1,364 research outputs found
Exact norm-conserving stochastic time-dependent Hartree-Fock
We derive an exact single-body decomposition of the time-dependent
Schroedinger equation for N pairwise-interacting fermions. Each fermion obeys a
stochastic time-dependent norm-preserving wave equation. As a first test of the
method we calculate the low energy spectrum of Helium. An extension of the
method to bosons is outlined.Comment: 21 pages, 3 figures, LaTeX fil
An experimental study of the sensitivity of helicopter rotor blade tracking to root pitch adjustment in hover
The sensitivity of blade tracking in hover to variations in root pitch was examined for two rotor configurations. Tests were conducted using a four bladed articulated rotor mounted on the NASA-Army aeroelastic rotor experimental system (ARES). Two rotor configurations were tested: one consisting of a blade set with flexible fiberglass spars and one with stiffer (by a factor of five in flapwise and torsional stiffnesses) aluminum spars. Both blade sets were identical in planform and airfoil distribution and were untwisted. The two configurations were ballasted to the same Lock number so that a direct comparison of the tracking sensitivity to a gross change in blade stiffness could be made. Experimental results show no large differences between the two sets of blades in the sensitivity of the blade tracking to root pitch adjustments. However, a measurable reduction in intrack coning of the fiberglass spar blades with respect to the aluminum blades is noted at higher rotor thrust conditions
Investigation of nanodispersion in polystyrene-montmorillonite nanocomposites by solid state NMR
Nanocomposites result from combinations of materials with vastly different properties in the nanometer scale. These materials exhibit many unique properties such as improved thermal stability, reduced flammability, and improved mechanical properties. Many of the properties associated with polymer–clay nanocomposites are a function of the extent of exfoliation of the individual clay sheets or the quality of the nanodispersion. This work demonstrates that solid-state NMR can be used to characterize, quantitatively, the nanodispersion of variously modified montmorillonite (MMT) clays in polystyrene (PS) matrices. The direct influence of the paramagnetic Fe3, embedded in the aluminosilicate layers of MMT, on polymer protons within about 1 nm from the clay surfaces creates relaxation sources, which, via spin diffusion, significantly shorten the overall proton longitudinal relaxation time (T1 H). Deoxygenated samples were used to avoid the particularly strong contribution to the T1 H of PS from paramagnetic molecular oxygen. We used T1 H as an indicator of the nanodispersion of the clay in PS. This approach correlated reasonably well with X-ray diffraction and transmission electron microscopy (TEM) data. A model for interpreting the saturation-recovery data is proposed such that two parameters relating to the dispersion can be extracted. The first parameter, f, is the fraction of the potentially available clay surface that has been transformed into polymer–clay interfaces. The second parameter is a relative measure of the homogeneity of the dispersion of these actual polymer–clay interfaces. Finally, a quick assay of T1 H is reported for samples equilibrated with atmospheric oxygen. Included are these samples as well as 28 PS/MMT nanocomposite samples prepared by extrusion. These measurements are related to the development of highthroughput characterization techniques. This approach gives qualitative indications about dispersion; however, the more time-consuming analysis, of a few deoxygenated samples from this latter set, offers significantly greater insight into the clay dispersion. A second, probably superior, rapid-analysis method, applicable to oxygen-containing samples, is also demonstrated that should yield a reasonable estimate of the f parameter. Thus, for PS/MMT nanocomposites, one has the choice of a less complete NMR assay of dispersion that is significantly faster than TEM analysis, versus a slower and more complete NMR analysis with sample times comparable to TEM, information rivaling that of TEM, and a substantial advantage that this is a bulk characterization method. © 2003 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 41: 3188–3213, 200
“some kind of thing it aint us but yet its in us”: David Mitchell, Russell Hoban, and metafiction after the millennium
This article appraises the debt that David Mitchell’s Cloud Atlas owes to the novels of Russell Hoban, including, but not limited to, Riddley Walker. After clearly mapping a history of Hoban’s philosophical perspectives and Mitchell’s inter-textual genre-impersonation practice, the article assesses the degree to which Mitchell’s metatextual methods indicate a nostalgia for by-gone radical aesthetics rather than reaching for new modes of its own. The article not only proposes several new backdrops against which Mitchell’s novel can be read but also conducts the first in-depth appraisal of Mitchell’s formal linguistic replication of Riddley Walker
Stochastic time-dependent current-density functional theory: a functional theory of open quantum systems
The dynamics of a many-body system coupled to an external environment
represents a fundamentally important problem. To this class of open quantum
systems pertains the study of energy transport and dissipation, dephasing,
quantum measurement and quantum information theory, phase transitions driven by
dissipative effects, etc. Here, we discuss in detail an extension of
time-dependent current-density-functional theory (TDCDFT), we named stochastic
TDCDFT [Phys. Rev. Lett. {\bf 98}, 226403 (2007)], that allows the description
of such problems from a microscopic point of view. We discuss the assumptions
of the theory, its relation to a density matrix formalism, and the limitations
of the latter in the present context. In addition, we describe a numerically
convenient way to solve the corresponding equations of motion, and apply this
theory to the dynamics of a 1D gas of excited bosons confined in a harmonic
potential and in contact with an external bath.Comment: 17 pages, 7 figures, RevTex4; few typos corrected, a figure modifie
Method of Fabricating a Composite Apparatus
A method for fabricating a piezoelectric macro-fiber composite actuator comprises making a piezoelectric fiber sheet by providing a plurality of wafers of piezoelectric material, bonding the wafers together with an adhesive material to from a stack of alternating layers of piezoelectric material and adhesive material, and cutting through the stack in a direction substantially parallel to the thickness of the stack and across the alternating layers of piezoelectric material and adhesive material to provide at least one piezoelectric fiber sheet having two sides comprising a plurality of piezoelectric fibers in juxtaposition to the adhesive material. The method further comprises bonding two electrically conductive films to the two sides of the piezoelectric fiber sheet. At least one conductive film has first and second conductive patterns formed thereon which are electrically isolated from one another and in electrical contact with the piezoelectric fiber sheet
Suppression of decoherence via strong intra-environmental coupling
We examine the effects of intra-environmental coupling on decoherence by
constructing a low temperature spin--spin-bath model of an atomic impurity in a
Debye crystal. The impurity interacts with phonons of the crystal through
anti-ferromagnetic spin-spin interactions. The reduced density matrix of the
central spin representing the impurity is calculated by dynamically integrating
the full Schroedinger equation for the spin--spin-bath model for different
thermally weighted eigenstates of the spin-bath. Exact numerical results show
that increasing the intra-environmental coupling results in suppression of
decoherence. This effect could play an important role in the construction of
solid state quantum devices such as quantum computers.Comment: 4 pages, 3 figures, Revtex fil
Wind-Tunnel Evaluation of the Effect of Blade Nonstructural Mass Distribution on Helicopter Fixed-System Loads
This report provides data obtained during a wind-tunnel test conducted to investigate parametrically the effect of blade nonstructural mass on helicopter fixed-system vibratory loads. The data were obtained with aeroelastically scaled model rotor blades that allowed for the addition of concentrated nonstructural masses at multiple locations along the blade radius. Testing was conducted for advance ratios ranging from 0.10 to 0.35 for 10 blade-mass configurations. Three thrust levels were obtained at representative full-scale shaft angles for each blade-mass configuration. This report provides the fixed-system forces and moments measured during testing. The comprehensive database obtained is well-suited for use in correlation and development of advanced rotorcraft analyses
Cross-Sectional Analysis of Nonhomogeneous Anisotropic Active Slender Structures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76969/1/AIAA-12451-957.pd
Topological complexity of the relative closure of a semi-Pfaffian couple
Gabrielov introduced the notion of relative closure of a Pfaffian couple as
an alternative construction of the o-minimal structure generated by
Khovanskii's Pfaffian functions. In this paper, use the notion of format (or
complexity) of a Pfaffian couple to derive explicit upper-bounds for the
homology of its relative closure.
Keywords: Pfaffian functions, fewnomials, o-minimal structures, Betti
numbers.Comment: 12 pages, 1 figure. v3: Proofs and bounds have been slightly improve
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