1,052 research outputs found
Identical Particle Scattering From A Weakly Coupled Bose-Einstein Condensed Gas
We calculate the scattering states and cross sections for a Bose-Einstein condensed dilute gas trapped in a spherical square well of finite depth. The interactions are treated in the scattering length approximation. We solve the Gross-Pitaevskii equation and the Bogoliubov equations for bound and scattering states. The results show that there are transparency effects reminiscent of those conjectured to occur for strongly coupled systems. When incident particle wavelengths λ are comparable to the well size a, exchange induced transparency enhancement is dramatic only for particular combinations of well depth, interaction strength, and particle number. For particles with large momenta (a/λ≫1),however, exchange with the condensate results in enhanced transmission for all coupling strengths. We calculated the rate of decay of the scattering states to leading order in anharmonic corrections to the Bogoliubov approximation and found the corresponding inelastic cross sections to be extremely small
High-quality variational wave functions for small 4He clusters
We report a variational calculation of ground state energies and radii for
4He_N droplets (3 \leq N \leq 40), using the atom-atom interaction HFD-B(HE).
The trial wave function has a simple structure, combining two- and three-body
correlation functions coming from a translationally invariant
configuration-interaction description, and Jastrow-type short-range
correlations. The calculated ground state energies differ by around 2% from the
diffusion Monte Carlo results.Comment: 5 pages, 1 ps figure, REVTeX, submitted to Phys. Rev.
Recommended from our members
Jahn Teller Effect of Cations in Water: The Cupric Ion in Water
We report a molecular dynamics model for the Jahn Teller effect in the solvation shell of a cation in solution in an aqueous liquid. We apply the model to the cupric ion and compare results with results of neutron scattering experiments on copper chlorate solutions. We conclude that the original interpretation of the experiments in terms of a Jan Teller effect may require modification
Identical particle scattering from a weakly coupled Bose-Einstein condensed gas
We calculate the scattering states and cross sections for a Bose-Einstein condensed dilute gas trapped in a spherical square well of finite depth. The interactions are treated in the scattering length approximation. We solve the Gross-Pitaevskii equation and the Bogoliubov equations for bound and scattering states. The results show that there are transparency effects reminiscent of those conjectured to occur for strongly coupled systems. When incident particle wavelengths λ are comparable to the well size a, exchange induced transparency enhancement is dramatic only for particular combinations of well depth, interaction strength, and particle number. For particles with large momenta (a/λ≫1),however, exchange with the condensate results in enhanced transmission for all coupling strengths. We calculated the rate of decay of the scattering states to leading order in anharmonic corrections to the Bogoliubov approximation and found the corresponding inelastic cross sections to be extremely small
Theory of Non-Reciprocal Optical Effects in Antiferromagnets: The Case Cr_2O_3
A microscopic model of non-reciprocal optical effects in antiferromagnets is
developed by considering the case of Cr_2O_3 where such effects have been
observed. These effects are due to a direct coupling between light and the
antiferromagnetic order parameter. This coupling is mediated by the spin-orbit
interaction and involves an interplay between the breaking of inversion
symmetry due to the antiferromagnetic order parameter and the trigonal field
contribution to the ligand field at the magnetic ion. We evaluate the matrix
elements relevant for the non-reciprocal second harmonic generation and
gyrotropic birefringence.Comment: accepted for publication in Phys. Rev.
Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces
We develop a microscopic theory of the scattering, transmission, and sticking
of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and
inelastic neutron scattering from the slab. The theory includes coupling
between different modes and allows for inelastic processes. We find a number of
essential aspects that must be observed in a physically meaningful and reliable
theory of atom transmission and scattering; all are connected with
multiparticle scattering, particularly the possibility of energy loss. These
processes are (a) the coupling to low-lying (surface) excitations
(ripplons/third sound) which is manifested in a finite imaginary part of the
self energy, and (b) the reduction of the strength of the excitation in the
maxon/roton region
Magnetic Raman Scattering in Two-Dimensional Spin-1/2 Heisenberg Antiferromagnets: Spectral Shape Anomaly and Magnetostrictive Effects
We calculate the Raman spectrum of the two-dimensional (2D) spin-1/2
Heisenberg antiferromagnet by exact diagonalization and quantum Monte Carlo
techniques on clusters of up to 144 sites and, on a 16-site cluster, by
considering the phonon-magnon interaction which leads to random fluctuations of
the exchange integral. Results are in good agreement with experiments on
various high-T_c precursors, such as La_2CuO_4 and YBa_2Cu_3O_{6.2}. In
particular, our calculations reproduce the broad lineshape of the two-magnon
peak, the asymmetry about its maximum, the existence of spectral weight at high
energies, and the observation of nominally forbidden A_{1g} scattering.Comment: 12 pages, REVTEX, 1 postscript figur
Kepler eclipsing binary stars. VII. the catalogue of eclipsing binaries found in the entire Kepler data set
The primary Kepler Mission provided nearly continuous monitoring of ~200,000 objects with unprecedented photometric precision. We present the final catalog of eclipsing binary systems within the 105 deg2 Kepler field of view. This release incorporates the full extent of the data from the primary mission (Q0-Q17 Data Release). As a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. We identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. We have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. The total number of identified eclipsing and ellipsoidal binary systems in the Kepler field of view has increased to 2878, 1.3% of all observed Kepler targets
Bibliometric Evidence for a Hierarchy of the Sciences
The hypothesis of a Hierarchy of the Sciences, first formulated in the 19(th) century, predicts that, moving from simple and general phenomena (e.g. particle dynamics) to complex and particular (e.g. human behaviour), researchers lose ability to reach theoretical and methodological consensus. This hypothesis places each field of research along a continuum of complexity and "softness", with profound implications for our understanding of scientific knowledge. Today, however, the idea is still unproven and philosophically overlooked, too often confused with simplistic dichotomies that contrast natural and social sciences, or science and the humanities. Empirical tests of the hypothesis have usually compared few fields and this, combined with other limitations, makes their results contradictory and inconclusive. We verified whether discipline characteristics reflect a hierarchy, a dichotomy or neither, by sampling nearly 29,000 papers published contemporaneously in 12 disciplines and measuring a set of parameters hypothesised to reflect theoretical and methodological consensus. The biological sciences had in most cases intermediate values between the physical and the social, with bio-molecular disciplines appearing harder than zoology, botany or ecology. In multivariable analyses, most of these parameters were independent predictors of the hierarchy, even when mathematics and the humanities were included. These results support a "gradualist" view of scientific knowledge, suggesting that the Hierarchy of the Sciences provides the best rational framework to understand disciplines' diversity. A deeper grasp of the relationship between subject matter's complexity and consensus could have profound implications for how we interpret, publish, popularize and administer scientific research
- …