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Splay-bend elasticity and rotational viscosity of liquid crystal mixtures of rod-like and bent-core molecules
No full textRestricted Access.We report temperature dependent measurements of birefringence (Delta n), splay (K(11)), bend (K(33)) elastic constants and rotational viscosity (gamma(1)) of mixtures of rod-like and bent-core molecules. K(11) and Delta n remain almost constant for all the mixtures whereas K(33) is always lower than K(11) and further decreases with increasing concentration of bent-core molecules in the mixtures. Apart from the large jump in Delta n at the nematic-isotropic transition (NI) a significant jump in Delta n at the nematic-smectic transition (NS) is also observed that increases with increasing mol% of the bent-core compound in the mixtures. Rotational viscosity increases by a factor of four when the concentration of the bent-core compound increased from 0 to 10 mol%. The results are discussed on the basis of their structural similarity and mutual alignment in the nematic phase
Anthraquinone-based discotic liquid crystals: new monomers and dimers
No full textRestricted Access.We report the design and synthesis of six new series of anthraquinone-based monomers and dimers and studies
on their structure–property relationship with respect to their liquid crystalline properties. The chemical structures
of these newly synthesised compounds are characterised by infrared (IR), nuclear magnetic resonance (NMR) and
mass spectroscopy. The liquid crystalline properties are investigated using polarising optical microscopy, differential
scanning calorimetry and X-ray diffraction studies. Most of the compounds synthesised here are found to
be liquid crystalline. In many cases, the mesophases stabilised up to room temperature. They exhibit a variety of
mesophases, viz., Colh and DL, in addition to an unidentified mesophase,Mx.We have made an effort to propose a
molecular model in the discotic lamellar phase of one of the dimer compounds based on the X-ray data obtained
Tops and writhing DNA
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The torsional elasticity of semiflexible polymers like DNA is of biological significance.
A mathematical treatment of this problem was begun by Fuller using the relation
between link, twist and writhe, but progress has been hindered by the non-local nature of the
writhe. This stands in the way of an analytic statistical mechanical treatment, which takes
into account thermal fluctuations, in computing the partition function. In this paper we use
the well known analogy with the dynamics of tops to show that when subjected to stretch and
twist, the polymer configurations which dominate the partition function admit a local writhe
formulation in the spirit of Fuller and thus provide an underlying justification for the use of
Fuller’s “local writhe expression” which leads to considerable mathematical simplification
in solving theoretical models of DNA and elucidating their predictions. Our result facilitates
comparison of the theoretical models with single molecule micromanipulation experiments
and computer simulation
First spectroscopic imaging observations of the sun at low radio frequencies with the Murchison widefield array prototype
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present the first spectroscopic images of solar radio transients from the prototype for the Murchison Widefield Array, observed on 2010 March 27. Our observations span the instantaneous frequency band 170.9-201.6 MHz. Though our observing period is characterized as a period of "low" to "medium" activity, one broadband emission feature and numerous short-lived, narrowband, non-thermal emission features are evident. Our data represent a significant advance in low radio frequency solar imaging, enabling us to follow the spatial, spectral, and temporal evolution of events simultaneously and in unprecedented detail. The rich variety of features seen here reaffirms the coronal diagnostic capability of low radio frequency emission and provides an early glimpse of the nature of radio observations that will become available as the next generation of low-frequency radio interferometers come online over the next few years
Suzaku observation of the transient X-ray pulsar GRO J1008−57
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report the timing and broad-band spectral properties of the Be transient high-mass X-ray binary pulsar GRO J1008−57 using a Suzaku observation in the declining phase of its 2007 November and December outbursts. Pulsations with a period of 93.737 s were clearly detected in the light curves of the pulsar up to the 80–100 keV energy band. The pulse profile was found to be strongly energy dependent, a double-peaked profile at soft X-ray energy bands (<8 keV) and a single-peaked smooth profile at hard X-rays. The broad-band energy spectrum of the pulsar, reported for the first instance in this paper, is well described with three different continuum models, namely (i) a high energy cut-off power law, (ii) a Negative and Positive power law with EXponential (NPEX) cut-off and (iii) a partial covering power law with high energy cut-off. In spite of large value of absorption column density in the direction of the pulsar, a blackbody component of temperature ∼0.17 keV for the soft excess was required for the first two continuum models. A narrow iron Kα emission line was detected in the pulsar spectrum. The partial covering model, however, is found to explain the phase-averaged and phase-resolved spectra well. The dip-like feature in the pulse profile can be explained by the presence of an additional absorption component with high column density and covering fraction at the same pulse phase. The details of the results are described in the paper
Second harmonic chalcone crystal: Synthesis, growth and characterization
No full textRestricted Access.The novel nonlinear optical chalcone derivative(2E)-3-[4-(methylsulfanyl) phenyl]-1-(3-bromophe-
nyl) prop-2-en-1-one(3Br4MSP) crystals have been grown by slow evaporation technique at ambient
temperature. The crystal was subjected to different types of characterization method in order to study
its possible application in nonlinear optics. The structure determination of the grown crystal was done
by single crystal X-ray diffraction study. The morphology of the crystal is studied. The crystal was
subjected to thermal analysis to f ind its thermal stability. The grown crystals were characterized for
their opticaltransmission and mechanical hardness. The second harmonic generation(SHG) efficiency of the crystal is obtained by classical powdered technique. The laser damage threshold for 3Br 4MSP
crystal was determined using Q-switched Nd:YAG laser
Calorimetric study of the effect of bent-shaped dopant molecules on the critical behavior at the nematic-smectic-Ad phase transition
No full textOpen AccessWe report results of calorimetric studies for the binary mixture of rodlike host n-alkyloxy-cyanobiphenyl
(nOCB, n = 8,9) and bent-shaped guest 1,3-phenylene-bis[4-(3-methylbenzoyloxy)]-4 -n-dodecylbiphenyl-4 -
carboxylate (BC12). The effect of bent-shaped dopant molecules on the critical behavior associated with the
nematic-smectic-Ad phase transition has been studied in detail. The transition temperature for the nematicsmectic-
Ad phase sharply decreases as the increase of the mole fraction of the dopant concentration (denoted X
for the BC12/9OCB mixture and Y for the BC12/8OCB mixture). The dependence of the critical exponent α on
X and Y is well explained in terms of the McMillan ratio. A nearly tricritical exponent has been obtained for the
X = 0.01 mixture. X = 0.02 − 0.03 mixtures, pure 8OCB, and Y = 0.01 − 0.03 mixtures exhibit nonuniversal
behaviorswith effective exponents lying between the 3D-XY and tricritical exponents. The heat capacity anomaly
for Y = 0.05 has been well described with the 3D-XY exponent. The critical amplitude ratio A−/A+ is close to 1
and insensitive to the dopant concentration. No Fisher renormalization of the critical exponent has been observed
even for nearly tricritical compositions, which indicates the smallness of the concentration plays a decisive role
rather than the steepness of the N-SmAd phase boundary
Intramolecular charge transfer and Z-scan studies of semiorganic nonlinear optical material sodium acid phthalate hemihydrate : a vibrational spectroscopic study
No full textRestricted Access.FT-IR and Raman spectra of the nonlinear optical material
sodium acid phthalate hemihydrate crystal have been recorded and analyzed.
The equilibrium geometry, bonding features, and harmonic vibrational
wavenumbers have been investigated with the help of the B3LYP density
functional theory method. A detailed interpretation of the vibrational spectra
was carried out with the aid of normal coordinate analysis following the scaled
quantum mechanical force field methodology. The natural bond orbital
analysis confirms the occurrence of strong intermolecular hydrogen bonding
in the molecule. Nonlinear optical absorption of the sample has been studied
at 532 nm using single 5 ns laser pulses, employing the open-aperture Z-scan
technique. It is found that the NaAPH molecule is a potential candidate for
optical limiting applications
Timing and spectral studies of the transient x-ray pulsar GX 304-1 during an outburst
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present the timing and spectral properties of the transient X-ray pulsarGX304−1 during its recent outburst in 2010 August, using observations carried out with the Proportional Counter Array (PCA) instrument on board the Rossi X-ray Timing Explorer (RXTE) satellite. We detected strong intensity- and energy-dependent variations in the pulse profiles during the
outburst. The pulse profile showed significant evolution over the outburst. It showed complex structures consisting of a main peak with steps on both sides during the start of the outburst.On some days, a sharp dip-like feature was seen which disappeared at the end of the outburst when the profile evolved into a sinusoidal shape. At low energies, the pulse profiles appeared complex, consisting of multiple peaks and a narrow minimum. The amplitude of the second
brightest peak in low energies decreased with energy, and above 12 keV the shape of the pulse profile changed to a single broad peak with a dip-like feature. The dip had energy dependence, both in phase and in width. We detected quasi-periodic oscillations (QPOs) at 0.125 Hz with a harmonic. The QPO feature had a low rms value of 2.9 per cent and it showed a positive energy dependence up to 40 keV with the rms value increasing to 9 per cent at 40 keV. The QPO frequency decreased from 0.128 to 0.108 Hz in 12 days. During most of the outburst, the 3–30 keV spectrum of GX 304−1 can be well fitted with a partial covering power-law model with a high-energy cut-off and iron fluorescent line emission. For a few of the observations carried out during the decay of the outburst, the partial covering absorption component is found to change to single-component absorption. We also found that the partial covering and high-energy cut-off parameters vary significantly with the pulse phase
Gravitational waveforms for binary black holes
No full textRestricted AccessOver the last decade gravitational waveforms of binary black holes have been investigated using a variety of approaches like the Multipolar post-Minkowskian formalism, Numerical Relativity and the Effective-One-Body method. We review these complementary approaches and summarize the current status of these investigations of relevance to construct the best templates for the next generation Advanced gravitational wave detectors