1,034 research outputs found
Habitat selection of an endangered primate, the samango monkey (Cercopithecus albogularis schwarzi): integrating scales to prioritise habitat for wildlife management
Aim: As habitat loss continues to accelerate with global human population growth, identifying landscape characteristics that influence species occurrence is a key conservation priority in order to prevent global biodiversity loss. In South Africa, the arboreal samango monkey (Cercopithecus albogularis sp.) is threatened due to loss and fragmentation of the indigenous forests it inhabits. The aim of this study was to determine the habitat preferences of the samango monkey at different spatial scales, and to identify key conservation areas to inform management plans for this species. Location: This study was carried out in the western Soutpansberg Mountains, which represents the northernmost population of samango monkeys within South Africa, and the only endangered subspecies (C. a. schwarzi). Methods: We used sequentially collected GPS points from two samango monkey groups followed between 2012 â 2017 to quantify the used and available habitat for this species within the western Soutpansberg Mountains. We developed 2nd (selection of ranging area), 3rd (selection within range) and 4th (feeding site selection) order resource selection functions (RSFs) to identify important habitat features at each scale. Through scale integration, we identified three key conservation areas for samango monkeys across Limpopo Province, South Africa. Results: Habitat productivity was the most important landscape variable predicting probability of use at each order of selection, indicating the dependence of these arboreal primates on tall-canopy indigenous forests. Critical habitat across Limpopo was highly fragmented, meaning complete isolation between subpopulations is likely. Main conclusions: Understanding the habitat characteristics that influence samango monkey distribution across South Africa is crucial for prioritising critical habitat for this species. Our results indicated that large, contiguous patches of tallcanopy indigenous forest are fundamental to samango monkey persistence. As such, protected area expansion of large forest patches and creation of forest corridors are identified as key conservation interventions for this species
Cosmology with a long range repulsive force
We consider a class of cosmological models in which the universe is filled
with a (non-electric) charge density that repels itself by means of a force
carried by a vector boson with a tiny mass. When the vector's mass depends upon
other fields, the repulsive interaction gives rise to an electromagnetic
barrier which prevents these fields from driving the mass to zero. This can
modify the cosmology dramatically. We present a very simple realization of this
idea in which the vector's mass arises from a scalar field. The electromagnetic
barrier prevents this field from rolling down its potential and thereby leads
to accelerated expansion.Comment: 15 pages, 8 figures, LaTeX (version accepted for publication in PRD).
3 new figures, extended discussion of observational consequence
Three sites and you are out: Ternary synergistic allostery controls aromatic amino acid biosynthesis in Mycobacterium tuberculosis.
3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyzes the first step in the shikimate
pathway, the pathway responsible for the biosynthesis of the aromatic amino acids Trp, Phe, and Tyr. Unlike
many other organisms that produce up to three isozymes, each feedback-regulated by one of the aromatic
amino acid pathway end products, Mycobacterium tuberculosis expresses a single DAH7PS enzyme that can
be controlled by combinations of aromatic amino acids. This study shows that the synergistic inhibition of this
enzyme by a combination of Trp and Phe can be significantly augmented by the addition of Tyr.We used X-ray
crystallography, mutagenesis, and isothermal titration calorimetry studies to show that DAH7PS from M.
tuberculosis possesses a Tyr-selective site in addition to the Trp and Phe sites, revealing an unusual and
highly sophisticated network of three synergistic allosteric sites on one enzyme. This ternary inhibitory
response, by a combination of all three aromatic amino acids, allows a tunable response of the protein to
changing metabolic demands
Qualitative Properties of Magnetic Fields in Scalar Field Cosmology
We study the qualitative properties of the class of spatially homogeneous
Bianchi VI_o cosmological models containing a perfect fluid with a linear
equation of state, a scalar field with an exponential potential and a uniform
cosmic magnetic field, using dynamical systems techniques. We find that all
models evolve away from an expanding massless scalar field model in which the
matter and the magnetic field are negligible dynamically. We also find that for
a particular range of parameter values the models evolve towards the usual
power-law inflationary model (with no magnetic field) and, furthermore, we
conclude that inflation is not fundamentally affected by the presence of a
uniform primordial magnetic field. We investigate the physical properties of
the Bianchi I magnetic field models in some detail.Comment: 12 pages, 2 figures in REVTeX format. to appear in Phys. Rev.
Particle production from axial fields
We study the production of massive fermions in arbitrary vector and
axial-vector classical backgrounds using effective action techniques. A
perturbative calculation shows the different features of each field and in
particular it is seen that pure temporal axial fields can produce particles
whereas it is not possible for a pure vector background. We also analyze from a
non-perturbative point of view a particular configuration with constant
electric and axial fields and show that the presence of the axial background
inhibits the production from the electric field.Comment: 10 pages, 1 figure, RevTeX; minor corrections, version to appear in
Phys. Rev.
The 22-Year Hale Cycle in cosmic ray flux: evidence for direct heliospheric modulation
The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar-cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted as qA>0 cycle) or negative (qA0 cycles than for qA0 and more sharply peaked for qA0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, we also demonstrate that these polarity-dependent heliospheric differences are evident during the space-age but are much less clear in earlier data: using geomagnetic reconstructions, we show that for the period of 1905 - 1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic-ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age
Untangling the complexities of processing and analysis for untargeted LC-MS data using open-source tools
Untargeted metabolomics is a powerful tool for measuring and understanding complex biological chemistries. However, employment, bioinformatics and downstream analysis of mass spectrometry (MS) data can be daunting for inexperienced users. Numerous open-source and free-to-use data processing and analysis tools exist for various untargeted MS approaches, including liquid chromatography (LC), but choosing the âcorrectâ pipeline isnât straight-forward. This tutorial, in conjunction with a user-friendly online guide presents a workflow for connecting these tools to process, analyse and annotate various untargeted MS datasets. The workflow is intended to guide exploratory analysis in order to inform decision-making regarding costly and time-consuming downstream targeted MS approaches. We provide practical advice concerning experimental design, organisation of data and downstream analysis, and offer details on sharing and storing valuable MS data for posterity. The workflow is editable and modular, allowing flexibility for updated/changing methodologies and increased clarity and detail as user participation becomes more common. Hence, the authors welcome contributions and improvements to the workflow via the online repository. We believe that this workflow will streamline and condense complex mass-spectrometry approaches into easier, more manageable, analyses thereby generating opportunities for researchers previously discouraged by inaccessible and overly complicated software
Effects of N, P and K on Striga asiatica (L.) Kuntze seed germination and infestation of sorghum
Sorghum (Sorghum bicolor (L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kgâ1 soil. With an increase of soil N, the Striga asiatica (L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induce Striga seed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1â1 range. The sorghum root exudate was considerably more active at 0 mg N 1â1, than at 30 mg N 1â1, and the stimulant produced at 150 mg N 1â1 failed to induce Striga seed germination. Presence of N in the growth medium considerably reduced the effectiveness of the stimulating substance produced by sorghum roots, whereas K promoted stimulant activity only in the absence of N. The presence or absence of P in the growth medium did not affect Striga seed germinability, probably due to the inability of this element to interfere with the production or activity of the stimulating substance from the host plants. It can be concluded, therefore, that sorghum plants seem to produce active root exudate only in conditions of N deficienc
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