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RP Andres T Bein M Dorogi S Feng JI Henderson CP Kubiak W Mahoney RG Osifchin R Reifenberger 《Science (New York, N.Y.)》1996,272(5266):1323-1325
Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms). 相似文献
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The local effects of isolated magnetic adatoms on the electronic properties of the surface of a superconductor were studied with a low-temperature scanning tunneling microscope. Tunneling spectra obtained near magnetic adsorbates reveal the presence of excitations within the superconductor's energy gap that can be detected over a few atomic diameters around the impurity at the surface. These excitations are locally asymmetric with respect to tunneling of electrons and holes. A model calculation based on the Bogoliubov-de Gennes equations can be used to understand the details of the local tunneling spectra. 相似文献
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A sheep reared outdoors in Victoria was found to be heavily infested with a stored product mite, Sancassania berlesei (Acaridae), apparently subsequent to an earlier flystrike. Laboratory observation revealed the infestation to be self-sustaining. Shearing rapidly resolved the infestation but treatment with diazinon was ineffective. The infestation could be transferred to other sheep only in the presence of moisture; once established it caused an extensive skin lesion with considerable fluid loss, apparently contributing to the death of one animal. This lesion was extremely attractive to blowflies. Animals infested with mites showed few signs of irritation. 相似文献
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Metronidazole, an antibiotic with specific activity against anaerobic bacteria, was assessed as a treatment for bovine pyometra. A preliminary experiment with metronidazole-neomycin was followed by an experiment in which metronidazole-ampicillin was compared with povidone iodine. Each treatment was given as a single intrauterine infusion. The success of therapy was judged by clinical examination, bacteriological examination before and after treatment and, in the second experiment, by post treatment reproductive performance. Before treatment 45 of the 84 cows in both experiments were infected with a mixture of anaerobic and aerobic bacteria, 23 cows were infected with aerobes alone and significant bacteria were not isolated from 16 cows. Complete bacteriological and clinical cures were achieved in 23 of 32 cows treated with metronidazole-neomycin, 15 of 32 cows treated with metronidazole-ampicillin and 1 of 20 cows treated with iodine. When only those cows with mixed anaerobe/aerobe infections were considered, complete cures occurred in 12 of 17 cows treated with metronidazole-neomycin, and 11 of 16 cows treated with metronidazole-ampicillin, but none of the 12 cows treated with iodine. Twenty-two of 29 cows treated with metronidazole-ampicillin conceived after treatment (mean 51.4 days), while 9 of 18 cows treated with iodine conceived (mean 58.7 days). Statistically, metronidazole-ampicillin treatment produced significantly better clinical and bacteriological cure rates than iodine treatment (P less than 0.05), but the differences in reproductive parameters were not significant. 相似文献
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