86,335 research outputs found
Interpretation of AIS Images of Cuprite, Nevada Using Constraints of Spectral Mixtures
A technique is outlined that tests the hypothesis Airborne Imaging Spectrometer (AIS) image spectra are produced by mixtures of surface materials. This technique allows separation of AIS images into concentration images of spectral endmembers (e.g., surface materials causing spectral variation). Using a spectral reference library it was possible to uniquely identify these spectral endmembers with respect to the reference library and to calibrate the AIS images
Spectral mixture modeling: Further analysis of rock and soil types at the Viking Lander sites
A new image processing technique was applied to Viking Lander multispectral images. Spectral endmembers were defined that included soil, rock and shade. Mixtures of these endmembers were found to account for nearly all the spectral variance in a Viking Lander image
The application of Floquet theory to the computation of small orbital perturbations over long time intervals using the Tschauner- Hempel equations
Calculation of path deviation of satellite from reference trajectory - perturbation theor
Compositional variability of the Martian surface
Spectral reflectance data from Viking Landers and Orbiters and from telescopic observations were analyzed with the objective of isolating compositional information about the Martian surface and assessing compositional variability. Two approaches were used to calibrate the data to reflectance to permit direct comparisons with laboratory reference spectra of well characterized materials. In Viking Lander multispectral images (six spectral bands) most of the spectral variation is caused by changes in lighting geometry within individual scenes, from scene to scene, and over time. Lighting variations are both wavelength independent and wavelength dependent. By calibrating lander image radiance values to reflectance using spectral mixture analysis, the possible range of compositions was assessed with reference to a collection of laboratory samples, also resampled to the lander spectral bands. All spectra from the lander images studied plot (in six-space) within a planar triangle having at the apexes the respective spectra of tan basaltic palagonite, gray basalt, and shale. Within this plane all lander spectra fit as mixtures of these three endmembers. Reference spectra that plot outside of the triangle are unable to account for the spectral variation observed in the images
The effects of estimation of censoring, truncation, transformation and partial data vectors
The purpose of this research was to attack statistical problems concerning the estimation of distributions for purposes of predicting and measuring assembly performance as it appears in biological and physical situations. Various statistical procedures were proposed to attack problems of this sort, that is, to produce the statistical distributions of the outcomes of biological and physical situations which, employ characteristics measured on constituent parts. The techniques are described
Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars
The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained
On the self-similarity in quantum Hall systems
The Hall-resistance curve of a two-dimensional electron system in the
presence of a strong perpendicular magnetic field is an example of
self-similarity. It reveals plateaus at low temperatures and has a fractal
structure. We show that this fractal structure emerges naturally in the
Hamiltonian formulation of composite fermions. After a set of transformations
on the electronic model, we show that the model, which describes interacting
composite fermions in a partially filled energy level, is self-similar. This
mathematical property allows for the construction of a basis of higher
generations of composite fermions. The collective-excitation dispersion of the
recently observed 4/11 fractional-quantum-Hall state is discussed within the
present formalism.Comment: 7 pages, 4 figures; version accepted for publication in Europhys.
Lett., new version contains energy calculations for collective excitations of
the 4/11 stat
Effective potential for Polyakov loops from a center symmetric effective theory in three dimensions
We present lattice simulations of a center symmetric dimensionally reduced
effective field theory for SU(2) Yang Mills which employ thermal Wilson lines
and three-dimensional magnetic fields as fundamental degrees of freedom. The
action is composed of a gauge invariant kinetic term, spatial gauge fields and
a potential for the Wilson line which includes a "fuzzy" bag term to generate
non-perturbative fluctuations. The effective potential for the Polyakov loop is
extracted from the simulations including all modes of the loop as well as for
cooled configuration where the hard modes have been averaged out. The former is
found to exhibit a non-analytic contribution while the latter can be described
by a mean-field like ansatz with quadratic and quartic terms, plus a
Vandermonde potential which depends upon the location within the phase diagram.Comment: 10 pages, 22 figures, v2: published version (minor clarifications,
update of reference list
Interfaces in driven Ising models: shear enhances confinement
We use a phase-separated driven two-dimensional Ising lattice gas to study
fluid interfaces exposed to shear flow parallel to the interface. The interface
is stabilized by two parallel walls with opposing surface fields and a driving
field parallel to the walls is applied which (i) either acts locally at the
walls or (ii) varies linearly with distance across the strip. Using computer
simulations with Kawasaki dynamics, we find that the system reaches a steady
state in which the magnetisation profile is the same as that in equilibrium,
but with a rescaled length implying a reduction of the interfacial width. An
analogous effect was recently observed in sheared phase-separated colloidal
dispersions. Pair correlation functions along the interface decay more rapidly
with distance under drive than in equilibrium and for cases of weak drive can
be rescaled to the equilibrium result.Comment: 4 pages, 3 figures Text modified, added Fig. 3b. To appear in Phys.
Rev. Letter
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