999 resultados para SOFT-GAMMA REPEATERS


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Communication: Coatings Of Yellow gamma-WO3 are deposited on glass by APCVD of WOCl4 and either ethanol or ethylacetate at 350-450degreesC. The yellow films show significant photoactivity for the destruction of stearic acid, and photoinduced superhydrophilicity. Preparation of blue reduced WO2.92 films from the same reaction at higher substrate temperatures of 500-600degreesC (Figure) is also found to be possible. These films show no photoactivity, but can be converted into the fully stoichiometric photoactive form simply by heating in air.

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Recombinant wild-type beta(1) gamma(1) dimers of signal-transducing guanine nucleotide-binding proteins (G proteins) and beta(1) gamma 1 dimers carrying a mutation known to block gamma-subunit isoprenylation (beta(1) gamma(1)C71S) were expressed in baculovirus-infected insect cells. Both wild-type and mutant beta(1) gamma(1) dimers were found in soluble fractions of infected cells upon subcellular fractionation. Anion exchange chromatographic and metabolic-radiolabeling studies revealed that the soluble beta(1) gamma(1) preparation contained approximately equal amounts of non-isoprenylated and isoprenylated beta(1) gamma(1) dimers. Soluble wild-type and mutant beta(1) gamma(1) dimers and native beta(1) gamma(1) dimers purified from bovine retina were reconstituted with recombinant phospholipase C-beta(2). Only isoprenylated beta(1) gamma(1) dimers were capable of stimulating phospholipase C-beta(2). The results show that gamma-subunit isoprenylation and/or additional post-translational processing of the protein are required for beta gamma subunit stimulation of phospholipase C.

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We have previously shown that isoprenylation and/or additional pest-translational processing of the G protein gamma(1) subunit carboxyl terminus is required for beta(1) gamma(1) subunit stimulation of phospholipase C-beta(2) (PLC beta(2)) [Dietrich, A., Meister, M., Brazil, D., Camps, M., & Gierschik, P. (1994) Eur. J. Biochem. 219, 171-178]. To examine whether isoprenylation of the gamma(1) subunit alone is sufficient for beta(1) gamma(1)-mediated PLC beta(2) stimulation or whether any of the two subsequent modifications, proteolytic removal of the carboxyl-terminal tripeptide and/or carboxylmethylation, is required for this effect, nonisoprenylated recombinant beta(1) gamma(1) dimers were produced in baculovirus-infected insect cells, purified to near homogeneity, and then isoprenylated in vitro using purified recombinant protein farnesyltransferase. Analysis of the beta(1) gamma(1) dimer after in vitro farnesylation by reversed phase high-performance liquid chromatography followed by delayed extraction matrix-assisted laser desorption/ionization mass spectrometry confirmed that the gamma(1) subunit was carboxyl-terminally farnesylated but not proteolyzed and carboxylmethylated. Functional reconstitution of in vitro-farnesylated beta(1) gamma(1) dimers with a recombinant PLC beta(2) isozyme revealed that farnesylation rendered recombinant nonisoprenylated beta(1) gamma(1) dimers capable of stimulating PLC beta(2) and that the degree of this stimulation was only approximately 45% lower for in vitro-farnesylated beta(1) gamma(1) dimers than for fully modified native beta(1) gamma(1) purified from bovine retinal rod outer segments. Taken together, these results suggest that isoprenylation of the gamma subunit is both necessary and sufficient for beta gamma dimer-mediated stimulation of phospholipase C.

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The propagation of a 1-ps laser pulse at intensities exceeding 10(19) Wcm(-2) in a low-density plasma channel was experimentally tested. The channel was produced by a lower intensity preceding pulse of the same duration. Plasma electrons were accelerated during the propagation of the main pulse, and high energy gamma -ray detectors were used to detect their bremsstrahlung emission. The gamma -ray yield was studied for different channel conditions, by varying the delay between the channel forming pulse and the high intensity pulse. These results are correlated with the interferograms of the propagation region into the plasma.

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The collisionally excited transient inversion scheme is shown to produce exceptionally high gain coefficients and gain-length products. Data are presented for the Ne-Like titanium and germanium and Ni-like silver X-ray lasers (XRL's) pumped using a combination of nanosecond and picosecond duration laser pulses. This method leads to a dramatic reduction of the required pump energy and makes down-sizing of XRL's possible, an important prerequisite if they are to become commonly used tools in the Long-term.

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Distributions of source intensity in two dimensions (designated the source model), averaged over a single laser pulse, based on experimental measurements of spatial coherence, are considered for radiation from the unresolved 23.2/23.6 nm spectral lines from the germanium collisional X-ray laser. The model derives from measurements of the visibility of Young slit interference fringes determined by a method based on the Wiener-Khinchin theorem. Output from amplifiers comprising three and four target elements have similar coherence properties in directions within the horizontal plane corresponding to strong plasma refraction effects and fitting the coherence data shows source dimensions (FWHM) are similar to 26 mu m (horizontal), significantly smaller than expected by direct imaging, and similar to 125 mu m (vertical: equivalent to the height of the driver excitation). (C) 1999 Elsevier Science B.V. All rights reserved.