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We report the room temperature synthesis of ZnS in the wurtzite phase by using ethylenediamine, which acts as a template as well as a capping agent. With the addition of ethylenediamine, structural transformation in ZnS from cubic to wurtzite phase is observed. This is accompanied by an increase in the real permittivity by an order of 2, and reduction in dielectric loss by a factor of 6 as compared to a sample without ethylenediamine. Thus, suggesting that ethylenediamine capped wurtzite ZnS is more suitable for miniaturied capactive devices. [ABSTRACT FROM AUTHOR]

Dielectric, textural, and electro-optical investigations have been carried out on a material exhibiting de Vries smectic A phase transition in sample cells of various thicknesses. Thickness independent memory effect has been observed in this special class of ferroelectric liquid crystals (FLCs) known as de Vries electroclinic liquid crystals. Unlike the FLC materials, surface anchoring energy does not play a role in the memory effect due to the fact that pitch is around 2 micron and basic assumption of SSFLC effect is not valid. The conversion of short-range azimuthal ([uppercase_phi_synonym]) ordering of molecules in Sm C* phase into a long-range azimuthal ordering under the influence of field could be one of the possible explanations. The transformation of molecular ordering in Sm C* phase under field may be mediated by dipolar interaction and viscoelastic properties. [ABSTRACT FROM AUTHOR]

This article is primarily addressed to the geometry of hard ellipsoidal molecules which is essentially required in the study of the fluid structure, thermodynamics and transport properties of the model hard-biaxial fluids or liquid crystals. A methodology has systematically been followed in obtaining the known as well as hitherto unknown results for a biaxial system. The computationally convenient and neat expressions have been achieved for the surface and volume elements of a biaxial molecule. New expressions have been obtained for the surface area S and the mean radius of curvature R of a rigid ellipsoid in terms of the elliptic integrals of the first and second kinds. In the limit when the two axes become equal, the expressions obtained for the ellipsoidal molecules reduce to those of the spheroidal systems. Exact expression has been obtained for the second virial coefficient of the ellipsoidal fluid and furthermore the significance of our analytical results for such a fluid are enunciated in the context of the study of the higher virial coefficients and equation of state. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

General expressions in terms of various square-bracket integrals for the thermal conductivity λ and its first-order approximation [λ]1 of a classical dilute binary gas mixture of nonspherical molecules have been obtained by extending the Taxman classical kinetic theory of transport phenomena within the framework of the Chapman–Enskog second approximation method for the mixture of spherical molecules. In the limit, [λ]1 formula tends to the corresponding formula for a dilute simple gas of nonspherical molecules or a dilute binary gas mixture of spherical molecules. The dimensionalities of the square-bracket integrals belonging to [λ]1 for the mixture of rigid spheroids having C∞v symmetry have been reduced by integrating analytically the velocity and angular velocity parts of the integrals. The resulting reduced quadratures are over the orientational coordinates of two colliding like or unlike spheroids. Two limiting checks are discussed which confirm that the quadrature formulas are correct. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

General expressions in terms of the square bracket integrals for the shear and volume viscosities of a classical dilute binary gas mixture of nonspherical molecules have been derived by extending the Taxman classical kinetic theory of transport phenomena within the framework of the Chapman–Enskog second approximation method for a mixture of spherical molecules. The dimensionality of integrals for the binary mixture of rigid spheroidal molecules having C∞v symmetry has been reduced analytically to get ultimately the forms wherein the integrals are to be performed only over the orientational coordinates of two colliding like or unlike spheroids. The general expressions for the nonspherical molecules as well as the final integrals for the spheroidal molecules are shown to be correct. The shear- and volume-viscosity formulas for a classical dilute binary gas mixture of hard sphere molecules have been retrieved as the limiting case of our corresponding expressions for the spheroidal systems. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The impedance of CrO2/Ag nanocomposite particles has been investigated in the frequency range of 100 Hz–1 MHz at a temperature of 300–475 K. The impedance in the form of Cole-Cole plot reveals that the resistivity contribution primarily comes from bulk grain interior below 375 K and above those from both the grain interior and grain boundaries. The grain interior resistance decreases from 163 kΩ at 300 K to 6 kΩ at 475 K with a typical semiconductor like behavior. Above 375 K, the impurities at grain boundaries are thermally activated and, thus, contribute to the dielectric relaxation. The electrical conductivity of the CrO2/Ag nanocomposite follows an Arrhenius law with an activation energy/dielectric transition from 0.18 to 0.82 eV at 400 K. The dielectric transition is explained as the change of the crystal field caused by the thermal expansion or by the surface bond contraction in the small CrO2/Ag particles. At 300 K, the nanocomposite has an increased coercivity of 650 Oe, with a saturation magnetization of 75 emu/g (equivalent to 1.13μB per Cr4+ ion), which is attributed to the spin pinning in the single domain CrO2/Ag particles. [ABSTRACT FROM AUTHOR]

Flash X-ray sources driven by pulsed power find applications in industrial radiography, and a portable X-ray source is ideal where the radiography needs to be taken at the test site. A compact and portable flash X-ray (FXR) system based on a Marx generator has been developed with the high voltage fed to the FXR tube via a cable feed-through arrangement. Hard bremsstrahlung X-rays of few tens of nanosecond duration are generated by impinging intense electron beams on an anode target of high Z material. An industrial X-ray source is developed with source size as low as 1 mm. The system can be operated from 150 kV to 450 kV peak voltages and a dose of 10 mR has been measured at 1 m distance from the source window. The modeling of the FXR source has been carried out using particle-in-cell and Monte Carlo simulations for the electron beam dynamics and X-ray generation, respectively. The angular dose profile of X-ray has been measured and compared with the simulation. [ABSTRACT FROM AUTHOR]

We highlight the relevance of demagnetizing-field corrections in the characterization of dense magnetic nanoparticle assemblies. By an analysis that employs in-plane and out-of-plane magnetometry on cylindrical assemblies, we demonstrate the suitability of a simple analytical formulabased correction method. This allows us to identify artifacts of the demagnetizing field in temperature-dependent susceptibility curves (e.g., shoulder peaks in curves from a disordered assembly of essentially bare magnetic nanoparticles). The same analysis approach is shown to be a straightforward procedure for determining the magnetic nanoparticle packing fraction in dense, disordered assemblies. [ABSTRACT FROM AUTHOR]

We present a method to fabricate top-gated field-effect devices in a LaAlO3/SrTiO3 two-dimensional electron gas (2-DEG). Prior to the gate deposition, the realisation of micron size conducting channels in the 2-DEG is achieved by an ion-irradiation with high-energy oxygen ions. After identifying the ion fluence as the key parameter that determines the electrical transport properties of the channels, we demonstrate the field-effect operation. At low temperature, the normal state resistance and the superconducting Tc can be tuned over a wide range by a top-gate voltage without any leakage. A superconductor-to-insulator quantum phase transition is observed for a strong depletion of the 2-DEG. [ABSTRACT FROM AUTHOR]

We report on experiments with deformed polymer microlasers that have a low refractive index and exhibit unidirectional light emission. We demonstrate that the highly directional emission is due to transport of light rays along the unstable manifold of the chaotic saddle in phase space. Experiments, ray-tracing simulations, and mode calculations show very good agreement. [ABSTRACT FROM AUTHOR]

In this paper, the measurements of vertical and horizontal aperture which are available for stable beam motion in Indus-2 at beam energy 2.5 GeV using movable beam scrapers are presented. These beam scrapers are installed in one of the long straight sections in the ring. With the movement of beam scrapers towards the beam centre, the beam lifetime is measured. The beam lifetime data obtained from the movement of vertical and horizontal beam scrapers are analyzed. The contribution of beam loss due to beam-gas scattering (vacuum lifetime) and electron-electron scattering within a beam bunch (Touschek lifetime) is separated from the measured beam lifetime at different positions of the beam scrapers. Vertical and horizontal beam sizes at scrapers location are estimated from the scraper movement towards the beam centre in quantum lifetime limit and their values closely agree with measured value obtained using X-ray diagnostic beamline. [ABSTRACT FROM AUTHOR]

We demonstrate here the tailoring of electro-optical properties of ferroelectric liquid crystals (FLCs) by doping different concentrations of Selenium Docosane (SD) capped palladium nanoparticles (PdNPs). The operating voltage is lowered by ∼50% in doped FLC as compared to undoped one. The remarkable increment in optical tilt angle of doped FLC is monitored, which is concentration-dependent. The steric interactions among alkyl chains of SD capped PdNPs and FLC molecules could be the probable reason for enhanced optical tilt angle. More importantly, present investigations on doped FLCs are indicative of their indispensible impact on next generation FLCs-based electro-optical devices. [ABSTRACT FROM AUTHOR]

The solution of the two-dimensional scalar Helmholtz wave equation is discussed in a domain consisting of N+2 boundaries wherein there is one central boundary and N circles are located symmetrically within a closed space such that the system as a whole has N-fold rotational symmetry. The general solution for this complicated domain has been found to reproduce the results corresponding to simpler structures with lesser number of boundaries. Furthermore, the rotational symmetry of the system is exploited to obtain the group-theoretic solution of the composite problem leading to symmetry-induced simplifications. The numerical results pertaining to the lowest and some of the higher modes are presented for N=1 and 2. The plot of the lowest eigenvalue as a function of eccentricity exhibits maximum for symmetric as well as antisymmetric modes whenever there are at least two inner boundaries. This behavior has universal character in the sense that the maximum shows up irrespective of the values of the geometrical parameters other than the eccentricity. The computations involving the group-theoretic aspects have been found to have fast convergence highlighting the significance of our approach to deal with the solution for a class of multidisciplinary problems coming within the purview of the Helmholtz equation. [ABSTRACT FROM AUTHOR]

A rigorous approach is discussed for solving the two-dimensional Helmholtz equation in a multiply-connected domain consisting of a ring of N circles distributed symmetrically within a closed space. The outer boundary has been taken to be such that the system as a whole has N-fold rotational symmetry. The Dirichlet boundary condition has been satisfied exactly at the outer as well as at each of the inner edges, using the addition theorems for the cylindrical Bessel functions in conjugation with the Fourier expansions. Numerical results, showing spatial configurational interference, are presented for the lowest cutoff value of the symmetric mode as a function of separation between centers of two inner circles, in the case N=2 with circular outer boundary. The application of the method to various problems of physics and engineering is enunciated. [ABSTRACT FROM AUTHOR]

Pulsed laser treatment of an individual multiwall carbon nanotube induced selective exfoliation of the amorphous carbon contamination layer. The multiwall carbon nanotube (MWCNT) was exposed to a 248 nm excimer laser. After the treatment, transmission electron microscopy images show that the amorphous layer has expanded and separated from the crystalline MWCNT walls. This interesting observation has implications for laser cleaning and possible thinning of MWCNTs to reduce the radial dimensions. [ABSTRACT FROM AUTHOR]

A correction is offered for the article "Effect of Zr Concentration on Conductivity Behavior of (1-x)PMN-xPZ Ceramic: An Impedance Spectroscopy Analysis" in a previous issue.

Exact solutions are obtained for the anisotropic Bianchi type-I model in normal gauge for Lyra’s geometry. The physical behavior of the models is examined in vacuum and in the presence of perfect fluids. [ABSTRACT FROM AUTHOR]

Examines the growth of indium antimonide (InSb) by molecular beam epitaxy. Optimization of InSb by reflection high energy electron diffraction; Use of InSb for large area detector arrays; Application of InSb in magnetoresistive sensors.

Structures and vibrational spectra of phenol-(acetylene) n (Ph(Ac) n ) clusters are studied by a combination of theoretical calculations and infrared (IR) spectroscopy. The molecular electrostatic potential features are utilized for generating trial geometries of the medium-sized Ph(Ac) n (n = 1, 2, 4, 6, and 7) clusters. These initial geometries are subjected to geometry optimization within the second-order Møller-Plesset (MP2) theory, employing correlation consistent aug-cc-pVDZ (aVDZ) basis set. Minimal nature of the reported structures is confirmed by doing vibrational frequency run at MP2/aVDZ level of theory using full calculations for n = 1 and 2 and employing grafting based molecular tailoring approach for the n = 4, 6, and 7. Several isomers for n ≥ 4 are found to lie in an energy window of 1 kcal mol -1 of each other. Considering the formidability of MP2 level investigation for the large number of isomers for n = 6 and 7, B97-D level theory is used for studying their energetics and IR spectra. It is seen that the number of energetically close isomers increases with increasing n. Moderately size-selected IR spectra of Ph(Ac) n (n = 4 and 7), prepared by a supersonic jet expansion, are measured for the acetylenic C-H and phenolic O-H stretch regions by infrared-ultraviolet (IR-UV) double resonance spectroscopy combined with time-of-flight mass spectrometry. Asymmetric line shape of the C-H stretch band and remarkable line broadening and weakening of the O-H stretch band are noteworthy features of the observed spectra. These findings of the experimental spectra are explained by the theoretical studies. The averaging of the vibrational spectrum of low-lying isomers of the Ph(Ac) n clusters lying in a narrow energy range is found to be responsible for the broadening and weakening of the O-H band.

A pragmatic method based on the molecular tailoring approach (MTA) for estimating the complete basis set (CBS) limit at Møller-Plesset second order perturbation (MP2) theory accurately for large molecular clusters with limited computational resources is developed. It is applied to water clusters, (H2O)n (n = 7, 8, 10, 16, 17, and 25) optimized employing aug-cc-pVDZ (aVDZ) basis-set. Binding energies (BEs) of these clusters are estimated at the MP2/aug-cc-pVNZ (aVNZ) [N = T, Q, and 5 (whenever possible)] levels of theory employing grafted MTA (GMTA) methodology and are found to lie within 0.2 kcal/mol of the corresponding full calculation MP2 BE, wherever available. The results are extrapolated to CBS limit using a three point formula. The GMTA-MP2 calculations are feasible on off-the-shelf hardware and show around 50%-65% saving of computational time. The methodology has a potential for application to molecular clusters containing ∼100 atoms.

Indus-2 storage ring is a 2.5 GeV third generation synchrotron radiation source. This source was commissioned using a moderate optics. Beam injection was accomplished using an off momentum electron beam to avoid difficulties faced in storage of beam at 550 MeV. The injection procedure and relevant beam dynamical studies are discussed. The switch over from the moderate optics to low emittance optics is done at 2.5 GeV after storing the electron beam. The procedure evolved to reduce the beam emittance and its implementation during the operation is discussed.

In a double bend achromat, Chasman-Green (CG) lattice represents the basic structure for low emittance synchrotron radiation sources. In the basic structure of CG lattice single focussing quadrupole (QF) magnet is used to form an achromat. In this paper, this CG lattice is discussed and an analytical relation is presented, showing the limitation of basic CG lattice to provide the theoretical minimum beam emittance in achromatic condition. To satisfy theoretical minimum beam emittance parameters, achromat having two, three, and four quadrupole structures is presented. In this structure, different arrangements of QF and defocusing quadruple (QD) are used. An analytical approach assuming quadrupoles as thin lenses has been followed for studying these structures. A study of Indus-2 lattice in which QF-QD-QF configuration in the achromat part has been adopted is also presented.

Structural bioinformatics and van der Waals density functional theory are combined to investigate the mechanochemical impact of a major class of histone-DNA interactions, namely, the formation of salt bridges between arginine residues in histones and phosphate groups on the DNA backbone. Principal component analysis reveals that the configurational fluctuations of the sugar-phosphate backbone display sequence-specific directionality and variability, and clustering of nucleosome crystal structures identifies two major salt-bridge configurations: a monodentate form in which the arginine end-group guanidinium only forms one hydrogen bond with the phosphate, and a bidentate form in which it forms two. Density functional theory calculations highlight that the combination of sequence, denticity, and salt-bridge positioning enables the histones to apply a tunable mechanochemical stress to the DNA via precise and specific activation of backbone deformations. The results suggest that selection for specific placements of van der Waals contacts, with high-precision control of the spatial distribution of intermolecular forces, may serve as an underlying evolutionary design principle for the structure and function of nucleosomes, a conjecture that is corroborated by previous experimental studies.

Synchrotron radiation sources Indus-1 and Indus-2 have a synchrotron as the common injector. A three kicker compensated bump injection scheme was employed for beam injection into this synchrotron. The stored beam current in the synchrotron is higher, when all the three kickers are operated at the same current than when kickers are operated at currents required to generate compensated bump. Beam dynamics studies have been done to understand why this happens. Theoretical studies indicate that higher stored current in the later case is attributed to smaller residual oscillations of injected beam. These studies also reveal that if the angle of the injected beam during beam injection is kept varying, the performance could be further improved. This is experimentally confirmed by injecting the beam on rising part of the injection septum magnet current pulse.

Characterization of transient intermediate or transition states is crucial for the description of biomolecular folding pathways, which is, however, difficult in both experiments and computer simulations. Such transient states are typically of low population in simulation samples. Even for simple systems such as RNA hairpins, recently there are mounting debates over the existence of multiple intermediate states. In this paper, we develop a computational approach to explore the relatively low populated transition or intermediate states in biomolecular folding pathways, based on a topological data analysis tool, MAPPER, with simulation data from large-scale distributed computing. The method is inspired by the classical Morse theory in mathematics which characterizes the topology of high-dimensional shapes via some functional level sets. In this paper we exploit a conditional density filter which enables us to focus on the structures on pathways, followed by clustering analysis on its level sets, which helps separate low populated intermediates from high populated folded/unfolded structures. A successful application of this method is given on a motivating example, a RNA hairpin with GCAA tetraloop, where we are able to provide structural evidence from computer simulations on the multiple intermediate states and exhibit different pictures about unfolding and refolding pathways. The method is effective in dealing with high degree of heterogeneity in distribution, capturing structural features in multiple pathways, and being less sensitive to the distance metric than nonlinear dimensionality reduction or geometric embedding methods. The methodology described in this paper admits various implementations or extensions to incorporate more information and adapt to different settings, which thus provides a systematic tool to explore the low-density intermediate states in complex biomolecular folding systems.

This paper presents the design and analysis of a multipurpose combined function magnet for use in accelerators. This magnet consists of three corrector magnets: (i) skew quadrupole, (ii) horizontal dipole, and (iii) vertical dipole magnets, along with the main sextupole magnet. The strength of the corrector magnets is smaller than that of the main sextupole magnet. The strength of all the four magnets can be varied independently. The excitation strength required to produce skew quadrupole gradient and the presence of various multipole components in the magnet are estimated using first order perturbation theory. The experimental data for the variation of the sextupole strength and its higher order multipoles in the presence of skew quadrupole excitations are presented and compared to the theoretical predictions. Simulation using two-dimensional fine element code, Poisson, is also done. Results obtained from all the above three methods are found to be in good agreement with each other. The variations of skew quadrupole gradient for different sextupole excitations are also measured. The validity of this theory is also checked for various combinations of excitations including the case where magnet gets saturated. The excitation strengths required for producing the horizontal and vertical dipole fields are estimated analytically along with the presence of various multipoles. Theoretical predictions of permissible multipoles are compared to the results obtained from simulation.

The contributions of auditory and cognitive factors to age-dependent differences in auditory spatial attention were investigated. In conditions of real spatial separation, the target sentence was presented from a central location and competing sentences were presented from left and right locations. In conditions of simulated spatial separation, different apparent spatial locations of the target and competitors were induced using the precedence effect. The identity of the target was cued by a callsign presented either prior to or following each target sentence, and the probability that the target would be presented at the three locations was specified at the beginning of each block. Younger and older adults with normal hearing sensitivity below 4 kHz completed all 16 conditions (2-spatial separation method X 2-callsign conditions X 4-probability conditions). Overall, younger adults performed better than older adults. For both age groups, performance improved with target location certainty, with a priori target cueing, and when location differences were real rather than simulated. For both age groups, the contributions of natural spatial cues were most pronounced when the target occurred at "unlikely" spatial listening locations. This suggests that both age groups benefit similarly from richer acoustical cues and a priori information in difficult listening environments.