1,332 research outputs found
Dating of ice cores from Vernagtferner (Austria) with fission products and lead-210
Fission product (90Sr_ 90y, I37CS, total beta) and 2tOPb_210pO activities were measured in core samples from the temperate vernagtferner (3150 m altitude, Oetztal Alps, Austria). The results show that the investigated fission products are transported with water resulting from melting processes, and are sorbed on dust or dirt horizons. These products are, therefore, not suited for dating temperate glaciers. 210Pb is also transported with water and displaced from its original deposition. However, despite large fluctuations, the specific activity of 210Pb decreases with depth, and can be used to estimate accumulation rates and the age of the ice. The average annual accumulation rate amounts to about 80 cm water equivalent, and the deepest sample (81 m i. e. "" 65 m w. e.) was deposited in the beginning of this century. These results agree with data obtained from other observations on this glacier and show that the 210Pb_method is suitable to date temperate glaciers, if the ice cores cover a time interval of about 100 years (i. e. "" 4 half-lives of 210Pb). The surface activity of 210Pb was found to be 5 ± I dpm per kg of ice in agreement with other locations in the Alps and with measurements of fresh snow
Coupling/decoupling between translational and rotational dynamics in a supercooled molecular liquid
We use molecular dynamics computer simulations to investigate the
coupling/decoupling between translational and rotational dynamics in a
glass-forming liquid of dumbbells. This is done via a careful analysis of the
-relaxation time of the incoherent
center-of-mass density correlator at the structure factor peak, the
-relaxation time of the reorientational correlator, and the
translational () and rotational () diffusion constants. We find
that the coupling between the relaxation times and
increases with decreasing temperature , whereas the coupling
decreases between the diffusivities and . In addition, the
-dependence of decouples from that of , which is
consistent with previous experiments and has been interpreted as a signature of
the "translation-rotation decoupling." We trace back these apparently
contradicting observations to the dynamical heterogeneities in the system. We
show that the decreasing coupling in the diffusivities and is
only apparent due to the inadequacy of the concept of the rotational diffusion
constant for describing the reorientational dynamics in the supercooled state.
We also argue that the coupling between and
and the decoupling between and , both of which strengthen
upon cooling, can be consistently understood in terms of the growing dynamic
length scale.Comment: revised manuscript, to appear in Phys. Rev. Let
Ab initio many-body calculation of excitons in solid Ne and Ar
Absorption spectra, exciton energy levels and wave functions for solid Ne and
Ar have been calculated from first principles using many-body techniques.
Electronic band structures of Ne and Ar were calculated using the GW
approximation. Exciton states were calculated by diagonalizing an exciton
Hamiltonian derived from the particle-hole Green function, whose equation of
motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to
n=5 for Ne and n=3 for Ar were obtained. Binding energies and
longitudinal-transverse splittings of n=1 excitons are in excellent agreement
with experiment. Plots of correlated electron-hole wave functions show that the
electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page
Peeling Bifurcations of Toroidal Chaotic Attractors
Chaotic attractors with toroidal topology (van der Pol attractor) have
counterparts with symmetry that exhibit unfamiliar phenomena. We investigate
double covers of toroidal attractors, discuss changes in their morphology under
correlated peeling bifurcations, describe their topological structures and the
changes undergone as a symmetry axis crosses the original attractor, and
indicate how the symbol name of a trajectory in the original lifts to one in
the cover. Covering orbits are described using a powerful synthesis of kneading
theory with refinements of the circle map. These methods are applied to a
simple version of the van der Pol oscillator.Comment: 7 pages, 14 figures, accepted to Physical Review
Scanning-gate-induced effects and spatial mapping of a cavity
Tailored electrostatic potentials are the foundation of scanning gate
microscopy. We present several aspects of the tip-induced potential on the
two-dimensional electron gas. First, we give methods on how to estimate the
size of the tip-induced potential. Then, a ballistic cavity is formed and
studied as a function of the bias-voltage of the metallic top gates and probed
with the tip-induced potential. It is shown how the potential of the cavity
changes by tuning the system to a regime where conductance quantization in the
constrictions formed by the tip and the top gates occurs. This conductance
quantization leads to a unprecedented rich fringe pattern over the entire
structure. Finally, the effect of electrostatic screening of the metallic top
gates is discussed.Comment: 10 pages, 6 figure
Locally induced quantum interference in scanning gate experiments
We present conductance measurements of a ballistic circular stadium
influenced by a scanning gate. When the tip depletes the electron gas below, we
observe very pronounced and regular fringes covering the entire stadium. The
fringes correspond to transmitted modes in constrictions formed between the
tip-induced potential and the boundaries of the stadium. Moving the tip and
counting the fringes gives us exquisite control over the transmission of these
constrictions. We use this control to form a quantum ring with a specific
number of modes in each arm showing the Aharonov-Bohm effect in low-field
magnetoconductance measurements.Comment: 10 pages, 4 figure
Sorption of Nickel and Cobalt on a Size-Fraction of Unconsolidated Glaciofluvial Deposits and on Clay Minerals
"Selbstscreen-Prodrom" - ein Selbstbeurteilungsinstrument zur Früherkennung von psychischen Erkrankungen und Psychosen
OBJECTIVE: In the past years, the significance of early detection of psychoses has been increasingly recognized. Screening for the onset of disorders should focus on individuals seeking treatment in an outpatient setting and should preferably operate stepwise. Within a prospective study for the early detection of psychoses (FePsy = Früh Erkennung von PSYchosen) the self-rating instrument "Self-screen Prodrome" was developed to differentiate between healthy individuals, individuals with psychosis or an at-risk mental state for psychosis and patients with other ICD-10 diagnoses. METHOD: The "Self-screen Prodrome" was developed by taking established risk factors and early signs of disease into account. In particular, prodromes and pre-psychotic symptoms were captured. A total score and a subscale were analyzed with regard to validity and reliability. RESULTS: The total score "Self-screen Prodrome" distinguished between outpatients with a mental disorder and healthy individuals (Cut-off < or = 6; sensitivity: 85 % specificity: 91 %). Additionally the subscale distinguished between psychosis-(risk)-individuals and outpatients with other ICD-10 psychiatric diagnoses (Cut-off < or = 2; sensitivity: 85 % specificity: 39 %). CONCLUSION: The "Self-screen Prodrome" is a useful instrument that a) separates mentally ill patients from healthy individuals and b) filters individuals with a risk of developing psychoses from patients with other ICD-10 diagnoses for further screening. The next step in the early detection of psychoses for identified individuals should be a detailed psychiatric exploration by experts
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