119,186 research outputs found
Center motions of nonoverlapping condensates coupled by long-range dipolar interaction in bilayer and multilayer stacks
We investigate the effect of anisotropic and long-range dipole-dipole
interaction (DDI) on the center motions of nonoverlapping Bose-Einstein
condensates (BEC) in bilayer and multilayer stacks. In the bilayer, it is shown
analytically that while DDI plays no role in the in-phase modes of center
motions of condensates, out-of-phase mode frequency () depends
crucially on the strength of DDI (). At the small- limit,
. In the multilayer stack, transverse
modes associated with center motions of coupled condensates are found to be
optical phonon like. At the long-wavelength limit, phonon velocity is
proportional to .Comment: 7 pages, 5 figure
Using modified Gaussian distribution to study the physical properties of one and two-component ultracold atoms
Gaussian distribution is commonly used as a good approximation to study the
trapped one-component Bose-condensed atoms with relatively small nonlinear
effect. It is not adequate in dealing with the one-component system of large
nonlinear effect, nor the two-component system where phase separation exists.
We propose a modified Gaussian distribution which is more effective when
dealing with the one-component system with relatively large nonlinear terms as
well as the two-component system. The modified Gaussian is also used to study
the breathing modes of the two-component system, which shows a drastic change
in the mode dispersion at the occurrence of the phase separation. The results
obtained are in agreement with other numerical results.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Oscillations of Bose condensates in a one-dimensional optical superlattice
Oscillations of atomic Bose-Einstein condensates in a 1D optical lattice with
a two-point basis is investigated. In the low-frequency regime, four branches
of modes are resolved, that correspond to the transverse in-phase and
out-of-phase breathing modes, and the longitudinal acoustic and optical phonon
modes of the condensates. Dispersions of these modes depend intimately on the
values of two intersite Josephson tunneling strengths, and , and the
on-site repulsion between the atoms. Observation of these mode dispersions
is thus a direct way to access them.Comment: 5 pages,2 figure
Toward optimal multi-objective models of network security: Survey
Information security is an important aspect of a successful business today. However, financial difficulties and budget cuts create a problem of selecting appropriate security measures and keeping networked systems up and running. Economic models proposed in the literature do not address the challenging problem of security countermeasure selection. We have made a classification of security models, which can be used to harden a system in a cost effective manner based on the methodologies used. In addition, we have specified the challenges of the simplified risk assessment approaches used in the economic models and have made recommendations how the challenges can be addressed in order to support decision makers
Covalent triazine framework with efficient photocatalytic activity in aqueous and solid media
Hardware simulation of shuttle Ku-band antenna acquisition, volume 5
For abstract, see N78-17252
Fatigue failure of materials under broad band random vibrations
The fatigue life of material under multifactor influence of broad band random excitations has been investigated. Parameters which affect the fatigue life are postulated to be peak stress, variance of stress and the natural frequency of the system. Experimental data were processed by the hybrid computer. Based on the experimental results and regression analysis a best predicting model has been found. All values of the experimental fatigue lives are within the 95% confidence intervals of the predicting equation
Unification of Gravitation, Gauge Field and Dark Energy
This paper is composed of two correlated topics: 1. unification of
gravitation with gauge fields; 2. the coupling between the daor field and other
fields and the origin of dark energy. After introducing the concept of ``daor
field" and discussing the daor geometry, we indicate that the complex daor
field has two kinds of symmetry transformations. Hence the gravitation and
SU(1,3) gauge field are unified under the framework of the complex connection.
We propose a first-order nonlinear coupling equation of the daor field, which
includes the coupling between the daor field and SU(1,3) gauge field and the
coupling between the daor field and the curvature, and from which Einstein's
gravitational equation can be deduced. The cosmological observations imply that
dark energy cannot be zero, and which will dominate the doom of our Universe.
The real part of the daor field self-coupling equation can be regarded as
Einstein's equation endowed with the cosmological constant. It shows that dark
energy originates from the self-coupling of the space-time curvature, and the
energy-momentum tensor is proportional to the square of coupling constant
\lambda. The dark energy density given by our scenario is in agreement with
astronomical observations. Furthermore, the Newtonian gravitational constant G
and the coupling constant \epsilon of gauge field satisfy G=
\lambda^{2}\epsilon^{2}.Comment: 24 pages, revised version; references added; typos correcte
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