Self-diffusion in sheared suspensions by dynamic simulation

The behaviour of the long-time self-diffusion tensor in concentrated colloidal dispersions is studied using dynamic simulation. The simulations are of a suspension of monodisperse Brownian hard spheres in simple shear flow as a function of the Péclet number, Pe, which measures the relative importance of shear and Brownian forces, and the volume fraction, [phi]. Here, Pe = &[gamma]dot;a^2/D0, where &[gamma]dot; is the shear rate, a the particle size and D0 = kT/6[pi][eta]a is the Stokes–Einstein diffusivity of an isolated particle of size a with thermal energy kT in a solvent of viscosity [eta]. Two simulations algorithms are used: Stokesian Dynamics for inclusion of the many-body hydrodynamic interactions, and Brownian Dynamics for suspensions without hydrodynamic interactions. A new procedure for obtaining high-quality diffusion data based on averaging the results of many short simulations is presented and utilized. At low shear rates, low Pe, Brownian diffusion due to a random walk process dominates and the characteristic scale for diffusion is the Stokes–Einstein diffusivity, D0. At zero Pe the diffusivity is found to be a decreasing function of [phi]. As Pe is slowly increased, O(Pe) and O(Pe^3/2) corrections to the diffusivity due to the flow are clearly seen in the Brownian Dynamics system in agreement with the theoretical results of Morris & Brady (1996). At large shear rates, large Pe, both systems exhibit diffusivities that grow linearly with the shear rate by the non-Brownian mechanism of shear-induced diffusion. In contrast to the behaviour at low Pe, this shear-induced diffusion mode is an increasing function of [phi]. Long-time rotational self-diffusivities are of interest in the Stokesian Dynamics system and show similar behaviour to their translational analogues. An off-diagonal long-time self-diffusivity, Dxy, is reported for both systems. Results for both the translational and rotational Dxy show a sign change from low Pe to high Pe due to different mechanisms in the two regimes. A physical explanation for the off-diagonal diffusivities is proposed

Structure, diffusion and rheology of Brownian suspensions by Stokesian Dynamics simulation

The non-equilibrium behaviour of concentrated colloidal dispersions is studied using Stokesian Dynamics, a molecular-dynamics-like simulation technique for analysing suspensions of particles immersed in a Newtonian fluid. The simulations are of a monodisperse suspension of Brownian hard spheres in simple shear flow as a function of the Péclet number, Pe, which measures the relative importance of hydrodynamic and Brownian forces, over a range of volume fraction 0.316 [less-than-or-eq, slant] [phi] [less-than-or-eq, slant] 0.49. For Pe < 10, Brownian motion dominates the behaviour, the suspension remains well-dispersed, and the viscosity shear thins. The first normal stress difference is positive and the second negative. At higher Pe, hydrodynamics dominate resulting in an increase in the long-time self-diffusivity and the viscosity. The first normal stress difference changes sign when hydrodynamics dominate. Simulation results are shown to agree well with both theory and experiment

Trade Studies Relating to a Long Range Mach 2.6 Supercruiser

A systems study was conducted on an aircraft concept, representative of a supersonic-cruise military aircraft (supercruiser). The study results indicate that supersonic ranges in excess of 4000 n.mi. at a Mach number of 2.62 are possible with a 500 lbf class aircraft. Trade studies, to determine the sensitivity of supersonic range to parameters which would improve maneuverability, indicate that thrust-weight ratios of as much as 0.5 can be used without significantly decreasing supersonic range; however, increasing the thrust-weight ratio to 1.0 decreases the range capability by about 1100 n.mi. The range penalty for increasing the aircraft limit load-factor from 4.0 to 9.0 is about 500 n.mi. The increased fuel volume of several configurations improved the supersonic range capability by about 1200 n.mi. but, due to associated losses in supersonic L/D, had an insignificant effect on the range at a Mach number of 2.62

On output feedback nonlinear model predictive control using high gain observers for a class of systems

In recent years, nonlinear model predictive control schemes have been derived that guarantee stability of the closed loop under the assumption of full state information. However, only limited advances have been made with respect to output feedback in connection to nonlinear predictive control. Most of the existing approaches for output feedback nonlinear model predictive control do only guarantee local stability. Here we consider the combination of stabilizing instantaneous NMPC schemes with high gain observers. For a special MIMO system class we show that the closed loop is asymptotically stable, and that the output feedback NMPC scheme recovers the performance of the state feedback in the sense that the region of attraction and the trajectories of the state feedback scheme are recovered for a high gain observer with large enough gain and thus leading to semi-global/non-local results

Bulk Milk Hauling Costs in the Sioux Valley Milkshed

Bulk handling of milk is a recent development in milk transportation. It is important to know the current cost data of transporting bulk milk. Cost structure is the important supply factor in determining hauling rates. Distance and volume are two important factors, but more detailed data are required to better determine the actual costs. The objective of this study was to determine the cost per hundredweight for transporting bulk milk from farm to plant within the Sioux Valley Milk Producers Association milk shed. The attainment of this objective involved the collection, classification, and analysis of several categories of data. Thus, it was necessary to: (1) determine the Grade A milk production within the milk shed; (2) determine the miles traveled by truckers in assembling the milk, (3) determine the time requirements for assembling the milk, and (4) determine the operating costs associated with assembling the milk. For purposes of data collection, the Sioux Valley Milk Producers Association provided the Grade A bulk production records along with records of routes, pickups, and loads. They also provided a detailed map showing the exact location of each product. Information on cost data was obtained by a study of relevant literature, along with interviews of business people

Design and Development of a SNAP-8 Mercury Pump Motor Assembly

Design and performance of mercury pump motor for SNAP 8 electrical generato

Single-Molecule Junction Conductance through Diaminoacenes

The study of electron transport through single molecules is essential to the development of molecular electronics. Indeed, trends in electronic conductance through organic nanowires have emerged with the increasing reliability of electron transport measurements at the single-molecule level. Experimental and theoretical work has shown that tunneling distance, HOMO-LUMO gap and molecular conformation influence electron transport in both saturated and pi-conjugated nanowires. However, there is relatively little experimental data on electron transport through fused aromatic rings. Here we show using diaminoacenes that conductivity depends not only on the number of fused aromatic rings in the molecule, which defines the molecular HOMO-LUMO gap, but also on the position of the amino groups on the rings. Specifically, we find that conductance is highest with minimal disruption of aromaticity in fused aromatic nanowires.Comment: 2 pages, 3 figure

Laser-free trapped ion entangling gates with AESE: Adiabatic Elimination of Spin-motion Entanglement

We discuss a laser-free, two-qubit geometric phase gate technique for generating high-fidelity entanglement between two trapped ions. The scheme works by ramping the spin-dependent force on and off slowly relative to the gate detunings, which adiabatically eliminates the spin-motion entanglement (AESE). We show how gates performed with AESE can eliminate spin-motion entanglement with multiple modes simultaneously, without having to specifically tune the control field detunings. This is because the spin-motion entanglement is suppressed by operating the control fields in a certain parametric limit, rather than by engineering an optimized control sequence. We also discuss physical implementations that use either electronic or ferromagnetic magnetic field gradients. In the latter, we show how to ``AESE" the system by smoothly turning on the \textit{effective} spin-dependent force by shelving from a magnetic field insensitive state to a magnetic field sensitive state slowly relative to the gate mode frequencies. We show how to do this with a Rabi or adiabatic rapid passage transition. Finally, we show how gating with AESE significantly decreases the gate's sensitivity to common sources of motional decoherence, making it easier to perform high-fidelity gates at Doppler temperatures