1,033,635 research outputs found
Assessment of wind energy potential of two sites in North-East, Nigeria
The study is used to assess the wind energy potential of Maiduguri and Potiskum, two sites in North-East,
Nigeria. 21 years (1987e2007) monthly mean wind data at 10 m height were assessed from the Nigeria
Meteorological department and subjected to 2-parameter Weibull and other statistical analyzes. The
result showed that average monthly mean wind speed variation for Potiskum ranged from 3.90 to
5.85 m/s, while for Maiduguri, it ranged from 4.35 to 6.33 m/s. Seasonally, data variation between the dry
and wet seasons revealed that, the mean wind speed variation for Potiskum ranged from 4.46 (for dry) to
5.16 m/s (for wet), while for Maiduguri it ranged from 5.10 (dry) to 5.59 m/s (wet). The wind power
density variation based on the Weibull analysis ranged from 102.54 to 300.15 W/m2 for Potiskum and it
ranged from 114.77 to 360.04 W/m2 for Maiduguri respectively. Moreover, Maiduguri was found to be the
better of the sites in terms of monthly and seasonal variation of mean wind speed, but they both can be
suitable for stand alone and medium scale wind power generation
A Survey of Proper Motion Stars. XVII. A Deficiency of Binary Stars on Retrograde Galactic Orbits and the Possibility that omega Centauri is Related to the Effect
We find a deficiency of binary stars moving on strongly retrograde Galactic
orbits. No binary deficiencies are seen for U or W velocities, however. From
theoretical analyses, we rule out preferential disruption of pre-existing
binary stars due to encounters with massive perturbers. We also rule out
globular clusters as the source of the effect since prograde motions are more
likely to create such an effect. We search for star streams and find one
possible candidate, but it is not on a retrograde orbit and probably represents
the remains of a cluster that has passed too near the Galactic center. Based on
a very small number of stars, we find that about the right fraction of stars on
retrograde Galactic orbits share some chemical similarities to the cluster
omega Cen, suggesting that its parent galaxy could be the explanation.Comment: To appear in the Astronomical Journal (March 2005 issue
Constitutive Modeling of Wind Energy Potential of Selected Sites in Nigeria: A Pre-Assessment Model
In this chapter, the authors present the result of a study carried out to develop a pre-assessment model
that can be used to carry out a preliminary study on the availability of wind energy resources of a site.
21 years’ (1987 – 2007) monthly average wind speeds for 18 locations in Nigeria were used to create
the simple constitutive model. The locations span across the six geopolitical zones of the nation with
three stations from each zone. Various statistical procedures were employed in the development of the
model. The outcome gave an empirical model, which if employed, will lead to determining the mod-
est range of wind energy potential of a site. Further, the results from this model were compared with
those from the well-established two-parameter Weibull statistical distribution function and found to be
reasonably adequate. Thus with this model, decision on site selection for complete assessment can be
made without much rigour
Assessment of Wind Power Potential and Wind Electricity Generation Using WECS of Two Sites in South West, Nigeria
The study was used to analyze the wind characteristics of Shaki (08.40’ N; 03.23’ E; Altitude 457.0 m; Air density 1.1723 kg/m3) and Iseyin (07.58’ N; 03.36’ E; Altitude 330.0 m; Air density 1.1869 kg/m3), two local sites in Oyo State, Nigeria. 21 years monthly mean wind speeds at 10 m height obtained from the Nigeria meteorological department were employed together with the Weibull 2-parameter distribution and other statistics to carry out monthly, seasonal and whole years’ analyses of the sites’ wind profiles for electricity generation. It was found that the whole data spread ranged between 0.9 and 9.1 m/s for the two sites while the 21 years’ average ranged between 3.2 and 5.1 m/s and 2.9 and 4.7 m/s for Shaki and Iseyin sites respectively. Three wind energy conversion systems were employed with the results and it was discovered that, the sites have capacity to generate MWh to GWh of electricity at an average cost/kWh of between € (0.025 and 0.049) and that a turbine with technical parameters of cut-in, cut-out and rated wind speeds of 3.0, 25 and 11.6 m/s is appropriate for the sites
Boundary conditions for coupled quasilinear wave equations with application to isolated systems
We consider the initial-boundary value problem for systems of quasilinear
wave equations on domains of the form , where is
a compact manifold with smooth boundaries . By using an
appropriate reduction to a first order symmetric hyperbolic system with maximal
dissipative boundary conditions, well posedness of such problems is established
for a large class of boundary conditions on . We show that our
class of boundary conditions is sufficiently general to allow for a well posed
formulation for different wave problems in the presence of constraints and
artificial, nonreflecting boundaries, including Maxwell's equations in the
Lorentz gauge and Einstein's gravitational equations in harmonic coordinates.
Our results should also be useful for obtaining stable finite-difference
discretizations for such problems.Comment: 22 pages, no figure
The Scattering Polarization of the Sr I 4607 \AA Line at the Diffraction Limit Resolution of a 1-m Telescope
One of the greatest challenges in solar and stellar physics in coming years
will be to observe the Second Solar Spectrum with a spatial resolution
significantly better than 1 arcsec. This type of scattering polarization
observations would probably allow us to discover hitherto unknown aspects of
the Sun's hidden magnetism. Here we report on some theoretical predictions for
the photospheric line of Sr I at 4607 \AA, which we have obtained by solving
the three-dimensional (3D) radiative transfer problem of scattering line
polarization in a realistic hydrodynamical model of the solar photosphere. We
have taken into account not only the anisotropy of the radiation field in the
3D medium and the Hanle effect of a tangled magnetic field, but also the
symmetry breaking effects caused by the horizontal atmospheric inhomogeneities
produced by the solar surface convection. Interestingly, the Q/I and U/I linear
polarization signals of the emergent spectral line radiation have sizable
values and fluctuations, even at the very center of the solar disk where we
meet the forward scattering case. The ensuing small-scale patterns in Q/I and
U/I turn out to be sensitive to the assumed magnetic field model, and are of
great diagnostic value. We argue that it should be possible to observe them
with the help of a 1-m telescope equipped with adaptive optics and a suitable
polarimeter.Comment: Accepted for publication in The Astrophysical Journal Letters (12
pages and 2 color figures
Cu(II) and Fe(III) complexes of sulphadoxine mixed with pyramethamine: Synthesis, characterization, antimicrobial and toxicology study
Two new mixed ligands metal complexes of sulphadoxine and pyramethamine were prepared by using CuCl2.6H2O and FeCl3.6H2O. The complexes were characterized by elemental analysis, melting point determination, molar conductivity, metal content analysis (AAS), IR, magnetic susceptibility measurements and UV-Visible spectroscopy. Based on the analytical and spectroscopic data, the complexes were proposed to have the formulae [M1L1L2(Cl)2] and [M2L1L2(Cl)3] (where M1 = Cu(II), M2 = Fe(III)), L1 = sulphadoxine, L2 = pyramethamine). The spectroscopic data proposed L1 to be a monodentate ligand and coordinated through N atom of the NH2 group in both complexes. Also, L2 was proposed to be tridentate ligand and coordinated through N atom of the NH2 groups and through N atom of imine group. However, [M1L1L2(Cl)2] and [M2L1L2(Cl)3] were proposed to possess distorted octahedral geometry. Conductivity measurement values supported the non-electrolytic nature of the complexes. The complexes have been tested in vitro against a number of pathogenic bacteria [g(+) Escherichia coli, g(+) Proteus species, g(+) Pseudomonas aeruginosa and g(+) Salmonella typhi] by using disc diffusion method. Obtained results indicated that the metal complexes exhibited better antibacterial activities as compared to the ligands. Toxicology tests against some tissues of albino rat (Rattus novergicuss) revealed toxicity of the complexes in the kidney as compared to the parent drugs. [M1L1L2(Cl)2] was found to be toxic to the sera, livers and kidneys of the rats used, while [M2L1L2(Cl)3] was found to be non-toxic to the sera, livers and kidneys of the rats as their alkaline phosphatase (ALP) values showed non-significant difference to the control value
Contextual barriers to mobile health technology in African countries: a perspective piece
On a global scale, healthcare practitioners are now beginning to move from traditional desktop-based computer technologies towards mobile computing environments[1]. Consequently, such environments have received immense attention from both academia and industry, in order to explore these promising opportunities, apparent limitations, and implications for both theory and practice[2]. The application of mobile IT within a medical context, referred to as mobile health or mHealth, has revolutionised the delivery of healthcare services as mobile technologies offer the potential of retrieving, modifying and entering patient-related data/information at the point-of-care. As a component of the larger health informatics domain mHealth may be referred as all portable computing devices (e.g. mobile phones, mobile clinical assistants and medical sensors) used in a healthcare context to support the delivery of healthcare services
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