865 resultados para African savanna


Relevância:

20.00% 20.00%

Publicador:

Resumo:

This article aims to propose a chronological subdivision in the history of African communication. African communication today is one of the most important axes for implementing development strategies, sustaining education, health, and schooling programmes, and so on. However, many of these programmes fail due to a lack of or ineffective communication between international organisations, local elite and lay people. The reasons for this situation must be found in Africa’s history of communication, which has undergone radical transformations in its different phases. Using the functionalist analysis drawn up by Jakobson, this article proposes a new chronological subdivision of Africa’s history of communication, reflecting on the current contradictions in contemporary communication in Africa.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Scorpion venoms are a particularly rich source of neurotoxic proteins/peptides that interact in a highly specific fashion with discrete subtypes of ion channels in excitable and non-excitable cells. Here we have employed a recently developed technique to effect molecular cloning and structural characterization of a novel putative potassium channel-blocking toxin from the same sample of venom from the North African scorpion, Androctonus amoreuxi. The deduced precursor open-reading frame is composed of 59 amino acid residues that consists of a signal peptide of approximately 22 amino acid residues followed by a mature toxin of 37 amino acid residues. The mature toxin contains two functionally important residues (Lys27 and Tyr36), constituting a functional dyad motif that may be critical for potassium channel-blocking activity that can be affirmed from structural homologs as occurring in the venoms from other species of Androctonus scorpions. Parallel proteomic/transcriptomic studies can thus be performed on the same scorpion venom sample without sacrifice of the donor animal.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Energy metabolism varies considerably between different groups of endotherms, yet there is little or no reported variation among extant groups of reptiles. We measured lower resting metabolic rates (RMRs) in Kalahari tent tortoises (Psammobate oculiferus) than in sympatric Leopard tortoises (Geochelone pardalis). G pardalis also had RMR values that were higher than the allometric prediction for reptiles whereas P oculiferus had RMR values that were not significantly different from the prediction. Differences in RMR between the two species may have occurred because of the large differences in body mass, differing body temperatures, differences in growth rates, or because there may have been differences in the heat increment of feeding.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

1. Free-living animals make complex decisions associated with optimizing energy and nutrient intake. In environments where ambient temperatures fall below the thermoneutral zone, homeotherms must choose whether or not to forage, how long and what to forage for, and whether or not to perform activities that conserve energy.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Seven ethnobotanically selected medicinal plants were screened for their antimycobacterial activity. The mininium inhibitory concentration (MIC) of four plants namely Artemisia afra, Dodonea angustifolia, Drosera capensis and Galenia africana ranged from 0.781 to 6.25 mg/mL against Mycobacterium smegmatis. G. africana showed the best activity exhibiting an MIC of 0.78 mg/mL and a minimum bactericidal concentration (MBC) of 1.56 mg/mL. The MICs of ethanol extracts of A angustifolia and G. africana against M. tuberculosis were found to be 5.0 and 1.2 mg/mL respectively. The mammalian cytotoxicity IC50 value of the most active antimycobacterial extract, from G. africana, was found to be 101.3 mu g/mL against monkey kidney Vero cells. Since the ethanol G. africana displayed the best antimycobacterial activity, it was subjected to fractionation which led to the isolation of a flavone, 5,7,2'-trihydroxyflavone. The MIC of this compound was found to be 0.031 mg/mL against M. smegmatis and 0.10 mg/mL against M. tuberculosis. This study gives some scientific basis to the 14 traditional use of these plants for TB-related symptoms. Copyright (C) 2008 John Wiley & Sons, Ltd.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We describe the isolation and structural characterization of a family of antimicrobial peptides related to kassinatuerin-2, from the skin secretion of the African hyperoliid frog, Kassina maculata. All four peptides, designated kassinatuerin-2Ma through Md, are C-terminally-amidated 20-mers with the consensus sequence – FX1GAIAAALPHVIX2AIKNAL – where X1 = L/F/V/I and X2 = S/N. All four peptides are encoded by precursors of 69 amino acids. Synthetic replicates of all kassinatuerin-2 related peptides displayed a potent inhibitory activity against Staphylococcus aureus with a minimal inhibitory concentration of 16 µM, at which concentration, however, they effected 18% haemolysis of horse erythrocytes after 2 h. Despite obvious membranolytic properties, all peptides were ineffective at inhibiting the growth of Escherichia coli at concentrations up to 200 µM and were relatively ineffective against Candida albicans (MIC 120 µM). The kassinatuerin-2 related peptides of K. maculata skin secretion thus possess a discrete antimicrobial and weak haemolytic activity in contrast to the prototype kassinatuerin-2 from the skin secretion of Kassina senegalensis.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This paper investigates if benchmark African equity indices exhibit the stylized facts reported for financial time-series returns. The returns distributions of the Africa All-Share, Large, Medium and Small Company Indices were found to be leptokurtotic, had fat-tails, over time experienced volatility clustering and exhibited long memory in volatility. Both the All-Share and Large Company Indices were found to exhibit leverage effects. In contrast, positive shocks had a greater impact on future volatility for the Small Company Index which implies a reverse leverage effect. This finding could reflect a bull/bubble market for small capitalisation stocks in Africa.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions(1). Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-richmiddle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few(2-4), especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (similar to 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.