ALBERT

Notes: During the Kenya Rift International Seismic Project (KRISP 90) a 450 km long E-W seismic-refraction/wide-angle-reflection profile involving the deployment of 250 instruments was shot across the Kenya Rift. A reflected phase recorded between distances of 260 and 350 km from a 1000 kg shot at the western end of the line in Lake Victoria has been interpreted as originating from about 60 km beneath the western margin of the rift.Detailed processing of this phase has resulted in defining its polarity in relation to the first-arrival diving wave at the same range. Extensive kinematic and dynamic modelling shows there is a high-velocity zone at depths below 60 km under the western flank of the rift. We cannot exclude the presence of a layered alternating high-low-velocity structure as found in the upper mantle beneath the northern part of the N-S seismic profile along the rift axis.Constraints from xenolith studies indicate that anisotropy may explain the high velocity found beneath the reflecting horizon (≥8.40km s−1). Petrological modelling shows that if the anisotropy is due to the preferred orientation of olivine crystals, then either a transverse isotropic structure, in which the ‘a’ and ‘c’ axes are randomly orientated in the horizontal plane, or an orthorhombic structure, in which the fast ‘a’ axis is orientated along the direction of the E-W seismic line, is possible. The reflection could also be caused by a pre-rift structure associated with the Proterozoic collisional orogen involving the Mozambique Orogenic Belt and the Archaean Nyanza Craton, whose contact is subparallel to and lies about 70 km to the west of the Tertiary rift. The evidence presented here delimits the lateral extent of the upper-mantle region of anomalously low-velocity material that is confined to below the surface expression of the rift itself at depths below 60 km.

Notes: Previous seismicity studies in the Kenya Rift have not been able to determine accurately depths of earthquakes, nor have most of them determined epicentres precisely enough to allow correlation of the seismicity with particular surface features. We operated a small dense seismic array for 3 months near Lake Bogoria in the Kenya Rift with the aim of locating microearthquakes in 3-D. 572 earthquakes, 81 per cent with ML 〈 1.0, have been located. The majority of the events are associated with the larger older faults on the Rift shoulder rather than the young ‘grid’ faults in the centre of the Rift. Seismic activity in the central trough cannot be related directly to the surface faulting; we infer that it indicates the presence of deep buried faults. This possibility has important implications for extension estimates and models of the Rift. Most of the activity occurs at depths less than 12 km, and no normal activity is deeper than 16 km. There is a peak in seismic activity at a depth of 9–10 km and the cut-off depth for brittle failure is taken at 12 km. The depth distribution of these earthquakes is similar to that found in other intracontinental areas with similar heat flow which suggests that the crust beneath the Kenya Rift is of normal rheology.

Notes: In August 1985 the crustal structure underlying the southern part of the Kenya Rift Valley was investigated by long-range explosion seismology. the experiment (KRISP 85) consisted of two seismic lines in the central sector of the rift, one along the axis and the other across it. Interpretation of the data, including time-term analysis and ray tracing has shown that the thickness of rift infill varies from about 6km below Lake Naivasha to about 2 and 1.5km below Lake Magadi and Lake Bogoria respectively. the underlying material has a P-wave velocity of 6.05 ± 0.03 km s-1 which suggests that the rift is underlain by Precambrian metamorphic basement. A localized high-velocity zone identified to the east of Nakuru may be due to basic intrusive material. the P-wave velocity increases discontinuously to 6.45 ± 0.2 km s-1 at a depth of 12.5 ± 1.0 km below sea level. This depth is similar to that inferred for the brittle-ductile transition zone from a study of local seismicity in the Lake Bogoria region. A high P-wave velocity layer (7.1 ± 0.2 km s-1) occurs at 22 ± 2 km depth below sea level which might be associated with a sill-like basic intrusion in the lower crust. an upper mantle velocity of 7.5 ± 0.2 km s-1 (unreversed) is reached at a depth of 34.0 ± 2.0 km below sea level. This implies that only moderate crustal thinning has occurred beneath the central sector of the rift. No evidence was obtained for the existence of a continuous‘axial intrusion’reaching to shallow levels below the rift and associated with crustal separation as suggested by previous studies.

Notes: This article presents experimental results for morphological assessment of sub-50-nm thick hydrogenated amorphous carbon (a-C:H) overcoats. The films were grown by rf plasma enhanced chemical vapor deposition using Ar/C2H2 gas mixture onto heterogeneous (Al2O3–TiC) ceramic substrates. They were analyzed using complementary information from scanning electron microscopy, energy dispersive x-ray analysis and atomic force microscopy. We found that the bias deposition voltage and the nature of the substrate (Al2O3 or TiC regions) adversely affect both growth rate and microstructure. Argon inclusion in the C2H2 plasma during the first stage of growth is responsible for the observed effects. These results suggest that the amorphous carbon layer is denser on the TiC than on the Al2O3 region. © 1999 American Institute of Physics.

Notes: Pulsed laser deposition (PLD) from a hot pressed manganese doped ZnS target using a KrF laser, has produced a high rate deposition method for growing luminescent thin films. Good stoichiometric quality and typical luminescent crystal structures have been observed with a predominant hexagonal phase and little evidence of the cubic phase. The luminescent characteristics were determined by cathodoluminescence and photoluminescence excitation and stable electroluminescence was observed under pulsed dc conditions with a minimum brightness of 150 cd/m2. PLD film characteristics are compared with those observed in radio-frequency sputtered samples.

Notes: [Auszug] The various granitic rocks of Leicestershire observed at Mountsorrel, Countesthorpe, Croft, Enderby, Stoney Stanton and in the recent NCB borehole at Kirby Lane, south-west of Melton Mowbray (Fig. 1) are considered to be the surface expression of a large calc-alkaline granitic pluton1'2. These ...

Notes: Summary Background Bone mineral density (BMD) is largely genetically determined and this influence is most powerful in the period of rapid skeletal development in childhood and late adolescence but environmental factors such as exercise and dietary calcium intake may influence up to 20%. Aims of the study The aims of the study were to examine healthy late adolescent females for the effects and benefits of a high calcium intake from dairy product foods on bone mineral density, body composition, lipids and biochemistry. The secondary aim is determine whether a high intake of dairy product foods in the diet is acceptable for this age group long term. Methods Ninety-one teenage girls who participated in a two-year randomised controlled study on the effect of dairy food supplementation on dietary patterns, body composition and bone density in post-pubertal teenage girls were approached one year after the cessation of the study to determine the effects of the cessation of dairy supplements on bone mineral density, dietary habits, biochemical markers, body composition and blood lipids. Bone mineral density and bone mineral content were assessed at the hip, spine and total body. Anthropometric data were collected, and exercise, Tanner, dietary assessment, preference and compliance questionnaires were administered. Lipid profiles, hydroxyproline excretion and urinary calcium and sodium excretion measurements were performed. Results There were no significant differences between the 2 groups for height, weight, lean and fat mass. The supplemented group had significantly higher calcium, phosphorus and protein intake during the supplementation period (p〈0.001). No differences were seen between the groups 12 months after supplementation finished. There were no significant differences in exercise level, preference or acceptability of dairy products or in the lipids and bone markers between baseline the end of supplementation and 1 year follow-up. There was a significant increase in trochanter (4.6%), lumbar spine (1.5%) and femoral neck (4.8%) BMD (p〈0.05) in the high calcium group at the end of supplementation. There was an increase in bone mineral content at the trochanter (p〈0.05) and lumbar spine; however the latter was not statistically significant, in the high calcium group at the end of supplementation. There was no difference in vertebral height or width at any stage of the study, indicating no influence on bone size. Conclusions In this 3 year study (2 years of supplementation, 1 year follow-up), teenage girls, aged 15–18 years, were able to significantly increase their BMD at the trochanter, femoral neck and lumbar spine when supplemented with dairy product foods to a mean calcium intake of 1160 mg/d. There was also an effect seen on the BMC particularly at the trochanter and to a lesser extent at the lumbar spine. The dietary calcium intake achieved did not adversely affect body weight, fat and lean mass or blood lipid profiles. Twelve months after the supplementation finished the girls had returned to their baseline diet, indicating self-selection of a high dairy product diet may be hard to achieve.