1,620 research outputs found
Anisotropic merging and splitting of dipolar Bose-Einstein condensates
We study the merging and splitting of quasi-two-dimensional Bose-Einstein
condensates with strong dipolar interactions. We observe that if the dipoles
have a non-zero component in the plane of the condensate, the dynamics of
merging or splitting along two orthogonal directions, parallel and
perpendicular to the projection of dipoles on the plane of the condensate are
different. The anisotropic merging and splitting of the condensate is a
manifestation of the anisotropy of the roton-like mode in the dipolar system.
The difference in dynamics disappears if the dipoles are oriented at right
angles to the plane of the condensate as in this case the Bogoliubov
dispersion, despite having roton-like features, is isotropic.Comment: 9 pages and 9 figure
Thermopower of the Hubbard model: Effects of multiple orbitals and magnetic fields in the atomic limit
We consider strongly-correlated systems described by the multi-orbital
Hubbard model in the atomic limit and obtain exact expressions for the chemical
potential and thermopower. We show that these expressions reduce to the Heikes
formula in the appropriate limits () and () and obtain
the full temperature dependence in between these regimes. We also investigate
the effect of a magnetic field introduced through a Zeeman term and observe
that the thermopower of the multi-orbital Hubbard model displays spikes as a
function of magnetic field at certain special values of the field. This effect
might be observable in experiments for materials with a large magnetic
coupling.Comment: 8 pages, 4 figures Typos in eqns. 3 and 4 and reference 17 correcte
Branching ratios in low-energy deuteron-induced reactions
We consider (d,p) and (d,n) reactions on light nuclei at low energies. A simple estimate using the second-order distorted-wave Born approximation shows that Coulomb-induced predissociation of the deuteron influences the relative rate by less than 10%. This disagrees with a previous explanation of experiments involving 6Li targets and invalidates speculations about such effects in "cold fusion" experiments
Seismic Bearing Capacity of Strip Footing Resting on Reinforced Earth Bed
With an increase in demand for construction the use of poor soils becomes imperative. Soil bearing capacity and settlement play an important role in the design of foundations. Seismicity of the site is another important parameter in the design of the foundation for a structure. Hence seismic bearing capacity of soil becomes an important component in the design. In weak soils often deep foundations are recommended on account of the low soil bearing capacity available. In poor soils, ground improvement techniques are commonly used to improve the soil bearing capacity. Reinforcing earth with geo synthetic is one such technique adopted in practice. This is preferred due to its cost effectiveness as in most of the engineering projects economy plays an important role. If the weak soil is improved by using geo synthetic, then it becomes feasible to use shallow foundations instead of deep foundations for the same structure, thus effecting economy. Shallow foundations still remain the most used foundation type in construction due to its economy and ease in construction. In this paper an attempt has been made to develop an analytical approach to obtain the seismic bearing capacity of a strip footing resting on reinforced earth. The approach is based on the analysis proposed by Binquet and Lee (1975b) for a strip footing subjected to static load. Both vertical and horizontal accelerations have been considered in terms of seismic coefficients, αh and αv. Results have been presented in the form of non - dimensional charts from which seismic bearing capacity can be obtained, conveniently. Both rupture strength and frictional resistance criteria, have been taken into account in preparing these charts. Charts incorporate horizontal seismic acceleration coefficient, αh = 0.0 and 0.10. The value of vertical seismic acceleration coefficient, αv, is taken as 2/3αh. An illustrative example has been included for a lucid understanding
Studies of orbital parameters and pulse profile of the accreting millisecond pulsar XTE J1807-294
The accreting millisecond pulsar XTE J1807-294 was observed by XMM-Newton on
March 22, 2003 after its discovery on February 21, 2003 by RXTE. The source was
detected in its bright phase with an observed average count rate of 33.3 cts/s
in the EPIC-pn camera in the 0.5-10 keV energy band (3.7 mCrab). Using the
earlier established best-fit orbital period of 40.0741+/-0.0005 minutes from
RXTE observations and considering a circular binary orbit as first
approximation, we derived a value of 4.8+/-0.1 lt-ms for the projected orbital
radius of the binary system and an epoch of the orbital phase of MJD
52720.67415(16). The barycentric mean spin period of the pulsar was derived as
5.2459427+/-0.0000004 ms. The pulsar's spin-pulse profile showed a prominent
(1.5 ms FWHM) pulse, with energy and orbital phase dependence in the amplitude
and shape. The measured pulsed fraction in four energy bands was found to be
3.1+/-0.2 % (0.5-3.0 keV), 5.4+/-0.4 % (3.0-6.0 keV), 5.1+/-0.7 % (6.0-10.0
keV) and 3.7+/-0.2 % (0.5-10.0 keV), respectively. Studies of spin-profiles
with orbital phase and energy showed significant increase in its pulsed
fraction during the second observed orbit of the neutron star, gradually
declining in the subsequent two orbits, which was associated with sudden but
marginal increase in mass accretion. From our investigations of orbital
parameters and estimation of other properties of this compact binary system, we
conclude that XTE J1807-294 is very likely a candidate for a millisecond radio
pulsar.Comment: 4 pages, 4 figures, Accepted for publication in Astronomy and
Astrophysics letter
Analysis of physical-chemical processes governing SSME internal fluid flows
The efforts to adapt CHAM's computational fluid dynamics code, PHOENICS, to the analysis of flow within the high pressure fuel turbopump (HPFTP) aft-platform seal cavity of the SSME are summarized. In particular, the special purpose PHOENICS satellite and ground station specifically formulated for this application are listed and described, and the preliminary results of the first part two-dimensional analyses are presented and discussed. Planned three-dimensional analyses are also briefly outlined. To further understand the mixing and combustion processes in the SSME fuelside preburners, a single oxygen-hydrogen jet element was investigated
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