5,189 research outputs found
Quantifying the effectiveness of silver ring splints to correct swan-neck deformity
Swan-neck deformity is a common symptom of rheumatoid arthritis affecting the fingers. It can be classified by hyperextension of the proximal interphalangeal (PIP) joint and flexion of the distal interphalangeal joint [1]. Methods to correct hyperextension of the PIP joint range from surgery to splinting techniques [2]. Silver ring splints (SRSs) were recently identified as a possible alternative to surgery and traditional thermoplastic splints because patient adherence was improved by their appearance [3]. The objective of this study was to investigate whether the SRSs restrict PIP joint hyperextension during a fine dexterity task
Spatiotemporal dynamics of quantum jumps with Rydberg atoms
We study the nonequilibrium dynamics of quantum jumps in a one-dimensional
chain of atoms. Each atom is driven on a strong transition to a short-lived
state and on a weak transition to a metastable state. We choose the metastable
state to be a Rydberg state so that when an atom jumps to the Rydberg state, it
inhibits or enhances jumps in the neighboring atoms. This leads to rich
spatiotemporal dynamics that are visible in the fluorescence of the strong
transition.Comment: 10 page
Nonadiabatic electron heat pump
We investigate a mechanism for extracting heat from metallic conductors based
on the energy-selective transmission of electrons through a spatially
asymmetric resonant structure subject to ac driving. This quantum refrigerator
can operate at zero net electronic current as it replaces hot by cold electrons
through two energetically symmetric inelastic channels. We present numerical
results for a specific heterostructure and discuss general trends. We also
explore the conditions under which the cooling rate may approach the ultimate
limit given by the quantum of cooling power.Comment: 4 pages, 3 figures; published version, typos correcte
Andreev reflection in bosonic condensates
We study the bosonic analog of Andreev reflection at a normal-superfluid
interface where the superfluid is a boson condensate. We model the normal
region as a zone where nonlinear effects can be neglected. Against the
background of a decaying condensate, we identify a novel contribution to the
current of reflected atoms. The group velocity of this Andreev reflected
component differs from that of the normally reflected one. For a
three-dimensional planar or two-dimensional linear interface Andreev reflection
is neither specular nor conjugate.Comment: 5 pages, 3 figures. Text revise
Anisotropic sub-Doppler laser cooling in dysprosium magneto-optical traps
Magneto-optical traps (MOTs) of Er and Dy have recently been shown to exhibit
population-wide sub-Doppler cooling due to their near degeneracy of excited and
ground state Lande g factors. We discuss here an additional, unusual intra-MOT
sub-Doppler cooling mechanism that appears when the total Dy MOT cooling laser
intensity and magnetic quadrupole gradient increase beyond critical values.
Specifically, anisotropically sub-Doppler-cooled cores appear, and their
orientation with respect to the quadrupole axis flips at a critical ratio of
the MOT laser intensity along the quadrupole axis versus that in the plane of
symmetry. This phenomenon can be traced to a loss of the velocity-selective
resonance at zero velocity in the cooling force along directions in which the
atomic polarization is oriented by the quadrupole field. We present data
characterizing this anisotropic laser cooling phenomenon and discuss a
qualitative model for its origin based on the extraordinarily large Dy magnetic
moment and Dy's near degenerate g factors.Comment: 4 pages, 5 figure
Two-Level Systems in Evaporated Amorphous Silicon
In -beam evaporated amorphous silicon (-Si), the densities of two-level
systems (TLS), and , determined from specific heat
and internal friction measurements, respectively, have been shown to
vary by over three orders of magnitude. Here we show that and
are proportional to each other with a constant of
proportionality that is consistent with the measurement time dependence
proposed by Black and Halperin and does not require the introduction of
additional anomalous TLS. However, and depend strongly
on the atomic density of the film () which depends on both film
thickness and growth temperature suggesting that the -Si structure is
heterogeneous with nanovoids or other lower density regions forming in a dense
amorphous network. A review of literature data shows that this atomic density
dependence is not unique to -Si. These findings suggest that TLS are not
intrinsic to an amorphous network but require a heterogeneous structure to
form
Coherent Control of Trapped Bosons
We investigate the quantum behavior of a mesoscopic two-boson system produced
by number-squeezing ultracold gases of alkali metal atoms. The quantum Poincare
maps of the wavefunctions are affected by chaos in those regions of the phase
space where the classical dynamics produces features that are comparable to
hbar. We also investigate the possibility for quantum control in the dynamics
of excitations in these systems. Controlled excitations are mediated by pulsed
signals that cause Stimulated Raman Adiabatic passage (STIRAP) from the ground
state to a state of higher energy. The dynamics of this transition is affected
by chaos caused by the pulses in certain regions of the phase space. A
transition to chaos can thus provide a method of controlling STIRAP.Comment: 17 figures, Appended a paragraph on section 1 and explained details
behind the hamiltonian on section
- …