Fredholm factorization of Wiener-Hopf scalar and matrix kernels

A general theory to factorize the Wiener-Hopf (W-H) kernel using Fredholm Integral Equations (FIE) of the second kind is presented. This technique, hereafter called Fredholm factorization, factorizes the W-H kernel using simple numerical quadrature. W-H kernels can be either of scalar form or of matrix form with arbitrary dimensions. The kernel spectrum can be continuous (with branch points), discrete (with poles), or mixed (with branch points and poles). In order to validate the proposed method, rational matrix kernels in particular are studied since they admit exact closed form factorization. In the appendix a new analytical method to factorize rational matrix kernels is also described. The Fredholm factorization is discussed in detail, supplying several numerical tests. Physical aspects are also illustrated in the framework of scattering problems: in particular, diffraction problems. Mathematical proofs are reported in the pape

The Quest for Bandwidth Estimation Techniques for large-scale Distributed Systems

In recent years the research community has developed many techniques to estimate the end-to-end available bandwidth of an Internet path. This important metric has been proposed for use in several distributed systems and, more recently, has even been considered to improve the congestion control mechanism of TCP. Thus, it has been suggested that some existing estimation techniques could be used for this purpose. However, existing tools were not designed for large-scale deployments and were mostly validated in controlled settings, considering only one measurement running at a time. In this paper, we argue that current tools, while offering good estimates when used alone, might not work in large-scale systems where several estimations severely interfere with each other. We analyze the properties of the measurement paradigms employed today and discuss their functioning, study their overhead and analyze their interference. Our testbed results show that current techniques are insufficient as they are. Finally, we will discuss and propose some principles that should be taken into account for including available bandwidth measurements in large-scale distributed systems. 1

Filamentation processes and dynamical excitation of light condensates in optical media with competing nonlinearities

We analyze both theoretically and by means of numerical simulations the phenomena of filamentation and dynamical formation of self-guided nonlinear waves in media featuring competing cubic and quintic nonlinearities. We provide a theoretical description of recent experiments in terms of a linear stability analysis supported with simulations, showing the possibility of experimental observation of the modulational instability suppression of intense light pulses travelling across such nonlinear media. We also show a novel mechanism of indirect excitation of {\em light condensates} by means of coalescence processes of nonlinear coherent structures produced by managed filamentation of high power laser beams.Comment: 6 pages, 4 figure

Cosmic-ray ionisation in circumstellar discs

Galactic cosmic rays are a ubiquitous source of ionisation of the interstellar gas, competing with UV and X-ray photons as well as natural radioactivity in determining the fractional abundance of electrons, ions and charged dust grains in molecular clouds and circumstellar discs. We model the propagation of different components of Galactic cosmic rays versus the column density of the gas. Our study is focussed on the propagation at high densities, above a few g cm$^{-2}$, especially relevant for the inner regions of collapsing clouds and circumstellar discs. The propagation of primary and secondary CR particles (protons and heavier nuclei, electrons, positrons, and photons) is computed in the continuous slowing down approximation, diffusion approximation, or catastrophic approximation, by adopting a matching procedure for the different transport regimes. A choice of the proper regime depends on the nature of the dominant loss process, modelled as continuous or catastrophic. The CR ionisation rate is determined by CR protons and their secondary electrons below $\approx 130$ g cm$^{-2}$ and by electron/positron pairs created by photon decay above $\approx600$ g cm$^{-2}$. We show that a proper description of the particle transport is essential to compute the ionisation rate in the latter case, since the electron/positron differential fluxes depend sensitively on the fluxes of both protons and photons. Our results show that the CR ionisation rate in high-density environments, like, e.g., the inner parts of collapsing molecular clouds or the mid-plane of circumstellar discs, is larger than previously assumed. It does not decline exponentially with increasing column density, but follows a more complex behaviour due to the interplay of different processes governing the generation and propagation of secondary particles.Comment: 19 pages, 11 figures, accepted by A&

S-AVE Semantic Active Vision Exploration and Mapping of Indoor Environments for Mobile Robots

Semantic mapping is fundamental to enable cognition and high-level planning in robotics. It is a difficult task due to generalization to different scenarios and sensory data types. Hence, most techniques do not obtain a rich and accurate semantic map of the environment and of the objects therein. To tackle this issue we present a novel approach that exploits active vision and drives environment exploration aiming at improving the quality of the semantic map

Identification of a Widespread Palmitoylethanolamide Contamination in Standard Laboratory Glassware.

Introduction: Fatty acid ethanolamides (FAEs) are a family of lipid mediators that participate in a host of biological functions. Procedures for the quantitative analysis of FAEs include organic solvent extraction from biological matrices (e.g., blood), followed by purification and subsequent quantitation by liquid chromatography-mass spectrometry (LC/MS) or gas chromatography-mass spectrometry. During the validation process of a new method for LC/MS analysis of FAEs in biological samples, we observed unusually high levels of the FAE, palmitoylethanolamide (PEA), in blank samples that did not contain any biological material. Materials and Methods: We investigated a possible source of this PEA artifact via liquid chromatography coupled to tandem mass spectrometry, as well as accurate mass analysis. Results: We found that high levels of a contaminant indistinguishable from PEA is present in new 5.75″ glass Pasteur pipettes, which are routinely used by laboratories to carry out lipid extractions. This artifact might account for discrepancies found in the literature regarding PEA levels in human blood serum and other tissues. Conclusions: It is recommended to take into account this pitfall by analyzing potential contamination of the disposable glassware during the validation process of any method used for analysis of FAEs

Towards smaller family size in Egypt, Morocco and Turkey: overall change over time or socio-economic compositional effect?

The whole region of the South and East Mediterranean exhibits a profound fertility transition with marked differences in the pace of fertility declines among the countries. The authors choose three representative countries: Egypt, Morocco and Turkey. Determinants of the propensity towards smaller family size are investigated as scrutinizing the development in the pattern of third births, which represents the critical step in the transitional process for these countries. The authors are particularly interested in verifying whether the decline of higher-order births is significantly driven by an overall societal change over time or by compositional change over different socio-economic segments of the female population. Evidence is found that overall societal changes have mainly driven the decline in large family size, though, to a much lesser extent, compositional changes are important too.Egypt, Morocco, Turkey, childbearing, family size, fertility decline