656 research outputs found
Back Reaction and Semiclassical Approximation of cosmological models coupled to matter
Bianchi -I, -III, and FRW type models minimally coupled to a massive
spatially homogeneous scalar field (i.e. a particle) are studied in the
framework of semiclassical quantum gravity. In a first step we discuss the
solutions of the corresponding equation for a Schr\"odinger particle
propagating on a classical background. The back reaction of the Schr\"odinger
particle on the classical metric is calculated by means of the Wigner function
and by means of the expectation value of the energy-momentum-tensor of the
field as a source. Both methods in general lead to different results.Comment: 4 pages, Latex, to appear in: Proceedings of the Second Meeting on
constrained Dynamics and Quantum Gravity (Santa Margherita Ligure 1996
Acute Immobilization Stress Modulate GABA Release from Rat Olfactory Bulb: Involvement of Endocannabinoids—Cannabinoids and Acute Stress Modulate GABA Release
We studied the effects of cannabinoids and acute immobilization stress on the regulation of GABA release in the olfactory bulb. Glutamate-stimulated 3H-GABA release was measured in superfused slices. We report that cannabinoids as WIN55, 212-2, methanandamide, and 2-arachidonoylglycerol were able to inhibit glutamate- and KCl-stimulated 3H-GABA release. This effect was blocked by the CB1 antagonist AM281. On the other hand, acute stress was able per se to increase endocannabinoid activity. This effect was evident since the inhibition of stimulated GABA release by acute stress was reversed with AM281 and tetrahydrolipstatin. Inhibition of the endocannabinoid transport or its catabolism showed reduction of GABA release, antagonized by AM281 in control and stressed animals. These results point to endocannabinoids as inhibitory modulators of GABA release in the olfactory bulb acting through an autocrine mechanism. Apparently, stress increases the endocannabinoid system, modulating GABAergic synaptic function in a primary sensory organ
BUDHIES I: characterizing the environments in and around two clusters at z~0.2
We present the optical spectroscopy for the Blind Ultra Deep HI Environmental
Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has
detected HI in over 150 galaxies in and around two Abell clusters at z~0.2.
With the aim of characterizing the environments of the HI-detected galaxies, we
obtained multi-fiber spectroscopy with the William Herschel Telescope. In this
paper, we describe the spectroscopic observations, report redshifts and EW[OII]
measurements for ~600 galaxies, and perform an environmental analysis. In
particular, we present cluster velocity dispersion measurements for 5 clusters
and groups in the BUDHIES volume, as well as a detailed substructure analysis.Comment: v2: Typos and small corrections after proofs added. 14 pages (plus
small appendix), 12 figures. Accepted for publication in MNRAS. Adobe Acrobat
Reader is required to correctly display the (3D) animated figures (Fig. 9).
Full data tables and supporting videos are also available at the BUDHIES
project website: http://www.astro.rug.nl/budhies
Acute Immobilization Stress Modulate GABA Release from Rat Olfactory Bulb: Involvement of Endocannabinoids-Cannabinoids and Acute Stress Modulate GABA Release
We studied the effects of cannabinoids and acute immobilization stress on the regulation of GABA release in the olfactory bulb. Glutamate-stimulated 3H-GABA release was measured in superfused slices. We report that cannabinoids as WIN55, 212-2, methanandamide, and 2-arachidonoylglycerol were able to inhibit glutamate-and KCl-stimulated 3H-GABA release. This effect was blocked by the CB1 antagonist AM281. On the other hand, acute stress was able per se to increase endocannabinoid activity. This effect was evident since the inhibition of stimulated GABA release by acute stress was reversed with AM281 and tetrahydrolipstatin. Inhibition of the endocannabinoid transport or its catabolism showed reduction of GABA release, antagonized by AM281 in control and stressed animals. These results point to endocannabinoids as inhibitory modulators of GABA release in the olfactory bulb acting through an autocrine mechanism. Apparently, stress increases the endocannabinoid system, modulating GABAergic synaptic function in a primary sensory organ
Geometrical Models of the Phase Space Structures Governing Reaction Dynamics
Hamiltonian dynamical systems possessing equilibria of stability type display \emph{reaction-type
dynamics} for energies close to the energy of such equilibria; entrance and
exit from certain regions of the phase space is only possible via narrow
\emph{bottlenecks} created by the influence of the equilibrium points. In this
paper we provide a thorough pedagogical description of the phase space
structures that are responsible for controlling transport in these problems. Of
central importance is the existence of a \emph{Normally Hyperbolic Invariant
Manifold (NHIM)}, whose \emph{stable and unstable manifolds} have sufficient
dimensionality to act as separatrices, partitioning energy surfaces into
regions of qualitatively distinct behavior. This NHIM forms the natural
(dynamical) equator of a (spherical) \emph{dividing surface} which locally
divides an energy surface into two components (`reactants' and `products'), one
on either side of the bottleneck. This dividing surface has all the desired
properties sought for in \emph{transition state theory} where reaction rates
are computed from the flux through a dividing surface. In fact, the dividing
surface that we construct is crossed exactly once by reactive trajectories, and
not crossed by nonreactive trajectories, and related to these properties,
minimizes the flux upon variation of the dividing surface.
We discuss three presentations of the energy surface and the phase space
structures contained in it for 2-degree-of-freedom (DoF) systems in the
threedimensional space , and two schematic models which capture many of
the essential features of the dynamics for -DoF systems. In addition, we
elucidate the structure of the NHIM.Comment: 44 pages, 38 figures, PDFLaTe
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
Classical and Quantum Transport Through Entropic Barriers Modelled by Hardwall Hyperboloidal Constrictions
We study the quantum transport through entropic barriers induced by hardwall
constrictions of hyperboloidal shape in two and three spatial dimensions. Using
the separability of the Schrodinger equation and the classical equations of
motion for these geometries we study in detail the quantum transmission
probabilities and the associated quantum resonances, and relate them to the
classical phase structures which govern the transport through the
constrictions. These classical phase structures are compared to the analogous
structures which, as has been shown only recently, govern reaction type
dynamics in smooth systems. Although the systems studied in this paper are
special due their separability they can be taken as a guide to study entropic
barriers resulting from constriction geometries that lead to non-separable
dynamics.Comment: 59 pages, 22 EPS figures
Computational Method for Phase Space Transport with Applications to Lobe Dynamics and Rate of Escape
Lobe dynamics and escape from a potential well are general frameworks
introduced to study phase space transport in chaotic dynamical systems. While
the former approach studies how regions of phase space are transported by
reducing the flow to a two-dimensional map, the latter approach studies the
phase space structures that lead to critical events by crossing periodic orbit
around saddles. Both of these frameworks require computation with curves
represented by millions of points-computing intersection points between these
curves and area bounded by the segments of these curves-for quantifying the
transport and escape rate. We present a theory for computing these intersection
points and the area bounded between the segments of these curves based on a
classification of the intersection points using equivalence class. We also
present an alternate theory for curves with nontransverse intersections and a
method to increase the density of points on the curves for locating the
intersection points accurately.The numerical implementation of the theory
presented herein is available as an open source software called Lober. We used
this package to demonstrate the application of the theory to lobe dynamics that
arises in fluid mechanics, and rate of escape from a potential well that arises
in ship dynamics.Comment: 33 pages, 17 figure
The Geometry of Mass Outflows and Fueling Flows in the Seyfert 2 Galaxy Mrk 3
We present a study of the resolved emission-line regions and an inner
dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope
observations. We show that the extended narrow-line region (ENLR), spanning ~4
kpc, is defined by the intersection of the ionizing bicone of radiation from
the AGN and the inner disk, which is not coplanar with the large-scale stellar
disk. This intersection leads to different position and opening angles of the
ENLR compared to the narrow-line region (NLR). A number of emission-line arcs
in the ENLR appear to be continuations of dust lanes in the disk, supporting
this geometry. The NLR, which consists of outflowing emission-line knots
spanning the central ~650 pc, is in the shape of a backwards S. This shape may
arise from rotation of the gas, or it may trace the original fueling flow close
to the nucleus that was ionized after the AGN turned on.Comment: 22 page, 7 figures, accepted for publication in the Astronomical
Journa
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