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Search Results: 1 - 10 of 557010 matches for " Alexander A.T. Smith "
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Comparative Genomics of Aeschynomene Symbionts: Insights into the Ecological Lifestyle of Nod-Independent Photosynthetic Bradyrhizobia
Damien Mornico,Lucie Miché,Gilles Béna,Nico Nouwen,André Verméglio,David Vallenet,Alexander A.T. Smith,Eric Giraud,Claudine Médigue,Lionel Moulin
Genes , 2012, DOI: 10.3390/genes3010035
Abstract: Tropical aquatic species of the legume genus Aeschynomene are stem- and root-nodulated by bradyrhizobia strains that exhibit atypical features such as photosynthetic capacities or the use of a nod gene-dependent (ND) or a nod gene-independent (NI) pathway to enter into symbiosis with legumes. In this study we used a comparative genomics approach on nine Aeschynomene symbionts representative of their phylogenetic diversity. We produced draft genomes of bradyrhizobial strains representing different phenotypes: five NI photosynthetic strains (STM3809, ORS375, STM3847, STM4509 and STM4523) in addition to the previously sequenced ORS278 and BTAi1 genomes, one photosynthetic strain ORS285 hosting both ND and NI symbiotic systems, and one NI non-photosynthetic strain (STM3843). Comparative genomics allowed us to infer the core, pan and dispensable genomes of Aeschynomene bradyrhizobia, and to detect specific genes and their location in Genomic Islands (GI). Specific gene sets linked to photosynthetic and NI/ND abilities were identified, and are currently being studied in functional analyses.
The Preservation and Conservation of Nigerian Cultural Heritage: An Impetus for Her Development
A.T. Ajayi
The Social Sciences , 2013,
Abstract: The preservation of the cultural heritage of a nation has become an impulse towards its development. Most states of the globe have come to realize that cultural heritage is an essential aspect of human life and its promotion and preservation an asset of a state. This study explores the problems inhibiting cultural integration in a developing country like Nigeria with plural and diversified cultures and the need to promote culture that stresses virtue, which is pivot to growth-oriented economy.
Anaesthesia and Job syndrome
A.T Bosenberg
Southern African Journal of Anaesthesia and Analgesia , 2008,
Abstract: No - Case Report
Construction and the role of Schematism in Kant's philosophy of mathematics A constru o e o papel do esquematismo na filosofia da matemática de Kant
A.T Winterbourne
Trans/Form/A??o , 1990, DOI: 10.1590/s0101-31731990000100008
The problems with multi-species conservation: do hotspots, ideal reserves and existing reserves coincide?
A.T. Lombard
African Zoology , 2011,
Abstract: South Africa urgently requires a national strategic plan for the conservation of the country's biodiversity. The formulation of such a plan would be relatively easy if centres (hotspots) of richness, endemism and rarity were congruent, both within and among many different taxa, if these hotspots captured a large proportion of the total species, and if hotspots fell within existing reserves. The investigation of six vertebrate taxa (viz freshwater fish, frogs, tortoises and terrapins, snakes, birds, and various mammal orders) at a national scale reveals that hotspots are not coincident within taxa. Centres of richness are concentrated in the north-eastern areas of the country, whereas endemism is concentrated in the south-west, and centres of rare and threatened (Red Data Book) species can be in either area. Paired comparisons among taxa reveal greatly varying proportional overlaps of species richness hotspots (0-72%). The proportion of total species falling in hotspots ranges from low (66% for fish) to high (92% for birds). Hotspots are thus not an efficient method of siting representative (ideal) reserves. In order to design a more representative reserve system to protect all vertebrate species, a complementarity algorithm was applied to all taxa separately, and then to all taxa combined. The combined analysis yielded more efficient results (66 reserves are required to represent all 1 074 species at least once) than the separate analyses (97 reserves). Many of these representative reserves coincide with both hotspots and existing reserves, and over 85% of the hotspots of most taxa coincide with existing reserves, thus South Africa's vertebrate fauna could be more effectively protected with only moderate acquisition of new, well-sited reserves. A biome analysis reveals that these reserves will also have to incorporate areas of those biomes that are currently inadequately protected, viz grassland, Succulent Karoo and Nama-Karoo. The methods outlined in this paper should be applied to as many other taxa as possible, in order to aid the formulation of a national strategic plan for biodiversity conservation.
The Ecology of Mangrove and Related Ecosystems Proceedings of the International Symposium held at Mombasa, Kenya 24-30 September 1990 Edited by Victor Jaccarini and Els Martens
A.T. Forbes
African Zoology , 2011,
Introduction to an evaluation of the protection status of South Africa's vertebrates
A.T. Lombard
African Zoology , 2011,
Abstract: During the Zoological Society of Southern Africa's 1994 Symposium in Pietermaritzburg, a theme session was convened to evaluate the protection status of selected groups of South African vertebrates (viz. freshwater fish, frogs, tortoises and terrapins, snakes, birds, and various mammal orders). The research papers presented during that session are reported in this number of the South African Journal of Zoology. The rationale behind the research, and the data and methods used, are described in this introductory paper. South Africa's national and international contractual obligations to conserve its biodiversity, and the urgent need for a national conservation strategy and national conservation information networks and databases, are also discussed.
Evolving perspectives on caribou population dynamics, have we got it right yet?
A.T. Bergerud
Rangifer , 1996,
Abstract: The roles of food, weather and predation are compared between sedentary and migratory caribou herds. Sedentary herds disperse (space out) at calving time while the cows of migratory herds move in masse (space away) to calving grounds to reduce predation risk. The sedentary ecotype calves on ranges near open water if tree cover is present or in rugged topography in the absence of tree cover. The migratory ecotype aggregates on calving grounds located on alpine mountain plateaus or on the tundra north of the Arctic tree line. The two herds with the greatest densities in North America, the sedentary Slate Islands Herd and the migratory George River Herd both had changes in abundance that followed summer food problems. The hypothesis that winter lichen supplies determine abundance and set the carrying capacity is rejected. Lichens are not a necessary food for caribou. A review of the mortality of young calves documented in the past 30 years provides no support for the hypothesis that hypothermia is a common mortality problem. Young calves documented can be born inviable at birth if their dams are severely malnourished. The migratory caribou in North America reached peak numbers in the 1980s after wolf populations were heavily harvested in the 1970s. The sedentary ecotype is frequently regulated by wolf predation that affects both recruitment (R) and the mortality of adults (M). The balance between R/M schedules commonly occurs when R (calves) represents, about 15% of the herd and when numbers (prorated to the area of the dispersed annual range) approximate 0.06 caribou/km2. Population limitation of migratory herds by predation has occurred in the NWT and in several herds in Alaska but only when wolf densities were > 6.5/1000 km2. Wolf predation halted the growth of the George River Herd in 1980 but then wolves contracted rabies and the herd again increased and degraded spring/summer ranges. The reduced summer phytomass resulted in lower birth rates and increased the vulnerability of calves and possibly adults to wolf predation. Stabilizing mechanisms for migratory herds include movements between herds above tree line and range contractions/expansions with resultant changes in demography. It is hypothesized that the most important ecological variable in all seasonal distributions of caribou is predation risk rather than to maximize forage supplies.
A Case Study of High-Resolution Gravity and Wenner-Schlumberger Resistivity for Geotechnical Engineering: An Example from North Jordan
A.T. Batayneh
Research Journal of Applied Sciences, Engineering and Technology , 2013,
Abstract: During 2011, high-resolution gravity and Direct Current (DC) Wenner-Schlumberger resistivity geophysical techniques were made over an area of 80×70 m at the location of a proposed educational building at Jarash City, north Jordan. The objectives of the study were (i) to evaluate the resolution of these geophysical techniques in field work in detecting and locating anomalies caused by subsurface structures and (ii) to provide additional rock stratigraphy information at the site. High-resolution gravity data were collected on 5 m grid station along survey lines spaced 5 m apart. Resistivity measurements were carried out utilizing the Wenner-Schlumberger array configuration with 2-m electrode spacing along thirteen profile lines. Results of the survey demonstrated a strong correlation between the two geophysical techniques and subsurface geology. The interpretations obtained from gravity of the field data provided useful information in detecting near-surface channels. The DC-resistivity surveys allowed the determination of the specific resistivity down to a depth of about 6.5 m. The results indicate zones of chalk, marl and chalky marl with limestone intercalation with low resistivity values. Moderate high resistivity values were detected and were attributed to the presence of marly limestone sedimentary rocks.
De natuurlijke aanwas der bevolking van Suriname.
A.T. Oliviera
Nieuwe West-Indische Gids , 1924,
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