Assessment of left ventricle dynamic from cardiac magnetic resonance imaging by means a correspondence approach

In this research, an approach to assess the heart dynamics is reported. The cardiac magnetic resonance images are considered for assessing the left ventricle motion and deformation. The shape of the cavity is obtained by means a segmentation procedure based on a clustering algorithm at an initial instant. This three-dimensional structure is used to establish a region of interest around the border of the structure. An optical flow method allows determining the displacement vector of this region and then defining the shapes of the cavity during the all cardiac cycle. The points of the left ventricle are followed using the displacement vectors in the cardiac cycle, obtaining thus, a dense motion field of the cavity. This approximate deformation field is refined with a correspondence method that working in the three-dimensional space. The mapping of the points that define the left ventricle in the cardiac cycle obtained with the correspondence procedure are then used for computing a set of clinical parameters that allows assessing the motion and deformation of this principal structure of the human heart. The torsion, radial and longitudinal contraction are quantified. The obtained results are promising for evaluating the heart dynamics

Effects of grade retention policies: a literature review of empirical studies applying causal inference

The identification of the causal effects of grade retention policies is of enormous relevance for researchers and policymakers alike. Taking advantage of the availability of more detailed longitudinal datasets, researchers have been able to apply different identification strategies that address the classical problems of selection bias and unobserved heterogeneity that have plagued previous studies on the effect of retention. We present a systematic literature review of empirical studies aiming to unveil the causal effects of retention. This study underlines the need to consider and evaluate different kinds of grade retention polices as their effects vary depending on several dimensions (such as timing of the policy, comparison groups, length of the effects or institutional settings). According to the results of our review, we conclude that grade retention is unlikely to be an efficient policy as the costs associated to the policy can easily outweigh the potential (weak) benefits of retention. It is therefore necessary to consider alternative policies to retention, or policies that can be used in combination with it, in order to enhance the performance of low achievers, in particular those students at risk characterized by a low ability profile

Effects of plot size, stand density, and scan density on the relationship between airborne laser scanning metrics and the gini coefficient of tree size inequality

© 2017, Canadian Science Publishing. All rights reserved. Estimation of the Gini coefficient (GC) of tree sizes using airborne laser scanning (ALS) can provide maps of forest structure across the landscape, which can support sustainable forest management. A challenge arise s in determining the optimal spatial resolution that maximizes the stability and precision of GC estimates, which in turn depends on stand density or ALS scan density. By subsampling different plot sizes within large field plots, we evaluated the optimal spatial resolution by observing changes in GC estimation and in its correlation with ALS metrics. We found that plot size had greater effects than either stand density or ALS scan density on the relationship between GC and ALS metrics. Uncertainty in GC estimates fell as plot size increased. Correlation with ALS metrics showed convex curves with maxima at 250–450m 2 , which thus was considered the optimal plot size and, consequently, the optimal spatial resolution. By thinning the density of the ALS point cloud, we deduced that at least 3 points·m −2 were needed for reliable GC estimates. Many nationwide ALS scan densities are sparser than this, so may be unreliable for GC estimation. Ours is a simple approach for evaluating the optimal spatial resolution in remote sensing estimation of any forest attribute

Cambios microestructurales y efecto sobre las proteínas miofibrilares de la carne del pescado yamú (Brycon amazonicus) durante la conservación en frío

El propósito de este trabajo consistió en evaluar el efecto de la conservación en frío sobre la carne del pescado yamú (Brycon amazonicus). La metodología consistió en analizar bajo dos temperaturas (0±1,6°C y -8±1°C), dos periodos de conservación (13 y 61 horas) y dos orígenes distintos (cultivo y rio), cambios en el perfil proteico, microestructural, propiedades fisicoquímicas (capacidad de retención de agua-CRA, pH, textura de la carne de filetes de yamú. Las alteraciones microestructurales fueron realizadas por medio de microscopia electrónica de barrido y óptica. Los resultados del análisis de las imágenes de la microestructura de la carne mostraron un efecto negativo de la conservación en frío sobre el músculo, evidenciándose una afectación en el tejido conectivo. Por otro lado, el análisis de perfil proteico permitió evidenciar que durante la conservación en frío de la carne de yamú, proteínas cómo la miosina de cadena pesada, la actina y la α-actinina presentaron degradación. Adicionalmente, el origen de los peces y la temperatura de almacenamiento tuvieron efecto significativo en los cambios de textura (P≤0.05) por su parte el tiempo de almacenamiento tuvo efecto significativo sobre las tres características tecnológicas de la carne (CRA, pH y Textura) (P≤0.05); y la temperatura de almacenamiento no afectó de manera significativa la CRA (P>0.05).This study aimed to evaluate the effect of cold storage on yamu fish meat (Brycon amazonicus). The methodology consisted of analyzing two temperatures (0±1.6°C and -8±1°C), two storage periods (13 and 61 hours) and two different sources (farm and river), and determine changes in the protein profile, microstructural, physical and chemical properties (water retention capacity-WRC, pH, texture of yamu meat fillets). The microstructural changes were observed with optical and scanning electron microscopy. The results of the image analysis of the meat microstructure showed a negative effect from cold storage on the muscle, affecting the connective tissue. Otherwise, the analysis of protein profile demonstrated protein degradation during the cold storage of the yamu meat, such as for heavy chain myosin, actin and α-actinin. In addition, the origin of the fish and the storage temperature had a significant effect on the texture changes (P≤0.05); meanwhile, the storage time had a significant effect on the three technological characteristics of the meat (WRC, pH and texture) (P≤0.05). The storage temperature did not significantly affect the WRC (P>0.05)

Measurement of nonlinear refractive index of organic materials by z-scan

The nonlinear effects characterization by using the Z-Scan transmission technique in many materials has generated great in forest according to the technological necessities. The majority part of the nonlinear effects can be described by the classic electromagnetic theory, with the electrical susceptibility in the constitutive equation that relates the electrical polarization with the electrical field. In this work the sign and refractive index magnitude and the nonlinear absorption coefficient of the following organic substance were determined: methylene-blue, rodamine LD, vegetable powder and gentian violet a hundred percent pure dissolved in isopropyl alcohol, a laser Nd: YAG was used as a source excitation. The bunch of laser was focused with a lens of ten centimeters of focal length; by using a displacement system the sweeping of twenty centimeters was realized. The following results of the normalized curves of the transmittance in function of the z position were obtained applying the Sheik- Bahae theory: The nonlinear refractive index of the dye shows an increase in function of its concentration and the power of exciting of the laser with negative nonlinear sign in the majority of the sample

Treinta y cinco años de investigación en gestión estratégica. Un análisis de países utilizando técnicas bibliométricas para el período 1987-2021

[EN] As a significant field of study, thirty-five years of strategic management research has accumulated a substantial amount of knowledge. This bibliometric study explores whether the unlimited flow of knowledge and the globalization of education & research in this time period, could drive away (or deter) the identification and specific interest of research in phenomena of national importance. Using bibliometric techniques and visualization of similarities (VOS) procedures of citation and co-citation analyses, this Paper explores research trends at the country level over 35 years using data from the Web of Science database. The aims are to identify: 1) the most visible and prominent actors at the country, regional, and global-level; 2) the evolution of the subjects of research into strategic management at the country, global, and supra-regional level; and 3) the evolution of journals publishing strategic management research articles by location. Findings suggest that common research subjects coexist at higher levels of aggregation, establishing the “paradigm” or general agreement about the field’s boundaries. Additionally, findings show that at the country level, rather than following a global trend, there is an enduring diversification of research agendas that bow to national and supranational factors from geographically close places.[ES] Como un campo de estudio importante, treinta y cinco años deinvestigación en gestión estratégica han acumulado una cantidad sustancial deconocimiento. Este estudio bibliométrico explora si el flujo ilimitado deconocimiento y la globalización de la educación y la investigación en esteperíodo de tiempo, podría alejar (o disuadir) la identificación y el interésespecífico de investigación de fenómenos de importancia nacional. Utilizandotécnicas bibliométricas y procedimientos de visualización de similitudes (VOS) de análisis de citas y co-citas, este documentoexplora las tendencias de investigación a nivel de país durante 35 añosutilizando datos de la base de datos Web of Science. Los objetivos se centranen identificar: 1) los actores más visibles y destacados a nivel nacional,regional y mundial; 2) la evolución de los temas de investigación de la gestiónestratégica a nivel país, global y suprarregional; y 3) la evolución de las revistas que publicanartículos de investigación de gestión estratégica por ubicación. Los hallazgossugieren que los temas de investigación comunes coexisten en niveles superioresde agregación, estableciendo el “paradigma” o acuerdo general sobre los límitesde campo de estudio. Además, los hallazgos muestran que, a nivel de países,existe una diversificación persistente de agendas de investigación, que seinclinan a estudiar eventos nacionales y supranacionales de lugaresgeográficamente cercanos, en vez de seguir una tendencia global

Uncertainty as key element in the analysis of X–ray angiography images

The X–ray angiography images are routinely used to assess the blood vessels. The acquisition procedure considers a medical imaging system which allows obtaining views of the vessel while the blood flows thought them. The X–ray source is influenced on the region to be viewed and then, the projection of the all anatomical structures in the champ of view is shown through an image intensifier. The information of the blood vessel is impacted for the other structures. Additionally, the blood and the contrast product required in the acquisition are not mixed homogeneously, producing artifacts in the images. Finally, the noise is also an impact factor in the quality of the angiography images. In the coronary vessel case, the branches of the network are superposed. In this paper, an enhancement procedure to diminish the uncertainty associated to X–ray angiography images is reported. The relation between two versions of the angiograms is determined using a fuzzy connector considering that this relation diminishes the images intrinsic uncertainty. These versions correspond with images filtered with low-pass and high-pass image filters, respectively. The technique is tested with images of the coronary and kidney vessels. The qualitative results show a good enhanced of the angiography images

Spinal cord metabolic signatures in models of fast- and slow-progressing SOD1G93A Amyotrophic Lateral Sclerosis

The rate of disease progression in amyotrophic lateral sclerosis (ALS) is highly variable, even between patients with the same genetic mutations. Metabolic alterations may affect disease course variability in ALS patients, but challenges in identifying the preclinical and early phases of the disease limit our understanding of molecular mechanisms underlying differences in the rate of disease progression. We examined effects of SOD1G93A on thoracic and lumbar spinal cord metabolites in two mouse ALS models with different rates of disease progression: the transgenic SOD1G93A-C57BL/6JOlaHsd (C57-G93A, slow progression) and transgenic SOD1G93A-129SvHsd (129S-G93A, fast progression) strains. Samples from three timepoints (presymptomatic, disease onset, and late stage disease) were analyzed using Gas Chromatography-Mass Spectrometry metabolomics. Tissue metabolome differences in the lumbar spinal cord were driven primarily by mouse genetic background, although larger responses were observed in metabolic trajectories after the onset of symptoms. The significantly affected lumbar spinal cord metabolites were involved in energy and lipid metabolism. In the thoracic spinal cord, metabolic differences related to genetic background, background-SOD1 genotype interactions, and longitudinal SOD1G93A effects. The largest responses in thoracic spinal cord metabolic trajectories related to SOD1G93A effects before onset of visible symptoms. More metabolites were significantly affected in the thoracic segment, which were involved in energy homeostasis, neurotransmitter synthesis and utilization, and the oxidative stress response. We find evidence that initial metabolic alterations in SOD1G93A mice confer disadvantages for maintaining neuronal viability under ALS-related stressors, with slow-progressing C57-G93A mice potentially having more favorable spinal cord bioenergetic profiles than 129S-G93A. These genetic background-associated metabolic differences together with the different early metabolic responses underscore the need to better characterize the impact of germline genetic variation on cellular responses to ALS gene mutations both before and after the onset of symptoms in order to understand their impact on disease development