Research for the future development of aquaculture in Ghana.

Aquaculture development, Conferences, Agribusiness, Agricultural and Food Policy, International Development,

What is the Brillouin Zone of an Anisotropic Photonic Crystal?

The concept of the Brillouin zone (BZ) in relation to a photonic crystal fabricated in an optically anisotropic material is explored both experimentally and theoretically. In experiment, we used femtosecond laser pulses to excite THz polaritons and image their propagation in lithium niobate and lithium tantalate photonic crystal (PhC) slabs. We directly measured the dispersion relation inside PhCs and observed that the lowest bandgap expected to form at the BZ boundary forms inside the BZ in the anisotropic lithium niobate PhC. Our analysis shows that in an anisotropic material the BZ - defined as the Wigner-Seitz cell in the reciprocal lattice - is no longer bounded by Bragg planes and thus does not conform to the original definition of the BZ by Brillouin. We construct an alternative Brillouin zone defined by Bragg planes and show its utility in identifying features of the dispersion bands. We show that for an anisotropic 2D PhC without dispersion, the Bragg plane BZ can be constructed by applying the Wigner-Seitz method to a stretched or compressed reciprocal lattice. We also show that in the presence of the dispersion in the underlying material or in a slab waveguide, the Bragg planes are generally represented by curved surfaces rather than planes. The concept of constructing a BZ with Bragg planes should prove useful in understanding the formation of dispersion bands in anisotropic PhCs and in selectively tailoring their optical properties.Comment: 9 pages, 6 figure

THz generation using a reflective stair-step echelon

We present a novel method for THz generation in lithium niobate using a reflective stair-step echelon structure. The echelon produces a discretely tilted pulse front with less angular dispersion compared to a high groove-density grating. The THz output was characterized using both a 1-lens and 3-lens imaging system to set the tilt angle at room and cryogenic temperatures. Using broadband 800 nm pulses with a pulse energy of 0.95 mJ and a pulse duration of 70 fs (24 nm FWHM bandwidth, 39 fs transform limited width), we produced THz pulses with field strengths as high as 500 kV/cm and pulse energies as high as 3.1 $\mu$J. The highest conversion efficiency we obtained was 0.33%. In addition, we find that the echelon is easily implemented into an experimental setup for quick alignment and optimization.Comment: 19 pages, 4 figure

Rice Fields Chemical and Physical Properties and the Implications on Breeding Strategie

Soil related constraints are major limiting factors in crop production in the Sahel. The objective of this study was to assess the properties of farmer's fields soil and irrigation water in Niger and the implications in rice improvement. Composite soil samples were collected from irrigated and non-irrigated fields. Sample of irrigation water was also collected. Physical and chemical analyses were performed in the laboratory. The results showed that most of rice fields were clayey and the non irrigated ones were mostly sandy. The soils were acidic and saline, the electrical conductivity ranged from 2.2 to 16.5 decisiemens per meter. The T-test showed that total dissolved salt, sodium adsorption ratio, cation exchange capacity, and organic matter percentage were significantly higher in irrigated fields than non-irrigated fields. The irrigated soils pH varied from 3.2 to 6.8, the electrical conductivity was greater than 4, and the sodium adsorption ratio was below 13 while the exchangeable sodium percentage was below 15. The irrigation water samples varied in term of ion content from site to site. The total sodium quantity estimated to be deposited varied from 87 kg/ha/year to 218 kg/ha/year. Rice fields' soils are saline and are getting worsened by irrigation water that contains salt. Therefore, the development of rice varieties that could withstand osmotic and ionic salt stress is necessary for sustainable production in the Sahel ecozone

A first checklist of cetaceans of Ghana, Gulf of Guinea, and a shore-based survey of interactions with coastal fisheries. Scientific Committee document SC/51/SM35, International Whaling Commission, May 1999, Grenada

To date, six cetacean species are confirmed to occur in coastal waters off Ghana: five odontocetes Stenella clymene, Steno bredanensis, Tursiops truncatus, Kogia simus, Physeter macrocephalus, and Megaptera novaeangliae. A stranded humpback whale calf raised questions about breeding stock. We found no evidence for the presence of the Atlantic hump-backed dolphin Sousa teuszii ; either it has become rare or it does not occur off Ghana. Unrestrained coastal development may pose a threat for nearshore species. Regular and year-round bycatches of small cetaceans are documented in artisanal gillnet fisheries from Apam, Jamestown (Accra), Kpone and Winneba. At Apam, drift gillnet fishermen intentionally capture dolphins with sharks and tuna. Annual takes at Apam and Jamestown probably count in the low hundreds, higher than at Kpone and Winneba. Bottlenose dolphins are also known to be taken in semi-industrial purse-seines (Jamestown). Carcasses are not filleted, but hacked into small portions including bone, and retailed locally for food. This explains why beach-combing around fishing villages did not yield any findings of skeletal parts. Field research and monitoring effort should continue

Relationship between Patient Anatomical Thickness and Radiographic Exposure Factors for Selected Radiologic Examinations

The most common cause of errors in radiographic examinations is inappropriate selection of exposure factors, which depends on the patient’s anatomical thickness. Inappropriate selection of exposure factors could lead to either underexposed or overexposed radiographs and unnecessary radiation exposure to the patient. The study sought to assess the relationship between patient anatomical thickness and their corresponding radiographic exposure factors used in the selected examinations. Anatomical thicknesses of patients aged 18 years and above, who presented for chest, lumbar spine or pelvis radiographic examinations at the Korle-Bu Polyclinic, from April to May 2014, were measured and recorded using a calliper of least count 0.1cm. The corresponding exposure factors (kVp and mAs) used for each examination were recorded as well as the demographic data of the patients. The study established a correlation between patient anatomical thickness and exposure factors. The results revealed a positive correlation between kVp, mAs and anatomical thickness in almost all the examinations under study. A low-negative correlation between mAs and kVp was recorded for lumbar spine lateral examinations. As mAs increases, kVp reduced marginally. KEYWORDS: kVp, mAs, anatomical thicknes

Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase

Ultrafast two-dimensional spectroscopy utilizes correlated multiple light-matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum. Its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. Here we report ultrafast two-dimensional terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by three terahertz field-dipole interactions. The nonlinear time-domain orientation signals are mapped into the frequency domain in two-dimensional rotational spectra which reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.Comment: 31 pages, 14 figure

Effect of Irrigation Management Methods on Growth, Grain Yield and Water Productivity of Three Lowland Rice (Oryza sativa L.) Varieties

It has been predicted that Ghana will face water shortage by the year 2025 due to increased demand of water resources from all sectors of the economy. Rice production will be negatively affected since rice consumes the highest amount of water in the agricultural sector. To develop a strategy to reduce water use for rice production while maintaining or increasing rice yield, a pot experiment was carried out in the screen house at Soil and Irrigation Research Centre - Kpong during 2016 and 2017 cropping seasons to determine the effect of irrigation management methods on growth, yield and water productivity of three rice varieties. A three by five (3 x 5) factorial experiment was laid out in a randomized complete block design and replicated six (6) times. The levels of the variety were: Agra (VA), Ex Baika (VB) and a hybrid (VH). Irrigation management methods included: continuous submergence (I1), alternate wet and dry soil condition (AWD) from transplanting to panicle initiation (PI) then submergence to harvest (I2), AWD from transplanting to booting then submergence to harvest (I3), AWD from transplanting to lowering then submergence to harvest (I4), and continuous AWD (I5). Results from the experiment revealed that, I3 saved 21.7% and 20.4% of water used when compared with I1 in 2016 and 2017, respectively however, these treatments produced similar growth and yield in both seasons. I3VH recorded 21.2% and 20.8% of water saved in 2016 and 2017, respectively however, it produced similar grain yield with I2VH and I1VH treatments in both seasons

Quality of Artesunate Tablets Sold in Pharmacies in Kumasi, Ghana

Purpose: The study was carried out to evaluate the quality of artesunate tablets sold in retail and wholesale pharmacies in Kumasi, Ghana. In particular, the study sought to ascertain the presence or otherwise of counterfeit artesunate tablets in Kumasi. Method: Artesunate tablets were purchased from pharmacies in Kumasi for the study. The mechanical properties of the tablets were evaluated, namely: uniformity of weight, breaking strength, friability and rate of disintegration in aqueous medium. Colorimetric methods were used to determine the presence of artesunate and to assay the tablets. Result: None of the artesunate tablets sampled was found to be a counterfeit. Most of the brands had acceptable mechanical properties in terms of mass uniformity, hardness, friability and disintegration time. However, the artesunate content of the tablets was variable (47.9-99.9 %). Six (35.3 %) of the samples passed the International Pharmacopoeia content uniformity test (93.7-99.9 %) while 11 (64.7 %) failed the test (47.9-89.4 %). However, only 3 (17.6 %) of the samples met the European Pharmacopoeia (Ph. Eur.) content requirements while 14 (82.4 %) failed to meet the requirements. Conclusion: The presence of substandard artesunate tablets on the Ghanaian market should alert drug regulatory authorities to be vigilant and continually monitor the quality of this life-saving drug. Keywords: Artesunate tablets, Artemisinins, Fast-red TR salt, Counterfeit drugs, Substandard drugs.Tropical Journal of Pharmaceutical Research Vol. 7(4) 2008: pp. 1179-118

Oxidation Behaviour and Bio-oxidation of Gold-bearing Sulphide Ores: Oxygen Capabilities and Challenges

The paper presents an overview of bio-oxidation of sulphidic refractory gold ores prior to gold cyanidation. This review discusses several factors, more importantly, oxygen requirements and oxygen limitations in biological oxidation of various sulphide minerals associated with gold ores. The availability of sufficient oxygen in bio-oxidation systems can speed up and enhance the oxidation of sulphide minerals, allowing the gold to be liberated for further extraction. However, oxygen supply and its low solubility in water have been the major limiting factors in bio-oxidation processes. More importantly, oxygen limitations are found to affect the rate of sulphide oxidation and the volume of materials that can be treated for gold leaching. First, the paper discusses the influence of dissolved oxygen on the oxidation behaviour of various sulphide minerals found in refractory gold ores or concentrates. Further discussed are the limiting factors in relation to dissolved oxygen during bio-oxidation of refractory gold ores. This review demonstrates that oxygen availability is a major challenge and therefore, oxygen enhancement techniques or strategies are vitally needed. As well, the review serves to inspire new research into efficient strategies to enhance oxygen availability