113 research outputs found
Preliminary Observations on the Relationships of Barbus Species From Cape Coastal Rivers, South Africa (Cypriniformes: Cyprinidae)
Observations on the phylogenetic relationships of Barbus species from the southern Cape Province are made in the light of new data on the post-cranial axial skeleton and other osteological and anatomical features. Particular attention is paid to the relationships of the ‘red fin’ Barbus species, and new evidence on the problematical relationships of the rare African cyprinid species Oreodaimon quathlambae, is presented
Evanescent wave optical trapping and transport of micro- and nanoparticles on tapered optical fibers
We investigate the manipulation of microscopic and nanoscopic particles using the evanescent optical field surrounding an optical fiber that is tapered to a micron-scale diameter, and propose that this scheme could be used to discriminate between, and thereby sort, metallic nanoparticles. First we show experimentally the concept of the transport of micron-sized spheres along a tapered fiber and measure the particle velocity. Having demonstrated the principle we then consider theoretically the application to the optical trapping and guiding of metallic nanoparticles, where the presence of a plasmon resonance is used to enhance optical forces. We show that the dynamics of the nanoparticles trapped by the evanescent field can be controlled by the state of polarization of the fiber mode, and by using more than one wavelength differently detuned from the nanoparticle plasmon resonance. Such a scheme could potentially be used for selectively trapping and transporting nano- or microscopic material from a polydisperse suspension
Mammalian production of an isotopically enriched outer domain of the HIV-1 gp120 glycoprotein for NMR spectroscopy
NMR spectroscopic characterization of the structure or the dynamics of proteins generally requires the production of samples isotopically enriched in 15N, 13C, or 2H. The bacterial expression systems currently in use to obtain isotopic enrichment, however, cannot produce a number of eukaryotic proteins, especially those that require post-translational modifications such as N-linked glycosylation for proper folding or activity. Here, we report the use of an adenovirus vector-based mammalian expression system to produce isotopically enriched 15N or 15N/13C samples of an outer domain variant of the HIV-1 gp120 envelope glycoprotein with 15 sites of N-linked glycosylation. Yields for the 15N- and 15N/13C-labeled gp120s after affinity chromatography were 45 and 44 mg/l, respectively, with an average of over 80% isotope incorporation. Recognition of the labeled gp120 by cognate antibodies that recognize complex epitopes showed affinities comparable to the unlabeled protein. NMR spectra, including 1H-15N and 1H-13C HSQCs, 15N-edited NOESY-HSQC, and 3D HNCO, were of high quality, with signal-to-noise consistent with an efficient level of isotope incorporation, and with chemical shift dispersion indicative of a well-folded protein. The exceptional protein yields, good isotope incorporation, and ability to obtain well-folded post-translationally modified proteins make this mammalian system attractive for the production of isotopically enriched eukaryotic proteins for NMR spectroscopy
Cryptic Diversity of African Tigerfish (Genus Hydrocynus) Reveals Palaeogeographic Signatures of Linked Neogene Geotectonic Events
The geobiotic history of landscapes can exhibit controls by tectonics over biotic evolution. This causal relationship positions ecologically specialized species as biotic indicators to decipher details of landscape evolution. Phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, including fishes, can reveal key events of drainage evolution, notably where geochronological resolution is insufficient. Where geochronological resolution is insufficient, phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, notably fishes, can reveal key events of drainage evolution. This study evaluates paleo-environmental causes of mitochondrial DNA (mtDNA) based phylogeographic records of tigerfishes, genus Hydrocynus, in order to reconstruct their evolutionary history in relation to landscape evolution across Africa. Strong geographical structuring in a cytochrome b (cyt-b) gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus. The dated phylogeny constrains the principal cladogenic events that have structured Hydrocynus diversity from the late Miocene to the Plio-Pleistocene (ca. 0–16 Ma). Phylogeographic tests reveal that the diversity and distribution of Hydrocynus reflects a complex history of vicariance and dispersals, whereby range expansions in particular species testify to changes to drainage basins. Principal divergence events in Hydrocynus have interfaced closely with evolving drainage systems across tropical Africa. Tigerfish evolution is attributed to dominant control by pulses of geotectonism across the African plate. Phylogenetic relationships and divergence estimates among the ten mtDNA lineages illustrates where and when local tectonic events modified Africa's Neogene drainage. Haplotypes shared amongst extant Hydrocynus populations across northern Africa testify to recent dispersals that were facilitated by late Neogene connections across the Nilo-Sahelian drainage. These events in tigerfish evolution concur broadly with available geological evidence and reveal prominent control by the African Rift System, evident in the formative events archived in phylogeographic records of tigerfish
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia
Primary Research PaperSpecific concepts of fluvial ecology are
well studied in riverine ecosystems of the temperate
zone but poorly investigated in the Afrotropical
region. Hence, we examined the longitudinal zonation
of fish and adult caddisfly (Trichoptera) assemblages
in the endorheic Awash River (1,250 km in length),
Ethiopia. We expected that species assemblages are
structured along environmental gradients, reflecting
the pattern of large-scale freshwater ecoregions. We
applied multivariate statistical methods to test for differences in spatial species assemblage structure and
identified characteristic taxa of the observed biocoenoses
by indicator species analyses. Fish and
caddisfly assemblages were clustered into highland
and lowland communities, following the freshwater
ecoregions, but separated by an ecotone with highest
biodiversity. Moreover, the caddisfly results suggest
separating the heterogeneous highlands into a forested
and a deforested zone. Surprisingly, the Awash
drainage is rather species-poor: only 11 fish (1
endemic, 2 introduced) and 28 caddisfly species (8
new records for Ethiopia) were recorded from the
mainstem and its major tributaries. Nevertheless,
specialized species characterize the highland forests, whereas the lowlands primarily host geographically
widely distributed species. This study showed that a
combined approach of fish and caddisflies is a
suitable method for assessing regional characteristics
of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio
Museum and herbarium collections for biodiversity research in Angola
The importance of museum and herbarium collections is especially great
in biodiverse countries such as Angola, an importance as great as the challenges
facing the effective and sustained management of such facilities. The interface that
Angola represents between tropical humid climates and semi-desert and desert
regions creates conditions for diverse habitats with many rare and endemic species.
Museum and herbarium collections are essential foundations for scientific studies,
providing references for identifying the components of this diversity, as well as
serving as repositories of material for future study. In this review we summarise the
history and current status of museum and herbarium collections in Angola and of
information on the specimens from Angola in foreign collections. Finally, we provide
examples of the uses of museum and herbarium collections, as well as a roadmap
towards strengthening the role of collections in biodiversity knowledge
generationinfo:eu-repo/semantics/publishedVersio
Biodiversity conservation: history, protected areas and hotspots
Angola is a large country of great physiographic, climatic and habitat
diversity, with a corresponding richness in animal and plant species. Legally protected
areas (National Parks and Game Reserves) were established from the 1930s
and occupied 6% of the country’s terrestrial area at the time of independence in
1975. As a consequence of an extended war, the Protected Areas were exposed to
serious neglect, poaching and land invasions. Many habitats of biogeographic
importance, and many rare and endemic species came under threat. The recently
strengthened administration gives cause for optimism that a new era for biodiversity
conservation is at hand. The Protected Areas system was greatly expanded in 2011,
and increasing resources are being made available towards achieving management
effectivenessinfo:eu-repo/semantics/publishedVersio
Mid-Crustal Focused Fluid Movement: Thermal Consequences and Silica Transport
Numerical models have been constructed to assess the thermal consequences and silica transport that would result if water released by regional metamorphic dehydration or cooling plutons were focused into large-scale (10 km) fracture zones. Two fracture zone model geometries have been considered, in one the fracture zone is planar, and in the other the fracture zone is radially symmetric. In both models dispersion and collection of fluids is simulated. The model results indicate that for planar or radially symmetric fracture zones, hydrothermal flow rates must approach 0.1 g/s (per m crack length) or 1 kg/s, respectively, to produce significant thermal effects. Given that regional metamorphic fluid fluxes are probably < 10−9 kg/m2−s, generation of a thermal ano-maly by fluids released during metamorphic dehydration into a planar fracture zone requires an unrealistic degree of lateral flow (>50 km). The collection area required to produce a detectable heating effect about a radially symmetric fracture zone is smaller (a radius of ∼ ∼ 15 km), but also implausibly large. These scales suggest tha
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