Noise reduction in 3D noncollinear parametric amplifier

We analytically find an approximate Bloch-Messiah reduction of a noncollinear parametric amplifier pumped with a focused monochromatic beam. We consider type I phase matching. The results are obtained using a perturbative expansion and scaled to a high gain regime. They allow a straightforward maximization of the signal gain and minimization of the parametric fluorescence noise. We find the fundamental mode of the amplifier, which is an elliptic Gaussian defining the optimal seed beam shape. We conclude that the output of the amplifier should be stripped of higher order modes, which are approximately Hermite-Gaussian beams. Alternatively, the pump waist can be adjusted such that the amount of noise produced in the higher order modes is minimized.Comment: 18 pages, 9 figures, accepted to Applied Physics

Shear Viscosity of a Unitary Fermi Gas

We present the first ab initio determination of the shear viscosity eta of the Unitary Fermi Gas, based on finite temperature quantum Monte Carlo calculations and the Kubo linear-response formalism. We determine the temperature dependence of the shear viscosity to entropy density ratio eta/s. The minimum of eta/s appears to be located above the critical temperature for the superfluid-to-normal phase transition with the most probable value being eta/s approx 0.2 hbar/kB, which almost saturates the Kovtun-Son-Starinets universal value hbar/(4 pi kB).Comment: 8 pages, 9 figures; supplemental materials include

Experimental Search for Pentaquarks

The experimental evidence for pentaquarks, both old an new, is discussed. Constraints due to $K^+N$ scattering data from previous decades is first reviewed, followed by experiments with positive evidence and those with null results. Finally, the problem of the narrow width of the Theta+ pentaquark is discussed, along with theoretical implications.Comment: Review article for Progress in Particle and Nuclear Physics (34 pages

Content-boosted Matrix Factorization Techniques for Recommender Systems

Many businesses are using recommender systems for marketing outreach. Recommendation algorithms can be either based on content or driven by collaborative filtering. We study different ways to incorporate content information directly into the matrix factorization approach of collaborative filtering. These content-boosted matrix factorization algorithms not only improve recommendation accuracy, but also provide useful insights about the contents, as well as make recommendations more easily interpretable

Numerical Analysis

Acknowledgements: This article will appear in the forthcoming Princeton Companion to Mathematics, edited by Timothy Gowers with June Barrow-Green, to be published by Princeton University Press.\ud \ud In preparing this essay I have benefitted from the advice of many colleagues who corrected a number of errors of fact and emphasis. I have not always followed their advice, however, preferring as one friend put it, to "put my head above the parapet". So I must take full responsibility for errors and omissions here.\ud \ud With thanks to: Aurelio Arranz, Alexander Barnett, Carl de Boor, David Bindel, Jean-Marc Blanc, Mike Bochev, Folkmar Bornemann, Richard Brent, Martin Campbell-Kelly, Sam Clark, Tim Davis, Iain Duff, Stan Eisenstat, Don Estep, Janice Giudice, Gene Golub, Nick Gould, Tim Gowers, Anne Greenbaum, Leslie Greengard, Martin Gutknecht, Raphael Hauser, Des Higham, Nick Higham, Ilse Ipsen, Arieh Iserles, David Kincaid, Louis Komzsik, David Knezevic, Dirk Laurie, Randy LeVeque, Bill Morton, John C Nash, Michael Overton, Yoshio Oyanagi, Beresford Parlett, Linda Petzold, Bill Phillips, Mike Powell, Alex Prideaux, Siegfried Rump, Thomas Schmelzer, Thomas Sonar, Hans Stetter, Gil Strang, Endre Süli, Defeng Sun, Mike Sussman, Daniel Szyld, Garry Tee, Dmitry Vasilyev, Andy Wathen, Margaret Wright and Steve Wright

Multiscale statistical analysis of coronal solar activity

Multi-filter images from the solar corona are used to obtain temperature maps which are analyzed using techniques based on proper orthogonal decomposition (POD) in order to extract dynamical and structural information at various scales. Exploring active regions before and after a solar flare and comparing them with quiet regions we show that the multiscale behavior presents distinct statistical properties for each case that can be used to characterize the level of activity in a region. Information about the nature of heat transport is also be extracted from the analysis.Comment: 24 pages, 18 figure

Improving Recommendation Quality by Merging Collaborative Filtering and Social Relationships

Matrix Factorization techniques have been successfully applied to raise the quality of suggestions generated\ud by Collaborative Filtering Systems (CFSs). Traditional CFSs\ud based on Matrix Factorization operate on the ratings provided\ud by users and have been recently extended to incorporate\ud demographic aspects such as age and gender. In this paper we\ud propose to merge CF techniques based on Matrix Factorization\ud and information regarding social friendships in order to\ud provide users with more accurate suggestions and rankings\ud on items of their interest. The proposed approach has been\ud evaluated on a real-life online social network; the experimental\ud results show an improvement against existing CF approaches.\ud A detailed comparison with related literature is also presen

Anti-Semitism, Securitization and the Media: Analyzing the role of media in relation to the increasing notion of anti-Semitism in Sweden - An issue for securitization?

This paper has examined the potential power of media in relation to ‘security’ for the Jews in the Swedish society. My intention was to find out whether media constitute a risk for the increasing notion of anti-Semitism which also enhances the threat for the Jews in Sweden to become a security matter and therefore result in a need for securitization. The analysis has been done partly through presentation of material which gives us the understanding that anti-Semitism is spreading in Sweden in relation to escalations of conflicts in the Middle East. A critical discourse analysis of two Swedish newspapers has been made, in order to see whether these papers did present a biased view over the ‘Cast Lead’ offensive in Gaza from Dec 27, 2008 to Jan 18, 2009 which eventually results in these negative notions against Jews in Sweden. The critical situation for the Jews has then been placed in relation to security where the paper looked closer upon whether the situation for the Jews has become severe to the extent that it is in need of a securitization act in order to protect the Jewish minority group in Sweden