Reaching the nonlinear regime of Raman amplification of ultrashort laser pulses

The intensity of a subpicosecond laser pulse was amplified by a factor of up to 1000 using the Raman backscatter interaction in a 2 mm long gas jet plasma. The process of Raman amplification reached the nonlinear regime, with the intensity of the amplified pulse exceeding that of the pump pulse by more than an order of magnitude. Features unique to the nonlinear regime such as gain saturation, bandwidth broadening, and pulse shortening were observed. Simulation and theory are in qualitative agreement with the measurements.open695

A Simple Separable Exact C*-Algebra not Anti-isomorphic to Itself

We give an example of an exact, stably finite, simple. separable C*-algebra D which is not isomorphic to its opposite algebra. Moreover, D has the following additional properties. It is stably finite, approximately divisible, has real rank zero and stable rank one, has a unique tracial state, and the order on projections over D is determined by traces. It also absorbs the Jiang-Su algebra Z, and in fact absorbs the 3^{\infty} UHF algebra. We can also explicitly compute the K-theory of D, namely K_0 (D) = Z[1/3] with the standard order, and K_1 (D) = 0, as well as the Cuntz semigroup of D.Comment: 16 pages; AMSLaTeX. The material on other possible K-groups for such an algebra has been moved to a separate paper (1309.4142 [math.OA]

Ultra-broadband Light Absorption by a Sawtooth Anisotropic Metamaterial Slab

We present an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.Comment: 12 pages, 4 picture

A Constrained Semi-Supervised Learning Approach to Data Association

Data association (obtaining correspondences) is a ubiquitous problem in computer vision. It appears when matching image features across multiple images, matching image features to object recognition models and matching image features to semantic concepts. In this paper, we show how a wide class of data association tasks arising in computer vision can be interpreted as a constrained semi-supervised learning problem. This interpretation opens up room for the development of new, more e#cient data association methods. In particular, it leads to the formulation of a new principled probabilistic model for constrained semi-supervised learning that accounts for uncertainty in the parameters and missing data. By adopting an ingenious data augmentation strategy, it becomes possible to develop an e#cient MCMC algorithm where the high-dimensional variables in the model can be sampled e#ciently and directly from their posterior distributions. We demonstrate the new model and algorithm on synthetic data and the complex problem of matching image features to words in the image captions

Pattern Recognition and Classification of Fatal Traffic Accidents in Israel A Neural Network Approach

This article provides a broad picture of fatal traffic accidents in Israel to answer an increasing need of addressing compelling problems, designing preventive measures, and targeting specific population groups with the objective of reducing the number of traffic fatalities. The analysis focuses on 1,793 fatal traffic accidents occurred during the period between 2003 and 2006 and applies Kohonen and feed-forward back-propagation neural networks with the objective of extracting from the data typical patterns and relevant factors. Kohonen neural networks reveal five compelling accident patterns: (1) single-vehicle accidents of young drivers, (2) multiple-vehicle accidents between young drivers, (3) accidents involving motorcyclists or cyclists, (4) accidents where elderly pedestrians crossed in urban areas, and (5) accidents where children and teenagers cross major roads in small urban areas. Feed-forward back-propagation neural networks indicate that sociodemographic characteristics of drivers and victims, accident location, and period of the day are extremely relevant factors. Accident patterns suggest that countermeasures are necessary for identified problems concerning mainly vulnerable road users such as pedestrians, cyclists, motorcyclists and young drivers. A "safe-system" integrating a system approach for the design of countermeasures and a monitoring process of performance indicators might address the priorities highlighted by the neural networks

MKP-1 inhibits high NaCl-induced activation of p38 but does not inhibit the activation of TonEBP/OREBP: Opposite roles of p38α and p38δ

High NaCl rapidly activates p38 MAPK by phosphorylating it, the phosphorylation presumably being regulated by a balance of kinases and phosphatases. Kinases are known, but the phosphatases are uncertain. Our initial purpose was to identify the phosphatases. We find that in HEK293 cells transient overexpression of MAPK phosphatase-1 (MKP-1), a dual-specificity phosphatase, inhibits high NaCl-induced phosphorylation of p38, and that overexpression of a dominant negative mutant of MKP-1 does the opposite. High NaCl lowers MKP-1 activity by increasing reactive oxygen species, which directly inhibit MKP-1, and by reducing binding of MKP-1 to p38. Because inhibition of p38 is reported to reduce hypertonicity-induced activation of the osmoprotective transcription factor, TonEBP/OREBP, we anticipated that MKP-1 expression might also. However, overexpression of MKP-1 has no significant effect on Ton EBP/OREBP activity. This paradox is explained by opposing effects of p38α and p38δ, both of which are activated by high NaCl and inhibited by MKP-1. Thus, we find that overexpression of p38α increases high NaCl-induced TonEBP/OREBP activity, but overexpression of p38δ reduces it. Also, siRNA-mediated knockdown of p38δ enhances the activation of TonEBP/OREBP. We conclude that high NaCl inhibits MKP-1, which contributes to the activation of p38. However, opposing actions of p38α and p38δ negate any effect on TonEBP/OREBP activity. Thus, activation of p38 isoforms by hypertonicity does not contribute to activation of TonEBP/OREBP because of opposing effects of p38α and p38δ, and effects of inhibitors of p38 depend on which isoform is affected, which can be misleading