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Nonequilibrium stationary state of a harmonic crystal with alternating masses
No full textOpen AccessWe analyze the nonequilibrium steady states (NESS) of a one-dimensional harmonic chain of N atoms with
alternating masses connected to heat reservoirs at unequal temperatures. We find that the temperature profile
defined through the local kinetic energy T (j ) ≡ p2
j
/mj oscillates with period two in the bulk of the system.
Depending on boundary conditions, either the heavier or the lighter particles in the bulk are hotter. We obtain
explicit integral expressions for the bulk temperature profile and steady state current in the limit N →∞. These
depend on whether N is odd or even.We also study similar temperature oscillations in the NESS of systems with
noise in the dynamics. These die out as N →∞
Strain glass analogue in a bent-core liquid crystal exhibiting the dark conglomerate phase
No full textRestricted Access.Vitrified states formed from the dark conglomerate liquid crystal (DCLC) phase, by two members of a homologous series made of bent-core molecules derived from 2,7-dihydroxynaphthalene under different cooling procedures, have been characterised using a variety of experimental techniques, such as optical microscopy, differential scanning calorimetry, X-ray diffraction, electro-optics, dielectric spectroscopy and atomic force microscopy. The experimental results show that though the vitrified state formed on gradual cooling of the sample from the DC phase has some glassy features, it is fragile and undergoes crystallisation over time. On the other hand, direct quenching of the DC phase to room temperature results in stronger glass formation. We propose that the vitrified state obtained on progressive cooling of the DC phase may have some analogy to strain glass and that the DC phase itself may be rather like unfrozen strain glas
Electron transfer and electrocatalytic studies on some organic and conducting polymer nanocomposite thin films
No full textLight scattering from a magnetically tunable dense random medium with weak dissipation : ferrofluid
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present a semi-phenomenological treatment of light transmission through and its reflection from a ferrofluid which we regard as a magnetically tunable system of dense random dielectric scatterers with dissipation. Partial spatial ordering is introduced by the application of a transverse magnetic field that superimposes a periodic modulation on the dielectric randomness. This causes Bragg scattering that effectively enhances the scattering due to the disorder alone, and thus reduces the elastic mean free path towards Anderson localization. A theoretical treatment, based on invariant imbedding, gives a simultaneous decrease of the transmission and the reflection without change of incident linear polarisation as the spatial order is tuned magnetically to the Bragg condition, namely the light wave vector being equal to half the Bragg vector (Q). Our experimental observations are in qualitative agreement with these results. We have also given expressions for the transit (sojourn) time of the light, and for the light energy stored in the random medium under a steady illumination. The ferrofluid thus provides an interesting physical realization of effectively a “Lossy Anderson-Bragg” (LAB) cavity with which to study the effect of interplay of the spatial disorder, partial order and the dissipation on light transport. Given current interests in the light propagation, optical limiting and the storage of light in ferrofluids, the present work seems topical
Simultaneous X-ray and optical observations of thermonuclear bursts in the LMXB EXO 0748-676
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations
H-shaped azoester-oxymethylene containing twin liquid crystalline compounds
No full textRestricted Access.Two mesogenic homologous series of H-shaped symmetrical dimers were synthesised and their thermotropic properties
studied by differential scanning calorimetry and on a hot-stage of a polarising microscope. These compounds
consisted of two mesogenic units of azoester interconnected through tetramethylene flexible spacers (n = 4) by ether
linkage resulting in the structure of ‘H-shaped’ dimeric compounds. The difference between the two series was in
the structure of terminal substituents (–CH3 for series I and –OCH3 for series II) attached on the azoestermesogens
at one terminus. All these compounds were found to be smectogenic. The mesomorphic properties of the series were
compared with each other and with other structurally related mesogenic H-shaped dimers. The trans-azobenzene
groups of the H-shaped dimeric compounds displayed a high-intensity π–π
∗ transition at about 365 nm and a low
intensity π–π
∗ transition at around 470 nm, therefore photochromism can be achieved by the introduction of the
azo linkage to the H-shaped dimeric compounds
H I in Arp 72 and similarities with M51-type systems
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present neutral hydrogen (H I) observations with the Giant Metrewave Radio Telescope (GMRT) of the interacting galaxies NGC 5996 and 5994, which make up the Arp 72 system. Arp 72 is an M51-type system and shows a complex distribution of H I tails and a bridge due to tidal interactions. H I column densities ranging from 0.8-1.8 × 1020 atoms cm-2 in the eastern tidal tail to 1.7-2 × 1021 atoms cm-2 in the bridge connecting the two galaxies are seen to be associated with star-forming regions. We discuss the morphological and kinematic similarities of Arp 72 with M51, the archetypal example of the M51-type systems, and Arp 86, another M51-type system studied with the GMRT, and suggest that a multiple passage model of Salo & Laurikainen may be preferred over the classical single passage model of Toomre & Toomre to reproduce the H I features in Arp 72 as well as in other M-51 systems depicting similar optical and H I features
Biopolymer elasticity: Mechanics and thermal fluctuations
No full textOpen AccessWe present an analytical study of the role of thermal fluctuations in shaping molecular elastic properties of semiflexible polymers. Our study interpolates between mechanics and statistical mechanics in a controlled way and shows how thermal fluctuations modify the elastic properties of biopolymers. We present a study of the minimum-energy configurations with explicit expressions for their energy and writhe and plots of the extension versus link for these configurations and a study of fluctuations around the local minima of energy and approximate analytical formulas for the free energy of stretched twisted polymers. The central result of our study is a closed-form expression for the leading thermal fluctuation correction to the free energy around the nonperturbative writhing family solution for the configuration of a biopolymer. From the derived formulas, the predictions of the wormlike chain model for molecular elasticity can be worked out for a comparison against numerical simulations and experiments
Counter-rotating stellar discs around a massive black hole: self-consistent, time-dependent dynamics
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We formulate the collisionless Boltzmann equation (CBE) for dense star clusters that lie within the radius of influence of a massive black hole in galactic nuclei. Our approach to these nearly Keplerian systems follows that of Sridhar and Touma (1999): Delaunay canonical variables are used to describe stellar orbits and we average over the fast Keplerian orbital phases. The stellar distribution function (DF) evolves on the longer time scale of precessional motions, whose dynamics is governed by a Hamiltonian, given by the orbit-averaged self-gravitational potential of the cluster. We specialize to razor-thin, planar discs and consider two counter-rotating ("") populations of stars. To describe discs of small eccentricities, we expand the Hamiltonian to fourth order in the eccentricities, with coefficients that depend self-consistently on the DFs. We construct approximate dynamical invariants and use Jeans' theorem to construct time-dependent DFs, which are completely described by their centroid coordinates and shape matrices. When the centroid eccentricities are larger than the dispersion in eccentricities, the centroids obey a set of 4 autonomous ordinary differential equations. We show that these can be cast as a two-degree of freedom Hamiltonian system which is nonlinear, yet integrable. We study the linear instability of initially circular discs and derive a criterion for the counter-rotating instability. We then explore the rich nonlinear dynamics of counter-rotating discs, with focus on the variety of steadily precessing eccentric configurations that are allowed. The stability and properties of these configurations are studied as functions of parameters such as the disc mass ratios and angular momentum