Curved Graphene Nanoribbons: Structure and Dynamics of Carbon Nanobelts

Carbon nanoribbons (CNRs) are graphene (planar) structures with large aspect ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into spiral-like structures, i. e., carbon nanoscrolls (CNSs) with large aspect ratio. In this work we investigated the energetics and dynamical aspects of CNBs formed from rolling up CNRs. We have carried out molecular dynamics simulations using reactive empirical bond-order potentials. Our results show that similarly to CNSs, CNBs formation is dominated by two major energy contribution, the increase in the elastic energy due to the bending of the initial planar configuration (decreasing structural stability) and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers (increasing structural stability). Beyond a critical diameter value these scrolled structures can be even more stable (in terms of energy) than their equivalent planar configurations. In contrast to CNSs that require energy assisted processes (sonication, chemical reactions, etc.) to be formed, CNBs can be spontaneously formed from low temperature driven processes. Long CNBs (length of $\sim$ 30.0 nm) tend to exhibit self-folded racket-like conformations with formation dynamics very similar to the one observed for long carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled structures. Possible synthetic routes to fabricate CNBs from graphene membranes are also addressed

Scaling properties of the Penna model

We investigate the scaling properties of the Penna model, which has become a popular tool for the study of population dynamics and evolutionary problems in recent years. We find that the model generates a normalised age distribution for which a simple scaling rule is proposed, that is able to reproduce qualitative features for all genome sizes.Comment: 4 pages, 4 figure

Tolerance After Liver Transplantation: Where Are We?

info:eu-repo/semantics/publishedVersio

Prospects for γγ→\gamma\gamma\to Higgs observation in ultraperipheral ion collisions at the Future Circular Collider

We study the two-photon production of the Higgs boson, $\rm \gamma\gamma\to H$, at the Future Circular Collider (FCC) in ultraperipheral PbPb and pPb collisions at $\sqrt{s_{NN}} = 39$ and 63 TeV. Signal and background events are generated with MADGRAPH 5, including $\gamma$ fluxes from the proton and lead ions in the equivalent photon approximation, yielding $\rm \sigma(\gamma\gamma\to H)$ = 1.75 nb and 1.5 pb in PbPb and pPb collisions respectively. We analyse the H$\,\to b\bar{b}$ decay channel including realistic reconstruction efficiencies for the final-state $b$-jets, showered and hadronized with PYTHIA 8, as well as appropriate selection criteria to reduce the dominant exclusive $\gamma\gamma\to b\bar{b}$ continuum background. Observation of $\rm PbPb\xrightarrow{\gamma\gamma}(Pb)\,H\,(Pb)$ is achievable in the first year with the expected PbPb integrated luminosities.Comment: 5 pages, 4 figures. PHOTON'17, CERN Proceedings, to appear. References adde

Evidence for quasi-chemically homogeneous evolution of massive stars up to solar metallicity

Long soft gamma ray bursts (LGRBs) are usually associated with the death of the most massive stars. A large amount of core angular momentum in the phases preceding the explosion is required to form LGRBs. A very high initial rotational velocity can provide this angular momentum. Such a velocity strongly influences the way the star evolves: it is chemically homogeneously mixed and evolves directly towards the blue part of the HR diagram from the main sequence. We have shown that chemically homogeneous evolution (CHE) takes place in the SMC, at low metallicity. We want to see if there is a metallicity threshold above which such an evolution does not exist. We perform a spectroscopic analysis of H-rich early-type WN stars in the LMC and the Galaxy. We use the code CMFGEN to determine the fundamental properties and the surface composition of the target stars. We then place the stars in the HR diagram and determine their evolution. We show that both the LMC and Galactic WNh stars we selected cannot be explained by standard stellar evolution. They are located on the left of the main sequence but show surface abundances typical of CN equilibrium. In addition, they still contain a large amount of hydrogen. They are thus core-H burning objects. Their properties are consistent with CHE. We determine the metallicity of the Galactic stars from their position and Galactic metallicity gradients, and conclude that they have 0.6<Z<1.0. A moderate coupling between the core and the envelope is required to explain that stellar winds do not extract to much angular momentum to prevent a blueward evolution. In view of the findings that some long gamma ray bursts appear in solar environments, CHE may be a viable way to form them over a wide range of metallicities.Comment: 10 pages, 10 figures. Accepted in Astronomy and Astrophysic

Polarized currents and spatial separation of Kondo state: NRG study of spin-orbital effect in a double QD

A double quantum dot device, connected to two channels that only see each other through interdot Coulomb repulsion, is analyzed using the numerical renormalization group technique. By using a two-impurity Anderson model, and parameter values obtained from experiment [S. Amasha {\it et al.}, Phys. Rev. Lett. {\bf 110}, 046604 (2013)], it is shown that, by applying a moderate magnetic field, and adjusting the gate potential of each quantum dot, opposing spin polarizations are created in each channel. Furthermore, through a well defined change in the gate potentials, the polarizations can be reversed. This polarization effect is clearly associated to a spin-orbital Kondo state having a Kondo peak that originates from spatially separated parts of the device. This fact opens the exciting possibility of experimentally probing the internal structure of an SU(2) Kondo state.Comment: 4+ pages; 4 figures; supplemental material (1 page, 2 figures