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991.
Experimental Mechanics - Digital image correlation (DIC) is a powerful experimental technique to determine displacement and strain fields. DIC methods usually require a large number of high... 相似文献
992.
P. S. Ghosh N. P. Ghosh S. Bhattacharya L. K. Samanta 《Crystal Research and Technology》1991,26(1):121-124
Using various Q switching techniques the performance potential of some Nd: glass rods have been analysed and compared with that of a standard rod. Second harmonics generated from such a Q-switched system have been separated from the fundamental using suitable dispersive element. 相似文献
993.
We present systematic studies of the temperature dependence of linewidths and lifetimes of excitonic transitions in quantum wells grown by molecular beam epitaxy using both photoluminescence(PL) and optical absorption. The temperature ranged from 6K to room temperature. Samples under investigation were lattice-matched GaAs/AlGaAs and InGaAs/InAlAs, and strained InGaAs/GaAs and InGaAs/AlGaAs quantum wellssystems. In addition, the effects of well-size variations in GaAs/AlGaAs quantum wells were measured and analyzed. In all cases we were able to observe the excitonic transitions up to room temperature. By a careful fitting of the experimental data we separated the exciton transitions from band-to-band transitions. By deconvoluting the excitonic transitions we obtained the homogeneous and inhomogeneous linewidths. The homogeneous linewidths were used to calculate the exciton lifetimes as a function of temperature using the Heisenberg uncertainty principle. We found the lifetime decreases significantly with temperature and increases with increasing well size. These results are interpreted in terms of the exciton-phonon interaction and are expected to be very useful for the design of semiconductor optical devices operating at different temperatures. 相似文献
994.
A new method that combines phase shifting photoelasticity and transmission Coherent Gradient Sensing (CGS) is developed to
determine the tensorial stress field in thin plates of photoelastic materials. A six step phase shifting photoelasticity method
determines principal stress directions and the difference of principal stresses. The transmission CGS method utilizes a standard
four step phase shifting method to measure the x and y first derivatives of the sum of principal stresses. These stress derivatives are numerically integrated using a weighted
preconditioned conjugate gradient (PCG) algorithm, which is also used for the phase unwrapping of the photoelastic and CGS
phases. With full-field measurement of the sum and difference of principal stresses, the principal stresses may be separated,
followed by the Cartesian and polar coordinate stresses using the principal stress directions. The method is demonstrated
for a compressed polycarbonate plate with a side V-shaped notch. The experimental stress fields compare well with theoretical
stress fields derived from Williams solution for a thin plate with an angular corner. 相似文献
995.
C. Thinaharan D. K. Aswal A. Singh S. Bhattacharya N. Joshi S. K. Gupta J. V. Yakhmi 《Crystal Research and Technology》2004,39(7):572-576
We have grown single crystals of recently discovered thermoelectric oxide material NaxCoO2 using NaCl flux. Crystals of sizes upto 1.5 x 1.5 x 1.5 mm3 having different morphological habits were reproducibly grown. The atomic force microscopic studies show that along c‐axis crystals grow via 2D layer‐by‐layer mechanism. The X‐ray diffraction analyses show that grown crystals are rich in Na content as compared to the starting charge indicating that NaCl flux also acts as a source of Na. The resistivity of the crystals exhibited a linear temperature dependence in the region between 30 and 300 K. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
996.
L. Tian L. Tevet-Deree G. deBotton K. Bhattacharya 《Journal of the mechanics and physics of solids》2012,60(1):181-198
The coupled electromechanical response of electroactive dielectric composites is examined in the setting of small deformation and moderate electric field. In this setting, the mechanical stress depends quadratically on the electric field through a combination of material electrostriction and Maxwell stress. It is rigorously shown that the macroscopic mechanical stress of the composite also depends quadratically on the macroscopic electric field. It is further demonstrated that the effective electromechanical coupling can be computed from the examination of the uncoupled electrostatic and elastic problems. The resulting expressions suggest that the effective electromechanical coupling may be very large for microstructures that lead to significant fluctuations of the electric field. This idea is explored through examples involving sequential laminates. It is demonstrated that the electromechanical coupling – the macroscopic strain induced in the composite through the application of a unit electric field – can be amplified by many orders of magnitude by either a combination of constituent materials with high contrast or by making a highly complex and polydisperse microstructure. These findings suggest a path forward for overcoming the main limitation hindering the development of electroactive polymers. 相似文献
997.
Somesh Kr. Bhattacharya Anjali Kshirsagar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(3):355-364
Density functional calculations of structural and electronic properties
of stoichiometric and nonstoichiometric
CdTe clusters, containing up to few tens of atoms, are carried out
using projector augmented wave method.
Molecular dynamics has been performed
for Cd12Te12 and Cd15Te15
to predict the structure corresponding to global energy minimum.
Cage type structures and bulk fragments, both in zinc blende and
wurtzite structures, are used as starting geometries and
conjugate gradient method is used to locate the local energy minima for other clusters.
The aim of these calculations is to get the energetically favorable probable
structures, to be compared with the experimentally known
structures. Clusters are relaxed both in vacuum and in
the presence of surface passivating ligands and the resulting structural
rearrangement is analyzed. As expected, passivation increases the stability of an
individual cluster, as indicated by specific properties like binding energy,
vertical detachment energy, electron affinity etc.
Passivation also locks the symmetry for three-dimensional structures but the small
CdnTen (1 ≤ n ≤ 6) clusters, which are planar, attain higher
symmetry structures on passivation.
We observe `self-healing' mechanism viz., opening of optical
gap on relaxation without the aid of passivating ligand, in CdTe clusters as
observed in CdSe clusters [A. Puzder et al., Phys. Rev. Lett. 92,
217401 (2004)]. However, we note that 'self-healing' is a stoichiometry dependent
phenomenon. Te atoms are found to achieve a total coordination of 4 on passivation,
a fact useful in chemical synthesis of nanoclusters. 相似文献
998.
Mithun Bhattacharya Subharanjan Biswas Srikanta Bandyopadhyay Anil K. Bhowmick 《先进技术聚合物》2012,23(3):596-610
Along with other properties, superior gas permeation behavior would impart an extra dimension to multifunctional natural rubber (NR) nanocomposites used in various applications, like tires. For the first time, the impact on thermodynamics and kinetics of oxygen transport has been evaluated for nano, micro, and dual filler based multifunctional NR nanocomposites through oxygen permeation studies at three different temperatures. It is seen that, the kinetics is less affected by platelet like nanofillers, while the thermodynamics and eventual permeability are not altered much by fibrous nanofillers. The permeability of the nanocomposites decreased in the presence of nanofillers due to high aspect ratio and exquisite dispersion, as ascertained from morphological studies, which caused increment in tortuosity and the reduction in free volume. Relative permeabilities were compared to predictions of existent permeation models and a novel function was successfully introduced to address deviations in a model. Finally, nearly 60% decrement in permeability of dual filler based nanocomposites explained by the formation of zeta potential driven filler associations indicate potency in development of thinner, but stronger and more durable multifunctional materials with longer air retention capabilities. These could be applied in tire research to reduce material, energy costs and increase fuel efficiencies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
999.
Sayaree Dhar Dipak Kumar Rana Somnath Singha Roy Swapnadip Roy Sudin Bhattacharya Subhash Chandra Bhattacharya 《Journal of luminescence》2012,132(4):957-964
The synthesis and solvatochromic behavior of the compound, 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM), a pervasive, bioactive coumarin derivative, which is expected to possess antioxidative properties and other important therapeutic activities of significant potency with low systematic toxicity, have been reported employing steady state and time resolved fluorescence techniques. Spectroscopic studies reveal that the solvatochromic behavior of the probe depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction of PCM in polar solvents modulated the order of the two close-lying lowest singlet states. The photophysical response of PCM in different solvents has been explained considering solute-solvent interactions. To corroborate these results, we performed the ground-state geometry, lowest energy transition and the UV–vis spectrum of PCM using the density functional theory (DFT) and the time-dependent density functional theory (TD–DFT) at B3LYP/6-31G? level. We found excellent correlation between the predicted and experimental spectral data, providing a useful tool in the design of new fluorogenic probes having potential therapeutic activity. 相似文献
1000.