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

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

Stress Corrosion Cracking of titanium alloys - SCC of aluminum alloys, polarization of titanium alloys in hydrogen chloride and correlation of titanium and aluminum SCC behavior Quarterly progress report, 1 Oct. 1968 - 31 Mar. 1969

Stress corrosion cracking of titanium alloys and aluminum alloy

Fundamental investigation of stress corrosion cracking

Two principle areas studied were stress corrosion crack growth rates of a titanium alloy in liquid environments containing halide ions and pitting corrosion of titanium in bromide solutions. Two initial assumptions were made, that the rate of propagation was controlled by a macroscopic solution parameter and that this parameter was viscosity. A series of solutions were prepared using lithium chloride as the solute and water, methanol, glycerin, formic acid, acetone, dimethyl sulphoxide, etc. As solvents, these solutions were prepared with a 5:1 solvent-solute ratio. Viscosity was varied by changing the temperature and it was found: (1) In all solvents the velocity of cracking was proportional to the reciprocal of the viscosity. (2) Each solvent gave a separate relationship, (3) The temperature dependence and numerical values for the apparent activation energy of cracking and viscosity were the same

Stress corrosion cracking of titanium alloys: Studies of cracks in thin specimens; SCC of Ti-6Al-4V in chloride, iodide and fluoride solutions; stress corrosion cracking in molten salts; electrochemistry of freshly generated titanium surfaces

Electrochemistry of freshly generated titanium surfaces and stress corrosion cracking in aqueous solutions and in molten salt

Observations of large raptors in northeast Sudan

During a targeted shorebird survey of wetlands along Sudan’s Red Sea Coast in January 2010 we took the opportunity to gather limited baseline information on large raptors within an understudied region. One 430 km transect was completed while driving from Atbara to Port Sudan on 19 January. Thirty Egyptian Vultures Neophron percnopterus were recorded at a mean of 7 birds per 100 km over 6.15 hours, and eight unidentified large vultures were seen. From subsequent ad hoc records gathered during 20 additional vehicle hours covering 450 km of coastline, we identified populations of Lappet-faced Vulture Torgos tracheliotos and Hooded Vulture Necrosyrtes monachus and migrant Steppe Eagle Aquila nipalensis

On the coupling between barotropic and baroclinic modes of extratropical atmospheric variability

The baroclinic and barotropic components of atmospheric dynamics are usually viewed as interlinked through the baroclinic life cycle, with baroclinic growth of eddies connected to heat fluxes, barotropic decay connected to momentum fluxes, and the two eddy fluxes connected through the Eliassen-Palm wave activity. However, recent observational studies have suggested that these two components of the dynamics are largely decoupled in their variability, with variations in the zonal mean flow associated mainly with the momentum fluxes, variations in the baroclinic wave activity associated mainly with the heat fluxes, and essentially no correlation between the two. These relationships are examined in a dry dynamical core model under different configurations and in Southern Hemisphere observations, considering different frequency bands to account for the different timescales of atmospheric variability. It is shown that at intermediate periods longer than 10 days the decoupling of the baroclinic and barotropic modes of variability can indeed occur as the eddy kinetic energy at those time scales is only affected by the heat fluxes and not the momentum fluxes. The baroclinic variability includes the oscillator model with periods of 20-30 days. At both the synoptic timescale and the quasi-steady limit the baroclinic and barotropic modes of variability are linked, consistent with baroclinic life cycles and the positive baroclinic feedback mechanism, respectively. In the quasi-steady limit the pulsating modes of variability and their correlations depend sensitively on the model climatology