5941 research outputs found
Sort by
A simple model for the rotation of a trapped chiral nematic droplet under the action of a linearly polarized laser beam
No full textRestricted Access.There have been recent reports of continuous rotation of chiral nematic droplets in restricted ranges of diameter/pitch (d /p) values, trapped by a linearly polarized laser beam. We have developed a simple model to calculate the distortion in the helical structure of a set of flat layers, caused by the action of the strong electric field of the propagating laser beam on the dielectric anisotropy of the medium. The resulting change in the polarization state of the beam passing through the sample is then used to calculate the torque on the sample as a function of the azimuthal angle of the first layer. The main results are: i) the torque tends to zero even with circularly polarized beam for samples with thicknesses around integral multiples of 0.5p ; ii) the undistorted sample takes an equilibrium orientation for linearly polarized beam, which jumps by π /2 rad at the same sample thicknesses; iii) these samples will have a nonzero torque at all azimuthal angles of the first slice when the helical structure is distorted by the linearly polarized beam. The calculations show that a propagating accordion mode, in which the helical pitch alternately expands and contracts, gives rise to the nonzero torque. The theoretical predictions are in broad agreement with experimental results
Light transmission through and its complete stoppage in an ultra slow wave optical medium
No full textOpen AccessLight Wave transmission -- its compression, amplification, and the optical energy storage -- in an Ultra Slow Wave Medium (USWM) is studied analytically. Our phenomenological treatment is based entirely on the continuity equation for the optical energy flux, and the well known distribution-product property of Dirac delta-function. The results so obtained provide a clear understanding of some recent experiments on light transmission and its complete stoppage in an USWM
Foreword written to Special issue on Gravitational Wave Detection and Fundamental Physics in Space to International Journal of Modern Physics D
No full textOpen AccessForwar
Novel N-substituted-5-phenyl-1H-pyrazole-4-ethyl carboxylates as potential NLO materials
No full textRestricted Access.In the present investigation we have synthesized a novel series of N-substituted-5-phenyl-1H-pyrazole-4-ethyl carboxylates, which are characterized by 1H NMR, UV–Vis and FT-IR spectroscopy methods. The optical nonlinearity of the compounds in chloroform solution has been studied at 532 nm using 5 ns laser pulses, employing the open-aperture z-scan technique. It is found that compound 3c having carboxylic acid group and ester substituent has maximum nonlinearity. From measurements we conclude that compounds 3c (4-[4-(ethoxycarbonyl)-5-phenyl-1H-pyrazol-1-yl]benzoic acid) and 3e (ethyl 1-(2-bromophenyl)-5-phenyl-1H-pyrazole-4-carboxylate) are potential candidates for optical limiting application
Signature of outflows in strong Mg II absorbers in quasar sightlines
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report a correlation between velocity offset (β = v/c) of strong Mg ii absorption systems and the bolometric luminosity (Lbol) of quasars in SDSS-DR7. We find that β shows a power-law increase with Lbol, with a slope ∼1/4. We find that such a relation of β with Lbol is expected for outflows driven by scattering of black hole radiation by dust grains, and which are launched from the innermost dust survival radius. Our results indicate that a significant fraction of the strong Mg ii absorbers, in the range of β = 0–0.4, may be associated with the quasars themselves
RRI-GBT multi-band receiver: motivation, design, and development
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report the design and development of a self-contained multi-band receiver (MBR) system, intended for use with a single large aperture to facilitate sensitive and high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span (100-1500 MHz) in a nearly log-periodic fashion. The development of this system was primarily motivated by need for tomographic studies of pulsar polar emission regions. Although the system design is optimized for the primary goal, it is also suited for several other interesting astronomical investigations. The system consists of a dual-polarization multi-band feed (with discrete responses corresponding to the 10 bands pre-selected as relatively radio frequency interference free), a common wide-band radio frequency front-end, and independent back-end receiver chains for the 10 individual sub-bands. The raw voltage time sequences corresponding to 16 MHz bandwidth each for the two linear polarization channels and the 10 bands are recorded at the Nyquist rate simultaneously. We present the preliminary results from the tests and pulsar observations carried out with the Robert C. Byrd Green Bank Telescope using this receiver. The system performance implied by these results and possible improvements are also briefly discussed
Synthesis and characterisation of novel alkoxycyanobiphenyl-substituted rufigallols
No full textRestricted Access.Microwave-assisted synthesis of novel alkoxycyanobiphenyl-substituted rufigallols are reported by systematically replacing one, two, four, five or six cyanobiphenyl-tethered alkoxy chains. The synthesis of the target compounds was challenging since classical reactions failed to produce these hybrids. Chemical structures of the hybrids were determined by 1H nuclear magnetic resonance (NMR), 13C NMR, infrared, ultraviolet spectroscopy and elemental analysis. The thermotropic liquid crystalline properties of the new compounds were investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffractometr
Giant radio galaxies – I. Intergalactic barometers
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present new wideband radio observations with the Australia Telescope Compact Array of a sample of 12 giant radio galaxies. The radio observations are part of a larger radio–optical study aimed at relating the radio structures with the ambient medium on large scales. With projected linear sizes larger than 0.7 Mpc, these objects are ideal candidates for the study of the warm-hot intergalactic medium (WHIM). The sample includes sources with sizes spanning 0.8–3.2 Mpc and total powers of 1.2 × 1024 to 4.0 × 1026 W Hz−1 at 2.1 GHz. Redshifts were limited to z ≤ 0.15 to permit spectroscopic observations of the hosts and neighbouring galaxies, which were obtained using the AAOmega spectrograph on the Anglo-Australian Telescope. We derive lobe energy densities from the radio observations via equipartition arguments. The inferred pressures in the lobes of the giant radio sources, which range from 1.1 × 10−15 to 2.0 × 10−14 Pa (80 to 1500 cm−3 K), are lower than previously inferred from X-ray observations of dense filaments. Comparison with the OverWhelmingly Large Simulations suggests that the WHIM in pressure balance with the radio lobes has a temperature in excess of ∼106.5 K or a particle overdensity in the range 50–500. This study highlights the capability of next generation surveys, such as the Evolutionary Map of the Universe survey with the Australian Square Kilometre Array Pathfinder, to study populations of giant radio sources at lower surface brightness and thereby discriminate between models for the cosmological evolution of the intergalactic medium and examine the validity of cosmological hydrodynamical simulations
Synthesis, growth and characterization of 4-bromo-4′-nitrobenzylidene aniline (BNBA): a novel nonlinear optical material with a (3+1)-dimensional incommensurately modulated structure
No full textRestricted Access
Corrigendum to “Novel N-substituted-5-phenyl-1H-pyrazole-4-ethyl carboxylates as potential NLO materials” [Arab. J. Chem. (6) (2013) 97–102]
No full textRestricted Access.The authors extend their appreciation to The Deanship of Scientific Research at King Saud University for funding the work through the research group project No. RGP-VPP-207.
Further, Hoong-Kun Fun was mistakenly not added to the list of authors. The correct list of authors and their affiliations is given below.The authors would like to apologise for any inconvenience caused