Finding needles in noisy haystacks

The theory of compressed sensing shows that samples in the form of random projections are optimal for recovering sparse signals in high-dimensional spaces (i.e., finding needles in haystacks), provided the measurements are noiseless. However, noise is almost always present in applications, and compressed sensing suffers from it. The signal to noise ratio per dimension using random projections is very poor, since sensing energy is equally distributed over all dimensions. Consequently, the ability of compressed sensing to locate sparse components degrades significantly as noise increases. It is possible, in principle, to improve performance by "shaping" the projections to focus sensing energy in proper dimensions. The main question addressed here is, can projections be adaptively shaped to achieve this focusing effect? The answer is yes, and we demonstrate a simple, computationally efficient procedure that does so

Kinetics of TNF-alpha and IFN-gamma mRNA expression in islets and spleen of NOD mice

Insulin-dependent diabetes mellitus is caused by autoimmune destruction of pancreatic ß cells. Non-obese diabetic (NOD) mice spontaneously develop diabetes similar to the human disease. Cytokines produced by islet-infiltrating mononuclear cells may be directly cytotoxic and can be involved in islet destruction coordinated by CD4+ and CD8+ cells. We utilized a semiquantitative RT-PCR assay to analyze in vitro the mRNA expression of TNF-alpha and IFN-gamma cytokine genes in isolated islets (N = 100) and spleen cells (5 x 10(5) cells) from female NOD mice during the development of diabetes and from female CBA-j mice as a related control strain that does not develop diabetes. Cytokine mRNAs were measured at 2, 4, 8, 14 and 28 weeks of age from the onset of insulitis to the development of overt diabetes. An increase in IFN-gamma expression in islets was observed for females aged 28 weeks (149 ± 29 arbitrary units (AU), P<0.05, Student t-test) with advanced destructive insulitis when compared with CBA-j mice, while TNF-alpha was expressed in both NOD and CBA-j female islets at the same level at all ages studied. In contrast, TNF-alpha in spleen was expressed at higher levels in NOD females at 14 weeks (99 ± 8 AU, P<0.05) and 28 weeks (144 ± 17 AU, P<0.05) of age when compared to CBA-j mice. The data suggest that IFN-gamma and TNF-alpha expression in pancreatic islets of female NOD mice is associated with ß cell destruction and overt diabetes.1347135

Dyonic Integrable Models

A class of non abelian affine Toda models arising from the axial gauged two-loop WZW model is presented. Their zero curvature representation is constructed in terms of a graded Kac-Moody algebra. It is shown that the discrete multivacua structure of the potential together with non abelian nature of the zero grade subalgebra allows soliton solutions with non trivial electric and topological charges. The dressing transformation is employed to explicitly construct one and two soliton solutions and their bound states in terms of the tau functions. A discussion of the classical spectra of such solutions and the time delays are given in detail.Comment: Latex 30 pages, corrected some typo

Multicharged Dyonic Integrable Models

We introduce and study new integrable models of A_n^{(1)}-Non-Abelian Toda type which admit U(1)\otimes U(1) charged topological solitons. They correspond to the symmetry breaking SU(n+1) \to SU(2)\otimes SU(2)\otimes U(1)^{n-2} and are conjectured to describe charged dyonic domain walls of N=1 SU(n+1) SUSY gauge theory in large n limit. It is shown that this family of relativistic IMs corresponds to the first negative grade q={-1} member of a dyonic hierarchy of generalized cKP type. The explicit relation between the 1-soliton solutions (and the conserved charges as well) of the IMs of grades q=-1 and q=2 is found. The properties of the IMs corresponding to more general symmetry breaking SU(n+1) \to SU(2)^{\otimes p}\otimes U(1)^{n-p} as well as IM with global SU(2) symmetries are discussed.Comment: 48pages, latex, v2. typos in eqns. (1.7) and (3.20) corrected, small improvements in subsection 2.2, new reference added;v3. improvements in text of Sect. 1,2 and 6; new Sect 7 and new refs. added; version to appear in Nucl. Phys.

Study of ATLAS sensitivity to FCNC top decays

The ATLAS experiment sensitivity to top quark Flavour Changing Neutral Current (FCNC) decays was studied at LHC using ttbar events. While one of the top quarks is expected to follow the dominant Standard Model decay t->bW, the other decays through a FCNC channel, i.e. t-> Z u(c), t-> gamma u(c) or t-> g u(c). Different types of analyses, applied to each FCNC decay mode, were compared. The FCNC branching ratio sensitivity (assuming a 5sigma signal significance) and 95% confidence level limits on the branching ratios (in the hypothesis of signal absence) were obtained

Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT

The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes, both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments in satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer (TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal counterpart only in the higher energy X- and gamma-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters were found difficult to be reconciled to a purely thermal emission component. We discuss possible mechanisms to explain the double spectral components at microwaves and in the THz ranges.Comment: Accepted version for publication in Solar Physic

Diffuse light and galaxy interactions in the core of nearby clusters

The kinematics of the diffuse light in the densest regions of the nearby clusters can be unmasked using the planetary nebulae (PNs) as probes of the stellar motions. The position-velocity diagrams around the brightest cluster galaxies (BCGs) identify the relative contributions from the outer halos and the intracluster light (ICL), defined as the light radiated by the stars floating in the cluster potential. The kinematics of the ICL can then be used to asses the dynamical status of the nearby cluster cores and to infer their formation histories. The cores of the Virgo and Coma are observed to be far from equilibrium, with mergers currently on-going, while the ICL properties in the Fornax and Hydra clusters show the presence of sub-components being accreted in their cores, but superposed to an otherwise relaxed population of stars. Finally the comparison of the observed ICL properties with those predicted from Lambda-CDM simulations indicates a qualitative agreement and provides insights on the ICL formation. Both observations and simulations indicate that BCG halos and ICL are physically distinct components, with the ``hotter" ICL dominating at large radial distances from the BCGs halos as the latter become progressively fainter.Comment: 14 pages, 5 figures. Invited review to appear in the proceedings of "Galaxies and their masks" eds. Block, D.L., Freeman, K.C. and Puerari, I., 2010, Springer (New York