478 research outputs found
Throughput and Delay Analysis for Real-Time Applications in Ad-Hoc Cognitive Networks
No full textWe consider a simple ad-hoc cognitive scenario with two data up-links, one licensed to use the spectral resource (primary) and the other unlicensed (secondary or cognitive). It is assumed that the cognitive link accesses the channel only when the channel is sensed idle. An ON-OFF channel model is used for the primary link, where traffic statistical characteristics are taken into account. A closed-form expression for the signal-to noise-plus interference (SINR) statistics of the cognitive nodes is derived that can be used for estimating the network performance. Moreover, a M/G/1 queueing model is exploited for deriving a simple expression for the average packet delay. Finally, a MAC strategy based on a channel-and-queue aware scheduling is introduced
Bayesian population inference for effective connectivity
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 157-169).A hierarchical model based on the Multivariate Autoregessive (MAR) process is proposed to jointly model functional neuroimaging time series collected from multiple subjects, and to characterize the distribution of MAR coefficients across the population from which those subjects were drawn. Thus, model-based inference about the interaction between brain regions, termed effective connectivity, may be generalized beyond those subjects studied. The posterior density of population- and subject-level connectivity parameters is estimated in a Variational Bayesian (VB) framework, and structural model parameters are chosen by the corresponding evidence criterion. The significance of resulting connectivity statistics are evaluated by permutation-based approximations to the null distribution. The method is demonstrated on simulated data and on actual multi-subject functional time series from electroencephalography (EEG) and functional magnetic resonance imaging (fMRI).by Eric Richard Cosman, Jr.Ph.D
The leukocyte Ig-like receptor (LIR)-1 for the Cytomegalovirus UL18 protein displays a broad specificity for different HLA class I alleles: analysis of LIR-1+ NK cell clones
No full textThe LIR-1 receptor for the cytomegalovirus UL18 protein displays a broad specificity for different HLA class I alleles.
No full textSoluble ULBP suppresses natural killer cell activity via down-regulating NKG2D expression
No full textNKG2D is an activating receptor that is expressed on most natural killer (NK) cells and CD8+ T cells. MHC class I-related chain A(MICA) and UL16-binding protein (ULBP) 1, 2, and 3 are well-known ligands for NKG2D. Human gastric cancer cell lines, SNU216 and SNU638 cells which expressed UL16-binding protein (ULBP) were susceptible to NK cells in a NKG2D-dependent manner. However, SNU484 and SNU620 cells which had no ULBP on their surface were resistant to NK cells. ULBP 1, 2, and 3 are glycosylphosphatidylinositol (GPI)-anchored proteins which are sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC). When SNU620 cells were treated with U73122, an inhibitor of PI-PLC, the surface expression of ULBP was elevated with increased NK susceptibility. Pre-incubating NK cells with culture supernatants of SNU620 or SNU638 cells, which contained soluble ULBP protein, reduced NK cell activity by decreasing surface expression of NKG2D in NK cells. Furthermore, recombinant ULBP-Fc induced the down-regulation of NKG2D expression in NK cells. Taken together, down-regulation of NKG2D by soluble ULBP provides a potential mechanism by which gastric cancer cells escape NKG2D-mediated attack by the immune cells.open
Human immunodeficiency virus 1 Nef protein downmodulates the ligands of the activating receptor NKG2D and inhibits natural killer cell-mediated cytotoxicity
No full textNatural killer (NK) cells are a major component of the host innate immune defence against various pathogens. Several viruses, including Human immunodeficiency virus 1 (HIV-1), have developed strategies to evade the NK-cell response. This study was designed to evaluate whether HIV-1 could interfere with the expression of NK cell-activating ligands, specifically the human leukocyte antigen (HLA)-I-like MICA and ULBP molecules that bind NKG21D, an activating receptor expressed by all NK cells. Results show that the HIV-1 Nef protein downmodulates cell-surface expression of MICA, ULBP1 and ULBP2, with a stronger effect on the latter molecule. The activity on MICA and ULBP2 is well conserved in Nef protein variants derived from HIV-1-infected patients. In HIV-1-infected cells, cell-surface expression of NKG2D ligands increased to a higher extent with a Nef-deficient virus compared with wild-type virus. Mutational analysis of Nef showed that NKG2D ligand downmodulation has structural requirements that differ from those of other reported Nef activities, including HLA-I downmodulation. Finally, data demonstrate that Nef expression has functional consequences on NK-cell recognition, causing a decreased susceptibility to NK cell-mediated lysis. These findings provide a novel insight into the mechanisms evolved by HIV-1 to escape from the NK-cell response
LIR-1 expression on lymphocytes, and cytomegalovirus disease in lung-transplant recipients
No full textOptimization of Multimedia Progressive Transmission Over MIMO Channels
No full textThis paper studies the optimal transmission of multimedia progressive sources, which require unequal target error rates in their bitstream, over multiple-input-multiple-output (MIMO) channels. First, we derive the information outage probability expression of a space-time code for an arbitrarily given piecewise-linear diversity-multiplexing tradeoff (DMT) function and the conditions for the existence of a crossover point of the information outage probability curves of the space-time codes. We prove that as long as the crossover point of the outage probabilities exists, as spectral efficiency increases, the crossover point in the signal-to-noise ratio (SNR) monotonically increases, whereas that of the outage probability monotonically decreases. This analysis can be applied to any space-time code, receiver, and propagation channel with a given DMT function. As a specific example, we analyze the two-layer diagonal Bell Labs space-time architecture (D-BLAST) with a group zero-forcing receiver, the vertical BLAST (V-BLAST) with a minimum mean-square error receiver, and orthogonal space-time block codes (OSTBCs), and prove the monotonic behavior of the crossover point for those codes. Based on that, with respect to D-BLAST, V-BLAST, and OSTBC, we derive a method for the optimal space-time coding of a sequence that contains numerous progressive packets. We show that by employing the optimization method rather than exhaustive search, the computational complexity involved with optimal space-time coding can be exponentially reduced without losing any peak SNR performance. © 2015 IEEE
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