Comprehensive Model for the Transformation of Zinc Nitride Metastable Layers.

In this work, we performed systematic studies on the oxidation of zinc nitride metastable layers using a climate chamber with controlled temperature and relative humidity. The electrical properties of the samples were in situ analyzed using a programmable microprocessor with a voltage divider, while the structural and optical properties were ex situ measured by scanning electron microscopy, elastic recoil detection analysis, and spectroscopic ellipsometry. Our results show that zinc nitride transformation proceeds in a top-down way, with a progressive substitution of N by O, which leads to the formation of pores and a remarkable swelling effect. The overall behavior is well explained by a universal logistic growth model. Considering this model, we successfully fabricated and tested a zinc nitride-based dehydration sensor for biomedical applications.

Biological and Mechanical Synergies to Deal With Proton Therapy Pitfalls: Minibeams, FLASH, Arcs, and Gantryless Rooms.

Proton therapy has advantages and pitfalls comparing with photon therapy in radiation therapy. Among the limitations of protons in clinical practice we can selectively mention: uncertainties in range, lateral penumbra, deposition of higher LET outside the target, entrance dose, dose in the beam path, dose constraints in critical organs close to the target volume, organ movements and cost. In this review, we combine proposals under study to mitigate those pitfalls by using individually or in combination: (a) biological approaches of beam management in time (very high dose rate "FLASH" irradiations in the order of 100 Gy/s) and (b) modulation in space (a combination of mini-beams of millimetric extent), together with mechanical approaches such as (c) rotational techniques (optimized in partial arcs) and, in an effort to reduce cost, (d) gantry-less delivery systems. In some cases, these proposals are synergic (e.g., FLASH and minibeams), in others they are hardly compatible (mini-beam and rotation). Fixed lines have been used in pioneer centers, or for specific indications (ophthalmic, radiosurgery,…), they logically evolved to isocentric gantries. The present proposals to produce fixed lines are somewhat controversial. Rotational techniques, minibeams and FLASH in proton therapy are making their way, with an increasing degree of complexity in these three approaches, but with a high interest in the basic science and clinical communities. All of them must be proven in clinical applications.

A Geant4 simulation for three-dimensional proton imaging of microscopic samples.

Proton imaging can be carried out on microscopic samples by focusing the beam to a diameter ranging from a few micrometers down to a few tens of nanometers, depending on the required beam intensity and spatial resolution. Three-dimensional (3D) imaging by tomography is obtained from proton transmission (STIM: Scanning Transmission Ion Microscopy) and/or X-ray emission (PIXE: Particle Induced X-ray Emission). In these experiments, the samples are dehydrated for under vacuum analysis. In situ quantification of nanoparticles has been carried out at CENBG in the frame of nanotoxicology studies, on cells and small organisms used as biological models, especially on Caenorhabditis elegans (C. elegans) nematodes. Tomography experiments reveal the distribution of mass density and chemical content (in g.cm-3) within the analyzed volume. These density values are obtained using an inversion algorithm. To investigate the effect of this data reduction process, we defined different numerical phantoms, including a (dehydrated) C. elegans phantom whose geometry and density were derived from experimental data. A Monte Carlo simulation based on the Geant4 toolkit was developed. Using different simulation and reconstruction conditions, we compared the resulting tomographic images to the initial numerical reference phantom. A study of the relative error between the reconstructed and the reference images lead to the result that 20 protons per shot can be considered as an optimal number for 3D STIM imaging. Preliminary results for PIXE tomography are also presented, showing the interest of such numerical phantoms to produce reference data for future studies on X-ray signal attenuation in thick samples.

Photoluminescence enhancement of monolayer MoS2 using plasmonic gallium nanoparticles.

2D monolayer molybdenum disulphide (MoS2) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency. Herein, we use gallium hemispherical nanoparticles (Ga NPs) deposited by thermal evaporation on top of chemical vapour deposited MoS2 monolayers in order to enhance its luminescence. The influence of the NP radius and the laser wavelength is reported in PL and Raman experiments. In addition, the physics behind the PL enhancement factor is investigated. The results indicate that the prominent enhancement is caused by the localized surface plasmon resonance of the Ga NPs induced by a charge transfer phenomenon. This work sheds light on the use of alternative metals, besides silver and gold, for the improvement of MoS2 luminescence.

Hipovitaminosis D en la población anciana institucionalizada: variables asociadas y valoración geriátrica / Hypovitaminosis D in elderly population in nursing home: associated variables and geriatric assessment

Introducción: Los datos más recientes sugieren que el déficit de vitamina D es frecuente en ancianos, especialmente en los mayores institucionalizados. La vitamina D desempeña un papel importante en la hemostasia del calcio, en el metabolismo del hueso y afecta en términos de salud tanto a la mortalidad como al riesgo de caídas. El objetivo de este estudio fue determinar la prevalencia de hipovitaminosis D, cuáles son los factores de riesgo asociados y la utilidad de las herramientas de valoración geriátrica. Método: Estudio descriptivo transversal. Población: 83 residentes de la Residencia de 3.ª edad ‘Gerontos’, Pedrezuela, Madrid, España. Fue desarrollado de enero del 2014 a diciembre del 2015. Variables sociodemográficas: edad y sexo; variables clínico-asistenciales: peso, talla e índice de masa corporal, y variables analíticas: niveles de hemoglobina, creatinina, urea, albúmina y 25 hidroxivitamina D; instrumentos de medida: escala de capacidad cognoscitiva e Índice de Barthel como escala de valoración funcional. Resultados: El análisis bivariado encontró asociación entre el déficit cognitivo y la hipovitaminosis D (p 0,007). La prevalencia de hipovitaminosis D fue del 80,7%. Conclusión: La prevalencia de hipovitaminosis D es alta entre población anciana en las residencias geriátricas. Aunque los estudios observacionales no establecen causalidad, nuestros resultados muestran que la hipovitaminosis D se asocia a deterioro cognitivo. La determinación de niveles de vitamina D en este grupo de población y la instauración de la suplementación farmacológica en pacientes con niveles inadecuados sería recomendable

Introduction: Most recent data suggest that the vitamin D deficiency is frequent in the elderly, and it is specially prevalent among patients in the nursing home. In addition, the vitamin D plays a significant role in calcium homeostasis and bone metabolism and affects other health outcomes like mortality and risk of falls. The objective of this study was to determine the prevalence of hypovitaminosis D, which risk factors are related and the utility of geriatric assessment tools. Method: A cross-sectional descriptive study. Population: 83 residents in the nursing home ‘Gerontos’, Pedrezuela, Madrid, Spain. It was developed from January 2014 to December 2015. Sociodemographic, clinical variables, blood test were measured: hemoglobin, creatinine, urea, albumin and 25 (OH) vitamin D. Functional status according to the Barthel Index and cognitive status by Mini-Mental State Examination were recorded. Results: The bivariate analyses identified an association between poor cognitive status and hypovitaminosis D (p 0,007). The prevalence of hipovitaminosis D was 80,7%. Conclusion: the prevalence of hypovitaminosis D is high in the elderly population in nursing home. Even though transversal study does not allow a causal link, our results show a relationship between hypovitaminosis D and cognitive impairment. The determination of vitamin D levels in this high risk group and the establishment of the pharmacological supplementation in patients with inadequate levels would be advisable