25,552 research outputs found
Analysis and Design of Multiple-Antenna Cognitive Radios with Multiple Primary User Signals
We consider multiple-antenna signal detection of primary user transmission
signals by a secondary user receiver in cognitive radio networks. The optimal
detector is analyzed for the scenario where the number of primary user signals
is no less than the number of receive antennas at the secondary user. We first
derive exact expressions for the moments of the generalized likelihood ratio
test (GLRT) statistic, yielding approximations for the false alarm and
detection probabilities. We then show that the normalized GLRT statistic
converges in distribution to a Gaussian random variable when the number of
antennas and observations grow large at the same rate. Further, using results
from large random matrix theory, we derive expressions to compute the detection
probability without explicit knowledge of the channel, and then particularize
these expressions for two scenarios of practical interest: 1) a single primary
user sending spatially multiplexed signals, and 2) multiple spatially
distributed primary users. Our analytical results are finally used to obtain
simple design rules for the signal detection threshold.Comment: Revised version (14 pages). Change in titl
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A novel element upstream of the Vgamma2 gene in the murine T cell receptor gamma locus cooperates with the 3 enhancer to act as a locus control region.
Transgenic expression constructs were employed to identify a cis-acting transcription element in the T cell receptor (TCR)-gamma locus, called HsA, between the Vgamma5 and Vgamma2 genes. In constructs lacking the previously defined enhancer (3E(Cgamma1)), HsA supports transcription in mature but not immature T cells in a largely position-independent fashion. 3E(Cgamma1), without HsA, supports transcription in immature and mature T cells but is subject to severe position effects. Together, the two elements support expression in immature and mature T cells in a copy number-dependent, position-independent fashion. Furthermore, HsA was necessary for consistent rearrangement of transgenic recombination substrates. These data suggest that HsA provides chromatin-opening activity and, together with 3E(Cgamma1), constitutes a T cell-specific locus control region for the TCR-gamma locus
Structural Properties of the Caenorhabditis elegans Neuronal Network
Despite recent interest in reconstructing neuronal networks, complete wiring
diagrams on the level of individual synapses remain scarce and the insights
into function they can provide remain unclear. Even for Caenorhabditis elegans,
whose neuronal network is relatively small and stereotypical from animal to
animal, published wiring diagrams are neither accurate nor complete and
self-consistent. Using materials from White et al. and new electron micrographs
we assemble whole, self-consistent gap junction and chemical synapse networks
of hermaphrodite C. elegans. We propose a method to visualize the wiring
diagram, which reflects network signal flow. We calculate statistical and
topological properties of the network, such as degree distributions, synaptic
multiplicities, and small-world properties, that help in understanding network
signal propagation. We identify neurons that may play central roles in
information processing and network motifs that could serve as functional
modules of the network. We explore propagation of neuronal activity in response
to sensory or artificial stimulation using linear systems theory and find
several activity patterns that could serve as substrates of previously
described behaviors. Finally, we analyze the interaction between the gap
junction and the chemical synapse networks. Since several statistical
properties of the C. elegans network, such as multiplicity and motif
distributions are similar to those found in mammalian neocortex, they likely
point to general principles of neuronal networks. The wiring diagram reported
here can help in understanding the mechanistic basis of behavior by generating
predictions about future experiments involving genetic perturbations, laser
ablations, or monitoring propagation of neuronal activity in response to
stimulation
A paracrine circuit of IL-1β/IL-1R1 between myeloid and tumor cells drives genotype-dependent glioblastoma progression
Monocytes and monocyte-derived macrophages (MDMs) from blood circulation infiltrate glioblastoma (GBM) and promote growth. Here, we show that PDGFB-driven GBM cells induce the expression of the potent proinflammatory cytokine IL-1β in MDM, which engages IL-1R1 in tumor cells, activates the NF-κB pathway, and subsequently leads to induction of monocyte chemoattractant proteins (MCPs). Thus, a feedforward paracrine circuit of IL-1β/IL-1R1 between tumors and MDM creates an interdependence driving PDGFB-driven GBM progression. Genetic loss or locally antagonizing IL-1β/IL-1R1 leads to reduced MDM infiltration, diminished tumor growth, and reduced exhausted CD8+ T cells and thereby extends the survival of tumor-bearing mice. In contrast to IL-1β, IL-1α exhibits antitumor effects. Genetic deletion of Il1a/b is associated with decreased recruitment of lymphoid cells and loss-of-interferon signaling in various immune populations and subsets of malignant cells and is associated with decreased survival time of PDGFB-driven tumor-bearing mice. In contrast to PDGFB-driven GBM, Nf1-silenced tumors have a constitutively active NF-κB pathway, which drives the expression of MCPs to recruit monocytes into tumors. These results indicate local antagonism of IL-1β could be considered as an effective therapy specifically for proneural GBM
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