High resolution carbon isotope stratigraphy of the basal Silurian stratotype (Dob's Linn, Scotland) and its global correlation

Since its designation as the Global Stratotype Section and Point (GSSP) for the base of the Silurian System, the choice of Dob's Linn, Southern Scotland, has received criticism due to the difficulties of relating its well constrained graptolite biostratigraphy to shallow water sequences elsewhere. Kerogen samples from across the Ordovician-Silurian boundary interval at Dob's Linn have yielded carbon stable isotope signatures consistent with those recorded elsewhere, in particular showing a clear positive δ13C excursion in the terminal Ordovician. The architecture of the δ13C curve from Dob's Linn enables very high resolution stratigraphic subdivision and direct correlation between the deep water Dob's Linn section and time equivalent carbonate shelf deposits. An integrated stratigraphic scheme using isotope stratigraphy and biostratigraphy of graptolites, conodonts and shelly faunas has been constructed. This direct correlation shows that the shallow water successions, including the former stratotype candidate at Anticosti Island, are generally incomplete, with hiatuses related to the rapid sea level changes during the Hirnantian stage. This confirms and greatly increases the global utility of Dob's Linn as a boundary stratotype

Surface passivation of InAs avalanche photodiodes for low-noise infrared imaging

The effect of surface passivation on the etched-mesa InAs diodes was investigated by carrying out the fabrication and passivation of InAs diodes. Extensive and detailed current-voltage characterization was done to determine the most suitable type of insulating material for the surface passivation. SU-8, silicon nitride, silicon dioxide and B-staged Bisbenzocyclobutene were used for the purpose of minimizing the conductivity of the etched mesa surface of InAs diodes. The forward- and reverse-biased characteristics of InAs diodes were measured at room temperature and 77 K in order to carefully investigate the effect of different surface passivation schemes. The results of this work categorically indicated that SU-8 is the most effective surface passivation material for InAs diodes, whereas silicon nitride and silicon dioxide have contributed to an even higher surface leakage current. Furthermore, SU-8 passivated InAs diodes were more sustainable to high bias voltages and its robustness increases the opportunity of its utilization for practical applications such as infrared imaging

RUNNING SHOE STIFFNESS:THE EFFECT ON WALKING GAIT

Sports shoes can be grouped into various categories based on their stability, protection capabilities, traction, impact characteristics and stiffness. The majority of shoe tests involve measures of traction and impact. Few studies have examined shoe sole stiffness. Therefore, the purpose of this study was to assess shoe sole stiffness by a materials testing procedure, and then examine the effect of shoe stiffness on walking gait. A damped oscillation technique, previously used on muscle-tendon complexes, was utilised to calculate the stiffness and the damping factor of six types of running shoes. The shoes used different rnidsole components which included air sacs, gel sacs, ethylene vinyl acetate (EVA), and kevlar reinforcing. Two shoes at the extremes of the range were then selected from the materials test results for use in the subsequent gait analysis. Nine males ranging in age from 25 to 45 years (mean =36 years) participated in the experiment. Heights ranged from 186cm to 176cm (mean=182cm) and weights ranged from 72.5kg to 89kg (mean=8lkg). No subjects had any musculoskeletal problems affecting the lower limb. Two dimensional video data were collected on the right leg using an Ariel Video Analysis system sampling at 50 Hz, as subjects walked at 5.1 km/hr on a motor driven treadmill. Markers were placed on the greater trochanter, lateral condyle of the femur, lateral malleolus of the fibular, the heel of the shoe and on the shoe at the level of the fifth metatarsal head. Three stride cycles were collected after the subjects had walked on the treadmill for one minute. Data were digitised and downloaded to FMAP software to calculate kinematic variables such as knee and ankle angle and knee and ankle angular velocity. Data were then normalised to 50 points and averaged across stride cycles and subjects. Although a comparison of the stiff and flexible shoes indicated no differences in the kinematic parameters (p>0.05), it may be that the muscles of the lower limb adjust their activity level for the stiffness of the shoe to maintain an invariant kinematic pattern

Advantages and challenges associated with implementing an ecosystem services approach to ecological risk assessment for chemicals

The ecosystem services (ES) approach is gaining broad interest in regulatory and policy arenas for use in landscape management and ecological risk assessment. It has the potential to bring greater ecological relevance to the setting of environmental protection goals and to the assessment of the ecological risk posed by chemicals. A workshop, organised under the auspices of the Society of Environmental Toxicology and Chemistry Europe, brought together scientific experts from European regulatory authorities, the chemical industry and academia to discuss and evaluate the challenges associated with implementing an ES approach to chemical ecological risk assessment (ERA). Clear advantages of using an ES approach in prospective and retrospective ERA were identified, including: making ERA spatially explicit and of relevance to management decisions (i.e. indicating what ES to protect and where); improving transparency in communicating risks and trade-offs; integrating across multiple stressors, scales, habitats and policies. A number of challenges were also identified including: the potential for increased complexity in assessments; greater data requirements; limitations in linking endpoints derived from current ecotoxicity tests to impacts on ES. In principle, the approach was applicable to all chemical sectors, but the scale of the challenge of applying an ES approach to general chemicals with widespread and dispersive uses leading to broad environmental exposure, was highlighted. There was agreement that ES-based risk assessment should be based on the magnitude of impact rather than on toxicity thresholds. The need for more bioassays/tests with functional endpoints was recognized, as was the role of modelling and the need for ecological production functions to link measurement endpoints to assessment endpoints. Finally, the value of developing environmental scenarios that can be combined with spatial information on exposure, ES delivery and service provider vulnerability was recognized

A Bayesian analysis of regularised source inversions in gravitational lensing

Strong gravitational lens systems with extended sources are of special interest because they provide additional constraints on the models of the lens systems. To use a gravitational lens system for measuring the Hubble constant, one would need to determine the lens potential and the source intensity distribution simultaneously. A linear inversion method to reconstruct a pixellated source brightness distribution of a given lens potential model was introduced by Warren & Dye. In the inversion process, a regularisation on the source intensity is often needed to ensure a successful inversion with a faithful resulting source. In this paper, we use Bayesian analysis to determine the optimal regularisation constant (strength of regularisation) of a given form of regularisation and to objectively choose the optimal form of regularisation given a selection of regularisations. We consider and compare quantitatively three different forms of regularisation previously described in the literature for source inversions in gravitational lensing: zeroth-order, gradient and curvature. We use simulated data with the exact lens potential to demonstrate the method. We find that the preferred form of regularisation depends on the nature of the source distribution.Comment: 18 pages, 10 figures; Revisions based on referee's comments after initial submission to MNRA

Come back Marshall, all is forgiven? : Complexity, evolution, mathematics and Marshallian exceptionalism

Marshall was the great synthesiser of neoclassical economics. Yet with his qualified assumption of self-interest, his emphasis on variation in economic evolution and his cautious attitude to the use of mathematics, Marshall differs fundamentally from other leading neoclassical contemporaries. Metaphors inspire more specific analogies and ontological assumptions, and Marshall used the guiding metaphor of Spencerian evolution. But unfortunately, the further development of a Marshallian evolutionary approach was undermined in part by theoretical problems within Spencer's theory. Yet some things can be salvaged from the Marshallian evolutionary vision. They may even be placed in a more viable Darwinian framework.Peer reviewedFinal Accepted Versio

Dark matter astrometry: accuracy of subhalo positions for the measurement of self-interaction cross-sections

Direct evidence for the existence of dark matter and measurements of its interaction cross-section have been provided by the physical offset between dark matter and intracluster gas in merging systems like the Bullet Cluster. Although a smaller signal, this effect is more abundant in minor mergers where infalling substructure dark matter and gas are segregated. In such low-mass systems the gravitational lensing signal comes primarily from weak lensing. A fundamental step in determining such an offset in substructure is the ability to accurately measure the positions of dark matter subpeaks. Using simulated Hubble Space Telescope observations, we make a first assessment of the precision and accuracy with which we can measure infalling groups using weak gravitational lensing. We demonstrate that using an existing and well-used mass reconstruction algorithm can measure the positions of 1.5 × 1013 M⊙ substructures that have parent haloes 10 times more massive with a bias of less than 0.3 arcsec. In this regime, our analysis suggests the precision is sufficient to detect (at 3σ statistical significance) the expected mean offset between dark matter and baryonic gas in infalling groups from a sample of ∼50 massive clusters

Microbial use of low molecular weight DOM in filtered and unfiltered freshwater:Role of ultra-small microorganisms and implications for water quality monitoring

Dissolved organic matter (DOM) plays a central role in regulating productivity and nutrient cycling in freshwaters. It is therefore vital that we can representatively sample and preserve DOM in freshwaters for subsequent analysis. Here we investigated the effect of filtration, temperature (5 and 25 °C) and acidification (HCl) on the persistence of low molecular weight (MW) dissolved organic carbon (DOC), nitrogen (DON) and orthophosphate in oligotrophic and eutrophic freshwater environments. Our results showed the rapid loss of isotopically-labelled glucose and amino acids from both filtered (0.22 and 0.45 μm) and unfiltered waters. We ascribe this substrate depletion in filtered samples to the activity of ultra-small (< 0.45 μm) microorganisms (bacteria and archaea) present in the water. As expected, the rate of C, N and P loss was much greater at higher temperatures and was repressed by the addition of HCl. Based on our results and an evaluation of the protocols used in recently published studies, we conclude that current techniques used to sample water for low MW DOM characterisation are frequently inadequate and lack proper validation. In contrast to the high degree of analytical precision and rigorous statistical analysis of most studies, we argue that insufficient consideration is still given to the presence of ultra-small microorganisms and potential changes that can occur in the low MW fraction of DOM prior to analysis

A New Method for the Detection of Galaxy Clusters in X-Ray Surveys

For many years the power of counting clusters of galaxies as a function of their mass has been recognized as a powerful cosmological probe; however, we are only now beginning to acquire data from dedicated surveys with sufcient sky coverage and sensitivity to measure the cluster population out to distances where the dark energy came to dominate the Universe’s evolution. One such survey uses the XMM X-ray telescope to scan a large area of sky, detecting the X-ray photons from the hot plasma that lies in the deep potential wells of massive clusters of galaxies. These clusters appear as extended (not point-like) objects, each providing just a few hundred photons in a typical observation. The detection of extended sources in such a low signal-to-noise situation is an important problem in astrophysics: we attempt to solve it by using as much prior information as possible, translating our experience with wellmeasured clusters to define a “template” cluster that can be varied and matched to the features seen in the XMM images. In this work we adapt an existing Monte Carlo analysis code for this problem. Two detection templates were dened and their suitability explored using simulated data; the method was then applied to a publically avalable XMM observation of a “blank” field. Presented are the encouraging results of this series of experiments, suggesting that this approach continue to be developed for future cluster-identication endeavours