93 research outputs found
Optimality of Orthogonal Access for One-dimensional Convex Cellular Networks
It is shown that a greedy orthogonal access scheme achieves the sum degrees
of freedom of all one-dimensional (all nodes placed along a straight line)
convex cellular networks (where cells are convex regions) when no channel
knowledge is available at the transmitters except the knowledge of the network
topology. In general, optimality of orthogonal access holds neither for
two-dimensional convex cellular networks nor for one-dimensional non-convex
cellular networks, thus revealing a fundamental limitation that exists only
when both one-dimensional and convex properties are simultaneously enforced, as
is common in canonical information theoretic models for studying cellular
networks. The result also establishes the capacity of the corresponding class
of index coding problems
Retrospective Interference Alignment
We explore similarities and differences in recent works on blind interference
alignment under different models such as staggered block fading model and the
delayed CSIT model. In particular we explore the possibility of achieving
interference alignment with delayed CSIT when the transmitters are distributed.
Our main contribution is an interference alignment scheme, called retrospective
interference alignment in this work, that is specialized to settings with
distributed transmitters. With this scheme we show that the 2 user X channel
with only delayed channel state information at the transmitters can achieve 8/7
DoF, while the interference channel with 3 users is able to achieve 9/8 DoF. We
also consider another setting where delayed channel output feedback is
available to transmitters. In this setting the X channel and the 3 user
interference channel are shown to achieve 4/3 and 6/5 DoF, respectively
Distributed Data Storage with Minimum Storage Regenerating Codes - Exact and Functional Repair are Asymptotically Equally Efficient
We consider a set up where a file of size M is stored in n distributed
storage nodes, using an (n,k) minimum storage regenerating (MSR) code, i.e., a
maximum distance separable (MDS) code that also allows efficient exact-repair
of any failed node. The problem of interest in this paper is to minimize the
repair bandwidth B for exact regeneration of a single failed node, i.e., the
minimum data to be downloaded by a new node to replace the failed node by its
exact replica. Previous work has shown that a bandwidth of B=[M(n-1)]/[k(n-k)]
is necessary and sufficient for functional (not exact) regeneration. It has
also been shown that if k < = max(n/2, 3), then there is no extra cost of exact
regeneration over functional regeneration. The practically relevant setting of
low-redundancy, i.e., k/n>1/2 remains open for k>3 and it has been shown that
there is an extra bandwidth cost for exact repair over functional repair in
this case. In this work, we adopt into the distributed storage context an
asymptotically optimal interference alignment scheme previously proposed by
Cadambe and Jafar for large wireless interference networks. With this scheme we
solve the problem of repair bandwidth minimization for (n,k) exact-MSR codes
for all (n,k) values including the previously open case of k > \max(n/2,3). Our
main result is that, for any (n,k), and sufficiently large file sizes, there is
no extra cost of exact regeneration over functional regeneration in terms of
the repair bandwidth per bit of regenerated data. More precisely, we show that
in the limit as M approaches infinity, the ratio B/M = (n-1)/(k(n-k))$
Janssen effect and the stability of quasi 2-D sandpiles
We present the results of three dimensional molecular dynamics study of
global normal stresses in quasi two dimensional sandpiles formed by pouring
mono dispersed cohesionless spherical grains into a vertical granular Hele-Shaw
cell. We observe Janssen effect which is the phenomenon of pressure saturation
at the bottom of the container. Simulation of cells with different thicknesses
shows that the Janssen coefficient is a function of the cell
thickness. Dependence of global normal stresses as well as on the
friction coefficients between the grains () and with walls () are
also studied. The results show that in the range of our simulations
usually increases with wall-grain friction coefficient. Meanwhile by increasing
while the other system parameters are fixed, we witness a gradual
increase in to a parameter dependent maximal value
Structure of bottle-brush brushes under good solvent conditions. A molecular dynamics study
We report a simulation study for bottle-brush polymers grafted on a rigid
backbone. Using a standard coarse-grained bead-spring model extensive molecular
dynamics simulations for such macromolecules under good solvent conditions are
performed. We consider a broad range of parameters and present numerical
results for the monomer density profile, density of the untethered ends of the
grafted flexible backbones and the correlation function describing the range
that neighboring grafted bottle-brushes are affected by the presence of the
others due to the excluded volume interactions. The end beads of the flexible
backbones of the grafted bottle-brushes do not access the region close to the
rigid backbone due to the presence of the side chains of the grafted
bottle-brush polymers, which stretch further the chains in the radial
directions. Although a number of different correlation lengths exist as a
result of the complex structure of these macromolecules, their properties can
be tuned with high accuracy in good solvents. Moreover, qualitative differences
with "typical" bottle-brushes are discussed. Our results provide a first
approach to characterizing such complex macromolecules with a standard bead
spring model.Comment: To appear in Journal of Physics Condensed Matter (2011
Epigenetic Modifications and Therapy in Chronic Obstructive Pulmonary Disease (COPD): An Update Review.
Chronic obstructive pulmonary disease (COPD) that is one of the most prevalent chronic adult diseases and the third leading cause of fatality until 2020. Elastase/anti-elastase hypothesis, chronic inflammation, apoptosis, oxidant-antioxidant balance and infective repair cause pathogenesis of COPD are among the factors at play. Epigenetic changes are post-translational modifications in histone proteins and DNA such as methylation and acetylation as well as dysregulation of miRNAs expression. In this update review, we have examined recent studies on the upregulation or downregulation of methylation in different genes associated with COPD. Dysregulation of HDAC activity which is caused by some factors and miRNAs plays a key role in the suppression and reduction of COPD development. Also, some therapeutic approaches are proposed against COPD by targeting HDAC2 and miRNAs, which have therapeutic effects
Locally Estimated Hemodynamic Response Function and Activation Detection Sensitivity in Heroin-Cue Reactivity Study
INTRODUCTION: A fixed hemodynamic response function (HRF) is commonly used for functional magnetic resonance imaging (fMRI) analysis. However, HRF may vary from region to region and subject to subject. We investigated the effect of locally estimated HRF (in functionally homogenous parcels) on activation detection sensitivity in a heroin cue reactivity study.
METHODS: We proposed a novel exploratory method for brain parcellation based on a probabilistic model to segregate the brain into spatially connected and functionally homogeneous components. Then, we estimated HRF and detected activated regions in response to an experimental task in each parcel using a joint detection estimation (JDE) method. We compared the proposed JDE method with the general linear model (GLM) that uses a fixed HRF and is implemented in FEAT (as a part of FMRIB Software Library, version 4.1).
RESULTS: 1) Regions detected by JDE are larger than those detected by fixed HRF, 2) In group analysis, JDE found areas of activation not detected by fixed HRF. It detected drug craving a priori regions-of-interest in the limbic lobe (anterior cingulate cortex [ACC], posterior cingulate cortex [PCC] and cingulate gyrus), basal ganglia, especially striatum (putamen and head of caudate), and cerebellum in addition to the areas detected by the fixed HRF method, 3) JDE obtained higher Z-values of local maxima compared to those obtained by fixed HRF.
CONCLUSION: In our study of heroin cue reactivity, our proposed method (that estimates HRF locally) outperformed the conventional GLM that uses a fixed HRF
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