5,770 research outputs found
A re-visit of the phase-resolved X-ray and \gamma-ray spectra of the Crab pulsar
We use a modified outer gap model to study the multi-frequency phase-resolved
spectra of the Crab pulsar. The emissions from both poles contribute to the
light curve and the phase-resolved spectra. Using the synchrotron self-Compton
mechanism and by considering the incomplete conversion of curvature photons
into secondary pairs, the observed phase-averaged spectrum from 100 eV - 10 GeV
can be explained very well. The predicted phase-resolved spectra can match the
observed data reasonably well, too. We find that the emission from the north
pole mainly contributes to Leading Wing 1. The emissions in the remaining
phases are mainly dominated by the south pole. The widening of the azimuthal
extension of the outer gap explains Trailing Wing 2. The complicated
phase-resolved spectra for the phases between the two peaks, namely Trailing
Wing 1, Bridge and Leading Wing 2, strongly suggest that there are at least two
well-separated emission regions with multiple emission mechanisms, i.e.
synchrotron radiation, inverse Compton scattering and curvature radiation. Our
best fit results indicate that there may exist some asymmetry between the south
and the north poles. Our model predictions can be examined by GLAST.Comment: 35 pages, 13 figures, accepted to publish in Ap
A systematic TMRT observational study of Galactic C/C ratios from Formaldehyde
We present observations of the C-band (4.8 GHz) and Ku-band
(14.5 GHz) K-doublet lines of HCO and the C-band
(4.6 GHz) line of HCO toward a large sample of
Galactic molecular clouds, through the Shanghai Tianma 65-m radio telescope
(TMRT). Our sample with 112 sources includes strong HCO sources from the
TMRT molecular line survey at C-band and other known HCO sources. All three
lines are detected toward 38 objects (43 radial velocity components) yielding a
detection rate of 34\%. Complementary observations of their continuum emission
at both C- and Ku-bands were performed. Combining spectral line parameters and
continuum data, we calculate the column densities, the optical depths and the
isotope ratio HCO/HCO for each source. To evaluate photon
trapping caused by sometimes significant opacities in the main isotopologue's
rotational mm-wave lines connecting our measured K-doublets, and to obtain
C/C abundance ratios, we used the RADEX non-LTE model accounting
for radiative transfer effects. This implied the use of the new collision rates
from \citet{Wiesenfeld2013}. Also implementing distance values from
trigonometric parallax measurements for our sources, we obtain a linear fit of
C/C = (5.081.10)D + (11.866.60), with a
correlation coefficient of 0.58. D refers to Galactocentric distances.
Our C/C ratios agree very well with the ones deduced from CN and
CO but are lower than those previously reported on the basis of HCO,
tending to suggest that the bulk of the HCO in our sources was formed on
dust grain mantles and not in the gas phase.Comment: 27 pages, 8 figures, 7 tables. Accepted for publication in The
Astrophysical Journa
Stacking up electron-rich and electron-deficient monolayers to achieve extraordinary mid- to far-infrared excitonic absorption: Interlayer excitons in the C3B/C3N bilayer
Our ability to efficiently detect and generate far-infrared (i.e., terahertz)
radiation is vital in areas spanning from biomedical imaging to interstellar
spectroscopy. Despite decades of intense research, bridging the terahertz gap
between electronics and optics remains a major challenge due to the lack of
robust materials that can efficiently operate in this frequency range, and
two-dimensional (2D) type-II heterostructures may be ideal candidates to fill
this gap. Herein, using highly accurate many-body perturbation theory within
the GW plus Bethe-Salpeter equation approach, we predict that a type-II
heterostructure consisting of an electron rich C3N and an electron deficient
C3B monolayers can give rise to extraordinary optical activities in the mid- to
far-infrared range. C3N and C3B are two graphene-derived 2D materials that have
attracted increasing research attention. Although both C3N and C3B monolayers
are moderate gap 2D materials, and they only couple through the rather weak van
der Waals interactions, the bilayer heterostructure surprisingly supports
extremely bright, low-energy interlayer excitons with large binding energies of
0.2 ~ 0.4 eV, offering an ideal material with interlayer excitonic states for
mid-to far-infrared applications at room temperature. We also investigate in
detail the properties and formation mechanism of the inter- and intra-layer
excitons.Comment: 15 pages, 6 figure
App Store at OpenNEX: A Gateway to Help Find Apps over Big Data on the Cloud
In this on-going work, we report our efforts of building App Store at OpenNEX, which aims to provide a data analytics software search engine to help researchers find reusable software components to facilitate the development of their own algorithms
Optically enhanced single- and multi-stacked 1.55 μm InAs/InAlGaAs/InP quantum dots for laser applications
For the development of InAs/InP quantum dot (QD) lasers for 1.55 μm telecom wavelength, there are two main challenges: (1) morphological preference for quantum dashes over QDs, and (2) generally poor size uniformity of QDs (dashes). This study addresses the issues, in synchronous, by demonstrating the improved optical properties of 1.55 μm InAs/InP QDs at room temperature with excellent reproducibility. A high-density (∼4 × 1010 cm−2) dot-like morphology was initially attained via adjusting the growth parameters, albeit with a large full-width at half-maximum (FWHM) of ∼80 meV and a peak position of a wavelength longer than 1.55 μm. For improvement, the indium-flush technique was employed, which enhanced the uniformity of InAs QDs and substantially lowered the FWHM of five (single) stacked QDs to 50.9 meV (47.9 meV). This technique also blue-shifted the emission peak to 1530.2 nm (1522 nm). The InAs/InP QDs presented are appropriate for the fabrication of high-performance 1.55 μm lasers on InP (001) and, potentially, emerging light sources on the important Si (001)
Entanglement control in one-dimensional random XY spin chain
The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.Comment: 13 pages, 4 figure
Risk of bias and methodological issues in randomised controlled trials of acupuncture for knee osteoarthritis: A cross-sectional study
© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.
Objective To assess risk of bias and to investigate methodological issues concerning the design, conduct and analysis of randomised controlled trials (RCTs) testing acupuncture for knee osteoarthritis (KOA). Methods PubMed, EMBASE, Cochrane Central Register of Controlled Trials and four major Chinese databases were searched for RCTs that investigated the effect of acupuncture for KOA. The Cochrane tool was used to examine the risk of bias of eligible RCTs. Their methodological details were examined using a standardised and pilot-Tested questionnaire of 48 items, together with the association between four predefined factors and important methodological quality indicators. Results A total of 248 RCTs were eligible, of which 39 (15.7%) used computer-generated randomisation sequence. Of the 31 (12.5%) trials that stated the allocation concealment, only one used central randomisation. Twenty-five (10.1%) trials mentioned that their acupuncture procedures were standardised, but only 18 (7.3%) specified how the standardisation was achieved. The great majority of trials (n=233, 94%) stated that blinding was in place, but 204 (87.6%) did not clarify who was blinded. Only 27 (10.9%) trials specified the primary outcome, for which 7 used intention-To-Treat analysis. Only 17 (6.9%) trials included details on sample size calculation; none preplanned an interim analysis and associated stopping rule. In total, 46 (18.5%) trials explicitly stated that loss to follow-up occurred, but only 6 (2.4%) provided some information to deal with the issue. No trials prespecified, conducted or reported any subgroup or adjusted analysis for the primary outcome. Conclusion The overall risk of bias was high among published RCTs testing acupuncture for KOA. Methodological limitations were present in many important aspects of design, conduct and analyses. These findings inform the development of evidence-based methodological guidance for future trials assessing the effect of acupuncture for KOA
Coupled KdV equations derived from atmospherical dynamics
Some types of coupled Korteweg de-Vries (KdV) equations are derived from an
atmospheric dynamical system. In the derivation procedure, an unreasonable
-average trick (which is usually adopted in literature) is removed. The
derived models are classified via Painlev\'e test. Three types of
-function solutions and multiple soliton solutions of the models are
explicitly given by means of the exact solutions of the usual KdV equation. It
is also interesting that for a non-Painlev\'e integrable coupled KdV system
there may be multiple soliton solutions.Comment: 19 pages, 2 figure
Entanglement dynamics of two-qubit system in different types of noisy channels
In this paper, we study entanglement dynamics of a two-qubit extended
Werner-like state locally interacting with independent noisy channels, i.e.,
amplitude damping, phase damping and depolarizing channels. We show that the
purity of initial entangled state has direct impacts on the entanglement
robustness in each noisy channel. That is, if the initial entangled state is
prepared in mixed instead of pure form, the state may exhibit entanglement
sudden death (ESD) and/or be decreased for the critical probability at which
the entanglement disappear.Comment: 11 pages, 6 figure
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