960 research outputs found
State selection in the noisy stabilized Kuramoto-Sivashinsky equation
In this work, we study the 1D stabilized Kuramoto Sivashinsky equation with
additive uncorrelated stochastic noise. The Eckhaus stable band of the
deterministic equation collapses to a narrow region near the center of the
band. This is consistent with the behavior of the phase diffusion constants of
these states. Some connections to the phenomenon of state selection in driven
out of equilibrium systems are made.Comment: 8 pages, In version 3 we corrected minor/typo error
Dynamical Semigroup Description of Coherent and Incoherent Particle-Matter Interaction
The meaning of statistical experiments with single microsystems in quantum
mechanics is discussed and a general model in the framework of non-relativistic
quantum field theory is proposed, to describe both coherent and incoherent
interaction of a single microsystem with matter. Compactly developing the
calculations with superoperators, it is shown that the introduction of a time
scale, linked to irreversibility of the reduced dynamics, directly leads to a
dynamical semigroup expressed in terms of quantities typical of scattering
theory. Its generator consists of two terms, the first linked to a coherent
wavelike behaviour, the second related to an interaction having a measuring
character, possibly connected to events the microsystem produces propagating
inside matter. In case these events breed a measurement, an explicit
realization of some concepts of modern quantum mechanics ("effects" and
"operations") arises. The relevance of this description to a recent debate
questioning the validity of ordinary quantum mechanics to account for such
experimental situations as, e.g., neutron-interferometry, is briefly discussed.Comment: 22 pages, latex, no figure
Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states
The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between
two remote physical systems is a primitive object on the study of quantum
entanglement. In order to understand the entanglement in canonical
continuous-variable systems, a pair of the EPR-like uncertainties is an
essential tool. Here, we consider a normalized pair of the EPR-like
uncertainties and introduce a state-overlap to a classically correlated mixture
of coherent states. The separable condition associated with this state-overlap
determines the strength of the EPR-like correlation on a coherent-state basis
in order that the state is entangled. We show that the coherent-state-based
condition is capable of detecting the class of two-mode Gaussian entangled
states. We also present an experimental measurement scheme for estimation of
the state-overlap by a heterodyne measurement and a photon detection with a
feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous
versions was moved into another paper: Journal of Atomic, Molecular, and
Optical Physics, 2012, 854693 (2012).
http://www.hindawi.com/journals/jamop/2012/854693
Macroscopic limit of a solvable dynamical model
The interaction between an ultrarelativistic particle and a linear array made
up of two-level systems (^^ ^^ AgBr" molecules) is studied by making use of
a modified version of the Coleman-Hepp Hamiltonian. Energy-exchange processes
between the particle and the molecules are properly taken into account, and the
evolution of the total system is calculated exactly both when the array is
initially in the ground state and in a thermal state. In the macroscopic limit
(), the system remains solvable and leads to interesting
connections with the Jaynes-Cummings model, that describes the interaction of a
particle with a maser. The visibility of the interference pattern produced by
the two branch waves of the particle is computed, and the conditions under
which the spin array in the limit behaves as a ^^ ^^
detector" are investigated. The behavior of the visibility yields good insights
into the issue of quantum measurements: It is found that, in the
thermodynamical limit, a superselection-rule space appears in the description
of the (macroscopic) apparatus. In general, an initial thermal state of the ^^
^^ detector" provokes a more substantial loss of quantum coherence than an
initial ground state. It is argued that a system decoheres more as the
temperature of the detector increases. The problem of ^^ ^^ imperfect
measurements" is also shortly discussed.Comment: 30 pages, report BA-TH/93-13
Non-Equilibrium Ionization States of GRB Environments
Iron spectral features are thought to be the best tracer of a progenitor of
gamma-ray bursts (GRBs). The detections of spectral features such as an iron
line and/or a Radiative Recombination edge and Continuum (RRC) were reported in
four X-ray afterglows of GRBs. However their properties were different each
other burst by burst. For example, Chandra observation of GRB 991216 reported
both the strong H-like iron line together with its RRC. On the contrary,
Yoshida et al. (2001) report only a detection of the strong RRC in GRB 970828
with ASCA. Since it is difficult to produce the strong RRC, we have to consider
special condition for the line and/or the RRC forming region. In this paper, we
point out a possibility of a ``non-equilibrium ionization state'' for the line
and the RRC forming region.Comment: 10pages, 2figures. Accepted for ApJL. This is a companion paper by
A.Yoshida et. a
Blunt apical dissection during anatomic radical retropubic prostatectomy
<p>Abstract</p> <p>Background</p> <p>Meticulous apical dissection during a radical prostatectomy is imperative to achieve desirable pathologic and quality of life outcomes.</p> <p>Findings</p> <p>We describe a novel technique using careful blunt dissection to better delineate the apex of the prostate, providing a simple means to potentially lessen positive surgical margins at the apex and promote better continence and erectile function in men undergoing an anatomic radical prostatectomy.</p> <p>Median operative time and blood loss were 190 minutes and 675 mL, respectively. Only 10 percent of the patients with positive surgical margins were found to have apical positive surgical margins. Ninety-three percent of patients reported no urinary leakage.</p> <p>Conclusion</p> <p>We believe our technique of isolating the DVC with blunt dissection and then ligating and transecting the DVC to be feasible approach that requires larger studies to truly confirm its utility.</p
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
Gamma-Ray Burst and Relativistic Shells: The Surface Filling Factor
The variability observed in many complex gamma-ray bursts (GRBs) is
inconsistent with causally connected variations in a single, symmetric,
relativistic shell interacting with the ambient material ("external shocks").
Rather, the symmetry of the shell must be broken on an angular scale much
smaller than Gamma^{-1} where Gamma is the bulk Lorentz factor for the shell.
The observed variability in the external shock models arises from the number of
causally connected regions that (randomly) become active. We define the
"surface filling factor" to be the ratio of the area of causally connected
regions that become active to the observable area of the shell. From the
observed variability in 52 BATSE bursts, we estimate the surface filling factor
to be typically 0.005 although some values are near unity. We find that the
surface filling factor is about 0.1 Delta T/T in both the constant Gamma phase
(which probably produces the GRB) and the deaccelerating phase (which probably
produces the x-ray afterglows). Here, \Delta T is a typical time scale of
variability and T is the time since the initial signal. We analyze the 2 hr
flare seen by ASCA 36 hr after the GRB and conclude that the surface filling
factor must be small (0.001) in the x-ray afterglow phase as well. Explanations
for low surface filling factor can either require more or less energy (by a
factor of about 1000) compared to that expected for a symmetric shell.Comment: 26 pages, 5 embedded figures, Latex, revised version as in press,
ApJ, added figure to show the possible expanding shell geometries that can
give low filling facto
- âŠ