13,000 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
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.
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
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
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
Interaction of vortices in thin superconducting films and Berezinskii-Kosterlitz-Thouless transition
The precondition for the BKT transition in thin superconducting films, the
logarithmic intervortex interaction, is satisfied at distances short relative
to , is the London penetration depth of the
bulk material and is the film thickness. For this reason, the search for
the transition has been conducted in samples of the size . It is
argued below that film edges turn the interaction into near exponential
(short-range) thus making the BKT transition impossible. If however the
substrate is superconducting and separated from the film by an insulated layer,
the logarithmic intervortex interaction is recovered and the BKT transition
should be observable.Comment: 4 pages, no figure
Diffraction and quasiclassical limit of the Aharonov--Bohm effect
Since the Aharonov-Bohm effect is the purely quantum effect that has no
analogues in classical physics, its persistence in the quasiclassical limit
seems to be hardly possible. Nevertheless, we show that the scattering
Aharonov-Bohm effect does persist in the quasiclassical limit owing to the
diffraction, i.e. the Fraunhofer diffraction in the case when space outside the
enclosed magnetic flux is Euclidean, and the Fresnel diffraction in the case
when the outer space is conical. Hence, the enclosed magnetic flux can serve as
a gate for the propagation of short-wavelength, almost classical, particles. In
the case of conical space, this quasiclassical effect which is in principle
detectable depends on the particle spin.Comment: 12 pages, minor changes, references update
Circular dielectric cavity and its deformations
The construction of perturbation series for slightly deformed dielectric
circular cavity is discussed in details. The obtained formulae are checked on
the example of cut disks. A good agreement is found with direct numerical
simulations and far-field experiments.Comment: 17 pages, 12 figure
The moving boundary problem in the presence of a dipole magnetic field
An exact analytic solution is obtained for a uniformly expanding, neutral,
infinitely conducting plasma sphere in an external dipole magnetic field. The
electrodynamical aspects related to the radiation and transformation of energy
were considered as well. The results obtained can be used in analyzing the
recent experimental and simulation data.Comment: 17 pages, 1 figure, Submitted to J. Phys. A, Math. and Genera
Total Angular Momentum Waves for Scalar, Vector, and Tensor Fields
Most calculations in cosmological perturbation theorydecompose those
perturbations into plane waves (Fourier modes). However, for some calculations,
particularly those involving observations performed on a spherical sky, a
decomposition into waves of fixed total angular momentum (TAM) may be more
appropriate. Here we introduce TAM waves, solutions of fixed total angular
momentum to the Helmholtz equation, for three-dimensional scalar, vector, and
tensor fields. The vector TAM waves of given total angular momentum can be
decomposed further into a set of three basis functions of fixed orbital angular
momentum (OAM), a set of fixed helicity, or a basis consisting of a
longitudinal (L) and two transverse (E and B) TAM waves. The symmetric
traceless rank-2 tensor TAM waves can be similarly decomposed into a basis of
fixed OAM or fixed helicity, or a basis that consists of a longitudinal (L),
two vector (VE and VB, of opposite parity), and two tensor (TE and TB, of
opposite parity) waves. We show how all of the vector and tensor TAM waves can
be obtained by applying derivative operators to scalar TAM waves. This operator
approach then allows one to decompose a vector field into three covariant
scalar fields for the L, E, and B components and symmetric-traceless-tensor
fields into five covariant scalar fields for the L, VE, VB, TE, and TB
components. We provide projections of the vector and tensor TAM waves onto
vector and tensor spherical harmonics. We provide calculational detail to
facilitate the assimilation of this formalism into cosmological calculations.
As an example, we calculate the power spectra of the deflection angle for
gravitational lensing by density perturbations and by gravitational waves. We
comment on an alternative approach to CMB fluctuations based on TAM waves. Our
work may have applications elsewhere in field theory and in general relativity.Comment: 32 pages, Published version in PR
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