1,140 research outputs found
Langzeituntersuchung der Kohlenstoff- und Stickstoffkreisläufe eines intensiven ökologischen Betriebssystems – am Beispiel des Versuchsgutes Scheyern
Carbon, nitrogen and energy flows are considered as an appropriate basis to characterize farming systems and to evaluate the environmental effects. Using the model REPRO the carbon and nitrogen flows of the experimental farm “Klostergut Scheyern” have been evaluated since 1991 on the basis of complete cultivation data as well as with the help of detailed site and weather data. Thus “Scheyern” is characterised as an intensive organic farming system with a high turnover of C and N
Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures
For the realisation of scalable solid-state quantum-bit systems, spins in
semiconductor quantum dots are promising candidates. A key requirement for
quantum logic operations is a sufficiently long coherence time of the spin
system. Recently, hole spins in III-V-based quantum dots were discussed as
alternatives to electron spins, since the hole spin, in contrast to the
electron spin, is not affected by contact hyperfine interaction with the
nuclear spins. Here, we report a breakthrough in the spin coherence times of
hole ensembles, confined in so called natural quantum dots, in narrow
GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently,
time-resolved Faraday rotation and resonant spin amplification techniques
deliver hole-spin coherence times, which approach in the low magnetic field
limit values above 70 ns. The optical initialisation of the hole spin
polarisation, as well as the interconnected electron and hole spin dynamics in
our samples are well reproduced using a rate equation model.Comment: 16 pages, 6 figure
Wirkungen differenzierter Bodenbearbeitungssysteme im Dauerversuch Scheyern
After a 12-year differing tillage in a 7-phase crop rotation with lay, potatoes, wheat, sunflowers, lay, wheat and rye it was found, that mouldboard-ploughing (P) resulted in less weed. Crop yields were as high as in the treatment with ploughing after lay and chiselling after potatoes and sunflowers (B). Lowest yields were obtained without ploughing but using the chisel (G). Weeds, esp. grasses, resulted in a huge competition for crops esp. after lay. Profit margins were highest in B due to lower expenditures for tillage and lowest in G. Soil organic carbon amounts differed by 1,5 t/ha and earthworm biomass by 0,25 t/ha between P and G after 12 years. It can be summed up for this experiment that G was not sustainable due to weeds and declining yields, and that B resulted in best economic profit, increasing SOM content and seems to be a sustainable compromise
Gate control of low-temperature spin dynamics in two-dimensional hole systems
We have investigated spin and carrier dynamics of resident holes in
high-mobility two-dimensional hole systems in GaAs/AlGaAs
single quantum wells at temperatures down to 400 mK. Time-resolved Faraday and
Kerr rotation, as well as time-resolved photoluminescence spectroscopy are
utilized in our study. We observe long-lived hole spin dynamics that are
strongly temperature dependent, indicating that in-plane localization is
crucial for hole spin coherence. By applying a gate voltage, we are able to
tune the observed hole g factor by more than 50 percent. Calculations of the
hole g tensor as a function of the applied bias show excellent agreement with
our experimental findings.Comment: 8 pages, 7 figure
Performance of HPGe Detectors in High Magnetic Fields
A new generation of high-resolution hypernuclear gamma$-spectroscopy
experiments with high-purity germanium detectors (HPGe) are presently designed
at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA,
the antiproton proton hadron spectrometer at the future FAIR facility. Both,
the FINUDA and PANDA spectrometers are built around the target region covering
a large solid angle. To maximise the detection efficiency the HPGe detectors
have to be located near the target, and therefore they have to be operated in
strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an
environment has not been well investigated so far. In the present work VEGA and
EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN
magnet at GSI. No significant degradation of the energy resolution was found,
and a change in the rise time distribution of the pulses from preamplifiers was
observed. A correlation between rise time and pulse height was observed and is
used to correct the measured energy, recovering the energy resolution almost
completely. Moreover, no problems in the electronics due to the magnetic field
were observed.Comment: submitted to Nucl. Instrum. Meth. Phys. Res. A, LaTeX, 19 pages, 9
figure
- …