2,127 research outputs found
Some preliminary results of the fine structure profiles of radio refractivity near the surface at Ota, Southwest Nigeria
Some preliminary results are presented of the fine structure profiles of surface radio refractivity, Ns,
over Ota, Southwest Nigeria (6° 42'N, 3° 14'E) computed from in-situ, one minute interval
measurements of surface pressure, temperature and relative humidity. A wireless Davis Vantage
Pro2 Weather Station instrument installed at the Department of Physics, Covenant University, Ota in
April 2012, was used to obtain the measured variables. Hourly, daily and monthly average values of
surface water vapour density, dry, wet and total radio refractivity were obtained for the months of
April 2012 to March 2013. The distance to the radio horizon for a given transmitter height may be
deduced from the observation that Ns is well correlated with the gradient of refractivity over the first
kilometer above ground. Refractivity gradients utilized for the work were those obtained in a previous
work for Oshodi, a meteorological weather station near the coast and close to Ota
Technology requirements for an orbiting fuel depot: A necessary element of a space infrastructure
Advanced planning within NASA has identified several bold space exploration initiatives. The successful implementation of these missions will require a supporting space infrastructure which would include a fuel depot, an orbiting facility to store, transfer and process large quantities of cryogenic fluids. In order to adequately plan the technology development programs required to enable the construction and operation of a fuel depot, a multidisciplinary workshop was convened to assess critical technologies and their state of maturity. Since technology requirements depend strongly on the depot design assumptions, several depot concepts are presented with their effect on criticality ratings. Over 70 depot-related technology areas are addressed
Lattice diffusion and surface segregation of B during growth of SiGe heterostructures by molecular beam epitaxy: effect of Ge concentration and biaxial stress
Si1-xGex/Si1-yGey/Si(100) heterostructures grown by Molecular Beam Epitaxy
(MBE) were used in order to study B surface segregation during growth and B
lattice diffusion. Ge concentration and stress effects were separated. Analysis
of B segregation during growth shows that: i) for layers in epitaxy on
(100)Si), B segregation decreases with increasing Ge concentration, i.e. with
increased compressive stress, ii) for unstressed layers, B segregation
increases with Ge concentration, iii) at constant Ge concentration, B
segregation increases for layers in tension and decreases for layers in
compression. The contrasting behaviors observed as a function of Ge
concentration in compressively stressed and unstressed layers can be explained
by an increase of the equilibrium segregation driving force induced by Ge
additions and an increase of near-surface diffusion in compressively stressed
layers. Analysis of lattice diffusion shows that: i) in unstressed layers, B
lattice diffusion coefficient decreases with increasing Ge concentration, ii)
at constant Ge concentration, the diffusion coefficient of B decreases with
compressive biaxial stress and increases with tensile biaxial stress, iii) the
volume of activation of B diffusion () is positive for biaxial stress while it
is negative in the case of hydrostatic pressure. This confirms that under a
biaxial stress the activation volume is reduced to the relaxation volume
Seasonal Variation of Surface Radio Refractivity and Water Vapour Density for 48 Stations in Nigeria
The monthly and seasonal variation of surface
refractivity and water vapour density were studied using thirtynine
years meteorological data for forty-eight stations in Nigeria.
The factors which influence the transmission of radio signals
operating within the troposphere are water vapour and
refractivity. The results show that the surface refractivity and
water vapour density generally have higher values during the
rainy season than dry season at all station studied. Furthermore
the results show that the value of surface refractivity and water
vapour density varies from about 263 N-units and 3 g/m3 in arid
region of Nigeria (North East) to about 393 N-units and 23 g/m3
in the coastal area of Nigeria (South West) respectively. For
optimal performance of terrestrial radio link across Nigeria it is
required to account for the variability of these parameters for
optimal systems design
Exploiting biomaterial approaches to manufacture an artificial trabecular meshwork: A progress report
Glaucoma is the second leading cause of irreversible blindness worldwide. Glaucoma is a progressive optic neuropathy in which permanent loss of peripheral vision results from neurodegeneration in the optic nerve head. The trabecular meshwork is responsible for regulating intraocular pressure, which to date, is the only modifiable risk factor associated with the development of glaucoma. Lowering intraocular pressure reduces glaucoma progression and current surgical approaches for glaucoma attempt to reduce outflow resistance through the trabecular meshwork. Many surgical approaches use minimally invasive glaucoma surgeries (MIGS) to control glaucoma. In this progress report, biomaterials currently employed to treat glaucoma, such as MIGS, and the issues associated with them are described. The report also discusses innovative biofabrication approaches that aim to revolutionise glaucoma treatment through tissue engineering and regenerative medicine (TERM). At present, there are very few applications targeted towards TM engineering in vivo, with a great proportion of these biomaterial structures being developed for in vitro model use. This is a consequence of the many anatomical and physiological attributes that must be considered when designing a TERM device for microscopic tissues, such as the trabecular meshwork. Ongoing advancements in TERM research from multi-disciplinary teams should lead to the development of a state-of-the-art device to restore trabecular meshwork function and provide a bio-engineering solution to improve patient outcomes
Multi-Technique Analysis of Precipitable Water Vapor Estimates in the sub-Sahel West Africa
Precipitable water vapor (PWV) is an important climate parameter indicative
of available moisture in the atmosphere, it is also an important greenhouse
gas. Observations of precipitable water vapor in sub-Sahel West Africa are
almost non-existent. Several Aerosol Robotic Network (AERONET) sites have been
established across West Africa, and observations from four of them, namely,
Ilorin (4.34o E, 8.32o N), Cinzana (5.93o W, 13.28o N), Banizoumbou (2.67o E,
13.54o N) and Dakar (16.96o W, 14.39o N) are being used in this study. Data
spanning the period from 2004 to 2014 have been selected, they include
conventional humidity parameters, remotely sensed aerosol and precipitable
water information and numerical model outputs. Since in Africa, only
conventional information on humidity parameters is available, it is important
to utilize the unique observations from the AERONET network to calibrate
empirical formulas frequently used to estimate precipitable water vapor from
humidity measurements. An empirical formula of the form PWV=aT_d+b where T_d is
the surface dew point temperature, a and b are constants, was fitted to the
data and is proposed as applicable to the climatic condition of the sub-Sahel.
Moreover, we have also used the AERONET information to evaluate the
capabilities of well-established numerical weather prediction (NWP) models such
as ERA Interim Reanalysis, NCEP-DOE Reanalysis II and NCEP-CFSR, to estimate
precipitable water vapor in the sub-Sahel West Africa, it was found that the
models tend to overestimate the amount of precipitable water at the selected
sites by about 25 %
Molecular Techniques Reveal Wide Phyletic Diversity of Heterotrophic Microbes Associated with Discodermia spp. (Porifera: Demospongiae)
Sponges are well known to harbor large numbers of heterotrophic microbes within their mesohyl. Studies to determine the diversity of these associated microbes have been attempted for only a few shallow water species. We cultured various microorganisms from several species of Discodermia collected from deep water using the \u27Johnson-Sea-Link\u27 manned submersibles, and characterised them by standard microbiological identification methods. Characterisation of a small proportion (ca. 10%) of the total and potential eubacterial isolate collection with molecular systematics techniques revealed a wide diversity of microbes. Phylogenetic analyses of 32 small subunit (SSU) 16S-like rRNA gene sequences from different micorbes indicated high levels of taxonomic diversity assoiated with this genus of sponge. For example, bacteria from at least five cubacterial subdivisions - gamma, alpha, beta, Cytophaga and Gram positive - were isolated from the mesohyl of Discodermia. Several strains were unidentifiable from current sequence databases. No overlap was found between sequences of 24 isolates and 8 sequences obtained by PCR and cloning directly from sponge samples. The abundance and diversity of microbes associated with sponges such as Discodermia suggest that they may play important roles in marine microbial ecology, dispersal and evolution
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