12,502 research outputs found
A flight test of laminar flow control leading-edge systems
NASA's program for development of a laminar flow technology base for application to commercial transports has made significant progress since its inception in 1976. Current efforts are focused on development of practical reliable systems for the leading-edge region where the most difficult problems in applying laminar flow exist. Practical solutions to these problems will remove many concerns about the ultimate practicality of laminar flow. To address these issues, two contractors performed studies, conducted development tests, and designed and fabricated fully functional leading-edge test articles for installation on the NASA JetStar aircraft. Systems evaluation and performance testing will be conducted to thoroughly evaluate all system capabilities and characteristics. A simulated airline service flight test program will be performed to obtain the operational sensitivity, maintenance, and reliability data needed to establish that practical solutions exist for the difficult leading-edge area of a future commercial transport employing laminar flow control
Age, growth, mortality, and radiometric age validation of gray snapper (Lutjanus griseus) from Louisiana
The gray snapper (Lutjanus griseus) is a temperate and tropical reef fish that is found along the Gulf of Mexico and Atlantic coasts of the southeastern United States. The recreational fishery for gray snapper has developed rapidly in south Louisiana with the advent of harvest and seasonal
restrictions on the established red snapper (L. campechanus) fishery. We examined the age and growth of
gray snapper in Louisiana with the use of cross-sectioned sagittae. A total of 833 specimens, (441 males, 387
females, and 5 of unknown sex) were opportunistically sampled from the recreational fishery from August 1998 to August 2002. Males ranged in size from 222 to 732 mm total length (TL) and from 280 g to 5700 g total weight (TW) and females ranged from 254 to 756 mm TL and from 340 g to 5800 g TW. Both edge analysis and bomb radiocarbon analyses were used to validate otolith-based age estimates. Ages were estimated for 718 individuals; both males and females ranged
from 1 to 28 years. The von Bertalanffy growth models derived from TL at age were Lt = 655.4{1–e[–0.23(t)]}
for males, Lt = 657.3{1–e[– 0.21(t)]} for females, and L t = 656.4{1–e[– 0.22 (t)]} for all specimens of known sex. Catch curves were used to produce a total mortality (Z) estimate of 0.17. Estimates of M calculated with various
methods ranged from 0.15 to 0.50; however we felt that M= 0.15 was the most appropriate estimate based on our estimate of Z. Full recruitment to the gray snapper recreational fishery began at age 4, was completed by age
8, and there was no discernible peak in the catch curve dome
Perturbations of Spatially Closed Bianchi III Spacetimes
Motivated by the recent interest in dynamical properties of topologically
nontrivial spacetimes, we study linear perturbations of spatially closed
Bianchi III vacuum spacetimes, whose spatial topology is the direct product of
a higher genus surface and the circle. We first develop necessary mode
functions, vectors, and tensors, and then perform separations of (perturbation)
variables. The perturbation equations decouple in a way that is similar to but
a generalization of those of the Regge--Wheeler spherically symmetric case. We
further achieve a decoupling of each set of perturbation equations into
gauge-dependent and independent parts, by which we obtain wave equations for
the gauge-invariant variables. We then discuss choices of gauge and stability
properties. Details of the compactification of Bianchi III manifolds and
spacetimes are presented in an appendix. In the other appendices we study
scalar field and electromagnetic equations on the same background to compare
asymptotic properties.Comment: 61 pages, 1 figure, final version with minor corrections, to appear
in Class. Quant. Gravi
BACK TO THE BASICS: WHAT DOES THE MARKET TELL US ABOUT BASIS?
This study explores market forces that affect harvest grain basis for corn, soybeans, and wheat in a grain deficit market. The findings indicate that implied basis (cash forward bid less harvest futures), nearby HHO price, and log of open interest on the harvest futures contract can be used to predict 33 to 99 percent of the variation in harvest basis at selected South Carolina locations.Marketing,
On the String Consensus Problem and the Manhattan Sequence Consensus Problem
In the Manhattan Sequence Consensus problem (MSC problem) we are given
integer sequences, each of length , and we are to find an integer sequence
of length (called a consensus sequence), such that the maximum
Manhattan distance of from each of the input sequences is minimized. For
binary sequences Manhattan distance coincides with Hamming distance, hence in
this case the string consensus problem (also called string center problem or
closest string problem) is a special case of MSC. Our main result is a
practically efficient -time algorithm solving MSC for sequences.
Practicality of our algorithms has been verified experimentally. It improves
upon the quadratic algorithm by Amir et al.\ (SPIRE 2012) for string consensus
problem for binary strings. Similarly as in Amir's algorithm we use a
column-based framework. We replace the implied general integer linear
programming by its easy special cases, due to combinatorial properties of the
MSC for . We also show that for a general parameter any instance
can be reduced in linear time to a kernel of size , so the problem is
fixed-parameter tractable. Nevertheless, for this is still too large
for any naive solution to be feasible in practice.Comment: accepted to SPIRE 201
Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy
We present the first scanning tunneling spectroscopy study on the Chevrel
phase PbMo6S8, an extreme type II superconductor with a coherence length only
slightly larger than in high-Tc cuprates. Tunneling spectra measured on
atomically flat terraces are spatially homogeneous and show well-defined
coherence peaks. The low-energy spectral weight, the zero bias conductance and
the temperature dependence of the gap are incompatible with a conventional
isotropic s-wave interpretation, revealing the presence of low-energy
excitations in the superconducting state. We show that our data are consistent
with the presence of nodes in the superconducting gap.Comment: To appear in PRB; 5 pages, 4 figure
The Momentum Constraints of General Relativity and Spatial Conformal Isometries
Transverse-tracefree (TT-) tensors on , with an
asymptotically flat metric of fast decay at infinity, are studied. When the
source tensor from which these TT tensors are constructed has fast fall-off at
infinity, TT tensors allow a multipole-type expansion. When has no
conformal Killing vectors (CKV's) it is proven that any finite but otherwise
arbitrary set of moments can be realized by a suitable TT tensor. When CKV's
exist there are obstructions -- certain (combinations of) moments have to
vanish -- which we study.Comment: 16 page
Exact Solution Methods for the -item Quadratic Knapsack Problem
The purpose of this paper is to solve the 0-1 -item quadratic knapsack
problem , a problem of maximizing a quadratic function subject to two
linear constraints. We propose an exact method based on semidefinite
optimization. The semidefinite relaxation used in our approach includes simple
rank one constraints, which can be handled efficiently by interior point
methods. Furthermore, we strengthen the relaxation by polyhedral constraints
and obtain approximate solutions to this semidefinite problem by applying a
bundle method. We review other exact solution methods and compare all these
approaches by experimenting with instances of various sizes and densities.Comment: 12 page
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