New Coherence and RIP Analysis for Weak Orthogonal Matching Pursuit

In this paper we define a new coherence index, named the global 2-coherence, of a given dictionary and study its relationship with the traditional mutual coherence and the restricted isometry constant. By exploring this relationship, we obtain more general results on sparse signal reconstruction using greedy algorithms in the compressive sensing (CS) framework. In particular, we obtain an improved bound over the best known results on the restricted isometry constant for successful recovery of sparse signals using orthogonal matching pursuit (OMP).Comment: arXiv admin note: substantial text overlap with arXiv:1307.194

High Order Methods for a Class of Volterra Integral Equations with Weakly Singular Kernels

The solution of the Volterra integral equation, $$( * )\qquad x(t) = g_1 (t) + \sqrt {t}g_2 (t) + \int _0^t \frac {K(t,s,x(s))} {\sqrt {t - s} } ds, \quad 0 \leqq t \leqq T,$$ where $g_1 (t)$, $g_2 (t)$ and $K(t,s,x)$ are smooth functions, can be represented as $x(t) = u(t) + \sqrt {t}v(t)$,$0 \leqq t \leqq T$, where $u(t)$, $v(t)$ are, smooth and satisfy a system of Volterra integral equations. In this paper, numerical schemes for the solution of (*) are suggested which calculate $x(t)$ via $u(t)$, $v(t)$ in a neighborhood of the origin and use (*) on the rest of the interval $0 \leqq t \leqq T$. In this way, methods of arbitrarily high order can be derived. As an example, schemes based on the product integration analogue of Simpson's rule are treated in detail. The schemes are shown to be convergent of order $h^{{7 / 2}}$. Asymptotic error estimates are derived in order to examine the numerical stability of the methods

The Stability of One-Step Schemes for First-Order Two-Point Boundary Value Problems

The stability of a finite difference scheme is related explicitly to the stability of the continuous problem being solved. At times, this gives materially better estimates for the stability constant than those obtained by the standard process of appealing to the stability of the numerical scheme for the associated initial value problem

Environmental isolation of black yeast-like fungi involved in human infection

The present study focuses on potential agents of chromoblastomycosis and other endemic diseases in the state of Paraná, Southern Brazil. Using a highly selective protocol for chaetothyrialean black yeasts and relatives, environmental samples from the living area of symptomatic patients were analysed. Additional strains were isolated from creosote-treated wood and hydrocarbon-polluted environments, as such polluted sites have been supposed to enhance black yeast prevalence. Isolates showed morphologies compatible with the traditional etiological agents of chromoblastomycosis, e.g. Fonsecaea pedrosoi and Phialophora verrucosa, and of agents of subcutaneous or systemic infections like Cladophialophora bantiana and Exophiala jeanselmei. Some agents of mild disease were indeed encountered. However, molecular analysis proved that most environmental strains differed from known etiologic agents of pronounced disease syndromes: they belonged to the same order, but mostly were undescribed species. Agents of chromoblastomycosis and systemic disease thus far are prevalent on the human host. The hydrocarbon-polluted environments yielded yet another spectrum of chaetothyrialean fungi. These observations are of great relevance because they allow us to distinguish between categories of opportunists, indicating possible differences in pathogenicity and virulence

Interconversion of Prony series for relaxation and creep

Various algorithms have been proposed to solve the interconversion equation of linear viscoelasticity when Prony series are used for the relaxation and creep moduli, G(t) and J(t). With respect to a Prony series for G(t), the key step in recovering the corresponding Prony series for J(t) is the determination of the coefficients {jk} of terms in J(t). Here, the need to solve a poorly conditioned matrix equation for the {jk} is circumvented by deriving elementary and easily evaluated analytic formulae for the {jk} in terms of the derivative dG(s)/ds of the Laplace transform G(s) of G(t)

Service Processes as a Sequence of Events

In this paper the service process is considered as a sequence ofevents. Using theory from economics and psychology a model isformulated that explains how the utility of each event affects theoverall evaluation of the service process. In this model we especiallyaccount for the peak-and-end rule and negative consumer timepreference. This model is tested in the context of telephone servicecalls in the financial service market. Our results show that both theaverage utility and the positive peak of the events positively affectcustomer satisfaction with the service call. Surprisingly, the end ofthe sequence has a negative effect. Theoretical and managerialimplications of these findings are discussed.satisfaction;economic psychology;consumers;sequence of events;services

Modulation of Voltage-Gated Ca2+ Channels by Retinoic Acid Signaling

Retinoic acid (RA), the active metabolite of vitamin A, has an established role in development of the nervous system, but has recently emerged as a critical regulator of adult nervous system function. RA is important for learning and memory in both vertebrates and invertebrates. It is also important for synaptic plasticity at rodent hippocampal synapses and is known to interact with Ca2+ signaling to regulate receptor expression and influence synaptic transmission. How RA signaling might mediate plasticity in an invertebrate nervous system has not yet been studied. Voltage-gated Ca2+ channels (CaV) represent a ubiquitous means of Ca2+ entry into a cell, and which regulate neuronal functioning (such as gene expression and neurotransmitter release). As such, CaV channels represent a potentially important locus for inducing plasticity in both vertebrates and invertebrates. It is not known in any species, whether RA might mediate changes in neuronal communication by influencing the functional properties of CaV channels. Here I show, utilizing cultured neurons from the molluscan pond snail, Lymnaea stagnalis, that RA signaling modulates CaV channel function. RA signaling inhibited CaV channel function by shifting the voltage dependence of channel activation to more depolarized potentials. I found that RA also produced spike broadening and activity-dependent complex spiking, an effect I determined was mediated by RA-induced inhibition of delayed rectifier voltage-gated K+ channels (KV), (and enhanced inactivation of these KV channels). Paradoxically, the effect of RA to induce spike broadening and activity-dependent complex spiking, enhanced Ca2+ influx through CaV channels. However, the concurrent inhibition of CaV2 channels limited this enhanced Ca2+ influx. I also provide evidence that constitutive/basal retinoid receptor signaling upregulates CaV channel function. I show that a retinoic acid receptor (RAR) antagonist produced G-protein-mediated voltage-dependent inhibition of CaV channels, a ubiquitous form of presynaptic plasticity that occurs at vertebrate synapses. I also show that a retinoid X receptor (RXR) antagonist produced a novel G-protein-independent form of voltage-dependent inhibition of CaV channels. Overall, my study indicates that retinoid signaling diversely regulates CaV channel function in this invertebrate species and provides insights into the mechanisms by which RA signaling might mediate neuronal and/or synaptic plasticity