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Articles by Xinyu Zhang
Total Records ( 5 ) for Xinyu Zhang
  Xinyu Zhang , Xuejun Sha and Ali Nawaz Khan
  The extremely narrow pulses with the order of nanoseconds and multipath in Time Hopping Ultra Wide Band system result in long mean acquisition time as well as low acquisition precision. A novel Variable Step Acquisition scheme, which aims to improve both mean acquisition time and acquisition precision, is proposed. The proposed acquisition scheme employs nonconsecutive search and adjusts searching steps according to several thresholds, which makes the acquisition process a fast acquisition with variable steps, i.e., from large steps to small ones. The mean acquisition time performances of the proposed scheme and conventional acquisition schemes are evaluated and compared. It is evident that proposed acquisition scheme significantly outperforms the conventional ones.
  Ali Nawaz Khan , Xuejun Sha and Xinyu Zhang
  In this study, we have presented and tested a method to calculate rate of handoff accurately by accounting for irregularities in cellular coverage area in next generation wireless and cellular communication networks. Traditionally, rate of handoff calculations are based on the assumption that cell boundaries can be represented by uniform geometrical shapes such as circle, square and hexagon. However, in real situations cell boundaries are irregular due to various signal-degradation factors and hence cannot be precisely represented by definite geometrical structures. The difference in calculated and measured values of rate of handoff introduces compounding error in probabilistic analysis of Next Generation Networks and hence, requires the multiplication of an appropriate correction factor with calculated rate of handoff to minimize the error. Extensive experimentation reveal that actual rate of handoff for a cellular environment is greater than the calculated rate by as much as 20% and is proportional to the degree of irregularity in the cell boundary.
  Xinyu Zhang , Xuejun Sha and Ali Nawaz Khan
  The influence of clock frequency offset between transmitter and receiver of IR UWB (Impulse Radio Ultra Wide Band) system is talked about in this study. Firstly, this study highlight the fact that clock frequency offset in UWB system will decrease the performance of the coherent receiver and then the necessity of frequency offset estimation before acquisition step is stated. To improve the acquisition failure situation caused by frequency offset, a new acquisition structure with frequency offset estimation, as well as a new method to estimate frequency offset, is proposed. The scheme employs the characteristics of the symmetry and linearity of correlation to approximate the frequency offset in a range of searching area and has good accuracy. As the simulation results reveal, the proposed acquisition structure with frequency offset estimation outperforms the traditional acquisition system and the acquisition failure caused by frequency offset is improved greatly.
  Guoyin Zhang , Bin Tang , Peng Wang , Yanxia Wu and Xinyu Zhang
  In-net caching is an important part of the content centric network architecture. So far, the default "Leave Copy Everywhere (LCE)" caching policy will cache all content without distinction, lead to a large number of cache content redundant in the nodes of network. Due to the limitation of node cache size, redundant reduced the verity of cache content cached in network, result in bad utilization of cache space. To boost the performance of the cache, many improved mechanisms have been put forward, including LCD, MCD and ProbCache caching policies. This article respectively experimented the LCE, LCD, MCD and ProbCache algorithm, judging by standards like content response delay, network link load, server stress, evaluation index, analyzed factors, such as network topology, content popularity and cache space, have what kind of effect on these policies’ performance.
  Alexandre F. Fernandes , Jilin Zhou , Xinyu Zhang , Qingning Bian , Janet Sparrow , Allen Taylor , Paulo Pereira and Fu Shang
  Oxidative stress and inflammation are implicated in the pathogenesis of many age-related diseases. Stress-induced overproduction of inflammatory cytokines, such as interleukin-8 (IL-8), is one of the early events of inflammation. The objective of this study was to elucidate mechanistic links between oxidative stress and overproduction of IL-8 in retinal pigment epithelial (RPE) cells. We found that exposure of RPE cells to H2O2, paraquat, or A2E-mediated photooxidation resulted in increased expression and secretion of IL-8. All of these oxidative stressors also inactivated the proteasome in RPE cells. In contrast, tert-butylhydroperoxide (TBH), a lipophilic oxidant that did not stimulate IL-8 production, also did not inactivate the proteasome. Moreover, prolonged treatment of RPE cells with proteasome-specific inhibitors recapitulated the stimulation of IL-8 production. These data suggest that oxidative inactivation of the proteasome is a potential mechanistic link between oxidative stress and up-regulation of the proinflammatory IL-8. The downstream signaling pathways that govern the production of IL-8 include NF-κB and p38 MAPK. Proteasome inhibition both attenuated the activation and delayed the turnoff of NF-κB, resulting in biphasic effects on the production of IL-8. Prolonged proteasome inhibition (>2 h) resulted in activation of p38 MAPK via activation of MKK3/6 and increased the production of IL-8. Chemically inhibiting the p38 MAPK blocked the proteasome inhibition-induced up-regulation of IL-8. Together, these data indicate that oxidative inactivation of the proteasome and the related activation of the p38 MAPK pathway provide a potential link between oxidative stress and overproduction of proinflammatory cytokines, such as IL-8.
 
 
 
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