122,513 research outputs found
Micromachined membrane particle filters
We report here several particle membrane filters (8 x 8 mm^2) with circular, hexagonal and rectangular through holes. By varying hole dimensions from 6 to 12 pm, opening factors from 4 to 45 % are achieved. In order to improve the filter robustness, a composite silicon nitride/Parylene membrane technology is developed. More importantly, fluid dynamic performance of the filters is also studied by both experiments and numerical simulations. It is found that the gaseous flow through the filters depends strongly on opening factors, and the measured pressure drops are much lower than that from numerical simulation using the Navier-Stokes equation. Interestingly, surface velocity slip can only account for a minor part of the discrepancy. This suggests that a very interesting topic for micro fluid mechanics research is identified
On the Energy and Centrality Dependence of Higher Order Moments of Net-Proton Distributions in Relativistic Heavy Ion Collisions
The higher order moments of the net-baryon distributions in relativistic
heavy ion collisions are useful probes for the QCD critical point and
fluctuations. Within a simple model we study the colliding energy and
centrality dependence of the net-proton distributions in the central rapidity
region. The model is based on considering the baryon stopping and pair
production effects in the processes. Based on some physical reasoning, the
dependence is parameterized. Predictions for the net-proton distributions for
Au+Au and Pb+Pb collisions at different centralities at =39 and
2760 GeV, respectively, are presented from the parameterizations for the model
parameters. A possible test of our model is proposed from investigating the net
proton distributions in the non-central rapidity region for different colliding
centralities and energies.Comment: 6 pages in revtex4, 8 eps figures. arXiv admin note: text overlap
with arXiv:1107.474
Performance of multiple-input multiple-output wireless communications systems using distributed antennas
In this contribution we propose and investigate a multiple-input multiple-output (MIMO) wireless communications system, where multiple receive antennas are distributed in the area covered by a cellular cell and connected with the base-station (BS). We first analyze the total received power by the BS through the distributed antennas, when assuming that the mobile's signal is transmitted over lognormal shadowed Rayleigh fading channels. Then, the outage probability of the distributed antenna MIMO systems is investigated, when considering various antenna distribution patterns. Furthermore, space-time coding at the mobile transmitter is considered for enhancing the outage performance of the distributed antenna MIMO system. Our study and simulation results show that the outage performance of a distributed antenna MIMO system can be significantly improved, when either increasing the number of distributed receive antennas or increasing the number of mobile transmit antennas
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