3,014 research outputs found
A Flexible and Fast Event-Driven Simulator for wireless MAC protocols
Many multiple-access (MAC) protocols have been or are being proposed for wireless networks. As most of these multiple-access protocols are designed for specific applications (such as telephony) and analyzed accordingly, the analysis results can not always be adapted to situations where each user has a different behavior. Wireless MAC protocols for data communication are not straightforward to analyse. To quickly make a reliable judgement of the usability of a MAC protocol for specific situations, we designed a simulator that makes it simple to implement the protocol and test it in different configurations and with differently behaving users. Our simulator generates a large amount of quantitative performance information that can be processed with standard graph drawing tools and an integrated trace analyze
Exact Gravity Dual of a Gapless Superconductor
A model of an exact gravity dual of a gapless superconductor is presented in
which the condensate is provided by a charged scalar field coupled to a bulk
black hole of hyperbolic horizon in asymptotically AdS spacetime. Below a
critical temperature, the black hole acquires its hair through a phase
transition while an electromagnetic perturbation of the background Maxwell
field determines the conductivity of the boundary theory.Comment: 21 pages, 8 figures, a section on the stability of the MTZ black hole
is added, references are added, version to be published in JHE
A new maximally supersymmetric background of IIB superstring theory
We present a maximally supersymmetric IIB string background. The geometry is
that of a conformally flat lorentzian symmetric space G/K with solvable G, with
a homogeneous five-form flux. We give the explicit supergravity solution,
compute the isometries, the 32 Killing spinors, and the symmetry superalgebra,
and then discuss T-duality and the relation to M-theory.Comment: 17 page
Autoimmune pancreatitis/IgG4-associated cholangitis and primary sclerosing cholangitis â Overlapping or separate diseases?
Autoimmune pancreatitis is a recently described fibroinflammatory disease which is characterised by raised serum levels of IgG4 (in >70% of cases), and an IgG4-positive lymphoplasmacytic tissue infiltrate. A favourable and rapid clinical response to oral steroid therapy is often seen. Biliary involvement is common, and the term IgG4-associated cholangitis has recently been coined. The cholangiographic appearances of IgG4-associated cholangitis and primary sclerosing cholangitis can be difficult to differentiate. Moreover, raised levels of serum IgG4 have been recently found in 9% of patients with primary sclerosing cholangitis (a much higher frequency than for other gastrointestinal diseases), and those with raised levels appear to progress more rapidly to liver failure. Here we review the similarities and differences between the biliary disease in autoimmune pancreatitis and primary sclerosing cholangitis, and address the issue of disease overlap. Improvements in understanding the relationship between these conditions might lead to an enhanced understanding of the aetiopathogenesis, and improved treatment of both conditions
Application of OCT to examination of easel paintings
We present results of applying low coherence interferometry to gallery paintings. Infrared low coherence interferometry is capable of non-destructive examination of paintings in 3D, which shows not only the structure of the varnish layer but also the paint layers
Moisture Absorption of Graphite-Epoxy Composites Immersed in Liquids and in Humid Air
Moisture absorption of graphite-epoxy composites immersed in liquids and in himid air were investigated. The moisture content as a function of time and temperature was measured for three materials: Fiberite T300/1034, Hercules AS/3501-5 and Narmco T300/5208. Tests were per formed a) with the materials immersed in No. 2 diesel fuel, in jet A fuel, in aviation oil, in saturated salt water, and in distilled water (in the range of 300 to 322 K) and b)with the materials exposed to humid air (in the range 322 to 366 K). The results obtained were compared to available composite and neat resin data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68153/2/10.1177_002199837901300205.pd
Null Wilson loops with a self-crossing and the Wilson loop/amplitude conjecture
The present study illuminates the relation between null cusped Wilson loops
and their corresponding amplitudes. We find that, compared to the case with no
self-crossing, the one loop expectation value of a self-intersecting Wilson
loop develops an additional 1/\epsilon singularity associated to the
intersection. Interestingly, the same 1/\epsilon pole exists in the finite part
of the one loop amplitude, appearing in the BDS conjecture, at the
corresponding kinematic limit. At two loops, we explore the behaviour of the
remainder function R, encoding the deviation of the amplitude from the BDS
conjecture. By analysing the renormalisation group equations for the Wilson
loop with a simple self-crossing, we argue that, when approaching the
configuration with a self-crossing (u_2 \to 1, u_1\approx u_3), R diverges in
the imaginary direction like R ~ i \pi \log^3(1-u_2). This behaviour can be
attributed to the non-trivial analytic continuation needed when passing from
the Euclidean to the physical region and suggests that R has a branch cut in
the negative u_2 axis when the two other cross ratios are approximately equal
(u_1 \approx u_3).Comment: 23 pages, 1 figure, typos corrected,references adde
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