Intermediate scattering functions of a rigid body monoclonal antibody protein in solution studied by dissipative particle dynamic simulation.

In the past decade, there was increased research interest in studying internal motions of flexible proteins in solution using Neutron Spin Echo (NSE) as NSE can simultaneously probe the dynamics at the length and time scales comparable to protein domain motions. However, the collective intermediate scattering function (ISF) measured by NSE has the contributions from translational, rotational, and internal motions, which are rather complicated to be separated. Widely used NSE theories to interpret experimental data usually assume that the translational and rotational motions of a rigid particle are decoupled and independent to each other.

Contact and stress anisotropies in start-up flow of colloidal suspensions.

Spatiotemporal correlations in start-up flows of attractive colloids are explored by numerical simulations as a function of their volume fraction and shear rate. The suspension is first allowed to flocculate during a time tw, then the stress necessary to induce its flow is computed. We find that, at low volume fractions, the stress is a universal function of the strain.

A comparison of viscosity-concentration relationships for emulsions.

Differential effective medium theory (D-EMT) has been used by a number of investigators to derive expressions for the shear viscosity of a colloidal suspension or an emulsion as a function of the volume fraction of the dispersed phase. Pal and Rhodes [R. Pal, E.

Cross-property correlations and permeability estimation in sandstone.

We computationally investigate cross-property correlations linking fluid permeability to conductive properties in sedimentary rock for a number of pore size parameters based on three-dimensional digitized rock images. In particular, we focus on correlations based on the pore volume-to-surface-area ratio (V(p)/S), a critical channel diameter (c) associated with mercury porosimetry measurements, length scales associated with the nuclear magnetic resonance relaxation time T2, as well as the mean survival time (tau). Differences between the length scales are discussed.

Breakup of a fluid thread in a confined geometry: droplet-plug transition, perturbation sensitivity, and kinetic stabilization with confinement.

We investigate the influence of geometrical confinement on the breakup of long fluid threads in the absence of imposed flow using a lattice Boltzmann model. Our simulations primarily focus on the case of threads centered coaxially in a tube filled with another Newtonian fluid and subjected to both impulsive and random perturbations. We observe a significant slowing down of the rate of thread breakup ("kinetic stabilization") over a wide range of the confinement, Lambda= R(tube)/R(thread) < or =10 and find that the relative surface energies of the liquid components influence this effect.

Relating Fresh Concrete Viscosity Measurements from Different Rheometers.

Concrete rheological properties need to be properly measured and predicted in order to characterize the workability of fresh concrete, including special concretes such as self-consolidating concrete (SCC). It was shown by a round-robin test held in 2000 [1,2] that different rheometer designs gave different values of viscosity for the same concrete. While empirical correlation between different rheometers was possible, for a procedure that is supposed to "scientifically" improve on the empirical slump tests, this situation is unsatisfactory.

Accelerating Scientific Discovery Through Computation and Visualization II.

This is the second in a series of articles describing a wide variety of projects at NIST that synergistically combine physical science and information science. It describes, through examples, how the Scientific Applications and Visualization Group (SAVG) at NIST has utilized high performance parallel computing, visualization, and machine learning to accelerate research. The examples include scientific collaborations in the following areas: (1) High Precision Energies for few electron atomic systems, (2) Flows of suspensions, (3) X-ray absorption, (4) Molecular dynamics of fluids, (5) Nanostructures, (6) Dendritic growth in alloys, (7) Screen saver science, (8) genetic programming.