Biomedical subjects

Turab Lookman

Publications and source records attributed to Turab Lookman.

6 recordsLinked to original sources

PubMed2006

Hydrodynamic self-consistent field theory for inhomogeneous polymer melts.

We introduce a mesoscale technique for simulating the structure and rheology of block-copolymer melts and blends in hydrodynamic flows. The technique couples dynamic self-consistent field theory with continuum hydrodynamics and flow penalization to simulate polymeric fluid flows in channels of arbitrary geometry. We demonstrate the method by studying phase separation of an ABC triblock copolymer melt in a submicron channel with neutral wall wetting conditions. We find that surface wetting effects and shear effects compete, producing wall-perpendicular lamellae in the absence of flow and wall-parallel lamellae in cases where the shear rate exceeds some critical Weissenberg number.

Journal Article↗

PubMed2005

Role of solvent for globular proteins in solution.

The properties of the solvent affect the behavior of the solution. We propose a model that accounts for the contribution of the solvent free energy to the free energy of globular proteins in solution. For the case of an attractive square-well potential, we obtain an exact mapping of the phase diagram of this model without solvent to the model that includes the solute-solvent contribution. In particular we find for appropriate choices of parameters upper critical points, lower critical points, and even closed loops with both upper and lower critical points similar to those found before [Macromolecules 36, 5843 (2003)]. In the general case of systems whose interactions are not attractive square wells, this mapping procedure can be a first approximation to understand the phase diagram in the presence of solvent. We also present simulation results for both the square-well model and a modified Lennard-Jones model.

Computer Simulation↗

PubMed2004

Viscoelastic properties of dynamically asymmetric binary fluids under shear flow.

We study theoretically the viscoelastic properties of sheared binary fluids that have strong dynamical asymmetry between the two components. The dynamical asymmetry arises due to asymmetry between the viscoelastic stresses, particularly the bulk stress. Our calculations are based on the two-fluid model that incorporates the asymmetric stress distribution. We simulate the phase separation process under an externally imposed shear and compare the asymmetric case with the usual phase separation under shear flow without viscoelastic effects. We also simulate the behavior of phase-separated stable morphologies under applied shear and compute the stress relaxation.

Journal Article↗

PubMed2004

Glassy behavior in systems with Kac-type step-function interaction.

We study a system with a weak, long-ranged repulsive Kac-type step-function interaction within the framework of a replicated effective phi(4) theory. The occurrence of extensive configurational entropy or an exponentially large number of metastable minima in the free energy (characteristic of a glassy state), is demonstrated. The underlying mechanism of mesoscopic patterning and defect organizations is discussed.

Journal Article↗

PubMed2003

Elastic deformation of polycrystals.

We propose a framework to model elastic properties of polycrystals by coupling crystal orientational degrees of freedom with elastic strains. Our model encodes crystal symmetries and takes into account explicitly the strain compatibility induced long-range interaction between grains. The coupling of crystal orientation and elastic interactions allows for the rotation of individual grains by an external load. We apply the model to simulate uniaxial tensile loading of a 2D polycrystal within linear elasticity and a system with elastic anharmonicities that describe structural phase transformations. We investigate the constitutive response of the polycrystal and compare it to that of single crystals with crystallographic orientations that form the polycrystal.

Journal Article↗

PubMed2002

Steps towards improving the security of chaotic encryption.

We present a method in which a chaotic signal is used to mask a message securely. It depends on separating the two tasks of synchronizing the chaotic oscillators and encrypting the message. A sporadic drive together with a function f of the ciphertext and response system variables is used to make extraction difficult. We give a choice of f that makes the method similar to a one-time pad, with pseudorandom numbers provided by the chaos.

Journal Article↗