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Erratum: Head-on infall of two compact objects: third post-Newtonian energy flux [Phys. Rev. D 82, 104005 (2010)]
No full textOpen Access
Enhanced optical limiting in functionalized hydrogen exfoliated graphene and its metal hybrids
No full textRestricted Access.We present the mechanism and performance of optical limiting (OL) in hydrogen exfoliated graphene (HEG), functionalized HEG (f-HEG) and its metal hybrids. At the wavelengths used, the mechanism of nonlinear absorption (NLA) involves two-photon absorption and excited state absorption in the nanosecond excitation regime, and saturable absorption in combination with two-photon absorption in the femtosecond (ultrafast) excitation regime. The role of defects in the OL performance of HEG and f-HEG is investigated with the help of their Raman spectra. OL efficiency of f-HEG is found to improve with Pt and Pd nanoparticle decoration due to an enhanced NLA, which arises mainly from interband transitions between the d band and the s–p conduction band in the metal NPs, and charge transfer between f-HEG and metal NPs. Thermally induced light scattering is negligible in these water dispersed systems
Superbubble breakout and galactic winds from disc galaxies
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We study the conditions for disc galaxies to produce superbubbles that can break out of the disc and produce a galactic wind. We argue that the threshold surface density of supernovae rate for seeding a wind depends on the ability of superbubble energetics to compensate for radiative cooling. We first adapt Kompaneets formalism for expanding bubbles in a stratified medium to the case of continuous energy injection and include the effects of radiative cooling in the shell. With the help of hydrodynamic simulations, we then study the evolution of superbubbles evolving in stratified discs with typical disc parameters. We identify two crucial energy injection rates that differ in their effects, the corresponding breakout ranging from being gentle to a vigorous one. (a) Superbubbles that break out of the disc with a Mach number of the order of 2-3 correspond to an energy injection rate of the order of 10-4 erg cm-2 s-1, which is relevant for disc galaxies with synchrotron emitting gas in the extra-planar regions. (b) A larger energy injection threshold, of the order of 10-3 erg cm-2 s-1, or equivalently, a star formation surface density of ˜0.1 M⊙ yr-1 kpc-2, corresponds to superbubbles with a Mach number ˜5-10. While the milder superbubbles can be produced by large OB associations, the latter kind requires super-starclusters. These derived conditions compare well with observations of disc galaxies with winds and the existence of multiphase halo gas. Furthermore, we find that contrary to the general belief that superbubbles fragment through Rayleigh-Taylor (RT) instability when they reach a vertical height of the order of the scaleheight, the superbubbles are first affected by thermal instability for typical disc parameters and that RT instability takes over when the shells reach a distance of approximately twice the scaleheight
Modelling carbon radio recombination line observations towards the ultracompact H II region W48A
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We model the carbon recombination line (CRL) emission from the photodissociation region (PDR) surrounding the ultracompact (UC) H ii region W48A. Our modelling shows that the inner regions (AV ∼ 1) of the C ii layer in the PDR contribute significantly to the CRL emission. Using models spanning over a large range of parameters that are typical for the environments of UCH ii regions, we explore the dependence of the line ratios of CRL emission on the density of the PDR and on the far-ultraviolet radiation incident in the region. We find that it is possible to constrain the density of the PDR by observing a suitable set of CRLs. If the neutral density in the PDR is high ( ≳ 107 cm−3), then the CRL emission is bright at high frequencies ( ≳ 20 GHz), and the absorption lines from such regions can be detected at low frequencies ( ≲ 10 GHz). By modelling CRL observations towards W48A, we can show that the UCH ii region is embedded in a molecular cloud with a density of about 4 × 107 cm−
Novel zigzag-shaped compounds exhibiting apolar columnar mesophases with oblique and rectangular lattices
No full textRestricted Access.The design, synthesis and characterisation of some compounds whose constituent molecules have a completely new shape have been carried out. A total of eight different series/part of series of these zigzag-shaped compounds that are either symmetrical or unsymmetrical were synthesised. Only two mesophases were observed, and on the basis of polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies, these have been characterised as columnar phases with a rectangular or an oblique lattice. Perhaps, these represent the first examples of a rigid zigzag-shaped compound exhibiting a mesophase
Electronic resources management at Raman Research Instiute Library
No full textRestricted Access Book chapter from Proceedings of UGC Sponsored 4th KSCLA National Conference, held at Shimoga, Karnataka. from Dec 27-28th 2013This paper aims to provide the significance of electronic resources at (RRI) Raman Research Institute library and the methods taken to access it. The RRI library has implemented new upcoming technologies to cater to its user needs. It has also adopted e-resources for better visibility and accessibility. Due to implementation of Information and communication, technology (ICT) RRI library has become hybrid library consisting of both print and digital recourses. In this article, an attempt has been made to explain how traditional modes of record keeping are transformed to digital format. This article will enumerate different types of E-resources used in RRI library and methods adopted to access it. Finally, it will conclude by discussing various problems encountered in managing electronic records
Generation of bright atomic and molecular solitons in hybrid atom-molecular Bose-Einstein condensates coupled through raman photoassociation.
No full textRestricted Access.We have explored the feasibility of designing atomic and molecular bright solitons in a hybrid atom-molecular BEC (Bose Einstein Condensate) system of 87Rb coupled through Raman Photoassociation. It is found that the atomic and molecular waves when allowed to evolve in a spherical one-dimensional trap, initially oscillate with time and assume solitonic nature as bright solitons with progress in time. After the trap is switched off, atomic and molecular waves propagate retaining its solitonic nature and the final amplitude and nature of the bright solitons depend on the time of evolution within the trap. For this study we have used system parameters which are experimentally realizable. We have imposed random perturbation (5%) on the initial atomic and molecular wavefunctions, which are the solution of time independent coupled equation (without decay) and studied the evolution of atomic and molecular solitons with trap on and off condition. A small regular or large irregular oscillation in the amplitude of atomic solitons during evolution of perturbed matter waves are imposed depending on the system parameters. However broad molecular solitons with slowly decaying amplitude are generated which oscillate symmetrically around the centre of the trap. It is found that the stability and the shape of the generated atomic and molecular bright solitons can be controlled by varying the system parameters e.g. initial number of atoms, decay rates of the excited molecule and the frequency of the trap. Since the boson-boson interaction and the atom-molecular coupling strength depend on the total number of atoms, one can control the interplay between boson-boson interaction (due to s-wave scattering) and the atom-molecular coupling (through Raman Photoassociation) by varying the total number of atoms. It is found that with the increase in trap frequency generation of atomic and molecular solitons in atom-molecular coupled system is feasible if the strength of atom-molecular coupling and two-photon detuning is increased. The shape and the stability of the bright solitonic waves depend significantly on the strength of induced decay from the excited molecular state to the two-atom continuum or to the bound vibrational levels of the ground state. Stable flat-top atomic and molecular matter wave pulse can be generated from this atom-molecular coupled system by increasing the decay rates of the excited molecules
Optical fiber-based force transducer for microscale samples
No full textOpen accessWe discuss the design, instrumentation, and calibration of a versatile force transducer with feedback control, called the Micro-Extensional Rheometer (MER). A force range of eight decades (1–108 pN) and a displacement range of four decades (10–105 nm) with a spatial resolution of the order of nanometers are accessible with the instrument. A feedback-loop algorithm is used to control the commanded force or the extensional strain on the sample and implement different rheometric protocols such as step-strain, step-force, exponential strain, among others. The device may also be used to measure the forces exerted by active suspensions, pulling neurons, et
Use of ultrasound attenuation spectroscopy to determine the size distribution of clay Tactoids in aqueous suspensions.
No full textRestricted Access.The dispersion processes of aqueous samples of clay are studied using ultrasound attenuation spectroscopy. The attenuation spectra that are acquired in the frequency range 10–100 MHz are used to determine the particle size distributions (PSDs) for different concentrations and ages of the clay suspensions. Our analysis, using equivalent spherical diameter (ESD) for circular discs under Stokes drag in samples of concentrations greater than 1.5% w/v, shows that a substantial fraction of the aggregates in suspension are actually tactoids that are composed of more than one platelet. This is in contrast to the general belief that clay disperses into individual platelets in the concentration range where their suspensions exhibit glassy behavior. We conclude that the incomplete fragmentation of the clay tactoids arises from the rapid enhancement of the intertactoid Coulombic repulsion