PROPERTIES OF ELECTROMAGNETIC SHIELDING CASE MADE OF PLYWOOD LAMINATED WITH CONDUCTIVE SHEETS

ABSTRACT Electromagnetic shielding cases have been regarded as an adequate solution for electromagnetic interference problems. Most electromagnetic shielding cases are made of metal, conductive plastics and carbon materials. Wood-based electromagnetic shielding cases have gained high levels of public interests due to their availability, cost, and renewability. In this study, the case was constructed of electromagnetic shielding plywood connected by copper foil. Shielding properties of the case were evaluated using shielded room testing. It was found that shielding effectiveness of the case ranged from 30.01 to 43.89 dB (30 MHz to 1 GHz), which indicated it met the secondary shielding effectiveness requirements of general cases for electronic equipment and could be used under the high requirements of electromagnetic compatibility. The results also showed seam leakage between the sides of cases resulted in a decrease of electromagnetic shielding effectiveness. The longer the seam length, the lower the shielding performance was. In addition, it was observed that rectangular waveguide resonance had an obvious influence on the case, which led to a sharp decrease of shielding effectiveness at the frequency of 720 MHz

A stability analysis of turning process considering the workpiece as a Timoshenko beam

In past studies, the elastic effects of a workpiece were usually ignored or a workpiece was just expressed with Euler-Bernoulli beam theory in turning process, which made the stability of cutting process less accurate. This paper considers the deformation of the workpiece expressed with a more accurate Timoshenko beam model in analysis for chatter of cutting process. The cutting stability of the turning process is analyzed by combining both the elastic effects of the tool and the workpiece with regenerative chatter mechanisms and compared with the stability analysis results that the deflection of workpiece is ignored. Besides, the influences of workpiece length, radius, the cutting tool damping and stiffness on the analytical model are also studied. At last, the present model is compared with those obtained from Euler-Bernoulli theory. It is found that the critical chip width when we consider workpiece as a Timoshenko beam is greater than the other two cases

Excellent HER and OER Catalyzing Performance of Se-vacancies in Defects-engineering PtSe2: From Simulation to Experiment

Facing with grave climate change and enormous energy demand, catalyzer gets more and more important due to its significant effect on reducing fossil fuels consumption. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by water splitting are feasible ways to produce clean sustainable energy. Here we systematically explored atomic structures and related STM images of Se defects in PtSe2. The equilibrium fractions of vacancies under variable conditions were detailly predicted. Besides, we found the vacancies are highly kinetic stable, without recovering or aggregation. The Se vacancies in PtSe2 can dramatically enhance the HER performance, comparing with, even better than Pt(111). Beyond, we firstly revealed that PtSe2 monolayer with Se vacancies is also a good OER catalyst. The excellent bipolar catalysis of Se vacancies were further confirmed by experimental measurements. We produced defective PtSe2 by direct selenization of Pt foil at 773 K using a CVD process. Then we observed the HER and OER performance of defective PtSe2 is much highly efficient than Pt foils by a series of measurements. Our work with compelling theoretical and experimental studies indicates PtSe2 with Se defects is an ideal bipolar candidate for HER and OER

Deadlock Prevention Policy with Behavioral Optimality or Suboptimality Achieved by the Redundancy Identification of Constraints and the Rearrangement of Monitors

This work develops an iterative deadlock prevention method for a special class of Petri nets that can well model a variety of flexible manufacturing systems. A deadlock detection technique, called mixed integer programming (MIP), is used to find a strict minimal siphon (SMS) in a plant model without a complete enumeration of siphons. The policy consists of two phases. At the first phase, SMSs are obtained by MIP technique iteratively and monitors are added to the complementary sets of the SMSs. For the possible existence of new siphons generated after the first phase, we add monitors with their output arcs first pointed to source transitions at the second phase to avoid new siphons generating and then rearrange the output arcs step by step on condition that liveness is preserved. In addition, an algorithm is proposed to remove the redundant constraints of the MIP problem in this paper. The policy improves the behavioral permissiveness of the resulting net and greatly enhances the structural simplicity of the supervisor. Theoretical analysis and experimental results verify the effectiveness of the proposed method