1,787 research outputs found
Land use classification in Bolivia
The Bolivian LANDSAT Program is an integrated, multidisciplinary project designed to provide thematic analysis of LANDSAT, Skylab, and other remotely sensed data for natural resource management and development in Bolivia, is discussed. Among the first requirements in the program is the development of a legend, and appropriate methodologies, for the analysis and classification of present land use based on landscape cover. The land use legend for Bolivia consists of approximately 80 categories in a hierarchical organization which may be collapsed for generalization, or expanded for greater detail. The categories, and their definitions, provide for both a graphic and textual description of the complex and diverse landscapes found in Bolivia, and are designed for analysis from LANDSAT and other remotely sensed data at scales of 1:1,000,000 and 1:250,000. Procedures and example products developed are described and illustrated, for the systematic analysis and mapping of present land use for all of Bolivia
Levy Flights in Inhomogeneous Media
We investigate the impact of external periodic potentials on superdiffusive
random walks known as Levy flights and show that even strongly superdiffusive
transport is substantially affected by the external field. Unlike ordinary
random walks, Levy flights are surprisingly sensitive to the shape of the
potential while their asymptotic behavior ceases to depend on the Levy index
. Our analysis is based on a novel generalization of the Fokker-Planck
equation suitable for systems in thermal equilibrium. Thus, the results
presented are applicable to the large class of situations in which
superdiffusion is caused by topological complexity, such as diffusion on folded
polymers and scale-free networks.Comment: 4 pages, 4 figure
STEPS - an approach for human mobility modeling
In this paper we introduce Spatio-TEmporal Parametric Stepping (STEPS) - a simple parametric mobility model which can cover a large spectrum of human mobility patterns. STEPS makes abstraction of spatio-temporal preferences in human mobility by using a power law to rule the nodes movement. Nodes in STEPS have preferential attachment to favorite locations where they spend most of their time. Via simulations, we show that STEPS is able, not only to express the peer to peer properties such as inter-ontact/contact time and to reflect accurately realistic routing performance, but also to express the structural properties of the underlying interaction graph such as small-world phenomenon. Moreover, STEPS is easy to implement, exible to configure and also theoretically tractable
Neutron star properties and the equation of state of neutron-rich matter
We calculate total masses and radii of neutron stars (NS) for pure neutron
matter and nuclear matter in beta-equilibrium. We apply a relativistic nuclear
matter equation of state (EOS) derived from Dirac-Brueckner-Hartree-Fock (DBHF)
calculations. We use realistic nucleon-nucleon (NN) interactions defined in the
framework of the meson exchange potential models. Our results are compared with
other theoretical predictions and recent observational data. Suggestions for
further study are discussed.Comment: 13 pages, 9 figures, 1 table; Revised version, accepted for
publication in Physical Review
Interplay of Three-Body Interactions in the EOS of Nuclear Matter
The equation of state of symmetric nuclear matter has been investigated
within Brueckner approach adopting the charge-dependent Argonne
two-body force plus a microscopic three-body force based on a meson-exchange
model. The effects on the equation of state of the individual processes giving
rise to the three-body force are explored up to high baryonic density. It is
found that the major role is played by the competition between the strongly
repulsive exchange term with virtual nucleon-antinucleon
excitation and the large attractive contribution due to
exchange with resonance excitation. The net result is a repulsive
term which shifts the saturation density corresponding to the only two-body
force much closer to the empirical value, while keeping constant the saturation
energy per particle. The contribution from exchange 3BF is shown
to be attractive and rather small. The analysis of the separate three-body
force contributions allows to make a comparison with the prediction of
Dirac-Brueckner approach which is supposed to incorporate via the {\it dressed}
Dirac spinors the same virtual nucleon-antinucleon excitations as in the
present three-body force. The numerical results suggest that the three-body
force components missing from the Dirac-Brueckner approach are not negligible,
especially at high density. The calculation of the nuclear mean field and the
effective mass shows that the three-body force affects to a limited extent such
properties.Comment: 12 pages 7 figure
In-medium chiral SU(3) dynamics and hypernuclear structure
A previously introduced relativistic energy density functional, successfully
applied to ordinary nuclei, is extended to hypernuclei. The density-dependent
mean field and the spin-orbit potential are consistently calculated for a
hyperon in the nucleus using the SU(3) extension of in-medium chiral
perturbation theory. The leading long range interaction arises from
kaon-exchange and -exchange with hyperon in the intermediate
state. Scalar and vector mean fields reflecting in-medium changes of the quark
condensates are constrained by QCD sum rules. The model, applied to oxygen as a
test case, describes spectroscopic data in good agreement with experiment. In
particular, the smallness of the spin-orbit interaction finds a
natural explanation in terms of an almost complete cancellation between
scalar-vector background contributions and long-range terms generated by
two-pion exchange.Comment: 10 pages, 2 figures, elsart class. Minor revision
Scales in nuclear matter: Chiral dynamics with pion nucleon form factors
A systematic calculation of nuclear matter is performed which includes the
long-range correlations between nucleons arising from one- and two-pion
exchange. Three-body effects from -exchange with excitations of virtual
-isobars are also taken into account in our diagrammatic
calculation of the energy per particle . In order to eliminate
possible high-momentum components from the interactions we introduce at each
pion-baryon vertex a form factor of monopole type. The empirical nuclear matter
saturation point, fm, MeV, is
well reproduced with a monopole mass of GeV. As in the recent approach based on the universal low-momentum
-potential , the inclusion of three-body effects is crucial
in order to achieve saturation of nuclear matter. We demonstrate that the
dependence of the pion-exchange contributions to on the
''resolution'' scale can be compensated over a wide range of
by counterterms with two ''running'' contact-couplings. As a further
application we study the in-medium chiral condensate beyond
the linear density approximation. For we find small
corrections from the derivative , which are stable
against variations of the monopole regulator mass .Comment: 13 pages, 6 figure
Progress in Understanding the Nuclear Equation of State at the Quark Level
At the present time there is a lively debate within the nuclear community
concerning the relevance of quark degrees of freedom in understanding nuclear
structure. We outline the key issues and review the impressive progress made
recently within the framework of the quark-meson coupling model. In particular,
we explain in quite general terms how the modification of the internal
structure of hadrons in-medium leads naturally to three- and four-body forces,
or equivalently, to density dependent effective interactions.Comment: Invited presentation at XXX Symposium on Nuclear Physics, Hacienda
Cocoyoc, Jan. 3-6, 200
3-Allyl-2-hydroxy-5,6,8-trimethoxynaphthalene-1,4-dione
In the crystal structure of the title compound, C16H16O6, a pair of naphthoquinone rings are linked via O—H⋯O—C hydrogen bonds in a nearly orthogonal arrangement. This dimeric unit is linked to a neighbouring dimer by π–π stacking interactions between the naphthoquinone rings, where the distance between the mean plane of the naphtoquinone backbones is 3.468 Å, and O—H⋯O—C hydrogen bonds
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