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Synthesis and nonlinear optical properties of Lead Telluride nanorods
No full textRestricted Access.Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (γ) are in the order of 10-22 m3 W-2 and for femtosecond excitation it is in the order of 10-29 m3 W-2. The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications
Optical limiting characteristics of Dichloridobis(1-ethyl-2, 6-dimethylpyridinium-4-olate-κO) zinc (II)
No full textRestricted Access.A newly synthesized metal-organic co-ordination compound Dichloridobis (1-ethyl-2,6-
dimethylpyridinium-4-olate-kO) zinc(II) (EDMPZC) is characterized by FTIR to confirm the molecular structure. It crystallizes in the monoclinic system with the centrosymmetric space group C2/c and the unit cell parameters are determined from the single crystal X-ray diffraction analysis. Optical energy band gap is found to be 3.5 eV by UVeVisible absorption studies. The third order nonlinear optical properties were investigated by open-aperture Z-scan measurements using Nd:YAG laser (532 nm, 5 ns). Two-photon absorption and reverse saturable absorption mechanisms at the excitation wavelength are found to cause the observed optical limiting behavior
Measurements of a cryogenic linear polarization modulator for mm-wavelengths
No full textOpen Access.Cryogenic Faraday phase modulators have been implemented in waveguide and tested in both a constant current mode and an alternating current mode. The loss of the phase shifter for DC currents that results in either a or phase shift is on average 1.45 dB over the entire W-band. In the modulating mode, it operates at frequencies as high as 4 Hz with transition times between the two phase states of 1.32 x 10-2 s
Experimental studies on statics and dynamics of some novel instabilities in lyotropic systems
No full textopen acces
Electrochemical and electrical conductivity studies of redox molecules and nanomaterials in some self-organised systems
No full textTheoretical estimates of two-point shear correlation functions using tangled magnetic fields
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The existence of primordial magnetic fields can induce matter perturbations with additional power at small scales
as compared to the usual ΛCDM model.We study its implication within the context of a two-point shear correlation
function from gravitational lensing. We show that a primordial magnetic field can leave its imprints on the shear
correlation function at angular scales a few arcminutes. The results are compared with CFHTLS data, which
yield some of the strongest known constraints on the parameters (strength and spectral index) of the primordial
magnetic field. We also discuss the possibility of detecting sub-nano Gauss fields using future missions such as
SNAP
RRL observations using ORT at 328 MHz and WSRT at 1.4 GHz from Eldwim
No full textRestricted Access.Radio recombination line (RRL or RL for short) observations from 10 Galactic positions using the Ooty Radio Telescope (ORT) at 328 MHz and the Westerbork Synthesis Radio Telescope (WSRT) at 1.4 GHz have been presented. ORT observations were made using a recently augmented New Digital Backend (NDB). NDB offered a bandwidth of 1 MHz that was used to observe H271α RL. The eight intermediate-frequency bands offered by WSRT in the incoherent addition mode were used to detect the seven H/Henα RLs with n = 165-171 and the H208β RL. RL observations common to WSRT and ORT have been put together to model the diffuse low-density ionized gas (extended low density warm ionized medium, ELDWIM). This modeling constrains the electron number density in ELDWIM to 1.0 cm-3 < ne < 10.0 cm-3 for a temperature range of 103-104 K for these 10 positions. An effective stellar temperature of the H II region picture for three positions showing He line detection has been presented using spherical cloud modeling. The lower limits on the stellar temperatures are >33,000 K for the obtained ratios of N He +/N H + toward these directions
A new layout optimization technique for interferometric arrays, applied to the Murchison Wide eld array
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21-cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed – even at the remote Australian location of the Murchison Widefield Array (MWA) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhances the PSF sidelobes and reduces the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution and snapshot PSF for this array choice
4-Nitrophenyl 4-hydroxy-3-methylbenzoate
No full textRestricted Access.The asymmetric unit of the title compound, C14H11NO5,
contains two independent molecules in which the dihedral
angles between the benzene rings are 89.27 (16) and
77.14 (12) . In the crystal, molecules are linked by O—
H O hydrogen bonds, generating C(8) chains propagating in
[010] for one molecule and [001] C(8) chains for the other. The
chains are connected by C—H O hydrogen bonds and –
interactions [shortest centroid–centroid distance =
3.5908 (12) ], generating a three-dimensional networ