6,260 research outputs found
Role of in the reaction near threshold
The role of the resonance in the reaction near threshold is studied within an effective Lagrangian
approach. We perform a calculation for the total and differential cross section
of the reaction by including the contributions
from the intermediate state decaying into
dominated by and mesons exchanges, the nucleon pole and
resonance decaying into dominated by exchanges of
and mesons. Besides, the non-resonance process and contact terms
to keep the total scattering amplitude gauge invariant are also considered.
With our model parameters, the total cross section of this reaction is of the
order of nanobarn at photon beam energy GeV. It is
expected that our model predictions could be tested by future experiments.Comment: Published versio
A search for 95 GHz class I methanol masers in molecular outflows
We have observed a sample of 288 molecular outflow sources including 123
high-mass and 165 low-mass sources to search for class I methanol masers at 95
GHz transition and to investigate relationship between outflow characteristics
and class I methanol maser emission with the PMO-13.7m radio telescope. Our
survey detected 62 sources with 95 GHz methanol masers above 3
detection limit, which include 47 high-mass sources and 15 low-mass sources.
Therefore the detection rate is 38% for high-mass outflow sources and 9% for
low-mass outflow sources, suggesting that class I methanol maser is relatively
easily excited in high-mass sources. There are 37 newly detected 95 GHz
methanol masers (including 27 high-mass and 10 low-mass sources), 19 of which
are newly identified (i.e. first identification) class I methanol masers
(including 13 high-mass and 6 low-mass sources). Statistical analysis for the
distributions of maser detections with the outflow parameters reveals that the
maser detection efficiency increases with outflow properties (e.g. mass,
momentum, kinetic energy and mechanical luminosity of outflows etc.).
Systematic investigations of relationships between the intrinsic luminosity of
methanol maser and the outflow properties (including mass, momentum, kinetic
energy, bolometric luminosity and mass loss rate of central stellar sources)
indicate a positive correlations. This further supports that class I methanol
masers are collisionally pumped and associated with shocks, where outflows
interact with the surrounding ambient medium.Comment: 32 pages, 5 figures, accepted by Ap
Genetic Algorithm with Evolutionary Chain-Based Mutation and Its Applications
Mutation is one of the important operators in genetic algorithm. In traditional genetic algorithm, mutation is activated stochastically. In this way it is unknown and cannot be controlled for which individuals to be mutated. Therefore, it is unavoidable that some good individuals are destroyed by mutation and then the evolutionary efficiency of the genetic algorithm is dampened. Owing to this kind of destructivity of mutation, the operator of mutation has to be limited within a very small probability, and the potentiality of mutation is consequently limited. In this paper, we present an evolutionary chain-based mutation and a control strategy of reasonable competition, in which the heuristic information provided by the evaluation function is well utilized. This method avoids the blindness of stochastic mutation. The performance improved in this method is shown by two examples, a fuzzy modeling for the identification of a nonlinear function and a typical combinatorial optimization problem-the traveling salesman problem
A New 95 GHz Methanol Maser Catalog: I. Data
The Purple Mountain Observatory 13.7 m radio telescope has been used to
search for 95 GHz (8--7A) class I methanol masers towards 1020
Bolocam Galactic Plane Survey (BGPS) sources, leading to 213 detections. We
have compared the line width of the methanol and HCO thermal emission in
all of the methanol detections and on that basis we find 205 of the 213
detections are very likely to be masers. This corresponds to an overall
detection rate of 95 GHz methanol masers towards our BGPS sample of 20%. Of the
205 detected masers 144 (70%) are new discoveries. Combining our results with
those of previous 95 GHz methanol masers searches, a total of four hundred and
eighty-one 95 GHz methanol masers are now known, we have compiled a catalog
listing the locations and properties of all known 95 GHz methanol masers.Comment: 18 pages, 7 figures, 8 tables, accepted for publication in ApJ
Linearized Tensor Renormalization Group Algorithm for Thermodynamics of Quantum Lattice Models
A linearized tensor renormalization group (LTRG) algorithm is proposed to
calculate the thermodynamic properties of one-dimensional quantum lattice
models, that is incorporated with the infinite time-evolving block decimation
technique, and allows for treating directly the two-dimensional transfer-matrix
tensor network. To illustrate its feasibility, the thermodynamic quantities of
the quantum XY spin chain are calculated accurately by the LTRG, and the
precision is shown to be comparable with (even better than) the transfer matrix
renormalization group (TMRG) method. Unlike the TMRG scheme that can only deal
with the infinite chains, the present LTRG algorithm could treat both finite
and infinite systems, and may be readily extended to boson and fermion quantum
lattice models.Comment: published versio
Let Graph be the Go Board: Gradient-free Node Injection Attack for Graph Neural Networks via Reinforcement Learning
Graph Neural Networks (GNNs) have drawn significant attentions over the years
and been broadly applied to essential applications requiring solid robustness
or vigorous security standards, such as product recommendation and user
behavior modeling. Under these scenarios, exploiting GNN's vulnerabilities and
further downgrading its performance become extremely incentive for adversaries.
Previous attackers mainly focus on structural perturbations or node injections
to the existing graphs, guided by gradients from the surrogate models. Although
they deliver promising results, several limitations still exist. For the
structural perturbation attack, to launch a proposed attack, adversaries need
to manipulate the existing graph topology, which is impractical in most
circumstances. Whereas for the node injection attack, though being more
practical, current approaches require training surrogate models to simulate a
white-box setting, which results in significant performance downgrade when the
surrogate architecture diverges from the actual victim model. To bridge these
gaps, in this paper, we study the problem of black-box node injection attack,
without training a potentially misleading surrogate model. Specifically, we
model the node injection attack as a Markov decision process and propose
Gradient-free Graph Advantage Actor Critic, namely G2A2C, a reinforcement
learning framework in the fashion of advantage actor critic. By directly
querying the victim model, G2A2C learns to inject highly malicious nodes with
extremely limited attacking budgets, while maintaining a similar node feature
distribution. Through our comprehensive experiments over eight acknowledged
benchmark datasets with different characteristics, we demonstrate the superior
performance of our proposed G2A2C over the existing state-of-the-art attackers.
Source code is publicly available at: https://github.com/jumxglhf/G2A2C}.Comment: AAAI 2023. v2: update acknowledgement section. arXiv admin note:
substantial text overlap with arXiv:2202.0938
Gas kinematics and star formation in the filamentary molecular cloud G47.06+0.26
We performed a multi-wavelength study toward the filamentary cloud
G47.06+0.26 to investigate the gas kinematics and star formation. We present
the 12CO (J=1-0), 13CO (J=1-0) and C18O (J=1-0) observations of G47.06+0.26
obtained with the Purple Mountain Observation (PMO) 13.7 m radio telescope to
investigate the detailed kinematics of the filament. The 12CO (J=1-0) and 13CO
(J=1-0) emission of G47.06+0.26 appear to show a filamentary structure. The
filament extends about 45 arcmin (58.1 pc) along the east-west direction. The
mean width is about 6.8 pc, as traced by the 13CO (J=1-0) emission. G47.06+0.26
has a linear mass density of about 361.5 Msun/pc. The external pressure (due to
neighboring bubbles and H II regions) may help preventing the filament from
dispersing under the effects of turbulence. From the velocity-field map, we
discern a velocity gradient perpendicular to G47.06+0.26. From the Bolocam
Galactic Plane Survey (BGPS) catalog, we found nine BGPS sources in
G47.06+0.26, that appear to these sources have sufficient mass to form massive
stars. We obtained that the clump formation efficiency (CFE) is about 18% in
the filament. Four infrared bubbles were found to be located in, and adjacent
to, G47.06+0.26. Particularly, infrared bubble N98 shows a cometary structure.
CO molecular gas adjacent to N98 also shows a very intense emission. H II
regions associated with infrared bubbles can inject the energy to surrounding
gas. We calculated the kinetic energy, ionization energy, and thermal energy of
two H II regions in G47.06+0.26. From the GLIMPSE I catalog, we selected some
Class I sources with an age of about 100000 yr, which are clustered along the
filament. The feedback from the H II regions may cause the formation of a new
generation of stars in filament G47.06+0.26.Comment: 10 pages, 11 figures, accepted for publication in A&
Об одном подходе к нахождению периодических решений нелинейного обычного дифференциального уравнения второго порядка
Запропоновано підхід до знаходження періодичних розв’язків нелінійного диференціального рівняння другого порядку, який базується на побудові функції Гріна для диференціального оператора, що визначений на функціях, які задовольняють періодичним крайовим умовам. Наведено необхідні та достатні умови існування періодичних розв’язків рівняння.The approach to determining of periodic solutions of the nonlinear differential second order equation is proposed. The approach is based on construction of the Green’s function for differential operator defined on the functions, which satisfy boundary conditions. Necessary and sufficient conditions for the existence of periodic solutions of the equation are shown.Предложен подход к нахождению периодических решений нелинейного дифференциального уравнения второго порядка, который базируется на построении функции Грина для дифференциального оператора, который определен на функциях, которые удовлетворяют периодическим краевым условиям. Приведено необходимые и достаточные условия существование периодических решений уравнения
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