1,339 research outputs found
Atomistic Theory of Coherent Spin Transfer between Molecularly Bridged Quantum Dots
Time-resolved Faradary rotation experiments have demonstrated coherent
transfer of electron spin between CdSe colloidal quantum dots coupled by
conjugated molecules. We employ here a Green's function approach, using
semi-empirical tight-binding to treat the nanocrystal Hamiltonian and Extended
Huckel theory to treat the linking molecule Hamiltonian, to obtain the coherent
transfer probabilities from atomistic calculations, without the introduction of
any new parameters. Calculations on 1,4-dithiolbenzene and
1,4-dithiolcyclohexane linked nanocrystals agree qualitatively with experiment
and provide support for a previous transfer Hamiltonian model. We find a
striking dependence on the transfer probabilities as a function of nanocrystal
surface site attachment and linking molecule conformation. Additionally, we
predict quantum interference effects in the coherent transfer probabilities for
2,7-dithiolnaphthalene and 2,6-dithiolnaphthalene linking molecules. We suggest
possible experiments based on these results that would test the coherent,
through-molecule transfer mechanism.Comment: 12 pages, 9 figures. Submitted Phys. Rev.
Quantum phases of dipolar rotors on two-dimensional lattices
The quantum phase transitions of dipoles confined to the vertices of two
dimensional (2D) lattices of square and triangular geometry is studied using
path integral ground state quantum Monte Carlo (PIGS). We analyze the phase
diagram as a function of the strength of both the dipolar interaction and a
transverse electric field. The study reveals the existence of a class of
orientational phases of quantum dipolar rotors whose properties are determined
by the ratios between the strength anisotropic dipole-dipole interaction, the
strength of the applied transverse field, and the rotational constant. For the
triangular lattice, the generic orientationally disordered phase found at zero
and weak values of both dipolar interaction strength and applied field, is
found to show a transition to a phase characterized by net polarization in the
lattice plane as the strength of the dipole-dipole interaction is increased,
independent of the strength of the applied transverse field, in addition to the
expected transition to a transverse polarized phase as the electric field
strength increases. The square lattice is also found to exhibit a transition
from a disordered phase to an ordered phase as the dipole-dipole interaction
strength is increased, as well as the expected transition to a transverse
polarized phase as the electric field strength increases. In contrast to the
situation with a triangular lattice, on square lattices the ordered phase at
high dipole-dipole interaction strength possesses a striped ordering. The
properties of these quantum dipolar rotor phases are dominated by the
anisotropy of the interaction and provide useful models for developing quantum
phases beyond the well-known paradigms of spin Hamiltonian models, realizing in
particular a novel physical realization of a quantum rotor-like Hamiltonian
that possesses an anisotropic long range interaction.Comment: Updated credit line and changed line spacin
Analytic, Group-Theoretic Density Profiles for Confined, Correlated N-Body Systems
Confined quantum systems involving identical interacting particles are to
be found in many areas of physics, including condensed matter, atomic and
chemical physics. A beyond-mean-field perturbation method that is applicable,
in principle, to weakly, intermediate, and strongly-interacting systems has
been set forth by the authors in a previous series of papers. Dimensional
perturbation theory was used, and in conjunction with group theory, an analytic
beyond-mean-field correlated wave function at lowest order for a system under
spherical confinement with a general two-body interaction was derived. In the
present paper, we use this analytic wave function to derive the corresponding
lowest-order, analytic density profile and apply it to the example of a
Bose-Einstein condensate.Comment: 15 pages, 2 figures, accepted by Physics Review A. This document was
submitted after responding to a reviewer's comment
Change in Metabolic Syndrome and Cardiorespiratory Fitness Following Exercise Training – The Ball State Adult Fitness Longitudinal Lifestyle Study (BALL ST)
This observational cohort study indicates an inverse relationship between the change in CRF and the change in MetS severity following exercise training. These results suggest that participation in a community-based exercise program yields significant improvements in CRF, MetS risk factors, the prevalence of the binary MetS, and the MetS severity score. Improvement in CRF through exercise training should be a primary prevention strategy for MetS
Entangling flux qubits with a bipolar dynamic inductance
We propose a scheme to implement variable coupling between two flux qubits
using the screening current response of a dc Superconducting QUantum
Interference Device (SQUID). The coupling strength is adjusted by the current
bias applied to the SQUID and can be varied continuously from positive to
negative values, allowing cancellation of the direct mutual inductance between
the qubits. We show that this variable coupling scheme permits efficient
realization of universal quantum logic. The same SQUID can be used to determine
the flux states of the qubits.Comment: 4 pages, 4 figure
Physical factors contributing to rural water supply functionality performance in Malawi
This report communicates the findings generated from one of the project surveys – deconstruction and forensic analysis of 50 individual water points in Malawi. The report presents the new data generated to Malawi’s groundwater resource potential; the nature and condition of hand-pump borehole installations; and the significance of both of these factors to service performance.
Based on the evidence collected, the main physical factor affecting functionality performance within Malawi is shown to be the poor condition of handpump components. Functionality of handpumps is considerably higher than in the other study countries, Ethiopia and Uganda, and the resource potential, depth to groundwater and recharge are generally favourable. Improved systems for rapid maintenance and repair would help increase functionality further.
This finding should not, however, be considered to be the only driving force of functionality outcomes in these regions of Malawi, and the results of this survey need to be examined alongside the wider project findings. Wider institutional arrangements, resources and dynamics, are likely to play a significant role in the implementation of appropriate borehole construction, siting and design; procurement processes; and the management capacity available for water points at national to local levels
Normalizing Cardiorespiratory Fitness To Fat-free Mass Improves Mortality Risk Prediction In Overweight Adults From The Ball St Cohort: 2361 Board #280 May 28 3:00 PM - 4:30 PM
Cardiorespiratory fitness(CRF) is a significant predictor of mortality outcomes in various populations, including overweight and obese adults. However, CRF is commonly expressed normalized to total body weight (VO2peakTBW) which may weaken the relationship in obese adults as fat-free mass (FFM) is directly related to CRF, and increased body fat is associated with lower CRF in adults. Therefore, this study aimed to assess the relationship between CRF normalized for FFM(VO2peakFFM) and all-cause mortality, as well as compare the predictive ability of VO2peakFFM and VO2peakTBW in a cohort of self-referred overweight and obese adults
Quantum dynamics of local phase differences between reservoirs of driven interacting bosons separated by simple aperture arrays
We present a derivation of the effective action for the relative phase of
driven, aperture-coupled reservoirs of weakly-interacting condensed bosons from
a (3+1)-D microscopic model with local U(1) gauge symmetry. We show that
inclusion of local chemical potential and driving velocity fields as a gauge
field allows derivation of the hydrodynamic equations of motion for the driven
macroscopic phase differences across simple aperture arrays. For a single
aperture, the current-phase equation for driven flow contains sinusoidal,
linear, and current-bias contributions. We compute the renormalization group
(RG) beta function of the periodic potential in the effective action for small
tunneling amplitudes and use this to analyze the temperature dependence of the
low-energy current-phase relation, with application to the transition from
linear to sinusoidal current-phase behavior observed in experiments by
Hoskinson et al. \cite{packard} for liquid He driven through nanoaperture
arrays. Extension of the microscopic theory to a two-aperture array shows that
interference between the microscopic tunneling contributions for individual
apertures leads to an effective coupling between apertures which amplifies the
Josephson oscillations in the array. The resulting multi-aperture current-phase
equations are found to be equivalent to a set of equations for coupled pendula,
with microscopically derived couplings.Comment: 16 pages, 5 figures v2: typos corrected, RG phase diagram correcte
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