588 research outputs found
Investigation of rising nitrate concentrations in groundwater in the Eden Valley, Cumbria: Phase 1 project scoping study
This is the Investigation of rising nitrate concentrations in groundwater in the Eden Valley, Cumbria report produced by the Environment Agency in 2003. This report focuses on groundwater nitrate concentrations in the Eden Valley. Most boreholes in the Eden Valley had nitrate concentrations less than 20 mg/l but a significant number had higher concentrations, some exceeding the EC maximum admissible concentration for drinking water of 50 mg/l. The main objectives of this report were to investigate the causes of rising nitrate concentrations in groundwater in the Permo-Triassic sandstone aquifers of the Eden Valley area and provide sufficient understanding of the groundwater and surface water flow system, including the sources of the nitrate contamination and the processes controlling nitrate movement, so that possible management options for reversing this trend can be considered
Global shape aftereffects in composite radial frequency patterns
YesIndividual radial frequency (RF) patterns are generated by modulating a circle's radius as a sinusoidal function of polar angle and have been shown to tap into global shape processing mechanisms. Composite RF patterns can reproduce the complex outlines of natural shapes and examining these stimuli may allow us to interrogate global shape mechanisms that are recruited in biologically relevant tasks. We present evidence for a global shape aftereffect in a composite RF pattern stimulus comprising two RF components. Manipulations of the shape, location, size and spatial frequency of the stimuli revealed that this aftereffect could only be explained by the attenuation of intermediate-level global shape mechanisms. The tuning of the aftereffect to test stimulus size also revealed two mechanisms underlying the aftereffect; one that was tuned to size and one that was invariant. Finally, we show that these shape mechanisms may encode some RF information. However, the RF encoding we found was not capable of explaining the full extent of the aftereffect, indicating that encoding of other shape features such as curvature are also important in global shape processing.This research was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) grant #BB/L007770/1
Rapid X-ray Variability of Seyfert 1 Galaxies
The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert
galaxies provided early support for the standard model in which Seyferts are
powered by a supermassive black hole fed from an accretion disc. However, since
EXOSAT there has been little opportunity to advance our understanding of the
most rapid X-ray variability. Observations with XMM-Newton have changed this.
We discuss some recent results obtained from XMM-Newton observations of Seyfert
1 galaxies. Particular attention will be given to the remarkable similarity
found between the timing properties of Seyferts and black hole X-ray binaries,
including the power spectrum and the cross spectrum (time delays and
coherence), and their implications for the physical processes at work in
Seyferts.Comment: To appear in From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht:
Kluwer
Topological mirror symmetry with fluxes
Motivated by SU(3) structure compactifications, we show explicitly how to
construct half--flat topological mirrors to Calabi--Yau manifolds with NS
fluxes. Units of flux are exchanged with torsion factors in the cohomology of
the mirror; this is the topological complement of previous
differential--geometric mirror rules. The construction modifies explicit SYZ
fibrations for compact Calabi--Yaus. The results are of independent interest
for SU(3) compactifications. For example one can exhibit explicitly which
massive forms should be used for Kaluza--Klein reduction, proving previous
conjectures. Formality shows that these forms carry no topological information;
this is also confirmed by infrared limits and old classification theorems.Comment: 35 pages, 5 figure
D-branes in Nongeometric Backgrounds
"T-fold" backgrounds are generically-nongeometric compactifications of string
theory, described by T^n fibrations over a base N with transition functions in
the perturbative T-duality group. We review Hull's doubled torus formalism,
which geometrizes these backgrounds, and use the formalism to constrain the
D-brane spectrum (to leading order in g_s and alpha') on T^n fibrations over
S^1 with O(n,n;Z) monodromy. We also discuss the (approximate) moduli space of
such branes and argue that it is always geometric. For a D-brane located at a
point on the base N, the classical ``D-geometry'' is a T^n fibration over a
multiple cover of N.Comment: 29 pages; uses harvmac.tex; v2: substantial revision throughou
Assessing pesticide pollution of groundwater: current knowledge and remaining gaps
This paper summarises recent research on pesticides in groundwater in both temperate and tropical regions. Results of field, laboratory and modelling studies highlight the factors which determine the fate and behaviour of pesticides in groundwater systems. These include transport pathways from the soil to the water table and thence to supply sources, and the processes such as adsorption and degradation which can help to attenuate pesticide movement and reduce concentrations. Studies of degradation show that most compounds are likely to be much more persistent in aquifers than in soils, but below the water table the long travel times and potential for dilution may greatly reduce concentrations. The greatest risks are likely to occur in fractured aquifers with their potential for much more rapid flow.
Important uncertainties and gaps in knowledge remain. Laboratory studies of degradation present difficulties of extrapolation to field conditions and provide evidence of wide variations in half-lives spatially and with time; making the choice of values for transport modelling problematic. Further work is required to improve understanding of such variations. Studies can also indicate that different degradation pathways can occur and different pesticide metabolites produced, depending onenvironmental conditions. The occurrence and behaviour of metabolites in groundwater systems is also poorly known
The Giant Inflaton
We investigate a new mechanism for realizing slow roll inflation in string
theory, based on the dynamics of p anti-D3 branes in a class of mildly warped
flux compactifications. Attracted to the bottom of a warped conifold throat,
the anti-branes then cluster due to a novel mechanism wherein the background
flux polarizes in an attempt to screen them. Once they are sufficiently close,
the M units of flux cause the anti-branes to expand into a fuzzy NS5-brane,
which for rather generic choices of p/M will unwrap around the geometry,
decaying into D3-branes via a classical process. We find that the effective
potential governing this evolution possesses several epochs that can
potentially support slow-roll inflation, provided the process can be arranged
to take place at a high enough energy scale, of about one or two orders of
magnitude below the Planck energy; this scale, however, lies just outside the
bounds of our approximations.Comment: 31 pages, 4 figures, LaTeX. v2: references added, typos fixe
Determination of time delay from the gravitational lens B1422+231
We present the radio light curves of lensed images of the gravitational lens
B1422+231. The observations have been carried out using the VLA at 8.4 and 15
GHz over a period of 197 days. We describe a method to estimate the time delay
from the observed light curves. Using this method, our cross-correlation
analysis shows that the time delay between images B and A is 1.51.4d,
between A and C is 7.62.5d, between B and C is 8.22.0d. When applied
to other lensed systems with measured time delays our new method gives
comparable results.Comment: 10 pages, 9 figures, accepted in MNRA
On the Taxonomy of Flux Vacua
We investigate several predictions about the properties of IIB flux vacua on
Calabi-Yau orientifolds, by constructing and characterizing a very large set of
vacua in a specific example, an orientifold of the Calabi-Yau hypersurface in
. We find support for the prediction of Ashok and Douglas
that the density of vacua on moduli space is governed by where and are curvature and K\"ahler forms on the moduli
space. The conifold point on moduli space therefore serves as an
attractor, with a significant fraction of the flux vacua contained in a small
neighborhood surrounding . We also study the functional dependence of
the number of flux vacua on the D3 charge in the fluxes, finding simple power
law growth.Comment: 22 pages, harvmac; v2 typos corrected, refs added; v3 minor error
correcte
Dibaryon Spectroscopy
The AdS/CFT correspondence relates dibaryons in superconformal gauge theories
to holomorphic curves in Kaehler-Einstein surfaces. The degree of the
holomorphic curves is proportional to the gauge theory conformal dimension of
the dibaryons. Moreover, the number of holomorphic curves should match, in an
appropriately defined sense, the number of dibaryons. Using AdS/CFT backgrounds
built from the generalized conifolds of Gubser, Shatashvili, and Nekrasov
(1999), we show that the gauge theory prediction for the dimension of
dibaryonic operators does indeed match the degree of the corresponding
holomorphic curves. For AdS/CFT backgrounds built from cones over del Pezzo
surfaces, we are able to match the degree of the curves to the conformal
dimension of dibaryons for the n'th del Pezzo surface, n=1,2,...,6. Also, for
the del Pezzos and the A_k type generalized conifolds, for the dibaryons of
smallest conformal dimension, we are able to match the number of holomorphic
curves with the number of possible dibaryon operators from gauge theory.Comment: 30 pages, 6 figures, corrected refs; v3 typos correcte
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