152 research outputs found
Diversity and biogeographical patterns of legumes (Leguminosae) indigenous to southern Africa
The principal aim of this study was to establish biogeographical patterns in the legume flora of southern
Africa so as to facilitate the selection of species with agricultural potential. Plant collection data from the
National Herbarium, South Africa, were analysed to establish the diversity and areas covered by legumes
(Leguminosae/Fabaceae) indigenous to South Africa, Lesotho and Swaziland. A total of 27,322 records
from 1,619 quarter degree grid cells, representing 1,580 species, 122 genera and 24 tribes were included
in the analyses. Agglomerative hierarchical clustering was applied to the presence or absence of legume
species in quarter degree grid cells, the resultant natural biogeographical regions (choria) being referred
to as leguminochoria. The description of the 16 uniquely formed leguminochoria focuses on defining
the associated bioregions and biomes, as well as on the key climate and soil properties. Legume species
with a high occurrence in a leguminochorion are listed as key species. The dominant growth form of key
species, species richness and range within each leguminochorion is discussed. Floristic links between the
leguminochoria are established, by examining and comparing key species common to clusters, using a
vegetation classification program. Soil pH and mean annual minimum temperature were found to be the main drivers for distinguishing among legume assemblages. This is the first time that distribution data for
legumes has been used to identify biogeographical areas covered by leguminochoria on the subcontinent.
One potential application of the results of this study is to assist in the selection of legumes for pasture
breeding and soil conservation programs, especially in arid and semi-arid environments.This paper is dedicated to the memory of Robert Howard (Bobby) Westfall
(17 December 1944–21 January 2016), vegetation ecologist and friend
whose sudden death during the preparation of this manuscript deprived
us of an invaluable collaborator.Financial assistance from the University of Pretoria is acknowledged
with thanks.http://phytokeys.pensoft.nethttp://opendatacommons.org/licenses/odbl/1.0/am2016Plant Scienc
Diversity and biogeographical patterns of legumes (Leguminosae) indigenous to southern Africa
This paper is dedicated to the memory of Robert Howard (Bobby) Westfall
(17 December 1944–21 January 2016), vegetation ecologist and friend
whose sudden death during the preparation of this manuscript deprived
us of an invaluable collaborator.The principal aim of this study was to establish biogeographical patterns in the legume flora of southern
Africa so as to facilitate the selection of species with agricultural potential. Plant collection data from the
National Herbarium, South Africa, were analysed to establish the diversity and areas covered by legumes
(Leguminosae/Fabaceae) indigenous to South Africa, Lesotho and Swaziland. A total of 27,322 records
from 1,619 quarter degree grid cells, representing 1,580 species, 122 genera and 24 tribes were included
in the analyses. Agglomerative hierarchical clustering was applied to the presence or absence of legume
species in quarter degree grid cells, the resultant natural biogeographical regions (choria) being referred
to as leguminochoria. The description of the 16 uniquely formed leguminochoria focuses on defining
the associated bioregions and biomes, as well as on the key climate and soil properties. Legume species
with a high occurrence in a leguminochorion are listed as key species. The dominant growth form of key
species, species richness and range within each leguminochorion is discussed. Floristic links between the
leguminochoria are established, by examining and comparing key species common to clusters, using a
vegetation classification program. Soil pH and mean annual minimum temperature were found to be the main drivers for distinguishing among legume assemblages. This is the first time that distribution data for
legumes has been used to identify biogeographical areas covered by leguminochoria on the subcontinent.
One potential application of the results of this study is to assist in the selection of legumes for pasture
breeding and soil conservation programs, especially in arid and semi-arid environments.Financial assistance from the University of Pretoria is acknowledged
with thanks.http://phytokeys.pensoft.nethttp://opendatacommons.org/licenses/odbl/1.0/am2016Plant Scienc
4th Biennial Employment Law Institute
Materials from the 4th Biennial Employment Law Institute held by UK/CLE in June 1994
Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy ion collisions
Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created during relativistic heavy-ion collisions. These
domains are predicted to lead to charge separation of quarks along the orbital
momentum of the system created in non-central collisions. To study this effect,
we investigate a three particle mixed harmonics azimuthal correlator which is a
\P-even observable, but directly sensitive to the charge separation effect. We
report measurements of this observable using the STAR detector in Au+Au and
Cu+Cu collisions at =200 and 62~GeV. The results are presented
as a function of collision centrality, particle separation in rapidity, and
particle transverse momentum. A signal consistent with several of the
theoretical expectations is detected in all four data sets. We compare our
results to the predictions of existing event generators, and discuss in detail
possible contributions from other effects that are not related to parity
violation.Comment: 17 pages, 14 figures, as accepted for publication in Physical Review
C
Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations
Charged-particle spectra associated with direct photon () and
are measured in + and Au+Au collisions at center-of-mass energy
GeV with the STAR detector at RHIC. A hower-shape
analysis is used to partially discriminate between and .
Assuming no associated charged particles in the direction (near
side) and small contribution from fragmentation photons (), the
associated charged-particle yields opposite to (away side) are
extracted. At mid-rapidity () in central Au+Au collisions,
charged-particle yields associated with and at high
transverse momentum ( GeV/) are suppressed by a factor
of 3-5 compared with + collisions. The observed suppression of the
associated charged particles, in the kinematic range and GeV/, is similar for and , and
independent of the energy within uncertainties. These
measurements indicate that the parton energy loss, in the covered kinematic
range, is insensitive to the parton path length.Comment: submitted to Phys. Rev. Lett, 6 pages, 4 figure
Charged and strange hadron elliptic flow in Cu+Cu collisions at = 62.4 and 200 GeV
We present the results of an elliptic flow analysis of Cu+Cu collisions
recorded with the STAR detector at 62.4 and 200GeV. Elliptic flow as a function
of transverse momentum is reported for different collision centralities for
charged hadrons and strangeness containing hadrons , ,
, in the midrapidity region . Significant reduction in
systematic uncertainty of the measurement due to non-flow effects has been
achieved by correlating particles at midrapidity, , with those at
forward rapidity, . We also present azimuthal correlations in
p+p collisions at 200 GeV to help estimating non-flow effects. To study the
system-size dependence of elliptic flow, we present a detailed comparison with
previously published results from Au+Au collisions at 200 GeV. We observe that
() of strange hadrons has similar scaling properties as were
first observed in Au+Au collisions, i.e.: (i) at low transverse momenta,
, scales with transverse kinetic energy, , and
(ii) at intermediate , , it scales with the number of
constituent quarks, . We have found that ideal hydrodynamic calculations
fail to reproduce the centrality dependence of () for
and . Eccentricity scaled values, , are larger
in more central collisions, suggesting stronger collective flow develops in
more central collisions. The comparison with Au+Au collisions which go further
in density shows depend on the system size, number of
participants . This indicates that the ideal hydrodynamic limit is
not reached in Cu+Cu collisions, presumably because the assumption of
thermalization is not attained.Comment: 18 pages, 14 figure
Identified high- spectra in Cu+Cu collisions at =200 GeV
We report new results on identified (anti)proton and charged pion spectra at
large transverse momenta (3<<10 GeV/c) from Cu+Cu collisions at
=200 GeV using the STAR detector at the Relativistic Heavy Ion
Collider (RHIC). This study explores the system size dependence of two novel
features observed at RHIC with heavy ions: the hadron suppression at
high- and the anomalous baryon to meson enhancement at intermediate
transverse momenta. Both phenomena could be attributed to the creation of a new
form of QCD matter. The results presented here bridge the system size gap
between the available pp and Au+Au data, and allow the detailed exploration for
the on-set of the novel features. Comparative analysis of all available 200 GeV
data indicates that the system size is a major factor determining both the
magnitude of the hadron spectra suppression at large transverse momenta and the
relative baryon to meson enhancement.Comment: Submitted to Phys. Rev. C, 9 pages, 5 figure
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV
We report on the observed differences in production rates of strange and
multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp
interactions at the same energy. The strange baryon yields in Au+Au collisions,
then scaled down by the number of participating nucleons, are enhanced relative
to those measured in pp reactions. The enhancement observed increases with the
strangeness content of the baryon, and increases for all strange baryons with
collision centrality. The enhancement is qualitatively similar to that observed
at lower collision energy sqrts =17.3 GeV. The previous observations are for
the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange
baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR
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