Search results for "Impact."
showing 10 items of 1677 documents
Highly siderophile elements (Re, Os, Ir, Ru, Rh, Pd, Au) in impact melts from three European impact craters (Sääksjärvi, Mien, and Dellen): Clues to …
1997
Twenty-two large (10 g) impact melt samples from three Scandinavian craters (i.e., Saaksjarvi, Finland; and Mien and Dellen, Sweden) were analyzed for highly siderophile elements (HSE: platinum group elements, Rh, and Au) by the nickel sulfide technique in combination with neutron activation. The ten impact melt samples from Saaksjarvi are enriched in Ir and other highly siderophile elements (Ir = 2.48 ± 0.73 ng/g) relative to average upper crust concentrations (0.03 ± 0.02 ng/g Ir). The twelve Dellen and Mien samples are marginally enriched in Ir (0.48 ± 0.23 ng/g for Dellen, and 0.37 ± 0.23 ng/g for Mien). The amount of meteoritic component corresponds to 0.5% of a nominal CI component fo…
Clues to the nature of the impacting bodies from platinum-group elements (rhenium and gold) in borehole samples from the Clearwater East crater (Cana…
1997
— Seven large (10 g) impact melt rock samples from boreholes from the Boltysh impact crater (Ukraine) and six samples from the East Clearwater crater (Canada) were analyzed for Os, Ir, Ru, Rh, Pd, Re and Au by the nickel sulfide technique in combination with neutron activation. Earlier analyses of Clearwater East impact melt rocks have shown that they are strongly enriched in Ir, Os, Pd and Re. In this work, I confirm earlier findings and demonstrate similarly high enrichments of Rh and Ru. The average Os/Ir, Ru/Ir, Pd/Ir, Rh/Ir and Ru/Rh ratios of the melt rock samples from Clearwater East are CI-chondritic and yield an average Ir content of 25.2 ± 6.5 ng/g relative to an average upper cru…
Catalytic processes activated by light
2010
Light-driven catalytic strategies are of great interest for the synthesis of useful products causing minimal environmental impact. Nature provides many examples of systems working in processes activated by light, and understanding them has been and, in the future, will be useful in the design of artificial catalysts.
Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on a longitudinally polarized deuterium target
2010
Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle $\phi$ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe-Heitler process. The results for the beam-charge and beam-helicity asymmetries from a tensor polarized deuterium target with vanishing vector polarization ar…
Single-Event Burnout Mechanisms in SiC Power MOSFETs
2018
Heavy ion-induced single-event burnout (SEB) is investigated in high-voltage silicon carbide power MOSFETs. Experimental data for 1200-V SiC power MOSFETs show a significant decrease in SEB onset voltage for particle linear energy transfers greater than 10 MeV/cm 2 /mg, above which the SEB threshold voltage is nearly constant at half of the rated maximum operating voltage for these devices. TCAD simulations show a parasitic bipolar junction transistor turn-on mechanism, which drives the avalanching of carriers and leads to runaway drain current, resulting in SEB. peerReviewed
Updated precision measurement of the average lifetime of B hadrons
1996
The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.}
Measurements of the b baryon lifetime
1995
Using about 1.5 million hadronic Z decays recorded with the ALEPH detector, the lifetime of the b baryons has been measured using two independent data samples. From a maximum likelihood fit to the impact parameter distribution of leptons in 519 Lambda l(-) combinations containing a b baryon sample of 290 decays, the measured b baryon lifetime is tau(b-baryon) = 1.05(-0.11)(+0.12)(stat) +/-0.09(syst) ps. The lifetime of the Lambda(b)(0) baryon from a maximum likelihood fit to the proper time distribution of 58 Lambda(c)(+)l(-) candidates containing a Lambda(b)(0) sample of 44 decays, is tau(Lambda b0) = 1.02(-0.18)(+0.23)(stat) +/- 0.06(syst) ps.
Measurement of the inclusive charmless and double-charm B branching ratios
1998
The DELPHI experiment at LEP has measured the inclusive charmless B hadron decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles per B decay, using the hadronic Z data taken between 1992 and 1995. The results are extracted from a fit to the b-tagging probability distribution based on the precise impact parameter measurements made using the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (c (c) over bar), is measured to be 0.033 +/- 0.021. The B branching ratio into two open charmed particles is 0.136 +/- 0.042. The mean number of charmed particles per B decay (including hidden …
Nuclear-mass dependence of azimuthal beam-helicity and beam-charge asymmetries in deeply virtual Compton scattering
2009
The nuclear-mass dependence of azimuthal cross section asymmetries with respect to charge and longitudinal polarization of the lepton beam is studiedfor hard exclusive electroproduction of real photons. The observed beam-charge and beam-helicity asymmetries are attributed to the interference between the Bethe-Heitler and deeply virtual Compton scattering processes. For various nuclei, the asymmetries are extracted for both coherent and incoherent-enriched regions, which involve different (combinations of) generalized parton distributions. For both regions, the asymmetries are compared to those for a free proton, and no nuclear-mass dependence is found.
Incoherent diffractiveJ/Ψproduction in high-energy nuclear deep-inelastic scattering
2011
We compute cross sections for incoherent diffractive $J/\ensuremath{\Psi}$ production in lepton-nucleus deep-inelastic scattering (DIS). The cross section is proportional to $A$ in the dilute limit and to ${A}^{1/3}$ in the black disk limit, with a large nuclear suppression due to saturation effects. The $t$ dependence of the cross section, if it can be measured accurately enough, is sensitive to the impact parameter profile of the gluons in the nucleus and their fluctuations, a quantity that determines the initial conditions of a relativistic heavy-ion collision. The nuclear suppression in incoherent diffraction shows how the transverse spatial distribution of the gluons in the nucleus gra…