14,273 research outputs found
Above-threshold ionization photoelectron spectrum from quantum trajectory
Many nonlinear quantum phenomena of intense laser-atom physics can be
intuitively explained with the concept of trajectory. In this paper, Bohmian
mechanics (BM) is introduced to study a multiphoton process of atoms
interacting with the intense laser field: above-threshold ionization (ATI).
Quantum trajectory of an atomic electron in intense laser field is obtained
from the Bohm-Newton equation first and then the energy of the photoelectron is
gained from its trajectory. With energies of an ensemble of photoelectrons, we
obtain the ATI spectrum which is consistent with the previous theoretical and
experimental results. Comparing BM with the classical trajectory Monte-Carlo
method, we conclude that quantum potential may play a key role to reproduce the
spectrum of ATI. Our work may present a new approach to understanding quantum
phenomena in intense laser-atom physics with the image of trajectory.Comment: 10 pages, 3 figure
Intermittent emission of particles from three coupled condensates in a one-dimensional lattice
We investigate particle emission, driven by periodically modulating the
interaction strength, from three coupled Bose-Einstein condensates in a
one-dimensional lattice. Within perturbative analyses, which lead to the
regimes of instabilities for different modes, we not only obtain two main
frequencies, under which the system can emit a large particle jet, but also
find that the emission is distinctly intermittent rather than continuous. The
time evolution of the trapped particles exhibits a stair-like decay, and a
larger drive induces a more significant intermittency. We further shed light on
the dynamics of the stimulating process, and demonstrate that instead of a real
suspension, the intermittency represents a build-up stage of the particles. The
theoretical framework might be generalized, to the explorations on other
multiple-condensate systems with analogous configurations and couplings.Comment: 7 pages, 10 figure
Present status of mangrove crab (Scylla serrata (Forskal)) culture in China
The status of mangrove crab (Scylla serrata) culture in China and suggestions on how this may become an important sector in the place are presented
A Critical Examination of Hypernova Remnant Candidates in M101. II. NGC 5471B
NGC 5471B has been suggested to contain a hypernova remnant because of its
extraordinarily bright X-ray emission. To assess its true nature, we have
obtained high-resolution images in continuum bands and nebular lines with the
Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt
Peak National Observatory 4-m echelle spectrograph. The images reveal three
supernova remnant (SNR) candidates in the giant HII region NGC 5471, with the
brightest one being the 77x60 pc shell in NGC 5471B. The Ha velocity profile of
NGC 5471B can be decomposed into a narrow component (FWHM = 41 km/s) from the
background HII region and a broad component (FWHM = 148 km/s) from the SNR
shell. Using the brightness ratio of the broad to narrow components and the Ha
flux measured from the WFPC2 Ha image, we derive an Ha luminosity of
(1.4+-0.1)x10^39 ergs/s for the SNR shell. The [SII]6716,6731 doublet ratio of
the broad velocity component is used to derive an electron density of ~700
cm^-3 in the SNR shell. The mass of the SNR shell is thus 4600+-500 Mo. With a
\~330 km/s expansion velocity implied by the extreme velocity extent of the
broad component, the kinetic energy of the SNR shell is determined to be
5x10^51 ergs. This requires an explosion energy greater than 10^52 ergs, which
can be provided by one hypernova or multiple supernovae. Comparing to SNRs in
nearby active star formation regions, the SNR shell in NGC 5471B appears truly
unique and energetic. We conclude that the optical observations support the
existence of a hypernova remnant in NGC 5471B.Comment: 27 pages, 9 figures, to appear in May 2002 issue of The Astronomical
Journa
- …