11,274 research outputs found
A seismic study of crustal structure in the region of the western isles of Scotland
In November 1979, the Department of Geological Sciences, University of Durham, in conjunction with the Department of Geology, University of Glasgow, carried out a marine seismic refraction survey between Barra In the Outer Hebrides and Girvan on the Ayrshire coast. In August/September 1981, a shorter profile, between Mull and Kintyre, was undertaken. Temporary recording stations were set up on land and explosives and alrguns used as sources at sea. In addition, data were obtained from the permanent recording networks in Scotland. The application of digital filtering techniques to the alrgun lines Is presented and reviewed. The explosive shot data were interpreted using time-term analysis, the plus- minus method and ray-tracing. Gravity and magnetic studies were used as a control on the interpretation. The depth to the basin has been examined, indicating sedimentary cover of between 1 and 3 km along the line. The variation in basement velocity has been determined. A velocity model for the upper crust has been developed indicating large lateral changes. A steep gradient Is thought to exist between Golonsay and Jura and a more gentle gradient beneath Mull. There does not seem to be evidence for a mid-crustal refractor with a sharp velocity transition across the boundary. Large changes In Pn time-terms across the Minch and Inner Hebrides basin are thought to be largely due to the varying velocity structure of the basement. The basin formation and deformation of the lower crust are thought to Involve movement within the mantle
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Plastic Microbial Acclimation and Optimisation of Composting and Anaerobic Digestion Processes may Improve Degradation Times
Fronto-striatal cognitive deficits at different stages of Parkinson's disease
Groups of patients with idiopathic Parkinson's disease, either medicated or unmedicated, were compared with matched groups of normal controls on a computerized battery previously shown to be sensitive to frontal lobe dysfunction, including tests of planning, spatial working memory and attentional set-shifting. In a series of problems based on the 'Tower of London' test, medicated patients with Parkinson's disease were shown to be impaired in the amount of time spent thinking about (planning) the solution to each problem. Additionally, an impairment in terms of the accuracy of the solution produced on this test was only evident in those patients with more severe clinical symptoms and was accompanied by deficits in an associated test of spatial short-term memory. Medicated patients with both mild and severe clinical symptoms were also impaired on a related test of spatial working memory. In contrast, a group of patients who were unmedicated and 'early in the course' of the disease were unimpaired in all three of these tests. However, all three Parkinson's disease groups were impaired in the test of attentional set-shifting ability, although unimpaired in a test of pattern recognition which is insensitive to frontal lobe damage. These data are compared with those previously published from a group of young neurosurgical patients with localized excisions of the frontal lobes and are discussed in terms of the specific nature of the cognitive deficit at different stages of Parkinson's disease
Pattern in Nonlinear Gravatational Clustering: A Numerical Investigation
The nonlinear clustering of dark matter particles in an expanding universe is
usually studied by N-body simulations. One can gain some insight into this
complex problem if simple relations between physical quantities in the linear
and nonlinear regimes can be extracted from the results of N-body simulations.
Hamilton et al. (1991) and Nityananda and Padmanabhan (1994) have made an
attempt in this direction by relating the mean relative pair velocities to the
mean correlation function in a useful manner. We investigate this relation and
other closely related issues in detail for the case of six different power
spectra: power laws with spectral indexes , cold dark matter (CDM),
and hot dark matter models with density parameter ; CDM including a
cosmological constant () with ,
; and model with . We find that: (i)
Power law spectra lead to self-similar evolution in an universe.
(ii) Stable clustering does not hold in an universe to the extent
our simulations can ascertain. (iii) Stable clustering is a better
approximation in the case of universe in which structure formation
freezes out at some low redshift. (iv) The relation between dimensionless pair
velocity and the mean correlation function, , is only approximately
independent of the shape of the power spectrum. At the nonlinear end, the
asymptotic value of the dimensionless pair velocity decreases with increasing
small scale power, because the stable clustering assumption is not universally
true. (v) The relation between the evolved and the linear regime
is also not universal but shows a weak spectrum dependence. We
present simple theoretical arguments for these conclusions.Comment: Princeton Univ Obs, in press ApJ (Aug 1, 1996) Figures (revised) also
available from ftp://astro.princeton.edu/cen/SCALIN
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Flexible Invariants Through Semantic Collaboration
Modular reasoning about class invariants is challenging in the presence of
dependencies among collaborating objects that need to maintain global
consistency. This paper presents semantic collaboration: a novel methodology to
specify and reason about class invariants of sequential object-oriented
programs, which models dependencies between collaborating objects by semantic
means. Combined with a simple ownership mechanism and useful default schemes,
semantic collaboration achieves the flexibility necessary to reason about
complicated inter-object dependencies but requires limited annotation burden
when applied to standard specification patterns. The methodology is implemented
in AutoProof, our program verifier for the Eiffel programming language (but it
is applicable to any language supporting some form of representation
invariants). An evaluation on several challenge problems proposed in the
literature demonstrates that it can handle a variety of idiomatic collaboration
patterns, and is more widely applicable than the existing invariant
methodologies.Comment: 22 page
Site-Selective Spectroscopy And Crystal-Field Analysis For Nd3+ In Strontium Fluorovanadate
Siteâselective spectroscopy reveals that Nd3+ ions occupy more than 40 different crystalâfield environments in Sr5(VO4)3F. Preferential energy transfer to the site responsible for 1 ÎŒm lasing occurs but becomes less complete with increasing temperature. The 4I and 4F3/2 Stark levels of the lasing site have been determined and an analysis of the crystal field performed. From the crystalâfield fitting parameters Bkq, a calculated energyâlevel spectrum is determined up to 17â500 cmâ1 with a rms deviation from the available experimental levels of 6 cmâ1
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