Search Results - (Author, Cooperation:P. J. Barrett)

2012-07-17

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Antarctic Regions ; Climate Change ; *Conservation of Natural Resources/trends ; *Ecosystem ; Forecasting ; Human Activities ; Humans ; Public Policy ; Travel

2012-06-02

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Amino Acid Motifs ; Amino Acid Sequence ; Amyloid beta-Protein Precursor/*chemistry/genetics/*metabolism ; Binding Sites ; Cholesterol/*metabolism ; Electron Spin Resonance Spectroscopy ; Humans ; Micelles ; Molecular Sequence Data ; Mutation ; Nuclear Magnetic Resonance, Biomolecular ; Peptide Fragments/*chemistry/genetics/*metabolism ; Protein Binding ; Protein Structure, Secondary ; Protein Structure, Tertiary

1089-7666

AIP Digital Archive

Physics

If plasma leaks through a negatively biased grid from a positively biased source chamber into an outer region where its potential is free to oscillate, the potential can go into a large-amplitude spontaneous oscillation at a frequency set by the ion transit time through the sheath. This is accompanied by density fluctuations that free stream away from the grid, spatially damped. The frequency and temporal growth rate are investigated under various plasma conditions.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

We performed a questionnaire survey to establish the current and intended practice of chair dental anaesthesia amongst recently appointed consultants, and senior registrars within the Mersey Region. Only 26% of the consultants surveyed practised chair dental anaesthesia, however, more consultants would have had their anaesthetic sessions allowed. Consultants performed 4.62 ± 3.5 sessions per month and anaesthetised 8.0 ± 2.27 patients per session. Cases were mostly performed in community dental centres. The most common reason for discontinuing the practice of chair dental anaesthesia was the Poswillo report and its implications. Sixty-eight per cent of senior registrars declared an interest in chair dental anaesthesia. This group had received significantly more training (p 〈 0.005) in dental anaesthesia than those with no interest. Most anaesthetists (52/71) felt that chair dental anaesthesia was acceptable in centres approved to Poswillo standards; 16 anaesthetists felt that it should be confined to a hospital environment and three felt that it should not be performed at all.

Electronic Resource

1365-3091

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

An attempt was made to distinguish aspects of the shape of rock particles, and to discover by analysis and empirical considerations the most appropriate parameters for describing these aspects. The shape of a rock particle can be expressed in terms of three independent properties: form (overall shape), roundness (large-scale smoothness) and surface texture. These form a three-tiered hierarchy of observational scale, and of response to geological processes. Form can be represented by only two independent measures from the three orthogonal axes normally measured. Of the four pairs of independent measures commonly used for bivariate plots, the two sphericity/shape factor pairs appear to be more efficient discriminators than simple axial ratios. Of the two, the most desirable pair is the maximum projection sphericity and oblate-prolate index for both measures show an arithmetic normal distribution for the range investigated. A measure of form that is independent of the three orthogonal axes, and measures derived from them, is the angularity measure of Lees. Roundness has measures of three types, those estimating average roundness of corners, those based on the sharpest corner, and a measure of convexity in the particle outline. Although each type measures a different aspect, they are not independent of each other. Only roundness from corners is considered in detail. As neither average nor sharpest corner measures are inherently more objective or more quantitative, purpose should determine which is more appropriate. Of the visual comparison charts for average roundness, Krumbein's appears best. The Modified Wentworth roundness is the most satisfactory for estimating roundness from the sharpest corner. The Cailleux Roundness index should not be used because it includes aspects of roundness and form. Shape is a difficult parameter to use for solving sedimentological problems. Even the best of the commonly used procedures are limited by observational subjectivity and a low discriminating power. Unambiguous interpretation of particle shape in terms of source material and processes will always be made difficult by the large number of natural variables and their interactions. For ancient sediments satisfactory results can be expected only from carefully planned studies or rather unusual geological situations.

Electronic Resource

1365-3091

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

The concept of the wave-graded continental shelf, with sea floor sediment coarsening from offshore mud to shoreface sand, has been well known from the time of Johnson (1919). Although most of the modern shelf shows textures unrelated to water depth on account of relict features or sediment starvation, the geological record is more likely to preserve sites where sediment is being fed to a subsiding inner-shelf. These consistently show the landward-coarsening pattern of the wave-graded shelf, recording past water depth history in accumulated sea floor sediment. The landward-coarsening pattern is driven primarily by wave-induced bed shear stress, which increases shoreward exponentially, although it also varies from place to place with wave climate, and can be influenced by sediment concentration and currents. In this study, the relationship between bed shear stress, sediment texture and water depth has been investigated by comparing per cent mud and wave climate data from shore-normal transects of three modern wave-graded coastal settings: Wellington Harbour (low energy) and the Manawatu coast (moderate energy) in New Zealand, and Monterey Bay in California (moderate–high energy). Samples from all three locations show a progressive change from poorly sorted mud offshore to well-sorted fine sand nearshore, with the sand–mud transition ranging from 3 m (low energy) to 50 m (moderate–high energy), reflecting differences in average bed shear. Repeat measurements of per cent mud on seasonal, annual and decadal time scales along a Manawatu coastal transect showed no measurable change, demonstrating equilibrium between sediment supply, wave energy, water depth and sediment texture. A simple model based on the relationship between wave climate, shear stress and per cent mud, and using data and conditions from the modern Manawatu coast, is applied to two mid-Pliocene cyclothems exposed 50 km inland, giving results comparable with estimates from foraminifera and the deep-sea isotope record. Per cent mud offers more detail for palaeobathymetric trends in shallow water shelf strata than other proxy depth recorders, although it is limited to depths above wave base and requires an independent estimate of wave climate if depths are to be quantified.

Electronic Resource

1365-3091

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

A 166 m thick Plio-Pleistocene sequence of glacial sediments has been cored in Ferrar Fiord in the southwestern corner of the Ross Sea, Antarctica. The core has the following lithofacies: massive diamictite (33% of the core; interpreted as lodgement or waterlain till), weakly stratified diamictite (25%; waterlain till or proximal glaciomarine sediment), well-stratified diamictite (8%; proximal glaciomarine or glaciolacustrine sediment), sandstone (25%; sand of aeolian or supraglacial origin), mudstone(7%; derived from subglacial debris and transported offshore in suspension), and minor amounts of rhythmite and tuff. The range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian-derived sand and the low proportion of mudstone facies.The core can be divided into two sequences based on composition and texture. The sequence from 162 to 100 mbsf (metres below the sea floor) comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds. It is Pliocene in age (4.9–2.0 Ma) and records several advances and retreats of ice through the Transantarctic Mountains and across the drill site from the west. The sequence from 100 mbsf to the sea floor, of Pleistocene age, consists of alternations of diamictite, interpreted as lodgement and waterlain till, and sandstone of aeolian origin deposited in a glaciolacustrine setting, similar to ice-covered lakes in the Dry Valleys today. These sediments have a high volcanic component, and hence are thought to have been derived by the grounding and advance of the Ross Ice Shelf from the east past volcanic Ross Island. This change in source is attributed to the rising Transantarctic Mountains increasingly containing East Antarctic ice.The Pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation, with alternations of till and glaciolacustrine sand. Mudstones from the Pliocene sequence beneath include palynomorphs, indicating times when the landscape was at least partially vegetated, but contain no evidence of meltwater influence.

Electronic Resource

1365-3091

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

N. C. Janke's criticism of my paper seems aimed more at the title than the paper itself. I acknowledge the importance of shape in determining the style and rate of movement of particles in fluids (Janke, 1966), but my paper attempted a different task, clarifying the basic concepts of shape, which I believe are spatial, not behavioural. It did occur to me at the time of writing that a complementary review of the relationships between the shape of particles and their behaviour in different situations would be useful, but I saw this as a separate problem. The main purpose of Janke's 1966 paper was not to provide a measure of some particular aspect of shape, but to find a formula using different predetermined aspects of shape to predict settling velocities of particles. Nevertheless, points do arise in his discussion that could usefully have been taken up in my review, notably his acceptance of Prandtl's (1952) view that shape, as it affects settling velocity at least, has two components, a form component and a surface area component. Although Janke had considerable success in finding an appropriate mix of each component to allow prediction of settling velocity from two shape measures, he does not argue a basis for the measures themselves. For example he replaces Corey's shape factor with his shape factor E because the latter ‘allows more discrimination’for shapes with equal axial lengths. Corey's factor assigns a value of 1 to spheres, equant cylinders, equal double cones and cubes, whereas Janke's E gives 1, 0·866, 1 and 0·775 respectively. However, I have difficulty imagining a useful concept of form in which spheres and double cones are in some sense equal and distinct from cylinders and cubes, and it seems to me important that measures like Janke's are conceptually clear as well as efficacious. I would very much like to see someone with experience like Dr Janke undertake the review I mentioned earlier in the hope of achieving such a clarification.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The ice rise is an elongate north-westerly-trending dome about 40 km long which reaches an elevation of 100 m. The ice of the rise is grounded2 and the northern and eastern margins are marked by extensive crevassing that continues for many kilometres north of the rise. This crevassing is believed ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The established view of Antarctic glacial history during the Cenozoic period is that considerable cooling occurred -40 Myr ago, with extensive ice first covering the continent 14 Myr ago, and persisting continuously to the present1. This is based on oxygen isotope variations in calcareous ...

Electronic Resource

1432-1920

Springer Online Journal Archives 1860-2000

Medicine

Résumé Le grand nombre de variantes anatomiques normales de la veine cérébrale interne peut être à l'origine de difficultés diagnostiques dans certains cas, C'est pourquoi les auteurs ont étudié les différentes positions et configurations de la veine cérébrale interne dans le velum interpositum afin de faciliter le diagnostic. Les conditions considérées étaient celles causant une dilatation ventriculaire sans déplacement latéral des structures médianes.

Zusammenfassung Durch die sehr großen anatomischen Variationsmöglichkeiten der V. cerebri interna können in einigen Fällen diagnostische Schwierigkeiten hervorgerufen werden. Messungen der Lage und der Konfiguration der V. cerebri interna im Velum interpositum dienen als diagnostische Hilfe.

Summary The wide anatomical range of normal variations in the internal cerebral vein can cause difficulty in diagnostic evaluation in some cases. Accordingly, a series of measurements of the position and configuration of the internal cerebral vein in the velum interpositum were derived as aids to diagnosis. The conditions considered were those causing ventricular enlargement without lateral dislocation of midline structures. The study reveals the usefulness of measurements in evaluating the configuration of the internal cerebral vein in certain conditions.

Electronic Resource