9,684 research outputs found
Constituting We the People
We study roles of the thermosphere and exosphere on the Martian ionospheric
structure and ion escape rates in the process of the solar wind-Mars
interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate
the Martian ionosphere and magnetosphere. The thermosphere background is
taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the
oxygen exosphere is adopted from the Mars exosphere Monte Carlo model -
Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the
combination of 1D (globally averaged) and 3D thermospheres and exospheres are
studied.
The ion escape rates calculated by adopting 1D and 3D atmospheres are
similar; however, the latter are required to adequately reproduce MAVEN
ionospheric observations. In addition, our simulations show that the 3D hot
oxygen corona plays an important role in preventing planetary molecular ions
(O and CO) escaping from Mars, mainly resulting from the mass
loading of the high-altitude exospheric O ions. The thermospheric
oxygen atom, however, is demonstrated to be the primary neutral source for
O ion escape during the relatively weak solar cycle 24.Comment: 21 pages, 10 figures, 4 tables, accepted for publication in Journal
of Geophysical Research-Space Physic
Improved PSO algorithm based on chaos theory and its application to design flood hydrograph
AbstractThe deficiencies of basic particle swarm optimization (bPSO) are its ubiquitous prematurity and its inability to seek the global optimal solution when optimizing complex high-dimensional functions. To overcome such deficiencies, the chaos-PSO (COSPSO) algorithm was established by introducing the chaos optimization mechanism and a global particle stagnation-disturbance strategy into bPSO. In the improved algorithm, chaotic movement was adopted for the particles' initial movement trajectories to replace the former stochastic movement, and the chaos factor was used to guide the particles' path. When the global particles were stagnant, the disturbance strategy was used to keep the particles in motion. Five benchmark optimizations were introduced to test COSPSO, and they proved that COSPSO can remarkably improve efficiency in optimizing complex functions. Finally, a case study of COSPSO in calculating design flood hydrographs demonstrated the applicability of the improved algorithm
Isospin dependence of projectile-like fragment production at intermediate energies
The cross sections of fragments produced in 140 MeV Ca + Be
and Ni + Be reactions are calculated by the statistical
abration-ablation(SAA) model and compared to the experimental results measured
at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State
University. The fragment isotopic and isotonic cross section distributions of
Ca and Ca, Ni and Ni, Ca and Ni, and
Ca and Ni are compared and the isospin dependence of the
projectile fragmentation is studied. It is found that the isospin dependence
decreases and disappears in the central collisions. The shapes of the fragment
isotopic and isotonic cross section distributions are found to be very similar
for symmetric projectile nuclei. The shapes of the fragment isotopic and
isotonic distributions of different asymmetric projectiles produced in
peripheral reactions are found very similar. The similarity of the
distributions are related to the similar proton and neutron density
distributions inside the nucleus in framework of the SAA model.Comment: 7 pages, 4 figures; to be published in Phys Rev
Local Geometric Distortions Resilient Watermarking Scheme Based on Symmetry
As an efficient watermark attack method, geometric distortions destroy the
synchronization between watermark encoder and decoder. And the local geometric
distortion is a famous challenge in the watermark field. Although a lot of
geometric distortions resilient watermarking schemes have been proposed, few of
them perform well against local geometric distortion like random bending attack
(RBA). To address this problem, this paper proposes a novel watermark
synchronization process and the corresponding watermarking scheme. In our
scheme, the watermark bits are represented by random patterns. The message is
encoded to get a watermark unit, and the watermark unit is flipped to generate
a symmetrical watermark. Then the symmetrical watermark is embedded into the
spatial domain of the host image in an additive way. In watermark extraction,
we first get the theoretically mean-square error minimized estimation of the
watermark. Then the auto-convolution function is applied to this estimation to
detect the symmetry and get a watermark units map. According to this map, the
watermark can be accurately synchronized, and then the extraction can be done.
Experimental results demonstrate the excellent robustness of the proposed
watermarking scheme to local geometric distortions, global geometric
distortions, common image processing operations, and some kinds of combined
attacks
Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca + Ca by Quantum Molecular Dynamics Model
Anisotropic flows (, , and ) of light fragments up till
the mass number 4 as a function of rapidity have been studied for 25
MeV/nucleon Ca + Ca at large impact parameters by Quantum
Molecular Dynamics model. A phenomenological scaling behavior of rapidity
dependent flow parameters (n = 1, 2, 3 and 4) has been found as a
function of mass number plus a constant term, which may arise from the
interplay of collective and random motions. In addition, keeps
almost independent of rapidity and remains a rough constant of 1/2 for all
light fragments.Comment: 4 pages, 5 figure
Scaling of Anisotropic Flows and Nuclear Equation of State in Intermediate Energy Heavy Ion Collisions
Elliptic flow () and hexadecupole flow () of light clusters have
been studied in details for 25 MeV/nucleon Kr + Sn at large
impact parameters by Quantum Molecular Dynamics model with different potential
parameters. Four parameter sets which include soft or hard equation of state
(EOS) with/without symmetry energy term are used. Both number-of-nucleon ()
scaling of the elliptic flow versus transverse momentum () and the scaling
of versus have been demonstrated for the light clusters
in all above calculation conditions. It was also found that the ratio of
keeps a constant of 1/2 which is independent of for all the
light fragments. By comparisons among different combinations of EOS and
symmetry potential term, the results show that the above scaling behaviors are
solid which do not depend the details of potential, while the strength of flows
is sensitive to EOS and symmetry potential term.Comment: 5 pages, 5 figure
Measuring Perceptual Color Differences of Smartphone Photographs
Measuring perceptual color differences (CDs) is of great importance in modern
smartphone photography. Despite the long history, most CD measures have been
constrained by psychophysical data of homogeneous color patches or a limited
number of simplistic natural photographic images. It is thus questionable
whether existing CD measures generalize in the age of smartphone photography
characterized by greater content complexities and learning-based image signal
processors. In this paper, we put together so far the largest image dataset for
perceptual CD assessment, in which the photographic images are 1) captured by
six flagship smartphones, 2) altered by Photoshop, 3) post-processed by
built-in filters of the smartphones, and 4) reproduced with incorrect color
profiles. We then conduct a large-scale psychophysical experiment to gather
perceptual CDs of 30,000 image pairs in a carefully controlled laboratory
environment. Based on the newly established dataset, we make one of the first
attempts to construct an end-to-end learnable CD formula based on a lightweight
neural network, as a generalization of several previous metrics. Extensive
experiments demonstrate that the optimized formula outperforms 33 existing CD
measures by a large margin, offers reasonable local CD maps without the use of
dense supervision, generalizes well to homogeneous color patch data, and
empirically behaves as a proper metric in the mathematical sense. Our dataset
and code are publicly available at https://github.com/hellooks/CDNet.Comment: 10 figures, 8 tables, 14 page
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