12,193 research outputs found
Developmental design, fabrication, and test of acoustic suppressors for fans of high bypass turbofan engines
An analysis procedure was developed for design of acoustically treated nacelles for high bypass turbofan engines. The plan was applied to the conceptual design of a nacelle for the quiet engine typical of a 707/DC-8 airplane installation. The resultant design was modified to a test nacelle design for the NASA Lewis quiet fan. The acoustic design goal was a 10 db reduction in effective perceived fan noise levels during takoff and approach. Detailed nacelle designs were subsequently developed for both the quiet engine and the quiet fan. The acoustic design goal for each nacelle was 15 db reductions in perceived fan noise levels from the inlet and fan duct. Acoustically treated nacelles were fabricated for the quiet engine and quiet fan for testing. Performance of selected inlet and fan duct lining configurations was experimentally evaluated in a flow duct. Results of the tests show that the linings perform as designed
Quantum Evaporation from Superfluid Helium at Normal Incidence
We study the scattering of atoms, rotons and phonons at the free surface of
He at normal incidence and calculate the evaporation, condensation and
reflection probabilities. Assuming elastic one-to-one processes and using
general properties of the scattering matrix, such as unitarity and time
reversal, we argue that all nonzero probabilities can be written in terms of a
single energy-dependent parameter. Quantitative predictions are obtained using
linearized time dependent density functional theory.Comment: 12 pages, REVTeX, 2 postscript figures, available also at
http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
Pressure of thermal excitations in superfluid helium
We find the pressure, due to the thermal excitations of superfluid helium, at
the interface with a solid. The separate contributions of phonons, rotons
and rotons are derived. The pressure due to rotons is shown to be
negative and partially compensates the positive contribution of rotons,
so the total roton pressure is positive but several times less than the
separate and roton contributions. The pressure of the quasiparticle
gas is shown to account for the fountain effect in . An experiment is
proposed to observe the negative pressure due to rotons.Comment: 14 pages, 4 figure
The resonance spectrum of the cusp map in the space of analytic functions
We prove that the Frobenius--Perron operator of the cusp map
, (which is an approximation of the
Poincar\'e section of the Lorenz attractor) has no analytic eigenfunctions
corresponding to eigenvalues different from 0 and 1. We also prove that for any
the spectrum of in the Hardy space in the disk
\{z\in\C:|z-q|<1+q\} is the union of the segment and some finite or
countably infinite set of isolated eigenvalues of finite multiplicity.Comment: Submitted to JMP; The description of the spectrum in some Hardy
spaces is adde
Isomorphism between Non-Riemannian gravity and Einstein-Proca-Weyl theories extended to a class of Scalar gravity theories
We extend the recently proved relation between certain models of
Non-Riemannian gravitation and Einstein- Proca-Weyl theories to a class of
Scalar gravity theories. This is used to present a Black-Hole Dilaton solution
with non-Riemannian connection.Comment: 13 pages, tex file, accepted in Class. Quant. Gra
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Depositional and Structural Challenges of the Wilcox Lobo Natural Gas Trend, South Texas
To increase understanding and utilization of gas resources in the Wilcox Lobo play of South Texas, this report reviews current geological knowledge of the Lobo trend. An additional objective of this report is to identify areas where advancements in geological understanding could lead to substantial improvements in efficient development of the Wilcox Lobo trend natural gas resource. According to published accounts, Lobo sandstones formed in a variety of depositional environments in both shallow and deep marine waters. During and after deposition, the Lobo experienced repeated episodes of erosion, faulting, and diagenesis. Thus, accurate prediction of reservoir sandstone attributes is difficult, and this difficulty is cited by operators as a significant challenge to efficiently targeting the remaining gas resource. Knowledge that would aid in the emergence of this resource includes information on sandstone correlation and accurate zone identification, depositional systems and facies interpretations, controls on fault pattern variability, and, to a lesser extent, recognition of diagenetic patterns and faults and fractures that are below seismic resolution. Geologic challenges of the Lobo trend are opportunities for targeting increasingly smaller and more difficult-to-detect compartments with advanced technology.Bureau of Economic Geolog
On a computer-aided approach to the computation of Abelian integrals
An accurate method to compute enclosures of Abelian integrals is developed.
This allows for an accurate description of the phase portraits of planar
polynomial systems that are perturbations of Hamiltonian systems. As an
example, it is applied to the study of bifurcations of limit cycles arising
from a cubic perturbation of an elliptic Hamiltonian of degree four
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