21,116 research outputs found
Ghost imaging without beam splitter
Many significant results have been achieved in the fields of ghost imaging,
in which the beam splitter is an indispensable optical component. This paper
introduces a method to realize ghost imaging without beam splitter. And we
study this method experimentally and theoretically. Finally, we suggest that
our device can be applied to implement the ghost imaging when we use the Sun
light as the light source
A New HDG Method for Dirichlet Boundary Control of Convection Diffusion PDEs II: Low Regularity
In the first part of this work, we analyzed a Dirichlet boundary control
problem for an elliptic convection diffusion PDE and proposed a new
hybridizable discontinuous Galerkin (HDG) method to approximate the solution.
For the case of a 2D polygonal domain, we also proved an optimal superlinear
convergence rate for the control under certain assumptions on the domain and on
the target state. In this work, we revisit the convergence analysis without
these assumptions; in this case, the solution can have low regularity and we
use a different analysis approach. We again prove an optimal convergence rate
for the control, and present numerical results to illustrate the convergence
theory
Energy Spectra of Anti-nucleons in Finite Nuclei
The quantum vacuum in a many-body system of finite nuclei has been
investigated within the relativistic Hartree approach which describes the bound
states of nucleons and anti-nucleons consistently. The contributions of the
Dirac sea to the source terms of the meson-field equations are taken into
account up to the one-nucleon loop and one-meson loop. The tensor couplings for
the - and -meson are included in the model. The overall nucleon
spectra of shell-model states are in agreement with the data. The calculated
anti-nucleon spectra in the vacuum differ about 20 -- 30 MeV with and without
the tensor-coupling effects.Comment: 4 pages, to appear in the Proceedings of MENU 2004 (Beijing, Aug. 29
-- Sept. 4, 2004
Improved cosmological constraints on the curvature and equation of state of dark energy
We apply the Constitution compilation of 397 supernova Ia, the baryon
acoustic oscillation measurements including the parameter, the distance
ratio and the radial data, the five-year Wilkinson microwave anisotropy probe
and the Hubble parameter data to study the geometry of the universe and the
property of dark energy by using the popular Chevallier-Polarski-Linder and
Jassal-Bagla-Padmanabhan parameterizations. We compare the simple
method of joined contour estimation and the Monte Carlo Markov chain method,
and find that it is necessary to make the marginalized analysis on the error
estimation. The probabilities of and in the
Chevallier-Polarski-Linder model are skew distributions, and the marginalized
errors are ,
, , and
. For the Jassal-Bagla-Padmanabhan model, the
marginalized errors are ,
, , and
. The equation of state parameter of dark energy
is negative in the redshift range at more than level.
The flat CDM model is consistent with the current observational data
at the level.Comment: 10 figures, 12 pages, Classical and Quantum Gravity in press; v2 to
match the pulished versio
Seething Horizontal Magnetic Fields in the Quiet Solar Photosphere
The photospheric magnetic field outside of active regions and the network has
a ubiquitous and dynamic line-of-sight component that strengthens from disk
center to limb as expected for a nearly horizontal orientation. This component
shows a striking time variation with an average temporal rms near the limb of
1.7 G at ~3" resolution. In our moderate resolution observations the nearly
horizontal component has a frequency variation power law exponent of -1.4 below
1.5 mHz and is spatially patchy on scales up to ~15 arcsec. The field may be a
manifestation of changing magnetic connections between eruptions and evolution
of small magnetic flux elements in response to convective motions. It shows no
detectable latitude or longitude variations.Comment: 7 pages, 6 figures, submitted to ApJ letters, quality of figures
significantly degraded here by compression requirement
Non-Parametric Estimation of Copula Parameters: Testing for Time-Varying Correlation
The correlation structure of financial assets is a key input with regard to portfolio and risk management. In this paper, we propose a non-parametric estimation method for the time-varying copula parameter. This is achieved in two steps: first, displaying the marginal distributions of financial asset returns by applying the empirical distribution function; second, by implementing the local likelihood method to estimate the copula parameters. The method for obtaining the optimal bandwidth through a maximum pseudo likelihood function and a statistical test on whether the copula parameter is time-varying are also introduced. A simulation study is conducted to show that our method is superior to its contender. Finally, we verify the proposed estimation methodology and time-varying statistical test by analysing the dynamic linkages between the Shanghai, Shenzhen and Hong Kong stock markets
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