2,061 research outputs found
Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study
The results of micro-Raman scattering measurements performed on three
different ``graphitic'' materials: micro-structured disks of highly oriented
pyrolytic graphite, graphene multi-layers thermally decomposed from carbon
terminated surface of 4H-SiC and an exfoliated graphene monolayer are
presented. Despite its multi-layer character, most parts of the surface of the
graphitized SiC substrates shows a single-component, Lorentzian shape, double
resonance Raman feature in striking similarity to the case of a single graphene
monolayer. Our observation suggests a very weak electronic coupling between
graphitic layers on the SiC surface, which therefore can be considered to be
graphene multi-layers with a simple (Dirac-like) band structure.Comment: 4 pages, 3 Figures Structure of the paper strongly modified, small
changes in Fig 2 and 3. Same interpretation and same result
Participatory plant breeding: a way to arrive at better-adapted onion varieties
The search for varieties that are better adapted to organic farming is a current topic in the organic sector. Breeding programmes specific for organic agriculture should solve this problem. Collaborating with organic farmers in such programmes, particularly in the selection process, can potentially result in varieties better adapted to their needs. Here, we assume that organic farmers' perceptive of plant health is broader than that of conventional breeders. Two organic onion farmers and one conventional onion breeder were monitored in their selection activities in 2004 and 2005 in order to verify whether and in which way this broader view on plant health contributes to improvement of organic varieties.
They made selections by positive mass selection in three segregating populations under organic conditions. The monitoring showed that the organic farmers selected in the field for earliness and downy mildew and after storage for bulb characteristics. The conventional breeder selected only after storage. Farmers and breeder applied identical selection directions for bulb traits as a round shape, better hardness and skin firmness. This resulted in smaller bulbs in the breeders’ populations, while the bulbs in the farmer populations were bigger than in the original population. In 2006 and 2007 the new onion populations will be compared with each other and the original populations to determine the selection response
Plasmon assisted transport through disordered array of quantum wires
Phononless plasmon assisted thermally activated transport through a long
disordered array of finite length quantum wires is investigated analytically.
Generically strong electron plasmon interaction in quantum wires results in a
qualitative change of the temperature dependence of thermally activated
resistance in comparison to phonon assisted transport. At high temperatures,
the thermally activated resistance is determined by the Luttinger liquid
interaction parameter of the wires.Comment: 7 pages, 1 figure, final version as publishe
Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial Graphene from Polarization Dependent Coherently Controlled Photocurrent Generation
Most experimental studies to date of multilayer epitaxial graphene on C-face
SiC have indicated that the electronic states of different layers are decoupled
as a consequence of rotational stacking. We have measured the third order
nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer
electronic coupling, by studying THz emission from coherently controlled
photocurrents as a function of the optical pump and THz beam polarizations. We
find that the polarization dependence of the coherently controlled THz emission
expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not
observed. We hypothesize that the observed angular dependence arises from weak
coupling between the layers; a model calculation of the angular dependence
treating the multilayer structure as a stack of independent bilayers with
variable interlayer coupling qualitatively reproduces the polarization
dependence, providing evidence for coupling.Comment: submitted to Nano Letter
Microscopic correlation between chemical and electronic states in epitaxial graphene on SiC(000-1)
We present energy filtered electron emission spectromicroscopy with spatial
and wave-vector resolution on few layer epitaxial graphene on SiC$(000-1) grown
by furnace annealing. Low energy electron microscopy shows that more than 80%
of the sample is covered by 2-3 graphene layers. C1s spectromicroscopy provides
an independent measurement of the graphene thickness distribution map. The work
function, measured by photoelectron emission microscopy (PEEM), varies across
the surface from 4.34 to 4.50eV according to both the graphene thickness and
the graphene-SiC interface chemical state. At least two SiC surface chemical
states (i.e., two different SiC surface structures) are present at the
graphene/SiC interface. Charge transfer occurs at each graphene/SiC interface.
K-space PEEM gives 3D maps of the k_|| pi - pi* band dispersion in micron scale
regions show that the Dirac point shifts as a function of graphene thickness.
Novel Bragg diffraction of the Dirac cones via the superlattice formed by the
commensurately rotated graphene sheets is observed. The experiments underline
the importance of lateral and spectroscopic resolution on the scale of future
electronic devices in order to precisely characterize the transport properties
and band alignments
Interfacial kinetics in a model emulsion polymerisation system using microelectrochemical measurements at expanding droplets (MEMED) and time lapse microscopy
Physicochemical processes that take place at the oil-water interface of an epoxy-amine emulsion polymerisation system influence the properties and structural morphology of the polymeric microparticles formed. Investigating these processes, such as the transport of monomers across the liquid/liquid interface brings new understanding which can be used to tune polymeric morphology. Two different approaches are used to provide new insights on these processes. Microelectrochemical measurements at expanding droplets (MEMED) are used to measure the transfer of amine from an organic phase comprised of epoxide and amine into an aqueous receptor phase. The rate of amine transfer across the liquid/liquid interface is characterised using MEMED and finite element method modelling and kinetic values are reported. Time lapse microscopy of epoxide droplets held in deionised water or an aqueous amine solution heated to different temperatures is further used to characterise epoxide dissolution into the aqueous phase. Mass-transport of epoxide into the aqueous phase is shown to be temperature-dependent. Epoxide homopolymerisation at the droplet-water interface is found to influence the rate of epoxide droplet dissolution. The rate of the epoxy- amine cure reaction is shown to be faster than the rate of the epoxide homopolymerisation reaction
Highly-ordered graphene for two dimensional electronics
With expanding interest in graphene-based electronics, it is crucial that
high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001)
Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce
epitaxial graphene sheets on a semiconductor. In this paper we show that
graphene grown from the SiC (C-terminated) surface are of higher
quality than those previously grown on SiC(0001). Graphene grown on the C-face
can have structural domain sizes more than three times larger than those grown
on the Si-face while at the same time reducing SiC substrate disorder from
sublimation by an order of magnitude.Comment: Submitted to Appl. Phys. Let
Rational use of <sup>18</sup>F-FDG PET/CT in patients with advanced cutaneous melanoma:A systematic review
18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is increasingly used in patients with advanced melanoma. Immune checkpoint inhibitors and BRAF/MEK-targeted therapy have transformed the therapeutic landscape of metastatic melanoma. Consequently, a need for markers predicting (early) response to treatment and for monitoring treatment (toxicity) has arisen. This systematic review appraises the current literature evidence for rational use of 18F-FDG PET/CT scans in staging, clinical decision-making, treatment monitoring and follow-up in advanced melanoma. 18F-FDG PET/CT has high overall accuracy for detection of distant metastases and is, combined with cerebral MRI, the preferred imaging strategy for staging metastatic melanoma. In contrast, strong evidence supporting the standard use of 18F-FDG PET/CT for predicting and monitoring therapy response and toxicity is currently lacking. Essential for determining the position of 18F-FDG PET/CT during treatment course in advanced melanoma are well-designed studies with standardized scanning protocols, incorporation of clinical parameters and comparison with contrast-enhanced CT alone
Ordered Self-Assembly Mechanism of a Spherical Oncoprotein Oligomer Triggered by Zinc Removal and Stabilized by an Intrinsically Disordered Domain
BACKGROUND: Self-assembly is a common theme in proteins of unrelated sequences or functions. The human papillomavirus E7 oncoprotein is an extended dimer with an intrinsically disordered domain, that can form large spherical oligomers. These are the major species in the cytosol of HPV transformed and cancerous cells. E7 binds to a large number of targets, some of which lead to cell transformation. Thus, the assembly process not only is of biological relevance, but represents a model system to investigate a widely distributed mechanism. METHODOLOGY/PRINCIPAL FINDINGS: Using various techniques, we monitored changes in secondary, tertiary and quaternary structure in a time course manner. By applying a robust kinetic model developed by Zlotnik, we determined the slow formation of a monomeric "Z-nucleus" after zinc removal, followed by an elongation phase consisting of sequential second-order events whereby one monomer is added at a time. This elongation process takes place at a strikingly slow overall average rate of one monomer added every 28 seconds at 20 µM protein concentration, strongly suggesting either a rearrangement of the growing complex after binding of each monomer or the existence of a "conformation editing" mechanism through which the monomer binds and releases until the appropriate conformation is adopted. The oligomerization determinant lies within its small 5 kDa C-terminal globular domain and, remarkably, the E7 N-terminal intrinsically disordered domain stabilizes the oligomer, preventing an insoluble amyloid route. CONCLUSION: We described a controlled ordered mechanism with features in common with soluble amyloid precursors, chaperones, and other spherical oligomers, thus sharing determining factors for symmetry, size and shape. In addition, such a controlled and discrete polymerization reaction provides a valuable tool for nanotechnological applications. Finally, its increased immunogenicity related to its supramolecular structure is the basis for the development of a promising therapeutic vaccine candidate for treating HPV cancerous lesions
Symmetry breaking in commensurate graphene rotational stacking; a comparison of theory and experiment
Graphene stacked in a Bernal configuration (60 degrees relative rotations
between sheets) differs electronically from isolated graphene due to the broken
symmetry introduced by interlayer bonds forming between only one of the two
graphene unit cell atoms. A variety of experiments have shown that non-Bernal
rotations restore this broken symmetry; consequently, these stacking varieties
have been the subject of intensive theoretical interest. Most theories predict
substantial changes in the band structure ranging from the development of a Van
Hove singularity and an angle dependent electron localization that causes the
Fermi velocity to go to zero as the relative rotation angle between sheets goes
to zero. In this work we show by direct measurement that non-Bernal rotations
preserve the graphene symmetry with only a small perturbation due to weak
effective interlayer coupling. We detect neither a Van Hove singularity nor any
significant change in the Fermi velocity. These results suggest significant
problems in our current theoretical understanding of the origins of the band
structure of this material.Comment: 7 pages, 6 figures, submitted to PR
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