Geometric origin of pair production by electric field in de sitter space

Particle production in de Sitter space provides an interesting model for understanding the curvature effect on Schwinger pair production by a constant electric field or the Schwinger mechanism on de Sitter radiation. For that purpose, we employ the recently introduced complex analysis method in which the quantum evolution in complex time explains pair production via the geometric transition amplitude and gives the pair-production rate as a contour integral. We compare the result from the contour integral with that of the phase-integral method.     

核壳型聚苯乙烯/聚甲基丙烯酸甲酯复合乳液的制备

以过硫酸铵(APS)为引发剂,用种子乳液聚合方法,合成出以聚苯乙烯(PSt)为核, 聚甲基丙烯酸甲酯(PMMA)为壳的复合乳液。透射电子显微镜观察了核壳复合乳胶粒的形态,光散射粒径分布仪(PCS)测量胶乳粒径大小及其分布。最终成功地制得了核壳型PS/PMMA复合乳液,所得复合乳胶粒粒径大小在60～90nm左右,且单分散性较好。     

Experimental and theoretical study on H2/CO2 separation by a five-step one-column psa process

An experimental and theoretical study is performed for bulk separation of H₂/CO₂ mixture (70/30 volume %) by PSA process with zeolite 5A, a process widely used commercially in conjunction with the catalytic steam reforming of natural gas or naphtha. For the optimized adsorption conditions of PSA, the characteristics of adsorption/desorption characteristics have been studied through breakthrough and desorption experiments under various conditions. The purge-to-feed ratio is important to the H₂ product purity only at a long adsorption step time. H₂ could be concentrated from 70% in the feed to 99.99% at H₂ recovery of 67.5%. The results of all five steps in PSA are successfully predicted by the LDF model considering an energy balance and nonlinear isotherm. For the model, the effective diffusivities (D,) are obtained separately from the uptake curves of H₂ and CO₂. The Langmuir-Freundlich isotherm is used to correlate the experimental equilibrium data and is very well fitted to the results.     

Microstructural Evolution of Gas-Pressure-Sintered Si3N4 with Yb2O3 as a Sintering Aid

Microstructural evolution of gas-pressure-sintered Si₃N₄ with Yb₂O₃ as a sintering aid was observed. Microstructures typical for in situ toughened Si₃N₄, i.e., large elongated grains randomly distributed in a fine matrix, were observed. However, the size of the elongated grains near the surface was much larger than that at the center, resulting in two distinct regions: an inner region and an outer region. The smaller the amount of Yb₂O₃ added, the larger the difference in the size of the elongated grains between the outer and inner regions. The difference between microstructures was diminished when 16 wt% Yb₂O₃ was added. The microstructural change with Yb₂O₃ content was attributed to the evaporation of Yb-containing liquid phase from the surface.     

基于ECT的高速数据采集系统设计

数据采集系统的速度制约了电容层析成像技术在航空发动机气路监测系统等高速设备中的应用。为此,设计了一种基于FPGA的新型电容数据采集系统,采用DDR2存储技术和PCI总线技术实现了数据的高速传输。同时应用卡尔曼滤波器代替传统的FIR滤波器,有效提高了滤波效率。测试结果表明,该系统具有抗干扰能力强、采样精度高、处理速度快等优点。     

Polypyrrole composite membrane with high permeability prepared by interfacial polymerization

Novel polypyrrole (PPy)/polydimethylsiloxane (PDMS) composite membrane was prepared by interfacial polymerization to make a very effective gas separation membrane. We found that Polymerized PPy films as thin as ～200 nm could be chemically synthesized as freestanding membranes by using the interfacial polymerization technique. Additionally, we show that difference morphology of PPys films was obtained by controlling polymerization rate and more dense films were formed at low polymerization rate. Wide X-ray diffraction study showed the d spacing value of the PPy film decreased from 4.89 å to 3.67 å by the rate of polymerization decreases. According to d spacing value decrease, selectivity of a PPy composite membrane was increased dramatically and permeability was reduced gradually. This high selectivity was derived from d spacing closed to the kinetic diameter of nitrogen. These results indicated that the permeability is controlled by the diffusion coefficient, reflecting the packed structure of the PPy film. The highest selectivity value of composite membrane that was prepared by interfacial polymerization was O₂/N₂=17.2 and permeability for O₂ was 40.2 barrer.     

Growth and formation mechanism of sea urchin-like ZnO nanostructures on Si

Sea urchin-like nanostructures of ZnO consisting of ZnO nanowires with blunt faceted ends were grown on Si (100) substrates by oxidation of metallic Zn at 600 °C. ZnO nanowires having a diameter of 30–60 nm and length of 2–4 Μm were in similar shape with uniform diameter along its entire length with well faceted blunt ends. X-ray diffraction and transmission electron microscope analysis showed that the as-grown nanostructures were highly crystalline with wurtzite hexagonal structure having lattice constants of a=b=3.25 å and c=5.21 å. Room temperature photoluminescence (PL) measurements showed a weak near band-edge emission at 380 nm, but a strong green emission at 500–530 nm. A model for vapor-solid (VS) growth mechanism of ZnO nanowires was presented, in which nucleation of ZnO is crucial for the growth of the nanostructures.     

EFFECTS OF ASYMMETRIC TEMPERATURE PROFILES ON THERMAL CONVECTION DURING PHYSICAL VAPOR TRANSPORT OF Hg2Cl2

Asymmetric horizontal thermal profiles can change the flow field structure in the physical vapor transport (PVT)of Hg₂Cl₂. It is found that for the ratios of horizontal to vertical thermal Rayleigh numbers Ra_H/Ra ≥ 1·5, the convetive flow structure changes from multicellular to unicellular for the base parametric state of Ra = 2·79 × 10⁴, Pr = 0·91, Le=l·01. Pe = 4·60, Ar= 0·2 and C_r = 1·01. The unicellular flow structure obtained by increasing ∇*_H(Ra_H) is not likely to support the conjecture of the presence of unicellular convective mode in the laser Doppler velocimetry (LDV) experiments for PVT process of Hg₂Cl₂ (Kim el al., 1996). When the six parameters of Ra, Pr, Le, Pe, Ar and C_r are fixed, the dimensional maximum magnitude of the velocity vector |U|_max is proportional to √∇T*_H.     

Updating the trusted connection of re-organized computing resource under the automated system management platform

The High-Performance Computing (HPC) is an infrastructure to support various research fields. The research using HPC requires big storage for large-scale of raw data and the huge computing resources to analyze. The consolidated operations of the computing center for supporting various researches using HPC are a very effective organization. The consolidated operations are able to increase the utilization. The computing center has to be re-organized continuously in order to support the various fields of research effectively and flexibly. Re-organization to reuse the limited resources enforces the update of the information for verification of the computing resources after the re-allocation of computing resources and the re-distribution of trusted connection between computing resources. Consequently, to maintain effective research support we need automated resource re-organization environment. In this paper, we build an automated update of the trusted connection for re-organized computing resource using puppet which is automated system management platform. Finally, we provide a unified verification point and efficient environment for the re-allocation and re-organization of the integrated computing center.     

A power-efficient vertical handover with MIH-based network scanning through consistency check

We propose an power-efficient scanning scheme considering the consistency of the Information Element (IE) for the Media Independent Handover (MIH) based Vertical Handover. Since the Green IT is one of the key issues of the science, we suggested the power saving scheme by extending the information and the event service of the MIH framework to reduce the number of full scanning. We proposed the criteria to select the update MT to quantify the power consumption alongside various network scanning methods. Since the frequent and multiple network scanning incurred by small mobile terminals (MT) is considerable, the scanning avoidance is essential for the framework we suggest. The MIH Information Service (MIIS) provides many usable factors and features for the scanning avoidance. However, because of the absence of the criteria to select the update node, these values are not actually usable. Therefore, we suggest an Energy Efficient Function, which tests the validity of MIIS values and makes a decision on whether to avoid the scanning or not.