Bias and temperature dependence of the noise in a single electron transistor

A single electron transistor based on Al-AlO_x-Nb tunnel junctions was fabricated by shadow evaporation and in situ barrier formation. Its output current noise was measured, using a transimpedance amplifier setup, as a function of bias voltage, gain, and temperature, in the frequency range 1...300 Hz. The spot noise at 10 Hz is dominated by a gain dependent component, indicating that the main noise contribution comes from fluctuations at the input of the transistor. Deviations from ideal input charge noise behaviour are found in the form of a bias dependence of the differential charge equivalent noise, i. e. the derivative of current noise with respect to gain. The temperature dependence of this effect could indicate that heating is activating the noise sources, and that they are located inside or in the near vicinity of the junctions.Comment: 16 pages, 9 figures (EPS

Grammatikbezogene Lernstrategien im Wirtschaftsdeutschunterricht aus Lehrer- und Lernerperspektive

Auf Basis ethnographischer Daten wird der Frage nachgegangen, ob und wie sich grammatikbezogene Lernstrategien im Wirtschaftsdeutschunterricht an der Universität von Hawai'i vermitteln lassen. Der Unterricht in zwei Deutschkursen wurde mehrere Monate beobachtet, die Kursteilnehmer- und -veranstalter interviewt und relevante Dokumente ausgewertet. Es wird gezeigt, wie forschungsinteressierte Lehrende adressatenspezifische Unterrichtskonzepte empirisch fundieren können

Gain Dependence of the Noise in the Single Electron Transistor

An extensive investigation of low frequency noise in single electron transistors as a function of gain is presented. Comparing the output noise with gain for a large number of bias points, it is found that the noise is dominated by external charge noise. For low gains we find an additional noise contribution which is compared to a model including resistance fluctuations. We conclude that this excess noise is not only due to resistance fluctuations. For one sample, we find a record low minimum charge noise of qn = 9*10^-6 e/sqrt(Hz) in the superconducting state and qn = 9*10^-6 e/sqrt(Hz) in the normal state at a frequency of 4.4 kHz.Comment: 10 pages, LaTex 2.09, 4 figures (epsfig

Spectral cutoffs in indirect dark matter searches

Indirect searches for dark matter annihilation or decay products in the cosmic-ray spectrum are plagued by the question of how to disentangle a dark matter signal from the omnipresent astrophysical background. One of the practically background-free smoking-gun signatures for dark matter would be the observation of a sharp cutoff or a pronounced bump in the gamma-ray energy spectrum. Such features are generically produced in many dark matter models by internal Bremsstrahlung, and they can be treated in a similar manner as the traditionally looked-for gamma-ray lines. Here, we discuss prospects for seeing such features with present and future Atmospheric Cherenkov Telescopes.Comment: 4 pages, 2 figures, 1 table; conference proceedings for TAUP 2011, Munich 5-9 Se

Chemicals regulation and the Porter Hypothesis:a critical review of the new European chemicals regulation

In this contribution, discussions about the Porter Hypothesis and the pros and cons of the new European chemicals regulation system REACH are tied together. The contribution seeks to apply the Porter Hypothesis to the field of European chemicals regulation. Porter’s claim of positive effects of regulation on innovations seems especially important for the chemicals sector pursuing differentiation. But, understanding Porter’s concept of strategic management indicates that certain segments of the chemicals industry will suffer negative effects on competition and innovation

The Maricunga Belt (chilean Precordillera) and its hydrothermal alteration zones as revealed by multispectral remote sensing and field studies

Remote sensing techniques offer a unique chance to analyse and map wide or nearly inaccessable areas under certain geoscientific aspects in relatively short time and at low cost. Therefore geological field campaigns together with multispectral image analysis were carried out for the Maricunga Belt in the chilenean Precordillera, south of the regional mining settlements San Salvador and Potrerillos (Atacama). On the basis of Landsat-TM 5, ASTER, radar-based DGM-data and field mapping/sampling the lithological/structural characteristics of several OH-bearing hydrothermal alteration zones of mostly Neogene age have been investigated because of their high value for future exploration. The often  unknown regional tectonic framework which seems to have controlled the alteration dimensions are also discussed. In order to obtain  reasonable lithological classification criteria for the remote sensing data fundamental statistical selection rules like the optimum index factor  (OIF) were applied to the combination of single TM bands. Furthermore specific band ratios (5/7; 5/4, 5/1) and principal components were  utilized to enhance the spectral properties of the argillized, bleached clay- and/or silica-rich alteration surfaces. Additional spectral measurements were carried out for each representative lithological unit of the alteration zones to estimate the quality of the calculated classifications/ratios for geological mapping. In some cases complementary geochemical data has been studied in order to obtain direct clues for understanding the type of some detected hydrothermal alterations. Finally the achieved data was compiled in a geological map which shows more than 20 hydrothermally altered surfaces in relation to the regional geology and the specific tectonic framework. The influence of three major fault systems (the N-S orientated West Fissure System, the NE-SW orientated Inca De Oro System and a poorly described NW-SE System) for the setting of the alterations seems to be obvious