938 research outputs found
The role of informal protected areas in maintaining biodiversity in the Western Ghats of India
Although it is widely believed that an important function of protected areas is to conserve species that are unable to survive elsewhere, there are very few empirical studies in which a comparison is made between biodiversity of protected areas and that of the cultivated landscape surrounding them. We examined the diversity of trees, birds, and macrofungi at 58 sites in three land-use types in a tree-covered landscape in Kodagu district in the Western Ghats of India. Ten forest reserve sites in the formal protected area, and 25 sacred groves and 23 coffee plantations in the neighboring cultivated landscape were sampled. A total of 215 tree, 86 bird, and 163 macrofungus species were recorded. The forest reserve had a large
number of trees that were restricted in their distribution, and the sacred groves had a large number of macrofungi. We observed that deciduous trees and non-forest-dwelling birds increased, and evergreen trees and forest-dwelling birds decreased with increasing intensity of land management. We found that trees having non-timber uses and macrofungi useful to the local people, as well as those with medicinal properties, were abundant in sacred groves. We found no significant differences in the distribution of endemic and threatened birds across the three land-use types. Although endemic trees were more abundant in the forest reserve than in sacred groves, threatened trees were more abundant in sacred groves than in the forest reserve. We attribute the high diversity in sacred groves to the native tree cover in shade coffee plantations. We conclude that informal protected areas are as important as formal ones for biodiversity conservation in Kodagu. We recommend that a conservation strategy that recognizes informal protection traditions is essential for successful biodiversity conservation in regions where formal reserves are surrounded by a matrix of cultivated land
Solving the Bethe-Salpeter equation for a pseudoscalar meson in Minkowski space
A new method of solution of the Bethe-Salpeter equation for a pseudoscalar
quark-antiquark bound state is proposed. With the help of an integral
representation, the results are directly obtained in Minkowski space. Dressing
of Green's functions is naturally taken into account, thus providing the
possible inclusion of a running coupling constant as well as quark propagators.
First numerical results are presented for a simplified ladder approximation
Schwinger functions and light-quark bound states
We examine the applicability and viability of methods to obtain knowledge
about bound-states from information provided solely in Euclidean space.
Rudimentary methods can be adequate if one only requires information about the
ground and first excited state and assumptions made about analytic properties
are valid. However, to obtain information from Schwinger functions about higher
mass states, something more sophisticated is necessary. A method based on the
correlator matrix can be dependable when operators are carefully tuned and
errors are small. This method is nevertheless not competitive when an
unambiguous analytic continuation of even a single Schwinger function to
complex momenta is available.Comment: 27 pages, 14 figure
Aspects and consequences of a dressed-quark-gluon vertex
Features of the dressed-quark-gluon vertex and their role in the gap and
Bethe-Salpeter equations are explored. It is argued that quenched lattice data
indicate the existence of net attraction in the colour-octet projection of the
quark-antiquark scattering kernel. This attraction affects the uniformity with
which solutions of truncated equations converge pointwise to solutions of the
complete gap and vertex equations. For current-quark masses less than the scale
set by dynamical chiral symmetry breaking, the dependence of the
dressed-quark-gluon vertex on the current-quark mass is weak. The study employs
a vertex model whose diagrammatic content is explicitly enumerable. That
enables the systematic construction of a vertex-consistent Bethe-Salpeter
kernel and thereby an exploration of the consequences for the strong
interaction spectrum of attraction in the colour-octet channel. With rising
current-quark mass the rainbow-ladder truncation is shown to provide an
increasingly accurate estimate of a bound state's mass. Moreover, the
calculated splitting between vector and pseudoscalar meson masses vanishes as
the current-quark mass increases, which argues for the mass of the pseudoscalar
partner of the \Upsilon(1S) to be above 9.4 GeV. The absence of
colour-antitriplet diquarks from the strong interaction spectrum is contingent
upon the net amount of attraction in the octet projected quark-antiquark
scattering kernel. There is a window within which diquarks appear. The amount
of attraction suggested by lattice results is outside this domain.Comment: 22 pages, 12 figure
Commentary on rainbow-ladder truncation for excited states and exotics
Ground-state, radially-excited and exotic scalar-, vector- and
flavoured-pseudoscalar-mesons are studied in rainbow-ladder truncation using an
interaction kernel that is consonant with modern DSE- and lattice-QCD results.
The inability of this truncation to provide realistic predictions for the
masses of excited- and exotic-states is confirmed and explained. On the other
hand, its application does provide information that is potentially useful in
proceeding beyond this leading-order truncation, e.g.: assisting with
development of projection techniques that ease the computation of excited state
properties; placing qualitative constraints on the long-range behaviour of the
interaction kernel; and highlighting and illustrating some features of hadron
observables that do not depend on details of the dynamics.Comment: 10 pages, 6 figures, 2 table
Pseudoscalar and vector mesons as q\bar{q} bound states
Two-body bound states such as mesons are described by solutions of the
Bethe-Salpeter equation. We discuss recent results for the pseudoscalar and
vector meson masses and leptonic decay constants, ranging from pions up to
c\bar{c} bound states. Our results are in good agreement with data. Essential
in these calculation is a momentum-dependent quark mass function, which evolves
from a constituent-quark mass in the infrared region to a current-quark mass in
the perturbative region. In addition to the mass spectrum, we review the
electromagnetic form factors of the light mesons. Electromagnetic current
conservation is manifest and the influence of intermediate vector mesons is
incorporated self-consistently. The results for the pion form factor are in
excellent agreement with experiment.Comment: 8 pages, 6 .eps figures, contribution to the proceedings of the first
meeting of the APS Topical Group on Hadron Physics, Fermilab, Oct. 200
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
Current quark mass dependence of nucleon magnetic moments and radii
A calculation of the current-quark-mass-dependence of nucleon static
electromagnetic properties is necessary in order to use observational data as a
means to place constraints on the variation of Nature's fundamental parameters.
A Poincare' covariant Faddeev equation, which describes baryons as composites
of confined-quarks and -nonpointlike-diquarks, is used to calculate this
dependence The results indicate that, like observables dependent on the
nucleons' magnetic moments, quantities sensitive to their magnetic and charge
radii, such as the energy levels and transition frequencies in Hydrogen and
Deuterium, might also provide a tool with which to place limits on the allowed
variation in Nature's constants.Comment: 23 pages, 2 figures, 4 tables, 4 appendice
Analysis of a quenched lattice-QCD dressed-quark propagator
Quenched lattice-QCD data on the dressed-quark Schwinger function can be
correlated with dressed-gluon data via a rainbow gap equation so long as that
equation's kernel possesses enhancement at infrared momenta above that
exhibited by the gluon alone. The required enhancement can be ascribed to a
dressing of the quark-gluon vertex. The solutions of the rainbow gap equation
exhibit dynamical chiral symmetry breaking and are consistent with confinement.
The gap equation and related, symmetry-preserving ladder Bethe-Salpeter
equation yield estimates for chiral and physical pion observables that suggest
these quantities are materially underestimated in the quenched theory: |<bar-q
q>| by a factor of two and f_pi by 30%.Comment: 9 pages, LaTeX2e, REVTEX4, 6 figure
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