8,986 research outputs found
Multi-tier Network Performance Analysis using a Shotgun Cellular System
This paper studies the carrier-to-interference ratio (CIR) and
carrier-to-interference-plus-noise ratio (CINR) performance at the mobile
station (MS) within a multi-tier network composed of M tiers of wireless
networks, with each tier modeled as the homogeneous n-dimensional (n-D, n=1,2,
and 3) shotgun cellular system, where the base station (BS) distribution is
given by the homogeneous Poisson point process in n-D. The CIR and CINR at the
MS in a single tier network are thoroughly analyzed to simplify the analysis of
the multi-tier network. For the multi-tier network with given system
parameters, the following are the main results of this paper: (1)
semi-analytical expressions for the tail probabilities of CIR and CINR; (2) a
closed form expression for the tail probability of CIR in the range
[1,Infinity); (3) a closed form expression for the tail probability of an
approximation to CIR in the entire range [0,Infinity); (4) a lookup table based
approach for obtaining the tail probability of CINR, and (5) the study of the
effect of shadow fading and BSs with ideal sectorized antennas on the CIR and
CINR. Based on these results, it is shown that, in a practical cellular system,
the installation of additional wireless networks (microcells, picocells and
femtocells) with low power BSs over the already existing macrocell network will
always improve the CINR performance at the MS.Comment: 6 pages, 3 figures, accepted at IEEE Globecom 201
Stochastic Ordering based Carrier-to-Interference Ratio Analysis for the Shotgun Cellular Systems
A simple analytical tool based on stochastic ordering is developed to compare
the distributions of carrier-to-interference ratio at the mobile station of two
cellular systems where the base stations are distributed randomly according to
certain non-homogeneous Poisson point processes. The comparison is conveniently
done by studying only the base station densities without having to solve for
the distributions of the carrier-to-interference ratio, that are often hard to
obtain.Comment: 10 pages, 0 figures, submitted for review to IEEE Wireless
Communications Letters on October 11, 201
Limitations for change detection in multiple Gabor targets
We investigate the limitations on the ability to detect when a target has changed, using Gabor targets as simple quantifiable stimuli. Using a partial report technique to equalise response variables, we show that the log of the Weber fraction for detecting a spatial frequency change is proportional to the log of the number of targets, with a set-size effect that is greater than that reported for visual search. This is not a simple perceptual limitation, because pre-cueing a single target out of four restores performance to the level found when only one target is present. It is argued that the primary limitation on performance is the division of attention across multiple targets, rather than decay within visual memory. However in a simplified change detection experiment without cueing, where only one target of the set changed, not only was the set size effect still larger, but it was greater at 2000 msec ISI than at 250 msec ISI, indicating a possible memory component. The steepness of the set size effects obtained suggests that even moderate complexity of a stimulus in terms of number of component objects can overload attentional processes, suggesting a possible low-level mechanism for change blindness
Formulations of the 3+1 evolution equations in curvilinear coordinates
Following Brown, in this paper we give an overview of how to modify standard
hyperbolic formulations of the 3+1 evolution equations of General Relativity in
such a way that all auxiliary quantities are true tensors, thus allowing for
these formulations to be used with curvilinear sets of coordinates such as
spherical or cylindrical coordinates. After considering the general case for
both the Nagy-Ortiz-Reula (NOR) and the Baumgarte-Shapiro-Shibata-Nakamura
(BSSN) formulations, we specialize to the case of spherical symmetry and also
discuss the issue of regularity at the origin. Finally, we show some numerical
examples of the modified BSSN formulation at work in spherical symmetry.Comment: 19 pages, 12 figure
Scaling of Pseudo-Critical Couplings in Two-Flavour QCD
We study the scaling behaviour of the pseudo-critical couplings for the
chiral phase transition in two-flavour QCD. We show that all existing results
from lattice simulations on lattices with temporal extent , 6 and 8
can be mapped onto a universal scaling curve. The relevant combination of
critical exponents, , is consistent with the scaling behaviour
expected for a second order phase transition with exponents. At present,
scaling according to the symmetry group can, however, not be ruled out.Comment: 8 pages, NSF-ITP 93-12
Setting a research agenda for progressive multiple sclerosis: The International Collaborative on Progressive MS
Despite significant progress in the development of therapies for relapsing MS, progressive MS remains comparatively disappointing. Our objective, in this paper, is to review the current challenges in developing therapies for progressive MS and identify key priority areas for research. A collaborative was convened by volunteer and staff leaders from several MS societies with the mission to expedite the development of effective disease-modifying and symptom management therapies for progressive forms of multiple sclerosis. Through a series of scientific and strategic planning meetings, the collaborative identified and developed new perspectives on five key priority areas for research: experimental models, identification and validation of targets and repurposing opportunities, proof-of-concept clinical trial strategies, clinical outcome measures, and symptom management and rehabilitation. Our conclusions, tackling the impediments in developing therapies for progressive MS will require an integrated, multi-disciplinary approach to enable effective translation of research into therapies for progressive MS. Engagement of the MS research community through an international effort is needed to address and fund these research priorities with the ultimate goal of expediting the development of disease-modifying and symptom-relief treatments for progressive MS
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