1,163 research outputs found
Investigation of Skylab imagery for regional planning
There are no author-identified significant results in this report
Investigation of Skylab imagery for regional planning
There are no author-identified significant results in this report
Interplay between microdynamics and macrorheology in vesicle suspensions
The microscopic dynamics of objects suspended in a fluid determines the
macroscopic rheology of a suspension. For example, as shown by Danker and
Misbah [Phys. Rev. Lett. {\bf 98}, 088104 (2007)], the viscosity of a dilute
suspension of fluid-filled vesicles is a non-monotonic function of the
viscosity contrast (the ratio between the viscosities of the internal
encapsulated and the external suspending fluids) and exhibits a minimum at the
critical point of the tank-treading-to-tumbling transition. By performing
numerical simulations, we recover this effect and demonstrate that it persists
for a wide range of vesicle parameters such as the concentration, membrane
deformability, or swelling degree. We also explain why other numerical and
experimental studies lead to contradicting results. Furthermore, our
simulations show that this effect even persists in non-dilute and confined
suspensions, but that it becomes less pronounced at higher concentrations and
for more swollen vesicles. For dense suspensions and for spherical (circular in
2D) vesicles, the intrinsic viscosity tends to depend weakly on the viscosity
contrast.Comment: 9 pages, 9 figures, to appear in Soft Matter (2014
Investigation of Satellite Imagery for Regional Planning
The author has identified the following significant results. Satellite multispectral imagery was found to be useful in regional planning for depicting general developed land patterns, wooded areas, and newly constructed highways by using visual photointerpretation methods. Other characteristics, such as residential and nonresidential development, street patterns, development density, and some vacant land components cannot be adequately detected using these standard methods
Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases: lattice-Boltzmann simulations
We report on the stress response of gyroidal and lamellar amphiphilic
mesophases to steady shear simulated using a bottom-up lattice-Boltzmann model
for amphiphilic fluids and sliding periodic (Lees-Edwards) boundary conditions.
We study the gyroid per se (above the sponge-gyroid transition, of high
crystallinity) and the molten gyroid (within such a transition, of
shorter-range order). We find that both mesophases exhibit shear-thinning, more
pronounced and at lower strain rates for the molten gyroid. At late times after
the onset of shear, the skeleton of the crystalline gyroid becomes a structure
of interconnected irregular tubes and toroidal rings, mostly oriented along the
velocity ramp imposed by the shear, in contradistinction with free-energy
Langevin-diffusion studies which yield a much simpler structure of disentangled
tubes. We also compare the shear stress and deformation of lamellar mesophases
with and without amphiphile when subjected to the same shear flow applied
normal to the lamellae. We find that the presence of amphiphile allows (a) the
shear stress at late times to be higher than in the case without amphiphile,
and (b) the formation of rich patterns on the sheared interface, characterised
by alternating regions of high and low curvature.Comment: 15 pages, 10 figures, Physical Review E, in pres
Penning traps with unitary architecture for storage of highly charged ions
Penning traps are made extremely compact by embedding rare-earth permanent
magnets in the electrode structure. Axially-oriented NdFeB magnets are used in
unitary architectures that couple the electric and magnetic components into an
integrated structure. We have constructed a two- magnet Penning trap with
radial access to enable the use of laser or atomic beams, as well as the
collection of light. An experimental apparatus equipped with ion optics is
installed at the NIST electron beam ion trap (EBIT) facility, constrained to
fit within 1 meter at the end of a horizontal beamline for transporting highly
charged ions. Highly charged ions of neon and argon, extracted with initial
energies up to 4000 eV per unit charge, are captured and stored to study the
confinement properties of a one-magnet trap and a two-magnet trap. Design
considerations and some test results are discussed
Two-dimensional Vesicle dynamics under shear flow: effect of confinement
Dynamics of a single vesicle under shear flow between two parallel plates is
studied using two-dimensional lattice-Boltzmann simulations. We first present
how we adapted the lattice-Boltzmann method to simulate vesicle dynamics, using
an approach known from the immersed boundary method. The fluid flow is computed
on an Eulerian regular fixed mesh while the location of the vesicle membrane is
tracked by a Lagrangian moving mesh. As benchmarking tests, the known vesicle
equilibrium shapes in a fluid at rest are found and the dynamical behavior of a
vesicle under simple shear flow is being reproduced. Further, we focus on
investigating the effect of the confinement on the dynamics, a question that
has received little attention so far. In particular, we study how the vesicle
steady inclination angle in the tank-treading regime depends on the degree of
confinement. The influence of the confinement on the effective viscosity of the
composite fluid is also analyzed. At a given reduced volume (the swelling
degree) of a vesicle we find that both the inclination angle, and the membrane
tank-treading velocity decrease with increasing confinement. At sufficiently
large degree of confinement the tank-treading velocity exhibits a
non-monotonous dependence on the reduced volume and the effective viscosity
shows a nonlinear behavior.Comment: 12 pages, 8 figure
A simplified particulate model for coarse-grained hemodynamics simulations
Human blood flow is a multi-scale problem: in first approximation, blood is a
dense suspension of plasma and deformable red cells. Physiological vessel
diameters range from about one to thousands of cell radii. Current
computational models either involve a homogeneous fluid and cannot track
particulate effects or describe a relatively small number of cells with high
resolution, but are incapable to reach relevant time and length scales. Our
approach is to simplify much further than existing particulate models. We
combine well established methods from other areas of physics in order to find
the essential ingredients for a minimalist description that still recovers
hemorheology. These ingredients are a lattice Boltzmann method describing rigid
particle suspensions to account for hydrodynamic long range interactions
and---in order to describe the more complex short-range behavior of
cells---anisotropic model potentials known from molecular dynamics simulations.
Paying detailedness, we achieve an efficient and scalable implementation which
is crucial for our ultimate goal: establishing a link between the collective
behavior of millions of cells and the macroscopic properties of blood in
realistic flow situations. In this paper we present our model and demonstrate
its applicability to conditions typical for the microvasculature.Comment: 12 pages, 11 figure
A Stability Diagram for Dense Suspensions of Model Colloidal Al2O3-Particles in Shear Flow
In Al2O3 suspensions, depending on the experimental conditions very different
microstructures can be found, comprising fluid like suspensions, a repulsive
structure, and a clustered microstructure. For technical processing in
ceramics, the knowledge of the microstructure is of importance, since it
essentially determines the stability of a workpiece to be produced. To
enlighten this topic, we investigate these suspensions under shear by means of
simulations. We observe cluster formation on two different length scales: the
distance of nearest neighbors and on the length scale of the system size. We
find that the clustering behavior does not depend on the length scale of
observation. If inter-particle interactions are not attractive the particles
form layers in the shear flow. The results are summarized in a stability
diagram.Comment: 15 pages, 10 figures, revised versio
An Adaptive, Kink-Based Approach to Path Integral Calculations
A kink-based expression for the canonical partition function is developed
using Feynman's path integral formulation of quantum mechanics and a discrete
basis set. The approach is exact for a complete set of states. The method is
tested on the 3x3 Hubbard model and overcomes the sign problem seen in
traditional path integral studies of fermion systems. Kinks correspond to
transitions between different N-electron states, much in the same manner as
occurs in configuration interaction calculations in standard ab initio methods.
The different N-electron states are updated, based on which states occur
frequently during a Monte Carlo simulation, giving better estimates of the true
eigenstates of the Hamiltonian.Comment: 24 pages, to be published in J. Chem. Phy
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