14,055 research outputs found
Economic Analysis in the Pacific Northwest Land Resources Project: Theoretical Considerations and Preliminary Results
The Pacific Northwest Land Resources Inventory Demonstration Project i s an a ttempt to combine a whole spectrum of heterogeneous geographic, institutional and applications elements in a synergistic approach to the evaluation of remote sensing techniques. This diversity is the prime motivating factor behind a theoretical investigation of alternative economic analysis procedures. For a multitude of reasons--simplicity, ease of understanding, financial constraints and credibility, among others--cost-effectiveness emerges as the most practical tool for conducting such evaluation determinatIons in the Pacific Northwest. Preliminary findings in two water resource application areas suggest, in conformity with most published studies, that Lands at-aided data collection methods enjoy substantial cost advantages over alternative techniques. The pntential for sensitivity analysis based on cost/accuracy tradeoffs is considered on a theoretical plane in the absence of current accuracy figures concerning the Landsat-aided approach
Soliton Stability in Systems of Two Real Scalar Fields
In this paper we consider a class of systems of two coupled real scalar
fields in bidimensional spacetime, with the main motivation of studying
classical or linear stability of soliton solutions. Firstly, we present the
class of systems and comment on the topological profile of soliton solutions
one can find from the first-order equations that solve the equations of motion.
After doing that, we follow the standard approach to classical stability to
introduce the main steps one needs to obtain the spectra of Schr\"odinger
operators that appear in this class of systems. We consider a specific system,
from which we illustrate the general calculations and present some analytical
results. We also consider another system, more general, and we present another
investigation, that introduces new results and offers a comparison with the
former investigations.Comment: 16 pages, Revtex, 3 f igure
Nonlinear modes in the harmonic PT-symmetric potential
We study the families of nonlinear modes described by the nonlinear
Schr\"odinger equation with the PT-symmetric harmonic potential . The found nonlinear modes display a number of interesting features. In
particular, we have observed that the modes, bifurcating from the different
eigenstates of the underlying linear problem, can actually belong to the same
family of nonlinear modes. We also show that by proper adjustment of the
coefficient it is possible to enhance stability of small-amplitude and
strongly nonlinear modes comparing to the well-studied case of the real
harmonic potential.Comment: 7 pages, 2 figures; accepted to Phys. Rev.
Structure-dependent ferroelectricity of niobium clusters (NbN, N=2-52)
The ground-state structures and ferroelectric properties of NbN (N=2-52) have
been investigated by a combination of density-functional theory (DFT) in the
generalized gradient approximation (GGA) and an unbiased global search with the
guided simulated annealing. It is found that the electric dipole moment (EDM)
exists in the most of NbN and varies considerably with their sizes. And the
larger NbN (N>=25) prefer the amorphous packing. Most importantly, our
numerical EDM values of NbN (N>=38) exhibit an extraordinary even-odd
oscillation, which is well consistent with the experimental observation,
showing a close relationship with the geometrical structures of NbN. Finally,
an inverse coordination number (ICN) function is proposed to account for the
structural relation of the EDM values, especially their even-odd oscillations
starting from Nb38.Comment: 11 pages and 4 figure
Welcher Weg? A trajectory representation of a quantum Young's diffraction experiment
The double slit problem is idealized by simplifying each slit by a point
source. A composite reduced action for the two correlated point sources is
developed. Contours of the reduced action, trajectories and loci of transit
times are developed in the region near the two point sources. The trajectory
through any point in Euclidian 3-space also passes simultaneously through both
point sources.Comment: 12 pages LaTeX2e, 9 figures. Typos corrected. Author's final
submission. A companion paper to "Interference, reduced action, and
trajectories", quant-ph/0605120. Keywords: interference, Young's experiment,
entanglement, nonlocality, trajectory representation, determinis
Force-extension relation of cross-linked anisotropic polymer networks
Cross-linked polymer networks with orientational order constitute a wide
class of soft materials and are relevant to biological systems (e.g., F-actin
bundles). We analytically study the nonlinear force-extension relation of an
array of parallel-aligned, strongly stretched semiflexible polymers with random
cross-links. In the strong stretching limit, the effect of the cross-links is
purely entropic, independent of the bending rigidity of the chains. Cross-links
enhance the differential stretching stiffness of the bundle. For hard
cross-links, the cross-link contribution to the force-extension relation scales
inversely proportional to the force. Its dependence on the cross-link density,
close to the gelation transition, is the same as that of the shear modulus. The
qualitative behavior is captured by a toy model of two chains with a single
cross-link in the middle.Comment: 7 pages, 4 figure
A Classical Treatment of Island Cosmology
Computing the perturbation spectrum in the recently proposed Island Cosmology
remains an open problem. In this paper we present a classical computation of
the perturbations generated in this scenario by assuming that the NEC-violating
field behaves as a classical phantom field. Using an exactly-solvable
potential, we show that the model generates a scale-invariant spectrum of
scalar perturbations, as well as a scale-invariant spectrum of gravitational
waves. The scalar perturbations can have sufficient amplitude to seed
cosmological structure, while the gravitational waves have a vastly diminished
amplitude.Comment: 8 pages, 1 figur
Two-dimensional shear modulus of a Langmuir foam
We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by
applying a mechanical perturbation, and simultaneously image it by Brewster
angle microscopy. We determine the foam stress tensor (through a determination
of the 2D gas-liquid line tension, 2.35 0.4 pJm) and the
statistical strain tensor, by analyzing the images of the deformed structure.
We deduce the 2D shear modulus of the foam, .
The foam effective rigidity is predicted to be , which agrees with the value obtained in an independent mechanical measurement.Comment: submitted May 12, 2003 ; resubmitted Sept 9, 200
Ion Trap Mass Spectrometers for Identity, Abundance and Behavior of Volatiles on the Moon
NASA GSFC and The Open University (UK) are collaborating to deploy an Ion Trap Mass Spectrometer on the Moon to investigate the lunar water cycle. The ITMS is flight-proven throughthe Rosetta Philae comet lander mission. It is also being developed under ESA funding to analyse samples drilled from beneath the lunar surface on the Roscosmos Luna-27 lander (2025).Now, GSFC and OU will now develop a compact ITMS instrument to study the near-surface lunar exosphere on board a CLPS Astrobotic lander at Lacus Mortis in 2021
Giant Magnetic Moments of Nitrogen Stabilized Mn Clusters and Their Relevance to Ferromagnetism in Mn Doped GaN
Using first principles calculations based on density functional theory, we
show that the stability and magnetic properties of small Mn clusters can be
fundamentally altered by the presence of nitrogen. Not only are their binding
energies substantially enhanced, but also the coupling between the magnetic
moments at Mn sites remains ferromagnetic irrespective of their size or shape.
In addition, these nitrogen stabilized Mn clusters carry giant magnetic moments
ranging from 4 Bohr magnetons in MnN to 22 Bohr magnetons in Mn_5N. It is
suggested that the giant magnetic moments of Mn_xN clusters may play a key role
in the ferromagnetism of Mn doped GaN which exhibit a wide range (10K - 940K)
of Curie temperatures
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