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 $N=4$ supergravity are described. The solutions describe the black holes in the throat limit, and consist of a tensor product of an $SU(2)$ WZW orbifold with the linear dilaton vacuum, supersymmetrized to $(1,0)$ world sheet SUSY. One dimension of the $SU(2)$ 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 $N=4$ 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, $\omega$ and $\rho$ 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