83 research outputs found
3D modelling of the impact of stellar activity on tidally locked terrestrial exoplanets: atmospheric composition and habitability
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
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
Vitamin K Supplementation in Postmenopausal Women with Osteopenia (ECKO Trial): A Randomized Controlled Trial
Angela Cheung and colleagues investigate whether vitamin K1 can prevent bone loss among postmenopausal women with osteopenia
D0-D4 brane tachyon condensation to a BPS state and its excitation spectrum in noncommutative super Yang-Mills theory
We investigate the D0-D4-brane system for different B-field backgrounds
including the small instanton singularity in noncommutative SYM theory. We
discuss the excitation spectrum of the unstable state as well as for the BPS
D0-D4 bound state. We compute the tachyon potential which reproduces the
complete mass defect. The relevant degrees of freedom are the massless (4,4)
strings. Both results are in contrast with existing string field theory
calculations. The excitation spectrum of the small instanton is found to be
equal to the excitation spectrum of the fluxon solution on R^2_theta x R which
we trace back to T-duality. For the effective theory of the (0,0) string
excitations we obtain a BFSS matrix model. The number of states in the
instanton background changes significantly when the B-field becomes self-dual.
This leads us to the proposal of the existence of a phase transition or cross
over at self-dual B-field.Comment: a4 11pt Latex2e 40 pages; v2: typos fixed, refined comments on
renormalisation, refs added, v3: ref added, version publishe
Moyal star product approach to the Bohr-Sommerfeld approximation
The Bohr-Sommerfeld approximation to the eigenvalues of a one-dimensional
quantum Hamiltonian is derived through order (i.e., including the
first correction term beyond the usual result) by means of the Moyal star
product. The Hamiltonian need only have a Weyl transform (or symbol) that is a
power series in , starting with , with a generic fixed point in
phase space. The Hamiltonian is not restricted to the kinetic-plus-potential
form. The method involves transforming the Hamiltonian to a normal form, in
which it becomes a function of the harmonic oscillator Hamiltonian.
Diagrammatic and other techniques with potential applications to other normal
form problems are presented for manipulating higher order terms in the Moyal
series.Comment: 27 pages, no figure
Solution conformations of early intermediates in Mos1 transposition
DNA transposases facilitate genome rearrangements by moving DNA transposons around and between genomes by a cut-and-paste mechanism. DNA transposition proceeds in an ordered series of nucleoprotein complexes that coordinate pairing and cleavage of the transposon ends and integration of the cleaved ends at a new genomic site. Transposition is initiated by transposase recognition of the inverted repeat sequences marking each transposon end. Using a combination of solution scattering and biochemical techniques, we have determined the solution conformations and stoichiometries of DNA-free Mos1 transposase and of the transposase bound to a single transposon end. We show that Mos1 transposase is an elongated homodimer in the absence of DNA and that the N-terminal 55 residues, containing the first helix-turn-helix motif, are required for dimerization. This arrangement is remarkably different from the compact, crossed architecture of the dimer in the Mos1 paired-end complex (PEC). The transposase remains elongated when bound to a single-transposon end in a pre-cleavage complex, and the DNA is bound predominantly to one transposase monomer. We propose that a conformational change in the single-end complex, involving rotation of one half of the transposase along with binding of a second transposon end, could facilitate PEC assembly
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