Phase change on transmission of microwaves through metal disc delay dielectrics

Expressions for the phase change Φ suffered by microwaves when transmitted through an artificial dielectric composed of metallic discs arranged in a three-dimensional array have been derived with different approaches as follows (i) molecular theory, (ii) electromagnetic theory and (iii) transmission line theory. The phase change depends on the distance t that the wave traverses inside the dielectric and also the spacing d between centre to centre of any two adjacent discs in the three principal directions. Molecular theory indicates Φ as an increasing function of t, whereas, the other two theories indicate Φ as an oscillatory function of t. The transmission line theory also exhibits Φ to be real or imaginary depending on t. Experimental values of Φ as a function of t have been obtained with the help of a microwave (3·2 cms wavelength) interferometer for two dielectrics having d as 1·91 cms and 2·22 cms respectively.

Separation Of Beta-Apocarotenals And Related Compounds By Reversed-Phase Paper And Thin-Layer Chromatography

Tlie sclxuntion and clraractcrization of vitamins Al and An nnd related compoundsby reversed-pllasc paper cliromatogrnpl~y as well as ly thin-lqxr chromategraphy have hen rcportccl carlicrl * $. Thin-lnycr chromatography has also been used for the separatinn and charncterizatio11 of carotenoids from natural sourccs3~ ‘1. I-Iowcver, 130tr.rc,1~1~ofib scrvccl that carotenoid misturcs cannot be separated on a sin& aclsorhnt with ;1 sin& solvent. The scparntion and clctermi1wtion of carotenoid alclclydes from plants, microorganisms and animnl tissues have lxxn carriecl out by nicans of thin-layer clirf.~li~ato~apI~~U. Apocarotcnals awl apocarotcnoic acid have been detected in ornnges by the same technique’*

Energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals

Thermotropic liquid crystals are known to display rich phase behavior on temperature variation. Although the nematic phase is orientationally ordered but translationally disordered, a smectic phase is characterized by the appearance of a partial translational order in addition to a further increase in orientational order. In an attempt to understand the interplay between orientational and translational order in the mesophases that thermotropic liquid crystals typically exhibit upon cooling from the high-temperature isotropic phase, we investigate the potential energy landscapes of a family of model liquid crystalline systems. The configurations of the system corresponding to the local potential energy minima, known as the inherent structures, are determined from computer simulations across the mesophases. We find that the depth of the potential energy minima explored by the system along an isochor grows through the nematic phase as temperature drops in contrast to its insensitivity to temperature in the isotropic and smectic phases. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures; the inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the isotropic-nematic transition. We find that this breakdown occurs at a temperature below which the system explores increasingly deeper potential energy minima.

Two-Phase Thermodynamic Model for Efficient and Accurate Absolute Entropy of Water from Molecular Dynamics Simulations

Presented here is the two-phase thermodynamic (2PT) model for the calculation of energy and entropy of molecular fluids from the trajectory of molecular dynamics (MD) simulations. In this method, the density of state (DoS) functions (including the normal modes of translation, rotation, and intramolecular vibration motions) are determined from the Fourier transform of the corresponding velocity autocorrelation functions. A fluidicity parameter (f), extracted from the thermodynamic state of the system derived from the same MD, is used to partition the translation and rotation modes into a diffusive, gas-like component (with 3Nf degrees of freedom) and a nondiffusive, solid-like component. The thermodynamic properties, including the absolute value of entropy, are then obtained by applying quantum statistics to the solid component and applying hard sphere/rigid rotor thermodynamics to the gas component. The 2PT method produces exact thermodynamic properties of the system in two limiting states: the nondiffusive solid state (where the fluidicity is zero) and the ideal gas state (where the fluidicity becomes unity). We examine the 2PT entropy for various water models (F3C, SPC, SPC/E, TIP3P, and TIP4P-Ew) at ambient conditions and find good agreement with literature results obtained based on other simulation techniques. We also validate the entropy of water in the liquid and vapor phases along the vapor-liquid equilibrium curve from the triple point to the critical point. We show that this method produces converged liquid phase entropy in tens of picoseconds, making it an efficient means for extracting thermodynamic properties from MD simulations.

Vapour phase synthesis of salol over solid acids via transesterification

The transesterification of methyl salicylate with phenol has been studied in vapour phase over solid acid catalysts such as ZrO2, MoO3 and SO42- or Mo(VI) ions modified zirconia. The catalytic materials were prepared and characterized for their total surface acidity, BET surface area and powder XRD patterns. The effect of mole-ratio of the reactants, catalyst bed temperature, catalyst weight, flow-rate of reactants, WHSV and time-on-stream on the conversion (%) of phenol and selectivity (%) of salol has been investigated. A good yield (up to 70%) of salol with 90% selectivity was observed when the reactions were carried out at a catalyst bed temperature of 200 degrees C and flow-rate of 10 mL/h in presence of Mo(VI)/ZrO2 as catalyst. The results have been interpreted based on the variation of acidic properties and powder XRD phases of zirconia on incorporation of SO42- or Mo(VI) ions. The effect of poisoning of acid sites of SO42- or Mo(VI) ions modified zirconia on total surface acidity, powder XRD phases and catalytic activity was also studied. Possible reaction mechanisms for the formation of salol and diphenyl ether over acid sites are proposed.

On Using Projective Relations for Calibration and Estimation in a Structured-Light Scanner

For structured-light scanners, the projective geometry between a projector-camera pair is identical to that of a camera-camera pair. Consequently, in conjunction with calibration, a variety of geometric relations are available for three-dimensional Euclidean reconstruction. In this paper, we use projector-camera epipolar properties and the projective invariance of the cross-ratio to solve for 3D geometry. A key contribution of our approach is the use of homographies induced by reference planes, along with a calibrated camera, resulting in a simple parametric representation for projector and system calibration. Compared to existing solutions that require an elaborate calibration process, our method is simple while ensuring geometric consistency. Our formulation using the invariance of the cross-ratio is also extensible to multiple estimates of 3D geometry that can be analysed in a statistical sense. The performance of our system is demonstrated on some cultural artifacts and geometric surfaces.

Electron diffraction patterns from the Al-Mn decagonal phase

The variety of electron diffraction patterns arising from the decagonal phase has been explored using a stereographic analysis for generating the important zone axes as intersection points corresponding to important relvectors. An indexing scheme employing a set of five vectors and an orthogonal vector has been followed. A systematic tilting from the decagonal axis to one of the twofold axes has been adopted to generate a set of experimental diffraction patterns corresponding to the expected patterns from the stereographic analysis with excellent agreement.

Effect of mode of rolling on development of texture and microstructure in two-phase (alpha plus beta) brass

The evolution of microstructure and texture during deformation of two-phase (alpha + beta) brass was studied for different initial microstructure and texture. The deformation processing involved unidirectional and multi-step cross-rolling. The bulk textures were determined by measuring the pole figures and calculating the orientation distribution function ODF for both alpha (fcc) and beta (bcc) phases, while the microstructure and other microstructural parameters were measured through optical microscopy and scanning electron microscopy with electron back scatter diffraction (SEM-EBSD). Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are significantly different. The variation in initial texture had a pronounced effect on the development of texture in the alpha phase during subsequent deformation. (C) 2010 Elsevier B.V. All rights reserved.

Orbital evolution and orbital phase resolved spectroscopy of the HMXB pulsar 4U 1538-52 with RXTE-PCA and BeppoSAX

We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3-20 keV energy range were fitted with a power law and a high energy cut-off along with a Gaussian line at similar to 6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at similar to 6.4keV in the restricted energy range of 0.3-10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.

Stress induced phase transition in monomolecular perfluroalkylsilane film self assembled on aluminium surface

We control the stiffnesses of two dual double cantelevers placed in series to control penetration into a perflurooctyltrichlorosilane monolayer self assembled on aluminium and silicon substrates. The top cantilever which carries the probe is displaced with respect to the bottom cantilever which carries the substrate, the difference in displacement recorded using capacitors gives penetration. We further modulate the input displacement sinusoidally to deconvolute the viscoelastic properties of the monolayer. When the intervention is limited to the terminal end of the molecule there is a strong viscous response in consonance with the ability of the molecule to dissipate energy by the generation of gauche defects freely. When the intervention reaches the backbone, at a contact mean pressure of 0.2GPa the damping disappears abruptly and the molecule registers a steep rise in elastic modulus and relaxation time constant, with increasing contact pressure. We offer a physical explanation of the process and describe this change as due to a phase transition from a liquid like to a solid like state.

Glowworm-inspired robot swarm for simultaneous taxis towards multiple radiation sources

This paper presents a glowworm metaphor based distributed algorithm that enables a collection of minimalist mobile robots to split into subgroups, exhibit simultaneous taxis-behavior towards, and rendezvous at multiple radiation sources such as nuclear/hazardous chemical spills and fire-origins in a fire calamity. The algorithm is based on a glowworm swarm optimization (GSO) technique that finds multiple optima of multimodal functions. The algorithm is in the same spirit as the ant-colony optimization (ACO) algorithms, but with several significant differences. The agents in the glowworm algorithm carry a luminescence quantity called luciferin along with them. Agents are thought of as glowworms that emit a light whose intensity is proportional to the associated luciferin. The key feature that is responsible for the working of the algorithm is the use of an adaptive local-decision domain, which we use effectively to detect the multiple source locations of interest. The glowworms have a finite sensor range which defines a hard limit on the local-decision domain used to compute their movements. Extensive simulations validate the feasibility of applying the glowworm algorithm to the problem of multiple source localization. We build four wheeled robots called glowworms to conduct our experiments. We use a preliminary experiment to demonstrate the basic behavioral primitives that enable each glowworm to exhibit taxis behavior towards source locations and later demonstrate a sound localization task using a set of four glowworms.