5,536 research outputs found
Global Mapping Function (GMF): A new empirical mapping function based on numerical weather model data
Troposphere mapping functions are used in the analyses of Global Positioning System and Very Long Baseline Interferometry observations to map a priori zenith hydrostatic and wet delays to any elevation angle. Most analysts use the Niell Mapping Function (NMF) whose coefficients are determined from site coordinates and the day of year. Here we present the Global Mapping Function (GMF), based on data from the global ECMWF numerical weather model. The coefficients of the GMF were obtained from an expansion of the Vienna Mapping Function (VMF1) parameters into spherical harmonics on a global grid. Similar to NMF, the values of the coefficients require only the station coordinates and the day of year as input parameters. Compared to the 6-hourly values of the VMF1 a slight degradation in short-term precision occurs using the empirical GMF. However, the regional height biases and annual errors of NMF are significantly reduced with GMF
Vertical quantum wire realized with double cleaved-edge overgrowth
A quantum wire is fabricated on (001)-GaAs at the intersection of two
overgrown cleaves. The wire is contacted at each end to n+ GaAs layers via
two-dimensional (2D) leads. A sidegate controls the density of the wire
revealing conductance quantization. The step height is strongly reduced from
2e^2/h due to the 2D-lead series resistance. We characterize the 2D density and
mobility for both cleave facets with four-point measurements. The density on
the first facet is modulated by the substrate potential, depleting a 2um wide
strip that defines the wire length. Micro-photoluminescence shows an extra peak
consistent with 1D electron states at the corner.Comment: 4 pages, 4 figure
Steigerung der Ausdauerleistungsfähigkeit von durchschnittlich trainierten Personen durch natürliche Sonnenstrahlung (Heliotherapie)
Problemstellung: Der UV-Strahlung wird unter anderem eine Steigerung der Ausdauerleistungsfähigkeit zugeschrieben; zahlreiche experimentelle Studien mit künstlicher Bestrahlung bestätigen dies. Aufgrund dieser Ergebnisse wird diskutiert, dass UV-Bestrahlung die gleichen Stoffwechselprozesse induziert wie ein Ausdauertraining. Diese Resultate wurden jedoch nur mit UVB-Bestrahlung erzielt; mit UVA-, Infrarot- oder sichtbarer Strahlung konnte keine Steigerung der Leistungsfähigkeit festgestellt werden. Es ist deshalb zusätzlich zu klären, ob die leistungssteigernden Effekte auch durch natürliches Sonnenlicht, welches wesentlich weniger UVB enthält, hervorgerufen werden können.
Gegenstand: Ziel der vorliegenden Studie war, die Auswirkungen der natürlichen Sonnenbestrahlung während Heliotherapie auf das Training der Ausdauerleistungsfähigkeit zu untersuchen. Insbesonders standen die metabolischen Effekte im Vordergrund der Untersuchung.
Versuchsplan: In Davos wurden 53 Neuroder-mitispatienten, die vom Herz-Kreislauf-System her gesund und durchschnittlich trainiert waren, einer 3wöchigen Heliotherapie unterzogen. Bei im übrigen gleichem Therapieregime wurden die Patienten zwei unterschiedlichen Therapiegruppen zugeteilt: Die 32 Patienten der „Sonnengruppe” haben während der 21tägigen Studiendauer im Mittel 19,3 Stunden, die Patienten der Kontrollgruppe dagegen nur 5,7 Stunden unbekleidet in der Sonne gelegen. Die Besonnung fand unter kontrollierten Bedingungen statt. Am Anfang und Ende der Kur wurde die Leistungssteigerung mittels Fahrradergometrie bestimmt. Meßparameter waren in erster Linie Puls und Laktat. Zusätzliche Aktivitäten der Patienten wurden in einem Tagebuch protokolliert.
Ergebnisse: Bei der Sonnengruppe ergab sich anhand der Laktatwerte eine signifikante Verbesserung des aeroben Metabolismus bei gleicher, submaximaler Belastung im Vergleich zur Kontrollgruppe (Differenz zwischen den Gruppen 0,5 mmol/l, p < 0,01). Die Pulswerte beider Gruppen unterscheiden sich am Kurende nur geringfügig (3 /min, n.s.).
Schlußfolgerung: Diese Ergebnisse bestätigen, dass durch UV-Bestrahlung dieselben Adaptationen im Muskelstoffwechsel wie durch ein mäßig dosiertes Ausdauertraining hervorgerufen werden. Auch die Größenordnung ist vergleichbar. Diese leichte Steigerung der Ausdauerleistungsfähigkeit läßt sich darüber hinaus nicht nur durch serielle künstliche UVB-Bestrahlung, sondern auch durch eine 3wöchige Heliotherapie erreichen
Electron spin relaxation in bulk GaAs for doping densities close to the metal-to-insulator transition
We have measured the electron spin relaxation rate and the integrated spin
noise power in n-doped GaAs for temperatures between 4 K and 80 K and for
doping concentrations ranging from 2.7 x 10^{-15} cm^{-3} to 8.8 x 10^{-16}
cm^{-3} using spin noise spectroscopy. The temperature dependent measurements
show a clear transition from localized to free electrons for the lower doped
samples and confirm mainly free electrons at all temperatures for the highest
doped sample. While the sample at the metal-insulator-transition shows the
longest spin relaxation time at low temperatures, a clear crossing of the spin
relaxation rates is observed at 70 K and the highest doped sample reveals the
longest spin relaxation time above 70 K.Comment: 6 pages, 4 figure
Direct Observation of Controlled Coupling in an Individual Quantum Dot Molecule
We report the direct observation of quantum coupling in individual quantum
dot molecules and its manipulation using static electric fields. A pronounced
anti-crossing of different excitonic transitions is observed as the electric
field is tuned. Comparison of our experimental results with theory shows that
the observed anti-crossing occurs between excitons with predominant spatially
\emph{direct} and \emph{indirect} character. The electron component of the
exciton wavefunction is shown to have molecular character at the anti-crossing
and the quantum coupling strength is deduced optically. In addition, we
determine the dependence of the coupling strength on the inter-dot separation
and identify a field driven transition of the nature of the molecular ground
state.Comment: 11 pages, 4 figures submitted to Physical Review Letter
Shock Waves in Nanomechanical Resonators
The dream of every surfer is an extremely steep wave propagating at the
highest speed possible. The best waves for this would be shock waves, but are
very hard to surf. In the nanoscopic world the same is true: the surfers in
this case are electrons riding through nanomechanical devices on acoustic waves
[1]. Naturally, this has a broad range of applications in sensor technology and
for communication electronics for which the combination of an electronic and a
mechanical degree of freedom is essential. But this is also of interest for
fundamental aspects of nano-electromechanical systems (NEMS), when it comes to
quantum limited displacement detection [2] and the control of phonon number
states [3]. Here, we study the formation of shock waves in a NEMS resonator
with an embedded two-dimensional electron gas using surface acoustic waves. The
mechanical displacement of the nano-resonator is read out via the induced
acoustoelectric current. Applying acoustical standing waves we are able to
determine the anomalous acoustocurrent. This current is only found in the
regime of shock wave formation. We ontain very good agreement with model
calculations.Comment: 14 Pages including 4 figure
Dynamic masses for the close PG1159 binary SDSSJ212531.92-010745.9
SDSSJ212531.92-010745.9 is the first known PG1159 star in a close binary with
a late main sequence companion allowing a dynamical mass determination. The
system shows flux variations with a peak-to-peak amplitude of about 0.7 mag and
a period of about 6.96h. In August 2007, 13 spectra of SDSSJ212531.92-010745.9
covering the full orbital phase range were taken at the TWIN 3.5m telescope at
the Calar Alto Observatory (Alm\'{e}ria, Spain). These confirm the typical
PG1159 features seen in the SDSS discovery spectrum, together with the Balmer
series of hydrogen in emission (plus other emission lines), interpreted as
signature of the companion's irradiated side. A radial velocity curve was
obtained for both components. Using co-added radial-velocity-corrected spectra,
the spectral analysis of the PG1159 star is being refined.
The system's lightcurve, obtained during three seasons of photometry with the
G\"ottingen 50cm and T\"ubingen 80cm telescopes, was fitted with both the
NIGHTFALL and PHOEBE binary simulation programs. An accurate mass determination
of the PG1159 component from the radial velocity measurements requires to first
derive the inclination, which requires light curve modelling and yields further
constraints on radii, effective temperature and separation of the system's
components. From the analysis of all data available so far, we present the
possible mass range for the PG1159 component of SDSSJ212531.92-010745.9.Comment: 8 pages, in "White dwarfs", proceedings of the 16th European White
Dwarf Workshop, eds. E. Garcia-Berro, M. Hernanz, J. Isern, S. Torres, to be
published in J. Phys.: Conf. Se
Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC10001893
KIC10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the
Kepler spacecraft in its primary mission. In addition to tens of pulsation
frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks
at very low frequencies, which is too low to be explained in terms of g modes.
The most convincing explanation is that we are seeing the orbital modulation of
three Earth-size planets (or planetary remnants) in very tight orbits, which
are illuminated by the strong stellar radiation. The orbital periods are
P1=5.273, P2=7.807, and P3=19.48 hours, and the period ratios P2/P1=1.481 and
P3/P2=2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of
the main pulsation modes of the star at 210.68 {\mu}Hz corresponds to the third
harmonic of the orbital frequency of the inner planet, suggesting that we see,
for the first time in an sdB star, g-mode pulsations tidally excited by a
planetary companion. The extreme planetary system that emerges from the Kepler
data is very similar to the recent discovery of two Earth-size planets orbiting
the sdB pulsator KIC05807616 (Charpinet et al. 2011a).Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
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