Synthesis of palladium concave Nanocubes with high‐index facets and their catalytic properties

Palladium nanocrystals with a variety of shapes have received particular interest in recent years due to their unique properties in catalysis. Herein, Pd concave nanocubes with high‐index facets (Pd‐CNs) was synthesized by a simple water‐based route without seeds using L‐ascorbic acid (AA) as the reduction agent in the presence of CTAB. X‐ray diffraction and transmission electron microscopy were employed to demonstrate the formation of concave structures with high‐index facets of the Pd‐CNs with an average size of 17.5 nm. The as‐prepared Pd‐CNs presented significantly higher catalytic activity than commercial Pd/C (an average particle size of 4.7 nm) in the electro‐oxidation of methanol, but exhibited weaker property in Suzuki coupling reaction, which provided an evidence for the effect of shape and size on different reactions.     

In situ studies of microbial inactivation during high pressure processing

High pressure processing (HPP) has been shown to reduce microbial concentration in foods. The mechanisms of microbial inactivation by HPP have been associated with damage to cell membranes. The real-time response of bacteria to HPP was measured to elucidate the mechanisms of inactivation, which can aid in designing more effective processes. Different pressure cycling conditions were used to expose Enterobacter aerogenes cells to HPP. Propidium iodide (PI) was used as a probe, which fluoresces after penetrating cells with damaged membranes and binding with nucleic acids. A HPP vessel with sapphire windows was used for measuring fluorescence in situ. Membrane damage was detected during pressurization and hold time, but not during depressurization. The drop in fluorescence was larger than expected after pressure cycles at higher pressure and longer times. This indicated possible reversible disassociation of ribosomes resulting in additional binding of PI to exposed RNA under pressure and its release after depressurization.     

Improvement of the weighted essentially nonoscillatory scheme based on the interaction of smoothness indicators

The weighted essentially nonoscillatory scheme is improved by introducing new smoothness indicators that evaluate the interactions among the classical smoothness indicators suggested by Jiang and Shu. The effect of the key parameters in the new smoothness indicators on the scheme is systematically investigated. The improved scheme has smaller dissipation with larger weight assignment to the discontinuous stencils and higher numerical accuracy with weights closer to the ideal weights. To verify the theory, benchmark problems governed by the linear transport equation, the 1‐dimensional nonlinear Burgers equation, and the Euler equations are conducted and analyzed, respectively. Better computational performances both on numerical resolution and accuracy are shown in the comparisons with other classical weighted essentially nonoscillatory schemes.     

Novel correction method for X-ray beam energy fluctuation of high energy DR system with a linear detector

A high energy digital radiography (DR) testing system has generated diverse scientific and technological interest in the field of industrial non-destructive testing. However, due to the limitations of manufacturing technology for accelerators, an energy fluctuation of the X-ray beam exists and leads to bright and dark streak artifacts in the DR image. Here we report the utilization of a new software-based method to correct the fluctuation artifacts. The correction method is performed using a high pass filtering operation to extract the high frequency information that reflects the X-ray beam energy fluctuation, and then subtracting it from the original image. Our experimental results show that this method is able to rule out the artifacts effectively and is readily implemented on a practical scanning system.     

改进实验仪器测量Bi／Ag线材的超导转变温度

对实验室现有的仪器进行改进并测量了Bi／Ag高温超导线材的Tc，结果为104．1K。     

Hydrothermal formation of tobermorite studied by in situ X‐ray diffraction under autoclave condition

Hydrothermal formation of tobermorite from a pre‐cured cake has been investigated by transmission X‐ray diffraction (XRD) using high‐energy X‐rays from a synchrotron radiation source in combination with a newly designed autoclave cell. The autoclave cell has a large and thin beryllium window for wide‐angle X‐ray diffraction; nevertheless, it withstands a steam pressure of more than 1.2 MPa, which enables in situ XRD measurements in a temperature range of 373 to 463 K under a saturated steam pressure. Formation and/or decomposition of several components has been successfully observed during 7.5 h of reaction time. From the intensity changes of the intermediate materials, namely non‐crystalline C–S–H and hydroxylellestadite, two pathways for tobermorite formation have been confirmed. Thus, the newly developed autoclave cell can be used for the analyses of reaction mechanisms under specific atmospheres and temperatures.     

C-V analysis of rapidly thermal annealed SF6 plasma treated AlGaN/GaN heterostructures

We studied influence of rapid thermal annealing on electrical parameters of SF₆ plasma treated AlGaN/GaN heterostructures. The main emphasis by the evaluation was laid on C-V measurement and simulation, but also I-V and SIMS measurement were used. It was found that the diminished sheet carrier concentration of a two-dimensional electron gas after plasma treatment recovered significantly at the temperature of 500 °C. By using C-V measurement, it was possible to assess besides the changes of the two-dimensional electron gas concentration after annealing also the changes in the Schottky barrier heights and to find out the doping concentration in AlGaN barrier and GaN channel layer. The trend in Schottky barrier height changes after annealing was confirmed also by I-V measurement.