652 research outputs found
SHRINKiT: Automated measurement of shrinkage limit for clay soils
This report describes the development at the British Geological Survey (BGS) of a new automated apparatus, titled ‘SHRINKiT’, for measuring the shrinkage limit of a clay soil. This has been developed at the BGS’s geotechnical laboratories, in part with NERC Innovations funding. The new method is intended to replace two British Standards (BS1377) methods which have fallen into disuse at BGS, in common with many other laboratories in the UK, and to some extent worldwide, partly as the result of safety concerns in their required use of large quantities of mercury. During the test the cylindrical specimen is allowed to air-dry and shrink. The apparatus carries out repeat measurements of diameter, height and weight; the dimension-measuring component being in effect a simple laser scanner. Each test takes a few days to complete; the duration depending on specimen size, soil type, initial water content and environmental conditions. The output of the test is a plot of water content vs. volume from which the shrinkage limit of the soil can be calculated using the graphical construction method described in BS1377. The shrinkage limit is defined as the water content below which there is little or no further structural shrinkage of the soil. Additional information may also be obtained from the results. The test may be carried out on a wide variety of soil types in an undisturbed, remoulded or compacted state
Dissimilatory nitrate reduction to ammonium coupled to Fe(II) oxidation in sediments of a periodically hypoxic estuary
Estuarine sediments are critical for the remediation of large amounts of anthropogenic nitrogen (N) loading via production of N<sub>2</sub> from nitrate by denitrification. However, nitrate is also recycled within sediments by dissimilatory nitrate reduction to ammonium (DNRA). Understanding the factors that influence the balance between denitrification and DNRA is thus crucial to constraining coastal N budgets. A potentially important factor is the availability of different electron donors (organic carbon, reduced iron and sulfur). Both denitrification and DNRA may be linked to ferrous iron oxidation, however the contribution of Fe(II)-fueled nitrate reduction in natural environments is practically unknown. This study investigated how nitrate-dependent Fe<sup>2+</sup> oxidation affects the partitioning between nitrate reduction pathways using <sup>15</sup>N-tracing methods in sediments along the salinity gradient of the periodically hypoxic Yarra River estuary, Australia. Increased dissolved Fe<sup>2+</sup> availability resulted in significant enhancement of DNRA rates from around 10–20% total nitrate reduction in control incubations to over 40% in those with additional Fe<sup>2+</sup>, at several sites. Increases in DNRA at some locations were accompanied by reductions in denitrification. Significant correlations were observed between Fe<sup>2+</sup> oxidation and DNRA rates, with reaction ratios corresponding to the stoichiometry of Fe<sup>2+</sup>-dependent DNRA. Our results provide experimental evidence for a direct coupling of DNRA to Fe<sup>2+</sup> oxidation across an estuarine gradient, suggesting that Fe<sup>2+</sup> availability may exert substantial control on the balance between retention and removal of bioavailable N. Thus, DNRA linked to Fe<sup>2+</sup> oxidation may be of general importance to environments with Fe-rich sediments
A new apparatus for determining the shrinkage limit of clay soils
A new apparatus for the determination of shrinkage limit is described. Two versions have been produced: a manually operated prototype ‘version1' followed by an automated version named SHRINKiT. Test results using the former for British and overseas clay soils are described and comparisons made with the British Standards preferred method. A further set of test results is described for SHRINKiT. However, it was not possible to compare these with the BS 1377 method owing to the introduction of a ban on the use of mercury in the British Geological Survey's geotechnical laboratories. The new method is set in the context of the huge cost of shrink/swell-related subsidence damage in Britain and the relative disuse of both BS 1377 methods for shrinkage limit, for reasons of safety. The shrinkage behaviour of different soils types and sample states is discussed, in addition to the advantages and disadvantages of the new method
Magneto-Acoustic Wave Oscillations in Solar Spicules
Some observations suggest that solar spicules show small amplitude and high
frequency oscillations of magneto-acoustic waves, which arise from photospheric
granular forcing. We apply the method of MHD seismology to determine the period
of kink waves. For this purposes, the oscillations of a magnetic cylinder
embedded in a field-free environment is investigated. Finally, diagnostic
diagrams displaying the oscillatory period in terms of some equilibrium
parameters are provided to allow a comparison between theoretical results and
those coming from observations.Comment: 10 pages, 4 fig
Multiplicative renormalizability of gluon and ghost propagators in QCD
We reformulate the coupled set of continuum equations for the renormalized
gluon and ghost propagators in QCD, such that the multiplicative
renormalizability of the solutions is manifest, independently of the specific
form of full vertices and renormalization constants. In the Landau gauge, the
equations are free of renormalization constants, and the renormalization point
dependence enters only through the renormalized coupling and the renormalized
propagator functions. The structure of the equations enables us to devise novel
truncations with solutions that are multiplicatively renormalizable and agree
with the leading order perturbative results. We show that, for infrared power
law behaved propagators, the leading infrared behavior of the gluon equation is
not solely determined by the ghost loop, as concluded in previous studies, but
that the gluon loop, the three-gluon loop, the four-gluon loop, and even
massless quarks also contribute to the infrared analysis. In our new Landau
gauge truncation, the combination of gluon and ghost loop contributions seems
to reject infrared power law solutions, but massless quark loops illustrate how
additional contributions to the gluon vacuum polarization could reinstate these
solutions. Moreover, a schematic study of the three-gluon and four-gluon loops
shows that they too need to be considered in more detail before a definite
conclusion about the existence of infrared power behaved gluon and ghost
propagators can be reached.Comment: 13 pages, 1 figure, submitted to Phys. Rev.
Morita Duality and Noncommutative Wilson Loops in Two Dimensions
We describe a combinatorial approach to the analysis of the shape and
orientation dependence of Wilson loop observables on two-dimensional
noncommutative tori. Morita equivalence is used to map the computation of loop
correlators onto the combinatorics of non-planar graphs. Several
nonperturbative examples of symmetry breaking under area-preserving
diffeomorphisms are thereby presented. Analytic expressions for correlators of
Wilson loops with infinite winding number are also derived and shown to agree
with results from ordinary Yang-Mills theory.Comment: 32 pages, 9 figures; v2: clarifying comments added; Final version to
be published in JHE
On the Stress Tensor of Kerr/CFT
The recently-conjectured Kerr/CFT correspondence posits a field theory dual
to dynamics in the near-horizon region of an extreme Kerr black hole with
certain boundary conditions. We construct a boundary stress tensor for this
theory via covariant phase space techniques. The structure of the stress tensor
indicates that any dual theory is a discrete light cone quantum theory, in
agreement with recent arguments by Balasubramanian et al. The key technical
step in our construction is the addition of an appropriate counter-term to the
symplectic structure, which is necessary to make the theory fully covariant and
to resolve a subtle problem involving the integrability of charges.Comment: 19 page
Stability of Attractive Bose-Einstein Condensates in a Periodic Potential
Using a standing light wave trap, a stable quasi-one-dimensional attractive
dilute-gas Bose-Einstein condensate can be realized. In a mean-field
approximation, this phenomenon is modeled by the cubic nonlinear Schr\"odinger
equation with attractive nonlinearity and an elliptic function potential of
which a standing light wave is a special case. New families of stationary
solutions are presented. Some of these solutions have neither an analog in the
linear Schr\"odinger equation nor in the integrable nonlinear Schr\"odinger
equation. Their stability is examined using analytic and numerical methods.
Trivial-phase solutions are experimentally stable provided they have nodes and
their density is localized in the troughs of the potential. Stable
time-periodic solutions are also examined.Comment: 12 pages, 18 figure
The Second Sound of SU(2)
Using the AdS/CFT correspondence, we calculate the transport coefficients of
a strongly interacting system with a non-abelian SU(2) global symmetry near a
second order phase transition. From the behavior of the poles in the Green's
functions near the phase transition, we determine analytically the speed of
second sound, the conductivity, and diffusion constants. We discuss
similarities and differences between this and other systems with vector order
parameters such as p-wave superconductors and liquid helium-3.Comment: 31 pages, 2 figures; v2 ref added, typo fixe
Constructing the fermion-boson vertex in QED3
We derive perturbative constraints on the transverse part of the
fermion-boson vertex in massive QED3 through its one loop evaluation in an
arbitrary covariant gauge. Written in a particular form, these constraints
naturally lead us to the first non-perturbative construction of the vertex,
which is in complete agreement with its one loop expansion in all momentum
regimes. Without affecting its one-loop perturbative properties, we also
construct an effective vertex in such a way that the unknown functions defining
it have no dependence on the angle between the incoming and outgoing fermion
momenta. Such a vertex should be useful for the numerical study of dynamical
chiral symmetry breaking, leading to more reliable results.Comment: 13 pages, 2 figure
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