1,966 research outputs found
Exact Black String Solutions in Three Dimensions
A family of exact conformal field theories is constructed which describe
charged black strings in three dimensions. Unlike previous charged black hole
or extended black hole solutions in string theory, the low energy spacetime
metric has a regular inner horizon (in addition to the event horizon) and a
timelike singularity. As the charge to mass ratio approaches unity, the event
horizon remains but the singularity disappears.Comment: 17 page
Photocatalytic production of organic compounds from CO and H2O in a simulated Martian atmosphere
[14C]CO2 and [14C]organic compounds are formed when a mixture of [14C]CO and water vapor diluted in [12C]CO2 or N2 is irradiated with ultraviolet light in the presence of soil or pulverized vycor substratum. The [14C]CO2 is recoverable from the gas phase, the [14C]organic products from the substratum. Three organic products have been tentatively identified as formaldehyde, acetaldehyde, and glycolic acid. The relative yields of [14C]CO2 and [14C]organics are wavelength- and surface-dependent. Conversion of CO to CO2 occurs primarily at wavelengths shorter than 2000 angstrom, apparently involves the photolysis of water, and is inhibited by increasing amounts of vycor substratum. Organic formation occurs over a broad spectral range below 3000 angstrom and increases with increasing amounts of substratum. It is suggested that organic synthesis results from adsorption of CO and H2O on surfaces, with excitation of one or both molecules occurring at wavelengths longer than those absorbed by the free gases. This process may occur on Mars and may have been important on the primitive earth
Influence of the Dirac sea on proton electromagnetic knockout
We use the relativistic distorted-wave impulse approximation (RDWIA) to study
the effects of negative-energy components of Dirac wave functions on the
left-right asymmetry for (e,e'p) reactions on 16-O with 0.2 < Q^2 < 0.8 and
12-C with 0.6 < Q^2 < 1.8 (GeV/c)^2. Spinor distortion is more important for
the bound state than for the ejectile and the net effect decreases with Q^2.
Spinor distortion breaks Godon equivalence and the data favor the CC2 operator
with intermediate coupling to the sea. The left-right asymmetry for Q^2 < 1.2
(GeV/c)^2 is described well by RDWIA calcuations, but at Q^2 = 1.8 (GeV/c)^2
the observed variation with missing momentum is flatter than predicted.Comment: 12 pages, 9 figures, to be submitted to PR
RDWIA analysis of 12C(e,e'p) for Q^2 < 2 (GeV/c)^2
We analyze data for 12C(e,e'p) with Q^2 < 2 (GeV/c)^2 using the relativistic
distorted-wave impulse approximation (RDWIA) based upon Dirac-Hartree wave
functions. The 1p normalization extracted from data for Q^2 > 0.6 (GeV/c)^2 is
approximately 0.87, independent of Q^2, which is consistent with the predicted
depletion by short-range correlations. The total 1p and 1s strength for E_m <
80 MeV approaches 100% of IPSM, consistent with a continuum contribution for 30
< E_m < 80 MeV of about 12% of IPSM. Similarly, a scale factor of 1.12 brings
RDWIA calculations into good agreement with 12C(e,e'p) data for transparency.
We also analyzed low Q^2 data from which a recent NDWIA analysis suggested that
spectroscopic factors might depend strongly upon the resolution of the probe.
We find that momentum distributions for their empirical Woods-Saxon wave
functions fit to low Q^2 data for parallel kinematics are too narrow to
reproduce data for quasiperpendicular kinematics, especially for larger Q^2,
and are partly responsible for reducing fitted normalization factors.Comment: 19 pages, 14 figures, to be submitted to PR
An Equivalence Between Momentum and Charge in String Theory
It is shown that for a translationally invariant solution to string theory,
spacetime duality interchanges the momentum in the symmetry direction and the
axion charge per unit length. As one application, we show explicitly that
charged black strings are equivalent to boosted (uncharged) black strings. The
extremal black strings (which correspond to the field outside of a fundamental
macroscopic string) are equivalent to plane fronted waves describing strings
moving at the speed of light.Comment: 10 page
Catatonia Associated with Initiating Paliperidone Treatment
We present a case of catatonia, which occurred shortly after starting a new antipsychotic, paliperidone, an active metabolite of risperidone. Catatonia may be caused by a variety of conditions, including metabolic, neurologic, psychiatric and toxic processes. Interestingly, risperidone, which has been thought to cause several cases of catatonia, has also been recommended as a potential treatment. We discuss potential mechanisms for causes of drug-induced catatonia as well as potential treatment options
Tilted String Cosmologies
Global symmetries of the string effective action are employed to generate
tilted, homogeneous Bianchi type VI_h string cosmologies from a previously
known stiff perfect fluid solution to Einstein gravity. The dilaton field is
not constant on the surfaces of homogeneity. The future asymptotic state of the
models is interpreted as a plane wave and is itself an exact solution to the
string equations of motion to all orders in the inverse string tension. An
inhomogeneous generalization of the Bianchi type III model is also found.Comment: 9 pages, Standard Latex Source. To appear in Physics Letters B Minor
change: Authors now alphabetically liste
The Extreme Kerr Throat Geometry: A Vacuum Analog of AdS_2 x S^2
We study the near horizon limit of a four dimensional extreme rotating black
hole. The limiting metric is a completely nonsingular vacuum solution, with an
enhanced symmetry group SL(2,R) x U(1). We show that many of the properties of
this solution are similar to the AdS_2 x S^2 geometry arising in the near
horizon limit of extreme charged black holes. In particular, the boundary at
infinity is a timelike surface. This suggests the possibility of a dual quantum
mechanical description. A five dimensional generalization is also discussed.Comment: 21 page
Cosmic Censorship and the Dilaton
We investigate extremal electrically charged black holes in
Einstein-Maxwell-dilaton theory with a cosmological constant inspired by string
theory. These solutions are not static, and a timelike singularity eventually
appears which is not surrounded by an event horizon. This suggests that cosmic
censorship may be violated in this theory.Comment: 16 pages, NSF-ITP-93-9
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