18,587 research outputs found
Hydrostatic pressure transducers of carbon and ytterbium Final report
Hydrostatic pressure coefficients of electrical resistivity for carbon and ytterbium pressure transducer
Renormalization of Drift and Diffusivity in Random Gradient Flows
We investigate the relationship between the effective diffusivity and
effective drift of a particle moving in a random medium. The velocity of the
particle combines a white noise diffusion process with a local drift term that
depends linearly on the gradient of a gaussian random field with homogeneous
statistics. The theoretical analysis is confirmed by numerical simulation. For
the purely isotropic case the simulation, which measures the effective drift
directly in a constant gradient background field, confirms the result
previously obtained theoretically, that the effective diffusivity and effective
drift are renormalized by the same factor from their local values. For this
isotropic case we provide an intuitive explanation, based on a {\it spatial}
average of local drift, for the renormalization of the effective drift
parameter relative to its local value. We also investigate situations in which
the isotropy is broken by the tensorial relationship of the local drift to the
gradient of the random field. We find that the numerical simulation confirms a
relatively simple renormalization group calculation for the effective
diffusivity and drift tensors.Comment: Latex 16 pages, 5 figures ep
Design, development, and fabrication of a prototype ice pack heat sink subsystem. Flight experiment physical phenomena experiment chest
The concept of a flight experiment physical phenomena experiment chest, to be used eventually for investigating and demonstrating ice pack heat sink subsystem physical phenomena during a zero gravity flight experiment, is described
High-spin intruder states in the fp shell nuclei and isoscalar proton-neutron correlations
We perform a systematic shell-model and mean-field study of fully-aligned,
high-spin f_{7/2}^{n} seniority isomers and d_{3/2}^{-1} f_{7/2}^{n+1} intruder
states in the A~44 nuclei from the lower-fp shell. The shell-model calculations
are performed in the full sdfp configuration space allowing 1p-1h cross-shell
excitations. The self-consistent mean-field calculations are based on the
Hartree-Fock approach with the Skyrme energy density functional that reproduces
empirical Landau parameters. While there is a nice agreement between
experimental and theoretical relative energies of fully-aligned states in N>Z
nuclei, this is no longer the case for the N=Z systems. The remaining deviation
from the data is attributed to the isoscalar proton-neutron correlations. It is
also demonstrated that the Coulomb corrections at high spins noticeably depend
on the choice of the energy density functional.Comment: 4 pages. submitted to Phys. Rev. Let
Correlation of finite-element structural dynamic analysis with measured free vibration characteristics for a full-scale helicopter fuselage
The correlation achieved with each program provides the material for a discussion of modeling techniques developed for general application to finite-element dynamic analyses of helicopter airframes. Included are the selection of static and dynamic degrees of freedom, cockpit structural modeling, and the extent of flexible-frame modeling in the transmission support region and in the vicinity of large cut-outs. The sensitivity of predicted results to these modeling assumptions are discussed. Both the Sikorsky Finite-Element Airframe Vibration analysis Program (FRAN/Vibration Analysis) and the NASA Structural Analysis Program (NASTRAN) have been correlated with data taken in full-scale vibration tests of a modified CH-53A helicopter
Some observations on the renormalization of membrane rigidity by long-range interactions
We consider the renormalization of the bending and Gaussian rigidity of model
membranes induced by long-range interactions between the components making up
the membrane. In particular we analyze the effect of a finite membrane
thickness on the renormalization of the bending and Gaussian rigidity by
long-range interactions. Particular attention is paid to the case where the
interactions are of a van der Waals type.Comment: 11 pages RexTex, no figure
Perturbation theory for the effective diffusion constant in a medium of random scatterer
We develop perturbation theory and physically motivated resummations of the
perturbation theory for the problem of a tracer particle diffusing in a random
media. The random media contains point scatterers of density uniformly
distributed through out the material. The tracer is a Langevin particle
subjected to the quenched random force generated by the scatterers. Via our
perturbative analysis we determine when the random potential can be
approximated by a Gaussian random potential. We also develop a self-similar
renormalisation group approach based on thinning out the scatterers, this
scheme is similar to that used with success for diffusion in Gaussian random
potentials and agrees with known exact results. To assess the accuracy of this
approximation scheme its predictions are confronted with results obtained by
numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style
The Cretaceous-Tertiary boundary marine extinction and global primary productivity collapse
The extinction of marine phyto-and zoo-plankton across the K-T boundary has been well documented. Such an event may have resulted in decreased photosynthetic fixation of carbon in surface waters and a collapse of the food chain in the marine biosphere. Because the vertical and horizontal distribution of the carbon isotopic composition of total dissolved carton (TDC) in the modern ocean is controlled by the transfer of organic carbon from the surface to deep reservoirs, it follows that a major disruption of the marine biosphere would have had a major effect on the distribution of carbon isotopes in the ocean. Negative carbon isotope excursions have been identified at many marine K-T boundary sequences worldwide and are interpreted as a signal of decreased oceanic primary productivity. However, the magnitude, duration and consequences of this productivity crisis have been poorly constrained. On the basis of planktonic and benthic calcareous microfossil carbon isotope and other geochemical data from DSDP Site 577 located on the Shatsky Rise in the north-central Pacific, as well as other sites, researchers have been able to provide a reasonable estimate of the duration and magnitude of this event
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