3,992 research outputs found
From knowledge presentation to knowledge representation to knowledge construction: Future directions for hypermedia
Relationships between human memory systems and hypermedia systems are discussed with particular emphasis on the underlying importance of associational memory. The distinctions between knowledge presentation, knowledge representation, and knowledge constructions are addressed. Issues involved in actually developing individualizable hypermedia based knowledge construction tools are presented
Contaminant mobility as a result of sediment inundation : literature review and laboratory scale pilot study on mining contaminated sediments
This report presents a literature review of soil and sediment inundation methodologies and
describes a pilot scale laboratory inundation study.
Changing weather conditions, subsequent flooding events, and the increased frequency of such
events both in the UK and worldwide is highlighting the need to research the area of contaminant
mobility from soils and sediments under inundated conditions. The findings of such
investigations impact on a wide variety of sectors, including human and ecological health,
agriculture, building, transport, world economy and climate change.
Standardised methodologies for the investigation of contaminant mobility resulting from
soil/sediment inundation episodes are not available. Most research has been conducted in the
agricultural sector for nutrient transport, as part of soil fertility and plant nutrition studies. Only
recently has work been undertaken for studying potentially harmful element transport in
inundated sediments/soils.
A pilot scale laboratory study was undertaken using contaminated bank sediment samples
collected from the Rookhope Burn catchment, Northern England, UK, with the aim to examine
the extent of contaminant mobilisation from flooded sediments. The catchment has been
affected by historical mining and processing of lead and zinc ore and is representative of several
catchments affected by the environmental legacy related to mining in the Northern Pennine
Orefield.
Bank sediment Pb and Zn concentrations were found significantly above both the TEL and PEL
sediment quality criteria, posing potentially a significant hazard to aquatic organisms. The source
of the Pb and Zn in the sediments is related to the underlying mineralisation, mining activities
and mine water discharges in the catchment. Abundances of original sulphide ore and authigenic
metal-bearing phases were expected to vary through the catchment.
The study design simulated rising flood water, a slow saturation of the sediment in order to
induce a slow change in physico-chemical properties, followed by a 3 month (88 day) stagnation
period. Natural day-night cycles were simulated by undertaking the study on the bench top
during the winter of 2009/2010 (November to February). The chemical changes in the
inundation water during the experiment were monitored and the sediment pore water at the end
of the inundation period analysed. The inundation water pH remained alkaline to neutral, while
redox measurements indicated oxic conditions in the water column throughout the inundation
period.
The pilot study showed that inundation of river bank sediments from the Rookhope Burn may be
a significant pathway for contaminants in the catchment and that mobilisation from the
sediments may pose a hazard to environmental receptors in the area, particularly with respect to
Pb and Zn contamination. The different degrees and different rates of metal losses to the
overlying water column observed during the flooding of the Rookhope Burn bank sediments
demonstrated that the significance of metal mobilisation was dictated by the sediment
composition.
The inundation water composition monitored during the sediment flooding was used to indirectly
infer possible processes that control contaminant fluxes from the sediments to the overlying
water. Dissolved Pb concentration in the inundation water reflected the original concentration in
the solid material and in sediments that had XRD-detectable galena and cerussite the dissolved
Pb concentration reached a maximum value of 395 μg l-1. Cerussite, which is commonly formed
as coatings on galena during the sulphide weathering, was close or supersaturated in those
solutions, suggesting that the lead carbonate mineral phase provided a continuous source of Pb to
these solutions.
The initial dissolved Zn in the inundation waters was independent of the original concentration
in the sediments. Sediments downstream a mine water discharge showed a greater availability of
easily mobilised Zn, producing high initial Zn concentration in the inundation water, despite the
relatively low Zn concentration in the inundated sediment. The Zn/SO4 and Cd/Zn molar ratios
were both consistent with sphalerite mineral oxidation. The final inundation water solutions had
the highest Zn concentrations for those sediment samples where sphalerite was detected by
XRD.
Redox sensitive elements such as Fe and Mn could not unequivocally indicate the presence of
reducing conditions within the flooded sediments and the redox measurements were carried out
only in the overlying water column (ORP above 200-350 mV). Low organic matter content and
sandy texture would not have favoured the rapid formation of an anoxic layer. Yet, only
extending the ORP measurements to the submerged sediment would determine the presence of
flooding-induced reducing conditions. Reductive dissolution of Mn oxyhydroxides would result
in release of Mn into solution, along with other trace metals, such as Pb and Zn. Mn increased in
the inundation water throughout most or all the inundation period for some of the studied
sediments. Their final pore water composition was significantly enriched in Mn (1300-
6500 μg l-1). Saturation indices indicated both rhodocrosite (MnCO3) and Mn oxides reached
saturation. Therefore, it was not possible to preclude either the role of rhodocrosite as solubility
controlling solid phase or the reductive dissolution of Mn oxides for accounting the enhanced
Mn concentrations in the pore water and overlying water column without a better
characterisation of the solid phase and monitoring of the sediment redox conditions.
Amendments to the inundation test design have been recommended, which comprise:
set-up to allow for the continuous monitoring of pore water dynamics and allow for the
collection of pore water at the different times and measurement of pore water pH and Eh;
inclusion of a blank test cell, to test the influence of the properties and the volume of the
inundation water;
inclusion of flow-cell tests to assess the influence of moving or stagnant inundation
water;
the inclusion of abiotic blanks to identify the role microbes play in the solubilisation of
contaminants.
complementary characterisation of the solid phase material and metal distribution in the
sediment before and after the inundation experiment
A technique for evaluating the application of the pin-level stuck-at fault model to VLSI circuits
Accurate fault models are required to conduct the experiments defined in validation methodologies for highly reliable fault-tolerant computers (e.g., computers with a probability of failure of 10 to the -9 for a 10-hour mission). Described is a technique by which a researcher can evaluate the capability of the pin-level stuck-at fault model to simulate true error behavior symptoms in very large scale integrated (VLSI) digital circuits. The technique is based on a statistical comparison of the error behavior resulting from faults applied at the pin-level of and internal to a VLSI circuit. As an example of an application of the technique, the error behavior of a microprocessor simulation subjected to internal stuck-at faults is compared with the error behavior which results from pin-level stuck-at faults. The error behavior is characterized by the time between errors and the duration of errors. Based on this example data, the pin-level stuck-at fault model is found to deliver less than ideal performance. However, with respect to the class of faults which cause a system crash, the pin-level, stuck-at fault model is found to provide a good modeling capability
Normal background concentrations (NBCs) of contaminants in English soils : final project report
The British Geological Survey (BGS) has been commissioned by the Department for Environment, Food and Rural Affairs (Defra) to give guidance on what are normal levels of contaminants in English soils in support of the Part 2A Contaminated Land Statutory Guidance. This has initially been done by studying the distribution of four contaminants – arsenic, lead, benzo[a]pyrene (BaP) and asbestos – in topsoils from England. This work was extended to a further four contaminants (cadmium, copper, nickel and mercury) which enabled methodologies developed to be tested on a larger range of contaminants. The first phase of the Project gathered data sets that were: nationally extensive; systematically collected so a broad range of land uses were represented; and collected and analysed to demonstrably and acceptable levels of quality. Information on the soil contaminant concentrations in urban areas was of particular importance as the normal background is considered to be a combination of both natural and diffuse anthropogenic contributions to the soil. Issues of soil quality are most important in areas where these affect most people, namely, the urban environment. The two principal data sets used in this work are the BGS Geochemical Baseline Survey of the Environment (G-BASE) rural and urban topsoils (37,269 samples) and the English NSI (National Soil Inventory) topsoils (4,864 samples) reanalysed at the BGS laboratories by X-ray fluorescence spectrometry (XRFS) so both data sets were highly compatible. These two data sets provide results for most inorganic element contaminants, though results explored for mercury and BaP are drawn from a variety of different and much less extensive data sets
Lenalidomide in the treatment of young patients with multiple myeloma: from induction to consolidation/maintenance therapy.
Numerical study of the scaling properties of SU(2) lattice gauge theory in Palumbo non-compact regularization
In the framework of a non-compact lattice regularization of nonabelian gauge
theories we look, in the SU(2) case, for the scaling window through the
analysis of the ratio of two masses of hadronic states. In the two-dimensional
parameter space of the theory we find the region where the ratio is constant,
and equal to the one in the Wilson regularization. In the scaling region we
calculate the lattice spacing, finding it at least 20% larger than in the
Wilson case; therefore the simulated physical volume is larger.Comment: 24 pages, 7 figure
Extremely Luminous Far-infrared Sources (ELFS)
The Infrared Astronomical Satellite (IRAS) survey uncovered a class of Extremely Luminous Far Infrared Sources (ELFS), exhibiting luminosities up to and occasionally exceeding 10 to the 12th power L sub 0. Arguments are presented to show that sources with luminosities L equal to or greater than 3 x 10 to the 10th power L sub 0 may represent gas rich galaxies in collision. The more conventional explanation of these sources as sites of extremely active star formation fails to explain the observed low optical luminosities of ELFS as well as their high infrared excess. In contrast, a collisional model heats gas to a temperature of approx. 10 to the 6th power K where cooling takes place in the extreme ultraviolet. The UV is absorbed by dust and converted into far infrared radiation (FIR) without generation of appreciable optical luminosity. Gas recombination as it cools generates a Lyman alpha photon only once for every two extreme ultraviolet approx. 50eV photons emitted by the 10 to the 6th power gas. That accounts for the high infrared excess. Finally, the model also is able to explain the observed luminosity distribution of ELFS as well as many other traits
The detection and tracking of mine-water pollution from abandoned mines using electrical tomography
Increasing emphasis is being placed on the environmental and societal impact of mining, particularly in the EU, where the environmental impacts of abandoned mine sites (spoil heaps and tailings) are now subject to the legally binding Water Framework and Mine Waste Directives.
Traditional sampling to monitor the impact of mining on surface waters and groundwater is laborious, expensive and often unrepresentative. In particular, sparse and infrequent borehole sampling may fail to capture the dynamic behaviour associated with important events such as flash flooding, mine-water break-out, and subsurface acid mine drainage. Current monitoring practice is therefore failing to provide the information needed to assess the socio-economic and environmental impact of mining on vulnerable eco-systems, or to give adequate early warning to allow preventative maintenance or containment. BGS has developed a tomographic imaging system known as ALERT ( Automated time-Lapse Electrical Resistivity Tomography) which allows the near real-time measurement of geoelectric properties "on demand", thereby giving early warning of potential threats to vulnerable water systems. Permanent in-situ geoelectric measurements are used to provide surrogate indicators of hydrochemical and hydrogeological properties. The ALERT survey concept uses electrode arrays, permanently buried in shallow trenches at the surface but these arrays could equally be deployed in mine entries or shafts or underground workings. This sensor network is then interrogated from the office by wireless telemetry (e.g: GSM, low-power radio, internet, and satellite) to provide volumetric images of the subsurface at regular intervals. Once installed, no manual intervention is required; data is transmitted automatically according to a pre-programmed schedule and for specific survey parameters, both of which may be varied remotely as conditions change (i.e: an adaptive sampling approach). The entire process from data capture to visualisation on the web-portal is seamless, with no manual intervention.
Examples are given where ALERT has been installed and used to remotely monitor (i) seawater intrusion in a coastal aquifer (ii) domestic landfills and contaminated land and (iii) vulnerable earth embankments. The full potential of the ALERT concept for monitoring mine-waste has yet to be demonstrated. However we have used manual electrical tomography surveys to characterise mine-waste pollution at an abandoned metalliferous mine in the Central Wales orefield in the UK. Hydrogeochemical sampling confirms that electrical tomography can provide a reliable surrogate for the mapping and long-term monitoring of mine-water pollution
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