Research on the Effect of High Power Microwave on Low Noise Amplifier and Limiter Based on the Injection Method

The reliability of electronic device is threatened in high power microwave (HPM) environment. In accordance with the situation that the emulation is ineffective in evaluating the accuracy and precision of the HPM effect to electronic device, the experimental method is used to resolve the problem. Low Noise Amplifier (LNA) and Limiter are selected as the objects for the experiments, the structural characteristic of the front-end of radar receiver is described, the phenomena and criterion are elaborated and analyzed using injection method due to its ability to get an accurate threshold avoiding the complex coupling, the basic principle of injection experiment is demonstrated, and the method and process of effect experiment about Low Noise Amplifier and Limiter are also explained. The experimental system is established, and the system is composed of low power microwave source such as TWT, test equipment for obtaining the effect parameters, and some of auxiliary equipments as camera, optical microscope or electron microscopy, attenuator, detector, and directional coupler etc. The microwave delivered from source is adjusted to the power infused by attenuator, and pour in the decanting point of effecter via directional coupler, then the couple signal created by directional coupler is input to the recording instrument after detecting by detector, finally the power of effecter is obtained. The value of power, which damages the effecter in the microwave pulse environment, is classified at the index of sensitivity, and the threshold is obtained by power diagnose and wave test. Some regular understandings of the HPM effect to electronic device are obtained based on the results of the experiments. It turns out that the index of electronic device is influenced significantly by the energy via front door coupling, the MOSFET made up of GaAs is the most wearing part to HPM in LNA, the damage threshold of LNA is about 40dBm under single pulse while in repetitive pulse the value is from 33.3dBm to 43.9dBm according to different wave band. The damage threshold of Limiter is about 56dBm to80dBm.

ELECTRONIC STRUCTURE OF THE LaNi_(5-x)Ga_x INTERMETALLIC COMPOUNDS

The equilibrium structures and electronic structure of LaNi5-xGax （x=0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and electron densities of LaNi5-xGax are plotted and analyzed. It is clear that the substitution of Ga at the Ni site leads to a progressive filling of the Ni-d bands, the ionic interaction between Ni and Ni, with Ga plays a dominant role in the stability of LaNi5-xGax compounds. The smaller the shift of EF toward higher energy region, the more stable the compounds will be. The increased contribution of the Ni-d-Ga-d interactions near EF and the low energy metal-gallium bonding bands indicate that the compounds become more stable. The results are compared with experimental data and discussed in light of previous studies.

Green Tea Consumption Reduces Oxidative Stress in Parkinson’s Disease Patients

Oxidative stress is one of the underlying causes of Parkinson’s disease (PD). Because of its antioxidant effect, we hypothesize that green tea consumption (3 cups daily for 3 months) would improve antioxidant status and reduces oxidative damage in Parkinson’s disease. Fifteen subjects who were within the first five years of PD, on stable PD medication, and not regular green tea consumers were recruited. Iron status, oxidative stress and PD status were evaluated before and after 3 months of green tea consumption. Hemoglobin, serum iron, iron saturation and ferritin concentrations were used to assess iron status. Antioxidant enzymes including catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPx) were measured to determine antioxidant status. Lipid peroxidation and protein carbonyls were measured as oxidative damage markers. There were no changes in total motor scores of the Unified Parkinson’s Disease Rating Scale (UPDRS), PDQ-39 total scores and various iron status markers after 3 months. Catalase (p < 0.05) and SOD activities (p < 0.005) were increased significantly indicating an improvement of antioxidant status. Both lipid peroxidation and protein carbonyls decreased by ~52% (p < 0.01) with green tea consumption, indicating less oxidative stress. In conclusion, 3 cups of green tea consumption for 3 months can improve antioxidant status and reduce oxidative damage in PD patients. Further studies are needed to determine if these changes result in slowing the disease progression.