40,566 research outputs found
Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires
Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces
Degeneracy of Ground State in Two-dimensional Electron-Lattice System
We discuss the ground state of a two dimensional electron-lattice system
described by a Su-Schrieffer-Heeger type Hamiltonian with a half-filled
electronic band, for which it has been pointed out in the previous paper [J.
Phys. Soc. Jpn. 69 (2000) 1769-1776] that the ground state distortion pattern
is not unique in spite of a unique electronic energy spectrum and the same
total energy. The necessary and sufficient conditions to be satisfied by the
distortion patterns in the ground state are derived numerically. As a result
the degrees of degeneracy in the ground state is estimated to be about
for with the linear dimension of the system.Comment: 2pages, 2figure
After heat distribution of a mobile nuclear power plant
A computer program was developed to analyze the transient afterheat temperature and pressure response of a mobile gas-cooled reactor power plant following impact. The program considers (in addition to the standard modes of heat transfer) fission product decay and transport, metal-water reactions, core and shield melting and displacement, and pressure and containment vessel stress response. Analyses were performed for eight cases (both deformed and undeformed models) to verify operability of the program options. The results indicated that for a 350 psi (241 n/sq cm) initial internal pressure, the containment vessel can survive over 100,000 seconds following impact before creep rupture occurs. Recommendations were developed as to directions for redesign to extend containment vessel life
Severity classification of ground-glass opacity via 2-D convolutional neural network and lung CT scans: a 3-day exploration
Ground-glass opacity is a hallmark of numerous lung diseases, including
patients with COVID19 and pneumonia, pulmonary fibrosis, and tuberculosis. This
brief note presents experimental results of a proof-of-concept framework that
got implemented and tested over three days as driven by the third challenge
entitled "COVID-19 Competition", hosted at the AI-Enabled Medical Image
Analysis Workshop of the 2023 IEEE International Conference on Acoustics,
Speech and Signal Processing (ICASSP 2023). Using a newly built virtual
environment (created on March 17, 2023), we investigated various pre-trained
two-dimensional convolutional neural networks (CNN) such as Dense Neural
Network, Residual Neural Networks (ResNet), and Vision Transformers, as well as
the extent of fine-tuning. Based on empirical experiments, we opted to
fine-tune them using ADAM's optimization algorithm with a standard learning
rate of 0.001 for all CNN architectures and apply early-stopping whenever the
validation loss reached a plateau. For each trained CNN, the model state with
the best validation accuracy achieved during training was stored and later
reloaded for new classifications of unseen samples drawn from the validation
set provided by the challenge organizers. According to the organizers, few of
these 2D CNNs yielded performance comparable to an architecture that combined
ResNet and Recurrent Neural Network (Gated Recurrent Units). As part of the
challenge requirement, the source code produced during the course of this
exercise is posted at https://github.com/lisatwyw/cov19. We also hope that
other researchers may find this light prototype consisting of few Python files
based on PyTorch 1.13.1 and TorchVision 0.14.1 approachable
Pinned modes in two-dimensional lossy lattices with local gain and nonlinearity
We introduce a system with one or two amplified nonlinear sites ("hot spots",
HSs) embedded into a two-dimensional linear lossy lattice. The system describes
an array of evanescently coupled optical or plasmonic waveguides, with gain
applied at selected HS cores. The subject of the analysis is discrete solitons
pinned to the HSs. The shape of the localized modes is found in
quasi-analytical and numerical forms, using a truncated lattice for the
analytical consideration. Stability eigenvalues are computed numerically, and
the results are supplemented by direct numerical simulations. In the case of
self-focusing nonlinearity, the modes pinned to a single HS are stable or
unstable when the nonlinearity includes the cubic loss or gain, respectively.
If the nonlinearity is self-defocusing, the unsaturated cubic gain acting at
the HS supports stable modes in a small parametric area, while weak cubic loss
gives rise to a bistability of the discrete solitons. Symmetric and
antisymmetric modes pinned to a symmetric set of two HSs are considered too.Comment: Philosophical Transactions of the Royal Society A, in press (a
special issue on "Localized structures in dissipative media"
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