1,109 research outputs found
Landau damping of transverse quadrupole oscillations of an elongated Bose-Einstein condensate
We study the interaction between low-lying transverse collective oscillations
and thermal excitations of an elongated Bose-Einstein condensate by means of
perturbation theory. We consider a cylindrically trapped condensate and
calculate the transverse elementary excitations at zero temperature by solving
the linearized Gross-Pitaevskii equations in two dimensions. We use them to
calculate the matrix elements between thermal excited states coupled with the
quasi-2D collective modes. The Landau damping of transverse collective modes is
investigated as a function of temperature. At low temperatures, the damping
rate due to the Landau decay mechanism is in agreement with the experimental
data for the decay of the transverse quadrupole mode, but it is too small to
explain the slow experimental decay of the transverse breathing mode. The
reason for this discrepancy is discussed.Comment: 6 pages, LaTeX, 1 figur
Synthesis of CdS/L-cys nanoparticles colloid solutions with predetermined optical properties
The purpose of this paper is to summarize experimental data of CdS/L-cystein nanoparticles (NPs) colloid solutions optical properties as function of 3-component mixture (Cd2+–S2 –L-cys) content. The NPs synthesis was carried out at pH 11 in the wide composition range based on literature data. The influence of the solutions composition on the colloids stability and the CdS/l-cys NPs size was monitored by
absorption and
fluorescence spectra observation at room temperature and studied by TEM. A polynomial
model was used for the responses produced from Scheffe’s simplex lattice design with fourth degree terms. The paper also compares the results of two statistical-experimental methods, namely 2D Scheffe’s simplex-lattice design and 3D-plot by STATISTICA v6 program. Both models were found to be adequate for prediction the optical properties of the solutions but with various approximation level
Synthesis of CdS/L-cys nanoparticles colloid solutions with predetermined optical properties
The purpose of this paper is to summarize experimental data of CdS/L-cystein nanoparticles (NPs) colloid solutions optical properties as function of 3-component mixture (Cd2+–S2 –L-cys) content. The NPs synthesis was carried out at pH 11 in the wide composition range based on literature data. The influence of the solutions composition on the colloids stability and the CdS/l-cys NPs size was monitored by
absorption and fluorescence spectra observation at room temperature and studied by TEM. A polynomial model was used for the responses produced from Scheffe’s simplex lattice design with fourth degree terms. The paper also compares the results of two statistical-experimental methods, namely 2D Scheffe’s simplex-lattice design and 3D-plot by STATISTICA v6 program. Both models were found to be adequate for prediction the optical properties of the solutions but with various approximation levels
Self-consistent calculation of the coupling constant in the Gross-Pitaevskii equation
A method is proposed for a self-consistent evaluation of the coupling
constant in the Gross-Pitaevskii equation without involving a pseudopotential
replacement. A renormalization of the coupling constant occurs due to medium
effects and the trapping potential, e.g. in quasi-1D or quasi-2D systems. It is
shown that a simplified version of the Hartree-Fock-Bogoliubov approximation
leads to a variational problem for both the condensate and a two-body wave
function describing the behaviour of a pair of bosons in the Bose-Einstein
condensate. The resulting coupled equations are free of unphysical divergences.
Particular cases of this scheme that admit analytical estimations are
considered and compared to the literature. In addition to the well-known cases
of low-dimensional trapping, cross-over regimes can be studied. The values of
the kinetic, interaction, external, and release energies in low dimensions are
also evaluated and contributions due to short-range correlations are found to
be substantial.Comment: 15 pages, ReVTEX, no figure
Radioglaciological studies on Hurd Peninsula glaciers, Livingston Island, Antarctica
We present the results of several radio-echo sounding surveys carried out on Johnsons and Hurd Glaciers, Livingston Island, Antarctica, between the 1999/2000 and 2004/05 austral summer campaigns, which included both radar profiling and common-midpoint measurements with low (20- 25 MHz)- and high (200MHz)-frequency radars. The latter have allowed us to estimate the radio-wave velocity in ice and firn and the corresponding water contents in temperate ice, which vary between 0 and 1.6% depending on the zone. Maximum ice thickness is ~200 m, with a mean value of 93.6 ± 2.5 m. Total ice volume is 0.968 ± 0.026 km3, for an area of 10.34 ± 0.03 km2. The subglacial relief of Johnsons Glacier is quite smooth, while that of Hurd Glacier shows numerous overdeepenings and peaks. The radar records suggest that Hurd Glacier has a polythermal structure, contrary to the usual assumption that glaciers in Livingston Island are temperate. This is also supported by other dynamical and geomorphological evidence
Group expansions for impurities in superconductors
A new method is proposed for practical calculation of the effective
interaction between impurity scatterers in superconductors, based on algebraic
properties of related Nambu matrices for Green functions. In particular, we
show that the density of states within the s-wave gap can have a non-zero
contribution (impossible either in Born and in T-matrix approximation) from
non-magnetic impurities with concentration , beginning from order.Comment: 5 pages, 1 figur
Overcoming laser diode nonlinearity issues in multi-channel radio-over-fiber systems
The authors demonstrate how external light injection into a directly modulated laser diode may be used to enhance the performance of a multi-channel radio-over-fiber system operating at a frequency of 6 GHz. Performance improvements of up to 2 dB were achieved by linearisation of the lasers-modulation response. To verify the experimental work a simulation of the complete system was carried out using Matlab. Good correlation was observed between experimental and simulated results
Positive Maps Which Are Not Completely Positive
The concept of the {\em half density matrix} is proposed. It unifies the
quantum states which are described by density matrices and physical processes
which are described by completely positive maps. With the help of the
half-density-matrix representation of Hermitian linear map, we show that every
positive map which is not completely positive is a {\em difference} of two
completely positive maps. A necessary and sufficient condition for a positive
map which is not completely positive is also presented, which is illustrated by
some examples.Comment: 4pages,The Institute of Theoretical Physics, Academia Sinica, Beijing
100080, P.R. Chin
The Spin-Dependent Structure Functions of Nuclei in the Meson-Nucleon Theory
A theoretical approach to the investigation of spin-dependent structure
functions in deep inelastic scattering of polarized leptons off polarized
nuclei, based on the effective meson-nucleon theory and operator product
expansion method, is proposed and applied to deuteron and . The explicit
forms of the moments of the deuteron and spin-dependent structure
functions are found and numerical estimates of the influence of nuclear
structure effects are presented.Comment: 42 pages revtex, 7 postscript figures available from above e-mail
upon request. Perugia preprint DFUPG 92/9
Relativistic Contributions to Deuteron Photodisintegration in the Bethe-Salpeter Formalism
In plane wave one-body approximation the reaction of deuteron
photodisintegration is considered in the framework of the Bethe-Salpeter
formalism for two-nucleon system. Results are obtained for deuteron vertex
function, which is the solution of the homogeneous Bethe-Salpeter equation with
a multi-rank separable interaction kernel, with a given analytical form. A
comparison is presented with predictions of non-relativistic, quasipotential
approaches and the equal time approximation. It is shown that important
contributions come from the boost in the arguments of the initial state vertex
function and the boost on the relative energy in the one-particle propagator
due to recoil.Comment: 29 pages, 6 figure
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