3,439 research outputs found
Significance of thermal fluctuations and hydrodynamic interactions in receptor-ligand mediated adhesive dynamics of a spherical particle in wall bound shear flow
The dynamics of adhesion of a spherical micro-particle to a ligand-coated
wall, in shear flow, is studied using a Langevin equation that accounts for
thermal fluctuations, hydrodynamic interactions and adhesive interactions.
Contrary to the conventional assumption that thermal fluctuations play a
negligible role at high Pclet numbers, we find that for particles
with low surface densities of receptors, rotational diffusion caused by
fluctuations about the flow and gradient directions aids in bond formation,
leading to significantly greater adhesion on average, compared to simulations
where thermal fluctuations are completely ignored. The role of wall
hydrodynamic interactions on the steady state motion of a particle, when the
particle is close to the wall, has also been explored. At high Pclet
numbers, the shear induced force that arises due to the stresslet part of the
Stokes dipole, plays a dominant role, reducing the particle velocity
significantly, and affecting the states of motion of the particle. The coupling
between the translational and rotational degrees of freedom of the particle,
brought about by the presence of hydrodynamic interactions, is found to have no
influence on the binding dynamics. On the other hand, the drag coefficient,
which depends on the distance of the particle from the wall, plays a crucial
role at low rates of bond formation. A significant difference in the effect of
both the shear force and the position dependent drag force, on the states of
motion of the particle, is observed when the Plet number is small.Comment: The manuscript has been accepted as an article in Physical Review E
Journa
Observation of Mixed Alkali Like Behaviour by Fluorine Ion in Mixed Alkali Oxyfluro Vanadate Glasses: Analysis from Conductivity Measurements
In this communication we report the fluorine ion dynamics in mixed alkali
oxyfluro vanadate glasses. We have measured the electrical conductivity using
impedance spectroscopy technique Room temperature conductivity falls to 5
orders of magnitude from its single alkali values at 33 mol% of rubidium
concentration. We have also estimated the distance between similar mobile ions
using the density values. Assuming this distance as the hopping distance
between the similar ions we have estimated the anionic (Fluorine ion in our
case) conductivity. It is observed that the fluorine ion dynamics mimics the
mixed alkali effect and scales as the onset frequency f0.Comment: submitted to DAE-SSDP 2018 Indi
Bose-Hubbard Models in Confining Potentials: An Inhomogeneous Mean-Field Theory
We present an extensive study of Mott insulator (MI) and superfluid (SF)
shells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic
traps. For this we develop an inhomogeneous mean-field theory. Our results for
the BH model with one type of spinless bosons agrees quantitatively with
quantum Monte Carlo (QMC) simulations. Our approach is numerically less
intensive than such simulations, so we are able to perform calculation on
experimentally realistic, large 3D systems, explore a wide range of parameter
values, and make direct contact with a variety of experimental measurements. We
also generalize our inhomogeneous mean-field theory to study BH models with
harmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two
species of bosons we obtain rich phase diagrams with a variety of SF and MI
phases and associated shells, when we include a quadratic confining potential.
For the spin-1 BH model we show, in a representative case, that the system can
display alternating shells of polar SF and MI phases; and we make interesting
predictions for experiments in such systems.Comment: 17 pages, 18 figure
Coupling of mixed layer processes and thermocline variations in the Arabian Sea
This study presents an analysis of observed data sets from multiple sources, including observations from a network of Argo floats during (2002–2003), with the aim of investigating the role of the southwest monsoon circulation in affecting the interactions between the oceanic mixed layer and the underlying thermocline in the northern Indian Ocean. Examination of the seasonal cycle of the upper-ocean thermal structure shows that the surface cooling of the Arabian Sea, during the southwest monsoon season, is accompanied by significant warming of the thermocline. It is seen that the thermocline is warmer by about 1.2°C in the south-central Arabian Sea during the southwest monsoon season relative to other months. Offline computations of the profiles of vertical diffusivity of heat reveal stronger and deeper penetration of heat into the Arabian Sea during the southwest monsoon season. The results presented in the paper demonstrate that the combined effects of strong wind-driven mixing by the monsoonal winds, weak density stratification in the upper-ocean, and downwelling in south-central Arabian Sea, along with strong vertical diffusivity, favor downward transfer of warm waters from the surface into the thermocline. Besides the climatological seasonal cycle, the present study also examines the impact of monsoon interannual variability on the upper-ocean response, by analysis of long-term observed records during (1955–2001) as well as the Argo observations for (2002–2003). It is found that the interannual variations in the ocean response reveal signatures of the influence of strong and weak southwest monsoons on the mixed layer and thermocline variabilities
Structural, Magnetic and Magneto-caloric studies of Ni50Mn30Sn20Shape Memory Alloy
We have synthesized a nominal composition of Ni50Mn30Sn20 alloy using arc
melting technique. Rietveld refinement confirms the austenite L21 structure in
Fm-3m space group. Electrical resistivity has been found to clearly exhibiting
two different phenomena viz. a magnetic transition from paramagnetic to
ferromagnetic and a structural transition from austenite to martensitic phase.
Thermo-magnetization measurements M(T) confirms ferromagnetic transition
temperature TC at 222 K and martensitic transition starting at 127 K(MS).
Magnetization measurement M(H) at 10 K confirms the ferromagnetic state.
Frequency dependence of ac susceptibility \c{hi}' at low temperature suggests
spin glass behavior in the system. The isothermal magnetic entropy change
values have been found to be 1.14 J/Kg.K, 2.69 J/Kg.K and 3.9 J/Kg.K, with
refrigeration capacities of 19.6 J/kg, 37.8 J/kg and 54.6 J/kg for the field
change of 1, 2 and 3 Tesla respectively at 227 K.Comment: 16 pages text + Figs. Ni50Mn30Sn20 alloy: reasonable refrigeration
capacity tunable to Room
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