89,657 research outputs found
Phase transformations induced by spherical indentation in ion-implanted amorphous silicon
The deformation behavior of ion-implanted (unrelaxed) and annealed ion-implanted (relaxed) amorphous silicon(a-Si) under spherical indentation at room temperature has been investigated. It has been found that the mode of deformation depends critically on both the preparation of the amorphous film and the scale of the mechanical deformation.Ex situmeasurements, such as Raman microspectroscopy and cross-sectional transmission electron microscopy, as well as in situ electrical measurements reveal the occurrence of phase transformations in all relaxed a-Si films. The preferred deformation mode of unrelaxed a-Si is plastic flow, only under certain high load conditions can this state of a-Si be forced to transform. In situ electrical measurements have revealed more detail of the transformation process during both loading and unloading. We have used ELASTICA simulations to obtain estimates of the depth of the metallic phase as a function of load, and good agreement is found with the experiment. On unloading, a clear change in electrical conductivity is observed to correlate with a “pop-out” event on load versus penetration curves
Nodal Domain Statistics for Quantum Maps, Percolation and SLE
We develop a percolation model for nodal domains in the eigenvectors of
quantum chaotic torus maps. Our model follows directly from the assumption that
the quantum maps are described by random matrix theory. Its accuracy in
predicting statistical properties of the nodal domains is demonstrated by
numerical computations for perturbed cat maps and supports the use of
percolation theory to describe the wave functions of general hamiltonian
systems, where the validity of the underlying assumptions is much less clear.
We also demonstrate that the nodal domains of the perturbed cat maps obey the
Cardy crossing formula and find evidence that the boundaries of the nodal
domains are described by SLE with close to the expected value of 6,
suggesting that quantum chaotic wave functions may exhibit conformal invariance
in the semiclassical limit.Comment: 4 pages, 5 figure
Deterministic dense coding and entanglement entropy
We present an analytical study of the standard two-party deterministic
dense-coding protocol, under which communication of perfectly distinguishable
messages takes place via a qudit from a pair of non-maximally entangled qudits
in pure state |S>. Our results include the following: (i) We prove that it is
possible for a state |S> with lower entanglement entropy to support the sending
of a greater number of perfectly distinguishable messages than one with higher
entanglement entropy, confirming a result suggested via numerical analysis in
Mozes et al. [Phys. Rev. A 71 012311 (2005)]. (ii) By explicit construction of
families of local unitary operators, we verify, for dimensions d = 3 and d=4, a
conjecture of Mozes et al. about the minimum entanglement entropy that supports
the sending of d + j messages, j = 2, ..., d-1; moreover, we show that the j=2
and j= d-1 cases of the conjecture are valid in all dimensions. (iii) Given
that |S> allows the sending of K messages and has the square roof of c as its
largest Schmidt coefficient, we show that the inequality c <= d/K, established
by Wu et al. [ Phys. Rev. A 73, 042311 (2006)], must actually take the form c <
d/K if K = d+1, while our constructions of local unitaries show that equality
can be realized if K = d+2 or K = 2d-1.Comment: 19 pages, 2 figures. Published versio
High resolution radio observations of the colliding-wind binary WR140
Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of
the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented
for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in
the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that
rotates as the orbit progresses. We interpret this rotation as due to the O
star moving from SE to approximately E of the WR star, which leads to solutions
for the orbit inclination of 122+/-5 deg, the longitude of the ascending node
of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to
WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a
supergiant. The inclination implies the mass of the WR and O star to be 20+/-4
and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of
0.22, with an expected half-opening angle for the WCR of 63 deg, consistent
with 65+/-10 deg derived from the VLBA observations. Total flux measurements
from Very Large Array (VLA) observations show the radio emission from WR140 is
very closely the same from one orbit to the next, pointing strongly toward
emission, absorption and cooling mechanism(s) that are controlled largely by
the orbital motion. The synchrotron spectra evolve dramatically through the
orbital phases observed, exhibiting both optically thin and optically thick
emission. We discuss a number of absorption and cooling mechanisms that may
determine the evolution of the synchrotron spectrum with orbital phase.Comment: Accepted by ApJ, to appear in v623, April 20, 2005. 14 pages, 13
figs, requires emulateapj.cls. A version with full resolution figs can be
obtained from http://www.drao.nrc.ca/~smd/preprint/wr140_data.pd
PACE and EISCAT radar observations of short-lived flow bursts on the nightside
Concurrent observations from two widely spaced radar experiments of quasi periodic flow bursts in the nightside are presented. The flow bursts closely resemble single radar observations reported by Williams et al. By using the Polar Anglo-American Conjugate Experiment (PACE) HF radar array at Halley Bay in conjunction with the EISCAT Common Program (CP) 2-D experiment, the flow bursts are shown to be a global phenomenon and important information as to their development and propagation can be determined
Loading Bose condensed atoms into the ground state of an optical lattice
We optimize the turning on of a one-dimensional optical potential, V_L(x,t) =
S(t) V_0 cos^2(kx) to obtain the optimal turn-on function S(t) so as to load a
Bose-Einstein condensate into the ground state of the optical lattice of depth
V_0. Specifically, we minimize interband excitations at the end of the turn-on
of the optical potential at the final ramp time t_r, where S(t_r) = 1, given
that S(0) = 0. Detailed numerical calculations confirm that a simple unit cell
model is an excellent approximation when the turn-on time t_r is long compared
with the inverse of the band excitation frequency and short in comparison with
nonlinear time \hbar/\mu where \mu is the chemical potential of the condensate.
We demonstrate using the Gross-Pitaevskii equation with an optimal turn-on
function S(t) that the ground state of the optical lattice can be loaded with
very little excitation even for times t_r on the order of the inverse band
excitation frequency
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