Radioactivity concentrations and their radiological significance in sediments of the Tema Harbour (Greater Accra, Ghana)

Abstract Studies on environmental radioactivity in tropical Africa are scarce. Therefore, a baseline study of natural ( 238 U, 210 Pb, 226 Ra, 232 Th, 228 Ra, 228 Th, 40 K) and anthropogenic ( 137 Cs) radionuclides was carried out on Tema Harbour (Greater Accra, Ghana) surface sediments and on their radiological significance. Grab surface sediment samples were collected from 21 stations within the Tema Harbour and their radioactivity concentrations measured by gamma spectrometry. The mean sediment radioactivity concentrations (Bq kg −1 dw) were 34 for 238 U, 210 for 210 Pb, 14 for 226 Ra, 30 for 232 Th, 29 for 228 Ra, 31 for 228 Th, 320 for 40 K, and 1.5 for 137 Cs. Large 238 U/ 226 Ra disequilibria were observed in the harbour sediments and a complex dynamics of several mixed sources of sediments within the Tema Harbour can be inferred from the spatial variations in the radioactivity concentrations. The estimated total absorbed dose rate in air ( D ), radium equivalent activity (Ra eq ), external hazard index ( H ex ), annual gonadal dose equivalent (AGDE) and annual effective dose equivalent (AEDE) indicated no significant radiological risks from the sediment radioactivity concentrations. Application of the Environmental Risk from Ionising Contaminants Assessment and Management tool (ERICA) confirmed that the potential dose rates to biota from the sediment radioactivity concentrations are unlikely to pose appreciable ecological risks. The radioactivity levels are compared with levels reported in sediments from other coastal areas of the world

Person-Specific Non-shared Environmental Influences in Intra-individual Variability : A Preliminary Case of Daily School Feelings in Monozygotic Twins

Most behavioural genetic studies focus on genetic and environmental influences on inter-individual phenotypic differences at the population level. The growing collection of intensive longitudinal data in social and behavioural science offers a unique opportunity to examine genetic and environmental influences on intra-individual phenotypic variability at the individual level. The current study introduces a novel idiographic approach and one novel method to investigate genetic and environmental influences on intra-individual variability by a simple empirical demonstration. Person-specific non-shared environmental influences on intra-individual variability of daily school feelings were estimated using time series data from twenty-one pairs of monozygotic twins (age = 10 years, 16 female pairs) over two consecutive weeks. Results showed substantial inter-individual heterogeneity in person-specific non-shared environmental influences. The current study represents a first step in investigating environmental influences on intra-individual variability with an idiographic approach, and provides implications for future behavioural genetic studies to examine developmental processes from a microscopic angle

Nutrient dynamics in the sediment of lake Grevelingen (SW Netherlands)

Het in dit proefschrift beschreven onderzoek richtte zlch op de ultwÍssellng van nutrÍënten tussen bodem en water in de Grevelingen, een in l97l afgesloten zeearm ln zuid-west Nederland. De afsluitlng verllep in twee fasen: in 1964 met de aanleg van de Grevelingendam aan de oostzijde en in 1971 door voltoollng van de Brouwersdam aan de westzijde. Zie: Samenvattin

Feasibility of a Small Scale Intensity Correlation Interferometer

Demand for high-resolution imaging capabilities for both space-based and ground-based imaging systems has created significant interest in improving the design of multi-aperture interferometry imaging systems. Interferometers are a desirable alternative to single aperture imaging systems due to the fact that the angular resolution of a single aperture system is dependent on the diameter of the aperture and the resolution of the image recording device (CCD or otherwise) which quickly results in increased size, weight, and cost. Interferometers can achieve higher angular resolutions with lower resolution recording mediums and smaller apertures by increasing the distance between the apertures. While these systems grow in both size, mechanical, and computational complexity, methods of testing large scale designs with small scale demonstration systems currently do not exist. This paper documents the performance of a small scale multi-aperture intensity correlation interferometer which is used to view a double slit image. The interferometer consists of 2 avalanche photo-diodes connected to a data acquisition computer. The image is produced by shining light through the double slit image an image containment system. The sensors are placed at the far end of the image containment system, and their voltages are recorded and digitally filtered. This study presents the formulation of the design parameters for the interferometer, the assembly and design of the interferometer, and then analyzes the results of the imaging experiment and the methods used to attempt to prevent unwanted noise from corrupting the expected interference pattern. Codes in C and C++ are used to collect and analyze the data, respectively, while Matlab® was used to produce plots of binary data. The results of the analysis are then used to show that a small scale intensity correlation interferometer is indeed feasible and has promising performance

Estimating total nitrogen and phosphorus losses in a data-poor Ethiopian catchment

Selecting a suitable model for a water quality study depends on the objectives, the characteristics of the study area, and the availability, appropriateness, and quality of data. In areas where in-stream chemical and hydrological data are limited but where estimates of nutrient loads are needed to guide management, it is necessary to apply more generalized models that make few assumptions about underlying processes. This paper presents the selection and application of a model to estimate total nitrogen (TN) and total phosphorus (TP) loads in two semiarid and adjacent catchments exposed to pollution risk in north-central Ethiopia. Using specific criteria to assess model suitability resulted in the use of the Pollution Load (PLOAD) model. The model relies on estimates of nutrient loads from point sources such as industries and export coefficients of land use, and it is calibrated using measured TN and TP loads from the catchments. The performance of the calibrated PLOAD model was increased, reducing the sum of errors by 89 and 5% for the TN and TP loads, respectively. The results were validated using independent field data. Next, two scenarios were evaluated: (i) use of riparian buffer strips, and (ii) enhanced treatment of industrial effluents. The model estimated that combined use of the two scenarios could reduce TN and TP loads by nearly 50%. Our modeling is particularly useful for initial characterization of nutrient pollution in catchments. With careful calibration and validation, PLOAD model can serve an important role in planning industrial and agricultural development in data-poor areas.</p