6,704 research outputs found
Atom Lithography with Near-Resonant Light Masks: Quantum Optimization Analysis
We study the optimal focusing of two-level atoms with a near resonant
standing wave light, using both classical and quantum treatments of the
problem. Operation of the focusing setup is considered as a nonlinear spatial
squeezing of atoms in the thin- and thick-lens regimes. It is found that the
near-resonant standing wave focuses the atoms with a reduced background in
comparison with far-detuned light fields. For some parameters, the quantum
atomic distribution shows even better localization than the classical one.
Spontaneous emission effects are included via the technique of quantum Monte
Carlo wave function simulations. We investigate the extent to which
non-adiabatic and spontaneous emission effects limit the achievable minimal
size of the deposited structures.Comment: 10 pages including 11 figures in Revte
Molecular Frisbee: Motion of Spinning Molecules in Inhomogeneous Fields
Several laser techniques have been suggested and demonstrated recently for
preparing polarizable molecules in rapidly spinning states with a disc-like
angular distribution. We consider motion of these spinning discs in
inhomogeneous fields, and show that the molecular trajectories may be precisely
controlled by the tilt of the plane of the laser-induced rotation. The
feasibility of the scheme is illustrated by optical deflection of linear
molecules twirled by two delayed cross-polarized laser pulses. These results
open new ways for many applications involving molecular focusing, guiding and
trapping, and may be suitable for separating molecular mixtures by optical and
static fields
Resonance Enhanced Tunneling
Time evolution of tunneling in thermal medium is examined using the real-time
semiclassical formalism previously developed. Effect of anharmonic terms in the
potential well is shown to give a new mechanism of resonance enhanced
tunneling. If the friction from environment is small enough, this mechanism may
give a very large enhancement for the tunneling rate. The case of the
asymmetric wine bottle potential is worked out in detail.Comment: 12 pages, LATEX file with 5 PS figure
Nondegenerate parametric down conversion in coherently prepared two-level atomic gas
We describe parametric down conversion process in a two-level atomic gas,
where the atoms are in a superposition state of relevant energy levels. This
superposition results in splitting of the phase matching condition into three
different conditions. Another, more important, peculiarity of the system under
discussion is the nonsaturability of amplification coefficients with increasing
pump wave intensity, under "sideband" generation conditions
Pneumatic compression devices for in-home management of lymphedema: two case reports
The two patients in this case series had experienced long-term difficulty controlling lymphedema at home. Both patients had used numerous home therapies, including older-generation intermittent pneumatic compression devices, without success. The Flexitouch® system, an advanced pneumatic device, was prescribed to assist them with in-home efforts by providing therapy to their affected limbs in addition to the lower trunk area for the patient with lymphedema of the lower extremity; and the trunk, chest wall, and shoulder areas for the patient with lymphedema of the upper extremity. Both patients achieved successful home maintenance of lymphedema, as judged by limb volume, clinical observations, and subjective patient impressions, after incorporating the Flexitouch® system. Neither patient experienced the deleterious effects (worsening genital edema; fibrotic cuff development) that they had experienced with the older-generation intermittent pneumatic compression devices they had previously used. Incorporating the Flexitouch® system as part of maintenance may improve success for lymphedema patients who have previously struggled with in-home management
Energy diffusion in strongly driven quantum chaotic systems
The energy evolution of a quantum chaotic system under the perturbation that
harmonically depends on time is studied for the case of large perturbation, in
which the rate of transition calculated from the Fermi golden rule exceeds the
frequency of perturbation. It is shown that the energy evolution retains its
diffusive character, with the diffusion coefficient that is asymptotically
proportional to the magnitude of perturbation and to the square root of the
density of states. The results are supported by numerical calculation. They
imply the absence of the quantum-classical correspondence for the energy
diffusion and the energy absorption in the classical limit .Comment: 12 pages, 3 figures, RevTe
Smearing of phase transition due to a surface effect or a bulk inhomogeneity in ferroelectric nanostructures
The boundary conditions, customarily used in the Landau-type approach to
ferroelectric thin films and nanostructures, have to be modified to take into
account that a surface of a ferroelectric (FE) is a defect of the ``field''
type. The surface (interface) field is coupled to a normal component of
polarization and, as a result, the second order phase transitions are generally
suppressed and anomalies in response are washed out. In FE films with a
compositional (grading) or some other type of inhomogeneity, the transition
into a monodomain state is suppressed, but a transition with formation of a
domain structure may occur.Comment: 5 pages, 1 figure; the effective bias field is very large, the
estimate is adde
ASSOCIATION OF BRITISH NEUROLOGISTS SUSTAINABILITY SPECIAL INTEREST GROUP (ABN SUSTAINABILITY SIG): FORMATION, OBJECTIVES AND INVITATION
We introduce the ABN Sustainability SIG. We present our aims & objectives, and practical ways of implementing sustainability strategies in Neurology.At the 2016 ABN annual meeting, a keynote speech by Dr. David Pencheon, then director of the National Health Service Sustainability Development Unit, highlighted the relevance and importance of Sustainability in Neurology. This planted the seed for our SIG’s formation. Initial interest was gathered from an ABN newsletter notice, via word-of-mouth and informal discussions at ABN annual meetings (2017, 2018). A series of teleconferences & email discussions enabled the formation of SIG byelaws and application to the ABN council.Our aims and objectivesTo be a positive force within the ABN to highlight issues surrounding global environmental sustainability.To provide a forum to consider the impact of choices made in neurology practice on global environmental sustainability. This will cover all aspects of neurology including, but not limited to, clinical practice, service provision, technological and digital developments, meetings and ABN resources and investments.To identify areas where the choice made could impact positively on global environmental sustainability and disseminate this information to the ABN membership to inform their decisions
Dynamics of barrier penetration in thermal medium: exact result for inverted harmonic oscillator
Time evolution of quantum tunneling is studied when the tunneling system is
immersed in thermal medium. We analyze in detail the behavior of the system
after integrating out the environment. Exact result for the inverted harmonic
oscillator of the tunneling potential is derived and the barrier penetration
factor is explicitly worked out as a function of time. Quantum mechanical
formula without environment is modifed both by the potential renormalization
effect and by a dynamical factor which may appreciably differ from the
previously obtained one in the time range of 1/(curvature at the top of
potential barrier).Comment: 30 pages, LATEX file with 11 PS figure
Ising model for distribution networks
An elementary Ising spin model is proposed for demonstrating cascading
failures (break-downs, blackouts, collapses, avalanches, ...) that can occur in
realistic networks for distribution and delivery by suppliers to consumers. A
ferromagnetic Hamiltonian with quenched random fields results from policies
that maximize the gap between demand and delivery. Such policies can arise in a
competitive market where firms artificially create new demand, or in a solidary
environment where too high a demand cannot reasonably be met. Network failure
in the context of a policy of solidarity is possible when an initially active
state becomes metastable and decays to a stable inactive state. We explore the
characteristics of the demand and delivery, as well as the topological
properties, which make the distribution network susceptible of failure. An
effective temperature is defined, which governs the strength of the activity
fluctuations which can induce a collapse. Numerical results, obtained by Monte
Carlo simulations of the model on (mainly) scale-free networks, are
supplemented with analytic mean-field approximations to the geometrical random
field fluctuations and the thermal spin fluctuations. The role of hubs versus
poorly connected nodes in initiating the breakdown of network activity is
illustrated and related to model parameters
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