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81.
Delay-bounded packet scheduling of bursty traffic over wireless channels   总被引:4,自引:0,他引:4  
In this paper, we study minimal power transmission of bursty sources over wireless channels with constraints on mean queuing delay. The power minimizing schedulers adapt power and rate of transmission based on the queue and channel state. We show that packet scheduling based on queue state can be used to trade queuing delay with transmission power, even on additive white Gaussian noise (AWGN) channels. Our extensive simulations show that small increases in average delay can lead to substantial savings in transmission power, thereby providing another avenue for mobile devices to save on battery power. We propose a low-complexity scheduler that has near-optimal performance. We also construct a variable-rate quadrature amplitude modulation (QAM)-based transmission scheme to show the benefits of the proposed formulation in a practical communication system. Power optimal schedulers with absolute packet delay constraints are also studied and their performance is evaluated via simulations.  相似文献   
82.
Spontaneous mouse mutations that cause severe immunodeficiency or autoimmunity are invaluable tools with which to investigate the mammalian immune system. Mutations at the 'motheaten' locus result in severe immunological dysfunction due to disruption of the structural gene encoding Src-homology 2-domain phosphatase-1 (SHP-1). This natural model for a specific protein-tyrosine-phosphatase deficiency is being widely utilized to determine the role of SHP-1 in the negative regulation of multiple signaling pathways in a number of hematopoietic lineages.  相似文献   
83.
Rajan Mahadevan evidences an exceptional memory for arrays of digits. The authors tested whether Rajan's spatial memory was likewise exceptional. Eight control Ss and Rajan were instructed to remember the position and orientation of 48 images of common objects shown either to the left or the right of fixation and facing either left or right. Rajan's accuracy for judging whether the position and orientation of these pictures had changed when they were shown in a different sequence was lower than that of control Ss for both judgments. Rajan's exceptional memory capacity apparently does not extend to spatial relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
84.
As a result of the varied applications of Hurwitz polynomials in the analysis and design of two-dimensional circuits and systems, several different classes of two-variable Hurwitz polynomials have been defined. The authors provide a comprehensive presentation of the definitions of different classes, the interrelationships among them, and their applications. The place and role of the newly defined principal Hurwitz polynomials among the various Hurwitz polynomials are also brought to light. Using a continuity property of the zeros of two-variable polynomials, new proofs for the test procedures of the different Hurwitz polynomials are presented. Applications of the Hurwitz polynomials in the study of the stability of two-dimensional systems and the properties of two-variable passive networks are summarized  相似文献   
85.
It is shown that two theorems regarding the existence of generalized linear processing orthogonal designs (GLPOD) are valid under more general conditions than those for which they have been stated and proved (for original paper see V. Tarokh et al., "Space-time block codes from orthogonal designs", ibid., vol. 45, p. 1456-1467 (1999)).  相似文献   
86.
Staphylococcal enterotoxins A and C1 (SEA or SEC1) bound to major histocompatibility-I (MHCI) molecules with high affinity (binding constants ranging from 1.1 microM to 79 nM). SEA and SEC1 directly bound MHCI molecules that had been captured by monoclonal antibodies specific for H-2Kk, H-2Dk, or both. In addition, MHCI-specific antibodies inhibited the binding of SEC1 to LM929 cells and SEA competitively inhibited SEC1 binding; indicating that the superantigens bound to MHCI on the cell surface. The affinity and number of superantigen binding sites differed depending on whether MHCI was expressed in the membrane of LM929 cells or whether it was captured. These data support the hypothesis that MHCI molecules can serve as superantigen receptors.  相似文献   
87.
An experimental study of transport phenomena at the wall of an agitated vessel with a propeller impeller under unsteady conditions is reported. The transient in heat transfer at the wall is caused by a step change in the speed of agitation from an initial static condition. The results are expressed in terms of a rise in modified “j-factor” above the initial free convection value and the number of revolutions taken by the impeller from the start of agitation. Also, an attempt has been made to find an analogy beween heat and momentum transfer. Results are given for the power in terms of Euler number plotted against the impeller Reynolds number. An empirical expression is also given for the transient heat transfer considering the system as a pure first order one with time delay. A “time-factor” constant which gives the number of impeller revolutions for 63.2% of the change from the initial to a final steady state is expressed as a function of impeller Reynolds number (102 to 106) and fluid Prandtl number (6 to 106).  相似文献   
88.
It is suggested that when a polymer is synthesized from a monomer and an added initiator in the presence of ultrasound, the process may produce polymers with predetermined structures and physical properties. An attempt is made to measure thermal diffusivity. Poly(methyl acrylate) (PMA) is synthesized using monomer methyl acrylate and an added initiator peroxodisulfate in the presence of ultrasound of frequency 35 kHz and power 100 W/cm2 at 50°C for various known sonication periods. PMA is obtained as a colorless, semitransparent solid. The solid PMA is cut into thin wafers in a highly symmetric direction to have uniform sizes. PMA samples are synthesized for 11 different sonication periods. These PMA samples are use to study their thermal diffusivity (α) by photoacoustic (PA) technique. Thermal diffusivity is calculated by measuring the amplitude and phase of the PA signal separately. A plot of the sonication period versus thermal diffusivity obtained from amplitude measurements of PMA indicates that there is an increase in thermal diffusivity from 2 × 10?6 to 4.7 × 10?6 m2/s when sonication period is increased from 30 to 330 min in steps of 30 min. The same trend is seen in a plot between sonication period and thermal diffusivity when the thermal diffusivity is calculated by PA phase measurements. There is a small difference in the experimental values obtained by the two measurements. Dependence of thermal diffusivity of PMA on ultrasonic sonication is discussed in detail. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 3756–3760, 2006  相似文献   
89.
Processing parameters and the resulting properties of a material are linked by the relationship between processing and microstructure. Characterizing the effect of processing variations on microstructure and determining its origin are essential to advanced material development. In this and a companion article, some readily applied techniques for producing quantitative data on grain size and shape, as well as grain and boundary crystallography, are described. The method described in Part I utilizes transmission electron microscopy and image analysis to measure grain size in large quantities (2000 to 3000 grains per sample), differentiated into orientation class subpopulation distributions. On application to Ni thin films produced by ion assisted deposition, the results have identified an orientation subpopulation that is predominantly responsible for the larger grain sizes observed in films grown under high ion flux. Larger grain size and the development of a preferred orientation have both been associated with increasing ion flux during growth, however, these results give the first experimental evidence connecting grain size and texture in these films.  相似文献   
90.
Glutamatergic retinotectal inputs mediated principally by NMDA receptors can be recorded from optic tectal neurons early during their morphological development in Xenopus tadpoles. As tectal cell dendrites elaborate, retinotectal synaptic responses acquire an AMPA receptor-mediated synaptic component, in addition to the NMDA component. Here, we tested whether glutamatergic activity was required for the elaboration of dendritic arbors in Xenopus optic tectal neurons. In vivo time-lapse imaging of single DiI-labeled neurons shows that the NMDA receptor antagonist APV (100 microM) blocked the early development of the tectal cell dendritic arbor, whereas the AMPA receptor antagonist CNQX (20 microM) or the sodium channel blocker TTX (1 microM) did not. The decreased dendritic development is attributable to failure to add new branches and extend preexisting branches. These observations indicate that NMDA-type glutamatergic activity promotes the initial development of the dendritic arbor. At later stages of tectal neuron development when AMPA receptor-mediated synaptic transmission is strong, both APV and CNQX decrease dendritic arbor branch length, consistent with a role for glutamatergic synaptic transmission in maintaining dendritic arbor structure. These results indicate that AMPA and NMDA receptors can differentially influence dendritic growth at different stages of neuronal development, in correlation with changes in the relative contribution of the receptor subtype to synaptic transmission.  相似文献   
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