969 research outputs found
Remote sensing applied to land-use studies in Wyoming
Impending development of Wyoming's vast fuel resources requires a quick and efficient method of land use inventory and evaluation. Preliminary evaluations of ERTS-1 imagery have shown that physiographic and land use inventory maps can be compiled by using a combination of visual and automated interpretation techniques. Test studies in the Powder River Basin showed that ERTS image interpretations can provide much of the needed physiographic and land use information. Water impoundments as small as one acre were detected and water bodies larger than five acres could be mapped and their acreage estimated. Flood plains and irrigated lands were successfully mapped, and some individual crops were identified and mapped. Coniferous and deciduous trees were mapped separately using color additive analysis on the ERTS multispectral imagery. Gross soil distinctions were made with the ERTS imagery, and were found to be closely related to the bedrock geology. Several broad unstable areas were identified. These were related to specific geologic and slope conditions and generally extended through large regions. Some new oil fields and all large open-cut coal mines were mapped. The most difficult task accomplished was that of mapping urban areas. Work in the urban areas provides a striking example of snow enhancement and the detail available from a snow enhanced image
New angles on D-branes
A low-energy background field solution is presented which describes several
D-membranes oriented at angles with respect to one another. The mass and charge
densities for this configuration are computed and found to saturate the BPS
bound, implying the preservation of one-quarter of the supersymmetries.
T-duality is exploited to construct new solutions with nontrivial angles from
the basic one.Comment: Latex, 12 pages, still no figures, references update
Towards the Classification of Non-Marginal Bound States of M-branes and Their Construction Rules
We present a systematic analysis of possible bound states of M-brane
solutions (including waves and monopoles) by using the solution generating
technique of reduction of M-brane to 10 dimensions, use of T-duality and then
lifting back to 11 dimensions. We summarize a list of bound states for one- and
two-charge cases including tilted brane solutions. Construction rules for these
non-marginal solutions are also discussed.Comment: Latex, 37 page
Microstates of Four-Dimensional Rotating Black Holes from Near-Horizon Geometry
We show that a class of four-dimensional rotating black holes allow
five-dimensional embeddings as black rotating strings. Their near-horizon
geometry factorizes locally as a product of the three-dimensional anti-deSitter
space-time and a two-dimensional sphere (AdS_3 x S^2), with angular momentum
encoded in the global space-time structure. Following the observation that the
isometries on the AdS_3 space induce a two-dimensional (super)conformal field
theory on the boundary, we reproduce the microscopic entropy with the correct
dependence on the black hole angular momentum.Comment: 11 pages, revte
Gauge Dependence in Chern-Simons Theory
We compute the contribution to the modulus of the one-loop effective action
in pure non-Abelian Chern-Simons theory in an arbitrary covariant gauge. We
find that the results are dependent on both the gauge parameter () and
the metric required in the gauge fixing. A contribution arises that has not
been previously encountered; it is of the form . This is possible as in three dimensions
is dimensionful. A variant of proper time regularization is used to render
these integrals well behaved (although no divergences occur when the
regularization is turned off at the end of the calculation). Since the original
Lagrangian is unaltered in this approach, no symmetries of the classical theory
are explicitly broken and is handled unambiguously
since the system is three dimensional at all stages of the calculation. The
results are shown to be consistent with the so-called Nielsen identities which
predict the explicit gauge parameter dependence using an extension of BRS
symmetry. We demonstrate that this dependence may potentially
contribute to the vacuum expectation values of products of Wilson loops.Comment: 17 pp (including 3 figures). Uses REVTeX 3.0 and epsfig.sty
(available from LANL). Latex thric
Theoretical study of finite temperature spectroscopy in van der Waals clusters. I. Probing phase changes in CaAr_n
The photoabsorption spectra of calcium-doped argon clusters CaAr_n are
investigated at thermal equilibrium using a variety of theoretical and
numerical tools. The influence of temperature on the absorption spectra is
estimated using the quantum superposition method for a variety of cluster sizes
in the range 6<=n<=146. At the harmonic level of approximation, the absorption
intensity is calculated through an extension of the Gaussian theory by Wadi and
Pollak [J. Chem. Phys. vol 110, 11890 (1999)]. This theory is tested on simple,
few-atom systems in both the classical and quantum regimes for which highly
accurate Monte Carlo data can be obtained. By incorporating quantum anharmonic
corrections to the partition functions and respective weights of the isomers,
we show that the superposition method can correctly describe the
finite-temperature spectroscopic properties of CaAr_n systems. The use of the
absorption spectrum as a possible probe of isomerization or phase changes in
the argon cluster is discussed at the light of finite-size effects.Comment: 17 pages, 9 figure
Hermitian D-brane solutions
A low-energy background field solution describing D-membrane configurations
is constructed which is distinguished by the appearance of a Hermitian metric
on the internal space. This metric is composed of a number of independent
harmonic functions on the transverse space. Thus this construction generalizes
the usual harmonic superposition rule. The BPS bound of these solutions is
shown to be saturated indicating that they are supersymmetric. By means of
T-duality, we construct more solutions of the IIA and IIB theories.Comment: 14 pages, Latex, no figure
Localized Branes and Black Holes
We address the delocalization of low dimensional D-branes and NS-branes when
they are a part of a higher dimensional BPS black brane, and the homogeneity of
the resulting horizon. We show that the effective delocalization of such branes
is a classical effect that occurs when localized branes are brought together.
Thus, the fact that the few known solutions with inhomogeneous horizons are
highly singular need not indicate a singularity of generic D- and NS-brane
states. Rather, these singular solutions are likely to be unphysical as they
cannot be constructed from localized branes which are brought together from a
finite separation.Comment: 13 pages, RevTex, no figures, few references and comments adde
Supergravity Duals to the Noncommutative N=4 SYM theory in the Infinite Momentum Frame
In this work the construction of supergravity duals to the noncommutative
SYM theory in the infinite momentum frame but with constant
momentum density is attempted. In the absence of the content of
noncommutativity, it has been known for some time that the previous
correspondence should be replaced by the
(with denoting the generalized Kaigorodov spacetime) correspondence
with the pp-wave propagating on the BPS brane worldvolume. Interestingly
enough, putting together the two contents, i.e., the introduction of
noncommutativity and at the same time that of the pp-wave along the brane
worldvolume, leads to quite nontrivial consequences such as the emergence of
``time-space'' noncommutativity in addition to the ``space-space''
noncommutativity in the manifold on which the dual gauge theory is defined.
Taking the gravity decoupling limit, it has been realized that for small ,
the solutions all reduce to geometry confirming our
expectation that the IR dynamics of the dual gauge theory should be unaffected
by the noncommutativity while as , the solutions start to deviate
significantly from limit indicating that the UV dynamics of
the dual gauge theory would be heavily distorted by the effect of
noncommutativity.Comment: 21 pages, Latex, One expression changed, a reference added, to appear
in Phys. Rev.
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