24,058 research outputs found
Morphology and flexibility of graphene and few-layer graphene on various substrates
We report on detailed microscopy studies of graphene and few-layer-graphene
produced by mechanical exfoliation on various semi-conducting substrates. We
demonstrate the possibility to prepare and analyze graphene on (001)-GaAs,
manganese p-doped (001)-GaAs and InGaAs substrates. The morphology of graphene
on these substrates was investigated by scanning electron and atomic force
microscopy and compared to layers on silicon oxide. It was found that graphene
sheets strongly follow the texture of the sustaining substrates independent on
doping, polarity or roughness. Furthermore resist residues exist on top of
graphene after a lithographic step. The obtained results provide the
opportunity to research the graphene-substrate interactions
Testing mechanisms of compensatory fitness of dioecy in a cosexual world
Questions: All else being equal, populations of dioecious species with a 50:50 sex ratio have only half the effective reproductive population size of bisexual species of equal abundance. Consequently, there is a need to explain how dioecious and bisexual species coexist. Increased mean individual seed mass, fecundity, and population density have all been proposed as attributes of unisexual individuals or populations that may contribute to the persistence or resilience of dioecious species. To date, no studies have compared sympatric dioecious and cosexual species with respect to all three components of fitness. In this study, we sought evidence for these compensatory advantages (higher seed mass, greater seed production per unit basal area, and higher population density) in dioecious species. Location: Five 20–25 ha forest dynamic plots spanning a latitudinal gradient in China, including two temperate, two subtropical, and one tropical forest. Methods: We used a phylogenetically corrected generalized linear modelling approach to assess the phylogenetic dependence and joint evolution of sexual system, seed mass and production, and ecological abundances among 48–333 species and 32,568–136,237 individuals per forest. Results: Across all five forests, we detected no consistent advantage for dioecious relative to sympatric cosexual species with respect to mean individual seed mass, seed production or the density of stems in any size class. Conclusions: Our study suggests that seed traits may provide compensatory mechanisms in some forests, but most often the coexistence of sexual systems cannot be explained by advantages of dioecy related to seed quality and demographic parameters. Future investigations of the factors that promote coexistence may increase our understanding by expanding the search to include attributes such as lifespan and tolerance or resistance to herbivores
General covariant geometric momentum, gauge potential and a Dirac fermion on a two-dimensional sphere
For a particle that is constrained on an ()-dimensional ()
curved surface, the Cartesian components of its momentum in -dimensional
flat space is believed to offer a proper form of momentum for the particle on
the surface, which is called the geometric momentum as it depends on the mean
curvature. Once the momentum is made general covariance, the spin connection
part can be interpreted as a gauge potential. The present study consists in two
parts, the first is a discussion of the general framework for the general
covariant geometric momentum. The second is devoted to a study of a Dirac
fermion on a two-dimensional sphere and we show that there is the generalized
total angular momentum whose three cartesian components form the
algebra, obtained before by consideration of dynamics of the particle, and we
demonstrate that there is no curvature-induced geometric potential for the
fermion.Comment: 8 pages, no figure. Presentation improve
Action Recognition Based on Joint Trajectory Maps Using Convolutional Neural Networks
Recently, Convolutional Neural Networks (ConvNets) have shown promising
performances in many computer vision tasks, especially image-based recognition.
How to effectively use ConvNets for video-based recognition is still an open
problem. In this paper, we propose a compact, effective yet simple method to
encode spatio-temporal information carried in skeleton sequences into
multiple images, referred to as Joint Trajectory Maps (JTM), and ConvNets
are adopted to exploit the discriminative features for real-time human action
recognition. The proposed method has been evaluated on three public benchmarks,
i.e., MSRC-12 Kinect gesture dataset (MSRC-12), G3D dataset and UTD multimodal
human action dataset (UTD-MHAD) and achieved the state-of-the-art results
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