Análisis de problemáticas urbanas a escala continental basado en datos abiertos: espacios verdes, forma urbana y sostenibilidad futura de las ciudades en África

Las próximas décadas serán de rápida urbanización y estrés climático en las ciudades africanas. Los espacios verdes pueden aumentar la resiliencia de las ciudades frente a las olas de calor, las inundaciones, los deslizamientos de tierra e incluso la erosión costera, además de mejorar la sostenibilidad al reparar la calidad del aire, proteger la biodiversidad y absorber carbono. Sin embargo, datos cuantitativos sobre la forma urbana, la disponibilidad de espacios verdes y la contaminación del aire son muy escasos y de difícil acceso para ciudades en África. En este trabajo usamos datos geoespaciales abiertos para analizar cuantitativamente las relaciones entre la forma urbana, la presencia de espacios verdes y la calidad del aire. Los resultados del análisis indican que la presencia de espacios verdes se relaciona con mejor calidad del aire, pero que deben estar acompañados de otras políticas para que su presencia sea realmente efectiva

Cellular EXchange Imaging (CEXI): Evaluation of a diffusion model including water exchange in cells using numerical phantoms of permeable spheres

Purpose: Biophysical models of diffusion MRI have been developed to characterize microstructure in various tissues, but existing models are not suitable for tissue composed of permeable spherical cells. In this study we introduce Cellular Exchange Imaging (CEXI), a model tailored for permeable spherical cells, and compares its performance to a related Ball \& Sphere (BS) model that neglects permeability. Methods: We generated DW-MRI signals using Monte-Carlo simulations with a PGSE sequence in numerical substrates made of spherical cells and their extracellular space for a range of membrane permeability. From these signals, the properties of the substrates were inferred using both BS and CEXI models. Results: CEXI outperformed the impermeable model by providing more stable estimates cell size and intracellular volume fraction that were diffusion time-independent. Notably, CEXI accurately estimated the exchange time for low to moderate permeability levels previously reported in other studies ($\kappa<25\mu m/s$). However, in highly permeable substrates ($\kappa=50\mu m/s$), the estimated parameters were less stable, particularly the diffusion coefficients. Conclusion: This study highlights the importance of modeling the exchange time to accurately quantify microstructure properties in permeable cellular substrates. Future studies should evaluate CEXI in clinical applications such as lymph nodes, investigate exchange time as a potential biomarker of tumor severity, and develop more appropriate tissue models that account for anisotropic diffusion and highly permeable membranes.Comment: 7 figures, 2 tables, 21 pages, under revie

Parameters Identification and Gas Behavior Characterization of DBD Systems

This paper proposes an efficient modeling and an identification method for dielectric barrier discharge (DBD) systems, based on input–output (current–voltage) experimental measurements. The DBD is modeled using an equivalent electric circuit associated with a differential equation that describes the dynamics of its conductance. This equation assumes a homogeneous behavior of the gas. This paper introduces a series of polynomial terms of the current of the gas into the conductance equation. These terms, after identification, are a very useful tool to analyze the physical mechanisms that take place in the gas. The identification process also returns the numerical values of other DBD parameters, such as associated capacitances and the breakdown voltage. In addition, an asymmetric model for the gas, which considers the direction of the current, is proposed to consider the possible geometrical dissimilarity between the two electrodes of the DBD setup. Experimental measurements taken on two different DBD applications are used for validating the proposed approach

Elaboración de un boletín de resultados de investigación y de trabajos fin de máster

Memoria ID-0150. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2009-2010.El objetivo del proyecto de innovación docente al que se refiere esta memoria era la creación de un sitio web con formato de revista electrónica, integrado en la página de la Universidad de Salamanca, que pudiera presentar resultados de la investigación obtenidos en el marco de la Escuela de Posgrado Estado de Derecho y Buen Gobierno, y que sirviera a los alumnos potenciales, actuales y pasados de los másteres en Democracia y Buen Gobierno, Análisis Económico del Derecho y las Políticas Públicas y Corrupción y Estado de Derecho como referencia para completar sus expectativas acerca de los programas formativos, para la preparación de asignaturas y, sobre todo, Trabajos Fin de Máster y como vínculo de contacto permanente una vez que son egresados de sus respectivos programas

Tractography dissection variability: What happens when 42 groups dissect 14 white matter bundles on the same dataset?

White matter bundle segmentation using diffusion MRI fiber tractography has become the method of choice to identify white matter fiber pathways in vivo in human brains. However, like other analyses of complex data, there is considerable variability in segmentation protocols and techniques. This can result in different reconstructions of the same intended white matter pathways, which directly affects tractography results, quantification, and interpretation. In this study, we aim to evaluate and quantify the variability that arises from different protocols for bundle segmentation. Through an open call to users of fiber tractography, including anatomists, clinicians, and algorithm developers, 42 independent teams were given processed sets of human whole-brain streamlines and asked to segment 14 white matter fascicles on six subjects. In total, we received 57 different bundle segmentation protocols, which enabled detailed volume-based and streamline-based analyses of agreement and disagreement among protocols for each fiber pathway. Results show that even when given the exact same sets of underlying streamlines, the variability across protocols for bundle segmentation is greater than all other sources of variability in the virtual dissection process, including variability within protocols and variability across subjects. In order to foster the use of tractography bundle dissection in routine clinical settings, and as a fundamental analytical tool, future endeavors must aim to resolve and reduce this heterogeneity. Although external validation is needed to verify the anatomical accuracy of bundle dissections, reducing heterogeneity is a step towards reproducible research and may be achieved through the use of standard nomenclature and definitions of white matter bundles and well-chosen constraints and decisions in the dissection process

Performance of non-invasive tests and histology for the prediction of clinical outcomes in patients with non-alcoholic fatty liver disease: an individual participant data meta-analysis

BackgroundHistologically assessed liver fibrosis stage has prognostic significance in patients with non-alcoholic fatty liver disease (NAFLD) and is accepted as a surrogate endpoint in clinical trials for non-cirrhotic NAFLD. Our aim was to compare the prognostic performance of non-invasive tests with liver histology in patients with NAFLD.MethodsThis was an individual participant data meta-analysis of the prognostic performance of histologically assessed fibrosis stage (F0–4), liver stiffness measured by vibration-controlled transient elastography (LSM-VCTE), fibrosis-4 index (FIB-4), and NAFLD fibrosis score (NFS) in patients with NAFLD. The literature was searched for a previously published systematic review on the diagnostic accuracy of imaging and simple non-invasive tests and updated to Jan 12, 2022 for this study. Studies were identified through PubMed/MEDLINE, EMBASE, and CENTRAL, and authors were contacted for individual participant data, including outcome data, with a minimum of 12 months of follow-up. The primary outcome was a composite endpoint of all-cause mortality, hepatocellular carcinoma, liver transplantation, or cirrhosis complications (ie, ascites, variceal bleeding, hepatic encephalopathy, or progression to a MELD score ≥15). We calculated aggregated survival curves for trichotomised groups and compared them using stratified log-rank tests (histology: F0–2 vs F3 vs F4; LSM: 2·67; NFS: 0·676), calculated areas under the time-dependent receiver operating characteristic curves (tAUC), and performed Cox proportional-hazards regression to adjust for confounding. This study was registered with PROSPERO, CRD42022312226.FindingsOf 65 eligible studies, we included data on 2518 patients with biopsy-proven NAFLD from 25 studies (1126 [44·7%] were female, median age was 54 years [IQR 44–63), and 1161 [46·1%] had type 2 diabetes). After a median follow-up of 57 months [IQR 33–91], the composite endpoint was observed in 145 (5·8%) patients. Stratified log-rank tests showed significant differences between the trichotomised patient groups (p<0·0001 for all comparisons). The tAUC at 5 years were 0·72 (95% CI 0·62–0·81) for histology, 0·76 (0·70–0·83) for LSM-VCTE, 0·74 (0·64–0·82) for FIB-4, and 0·70 (0·63–0·80) for NFS. All index tests were significant predictors of the primary outcome after adjustment for confounders in the Cox regression.InterpretationSimple non-invasive tests performed as well as histologically assessed fibrosis in predicting clinical outcomes in patients with NAFLD and could be considered as alternatives to liver biopsy in some cases

The Diffusion-Simulated Connectivity Dataset

The Diffusion-Simulated Connectivity Dataset is generated from a numerical phantom and Monte-Carlo simulation of the diffusion-weighted MRI signal [Rafael-Patino et al., Frontiers in Neuroinformatics, 2020]. The dataset was created to evaluate diffusion-weighted MRI-based structural connectome estimation techniques such as voxel-wise fibre orientation estimation, tractography, and structural connectome estimation. The phantom is constructed from 12,196 synthetic tubular fibres (strands) ranging in diameter from 1.4μm to 4.2μm. The phantom geometry was obtained using the optimisation procedure included in the Numerical Fiber Generator [Close et al., NeuroImage, 2009]. Sixteen regions of interest (ROIs) located on the surface of a sphere are connected through a variable number of strands. The strands form complex white matter configurations that include kissing, branching, and crossing at different angles. The weights of the 16x16 ground truth connectivity matrix are defined by the total cross-sectional area of the strands forming the connections. The phantom has a volume of 1 cubic millimetre and is divided into a 40x40x40 voxel image matrix. After the Monte-Carlo simulation of the diffusion-weighted MRI signals, the image header is set to a voxel size of 1.0 mm isotropic, creating a final image size of 4x4x4 cm³, compatible with conventional diffusion-weighted MRI methods. The diffusion-weighted MRI simulation protocol includes 360 diffusion-weighted images and 4 non-diffusion-weighted images (b=0 s/mm²). The diffusion-weighted MRI signals are distributed on 4 b-shells (b=1000, 1925, 3094, 13191 s/mm²). The dataset includes the signal generated with the Monte Carlo simulation and the same signal corrupted with various levels of Rician noise. Additionally, the dataset contains the relevant phantom’s ground-truth information including, i) a voxel map indicating the volume fraction occupied by the strands, ii) a label map of the location of the 16 ROIs, iii) the 12,196 strands' centerline trajectories, as well as their diameter and ending ROIs, and iv) the three-dimensional substrate mesh used for the Monte Carlo simulation