Coexistence of Quantum Theory and Special Relativity in signaling scenarios

The coexistence between Quantum Mechanics and Special Relativity is usually formulated in terms of the no-signaling condition. Several authors have even suggested that this condition should be included between the basic postulates of Quantum Theory. However, there are several scenarios where signaling is, in principle, possible: based on previous results and the analysis of the relation between unitarity and signaling we present an example of a two-particle interferometric arrangement for which the dynamics is, in principle, compatible with superluminal transmission of information. This type of non-locality is not in the line of Bell's theorem, but closer in spirit to the one-particle acausality studied by Hegerfeldt and others. We analyze in this paper the meaning of this non-locality and how to preserve the coexistence of the two fundamental theories in this signaling scenario.Comment: See also the comment by G C Hegerfeldt in the online version of the journal, including more reference

Self-sustained spatiotemporal oscillations induced by membrane-bulk coupling

We propose a novel mechanism leading to spatiotemporal oscillations in extended systems that does not rely on local bulk instabilities. Instead, oscillations arise from the interaction of two subsystems of different spatial dimensionality. Specifically, we show that coupling a passive diffusive bulk of dimension d with an excitable membrane of dimension d-1 produces a self-sustained oscillatory behavior. An analytical explanation of the phenomenon is provided for d=1. Moreover, in-phase and anti-phase synchronization of oscillations are found numerically in one and two dimensions. This novel dynamic instability could be used by biological systems such as cells, where the dynamics on the cellular membrane is necessarily different from that of the cytoplasmic bulk.Comment: Accepted for publication in Physical Review Letter

Characterisation of the artist John Opie’s pigments, dated 1806

This paper discusses the contents of an artist’s paint box currently in the possession of St. Agnes Museum, Cornwall, UK, containing a selection of historic pigments. On its lid is a metal plaque that reads ‘John Opie 1806’. Very little is known about this paint box, so this piece of research aims to uncover some of the hidden information stored within it through identification of some of the pigments it contains. The main body of this research shows the first results obtained by the identification of a selection of the pigments from the paint box, using Fourier Transform Infra Red spectroscopy (FTIR) and optical microscopy techniques. These findings will be considered in relation to what this tells us about the artist John Opie, the authenticity of the pigments within the paint box, and the use of pigments in the early nineteenth century

First Principles Studies on 3-Dimentional Strong Topological Insulators: Bi2Te3, Bi2Se3 and Sb2Te3

Bi2Se3, Bi2Te3 and Sb2Te3 compounds are recently predicted to be 3-dimentional (3D) strong topological insulators. In this paper, based on ab-initio calculations, we study in detail the topological nature and the surface states of this family compounds. The penetration depth and the spin-resolved Fermi surfaces of the surface states will be analyzed. We will also present an procedure, from which highly accurate effective Hamiltonian can be constructed, based on projected atomic Wannier functions (which keep the symmetries of the systems). Such Hamiltonian can be used to study the semi-infinite systems or slab type supercells efficiently. Finally, we discuss the 3D topological phase transition in Sb2(Te1-xSex)3 alloy system.Comment: 8 pages,17 figure

Fullerene based devices for molecular electronics

We have investigated the electronic properties of a C_60 molecule in between carbon nanotube leads. This problem has been tackled within a quantum chemical treatment utilizing a density functional theory-based LCAO approach combined with the Landauer formalism. Owing to low-dimensionality, electron transport is very sensitive to the strength and geometry of interfacial bonds. Molecular contact between interfacial atoms and electrodes gives rise to a complex conductance dependence on the electron energy exhibiting spectral features of both the molecule and electrodes. These are attributed to the electronic structure of the C_60 molecule and to the local density of states of the leads, respectively.Comment: 4 pages, 2 figures, to appear in Physica

Nonequilibrium fluctuation induced escape from a metastable state

Based on a simple microscopic model where the bath is in a non-equilibrium state we study the escape from a metastable state in the over-damped limit. Making use of Fokker-Planck-Smoluchowski description we derive the time dependent escape rate in the non-stationary regime in closed analytical form which brings on to fore a strong non-exponential kinetic of the system mode.Comment: 4 pages, no figures, EPJ class file include

Hole Pairs in the Two-Dimensional Hubbard Model

The interactions between holes in the Hubbard model, in the low density, intermediate to strong coupling limit, are investigated. Dressed spin polarons in neighboring sites have an increased kinetic energy and an enhanced hopping rate. Both effects are of the order of the hopping integral and lead to an effective attraction at intermediate couplings. Our results are derived by systematically improving mean field calculations. The method can also be used to derive known properties of isolated spin polarons.Comment: 4 page

Diet of three large pelagic fishes associated with drifting fish aggregating devices (DFADs) in the western equatorial Indian Ocean

Dieta de tres peces pelágicos de gran tamaño asociados a agregaciones de peces bajo objetos flotantes (DFADs) en el Océano Índico ecuatorial occidental Los objetos flotantes congregan distintas especies de peces en aguas tropicales marinas. Se capturaron tres especies depredadoras: atún de aleta amarilla (Thunnus albacares), petos (Acanthocybium solandri) y llampugas (Coryphaena hippurus) en agregaciones bajo objetos flotantes en el Océano Índico occidental, para caracterizar su dieta y determinar si se alimentan de organismos asociados a las DFADs. Los atunes de aleta amarilla no se alimentaron de presas asociadas a objetos flotantes, mientras los petos y llampugas sí explotaron los recursos agregados a estos objetos flotantes, aunque predominantemente se alimentaron de otros organismos no asociados a ellos. En atunes de aleta amarilla y en llampugas asociados a FADs se observó una predación oportunista en la superficie de agrupaciones de crustáceos estomatópodos pero no así en los petos. Palabras clave: Dispositivos agregadores de peces, Atún de aleta amarilla, Llampuga, Peto, Contenidos estomacales, Dieta.Several species of fish, aggregate around DFADs in marine tropical waters. We captured three predatory species: yellow fin tuna (Thunnus albacares), wahoo (Acanthocybium solandri) and dolphinfish (Coryphaena hippurus) from aggregations under DFADs in the Western Indian Ocean to characterize their diet and determine whether they fed on other DFAD associated organisms. Yellowfin tuna did not feed on DFAD–associated prey, while wahoo and dolphinfish did exploit resources aggregated by the DFADs, though they predominantly fed on other non–associated organisms. Opportunistic feeding on surface swarming stomatopod crustaceans was observed in yellowfin tuna and dolphinfish associated with FADs, but was not observed in wahoo. Key words: FAD, Yellowfin tuna, Dolphinfish, Wahoo, Stomach contents, Diet.Dieta de tres peces pelágicos de gran tamaño asociados a agregaciones de peces bajo objetos flotantes (DFADs) en el Océano Índico ecuatorial occidental Los objetos flotantes congregan distintas especies de peces en aguas tropicales marinas. Se capturaron tres especies depredadoras: atún de aleta amarilla (Thunnus albacares), petos (Acanthocybium solandri) y llampugas (Coryphaena hippurus) en agregaciones bajo objetos flotantes en el Océano Índico occidental, para caracterizar su dieta y determinar si se alimentan de organismos asociados a las DFADs. Los atunes de aleta amarilla no se alimentaron de presas asociadas a objetos flotantes, mientras los petos y llampugas sí explotaron los recursos agregados a estos objetos flotantes, aunque predominantemente se alimentaron de otros organismos no asociados a ellos. En atunes de aleta amarilla y en llampugas asociados a FADs se observó una predación oportunista en la superficie de agrupaciones de crustáceos estomatópodos pero no así en los petos. Palabras clave: Dispositivos agregadores de peces, Atún de aleta amarilla, Llampuga, Peto, Contenidos estomacales, Dieta

Nitrogen-Fixing Symbiotic Paraburkholderia Species: Current Knowledge and Future Perspectives

A century after the discovery of rhizobia, the first Beta-proteobacteria species (beta-rhizobia) were isolated from legume nodules in South Africa and South America. Since then, numerous species belonging to the Burkholderiaceae family have been isolated. The presence of a highly branching lineage of nodulation genes in beta-rhizobia suggests a long symbiotic history. In this review, we focus on the beta-rhizobial genus Paraburkholderia, which includes two main groups: the South American mimosoid-nodulating Paraburkholderia and the South African predominantly papilionoid-nodulating Paraburkholderia. Here, we discuss the latest knowledge on Paraburkholderia nitrogen-fixing symbionts in each step of the symbiosis, from their survival in the soil, through the first contact with the legumes until the formation of an efficient nitrogen-fixing symbiosis in root nodules. Special attention is given to the strain P. phymatum STM815T that exhibits extraordinary features, such as the ability to: (i) enter into symbiosis with more than 50 legume species, including the agriculturally important common bean, (ii) outcompete other rhizobial species for nodulation of several legumes, and (iii) endure stressful soil conditions (e.g., high salt concentration and low pH) and high temperatures