7,449 research outputs found
Josephson tunneling of dark solitons in a double-well potential
We study the dynamics of matter waves in an effectively one-dimensional
Bose-Einstein condensate in a double well potential. We consider in particular
the case when one of the double wells confines excited states. Similarly to the
known ground state oscillations, the states can tunnel between the wells
experiencing the physics known for electrons in a Josephson junction, or be
self-trapped. As the existence of dark solitons in a harmonic trap are
continuations of such non-ground state excitations, one can view the
Josephson-like oscillations as tunnelings of dark solitons. Numerical existence
and stability analysis based on the full equation is performed, where it is
shown that such tunneling can be stable. Through a numerical path following
method, unstable tunneling is also obtained in different parameter regions. A
coupled-mode system is derived and compared to the numerical observations.
Regions of (in)stability of Josephson tunneling are discussed and highlighted.
Finally, we outline an experimental scheme designed to explore such dark
soliton dynamics in the laboratory.Comment: submitte
Geothermal reservoir engineering research
The Stanford University research program on the study of stimulation and reservoir engineering of geothermal resources commenced as an interdisciplinary program in September, 1972. The broad objectives of this program have been: (1) the development of experimental and computational data to evaluate the optimum performance of fracture-stimulated geothermal reservoirs; (2) the development of a geothermal reservoir model to evaluate important thermophysical, hydrodynamic, and chemical parameters based on fluid-energy-volume balances as part of standard reservoir engineering practice; and (3) the construction of a laboratory model of an explosion-produced chimney to obtain experimental data on the processes of in-place boiling, moving flash fronts, and two-phase flow in porous and fractured hydrothermal reservoirs
Decomposition of NO studied by infrared emission and CO laser absorption
A diagnostic technique for monitoring the concentration of NO using absorption of CO laser radiation was developed and applied in a study of the decomposition kinetics of NO. Simultaneous measurements of infrared emission by NO at 5.3 microns were also made to validate the laser absorption technique. The data were obtained behind incident shocks in NO-N2O-Ar (or Kr) mixtures, with temperatures in the range 2400-4100 K. Rate constants for dominant reactions were inferred from comparisons with computer simulations of the reactive flow
The supporting-cell antigen: a receptor-like protein tyrosine phosphatase expressed in the sensory epithelia of the inner ear
After noise- or drug-induced hair-cell loss, the sensory epithelia of the avian inner ear can regenerate new hair cells. Few molecular markers are available for the supporting-cell precursors of the hair cells that regenerate, and little is known about the signaling mechanisms underlying this regenerative response. Hybridoma methodology was used to obtain a monoclonal antibody (mAb) that stains the apical surface of supporting cells in the sensory epithelia of the inner ear. The mAb recognizes the supporting-cell antigen (SCA), a protein that is also found on the apical surfaces of retinal Müller cells, renal tubule cells, and intestinal brush border cells. Expression screening and molecular cloning reveal that the SCA is a novel receptor-like protein tyrosine phosphatase (RPTP), sharing similarity with human density-enhanced phosphatase, an RPTP thought to have a role in the density-dependent arrest of cell growth. In response to hair-cell damage induced by noise in vivo or hair-cell loss caused by ototoxic drug treatment in vitro, some supporting cells show a dramatic decrease in SCA expression levels on their apical surface. This decrease occurs before supporting cells are known to first enter S-phase after trauma, indicating that it may be a primary rather than a secondary response to injury. These results indicate that the SCA is a signaling molecule that may influence the potential of nonsensory supporting cells to either proliferate or differentiate into hair cell
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
VARIABLY CURING RESINS FOR MOUNTING METALLOGRAPHIC SAMPLES
In the past, heat-and-pressure-curing resins have been used almost exclusively as mounting materials for metallographic samples. Now, however, certain polyester resins, which are curable at room temperature, are equally as good for this purpose, and with their versatility they adapt readily to a variety of mounting conditions. A study of the epoxies and polyesters was made to determine which type of resin would satisfy the desirable properties of a metallographic mount. Four polyester resins were selected and investigated intensively to ascertain the variables associated with their curing processes. The results are compared with the standard thermosetting mounting material, Bakelite. (auth
Dynamical density functional theory for the evaporation of droplets of nanoparticle suspension
We develop a lattice gas model for the drying of droplets of a nanoparticle
suspension on a planar surface, using dynamical density functional theory
(DDFT) to describe the time evolution of the solvent and nanoparticle density
profiles. The DDFT assumes a diffusive dynamics but does not include the
advective hydrodynamics of the solvent, so the model is relevant to highly
viscous or near to equilibrium systems. Nonetheless, we see an equivalent of
the coffee-ring stain effect, but in the present model it occurs for
thermodynamic rather the fluid-mechanical reasons. The model incorporates the
effect of phase separation and vertical density variations within the droplet
and the consequence of these on the nanoparticle deposition pattern on the
surface. We show how to include the effect of slip or no-slip at the surface
and how this is related to the receding contact angle. We also determine how
the equilibrium contact angle depends on the microscopic interaction
parameters.Comment: 35 pages, 10 figure
Symmetry of re-entrant tetragonal phase in Ba1-xNaxFe2As2: Magnetic versus orbital ordering mechanism
Magneto-structural phase transitions in Ba1-xAxFe2As2 (A = K, Na) materials
are discussed for both magnetically and orbitally driven mechanisms, using a
symmetry analysis formulated within the Landau theory of phase transitions.
Both mechanisms predict identical orthorhombic space-group symmetries for the
nematic and magnetic phases observed over much of the phase diagram, but they
predict different tetragonal space-group symmetries for the newly discovered
re-entrant tetragonal phase in Ba1-xNaxFe2As2 (x ~ 0.24-0.28). In a magnetic
scenario, magnetic order with moments along the c-axis, as found
experimentally, does not allow any type of orbital order, but in an orbital
scenario, we have determined two possible orbital patterns, specified by
P4/mnc1' and I4221' space groups, which do not require atomic displacements
relative to the parent I4/mmm1' symmetry and, in consequence, are
indistinguishable in conventional diffraction experiments. We demonstrate that
the three possible space groups are however, distinct in resonant X-ray Bragg
diffraction patterns created by Templeton & Templeton scattering. This provides
an experimental method of distinguishing between magnetic and orbital models
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