465 research outputs found
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Reactive Oxygen Species as Signaling Molecules in Neutrophil Chemotaxis
Neutrophil chemotaxis is a critical component in innate immunity. Recently, using a small-molecule functional screening, we identified NADPH-oxidase-dependent Reactive Oxygen Species (ROS) as key regulators of neutrophil chemotactic migration. Neutrophils depleted of ROS form more frequent multiple pseudopodia and lost their directionality as they migrate up a chemoattractant concentration gradient. Here, we further studied the role of ROS in neutrophil chemotaxis and found that multiple pseudopodia formation induced by NADPH inhibitor diphenyleneiodonium chloride (DPI) was more prominent in relatively shallow chemoattractant gradient. It was reported that, in shallow chemoattractant gradients, new pseudopods are usually generated when existing ones bifurcate. Directional sensing is mediated by maintaining the most accurate existing pseudopod, and destroying pseudopods facing the wrong direction by actin depolymerization. We propose that NADPH-mediated ROS production may be critical for disruption of misoriented pseudopods in chemotaxing neutrophils. Thus, inhibition of ROS production will lead to formation of multiple pseudopodia
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Phosphoinositide Lipid Posphatase SHIP1 and PTEN Coordinate to Regulate Cell Migration and Adhesion
The second messenger phosphatidylinositol is formed by stimulation of various receptors, including G protein–coupled receptors and integrins. The lipid phosphatases PTEN and SHIP1 are critical in regulating the level of PtdIns during chemotaxis. Observations that loss of PTEN had minor and loss of SHIP1 resulted in a severe chemotaxis defect in neutrophils led to the belief that SHIP1 rather than PTEN acts as a predominant phospholipid phosphatase in establishing a PtdIns compass. In this study, we show that SHIP1 regulates PtdIns production in response to cell adhesion and plays a limited role when cells are in suspension. neutrophils lose their polarity upon cell adhesion and are extremely adherent, which impairs chemotaxis. However, chemotaxis can be restored by reducing adhesion. Loss of SHIP1 elevates Akt activation following cell adhesion due to increased PtdIns production. From our observations, we conclude that SHIP1 prevents formation of top-down PtdIns polarity to facilitate proper cell attachment and detachment during chemotaxis
MHD Simulation of The Inner Galaxy with Radiative Cooling and Heating
We investigate the role of magnetic field on the gas dynamics in the Galactic
bulge region by three dimensional simulations with radiative cooling and
heating. While high-temperature corona with is formed in the
halo regions, the temperature near the Galactic plane is following the thermal equilibrium curve determined by the radiative cooling
and heating. Although the thermal energy of the interstellar gas is lost by
radiative cooling, the saturation level of the magnetic field strength does not
significantly depend on the radiative cooling and heating. The magnetic field
strength is amplified to on average, and reaches several
hundred locally. We find the formation of magnetically dominated
regions at mid-latitudes in the case with the radiative cooling and heating,
which is not seen in the case without radiative effect. The vertical thickness
of the mid-latitude regions is at the radial location of
from the Galactic center, which is comparable to the
observed vertical distribution of neutral atomic gas. When we take the average
of different components of energy density integrated over the Galactic bulge
region, the magnetic energy is comparable to the thermal energy. We conclude
that the magnetic field plays a substantial role in controlling the dynamical
and thermal properties of the Galactic bulge region.Comment: Submitted to ApJ; 21 pages, 18 figures 3 tables. Comment are welcom
Braneworld Flux Inflation
We propose a geometrical model of brane inflation where inflation is driven
by the flux generated by opposing brane charges and terminated by the collision
of the branes, with charge annihilation. We assume the collision process is
completely inelastic and the kinetic energy is transformed into the thermal
energy after collision. Thereafter the two branes coalesce together and behave
as a single brane universe with zero effective cosmological constant. In the
Einstein frame, the 4-dimensional effective theory changes abruptly at the
collision point. Therefore, our inflationary model is necessarily 5-dimensional
in nature. As the collision process has no singularity in 5-dimensional
gravity, we can follow the evolution of fluctuations during the whole history
of the universe. It turns out that the radion field fluctuations have a steeply
tilted, red spectrum, while the primordial gravitational waves have a flat
spectrum. Instead, primordial density perturbations could be generated by a
curvaton mechanism.Comment: 11 pages, 6 figures, references adde
Inhomogeneity of Spatial Curvature for Inflation
We study how the initial inhomogeneities of the spatial curvature affect the
onset of inflation in the closed universe. We consider a cosmological model
which contains a radiation and a cosmological constant. In order to treat the
inhomogeneities in the closed universe, we improve the long wavelength
approximation such that the non-small spatial curvature is tractable in the
lowest order. Using the improved scheme, we show how large inhomogeneities of
the spatial curvature prevent the occurrence of inflation.Comment: 17 pages, revtex, 6 figures included using eps
On the Canonical Formalism for a Higher-Curvature Gravity
Following the method of Buchbinder and Lyahovich, we carry out a canonical
formalism for a higher-curvature gravity in which the Lagrangian density is given in terms of a function of the salar curvature as . The local Hamiltonian is obtained by a
canonical transformation which interchanges a pair of the generalized
coordinate and its canonical momentum coming from the higher derivative of the
metric.Comment: 11 pages, no figures, Latex fil
Black holes and a scalar field in an expanding universe
We consider a model of an inhomogeneous universe including a massless scalar
field, where the inhomogeneity is assumed to consist of many black holes. This
model can be constructed by following Lindquist and Wheeler, which has already
been investigated without including scalar field to show that an averaged scale
factor coincides with that of the Friedmann model. In this work we construct
the inhomogeneous universe with an massless scalar field, where we assume that
the averaged scale factor and scalar field are given by those of the Friedmann
model including a scalar field. All of our calculations are carried out in the
framework of Brans-Dicke gravity. In constructing the model of an inhomogeneous
universe, we define the mass of a black hole in the Brans-Dicke expanding
universe which is equivalent to ADM mass if the mass evolves adiabatically, and
obtain an equation relating our mass to the averaged scalar field and scale
factor. As the results we find that the mass has an adiabatic time dependence
in a sufficiently late stage of the expansion of the universe, and that the
time dependence is qualitatively diffenrent according to the sign of the
curvature of the universe: the mass increases decelerating in the closed
universe case, is constant in the flat case and decreases decelerating in the
open case. It is also noted that the mass in the Einstein frame depends on
time. Our results that the mass has a time dependence should be retained even
in the general scalar-tensor gravitiy with a scalar field potential.
Furthermore, we discuss the relation of our results to the uniqueness theorem
of black hole spacetime and gravitational memory effect.Comment: 16 pages, 3 tables, 5 figure
Anisotropic Power-law Inflation
We study an inflationary scenario in supergravity model with a gauge kinetic
function. We find exact anisotropic power-law inflationary solutions when both
the potential function for an inflaton and the gauge kinetic function are
exponential type. The dynamical system analysis tells us that the anisotropic
power-law inflation is an attractor for a large parameter region.Comment: 14 pages, 1 figure. References added, minor corrections include
CP and T violation test in neutrino oscillation
We examine how large violation of CP and T is allowed in long base line
neutrino experiments. When we attribute only the atmospheric neutrino anomaly
to neutrino oscillation we may have large CP violation effect. When we
attribute both the atmospheric neutrino anomaly and the solar neutrino deficit
to neutrino oscillation we may have a sizable T violation effect proportional
to the ratio of two mass differences; it is difficult to see CP violation since
we can't ignore the matter effect. We give a simple expression for T violation
in the presence of matter.Comment: 12 pages + 2 eps figures, Latex, In order to avoid misunderstanding
we have refined our English and rewritten the parts which might be
misleading. Several typographical errors are correcte
CP Violation and Matter Effect in Long Baseline Neutrino Oscillation Experiments
We show simple methods how to separate pure CP violating effect from matter
effect in long baseline neutrino oscillation experiments with three generations
of neutrinos. We give compact formulae for neutrino oscillation probabilities
assuming one of the three neutrino masses (presumably tau-neutrino mass) to be
much larger than the other masses and the effective mass due to matter effect.
Two methods are shown: One is to observe envelopes of the curves of oscillation
probabilities as functions of neutrino energy; a merit of this method is that
only a single detector is enough to determine the presence of CP violation. The
other is to compare experiments with at least two different baseline lengths;
this has a merit that it needs only narrow energy range of oscillation data.Comment: 17 pages + 9 eps figures, LaTeX, errors are correcte
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