1,903 research outputs found
Large-scale Binary Quadratic Optimization Using Semidefinite Relaxation and Applications
In computer vision, many problems such as image segmentation, pixel
labelling, and scene parsing can be formulated as binary quadratic programs
(BQPs). For submodular problems, cuts based methods can be employed to
efficiently solve large-scale problems. However, general nonsubmodular problems
are significantly more challenging to solve. Finding a solution when the
problem is of large size to be of practical interest, however, typically
requires relaxation. Two standard relaxation methods are widely used for
solving general BQPs--spectral methods and semidefinite programming (SDP), each
with their own advantages and disadvantages. Spectral relaxation is simple and
easy to implement, but its bound is loose. Semidefinite relaxation has a
tighter bound, but its computational complexity is high, especially for large
scale problems. In this work, we present a new SDP formulation for BQPs, with
two desirable properties. First, it has a similar relaxation bound to
conventional SDP formulations. Second, compared with conventional SDP methods,
the new SDP formulation leads to a significantly more efficient and scalable
dual optimization approach, which has the same degree of complexity as spectral
methods. We then propose two solvers, namely, quasi-Newton and smoothing Newton
methods, for the dual problem. Both of them are significantly more efficiently
than standard interior-point methods. In practice, the smoothing Newton solver
is faster than the quasi-Newton solver for dense or medium-sized problems,
while the quasi-Newton solver is preferable for large sparse/structured
problems. Our experiments on a few computer vision applications including
clustering, image segmentation, co-segmentation and registration show the
potential of our SDP formulation for solving large-scale BQPs.Comment: Fixed some typos. 18 pages. Accepted to IEEE Transactions on Pattern
Analysis and Machine Intelligenc
A Helium-Surface Interaction Potential of BiTe(111) from Ultrahigh-Resolution Spin-Echo Measurements
We have determined an atom-surface interaction potential for the
HeBiTe(111) system by analysing ultrahigh resolution measurements of
selective adsorption resonances. The experimental measurements were obtained
using He spin-echo spectrometry. Following an initial free-particle model
analysis, we use elastic close-coupling calculations to obtain a
three-dimensional potential. The three-dimensional potential is then further
refined based on the experimental data set, giving rise to an optimised
potential which fully reproduces the experimental data. Based on this analysis,
the HeBiTe(111) interaction potential can be described by a
corrugated Morse potential with a well depth , a
stiffness and a surface electronic
corrugation of % of the lattice constant. The improved
uncertainties of the atom-surface interaction potential should also enable the
use in inelastic close-coupled calculations in order to eventually study the
temperature dependence and the line width of selective adsorption resonances
Counterpropagating beams in biased photorefractive crystals: anisotropic theory
We formulate an anisotropic nonlocal theory of the space charge field induced by the coherent counterpropagating
beams in biased photorefractive crystals. We establish that the competition between the drift and
diffusion terms has to be taken into account when the crystal cË axis is tilted with respect to the propagation
direction of the beams. We demonstrate that this configuration combines the features of both spatial soliton
formation without energy exchange and two-wave mixing with energy exchange leading to pattern formation
The SFR-M <sub>â</sub> Correlation Extends to Low Mass at High Redshift
To achieve a fuller understanding of galaxy evolution, SED fitting can be
used to recover quantities beyond stellar masses (M) and star formation
rates (SFRs). We use Star Formation Histories (SFHs) reconstructed via the
Dense Basis method of Iyer \& Gawiser (2017) for a sample of galaxies
at in the CANDELS GOODS-S field to study the nature and evolution of
the SFR-M correlation. The reconstructed SFHs represent trajectories in
SFR-M space, enabling us to study galaxies at epochs earlier than observed
by propagating them backwards in time along these trajectories. We study the
SFR-M correlation at using both direct fits to galaxies
observed at those epochs and SFR-M trajectories of galaxies observed at
lower redshifts. The SFR-M correlations obtained using the two approaches
are found to be consistent with each other through a KS test. Validation tests
using SFHs from semi-analytic models and cosmological hydrodynamical
simulations confirm the sensitivity of the method to changes in the slope,
normalization and shape of the SFR-M correlation. This technique allows us
to further probe the low-mass regime of the correlation at high-z by
dex and over an effective volume of larger than possible with
just direct fits. We find that the SFR-M correlation is consistent with
being linear down to M at . The evolution of the
correlation is well described by , where is the age of the universe in Gyr.Comment: 22 pages, 10 figures. Accepted for publication in Ap
Heralded generation of entangled photon pairs
Entangled photons are a crucial resource for quantum communication and linear
optical quantum computation. Unfortunately, the applicability of many
photon-based schemes is limited due to the stochastic character of the photon
sources. Therefore, a worldwide effort has focused in overcoming the limitation
of probabilistic emission by generating two-photon entangled states conditioned
on the detection of auxiliary photons. Here we present the first heralded
generation of photon states that are maximally entangled in polarization with
linear optics and standard photon detection from spontaneous parametric
down-conversion. We utilize the down-conversion state corresponding to the
generation of three photon pairs, where the coincident detection of four
auxiliary photons unambiguously heralds the successful preparation of the
entangled state. This controlled generation of entangled photon states is a
significant step towards the applicability of a linear optics quantum network,
in particular for entanglement swapping, quantum teleportation, quantum
cryptography and scalable approaches towards photonics-based quantum computing
Comparison of Different Approaches to Surface Functionalization of Biodegradable Polycaprolactone Scaffolds
Due to their good mechanical stability compared to gelatin, collagen or polyethylene glycol nanofibers and slow degradation rate, biodegradable poly-epsilon-caprolactone (PCL) nanofibers are promising material as scaffolds for bone and soft-tissue engineering. Here, PCL nanofibers were prepared by the electrospinning method and then subjected to surface functionalization aimed at improving their biocompatibility and bioactivity. For surface modification, two approaches were used: (i) COOH-containing polymer was deposited on the PCL surface using atmospheric pressure plasma copolymerization of CO2 and C2H4, and (ii) PCL nanofibers were coated with multifunctional bioactive nanostructured TiCaPCON film by magnetron sputtering of TiC-CaO-Ti3POx target. To evaluate bone regeneration ability in vitro, the surface-modified PCL nanofibers were immersed in simulated body fluid (SBF, 1x) for 21 days. The results obtained indicate different osteoblastic and epithelial cell response depending on the modification method. The TiCaPCON-coated PCL nanofibers exhibited enhanced adhesion and proliferation of MC3T3-E1 cells, promoted the formation of Ca-based mineralized layer in SBF and, therefore, can be considered as promising material for bone tissue regeneration. The PCL-COOH nanofibers demonstrated improved adhesion and proliferation of IAR-2 cells, which shows their high potential for skin reparation and wound dressing
No More Active Galactic Nuclei in Clumpy Disks Than in Smooth Galaxies at z~2 in CANDELS / 3D-HST
We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to
investigate if active galactic nuclei (AGNs) are preferentially fueled by
violent disk instabilities funneling gas into galaxy centers at 1.3<z<2.4. We
select galaxies undergoing gravitational instabilities using the number of
clumps and degree of patchiness as proxies. The CANDELS visual classification
system is used to identify 44 clumpy disk galaxies, along with mass-matched
comparison samples of smooth and intermediate morphology galaxies. We note
that, despite being being mass-matched and having similar star formation rates,
the smoother galaxies tend to be smaller disks with more prominent bulges
compared to the clumpy galaxies. The lack of smooth extended disks is probably
a general feature of the z~2 galaxy population, and means we cannot directly
compare with the clumpy and smooth extended disks observed at lower redshift.
We find that z~2 clumpy galaxies have slightly enhanced AGN fractions selected
by integrated line ratios (in the mass-excitation method), but the spatially
resolved line ratios indicate this is likely due to extended phenomena rather
than nuclear AGNs. Meanwhile the X-ray data show that clumpy, smooth, and
intermediate galaxies have nearly indistinguishable AGN fractions derived from
both individual detections and stacked non-detections. The data demonstrate
that AGN fueling modes at z~1.85 - whether violent disk instabilities or
secular processes - are as efficient in smooth galaxies as they are in clumpy
galaxies.Comment: ApJ accepted. 17 pages, 17 figure
Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems
Quantum simulators are controllable quantum systems that can reproduce the
dynamics of the system of interest, which are unfeasible for classical
computers. Recent developments in quantum technology enable the precise control
of individual quantum particles as required for studying complex quantum
systems. Particularly, quantum simulators capable of simulating frustrated
Heisenberg spin systems provide platforms for understanding exotic matter such
as high-temperature superconductors. Here we report the analog quantum
simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type
interactions among four spin-1/2 particles . Depending on the interaction
strength, frustration within the system emerges such that the ground state
evolves from a localized to a resonating valence-bond state. This spin-1/2
tetramer is created using the polarization states of four photons. The
single-particle addressability and tunable measurement-induced interactions
provide us insights into entanglement dynamics among individual particles. We
directly extract ground-state energies and pair-wise quantum correlations to
observe the monogamy of entanglement
Antioxidant intervention in rheumatoid arthritis: results of an open pilot study
There is evidence that reactive oxygen species play a causal role in auto-immune diseases, such as rheumatoid arthritis (RA). Despite the supporting evidence for a beneficial effect of antioxidants on clinical characteristics of RA, the right balance for optimal effectiveness of antioxidants is largely unknown. To determine the potential beneficial effects of an antioxidant intervention on clinical parameters for RA, an open pilot study was designed. Eight non-smoking female patients with rheumatoid factor + RA and a Disease Activity Score (DAS 28) higher than 2.5 were enrolled in the study. Patients had to be receiving stable non-steroidal anti-inflammatory drug treatment and/or âsecond lineâ medication for at least 3Â months. The pilot group consumed 20Â g of antioxidant-enriched spread daily during a period of 10Â weeks. The intervention was stopped after 10Â weeks and was followed by a âwash-outâ period of 4Â weeks. At tâ=â0, tâ=â10Â weeks and tâ=â14Â weeks, patientsâ condition was assessed by means of DAS. In addition, standard laboratory analyses were performed, and blood-samples for antioxidants were taken. The antioxidant-enriched spread was well tolerated. All laboratory measures of inflammatory activity and oxidative modification were generally unchanged. However, the number of swollen and painful joints were significantly decreased and general health significantly increased, as reflected by a significantly improved (1.6) DAS at tâ=â10Â weeks. The antioxidant effect was considered beneficial as, compared to the scores at tâ=â0, the DAS significantly reduced at tâ=â10Â weeks. Increase of the DAS (0.7) after the âwash-out periodâ at tâ=â14 confirmed a causal relation between changes in clinical condition and antioxidants. This open pilot study aimed to assess the clinical relevance of an antioxidant intervention as a first step in assessing potential beneficial effects of antioxidants on rheumatoid arthritis. These conclusions need to be validated in a larger controlled study population
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