1,954 research outputs found
Recovering the lost gold of the developing world : bibliographic database
This report contains a library of 181 references, including abstracts, prepared for Project
R 7120 "Recovering the lost gold of the developing world" funded by the UK' s
Department for International Development (DFID) under the Knowledge and Research
(KAR) programme. As part of an initial desk study, a literature review of gold processing
methods used by small-scale miners was carried out using the following sources; the lSI
Science Citation Index accessed via Bath Information and Data Services (BIDS), a
licensed GEOREF CD-ROM database held at the BGS's Library in Keyworth and
IMMage a CD-ROM database produced by the Institution of Mining and Metallurgy held
by the Minerals group ofBGS. Information on the search terms used is available from the
author
Characterisation of Quaternary sediments from East Anglia
This report describes the mineralogical investigations of Quaternary sediments,mainly Cromer Till, collected from East Anglia. The main aim of the work was to characterise the mineralogical and physical properties of the till samples to facilitate correlation between tills from different localities. The clast composition of the samples was determined using a binocular microscope and the mineralogy of the matrix was determined using X-ray diffraction and thermogravimetry. Calibration charts were used to quantify the amount of quartz and calcite present. Cumulative frequency graphs were plotted from the particle-size data to determine the mean, median, standard deviation and skewness. Also ternary sand/silt/clay diagrams were
plotted. The Cromer Till samples typically contained 2% gravel (mainly flint, sandstone, quartz and chalk), 45% sand, 31 % silt and 22% clay. The Starston Till contained 12% gravel (mainly flint), 46% sand, 16% silt and 26% clay. The 'Clay' from Sea Palling contained 1 % gravel (mainly flint), 10% sand, 78% silt and 11 % clay. The Lowestoft Till samples had different particle-size distributions and the gravel consisted mainly of chalk.The Crag Clay samples contained 1 % gravel (mainly sandstone), 11 % sand, 49% silt and 39% clay. The Blue Clay samples contained virtually no gravel, 4% sand, 59% silt and 37% silt. The Holocene sample contained 1 % gravel (mainly flint), 21% sand, 39% silt and 39% clay. The CaC03 contents and particle-size distributions of the Cromer Till samples were
compared with published data (Lunkka, 1994). Based upon this comparison the samples were tentatively classified as either Walcott Diamicton, Happisburgh Diamicton or Norwich Brickearth. The 'Blue Clay' samples were also tentatively
classified as Crag Clay. Recommendations for further work include detailed logging and sampling of coastal sections; collection of large samples for more accurate clast analysis ; and heavy mineral analysis
Tunneling and Metastability of continuous time Markov chains
We propose a new definition of metastability of Markov processes on countable
state spaces. We obtain sufficient conditions for a sequence of processes to be
metastable. In the reversible case these conditions are expressed in terms of
the capacity and of the stationary measure of the metastable states
Evidence of absence: no relationship between behaviourally measured prediction error response and schizotypy
Introduction: The predictive processing framework has attracted much interest in the field of schizophrenia research in recent years, with an increasing number of studies also carried out in healthy individuals with nonclinical psychosis-like experiences. The current research adopted a continuum approach to psychosis and aimed to investigate different types of prediction error responses in relation to psychometrically defined schizotypy. Methods: One hundred and two healthy volunteers underwent a battery of behavioural tasks including (a) a force-matching task, (b) a Kamin blocking task, and (c) a reversal learning task together with three questionnaires measuring domains of schizotypy from different approaches. Results: Neither frequentist nor Bayesian statistical methods supported the notion that alterations in prediction error responses were related to schizotypal traits in any of the three tasks. Conclusions: These null results suggest that deficits in predictive processing associated with clinical states of psychosis are not always present in healthy individuals with schizotypal traits
Irrigation Management
Competition for limited water supplies continues to restrict water available for irrigation. Irrigated agricultural must continually improve irrigation management to continue producing food, fiber and fuel for a growing world population. Precision irrigation is the process of applying the right amount of water at the right time and place to obtain the best use of available water. Precision irrigation management is needed on large irrigation projects so water delivery matches irrigation needs and on individual fields to apply the right amount of water at the right time and place. Technology is commercially available to precisely apply water when and where it is needed by crops, however, user-friendly decision tools are still needed to quantify specific irrigation needs and control water application within fields. Integrating information from various sensors and systems into a decision support program will be critical to highly managed, spatially varied irrigation
Geomorphological controls on fluvial carbon storage in headwater peatlands
Geomorphological controls and catchment sediment characteristics control the formation of floodplains and affect their capacity to sequester carbon. Organic carbon stored in floodplains is typically a product of pedogenic development between periods of mineral sediment deposition. However, in organically‐dominated upland catchments with a high sediment load, eroded particulate organics may also be fluvially deposited with potential for storage and/or oxidation. Understanding the redistribution of terrestrial carbon laterally, beyond the bounds of river channels is important, especially in eroding peatland systems where fluvial particulate organic carbon exports are often assumed to be oxidised. Floodplains have the potential to be both carbon cycling hotspots and areas of sequestration. Understanding of the interaction of carbon cycling and the sediment cascade through floodplain systems is limited. This paper examines the formation of highly organic floodplains downstream of heavily eroded peatlands in the Peak District, UK. Reconstruction of the history of the floodplains suggests that they have formed in response to periods of erosion of organic soils upstream. We present a novel approach to calculating a carbon stock within a floodplain, using XRF and radiograph data recorded during Itrax core scanning of sediment cores. This carbon stock is extrapolated to the catchment scale, to assess the importance of these floodplains in the storage and cycling of organic carbon in this area. The carbon stock estimate for the floodplains across the contributing catchments is between 3482‐13460 tonnes, equating on an annualised basis to 0.8‐4.5% of the modern‐day POC flux. Radiocarbon analyses of bulk organic matter in floodplain sediments revealed that a substantial proportion of organic carbon was associated with re‐deposited peat and has been used as a tool for organic matter source determination. The average age of these samples (3010 years BP) is substantially older than Infrared Stimulated Luminesence dating which demonstrated that the floodplains formed between 430 and 1060 years ago. Our data suggest that floodplains are an integral part of eroding peatland systems, acting as both significant stores of aged and eroded organic carbon and as hotspots of carbon turnover
An assessment of Evans' unified field theory I
Evans developed a classical unified field theory of gravitation and
electromagnetism on the background of a spacetime obeying a Riemann-Cartan
geometry. This geometry can be characterized by an orthonormal coframe theta
and a (metric compatible) Lorentz connection Gamma. These two potentials yield
the field strengths torsion T and curvature R. Evans tried to infuse
electromagnetic properties into this geometrical framework by putting the
coframe theta to be proportional to four extended electromagnetic potentials A;
these are assumed to encompass the conventional Maxwellian potential in a
suitable limit. The viable Einstein-Cartan(-Sciama-Kibble) theory of gravity
was adopted by Evans to describe the gravitational sector of his theory.
Including also the results of an accompanying paper by Obukhov and the author,
we show that Evans' ansatz for electromagnetism is untenable beyond repair both
from a geometrical as well as from a physical point of view. As a consequence,
his unified theory is obsolete.Comment: 39 pages of latex, modified because of referee report, mistakes and
typos removed, partly reformulated, taken care of M.W.Evans' rebutta
Holographic RG Flows and Universal Structures on the Coulomb Branch of N=2 Supersymmetric Large n Gauge Theory
We report on our results of D3-brane probing a large class of generalised
type IIB supergravity solutions presented very recently in the literature. The
structure of the solutions is controlled by a single non-linear differential
equation. These solutions correspond to renormalisation group flows from pure
N=4 supersymmetric gauge theory to an N=2 gauge theory with a massive adjoint
scalar. The gauge group is SU(n) with n large. After presenting the general
result, we focus on one of the new solutions, solving for the specific
coordinates needed to display the explicit metric on the moduli space. We
obtain an appropriately holomorphic result for the coupling. We look for the
singular locus, and interestingly, the final result again manifests itself in
terms of a square root branch cut on the complex plane, as previously found for
a set of solutions for which the details are very different. This, together
with the existence of the single simple non-linear differential equation, is
further evidence in support of an earlier suggestion that there is a very
simple model --perhaps a matrix model with relation to the Calogero-Moser
integrable system-- underlying this gauge theory physics.Comment: 14 pages, LaTeX, 1 figur
Simulated Optimisation of Disordered Structures with negative Poisson’s ratios
Copyright © 2009 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Mechanics of Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Mechanics of Materials, Vol. 41 Issue 8 (2009). DOI: 10.1016/j.mechmat.2009.04.008Two-dimensional regular theoretical units that give a negative Poisson’s ratio (NPR) are well documented and well understood. Predicted mechanical properties resulting from these models are reasonably accurate in two dimensions but fall down when used for heterogeneous real-world materials. Manufacturing processes are seldom perfect and some measure of heterogeneity is therefore required to account for the deviations from the regular unit cells in this real-life situation. Analysis of heterogeneous materials in three dimensions is a formidable problem; we must first understand heterogeneity in two dimensions. This paper approaches the problem of finding a link between heterogeneous networks and its material properties from a new angle. Existing optimisation tools are used to create random two-dimensional topologies that display NPR, and the disorder in the structure and its relationship with NPR is investigated
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