The significance of sedimentation and sediments to phytoplankton growth in drinking-water reservoirs

In the mesotrophic-eutrophic Saidenbach Reservoir in Saxony, the nanoplankton and cyanobacteria have increased at the expense of diatom dominance, due to a doubling of the external phosphorus load in the last 15 years. However, the phosphorus sedimentation flux is still very high (up to 80% of the input), corresponding to more than 2 g m2 d-1 in terms of dry weight. There is a strong correlation between the abundance of diatoms in the euphotic zone and their sedimentation flux (with a delay of about 2 weeks). Only about 25% of the deposited material could be clearly attributed to plankton biomass; the remainder resulted from flocculation and precipitation processes or directly from the inflow of clay minerals. The ash content of the deposited material was high (73%). Thus the sedimentation flux can be considered to operate as an internal water-treatment/oligotrophication process within the lake. The neighbouring Neunzehnhain Reservoir still has a very clear water with a transparency up to 18 m depth. Though the sediment was not much lower than Saidenbach sediment in total phosphorus and total numbers of bacteria, sulphide was always absent and the ratio of Fe 2+ to Fe 3+ was very low in the upper (0- 5 cm) layer. Thus the external and internal phosphorus loads do not attain the critical level necessary to induce a ”phosphorus - phytoplankton” feedback loop

Which preferences associate with school performance? Lessons from an exploratory study with university students

<div><p>Success in life is determined to a large extent by school performance so it is important to understand the effect of the factors that influence it. In this exploratory study, in addition to cognitive abilities, we attempt to link measures of preferences with outcomes of school performance. We measured in an incentivized way risk, time, social and competitive preferences and cognitive abilities of university students to look for associations between these measures and two important academic outcome measures: exam results and GPA. We find consistently that cognitive abilities (proxied by the Cognitive Reflection Test) are very well correlated with school performance. Regarding non-cognitive skills, we report suggestive evidence for many of our measured preferences. We used two alternative measures of time preference: patience and present bias. Present bias explains exam grades better, while patience explains GPA relatively better. Both measures of time preferences have a non-linear relation to school performance. Competitiveness matters, as students, who opt for a more competitive payment scheme in our experimental task have a higher average GPA. We observe also that risk-averse students perform a little better than more risk-tolerant students. That makes sense in case of multiple choice exams, because more risk-tolerant students may want to try to pass the exam less prepared, as the possibility of passing an exam just by chance is not zero. Finally, we have also detected that cooperative preferences—the amount of money offered in a public good game—associates strongly with GPA in a non-linear way. Students who offered around half of their possible amounts had significantly higher GPAs than those, who offered none or all their money.</p></div

Using a neural network approach for muon reconstruction and triggering

The extremely high rate of events that will be produced in the future Large Hadron Collider requires the triggering mechanism to take precise decisions in a few nano-seconds. We present a study which used an artificial neural network triggering algorithm and compared it to the performance of a dedicated electronic muon triggering system. Relatively simple architecture was used to solve a complicated inverse problem. A comparison with a realistic example of the ATLAS first level trigger simulation was in favour of the neural network. A similar architecture trained after the simulation of the electronics first trigger stage showed a further background rejection.Comment: A talk given at ACAT03, KEK, Japan, November 2003. Submitted to Nuclear Instruments and Methods in Physics Research, Section

Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs

We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configuration-interaction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d5 configuration that maximizes the local Mn moment. Nanoscaling and strain significantly alter the properties of MnAs. Internal strain in the nanocrystals results in reduced p-d hybridization and enhanced ionic character of the Mn-As bonding interactions. The spatial confinement and reduced p-d hybridization in the nanocrystals lead to enhanced d-electron localization, triggering d-d electron correlations and enhancing local Mn moments. These changes in the electronic structure of MnAs have an advantageous effect on the Curie temperature of the nanocrystals, which is measured to be remarkably higher than that of bulk MnAs.Comment: 4 figures, 2 table

CORE Technology and Exact Hamiltonian Real-Space Renormalization Group Transformations

The COntractor REnormalization group (CORE) method, a new approach to solving Hamiltonian lattice systems, is presented. The method defines a systematic and nonperturbative means of implementing Kadanoff-Wilson real-space renormalization group transformations using cluster expansion and contraction techniques. We illustrate the approach and demonstrate its effectiveness using scalar field theory, the Heisenberg antiferromagnetic chain, and the anisotropic Ising chain. Future applications to the Hubbard and t-J models and lattice gauge theory are discussed.Comment: 65 pages, 9 Postscript figures, uses epsf.st

The χ2\chi^2 - divergence and Mixing times of quantum Markov processes

We introduce quantum versions of the $\chi^2$-divergence, provide a detailed analysis of their properties, and apply them in the investigation of mixing times of quantum Markov processes. An approach similar to the one presented in [1-3] for classical Markov chains is taken to bound the trace-distance from the steady state of a quantum processes. A strict spectral bound to the convergence rate can be given for time-discrete as well as for time-continuous quantum Markov processes. Furthermore the contractive behavior of the $\chi^2$-divergence under the action of a completely positive map is investigated and contrasted to the contraction of the trace norm. In this context we analyse different versions of quantum detailed balance and, finally, give a geometric conductance bound to the convergence rate for unital quantum Markov processes

A General Framework for Recursive Decompositions of Unitary Quantum Evolutions

Decompositions of the unitary group U(n) are useful tools in quantum information theory as they allow one to decompose unitary evolutions into local evolutions and evolutions causing entanglement. Several recursive decompositions have been proposed in the literature to express unitary operators as products of simple operators with properties relevant in entanglement dynamics. In this paper, using the concept of grading of a Lie algebra, we cast these decompositions in a unifying scheme and show how new recursive decompositions can be obtained. In particular, we propose a new recursive decomposition of the unitary operator on $N$ qubits, and we give a numerical example.Comment: 17 pages. To appear in J. Phys. A: Math. Theor. This article replaces our earlier preprint "A Recursive Decomposition of Unitary Operators on N Qubits." The current version provides a general method to generate recursive decompositions of unitary evolutions. Several decompositions obtained before are shown to be as a special case of this general procedur

Vacuum State of Lattice Gauge Theory with Fermions in 2+1 Dimensions

We investigate the vacuum state of the lattice gauge theory with fermions in 2+1 dimensions. The vacuum in the Hermite form for the fermion part is obtained; the vacuum in the unitary form has been proposed by Luo and Chen. It is shown that the Hermite vacuum has a lower energy than the unitary one through the variational method.Comment: 16 pages, 5 embedded PS figures, LaTeX with special styl