91 research outputs found
Multi-mission Ni-H2 battery cells for the 1990's
A sufficient production, test and operational database is now available to permit design technology optimization for the next decade. The evolved battery cell design features standardized technology intended to support multiple type missions (e.g., both GEO and LEO). Design analysis and validation test cells demonstrate that improved performance plus attractive specific-energy characteristics will be achieved
Multi-mission Ni-H2 battery cell for the 1990's
A sufficient production, test and operational database is now available to permit design technology optimization for the next decade. The evolved battery cell design features standardized technology intended to support multiple type missions (e.g., both GEO and LEO). Design analyses and validation test cells demonstrate improved performance plus attractive specific-energy characteristics will be achieved
\u3cem\u3eRhizobium japonicum\u3c/em\u3e Mutants Defective in Symbiotic Nitrogen Fixation
Rhizobium japonicum strains 3I1b110 and 61A76 were mutagenized to obtain 25 independently derived mutants that produced soybean nodules defective in nitrogen fixation, as assayed by acetylene reduction. The proteins of both the bacterial and the plant portions of the nodules were analyzed by two-dimensional polyacrylamide gel electrophoresis. All of the mutants had lower-than-normal levels of the nitrogenase components, and all but four contained a prominent bacteroid protein not observed in wild-type bacteroids. Experiments with bacteria grown ex planta suggested that this protein was derepressed by the absence of ammonia. Nitrogenase component II of one mutant was altered in isoelectric point. The soluble plant fraction of the nodules of seven mutants had very low levels of heme, yet the nodules of five of these seven mutants contained the polypeptide of leghemoglobin. Thus, the synthesis of the globin may not be coupled to the content of available heme in soybean nodules. The nodules of the other two of these seven mutants lacked not only leghemoglobin but most of the other normal plant and bacteroid proteins. Ultrastructural examination of nodules formed by these two mutants indicated normal ramification of infection threads but suggested a problem in subsequent survival of the bacteria and their release from the infection threads
When Black Holes Meet Kaluza-Klein Bubbles
We explore the physical consequences of a recently discovered class of exact
solutions to five dimensional Kaluza-Klein theory. We find a number of
surprising features including: (1) In the presence of a Kaluza-Klein bubble,
there are arbitrarily large black holes with topology S^3. (2) In the presence
of a black hole or a black string, there are expanding bubbles (with de Sitter
geometry) which never reach null infinity. (3) A bubble can hold two black
holes of arbitrary size in static equilibrium. In particular, two large black
holes can be close together without merging to form a single black hole.Comment: 23 pages, 5 figures, v2: few comments on stability modifie
Convex Functions and Spacetime Geometry
Convexity and convex functions play an important role in theoretical physics.
To initiate a study of the possible uses of convex functions in General
Relativity, we discuss the consequences of a spacetime or an
initial data set admitting a suitably defined convex
function. We show how the existence of a convex function on a spacetime places
restrictions on the properties of the spacetime geometry.Comment: 26 pages, latex, 7 figures, improved version. some claims removed,
references adde
The AdS/CFT Correspondence and a New Positive Energy Conjecture for General Relativity
We examine the AdS/CFT correspondence when the gauge theory is considered on
a compactified space with supersymmetry breaking boundary conditions. We find
that the corresponding supergravity solution has a negative energy, in
agreement with the expected negative Casimir energy in the field theory.
Stability of the gauge theory would imply that this supergravity solution has
minimum energy among all solutions with the same boundary conditions. Hence we
are lead to conjecture a new positive energy theorem for asymptotically locally
Anti-de Sitter spacetimes. We show that the candidate minimum energy solution
is stable against all quadratic fluctuations of the metric.Comment: 25 pages, harvma
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
Supergravity p-branes revisited: extra parameters, uniqueness, and topological censorship
We perform a complete integration of the Einstein-dilaton-antisymmetric form
action describing black p-branes in arbitrary dimensions assuming the
transverse space to be homogeneous and possessing spherical, toroidal or
hyperbolic topology. The generic solution contains eight parameters satisfying
one constraint. Asymptotically flat solutions form a five-parametric subspace,
while conditions of regularity of the non-degenerate event horizon further
restrict this number to three, which can be related to the mass and the charge
densities and the asymptotic value of the dilaton. In the case of a degenerate
horizon, this number is reduced by one. Our derivation constitutes a
constructive proof of the uniqueness theorem for -branes with the
homogeneous transverse space. No asymptotically flat solutions with toroidal or
hyperbolic transverse space within the considered class are shown to exist,
which result can be viewed as a demonstration of the topological censorship for
p-branes. From our considerations it follows, in particular, that some
previously discussed p-brane-like solutions with extra parameters do not
satisfy the standard conditions of asymptotic flatness and absence of naked
singularities. We also explore the same system in presence of a cosmological
constant, and derive a complete analytic solution for higher-dimensional
charged topological black holes, thus proving their uniqueness.Comment: Revtex4, no figure
Phase transitions in LaFeAsO: structural, magnetic, elastic, and transport properties, heat capacity and Mossbauer spectra
We present results from a detailed experimental investigation of LaFeAsO, the
parent material in the series of "FeAs" based oxypnictide superconductors. Upon
cooling this material undergoes a tetragonal-orthorhombic crystallographic
phase transition at ~160 K followed closely by an antiferromagnetic ordering
near 145 K. Analysis of these phase transitions using temperature dependent
powder X-ray and neutron diffraction measurements is presented. A magnetic
moment of ~0.35 Bohr magnetons per iron is derived from Mossbauer spectra in
the low temperature phase. Evidence of the structural transition is observed at
temperatures well above the structural transition (up to near 200 K) in the
diffraction data as well as the polycrystalline elastic moduli probed by
resonant ultrasound spectroscopy measurements. The effects of the two phase
transitions on the transport properties (resistivity, thermal conductivity,
Seebeck coefficient, Hall coefficient), heat capacity, and magnetization of
LaFeAsO are also reported, including a dramatic increase in the magnitude of
the Hall coefficient below 160 K. The results suggest that the structural
distortion leads to a localization of carriers on Fe, producing small local
magnetic moments which subsequently order antiferromagnetically upon further
cooling. Evidence of strong electron-phonon interactions in the
high-temperature tetragonal phase is also observed.Comment: Revised and expanded magnetization and Mossbauer spectroscopy
section. Clarified sample preparation description. This paper contains some
results from arXiv:0804.0796. 10 figure
Pathogenic huntingtin inhibits fast axonal transport by activating JNK3 and phosphorylating kinesin
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature America for personal use, not for redistribution. The definitive version was published in Nature Neuroscience 12 (2009): 864-871, doi:10.1038/nn.2346.Selected vulnerability of neurons in Huntington’s disease (HD) suggests alterations in a cellular
process particularly critical for neuronal function. Supporting this idea, pathogenic Htt (polyQ-Htt)
inhibits fast axonal transport (FAT) in various cellular and animal HD models (mouse and squid),
but the molecular basis of this effect remains unknown. Here we show that polyQ-Htt inhibits FAT
through a mechanism involving activation of axonal JNK. Accordingly, increased activation of JNK
was observed in vivo in cellular and animal HD models. Additional experiments indicate that
polyQ-Htt effects on FAT are mediated by the neuron-specific JNK3, and not ubiquitously
expressed JNK1, providing a molecular basis for neuron-specific pathology in HD. Mass
spectrometry identified a residue in the kinesin-1 motor domain phosphorylated by JNK3, and this
modification reduces kinesin-1 binding to microtubules. These data identify JNK3 as a critical
mediator of polyQ-Htt toxicity and provides a molecular basis for polyQ-Htt-induced inhibition of
FAT.This work was supported by 2007/2008 MBL summer fellowship to GM; an HDSA
grant to GM; NIH grants MH066179 to GB; and ALSA, Muscular Dystrophy Association, and NIH
(NS23868, NS23320, NS41170) grants to STB
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