20,173 research outputs found
Using LANDSAT digital data for estimating green biomass
The author has identified the following significant results. Relationships between the quantity of mixed prairie rangeland vegetation and LANDSAT MSS response were studied during four growing seasons at test sites throughout the United States Great Plans region. A LANDSAT derived parameter, the normalized difference was developed from theoretical considerations fro statistical estimation of the amount and seasonal condition of rangeland vegetation. This parameter was tested for application to local assessment of green forage biomass and regional monitoring of range feed conditions and drought. Results show that for grasslands in the Great Plains with near continuous vegetative cover and free of heavy brush and forbs, the LANDSAT digital data can provide a useful estimate of the quantity of green forage biomass (within 250 kg/ha), and at least five levels of pasture and range feed conditions can be adequately mapped for extended regions
Comparison of classical and second quantized description of the dynamic Stark shift
We compare the derivation of the dynamic Stark shift of hydrogenic energy
levels in a classical framework with an adiabatically damped laser-atom
interaction, which is equivalent to the Gell-Mann-Low-Sucher formula, and a
treatment based on time-independent perturbation theory, with a
second-quantized laser-atom dipole interaction Hamiltonian. Our analysis
applies to a laser that excites a two-photon transition in atomic hydrogen or
in a hydrogenlike ion with low nuclear charge number. Our comparisons serve to
demonstrate why the dynamic Stark shift may be interpreted as a stimulated
radiative correction and illustrates connections between the two derivations.
The simplest of the derivations is the fully quantized approach. The classical
and the second-quantized treatment are shown to be equivalent in the limit of
large photon numbers.Comment: 5 page
BCS theory of nodal superconductors
This course has a dual purpose. First we review the successes of the
weak-coupling BCS theory in describing new classes of superconductors
discovered since 1979. They include the heavy-fermion superconductors, high-Tc
cuprate superconductors, organic superconductors, Sr2RuO4, etc. Second, we
present the quasiclassical approximation introduced by Volovik, which we extend
to describe the thermodynamics and the thermal conductivity of the vortex state
in nodal superconductors. This approach provides the most powerful tool to
identify the symmetry of the energy gap function Delta(k) in these new
superconductors.Comment: 31 pages, 33 figure
New World of Gossamer Superconductivity
Since the discovery of the high-T cuprate superconductor
LaBaCuO in 1986 by Bednorz and M\"{u}ller, controversy regarding
the nature or origin of this remarkable superconductivity has continued.
However, d-wave superconductivity in the hole-doped cuprates, arising due to
the anti-paramagnon exchange, was established around 1994. More recently we
have shown that the mean field theory, like the BCS theory of superconductivity
and Landau's Fermi liquid theory are adequate to describe the cuprates. The
keys for this development are the facts that a)the pseudogap phase is d-wave
density wave (dDW) and that the high-T cuprate superconductivity is
gossamer (i.e. it exists in the presence of dDW).Comment: 6 pages, 4 figure
Probing the Light Pseudoscalar Window
Very light pseudoscalars can arise from the symmetry-breaking sector in many
extensions of the Standard Model. If their mass is below 200 MeV, they can be
long-lived and have interesting phenomenology. We discuss the experimental
constraints on several models with light pseudoscalars, including one in which
the pseudoscalar is naturally fermiophobic. Taking into account the stringent
bounds from rare K and B decays, we find allowed parameter space in each model
that may be accessible in direct production experiments. In particular, we
study the photoproduction of light pseudoscalars at Jefferson Lab and conclude
that a beam dump experiment could explore some of the allowed parameter space
of these models.Comment: 22 pages, 4 figure
Monitoring vegetation conditions from LANDSAT for use in range management
A summary of the LANDSAT Great Plains Corridor projects and the principal results are presented. Emphasis is given to the use of satellite acquired phenological data for range management and agri-business activities. A convenient method of reducing LANDSAT MSS data to provide quantitative estimates of green biomass on rangelands in the Great Plains is explained. Suggestions for the use of this approach for evaluating range feed conditions are presented. A LANDSAT Follow-on project has been initiated which will employ the green biomass estimation method in a quasi-operational monitoring of range readiness and range feed conditions on a regional scale
Monitoring the vernal advancement and retrogradation (green wave effect) of natural vegetation
The author has identified the following significant results. The Great Plains Corridor rangeland project utilizes natural vegetation systems as phenological indicators of seasonal development and climatic effects upon regional growth conditions. A method has been developed for quantitative measurement of vegetation conditions over broad regions using ERTS-1 MSS data. Radiance values recorded in ERTS-1 spectral bands 5 and 7, corrected for sun angle, are used to compute a band ratio parameter which is shown to be correlated with green biomass and vegetation moisture content. This report details the progress being made toward determining factors associated with the transformed vegetation index (TVI) and limitations on the method. During the first year of ERTS-1 operation (cycles 1-20), an average of 50% usable ERTS-1 data was obtained for the ten Great Plains Corridor test sites
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