2,246 research outputs found
Landuse and enviromental change in the Lake Chad Basin of Nigeria
The Lake Chad Basin is a major geographical region in the central part of the Sudan zone of Africa. The northern parts, however, extend into the Sahel and the southern parts of the Sahara desert. It consists of an extensive shallow depression of about 1.536.000 km2 (600.000 miles2) of which about 10% lies in Nigeria. The greater part is shared between the three countries of Cameroon, Chad and Niger. Climatically and agriculturally, the Chad Basin lies within the dry or semi-arid zone of Nigeria. It is a marginal area which has experienced severe droughts and considerable environmental changes in recent years. The natural environment, its use and misuse, and the threat of life posed by environmental pollution dominate discussions on environmental change. But in addition to the natural or physical environment, there are other equally important 'environments' which deserve some attention in view of the role that they play in generating economic growth and in ensuring sustainable development which is the central issue in our concern about the environment. These other environments are the cultural environment, the political environment and the economic environment, both internal and external. In the Chad Basin, all these other environments, along with the natural environment have been greatly influenced by its land locked location in the heart of Africa
VO2: A Novel View from Band Theory
New calculations for vanadium dioxide, one of the most controversely
discussed materials for decades, reveal that band theory as based on density
functional theory is well capable of correctly describing the electronic and
magnetic properties of the metallic as well as both the insulating M1 and M2
phases. Considerable progress in the understanding of the physics of VO2 is
achieved by the use of the recently developed hybrid functionals, which include
part of the electron-electron interaction exactly and thereby improve on the
weaknesses of semilocal exchange functionals as provided by the local density
and generalized gradient approximations. Much better agreement with
photoemission data as compared to previous calculations is found and a
consistent description of the rutile-type early transition-metal dioxides is
achieved.Comment: 5 pages, 4 figure
Strong coupling of a qubit to shot noise
We perform a nonperturbative analysis of a charge qubit in a double quantum
dot structure coupled to its detector. We show that strong detector-dot
interaction tends to slow down and halt coherent oscillations. The transitions
to a classical and a low-temperature quantum overdamping (Zeno) regime are
studied. In the latter, the physics of the dissipative phase transition
competes with the effective shot noise.Comment: 5 pages, 4 figure
Molecular structure of the 8.0 kDa subunit of cytochrome-c reductase from potato and its Δψ-dependent import into isolated mitochondria
AbstractThe cytochrome-c reductase (EC 1.10.2.2) of the mitochondrial respiratory chain couples electron transport from ubiquinol to cytochrome c with proton translocation across the inner mitochondrial membrane. The enzyme from potato was shown to be composed of 10 subunits. Isolation and characterization of cDNA clones for the second smallest subunit reveal an open reading frame of 216 bp encoding a protein of 8.0 kDa. The protein exhibits similarities to a 7.2/7.3 kDa subunit of cytochrome-c reductase from bovine and yeast, that is localized on the intermembrane space side of the enzyme complex. It also shows similarity to a previously unidentified 7.8 kDa protein of cytochrome-c reductase from Euglena. The potato 8.0 kDa protein has a segmental structure, as its sequence can be devided into four parts, each comprising a central Arg-(Xaa)5-Val motif. N-terminal sequencing of the mature 8.0 kDa protein indicates the absence of a cleavable mitochondrial targeting sequence. Import of the in vitro synthesized 8.0 kDa protein into isolated potato mitochondria confirms the lack of a presequence and reveals a dependence of the transport on the membrane potatial Δψ across the inner mitochondrial membrane. These features are unique among the intermembrane space proteins known so far
STRUCTURE–ACTIVITY RELATIONSHIPS FOR CHLORO- AND NITROPHENOL TOXICITY IN THE POLLEN TUBE GROWTH TEST
Effective Confinement as Origin of the Equivalence of Kinetic Temperature and Fluctuation-Dissipation Ratio in a Dense Shear Driven Suspension
We study response and velocity autocorrelation functions for a tagged
particle in a shear driven suspension governed by underdamped stochastic
dynamics. We follow the idea of an effective confinement in dense suspensions
and exploit a time-scale separation between particle reorganization and
vibrational motion. This allows us to approximately derive the
fluctuation-dissipation theorem in a "hybrid" form involving the kinetic
temperature as an effective temperature and an additive correction term. We
show numerically that even in a moderately dense suspension the latter is
negligible. We discuss similarities and differences with a simple toy model, a
single trapped particle in shear flow
Behavioural and olfactory responses of Sitophilus zeamais (Coleoptera: Curculionidae) to Aframomum melegueta and Zingiber officinale oleoresins.
The oleoresins extracted from the seeds of alligator pepper, Aframomum melegueta and ginger, Zingiber officinale rhizome using methanol, was evaluated for bioactivity against the maize weevil, Sitophilus zeamais in the laboratory. Using a 4-arm olfactometer, solutions of the oleoresins at a concentration of 1 mg/ml exhibited significant olfactory repellent activity against male and female S. zeamais when tested alone, and in combination with maize seeds. These findings provide a scientific basis for the observed repellent properties of the oleoresins and demonstrate the need for their development in stored product pest protection in Africa where these plants are readily available.KEYWORDS: Oleoresin, Aframomum melegueta, Zingiber officinale, Sitophilus zeamais, Olfactometer
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