Interfaces within graphene nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins

A search for neutrino-antineutrino mass inequality by means of sterile neutrino oscillometry

The investigation of the oscillation pattern induced by the sterile neutrinos might determine the oscillation parameters, and at the same time, allow to probe CPT symmetry in the leptonic sector through neutrino-antineutrino mass inequality. We propose to use a large scintillation detector like JUNO or LENA to detect electron neutrinos and electron antineutrinos from MCi electron capture or beta decay sources. Our calculations indicate that such an experiment is realistic and could be performed in parallel to the current research plans for JUNO and RENO. Requiring at least 5$\sigma$ confidence level and assuming the values of the oscillation parameters indicated by the current global fit, we would be able to detect neutrino-antineutrino mass inequality of the order of 0.5% or larger, which would imply a signal of CPT anomalies.Comment: 14 pages, 10 figure

Recognition of two distinct elements in the RNA substrate by the RNA-binding domain of the T. thermophilus DEAD box helicase Hera

DEAD box helicases catalyze the ATP-dependent destabilization of RNA duplexes. Whereas duplex separation is mediated by the helicase core shared by all members of the family, flanking domains often contribute to binding of the RNA substrate. The Thermus thermophilus DEAD-box helicase Hera (for “heat-resistant RNA-binding ATPase”) contains a C-terminal RNA-binding domain (RBD). We have analyzed RNA binding to the Hera RBD by a combination of mutational analyses, nuclear magnetic resonance and X-ray crystallography, and identify residues on helix α1 and the C-terminus as the main determinants for high-affinity RNA binding. A crystal structure of the RBD in complex with a single-stranded RNA resolves the RNA–protein interactions in the RBD core region around helix α1. Differences in RNA binding to the Hera RBD and to the structurally similar RBD of the Bacillus subtilis DEAD box helicase YxiN illustrate the versatility of RNA recognition motifs as RNA-binding platforms. Comparison of chemical shift perturbation patterns elicited by different RNAs, and the effect of sequence changes in the RNA on binding and unwinding show that the RBD binds a single-stranded RNA region at the core and simultaneously contacts double-stranded RNA through its C-terminal tail. The helicase core then unwinds an adjacent RNA duplex. Overall, the mode of RNA binding by Hera is consistent with a possible function as a general RNA chaperone

Scanning for melanoma

Non-invasive diagnostic tools aim at increasing accuracy of melanoma diagnosis. Clinical naked eye observation in combination with dermoscopy can be regarded as the practical reference standard to identify lesions for histopathological evaluation. Pigmented lesions need to be evaluated in the context of patient history to identify risk factors for melanoma, followed by a dermoscopically-aided entire skin examination. Patients with identified risk factors should be further examined. Total body photography is widely used in the follow-up of high-risk patients (particularly those with numerous and dysplastic naevi) and can be coupled with digital dermoscopy or videodermoscopy. New noninvasive diagnostic aids comprise multispectral image analysis, reflectance confocal microscopy and computer assisted diagnostic systems. Also, molecular profiling of lesions is an emerging technique under investigation for melanoma diagnosis. © Copyright 2010 National Prescribing Service Ltd

What residualizing predictors in regression analyses does (and what it does not do)

Psycholinguists are making increasing use of regression analyses and mixed-effects modeling. In an attempt to deal with concerns about collinearity, a number of researchers orthogonalize predictor variables by residualizing (i.e., by regressing one predictor onto another, and using the residuals as a stand-in for the original predictor). In the current study, the effects of residualizing predictor variables are demonstrated and discussed using ordinary least-squares regression and mixed-effects models. Some of these effects are almost certainly not what the researcher intended and are probably highly undesirable. Most importantly, what residualizing does not do is change the result for the residualized variable, which many researchers probably will find surprising. Further, some analyses with residualized variables cannot be meaningfully interpreted. Hence, residualizing is not a useful remedy for collinearity

Edge effects in graphene nanostructures: I. From multiple reflection expansion to density of states

We study the influence of different edge types on the electronic density of states of graphene nanostructures. To this end we develop an exact expansion for the single particle Green's function of ballistic graphene structures in terms of multiple reflections from the system boundary, that allows for a natural treatment of edge effects. We first apply this formalism to calculate the average density of states of graphene billiards. While the leading term in the corresponding Weyl expansion is proportional to the billiard area, we find that the contribution that usually scales with the total length of the system boundary differs significantly from what one finds in semiconductor-based, Schr\"odinger type billiards: The latter term vanishes for armchair and infinite mass edges and is proportional to the zigzag edge length, highlighting the prominent role of zigzag edges in graphene. We then compute analytical expressions for the density of states oscillations and energy levels within a trajectory based semiclassical approach. We derive a Dirac version of Gutzwiller's trace formula for classically chaotic graphene billiards and further obtain semiclassical trace formulae for the density of states oscillations in regular graphene cavities. We find that edge dependent interference of pseudospins in graphene crucially affects the quantum spectrum.Comment: to be published in Phys. Rev.

Interfaces Within Graphene Nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.Comment: 19 pages, published version, several references added, small changes to conclusion

Curupira

Portuguese: Vou falar um pouco da lenda do Curupira que é um personagem da Amazônia e ela diz assim, bom, minha avó fala que a avó dela contava para ela que a lenda nos conta que o Curupira é a defensor dos animais, sendo ele um dos mais populares personagens do folclore brasileiro. Então é isso, entendeu? Só que ela continua dizendo que o Curupira gosta de sentar na sombra das mangeiras para comer os frutos. Lá fica entretido deliciando cada manga mas percebendo que está sendo observado, logo sai correndo numa velocidade tão grande que a humana não consegue acompanhar. Não adianta correr atrás de um curupira. Eu: Como o Curupira defende a floresta? Israel: O Curupira, ele defende a mata, a fauna, a flora...eh, dos predadores tipo cortadores, destruidores demais, esse negócio todo entendeu, então ele só parece para as pessoas que vao fazer mal pra floresta. Assim minha avó contava que ela viu uma vez o Curupira também em vida quando ela tinha vinte anos aquele negócio todo que ela morava no interior Urucurituba. Mas esse mesmo a história do Curupira. [Dito depois de uma segunda lenda contada na mesma mensagem] Então essas duas lendas estou contando para você. Se alguém tiver dúvida aí, pode falar para vim em Manaus, em Amazonas, e eles podem ver que é real, o encontro das águas e histórias reais e os antigos contam bem melhor que eu. Estou só te contando o que minha avó contou para mim, entendeu? English Translation: Israel: I will talk a little about the legend of the Curupira that is a person from the Amazon and the legend says this, well, my grandma said that her grandpa told her this legend and told us that the Curupira is the defender of the animals, hime being one of the most popular people in Brazilian folklore. So it is this, understand? Only that my grandma continued saying that the Curupira likes to sit in the shade of the mango trees to eat the fruits. There it stays enjoying every mango but noticing that it is being observed, right away it leaves running at a velocity so fast that humans can’t follow. It’s no use running after a curupira. Me: How does the Curupira defend the forest? Israel: The Curupira, he defends the jungle, the animals, the plants…um, from the predators like those who cut down trees, people who destroy too much, this whole kind of thing understand, so he only appears for the people who will harm the forest. Like that my grandma said that saw a Curupira once in real life when she was twenty years old that whole thing when she lived in the interior of Urucurituba. But this is the story of the Curupira. [After another legend told in the same conversation he said this] So these two legends that I’m telling you. If anyone has doubt there, you can tell them to come to Manaus, to Amazonas, and they can see that it is real, the meeting of the waters and the real stories and the elderly tell them way better than me. I’m just telling you what my grandma told to me, understand

Impurity and edge roughness scattering in armchair graphene nanoribbons: Boltzmann approach

The conductivity of armchair graphene nanoribbons in the presence of short-range impurities and edge roughness is studied theoretically using the Boltzmann transport equation for quasi-one-dimensional systems. As the number of occupied subbands increases, the conductivity due to short-range impurities converges towards the two-dimensional case. Calculations of the magnetoconductivity confirm the edge-roughness-induced dips at cyclotron radii close to the ribbon width suggested by the recent quantum simulations