Development of a universal stress sensor for graphene and carbon fibres

Carbon fibres are a significant volume fraction of modern structural airframes. Embedded into polymer matrices, they provide significant strength and stiffness gains by unit weight compared with competing structural materials. Here we use the Raman G peak to assess the response of carbon fibres to the application of strain, with reference to the response of graphene itself. Our data highlight the predominance of the in-plane graphene properties in all graphitic structures examined. A universal master plot relating the G peak strain sensitivity to tensile modulus of all types of carbon fibres, as well as graphene, is presented. We derive a universal value of - average - phonon shift rate with axial stress of around -5ω0 -1 (cm -1 Mpa-1), where ω0 is the G peak position at zero stress for both graphene and carbon fibre with annular morphology. The use of this for stress measurements in a variety of applications is discussed. © 2011 Macmillan Publishers Limited. All rights reserved.

Discrete dislocation plasticity analysis of size effects in single crystals

The effect of size and slip system configuration on the tensile stress-strain response of micron-sized planar crystals as obtained from discrete dislocation plasticity simulations is presented. The crystals are oriented for either single or symmetric double slip. With the rotation of the tensile axis unconstrained, there is a strong size dependence, with the flow strength increasing with decreasing specimen size. Below a certain specimen size, the flow strength of the crystals is set by the nucleation strength of the initially present Frank-Read sources. The main features of the size dependence are the same for both the single and symmetric double slip configurations.

固氮蓝藻培养和应用的结果与展望

<正> 固氮蓝藻是一类低等原核植物。它能进行固氮作用,固定空气中分子态氮成为氮素化合物;又能进行光合作用,将二氧化碳变为碳素化合物并放出氧气,为自身的固氮提供能源和还原剂。由于具有以上功能,它们适应性很强往往是贫瘠土壤的先驱植物,因此,很早就引起了人们的重视。早在1889年Frank首先发现生长着蓝藻的土壤在光照下,氮化合物的含量有所增加;1901年Beijerinck发现在仅有一点土壤的缺氮水中的小链鱼腥藻

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al0.3Ga0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well. (c) 2004 Elsevier B.V. All rights reserved.

Molecular evidence for double maternal origins of the diploid hybrid Hippophae goniocarpa (Elaeagnaceae)

Homoploid hybrid plant species are rare, and the mechanisms of their speciation are largely unknown, especially for homoploid hybrid tree species. Two contrasting hypotheses have been proposed to explain the origin of Hippophae goniocarpa: (1) it is a diploid hybrid originating from H. rhamnoides ssp. sinensis x H. neurocarpa ssp. neurocarpa, and (2) it originated via marginal differentiation from H. rhamnoides ssp. sinensis. Regardless of which of these hypotheses is true (if either), previous studies have suggested that H. rhamnoides ssp. sinensis is the only maternal donor for this hybrid species. In this study, we aim to elucidate the maternal composition of H. goniocarpa and to test the two hypotheses. For this purpose, we sequenced the maternal chloroplast DNA trnL-F region of 75 individuals representing H. goniocarpa, H. rhamnoides ssp. sinensis, and H. neurocarpa ssp. neurocarpa in two co-occurring sites of the taxa. Seven haplotypes were identified from three taxonomic units, and their phylogenetic relationships were further constructed by means of maximum parsimony, maximum likelihood, and network analyses. These seven haplotypes clustered into two distinct, highly divergent lineages. Two haplotypes from one lineage were found in H. rhamnoides ssp. sinensis, and five (representing the other lineage) in H. neurocarpa ssp. neurocarpa. Hippophae goniocarpa shared four common haplotypes from both lineages, but the haplotypes detected from the two populations differed to some extent, and in each case were identical to local haplotypes of the putative parental species. Thus, both H. rhamnoides ssp. sinensis and H. neurocarpa ssp. neurocarpa appear to have together contributed to the maternal establishment of H. goniocarpa. These results clearly demonstrate that the marginal origin hypothesis should be rejected, and support the hybrid origin hypothesis. Hippophae goniocarpa exhibits a sympatric distribution with its two parent species, without occupying new niches or displaying complete ecological isolation. However, this species has effectively developed reproductive isolation from its sympatric parent species. Our preliminary results suggest that H. goniocarpa may provide a useful model system for studying diploid hybrid speciation in trees. (c) 2008 The Linnean Society of London.

Identificação dos principais fungos das sementes de trigo.

Procedimento para identificação dos fungos das sementes de trigo; Descrição diagnostica dos principais fungos das sementes de trigo; Sclerotium Tode; Rhizoctonia DC; Chaetomium Kunze; Pleospora Rabenh; Sporobolomyces Kluy. & Niel; Rhodotorula Harrison; Phoma Sacc.; Septoria tritici Rob; Stagonospora nodorum (Berk.) Cas. & Germ.; Stagonospora avenae (Frank) Bisset f. sp. triticae; Colletotrichum graminicola (Ces.) Wilson; Fusarium tricinctum (Corda) Sacc; Fusarium moniliforme Sheldon; Fusarium avenaceum (Fr.) Sacc; Fusarium acuminatum Ell. & Kellerm; Fusarium equiseti (Corda) Sacc.; Fusarium graminearum Schw.; Mucor Micheli; Rhizopus Ehrenb; Aspergillus Link.; Penicillium Link.; Alternaria Nees; Epicoccum Link; Cladosporium Link; Nigrospora Zimm; Curvularia Boedijn; Drechslera tritici-repentis (Died.) Drech; Bipolaris sorokiniana (Sacc. in Sorok.) Shoem; Chave sistemática dos principais fungos de sementes de trigo; Ilustrações dos principais fungos encontrados em sementes de trigo.

Seleção massal na população de feijoeiro comum (Phaseolus vulgaris L.)"Carioca Pitoco" em Rio Branco, Acre.

O sistema de cultivo do feijoeiro comum, no Estado do Acre, é típico de pequenos agricultores, o uso de insumos e máquinas é mínimo e toda mão-de-obra do processo produtivo é familiar. As áreas de cultivo dificilmente ultrapassam 5 ha, a produtividade é baixa e o excedente da produção é comercializado exclusivamente no mercado estadual. Esta cultura é a principal fonte de proteínas disponível por todo o ano nas pequenas propriedades, demonstrando importância nutricional e social para as famílias de baixa renda. As variedades de maior preferência dos agricultores e consumidores locais são o feijão Carioca Comum e o Rosinha de porte determinado. Entretanto, os materiais utilizados têm sido severamente prejudicados pela incidência da "mela" (Thanatephorus cucumeris (Frank) Donk). Estudos têm sido realizados no sentido de controlar ou minimizar esta doença, no entanto, até o momento não foi obtido um controle efetivo. A adoção de práticas culturais, como a cobertura do solo com restos culturais, diminui bastante os prejuízos, entretanto, esta prática por si só, não resolve o problema. A Embrapa Acre, desde a sua implantação, vem desenvolvendo trabalhos de introdução e avaliação de genótipos de feijão, visando a seleção e recomendação de materiais com características que superem os problemas da baixa produtividade e resistência à meia na região, bem como atender às exigências do mercado local, principalmente no que se refere ao tipo de grão. A introdução de genótipos, embora seja de fundamental importância para programas de melhoramento, nem sempre proporciona resultados imediatos e de interesse para a região, tendo em vista, principalmente, problemas de adaptação às novas condições edafoclimáticas.