Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living supra-specific taxa of Chondrichthyan fishes. Part B: Batomorphii. 4a: Order Rajiformes - Suborder Myliobatoidei - Superfamily Dasyatoidea - Family Dasyatidae - Subfamily Dasyatinae - Genera: <i>Amphotistius, Dasyatis, Himantura, Pastinachus, Pteroplatytrygon, Taeniura, Urogymnus</i> and <i>Urolophoides</i> (incl. supraspecific taxa of uncertain status and validity), Superfamily Myliobatoidea - Family Gymnuridae - Genera: <i>Aetoplatea</i> and <i>Gymnura</i>, Superfamily Plesiobatoidea - Family Hexatrigonidae - Genus: <i>Hexatrygon</i>

Part B of this series, comprising the Batomorphii is continued with taxa of the Myliobatoidei. The tooth morphology of representatives of eight genera (incl. supraspecific taxa of uncertain status and validity) of the family Dasyatidae, two of Gymnuridae and one of Hexatrygonidae is described and illustrated by SEM-photographs. A differential diagnosis for a final conclusions on myliobatoid odontology will be given in a forthcoming issue dealing with the last myliobatoid taxa

Comparing powder magnetization and transport critical current of Bi,Pb(2223) tapes

The magnetic field dependence of the critical current in (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+x/ tapes is compared with the magnetization response of isolated grains extracted from the tapes. Special attention is paid to the low-field behavior. The goal of the experiment is to test the widely-used hypothesis that current paths in these tapes contain both weak- and strong- linked branches, which in low field act in parallel. The data agree with this hypothesis; at temperatures above 50 K the powder magnetization drops off exponentially from the self-field to the irreversibility field, while the transport and magnetization currents in the intact tapes show an extra low-field component. Below 50 K the powder behavior becomes less straightforward, but the parallel-path picture in the tapes still holds

Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living supraspecific taxa of Chondrichthyan fishes. Part A. Selachii. 1b: Order: Hexanchiformes - Family: Chlamydoselachidae. 5: Order: Heterodontiformes - Family: Heterodontidae. 6: Order: Lamniformes - Families: Cetorhinidae, Megachasmidae; Addendum 1 to 3: Order Squaliformes; Addendum 1 to 4: Order: Orectolobiformes; General Glossary; Summary part A

The morphology of the microteeth of the following taxa is described and illustrated with SEM-photographs in order to elucidate the interrelationships within the shark orders and families concerned and also from odontological point of view. Contribution 1b: The monotypic single genus of the hexanchiform Chlamydoselachidae. The tooth morphology of C. anguineus is compared with that of taxa of the only other hexanchiformes. The dental histology is commented on, and the dental vascular type is re-examined in order to understand the root form. The results are summarized in an odontological diagnosis for the genus. Investigational results on dental morphology, histology and vascularization recommend a reconsideration of the systematic position of the Chlamydoselachidae, which show a closer relation to Orectolobiformes than to Hexanchidae. Contribution 5: The three genera Tropidodus, Gyropleurodus and Heterodontus of the heterodontiform family Heterodontidae as once proposed by Gill, 1862. The differences in tooth morphology are only of interspecific signification. Contribution 6: The genera of the monotypic families Cetorhinidae and Megachasmidae. The morphology of the small teeth in both families is characteristic for filter-feeders. Cetorhinus exhibits irregular size and shape of its small teeth and a distinct ontogenetic heterodonty in its dentition. Megachasma, in contrast, shows small teeth of equal size and shape indicating a relatively recent adaptation to filter-feeding. Contribution 3, addendum 1: The squalid species Scymnodon squamulosus and Scymnodon obscurus attributable to the genus Zameus, proposed by Jordan and Fowler in 1903 and revalidated by Taniuchi and Garrick in 1986. Odontological investigations indicate a synonymy of Zameus and Scymnodalatias with Scymnodon. Contribution 4, addendum 1: The type species of the monotypic orectolobid genus Sutorectus. The results are summarized in a diagnosis for the genus and offer hardly any odontological arguments for distinguishing Sutorectus from Orectolobus

Strain effects in high temperature superconductors investigated with magneto-optical imaging

In order to determine the influence of intermediate deformation steps on the mechanical behavior of Bi-based tapes, the effect of longitudinal applied strain is investigated by means of magneto-optical imaging. The strain is applied in a helium flow-cryostat. Cracks appear soon after the critical current in Bi-based tapes is degraded. All filaments form multiple cracks that grow into tape-wide cracks, running from one filament to the next. The crack location is not caused by stress concentrations in the matrix, but by the mechanically weak colony boundaries. Because of the absence of intermediate rolling steps in the production of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ tapes, a different crack structure is observed compared to Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tapes. The relation between the critical current and the formation of cracks is studied. The degradation in critical current before the critical strain is reached may be caused by microcracks that remain undetected by magneto-optical imaging. The influence of strain on the microstructure of YBa/sub 2/Cu/sub 3/O/sub x/ coated conductors is also investigated with magneto-optical imaging. The formation of cracks is believed to be determined by the nickel substrate and related to the Ni-grain size

Critical current versus strain research at the University of Twente

At the University of Twente a U-shaped spring has been used to investigate the mechanical properties of a large variety of superconducting tapes and wires. Several mechanisms are responsible for the degradation of critical current as a function of applied strain. A change in its intrinsic parameters causes a reversible critical current dependence in Nb3Sn. The critical current reaches a maximum at a wire-dependent tensile strain level, and decreases when this tensile strain is either released or further increased. In Bi-based tapes the critical current is virtually insensitive to tensile strain up to a sample-dependent irreversible strain limit. When this limit is exceeded, the critical current decreases steeply and irreversibly. This behaviour is attributed to microstructural damage to the filaments. This cracking of the filaments is verified by a magneto-optical strain experiment. Recent experiments suggest that in MgB2 the degradation of critical current is caused by a change in intrinsic properties and damage to the microstructure. Magneto-optical imaging can be used to investigate the influence of applied strain on the microstructure of MgB2, as is done successfully with Bi-based tapes. In all these conductors the thermal precompression of the filaments plays an important role. In Nb3Sn it determines the position of the maximum and in Bi-based and MgB2 conductors it is closely related to the irreversible strain limit

Congested Traffic States in Empirical Observations and Microscopic Simulations

We present data from several German freeways showing different kinds of congested traffic forming near road inhomogeneities, specifically lane closings, intersections, or uphill gradients. The states are localized or extended, homogeneous or oscillating. Combined states are observed as well, like the coexistence of moving localized clusters and clusters pinned at road inhomogeneities, or regions of oscillating congested traffic upstream of nearly homogeneous congested traffic. The experimental findings are consistent with a recently proposed theoretical phase diagram for traffic near on-ramps [D. Helbing, A. Hennecke, and M. Treiber, Phys. Rev. Lett. {\bf 82}, 4360 (1999)]. We simulate these situations with a novel continuous microscopic single-lane model, the ``intelligent driver model'' (IDM), using the empirical boundary conditions. All observations, including the coexistence of states, are qualitatively reproduced by describing inhomogeneities with local variations of one model parameter. We show that the results of the microscopic model can be understood by formulating the theoretical phase diagram for bottlenecks in a more general way. In particular, a local drop of the road capacity induced by parameter variations has practically the same effect as an on-ramp.Comment: Now published in Phys. Rev. E. Minor changes suggested by a referee are incorporated; full bibliographic info added. For related work see http://www.mtreiber.de/ and http://www.helbing.org