2,861 research outputs found
Casimir effect with a helix torus boundary condition
We use the generalized Chowla-Selberg formula to consider the Casimir effect
of a scalar field with a helix torus boundary condition in the flat
()-dimensional spacetime.
We obtain the exact results of the Casimir energy density and pressure for
any for both massless and massive scalar fields. The numerical calculation
indicates that once the topology of spacetime is fixed, the ratio of the sizes
of the helix will be a decisive factor. There is a critical value of
the ratio of the lengths at which the pressure vanishes. The pressure
changes from negative to positive as the ratio passes through
increasingly. In the massive case, we find the pressure tends to the result of
massless field when the mass approaches zero. Furthermore, there is another
critical ratio of the lengths and the pressure is
independent of the mass at in the D=3 case.Comment: 11 pages, 3 figures, to be published in Mod. Phys. Lett.
From Rayleigh-B\'enard convection to porous-media convection: how porosity affects heat transfer and flow structure
We perform a numerical study of the heat transfer and flow structure of
Rayleigh-B\'enard (RB) convection in (in most cases regular) porous media,
which are comprised of circular, solid obstacles located on a square lattice.
This study is focused on the role of porosity in the flow properties
during the transition process from the traditional RB convection with
(so no obstacles included) to Darcy-type porous-media convection with
approaching 0. Simulations are carried out in a cell with unity aspect ratio,
for the Rayleigh number from to and varying porosities
, at a fixed Prandtl number , and we restrict ourselves to the
two dimensional case. For fixed , the Nusselt number is found to vary
non-monotonously as a function of ; namely, with decreasing , it
first increases, before it decreases for approaching 0. The
non-monotonous behaviour of originates from two competing effects of
the porous structure on the heat transfer. On the one hand, the flow coherence
is enhanced in the porous media, which is beneficial for the heat transfer. On
the other hand, the convection is slowed down by the enhanced resistance due to
the porous structure, leading to heat transfer reduction. For fixed ,
depending on , two different heat transfer regimes are identified, with
different effective power-law behaviours of vs , namely, a steep one
for low when viscosity dominates, and the standard classical one for large
. The scaling crossover occurs when the thermal boundary layer thickness
and the pore scale are comparable. The influences of the porous structure on
the temperature and velocity fluctuations, convective heat flux, and energy
dissipation rates are analysed, further demonstrating the competing effects of
the porous structure to enhance or reduce the heat transfer
Heavy quark polarizations of in the general two Higgs doublet model
The polarizations of the heavy quark ( or ) in the process have been calculated in the general two Higgs doublet model.
The CP violating normal polarization of the top quark can reach 8%, and for the bottom quark, while it is zero in the standard model. The
longitudinal and transverse polarizations of the bottom quark can be
significantly different from those in SM and consequently could aslo be used as
the probe of the new physics.Comment: 12 pages, discussion on statistic significance added, version to
appear in PR
Large-Scale Gravitational Instability and Star Formation in the Large Magellanic Cloud
Large-scale star formation in disk galaxies is hypothesized to be driven by
global gravitational instability. The observed gas surface density is commonly
used to compute the strength of gravitational instability, but according to
this criterion star formation often appears to occur in gravitationally stable
regions. One possible reason is that the stellar contribution to the
instability has been neglected. We have examined the gravitational instability
of the Large Magellanic Cloud (LMC) considering the gas alone, and considering
the combination of collisional gas and collisionless stars. We compare the
gravitationally unstable regions with the on-going star formation revealed by
Spitzer observations of young stellar objects. Although only 62% of the massive
young stellar object candidates are in regions where the gas alone is unstable,
some 85% lie in regions unstable due to the combination of gas and stars. The
combined stability analysis better describes where star formation occurs. In
agreement with other observations and numerical models, a small fraction of the
star formation occurs in regions with gravitational stability parameter Q > 1.
We further measure the dependence of the star formation timescale on the
strength of gravitational instability, and quantitatively compare it to the
exponential dependence expected from numerical simulations.Comment: Accepted for publication in ApJ, 10 pages, 5 figure
Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections
We estimate the decay rates of ,
, and ,
, by taking into account both relativistic and
QCD radiative corrections. The decay amplitudes are derived in the
Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired
interquark potential are used to calculate the wave functions and decay widths
for these states. We find that the relativistic correction to the
ratio is negative and tends to compensate the positive contribution from
the QCD radiative correction. Our estimate gives and ,
which are smaller than their nonrelativistic values. The hadronic widths
and are then indicated accordingly to the first order
QCD radiative correction, if . The decay widths for
states are also estimated. We show that when making the assmption
that the quarks are on their mass shells our expressions for the decay widths
will become identical with that in the NRQCD theory to the next to leading
order of and .Comment: 14 pages LaTex (2 figures included
Microarray studies on effects of Pneumocystis carinii infection on global gene expression in alveolar macrophages
<p>Abstract</p> <p>Background</p> <p><it>Pneumocystis </it>pneumonia is a common opportunistic disease in AIDS patients. The alveolar macrophage is an important effector cell in the clearance of <it>Pneumocystis </it>organisms by phagocytosis. However, both the number and phagocytic activity of alveolar macrophages are decreased in <it>Pneumocystis </it>infected hosts. To understand how <it>Pneumocystis </it>inactivates alveolar macrophages, Affymetrix GeneChip<sup>® </sup>RG-U34A DNA microarrays were used to study the difference in global gene expression in alveolar macrophages from uninfected and <it>Pneumocystis carinii</it>-infected Sprague-Dawley rats.</p> <p>Results</p> <p>Analyses of genes that were affected by <it>Pneumocystis </it>infection showed that many functions in the cells were affected. Antigen presentation, cell-mediated immune response, humoral immune response, and inflammatory response were most severely affected, followed by cellular movement, immune cell trafficking, immunological disease, cell-to-cell signaling and interaction, cell death, organ injury and abnormality, cell signaling, infectious disease, small molecular biochemistry, antimicrobial response, and free radical scavenging. Since rats must be immunosuppressed in order to develop <it>Pneumocystis </it>infection, alveolar macrophages from four rats of the same sex and age that were treated with dexamethasone for the entire eight weeks of the study period were also examined. With a filter of false-discovery rate less than 0.1 and fold change greater than 1.5, 200 genes were found to be up-regulated, and 144 genes were down-regulated by dexamethasone treatment. During <it>Pneumocystis </it>pneumonia, 115 genes were found to be up- and 137 were down-regulated with the same filtering criteria. The top ten genes up-regulated by <it>Pneumocystis </it>infection were Cxcl10, Spp1, S100A9, Rsad2, S100A8, Nos2, RT1-Bb, Lcn2, RT1-Db1, and Srgn with fold changes ranging between 12.33 and 5.34; and the top ten down-regulated ones were Lgals1, Psat1, Tbc1d23, Gsta1, Car5b, Xrcc5, Pdlim1, Alcam, Cidea, and Pkib with fold changes ranging between -4.24 and -2.25.</p> <p>Conclusions</p> <p>In order to survive in the host, <it>Pneumocystis </it>organisms change the expression profile of alveolar macrophages. Results of this study revealed that <it>Pneumocystis </it>infection affects many cellular functions leading to reduced number and activity of alveolar macrophages during <it>Pneumocystis </it>pneumonia.</p
SDSS J143030.22-001115.1: A misclassified narrow-line Seyfert 1 galaxy with flat X-ray spectrum
We used multi-component profiles to model H and [O III]4959,5007 lines for SDSS J143030.22-001115.1, a narrow-line Seyfert 1
galaxy (NLS1) in a sample of 150 NLS1s candidates selected from the Sloan
Digital Sky Survey (SDSS) Early Data Release (EDR). After subtracting the
H contribution from narrow line regions (NLRs), we found that its full
width half maximum (FWHM) of broad H line is nearly 2900 \kms,
significantly larger than the customarily adopted criterion of 2000 \kms. With
its weak Fe II multiples, we think that SDSS J143030.22-001115.1 can't be
classified as a genuine NLS1. When we calculate the virial black hole masses of
NLS1s, we should use the H linewidth after subtracting the H
contribution from NLRs.Comment: 7 pages, 1 table, accepted by ChJA
The Gevrey hypoellipticity for kinetic equations
In this paper, we study the Gevrey regularity of weak solutions for a class
of linear and semi-linear kinetic equations, which are the linear model of
spatially inhomogeneous Boltzmann equations without an angular cutoff
- …