PubMed Health⌕ Search

Biomedical subjects

W Schirmacher

Publications and source records attributed to W Schirmacher.

12 recordsLinked to original sources
PubMed2004

Collective nature of the boson peak and universal transboson dynamics of glasses.

Using probe molecules with resonant nuclei and nuclear inelastic scattering, we are able to measure the density of states exclusively for collective motions with a correlation length of more than approximately 20 A. Such spectra exhibit an excess of low-energy modes (boson peak). This peak behaves in the same way as that observed by conventional methods. This shows that a significant part of the modes constituting the boson peak is of collective character. At energies above the boson peak, the reduced density of states of the collective motions universally exhibits an exponential decrease.

Journal Article↗
PubMed2001

Electronic correlation effects and the Coulomb gap at finite temperature.

We have investigated the effect of the long-range Coulomb interaction on the one-particle excitation spectrum of n-type germanium, using tunneling spectroscopy on mechanically controllable break junctions. At low temperatures, the tunnel conductance shows a minimum at zero bias voltage due to the Coulomb gap. Above 1 K, the gap is filled by thermal excitations. This behavior is reflected in the variable-range hopping resistivity measured on the same samples: up to a few degrees Kelvin the Efros-Shklovskii lnR infinity T(-1/2) law is obeyed, whereas at higher temperatures deviations from this law occur. The type of crossover differs from that considered previously in the literature.

Journal Article↗
PubMed2000

Quantum chaotic scattering with a mixed phase space: the three-disk billiard in a magnetic field

We study the classical and semiclassical scattering behavior of electrons in an open three-disk billard in the presence of a homogeneous magnetic field, which is confined to the inner part of the scattering region. As the magnetic field is increased the phase space of the invariant set of the classical scattering trajectories changes from hyperbolic (fully chaotic) to a mixed situation, where KAM tori are present. The "stickiness" of the stable trajectories leads to a much slower decay of the survival probability of trajectories as compared to the hyperbolic case. We show that this effect influences strongly the quantum fluctuations of the scattering amplitude and cross sections.

Journal Article↗
PubMed1990

Percolation model of ionic channel dynamics.

The nonexponential closed-time distributions observed for ionic channels have been explained recently by quasi-one-dimensional models of structural diffusion (Millhauser, G. L., E. E. Salpeter, and R. E. Oswald. 1988. Proc. Natl. Acad. Sci. USA. 85: 1503-1507; Condat, C. A., and J. Jäckle. 1989. Biophys. J. 55: 915-925; Levitt, D. G. 1989. Biophys. J. 55: 489-498). We generalize this treatment by allowing for more complex trajectories using percolation theory. We assume that the gating transition depends on marginally connected conformational states leading to the observed spread in time scales.

Computer Simulation↗
PubMed1989

Evaluating mite (Acari) allergenicity of house dust by guanine quantification.

The development of a quick color reaction for guanine in house dust has made it possible to screen many homes for mite products of allergenic consequence. The azo dye methods are specific enough to be useful for the development of a sanitary standard. Comparing the guanine quantification results with mite counts and determinations of the mite antigen P1 (Der p I) leads to the conclusion that the provisional standard for mattress dust of 0.6 mg guanine/g dust can be extended to dust from floor coverings and padded furniture, at least in western Europe. Below this level, the sensitization risk to patients allergic to house dust mites seems to be minimal.

Animals↗
PubMed1987

Investigations of allergen-containing dust samples from the interior of the house.

Using ACAREX test, it is straightforward to determine the allergen-containing excreta of housedust mites in dust samples and to detect the source of a contamination. Investigation of the antigen content by RAST inhibition shows that there is correlation between guanine and allergen content in a dust sample. There is no direct relation with the number of live (or dead) housedust mites, nor is this to be expected.

Allergens↗