1,576 research outputs found
Observing the emergence of chaos in a many-particle quantum system
Accessing the connection between classical chaos and quantum many-body
systems has been a long-standing experimental challenge. Here, we investigate
the onset of chaos in periodically driven two-component Bose-Einstein
condensates, whose small quantum uncertainties allow for exploring the phase
space with high resolution. By analyzing the uncertainties of time-evolved
many-body states, we find signatures of elliptic and hyperbolic periodic orbits
generated according to the Poincar\'e-Birkhoff theorem, and the formation of a
chaotic region at increasing driving strengths. The employed fluctuation
analysis allows for probing the phase-space structure by use of only short-time
quantum dynamics.Comment: 5+2 pages, 4 figure
On the appearance of hyperons in neutron stars
By employing a recently constructed hyperon-nucleon potential the equation of
state of \beta-equilibrated and charge neutral nucleonic matter is calculated.
The hyperon-nucleon potential is a low-momentum potential which is obtained
within a renormalization group framework. Based on the Hartree-Fock
approximation at zero temperature the densities at which hyperons appear in
neutron stars are estimated. For several different bare hyperon-nucleon
potentials and a wide range of nuclear matter parameters it is found that
hyperons in neutron stars are always present. These findings have profound
consequences for the mass and radius of neutron stars.Comment: 12 pages, 12 figures, RevTeX4; summary and conclusions are
strengthened, to appear in PR
Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
Several studies have shown that the distribution of cation
adsorption sites (CASs) is patchy at a millimetre to centimetre scale. Often,
larger concentrations of CASs in biopores or aggregate coatings have been
reported in the literature. This heterogeneity has implications on the
accessibility of CASs and may influence the performance of soil system models
that assume a spatially homogeneous distribution of CASs. In this study, we
present a new method to quantify the abundance and 3-D distribution of CASs in
undisturbed soil that allows for investigating CAS densities with distance to
the soil macropores. We used X-ray imaging with Ba<sup>2+</sup> as a contrast
agent. Ba<sup>2+</sup> has a high adsorption affinity to CASs and is widely used as
an index cation to measure the cation exchange capacity (CEC). Eight soil
cores (approx. 10 cm<sup>3</sup>) were sampled from three locations with
contrasting texture and organic matter contents. The CASs of our samples were
saturated with Ba<sup>2+</sup> in the laboratory using BaCl<sub>2</sub> (0.3 mol L<sup>−1</sup>). Afterwards, KCl (0.1 mol L<sup>−1</sup>) was used to rinse out Ba<sup>2+</sup>
ions that were not bound to CASs. Before and after this process the samples
were scanned using an industrial X-ray scanner. Ba<sup>2+</sup> bound to CASs was
then visualized in 3-D by the difference image technique. The resulting
difference images were interpreted as depicting the Ba<sup>2+</sup> bound to CASs
only. The X-ray image-derived CEC correlated significantly with results of
the commonly used ammonium acetate method to determine CEC in well-mixed
samples. The CEC of organic-matter-rich samples seemed to be systematically
overestimated and in the case of the clay-rich samples with less organic
matter the CEC seemed to be systematically underestimated. The results showed
that the distribution of the CASs varied spatially within most of our samples
down to a millimetre scale. There was no systematic relation between the
location of CASs and the soil macropore structure. We are convinced that the approach proposed here will strongly aid the development of more realistic
soil system models
Io: IUE observations of its atmosphere and the plasma torus
Two of the main components of the atmosphere of Io, neutral oxygen and sulfur, were detected with the IUE. Four observations yield brightnesses that are similar, regardless of whether the upstream or the downstream sides of the torus plasma flow around Io is observed. A simple model requires the emissions to be produced by the interaction of O and S columns in the exospheric range with 2 eV electrons. Cooling of the 5 eV torus electrons is required prior to their interaction with the atmosphere of Io. Inconsistencies in the characteristics of the spectra that cannot be accounted for in this model require further analysis with improved atomic data. The Io plasma torus was monitored with the IUE. The long-term stability of the warm torus is established. The observed brightnesses were analyzed using a model of the torus, and variations of less than 30 percent in the composition are observed, the quantitative results being model dependent
Anti factor H autoantibodies block C-terminal recognition function of factor H in hemolytic uremic syndrome
The atypical form of the kidney disease hemolytic uremic syndrome (aHUS) is associated with defective complement regulation. In addition to mutations in complement regulators, factor H (FH)-specific autoantibodies have been reported for aHUS patients. The aim of the present study was to understand the role of these autoantibodies in aHUS. First, the binding sites of FH autoantibodies from 5 unrelated aHUS patients were mapped using recombinant FH fragments and competitor antibodies. For all 5 autoantibodies, the binding site was localized to the FH C-terminus. In a functional assay, isolated patient IgG inhibited FH binding to C3b. In addition, autoantibody-positive patients' plasma caused enhanced hemolysis of sheep erythrocytes, which was reversed by adding FH in excess. These results suggest that aHUS-associated FH autoantibodies mimic the effect of C-terminal FH mutations, as they inhibit the regulatory function of FH at cell surfaces by blocking its C-terminal recognition region
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