Results 1 - 10 of 2460
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[en] Full text: Neutron holography constitutes a novel technique to obtain structural information on an atomic scale. It is based on the recording of the interference of neutron waves coherently scattered by atomic nuclei with an appropriate reference wave. The method can be implemented by using appropriate holographic probe nuclei which can either, due to their strong incoherent scattering, serve as internal neutron sources or, due to their high absorption cross section, serve as internal neutron detectors. Several successful experiments applying both of these approaches have been performed over the last years and have confirmed the underlying physical concepts. More recently, it could be demonstrated that the method is capable to determine the atomic positions within several neighbour shells around holographic probe nuclei with a precision approaching one picometer thus allowing for the quantitative determination of lattice distortions. It is expected that use of the technique can be considerably extended due to the availability of a significant number of elements/isotopes which appear well suited to serve as holographic probes. A particular promise lies in the investigation of substances containing hydrogen. We discuss the current status of neutron holography, its present technical limitations, and perspectives of possible applications. (author)
[en] When a resonant laser sent on an optically thick cold atomic cloud is abruptly switched off, a coherent flash of light is emitted in the forward direction. This transient phenomenon is observed due to the highly resonant character of the atomic scatterers. We analyze quantitatively its temporal properties and show very good agreement with theoretical predictions. Based on complementary experiments, the phase of the coherent field is reconstructed without interferometric tools.
[en] In this paper, the fluorescence spectrum produced by a two-photon Jaynes-Cummings model (JCM) is analyzed using the infinity of transitions among the dressed states of its Hamiltonian. A large number of resonances in the spectra are observed which are sensitive to the mean photon numbers of the quantized coherent field. Also, the qualitative nature of these spectra are in contrast to that of the corresponding spectra of standard JCM
[en] Complete text of publication follows. In this paper, we discuss the evolution of the nightside high latitude ionospheric convection and the relevant current systems associated with substorms, with particular emphasis on those features near the Harang reversal region. Two different types of radars, including the SuperDARN coherent-scatter radars and the new advanced PFISR radar, as well as other complementary instruments, such as the IMAGE satellite and the THEMIS ASI array, have been utilized. We found that the auroral activity at substorm onset is located in the center of the Harang reversal and the nightside convection flows exhibit repeatable distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. By synthesizing observations from these observations, a 2-D picture of the evolution of ionospheric substorm electrodynamics has been established, which reveals features of an important relationship between the Region 2 and the substorm current systems. We believe these observations can shed new light on the substorm-related magnetosphere-ionosphere coupling process and contribute to the building of a holistic picture of the substorm dynamics.
[en] The analysis of the peculiarities of the anomalous coherent scattering of thee-level atoms in the field of standing waves is presented. It is shown that at the anomalous scattering (occurring in strong fields) the diffraction pattern undergoes qualitative changes (an asymmetry occurs and a partial inhibition trapping takes place) which would be taken into account when projecting effective schemes for atomic selection or beam-splitting. 11 refs
[en] Using Geant4 toolkit, the differential cross-section and the atomic form factor for coherent scattering of 25.2 heV photons in some tissue - equivalent compounds at 90 degree were calcuated. The results gave good agreement with those calculated theoretically. (author).