Showing papers by "Pijush Ghosh published in 2008"
12 Jun 2008
TL;DR: In this article, the first spin alignment measurements for the K*{sup 0}(892) and (1020) vector mesons produced at midrapidity with transverse momenta up to 5 GeV/c at {radical}s{sub NN} = 200 GeV at RHIC.
Abstract: We present the first spin alignment measurements for the K*{sup 0}(892) and (1020) vector mesons produced at midrapidity with transverse momenta up to 5 GeV/c at {radical}s{sub NN} = 200 GeV at RHIC. The diagonal spin-density matrix elements with respect to the reaction plane in Au+Au collisions are {rho}{sub 00} = 0.32 {+-} 0.04 (stat) {+-} 0.09 (syst) for the K*{sup 0} (0.8 < p{sub T} < 5.0 GeV/c) and {rho}{sub 00} = 0.34 {+-} 0.02 (stat) {+-} 0.03 (syst) for the {phi} (0.4 < p{sub T} < 5.0 GeV/c) and are constant with transverse momentum and collision centrality. The data are consistent with the unpolarized expectation of 1/3 and thus no evidence is found for the transfer of the orbital angular momentum of the colliding system to the vector-meson spins. Spin alignments for K*{sup 0} and {phi} in Au+Au collisions were also measured with respect to the particle's production plane. The {phi} result, {rho}{sub 00} = 0.41 {+-} 0.02 (stat) {+-} 0.04 (syst), is consistent with that in p+p collisions, {rho}{sub 00} = 0.39 {+-} 0.03 (stat) {+-} 0.06 (syst), also measured in this work. The measurements thus constrain the possible size of polarization phenomena in the production dynamicsmore » of vector mesons.« less
47 citations
TL;DR: The nacre structure consists of laminated interlocked mineral platelets separated by nanoscale organic layers and the role of close proximity of mineral to the proteins on mechanical behavior of the protein is investigated through steered molecular dynamics simulations.
Abstract: The nacre structure consists of laminated interlocked mineral platelets separated by nanoscale organic layers. Here, the role of close proximity of mineral to the proteins on mechanical behavior of the protein is investigated through steered molecular dynamics simulations. Our simulations indicate that energy required for unfolding protein in the proximity of mineral aragonite is several times higher than that for isolated protein in the absence of the mineral. Here, we present details of specific mechanisms which result in higher energy for protein unfolding in the proximity of mineral. At the early stage of pulling, peaks in the load-displacement (LD) plot at mineral proximity are quantitatively correlated to the interaction energy between atoms involved in the latching phenomenon of amino acid side chain to aragonite surface. Water plays an important role during mineral and protein interaction and water molecules closer to the mineral surface are highly oriented and remain rigidly attached as the protein strand is pulled. Also, the high magnitude of load for a given displacement originates from attractive interactions between the protein, protein-bound water, and mineral. This study provides an insight into mineral-protein interactions that are predominant in biological nanocomposites and also provides guidelines towards design of biomimetic nanocomposites.
21 citations
01 Jan 2008
TL;DR: In this article, the structure of nacre is modeled using 3D finite element models and features up to 50 nm are incorporated into the 3D models and the molecular structure which pertains to the interfacial mechanics of the organic-inorganic interfaces is modelled using steered molecular dynamics.
Abstract: Nacre the inner iridescent layer of molluscan seashells is a model biomimetic system for design of next generation nanocomposites. Here, we present results of multiscale modelling and experimental investigation of the mechanics of nacre. The structure of nacre which is an organized polygonal laminated platelet structure at the micrometer length scale, is modelled using 3D finite element models and the features up to 50 nm are incorporated into the 3D models. The molecular structure which pertains to the interfacial mechanics of the organic-inorganic interfaces is modelled using steered molecular dynamics. In addition, we have utilized several characterization techniques to evaluate the mechanics of this system at many length scales. Tensile testing and 3-point bend tests are performed at the macro-scale. At the micro-nm length scale we have conducted nanomechanics experiments using atomic force microscopy and nanoindentation. The molecular nature of the organic inorganic interface is investigated using photoacoustic spectroscopy techniques. Our simulations and experiments indicate important results on the specific roles of nano and microstructural details of nacre. We have shown that the organic phase exhibits a very large modulus (~20 GPa) while also undergoing very large deformations. The mineral bridges that connect one layer of mineral platelets to the next have marginal role on the deformation mechanics of nacre and as also the nanoscale roughness or asperities. We have also discovered the presence of platelet-platelet interlocks in nacre and shown that these interlocks have a very significant role on mechanics of nacre. The deformation of the mineral at nanoscale indicates visco-elastic behaviour which arises from presence of water within and adsorbed on surfaces of the nacre platelets. Our simulations with application of force on molecular models of aragonite and proteins indicate that the deformation of the protein itself is very significantly influenced by the non-bonded interactions that are present at the organic-inorganic interfaces in nacre. These results are significant both for developing understanding of this important material system and also for describing methods and techniques in understanding multiscale mechanics which is applicable and necessary for the next generation advanced material systems.