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H M Singer

Publications and source records attributed to H M Singer.

6 recordsLinked to original sources
PubMed2006

Analysis and visualization of multiply oriented lattice structures by a two-dimensional continuous wavelet transform.

The phase-field-crystal model [K. R. Elder and M. Grant, Phys. Rev. E 70, 051605 (2004)] produces multigrain structures on atomistic length scale but on diffusive time scales. Since individual atoms are resolved but are treated identically it is difficult to distinguish the exact position of grain boundaries and defects within grains. In order to analyze and visualize the whole grains a two-dimensional wavelet transform has been developed, which is capable of extracting grain boundaries and the lattice orientation of a grain relative to a laboratory frame of reference. This transformation makes it possible not only to easily visualize the multigrain structure, but also to perform exact measurements on low- and high-angle boundaries, grain size distributions and boundary-angle distributions, which can then be compared to experimental data. The presented wavelet transform can also be applied to results of other atomistic simulations, e.g., molecular dynamics or granular materials.

Journal Article↗
PubMed2006

Measurements of the three-dimensional shape of ice crystals in supercooled water.

Experimentally grown ice crystals from ultrapure supercooled water are imaged by means of Mach-Zehnder interferometry. By analyzing the fringe patterns the phase information and thus the three-dimensional shape of the ice crystals is recovered quantitatively. The integral parameters height of the basal plane, volume, and surface of the crystals are measured as a function of time and supercooling. It is found that all measured parameters follow a power law as a function of time and the exponents are found to be independent of the supercooling. The shape transition from the prismatic to the basal face along the main growth direction of the ice dendrites as a function of the distance from the tip is found to be a power law as well. Our findings support the validity of universal growth laws in pattern forming systems.

Journal Article↗
PubMed2004

Quantitative description of morphological transitions in diffusion-limited growth of xenon crystals.

Changes of growth morphologies are induced by a perturbation of the temperature distribution in the surrounding of a growing xenon crystal. Apart from the dendritic morphology seaweed and doublon morphologies are found. We present a method which quantitatively describes growth morphologies by means of rotational, scale, and translational invariant transformations. Evolutions of growth morphologies are represented as paths in the morphology space. The presented method could be of some use for other fields of research where qualitative and quantitative information of different classes of images has to be identified.

Journal Article↗
PubMed2004

Generalized length scales for three-dimensional dendritic growth.

The crucial length scale of dendritic growth is the tip radius. Usually it is determined by fitting the data to a theoretical function. We present a method of a generalized tip radius which is entirely based on geometric considerations and is not dependent on an underlying assumption of the shape of the tip. Furthermore the results are stable and the average change of the tip radius between successive images is less than 6%.

Journal Article↗
PubMed1998

The relation between scabies and hypersensitivity to antigens of house dust mites and storage mites.

Twenty five non-atopic scabietic patients were examined to estimate their reaction to crude house dust mite Dermatophagoides farinae (D. farinae) and storage mite Tyrophagus putrescentia (T. putrescentiae) antigens. Skin prick testing (SPT) by extracts of both mites antigens showed significant higher positive results in scabietics when compared to non-scabietic control subjects. Moreover, 60% and 56% of scabietic patients showed positive levels of specific anti-D. farinae and T. putrescentia IgE respectively in comparison to 13.4% & 20% of control subjects. A significant difference has been obtained when the total number of positive results were compared to the total number of negative ones. The results revealed that there is an evidence of cross reactivity between Sarcoptes scabiei antigens and extracts of D. farinae and T. putrescentiae, and the hypersensitivity to house dust mite and storage mite antigens was significantly higher in scabietics than in controls. It could be concluded that there is some proof that other mites rather than Sarcoptes scabiei may have a role in the pathogenesis of scabies and the cross reactivity between S. scabiei and house dust mite and storage mite may explain the persistence of symptoms in some cases even after proper treatment of the disease.

Adolescent↗