259 research outputs found
Existence and uniqueness of the integrated density of states for Schr\"odinger operators with magnetic fields and unbounded random potentials
The object of the present study is the integrated density of states of a
quantum particle in multi-dimensional Euclidean space which is characterized by
a Schr\"odinger operator with a constant magnetic field and a random potential
which may be unbounded from above and from below. For an ergodic random
potential satisfying a simple moment condition, we give a detailed proof that
the infinite-volume limits of spatial eigenvalue concentrations of
finite-volume operators with different boundary conditions exist almost surely.
Since all these limits are shown to coincide with the expectation of the trace
of the spatially localized spectral family of the infinite-volume operator, the
integrated density of states is almost surely non-random and independent of the
chosen boundary condition. Our proof of the independence of the boundary
condition builds on and generalizes certain results by S. Doi, A. Iwatsuka and
T. Mine [Math. Z. {\bf 237} (2001) 335-371] and S. Nakamura [J. Funct. Anal.
{\bf 173} (2001) 136-152].Comment: This paper is a revised version of the first part of the first
version of math-ph/0010013. For a revised version of the second part, see
math-ph/0105046. To appear in Reviews in Mathematical Physic
Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach
Vivianite, Fe3(PO4)2 · 8 H2O, is a ferrous iron
phosphate mineral which forms in waterlogged soils and
sediments. The phosphorus (P) bound in its crystal lattice is
considered to be immobilised because vivianite is stable under
anoxic, reducing, sedimentary conditions. Thus, vivianite formation
can make a major contribution to P retention during early
diagenesis. Much remains unknown about vivianite in sediments,
because technical challenges have rendered direct identification and
quantification difficult. To identify vivianite and assess its
significance for P burial during early diagenesis we studied the
consequences of a 1992/1993 in-lake application of FeCl3 and
Fe(OH)3 aimed at restoring Lake Groß-Glienicke (Berlin,
Germany). In a novel approach, we firstly applied a heavy-liquid
separation to the iron-rich surface sediments which allowed direct
identification of vivianite by X-ray diffraction in the high-density
(ρ > 2.3 g cm−3) sediment fraction. Secondly, we
assessed the contribution of vivianite to P retention, combining
results from chemical digestion with magnetic susceptibility data
derived from magnetic hysteresis measurements. Scanning electron
microscopy revealed that the dark blue spherical vivianite nodules
were 40–180 μm in diameter, and formed of platy- and
needle-shaped crystal aggregates. Although equilibrium calculations
indicated supersaturation of vivianite throughout the upper
30 cm of the sediment, the vivianite deposits were
homogeneously distributed within, and restricted to, the upper
23 cm only. Thus, supersaturated pore water alone cannot
serve as a reliable predictor for the in situ formation of
vivianite. In Lake Groß -Glienicke, vivianite formation continues
to be triggered by the artificial iron amendment more than
20 yr ago, significantly contributing to P retention in
surface sediments
Lifshitz Tails in Constant Magnetic Fields
We consider the 2D Landau Hamiltonian perturbed by a random alloy-type
potential, and investigate the Lifshitz tails, i.e. the asymptotic behavior of
the corresponding integrated density of states (IDS) near the edges in the
spectrum of . If a given edge coincides with a Landau level, we obtain
different asymptotic formulae for power-like, exponential sub-Gaussian, and
super-Gaussian decay of the one-site potential. If the edge is away from the
Landau levels, we impose a rational-flux assumption on the magnetic field,
consider compactly supported one-site potentials, and formulate a theorem which
is analogous to a result obtained in the case of a vanishing magnetic field
Non-inversion conservation tillage as an underestimated driver of tillage erosion
Tillage erosion is a widely underestimated process initiating soil degradation especially in case of large agricultural fields located in rolling topography. It is often assumed that, conservation, non-inversion tillage causes less tillage erosion than conventional inversion tillage. In this study, tillage erosion was determined on three paired plots comparing non-inversion chisel versus inversion mouldboard tillage. The experiments were performed at three sites in Northeast Germany with gentle, moderate, and steep slope, while tillage depth (0.25 m) and speed (≈ 6 km h−1) were kept constant during all experiments. The results indicate that non-inversion tillage produces significantly more soil movement compared to inversion tillage. The soil translocation distance was by a factor of 1.3–2.1 larger in case of chisel tillage. The largest difference in translocation distance and tillage transport coefficient (ktil) was found on the gentle slope exhibiting the lowest soil cohesion. Our results together with an evaluation of ktil values derived from literature and standardised for 0.25 m tillage depth contradict the general assumption that non-inversion tillage reduces tillage erosion. In tillage erosion dominated areas, non-inversion tillage applied with high tillage speed and depth potentially increases tillage erosion and fails its purpose to serve as soil conservation measure
-approximation of the integrated density of states for Schr\"odinger operators with finite local complexity
We study spectral properties of Schr\"odinger operators on \RR^d. The
electromagnetic potential is assumed to be determined locally by a colouring of
the lattice points in \ZZ^d, with the property that frequencies of finite
patterns are well defined. We prove that the integrated density of states
(spectral distribution function) is approximated by its finite volume
analogues, i.e.the normalised eigenvalue counting functions. The convergence
holds in the space where is any finite energy interval and is arbitrary.Comment: 15 pages; v2 has minor fixe
Hijacking the mustard-oil bomb: How a glucosinolate-sequestering flea beetle copes with plant myrosinases
Myrosinase enzymes play a key role in the chemical defense of plants of the order Brassicales. Upon herbivory, myrosinases hydrolyze the β-S-linked glucose moiety of glucosinolates, the characteristic secondary metabolites of brassicaceous plants, which leads to the formation of different toxic hydrolysis products. The specialist flea beetle, Phyllotreta armoraciae, is capable of accumulating high levels of glucosinolates in the body and can thus at least partially avoid plant myrosinase activity. In feeding experiments with the myrosinase-deficient Arabidopsis thaliana tgg1 × tgg2 (tgg) mutant and the corresponding Arabidopsis Col-0 wild type, we investigated the influence of plant myrosinase activity on the metabolic fate of ingested glucosinolates in adult P. armoraciae beetles. Arabidopsis myrosinases hydrolyzed a fraction of ingested glucosinolates and thereby reduced the glucosinolate sequestration rate by up to 50% in adult beetles. These results show that P. armoraciae cannot fully prevent glucosinolate hydrolysis; however, the exposure of adult beetles to glucosinolate hydrolysis products had no impact on the beetle’s energy budget under our experimental conditions. To understand how P. armoraciae can partially prevent glucosinolate hydrolysis, we analyzed the short-term fate of ingested glucosinolates and found them to be rapidly absorbed from the gut. In addition, we determined the fate of ingested Arabidopsis myrosinase enzymes in P. armoraciae. Although we detected Arabidopsis myrosinase protein in the feces, we found only traces of myrosinase activity, suggesting that P. armoraciae can inactivate plant myrosinases in the gut. Based on our findings, we propose that the ability to tolerate plant myrosinase activity and a fast glucosinolate uptake mechanism represent key adaptations of P. armoraciae to their brassicaceous host plants
Upper bounds on the density of states of single Landau levels broadened by Gaussian random potentials
We study a non-relativistic charged particle on the Euclidean plane R^2
subject to a perpendicular constant magnetic field and an R^2-homogeneous
random potential in the approximation that the corresponding random Landau
Hamiltonian on the Hilbert space L^2(R^2) is restricted to the eigenspace of a
single but arbitrary Landau level. For a wide class of Gaussian random
potentials we rigorously prove that the associated restricted integrated
density of states is absolutely continuous with respect to the Lebesgue
measure. We construct explicit upper bounds on the resulting derivative, the
restricted density of states. As a consequence, any given energy is seen to be
almost surely not an eigenvalue of the restricted random Landau Hamiltonian.Comment: 16 pages, to appear in "Journal of Mathematical Physics
Detection of triplex PCR for the modified qualitative soybean and maize genetically
A molecular screening method based on multiplex PCR that involves amplification of specific soybean or maize sequences from plant DNA (lectin or zein) and the amplification of 35S promoter and NOS terminator,for the detection of genetically modified soybean and maize was developed. The new method is proposed,for the simulicmeous cletcctimt of tree genetic elements in the.same run as reliable method for rapid detection of genetically, modified plants with sensitivity of 0.1%
Structure and activity of lacustrine sediment bacteria involved in nutrient and iron cycles
Knowledge about the bacterial community structure in sediments is essential to better design restoration strategies for eutrophied lakes. In that regard, the aim of this study was to quantify the abundance and activity of bacteria involved in nutrient and iron cycling in sediments from four Azorean lakes with distinct trophic states (Verde, Azul, Furnas and Fogo). Inferred from quantitative PCR, bacteria performing anaerobic ammonia oxidation, were the most abundant in the eutrophic lakes Verde, Azul and Furnas (4.5 % to 16.6 %), followed by nitrifying bacteria (0.8 % to 13.0 %), denitrifying bacteria (0.5 % to 6.8 %), iron-reducing bacteria (0.2 % to 1.4 %), and phosphorus-accumulating organisms (<0.3 %). In contrast, denitrifying bacteria dominated sediments from the oligo-mesotrophic lake Fogo (8.8 %). Activity assays suggested that bacteria performing ammonia oxidation (aerobic and anaerobic), nitrite oxidation, heterothrophic nitrate reduction, iron reduction and biological phosphorus storage/release were present and active in all Azorean lake sediments. The present work also suggested that the activity of denitrifying bacteria might contribute to the release of phosphorus from sediments.The authors are indebted and grateful to the Regional Department of Water Resources and Land Planning (Azores) for the grant (Contrato Excepcionado no. 4/2008/ DROTRH) and its staff (Dina Pacheco), and to Virgilio Cruz and Paulo Antunes (Geosciences Department, University of Azores) for the useful help in sediments' collection, to the technical staff of the Department of Environmental Engineering - DTU for chemical analysis, to Laurent Philippot (INRA - University of Burgundy) for positive controls for DNB, to Richard Glaven and Derek Lovley (Department of Microbiology, University of Massachusetts) for Geobacter strains, to Paul Bodelier, Marzia Milleto and Marion Meima (Netherlands Institute of Ecology, NIOO-KNAW) for SRB clones and to Yunhong Kong and Per Halkjaer Nielsen (Department of Life Sciences, Section of Environmental Engineering, Aalborg University) for PAO clones. The authors also acknowledge the Grant SFRH/BD/25639/2005 from the Foundation for Science and Technology/M.C.T.(Portugal) awarded to G. M. and a Marie Curie Excellence Award (EC FP6) to B.F.S
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