3,859 research outputs found
MT SCORP: Behavioral Risk Factor Surveillance System: Outdoor Recreation and Resident Health
The Behavioral Risk Factor Surveillance System (BRFSS) provides state-based data on health and risk behaviors among adults. Several supplemental outdoor recreation related questions were included in the 2011 questionnaire to assist with the State Comprehensive Outdoor Recreation Plan process and are analyzed in this report
Optical properties of V2O3 in its whole phase diagram
Vanadium sesquioxide V2O3 is considered a textbook example of Mott-Hubbard
physics. In this paper we present an extended optical study of its whole
temperature/doping phase diagram as obtained by doping the pure material with
M=Cr or Ti atoms (V1-xMx)2O3. We reveal that its thermodynamically stable
metallic and insulating phases, although macroscopically equivalent, show very
different low-energy electrodynamics. The Cr and Ti doping drastically change
both the antiferromagnetic gap and the paramagnetic metallic properties. A
slight chromium content induces a mesoscopic electronic phase separation, while
the pure compound is characterized by short-lived quasiparticles at high
temperature. This study thus provides a new comprehensive scenario of the
Mott-Hubbard physics in the prototype compound V2O3
Manipulation of Single Neutral Atoms in Optical Lattices
We analyze a scheme to manipulate quantum states of neutral atoms at
individual sites of optical lattices using focused laser beams. Spatial
distributions of focused laser intensities induce position-dependent energy
shifts of hyperfine states, which, combined with microwave radiation, allow
selective manipulation of quantum states of individual target atoms. We show
that various errors in the manipulation process are suppressed below
with properly chosen microwave pulse sequences and laser parameters. A similar
idea is also applied to measure quantum states of single atoms in optical
lattices.Comment: 5 pages, 3 figure
Coherent Control of Ultracold Collisions with Chirped Light: Direction Matters
We demonstrate the ability to coherently control ultracold atomic Rb
collisions using frequency-chirped light on the nanosecond time scale. For
certain center frequencies of the chirp, the rate of inelastic trap-loss
collisions induced by negatively chirped light is dramatically suppressed
compared to the case of a positive chirp. We attribute this to a fundamental
asymmetry in the system: an excited wavepacket always moves inward on the
attractive molecular potential. For a positive chirp, the resonance condition
moves outward in time, while for a negative chirp, it moves inward, in the same
direction as the excited wavepacket; this allows multiple interactions between
the wavepacket and the light, enabling the wavepacket to be returned coherently
to the ground state. Classical and quantum calculations support this
interpretation
Quasiparticle evolution and pseudogap formation in V2O3: An infrared spectroscopy study
The infrared conductivity of V2O3 is measured in the whole phase diagram.
Quasiparticles appear above the Neel temperature TN and eventually disappear
further enhancing the temperature, leading to a pseudogap in the optical
spectrum above 425 K. Our calculations demonstrate that this loss of coherence
can be explained only if the temperature dependence of lattice parameters is
considered. V2O3 is therefore effectively driven from the metallic to the
insulating side of the Mott transition as the temperature is increased.Comment: 5 pages, 3 figure
Bichromatic Slowing of Metastable Helium
We examine two approaches for significantly extending the velocity range of
the optical bichromatic force (BCF), to make it useful for laser deceleration
of atomic and molecular beams. First, we present experimental results and
calculations for BCF deceleration of metastable helium using very large BCF
detunings, and discuss the limitations of this approach. We consider in detail
the constraints, both inherent and practical, that set the usable upper limit
of the BCF. We then show that a more promising approach is to utilize a BCF
profile with a relatively small velocity range in conjunction with chirped
Doppler shifts, to keep the force resonant with the atoms as they are slowed.
In an initial experimental test of this chirped BCF method, helium atoms are
slowed by m/s using a BCF profile with a velocity width of m/s. Straightforward scaling of the present results indicates that a
decelerator for He* capable of loading a magneto-optical trap (MOT) can yield a
brightness comparable to a much larger Zeeman slower.Comment: 11 pages, 9 figures. Published in Phys. Rev.
Levy distribution in many-particle quantum systems
Levy distribution, previously used to describe complex behavior of classical
systems, is shown to characterize that of quantum many-body systems. Using two
complimentary approaches, the canonical and grand-canonical formalisms, we
discovered that the momentum profile of a Tonks-Girardeau gas, -- a
one-dimensional gas of impenetrable (hard-core) bosons, harmonically
confined on a lattice at finite temperatures, obeys Levy distribution. Finally,
we extend our analysis to different confinement setups and demonstrate that the
tunable Levy distribution properly reproduces momentum profiles in
experimentally accessible regions. Our finding allows for calibration of
complex many-body quantum states by using a unique scaling exponent.Comment: 7 pages, 6 figures, results are generalized, new examples are adde
Structural dichroism in the antiferromagnetic insulating phase of V_2O_3
We performed near-edge x-ray absorption spectroscopy (XANES) at V K edge in
the antiferromagnetic insulating (AFI) phase of a 2.8% Cr-doped V_2O_3 single
crystal. Linear dichroism of several percent is measured in the hexagonal plane
and found to be in good agreement with ab-initio calculations based on multiple
scattering theory. This experiment definitively proves the structural origin of
the signal and therefore solves a controversy raised by previous
interpretations of the same dichroism as non-reciprocal. It also calls for a
further investigation of the role of the magnetoelectric annealing procedure in
cooling to the AFI phase.Comment: 4 pages 3 figures. To be published in Phys. Rev. B (2005
Loss of molecules in magneto-electrostatic traps due to nonadiabatic transitions
We analyze the dynamics of a paramagnetic, dipolar molecule in a generic
"magneto-electrostatic'' trap where both magnetic and electric fields may be
present. The potential energy that governs the dynamics of the molecules is
found using a reduced molecular model that incorporates the main features of
the system. We discuss the shape of the trapping potentials for different field
geometries, as well as the possibility of nonadiabatic transitions to untrapped
states, i.e., the analog of Majorana transitions in a quadrupole magnetic
atomic trap. Maximizing the lifetime of molecules in a trap is of great concern
in current experiments, and we assess the effect of nonadiabatic transitions on
obtainable trap lifetimes.Comment: 13 pages, 6 figure
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