A geophysical investigation of the south-east Greenland continental margin

During the summers of 1973 and 1974 geophysical observations were made, aboard R.R.S. Shackleton, across the south east Greenland continental margin, between 58 and 65 N. The thesis describes the reduction and interpretation of the magnetic, bathymetric, gravimetric, and deep seismic reflection data and gives details of the digital deconvolution and C.D.P. stacking techniques developed for processing the reflection data. The magnetic results indicate that, south of 63 N., anomaly 24 is the earliest recognisable oceanic magnetic anomaly. North of 63 N., anomalies 22-24 cut out against the margin, and a complementary widening of ocean floor of this age, on the opposite Rockall margin, north of Hatton Bank, indicates that a local westward migration of the spreading axis occurred, north of 63 N., shortly after the split. Igneous intrusives, outcropping on the rise, post-date the continental split by several million years, indicating that the volcanic activity of East Greenland may have occurred some time after continental separation started. Airgun and sparker profiles show three major sediment groups. Two groups of Tertiary age are separated by an erosional unconformity, beneath the rise north of 62 N. The upper sediments are interpreted as contour current deposits of Miocene and later age, and the lower sediments as lithified oozes of about Eocene age. Below these Tertiary sediments, older, seaward dipping reflectors occur between anomaly 24 and the scarp. These are interpreted as Mesozoic sediments overlying subsided continental crust. The oceanic-continental crustal boundary, as recognised from magnetic anomalies, occurs to the east of this subsided region and lies up to 80 km seaward of the scarp, which is an erosional feature cut by contour currents. Gravity profiles indicate that the main change in crustal thickness beneath the margin lies up to 80 km landward of the scarp north of 63.5 N; but corresponds more nearly with the scarp further south

Evaluating EGM2008 over East Antarctica

The release of EGM2008 and associated products such as grids of mean dynamic ocean topography offer the possibility of utilising the extensive historical record in Antarcticawith today's modern satellite sensing techniques. In this study, we use data acquired at the Mawson, Davis, Casey and Scott and McMurdo stations in East Antarctica to investigate the performance of EGM2008 over this region. EGM2008 over Antarctica is entirely dependent on the EGM2008-adopted global GRACE satellite-derived gravity field. This is in contrast to most other regions of the Earth, where there are also contributions from terrestrial gravity and/or altimeter satellites. We determine, over East Antarctica, and at our four test sites that EGM2008 should be used with caution when precisions better than one metre are required. The precisions at the test sites are better than this, but the evidence is that the four test sites are probably not representative of the large area of East Antarctica they are being forced to represent. Notwithstanding any of the above, EGM2008 represents a significant step forward in East Antarctica and that the use of test stations and regions where there is little or no complementary data is a valid method of investigating the performance of the model

The Role of Coordinate Systems, Coordinates and Heights in Horizontal Datum Transformations

This paper reviews the fundamental definitions of geodetic and geocentric coordinate systems, whilst clarifying the distinction between coordinates and coordinate systems. It is then argued that the transformation of coordinates from a local geodetic datum to a geocentric datum should first employ a change of the coordinate system using a six- or four-parameter transformation, followed by further modelling of the distortion in the coordinates. It is also argued that the horizontal coordinate transformation should not include height information, since this forms an entirely different coordinate in another coordinate system

On the geodetic datums in Sri Lanka

The geodetic datums in Sri Lanka (formerly Ceylon) for latitude and longitude, height and gravity are described and discussed, because this information is not available in the open literature. It is recommended that most of these datums require some upgrading

Assessment of EGM2008 over Sri Lanka, an area where 'fill-in' data were used in EGM2008

The tide-free EGM2008 combined global geopotential model is compared with land and marine gravity observations and co-located GPS-levelling on and around Sri Lanka (formerly Ceylon). Not all these data are in the public domain, so offer an informative test of how the 'fill-in' methodology used in EGM2008 performs versus observed data. Sri Lanka is also in an area where the geoid exhibits its lowest elevation with respect to a geocentric reference ellipsoid. A -1.75 m bias between the GPS-levelling and EGM2008 led to an investigation into the Sri Lankan geodetic datums, showing a bias in the ellipsoidal heights. After rejection of 15 outliers, the standard deviation of the difference between 207 Sri Lankan GPS-levelling points and EGM2008 is 0.184 m. The difference between the gravity anomalies and EGM2008 showed that the Sri Lankan gravity data is based on the old Potsdam datum. The Sri Lankan land gravity data, after rejection of outliers, yielded standard deviations of 6.743 mGal for 20 GPS-coordinated gravity points on fundamental benchmarks, 14.704 mGal for 42 gravity points on fundamental benchmarks but with coarse locations, and 6.367 mGal for 1032 digitised and reconstructed free-air anomalies from a Bouguer anomaly map. The ship-track gravity data have not been crossover adjusted, and yield a standard deviation of 43.683 mGal. Importantly, the ability of EGM2008 to identify datum deficiencies is an implicit validation and leads to its applicationin other areas to search for datum deficiencies

The Divisive Power of Humour: Comedy, Taste and Symbolic Boundaries

Using British and Dutch interview data, this article demonstrates how people from different social classes draw strong symbolic boundaries on the basis of comedy taste. Eschewing the omnivorousness described in recent studies of cultural consumption, comedy audiences make negative aesthetic and moral judgements on the basis of comedy taste, and often make harsh judgements without the disclaimers, apologies and ambivalence so typical of ‘taste talk’ in contemporary culture. The article demonstrates how, in particular, Dutch and British middle class audiences use their comedy taste to communicate distinction and cultural superiority. We discuss several reasons why such processes of social distancing exist in comedy taste and not other cultural areas: the traditionally low status of comedy; the strong relation between humour and personhood; the continuity between comedy tastes and humour styles in everyday life; as well as the specific position of comedy in the British and Dutch cultural fields

Delivery Challenges for Fluoride, Chlorhexidine and Xylitol

The progression or reversal of dental caries is determined by the balance between pathological and protective factors. It is well established that a) fluoride inhibits demineralization and enhances remineralization, b) chlorhexidine reduces the cariogenic bacterial challenge, and c) xylitol is non-cariogenic and has antibacterial properties. The challenge that we face is how best to deliver these anti-caries entities at true therapeutic levels, over time, to favorably tip the caries balance. High caries risk people, including children with Early Childhood Caries (ECC), are a special challenge, since high cariogenic bacterial activity can override fluoride therapy. Current fluoride and chlorhexidine varnishes deliver all their activity within about 24 hours. Early studies with experimental slow release fluoride devices retained elevated levels of fluoride for months in a therapeutic range but have not been pursued. Preventive dentistry has largely ignored the benefits of reducing the bacterial challenge, partially due to primitive and inadequate delivery systems. For example, Chlorhexidine applied as a rinse partially reduces some bacteria but not others that are hiding within the biofilm. Better antibacterials and better delivery systems are needed. Xylitol delivered by gum or lozenge appears to be effective clinically in reducing cariogenic bacteria and caries levels, but novel systems that deliver therapeutic amounts when needed would be a major advance, especially for young children. Reducing the cariogenic bacterial challenge and enhancing the effect of fluoride by the use of new sustained-delivery systems would have a major effect on dealing with caries as a disease

The effect of EGM2008-based normal, normal-orthometric and Helmert orthometric height systems on the Australian levelling network

This paper investigates the normal-orthometric correction used in the definition of the Australian Height Datum, and also computes and evaluates normal and Helmert orthometric corrections for the Australian National Levelling Network (ANLN). Testing these corrections in Australia is important to establish which height system is most appropriate for any new Australian vertical datum. An approximate approach to assigning gravity values to ANLN benchmarks (BMs) is used, where the EGM2008-modelled gravity field is used to "re-construct" observed gravity at the BMs. Network loop closures (for first- and second-order levelling) indicate reduced misclosures for all height corrections considered, particularly in the mountainous regions of south eastern Australia. Differences between Helmert orthometric and normal-orthometric heights reach 44 cm in the Australian Alps, and differences between Helmert orthometric and normal heights are about 26 cm in the same region. Normal orthometric heights differ from normal heights by up to 18 cm in mountainous regions >2,000 m. This indicates that the quasigeoid is not compatible with normal-orthometric heights in Australia