279 research outputs found
Multifarious transparent glass nanocrystal composites
Glasses comprising well known ferroelectric crystalline phases have been a subject of curious investigation from the point of view of exploiting these composites for dielectric, pyroelectric, ferroelectric, electro and non-linear optical devices. Transparent glass-ceramics containing ferroelectric crystallites at nano scale have been of much interest owing to their promising physical properties. The advantages that are associated with glass-ceramics include very low levels of porosity and hence high break down voltages. It is of our interest to nanocrystallize Aurivillius family of ferroelectric oxides and tetragonal tungsten bronzes on borate and tellurite based glass matrices and demonstrate their promising optical and nonlinear optical properties. Apart from the above, the nanocrystallites of well known ferroelectric material LiNbO3 was grown in a reactive glass matrix. These nanocrystals of LiNbO3 exhibited intense second harmonic signals in transmission mode when exposed to IR light at 1064 nm. The most interesting result was the demonstration of optical diffraction of the second harmonic signals which was attributed to the presence of self- organized sub-micrometer sized LiNbO3 crystallites that were indeed inscribed by the IR laser light which was used to probe in the NLO property of these materials
Diffusion of a chemically reactive species of a power-law fluid past a stretching surface
A numerical solution for the steady magnetohydrodynamic (MHD) non-Newtonian power-law fluid flow over a continuously moving surface with species concentration and chemical reaction has been obtained. The viscous flow is driven solely by the linearly stretching sheet, and the reactive species emitted from this sheet undergoes an isothermal and homogeneous one-stage reaction as it diffuses into the surrounding fluid. Using a similarity transformation, the governing non-linear partial differential equations are transformed into coupled nonlinear ordinary differential equations. The governing equations of the mathematical model show that the flow and mass transfer characteristics depend on six parameters, namely, the power-law index, the magnetic parameter, the local Grashof number with respect to species diffusion, the modified Schmidt number, the reaction rate parameter, and the wall concentration parameter. Numerical solutions for these coupled equations are obtained by the KellerBox method, and the solutions obtained are presented through graphs and tables. The numerical results obtained reveal that the magnetic field significantly increases the magnitude of the skin friction, but slightly reduces the mass transfer rate. However, the surface mass transfer strongly depends on the modified Schmidt number and the reaction rate parameter; it increases with increasing values of these parameters. The results obtained reveal many interesting behaviors that warrant further study of the equations related to non-Newtonian fluid phenomena, especially shear-thinning phenomena. Shear thinning reduces the wall shear stress. © 2011 Elsevier Ltd. All rights reserved
Massless monopoles and the moduli space approximation
We investigate the applicability of the moduli space approximation in
theories with unbroken non-Abelian gauge symmetries. Such theories have
massless magnetic monopoles that are manifested at the classical level as
clouds of non-Abelian field surrounding one or more massive monopoles. Using an
SO(5) example with one massive and one massless monopole, we compare the
predictions of the moduli space approximation with the results of a numerical
solution of the full field equations. We find that the two diverge when the
cloud velocity becomes of order unity. After this time the cloud profile
approximates a spherical wavefront moving at the speed of light. In the region
well behind this wavefront the moduli space approximation continues to give a
good approximation to the fields. We therefore expect it to provide a good
description of the motion of the massive monopoles and of the transfer of
energy between the massive and massless monopoles.Comment: 18 pages, 5 figure
Addition of NOCl to cyclic vinylsilanes: An unexpected reversal of regiochemistry
NOCl adds to cyclic vinylsilanes in a syn manner with NO+ bonding to the β-carbon and Cl- to the α-carbon, which is a reversal of the regiochemistry expected from the β-silicon effect. The adducts dimerize to a single diastereomer containing enantiomeric pairs and/or give secondary products on further reaction. © 2001 Elsevier Science Ltd
More on scattering of Chern-Simons vortices
I derive a general formalism for finding kinetic terms of the effective
Lagrangian for slowly moving Chern-Simons vortices. Deformations of fields
linear in velocities are taken into account. From the equations they must
satisfy I extract the kinetic term in the limit of coincident vortices. For
vortices passing one over the other there is locally the right-angle
scattering. The method is based on analysis of field equations instead of
action functional so it may be useful also for nonvariational equations in
nonrelativistic models of Condensed Matter Physics.Comment: discussion around Eq.(45) is generalised, one more condition for the
local right-angle scattering is adde
Ferroelectric Properties and Transmission Response ofPZN-PT Single Crystals for Underwater Communication
Single crystal of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZN-PT) at the composition of morphotropicphase boundary (MPB) shows a very high electromechanical coupling coefficient, piezoelectriccoefficient, and dielectric constant compared to conventional PZT ceramics. These exceptionalproperties of these single crystals find enormous applications in medical ultrasound imaging andunderwater communication (Sonar). The growth of PZN-PT single crystals has been carried outby bottom-supported flux Bridgman method. There are many growth issues to be addressedduring the process of growth. The grown crystals are oriented and cut along <001> directionwith the crystal dimension of 8 x 6 x 1.5 mm3 for further analysis. The oriented crystals were poledat a rate of 1 kV/mm. The poled crystals have been characterised for dielectric, strain andpiezoelectric values. Further, the poled specimen were tested for transmitting response at variousfrequencies in acoustic test facility and the difficulties in their growth
ChemInform Abstract: Addition of NOCl to Cyclic Vinylsilanes: An Unexpected Reversal of Regiochemistry.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
We propose a cosmological scenario in which the hot big bang universe is
produced by the collision of a brane in the bulk space with a bounding orbifold
plane, beginning from an otherwise cold, vacuous, static universe. The model
addresses the cosmological horizon, flatness and monopole problems and
generates a nearly scale-invariant spectrum of density perturbations without
invoking superluminal expansion (inflation). The scenario relies, instead, on
physical phenomena that arise naturally in theories based on extra dimensions
and branes. As an example, we present our scenario predominantly within the
context of heterotic M-theory. A prediction that distinguishes this scenario
from standard inflationary cosmology is a strongly blue gravitational wave
spectrum, which has consequences for microwave background polarization
experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde
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