866 research outputs found
First Order Sea Clutter Cross Section for HF Hybrid Sky-Surface Wave Radar
This paper presents a modified method to simulate the first order sea clutter cross section for high frequency (HF) hybrid sky-surface wave radar, based on the existent model applied in the bistatic HF surface wave radar. The modification focuses on the derivation of Bragg scattering frequency and the ionosphere dispersive impact on the clutter resolution cell. Meanwhile, an analytic expression to calculate the dispersive transfer function is derived on condition that the ionosphere is spherical stratified. Simulation results explicate the variance of the cross section after taking account of the influence triggered by the actual clutter resolution cell, and the spectral width of the first order sea clutter is defined so as to compare the difference. Eventually, experiment results are present to verify the rationality and validity of the proposed method
Space-time Characteristics and Experimental Analysis of Broadening First-order Sea Clutter in HF Hybrid Sky-surface Wave Radar
In high frequency (HF) hybrid sky-surface wave radar, the first-order sea clutter broadening is very complex and serious under the influence of ionosphere and bistatic angle, which affects the detection of ship target. This paper analyzes the space-time characteristics based on the HF sky-surface wave experimental system. We first introduce the basic structure, working principle and position principle based on our experimental system. Also analyzed is the influence of ionosphere and bistatic angle on the space-time coupling characteristics of broadening first-order sea clutter and the performance of space-time adaptive processing (STAP). Finally, the results of theoretic analysis are examined with the experimental data. Simulation results show that the results of experiment consist with that of theoretic analysis
Interacting Agegraphic Dark Energy
A new dark energy model, named "agegraphic dark energy", has been proposed
recently, based on the so-called K\'{a}rolyh\'{a}zy uncertainty relation, which
arises from quantum mechanics together with general relativity. In this note,
we extend the original agegraphic dark energy model by including the
interaction between agegraphic dark energy and pressureless (dark) matter. In
the interacting agegraphic dark energy model, there are many interesting
features different from the original agegraphic dark energy model and
holographic dark energy model. The similarity and difference between agegraphic
dark energy and holographic dark energy are also discussed.Comment: 10 pages, 5 figures, revtex4; v2: references added; v3: accepted by
Eur. Phys. J. C; v4: published versio
China’s emerging global role: dissatisfied responsible great power
China has (re)emerged as a great power in a world not of its own making. The distribution of power in major organisations and the dominant norms of international interactions are deemed to unfairly favour the existing Western powers, and at times obstruct China’s ability to meet national development goals. Nevertheless, engaging the global economy has been a key source of economic growth (thus helping to maintain regime stability), and establishing China’s credentials as a responsible global actor is seen as a means of ensuring continued access to what China needs. As an emerging great power that is also still in many respects a developing country, China’s challenge is to change the global order in ways that do not cause global instability or generate crises that would damage China’s own ability to generate economic growth and ensure political stability
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
On Vanishing Theorems For Vector Bundle Valued p-Forms And Their Applications
Let be a strictly increasing function
with . We unify the concepts of -harmonic maps, minimal
hypersurfaces, maximal spacelike hypersurfaces, and Yang-Mills Fields, and
introduce -Yang-Mills fields, -degree, -lower degree, and generalized
Yang-Mills-Born-Infeld fields (with the plus sign or with the minus sign) on
manifolds. When and
the -Yang-Mills field becomes an ordinary Yang-Mills field,
-Yang-Mills field, a generalized Yang-Mills-Born-Infeld field with the plus
sign, and a generalized Yang-Mills-Born-Infeld field with the minus sign on a
manifold respectively. We also introduce the energy functional (resp.
-Yang-Mills functional) and derive the first variational formula of the
energy functional (resp. -Yang-Mills functional) with
applications. In a more general frame, we use a unified method to study the
stress-energy tensors that arise from calculating the rate of change of various
functionals when the metric of the domain or base manifold is changed. These
stress-energy tensors, linked to -conservation laws yield monotonicity
formulae. A "macroscopic" version of these monotonicity inequalities enables us
to derive some Liouville type results and vanishing theorems for forms with
values in vector bundles, and to investigate constant Dirichlet boundary value
problems for 1-forms. In particular, we obtain Liouville theorems for
harmonic maps (e.g. -harmonic maps), and Yang-Mills fields (e.g.
generalized Yang-Mills-Born-Infeld fields on manifolds). We also obtain
generalized Chern type results for constant mean curvature type equations for
forms on and on manifolds with the global doubling property
by a different approach. The case and is due to Chern.Comment: 1. This is a revised version with several new sections and an
appendix that will appear in Communications in Mathematical Physics. 2. A
"microscopic" approach to some of these monotonicity formulae leads to
celebrated blow-up techniques and regularity theory in geometric measure
theory. 3. Our unique solution of the Dirichlet problems generalizes the work
of Karcher and Wood on harmonic map
Structure of ternary additive hard-sphere fluid mixtures
Monte Carlo simulations on the structural properties of ternary fluid
mixtures of additive hard spheres are reported. The results are compared with
those obtained from a recent analytical approximation [S. B. Yuste, A. Santos,
and M. Lopez de Haro, J. Chem. Phys. 108, 3683 (1998)] to the radial
distribution functions of hard-sphere mixtures and with the results derived
from the solution of the Ornstein-Zernike integral equation with both the
Martynov-Sarkisov and the Percus-Yevick closures. Very good agreement between
the results of the first two approaches and simulation is observed, with a
noticeable improvement over the Percus-Yevick predictions especially near
contact.Comment: 11 pages, including 8 figures; A minor change; accepted for
publication in PR
Entropic Corrections to Coulomb's Law
Two well-known quantum corrections to the area law have been introduced in
the literatures, namely, logarithmic and power-law corrections. Logarithmic
corrections, arises from loop quantum gravity due to thermal equilibrium
fluctuations and quantum fluctuations, while, power-law correction appears in
dealing with the entanglement of quantum fields in and out the horizon.
Inspired by Verlinde's argument on the entropic force, and assuming the quantum
corrected relation for the entropy, we propose the entropic origin for the
Coulomb's law in this note. Also we investigate the Uehling potential as a
radiative correction to Coulomb potential in 1-loop order and show that for
some value of distance the entropic corrections of the Coulomb's law is
compatible with the vacuum-polarization correction in QED. So, we derive
modified Coulomb's law as well as the entropy corrected Poisson's equation
which governing the evolution of the scalar potential . Our study further
supports the unification of gravity and electromagnetic interactions based on
the holographic principle.Comment: 17 pages, 5 figures, accepted in IJT
Use of traditional and complementary medicine as self-care strategies in community health centers
In China, Community Health Centers (CHCs) are major providers of primary care services, but their potential in empowering patients’ self-management capacity has not been assessed. This study aims to describe self-care practice patterns amongst CHC attendees in urban China.
In this cross-sectional quantitative study, 3360 CHC patients from 6 cities within the Pearl Delta Region were sampled using multistage cluster sampling.
Thirty-seven per cent had used with over-the-counter Chinese herbal medicines (OTC CHMs) in the past year and majority of respondents found OTC CHMs effective. OTC CHMs were more popular amongst those who needed to pay out of pocket for CHC services. Less than 10% used vitamins and minerals, and those with a lower socioeconomic background have a higher propensity to consume. Although doubts on their usefulness are expressed, their use by the vulnerable population may reflect barriers to access to conventional health care, cultural affinity, or a defense against negative consequences of illnesses. About 25% performed physical exercise, but the prevalence is lower amongst women and older people. Taiji seems to be an alternative for these populations with promising effectiveness, but overall only 6% of CHC attendees participated.
These results suggest that CHCs should start initiatives in fostering appropriate use of OTC CHM, vitamins, and minerals. Engaging community pharmacists in guiding safe and effective use of OTC CHM amongst the uninsured is essential given their low accessibility to CHC services. Prescription of Taiji instead of physical exercises to women and older people could be more culturally appropriate, and the possibility of including this as part of the CHC services worth further exploration
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