和钛酸丁酯为原料,以冰醋酸为抑制剂,采用溶胶-凝胶法制备了晶态Li4Ti5O12负极材料。与自制的3种电解液和实验室常用的电解液分别组装成锂/钛酸锂半电池。采用恒流充放电测试、循环伏安法(CV)及交流阻抗法(EIS)对其电化学性能进行研究。研究结果发现:在以环状碳酸酯类(EC、PC)和线性碳酸酯类(MEC)为溶剂、以六氟磷酸锂(LiPF6)为电解质的电解液中添加双乙二酸硼酸锂(LiBOB),有利于提高半电池的性能,首次放电比电容达到了198mA.h.g-1,且放电比电容经多次充放电后衰减得较小。而在电解液中加入碳酸亚乙烯酯(VC),半电池的性能有所下降。Li4Ti5O12对电解液表现出较明显的兼容性。     

Construction of rectangular displacement-based element for thick/thin plates

In this paper, a method of constructing displacement-based element for thick/thin plates is developed by using the technique of generalized compatibility, and a rectangular displacement based element with 12 degrees of freedom for thick/thin plates is presented. This method enjoys a good accuracy with simple formulation and is free of shear locking as the thickness of the plate approaches zero. The project supported by National Natural Science Foundation of China through Grant No. 59208075     

Some Properties of the Boundary Value Problem of Linear Elasticity in Terms of Stresses

The relation between the classical formulation of linear elastic problems in displacements and the stress formulation proposed by Pobedria is studied. It is shown that if the Navier and Pobedria differential operators are elliptic then corresponding boundary value problems are equivalent. The values of parameters for which Pobedria's boundary value problem has the Fredholm property are found. The homogeneous Pobedria's system is considered as a spectral problem with Poisson's ratio as a spectral parameter. The points of the essential spectrum are found and classified. The example of solving Pobedria's system for the Lamé problem for a spherical shell is presented.     

Thermoelastic Solution for Stresses

A new solution to the three-dimensional thermoelastic problem for stresses is proposed. It satisfies the static equation and compatibility condition. The stress tensor is expressed in terms of a harmonic vector. With such a solution, the boundary conditions for some elastic bodies can be satisfied quite easily__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 3, pp. 46–54, March 2005.