1,403 research outputs found
Effects of old landfills on groundwater quality. Phase 2, investigation of the Thriplow landfill 1996â1997
Disused sand and gravel excavations overlying the major Chalk aquifer at Thriplow in Cambridgeshire have
been filled with domestic waste in two phases. One area (Phase 1) was filled between 1957â77 with little compaction
of the refuse and was left uncapped, while Phase 2 was deposited between 1981â87 and capped with
clay. Aerial photography and surface resistivity surveys indicate that the site geometry is complex, with several
phases of landfilling into excavations of differing depths. Drilling through the waste indicates that leachate production
and waste stabilisation proceed at different rates in capped and uncapped landfills. Analysis of leachate
obtained by centrifugation or squeezing appears to give more insight into the pollution potential than do leach
tests with distilled water. The Biological Methane Potential (BMP) of the waste appears to be related to the
quantity of decomposable material but the chemical oxygen demand (COD) values are distorted by the presence
of reduced metals. Too few boreholes have been drilled to define the leachate source in terms of its spatial distribution
and little is known of how its composition has changed with time. However, hydraulic conductivity measurements
on the landfill caps suggest that it is sufficiently permeable for all rainfall to potentially infiltrate the
waste.
Boreholes outside the landfill penetrate the Upper and Lower Chalk, and identify the Melbourn Rock and underlying
Plenus Marls at the junction of the two formations about 20 m below ground level (bgl). Surface resistivity
surveys using the BGS RESCAN system, confirm aerial photographs of the extent of the landfill and also
suggest that leachate has migrated beyond the base of the landfill. Evidence of leachate migration in pre-existing
screened boreholes completed above and below the Plenus Marls suggests that leachate is flowing above the
Plenus Marls. Hydraulic head measurements whilst drilling a borehole to the base of the lower Chalk approx. 70
m bgl revealed the potential for upward groundwater flow through the Plenus Marls. Thus, previously-drilled
boreholes penetrating the Plenus Marls are expected to recharge upwards into the shallow aquifer above the
Plenus Marls diluting any leachate in the upper aquifer and distorting the flow regime. Several of these boreholes
have subsequently been modified to stem the flow across the Plenus Marls.
One borehole down-gradient to the west of the site revealed a large thickness of drift composed of both sand and
clay rich material. This suggests the existence of a buried channel, the hydrogeological significance of which has
yet to be assessed.
Groundwater chemistry appears to be influenced by three major factors. (a) the landfill leachate (b) the composition
of shallow groundwater in the top 10 m of the Chalk, and (c) the composition of water from the Lower
Chalk. Limited groundwater monitoring data appear to display a cyclic variation in chloride concentration. The
origin for this is not clear but it may correlate with cyclic variations in groundwater levels when the water table
rises into the waste. Cyclic flushing of the landfill may release leachate into the aquifer giving rise to pulses of
chloride. Alternatively changes in chloride may arise by the changing direction of groundwater flow which as yet
has not been assessed.
A conceptual hydrogeological model in which flow is limited to above the Plenus Marls has been used to
develop a more appropriate groundwater flow and solute transport model. However, the model lacks data on
aquifer properties, on contaminant inputs concentrations, fluxes and spatial variations, and there is a paucity of
monitoring data for calibration. Nonetheless preliminary transport modelling using an equivalent porous medium
approach shows that an effective porosity of about 5% best fits the regional data. Since this is much less than the
total porosity of about 40% for the Chalk, it would appear that only part of the Chalk is available for flow but
that matrix diffusion could play an important role in leachate attenuation. Discrete fracture modelling using the
FRACTRAN code has allowed some scoping to be made of the hydraulic properties of the aquifer by comparison
with chloride hydrographs, but these again need to be better conditioned by in-situ measurement of fracture
distributions and transmissivities.
A number of additional activities are required to improve the understanding of flow and contaminant transport at
the site. These include better spatial definition of the waste distribution, improved data on the hydraulic properties
of the Chalk aquifer, and the use of automatic monitoring to record temporal changes in groundwater chemistry
and groundwater levels
Defining the origins of multiple emission/excitation in rhenium-bisthiazole complexes
The underlying mechanism of the unusual emissive behavior of [Re(CO) 3 -1,1-bis-4-thiazole-(1,4)-diaminobutane)] bromide (4-BT) has been investigated. Synthesis and spectroscopic characterization of structurally similar isomers ([Re(CO) 3 -1,1-bis-2-thiazole-(1,4)-diaminobutane)] bromide (2-BT)) and the location of triplet states, solid state and low temperature spectroscopic measurements, and DFT calculations show that the photophysical properties are not due to photoisomerization as previously hypothesized. The results show that the unusual emissive behavior is not observed in structural isomers, is specific to the previously reported complex, 4-BT, and may arise from vibrational energy relaxation and vibrational cooling. Translation of the unusual emissive behavior to the solid state offers an interesting platform allowing this complex to be potentially utilized as a probe, sensor or photonic device
First detection of Edwardsiella ictaluri (Proteobacteria: Enterobacteriaceae) in wild Australian catfish
The bacterium Edwardsiella ictaluri is considered to be one of the most significant pathogens of farmed catfish in the United States of America and has also caused mortalities in farmed and wild fishes in many other parts of the world. E. ictaluri is not believed to be present in wild fish populations in Australia, although it has previously been detected in imported ornamental fishes held in quarantine facilities. In an attempt to confirm freedom from the bacterium in Australian native fishes, we undertook a risk-based survey of wild catfishes from 15 sites across northern Australia. E. ictaluri was detected by selective culturing, followed by DNA testing, in Wet Tropics tandan (Tandanus tropicanus) from the Tully River, at a prevalence of 0.40 (95% CI 0.21â0.61). The bacterium was not found in fishes sampled from any of the other 14 sites. This is the first report of E. ictaluri in wild fishes in Australia
Microclusters of inhibitory killer immunoglobulinâlike receptor signaling at natural killer cell immunological synapses
We report the supramolecular organization of killer Igâlike receptor (KIR) phosphorylation using a technique applicable to imaging phosphorylation of any green fluorescent proteinâtagged receptor at an intercellular contact or immune synapse. Specifically, we use fluorescence lifetime imaging (FLIM) to report Förster resonance energy transfer (FRET) between GFP-tagged KIR2DL1 and a Cy3-tagged generic anti-phosphotyrosine monoclonal antibody. Visualization of KIR phosphorylation in natural killer (NK) cells contacting target cells expressing cognate major histocompatibility complex class I proteins revealed that inhibitory signaling is spatially restricted to the immune synapse. This explains how NK cells respond appropriately when simultaneously surveying susceptible and resistant target cells. More surprising, phosphorylated KIR was confined to microclusters within the aggregate of KIR, contrary to an expected homogeneous distribution of KIR signaling across the immune synapse. Also, yellow fluorescent proteinâtagged Lck, a kinase important for KIR phosphorylation, accumulated in a multifocal distribution at inhibitory synapses. Spatial confinement of receptor phosphorylation within the immune synapse may be critical to how activating and inhibitory signals are integrated in NK cells
Topological Defects and CMB anisotropies : Are the predictions reliable ?
We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR
Rotational Surfaces in and Solutions in the Nonlinear Sigma Model
The Gauss map of non-degenerate surfaces in the three-dimensional Minkowski
space are viewed as dynamical fields of the two-dimensional O(2,1) Nonlinear
Sigma Model. In this setting, the moduli space of solutions with rotational
symmetry is completely determined. Essentially, the solutions are warped
products of orbits of the 1-dimensional groups of isometries and elastic curves
in either a de Sitter plane, a hyperbolic plane or an anti de Sitter plane. The
main tools are the equivalence of the two-dimensional O(2,1) Nonlinear Sigma
Model and the Willmore problem, and the description of the surfaces with
rotational symmetry. A complete classification of such surfaces is obtained in
this paper. Indeed, a huge new family of Lorentzian rotational surfaces with a
space-like axis is presented. The description of this new class of surfaces is
based on a technique of surgery and a gluing process, which is illustrated by
an algorithm.Comment: PACS: 11.10.Lm; 11.10.Ef; 11.15.-q; 11.30.-j; 02.30.-f; 02.40.-k. 45
pages, 11 figure
Empathy: a review of the concept
The inconsistent definition of empathy has had a negative impact on both research and practice. The aim of this article is to review and critically appraise a range of definitions of empathy and, through considered analysis, to develop a new conceptualisation. From the examination of 43 discrete definitions, 8 themes relating to the nature of empathy emerged: âdistinguishing empathy from other conceptsâ; âcognitive or affective?â; âcongruent or incongruent?â; âsubject to other stimuli?â; âself/other distinction or merging?â; âtrait or state influences?â; âhas a behavioural outcome?â; and âautomatic or controlled?â The relevance and validity of each theme is assessed and a new conceptualisation of empathy is offered. The benefits of employing a more consistent and complete definition of empathy are discussed
Menus for Feeding Black Holes
Black holes are the ultimate prisons of the Universe, regions of spacetime
where the enormous gravity prohibits matter or even light to escape to
infinity. Yet, matter falling toward the black holes may shine spectacularly,
generating the strongest source of radiation. These sources provide us with
astrophysical laboratories of extreme physical conditions that cannot be
realized on Earth. This chapter offers a review of the basic menus for feeding
matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to
appear in hard cover in the Space Sciences Series of ISSI "The Physics of
Accretion onto Black Holes" (Springer Publisher
Simulation of dimensionality effects in thermal transport
The discovery of nanostructures and the development of growth and fabrication
techniques of one- and two-dimensional materials provide the possibility to
probe experimentally heat transport in low-dimensional systems. Nevertheless
measuring the thermal conductivity of these systems is extremely challenging
and subject to large uncertainties, thus hindering the chance for a direct
comparison between experiments and statistical physics models. Atomistic
simulations of realistic nanostructures provide the ideal bridge between
abstract models and experiments. After briefly introducing the state of the art
of heat transport measurement in nanostructures, and numerical techniques to
simulate realistic systems at atomistic level, we review the contribution of
lattice dynamics and molecular dynamics simulation to understanding nanoscale
thermal transport in systems with reduced dimensionality. We focus on the
effect of dimensionality in determining the phononic properties of carbon and
semiconducting nanostructures, specifically considering the cases of carbon
nanotubes, graphene and of silicon nanowires and ultra-thin membranes,
underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
La ricerca in Psicologia Clinica Perinatale : fattori di rischio e protezione per la tutela della salute mentale
- âŠ