4,104 research outputs found
Investigation of sterilization of secondary batteries Final report, Oct. 26, 1965 - Jun. 26, 1966
Thermally sterilized nickel cadmium battery developmen
Investigation of sterilization of secondary batteries Quarterly progress report no. 1, Oct. 26, 1965 - Jan. 26, 1966
Asbestos and polypropylene separators for nickel-cadmium cells which are sterilize
A fast immersed boundary method for external incompressible viscous flows using lattice Green's functions
A new parallel, computationally efficient immersed boundary method for
solving three-dimensional, viscous, incompressible flows on unbounded domains
is presented. Immersed surfaces with prescribed motions are generated using the
interpolation and regularization operators obtained from the discrete delta
function approach of the original (Peskin's) immersed boundary method. Unlike
Peskin's method, boundary forces are regarded as Lagrange multipliers that are
used to satisfy the no-slip condition. The incompressible Navier-Stokes
equations are discretized on an unbounded staggered Cartesian grid and are
solved in a finite number of operations using lattice Green's function
techniques. These techniques are used to automatically enforce the natural
free-space boundary conditions and to implement a novel block-wise adaptive
grid that significantly reduces the run-time cost of solutions by limiting
operations to grid cells in the immediate vicinity and near-wake region of the
immersed surface. These techniques also enable the construction of practical
discrete viscous integrating factors that are used in combination with
specialized half-explicit Runge-Kutta schemes to accurately and efficiently
solve the differential algebraic equations describing the discrete momentum
equation, incompressibility constraint, and no-slip constraint. Linear systems
of equations resulting from the time integration scheme are efficiently solved
using an approximation-free nested projection technique. The algebraic
properties of the discrete operators are used to reduce projection steps to
simple discrete elliptic problems, e.g. discrete Poisson problems, that are
compatible with recent parallel fast multipole methods for difference
equations. Numerical experiments on low-aspect-ratio flat plates and spheres at
Reynolds numbers up to 3,700 are used to verify the accuracy and physical
fidelity of the formulation.Comment: 32 pages, 9 figures; preprint submitted to Journal of Computational
Physic
Dynamic Factors in the Presence of Block Structure
Macroeconometric data often come under the form of large panels of time series, themselves decomposing into smaller but still quite large subpanels or blocks. We show how the dynamic factor analysis method proposed in Forni et al (2000), combined with the identification method of Hallin and Liska (2007), allows for identifying and estimating joint and block-specific common factors. This leads to a more sophisticated analysis of the structures of dynamic interrelations within and between the blocks in such datasets, along with an informative decomposition of explained variances. The method is illustrated with an analysis of the Industrial Production Index data for France, Germany, and Italy.Panel data; Time series; High dimensional data; Dynamic factor model; Business cycle; Block specific factors; Dynamic principal components; Information criterion.
Spinning probes and helices in AdS
We study extremal curves associated with a functional which is linear in the
curve's torsion. The functional in question is known to capture the properties
of entanglement entropy for two-dimensional conformal field theories with
chiral anomalies and has potential applications in elucidating the equilibrium
shape of elastic linear structures. We derive the equations that determine the
shape of its extremal curves in general ambient spaces in terms of geometric
quantities. We show that the solutions to these shape equations correspond to a
three-dimensional version of Mathisson's helical motions for the centers of
mass of spinning probes. Thereafter, we focus on the case of maximally
symmetric spaces, where solutions correspond to cylindrical helices and find
that the Lancret ratio of these equals the relative speed between the
Mathisson-Pirani and the Tulczyjew-Dixon observers. Finally, we construct all
possible helical motions in three-dimensional manifolds with constant negative
curvature. In particular, we discover a rich space of helices in AdS which
we explore in detail.Comment: 28 pages, 5 figure
Accurate computation of surface stresses and forces with immersed boundary methods
Many immersed boundary methods solve for surface stresses that impose the
velocity boundary conditions on an immersed body. These surface stresses may
contain spurious oscillations that make them ill-suited for representing the
physical surface stresses on the body. Moreover, these inaccurate stresses
often lead to unphysical oscillations in the history of integrated surface
forces such as the coefficient of lift. While the errors in the surface
stresses and forces do not necessarily affect the convergence of the velocity
field, it is desirable, especially in fluid-structure interaction problems, to
obtain smooth and convergent stress distributions on the surface. To this end,
we show that the equation for the surface stresses is an integral equation of
the first kind whose ill-posedness is the source of spurious oscillations in
the stresses. We also demonstrate that for sufficiently smooth delta functions,
the oscillations may be filtered out to obtain physically accurate surface
stresses. The filtering is applied as a post-processing procedure, so that the
convergence of the velocity field is unaffected. We demonstrate the efficacy of
the method by computing stresses and forces that converge to the physical
stresses and forces for several test problems
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