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2.
Giaccone P. Prabhakar B. Shah D. 《Selected Areas in Communications, IEEE Journal on》2003,21(4):546-559
The aggregate bandwidth of a switch is its port count multiplied by its operating line rate. We consider switches with high-aggregate bandwidths; for example, a 30-port switch operating at 40 Gb/s or a 1000-port switch operating at 1 Gb/s. Designing high-performance schedulers for such switches with input queues is a challenging problem for the following reasons: (1) high performance requires finding good matchings; (2) good matchings take time to find; and (3) in high-aggregate bandwidth switches there is either too little time (due to high line rates) or there is too much work to do (due to a high port count). We exploit the following features of the switching problem to devise simple-to-implement, high-performance schedulers for high-aggregate bandwidth switches: (1) the state of the switch (carried in the lengths of its queues) changes slowly with time, implying that heavy matchings will likely stay heavy over a period of time and (2) observing arriving packets will convey useful information about the state of the switch. The above features are exploited using hardware parallelism and randomization to yield three scheduling algorithms - APSARA, LAURA, and SERENA. These algorithms are shown to achieve 100% throughput and simulations show that their delay performance is quite close to that of the maximum weight matching, even when the traffic is correlated. We also consider the stability property of these algorithms under generic admissible traffic using the fluid-model technique. The main contribution of this paper is a suite of simple to implement, high-performance scheduling algorithms for input-queued switches. We exploit a novel operation, called MERGE, which combines the edges of two matchings to produce a heavier match, and study of the properties of this operation via simulations and theory. The stability proof of the randomized algorithms we present involves a derandomization procedure and uses methods which may have wider applicability. 相似文献
3.
Prabhakar R. Bandaru 《Journal of Materials Science》2007,42(5):1809-1818
A review on the syntheses and electrical characterization of Y-shaped multi-walled carbon nanotube morphologies is presented.
Modified thermal CVD processes, using Ti precursors, are used to grow Y-junctions of different geometries and distribution
of catalyst particles. It has been established that novel electrical switching behavior is feasible, where any one of the
three branches of the Y-junction can be used for modulating the electrical current flow through the other two branches. Current
blocking behavior, leading to perfect rectification, is seen which could be related to the interplay of the carrier lifetime
and the transit time. The overall goal is to investigate the possibility of obtaining novel functionality at the nanoscale,
which can lead to new device paradigms. 相似文献
4.
JA Skinner G Prabhakar DG Genecov K Granke DE McDowell 《Canadian Metallurgical Quarterly》1997,90(10):993-996
BACKGROUND: Spontaneous rupture of abdominal aortic aneurysm into the inferior vena cava is rare. The clinical presentation is highly variable, and the diagnosis can be difficult, often being made only at operation. The aortocaval fistula results in a large left-to-right shunt, which can cause cardiac failure. Once the diagnosis is made, treatment is by surgical closure of the fistula and repair of the aneurysm with a graft. METHODS: This is a retrospective review of a single surgeon's experience with aortocaval fistula complicating abdominal aortic aneurysms. RESULTS: Over a 15-year period, we had five patients with spontaneous aortocaval fistula who were treated operatively. Preoperative diagnosis was made in two, suspected in one, and not made in two, one of whom died (the only perioperative death in the series). CONCLUSIONS: Spontaneous aortocaval fistulas are uncommon, and their preoperative recognition is difficult. Hematuria in association with an abdominal aortic aneurysm should raise the suspicion of an aortocaval fistula. Surgical correction is possible, with survival rates comparable to those associated with rupture of aneurysms into the retroperitoneum. Early operative control of the fistula is important to optimize the preload to the heart. 相似文献
5.
A new finite element crack growth algorithm has been developed to simulate dynamic fracture. In this algorithm, pseudo elements with very high initial density are placed below the crack plane and the density is reduced to zero in a gradual manner as the crack passes the element. A number of linear elastic and elasto-viscoplastic problems have been carried out to test the new algorithm. The results are compared with some of the existing crack growth models. 相似文献
6.
Divakaruni R. Prabhakar V. Viswanathan C.R. 《Electron Devices, IEEE Transactions on》1994,41(8):1405-1413
The response of semiconductor devices at low temperatures to changes in the voltage across the depletion region is limited by the dielectric relaxation time of the majority carriers in the bulk region. This results in a dispersion of the C-V curves at low temperatures. In this paper, we report a study of the dispersion seen in the accumulation and depletion regions of the C-V curve in n- and p-channel MOS transistors as well as in reverse biased one-sided abrupt junctions. From the admittance measured as a function of temperature and frequency, the dopant energy level is determined. The values of the activation energy measured using the diodes agree well with the corresponding values obtained using MOS devices 相似文献
7.
Entropy and the timing capacity of discrete queues 总被引:1,自引:0,他引:1
Prabhakar B. Gallager R. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(2):357-370
Queueing systems which map Poisson input processes to Poisson output processes have been well-studied in classical queueing theory. This paper considers two discrete-time queues whose analogs in continuous-time possess the Poisson-in-Poisson-out property. It is shown that when packets arriving according to an arbitrary ergodic stationary arrival process are passed through these queueing systems, the corresponding departure process has an entropy rate no less (some times strictly more) than the entropy rate of the arrival process. Some useful by-products are discrete-time versions of: (i) a proof of the celebrated Burke's (1956) theorem, (ii) a proof of the uniqueness, amongst renewal inputs, of the Poisson process as a fixed point for exponential server queues proposed by Anantharam (1993), and (iii) connections with the timing capacity of queues described by Anantharam and Verdu (1996). 相似文献
8.
We propose an exact algorithm for counting the models of propositional formulas in conjunctive normal form. Our algorithm is based on the detection of strong backdoor sets of bounded size; each instantiation of the variables of a strong backdoor set puts the given formula into a class of formulas for which models can be counted in polynomial time. For the backdoor set detection we utilize an efficient vertex cover algorithm applied to a certain “obstruction graph” that we associate with the given formula. This approach gives rise to a new hardness index for formulas, the clustering-width. Our algorithm runs in uniform polynomial time on formulas with bounded clustering-width. It is known that the number of models of formulas with bounded clique-width, bounded treewidth, or bounded branchwidth can be computed in polynomial time; these graph parameters are applied to formulas via certain (hyper)graphs associated with formulas. We show that clustering-width and the other parameters mentioned are incomparable: there are formulas with bounded clustering-width and arbitrarily large clique-width, treewidth, and branchwidth. Conversely, there are formulas with arbitrarily large clustering-width and bounded clique-width, treewidth, and branchwidth. 相似文献
9.
Autoantibodies to the thyrotropin receptor (TSHR) can act as thyrotropin agonists or antagonists, or can cause thyroid hypertrophy. Neither the autoantibody-binding sites on the TSHR nor the intracellular mechanisms by which the autoantibodies mediate their diverse functional effects are completely understood. This article reviews how cloning of the TSHR has contributed to our understanding of its structure and function, and has allowed induction of experimental autoimmunity to the TSHR. 相似文献
10.
A. G. Gopala Krishna J. V. Prabhakar 《Journal of the American Oil Chemists' Society》1994,71(6):645-647
Antioxidant efficacy of the amino acids methionine, tryptophan, aspartic acid, serine, alanine and arginine in methyl linoleate
were compared to a methyl linoleate control at 2,50 or 79% relative humidity (RH) at 37°C. Antioxidant efficacy varied with
RH and the individual amino acids. Arginine had the highest antioxidant efficacy at all RH values compared to the control.
The efficacy of alanine was equal to that of arginine at RHs of 50 and 79% but was lower at 2% RH. The presence of aliphatic,
alkaline amino, hydroxyl or thiol groups in the side chain of the amino acids increased the antioxidant efficacy at high RHs. 相似文献