5,428 research outputs found

    Effective constructions in plethysms and Weintraub's conjecture

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    We give a short proof of Weintraub's conjecture by constructing explicit highest weight vectors in the symmetric power of an even exterior power

    Distribution of phytoplasma in grapevines in the Golan Heights, Israel, and development of a new universal primer

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    Our survey, made in 1999 and 2000, sampled 4 of the most prevalent grapevine cultivars in northern, central and southern regions of the Golan Heights. There were significant differences in the levels of phytoplasma infection between different sub-regions of the Golan Heights; highest levels were found in the south, followed by the center, and the lowest levels in the north. Stolbur was found to be the predominant phytoplasma (~70 %), although aster yellow (~11 %), western-X (~5 %) and mixtures of two phytoplasmas (13 % of all infections, 90 % of which involved Stol and AY) were also found. Prior research on phytoplasmas of grapevines in Israel involved the use of two sets of universal primers. Primers were developed specifically for phytoplasmas occurring in Israel in which there were homologies of 90,85 and 78 % for Stol,AY and W-X phytoplasmas, respectively.

    Detection of Molecular Hydrogen Orbiting a "Naked" T Tauri Star

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    Astronomers have established that for a few million years newborn stars possess disks of orbiting gas and dust. Such disks, which are likely sites of planet formation, appear to disappear once these stars reach ages of 5-10 times 10^6 yr; yet, >= 10^7 yr is thought necessary for giant planet formation. If disks dissipate in less time than is needed for giant planet formation, such planets may be rare and those known around nearby stars would be anomalies. Herein, we report the discovery of H_2 gas orbiting a weak-lined T Tauri star heretofore presumed nearly devoid of circumstellar material. We estimate that a significant amount of H_2 persists in the gas phase, but only a tiny fraction of this mass emits in the near-infrared. We propose that this star possesses an evolved disk that has escaped detection thus far because much of the dust has coagulated into planetesimals. This discovery suggests that the theory that disks are largely absent around such stars should be reconsidered. The widespread presence of such disks would indicate that planetesimals can form quickly and giant planet formation can proceed to completion before the gas in circumstellar disks disperses.Comment: latex 12 pages, including 1 figur

    The Sea Ice Topography of M'Clure Strait in Winter and Summer of 1960 from Submarine Profiles

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    Submarine profiles of the ice underside in M'Clure Strait were obtained by USS Sargo in February 1960 and by USS Seadragon in August 1960. They gave the first quantitative measurements of the ice draft distribution in the strait and in the nearby Beaufort Sea shelf zone, as well as providing a seasonal comparison of ice conditions within a single year. Analysis of the profiles reveals a region of very high mean ice draft (7.8 m) and heavy ridging off the southwest tip of Prince Patrick Island in winter. Within M'Clure Strait itself the mean ice draft lay in the 4-5 m range and the draft distribution showed that the ice was mainly first-year, as opposed to the mixture of first-and multi-year ice that exists out in the Beaufort Sea. This suggests a local origin for the ice in the strait. Pressure ridges were much more frequent in summer than in winter, as were polynyas. Both the pressure ridge draft distribution (in summer) and the ice draft distribution at great depths (in summer and winter) fitted a negative exponential distribution, in common with other ice profiles which have been analysed.Key words: sea ice, pressure ridges, sonar, M'Clure Strait, Viscount Melville SoundMots clés: glace de la mer, crêtes de pression, sonar, le détroit M'Clure, le détroit Viscount Melvill

    Interventional cardiology : Cost-effectiveness of PCI guided by fractional flow reserve

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    Coronary revascularization strategies have been evaluated in numerous clinical trials. As coronary revascularization has become more common, concerns over financial costs have increased
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