9,318 research outputs found
Quantum transport of disordered Weyl semimetals at the nodal point
Weyl semimetals are paradigmatic topological gapless phases in three
dimensions. We here address the effect of disorder on charge transport in Weyl
semimetals. For a single Weyl node with energy at the degeneracy point and
without interactions, theory predicts the existence of a critical disorder
strength beyond which the density of states takes on a nonzero value.
Predictions for the conductivity are divergent, however. In this work, we
present a numerical study of transport properties for a disordered Weyl cone at
zero energy. For weak disorder our results are consistent with a
renormalization group flow towards an attractive pseudoballistic fixed point
with zero conductivity and a scale-independent conductance; for stronger
disorder diffusive behavior is reached. We identify the Fano factor as a
signature that discriminates between these two regimes
Thymelaea Passerina, A new Weed in the United States
During a survey of the loess bluffs flora of the Missouri River border of Iowa, Morrill (1953) discovered a few individuals of an unknown weed growing on bare vertical loess south of Council Bluffs. It proved impossible to identify this plant with any of the usual American manuals. It eventually was determined to be Thymelaea passerina (L.) Coss. and Germ. Inquiries addressed to the principal American herbaria revealed that only one specimen of the plant had been previously collected in this country. This was found in a pasture in Cedar County, Nebraska, in the northeastern corner of the state
Vitis rotundifolia Michx.
https://thekeep.eiu.edu/herbarium_specimens_byname/19798/thumbnail.jp
Introduced Weedy Grasses in Iowa
Chloris verticillata Nutt., Eriochloa villosa (Thunb.) Kunth, and Miscanthus sacchariflorus (Maxim.) Hack., are reported as three grasses new to the Iowa flora
A Rapid Softening Agent for Dried Plant Structures
In the past, dried plant materials, such as fragments of herbarium specimens, have generally been softened for dissection by boiling in water. Such a process has obvious disadvantages: slowness, fire hazard, and inconvenience. Furthermore, it is impossible to apply the boiling technique to mounted herbarium specimens without removing portions of the plant. While the author was engaged in the examination of the ligules of large numbers of grass specimens, it became evident that a solution which could be applied directly to the mounted specimen to soften it in situ would be of great advantage in preventing unnecessary breakage. A little experimentation led to the formulation of the solution whose composition is stated below. It proved very satisfactory for softening most plant specimens quickly, without boiling
Pennisetum petiolare, a pseudopetiolate African Grass Adventive in lowa
Pennisetum petiolare, a grass native to the Sudan and Ethiopia and never previously reported from North America, occurred in a lawn in Ames, Iowa. The source of the seed was contaminated Niger thistle (Guizotia abyssinica) seed used in a bird feeder directly above the location of the plant. The occurrence of at least 15 other seeds or fruits as contaminants in the sample indicates that Niger thistle seed may serve as a medium for the introduction of weed seed into the United States
Morphology and Cytology of Some Hybrids Between Elymus canadensis and E. virginicus
Substances which inhibit the action of human plasma cholinesterase in vitro have been found in aqueous extracts of various members of the plant family Solanaceae. A preliminary survey of some weedy and cultivated midwestern representatives of this family revealed eleven active species in six genera: Datura, Lycopersicon, Nicotiana, Petunia, Physalis, and Solanum. A member each of the genera Capsicum and Lycium were inactive. Inhibitory substances were not found in thirty-one species representing nineteen plant families other than Solanaceae
Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots
A systematic variation of the exciton fine-structure splitting with quantum
dot size in single InAs/GaAs quantum dots grown by metal-organic chemical vapor
deposition is observed. The splitting increases from -80 to as much as 520
eV with quantum dot size. A change of sign is reported for small quantum
dots. Model calculations within the framework of eight-band k.p theory and the
configuration interaction method were performed. Different sources for the
fine-structure splitting are discussed, and piezoelectricity is pinpointed as
the only effect reproducing the observed trend.Comment: 5 pages, 5 figure
High-current Capability of Coaxial Cables in Magnetoforming Applications
Magnetoforming technology often requires impulse current amplitudes of several hundred kiloamps, at pulse durations between 30 µs and > 100 µs. Often, it is required to provide the impulse via a flexible transmission line (cable) in order to allow the forming coil to be positioned correctly. These cables have to withstand the high pulse currents without deterioration for a large number of pulses. In addition, it is necessary to minimise the inductance of the cable connection, as an increase in inductance negatively influences the efficiency of the installation as a whole, whence low-inductance coaxial cables are required which are able to fulfil all of these requirements simultaneously. Manufacturers normally do not specify the impulse current capability of coaxial cables, as this is not necessary for most standard applications. Therefore, experiments were performed to explore the limits of commercial medium high voltage cables in regard of their impulse current withstand capability for these specific impulse parameters. A coaxial medium voltage cable has been tested at single pulses of ca. 100 µs duration, at amplitudes between 30 and 140 kA. The radial deformation (expansion) of the cable was detected with a high-resolution, high-speed camera. At a frame rate of 9000 frames/s the expansion of the cable has been determined as a function of the current amplitude. We observed dynamic changes of the cable diameter at currents above 81 kA, reaching up to 1.26 mm increase in diameter at 142 kA pulse amplitude. Above 100 kA, part of the deformation becomes irreversible, with cumulated permanent changes of up to 1 mm. The measurements are used to estimate the operating range of these cables
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