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Prefrontal cortex involvement during dual-task stair climbing in healthy older adults: An fNIRS study
No full textExecutive function and motor control deficits adversely affect gait performance with age, but the neural correlates underlying this interaction during stair climbing remains unclear. Twenty older adults (72.7 ± 6.9 years) completed single tasks: standing and responding to a response time task (SC), ascending or descending stairs (SMup, SMdown); and a dual-task: responding while ascending or descending stairs (DTup, DTdown). Prefrontal hemodynamic response changes (∆HbO2, ∆HbR) were examined using functional near-infrared spectroscopy (fNIRS), gait speed was measured using in-shoe smart insoles, and vocal response time and accuracy were recorded. Findings revealed increased ∆HbO2 (p = 0.020) and slower response times (p < 0.001) during dual-versus single tasks. ∆HbR (p = 0.549), accuracy (p = 0.135) and gait speed (p = 0.475) were not significantly different between tasks or stair climbing conditions. ∆HbO2 and response time findings suggest that executive processes are less efficient during dual-tasks. These findings, in addition to gait speed and accuracy maintenance, may provide insights into the neural changes that precede performance declines. To capture the subtle differences between stair ascent and descent and extend our understanding of the neural correlates of stair climbing in older adults, future studies should examine more difficult cognitive tasks. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Psychological characteristics of sports performance: Analysis of professional and semiprofessional football referees
No full textSports psychology acknowledges the importance of referees in sports. However, evidence is still needed on psychological variables related to refereeing decisions. Psychological characteristics related to sports performance (Stress Control, Influence of Performance Evaluation, Motivation, Mental Skills, and Team Cohesion) were assessed and compared to referee role (referees vs assistant referees), experience, age, and education level. A cross-sectional design was realized, sixty-one professional and semiprofessional referees from Colombia (Mage = 22.5; SD = 4.1) completed the questionnaire for Psychological Characteristics related to Sports Performance adapted for Football Referees (CPRD-AF, for its Spanish acronym). Findings revealed that psychological characteristics are consistent regarding the referee role and experience. Differences were found between stress control and age [FSC (3, 57) =3.83, p =.27, η2 =.38], were the 28-34-year-old group was significantly higher than the 16-21-year-old group. Significant differences were found between stress control and education level [FSC(4, 56) =3.19, p =.030, η2 =.14], postgraduate referees had higher stress control compared with undergraduate referees (p <.027). Performance evaluation has a significantly higher influence on postgraduate referees than college referees (p<.036). Future research needs to evaluate social factor and psychological characteristics related to refereeing performance and include different types of referees role. © JPES
Model for the prediction of noise from wind turbines
No full textThis article presents a prediction model that can be applied to estimate the propagation of noise generated by wind turbines through an easy calculation procedure. The proposed prediction model is semi-empirical and based on the analysis of phenomena related to the generation and propagation of sound levels and field measurements. An experimental program was designed that included the measurement of sound pressure levels with a sound level meter to different weather conditions and distances within a wind farm to compare them with the levels estimated by ISO 9613 Part 2. A statistical analysis of the data recorded in field was performed to observe the dependence on the meteorological variables recorded during the measurements. The model explains 92.5% of the variability of the residual sound pressure level and has an average absolute error of 2.9 dB. After eliminating 5.0% of the data considered atypical, the proposed model explains 94.7% of the variability of the residual sound pressure level, with an average absolute error of 2.5 dB. A statistically significant relationship exists between the variables with a confidence level of 95.0%. The results have provided a rather satisfactory model for predicting noise from wind turbines up to distances of 900 m, greatly improving what has been achieved so far by the method established in standard ISO 9613 Part 2. literature for that particular subject. © 2018 Universidad de Antioquia.Este artículo presenta un modelo de predicción aplicable a la propagación del ruido proveniente de los aerogeneradores a través de un procedimiento de cálculo de fácil implementación. El modelo de predicción propuesto es semi-empírico y se basa en el análisis de los fenómenos relacionados con la generación y propagación de los niveles sonoros y las mediciones de campo. Se diseñó un programa experimental que comprendió la medición de los niveles de presión sonora con un sonómetro en determinadas condiciones meteorológicas y diferentes distancias al interior de un parque eólico para compararlos con los niveles estimados por la norma ISO 9613 Parte 2. Se realizó un análisis estadístico de los datos registrados en campo para observar la dependencia con las variables meteorológicas registradas durante las mediciones. El modelo propuesto explica el 92,5 % de la variabilidad del nivel de presión sonora residual y tiene un error absoluto medio de 2.9 dB. Al eliminar el 5,0 % de los datos por considerarlos atípicos, el modelo propuesto explica el 94,7 % de la variabilidad del nivel de presión sonora residual con un error absoluto medio de 2,5 dB. Hay una relación estadísticamente significativa entre las variables en un nivel de confianza del 95,0%. Los resultados han arrojado un modelo bastante satisfactorio para predecir el ruido proveniente de los aerogeneradores hasta distancias de 900 m, mejorando en gran medida lo obtenido hasta el momento por el método establecido en la norma ISO 9613 Parte 2. © 2018 Universidad de Antioquia
Local and Global: The State against transnational crime [Local y global: El Estado frente al delito transnacional]
No full textTransnational organized crime (cot) is one of the main affectations to nation states in the contemporary world, to such an extent that in many occasions criminal networks exceed the capacity of institutions. The objective of this article is to show the legal limits of the nation state against this phenomenon from a historical-hermeneutical analysis. This qualitative research has an interpretative level and is developed from a dual perspective, taking elements of the institutionalism proper to political science and the analysis of international law and criminal law. The idea is sustained that the nation state can overcome its crisis as long as it recognizes a fragmented sovereignty that allows not only the hybridization of the law, but also the hybridization of state institutions and functions in terms of security and prosecution of transnational crime. That is, the States must migrate to a network operation, as do the groups associated with transnational organized crime. © 2020 Universidad Externado de Colombia. All rights reserved
Characterization of titanium powders processed in n-hexane by high-energy ball milling
No full textThe effect of speed and milling time on the morphology, crystallite size, and phase composition of Ti Cp powders processed in n-hexane by high-energy ball milling (HEBM) using a E-max Retsch equipment was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Lattice parameters, mean crystallite size, lattice strain, and dislocation density were obtained from Rietveld analysis. The XRD and TEM results show that the HEBM process of the Ti Cp promotes the transition from HCP to FCC after 6 h of milling at 1400 rpm. The transformation process could be attributed to the energy generated in the milling process which induces high deformation and presence of high-density dislocations in the powder. Graphical Abstract[Figure not available: see fulltext.]. © 2020, Springer-Verlag London Ltd., part of Springer Nature
Advances in attractive ellipsoid method for robust control design
No full textOur contribution is devoted to a further theoretic development of the attractive ellipsoid method (AEM). We consider dynamic models given by nonlinear ordinary differential equations in the presence of bounded disturbances. The resulting robustness analysis of the closed-loop system incorporates the celebrated Clarke invariancy concept (an analytic extension of the celebrated Lyapunov methodology). We finally obtain a new general geometric characterization of the AEM-based approach to the robust systems design. Moreover, we also discuss the corresponding numerical aspects of the proposed theoretical extensions of the method. The theoretic results obtained in this contribution are finally illustrated by a practically oriented computational example. © 2018 John Wiley & Sons, Ltd
Diels-Alder reaction mechanisms of substituted chiral anthracene: A theoretical study based on the reaction force and reaction electronic flux
No full textQuantum chemical calculations were used to study the mechanism of Diels-Alder reactions involving chiral anthracenes as dienes and a series of dienophiles. The reaction force analysis was employed to obtain a detailed scrutiny of the reaction mechanisms, it has been found that thermodynamics and kinetics of the reactions are quite consistent: the lower the activation energy, the lower the reaction energy, thus following the Bell-Evans-Polanyi principle. It has been found that activation energies are mostly due to structural rearrangements that in most cases represented more than 70% of the activation energy. Electronic activity mostly due to changes in σ and π bonding were revealed by the reaction electronic flux (REF), this property helps identify whether changes on σ or π bonding drive the reaction. Additionally, new global indexes describing the behavior of the electronic activity were introduced and then used to classify the reactions in terms of the spontaneity of their electronic activity. Local natural bond order electronic population analysis was used to check consistency with global REF through the characterization of specific changes in the electronic density that might be responsible for the activity already detected by the REF. Results show that reactions involving acetoxy lactones are driven by spontaneous electronic activity coming from bond forming/strengthening processes; in the case of maleic anhydrides and maleimides it appears that both spontaneous and non-spontaneous electronic activity are quite active in driving the reactions. © 2020 Wiley Periodicals LL
Experimental exploration of dynamic phase transitions and associated metamagnetic fluctuations for materials with different Curie temperatures
No full textWe study dynamic magnetic behavior in the vicinity of the dynamic phase transition (DPT) for a suitable series of samples that have different Curie temperatures TC, which thus enables us to experimentally explore the role of the reduced temperature T/TC in the DPT. For this purpose, we fabricate Co1-xRux epitaxial thin films with uniaxial in-plane anisotropy by means of sputter deposition in the concentration range 0.0≤x≤0.26. All samples are ferromagnetic at room temperature, exhibit an abrupt magnetization reversal along their easy axis, and represent a unique TC and thus T/TC ratio according to their Ru concentration. The dynamic magnetic behavior is measured by using an ultrasensitive transverse magneto-optical detection method and the resulting dynamic states are explored as a function of the applied magnetic field amplitude H0 and period P, as well as an additional bias field Hb, which is the conjugate field of the dynamic order parameter Q. Our experimental results demonstrate that the qualitative behavior of the dynamic phase diagram is independent of the T/TC ratio and that for all T/TC values we observe metamagnetic anomalies in the dynamic paramagnetic state, which do not exist in the corresponding thermodynamic phase diagram. However, quantitatively, these metamagnetic anomalies are very strongly dependent on the T/TC ratio, leading to an about 20-fold increase of large metamagnetic fluctuations in the paramagnetic regime as the T/TC ratio increases from 0.37 to 0.68. Also, the phase space range in which these anomalous metamagnetic fluctuations occur extends closer and closer to the critical point as T/TC increases. © 2020 American Physical Society
CO, CO 2 , and H 2 Interactions with (0001) and (001) Tungsten Carbide Surfaces: Importance of Carbon and Metal Sites
No full textIn this work, a systematic study on the adsorption of atomic and molecular hydrogen and carbon oxides on cubic (001) and hexagonal (0001) WC surfaces by periodical density functional theory is reported. Calculations have been performed by employing the Perdew-Burke-Ernzerhof exchange correlation functional with van der Waals corrections to account for the dispersive force term. In addition, dipole corrections were applied for W- and C-terminated hexagonal WC(0001) surfaces. Good agreement is found between calculated and reported data for representative bulk properties. Regarding surface properties, our results indicate that atomic hydrogen adsorbs quite strongly while H 2 does, in general, dissociatively on the studied surfaces, with very small energy barriers (<0.35 eV) for the cleavage of the H-H bonds. The C sites of the carbide play an essential role in the binding of H atoms and the cleavage of H-H bonds. Studies examining the interaction of tungsten carbide with CO and CO 2 also evidence the importance of C sites. The reactivity of C- and W-terminated (0001) hexagonal WC surfaces significantly differs. Atomic hydrogen, carbon monoxide, and CO 2 are more stable on a C- than on a W-terminated surface, and only this latter termination is able to cleave spontaneously a C-O bond of the CO 2 molecule. This difference in reactivity may open a number of possibilities for fine-tuning the selectivity of the resulting material or designing compounds catalytically active for specific reactions by carefully adjusting the proportion of C, W, and mixed terminations during the synthesis procedure. © 2019 American Chemical Society
A Path for the Implementation of Best Practices for Software Requirements Management Process Using a Multimodel Environment
No full textContinuous improvement is one of the topics of interest for organizations seeking positioning opportunities in the world market. However, software development organizations have high levels of difficulty to implement best practices that address continuous improvement. This paper presents a path to follow to facilitate the work of continuous improvement in a software development organization and that seeks to implement best practices in the software requirements management process. The path is drawn from an analysis of software process improvement models and standards related to software development best practices, under a multimodel environment. The path is structured with a set of techniques, tools, activities, and outputs associated with identified best practices, to facilitate the implementation of improvements in the software requirements management process. Besides, the established path is proposed as an alternative to facilitate the process improvement using a multimodel environment, this way allows establishing balance and instances of collaboration among best practices independent of the model or standard to be implemented. © 2020, Springer Nature Switzerland AG