1,755 research outputs found
Quantum trajectories for time-dependent adiabatic master equations
We develop a quantum trajectories technique for the unraveling of the quantum
adiabatic master equation in Lindblad form. By evolving a complex state vector
of dimension instead of a complex density matrix of dimension ,
simulations of larger system sizes become feasible. The cost of running many
trajectories, which is required to recover the master equation evolution, can
be minimized by running the trajectories in parallel, making this method
suitable for high performance computing clusters. In general, the trajectories
method can provide up to a factor advantage over directly solving the
master equation. In special cases where only the expectation values of certain
observables are desired, an advantage of up to a factor is possible. We
test the method by demonstrating agreement with direct solution of the quantum
adiabatic master equation for -qubit quantum annealing examples. We also
apply the quantum trajectories method to a -qubit example originally
introduced to demonstrate the role of tunneling in quantum annealing, which is
significantly more time consuming to solve directly using the master equation.
The quantum trajectories method provides insight into individual quantum jump
trajectories and their statistics, thus shedding light on open system quantum
adiabatic evolution beyond the master equation.Comment: 17 pages, 7 figure
Long wavelength optical coherence tomography for painted objects
Optical Coherence Tomography has been successfully applied to the imaging of painted objects in recent years. However, a significant limitation is the low penetration depth of OCT in paint because of the high opacity of paint due to either scattering or absorption. It has been shown that the optimum spectral window for OCT imaging of paint layers is around 2.2μm in wavelength. In this paper, we demonstrate a 1950nm OCT for imaging painted objects using a superfluorescent fiber source at low power
High resolution fourier domain optical coherence tomography at 2 microns for painted objects
Optical Coherence Tomography has been successfully applied to the non-invasive imaging of subsurface microstructure of a variety of materials from biological tissues to painted objects of art. One of the limitations of the technique is the low depth of penetration due to the strong scattering and absorption in the material. Previous studies found that for paint materials, the optimum window for large depth of penetration is around 2.2 microns. This is also true for many other materials with low water content. We have previously demonstrated OCT systems in this wavelength regime for imaging with improved depth of penetration. In this paper, we present an improved 2 micron high resolution Fourier domain OCT system using a broadband supercontinuum source. The system achieved a depth resolution of 9 microns in air (or 6 microns in paint or any polymer)
Content Analysis Of Board Reports On Corporate Governance, Internal Controls And Risk Management: Evidence From France
The French legislature has mandated in 2008 that the board chairperson reports on governance, internal controls, and risk management approach with the objective to enhance corporate disclosures to investors. This study examines the content of board chair reports to assess their relevance and compliance with mandated disclosure requirements. Based on a sample of 109 french publicly listed comapnies in 2009, Our results show that, with the exception of banks subject to a more stringent regulatory standard, the mandatory nature of the legislation did not translate in extended disclosures about internal controls and risk management practices. We further observe significant variations among the different indices of disclosure particularly with regards internal accounting and financial control. The multivaraite results validate the influence of the chosen internal control framework as well as firm characteristics on the content of the information disclosed about governance, internal control, and risk management practices
Species delineation using Bayesian model-based assignment tests: a case study using Chinese toad-headed agamas (genus Phrynocephalus)
<p>Abstract</p> <p>Background</p> <p>Species are fundamental units in biology, yet much debate exists surrounding how we should delineate species in nature. Species discovery now requires the use of separate, corroborating datasets to quantify independently evolving lineages and test species criteria. However, the complexity of the speciation process has ushered in a need to infuse studies with new tools capable of aiding in species delineation. We suggest that model-based assignment tests are one such tool. This method circumvents constraints with traditional population genetic analyses and provides a novel means of describing cryptic and complex diversity in natural systems. Using toad-headed agamas of the <it>Phrynocephalus vlangalii </it>complex as a case study, we apply model-based assignment tests to microsatellite DNA data to test whether <it>P. putjatia</it>, a controversial species that closely resembles <it>P. vlangalii </it>morphologically, represents a valid species. Mitochondrial DNA and geographic data are also included to corroborate the assignment test results.</p> <p>Results</p> <p>Assignment tests revealed two distinct nuclear DNA clusters with 95% (230/243) of the individuals being assigned to one of the clusters with > 90% probability. The nuclear genomes of the two clusters remained distinct in sympatry, particularly at three syntopic sites, suggesting the existence of reproductive isolation between the identified clusters. In addition, a mitochondrial ND2 gene tree revealed two deeply diverged clades, which were largely congruent with the two nuclear DNA clusters, with a few exceptions. Historical mitochondrial introgression events between the two groups might explain the disagreement between the mitochondrial and nuclear DNA data. The nuclear DNA clusters and mitochondrial clades corresponded nicely to the hypothesized distributions of <it>P. vlangalii </it>and <it>P. putjatia</it>.</p> <p>Conclusions</p> <p>These results demonstrate that assignment tests based on microsatellite DNA data can be powerful tools for distinguishing closely related species and support the validity of <it>P. putjatia</it>. Assignment tests have the potential to play a significant role in elucidating biodiversity in the era of DNA data. Nonetheless, important limitations do exist and multiple independent datasets should be used to corroborate results from assignment programs.</p
High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source
A 220 nm bandwidth supercontinuum source in the two-micron wavelength range has been developed for use in a Fourier domain optical coherence tomography (FDOCT) system. This long wavelength source serves to enhance probing depth in highly scattering material with low water content. We present results confirming improved penetration depth in high opacity paint samples while achieving the high axial resolution needed to resolve individual paint layers. This is the first FDOCT developed in the 2 μm wavelength regime that allows fast, efficient capturing of 3D image cubes at a high axial resolution of 13 μm in air (or 9 μm in paint)
Standard quantum annealing outperforms adiabatic reverse annealing with decoherence
We study adiabatic reverse annealing (ARA) in an open system. In the closed
system (unitary) setting, this annealing protocol allows avoidance of
first-order quantum phase transitions of selected models, resulting in an
exponential speedup compared with standard quantum annealing, provided that the
initial state of the algorithm is close in Hamming distance to the target one.
Here, we show that decoherence can significantly modify this conclusion: by
resorting to the adiabatic master equation approach, we simulate the dynamics
of the ferromagnetic -spin model with under independent and collective
dephasing. For both models of decoherence, we show that the performance of open
system ARA is far less sensitive to the choice of the initial state than its
unitary counterpart, and, most significantly, that open system ARA by and large
loses its time to solution advantage compared to standard quantum annealing.
These results suggest that as a stand-alone strategy, ARA is unlikely to
experimentally outperform standard "forward" quantum annealing, and that error
mitigation strategies will likely be required in order to realize the benefits
of ARA in realistic, noisy settings.Comment: 12 pages, 11 figure
Spectral Decomposition of Broad-Line AGNs and Host Galaxies
Using an eigenspectrum decomposition technique, we separate the host galaxy
from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from
the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75.
The decomposition technique uses separate sets of galaxy and quasar
eigenspectra to efficiently and reliably separate the AGN and host
spectroscopic components. The technique accurately reproduces the host galaxy
spectrum, its contributing fraction, and its classification. We show how the
accuracy of the decomposition depends upon S/N, host galaxy fraction, and the
galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN
host galaxies spans a wide range of spectral types, but the distribution
differs significantly from inactive galaxies. In particular, post-starburst
activity appears to be much more common among AGN host galaxies. The
luminosities of the hosts are much higher than expected for normal early-type
galaxies, and their colors become increasingly bluer than early-type galaxies
with increasing host luminosity. Most of the AGNs with detected hosts are
emitting at between 1% and 10% of their estimated Eddington luminosities, but
the sensitivity of the technique usually does not extend to the Eddington
limit. There are mild correlations among the AGN and host galaxy
eigencoefficients, possibly indicating a link between recent star formation and
the onset of AGN activity. The catalog of spectral reconstruction parameters is
available as an electronic table.Comment: 18 pages; accepted for publication in A
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