Improvements of the Variable Thermal Resistance

A flat mounting unit with electronically variable thermal resistance [1] has been presented in the last year [2]. The design was based on a Peltier cell and the appropriate control electronics and software. The device is devoted especially to the thermal characterization of packages, e.g. in dual cold plate arrangements. Although this design meets the requirements of the static measurement we are intended to improve its parameters as the settling time and dynamic thermal impedance and the range of realized thermal resistance. The new design applies the heat flux sensor developed by our team as well [3], making easier the control of the device. This development allows even the realization of negative thermal resistances.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Investigations on alternative substances for control of apple scab - Results from Conidia germinating tests and experiments with plant extracts

The intention of this research project, which was supported within the "Bundesprogramm Ökologischer Landbau", was to find alternatives for the control of Venturia inaequalis for the organic fruitgrower. Beside the investigations on reducing the ascospore potential on fallen leaves, experiments were conducted in laboratory, greenhouses and in orchard to test direct control of scab with different plant extracts, concentrations and methods of extraction. Extracts from Inula viscosa, Quillaja saponaria-bark, citrus-species (AGROMIL) and Saponaria officinalis revealed a distinct efficacy against apple scab in greenhouse studies on apple seedlings. ELOT-VIS, CHITOPLANT, COMCAT, MOOSEXTRAKT, SILIOPLANT und FZB 24 did not show sufficient efficacy with the application schedule used for control of scab. Mixtures of Quillaja-saponine and sulphur reduced effectively apple scab incidence. In an experiment concerning rain stability Citrus-extract and Quillaja-saponine showed a lower efficacy against scab after a simulated rain of 5 mm. The screening of different supplements to Citrus-extract as surfactants and adhesives revealed GREEMAX and BIOPLUSS as promising additives. Both combinations showed an efficacy comparable to copperoxychloride corresponding to 400 g elementary copper per ha

Investigations on alternative substances for control of apple scab - results from sanitation trials

The intention of this research project, which was supported within the "Bundesprogramm Ökologischer Landbau", was to look for alternatives in organic fruit growing to control apple scab, Venturia inaequalis. One important part of the investigations was the application of different substances like microbiological nutrient media, enzymes usually used for production of fruit juices and organic fertilizers on their effect on the ascospore potential on depots of fallen leaves. Some substances like TRYPTIC SOY BROTH increased the decomposition of the leaves significantly, other like BACTOFIL B and HUMOFIX showed nearly no effect on the decomposition, but reduced the ascospore potential in early spring by 80 % compared to the untreated control

The moduli space of hypersurfaces whose singular locus has high dimension

Let $k$ be an algebraically closed field and let $b$ and $n$ be integers with $n\geq 3$ and $1\leq b \leq n-1.$ Consider the moduli space $X$ of hypersurfaces in $\mathbb{P}^n_k$ of fixed degree $l$ whose singular locus is at least $b$-dimensional. We prove that for large $l$, $X$ has a unique irreducible component of maximal dimension, consisting of the hypersurfaces singular along a linear $b$-dimensional subspace of $\mathbb{P}^n$. The proof will involve a probabilistic counting argument over finite fields.Comment: Final version, including the incorporation of all comments by the refere

Tunneling gap of laterally separated quantum Hall states

We use a method of matched asymptotics to determine the energy gap of two counter-propagating, strongly interacting, quantum Hall edge states. The microscopic edge state dispersion and Coulomb interactions are used to precisely constrain the short-distance behavior of an integrable field theory, which then determines the low energy spectrum. We discuss the relationship of our results to the tunneling measurements of Kang et al., Nature 403, 59 (2000).Comment: 4 pages, 1 figur

Ferromagnetism in the two dimensional t-t' Hubbard model at the Van Hove density

Using an improved version of the projection quantum Monte Carlo technique, we study the square-lattice Hubbard model with nearest-neighbor hopping t and next-nearest-neighbor hopping t', by simulation of lattices with up to 20 X 20 sites. For a given R=2t'/t, we consider that filling which leads to a singular density of states of the noninteracting problem. For repulsive interactions, we find an itinerant ferromagnet (antiferromagnet) for R=0.94 (R=0.2). This is consistent with the prediction of the T-matrix approximation, which sums the most singular set of diagrams.Comment: 10 pages, RevTeX 3.0 + a single postscript file with all figure

New theoretical approaches for correlated systems in nonequilibrium

Abstract.: We review recent developments in the theory of interacting quantum many-particle systems that are not in equilibrium. We focus mainly on the nonequilibrium generalizations of the flow equation approach and of dynamical mean-field theory (DMFT). In the nonequilibrium flow equation approach one first diagonalizes the Hamiltonian iteratively, performs the time evolution in this diagonal basis, and then transforms back to the original basis, thereby avoiding a direct perturbation expansion with errors that grow linearly in time. In nonequilibrium DMFT, on the other hand, the Hubbard model can be mapped onto a time-dependent self-consistent single-site problem. We discuss results from the flow equation approach for nonlinear transport in the Kondo model, and further applications of this method to the relaxation behavior in the ferromagnetic Kondo model and the Hubbard model after an interaction quench. For the interaction quench in the Hubbard model, we have also obtained numerical DMFT results using quantum Monte Carlo simulations. In agreement with the flow equation approach they show that for weak coupling the system relaxes to a "prethermalized” intermediate state instead of rapid thermalization. We discuss the description of nonthermal steady states with generalized Gibbs ensemble

S-COL: A Copernican turn for the development of flexibly reusable collaboration scripts

Collaboration scripts are usually implemented as parts of a particular collaborative-learning platform. Therefore, scripts of demonstrated effectiveness are hardly used with learning platforms at other sites, and replication studies are rare. The approach of a platform-independent description language for scripts that allows for easy implementation of the same script on different platforms has not succeeded yet in making the transfer of scripts feasible. We present an alternative solution that treats the problem as a special case of providing support on top of diverse Web pages: In this case, the challenge is to trigger support based on the recognition of a Web page as belonging to a specific type of functionally equivalent pages such as the search query form or the results page of a search engine. The solution suggested has been implemented by means of a tool called S-COL (Scripting for Collaborative Online Learning) and allows for the sustainable development of scripts and scaffolds that can be used with a broad variety of content and platforms. The tool’s functions are described. In order to demonstrate the feasibility and ease of script reuse with S-COL, we describe the flexible re-implementation of a collaboration script for argumentation in S-COL and its adaptation to different learning platforms. To demonstrate that a collaboration script implemented in S-COL can actually foster learning, an empirical study about the effects of a specific script for collaborative online search on learning activities is presented. The further potentials and the limitations of the S-COL approach are discussed

Exact analytic results for the Gutzwiller wave function with finite magnetization

We present analytic results for ground-state properties of Hubbard-type models in terms of the Gutzwiller variational wave function with non-zero values of the magnetization m. In dimension D=1 approximation-free evaluations are made possible by appropriate canonical transformations and an analysis of Umklapp processes. We calculate the double occupation and the momentum distribution, as well as its discontinuity at the Fermi surface, for arbitrary values of the interaction parameter g, density n, and magnetization m. These quantities determine the expectation value of the one-dimensional Hubbard Hamiltonian for any symmetric, monotonically increasing dispersion epsilon_k. In particular for nearest-neighbor hopping and densities away from half filling the Gutzwiller wave function is found to predict ferromagnetic behavior for sufficiently large interaction U.Comment: REVTeX 4, 32 pages, 8 figure

Toward a script theory of guidance in computer-supported collaborative learning

This article presents an outline of a script theory of guidance for computer-supported collaborative learning (CSCL). With its four types of components of internal and external scripts (play, scene, role, and scriptlet) and seven principles, this theory addresses the question how CSCL practices are shaped by dynamically re-configured internal collaboration scripts of the participating learners. Furthermore, it explains how internal collaboration scripts develop through participation in CSCL practices. It emphasizes the importance of active application of subject matter knowledge in CSCL practices, and it prioritizes transactive over non-transactive forms of knowledge application in order to facilitate learning. Further, the theory explains how external collaboration scripts modify CSCL practices and how they influence the development of internal collaboration scripts. The principles specify an optimal scaffolding level for external collaboration scripts and allow for the formulation of hypotheses about the fading of external collaboration scripts. Finally, the article points towards conceptual challenges and future research questions