447 research outputs found
Unsupervised Learning of Surgical Smoke Removal from Simulation
The surgical smoke produced during minimally invasive surgery can not only reduce the visibility of the surgeons, but also severally affect the performance of image processing algorithms used for image guided surgery such as image tracking, segmentation, detection and retrieval. Besides from physical smoke evacuation devices, many research works address this issue by using vision-based methods to filter out the smoke and try to recover the clear images. More recently, end-to-end deep learning approaches have been introduced to solve the de-hazing and de-smoking problems. However, it is extremely difficult to collect large amounts of data for the effective learning of the implicit de-smoking function, especially for surgical scenes. In this paper, we propose a computational framework for unsupervised learning of smoke removal from rendering smoke on laparoscopic video. Compared to conventional image processing approaches, our proposed framework is able to remove local smoke and recover more realistic tissue colour but will not affect the areas without smoke. Although trained on synthetic images, the experimental results show that our network is able to effectively remove smoke on laparoscopic images with real surgical smoke
De-smokeGCN: Generative Cooperative Networks for Joint Surgical Smoke Detection and Removal
Surgical smoke removal algorithms can improve the quality of intra-operative imaging and reduce hazards in image-guided surgery, a highly desirable post-process for many clinical applications. These algorithms also enable effective computer vision tasks for future robotic surgery. In this paper, we present a new unsupervised learning framework for high-quality pixel-wise smoke detection and removal. One of the well recognized grand challenges in using convolutional neural networks (CNNs) for medical image processing is to obtain intra-operative medical imaging datasets for network training and validation, but availability and quality of these datasets are scarce. Our novel training framework does not require ground-truth image pairs. Instead, it learns purely from computer-generated simulation images. This approach opens up new avenues and bridges a substantial gap between conventional non-learning based methods and which requiring prior knowledge gained from extensive training datasets. Inspired by the Generative Adversarial Network (GAN), we have developed a novel generative-collaborative learning scheme that decomposes the de-smoke process into two separate tasks: smoke detection and smoke removal. The detection network is used as prior knowledge, and also as a loss function to maximize its support for training of the smoke removal network. Quantitative and qualitative studies show that the proposed training framework outperforms the state-of-the-art de-smoking approaches including the latest GAN framework (such as PIX2PIX). Although trained on synthetic images, experimental results on clinical images have proved the effectiveness of the proposed network for detecting and removing surgical smoke on both simulated and real-world laparoscopic images
Constraining the variation of the coupling constants with big bang nucleosynthesis
We consider the possibility of the coupling constants of the gauge interactions at the time of big bang nucleosynthesis
having taken different values from what we measure at present, and investigate
the allowed difference requiring the shift in the coupling constants not
violate the successful calculation of the primordial abundances of the light
elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a
model in which their relative variations are governed by a single scalar field,
dilaton, as found in string theory. The results include a limit on the fine
structure constant
, which is
two orders stricter than the limit obtained by considering the variation of
alone.Comment: 7 page
A first-principles study of MgB2 (0001) surfaces
We report self-consistent {\it ab initio} calculations of structural and
electronic properties for the B- and Mg-terminated MgB (0001) surfaces.
We employ ultra-soft pseudopotentials and plane wave basis sets within the
generalized gradient approximation. The surface relaxations are found to be
small for both B- and Mg-terminated surfaces. For the B-terminated surface,
both B and surface bands appear, while only one B
surface band exists near the Fermi level for the Mg-terminated surface. The
superconductivity of the MgB surfaces is discussed. The work function is
predicted to be 5.95 and 4.25 eV for the B- and Mg-terminated surfaces
respectively. The simulated scanning tunneling microscopy images of the
surfaces are not sensitive to the sign and value of the bias voltages, but
depend strongly on the tip-sample distance. An image reversal is predicted for
the Mg-terminated surface.Comment: 3 pages, 4 figures, Revte
Quantum oscillations in underdoped YBa_2Cu_3O_6.5
Shubnikov-de Haas and de Haas-van Alphen effects have been measured in the
underdoped high temperature superconductor YBaCuO. Data are in
agreement with the standard Lifshitz-Kosevitch theory, which confirms the
presence of a coherent Fermi surface in the ground state of underdoped
cuprates. A low frequency T is reported in both measurements,
pointing to small Fermi pocket, which corresponds to 2% of the first Brillouin
zone area only. This low value is in sharp contrast with that of overdoped
TlBaCuO, where a high frequency kT has been
recently reported and corresponds to a large hole cylinder in agreement with
band structure calculations. These results point to a radical change in the
topology of the Fermi surface on opposing sides of the cuprate phase diagram.Comment: proceeding of the ECRYS-200
Does black-hole growth depend on the cosmic environment?
It is well known that environment affects galaxy evolution, which is broadly related to supermassive black hole (SMBH) growth. We investigate whether SMBH evolution also depends on host-galaxy local (sub-Mpc) and global (≈1–10 Mpc) environment. We construct the surface-density field (local environment) and cosmic web (global environment) in the Cosmic Evolution Survey (COSMOS) field at z = 0.3–3.0. The environments in COSMOS range from the field to clusters (Mhalo ≲ 1014 M⊙), covering the environments where ≈99 per cent of galaxies in the Universe reside. We measure sample-averaged SMBH accretion rate ( BHAR¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ) from X-ray observations, and study its dependence on overdensity and cosmic-web environment at different redshifts while controlling for galaxy stellar mass (M⋆). Our results show that BHAR¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ does not significantly depend on overdensity or cosmic-web environment once M⋆ is controlled, indicating that environment-related physical mechanisms (e.g. tidal interaction and ram-pressure stripping) might not significantly affect SMBH growth. We find that BHAR¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ is strongly related to host-galaxy M⋆, regardless of environment
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal
nonlinear response function, we derive a nonliear equation in which the mixed
state Hall resistivity can be expressed as an analytical function of magnetic
field, temperature and applied current. This equation enables one to compare
quantitatively the experimental data with theoretical model. We also find some
new scaling relations of the temperature and field dependency of Hall
resistivity. The comparison between our theoretical curves and experimental
data shows a fair agreement.Comment: 4 pages, 3 figure
Muon-spin-relaxation study of the magnetic penetration depth in MgB2
The magnetic vortex lattice (VL) of polycrystalline MgB2 has been
investigated by transverse-field muon-spin-relaxation (TF-MuSR). The evolution
of TF-MuSR depolarization rate, sigma, that is proportional to the second
moment of the field distribution of the VL has been studied as a function of
temperature and applied magnetic field. The low temperature value s exhibits a
pronounced peak near Hext = 75 mT. This behavior is characteristic of strong
pinning induced distortions of the VL which put into question the
interpretation of the low-field TF-MuSR data in terms of the magnetic
penetration depth lambda(T). An approximately constant value of sigma, such as
expected for an ideal VL in the London-limit, is observed at higher fields of
Hext > 0.4 T. The TF-MuSR data at Hext = 0.6 T are analyzed in terms of a
two-gap model. We obtain values for the gap size of D1 = 6.0 meV (2D1/kBTc =
3.6), D2 = 2.6 meV (2D2/kBTc = 1.6), a comparable spectral weight of the two
bands and a zero temperature value for the magnetic penetration depth of lambda
= 100 nm. In addition, we performed MuSR-measurements in zero external field
(ZF-MuSR). We obtain evidence that the muon site (at low temperature) is
located on a ring surrounding the center of the boron hexagon. Muon diffusion
sets in already at rather low temperature of T > 10 K. The nuclear magnetic
moments can account for the observed relaxation rate and no evidence for
electronic magnetic moments has been obtained.Comment: 15 pages, 4 figure
Chaotic Diffusion on Periodic Orbits: The Perturbed Arnol'd Cat Map
Chaotic diffusion on periodic orbits (POs) is studied for the perturbed
Arnol'd cat map on a cylinder, in a range of perturbation parameters
corresponding to an extended structural-stability regime of the system on the
torus. The diffusion coefficient is calculated using the following PO formulas:
(a) The curvature expansion of the Ruelle zeta function. (b) The average of the
PO winding-number squared, , weighted by a stability factor. (c) The
uniform (nonweighted) average of . The results from formulas (a) and (b)
agree very well with those obtained by standard methods, for all the
perturbation parameters considered. Formula (c) gives reasonably accurate
results for sufficiently small parameters corresponding also to cases of a
considerably nonuniform hyperbolicity. This is due to {\em uniformity sum
rules} satisfied by the PO Lyapunov eigenvalues at {\em fixed} . These sum
rules follow from general arguments and are supported by much numerical
evidence.Comment: 6 Tables, 2 Figures (postscript); To appear in Physical Review
Single-Proton Removal Reaction Study of 16B
The low-lying level structure of the unbound system B has been
investigated via single-proton removal from a 35 MeV/nucleon C beam. The
coincident detection of the beam velocity B fragment and neutron allowed
the relative energy of the in-flight decay of B to be reconstructed. The
resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is
argued that this feature corresponds to a very narrow (100 keV)
resonance, or an unresolved multiplet, with a dominant + configuration which decays by d-wave neutron
emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.
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