We present the results from an experimental study of the magneto-transport of superconducting wires of amorphous Indium-Oxide, having widths in the range 40 -120 nm. We find that, below the superconducting transition temperature, the wires exhibit clear, reproducible, oscillations in their resistance as a function of magnetic field. The oscillations are reminiscent of those which underlie the operation of a superconducting quantum interference device.PACS numbers: 74.78. Na, 85.35.Ds, 73.21.Hb The central challenge in the study of thin superconducting wires is to understand how superconductivity is affected when approaching the one-dimensional (1D) limit. Earlier studies have predicted that intrinsic thermal [1, 2] and quantum [3,4,5] fluctuations play an increasingly important role in this limit, causing the wires to remain resistive much below the superconducting transition temperature, T c . Recent theories [6,7], incorporating the effect of electron-electron interactions, describe the suppression of T c when approaching the 1D limit, which was observed in experiments [8].In recent years new experimental techniques enabling the fabrication of superconducting wires with a diameter approaching the 1D limit were developed. The experiments that followed [9] focused primarily on whether the quantum resistance for a Cooper-pair, R Q = h/4e 2 ≈ 6.45 kΩ (h is Planck's constant and e is the charge of the electron) is the resistance scale that solely controls the existence of superconductivity. While some works [9,10] provided evidence that wires with a normal state resistance R N < R Q are superconducting and those with R N > R Q become insulating at low T , this point is still under debate [11].In this letter we report on an experimental study of the magnetic field (B) dependence of the resistance of superconducting wires whose dimensions are close to the 1D limit. We find that, while a strong B drives our wires into an insulating state, the magnetoresistance is dominated by reproducible periodic oscillations similar to those observed in superconducting quantum interference devices (SQUIDs) [12]. We also find that wires with R N >> R Q can exhibit superconductivity.In order to fabricate our 1D wires we utilized the method of Bezryadin et al. [9], in which a non-conducting nanotube, suspended across a narrow gap etched in a semiconductor substrate, is used as a template on which the superconductor is deposited. There are two experimental differences between our work and that of Ref.[9]. First, instead of carbon, our nanotubes were made of WS 2 [13]. Being a semiconductor with a bandgap of about 2 eV [14], WS 2 nanotubes are electrically insulating at low T and do not create a parallel conduction channel. We have verified that the nanotubes are insulating before depositing the superconducting material.Second, and more importantly, for the disordered superconductor we chose amorphous indium-oxide (a:InO). This choice was influenced by several of its properties. Since a:InO is known to form relatively uniform, superco...

Site-specific x-ray photoelectron spectroscopy together with density functional theory calculations based on the local density approximation have identified the chemical bonding, single-particle matrix element, and many-body effects in the x-ray photoelectron spectrum of corundum V 2 O 3 . Significant covalent bonding in both the upper and lower lobes of the photoelectron spectrum is found, despite the localized nature of the V 3d electrons that are responsible for the Mott behavior. We show that the approximate treatment of correlation dominates the discrepancy between theory and experiment in the near-Fermi-edge region and that many-body effects of the photoemission process can be modeled by Doniach-Šunjić ͓J. Phys. C 3, 285 ͑1970͔͒ asymmetric loss. Correlation effects govern the relative intensity and energy position of the higher level electron bands, and many-body effects dominate the "tail" region of both the upper and lower lobes of the photoemission spectrum.

Pollen dispersal is fundamental in a plant's reproductive ecology and as a result of fragmentation of the landscape, questions have been raised on how isolated plant populations can still exchange genetic information. A common mechanism for gene exchange is wind pollination (anemophily). A successful anemophilous species native to North America is ragweed (Ambrosia), a weed that is hard to eradicate after it takes root on crop fields and its pollen causes very strong allergenic effects (hay fever). Despite the extremely clumpy nature of ragweed pollen that should limit its long distance dispersal, ragweed has spread rapidly across the world during the last century while maintaining a high genetic diversity. One of the reasons for its success may be prolific pollen production as well as an efficient pollen clump release and breakup mechanism. Efficient pollen entrainment and dispersal into the atmosphere is highly influenced by flow field characteristics as pollen released into the atmosphere initially encounters flow structures created by the plant's morphology. Here, the flow field in the wake of a mature ragweed spike having multiple staminate flowers as well as pollen release was studied using Particle Image Velocimetry and high‐speed, inline holographic cinematography. The latter enabled to track the pollen in a 3D volume. The spike was set up in a wind tunnel and exposed to wind speeds ranging from 1 to 2 m/s. Results indicated that ragweed pollen was released in multiple sized clumps containing tens to several thousand single grains. Clumps were both “pulled apart” at the point of entrainment while exiting the flowers as well as broke up in smaller sized clumps in high shear rate flow regions not far from the spike. In addition, the largest clumps that did not travel far, deposited in the vicinity of the spike, breaking apart into many small clumps upon deposition. Based on our results, initial release and dispersal of ragweed pollen clumps is characterized by three concomitant mechanisms of clump breakup occurring at entrainment, in mid‐air and on deposition, which make it perfectly suited to disperse pollen over a wide range of spatial scales.

The very variable complex of plants until now ascribed to Cheilanthes hirta Swartz, together with some derived or allied species, is investigated. The type of the species as established by N. C. Anthony (1984), is accepted. Three new varieties are distinguished: Cheilanthes hirta Swartz var. brevipilosa W. N. Jacobsen, var. inferacampestris W. N.Jacobsen and var. nemorosa W. N. Jacobsen. One new form of Cheilanthes hirta var. brevipilosa W. N. Jacobsen is recognized: forma waterbergensis W. N. Jacobsen. Var.  laxa Kunze (1836) is given the new status of forma:  Chei­lanthes hirta var. brevipilosa W. N. Jacobsen forma laxa (Kunze) W. N. Jacobsen. Three allied species are discussed and included in the key to all taxa mentioned. Taxa are described and information given includes notes on distribution and ecology. Special attention is paid to spore morphology. Most taxa are illustrated by a habit photo, and all by line drawings and scanning electron micrographs (SEM) of the spores. Possible evolutionary conclusions, particularly on the nature of the spores and on frond dimensions in relation to geographical distribution and climate are discussed.

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