Nonlinear Breit-Wheeler pair creation with bremsstrahlung γ\gamma rays

Electron-positron pairs are produced through the Breit-Wheeler process when energetic photons traverse electromagnetic fields of sufficient strength. Here we consider a possible experimental geometry for observation of pair creation in the highly nonlinear regime, in which bremsstrahlung of an ultrarelativistic electron beam in a high-$Z$ target is used to produce $\gamma$ rays that collide with a counterpropagating laser pulse. We show how the target thickness may be chosen to optimize the yield of Breit-Wheeler positrons, and verify our analytical predictions with simulations of the cascade in the material and in the laser pulse. The electron beam energy and laser intensity required are well within the capability of today's high-intensity laser facilities.Comment: 12 pages, 5 figure

Solenoid valve performance characteristics studied

Current and voltage waveforms of a solenoid coil are recorded as the valve opens and closes. Analysis of the waveforms with respect to time and the phase of the valve cycle accurately describes valve performance

Minimum Wages and Poverty

The principal justification for minimum wage legislation resides in improving the economic condition of low-wage workers. Most previous analyses of the distributional effects of minimum wages have been confined to simulation exercises employing rather restrictive assumptions that guarantee the conclusion that an increase in the minimum wage reduces poverty. In contrast, we adopt a more flexible "reduced-form" approach that links increases in both federal and state minima to contemporaneous changes in poverty rates. For the period 1983-96, we find indication of a poverty-reducing effect of minimum wages among older junior-high dropouts and among teenagers. --

Stress corrosion cracking of titanium alloys: SCC velocity: concentration of TiCl3

Stress corrosion cracking of titanium alloys, velocity of cracking in aqueous and methanol solutions and halogenated organic solvents, concentration of TiCl3 in crack

Distinct difference configurations: multihop paths and key predistribution in sensor networks

A distinct difference configuration is a set of points in Z2 with the property that the vectors (difference vectors) connecting any two of the points are all distinct. Many specific examples of these configurations have been previously studied: the class of distinct difference configurations includes both Costas arrays and sonar sequences, for example. Motivated by an application of these structures in key predistribution for wireless sensor networks, we define the k-hop coverage of a distinct difference configuration to be the number of distinct vectors that can be expressed as the sum of k or fewer difference vectors. This is an important parameter when distinct difference configurations are used in the wireless sensor application, as this parameter describes the density of nodes that can be reached by a short secure path in the network. We provide upper and lower bounds for the k-hop coverage of a distinct difference configuration with m points, and exploit a connection with Bh sequences to construct configurations with maximal k-hop coverage. We also construct distinct difference configurations that enable all small vectors to be expressed as the sum of two of the difference vectors of the configuration, an important task for local secure connectivity in the application

The Effect of NAG–thiazoline on Morphology and Surface Hydrophobicity of Escherichia Coli

The β-hexosaminidase inhibitor and structural analog of the putative oxazolium reaction intermediate of lytic transglycosylases, N-acetylglucosamine thiazoline (NAG–thiazoline), was synthesized in 46% overall yield and tested as an inhibitor of Escherichia coli growth. NAG–thiazoline, at concentrations up to 1 mg/ml, was not found to affect the viability of E. coli DH5α

Two-dimensional patterns with distinct differences; constructions, bounds, and maximal anticodes

A two-dimensional (2-D) grid with dots is called a configuration with distinct differences if any two lines which connect two dots are distinct either in their length or in their slope. These configurations are known to have many applications such as radar, sonar, physical alignment, and time-position synchronization. Rather than restricting dots to lie in a square or rectangle, as previously studied, we restrict the maximum distance between dots of the configuration; the motivation for this is a new application of such configurations to key distribution in wireless sensor networks. We consider configurations in the hexagonal grid as well as in the traditional square grid, with distances measured both in the Euclidean metric, and in the Manhattan or hexagonal metrics. We note that these configurations are confined inside maximal anticodes in the corresponding grid. We classify maximal anticodes for each diameter in each grid. We present upper bounds on the number of dots in a pattern with distinct differences contained in these maximal anticodes. Our bounds settle (in the negative) a question of Golomb and Taylor on the existence of honeycomb arrays of arbitrarily large size. We present constructions and lower bounds on the number of dots in configurations with distinct differences contained in various 2-D shapes (such as anticodes) by considering periodic configurations with distinct differences in the square grid

Minimum Wage Increases Under Straightened Circumstances

Do apparently large minimum wage increases in an environment of recession produce clearer evidence of disemployment effects than is typically observed in the new minimum wage literature? This paper augments the sparse literature on the most recent increases in the U.S. minimum wage, using three different data sets and the two main estimation strategies for handling geographically-disparate trends. The evidence is generally unsupportive of negative employment effects, still less of a 'recessionary multiplier.' Minimum wage workers seem to be concentrated in sectors of the economy for which the labor demand response to wage mandates is minimal.minimum wages, disemployment, earnings, low-wage sectors, geographically-disparate employment trends, recession