233 research outputs found
Objective method for measuring the macular pigment optical density in the eye
Macular pigment is a yellowish pigment of purely dietary origin, which is thought to have a protective role in the retina. Recently, it was linked to age-related macular degeneration and improved visual function. In this work, we present a method and a corresponding optical instrument for the rapid measurement of its optical density. The method is based on fundus reflectometry and features a photodetector for the measurement of reflectance at different wavelengths and retinal locations. The method has been tested against a commercially available instrument on a group of healthy volunteers and has shown good correlation. The proposed instrument can serve as a rapid, non-midriatic, low-cost tool for the measurement of macular pigment optical density
Magnetic field dependence of the density of states in the multiband superconductor -BiPd
We present very low temperature scanning tunneling microscopy (STM)
experiments on single crystalline samples of the superconductor
-BiPd. We find a single fully isotropic superconducting gap.
However, the magnetic field dependence of the intervortex density of states is
higher than the one expected in a single gap superconductor, and the hexagonal
vortex lattice is locked to the square atomic lattice. Such increase in the
intervortex density of states and vortex lattice locking have been found in
superconductors with multiple superconducting gaps and anisotropic Fermi
surfaces. We compare the upper critical field obtained in our
sample with previous measurements and explain available data within multiband
supercondutivity. We propose that -BiPd is a single gap multiband
superconductor. We anticipate that single gap multiband superconductivity can
occur in other compounds with complex Fermi surfaces.Comment: 8 pages, 7 figure
Single-molecule kinetic energy of condensed normal deuterium
8 págs.; 9 figs.; 1 tab.Inelastic scattering of 300-meV neutrons allows the study of the liquid (T=20 and 30 K, saturated vapor pressure) and solid (T=4.2 K, saturated vapor pressure) phases of the normal deuterium mixture (2/3 o-D2+1/3 p -D2) in the region of momentum transfer where a single-molecule response is expected. The spectra are analyzed within the impulse approximation and assuming Gaussian momentum distributions for the translation of the molecules. For the solid, the estimated value of the single-molecule average kinetic energy does not compare unfavorably with those obtained scaling experimental results in parahydrogen solids. In the liquid state, substantial departures seem to exist from the classical liquid behavior, even if up to second-order quantum corrections are taken into account. ©1996 American Physical SocietyThis research has been made possible in part by the Spanish DGICYT through Grant
No. PB92-0015.Peer Reviewe
Análisis tiempo-frecuencia de mapas de activación cardíaca en fibrilación ventricular
El análisis de mapas de activación permite investigar la
estructura de la fibrilación ventricular cardíaca (FV). El
presente trabajo plantea una revisión de la utilización de
objetos de interés (blobs), usados en procesado de
imágenes y aplicados también a mapas de activación
cerebral y cardíaca, mediante su generación a partir de
representaciones tiempo-frecuencia de registros FV. Su
estudio proporciona información sobre qué frecuencias
de la señal están presentes en un instante dado, así como
su distribución espacial. También permiten determinar el
momento en que una determinada frecuencia aparece y
desaparece de cada electrodo, por lo que constituye una
herramienta interesante para analizar los mecanismos de
generación y mantenimiento de la FV
Magnetic phase diagram, magnetotransport and inverse magnetocaloric effect in the noncollinear antiferromagnet Mn5Si3
This Accepted Manuscript will be available for reuse under a CC BY-NC-ND licence after 24 months of embargo periodThe antiferromagnet Mn5Si3 has recently attracted attention because a noncollinear spin arrangement has been shown to produce a topological anomalous Hall effect and an inverse magnetocaloric effect. Here we synthesize single crystals of Mn5Si3 using flux growth. We determine the phase diagram through magnetization and measure the magnetoresistance and the Hall effect. We find the collinear and noncollinear antiferromagnetic phases at low temperatures and, in addition, a third magnetic phase, in between the two antiferromagnetic phases. The latter magnetic phase might be caused by strain produced by Cu inclusions. This suggests that fluctuations of the mixed character magnetic ordering in this compound can be easily quenched by stressThis work was supported by the Spanish MINECO (Consolider Ingenio Molecular Nanoscience CSD2007-00010 program, FIS2017-84330-R, MDM-2014-0377, MAT2014-52405-C2-2-R, FJCI-2015-25427 and CSD2009-00013), by the Comunidad de Madrid through program NANOMAGCOST-CM (S2018 NMT-4321) and MAD2D-CM (S2013/MIT-3007) and by EU (Graphene Core1 contract No. 696656, Nanopyme FP7-NMP-2012 SMALL-6 NMP3-SL-2012 310516 and COST CA16218
Room Temperature In-plane <100> Magnetic Easy Axis for Fe3O4/SrTiO3(001):Nb Grown by Infrared PLD
We examine the magnetic easy-axis directions of stoichiometric magnetite
films grown on SrTiO3:Nb by infrared pulsed-laser deposition. Spin-polarized
low-energy electron microscopy reveals that the individual magnetic domains are
magnetized along the in-plane film directions. Magneto-optical Kerr
effect measurements show that the maxima of the remanence and coercivity are
also along in-plane film directions. This easy-axis orientation differs
from bulk magnetite and films prepared by other techniques, establishing that
the magnetic anisotropy can be tuned by film growth.Comment: 3 pages, 3 figure
Versatile Graphene-Based Platform for Robust Nanobiohybrid Interfaces
Technologically useful and robust graphene-based interfaces for devices
require the introduction of highly selective, stable, and covalently bonded
functionalities on the graphene surface, whilst essentially retaining the
electronic properties of the pristine layer. This work demonstrates that highly
controlled, ultrahigh vacuum covalent chemical functionalization of graphene
sheets with a thiol-terminated molecule provides a robust and tunable platform
for the development of hybrid nanostructures in different environments. We
employ this facile strategy to covalently couple two representative systems of
broad interest: metal nanoparticles, via S-metal bonds, and thiol-modified DNA
aptamers, via disulfide bridges. Both systems, which have been characterized by
a multi-technique approach, remain firmly anchored to the graphene surface even
after several washing cycles. Atomic force microscopy images demonstrate that
the conjugated aptamer retains the functionality required to recognize a target
protein. This methodology opens a new route to the integration of high-quality
graphene layers into diverse technological platforms, including plasmonics,
optoelectronics, or biosensing. With respect to the latter, the viability of a
thiol-functionalized chemical vapor deposition graphene-based solution-gated
field-effect transistor array was assessed
Morphological stabilization and KPZ scaling by electrochemically induced co-deposition of nanostructured NiW alloy films
We have assessed the stabilizing role that induced co-deposition has in the growth of nanostructured NiW alloy films by electrodeposition on polished steel substrates, under pulsed galvanostatic conditions. We have compared the kinetic roughening properties of NiW films with those of Ni films deposited under the same conditions, as assessed by Atomic Force Microscopy. The surface morphologies of both systems are super-rough at short times, but differ at long times: while a cauliflower-like structure dominates for Ni, the surfaces of NiW films display a nodular morphology consistent with more stable, conformal growth, whose height fluctuations are in the Kardar-Parisi- Zhang universality class of rough two-dimensional interfaces. These differences are explained by the mechanisms controlling surface growth in each case: mass transport through the electrolyte (Ni) and attachment of the incoming species to the growing interface (NiW). Thus, the long-time conformal growth regime is characteristic of electrochemical induced co-deposition under current conditions in which surface kinetics is hindered due to a complex reaction mechanism. These results agree with a theoretical model of surface growth in diffusion-limited systems, in which the key parameter is the relative importance of mass transport with respect to the kinetics of the attachment reaction.Facultad de Ciencias Exacta
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