678 research outputs found
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Structure and Electrochemical Properties of LiMn2O4 Thin Films
The structure and electrochemical properties of LiMn{sub 2}O{sub 4} films depend upon the deposition and annealing conditions. Films which were deposited by rf magnetron sputtering of LiMn{sub 2}O{sub 4} in Ar + N{sub 2} gas mixtures and annealed in O{sub 2} at temperatures between 400 to 1000{degrees}C had the cubic spinel structure with an a-axis length that increased linearly from 8.13 to 8.25 {Angstrom} with increasing anneal temperature. Thin-film lithium cells with cathodes of different a-axis lengths exhibited marked differences in their voltage profiles. In particular, the ratio of the capacities at 4 V and 3 V increased with the a-axis length. A defect model of LiMn{sub 2}O{sub 4} which is consistent with the structural and electrochemical data is represented by [Li{sub 1-y+z}Mn{sup 2+}{sub y-z}]{sub 8a}[Mn{sup 2+}{sub z}]{sub 16c}[Li{sub x}Mn{sub 2-x}]{sub 16d}O{sub 4}. Based on this model and the results of in-situ XRD measurements, it is proposed that Mn ions migrate from 8(a) tetrahedral sites to 16(c) octahedral sites on charging the cells in the 5V plateau
5D Black Rings and 4D Black Holes
It has recently been shown that the M theory lift of a IIA 4D BPS Calabi-Yau
black hole is a 5D BPS black hole spinning at the center of a Taub-NUT-flux
geometries, and a certain linear relation between 4D and 5D BPS partition
functions was accordingly proposed. In the present work we fortify and enrich
this proposal by showing that the M-theory lift of the general 4D multi-black
hole geometry are 5D black rings in a Taub-NUT-flux geometry.Comment: 8 pages; version 2, with additional references and explanation
Supergravity Microstates for BPS Black Holes and Black Rings
We demonstrate a solution generating technique, modulo some constraints, for
a large class of smooth supergravity solutions with the same asymptotic charges
as a five dimensional 3-charge BPS black hole or black ring, dual to a D1/D5/P
system. These solutions are characterized by a harmonic function with both
positive and negative poles, which induces a geometric transition whereby
singular sources have disappeared and all of the net charge at infinity is
sourced by fluxes through two-cycles joining the poles of the harmonic
function.Comment: 25 pages, 1 figure. Fixed minor typos, references added, extra
comment on gauge choic
Characterization of all the supersymmetric solutions of gauged N=1,d=5 supergravity
We find a complete characterization of all the supersymmetric solutions of
non-Abelian gauged N=1,d=5 supergravity coupled to vector multiplets and
hypermultiplets: the generic forms of the metrics as functions of the scalars
and vector fields plus the equations that all these must satisfy. These
equations are now a complicated non-linear system and there it seems impossible
to produce an algorithm to construct systematically all supersymmetric
solutions.Comment: Some references and two comments adde
Kinetics of Ordering in Fluctuation-Driven First-Order Transitions: Simulations and Dynamical Renormalization
Many systems where interactions compete with each other or with constraints
are well described by a model first introduced by Brazovskii. Such systems
include block copolymers, alloys with modulated phases, Rayleigh-Benard Cells
and type-I superconductors. The hallmark of this model is that the fluctuation
spectrum is isotropic and has a minimum at a nonzero wave vector represented by
the surface of a d-dimensional hyper-sphere. It was shown by Brazovskii that
the fluctuations change the free energy structure from a to a
form with the disordered state metastable for all quench depths.
The transition from the disordered to the periodic, lamellar structure changes
from second order to first order and suggests that the dynamics is governed by
nucleation. Using numerical simulations we have confirmed that the equilibrium
free energy function is indeed of a form. A study of the dynamics,
however, shows that, following a deep quench, the dynamics is described by
unstable growth rather than nucleation. A dynamical calculation, based on a
generalization of the Brazovskii calculations shows that the disordered state
can remain unstable for a long time following the quench.Comment: 18 pages, 15 figures submitted to PR
All the supersymmetric solutions of N=1,d=5 ungauged supergravity
We classify the supersymmetric solutions of ungauged N=1 d=5 SUGRA coupled to
vector multiplets and hypermultiplets. All the solutions can be seen as
deformations of solutions with frozen hyperscalars. We show explicitly how the
5-dimensional Reissner-Nordstrom black hole is deformed when hyperscalars are
living on SO(4,1)/SO(4) are turned on, reducing its supersymmetry from 1/2 to
1/8. We also describe in the timelike and null cases the solutions that have
one extra isometry and can be reduced to N=2,d=4 solutions. Our formulae allows
the uplifting of certain N=2,d=4 black holes to N=1,d=5 black holes on KK
monopoles or to pp-waves propagating along black strings.Comment: Some typos fixed and some paragraphs improved. 44 pages, Latex 2e
file, no figures. Version to be published in JHE
Mergers and Typical Black Hole Microstates
We use mergers of microstates to obtain the first smooth horizonless
microstate solutions corresponding to a BPS three-charge black hole with a
classically large horizon area. These microstates have very long throats, that
become infinite in the classical limit; nevertheless, their curvature is
everywhere small. Having a classically-infinite throat makes these microstates
very similar to the typical microstates of this black hole. A rough CFT
analysis confirms this intuition, and indicates a possible class of dual CFT
microstates.
We also analyze the properties and the merging of microstates corresponding
to zero-entropy BPS black holes and black rings. We find that these solutions
have the same size as the horizon size of their classical counterparts, and we
examine the changes of internal structure of these microstates during mergers.Comment: 49 pages, 5 figures. v2 references adde
Bubbles on Manifolds with a U(1) Isometry
We investigate the construction of five-dimensional, three-charge
supergravity solutions that only have a rotational U(1) isometry. We show that
such solutions can be obtained as warped compactifications with a singular
ambi-polar hyper-Kahler base space and singular warp factors. We show that the
complete solution is regular around the critical surface of the ambi-polar
base. We illustrate this by presenting the explicit form of the most general
supersymmetric solutions that can be obtained from an Atiyah-Hitchin base space
and its ambi-polar generalizations. We make a parallel analysis using an
ambi-polar generalization of the Eguchi-Hanson base space metric. We also show
how the bubbling procedure applied to the ambi-polar Eguchi-Hanson metric can
convert it to a global AdS_2xS^3 compactification.Comment: 33 pages, 5 figures, LaTeX; references adde
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Sputter deposition and characterization of lithium cobalt oxide thin films and their applications in thin-film rechargeable lithium batteries
Li Co oxide thin films were deposited by rf magnetron sputtering of a LiCoO{sub 2} target in a 3:1 Ar/O{sub 2} mixture gas. From proton-induced gamma-ray emission analysis and Rutherford backscattering spectrometry, the average composition of these films was determined to be Li{sub 1.15}CoO{sub 2.16}. X-ray powder diffraction patterns of films annealed in air at 500-700 C were consistent with regular rhombohedral structure of crystalline LiCoO{sub 2}. Discharge curves of thin film lithium cells with amoprohous LiCoO{sub 2} showed no obvious structural transition between 4.2 and 1.5 V. Shape of discharge curves of cells with polycrystalline cathodes were consistent with a two-phase voltage plateau at {similar_to}3.9 V with a relatively large capacity and two additional smaller plateaus at higher voltages. Cells with the 700 C annealed cathodes showed a capacity loss of {similar_to} after 1000 cycles between 4.2 and 3.0 V
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