1,493 research outputs found
The Multiphoton Interaction of Lambda Model Atom and Two-Mode Fields
The system of two-mode fields interacting with atom by means of multiphotons is addressed, and the non-classical statistic quality of two-mode fields with interaction is discussed. Through mathematical calculation, some new rules of non-classical effects of two-mode fields which evolue with time, are established
Interplay between Quantum Size Effect and Strain Effect on Growth of Nanoscale Metal Thin Film
We develop a theoretical framework to investigate the interplay between
quantum size effect (QSE) and strain effect on the stability of metal
nanofilms. The QSE and strain effect are shown to be coupled through the
concept of "quantum electronic stress. First-principles calculations reveal
large quantum oscillations in the surface stress of metal nanofilms as a
function of film thickness. This adds extrinsically additional strain-coupled
quantum oscillations to surface energy of strained metal nanofilms. Our theory
enables a quantitative estimation of the amount of strain in experimental
samples, and suggests strain be an important factor contributing to the
discrepancies between the existing theories and experiments
First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope
Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by
colliding with the dense interstellar medium (ISM). Arp 220 is the nearest
ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme
levels, so it has long been predicted to emit high-energy gamma-rays. However,
no evidence of gamma-ray emission was found despite intense efforts of search.
Here we report the discovery of high-energy gamma-ray emission above 200 MeV
from Arp 220 at a confidence level of using 7.5 years of
\textsl {Fermi} Large Area Telescope observations. The gamma-ray emission shows
no significant variability over the observation period and it is consistent
with the quasi-linear scaling relation between the gamma-ray luminosity and
total infrared luminosity for star-forming galaxies, suggesting that these
gamma-rays arise from CR interactions. As the high density medium of Arp 220
makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to
measure the efficiency of powering CRs by supernova (SN) remnants given a known
supernova rate in Arp 220. We find that this efficiency is about
for CRs above 1 GeV.Comment: Accepted by ApJL, 6 pages, 3 figure
Tier Balancing: Towards Dynamic Fairness over Underlying Causal Factors
The pursuit of long-term fairness involves the interplay between
decision-making and the underlying data generating process. In this paper,
through causal modeling with a directed acyclic graph (DAG) on the
decision-distribution interplay, we investigate the possibility of achieving
long-term fairness from a dynamic perspective. We propose Tier Balancing, a
technically more challenging but more natural notion to achieve in the context
of long-term, dynamic fairness analysis. Different from previous fairness
notions that are defined purely on observed variables, our notion goes one step
further, capturing behind-the-scenes situation changes on the unobserved latent
causal factors that directly carry out the influence from the current decision
to the future data distribution. Under the specified dynamics, we prove that in
general one cannot achieve the long-term fairness goal only through one-step
interventions. Furthermore, in the effort of approaching long-term fairness, we
consider the mission of "getting closer to" the long-term fairness goal and
present possibility and impossibility results accordingly
Keystroke Biometrics for Freely Typed Text Based on CNN model
Keystroke biometrics, as an authentication method with advantages of no extra hardware cost, easy-to-integrate and high-security, has attracted much attention in user authentication. However, a mass of researches on keystroke biometrics have focused on the fixed-text analysis, while only a few took free-text analysis into consideration. And in the field of free-text analysis, most researchers usually devote their efforts to extracting the most appropriate keystroke features on their own experience. These methods were inevitably questionable due to their strong subjectivity. In this paper we proposed a multi-user keystroke authentication scheme based on CNN model, which can automatically figure out the appropriate features for the model, adjust and optimize the model constantly to further enhance the performance of model. In the experiment on a small sample set, the performance is improved more than 10% compared with the benchmark. Our model achieves an average recognition accuracy of 92.58%, with FAR of 0.24% and FRR of 7.34%
Evidence of a spectral break in the gamma-ray emission of the disk component of Large Magellanic Cloud: a hadronic origin?
It has been suggested that high-energy gamma-ray emission ()
of nearby star-forming galaxies may be produced predominantly by cosmic rays
colliding with the interstellar medium through neutral pion decay. The
pion-decay mechanism predicts a unique spectral signature in the gamma-ray
spectrum, characterized by a fast rising spectrum and a spectral break below a
few hundreds of MeV. We here report the evidence of a spectral break around 500
MeV in the disk emission of Large Magellanic Cloud (LMC), which is found in the
analysis of the gamma-ray data extending down to 60 MeV observed by {\it
Fermi}-Large Area Telescope. The break is well consistent with the pion-decay
model for the gamma-ray emission, although leptonic models, such as the
electron bremsstrahlung emission, cannot be ruled out completely.Comment: 11 pages, 4 figures, Accepted by Ap
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