Orbital eigenchannel analysis for ab-initio quantum transport calculations

We show how to extract the orbital contribution to the transport eigenchannels from a first-principles quantum transport calculation in a nanoscopic conductor. This is achieved by calculating and diagonalizing the first-principles transmission matrix reduced to selected scattering cross-sections. As an example, the orbital nature of the eigenchannels in the case of Ni nanocontacts is explored, stressing the difficulties inherent to the use of non-orthogonal basis sets and first-principles Hamiltonians.Comment: 5 pages, 5 figurs; replaced with final version, introduction revised; to be published in PR

How coloniality shapes the making of Latin American psychologists: ethnographic evidence from Ecuador

This paper provides ethnographic evidence on how coloniality shapes the making of Latin American psychologists. A critical ethnography was conducted at a psychology training institution in Ecuador, consisting of twelve months of participant observation; forty-one semi-structured interviews; and analysis of academic discourse, photos, videos and relevant social media content. The research was guided by the tradition of Critical Psychology – specifically Liberation Psychology – and Critical Discourse Analysis. Findings suggest the pervasiveness of coloniality in the making of Ecuadorian psychologists and, hypothetically, of others in Latin America and the wider Global South. Interpretations also highlight the non-essentialist, non-dichotomist, ‘messy’ nature of such processes, a consideration which may advance current ethical and analytical debates on decolonisation. Echoing ongoing critical arguments, authors suggest that a ‘help-as-war’ metaphor is a category with potential value to contribute to such advancement, an approach that has important theoretical and pragmatic implications for researchers and practitioners

Los artefactos líticos del Alero Carriqueo : informe de avance 2010

El denominado alero Carriqueo se ubica en Nordpatagonia, en la cuenca del río Limay. El actual sitio arqueológico fue recurrentemente habitado durante un amplio período. Hasta el presente el registro arqueológico, abundante y variado, se puede vincular al período ceramolítico de la región. En este trabajo brindamos información acerca de los resultados obtenidos luego del estudio morfológico-descriptivo de una muestra de artefactos líticos que hemos dividido en débitage lato sensu por un lado (débitage stricto sensu más las matrices bifaciales y los núcleos) y por el otro, en instrumentos. Todos proceden de las excavaciones realizadas en el sitio hasta la actualidad.The Carriqueo Nordpatagonia rock shelter is located in the Lima)/ River basin. The current archaeological site was occupied repeatedly over an extended period. So far the archaeological record, generous and varied, can be linked to the region ceramolítico period. In this paper we provide information about the results after morphologicaldescriptive study of a sample of lithic debitage we divided into sensu lato on one side (sensu stricto debitage more bifacial matrix and cores) and the other in instruments. All come from the excavations at the site until today.Fil: Palacios, Oscar M. . Universidad de Buenos AiresFil: Ramos, Mariano S. . Universidad Nacional de Lujá

Magnetic and orbital blocking in Ni nanocontacts

We address the fundamental question of whether magneto-resistance (MR) of atomic-sized contacts of Nickel is very large because of the formation of a domain wall (DW) at the neck. Using {\em ab initio} transport calculations we find that, as in the case of non-magnetic electrodes, transport in Ni nanocontacts depends very much on the orbital nature of the electrons. Our results are in agreement with several experiments in the average value of the conductance. On the other hand, contrary to existing claims, DW scattering does {\em not} account for large MR in Ni nanocontacts.Comment: 5 pages, 3 Figure

Spin dynamics in a dissipative environment: from quantal to classical

We address the problem of spin dynamics in the presence of a thermal bath, by solving exactly the appropriate quantum master equations with continued-fraction methods. The crossover region between the quantum and classical domains is studied by increasing the spin value S, and the asymptote for the classical absorption spectra is eventually recovered. Along with the recognized relevance of the coupling strength, we show the critical role played by the structure of the system-environment interaction in the emergence of classical phenomenology.Comment: 4 pp., 3 figs., resubmitted to Phys. Rev. Lett. with minor change

Electronic structure of the substitutional vacancy in graphene: Density-functional and Green's function studies

We study the electronic structure of graphene with a single substitutional vacancy using a combination of the density-functional, tight-binding, and impurity Green's function approaches. Density functional studies are performed with the all-electron spin-polarized linear augmented plane wave (LAPW) method. The three $sp^2 \sigma$ dangling bonds adjacent to the vacancy introduce localized states (V$\sigma$) in the mid-gap region, which split due to the crystal field and a Jahn-Teller distortion, while the $p_z \pi$ states introduce a sharp resonance state (V$\pi$) in the band structure. For a planar structure, symmetry strictly forbids hybridization between the $\sigma$ and the $\pi$ states, so that these bands are clearly identifiable in the calculated band structure. As for the magnetic moment of the vacancy, the Hund's-rule coupling aligns the spins of the four localized V$\sigma_1 \uparrow \downarrow$, V$\sigma_2 \uparrow$, and the V$\pi \uparrow$ electrons resulting in a S=1 state, with a magnetic moment of $2 \mu_B$, which is reduced by about $0.3 \mu_B$ due to the anti-ferromagnetic spin-polarization of the $\pi$ band itinerant states in the vicinity of the vacancy. This results in the net magnetic moment of $1.7 \mu_B$. Using the Lippmann-Schwinger equation, we reproduce the well-known $\sim 1/r$ decay of the localized V$\pi$ wave function with distance and in addition find an interference term coming from the two Dirac points, previously unnoticed in the literature. The long-range nature of the V$\pi$ wave function is a unique feature of the graphene vacancy and we suggest that this may be one of the reasons for the widely varying relaxed structures and magnetic moments reported from the supercell band calculations in the literature.Comment: 24 pages, 15 figures. Accepted for publication in New Journal of Physic

Image Calibration

Calibrate_Image calibrates images obtained from focal plane arrays so that the output image more accurately represents the observed scene. The function takes as input a degraded image along with a flat field image and a dark frame image produced by the focal plane array and outputs a corrected image. The three most prominent sources of image degradation are corrected for: dark current accumulation, gain non-uniformity across the focal plane array, and hot and/or dead pixels in the array. In the corrected output image the dark current is subtracted, the gain variation is equalized, and values for hot and dead pixels are estimated, using bicubic interpolation techniques

Vortex structure of thin mesoscopic disks in the presence of an inhomogeneous magnetic field

The vortex states in a thin mesoscopic disk are investigated within the phenomenological Ginzburg-Landau theory in the presence of different ''model'' magnetic field profiles with zero average field which may result from a ferromagnetic disk or circulating currents in a loop near the superconductor. We calculated the dependences of both the ground and metastable states on the magnitude and shape of the magnetic field profile for different values of the order parameter angular moment, i.e. the vorticity. The regions of existence of the multi-vortex state and the giant vortex state are found. We analysed the phase transitions between these states and studied the contribution from ring-shaped vortices. A new transition between different multi-vortex configurations as the ground state is found. Furthermore, we found a vortex state consisting of a central giant vortex surrounded by a collection of anti-vortices which are located in a ring around this giant vortex. The limit to a disk with an infinite radius, i.e. a film, will also be discussed. We also extended our results to ''real'' magnetic field profiles and to the case in which an external homogeneous magnetic field is present.Comment: 17 pages, 23 figures. Submitted to PR

Capas finas de ZrO2 para mejorar la resistencia química de los vidriados mates de calcio

La resistencia al ataque químico de vidriados cerámicos susceptibles al mismo, concretamente formulados a partir de una frita mate de calcio, se ha mejorado depositando en la superficie una capa delgada de óxido de circonio. Un sol de circonio estabilizado es el precursor de la capa, el cual se deposita mediante aerografía sobre el vidriado cocido y con un tratamiento térmico suave (Tmax ≈ 400 ºC), es transformado en ZrO2 y anclado a la superficie. Los ensayos de resistencia química demuestran que el vidriado protegido no sufre un ataque apreciable visualmente por parte del ácido clorhídrico concentrado, condiciones en las que el mismo vidriado sin el recubrimiento resulta gravemente dañado. El precursor utilizado genera una capa de óxido de circonio que protege el vidriado subyacente, de modo que el ataque químico por parte del ácido clorhídrico queda confinado al entorno de las grietas y discontinuidades de la capa depositadaPeer reviewe