818 research outputs found
High arsenic (As) concentrations in the shallow groundwaters of southern Louisiana: Evidence of microbial controls on As mobilization from sediments
Citation: Yang, N., Shen, Z., Datta, S., & Johannesson, K. H. (2016). High arsenic (As) concentrations in the shallow groundwaters of southern Louisiana: Evidence of microbial controls on As mobilization from sediments. Journal of Hydrology: Regional Studies, 5, 100-113. doi:10.1016/j.ejrh.2015.11.023Study region: The Mississippi Delta in southern Louisiana, United States. Study focus: The probable role that microbial respiration plays in As release from the shallow aquifer sediments. New hydrological insights for the region: Shallow groundwaters in southern Louisiana have been reported to contain elevated As concentrations, whereas mechanisms responsible for As release from sediments have rarely been studied in this region. Microbial respiration is generally considered the main mechanism controlling As release in reducing anoxic aquifers such as the shallow aquifers in southern Louisiana and those of the Bengal basin. This study investigates the role microbial respiration plays in As release from shallow aquifer sediments in southern Louisiana through sediment incubation experiments and porewater analysis. Arsenic concentrations were the lowest in the sterilized control experiments, slightly higher in the un-amended experiments, and the highest in the experiments amended with acetate, and especially those amended with both acetate and AQDS (9,10-anthraquinone-2,6-disulfonic acid). Although Fe and Mn generally decreased at the beginning of all the experiments, they did follow a similar trend to As after the decrease. Porewater analysis showed that As and Fe concentrations were generally positively correlated and were higher in the coarse-grained sediments than in the fine-grained sediments. Results of the investigation are consistent with microbial respiration playing a key role in As release from the shallow aquifers sediments in southern Louisiana. © 2015 The Authors
Enhanced Two-Channel Kondo Physics in a Quantum Box Device
We propose a design for a one-dimensional quantum box device where the charge
fluctuations are described by an anisotropic two-channel Kondo model. The
device consists of a quantum box in the Coulomb blockade regime, weakly coupled
to a quantum wire by a single-mode point contact. The electron correlations in
the wire produce strong back scattering at the contact, significantly
increasing the Kondo temperature as compared to the case of non-interacting
electrons. By employing boundary conformal field theory techniques we show that
the differential capacitance of the box exhibits manifest two-channel Kondo
scaling with temperature and gate voltage, uncontaminated by the
one-dimensional electron correlations. We discuss the prospect to
experimentally access the Kondo regime with this type of device.Comment: EPL style, 5 pages, 1 figure, final published versio
The effect of multiple paternity on genetic diversity during and after colonisation
In metapopulations, genetic variation of local populations is influenced by
the genetic content of the founders, and of migrants following establishment.
We analyse the effect of multiple paternity on genetic diversity using a model
in which the highly promiscuous marine snail Littorina saxatilis expands from a
mainland to colonise initially empty islands of an archipelago. Migrant females
carry a large number of eggs fertilised by 1 - 10 mates. We quantify the
genetic diversity of the population in terms of its heterozygosity: initially
during the transient colonisation process, and at long times when the
population has reached an equilibrium state with migration. During
colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in
comparison with the case of single paternity. The equilibrium state, by
contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 %
higher heterozygosity compared with single paternity. Further we find that far
from the mainland, new mutations spreading from the mainland cause bursts of
high genetic diversity separated by long periods of low diversity. This effect
is boosted by multiple paternity. We conclude that multiple paternity
facilitates colonisation and maintenance of small populations, whether or not
this is the main cause for the evolution of extreme promiscuity in Littorina
saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia
Editorial: Further rare earth elements environmental dissemination: Observation, analysis, and impacts
The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra
We present novel evidence for a fine structure observed in the net-circular
polarization (NCP) of a sunspot penumbra based on spectropolarimetric
measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first
time we detect a filamentary organized fine structure of the NCP on spatial
scales that are similar to the inhomogeneities found in the penumbral flow
field. We also observe an additional property of the visible NCP, a
zero-crossing of the NCP in the outer parts of the center-side penumbra, which
has not been recognized before. In order to interprete the observations we
solve the radiative transfer equations for polarized light in a model penumbra
with embedded magnetic flux tubes. We demonstrate that the observed
zero-crossing of the NCP can be explained by an increased magnetic field
strength inside magnetic flux tubes in the outer penumbra combined with a
decreased magnetic field strength in the background field. Our results strongly
support the concept of the uncombed penumbra
Pareto-optimal alloys
Large databases that can be used in the search for new materials with
specific properties remain an elusive goal in materials science. The search
problem is complicated by the fact that the optimal material for a given
application is usually a compromise between a number of materials properties
and the price. In this letter we present a database consisting of the lattice
parameters, bulk moduli, and heats of formation for over 64,000 ordered
metallic alloys, which has been established by direct first-principles
density-functional-theory calculations. Furthermore, we use a concept from
economic theory, the Pareto-optimal set, to determine optimal alloy solutions
for the compromise between low compressibility, high stability and price.Comment: 5 pages, 2 figures, To be published in Appl. Phys. Let
Hidden Kondo Effect in a Correlated Electron Chain
We develop a general Bethe Ansatz formalism for diagonalizing an integrable
model of a magnetic impurity of arbitrary spin coupled ferro- or
antiferromagnetically to a chain of interacting electrons. The method is
applied to an open chain, with the exact solution revealing a ``hidden'' Kondo
effect driven by forward electron scattering off the impurity. We argue that
the so-called ``operator reflection matrices'' proposed in recent Bethe Ansatz
studies of related models emulate only forward electron-impurity scattering
which may explain the absence of complete Kondo screening for certain values of
the impurity-electron coupling in these models.Comment: 5 pages, RevTex; to appear in Phys. Rev. Let
Reciprocal transplants support a plasticity-first scenario during colonisation of a large hyposaline basin by a marine macro alga
Boundary Effects on Spectral Properties of Interacting Electrons in One Dimension
The single electron Green's function of the one-dimensional
Tomonaga-Luttinger model in the presence of open boundaries is calculated with
bosonization methods. We show that the critical exponents of the local spectral
density and of the momentum distribution change in the presence of a boundary.
The well understood universal bulk behavior always crosses over to a boundary
dominated regime for small energies or small momenta. We show this crossover
explicitly for the large-U Hubbard model in the low-temperature limit.
Consequences for photoemission experiments are discussed.Comment: revised and reformatted paper to appear in Phys. Rev. Lett. (Feb.
1996). 5 pages (revtex) and 3 embedded figures (macro included). A complete
postscript file is available from http://FY.CHALMERS.SE/~eggert/luttinger.ps
or by request from [email protected]
An extended massless phase and the Haldane phase in a spin-1 isotropic antiferromagnetic chain
We study the phase transition of isotropic spin-1 models in the vicinity of
the Uimin-Lai-Sutherland model by using the SU(3)_1 WZW model with certain
marginal perturbations. The unstable RG trajectory by a marginally relevant
perturbation generates a mass gap for the Haldane phase, and thus the
universality class of the transition from the massless phase to the Haldane
phase at ULS point becomes the BKT type. Our results support recent numerical
studies by F\'ath and S\'olyom. In the massless phase, we calculate logarithmic
finite-size corrections of the energy for the SU(\nu)-symmetric and asymmetric
models.Comment: 19 pages, RevTe
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