Timing of volcanism and evolution of the northern Kenya Rift

Journal ArticleThe northern Kenya Rift is bounded on the west by uplands of Turkana which comprise horst-like blocks that include metamorphic basement rocks, locally overlain unconformably by the Cretaceous Lubur Sandstone, in turn overlain by predominantly volcanic sequences in which relatively thin sedimentary packages occur. Amphibolite facies crystalline rocks of the basement yield Early Palaeozoic K-Ar cooling ages reflecting the Pan-African Orogeny. Volcanism in Turkana was initiated through voluminous eruptions of transitional tholeiitic basalts commencing about 36 Ma ago in the Late Eocene, with some evidence for concomitant rhyolitic volcanism. Volcanism became dominantly rhyolitic in the interval from about 27 to 23 Ma ago, but remained bimodal as basaltic lavas are also known from this period. From about 19 to 15 Ma or younger, basaltic volcanism again dominated, often alkaline in nature, with thin but significant sedimentary sequences interleaved that have yielded important vertebrate faunal assemblages. Parallels exist between the volcanic history recorded in Turkana and that found in the Nabwal Hills east of Lake Turkana. In the southern Turkana region, oil exploration by seismic methods and deep drill holes has shown the existence of northerly-trending half-graben with up to 7 km of fill, and that these developed from at least Oligocene and possibly Late Eocene times. This suggests that the widespread basaltic volcanism at about 36 Ma ago (Late Eocene) heralds an earlier initiation of the Kenya Rift in northern Kenya than most workers have previously suggested

Nanoscintometry : a pathway to absolute dosimetry of ionising radiations.

It is now accepted that the deleterious effects induced by ionising radiations in mammalian cells are caused by the simultaneous breaking of both strands of the DNA helix by a single track. These effects are optimised when the mean free path of primary ionisation. lambda, matches the 2 nanometre mean chord distribution of DNA. However, there is currently no method of measuring radiation damage in terms of lambda. The aim of this project has been to design and construct a detector with a lambda response function capable of providing a measure of the absolute biological effectiveness of a radiation, independent of radiation type. Organic scintillation molecules, in the condensed phase, have been identified as being most suitable for bio-effectiveness measurements. Tissue equivalent and of comparable interaction cross-section, these nanodetectors are capable of signalling individual interactions with the emission of a scintillation photon, or scinton. Using a 20 mum scintillation film and DEP hybrid photodiode, spectra containing single and plural scinton events were recorded. These spectra reveal unique differences in the radiation quality of photon-emitting radioisotopes. A model of radiation action on scintillators in the condensed phase, analogous to the direct and indirect actions observed in intra-cellular DNA, has been developed and used to predict the characteristic yields of single and plural scinton events. The model was further developed to provide probabilities of paired' scinton events originating from fluor sites with a mean spacing of 2 nm. These critical 'paired' events are representative of double strand breaks and interpretation of these events that will yield bio-effectiveness data. Using Poisson distributions, a scintillator with optimised fluor concentration was developed for use in bio-effectiveness detectors. Loss calculations within the detector revealed an inconsistency in exponential attenuation theory, which appears to be inadequate when applied to light-guides. Consequently a new model of photon transport in light-pipes based on a Monte Carlo simulation has been developed and offers a more rigorous alternative. Calibration of the detector highlighted the need for a simple yet effective technique for photomultiplier tube (PMT) gain calibration in the laboratory. A technique using Cerenkov radiation was developed and provides good correlation with published gain figures. Although this prototype detector has not yet been fully tested, nor the associated bio-effect model fully developed to allow extraction of bio-effectiveness data from the collected spectra, preliminary results suggest this technique to be promising alternative and offers a route towards the measurement of absolute dosimetry with potential application in radiotherapy and radiation protection

A study of the Tasmanian dolerites with particular reference to the differentiation of the Red Hill dolerite-granophyre association

187, 16 p. : ill., mapsThe Tasmanian dolerites were intruded into essentially flat-lying Permian and Triassic sediments in the form of sheets, commonly exceeding 1000 feet in thickness, large dyke-like intrusions up to one mile in width, and transgressive bodies. The dolerite is post Triassic and pre-Tertiary in age, and Hills and Carey (194-9, 54-) and Banks (1958, 234-) suggest that the intrusions took place in the Jurassic. They crop out over more than 6,000 square miles, and Edwards (1942, 452) has estimated that the volume of magma intruded was of the order of 3,000 cubic miles. (First paragraph of Introduction)

Some aspects of the pure theory of international trade

iv, 242 leavesA traditional dichotomy exists in the theory of international trade between, on the one hand, the monetary theory and its associated problems which arise because different money circulates in different countries, because each country has its own central bank and controls its own monetary policy, and because money is treated as a commodity with a direct utility of its own and, on the other hand, the pure theory which is concerned with the real factors underlying the monetary problems. This thesis is concerned solely with the latter. More precisely, our interest centres upon the application of the neo-Walrasian analysis of value and welfare to some of the traditional questions posed in trade theory. The pure theory of international trade itself can be subdivided broadly between 'positive' contributions, intended for purposes of explanation and prediction, and normative contributions relating international trade to economic welfare. In the positive field, and it is with problems arising here that we are primarily concerned, there has been a recent trend towards the empirical verification of different hypotheses. However, though this trend is quite marked in the theory of comparative costs [107] and in connection with the Heckscher-Ohlin theorem that a country's exports use intensively the country's abundant factor of production [108; 109]> id is scarcely noticeable among the great bulk of pure theory writings which are concerned with the formulation of ' logically true' propositions which, in the nature of things, cannot be refuted empirically. The majority of these have been developed within the context of the familiar two-good, two factor model with its additional assumptions of linear and homogeneous production functions with diminishing return*along isoquants, full employment, profit maximisation and perfect competition

Upper Miocene and Pliocene geomagnetic secular variation in the Borgarfjördur area of Western Iceland

Copyright 1977; Oxford University PressA total of 362 successive lava flows, which were extruded at a regular rate between t= 6.7 and 1.6 Myr in the Borgarfjördur area of Western Iceland, have been subjected to palaeomagnetic study. In contrast to the result of a study by Wilson & McElhinny of palaeo‐magnetic data from a long sequence of lava flows in Eastern Iceland, there does not exist any long‐term increase of geomagnetic inclination in Western Iceland between t= 7 and 3 Myr which, as they show, would produce a change in the distance to the associated virtual geomagnetic poles (VGP's) from greater than the geographic co‐latitude to less than the co‐latitude (or, with respect to the site, from ‘far side’ of the geographic pole to ‘near‐side’ of the geographic pole). Instead the geomagnetic inclination is less than that required for an axial dipole field, providing ‘far‐side’ VGP positions for all data groups. The mean VGP positions are almost identical for four successive polarity epochs (two of reversed polarity, and two of normal polarity), consistent with reversal of the main dipole being accompanied by reversal of the non‐dipole field. S F the angular standard deviation of groups of VGP positions, is used as an expression of palaeosecular variation of the magnetic field. It is shown to be almost constant throughout the 5‐Myr period, suggesting that standing and drifting non‐dipole fields have not combined to produce strong secular variation which is in principle possible in high latitudes. This conclusion is weakened by the suspicion that the conventional exclusion of data from lavas with low‐latitude VGP positions has discriminated against the discovery of high palaeosecular variation rates.Peer reviewe

Assassins and apples: the environmental constraints of two snails that threaten Australian aquatic systems

Context: Alien freshwater snails pose a substantial risk to Australian native aquatic biota.Aims: This study aims to determine the thermal and salinity ranges of two introduced species within Australia, Pomacea sp. and Anentome sp., to facilitate predictions of their potential geographic range should they become widely established.Methods: Laboratory tests were conducted to assess behavioural responses of snails to altered temperature or salinity after different acclimation regimes.Key results: After acclimation at 25°C, Pomacea sp. had a median activity range of 13.5–38°C and Anentome sp. of 12–38.5°C. Higher acclimation temperatures produced observable effects, whereas lower acclimation temperatures did not. Salinity tolerances differed, with Pomacea sp. remaining active at up to 8 parts per thousand (ppt) (after acclimation at 25°C), with acclimation at 20°C resulting in a lower salinity tolerance. By contrast, Anentome sp. snails were active at up to 5 ppt after low salinity acclimation, demonstrating enhanced salinity tolerance compared with non-salinity acclimations.Conclusions: These results showed that both snails are capable of surviving temperatures and salinities that would allow invasion into subtropical and warm-temperate Australian aquatic systems.Implications: Free from the constraints of natural predators, competitors, and parasites, these snails should be of great concern to biosecurity agencies in Australia

Aryl hydrocarbon receptor activation during in vitro and in vivo digestion of raw and cooked broccoli (brassica oleracea var. Italica)

Broccoli is rich in glucosinolates, which can be converted upon chewing and processing into Aryl hydrocarbon Receptor (AhR) ligands. Activation of AhR plays an important role in overall gut homeostasis but the role of broccoli processing on the generation of AhR ligands is still largely unknown. In this study, the effects of temperature, cooking method (steaming versus boiling), gastric pH and further digestion of broccoli on AhR activation were investigated in vitro and in ileostomy subjects. For the in vitro study, raw, steamed (t = 3 min and t = 6 min) and boiled (t = 3 min and t = 6 min) broccoli were digested in vitro with different gastric pH. In the in vivo ileostomy study, 8 subjects received a broccoli soup or a broccoli soup plus an exogenous myrosinase source. AhR activation was measured in both in vitro and in vivo samples by using HepG2-Lucia™ AhR reporter cells. Cooking broccoli reduced the AhR activation measured after gastric digestion in vitro, but no effect of gastric pH was found. Indole AhR ligands were not detected or detected at very low levels both after intestinal in vitro digestion and in the ileostomy patient samples, which resulted in no AhR activation. This suggests that the evaluation of the relevance of glucosinolates for AhR modulation in the gut cannot prescind from the way broccoli is processed, and that broccoli consumption does not necessarily produce substantial amounts of AhR ligands in the large intestine

Colon-available raspberry polyphenols exhibit anti-cancer effects on in vitro models of colon cancer

BACKGROUND: There is a probable association between consumption of fruit and vegetables and reduced risk of cancer, particularly cancer of the digestive tract. This anti-cancer activity has been attributed in part to anti-oxidants present in these foods. Raspberries in particular are a rich source of the anti-oxidant compounds, such as polyphenols, anthocyanins and ellagitannins. METHODS: A "colon-available" raspberry extract (CARE) was prepared that contained phytochemicals surviving a digestion procedure that mimicked the physiochemical conditions of the upper gastrointestinal tract. The polyphenolic-rich extract was assessed for anti-cancer properties in a series of in vitro systems that model important stages of colon carcinogenesis, initiation, promotion and invasion. RESULTS: The phytochemical composition of CARE was monitored using liquid chromatography mass spectrometry. The colon-available raspberry extract was reduced in anthocyanins and ellagitannins compared to the original raspberry juice but enriched in other polyphenols and polyphenol breakdown products that were more stable to gastrointestinal digestion. Initiation – CARE caused significant protective effects against DNA damage induced by hydrogen peroxide in HT29 colon cancer cells measured using single cell microgelelectrophoresis. Promotion – CARE significantly decreased the population of HT29 cells in the G(1 )phase of the cell cycle, effectively reducing the number of cells entering the cell cycle. However, CARE had no effect on epithelial integrity (barrier function) assessed by recording the trans-epithelial resistance (TER) of CACO-2 cell monolayers. Invasion – CARE caused significant inhibition of HT115 colon cancer cell invasion using the matrigel invasion assay. CONCLUSION: The results indicate that raspberry phytochemicals likely to reach the colon are capable of inhibiting several important stages in colon carcinogenesis in vitro