4,680 research outputs found
Instantaneous ionization rate as a functional derivative
We describe an approach defining instantaneous ionization rate (IIR) as a
functional derivative of the total ionization probability. The definition is
based on physical quantities which are directly measurable, such as the total
ionization probability and the waveform of the pulse. The definition is,
therefore, unambiguous and does not suffer from gauge non-invariance. We
compute IIR by solving numerically the time-dependent Schrodinger equation for
the hydrogen atom in a strong laser field. We find that the IIR lags behind the
electric field, but this lag is entirely due to the long tail effect of the
Coulomb field. In agreement with the previous results using attoclock
methodology, therefore, the IIR we define does not show measurable delay in
strong field tunnel ionization
Absorption cross section and Hawking radiation in two-dimensional AdS black hole
We calculate the absorption coefficient of scalar field on the background of
the two-dimensional AdS black hole, which is of relevance to Hawking radiation.
For the massless scalar field, we find that there does not exist any massless
radiation.Comment: 6 pages, revtex, no figure
Exact soluble two-dimensional charged wormhole
We present an exactly soluble charged wormhole model in two dimensions by
adding infalling chiral fermions on the static wormhole. The infalling energy
due to the infalling charged matter requires the classical back reaction of the
geometry, which is solved by taking into account of the nontrivial nonchiral
exotic energy. Finally, we obtain the exact expression for the size of the
throat depending on the total amount of the infalling net energy and discuss
the interesting transition from the AdS spacetime to the wormhole geometry.Comment: 8 pages, no figure
FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents
The U.S. Department of Energy is performing research and development that focuses on key phenomena that are important during challenging scenarios that may occur in the Next Generation Nuclear Plant (NGNP)/Generation IV very high temperature reactor (VHTR). Phenomena Identification and Ranking studies to date have identified the air ingress event, following on the heels of a VHTR depressurization, as very important. Consequently, the development of advanced air ingress-related models and verification & validation are of very high priority for the NGNP Project. Following a loss of coolant and system depressurization incident, air ingress will occur through the break, leading to oxidation of the in-core graphite structure and fuel. This study indicates that depending on the location and the size of the pipe break, the air ingress phenomena are different. In an effort to estimate the proper safety margin, experimental data and tools, including accurate multidimensional thermal-hydraulic and reactor physics models, a burn-off model, and a fracture model are required. It will also require effective strategies to mitigate the effects of oxidation, eventually. This 3-year project (FY 2008–FY 2010) is focused on various issues related to the VHTR air-ingress accident, including (a) analytical and experimental study of air ingress caused by density-driven, stratified, countercurrent flow, (b) advanced graphite oxidation experiments, (c) experimental study of burn-off in the core bottom structures, (d) structural tests of the oxidized core bottom structures, (e) implementation of advanced models developed during the previous tasks into the GAMMA code, (f) full air ingress and oxidation mitigation analyses, (g) development of core neutronic models, (h) coupling of the core neutronic and thermal hydraulic models, and (i) verification and validation of the coupled models
Polarization-sensitive quantum-optical coherence tomography
We set forth a polarization-sensitive quantum-optical coherence tomography
(PS-QOCT) technique that provides axial optical sectioning with
polarization-sensitive capabilities. The technique provides a means for
determining information about the optical path length between isotropic
reflecting surfaces, the relative magnitude of the reflectance from each
interface, the birefringence of the interstitial material, and the orientation
of the optical axis of the sample. PS-QOCT is immune to sample dispersion and
therefore permits measurements to be made at depths greater than those
accessible via ordinary optical coherence tomography. We also provide a general
Jones matrix theory for analyzing PS-QOCT systems and outline an experimental
procedure for carrying out such measurements.Comment: 15 pages, 5 figures, to appear in Physical Review
Quantum Nucleation in a Ferromagnetic Film Placed in a Magnetic Field at an Arbitrary Angle
We study the quantum nucleation in a thin ferromagnetic film placed in a
magnetic field at an arbitrary angle. The dependence of the quantum nucleation
and the temperature of the crossover from thermal to quantum regime on the
direction and the strength of the applied field are presented. It is found that
the maximal value of the rate and that of the crossover temperature are
obtained at a some angle with the magnetic field, not in the direction of the
applied field opposite to the initial easy axis.Comment: 15 pages, RevTex, 3 PostScript figures. To appear in Phys. Rev.
Three-Dimensional Spectral-Domain Optical Coherence Tomography Data Analysis for Glaucoma Detection
Purpose: To develop a new three-dimensional (3D) spectral-domain optical coherence tomography (SD-OCT) data analysis method using a machine learning technique based on variable-size super pixel segmentation that efficiently utilizes full 3D dataset to improve the discrimination between early glaucomatous and healthy eyes. Methods: 192 eyes of 96 subjects (44 healthy, 59 glaucoma suspect and 89 glaucomatous eyes) were scanned with SD-OCT. Each SD-OCT cube dataset was first converted into 2D feature map based on retinal nerve fiber layer (RNFL) segmentation and then divided into various number of super pixels. Unlike the conventional super pixel having a fixed number of points, this newly developed variable-size super pixel is defined as a cluster of homogeneous adjacent pixels with variable size, shape and number. Features of super pixel map were extracted and used as inputs to machine classifier (LogitBoost adaptive boosting) to automatically identify diseased eyes. For discriminating performance assessment, area under the curve (AUC) of the receiver operating characteristics of the machine classifier outputs were compared with the conventional circumpapillary RNFL (cpRNFL) thickness measurements. Results: The super pixel analysis showed statistically significantly higher AUC than the cpRNFL (0.855 vs. 0.707, respectively, p = 0.031, Jackknife test) when glaucoma suspects were discriminated from healthy, while no significant difference was found when confirmed glaucoma eyes were discriminated from healthy eyes. Conclusions: A novel 3D OCT analysis technique performed at least as well as the cpRNFL in glaucoma discrimination and even better at glaucoma suspect discrimination. This new method has the potential to improve early detection of glaucomatous damage. © 2013 Xu et al
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