Regulierung der Krautfäule(Phytophthora infestans) mit reduzierten Kupfer-Aufwandmengen im Kartoffelanbau

Four field experiments were conducted in 2004 to analyse the efficacy of reduced rates of copper fungicides against Phytophthora infestans (3 x organic and 1 x conventional growing). Copper (Cu-hydroxide, Cu-oxychloride or Cu-octanoate) was sprayed in a weekly routine or according to the decision support system SIMPHYT with total dosages ranging from 0.57 kg/ha to 4.0 kg/ha. The results revealed in almost all treatments a significant reduction of late blight, except for the lowest rates (e.g. 4 x 0.14 kg/ha Cu as Cu-octanoate or 6 x 0.15 kg/ha Cu as Cu-hydroxide). There was a clear dose-response relation between increasing rates of copper and control of late blight in each experiment. Marketable yields varied from 132 dt/ha to 238 dt/ha in organic field trials depending on trial site and copper treatment. Generally, an effect of copper treatment and late blight on yield could be shown. Even a slight reduction of P. infestans increased yield by 10 % to 20 %. The influence of copper dosage on late blight was more obvious than influence of copper spraying on yield. A dropleg spraying system (copper application within the crop canopy) which was tested on one trial site did not improve blight control compared to conventional application

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO$_2$ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross section for cold elastic Li-Cs collisions.Comment: 10 pages 9 figures, submitted to Appl. Phys. B; v2: Corrected evaporation formulas and some postscript problem

Kupferminimierungsstrategien im ökologischen Kartoffelanbau – Projekt “ÖKO-SIMPHYT“: Erste Erfahrungen aus dem norddeutschen Freiland

In the research project „ÖKO-SIMPHYT“ different strategies are tested to reduce the copper application for Phytophthora infestans in organic potato cultivation. Within the first two years of our research a reduction of the total amount of copper per hectare could be accomplished when applying the new developed forecast system ÖKO-SIMPHYT. With this decision support system a reduction of copper up to 46% was possible, when the infection pressure was relatively low. These first results have now to be proven under high infection pressure conditions. Experiments were carried out in the greenhouse to test the rain stability of copper and contacting agents. It could be proved that precipitation of 30 mm is able to reduce the degree of a copper treatment by up to 25%

Phytophthora-Sekundärbefall - Kupferminimierungsstrategien im ökologischen Kartoffelanbau

Auf Grund der negativen Auswirkungen von Kupfer auf Nicht-Ziel-Organismen, wie z.B. aquatische Organismen und Regenwürmern sowie der Anreicherungsproblematik im Boden, ist eine weitere Reduzierung des Kupfereinsatzes dringend erforderlich. Deshalb werden im Rahmen des Forschungsprojekts „ÖKO-SIMPHYT“ Kupferminimierungsstrategien für den ökologischen Kartoffelanbau zur Kontrolle des Sekundärbefalls von Phytophthora infestans entwickelt

Current-Carrying Ground States in Mesoscopic and Macroscopic Systems

We extend a theorem of Bloch, which concerns the net orbital current carried by an interacting electron system in equilibrium, to include mesoscopic effects. We obtain a rigorous upper bound to the allowed ground-state current in a ring or disc, for an interacting electron system in the presence of static but otherwise arbitrary electric and magnetic fields. We also investigate the effects of spin-orbit and current-current interactions on the upper bound. Current-current interactions, caused by the magnetic field produced at a point r by a moving electron at r, are found to reduce the upper bound by an amount that is determined by the self-inductance of the system. A solvable model of an electron system that includes current-current interactions is shown to realize our upper bound, and the upper bound is compared with measurements of the persistent current in a single ring.Comment: 7 pager, Revtex, 1 figure available from [email protected]

Thermal expansion, heat capacity and magnetostriction of RAl3_3 (R = Tm, Yb, Lu) single crystals

We present thermal expansion and longitudinal magnetostriction data for cubic RAl3 (R = Tm, Yb, Lu) single crystals. The thermal expansion coefficient for YbAl3 is consistent with an intermediate valence of the Yb ion, whereas the data for TmAl3 show crystal electric field contributions and have strong magnetic field dependencies. de Haas-van Alphen-like oscillations were observed in the magnetostriction data of YbAl3 and LuAl3, several new extreme orbits were measured and their effective masses were estimated. Zero and 140 kOe specific heat data taken on both LuAl3 and TmAl3 for T < 200 K allow for the determination of a CEF splitting scheme for TmAl3

Possibility of long-range order in clean mesoscopic cylinders

A microscopic Hamiltonian of the magnetostatic interaction is discussed. This long-range interaction can play an important role in mesoscopic systems leading to an ordered ground state. The self-consistent mean field approximation of the magnetostatic interaction is performed to give an effective Hamiltonian from which the spontaneous, self-sustaining currents can be obtained. To go beyond the mean field approximation the mean square fluctuation of the total momentum is calculated and its influence on self-sustaining currents in mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then, by the use of the microscopic Hamiltonian of the magnetostatic interaction for a set of stacked rings, the problem of long-range order is discussed. The temperature $T^{*}$ below which the system is in an ordered state is determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.

Electron Dephasing in Mesoscopic Metal Wires

The low-temperature behavior of the electron phase coherence time, $\tau_{\phi}$, in mesoscopic metal wires has been a subject of controversy recently. Whereas theory predicts that $\tau_{\phi}(T)$ in narrow wires should increase as $T^{-2/3}$ as the temperature $T$ is lowered, many samples exhibit a saturation of $\tau_{\phi}$ below about 1 K. We review here the experiments we have performed recently to address this issue. In particular we emphasize that in sufficiently pure Ag and Au samples we observe no saturation of $\tau_{\phi}$ down to our base temperature of 40 mK. In addition, the measured magnitude of $\tau_{\phi}$ is in excellent quantitative agreement with the prediction of the perturbative theory of Altshuler, Aronov and Khmelnitskii. We discuss possible explanations why saturation of $\tau_{\phi}$ is observed in many other samples measured in our laboratory and elsewhere, and answer the criticisms raised recently by Mohanty and Webb regarding our work.Comment: 14 pages, 3 figures; to appear in proceedings of conference "Fundamental Problems of Mesoscopic Physics", Granada, Spain, 6-11 September, 200