Bound states in the continuum driven by AC fields

We report the formation of bound states in the continuum driven by AC fields. This system consists of a quantum ring connected to two leads. An AC side-gate voltage controls the interference pattern of the electrons passing through the system. We model the system by two sites in parallel connected to two semi-infinite lattices. The energy of these sites change harmonically with time. We obtain the transmission probability and the local density of states at the ring sites as a function of the parameters that define the system. The transmission probability displays a Fano profile when the energy of the incoming electron matches the driving frequency. Correspondingly, the local density of states presents a narrow peak that approaches a Dirac delta function in the weak coupling limit. We attribute these features to the presence of bound states in the continuum.Comment: 5 pages, 3 figure

Localisation and finite-size effects in graphene flakes

We show that electron states in disordered graphene, with an onsite potential that induces inter-valley scattering, are localised for all energies at disorder as small as of the band width of clean graphene. We clarify that, in order for this Anderson-type localisation to be manifested, graphene flakes of size or larger are needed. For smaller samples, due to the surprisingly large extent of the electronic wave functions, a regime of apparently extended (or even critical) states is identified. Our results complement earlier studies of macroscopically large samples and can explain the divergence of results for finite-size graphene flakes

Characterization of ten white matter tracts in a representative sample of Cuban population

Background: The diffusion tensor imaging technique (DTI) combined with tractography methods, has achieved the tridimensional reconstruction of white matter tracts in the brain. It allows their characterization in vivo in a non-invasive way. However, one of the largest sources of variability originates from the location of regions of interest, is therefore necessary schemes which make it possible to establish a protocol to be insensitive to variations in drawing thereof. The purpose of this paper is to stablish a reliable protocol to reconstruct ten prominent tracts of white matter and characterize them according to volume, fractional anisotropy and mean diffusivity. Also we explored the relationship among these factors with gender and hemispheric symmetry. Methods: This study aims to characterize ten prominent tracts of white matter in a representative sample of Cuban population using this technique, including 84 healthy subjects. Diffusion tensors and subsequently fractional anisotropy and mean diffusivity maps were calculated from each subject's DTI scans. The trajectory of ten brain tracts was estimated by using deterministic tractography methods of fiber tracking. In such tracts, the volume, the FA and MD were calculated, creating a reference for their study in the Cuban population. The interactions between these variables with age, cerebral hemispheres and gender factors were explored using Repeated Measure Analysis of Variance. Results: The volume values showed that a most part of tracts have bigger volume in left hemisphere. Also, the data showed bigger values of MD for males than females in all the tracts, an inverse behavior than FA values. Conclusions: This work showed that is possible reconstruct white matter tracts using a unique region of interest scheme defined from standard to native space. Also, this study indicates differing developmental trajectories in white matter for males and females and the importance of taking gender into account in developmental DTI studies and in underlie gender-related cognitive differences

Klein paradox between transmitted and reflected Dirac waves on Bour surfaces

It is supposed the existence of a curved graphene sheet with the geometry of a Bour surface $B_{n}$, such as the catenoid (or helicoid), $B_{0}$, and the classical Enneper surface, $B_{2}$, among others. In particular, in this work, the propagation of the electronic degrees of freedom on these surfaces is studied based on the Dirac equation. As a consequence of the polar geometry of $B_{n}$, it is found that the geometry of the surface causes the Dirac fermions to move as if they would be subjected to an external potential coupled to a spin-orbit term. The geometry-induced potential is interpreted as a barrier potential, which is asymptotically zero. Furthermore, the behaviour of asymptotic Dirac states and scattering states are studied through the Lippmann-Schwinger formalism. It is found that for surfaces $B_{0}$ and $B_{1}$, the total transmission phenomenon is found for sufficiently large values of energy, while for surfaces $B_{n}$, with $n\geq 2$, it is shown that there is an energy point $E_{K}$ where Klein's paradox is realized, while for energy values $E\gg E_{K}$ it is found that the conductance of the hypothetical material is completely suppressed, $\mathcal{G}(E)\to 0$.Comment: 31 pages, 9 figure

Physical and Excess Properties for Binary Systems Containing an Alcohol and Ionic Liquid at T = 298.15K

AbstractIn this paper, density, speed of sound and refractive index of six binary systems (alcohol + ionic liquid) were measured, along the whole composition range, at T = 298.15K and atmospheric pressure. The ionic liquids used in this work are constituted by different cations (pyridinium and pyrrolidinium), anions (trifluoromethanesulfonate and dicyanamide) and alkyl-side chain (propyl- and butyl-). From the experimental data, excess molar volumes, excess molar isentropic compressions and excess refractive index were calculated and satisfactorily fitted using the Redlich-Kister equation. The obtained results show that the physical and excess properties studied in this work are dependent on the structure of the ILs, especially on the anion

Proyecto para la creación de una empresa de confección de camisetas a base de algodón orgánico en la ciudad de Guayaquil

Este documento presenta un análisis de viabilidad y factibilidad de implantar una fábrica que confeccione camisetas en la ciudad de Guayaquil y muestra el plan de negocios para esta empresa. Para esto se realizó un análisis del sector textil e investigación de mercados para identificar estrategias y acciones a seguir. La investigación incluyó a compradores en centros comerciales y competencia en el mercado. En base a la investigación sectorial y a resultados del análisis de la investigación se llegó a la conclusión que el proyecto es totalmente viable; debido a que hay una gran disposición ecologista de la gente y que estarían dispuestos a comprar, y es también factible; porque a través de la aplicación de estrategia de nicho de mercado y diferentes tácticas, la fábrica logrará participación de mercado y sobre todo alta rentabilidad.FEN-ESPO

Molecular identification of hammerhead shark trunks from the southern Gulf of California using multiplex PCR

The demand for shark fins in Asiatic markets has resulted in excessive increases in shark catches, even for species that may be under protection or subject to management. As such, it has been necessary to develop and promote monitoring efforts for exploited species and taxonomic groups in order to improve fishing management strategies for elasmobranchs. Identifying species from landings is one of many fishing management problems because landed organisms have usually already been processed and are therefore incomplete, which makes identification problematic, impedes the generation of proper species records, and leads to poor fishery assessments. Tools that can correctly identify species, such as various molecular techniques, have become essential for accurate fishery assessments. In this study, 30 hammerhead trunks from artisanal fisheries from the southern portion of the Gulf of California were identified using multiplex PCR (17 Sphyrna lewini and 13 Sphyrna zygaena). The total fee to identify each trunk with this technique was ~ $3.80 and the procedure required 2 to 5 days. When compared with other widely-used methods, such as PCR-RFLP or barcoding, multiplex PCR is fast, efficient, low-cost, and easy to implement in a laboratory