排序方式: 共有31条查询结果,搜索用时 15 毫秒
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Rudenko A Foucar L Kurka M Ergler T Kühnel KU Jiang YH Voitkiv A Najjari B Kheifets A Lüdemann S Havermeier T Smolarski M Schössler S Cole K Schöffler M Dörner R Düsterer S Li W Keitel B Treusch R Gensch M Schröter CD Moshammer R Ullrich J 《Physical review letters》2008,101(7):073003
Recoil-ion momentum distributions for two-photon double ionization of He and Ne (variant Planck's over omega=44 eV) have been recorded with a reaction microscope at FLASH (the free-electron laser at Hamburg) at an intensity of approximately 1 x 10(14) W/cm2 exploring the dynamics of the two fundamental two-photon-two-electron reaction pathways, namely, sequential and direct (or nonsequential) absorption of the photons. We find strong differences in the recoil-ion momentum patterns for the two mechanisms pointing to the significantly different two-electron emission dynamics and thus provide serious constraints for theoretical models. 相似文献
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Schulz M Wang X Gundmundsson M Schneider K Kelkar A Voitkiv AB Najjari B Schöffler M Schmidt LP Dörner R Ullrich J Moshammer R Fischer D 《Physical review letters》2012,108(4):043202
We studied three-dimensional angular distributions and longitudinal momentum spectra of electrons ejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron, for ion-helium collisions. We observe a pronounced structure strongly focused opposite to the projectile beam direction, which we associate with a new correlated TI mechanism proposed recently. This process contributes significantly to the total cross sections over a broad range of perturbations η, even at η as large as 0.5, where uncorrelated TI mechanisms were thought to be dominant. 相似文献
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Photoionization of an atom A, in the presence of a neighboring atom B, can proceed both directly and via resonant excitation of B with subsequent energy transfer to A through two-center electron-electron correlation. We show that in such a case the photoionization process can be very strongly enhanced and acquire interesting characteristic features, both in its time development and the electron spectrum. 相似文献
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Clément Louriou Hanène Ouerfelli Marc Prat Mustapha Najjari Sassi Ben Nasrallah 《Transport in Porous Media》2012,91(1):153-171
We study numerically and experimentally the displacement of a liquid by a gas in a two-dimensional model porous medium. In
contrast with previous pore network studies on drainage in porous media, the gas pressurization is fully taken into account.
The influence of the gas injection rate on the displacement pattern, breakthrough time and the evolution of the pressure in
the gas phase due in part to gas compressibility are investigated. A good agreement is found between the simulations and the
experiments as regards the invasion patterns. The agreement is also good on the drainage kinetics when the dynamic liquid
films are taken into account. 相似文献
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Dorn A Kheifets A Schröter CD Najjari B Höhr C Moshammer R Ullrich J 《Physical review letters》2001,86(17):3755-3758
The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)]. 相似文献
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We study mutual ionization in relativistic collisions between hydrogenlike projectiles and helium atoms: X(Z+)(1s)+He(1s(2))-->X((Z+1)+)+ He+(1s)+2e(-). At high collision velocities and for not too heavy projectiles, 2Z/v<1 (v is the collision velocity), the mutual ionization proceeds via the direct interaction between two electrons bound (initially) to different colliding particles. Considering for the first time this fundamental process in the case of relativistic collisions, we calculate ionization cross sections and discuss manifestations of relativistic effects. In particular, we predict two novel and interesting phenomena: (i) considerable relativistic effects in collisions with low Lorentz factors gamma and (ii) the rapid saturation of these effects at higher gamma. Estimates show that the predicted effects can be experimentally tested using existing facilities and spectrometers. 相似文献
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Viscous dissipation and its contribution to turbulent kinetic energy (TKE) budget are investigated in the asymmetric jet–wake flow of a forward-curved centrifugal turbomachine. Single-plane three-dimensional turbulent data are obtained using stereoscopic particle image velocimetry (SPIV). Viscous dissipation is indirectly estimated from subgrid-scale (SGS) dissipation (SGS energy flux) by filtering velocity field using a top-hat filter. The filter scale should be within the inertial sub-range and this is ensured by spectral analysis of the measured field. Reduction of turbulent energy flux for smaller filter scales plus underestimation of viscous dissipation as compared with other TKE terms both suggest the presence of spectral shortcut. This bypass energy transfer (from intermediate scales towards dissipative scales) works in parallel with direct SGS energy transfer and affects the classical energy cascade. Analysis of TKE budget in the rotor exit region shows significant radial/circumferential variations in the contributing terms. These variations are mainly due to jet–wake–volute interactions, circumferential asymmetry of volute area and expansion of flow toward the fan outlet. 相似文献