48,757 research outputs found
Bose-Einstein condensate of kicked rotators with time-dependent interaction
A modification of the quantum kicked rotator is suggested with a
time-dependent delta-kicked interaction parameter which can be realized by a
pulsed turn-on of a Feshbach resonance. The mean kinetic energy increases
exponentially with time in contrast to a merely diffusive or linear growth for
the first few kicks for the quantum kicked rotator with a constant interaction
parameter. A recursive relation is derived in a self-consistent random phase
approximation which describes this superdiffusive growth of the kinetic energy
and is compared with numerical simulations. Unlike in the case of the quantum
rotator with constant interaction, a Lax pair is not found. In general the
delta-kicked interaction is found to lead to strong chaotic behaviour.Comment: 4 pages, 3 figure
Removal of acid gases and oxides of nitrogen from space cabin atmospheres
Removal of acid gases and oxides of nitrogen from spacecraft cabin atmospheres at ambient temperature
Experimental Design for the Gemini Planet Imager
The Gemini Planet Imager (GPI) is a high performance adaptive optics system
being designed and built for the Gemini Observatory. GPI is optimized for high
contrast imaging, combining precise and accurate wavefront control, diffraction
suppression, and a speckle-suppressing science camera with integral field and
polarimetry capabilities. The primary science goal for GPI is the direct
detection and characterization of young, Jovian-mass exoplanets. For plausible
assumptions about the distribution of gas giant properties at large semi-major
axes, GPI will be capable of detecting more than 10% of gas giants more massive
than 0.5 M_J around stars younger than 100 Myr and nearer than 75 parsecs. For
systems younger than 1 Gyr, gas giants more massive than 8 M_J and with
semi-major axes greater than 15 AU are detected with completeness greater than
50%. A survey targeting young stars in the solar neighborhood will help
determine the formation mechanism of gas giant planets by studying them at ages
where planet brightness depends upon formation mechanism. Such a survey will
also be sensitive to planets at semi-major axes comparable to the gas giants in
our own solar system. In the simple, and idealized, situation in which planets
formed by either the "hot-start" model of Burrows et al. (2003) or the core
accretion model of Marley et al. (2007), a few tens of detected planets are
sufficient to distinguish how planets form.Comment: 15 pages, 9 figures, revised after referee's comments and resubmitted
to PAS
Universality of the Small-Scale Dynamo Mechanism
We quantify possible differences between turbulent dynamo action in the Sun
and the dynamo action studied in idealized simulations. For this purpose we
compare Fourier-space shell-to-shell energy transfer rates of three
incrementally more complex dynamo simulations: an incompressible, periodic
simulation driven by random flow, a simulation of Boussinesq convection, and a
simulation of fully compressible convection that includes physics relevant to
the near-surface layers of the Sun. For each of the simulations studied, we
find that the dynamo mechanism is universal in the kinematic regime because
energy is transferred from the turbulent flow to the magnetic field from
wavenumbers in the inertial range of the energy spectrum. The addition of
physical effects relevant to the solar near-surface layers, including
stratification, compressibility, partial ionization, and radiative energy
transport, does not appear to affect the nature of the dynamo mechanism. The
role of inertial-range shear stresses in magnetic field amplification is
independent from outer-scale circumstances, including forcing and
stratification. Although the shell-to-shell energy transfer functions have
similar properties to those seen in mean-flow driven dynamos in each simulation
studied, the saturated states of these simulations are not universal because
the flow at the driving wavenumbers is a significant source of energy for the
magnetic field.Comment: 16 pages, 9 figures, accepted for publication in Ap
Supersymmetric minisuperspace with non-vanishing fermion number
The Lagrangean of supergravity is dimensionally reduced to one
(time-like) dimension assuming spatial homogeneity of any Bianchi type within
class A of the classification of Ellis and McCallum. The algebra of the
supersymmetry generators, the Lorentz generators, the diffeomorphism generators
and the Hamiltonian generator is determined and found to close. In contrast to
earlier work, infinitely many physical states with non-vanishing even fermion
number are found to exist in these models, indicating that minisuperspace
models in supergravity may be just as useful as in pure gravity.Comment: 4 page
The exact cosmological solution to the dynamical equations for the Bianchi IX model
Quantum geometrodynamics in extended phase space describes phenomenologically
the integrated system ``a physical object + observation means (a gravitational
vacuum condensate)''. The central place in this version of QGD belongs to the
Schrodinger equation for a wave function of the Universe. An exact solution to
the ``conditionally-classical'' set of equations in extended phase space for
the Bianchi-IX model and the appropriate solution to the Schrodinger equation
are considered. The physical adequacy of the obtained solutions to existing
concepts about possible cosmological scenarios is demonstrated. The
gravitational vacuum condensate is shown to be a cosmological evolution factor.Comment: LaTeX, 14 pages, to be published in Int. J. Mod. Phys.
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