294 research outputs found
Effect of electro-co-deposition parameters on surface mechanical properties of Cu-TiO2 composite coating
The present work describes processing and properties of Cu–TiO2 electrodeposited coating on copper substrate with optimized current density and ultrafine ceramic TiO2 powder in the plating bath. Direct current electrodeposition process was employed to develop the composite coating with Cu matrix and ceramic oxide (TiO2) nanoparticles as reinforcement on copper substrate. The coatings were developed with 0 (unreinforced), 10 and 30 g l −1 TiO2 powder in bath, at four different current densities (5, 8, 11 and 14 A dm −2 ) to study the effect of current density and particle concentration in bath on the structure and properties of the developed coatings. Phase, microstructure and compositional analysis of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. Hardness and wear resistance of the coatings were analysed by using microhardness tester and ball on plate wear tester and improvement in these properties was observed due to particle reinforcement and crystallographic texture
S-duality and cosmological constant in string theory
The S-duality invariance of equations of motion of four dimensional string effective action with cosmological constant, \Lambda , is studied. It is demonstrated that the S-duality symmetry of the field equations are broken for nonzero \Lambda. The naturalness hypothesis is invoked to argue that \Lambda should remain small since exact S-duality symmetry will force the cosmological constant to vanish in the string effective action
Monodromy Matrix in the PP-Wave Limit
We construct the monodromy matrix for a class of gauged WZWN models in the
plane wave limit and discuss various properties of such systems.Comment: 16 page
Cosmological solutions, p-branes and the Wheeler-DeWitt equation
The low energy effective actions which arise from string theory or M-theory
are considered in the cosmological context, where the graviton, dilaton and
antisymmetric tensor field strengths depend only on time. We show that previous
results can be extended to include cosmological solutions that are related to
the E_N Toda equations. The solutions of the Wheeler-DeWitt equation in
minisuperspace are obtained for some of the simpler cosmological models by
introducing intertwining operators that generate canonical transformations
which map the theories into free theories. We study the cosmological properties
of these solutions, and also briefly discuss generalised Brans-Dicke models in
our framework. The cosmological models are closely related to p-brane solitons,
which we discuss in the context of the E_N Toda equations. We give the explicit
solutions for extremal multi-charge (D-3)-branes in the truncated system
described by the D_4 =O(4,4) Toda equations.Comment: 11 pages (2-column), Revte
Symmetries of the near horizon of a Black Hole by Group Theoretic methods
We use group theoretic methods to obtain the extended Lie point symmetries of
the quantum dynamics of a scalar particle probing the near horizon structure of
a black hole. Symmetries of the classical equations of motion for a charged
particle in the field of an inverse square potential and a monopole, in the
presence of certain model magnetic fields and potentials are also studied. Our
analysis gives the generators and Lie algebras generating the inherent
symmetries.Comment: To appear in Int. J. Mod. Phys.
Covariant Duality Symmetric Actions
A manifestly Lorentz and diffeomorphism invariant form for the abelian gauge
field action with local duality symmetry of Schwarz and Sen is given. Some of
the underlying symmetries of the covariant action are further considered. The
Noether conserved charge under continuous local duality rotations is found. The
covariant couplings with gravity and the axidilaton field are discussed.Comment: 9 pages, revtex, no figures; (To appear in Physical Review D
Kaluza-Klein Black Holes in String Theory
Exact solutions of heterotic string theory corresponding to four-dimensional
magnetic black holes in supergravity are described. The solutions
describe the black holes in the throat limit, and consist of a tensor product
of an WZW orbifold with the linear dilaton vacuum, supersymmetrized to
world sheet SUSY. One dimension of the model is interpreted as
a compactified fifth dimension, leading to a four dimensional solution with a
Kaluza-Klein gauge field having a magnetic monopole background; this
corresponds to a solution in supergravity, since that theory is obtained
by dimensional reduction of string theory.Comment: 13p. uses Harvma
Warped Spectroscopy: Localization of Frozen Bulk Modes
We study the 10D equation of motion of dilaton-axion fluctuations in type IIB
string compactifications with three-form flux, taking warping into account.
Using simplified models with physics comparable to actual compactifications, we
argue that the lightest mode localizes in long warped throats and takes a mass
of order the warped string scale. Also, Gukov-Vafa-Witten superpotential is
valid for the lightest mass mode; however, the mass is similar to the
Kaluza-Klein scale, so the dilaton-axion should be integrated out of the
effective theory in this long throat regime (leaving a constant
superpotential). On the other hand, there is a large hierarchy between
flux-induced and KK mass scales for moderate or weak warping. This hierarchy
agrees with arguments given for trivial warping. Along the way, we also
estimate the effect of the other 10D supergravity equations of motion on the
dilaton-axion fluctuation, since these equations act as constraints. We argue
that they give negligible corrections to the simplest approximation.Comment: 24pp + appendices, 6 figs, JHEP3 class; v2. corrected reference; v3.
added clarifications; v4. corrected typo
Asymmetric nuclear matter : a variational approach
We discuss here a self-consistent method to calculate the properties of the
cold asymmetric nuclear matter. In this model, the nuclear matter is dressed
with s-wave pion pairs and the nucleon-nucleon (N-N) interaction is mediated by
these pion pairs, and mesons. The parameters of these
interactions are calculated self-consistently to obtain the saturation
properties like equilibrium binding energy, pressure, compressibility and
symmetry energy. The computed equation of state is then used in the Tolman-
Oppenheimer-Volkoff (TOV) equation to study the mass and radius of a neutron
star in the pure neutron matter limit.Comment: 10 pages, 5 figures and 1 tabl
Master Ward Identity for Nonlocal Symmetries in D=2 Principal Chiral Models
We derive, in path integral approach, the (anomalous) master Ward identity
associated with an infinite set of nonlocal conservation laws in
two-dimensional principal chiral modelsComment: 12 pages, harvmac, minors correction
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