Elliot-Yafet mechanism in graphene

The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction.Comment: 4 pages + \epsilon + S

Quark mass hierarchy in 3-3-1 models

We study the mass spectrum of the quark sector in an special type I-like model with gauge symmetry $SU(3)_c \otimes SU(3)_L \otimes U(1)_X$. By considering couplings with scalar triplets at large ($\sim TeV$) and small ($\sim GeV$) scales, we obtain specific zero-texture mass matrices for the quarks which predict three massless quarks ($u,d,s$) and three massive quarks ($c,b,t$) at the electroweak scale ($\sim$ GeV). Taking into account mixing couplings with three heavy quarks at large scales predicted by the model, the three massless quarks obtain masses at small order that depends on the inverse of the large scale. Thus, masses of the form $m_u \lesssim m_d < m_s \sim MeV$ and $m_{c,b,t} \sim GeV$ can be obtained naturally from the gauge structure of the model

Constraining the Noncommutative Spectral Action via Astrophysical Observations

The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. Thus, noncommutative geometry provides a geometric interpretation of particle physics coupled to curvature. In this letter we use observations of pulsar timings, assuming that no deviation from General Relativity has been observed, to constrain the gravitational sector of this theory. Thus, we directly constrain noncommutative geometry, a potential grand unified theory of physics, via astrophysical observations. Whilst the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from General Relativity in other settings and are likely to be further constrained by future observations.Comment: 5 pages; slightly shorter version to match the one will appear in Phys. Rev. Let

Interactions and magnetic moments near vacancies and resonant impurities in graphene

The effect of electronic interactions in graphene with vacancies or resonant scatterers is investigated. We apply dynamical mean-field theory in combination with quantum Monte Carlo simulations, which allow us to treat non-perturbatively quantum fluctuations beyond Hartree-Fock approximations. The interactions narrow the width of the resonance and induce a Curie magnetic susceptibility, signaling the formation of local moments. The absence of saturation of the susceptibility at low temperatures suggests that the coupling between the local moment and the conduction electrons is ferromagnetic

Colangiocarcinoma hepático en un felino y hallazgos anatomopatólogicos, y clínicos compatibles con peritonitis infecciosa felina

Se presentan los hallazgos patomorfológicos de colangiocarcinoma hepático (CGC) con efusión peritoneal en un gato doméstico geronte y se relaciona con la sintomatología clínica y los hallazgos anatomopatológicos compatibles con la peritonitis infecciosa felina (PIF). Se atendió en la clínica veterinaria de la Universidad de los Llanos un paciente felino de 8 años de edad, criollo, con aumento de la silueta abdominal y depresión. Clínicamente se encontró deshidratación del 7%, hipotermia (37.2ºC), mucosas pálidas, disnea y hepatomegalia. Mediante abdominocentesis se obtuvo un exudado no séptico y un cuadro citológico compatible con CGC con células columnares bajas dispuestas en panal de abeja, presentando anisocariosis, hipercromacia moderada, citoplasmas claros y vacuolados acompañados de un fondo sucio inflamatorio y hemorrágico con detritos celulares. En el análisis radiográfico se observó hepatomegalia con un patrón de punteado característico de formación neoplásica y ascitis. A la necropsia se presentó hemotórax e hidropericardio, ascitis y nódulos neoplásicos blancos duros al corte en el 45% del parénquima hepático y un patrón nodular sobre la superficie visceral del estomago, intestinos delgado, grueso y mesenterio. Las muestras se fijaron en formalina buferada al 10%, se procesaron mediante métodos rutinarios para microscopía óptica. Por histopatología se diagnosticó CGC moderadamente diferenciado con intensa desmoplasia. Citológica e histopatológicamente se evidenció un CGC hepático con efusión peritoneal que se relacionó con la sintomatología clínica y los hallazgos anatomopatológicos compatibles con la PIF

Nanotailoring Stereolithography Resins for Unique Applications using Carbon Nanotubes

Nanostructured materials and exploiting their properties in stereolithography (SL) may open new markets for unique rapidly manufactured functional devices. Controlled amounts of multiwalled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and complex three-dimensional (3D) parts were successfully fabricated by means of a multi-material SL setup. The effect of the nanosized filler was evaluated using mechanical testing. Small dispersions of MWCNTs resulted in significant effects on the physical properties of the polymerized resin. A MWCNT concentration of .05 wt% (w/v) in DSM Somos® WaterShed™ 11120 resin increased the ultimate tensile stress and fracture stress an average of 17% and 37%, respectively. Electron microscopy was used to examine the morphology of the nanocomposite and results showed affinity between the MWCNTs and SL resin and identified buckled nanotubes that illustrated strong interfacial bonding. These improved physical properties may provide opportunities for using nanocomposite SL resins in end-use applications. Varying types and concentrations of nanomaterials can be used to tailor existing SL resins for particular applications.Mechanical Engineerin

Novel effects of strains in graphene and other two dimensional materials

The analysis of the electronic properties of strained or lattice deformed graphene combines ideas from classical condensed matter physics, soft matter, and geometrical aspects of quantum field theory (QFT) in curved spaces. Recent theoretical and experimental work shows the influence of strains in many properties of graphene not considered before, such as electronic transport, spin-orbit coupling, the formation of Moir\'e patterns, optics, ... There is also significant evidence of anharmonic effects, which can modify the structural properties of graphene. These phenomena are not restricted to graphene, and they are being intensively studied in other two dimensional materials, such as the metallic dichalcogenides. We review here recent developments related to the role of strains in the structural and electronic properties of graphene and other two dimensional compounds.Comment: 75 pages, 15 figures, review articl