4,852 research outputs found
Bianchi Type III String Cosmological Models with Time Dependent Bulk Viscosity
Bianchi type III string cosmological models with bulk viscous fluid for
massive string are investigated. To get the determinate model of the universe,
we have assumed that the coefficient of bulk viscosity () is inversely
proportional to the expansion () in the model and expansion ()
in the model is proportional to the shear (). This leads to , and are constants. The behaviour of the model in presence
and absence of bulk viscosity, is discussed. The physical implications of the
models are also discussed in detail.Comment: 11 pages, no figur
Bianchi Type I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity
Bianchi type I massive string cosmological model with magnetic field of
barotropic perfect fluid distribution through the techniques used by Latelier
and Stachel, is investigated. To get the deterministic model of the universe,
it is assumed that the universe is filled with barotropic perfect fluid
distribution. The magnetic field is due to electric current produced along
x-axis with infinite electrical conductivity. The behaviour of the model in
presence and absence of magnetic field together with other physical aspects is
further discussed.Comment: 10 pages, no figure. Chin. Phys. Lett., Vol. 24, No. 8 (2007), to
appea
Neuroretinal Rim Area and Body Mass Index
Purpose: To examine associations between neuroretinal rim area, pressure related factors and anthropometric parameters in a population-based setting. Methods: The population-based cross-sectional Beijing Eye Study 2006 included 3251 subjects with an age of 45+ years. The participants underwent a detailed ophthalmic examination. Exclusion criteria for our study were high myopia of more than-8 diopters and angle-closure glaucoma. Results: The study included 2917 subjects with a mean age of 59.869.8 years (range: 45–89 years). Mean neuroretinal rim area was 1.9760.38 mm 2, mean intraocular pressure 15.663.0 mmHg, mean diastolic blood pressure 79.065.9 mm Hg, mean systolic blood pressure 133.5611.1 mmHg, and mean body mass index was 25.563.7. In univariate analysis, neuroretinal rim area was significantly associated with optic disc size, open-angle glaucoma, refractive error, age and gender. After adjustment for these parameters in a multivariate analysis, a larger neuroretinal rim area was significantly correlated with a higher body mass index (P,0.001), in addition to be associated with a lower intraocular pressure (P = 0.004), lower mean blood pressure (P = 0.02), and higher ocular perfusion pressure. Conclusions: In a general population, neuroretinal rim as equivalent of the optic nerve fibers is related to a higher body mass index, after adjustment for disc area, refractive error, age, gender, open-angle glaucoma, intraocular pressure, blood pressure and ocular perfusion pressure. Since body mass index is associated with cerebrospinal fluid pressure, the latter ma
String Cosmology in Anisotropic Bianchi-II Space-time
The present study deals with a spatially homogeneous and anisotropic
Bianchi-II cosmological model representing massive strings. The energy-momentum
tensor, as formulated by Letelier (1983), has been used to construct a massive
string cosmological model for which the expansion scalar is proportional to one
of the components of shear tensor. The Einstein's field equations have been
solved by applying a variation law for generalized Hubble's parameter that
yields a constant value of deceleration parameter in Bianchi-II space-time. A
comparative study of accelerating and decelerating modes of the evolution of
universe has been carried out in the presence of string scenario. The study
reveals that massive strings dominate the early Universe. The strings
eventually disappear from the Universe for sufficiently large times, which is
in agreement with the current astronomical observations.Comment: 11 pages, 6 figures (To appear in Mod. Phys. Lett. A) In this
version, the cosmic string has been directed along z-direction and the
resultant field equations have been solved exactl
The decay rate of to in SM and beyond
With rapid growth of the database of the BES III and the proposed super
flavor factory, measurement on the rare decays may be feasible,
especially the weak decays into baryon final states. In this work we study the
decay rate of to in the SM and
physics beyond the SM (here we use the unparticle model as an example). The QPC
model is employed to describe the creation of a pair of from vacuum.
We find that the rate of is
at order of in the SM, whereas the contribution of the unparticle is
too small to be substantial. Therefore if a large branching ratio is observed,
it must be due to new physics beyond SM, but by no means the unparticle.Comment: 9 pages, 1 figure
Phenomenological study of hadron interaction models
We present a phenomenological study of three models with different effective
degrees of freedom: a Goldstone Boson Exchange (GBE) model which is based on
quark-meson couplings, the quark delocalization, color screening model (QDCSM)
which is based on quark-gluon couplings with delocalized quark wavefunctions,
and the Fujiwara-Nijmegen (FN) mixed model which includes both quark-meson and
quark-gluon couplings. We find that for roughly two-thirds of 64 states
consisting of pairs of octet and decuplet baryons, the three models predict
similar effective baryon-baryon interactions. This suggests that the three very
different models, based on different effective degrees of freedom, are
nonetheless all compatible with respect to baryon spectra and baryon-baryon
interactions. We also discuss the differences between the three models and
their separate characteristics.Comment: 30 pages latex, 7 tables, 12 figs; submitted to Phys. Rev.
Proteasome Inhibition Augments Cigarette Smoke-Induced GM-CSF Expression in Trophoblast Cells via the Epidermal Growth Factor Receptor
Maternal cigarette smoking has adverse effects on pregnancy outcomes. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is an essential cytokine for a normal pregnancy. We investigated the impact of cigarette smoke extract (CSE) on GM-CSF expression in human cytotrophoblast cells and suggested a cellular mechanism underlying the CSE-induced GM-CSF expression. An immortalized normal human trophoblast cell line (B6Tert-1) was treated with CSE. The viability and proliferation of the CSE-treated B6Tert-1 cells were evaluated, and the expression of GM-CSF in these cells was quantified at the mRNA and the protein levels by means of reverse-transcription and quantitative polymerase chain reaction (RT-qPCR); and enzyme-linked immunosorbent assay (ELISA), respectively. Human trophoblast cells treated with CSE had an increased expression of GM-CSF at both the mRNA and the protein levels. The CSE-induced GM-CSF expression was synergistically enhanced by the addition of the proteasome inhibitor MG-132, but inhibited by AG-1478, an inhibitor of the epidermal growth factor receptor (EGFR) kinase. Furthermore, CSE treatment increased the phosphorylation of the extracellular-signal regulated kinases (ERK1/2) in the trophoblast cells. The expression of other growth factors such as heparin-binding epidermal growth factor-like growth factor (HB-EGF) and vascular endothelial growth factor (VEGF) was also evaluated. Our data suggested that cigarette smoking and proteasome inhibition synergistically up-regulate GM-CSF cytokine expression by activating the EGFR signaling pathway
Tunable Dirac Fermion Dynamics in Topological Insulators
Three-dimensional topological insulators are characterized by insulating bulk
state and metallic surface state involving Dirac fermions that behave as
massless relativistic particles. These Dirac fermions are responsible for
achieving a number of novel and exotic quantum phenomena in the topological
insulators and for their potential applications in spintronics and quantum
computations. It is thus essential to understand the electron dynamics of the
Dirac fermions, i.e., how they interact with other electrons, phonons and
disorders. Here we report super-high resolution angle-resolved photoemission
studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3
topological insulators. We have directly revealed signatures of the
electron-phonon coupling in these topological insulators and found that the
electron-disorder interaction is the dominant factor in the scattering process.
The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned
by varying the composition, x, or by controlling the charge carriers. Our
findings provide crucial information in understanding the electron dynamics of
the Dirac fermions in topological insulators and in engineering their surface
state for fundamental studies and potential applications.Comment: 14 Pages, 4 Figure
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