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41.
Hoffman JE McElroy K Lee DH Lang KM Eisaki H Uchida S Davis JC 《Science (New York, N.Y.)》2002,297(5584):1148-1151
Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials. 相似文献
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Welfare dependence within and across generations 总被引:2,自引:0,他引:2
A central question in the debate about the effects of welfare programs is whether their intended positive results--providing needed resources to recipients and their children--outweigh any unintended negative results--for example, the breaking up of families, reduction in work effort, or the fostering of a welfare "culture" that is passed on from parent to child. Recent research shows that although work effort is affected adversely by the generosity of welfare programs, effects on family structure appear quite weak, most welfare experiences are relatively short, and the majority of women who grew up in homes heavily dependent on welfare do not rely on those programs when they are young adults. 相似文献
45.
Experimentally damaged leaves of Cucurbita moschata mobilize substances to the damaged region within 40 minutes. These substances stimulate feeding by Acalymma vittata (Coleoptera: Chrysomelidae) and inhibit feeding by Epilacha tredecimnotata (Coleoptera: Coccinelidae). Under natural conditions, Epilachna cuts a circular trench in the leaf before feeding on the encircled leaf material, thus preventing mobilization of the deterrent substances to the feeding area. 相似文献
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Naturally acquired antibodies to sporozoites do not prevent malaria: vaccine development implications 总被引:12,自引:0,他引:12
S L Hoffman C N Oster C V Plowe G R Woollett J C Beier J D Chulay R A Wirtz M R Hollingdale M Mugambi 《Science (New York, N.Y.)》1987,237(4815):639-642
The first human vaccines against the malaria parasite have been designed to elicit antibodies to the circumsporozoite protein of Plasmodium falciparum. However, it is not known whether any level of naturally acquired antibodies to the circumsporozoite protein can predict resistance to Plasmodium falciparum malaria. In this study, 83 adults in a malaria-endemic region of Kenya were tested for circumsporozoite antibodies and then treated for malaria. They were monitored for the development of new malaria infections for 98 days. Antibody levels, as determined by four assays in vitro, were indistinguishable between the 60 individuals who did and the 23 who did not develop parasitemia during follow-up, and there was no apparent relation between day of onset of parasitemia and level of antibodies to circumsporozoite protein. Unless immunization with sporozoite vaccines induces antibodies that are quantitatively or qualitatively superior to the circumsporozoite antibodies in these adults, it is unlikely that such antibodies will prevent infection in areas with as intense malaria transmission as western Kenya. 相似文献
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Genetic restriction of energy conservation in Schizophyllum 总被引:2,自引:0,他引:2
A genetically determined malfunction of energy conservation reduces assimilation of substrate to half or less its normal level while leaving oxidative processes apparently unchanged. This metabolic defect, which differs in many ways from any previously described, is related to the function of the B incompatibility factor and occurs both in the common A heterokaryon (A = B not equal)-in which two compatible, wild B factors interact-and in mutant-B homokaryons. 相似文献
50.
Outeiro TF Kontopoulos E Altmann SM Kufareva I Strathearn KE Amore AM Volk CB Maxwell MM Rochet JC McLean PJ Young AB Abagyan R Feany MB Hyman BT Kazantsev AG 《Science (New York, N.Y.)》2007,317(5837):516-519
The sirtuins are members of the histone deacetylase family of proteins that participate in a variety of cellular functions and play a role in aging. We identified a potent inhibitor of sirtuin 2 (SIRT2) and found that inhibition of SIRT2 rescued alpha-synuclein toxicity and modified inclusion morphology in a cellular model of Parkinson's disease. Genetic inhibition of SIRT2 via small interfering RNA similarly rescued alpha-synuclein toxicity. Furthermore, the inhibitors protected against dopaminergic cell death both in vitro and in a Drosophila model of Parkinson's disease. The results suggest a link between neurodegeneration and aging. 相似文献