Probabilistic calibration of discrete element simulations using the sequential quasi-Monte Carlo filter

The calibration of discrete element method (DEM) simulations is typically accomplished in a trial-and-error manner. It generally lacks objectivity and is filled with uncertainties. To deal with these issues, the sequential quasi-Monte Carlo (SQMC) filter is employed as a novel approach to calibrating the DEM models of granular materials. Within the sequential Bayesian framework, the posterior probability density functions (PDFs) of micromechanical parameters, conditioned to the experimentally obtained stress–strain behavior of granular soils, are approximated by independent model trajectories. In this work, two different contact laws are employed in DEM simulations and a granular soil specimen is modeled as polydisperse packing using various numbers of spherical grains. Knowing the evolution of physical states of the material, the proposed probabilistic calibration method can recursively update the posterior PDFs in a five-dimensional parameter space based on the Bayes’ rule. Both the identified parameters and posterior PDFs are analyzed to understand the effect of grain configuration and loading conditions. Numerical predictions using parameter sets with the highest posterior probabilities agree well with the experimental results. The advantage of the SQMC filter lies in the estimation of posterior PDFs, from which the robustness of the selected contact laws, the uncertainties of the micromechanical parameters and their interactions are all analyzed. The micro–macro correlations, which are byproducts of the probabilistic calibration, are extracted to provide insights into the multiscale mechanics of dense granular materials.     

电子装置内的热移动研究——温度分布及速度分布

在高60cm,宽45cm 的模拟电子装置内,进行装置内热移动研究,得到不同条件下的温度分布及速度分布.在理论解析及数值计算基础上,进行无因次准数关联,得出实验式.实验结果及解析结果基本一致.利用所得实验式对正在运转或有待开发的新的电子装置有关参数进行推算,对于传热设计具有很强的实用性.     

Gold nanoparticle distribution monitor for drug delivery system based on optically assisted ultrasonic velocity-change imaging

Optical absorption images of the tissue mimic phantom including gold nanoparticles were obtained by detecting the ultrasonic velocity-change caused by light irradiation. A series of experimental results showed the possibility as a nanoparticle distribution monitor for the drug delivery system.     

Superconductivity and spin correlation study by Fe3+ - ESR in (La1−xSrx)2Cu1−yFeyO4−z

Fe³⁺-ESR measurements are carried out for the samples of (La_1–xSr_x)₂Cu_1–yFe_yO_4–z. Peak-peak width H_pp of the signals decreases with falling temperature until minimum value and rises sharply with further decreasing temperature, which is approximated by H_pp = C₀ +C₁/T + BT. The H_pp behavior at high temperature and at low temperature can be analyzed by Korringa mechanism and slowing down of Fe₃₊ spin fluctuation, respectively. From the analysis of coefficient B's of Korringa terms, C₀ and g-shift, it is revealed that the magnetic interaction of Fe³⁺ with hole carriers and Ce²⁺ spins depends strongly on hole density.     

Primary structure of Streptomyces griseus metalloendopeptidase II

Streptomyces griseus metalloendopeptidase II (SGMPII) is a unique protease, since it shows anomalous susceptibility to the proteinaceous "serine protease inhibitors" produced by Streptomyces, such as Streptomyces subtilisin inhibitor (SSI) and its homologous proteins. In this study, we analyzed the amino acid sequence of SGMPII by analyzing various peptide fragments produced enzymatically. The sequence of SGMPII, which is composed of 334 amino acids, showed no extensive similarity to SSI-insensitive metalloproteases produced by other species of Streptomyces, except for the amino acid residues essential for catalysis and zinc binding. However, SGMPII is 35-41% similar to thermolysin and its related metalloproteases, which are not inhibited by SSI, and the residues presumed to be critical for catalysis and zinc-binding are well conserved in SGMPII. Glu137 in a "His-Glu-Xaa-His" motif of SGMPII was identified as the residue modified by CICH2 CO-DL-(N-OH)Leu-Ala-Gly-NH2, an active-site-directed irreversible inhibitor of thermolysin-like metalloproteases. Based on the sequence comparison of SGMPII and other bacterial metalloproteases, we discuss the structural basis for the differences in substrate specificity and stability between SGMPII and other thermolysin-like proteases. A possible SSI-binding locus of SGMPII is also proposed.     

Contribution of primary radical termination to radical polymerization of diethyl fumarate estimated from absolute rate constants

Summary Diethyl fumarate was radically polymerized under UV irradiation and concentration of the propagating radical was determined to be of the order of 10^-5 mol/L by scavenge with a stable free radical. The absolute rate constant for propagation (k_p) was evaluated from the overall rate of polymerization at 30°C: K_p =(2.9 ± 0.3) × 10^-2 L/mol · s. The rate constant for mutual termination of the polymer radical (k_t) was calculated from the decreasing rate of the radical concentration in the dark: k_t=8.0 L/mol·s. The k_t value determined is one twentieth of that evaluated previously by a rotating sector method. This discrepancy is accounted for by contribution of much faster primary radical termination.     

Corrosion characteristics of reduced activation ferritic steel, JLF-1 (8.92Cr–2W) in molten salts Flibe and Flinak

Static corrosion tests were performed in molten salts, LiF–BeF₂ (Flibe) and LiF–NaF–KF (Flinak), at 500 °C and 600 °C for 1000 h. The purpose is to investigate the corrosion characteristics of reduced activation ferritic steels, JLF-1 (8.92Cr–2W) in the fluids. The concentration of hydrogen fluoride (HF) in the fluids was measured by slurry pH titration method before and after the exposure. The HF concentration determined the fluoridation potential. The corrosion was mainly caused by dissolution of Fe and Cr into the fluids due to fluoridation and/or electrochemical corrosion. Carbon on the surface might be dissolved into the fluids due to the corrosion, and this resulted to the decrease of carbide on the surface. The corrosion depth of the JLF-1 specimen, which was obtained from the weight losses, was 0.637 μm in Flibe at 600 °C and 6.73 μm in Flinak at 600 °C.