447 research outputs found
Different populations of RNA polymerase II in living mammalian cells
RNA polymerase II is responsible for transcription of most eukaryotic genes, but, despite exhaustive analysis, little is known about how it transcribes natural templates in vivo. We studied polymerase dynamics in living Chinese hamster ovary cells using an established line that expresses the largest (catalytic) subunit of the polymerase (RPB1) tagged with the green fluorescent protein (GFP). Genetic complementation has shown this tagged polymerase to be fully functional. Fluorescence loss in photobleaching (FLIP) reveals the existence of at least three kinetic populations of tagged polymerase: a large rapidly-exchanging population, a small fraction resistant to 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole (DRB) but sensitive to a different inhibitor of transcription (i.e. heat shock), and a third fraction sensitive to both inhibitors. Quantitative immunoblotting shows the largest fraction to be the inactive hypophosphorylated form of the polymerase (i.e. IIA). Results are consistent with the second (DRB-insensitive but heat-shock-sensitive) fraction being bound but not engaged, while the third (sensitive to both DRB and heat shock) is the elongating hyperphosphorylated form (i.e. IIO)
Decoherent Scattering of Light Particles in a D-Brane Background
We discuss the scattering of two light particles in a D-brane background. It
is known that, if one light particle strikes the D brane at small impact
parameter, quantum recoil effects induce entanglement entropy in both the
excited D brane and the scattered particle. In this paper we compute the
asymptotic `out' state of a second light particle scattering off the D brane at
large impact parameter, showing that it also becomes mixed as a consequence of
quantum D-brane recoil effects. We interpret this as a non-factorizing
contribution to the superscattering operator S-dollar for the two light
particles in a Liouville D-brane background, that appears when quantum D-brane
excitations are taken into account.Comment: 18 pages LATEX, one figure (incorporated
Static axially symmetric solutions of Einstein-Yang-Mills equations with a negative cosmological constant: black hole solutions
We investigate static axially symmetric black hole solutions in a
four-dimensional Einstein-Yang-Mills-SU(2) theory with a negative cosmological
constant . These solutions approach asymptotically the anti-de Sitter
spacetime and possess a regular event horizon. A discussion of the main
properties of the solutions and the differences with respect to the
asymptotically flat case is presented. The mass of these configurations is
computed by using a counterterm method. We note that the
configurations have an higher dimensional interpretation in context of
supergravity. The existence of axially symmetric monopole and dyon solutions in
a fixed Schwarzschild-anti-de Sitter background is also discussed. An exact
solution of the Einstein-Yang-Mills equations is presented in Appendix.Comment: 47 pages, 47 figure
Vacuum polarization for lukewarm black holes
We compute the renormalized expectation value of the square of a quantum scalar field on a Reissner-Nordström–de Sitter black hole in which the temperatures of the event and cosmological horizons are equal (“lukewarm” black hole). Our numerical calculations for a thermal state at the same temperature as the two horizons indicate that this renormalized expectation value is regular on both the event and cosmological horizons. We are able to show analytically, using an approximation for the field modes near the horizons, that this is indeed the case
Abelian Higgs Hair for a Static Charged Black String
We study the problem of vortex solutions in the background of an electrically
charged black string. We show numerically that the Abelian Higgs field
equations in the background of a four-dimensional black string have vortex
solutions. These solutions which have axial symmetry, show that the black
string can support the Abelian Higgs field as hair. This situation holds also
in the case of the extremal black string. We also consider the self-gravity of
the Abelian Higgs field and show that the effect of the vortex is to induce a
deficit angle in the metric under consideration.Comment: REVTEX4, 12 pages, 6 figures, The version to be appeared in Phys.
Rev.
Quasi-normal modes of toroidal, cylindrical and planar black holes in anti-de Sitter spacetimes: scalar, electromagnetic and gravitational perturbations
We study the quasi-normal modes (QNM) of scalar, electromagnetic and
gravitational perturbations of black holes in general relativity whose horizons
have toroidal, cylindrical or planar topology in an asymptotically anti-de
Sitter (AdS) spacetime. The associated quasinormal frequencies describe the
decay in time of the corresponding test field in the vicinities of the black
hole. In terms of the AdS/CFT conjecture, the inverse of the frequency is a
measure of the dynamical timescale of approach to thermal equilibrium of the
corresponding conformal field theory.Comment: Latex, 16 pages. Minor change
Charged black holes in generalized dilaton-axion gravity
We study generic Einstein-Maxwell-Kalb-Ramond-dilaton actions, and derive
conditions under which they give rise to static, spherically symmetric black
hole solutions. We obtain new asymptotically flat and non-flat black hole
solutions which are in general electrically and magnetically charged. They have
positive definite and finite quasi-local masses. Existing non-rotating black
hole solutions (including those appearing in low energy string theory) are
recovered in special limits.Comment: Replaced with revised version, 33 pages, No figure
The Role of Serotonin in the Regulation of Patience and Impulsivity
Classic theories suggest that central serotonergic neurons are involved in the behavioral inhibition that is associated with the prediction of negative rewards or punishment. Failed behavioral inhibition can cause impulsive behaviors. However, the behavioral inhibition that results from predicting punishment is not sufficient to explain some forms of impulsive behavior. In this article, we propose that the forebrain serotonergic system is involved in “waiting to avoid punishment” for future punishments and “waiting to obtain reward” for future rewards. Recently, we have found that serotonergic neurons increase their tonic firing rate when rats await food and water rewards and conditioned reinforcer tones. The rate of tonic firing during the delay period was significantly higher when rats were waiting for rewards than for tones, and rats were unable to wait as long for tones as for rewards. These results suggest that increased serotonergic neuronal firing facilitates waiting behavior when there is the prospect of a forthcoming reward and that serotonergic activation contributes to the patience that allows rats to wait longer. We propose a working hypothesis to explain how the serotonergic system regulates patience while waiting for future rewards
Hawking emission from quantum gravity black holes
We address the issue of modelling quantum gravity effects in the evaporation
of higher dimensional black holes in order to go beyond the usual
semi-classical approximation. After reviewing the existing six families of
quantum gravity corrected black hole geometries, we focus our work on
non-commutative geometry inspired black holes, which encode model independent
characteristics, are unaffected by the quantum back reaction and have an
analytical form compact enough for numerical simulations. We consider the
higher dimensional, spherically symmetric case and we proceed with a complete
analysis of the brane/bulk emission for scalar fields. The key feature which
makes the evaporation of non-commutative black holes so peculiar is the
possibility of having a maximum temperature. Contrary to what happens with
classical Schwarzschild black holes, the emission is dominated by low frequency
field modes on the brane. This is a distinctive and potentially testable
signature which might disclose further features about the nature of quantum
gravity.Comment: 36 pages, 18 figures, v2: updated reference list, minor corrections,
version matching that published on JHE
On classical super-radiance in Kerr-Newman-anti-de Sitter black holes
We study in detail the modes of a classical scalar field on a
Kerr-Newman-anti-de Sitter (KN-AdS) black hole. We construct sets of basis
modes appropriate to the two possible boundary conditions (``reflective'' and
``transparent'') at time-like infinity, and consider whether super-radiance is
possible. If we employ ``reflective'' boundary conditions, all modes are
non-super-radiant. On the other hand, for ``transparent'' boundary conditions,
the presence of super-radiance depends on our definition of positive frequency.
For those KN-AdS black holes having a globally time-like Killing vector, the
natural choice of positive frequency leads to no super-radiance. For other
KN-AdS black holes, there is a choice of positive frequency which gives no
super-radiance, but for other choices there will, in general, be
super-radiance.Comment: 23 pages, 3 figures, v2: minor changes, references adde
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