Nonperturbative analysis of coupled quantum dots in a phonon bath

Transport through coupled quantum dots in a phonon bath is studied using the recently developed real-time renormalization-group method. Thereby, the problem can be treated beyond perturbation theory regarding the complete interaction. A reliable solution for the stationary tunnel current is obtained for the case of moderately strong couplings of the dots to the leads and to the phonon bath. Any other parameter is arbitrary, and the complete electron-phonon interaction is taken into account. Experimental results are quantitatively reproduced by taking into account a finite extension of the wavefunctions within the dots. Its dependence on the energy difference between the dots is derived.Comment: 8 pages, 6 figure

Effects of saline irrigation on growth, physiology and quality of Mesembryanthemum crystallinum L., a rare vegetable crop.

World wide increased desertification due to recent global changes enhances the need of irrigation, which, in turn, provokes the risk of soil salinization. Furthermore, limited fresh water resources may increasingly constrain the use of low quality irrigation water. Hence, intensified use of halotolerant crop plants will be necessary, even in Europe.Commercial use of halophytes as fresh food is limited. Several facultative halophytic members of Aizoaceae are nowadays used as special crop plants. A rare leafy vegetable species is the common ice plant Mesembryanthemum crystallinum, a Crassulacean acid metabolism (CAM) species, which is mostly cultivated in India, California, Australia, and New Zealand. It is also known in Europe as a quickly cooked tender vegetable. With their succulent, mellow, slightly salty tasting leaves and young shoots, M. crystallinum is getting interesting as delicious cool flavored salad greens during recent years. However, it is a perishable product and thus, shelf live is short. On the other hand, CAM capacity of M. crystallinum can be largely enhanced by saline irrigation. Increased CAM potentially reduces water and carbon losses.In this project we studied whether moderate salt treatment affects physiology, growth and yield of this rare crop plant. Furthermore, we investigated whether such treatment that enhances the irreversible C3 to CAM shift in young leaves of this CAM species, potentially prolongs shelf live. Results showed that moderate salt treatment did not negatively influence growth, yield and sensory quality. When in CAM, leaves showed reduced transpiration water losses and CAM also reduced carbon losses during storage

Effect of Muons on the Phase Transition in Magnetised Proto-Neutron Star Matter

We study the effect of inclusion of muons and the muon neutrinos on the phase transition from nuclear to quark matter in a magnetised proto-neutron star and compare our results with those obtained by us without the muons. We find that the inclusion of muons changes slightly the nuclear density at which transition occurs.However the dependence of this transition density on various chemical potentials, temperature and the magnetic field remains quantitatively the same.Comment: LaTex2e file with four postscript figure

Evolution of Proto-Neutron stars with kaon condensates

We present simulations of the evolution of a proto-neutron star in which kaon-condensed matter might exist, including the effects of finite temperature and trapped neutrinos. The phase transition from pure nucleonic matter to the kaon condensate phase is described using Gibbs' rules for phase equilibrium, which permit the existence of a mixed phase. A general property of neutron stars containing kaon condensates, as well as other forms of strangeness, is that the maximum mass for cold, neutrino-free matter can be less than the maximum mass for matter containing trapped neutrinos or which has a finite entropy. A proto-neutron star formed with a baryon mass exceeding that of the maximum mass of cold, neutrino-free matter is therefore metastable, that is, it will collapse to a black hole at some time during the Kelvin-Helmholtz cooling stage. The effects of kaon condensation on metastable stars are dramatic. In these cases, the neutrino signal from a hypothetical galactic supernova (distance $\sim8.5$ kpc) will stop suddenly, generally at a level above the background in the SuperK and SNO detectors, which have low energy thresholds and backgrounds. This is in contrast to the case of a stable star, for which the signal exponentially decays, eventually disappearing into the background. We find the lifetimes of kaon-condensed metastable stars to be restricted to the range 40--70 s and weakly dependent on the proto-neutron star mass, in sharp contrast to the significantly larger mass dependence and range (1--100 s) of hyperon-rich metastable stars.Comment: 25 pages, 14 figures. Submitted to Astrophysical Journa

Prognosegesteuerte Bekämpfungsstrategien im Ökologischen Kartoffelanbau- mögliche Kupfereinsparungspotentiale und Vergleich der Bekämpfungserfolge

Im Rahmen des Forschungsprojektes ÖKOSIMPHYT liegen mittlerweile dreijährige Versuchsergebnisse zur Bekämpfung der Kraut- und Knollenfäule (Phytophthora infestans) im Ökologischen Kartoffelanbau vor, in denen die Anwendung des neuen Prognosesystems ÖKOSIMPHYT im Freiland getestet wurde. Ziel des Projektes ist, durch eine zielgerichtete Applikation den Kupfereinsatz sowohl aus Bekämpfung- als auch aus ökologischer Sicht zu optimieren

Möglichkeiten zur Optimierung der Kupferwirkung gegen Krautfäule im Ökologischen Kartoffelanbau

Die Regulierung der Kraut- und Knollenfäule, verursacht durch Phytophthora infestans, stellt im ökologischen Landbau nach wie vor ein nur schwer zu lösendes Problem dar. Bislang ist eine befriedigende Befallsreduktion nur durch den Einsatz kupferhaltiger Pflanzenschutzmittel möglich, deren Einsatz durch die Anbauverbände, sofern überhaupt gestattet, auf 3kg pro Jahr begrenzt ist. Im Rahmen des Projekts „ÖKO-SIMPHYT“ wurden daher verschiedene Kupferapplikationsverfahren zur Bekämpfung der Phytophthora infestans-Sekundärinfektionen untersucht, um die zur Verfügung stehenden Kupfermengen optimal einzusetzen

A Fresh Look at Axions and SN 1987A

We re-examine the very stringent limits on the axion mass based on the strength and duration of the neutrino signal from SN 1987A, in the light of new measurements of the axial-vector coupling strength of nucleons, possible suppression of axion emission due to many-body effects, and additional emission processes involving pions. The suppression of axion emission due to nucleon spin fluctuations induced by many-body effects degrades previous limits by a factor of about 2. Emission processes involving thermal pions can strengthen the limits by a factor of 3-4 within a perturbative treatment that neglects saturation of nucleon spin fluctuations. Inclusion of saturation effects, however, tends to make the limits less dependent on pion abundances. The resulting axion mass limit also depends on the precise couplings of the axion and ranges from 0.5x10**(-3) eV to 6x10**(-3) eV.Comment: 32 latex pages, 13 postscript figures included, uses revtex.sty, submitted to Physical Review

NP-hardness of the cluster minimization problem revisited

The computational complexity of the "cluster minimization problem" is revisited [L. T. Wille and J. Vennik, J. Phys. A 18, L419 (1985)]. It is argued that the original NP-hardness proof does not apply to pairwise potentials of physical interest, such as those that depend on the geometric distance between the particles. A geometric analog of the original problem is formulated, and a new proof for such potentials is provided by polynomial time transformation from the independent set problem for unit disk graphs. Limitations of this formulation are pointed out, and new subproblems that bear more direct consequences to the numerical study of clusters are suggested.Comment: 8 pages, 2 figures, accepted to J. Phys. A: Math. and Ge