Size-dependent ignition temperature of metallic compounds fabricated by self-propagating high-temperature synthesis

Considering the diffusion reaction at solid interfaces, the ignition temperature of compounds fabricated by self-propagating high-temperature synthesis (SHS) is modelled with the help of size-dependent activation energy. As reactant size decreases, ignition temperature also decreases. This is because of increased contact areas between the reactants and the lowered diffusion barrier, both of which must be calculated specifically for reactants in nanoscale. The model predictions and experimental results are consistent for some metallic compounds.     

Dislocation decoration and raft formation in irradiated materials

Experimental observations of dislocation decoration with self-interstitial atom (SIA) clusters and of SIA cluster rafts are analysed to establish the mechanisms controlling these phenomena in bcc metals. The elastic interaction between SIA clusters, and between clusters and dislocations is included in kinetic Monte Carlo (KMC) simulations of damage evolution in irradiated bcc metals. The results indicate that SIA clusters, which normally migrate by 1D glide, rotate due to their elastic interactions, and that this rotation is necessary to explain experimentally-observed dislocation decoration and raft formation in neutron-irradiated pure iron. The critical dose for raft formation in iron is shown to depend on the intrinsic glide/rotation characteristics of SIA clusters. The model is compared with experimental observations for the evolution of defect cluster densities (sessile SIA clusters and nano-voids), dislocation decoration characteristics and the conditions for raft formation.     

Cooling-induced increase of methane cluster size investigated under a Coulomb explosion scheme

In this letter, we discuss the increase in the average cluster size by lowering the stagnation temperature of the methane （CH4） gas. The Coulomb explosion experiments are conducted to estimate the cluster size and the size distribution. The average CH4 cluster sizes Nay of 6 230 and 6 580 are acquired with the source conditions of 30 bars at 240 K and 60 bars at 296 K, respectively. Empirical estimation suggests a five-fold increase in the average size of the CH4 clusters at 240 K compared with that at room temperature under a backing pressure of 30 bars. A strong nonlinear Hagena parameter relation （Г^＊∝ T0^-3.3） for the CH4 clusters is revealed. The results may be favorable for the production of large-sized clusters by using gases at low temperature and high back pressures.     

Manipulation of atom-to-molecule conversion in a magnetic lattice

Atom-to-molecule conversion by the technique of optical Feshbach resonance in a magnetic lattice is studied in the mean-field approximation. For the case of a shallow lattice, we give the dependence of the atomto-molecule conversion efficiency on tunnelling strength and atomic interaction by taking a double-well as an example. We find that one can obtain a high atom-to-molecule conversion by tuning the tunnelling and interaction strengths of the system. For the case of a deep lattice, we show that the existence of the lattice can improve the atom-to-molecule conversion for certain initial states.     

高效液相色谱法同时测定生物质乳酸发酵液中有机酸及糖类化合物

建立了高效液相色谱(HPLC)同时测定生物质乳酸发酵液中有机酸及糖类的分析方法。使用Bio-Rad Aminex HPX-87H色谱柱,以5 mmol/L的H2SO4为流动相,在柱温55 ℃,流速0.6 mL/min条件下,采用示差折光检测器进行检测。结果表明,该方法可在17 min内实现发酵液中各种有机酸和糖类化合物等的完全分离与定量,6种有机酸和3种糖类化合物在0.15～5.19 g/L范围内的线性关系良好,回归方程的线性相关系数在0.9998以上。将该法用于米根霉发酵液的检测,两个水平的加标回收率为96.91%～103.11%,相对标准偏差(n=6)为0.81%～4.61%。该法适用于微生物发酵液中多种有机酸和糖类的快速、高效分离和定量测定。     

Immobilized palladium on surface-modified Fe3O4/SiO2 nanoparticles: as a magnetically separable and stable recyclable high-performance catalyst for Suzuki and Heck cross-coupling reactions

A palladium-based catalyst (Fe₃O₄/SiO₂/HPG–OPPh₂–PNP) supported on chlorodiphenylphosphine-functionalized magnetic nanoparticles was successfully prepared from Fe₃O₄/SiO₂ with sequential attachment of glycerol and chlorodiphenylphosphine, followed by treatment of an ethanolic solution of palladium chloride with hydrazine. The as-prepared catalyst was characterized by ICP-AES, FTIR, XRD, SEM, and TEM. The Fe₃O₄/SiO₂/HPG–OPPh₂–PNP was found as a magnetically separable and highly active catalyst for Suzuki coupling reactions of aryl iodides, bromides, and chlorides as well as Heck reactions of aryl iodides and bromides. Under appropriate conditions, all reactions afforded the desired products in moderate to excellent yields. Moreover, this catalyst can be easily recovered by using a magnetic field and directly reused for at least six cycles without significant loss of its activity.