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Rotational rectification of an alternating magnetic field
No full textOpen AccessIn this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. “Classroom” is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science
Pulse phase resolved spectroscopy of Vela X-1 with Suzaku
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations). The article will be made open-access at the journal site after 24 months.We present a detailed pulse-phase-resolved spectral analysis of the persistent high-mass X-ray binary pulsar Vela X-1 observed with Suzaku during 2008 June. The pulse profiles exhibit both intensity and energy dependence with multiple peaks at low energies and double peaks at higher energies. The source shows some spectral evolution over the duration of the observation and care has been taken to average over data with minimum spectral variability for the analysis. We model the continuum with a phenomenological partial covering high-energy cutoff model and a more physical partial covering thermal Comptonization model (CompTT) excluding the time ranges having variable hardness ratio and intensity dependence. For both the models, we detect a cyclotron resonant scattering feature (CRSF) and its harmonic at ~25 keV and ~50 keV. Both the CRSF fundamental and harmonics parameters are strongly variable over the pulse phase, with the ratio of the two line energies deviating from the classical value of 2. The continuum parameters also show significant variation over the pulse phase and give us some idea about the changing physical conditions that are seen with the changing viewing angle at different pulse phases and obscuration by the accretion stream at some pulse phases
Boundary term contribution to the volume of a small causal diamond
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)In his calculation of the spacetime volume of a small Alexandrov interval in four dimensions, Myrheim introduced a term which he referred to as a surface integral (Myrheim 1978 CERN preprint TH-2538). The evaluation of this term has remained opaque and led subsequent authors to obtain a formula for the volume using other techniques (Gibbons and Solodukhin 2007 Phys. Lett. B 649 317). It is the purpose of this work to explicitly calculate this integral and in the process complete the proof for the volume formula in arbitrary dimensions. We point out that it arises from the difference in the flat spacetime volumes of the curved and flat spacetime intervals. We use first-order degenerate perturbation theory to evaluate this difference and find that it adds a dimension-independent factor to the volume of the flat spacetime interval as the lowest order correction. Our analysis admits a simple extension to a more general class of integrals over the same domain. Using a combination of techniques we also find that the next-order correction to the volume vanishes
Thiophene-based donor–acceptor conjugated polymer as potential optoelectronic and photonic material
No full textOpen AccessIn this paper, we report the synthesis, characterization and optical properties of a donor–acceptor conjugated polymer, PTh-CN, containing 3,4-didodecyloxythiophene and cyanovinylene units. The polymer possesses a low band gap of 1.75 eV as calculated from the onset absorption edge. From the electrochemical study, the HOMO and LUMO energy levels of the polymer are figured out to be −5.52 eV and −3.52 eV, respectively. Polymer light-emitting diodes are fabricated using PTh-CN as the emissive layer with a device configuration of ITO/PEDOT:PSS/PTh-CN/Al. The device showed stable saturated red electroluminescence with CIE coordinate values (0.65, 0.32) at 12 V, which are very close to the values for standard red demanded by the NTSC. In addition, the device showed good colour stability under different bias voltages and the threshold voltage of the PLED device is found to be as low as 3.1 V. Further, a nanocomposite of the polymer and TiO2 nanoparticles is prepared by the dispersion method. The nonlinear optical properties of PTh-CN and PTh-CN/TiO 2 nanocomposite are studied using z-scan technique. The polymer solution, polymer film and polymer/TiO2 nanocomposite film show a strong saturable absorption behaviour. The value of saturation intensity (Is) is found to be of the order 1011–1012 W/m2, indicating that the materials are useful candidates for photonic applications
Method to display an image on a display device
No full textRestricted AccessIn one embodiment, a method a method of displaying an image on a display device is described. The display device includes a plurality of clusters. Each cluster has a plurality of pixels and an independent light source associated therewith. Each of the plurality of clusters are illuminated with their associated independent light source. The plurality of pixels in a cluster are refreshed with bits of gray scale. Simultaneously with the refreshing, the light source associated with the cluster where the plurality of pixels are being refreshed is switched off. When the plurality of pixels have been refreshed, the light source is switched on with a predetermined intensity of light. Each of the clusters are refreshed at a rate that is fast enough to eliminate flicker
Astrosat : some key science prospects
No full textRestricted Access.ASTROSAT is an astronomy satellite designed for simultaneous multi-wavelength studies in the Optical/UV and a broad X-ray energy range. With four X-ray instruments and a pair of UV-Optical telescopes, ASTROSAT will provide unprecedented opportunity for simultaneous multi-wavelength observations, which is of immense value in study of highly variable sources, especially X-ray binaries and active galactic nuclei. The Large Area X-ray Proportional Counters (LAXPC) of ASTROSAT, which has the largest effective area in the hard X-ray band compared to all previous X-ray missions, will enable high time resolution X-ray measurements in the 2–80 keV band with moderate energy resolution. Here we give a brief summary of the payload characteristics of ASTROSAT and discuss some of the main science topics that will be addressed with the LAXPC, and with simultaneous observations with the UVIT telescopes, with particular emphasis on X-ray binaries and compact objects. The possibility of aiding gravitational wave experiments is also briefly mentioned
Nonaffine displacements in crystalline solids in the harmonic limit
No full textOpen Access.A systematic coarse graining of microscopic atomic displacements generates a local elastic deformation tensor D as well as a positive definite scalar χ measuring nonaffinity, i.e., the extent to which the displacements are not representable as affine deformations of a reference crystal. We perform an exact calculation of the statistics of χ and D and their spatial correlations for solids at low temperatures, within a harmonic approximation and in one and two dimensions. We obtain the joint distribution P(χ,D) and the two-point spatial correlation functions for χ and D. We show that nonaffine and affine deformations are coupled even in a harmonic solid, with a strength that depends on the size of the coarse-graining volume Ω and dimensionality. As a corollary to our work, we identify the field hχ conjugate to χ and show that this field may be tuned to produce a transition to a state where the ensemble average <χ> and the correlation length of χ diverge. Our work should be useful as a template for understanding nonaffine displacements in realistic systems with or without disorder and as a means for developing computational tools for studying the effects of nonaffine displacements in melting, plastic flow, and the glass transition
