6,587 research outputs found
Spectral Analyses of the Nearest Persistent Ultraluminous X-Ray Source M33 X-8
We provide a detailed analysis of 12 XMM observations of the nearest
persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No
significant spectral evolution is detected between the observations, therefore
we combine the individual observations to increase the signal-to-noise ratio
for spectral fitting. The combined spectra are best fitted by the
self-consistent p-free disk plus power-law component model with p =
0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio
of the p-free disk component to the power-law component being 0.63:0.37 in the
0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of
\sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}),
and the phase of the accretion disk is close to a slim disk (p = 0.5). We
report, for the first time, that an extra power-law component is required in
addition to the p-free disk model for ULXs. In super-Eddington cases, the
power-law component may possibly result from the optically thin inner region f
the disk or a comptonized corona similar to that of a standard thin disk.Comment: 11 pages, 1 table, 2 figures, accepted by PAS
Microscopic origin of local moments in a zinc-doped high- superconductor
The formation of a local moment around a zinc impurity in the high-
cuprate superconductors is studied within the framework of the bosonic
resonating-valence-bond (RVB) description of the model. A topological
origin of the local moment has been shown based on the phase string effect in
the bosonic RVB theory. It is found that such an moment distributes
near the zinc in a form of staggered magnetic moments at the copper sites. The
corresponding magnetic properties, including NMR spin relaxation rate, uniform
spin susceptibility, and dynamic spin susceptibility, etc., calculated based on
the theory, are consistent with the experimental measurements. Our work
suggests that the zinc substitution in the cuprates provide an important
experimental evidence for the RVB nature of local physics in the original (zinc
free) state.Comment: The topological reason of local moment formation is given. One figure
is adde
On strain hardening mechanism in gradient nanostructures
Experiments have shown that a gradient design, in which grain size spans over four orders of magnitude, can make strong nanomaterials ductile. The enhanced ductility is attributed to the considerable strain hardening capability obtained in the gradient metals. A non-uniform deformation on the lateral sample surface is also observed. This might inject geometrically necessary dislocations (GNDs) into the sample. However, no direct evidence has been provided. Therefore the issues remain: why can the gradient structure generate high strain hardening, and how does it reconcile the strength-ductility synergy of gradient nanostructures? Here for the first time we quantitatively investigate the strain hardening of a gradient interstitial-free steel by developing a dislocation density-based continuum plasticity model, in which the interaction of the component layers in the gradient structure is represented by incorporating GNDs and back stress. It is demonstrated that both the surface non-uniform deformation and the strain-hardening rate up-turn can be quantitatively well predicted. The results also show that the strain hardening rate of the gradient sample can reach as high as that of the coarse-grained counterpart. A strength-ductility map is then plotted, which clearly show that the gradient samples perform much more superior to their homogeneous counterparts in strength-ductility synergy. The predicted map has been verified by a series of experimental data. A detailed analysis on GNDs distribution and back stress evolution at the end further substantiates our view that the good strain hardening capability results from the generation of abundant GNDs by the surface non-uniform deformation into the nano-grained layers of the gradient sample. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Bus travel time reliability analysis: A case study
The travel time reliability of buses has become increasingly important for public transit companies. In this study, a novel approach is proposed to evaluate and analyse the travel time reliability of bus services provided by TransLink in Queensland, Australia. In view of their stochastic features, the two components of travel time-dwell time and driving time-are represented by discrete distributed and normally distributed random variables respectively. Accordingly, the travel time could be described by Gaussian mixture models. Based on the proposed model, impact analysis shows that bus line reliability would increase by around 15% if onboard top-up for 'go cards' (electronic tickets) was not offered by TransLink. It was found that not providing this top-up method would not significantly harm the benefit of go card users, but it would substantially increase the total social benefit thanks to improved bus line reliability
Optical spectroscopy study of Nd(O,F)BiS2 single crystals
We present an optical spectroscopy study on F-substituted NdOBiS
superconducting single crystals grown using KCl/LiCl flux method. The
measurement reveals a simple metallic response with a relatively low screened
plasma edge near 5000 \cm. The plasma frequency is estimated to be 2.1 eV,
which is much smaller than the value expected from the first-principles
calculations for an electron doping level of x=0.5, but very close to the value
based on a doping level of 7 of itinerant electrons per Bi site as
determined by ARPES experiment. The energy scales of the interband transitions
are also well reproduced by the first-principles calculations. The results
suggest an absence of correlation effect in the compound, which essentially
rules out the exotic pairing mechanism for superconductivity or scenario based
on the strong electronic correlation effect. The study also reveals that the
system is far from a CDW instability as being widely discussed for a doping
level of x=0.5.Comment: 5 pages, 5 figure
Evolution of structural and electronic properties of highly mismatched InSb films
We have investigated the evolution of structural and electronic properties of highly mismatched InSb films, with thicknesses ranging from 0.1 to 1.5 μm. Atomic force microscopy, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction show that the 0.1 μm films are nearly fully relaxed and consist of partially coalesced islands, which apparently contain threading dislocations at their boundaries. As the film thickness increases beyond 0.2 μm, the island coalescence is complete and the residual strain is reduced. Although the epilayers have relaxed equally in the 〈110〉 in-plane directions, the epilayer rotation about an in-plane axis (epilayer tilt) is not equal in both 〈110〉 in-plane directions. Interestingly, the island-like surface features tend to be preferentially elongated along the axis of epilayer tilt. Furthermore, epilayer tilt which increases the substrate offcut (reverse tilt) is evident in the [110] direction. High-resolution transmission electron microscopy indicates that both pure-edge and 60° misfit dislocations contribute to the relaxation of strain. In addition, as the film thickness increases, the threading dislocation density decreases, while the corresponding room-temperature electron mobility increases. The other structural features, including the residual strain, and the surface and interface roughness, do not appear to impact the electron mobility in these InSb films. Together, these results suggest that free-carrier scattering from the threading dislocations is the primary room-temperature mobility-limiting mechanism in highly mismatched InSb films. Finally, we show quantitatively that free-carrier scattering from the lattice dilation associated with threading dislocations, rather than scattering from a depletion potential surrounding the dislocations, is the dominant factor limiting the electron mobility. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70332/2/JAPIAU-88-11-6276-1.pd
Formation mechanisms of embedded wurtzite and zincblende indium nitride nanocrystals
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98698/1/ApplPhysLett_99_093108.pd
Stage-Aware Feature Alignment Network for Real-Time Semantic Segmentation of Street Scenes
Over the past few years, deep convolutional neural network-based methods have made great progress in semantic segmentation of street scenes. Some recent methods align feature maps to alleviate the semantic gap between them and achieve high segmentation accuracy. However, they usually adopt the feature alignment modules with the same network configuration in the decoder and thus ignore the different roles of stages of the decoder during feature aggregation, leading to a complex decoder structure. Such a manner greatly affects the inference speed. In this paper, we present a novel Stage-aware Feature Alignment Network (SFANet) based on the encoder-decoder structure for real-time semantic segmentation of street scenes. Specifically, a Stage-aware Feature Alignment module (SFA) is proposed to align and aggregate two adjacent levels of feature maps effectively. In the SFA, by taking into account the unique role of each stage in the decoder, a novel stage-aware Feature Enhancement Block (FEB) is designed to enhance spatial details and contextual information of feature maps from the encoder. In this way, we are able to address the misalignment problem with a very simple and efficient multi-branch decoder structure. Moreover, an auxiliary training strategy is developed to explicitly alleviate the multi-scale object problem without bringing additional computational costs during the inference phase. Experimental results show that the proposed SFANet exhibits a good balance between accuracy and speed for real-time semantic segmentation of street scenes. In particular, based on ResNet-18, SFANet respectively obtains 78.1% and 74.7% mean of class-wise Intersection-over-Union (mIoU) at inference speeds of 37 FPS and 96 FPS on the challenging Cityscapes and CamVid test datasets by using only a single GTX 1080Ti GPU
Ultrathin silica films on Pd(111): Structure and adsorption properties
We studied the preparation of thin silica films on Pd(111) using low energy electron diffraction (LEED), infrared reflection-absorption spectroscopy (IRAS), and scanning tunneling microscopy (STM). The films grow from the onset as a double-layer (bilayer) silicate and show no long-range ordering as judged by LEED, thus bearing close similarities to the silicate films grown on a Pt(111) support. The results provide further evidence that the principal structure (monolayer vs bilayer) of ultrathin silica films on metal substrates is primarily governed by the affinity of a metal substrate to oxygen. Individual adsorption of CO and D2 on the prepared films showed that both molecules penetrate through the film and chemisorb on the Pd(111) surface. Density functional theory (DFT) calculations showed that CO bonding on Pd(111) underneath the silica film becomes weaker as compared to the bare Pd(111) surface, but the vibrational frequencies remain unaffected, that is in nice agreement with the experimental results
Co-reductive fabrication of carbon nanodots with high quantum yield for bioimaging of bacteria
A simple and straightforward synthetic approach for carbon nanodots (C-dots) is proposed. The strategy is based on a one-step hydrothermal chemical reduction with thiourea and urea, leading to high quantum yield C-dots. The obtained C-dots are welldispersed with a uniform size and a graphite-like structure. A synergistic reduction mechanism was investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The findings show that using both thiourea and urea during the one-pot synthesis enhances the luminescence of the generated C-dots. Moreover, the prepared C-dots have a high distribution of functional groups on their surface. In this work, C-dots proved to be a suitable nanomaterial for imaging of bacteria and exhibit potential for application in bioimaging thanks to their low cytotoxicity
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