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Biomedical subjects

M S Jhon

Publications and source records attributed to M S Jhon.

At least 19 recordsLinked to original sources
PubMed2005

Comment on "Preparation and electrorheological property of rare earth modified amorphous Ba(x)Sr(1-x)TiO3 gel electrorheological fluid".

The comments on the recent results on electrorheological (ER) property of rare earth modified amorphous barium strontium titanate gel based ER fluid are given via analysis of its dynamic yield stress data as a function of applied electric field strengths. Using our previously reported universal yield stress equation, we obtained the critical electric field strength and collapsed their data onto a single curve.

Journal Article↗
PubMed1999

Monte Carlo simulations of liquid spreading on a solid surface: effect of end-group functionality.

The spreading of liquid droplets composed of molecules with or without reactive end groups over a solid surface has been studied using Monte Carlo simulations. For molecules without reactive end groups, a molecular layering in the spreading profiles is predicted, depending on the ratio of the magnitude of intermolecular interactions to thermal energy. As intermolecular interactions become smaller than thermal energy, the layered structure vanishes. For molecules with reactive end groups, interactions between end groups and between end groups and the surface complicate the situation. By assuming an end-to-end interaction between molecules and the pinning of end groups to the surface, a complex layered structure is obtained. Our simulation predicts spreading profiles that accurately describe the broad spectrum of data obtained from scanning microellipsometry for perfluoropolyalkylethers with and without reactive end groups.

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PubMed1991

High directional Monte Carlo procedure coupled with the temperature heating and annealing as a method to obtain the global energy minimum structure of polypeptides and proteins.

A high directional Monte Carlo procedure that predicts the topology of the energy hypersurface before it walks, is developed as a method to obtain a global energy minimum structure of polypeptides and proteins. It calculates its covariance matrix, which controls the individual trial step distribution of the next set of steps, from the second moment of the actual walk segment in the previous set. The method is successfully applied to the pentapeptide Metenkephalin system. And it is shown that some initial heating process, which provides the more flexible molecule, is necessary in order to overcome the energy barriers that can be overestimated by some biases in the empirical description of the system. The sampling efficiency, traced by an average conformational changes, is found to be at least 20 times greater than the one in the conventional Metropolis Monte Carlo methods, and it is expected that this increases in efficiency will be more prominent when the system is larger.

Enkephalin, Methionine↗
PubMed1986

Flow-induced anisotropy in the susceptibility of a particle suspension.

The initial susceptibility, or low-field high-frequency permeability, of a rod-like particle suspension or polymer solution can become anisotropic when the particles or molecules interact with a magnetic field in a directional manner and are nonrandomly oriented by certain types of flow field. This is the alignment that leads to thixotropy and deviatoric stresses during rheological measurements on these fluids. A general expression for the particle order parameter and the fluid permeability in terms of Legendre polynomials is derived by calculating the ensemble average over all possible orientation angles. This is an integral containing the orientation angle-dependent orientation probability function. The example case of single-domain magnetic particles suspended in extensional flow of a newtonian fluid is examined by using the following well-known models: chain-of-spheres model for the magnetic properties of a particle and the Kirkwood-Auer theory for the orientation probability function. From this, the particle orientation in the flow direction downstream from a sharp circular convergence is predicted to dramatically increase with an increase in the ratio of the extension rate to the particle rotary diffusion coefficient. Consequently, the measured permeability of the fluid is predicted to decrease parallel to, and to increase perpendicular to, the flow direction.

Journal Article↗
PubMed1981

Radial distribution function of liquid argon according to significant structure theory.

The significant structure theory of liquids is tested by evaluating the radial distribution function. The calculations are based on face-centered cubic quasi-lattice structure, and the fluctuation in volume is used to describe the thermal displacements of molecules. It is shown that the local structure of liquids has inhomogeneous distributions. The correlation at long ranges becomes negligible because of the fluidized vacancies in our model. The calculations are performed for liquid argon, and the results are in good agreement with experiments.

Journal Article↗
PubMed1980

Significant structure theory applied to liquid He.

The large kinetic zero-point motion of (4)He molecules has been properly taken into account in the significant structure theory of liquids in order to describe the liquidity of liquid (4)He. The Debye and the Bose-Einstein partition functions are used for the solid-like molecules of the normal fluid component and for the whole gas-like molecules, respectively. The solid-like molecules of the superfluid component are considered as ground state molecules without having positional degeneracies. The Bragg-Williams approximation of an order/disorder phase transition has been applied to the lambda transition of liquid (4)He. Thermodynamic and surface properties of liquid (4)He have been calculated up to the critical point. The results are satisfactory when compared with the observed values.

Journal Article↗
PubMed1979

Theoretical study of hydration of RNA.

The hydration phenomena of A-RNA double helix and the anticodon loop of transfer RNA have been theoretically investigated using the empirical potential energy functions. The hydration schemes of a model compound of A-RNA and a polynucleotide which has the structure of the anticodon loop of yeast tRNAPhe have been determined, and their stabilization energies produced by the introduction of water in the first hydration shell were calculated by considering the hydrated ones as supermolecules. The results indicate that hydration scheme of A-RNA considerably differs from that of B-DNA and stabilization energy due to hydration of A-RNA is not so great as B-DNA. In the anticodon loop structure, however, stabilizing effect of the bound water molecules upon the structure is significant. From the results, the reason why the structure of RNA remains unchanged with the change of hydration degree while that of DNA is altered was studied.

Anticodon↗
PubMed1979

Significant structure theory applied to electrolyte solution.

The significant structure theory has been successfully applied to an aqueous NaCl solution. Liquid water is assumed to have a domain structure and the ions are hydrated by water molecules. The partition function is composed of the partition function for the water and that for the salt, and the excess free energy term from the Debye-Hückel theory is also added. The thermodynamic properties, such as molar volume, vapor pressure, entropy of vaporization, and heat capacity, as well as the dielectric constant are calculated over the whole concentration ranges and wide temperature ranges. The agreement between theory and experiment is satisfactory.

Journal Article↗
PubMed1977

Theoretical study of the hydration of B-DNA.

A theoretical study of the hydration of the B-form of DNA has been carried out using empirical potential energy functions. In the first stage the hydration scheme of a model compound representing the B-DNA has been determined and the results have been shown to agree to a large extent with those of refined ab initio SCF computations. In the second stage, the stabilization energy due to the presence of water in the first hydration shell was computed by considering the hydrated helix as a supermolecule. The computations indicate appreciable stabilization. The different components contributing to the overall stabilization are determined and analysed.

Binding Sites↗
PubMed1977

Significant structure theory applied to phase separation.

The significant structure theory of liquids has been applied to the partially miscible system of the O(3)-O(2) mixture, which exhibits partial miscibility in the temperature range from -195.5 degrees C to -179.9 degrees C. The thermodynamic condition for phase separation is given by the following inequality: [Formula: see text] A partition function for the binary liquid mixture is developed using significant liquid structure theory. Here X(i) is the mole fraction of either of the two components. We obtain the coexistence curve of the O(3)-O(2) system by varying the mole fractions of the components to find the temperature at which the two liquids separate. The agreement between theory and experiment is satisfactory.

Journal Article↗
PubMed1977

Significant structure theory applied to liquid helium-3.

The significant structure theory of liquids is successfully applied to the quantum liquid (3)He. The partition function uses the Debye partition function for the solid-like molecules and the Fermi-Dirac partition function for the gas-like degrees of freedom. To evaluate the gas-like partition function, numerical calculations are performed and some integral functions appearing in the equation of state of the ideal Fermi-Dirac gas are tabulated. In the solid-like molecules, the molar volume V(s) depends on the temperature, and a linear dependence is used.The thermodynamic properties, such as molar volume, vapor pressure, entropy, heat capacity, and the critical constants as well as the surface tension of liquid (3)He are calculated. The agreement between theory and experiment is satisfactory.

Journal Article↗
PubMed1974

The significant structure theory applied to amorphous and crystalline polyethylene.

The significant structure theory of liquids has been applied to amorphous and crystalline polyethylene. In this theory the amorphous state, like liquids in general, is assumed to have solid-like structure, gaslike structure, and positional degeneracy which arises from the motion of kinetic segments and from the libration of CH(2) units. This concept leads to a partition function giving the Helmholtz free energy in terms of volume, temperature, and composition.Thermodynamic and transport properties are calculated for amorphous polyethylene. The thermodynamic properties are also calculated for the crystalline solid. The calculated results are in reasonable agreement with the experimental values. No such detailed calculations of polymer properties from a partition function, depending on both volume and temperature, have been previously attempted.

Journal Article↗
PubMed1972

Molecular orbital studies of ethylenediamine conformations.

Semiempirical quantum mechanical treatments are applied to the ethylenediamine di-cation, mono-action, and neutral molecule by the use of the extended Huckel theory.The minimum energies of conformations of molecules for rotation about the CH(2)-CH(2) axis is found. The theoretical predictions for the conformation with minimum values. The importance of the ethylenediamine conformations are discussed.

Journal Article↗
PubMed1972

Physical adsorption of the quantum gas.

The significant structure theory of quantum liquids such as hydrogen, deuterium, and helium has been applied to the physical adsorption occurring in the submonolayer region. The partition function for the two-dimensional adsorbed fluid has been derived. The properties of isothermal and isosteric heat show good agreement with the available data from the literature.

Journal Article↗
PubMed1969

An improved iteration method for the calculation of surface tension using the significant structure theory of liquids.

An improved iteration method for calculating the surface tension developed by Chang et al. is presented. To test it, the surface tensions of the following liquids are calculated: A, N(2), CH(4), PH(2), Br(2), C(6)H(6), HgCl(2), and TiCl(4).The calculated results show the present method is an improvement over that of Chang et al. In addition to the change in the energy of sublimation of a molecule in a surface layer, which Chang et al. considered, the less important but not negligible effects on the number of nearest neighbors, eta(i), and the characteristic temperature, theta(i), are now included. eta(i) is proportional to the effective local density, and theta(i) is proportional to the square root of the effective local density. The calculated values fit the experimental data somewhat more closely than those calculated by the original method of Chang et al.

Journal Article↗