Surface-Enriched Boron-Doped TiO2 Nanoparticles as Photocatalysts for Propene Oxidation.

A series of nanostructured boron-TiO2 photocatalysts (B-X-TiO2-T) were prepared by sol-gel synthesis using titanium tetraisopropoxide and boric acid. The effects of the synthesis variables, boric acid amount (X) and crystallization temperature (T), on structural and electronic properties and on the photocatalytic performance for propene oxidation, are studied. This reaction accounts for the remediation of pollution caused by volatile organic compounds, and it is carried out at low concentrations, a case in which efficient removal techniques are difficult and costly to implement. The presence of boric acid during the TiO2 synthesis hinders the development of rutile without affecting the textural properties. X-ray photoelectron spectroscopy analysis reveals the interstitial incorporation of boron into the surface lattice of the TiO2 nanostructure, while segregation of B2O3 occurs in samples with high boron loading, also confirmed by X-ray diffraction. The best-performing photocatalysts are those with the lowest boron loading. Their high activity, outperforming the equivalent sample without boron, can be attributed to a high anatase and surface hydroxyl group content and efficient photo-charge separation (photoelectrochemical characterization, PEC), which can explain the suppression of visible photoluminescence (PL). Crystallization at 450 °C renders the most active sample, likely due to the development of a pure anatase structure with a large surface boron enrichment. A shift in the wavelength-dependent activity profile (PEC data) and the lowest electron-hole recombination rate (PL data) are also observed for this sample.

Impact of kinetics on the growth of GaN on graphene by plasma-assisted molecular beam epitaxy.

The growth of GaN on graphene by molecular beam epitaxy was investigated. The most stable epitaxial relationship, i.e. [00.1]-oriented grains, is obtained at high temperature and N-rich conditions, which match those for nanowire growth. Alternatively, at moderate temperature and Ga-rich conditions, several metastable orientations are observed at the nucleation stage, which evolve preferentially towards [00.1]-oriented grains. The dependence of the nucleation regime on growth conditions was assigned to Ga adatom kinetics. This statement is consistent with the calculated graphene/GaN in-plane lattice coincidence and supported by a combination of transmission electron microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy experiments.

Assessment of Polarity in GaN Self-Assembled Nanowires by Electrical Force Microscopy.

In this work, we demonstrate the capabilities of atomic force microscopies (AFMs) for the nondestructive determination of the polarity of GaN nanowires (NWs). Three complementary AFMs are analyzed here: Kelvin probe force microscopy (KPFM), light-assisted KPFM, and piezo-force microscopy (PFM). These techniques allow us to assess the polarity of individual NWs over an area of tens of µm(2) and provide statistics on the polarity of the ensemble with an accuracy hardly reachable by other methods. The precise quantitative analysis of the tip-sample interaction by multidimensional spectroscopic measurements, combined with advanced data analysis, has allowed the separate characterization of electrostatic and van der Waals forces as a function of tip-sample distance. Besides their polarity, the net surface charge density of individual NWs was estimated.

Prevalencia de patología cardíaca en la enfermedad de Chagas: años 2004-2012. Programa y Red de Chagas de CABA / Prevalence of cardiac pathology in Chagas disease: 2004 -2012. Program and Chagas CABA network

El Instituto Universitario de Ciencias de las Salud ha mostrado un particular compromiso con la formación de sus estudiantes en la estrategia de Atención Primaria de la Salud, con las prácticas asistenciales dedicadas al 1er nivel de atención ambulatoria y a las patologías prevalentes en ese ámbito. Del mismo modo se han desenvuelto las actividades de formación en investigación. Como exponente de esa orientación, la revista Ciencias de la Salud publicó en el Vol. 2, N°1, 2011:4-9, el artículo “Prevalencia de la Enfermedad de Chagas” de Érica G. Morais, que había obtenido el premio “Futuros Líderes”, otorgado por el Curso Anual Internacional de Investigación en Ciencias de la Salud (IUCS-AMA, Prof. Carlos Álvarez Bermúdez). Aquella investigación formaba parte de un proyecto más amplio realizado en el Hospital Teodoro Álvarez entre 2004 y 2012, en el que participaron un conjunto de investigadores, que compartieron la autoría de la actual publicación. El Dr. Jorge Mitelman, Prosecretario de Ciencia y Técnica del IUCS e integrante de ese equipo, preparó además una reseña sobre la jornada del INCOSUR, realizada en abril del presente año, describiendo asimismo el proceso de desarrollo de la Ciudad de Buenos Aires, como área no endémica, para encarar las consecuencias de la enfermedad de Chagas

Spontaneous core­shell elemental distribution in In-rich In(x)Ga1-xN nanowires grown by molecular beam epitaxy.

The elemental distribution of self-organized In-rich In(x)Ga1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques has provided sufficient sensitivity and spatial resolution to prove the spontaneous formation of a core­shell nanowire and to quantify the thicknesses and alloy compositions of the core and shell regions. A theoretical model based on continuum elastic theory has been used to estimate the strain fields present in such inhomogeneous nanowires. These results suggest new strategies for achieving high quality nonpolar heterostructures.

InN thin film lattice dynamics by grazing incidence inelastic x-ray scattering.

Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations of thin wurtzite indium nitride films. Indium nitride is an especially relevant example, due to the technological interest for optoelectronic and solar cell applications in combination with other group III nitrides.

X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC.

By means of x-ray absorption near-edge structure (XANES) several Ga(1-x)Mn(x)N (0.03

Coherent control of optical emission from a conjugated polymer.

We have observed that resonant Rayleigh scattering dominates the emission from poly(p-phenylene vinylene) excited with photons at energies below the threshold at which excitonic migration is reduced. The intensity of the resonant emission decays exponentially with a lifetime of up to 450 fs after pulsed excitation. The coherent nature of the emission was confirmed by angular variations in the far-field emission intensity-bright and dark speckles. Persistence of a coherent polarization was demonstrated by coherent control using phase-locked pulses.

[Development of gastric carcinoma at the site of a preceding peptic ulcer after 10 years]. / Sviluppo di un carcinoma gastrico nella sede di una precedente ulcera peptica dopo 10 anni.

We have observed an adenocarcinoma of the stomach which developed on the site where an apparently benign active gastric ulcer had been diagnosed radiologically 10 and 7 years previously. The patient had complained of recurrent episodes of epigastric pain over ten years, which were well controlled by the medical treatment. The length of clinical history in this patient makes it unlikely that his ulcer was neoplastic at the time of onset. This appears to be, therefore, one of the rare instances of development of a gastric carcinoma on the site of a previously benign peptic ulcer.