Dynamics of Diblock Copolymers in Dilute Solutions

We consider the dynamics of freely translating and rotating diblock (A-B), Gaussian copolymers, in dilute solutions. Using the multiple scattering technique, we have computed the diffusion and the friction coefficients D_AB and Zeta_AB, and the change Eta_AB in the viscosity of the solution as functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments of the A block and of the whole copolymer, respectively, and l_A, l_B are the Kuhn lengths of the A and B blocks. Specific regimes that maximize the efficiency of separation of copolymers with distinct "t" values, have been identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty, submitted to Macromolecule

Therapeutic Efficacy of Vishnu Chakara Mathirai - A Siddha Formulation in the management of Valippu Noi (Convulsive Disorders): A Pre-Clinical study

The Vishnu Chakara Mathirai possess the specified charcters as mentioned by the Pharmacopoeial Laboratory for Indian Medicine, Ministry of AYUSH. • The phytochemical analysis revealed the presence of alkaloids and phenols which may helpful for the therapeutic efficacy. • The ICP OES analysis revealed that the toxic elements like mercury, arsenic, cadmium, lead and sulphur were found to be WHO permissible limits. • The spectral studies revealed the fingerprint of VCM which can be used for its bulk production. • The SEM and EXAX analysis showed the basic elements present in VCM as well as the external morphology of Vishnu Chakara Mathirai. • The TLC and HPTLC finger printing is much helpful in identifying the active principle in VCM. • The drug VCM was found to the safe as the LD50 level was fall above 2000mg/kg.b.wt. • The NOEAL level was found to be > 200 mg/kg b.wt. • The subacute and subchronic toxicity study revealed no toxic effects in the animals. • Efficacy studies revealed good antiepileptic activity as it controls the maximum electro shock in rats, Picrotoxin induced seizures in mice, Picrotoxin induced kindling as well as seizures and N-Methyl-D-Aspartate (NMDA) test in mice. CONCLUSION: The present study was undertaken to establish the literature that Vishu Chakara Mathirai (VCM), a herbo mineral formulation of Siddha system of medicine, would be effectively used against epilepsy (Valippu Noi), through various animal models. The safety as well as efficacy of VCM was studied extensively using standard and recommended scientific techniques. The trial drug VCM was found to be both safe and effective in epilepsy among animal models. The findings are strongly supportive of the traditional claim and use of VCM as an anti-epleptic medicine. From this study findings, it is also recommended that the medicine VCM can be taken for further research in the form of pharmacokinetic and pharmacodynamic studies as well clinical trials among human subjects to further establish the finding of this study. RECOMMENDATIONS: As VCM shows very good anti epileptic activity in animal models, therefore it is recommended for a pharmacokinetic and pharmacodynamic study. The drug is also be recommended for a clinical trial in epileptic patients

Polymers pushing Polymers: Polymer Mixtures in Thermodynamic Equilibrium with a Pore

We investigate polymer partitioning from polymer mixtures into nanometer size cavities by formulating an equation of state for a binary polymer mixture assuming that only one (smaller) of the two polymer components can penetrate the cavity. Deriving the partitioning equilibrium equations and solving them numerically allows us to introduce the concept of "polymers-pushing-polymers" for the action of non-penetrating polymers on the partitioning of the penetrating polymers. Polymer partitioning into a pore even within a very simple model of a binary polymer mixture is shown to depend in a complicated way on the composition of the polymer mixture and/or the pore-penetration penalty. This can lead to enhanced as well as diminished partitioning, due to two separate energy scales that we analyse in detail.Comment: 10 pages, 6 figure

Microphase separation in polyelectrolytic diblock copolymer melt : weak segregation limit

We present a generalized theory of microphase separation for charged-neutral diblock copolymer melt. Stability limit of the disordered phase for salt-free melt has been calculated using Random Phase Approximation (RPA) and self-consistent field theory (SCFT). Explicit analytical free energy expressions for different classical ordered microstructures (lamellar, cylinder and sphere) are presented. We demonstrate that chemical mismatch required for the onset of microphase separation ($\chi^{\star} N$) in charged-neutral diblock melt is higher and the period of ordered microstructures is lower than those for the corresponding neutral-neutral diblock system. Theoretical predictions on the period of ordered structures in terms of Coulomb electrostatic interaction strength, chain length, block length, and the chemical mismatch between blocks are presented. SCFT has been used to go beyond the stability limit, where electrostatic potential and charge distribution are calculated self-consistently. Stability limits calculated using RPA are in perfect agreement with the corresponding SCFT calculations. Limiting laws for stability limit and the period of ordered structures are presented and comparisons are made with an earlier theory. Also, transition boundaries between different morphologies have been investigated

Efficient Set Sharing Using ZBDDs

Set sharing is an abstract domain in which each concrete object is represented by the set of local variables from which it might be reachable. It is a useful abstraction to detect parallelism opportunities, since it contains definite information about which variables do not share in memory, i.e., about when the memory regions reachable from those variables are disjoint. Set sharing is a more precise alternative to pair sharing, in which each domain element is a set of all pairs of local variables from which a common object may be reachable. However, the exponential complexity of some set sharing operations has limited its wider application. This work introduces an efficient implementation of the set sharing domain using Zero-suppressed Binary Decision Diagrams (ZBDDs). Because ZBDDs were designed to represent sets of combinations (i.e., sets of sets), they naturally represent elements of the set sharing domain. We show how to synthesize the operations needed in the set sharing transfer functions from basic ZBDD operations. For some of the operations, we devise custom ZBDD algorithms that perform better in practice. We also compare our implementation of the abstract domain with an efficient, compact, bit set-based alternative, and show that the ZBDD version scales better in terms of both memory usage and running time

Anomalous Dynamics of Forced Translocation

We consider the passage of long polymers of length N through a hole in a membrane. If the process is slow, it is in principle possible to focus on the dynamics of the number of monomers s on one side of the membrane, assuming that the two segments are in equilibrium. The dynamics of s(t) in such a limit would be diffusive, with a mean translocation time scaling as N^2 in the absence of a force, and proportional to N when a force is applied. We demonstrate that the assumption of equilibrium must break down for sufficiently long polymers (more easily when forced), and provide lower bounds for the translocation time by comparison to unimpeded motion of the polymer. These lower bounds exceed the time scales calculated on the basis of equilibrium, and point to anomalous (sub-diffusive) character of translocation dynamics. This is explicitly verified by numerical simulations of the unforced translocation of a self-avoiding polymer. Forced translocation times are shown to strongly depend on the method by which the force is applied. In particular, pulling the polymer by the end leads to much longer times than when a chemical potential difference is applied across the membrane. The bounds in these cases grow as N^2 and N^{1+\nu}, respectively, where \nu is the exponent that relates the scaling of the radius of gyration to N. Our simulations demonstrate that the actual translocation times scale in the same manner as the bounds, although influenced by strong finite size effects which persist even for the longest polymers that we considered (N=512).Comment: 13 pages, RevTeX4, 16 eps figure

What drives the translocation of stiff chains?

We study the dynamics of the passage of a stiff chain through a pore into a cell containing particles that bind reversibly to it. Using Brownian Molecular Dynamics simulations we investigate the mean-first-passage time as a function of the length of the chain inside, for different concentrations of binding particles. As a consequence of the interactions with these particles, the chain experiences a net force along its length whose calculated value from the simulations accounts for the velocity at which it enters the cell. This force can in turn be obtained from the solution of a generalized diffusion equation incorporating an effective Langmuir adsorption free energy for the chain plus binding particles. These results suggest a role of binding particles in the translocation process which is in general quite different from that of a Brownian ratchet. Furthermore, non-equilibrium effects contribute significantly to the dynamics, \emph{e.g.}, the chain often enters the cell faster than particle binding can be saturated, resulting in a force several times smaller than the equilibrium value.Comment: 7 pages, 4 figure

Electronic structure of strongly correlated d-wave superconductors

We study the electronic structure of a strongly correlated d-wave superconducting state. Combining a renormalized mean field theory with direct calculation of matrix elements, we obtain explicit analytical results for the nodal Fermi velocity, v_F, the Fermi wave vector, k_F, and the momentum distribution, n_k, as a function of hole doping in a Gutzwiller projected d-wave superconductor. We calculate the energy dispersion, E_k, and spectral weight of the Gutzwiller-Bogoliubov quasiparticles, and find that the spectral weight associated with the quasiparticle excitation at the antinodal point shows a non monotonic behavior as a function of doping. Results are compared to angle resolved photoemission spectroscopy (ARPES) of the high temperature superconductors.Comment: final version, comparison to experiments added, 4+ pages, 4 figure

Dynamics of a Suspension of Spheres and Rigid Polymers: Effect of Geometrical Mismatch

An effective medium approach together with a multiple scattering formalism is considered to study the steady-state dynamics of suspensions of spheres and rigid stiff polymer chains (Gaussian) without excluded volume interactions. The translational diffusion coefficients of the moving probe sphere and of the probe polymer chain, and the shear viscosity of the suspensions have been derived for finite volume fractions of spheres FSP and of polymers FPOL. The role of the geometrical parameter t=R_g/a ("a" is the radius of any sphere and R_g the radius of gyration of a polymer chain) is discussed. Dynamics of the probe objects is frozen when FPOL approaches 0.31. An optimum range of FSP that maximizes the difference in the diffusion coefficients of polymer chains characterized by distinct "t" values has been noticed.Comment: 30 pages, RevTex using multicol.sty (required), 21 Postscript figs. included using epsf.tex (required