230 research outputs found
Average velocities of some ocean currents as deduced from the recovery of plastic drift cards
Twenty-four drift cards, released in 1964 through 1966 in the vicinity of Cape Town and at various locations in the Atlantic Ocean, have been recovered on the coasts of: North and South America, three islands in the South Atlantic, England, France, Nigeria, and Australia. The travel times indicated by 19 of these cards have been used to estimate the mean velocities of the presumed current systems involved. The rate of card recovery and the long distances traveled by the cards have proved conclusively that the solid polythene drift card is durable
Electronic transport in polycrystalline graphene
Most materials in available macroscopic quantities are polycrystalline.
Graphene, a recently discovered two-dimensional form of carbon with strong
potential for replacing silicon in future electronics, is no exception. There
is growing evidence of the polycrystalline nature of graphene samples obtained
using various techniques. Grain boundaries, intrinsic topological defects of
polycrystalline materials, are expected to dramatically alter the electronic
transport in graphene. Here, we develop a theory of charge carrier transmission
through grain boundaries composed of a periodic array of dislocations in
graphene based on the momentum conservation principle. Depending on the grain
boundary structure we find two distinct transport behaviours - either high
transparency, or perfect reflection of charge carriers over remarkably large
energy ranges. First-principles quantum transport calculations are used to
verify and further investigate this striking behaviour. Our study sheds light
on the transport properties of large-area graphene samples. Furthermore,
purposeful engineering of periodic grain boundaries with tunable transport gaps
would allow for controlling charge currents without the need of introducing
bulk band gaps in otherwise semimetallic graphene. The proposed approach can be
regarded as a means towards building practical graphene electronics.Comment: accepted in Nature Material
Klein tunneling in graphene: optics with massless electrons
This article provides a pedagogical review on Klein tunneling in graphene,
i.e. the peculiar tunneling properties of two-dimensional massless Dirac
electrons. We consider two simple situations in detail: a massless Dirac
electron incident either on a potential step or on a potential barrier and use
elementary quantum wave mechanics to obtain the transmission probability. We
emphasize the connection to related phenomena in optics, such as the
Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot
resonances, negative refraction index materials (the so called meta-materials),
etc. We also stress that Klein tunneling is not a genuine quantum tunneling
effect as it does not necessarily involve passing through a classically
forbidden region via evanescent waves. A crucial role in Klein tunneling is
played by the conservation of (sublattice) pseudo-spin, which is discussed in
detail. A major consequence is the absence of backscattering at normal
incidence, of which we give a new shorten proof. The current experimental
status is also thoroughly reviewed. The appendix contains the discussion of a
one-dimensional toy model that clearly illustrates the difference in Klein
tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added,
several figures slightly modifie
Chronic nodular prurigo: clinical profile and burden. A European cross-sectional study
Background: Chronic nodular prurigo (CNPG) is a condition characterized by chronic itch, a prolonged scratching behaviour and the presence of pruriginous nodules. A comprehensive understanding of this condition, especially regarding its clinical characteristics and impact on quality of life is still lacking. Objectives: Aim of this pan-European multicentre cross-sectional study was to establish the clinical profile of CNPG, including its associated burden. Methods: Fifteen centres from 12 European countries recruited CNPG patients presenting at the centre or using the centres' own databases. Patients were asked to complete a questionnaire in paper or electronic format. Demography, current co-morbidities, underlying disease, itch intensity, additional sensory symptoms, quality of life, highest burden and emotional experience of itch were assessed. Results: A total of 509 patients (210 male, median age: 64 years [52; 72]) were enrolled. Of these, 406 reported itch and CNPG lesions in the previous 7 days and qualified to complete the whole questionnaire. We recorded moderate to severe worst itch intensity scores in the previous 24 h. Scores were higher in patients with lower educational levels and those coming from Eastern or Southern Europe. Most patients experience itch often or always (71%) and report that their everyday life is negatively affected (53%). Itch intensity was considered to be the most burdensome aspect of the disease by 49% of the patients, followed by the visibility of skin lesions (21%) and bleeding of lesions (21%). The majority of patients was unaware of an underlying condition contributing to CNPG (64%), while psychiatric diseases were the conditions most often mentioned in association with CNPG (19%). Conclusions: This multicentre cross-sectional study shows that itch is the dominant symptom in CNPG and reveals that the profile of the disease is similar throughout Europe
An evaluation of metal removal during wastewater treatment: The potential to achieve more stringent final effluent standards
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2011 Taylor & Francis.Metals are of particular importance in relation to water quality, and concern regarding the impact of these contaminants on biodiversity is being encapsulated within the latest water-related legislation such as the Water Framework Directive in Europe and criteria revisions to the Clean Water Act in the United States. This review undertakes an evaluation of the potential of 2-stage wastewater treatment consisting of primary sedimentation and biological treatment in the form of activated sludge processes, to meet more stringent discharge consents that are likely to be introduced as a consequence. The legislation, sources of metals, and mechanisms responsible for their removal are discussed, to elucidate possible pathways by which the performance of conventional processes may be optimized or enhanced. Improvements in effluent quality, achievable by reducing concentrations of suspended solids or biochemical oxygen demand, may also reduce metal concentrations although meeting possible requirements for the removal of copper my be challenging
A microbial supply chain for production of the anti-cancer drug vinblastine
International audienceAbstract Monoterpene indole alkaloids (MIAs) are a diverse family of complex plant secondary metabolites with many medicinal properties, including the essential anti-cancer therapeutics vinblastine and vincristine 1 . As MIAs are difficult to chemically synthesize, the worldâs supply chain for vinblastine relies on low-yielding extraction and purification of the precursors vindoline and catharanthine from the plant Catharanthus roseus , which is then followed by simple in vitro chemical coupling and reduction to form vinblastine at an industrial scale 2,3 . Here, we demonstrate the de novo microbial biosynthesis of vindoline and catharanthine using a highly engineered yeast, and in vitro chemical coupling to vinblastine. The study showcases a very long biosynthetic pathway refactored into a microbial cell factory, including 30 enzymatic steps beyond the yeast native metabolites geranyl pyrophosphate and tryptophan to catharanthine and vindoline. In total, 56 genetic edits were performed, including expression of 34 heterologous genes from plants, as well as deletions, knock-downs and overexpression of ten yeast genes to improve precursor supplies towards de novo production of catharanthine and vindoline, from which semisynthesis to vinblastine occurs. As the vinblastine pathway is one of the longest MIA biosynthetic pathways, this study positions yeast as a scalable platform to produce more than 3,000 natural MIAs and a virtually infinite number of new-to-nature analogues
Magnetodielectric effect of Graphene-PVA Nanocomposites
Graphene-Polyvinyl alcohol (PVA) nanocomposite films with thickness were synthesized by solidification of PVA in a solution with dispersed
graphene nanosheets. Electrical conductivity data were explained as arising due
to hopping of carriers between localized states formed at the graphene-PVA
interface. Dielectric permittivity data as a function of frequency indicated
the occurrence of Debye-type relaxation mechanism. The nanocomposites showed a
magnetodielectric effect with the dielectric constant changing by 1.8% as the
magnetic field was increased to 1 Tesla. The effect was explained as arising
due to Maxwell-Wagner polarization as applied to an inhomogeneous
two-dimensional,two-component composite model. This type of nanocomposite may
be suitable for applications involving nanogenerators.Comment: 13 pages, 11 figure
Reward and punishment in climate change dilemmas
Mitigating climate change effects involves strategic decisions by individuals that may choose to limit their emissions at a cost. Everyone shares the ensuing benefits and thereby individuals can free ride on the effort of others, which may lead to the tragedy of the commons. For this reason, climate action can be conveniently formulated in terms of Public Goods Dilemmas often assuming that a minimum collective effort is required to ensure any benefit, and that decision-making may be contingent on the risk associated with future losses. Here we investigate the impact of reward and punishment in this type of collective endeavors - coined as collective-risk dilemmas - by means of a dynamic, evolutionary approach. We show that rewards (positive incentives) are essential to initiate cooperation, mostly when the perception of risk is low. On the other hand, we find that sanctions (negative incentives) are instrumental to maintain cooperation. Altogether, our results are gratifying, given the a-priori limitations of effectively implementing sanctions in international agreements. Finally, we show that whenever collective action is most challenging to succeed, the best results are obtained when both rewards and sanctions are synergistically combined into a single policy.This research was supported by Fundacao para a Ciencia e Tecnologia (FCT) through grants PTDC/EEISII/5081/2014 and PTDC/MAT/STA/3358/2014 and by multiannual funding of INESC-ID and CBMA (under the projects UID/CEC/50021/2019 and UID/BIA/04050/2013). F.P.S. acknowledges support from the James S. McDonnell Foundation 21st Century Science Initiative in Understanding Dynamic and Multi-scale Systems Postdoctoral Fellowship Award. All authors declare no competing financial or non-financial interests in relation to the work described
Impact of different privacy conditions and incentives on survey response rate, participant representativeness, and disclosure of sensitive information: a randomized controlled trial
Maternal serum but not breast milk IL-5, IL-6, and IL-13 immune markers are associated with scratching among infants
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