1,721,032 research outputs found
Wave packet dynamics in stabilization of ionization in a circularly polarized laser field
No full textWe present the results of a quantum dynamical study of ionization stabilization of a two-dimensional hydrogen atom in an intense circularly polarized laser field. We show that stabilization can be explained by the formation of a nonspreading electron wave packet rotating with the laser frequency. The radius of the circular orbit is found to be greater than the radius of the classical circular motion of a free electron under the same laser field. We also investigate the classical nonlinear dynamics of the electron and examine the relationship between nonlinear resonance islands and the wave packet dynamics.This research was supported by the Ministry of Science and Technology of Korea through the Creative Research Initiative Program, by the the Korea Research Foundation under Contract No. 2001-015-0107, and by the the
Korea Atomic Energy Research Institute
Chaos and reconnection in relativistic cyclotron motion in an elliptically polarized electric field
No full textA theoretical study of the relativistic cyclotron motion occurring in a uniform magnetic field and an oscillating electric field of arbitrary polarization is performed, which aims at determining the effect of the ellipticity and the strength of the electric field upon the integrability or nonintegrability of the system. Unless a circularly polarized electric field is used, the cyclotron system is nonintegrable and displays stochastic behavior in the region where resonance islands overlap. It is found, however, that the stochastic layers become increasingly thin as the polarization angle is moved closer coward pi/2 (circular polarization). If the polarization angle is held fixed and the electric field amplitude is increased, the Kolmogorov-Arnold-Moser curve a separating the resonance islands experience a reconnection process through which the islands are topologically rearranged. When the rearrangement is accomplished, the phase space is occupied mostly by regular trajectories. [S1063-651X(99)02710-5].This research was supported in part by the Agency for Defense Development(ADD) of Korea and by the Korea Atomic Energy Research Institute(KAERI)
Relativistic cyclotron motion in a polarized electric field
No full textThe relativistic cyclotron motion in a uniform magnetic field and in a transverse time-periodic electric field is studied, with particular attention to qualitative differences in the nature of the motion under linearly and circularly polarized electric fields. Theoretical analysis based on the Lagrangian formulation of the cyclotron motion allows a direct comparision for the two polarizations and confirms the earlier observation that the cyclotron motion is always integrable when the electric field is circularly polarized, but is not under a linearly polarized electric field
Stabilization dynamics in an intense circularly polarized laser field
No full text©2002 The American Physical Society
URL: http://link.aps.org/abstract/PRA/v65/e055401
DOI: 10.1103/PhysRevA.65.055401
PACS: 42.50.Hz, 32.80.Fb, 32.80.WrWe study quantum and classical dynamics of the electron in ionization stabilization of the two-dimensional hydrogen atom irradiated by an intense circularly polarized laser. When the quantum time evolution of the wave packet is stable but the corresponding classical time evolution is diffusive, stabilization can be understood to arise from the effect of quantum localization that suppresses classically chaotic diffusion. When both the quantum and classical time evolutions exhibit a stable behavior, stabilization can be regarded as originating from stable classical orbits generated by nonlinear resonance. We also investigate the effect of the bare Coulomb singularity on ionization stabilization.This research was supported by the Korea Atomic Energy Research Institute, by the Korea Research Foundation under Contract No. 2001-015-DP0088, and by the Ministry of Science and Technology of Korea through the Creative Research Initiative Program
Simultaneous multiple Helicobacter pylori infection identified by repetitive sequence-based polymerase chain reaction (REP-PCR) in duodenal ulcer patients.
No full textRepetitive sequence-based PCR (REP-PCR) detects simultaneous, multiple strain infection in duodenal ulcer patients
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Demonstration of unexpected antibiotic resistance of genotypically identical Helicobacter pylori isolates.
No full textWith use of multiple- and single-colony expansion procedures, the results of susceptibility testing of Helicobacter pylori isolates from patients with duodenal ulcer were assessed by Etest. The H. pylori genotype was assessed by repetitive extragenic palindrome-based polymerase chain reaction (REP-PCR). There was a high degree of genotypic heterogeneity between different patients, but a single REP-PCR pattern was found for 92% of patients. In contrast, a high degree of phenotypic heterogeneity was shown among the isolated colonies. Antibiogram susceptibility patterns differed only with respect to metronidazole but not with respect to clarithromycin or amoxicillin. The 42% rate of resistance to metronidazole determined with use of the conventional multiple-strains expansion method was increased to 92% when the single-colony expansion method was used. Similarly, dual clarithromycin/metronidazole resistance was increased from 8% to 42% with single-colony expansion. Despite evidence of a single genotype in most patients, single-colony expansion shows that routine susceptibility testing may greatly underestimate the frequency of metronidazole resistance
Mechanism of acquired-multidrug resistance in Helicobacter pylori: Alterations of outer membrane proteins and lipopolysaccharide
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