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排序方式: 共有659条查询结果,搜索用时 250 毫秒
101.
Using channel state dependent packet scheduling to improve TCPthroughput over wireless LANs 总被引:1,自引:0,他引:1
Pravin Bhagwat Partha Bhattacharya Arvind Krishna Satish K. Tripathi 《Wireless Networks》1997,3(1):91-102
In recent years, a variety of mobile computers equipped with wireless communication devices have become popular. These computers
use applications and protocols, originally developed for wired desktop hosts, to communicate over wireless channels. Unlike
wired networks, packets transmitted on wireless channels are often subject to burst errors which cause back to back packet
losses. In this paper we study the effect of burst packet errors and error recovery mechanisms employed in wireless MAC protocols
on the performance of transport protocols such as TCP. Most wireless LAN link layer protocols recover from packet losses by
retransmitting lost segments. When the wireless channel is in a burst error state, most retransmission attempts fail, thereby
causing poor utilization of the wireless channel. Furthermore, in the event of multiple sessions sharing a wireless link,
FIFO packet scheduling can cause the HOL blocking effect, resulting in unfair sharing of the bandwidth. This observation leads
to a new class of packet dispatching methods which explicitly take wireless channel characteristics into consideration in
making packet dispatching decisions. We compare a variety of channel state dependent packet (CSDP) scheduling methods with
a view towards enhancing the performance of transport layer sessions. Our results indicate that by employing a CSDP scheduler
at the wireless LAN device driver level, significant improvement in channel utilization can be achieved in typical wireless
LAN configurations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
102.
The problem of isothermal diffusion-reaction in a slab catalyst with bimolecular Langmuir—Hinshelwood kinetics is studied. Analytic solutions for the concentration profile and the catalytic effectiveness factor are reported for the full range of Thiele modulus values, in the limit of large adsorption inhibition constant. In this limit, connections with negative first-order kinetics are shown, and rather good explicit estimates of the region of multiple steady states are provided. Comparisons with numerical calculations are also made. 相似文献
103.
AG Corry DK Arvind GLS Connolly RR Korya IN Parker 《Microprocessors and Microsystems》1983,7(10):482-486
The development and implementation of systems for the more complex realtime image processing and scene understanding tasks, such as robot vision and remote surveillance, calls for faster computation than that possible using the traditional serial computer. The advent of VLSI has made feasible the consideration of more specialized processing architectures, designed to support these datarates, while keeping systems compact and relatively cheap. Two approaches are discussed: the use of a programmable processor array, and the customizing of image processing algorithms in silicon. This paper examines designs based upon each approach in the light of the techniques and constraints of VLSI. In particular we describe in some detail an example of a VLSI parallel array processor, the Grid (GEC rectangular image and data processor), and a number of special-purpose CMOS/SOS chips based on systolic design techniques. 相似文献
104.
Andreas Mettler Nicolas Wyrsch Michael Goetz Arvind Shah 《Solar Energy Materials & Solar Cells》1994,34(1-4)
We present systematic measurements of CPM on two independent series of slightly phosphorous and boron doped films. For “n-type” samples of both series, the CPM deep defect absorption is proportional to the square root of the gas dopant ratio. For these samples we discuss the influence of Fermi level on the CPM spectra. For slightly “p-type” samples, CPM deep defect absorption as evaluated by CPM becomes higher than the corresponding PDS-values. This fundamental problem can be traced back to the violation of two basic conditions necessary for a correct evaluation of the absorption from CPM measurements: (1) the power law exponent γ (Rose factor) of the photoconductivity must be spectrally independent, and (2) the generation rate G, which corresponds to the CPM photocurrent, also has to be spectrally independent. Further, we compare the annealed and the “saturated” light soaked states of selected slightly doped samples and an undoped sample: the variations in the CPM deep defect absorption and in photoconductivity due to light-soaking are discussed. 相似文献
105.
The sintering and graphitization behavior of mesocarbon microbeads (MCMB) at high temperatures (1900-2800 K) is investigated. It is shown that while the low temperature sintering performance of MCMB is unique, at high temperature it appears to be similar to that of conventional materials. In contrast, the obtained activation energy for MCMB high-temperature graphitization is ∼100 kcal/mol, which is smaller than that (∼240 kcal/mol) for typical carbon systems. It is concluded that the combination of such unique properties as excellent compressibility, low temperature sinterability, and rapid graphitization makes MCMB an attractive precursor for manufacturing carbon-based materials. 相似文献
106.
Arvind Bharti 《Bulletin of Materials Science》1988,11(2-3):191-212
A brief state-of-the-art review of laser welding has been presented. Results of our experimental studies on laser welding
of Ti-6Al-4V have been reported. Results of weld evaluation including microstructure, mechanical properties and microchemistry
have also been presented. 相似文献
107.
Arvind Mishra A. G. Gopalakrishna J. V. Prabhakar 《Journal of the American Oil Chemists' Society》1988,65(10):1605-1609
Components of rice bran oil have been assessed for their effect on refining losses. Rice bran oil used in the study had the following (percent) analysis: free fatty acids, 6.8; phosphatides, 1.25; wax, 2.85; monoglycerides, 1.67; diglycerides, 4.84, and oryzanol, 1.85; the rest (80.74) was mostly triglycerides. The phosphatides and mono- and diglycerides had no noticeable effect on refining losses at levels of up to 2% in the oil. Waxes and oryzanol increased the refining losses substantially. In model experiments where these were incorporated into peanut oil individually and in combination, the wax at as low a level as 1% increased the refining losses by about 80% more than control and the refining losses increased with concentration of wax. Oryzanol had a similar effect. When wax and oryzanol were present together in the oil, the effect was synergistic—the refining losses were higher than the sum of their individual effects. Phosphatides, mono- and diglycerides tended to reduce the adverse effect of wax and oryzanol. The main components responsible for higher than normal refining losses in rice bran oil have been identified as wax and oryzanol. 相似文献
108.
The possibility of shape normalization of catalyst pellets with non-uniform catalytic activity profiles is examined. A first order isothermal reaction occurring in slab or spherical catalyst pellets, with a variety of activity profiles, is considered. Analytic solutions for the effectiveness factor are reported in all cases. When the catalytic activity at the external surface of the pellet is non-zero, a physically significant normalization of the Thiele modulus is suggested which makes the asymptotic behavior of the effectiveness factor identical for all pellet shapes and all activity profiles. For an operational range intermediate between kinetic and diffusion control, however, the normalization can lead to significant errors. No such normalization exists when the surface catalytic activity is zero. 相似文献
109.
Autothermal reforming is an attractive method for on-site production of hydrogen for use in proton exchange membrane (PEM) fuel cells. The use of liquid hydrocarbons as feedstock, however, remains a challenge as these fuels cause severe coking of the currently available catalysts. In this work, cerium- and nickel-substituted LaFeO3 perovskites were investigated as potential low cost coking resistant catalysts for autothermal reforming of a JP-8 fuel surrogate. The high surface area complex oxides were prepared using aqueous (solution) combustion synthesis at fuel-rich conditions and characterized by BET and XRD techniques. The catalysts exhibited excellent stability during autothermal reforming at and 1 atm, with near-equilibrium hydrogen yield even at high GHSV values (). The addition of cerium significantly improved coking resistance, attributed to improved oxygen ion conductivity, resulting in carbon oxidation on the catalyst surface. 相似文献
110.
Das B.P. Amrutur B. Jamadagni H.S. Arvind N.V. Visvanathan V. 《Semiconductor Manufacturing, IEEE Transactions on》2009,22(2):256-267
We report the design and characterization of a circuit technique to measure the on-chip delay of an individual logic gate (both inverting and noninverting) in its unmodified form. The test circuit comprises of digitally reconfigurable ring oscillator (RO). The gate under test is embedded in each stage of the ring oscillator. A system of linear equations is then formed with different configuration settings of the RO, relating the individual gate delay to the measured period of the RO, whose solution gives the delay of the individual gates. Experimental results from a test chip in 65-nm process node show the feasibility of measuring the delay of an individual inverter to within 1 ps accuracy. Delay measurements of different nominally identical inverters in close physical proximity show variations of up to 28% indicating the large impact of local variations. As a demonstration of this technique, we have studied delay variation with poly-pitch, length of diffusion (LOD) and different orientations of layout in silicon. The proposed technique is quite suitable for early process characterization, monitoring mature process in manufacturing and correlating model-to-hardware. 相似文献