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排序方式: 共有791条查询结果,搜索用时 15 毫秒
61.
Vivek Ganvir Ashish Lele Rochish Thaokar B.P. Gautham 《ournal of non Newtonian Fluid Mechanics》2009,156(1-2):21-28
Accurate prediction of extrudate (die) swell in polymer melt extrusion is important as this helps in appropriate die design for profile extrusion applications. Extrudate swell prediction has shown significant difficulties due to two key reasons. The first is the appropriate representation of the constitutive behavior of the polymer melt. The second is regarding the simulation of the free surface, which requires special techniques in the traditionally used Eulerian framework. In this paper we propose a method for simulation of extrudate swell using an Arbitrary Lagrangian Eulerian (ALE) technique based finite element formulation. The ALE technique provides advantages of both Lagrangian and Eulerian frameworks by allowing the computational mesh to move in an arbitrary manner, independent of the material motion. In the present method, a fractional-step ALE technique is employed in which the Lagrangian phase of material motion and convection arising out of mesh motion are decoupled. In the first step, the relevant flow and constitutive equations are solved in Lagrangian framework. The simpler representation of polymer constitutive equations in a Lagrangian framework avoids the difficulties associated with convective terms thereby resulting in a robust numerical formulation besides allowing for natural evolution of the free surface with the flow. In the second step, mesh is moved in ALE mode and the associated convection of the variables due to relative motion of the mesh is performed using a Godunov type scheme. While the mesh is fixed in space in the die region, the nodal points of the mesh on the extrudate free surface are allowed to move normal to flow direction with special rules to facilitate the simulation of swell. A differential exponential Phan Thien Tanner (PTT) model is used to represent the constitutive behavior of the melt. Using this method we simulate extrudate swell in planar and axisymmetric extrusion with abrupt contraction ahead of the die exit. This geometry allows the extrudate to have significant memory for shorter die lengths and acts as a good test for swell predictions. We demonstrate that our predictions of extrudate swell match well with reported experimental and numerical simulations. 相似文献
62.
Himanshu Goel Anthony Hazel Vincent D. Ustach Sunhwan Jo Wenbo Yu Alexander D. MacKerell Jr 《Chemical science》2021,12(25):8844
Predicting relative protein–ligand binding affinities is a central pillar of lead optimization efforts in structure-based drug design. The site identification by ligand competitive saturation (SILCS) methodology is based on functional group affinity patterns in the form of free energy maps that may be used to compute protein–ligand binding poses and affinities. Presented are results obtained from the SILCS methodology for a set of eight target proteins as reported originally in Wang et al. (J. Am. Chem. Soc., 2015, 137, 2695–2703) using free energy perturbation (FEP) methods in conjunction with enhanced sampling and cycle closure corrections. These eight targets have been subsequently studied by many other authors to compare the efficacy of their method while comparing with the outcomes of Wang et al. In this work, we present results for a total of 407 ligands on the eight targets and include specific analysis on the subset of 199 ligands considered previously. Using the SILCS methodology we can achieve an average accuracy of up to 77% and 74% when considering the eight targets with their 199 and 407 ligands, respectively, for rank-ordering ligand affinities as calculated by the percent correct metric. This accuracy increases to 82% and 80%, respectively, when the SILCS atomic free energy contributions are optimized using a Bayesian Markov-chain Monte Carlo approach. We also report other metrics including Pearson''s correlation coefficient, Pearlman''s predictive index, mean unsigned error, and root mean square error for both sets of ligands. The results obtained for the 199 ligands are compared with the outcomes of Wang et al. and other published works. Overall, the SILCS methodology yields similar or better-quality predictions without a priori need for known ligand orientations in terms of the different metrics when compared to current FEP approaches with significant computational savings while additionally offering quantitative estimates of individual atomic contributions to binding free energies. These results further validate the SILCS methodology as an accurate, computationally efficient tool to support lead optimization and drug discovery.Predicting relative protein–ligand binding affinities is a central pillar of lead optimization efforts in structure-based drug design. 相似文献
63.
Gagandeep Singh Naman Gupta Vivek Gupta Mohan Paul Singh Ishar 《Tetrahedron letters》2017,58(25):2456-2459
Reductive ring opening of isoxazolidine moiety of chromano–piperidine-fused isoxazolidines (3a–c) with HCOONH4 and 10% Pd/C in a mixture of solvents (THF/MeOH) at ambient temperature, affords novel 2-(methylamino)-4-oxo-N-phenyl-N-propyl-4H-chromene-3-carboxamide (4), which is apparently derived from reductive NO bond cleavage followed by tandem intramolecular rearrangements. Plausible mechanistic rationale for the formation of compound 4 is proffered. 相似文献
64.
V. R. Sinha Amita Renu Chadha Honey Goel 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(3-4):381-392
The objectives of the present investigation were to prepare and characterize solid inclusion complexes of Etodolac (ETD) with β-cyclodextrin (β-CD) in order to study the effect of complexation on the dissolution rate of ETD, a hydrophobic guest molecule. Phase solubility curve was classified as a typical AL-type for the cyclodextrins (CD’s), showing that soluble complex was formed. The inclusion complexes in the molar ratio of 1:1 and 1:2 (β-CD–ETD) were prepared by various methods such as kneading, co-evaporation and in molar ratio of 1:1 by spray dried technique respectively. The molecular behaviors of ETD in all samples were characterized by nuclear magnetic resonance (NMR) spectroscopy, fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) studies and Scanning Electron microscopy (SEM) analysis. The results of these studies indicated that complexes prepared by kneading, co-evaporation and spray drying techniques showed inclusion of the ETD molecule into the CD’s cavities. The highest improvement in in vitro dissolution profiles was observed in complexes prepared with spray dried technique. Mean in vitro dissolution time indicated significant difference between the release profiles of ETD from complexes and physical mixtures and from pure ETD. 相似文献
65.
Teena Goel Manoj Kumbhakar Tulsi Mukherjee Haridas Pal 《Journal of photochemistry and photobiology. A, Chemistry》2010,209(1):41-48
The effect of different hydrotropic salts on the microenvironment at the anionic head group region of sodium dodecyl sulphate (SDS) micelle has been studied through time-resolved fluorescence anisotropy measurements of a solubilized probe, coumarin-153 (C153). The organic cations of the hydrotropic salts used in this study, i.e. aniline hydrochloride (AHC) and o-, m- and p-toluidine hydrochlorides (OTHC, MTHC and PTHC, respectively), differ in their charge to size ratio and hydrophobicity. Present study utilizes the sensitivity of the fluorescence technique to understand the changes in the micropolarity and microviscosity experienced by the fluorescent probe, C153, solubilized in the micellar Stern layer, on addition of different hydrotropic salts. Significant changes are observed in the rotational relaxation dynamics of the probe with increasing concentration of the salts. The changes in the rotational relaxation dynamics clearly reflect the sphere to rod transition in the SDS micelles and correspond nicely with the reported results from dynamic light scattering measurements. The growth behavior of SDS micelles is found to be sensitive to the hydrophobicity of the organic cations. The charge to size ratio of the organic cations also indicated to play a role in inducing the sphere to rod transition in the SDS micelles. The interesting observation made from this study is that the sphere to rod transition of SDS micelles is largely facilitated by the presence of the hydrotropic salts and such a transition is successfully indicated by the simple fluorescence anisotropy measurements of a probe in the micelle carried out in the presence of different hydrotropic salts. 相似文献
66.
67.
Volume changes associated with point defects in space charge layers can produce strains that substantially alter thermodynamic equilibrium near surfaces in ionic solids. For example, near-surface compressive stresses exceeding -10 GPa are predicted for ceria. The magnitude of this effect is consistent with anomalous lattice parameter increases that occur in ceria nanoparticles. These stresses should significantly alter defect concentrations and key transport properties in a wide range of materials (e.g., ceria electrolytes in fuel cells). 相似文献
68.
Abstract
The crystal structure of the title compound, 3β-hydroxy-16α-methylpregn-5-en-20-one, C22H34O2, was determined by direct methods using single crystal X-ray diffraction data. The compound crystallizes in the triclinic space group P1 with unit-cell parameters: a = 6.235(1) ?, b = 6.282(1) ?, c = 12.877(3) ?, α = 96.672(4)°, β = 98.746(4)°, γ = 106.838(4)°, Z = 1. The structure was refined by full-matrix least-squares to R = 0.0573 for 2,196 observed reflections. Rings A and C of the compound are in chair conformation whereas ring B is in half-chair conformation. Ring D is in envelope conformation. The A/B ring junction is quasi-trans, while ring systems B/C and C/D are trans fused about the C8–C9 and C13–C14 bonds, respectively. The steroid nucleus has a small twist, as shown by the C19–C10···C13–C18 pseudo-torsion angle of 8.0°. Molecules are connected via C–H···O hydrogen bonds to form straight chains along the c-axis of the unit cell. The straight chains are packed together to form layers. 相似文献69.
70.
G. Kavitha S. R. C. Vivek A. Govindaraj Chandrabhas Narayana 《Journal of Chemical Sciences》2003,115(5-6):689-694
The paper discusses the design of a low cost Raman spectrometer. Single-walled nanotubes (SWNT) have been studied to demonstrate
the reach of such a system. We observe both the radial-breathing mode (RBM) and the tangential mode from the SWNT. The tube
diameters of the SWNT used in these experiments have been determined using RBM to be predominantly 1.4 and 1.6 nm. These are
consistent with the TEM images taken of the same sample. The new method of producing SWNT using Ni-Y catalyst in electric-arc
discharge method produces nanotubes with very small dispersion in diameter and high yields. The chirality of the SWNT can
be deduced from their radial breathing modes, and it suggests that they are metallic in nature.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献