21,573 research outputs found
Visible and near-IR spectral reflectance of geologically important materials: A short review
Examples of reflectance spectra are presented and discussed for various mineral groups including pyroxenes, olivene, phylosilicates, amphiboles, feldspars, oxides and hydroxides, carbonates, and mixtures of minerals. The physical sources of some spectral features are also reviewed such as charge transfer and conduction bands, crystal field absorptions, and vibrational absorptions
A next-generation mapping spectrometer
Operational and design characteristics for a remote sensing instrument for aircraft and orbital use are defined. The ideal instrument would be based around two-dimensional detector arrays, silicon for the visible and very-near infrared (0.4 to 1.0 microns) and InSb or PbS for the rest of the near-infrared (out to about 2.6 microns). Spectral information would be dispersed along one axis. Thus one exposure or frame would simultaneously record a full spectrum for each pixel in a row perpendicular to the ground track. The instrument should be smart and versatile, with extensive pre-processing capability programmable from the ground. Spatial and spectral resolution, signal to noise radio, data precision, and calibration and atmospheric corrections are also discussed
Development assistance gone wrong : why support services have failed to expand exports
This study shows that in developing countries with no more than partly favorable policies toward manufactured exports, outside assistance to services that promote and support manufactured exports has had little discernible impact on exports and has rarely been effective in expanding them. The principal reasons for this lack of impact appear to be the after effects of inward-looking development policies, neglect of assistance to enterprises in the production and supply aspects of exporting, insufficient donor concern about the direct impact of their assistance on exports, and reliance on an inappropriate delivery mechanism. Recommendations which suggest new guidelines for donor assistance, project components and new country policies are explained in a companion paper, WPS 544.Economic Theory&Research,Environmental Economics&Policies,Health Economics&Finance,ICT Policy and Strategies,Poverty Assessment
Fractional analytic index
For a finite rank projective bundle over a compact manifold, so associated to
a torsion, Dixmier-Douady, 3-class, w, on the manifold, we define the ring of
differential operators `acting on sections of the projective bundle' in a
formal sense. In particular, any oriented even-dimensional manifold carries a
projective spin Dirac operator in this sense. More generally the corresponding
space of pseudodifferential operators is defined, with supports sufficiently
close to the diagonal, i.e. the identity relation. For such elliptic operators
we define the numerical index in an essentially analytic way, as the trace of
the commutator of the operator and a parametrix and show that this is homotopy
invariant. Using the heat kernel method for the twisted, projective spin Dirac
operator, we show that this index is given by the usual formula, now in terms
of the twisted Chern character of the symbol, which in this case defines an
element of K-theory twisted by w; hence the index is a rational number but in
general it is not an integer.Comment: 23 pages, Latex2e, final version, to appear in JD
Oxidation of basaltic tephras: Influence on reflectance in the 1 micron region
As part of a ongoing study into the products of hydrovolcanism, tuffs were examined from the Cerro Colorado and Pavant Butte tuff cones. The former resides in the northeastern corner of the Pinacate Volcanic Field in Sonara, Mexico and the latter is in the Black Rock Desert of southern Utah. Numerous samples were collected and many of these had their Vis/IR reflectance measured. It seems likely that in the palagonite tuffs there is a combination of nanocrystalline ferric oxide phases contributing to the UV absorption edge, but not to the 1 micron band, plus more crystalline ferric oxides which do contribute to that band as well as ferrous iron within unaltered sideromelane which is skewing the band center to longer wavelengths. This work has implications for the study of Mars. The present work indicates that when ferrous and ferric iron phases are both present, their combined spectral contribution is a single band in the vicinity of 1 micron. The center, depth, and width of that feature has potential to be used to gauge the relative proportions of ferrous and ferric iron phases
Spectral effects of dehydration on phyllosilicates
Six phyllosilicates were progressively dehydrated under controlled conditions in an effort to study the spectral effects of their dehydration. The spectra obtained at each level of hydration provide information that may be used in future spectroscopic observations of the planets, as well as a data set which compliments the existing body of terrestrial soil knowledge
Variable features in the Valles Marineris region of Mars
Transient phenomena on Mars have long been recognized in Mariner and Viking images as well as in decades of Earth based telescopic observations. These events are of interest because of the information they present on currently active meteorological and geological processes. Changes in surface albedo patterns and atmospheric conditions can also affect the analysis and interpretation of data based on spectral or morphological properties of geologic units on the surface. The mechanism responsible for albedo pattern change is currently under investigation. Generation and subsequent transportation and deposition of dark sands has been interpreted in the Valles. However, the removal of a bright dust layer is more consistent with the rapid time period of the change (about two months) and with preliminary multispectral mapping results which suggest that the dark streak south of Eos and Coprates Chasmata is spectrally distinguishable from the dark saltating materials found elsewhere in the canyon system. If a layer of bright dust was removed to affect the albedo change, questions concerning how such micron-sized particles are mobilized by the winds during a normally quiescent season (Southern Hemisphere Autumn) should be addressed
The interaction energy of well-separated Skyrme solitons
We prove that the asymptotic field of a Skyrme soliton of any degree has a
non-trivial multipole expansion. It follows that every Skyrme soliton has a
well-defined leading multipole moment. We derive an expression for the linear
interaction energy of well-separated Skyrme solitons in terms of their leading
multipole moments. This expression can always be made negative by suitable
rotations of one of the Skyrme solitons in space and iso-space.We show that the
linear interaction energy dominates for large separation if the orders of the
Skyrme solitons' multipole moments differ by at most two. In that case there
are therefore always attractive forces between the Skyrme solitons.Comment: 27 pages amslate
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