Srinivasan V.,IISER |
Srinivasan V.,Princeton University |
Sebastiani D.,Free University of Berlin |
Sebastiani D.,Max Planck Institute for Polymer Research
Journal of Physical Chemistry C | Year: 2011
We investigate the quantum-mechanical localization of 1H and 2H isotopes in the symmetric low-barrier hydrogen-bonds of potassium dihydrogen phosphate (KDP) crystals in the paraelectric phase. The spatial density distributions of these hydrogen atoms are suspected to be responsible for the surprisingly large isotope effect observed for the ferroelectric phase transition in KDP. We employ ab initio path integral molecular dynamics simulations to obtain the nuclear real-space and momentum-space densities n(R) and n(k) of 1H and 2H, of which the latter densitites are compared to experimental neutron compton scattering data. Our results suggest a qualitative difference in the nature of the paraelectric phase in KDP between the two isotopes. Whereas both paraelectric states result from quantum delocalization, the essential difference is the change from a probably coherent to incoherent tunneling behavior of the hydrogen atoms across the hydrogen-bonds. © 2011 American Chemical Society.
Arora B.,IISER |
Safronova M.S.,University of Delaware |
Clark C.W.,U.S. National Institute of Standards and Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011
Using first-principles calculations, we identify "tune-out" optical wavelengths, λzero, for which the ground-state frequency-dependent polarizabilities of alkali-metal atoms vanish. Our approach uses high-precision, relativistic all-order method in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. We discuss the use of tune-out wavelengths for sympathetic cooling in two-species mixtures of alkali metals with group II and other elements of interest. Special cases in which these wavelengths coincide with strong resonance transitions in a target system are identified. © 2011 American Physical Society.
Deb N.,University of Burdwan |
Bagchi S.,IISER |
Mukherjee A.K.,University of Burdwan
Molecular Physics | Year: 2010
Electron donor-acceptor interaction of the reverse micelle (RM) of TX-100 in CCl4 medium with a number of π-acceptors has been established by analysing the charge transfer (CT) absorption bands in the light of Mulliken's theory. Aggregation number (n) and operational critical micellisation concentration of the RM and formation constants of the RM-p-chloranil and RM-o-chloranil complexes have been determined by UV-visible spectrophotometry. Values of n thus obtained (20-30) are close to that of TX-100/cyclohexane dry reverse micelles determined by other methods and also to a theoretically calculated value of n for AOT/CCl4 dry RM. © 2010 Taylor & Francis.
Kumar A.,IISER |
Yadav K.L.,Indian Institute of Technology Roorkee
Journal of Applied Physics | Year: 2014
One of the induced multiferroic materials, CuO has the magnetic as well as ferroelectric phase transition at same temperature (TN1 ∼213K, TC and TN2 ∼230K). These type of materials can show two types of entropy; magnetic field induced entropy (Magnetocaloric Effect) as well as electeric field induced entropy (Electrocaloric Effect). The presence of both type of entropy may be called "Multicaloric Entropy" (M. Vopson, Solid State Commun. 152, 2067 (2012) and Meng et al., Phys. Lett. A 377, 567 (2013)). We observed that "Multicaloric Entropy" in the induced multiferroic materials also depends on the magnetoelectric interaction (γ). Therofore, this numerical attempt to calculate the entropy of CuO may be useful for the future "electro-magnetic" based refrigerator technology. © 2014 AIP Publishing LLC.
Ranjan R.K.,Jawaharlal Nehru University |
Routh J.,IISER |
Ramanathan A.L.,Jawaharlal Nehru University
Applied Geochemistry | Year: 2010
The Pichavaram mangrove ecosystem is located between the Vellar and Coleroon Estuaries in south-eastern India. To document the spatial-depth-based variabilities in organic matter (OM) input and cycling, five sediment cores were collected. A comparative study was carried out of grain-size composition, pore water salinity, dissolved organic C (DOC), loss-on-ignition (LOI), elemental ratios (C/N and H/C), pigments (Chl a, Chl b, and total carotenoids), and humification indices. Sand is the major fraction in these cores ranging from 60% to 99% followed by silt and clay; cores from the estuarine margin have high sand content. In mangrove forests, pore-water DOC concentrations are high (32±14mgL-1), whereas salinity levels are low (50±5.5‰). Likewise, LOI, organic C and N, and pigment concentrations are high in mangroves. OM is mainly derived from upstream terrestrial matter and/or mangrove litter, and marine OM. The humification indices do not vary significantly with depth because of rapid OM turnover. The bulk parameters indicate that the Vellar and Coleroon Estuaries are more affected by anthropogenic processes than mangrove forests. Finally, greater variability and sometimes lack of specific trends in bulk parameters implies that the 2004 tsunami caused extensive mixing in sediments. © 2010 Elsevier Ltd.