Y. Singh

Ocular hazards during birth.

In a study of over 2,000 consecutive live births, 243 newborns (12%) suffered birth trauma to the eye and its adnexa. Two hundred twenty-one cases (11%) had multiple retinal hemorrhages. Severe ocular accidents by forceps delivery were seen in the form of hyphema, Purtschers retinopathy, corneal edema, facial palsy, and corneal abscess. Purtschers retinopathy and corneal abscess are rare birth injuries that have not been reported so far in newborn babies.

Equilibrium properties of simple molecular fluids

The application of thermodynamic perturbation theory in which all tensor interactions are taken as perturbation of the pair central potential to the computation of the equilibrium properties of uniform molecular fluids is considered. Comparisons with experiment are made for nitrogen, oxygen, carbon monoxide, carbon dioxide, and methane. Theoretical expressions are given and calculations made for Helmholtz free energy, configurational energy, entropy, and pressure, taking into account the influence of permanent electric multipole moments, induced dipole moments, anisotropic dispersion, and overlap forces. The influence of three‐body nonadditive interaction arising from dispersion and classical electric induction interactions between asymmetric molecules on the thermodynamic properties is also considered. Excellent agreement with experiment is obtained for all systems.

A simple and exactly solvable model for a semiflexible polymer chain interacting with a surface

We use the lattice model of directed walks to investigate the conformational as well as the adsorption properties of a semiflexible homopolymer chain immersed in a good solvent in 2D and 3D. To account for the stiffness in the chain we have introduced energy barrier for each bend in the walk and have calculated the persistent length as a function of this energy. For the adsorption on an impenetrable surface perpendicular to the preferred direction of the walk we have solved the model exactly and have found the critical value of the surface attractions for the adsorption in both 2D and 3D. We have also enumerated all possible walks on square and cubic lattices for the number of steps N⩽30 for 2D and N⩽20 for 3D and have used ratio method for extrapolation. The transition located using this method is in excellent agreement with the results found from the analytical method. We have compared the results of surface adsorption for two different surface orientations. In one of the orientation, surface is considered parallel to the preferred direction and in another it is perpendicular to the preferred direction. Results found in both the cases indicate that for stiffer chains adsorption transition takes place at higher temperature compared to that of flexible chain

Perturbation theory for fluids of non-spherical molecules in the presence of three-body forces

The application of perturbation theory to a fluid of non-spherical molecules of arbitrary symmetry is considered. The influence of a large number of angle-dependent pair interactions and three-body non-additive interactions on the Helmholtz free energy and on the pair and triplet distribution functions, in some cases through the third order of the perturbation theory, is evaluated. Explicit expressions are given for the Helmholtz free energy for molecules possessing axial and tetrahedral symmetries in terms of molecular parameters and the reference systems pair and triplet distribution functions. The contributions of the various terms discussed in this paper are expected to be substantial at low temperatures for a real fluid.

Virial coefficients of the equation of state of a gas of nonspherical molecules

The second and third virial coefficient of a gas of nonspherical molecules of arbitrary symmetry have been calculated for a set of force parameters which has been found suitable to explain the dilute gas viscosity data. The influence of a large number of orientation dependent pair- and three-body nonadditive interactions has been taken into account. The relative contribution of each branch of pair and triplet interactions has been evaluated as a function of temperature. The theoretical results have been compared with the experimental data of N2, CO, CO2, CS2, C2H4 and C6H6. The agreement between theory and experiment is very satisfactory for all the systems.

Effect of shape of molecules on transport and equilibrium properties of nonpolar polyatomic gases

Collision integrals for nonpolar polyatomic gases have been evaluated on the assumption of fixed relative orientation per collision, with a 12–12–6 potential model, for a range of reduced temperatures and shape parameters. The effect of shape of molecules on diffusion and viscosity is small but not negligible. Thermal diffusion factors are most strongly affected; the presence of interaction due to nonsphericity in the shape of molecules can wipe out the thermal‐diffusion inversion temperatures. The parameters of the spherical component of the potential have been obtained from the viscosity data for nine gases. These parameters have been used in conjunction with the second viral coefficient data to determine the quadrupole moments and shape parameters of the molecules. The quadrupole moments and shape parameters obtained are very reasonable.

Semiclassical statistical mechanics of a two dimensional fluid

Expansions are obtained for the two and three body ‘modified’ Ursell functions for a hard disc fluid in the semiclassical limit. These results are used to obtain a high temperature expansion for the density independent part of the radial distribution function and the first order density correction to it. Quantum corrections to the second and third virial coefficients are also discussed.

Does a surface attached globule phase exist

A long flexible neutral polymer chain immersed in a poor solvent and interacting with an impenetrable attractive surface exhibits a phase known as surface attached globule (SAG) in addition to other adsorbed and desorbed phases. In the thermodynamic limit, the SAG phase has the same free energy per monomer as the globular phase, and the transition between them is a surface transition. We have investigated the phase diagrams of such a chain in both two- and three-dimensions and calculated the distribution of monomers in different domains of the phase diagram.

Quantum mechanical second virial coefficient of a gas with square‐well plus hard‐core potential

The quantum mechanical second virial coefficient of a gas with square‐well plus hard‐core potential is evaluated at low and high temperatures. The low temperature result is given in a series in the ascending powers of (a/λ), and the first four coefficients are given. The direct part of the second virial coefficient at high temperature is given in a series in the ascending powers of (λ/a), and the first three coefficients are given. Our result for the first coefficient in the high temperature series is in agreement with the result of previous workers.

Equilibrium properties of molecular fluid mixtures

The application of perturbation theory in which all tensor interactions are taken as a perturbation of the central potential to a multicomponent fluid mixture of nonspherical molecules of arbitrary symmetry is considered. The influence of angle‐dependent pair interactions arising from permanent electric multipole moments, induced dipole moments, anisotropic dispersion and overlap forces, and three‐body nonadditive interactions arising from dispersion and classical electric induction interaction between asymmetric molecules on the Helmholtz free energy, in some cases through the third‐order of the perturbation theory, is evaluated. The theory is applied to binary mixtures consisting of (i) a component of spherically symmetric molecules and another of axially symmetric molecules and (ii) both components of axially symmetric molecules. Comparisons with experiments are made for Ar–N2, Ar–O2, Ar–CO, N2–O2 and N2–CO binary mixtures at zero pressure isobar and T=83.82u2009°K as a function of composition for excess G...