189 research outputs found
Reconstruction of inhomogeneous metric perturbations and electromagnetic four-potential in Kerr spacetime
We present a procedure that allows the construction of the metric
perturbations and electromagnetic four-potential, for gravitational and
electromagnetic perturbations produced by sources in Kerr spacetime. This may
include, for example, the perturbations produced by a point particle or an
extended object moving in orbit around a Kerr black hole. The construction is
carried out in the frequency domain. Previously, Chrzanowski derived the vacuum
metric perturbations and electromagnetic four-potential by applying a
differential operator to a certain potential . Here we construct
for inhomogeneous perturbations, thereby allowing the application of
Chrzanowski's method. We address this problem in two stages: First, for vacuum
perturbations (i.e. pure gravitational or electromagnetic waves), we construct
the potential from the modes of the Weyl scalars or .
Second, for perturbations produced by sources, we express in terms of
the mode functions of the source, i.e. the energy-momentum tensor or the electromagnetic current vector .Comment: 20 pages; few typos corrected and minor modifications made; accepted
to Phys. Rev.
Photon Total Cross-sections
We discuss present predictions for the total and
cross-sections, highlighting why predictions differ. We present results from
the Eikonal Minijet Model and improved predictions based on soft gluon
resummation.Comment: 7 pages, 10 figures, LaTeX, requires espcrc2.sty, Talk presented by
G. Pancheri at PHOTON-2003, International Meeting on Structure and
Interactions of the Photon, Frascati, Italy, April 7-11, 200
An Abrupt Aging of Dissolved Organic Carbon in Large Arctic Rivers
Permafrost thaw in Arctic watersheds threatens to mobilize hitherto sequestered carbon. We examine the radiocarbon activity (F14C) of dissolved organic carbon (DOC) in the northern Mackenzie River basin. From 2003‐2017, DOC‐F14C signatures (1.00 ± 0.04; n = 39) tracked atmospheric 14CO2, indicating export of “modern” carbon. This trend was interrupted in June 2018 by the widespread release of aged DOC (0.85 ± 0.16, n = 28) measured across three separate catchment areas. Increased nitrate concentrations in June 2018 lead us to attribute this pulse of 14C‐depleted DOC to mobilization of previously frozen soil organic matter. We propose export through lateral perennial thaw zones occurred at the base of the active layer weakened by preceding warm summer and winter seasons. Although we are not yet able to ascertain the broader significance of this “anomalous” mobilization event, it highlights the potential for rapid and large‐scale release of aged carbon from permafrost
First order optical potentials and 25 to 40 MeV proton elastic scattering
The differential cross sections and analyzing powers from the elastic
scattering of 25 and 40 MeV protons from many nuclei have been studied.
Analyses have been made using a fully microscopic model of proton-nucleus
scattering seeking to establish a means appropriate for use in analyses of
radioactive beam scattering from hydrogen with ion energies 25A and 40A MeV.Comment: 9 pages, RevTeX, 4 figure
Curcumin Ingestion Inhibits Mastocytosis and Suppresses Intestinal Anaphylaxis in a Murine Model of Food Allergy
IgE antibodies and mast cells play critical roles in the establishment of allergic responses to food antigens. Curcumin, the active ingredient of the curry spice turmeric, has anti-inflammatory properties, and thus may have the capacity to regulate Th2 cells and mucosal mast cell function during allergic responses. We assessed whether curcumin ingestion during oral allergen exposure can modulate the development of food allergy using a murine model of ovalbumin (OVA)-induced intestinal anaphylaxis. Herein, we demonstrate that frequent ingestion of curcumin during oral OVA exposure inhibits the development of mastocytosis and intestinal anaphylaxis in OVA-challenged allergic mice. Intragastric (i.g.) exposure to OVA in sensitized BALB/c mice induced a robust IgE-mediated response accompanied by enhanced OVA-IgE levels, intestinal mastocytosis, elevated serum mMCP-1, and acute diarrhea. In contrast, mice exposed to oral curcumin throughout the experimental regimen appeared to be normal and did not exhibit intense allergic diarrhea or a significant enhancement of OVA-IgE and intestinal mast cell expansion and activation. Furthermore, allergic diarrhea, mast cell activation and expansion, and Th2 responses were also suppressed in mice exposed to curcumin during the OVA-challenge phase alone, despite the presence of elevated levels of OVA-IgE, suggesting that curcumin may have a direct suppressive effect on intestinal mast cell activation and reverse food allergy symptoms in allergen-sensitized individuals. This was confirmed by observations that curcumin attenuated the expansion of both adoptively transferred bone marrow-derived mast cells (BMMCs), and inhibited their survival and activation during cell culture. Finally, the suppression of intestinal anaphylaxis by curcumin was directly linked with the inhibition of NF-kappaB activation in curcumin-treated allergic mice, and curcumin inhibited the phosphorylation of the p65 subunit of NF-kappaB in BMMCs. In summary, our data demonstrates a protective role for curcumin during allergic responses to food antigens, suggesting that frequent ingestion of this spice may modulate the outcome of disease in susceptible individuals
Lodged in the throat: Internal infinities and AdS/CFT
In the context of AdS3/CFT2, we address spacetimes with a certain sort of
internal infinity as typified by the extreme BTZ black hole. The internal
infinity is a null circle lying at the end of the black hole's infinite throat.
We argue that such spacetimes may be described by a product CFT of the form
CFT-L * CFT-R, where CFT-R is associated with the asymptotically AdS boundary
while CFT-L is associated with the null circle. Our particular calculations
analyze the CFT dual of the extreme BTZ black hole in a linear toy model of
AdS3/CFT2. Since the BTZ black hole is a quotient of AdS3, the dual CFT state
is a corresponding quotient of the CFT vacuum state. This state turns out to
live in the aforementioned product CFT. We discuss this result in the context
of general issues of AdS/CFT duality and entanglement entropy.Comment: 11 pages, 2 figures; v2 - some typos corrected, minor revision
Total photoproduction cross-section at very high energy
In this paper we apply to photoproduction total cross-section a model we have
proposed for purely hadronic processes and which is based on QCD mini-jets and
soft gluon re-summation. We compare the predictions of our model with the HERA
data as well as with other models. For cosmic rays, our model predicts
substantially higher cross-sections at TeV energies than models based on
factorization but lower than models based on mini-jets alone, without soft
gluons. We discuss the origin of this difference.Comment: 13 pages, 9 figures. Accepted for publication in EPJC. Changes
concern added references, clarifications of the Soft Gluon Resummation method
used in the paper, and other changes requested by the Journal referee which
do not change the results of the original versio
On the Resolution of the Time-Like Singularities in Reissner-Nordstrom and Negative-Mass Schwarzschild
Certain time-like singularities are shown to be resolved already in classical
General Relativity once one passes from particle probes to scalar waves. The
time evolution can be defined uniquely and some general conditions for that are
formulated. The Reissner-Nordstrom singularity allows for communication through
the singularity and can be termed "beam splitter" since the transmission
probability of a suitably prepared high energy wave packet is 25%. The high
frequency dependence of the cross section is w^{-4/3}. However, smooth
geometries arbitrarily close to the singular one require a finite amount of
negative energy matter. The negative-mass Schwarzschild has a qualitatively
different resolution interpreted to be fully reflecting. These 4d results are
similar to the 2d black hole and are generalized to an arbitrary dimension d>4.Comment: 47 pages, 5 figures. v2: See end of introduction for an important
note adde
Minijets, soft gluon resummation and photon cross-sections
We compare the high energy behaviour of hadronic photon-photon cross-sections
in different models. We find that the photon-photon cross-section appears to
rise faster than the purely hadronic ones (proton-proton and
proton-antiproton).Comment: 7 pages, 5 figures. Presented at Photon2007, Paris, July 2007.
Requires photon2007.cl
Engineering the Photonic Density of States with metamaterials
The photonic density of states (PDOS), like its' electronic coun- terpart, is
one of the key physical quantities governing a variety of phenom- ena and hence
PDOS manipulation is the route to new photonic devices. The PDOS is
conventionally altered by exploiting the resonance within a device such as a
microcavity or a bandgap structure like a photonic crystal. Here we show that
nanostructured metamaterials with hyperbolic dispersion can dramatically
enhance the photonic density of states paving the way for metamaterial based
PDOS engineering
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