440 research outputs found
Coupled-channel pseudo-potential description of the Feshbach resonance in two dimensions
We derive pseudo-potentials that describe the scattering between two
particles in two spatial dimensions for any partial wave m, whose scattering
strength is parameterized in terms of the m-dependent phase shift. Using our
m=0 pseudo-potential, we develop a coupled channel model with 2D zero-range
interactions, which describes the two-body physics across a Feshbach resonance.
Our model predicts the scattering length, the binding energy and the "closed
channel molecular fraction" of two particles; these observables can be measured
in experiments on ultracold quasi-2D atomic Bose and Fermi gases with
present-day technology.Comment: 4 pages, 3 figure
Data-driven pattern identification and outlier detection in time series
We address the problem of data-driven pattern identification and outlier
detection in time series. To this end, we use singular value decomposition
(SVD) which is a well-known technique to compute a low-rank approximation for
an arbitrary matrix. By recasting the time series as a matrix it becomes
possible to use SVD to highlight the underlying patterns and periodicities.
This is done without the need for specifying user-defined parameters. From a
data mining perspective, this opens up new ways of analyzing time series in a
data-driven, bottom-up fashion. However, in order to get correct results, it is
important to understand how the SVD-spectrum of a time series is influenced by
various characteristics of the underlying signal and noise. In this paper, we
have extended the work in earlier papers by initiating a more systematic
analysis of these effects. We then illustrate our findings on some real-life
data
Pseudo-potential treatment of two aligned dipoles under external harmonic confinement
Dipolar Bose and Fermi gases, which are currently being studied extensively
experimentally and theoretically, interact through anisotropic, long-range
potentials. Here, we replace the long-range potential by a zero-range
pseudo-potential that simplifies the theoretical treatment of two dipolar
particles in a harmonic trap. Our zero-range pseudo-potential description
reproduces the energy spectrum of two dipoles interacting through a
shape-dependent potential under external confinement very well, provided that
sufficiently many partial waves are included, and readily leads to a
classification scheme of the energy spectrum in terms of approximate angular
momentum quantum numbers. The results may be directly relevant to the physics
of dipolar gases loaded into optical lattices.Comment: 9 pages, 4 figure
Low-energy resonances and bound states of aligned bosonic and fermionic dipoles
The low-energy scattering properties of two aligned identical bosonic and
identical fermionic dipoles are analyzed. Generalized scattering lengths are
determined as functions of the dipole moment and the scattering energy. Near
resonance, where a new bound state is being pulled in, all non-vanishing
generalized scattering lengths diverge, with the and
scattering lengths being dominant for identical bosons and identical fermions,
respectively, near both broad and narrow resonances. Implications for the
energy spectrum and the eigenfunctions of trapped two-dipole systems and for
pseudo-potential treatments are discussed.Comment: 4 pages, 4 figure
Au9+ swift heavy ion irradiation of Zn[CS(NH2)2]3SO4 crystal: Crystalline perfection and optical properties
The single crystal of tris(thiourea)zinc sulphate (Zn[CS(NH2)2]3SO4) was
irradiated by 150 MeV Au9+ swift heavy ions and analyzed in comparison with
pure crystal for crystalline perfection and optical properties. The Fourier
transform infrared and x-ray powder diffraction inferred that swift ions lead
the disordering and breaking of molecular bonds in lattice without formation of
new structural phases. High resolution X-ray diffraction (HRXRD) revealed the
abundance of point defects, and formation of mosaics and low angle grain
boundaries in the irradiated region of crystal. The swift ion irradiation found
to affect the lattice vibrational modes and functional groups significantly.
The defects induced by heavy ions act as the color centers and resulted in
enhance of photoluminescence emission intensity. The optical transparency and
band gap found to be decreased.Comment: 7 page
Effect of swift heavy ion irradiation on surface resistance of DyBa2Cu3O7−δ thin films at microwave frequencies
We report the observation of a pronounced peak in surface resistance at microwave frequencies of 4.88 GHz and 9.55 GHz and its disappearance after irradiation with swift ions in laser ablated DyBa2Cu3O7−δ (DBCO) thin films. The measurements were carried out in zero field as well as in the presence of magnetic fields (up to 0.8 T). The films were irradiated using 90 MeV oxygen ions at Nuclear Science Centre, New Delhi at a fluence of 3 × 10^13 ions/cm2. Introduction of point defects and extended defects after irradiation suppresses the peak at 9.55 GHz whereas no suppression is observed at 4.88 GHz. These results and the vortex dynamics in the films at microwave frequencies before and after irradiation are discussed
- …