11,424 research outputs found
The Generalised Raychaudhuri Equations : Examples
Specific examples of the generalized Raychaudhuri Equations for the evolution
of deformations along families of dimensional surfaces embedded in a
background dimensional spacetime are discussed. These include string
worldsheets embedded in four dimensional spacetimes and two dimensional
timelike hypersurfaces in a three dimensional curved background. The issue of
focussing of families of surfaces is introduced and analysed in some detail.Comment: 8 pages (Revtex, Twocolumn format). Corrected(see section on string
worldsheets), reorganised and shortened slightl
Path integrals and wavepacket evolution for damped mechanical systems
Damped mechanical systems with various forms of damping are quantized using
the path integral formalism. In particular, we obtain the path integral kernel
for the linearly damped harmonic oscillator and a particle in a uniform
gravitational field with linearly or quadratically damped motion. In each case,
we study the evolution of Gaussian wavepackets and discuss the characteristic
features that help us distinguish between different types of damping. For
quadratic damping, we show that the action and equation of motion of such a
system has a connection with the zero dimensional version of a currently
popular scalar field theory. Furthermore we demonstrate that the equation of
motion (for quadratic damping) can be identified as a geodesic equation in a
fictitious two-dimensional space.Comment: 15 pages, 6 figure
Decoupling of silicon carbide optical sensor response for temperature and pressure measurements (Erratum)
Single crystal silicon carbide is a chemically inert transparent material with superior oxidation-resistant properties at elevated temperatures compared to black polycrystalline silicon carbide substrates. These improved properties make crystalline silicon carbide a good optical sensor material for harsh environments such as combustion chambers and turbine systems. Interferometric optical sensors are orders of magnitude more sensitive than electrical sensors and are proposed for these applications. Silicon carbide itself behaves as a Fabry-Perot etalon eliminating the need for an external interferometer for any measurement using this silicon carbide as a sensor. The principle of the optical sensor in this study is the temperature- and pressure-dependent refractive index of silicon carbide, which can be used to determine the temperatures and pressures of gases that are in contact with silicon carbide. Interference patterns produced by a silicon carbide (4H-SiC) wafer due to multiple reflections of a helium-neon laser beam of wavelength of 632.8 nm have been obtained at temperatures up to 500 degrees C and pressures up to 600 psi. The pattern changes for the same gas at different temperatures and pressures and for different gases at the same temperature and pressure. The refractive index at the wafer-gas interface is calculated from the interference pattern and the refractive index gradients with respect to temperature and pressure, respectively, are also determined. Decoupling temperature and pressure using these gradients and the measured reflectivity data are discussed in this paper
On a Raychaudhuri equation for hot gravitating fluids
We generalize the Raychaudhuri equation for the evolution of a self
gravitating fluid to include an Abelian and non-Abelian hybrid magneto fluid at
a finite temperature. The aim is to utilize this equation for investigating the
dynamics of astrophysical high temperature Abelian and non-Abelian plasmas.Comment: 13 pages, Invited contribution to Pramana special issue dedicated to
A.K. Raychaudhuri, "The Raychaudhuri equation and its role in Modern
Cosmology". Pramana style files include
Exciton-photon coupling in a ZnSe based microcavity fabricated using epitaxial liftoff
We report the observation of strong exciton-photon coupling in a ZnSe based
microcavity fabricated using epitaxial liftoff. Molecular beam epitaxial grown
ZnSe/ZnCdSe quantum wells with a one wavelength optical length
at the exciton emission were transferred to a SiO/TaO mirror with a
reflectance of 96% to form finesse matched microcavities. Analysis of our angle
resolved transmission spectra reveals key features of the strong coupling
regime: anticrossing with a normal mode splitting of at ;
composite evolution of the lower and upper polaritons; and narrowing of the
lower polariton linewidth near resonance. The heavy hole exciton oscillator
strength per quantum well is also deduced to be .Comment: 3 pages, 3 figure
Correction to “Analysis of the summertime buildup of tropospheric ozone abundances over the Middle East and North Africa as observed by the Tropospheric Emission Spectrometer Instrument”
Focusing of timelike worldsheets in a theory of strings
An analysis of the generalised Raychaudhuri equations for string world sheets
is shown to lead to the notion of focusing of timelike worldsheets in the
classical Nambu-Goto theory of strings. The conditions under which such effects
can occur are obtained . Explicit solutions as well as the Cauchy initial value
problem are discussed. The results closely resemble their counterparts in the
theory of point particles which were obtained in the context of the analysis of
spacetime singularities in General Relativity many years ago.Comment: 14 pages, RevTex, no figures, extended, to appear in Phys Rev
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