11,814 research outputs found
An introduction to a new space debris evolution model -- SOLEM
SOLEM is the first space debris long-term evolution model of China. This
paper describes the principles, components and workflow of the SOLEM. The
effects of different mitigation measures based on SOLEM model are analyzed and
presented. The limitation of the model is pointed out and its future
improvement work-plan is prospected.Comment: 16 pages, 14 figure
Quantum Fisher information and symmetric logarithmic derivative via anti-commutators
Symmetric logarithmic derivative (SLD) is a key quantity to obtain quantum
Fisher information (QFI) and to construct the corresponding optimal
measurements. Here we develop a method to calculate the SLD and QFI via
anti-commutators. This method is originated from the Lyapunov representation
and would be very useful for cases that the anti-commutators among the state
and its partial derivative exhibits periodic properties. As an application, we
discuss a class of states, whose squares linearly depend on the states
themselves, and give the corresponding analytical expressions of SLD and QFI. A
noisy scenario of this class of states is also considered and discussed.
Finally, we readily apply the method to the block-diagonal states and the
multi-parameter estimation problems.Comment: 12 pages, no figur
Quantum Fisher information for density matrices with arbitrary ranks
We provide a new expression of the quantum Fisher information(QFI) for a
general system. Utilizing this expression, the QFI for a non-full rank density
matrix is only determined by its support. This expression can bring convenience
for a infinite dimensional density matrix with a finite support. Besides, a
matrix representation of the QFI is also given.Comment: 6 pages, no figur
Maximal quantum Fisher information for general su(2) parametrization processes
Quantum Fisher information is a key concept in the field of quantum
metrology, which aims to enhance the parameter accuracy by using quantum
resources. In this paper, utilizing a representation of quantum Fisher
information for a general unitary parametrization process, we study unitary
parametrization processes governed by su(2) dynamics. We obtain the analytical
expression for the Hermitian operator of the parametrization and the maximal
quantum Fisher information. We find that the maximal quantum Fisher information
over the parameter space consists of two parts, one is quadratic in the time
and the other oscillates with the time. We apply our result to the estimation
of a magnetic field and obtained the maximal quantum Fisher information. We
further discuss a driving field with a time-dependent Hamiltonian and find the
maximal quantum Fisher information of the driving frequency attains optimum
when it is in resonance with the atomic frequency.Comment: 6 pages, 2 figures, published versio
Non-unital non-Markovianity of quantum dynamics
We show that Breuer-Laine-Piilo (BLP) non-Markovianity cannot capture the
dynamical information in the non-unital aspect of the quantum dynamics.
Moreover, we provide a measure on the effect of the non-unitality of quantum
processes on the infinitesimal non-divisibility. This measure can be used as a
supplement to BLP non-Markovianity for non-unital quantum processes. A measure
on the degree of the non-unital behavior of quantum processes is also given in
this paper.Comment: accepted by Phys. Rev.
Hadronic decays of in the perturbative QCD approach
We calculate the branching ratios and polarization fractions of the decays in the perturbative QCD(pQCD) approach at leading order, where
() stands for the axial-vector state. By
combining the phenomenological analyses with the perturbative calculations, we
find the following results: (a) the large decay rates around to
of the decays dominated by the longitudinal
polarization(except for the mode) are predicted and
basically consistent with those in the QCD factorization(QCDF) within errors,
which are expected to be tested by the Large Hadron Collider and Belle-II
experiments. The large branching ratio could provide
hints to help explore the mechanism of the color-suppressed decays. (b) the
rather different QCD behaviors between the and mesons result in the
destructive(constructive) contributions in the nonfactorizable spectator
diagrams with emission. Therefore, an interesting pattern of the
branching ratios appears for the color-suppressed and modes in the pQCD approach, , which is different
from in the QCDF and would be verified at future experiments. (c) the
large naive factorization breaking effects are observed in these decays. Specifically, the large nonfactorizable spectator(weak
annihilation) amplitudes contribute to the mode(s), which demand confirmations
via the precise measurements.Comment: 13 pages, 1 figure, 5 tables, revtex fil
A Collision Probability Estimation Algorithm Used in the Space Debris Evolutionary Model
An in-depth analysis is performed on the problem that one parameter of the
Cube model can affects the final simulation results of space debris long-term
evolution model, which weakens the representativeness of the space debris
evolution model. We made some improvements and proposed an Improved-Cube
(I-Cube) model. By multiple Monte Carlo simulations, it is indicated that the
I-Cube model offered a more accurate and more reasonable option for collision
probability estimation in the space debris evolution process. The simulation
results of space debris long-term evolution model are no longer sensitive to
the collision probability estimation model parameters, thus improved the
reliability of space debris long-term evolution model.Comment: 8pages, in Chinese, 7figure
Strongly screening electron capture rates of chromium isotopes in presupernova
Taking into account the effect of electron screening on the electron energy
and electron capture threshold energy, by using the method of Shell-Model Monte
Carlo and Random Phase Approximation theory, we investigate the strong electron
screening capture rates of chromium isotopes according to the linear response
theory screening model. The strong screening rates can decrease by about
40.43\% (e.g., for Cr at ). Our conclusions may be
helpful to the researches of supernova explosion and numerical simulation.Comment: 9 pages, 2 figures,Accepted for publication in Astronomy and
Astrophysics (RAA
Beam Dump Window Design for CSNS
Beam dump window is one of the most important parts of beam dump of China
Spallation Neutron Source(CSNS). The material, structure and other concerned
issue have been discussed in this paper. Thermal analyses have been applied for
the beam dump window design. By comparison, GlidcopAL-15 and 316L have been
chosen as window material. The window section has been designed as inner convex
spherical surface and the window thickness has been set 1.5mm to 3mm by
structure optimization. The window safety has been confirmed under the damage
of magnet. All these analyses proved that the window can meet the requirements
of CSNS beam dump well.Comment: 7 pages,5 figure
Excitonic pairing of two-dimensional Dirac fermions near the antiferromagnetic quantum critical point
Two-dimensional Dirac fermions are subjected to two types of interactions,
namely the long-range Coulomb interaction and the short-range on-site
interaction. The former induces excitonic pairing if its strength is
larger than some critical value , whereas the latter drives an
antiferromagnetic Mott transition when its strength exceeds a threshold
. Here, we study the impacts of the interplay of these two interactions on
excitonic pairing with the Dyson-Schwinger equation approach. We find that the
critical value is increased by weak short-range interaction. As
increases to approach , the quantum fluctuation of antiferromagnetic order
parameter becomes important and interacts with the Dirac fermions via the
Yukawa coupling. After treating the Coulomb interaction and Yukawa coupling
interaction on an equal footing, we show that is substantially
increased as . Thus, the excitonic pairing is strongly
suppressed near the antiferromagnetic quantum critical point. We obtain a
global phase diagram on the - plane, and illustrate that the
excitonic insulating and antiferromagnetic phases are separated by an
intermediate semimetal phase. These results provide a possible explanation of
the discrepancy between recent theoretical progress on excitonic gap generation
and existing experiments in suspended graphene.Comment: 12 pages, 9 figures, 1 tabl
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