1,235 research outputs found
Reflection of light from a disordered medium backed by a phase-conjugating mirror
This is a theoretical study of the interplay of optical phase-conjugation and
multiple scattering. We calculate the intensity of light reflected by a
phase-conjugating mirror when it is placed behind a disordered medium. We
compare the results of a fully phase-coherent theory with those from the theory
of radiative transfer. Both methods are equivalent if the dwell time
\tau_{dwell} of a photon in the disordered medium is much larger than the
inverse of the frequency shift 2\Delta\omega acquired at the phase-conjugating
mirror. When \tau_{dwell} \Delta\omega < 1, in contrast, phase coherence
drastically affects the reflected intensity. In particular, a minimum in the
dependence of the reflectance on the disorder strength disappears when
\Delta\omega is reduced below 1/\tau_{dwell}. The analogies and differences
with Andreev reflection of electrons at the interface between a normal metal
and a superconductor are discussed.Comment: 27 pages RevTeX with 11 figures included with psfi
Different carbon isotope fractionation patterns during the development of phototrophic freshwater and marine biofilms
Natural phototrophic biofilms are influenced by a broad array of abiotic and biotic factors and vary over temporal and spatial scales. Different developmental stages can be distinguished and growth rates will vary due to the thickening of the biofilm, which is expected to lead to a limitation of light or mass transport. This study shows that variation in CO<sub>2(aq)</sub> availability leads to a fractionation shift and thereby affects &delta;<sup>13</sup>C signatures during biofilm development. For phototrophic freshwater biofilms it was found that the &delta;<sup>13</sup>C value became less negative with the thickening of the biofilm, while the opposite trend was found in marine biofilms. Modeling and pH profiling indicated that the trend in the freshwater system was caused by an increase in CO<sub>2(aq)</sub> limitation resulting in an increase of HCO<sub>3</sub><sup>&minus;</sup> as C-source. The opposite trend in the marine system could be explained by a higher heterotrophic biomass and activity causing a higher carbon recycling and thereby lower &delta;<sup>13</sup>C values. We conclude that &delta;<sup>13</sup>C was more related to the net areal photosynthesis rate and carbon recycling, rather than to the growth rate of the biofilms
Spectral Statistics in Chiral-Orthogonal Disordered Systems
We describe the singularities in the averaged density of states and the
corresponding statistics of the energy levels in two- (2D) and
three-dimensional (3D) chiral symmetric and time-reversal invariant disordered
systems, realized in bipartite lattices with real off-diagonal disorder. For
off-diagonal disorder of zero mean we obtain a singular density of states in 2D
which becomes much less pronounced in 3D, while the level-statistics can be
described by semi-Poisson distribution with mostly critical fractal states in
2D and Wigner surmise with mostly delocalized states in 3D. For logarithmic
off-diagonal disorder of large strength we find indistinguishable behavior from
ordinary disorder with strong localization in any dimension but in addition
one-dimensional Dyson-like asymptotic spectral singularities. The
off-diagonal disorder is also shown to enhance the propagation of two
interacting particles similarly to systems with diagonal disorder. Although
disordered models with chiral symmetry differ from non-chiral ones due to the
presence of spectral singularities, both share the same qualitative
localization properties except at the chiral symmetry point E=0 which is
critical.Comment: 13 pages, Revtex file, 8 postscript files. It will appear in the
special edition of J. Phys. A for Random Matrix Theor
Phase III randomised controlled trial on PSMA PET/CT guided hypofractionated salvage prostate bed radiotherapy of biochemical failure after radical prostatectomy for prostate cancer (PERYTON-trial):study protocol
BACKGROUND: Salvage external beam radiotherapy (sEBRT) for patients with a biochemical recurrence (BCR) after radical prostatectomy provides a 5-year biochemical progression-free survival up to 60%. Multiple studies have shown that dose escalation to the primary prostate tumour improves treatment outcome. However, data is lacking on the role of dose escalation in the recurrent salvage setting. The main objective of the PERYTON-trial is to investigate whether treatment outcome of sEBRT for patients with a BCR after prostatectomy can be improved by increasing the biological effective radiation dose using hypofractionation. Moreover, patients will be staged using the PSMA PET/CT scan, which is superior to conventional imaging modalities in detecting oligometastases. METHODS: The PERYTON-study is a prospective multicentre open phase III randomised controlled trial. We aim to include 538 participants (269 participants per treatment arm) with a BCR after prostatectomy, a PSA-value of < 1.0 ng/mL and a recent negative PSMA PET/CT scan. Participants will be randomised in a 1:1 ratio between the conventional fractionated treatment arm (35 × 2 Gy) and the experimental hypofractionated treatment arm (20 × 3 Gy). The primary endpoint is the 5-year progression-free survival after treatment. The secondary endpoints include toxicity, quality of life and disease specific survival. DISCUSSION: Firstly, the high rate of BCR after sEBRT may be due to the presence of oligometastases, for which local sEBRT is inappropriate. With the use of the PSMA PET/CT before sEBRT, patients with oligometastases will be excluded from intensive local treatment to avoid unnecessary toxicity. Secondly, the currently applied radiation dose for sEBRT may be too low to achieve adequate local control, which may offer opportunity to enhance treatment outcome of sEBRT by increasing the biologically effective radiotherapy dose to the prostate bed. TRIAL REGISTRATION: This study is registered at ClinicalTrials.gov (Identifier: NCT04642027). Registered on 24 November 2020 – Retrospectively registered. The study protocol was approved by the accredited Medical Ethical Committee (METc) of all participating hospitals (date METc review: 23-06-2020, METc registration number: 202000239). Written informed consent will be obtained from all participants
Effect of inelastic scattering on parametric pumping
Pumping of charge in phase-coherent mesoscopic systems due to the
out-of-phase modulation of two parameters has recently found considerable
interest. We investigate the effect of inelastic processes on the adiabatically
pumped current through a two terminal mesoscopic sample. We find that the loss
of coherence does not suppress the pumped charge but rather an additional
physical mechanism for an incoherent pump effect comes into play. In a fully
phase incoherent system the pump effect is similar to a rectification effect
Non-perturbative calculation of the probability distribution of plane-wave transmission through a disordered waveguide
A non-perturbative random-matrix theory is applied to the transmission of a
monochromatic scalar wave through a disordered waveguide. The probability
distributions of the transmittances T_{mn} and T_n=\sum_m T_{mn} of an incident
mode n are calculated in the thick-waveguide limit, for broken time-reversal
symmetry. A crossover occurs from Rayleigh or Gaussian statistics in the
diffusive regime to lognormal statistics in the localized regime. A
qualitatively different crossover occurs if the disordered region is replaced
by a chaotic cavity. ***Submitted to Physical Review E.***Comment: 7 pages, REVTeX-3.0, 5 postscript figures appended as self-extracting
archive. A complete postscript file with figures and text (4 pages) is
available from http://rulgm4.LeidenUniv.nl/preprints.htm
Proposal For A Quantum Hall Pump
A device is proposed that is similar in spirit to the electron turnstile
except that it operates within a quantum Hall fluid. In the integer quantum
Hall regime, this device pumps an integer number of electrons per cycle. In the
fractional regime, it pumps an integer number of fractionally charged
quasiparticles per cycle. It is proposed that such a device can make an
accurate measurement of the charge of the quantum Hall effect quasiparticles.Comment: 4 pages, LaTeX, 4 figures include
Density of states for the -flux state with bipartite real random hopping only: A weak disorder approach
Gade [R. Gade, Nucl. Phys. B \textbf{398}, 499 (1993)] has shown that the
local density of states for a particle hopping on a two-dimensional bipartite
lattice in the presence of weak disorder and in the absence of time-reversal
symmetry(chiral unitary universality class) is anomalous in the vicinity of the
band center whenever the disorder preserves the sublattice
symmetry. More precisely, using a nonlinear-sigma-model that encodes the
sublattice (chiral) symmetry and the absence of time-reversal symmetry she
argues that the disorder average local density of states diverges as
with some non-universal
positive constant and a universal exponent. Her analysis has been
extended to the case when time-reversal symmetry is present (chiral orthogonal
universality class) for which the same exponent was predicted.
Motrunich \textit{et al.} [O. Motrunich, K. Damle, and D. A. Huse, Phys. Rev. B
\textbf{65}, 064206 (2001)] have argued that the exponent does not
apply to the typical density of states in the chiral orthogonal universality
class. They predict that instead. We confirm the analysis of
Motrunich \textit{et al.} within a field theory for two flavors of Dirac
fermions subjected to two types of weak uncorrelated random potentials: a
purely imaginary vector potential and a complex valued mass potential. This
model is believed to belong to the chiral orthogonal universality class. Our
calculation relies in an essential way on the existence of infinitely many
local composite operators with negative anomalous scaling dimensions.Comment: 30 pages, final version published in PR
Breakdown of the Mott insulator: Exact solution of an asymmetric Hubbard model
The breakdown of the Mott insulator is studied when the dissipative tunneling
into the environment is introduced to the system. By exactly solving the
one-dimensional asymmetric Hubbard model, we show how such a breakdown of the
Mott insulator occurs. As the effect of the tunneling is increased, the Hubbard
gap is monotonically decreased and finally disappears, resulting in the
insulator-metal transition. We discuss the origin of this quantum phase
transition in comparison with other non-Hermitian systems recently studied.Comment: 7 pages, revte
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