5,521 research outputs found
Center of mass rotation and vortices in an attractive Bose gas
The rotational properties of an attractively interacting Bose gas are studied
using analytical and numerical methods. We study perturbatively the ground
state phase space for weak interactions, and find that in an anharmonic trap
the rotational ground states are vortex or center of mass rotational states;
the crossover line separating these two phases is calculated. We further show
that the Gross-Pitaevskii equation is a valid description of such a gas in the
rotating frame and calculate numerically the phase space structure using this
equation. It is found that the transition between vortex and center of mass
rotation is gradual; furthermore the perturbative approach is valid only in an
exceedingly small portion of phase space. We also present an intuitive picture
of the physics involved in terms of correlated successive measurements for the
center of mass state.Comment: version2, 17 pages, 5 figures (3 eps and 2 jpg
Electromagnetic surface states in structured perfect-conductor surfaces
Surface-bound modes in metamaterials forged by drilling periodic hole arrays
in perfect-conductor surfaces are investigated by means of both analytical
techniques and rigorous numerical solution of Maxwell's equations. It is shown
that these metamaterials cannot be described in general by local,
frequency-dependent permittivities and permeabilities for small periods
compared to the wavelength, except in certain limiting cases that are discussed
in detail. New related metamaterials are shown to exhibit exciting optical
properties that are elucidated in the light of our simple analytical approach.Comment: 5 figure
Containerless high temperature property measurements
Containerless processing in the low gravity environment of space provides the opportunity to increase the temperature at which well controlled processing of and property measurements on materials is possible. This project was directed towards advancing containerless processing and property measurement techniques for application to materials research at high temperatures in space. Containerless high temperature material property studies include measurements of the vapor pressure, melting temperature, optical properties, and spectral emissivities of solid boron. The reaction of boron with nitrogen was also studied by laser polarimetric measurement of boron nitride film growth. The optical properties and spectral emissivities were measured for solid and liquid silicon, niobium, and zirconium; liquid aluminum and titanium; and liquid Ti-Al alloys of 5 to 60 atomic pct. titanium. Alternative means for noncontact temperature measurement in the absence of material emissivity data were evaluated. Also, the application of laser induced fluorescence for component activity measurements in electromagnetic levitated liquids was studied, along with the feasibility of a hybrid aerodynamic electromagnetic levitation technique
Dynamical quantum phase transition of a two-component Bose-Einstein condensate in an optical lattice
We study dynamics of a two-component Bose-Einstein condensate where the two
components are coupled via an optical lattice. In particular, we focus on the
dynamics as one drives the system through a critical point of a first order
phase transition characterized by a jump in the internal populations. Solving
the time-dependent Gross-Pitaevskii equation, we analyze; breakdown of
adiabaticity, impact of non-linear atom-atom scattering, and the role of a
harmonic trapping potential. Our findings demonstrate that the phase transition
is resilient to both contact interaction between atoms and external trapping
confinement.Comment: 8 pages, 8 figure
- …