77823 research outputs found
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A study on an optimal analytical and an accurate algorithmic landing techniques
Get PDFLanding trajectory optimization is a fundamental challenge in aerospace engineering, traditionally approached by optimal control problem formulation. In practice, for Earth landing, the vehicle is subject to strongly non-linear perturbations, such as drag, wind, and gravity. Indirect control methods cannot deal with these problems, leading to large errors, while direct methods require high computation times when perturbations are not continuous. Thus, in this work, we propose a hybrid algorithm to approximate the solution of nonlinear optimization problems, based on the iteration of the indirect control analytical solution of the non-autonomous linear problem. The algorithm’s performance has been studied for the problem of landing rockets on the Earth’s surface and compared with a standard boundary value problem solver. The results show that the proposed algorithm tolerates strong discontinuous perturbations, with very small landing error and computation time
Dynamic small-scale green ammonia non-renewable and renewable exergy costs up to 2050: Short and long-term projections under IEA energy transition scenarios
No full textAmmonia is currently indispensable for fertilizers and is projected to be a fundamental renewable energy vector. This study analyzes the non-renewable and renewable exergy costs associated with a small-scale green ammonia plant under different combinations of water electrolysis technologies (AWE, PEM, SOEC, and AEM) with electricity sources (hydro, wind, photovoltaic, and electricity grid). Our method accounts for both the exergy conversion efficiencies of primary energy sources and the required materials on the infrastructures of the renewables and electrolyzers. Our research projects current, short-term (2030) and long-term (2050) ammonia’s exergy cost based on different IEA’s energy transition scenarios. Our findings highlight the impact of non-renewable exergy consumption on the renewables and electrolyzers infrastructures on ammonia exergy costs. In 2025, these values range between 12.5 and 32.5 MWh/tNH3 whereas in 2050 they might range between 11.5 and 19.1 MWh/tNH3 for SOEC-hydro and PEM-AWE-electricity grid scenarios, respectively. A Grassmann diagram illustrates how non-renewable and renewable exergy costs are split throughout the natural resources of our plant. A discussion about the model’s main features, restrictions and future industrial symbiosis possibilities (Ar, H2, O2) is presented. Our innovative methodology emphasizes the origins of natural resources by conscientiously evaluating their non-renewable and renewable exergy costs
A simultaneous relationship between digitalization and servitization? An application to Spanish importer manufacturing firms
No full textPurpose: This work aims to study the relationships between digitalization and servitization of manufacturing firms and whether this relationship is stronger for importer firms. Design/methodology/approachUsing: a dataset of Spanish manufacturing firms taken from the 2022 Spanish Survey on Business Strategies, a 3SLS (three-stage least squares) model was applied to 2028 firms. In addition, various models were fitted to subsamples to explore the effects of imports on the relationship between digital technologies and servitization. Findings: The results indicate that there are differences in the two opposite directions and that digital technologies affect servitization positively and not conversely; this is especially the case for small manufacturing firms. In addition, the results suggest that importing intermediate goods, considering the intensity and geographical diversification positively influences the relationship between digitalization and servitization only for high-import intensity firms. Research limitations/implications: This study contributes to the literature on digital servitization by providing support for the idea that digital technologies can positively affect servitization. In addition, these results address the need for a more nuanced discussion through importer intensity. Practical implications: Managers, especially from small manufacturing firms, should consider appropriate technology portfolio management and also consider the relationship between digital technologies and servitization as the initial step in the journey towards digital transformation. In addition, an international dimension should be considered when designing their digital servitization strategy. Originality/value: This work provides a basis for understanding the importance of importing intermediary goods when manufacturing firms are developing a digital servitization strategy
New trends in the design and evaluation of accessible human-computer interfaces
No full textIn today’s connected world, there are numerous situations in which people need to make use of devices with a human-computer interface. The variety of interfaces, with approaches such as multimodal interfaces, virtual reality, augmented reality and many others, makes it difficult to take advantage of the knowledge and techniques from working with traditional interfaces. Thus, it is necessary to work with these new interfaces from new points of view. Of course, accessibility is a key point in the success of interfaces, and the proposed approaches must take into account that interfaces need to be accessible..
Testing extreme warming and geographical heterogeneity
No full textExtreme climate events represent a critical climate risk and a global challenge. Understanding the heterogeneity in worldwide temperatures is crucial for predicting future climate change dynamics and guiding effective policy responses. This paper addresses both issues by analyzing the presence of trends in the tail decay of the realized distribution of annual temperatures for eight regions spanning the globe over the period 1960 to 2022. Our empirical findings reveal that extreme warming exhibits heterogeneity across regions and seasons, with a pronounced distinction between the Northern and Southern hemispheres. Importantly, extreme warming predominantly occurs in both hemispheres during the period from June to September
Interpretation of three-dimensional polarization states through the smart decomposition of the polarization matrix
No full textA complete description of a three-dimensional (3D) polarization state is provided by the two most significant eigenstates of the polarization matrix, together with the two indices of polarimetric purity. By means of the so-called smart decomposition, such information can be arranged to represent the state as a combination of two components, one partially polarized (active component) and one unpolarized. Contrary to what happens for two-dimensional (2D) polarization states (with the electric field fluctuating within a fixed plane), whose active component is constituted by a single totally polarized state, in the general case of 3D polarization states the active component is given by a weighted incoherent composition of the two above-mentioned eigenstates. We show that a detailed description of the intensity and spin anisotropies is encompassed by the active component of the state, which admits a simple interpretation and geometric representation. In addition, it is found that the degree of nonregularity can be viewed as a distance of the state to a regular state
Aproximaciones didácticas activas en el "Prácticum" de Investigación para la capacitación de estudiantes de Trabajo Social
No full textEste artículo aborda la implementación de metodologías activas de enseñanza-aprendizaje en el contexto universitario, específicamente en la asignatura del "Prácticum" del Grado en Trabajo Social. El problema central que se plantea es la necesidad de desarrollar en los estudiantes de Trabajo Social competencias cognitivas y epistemológicas relacionadas con la investigación social, a través de enfoques pedagógicos más dinámicos e interactivos. Para ello, el estudio utiliza técnicas de observación participante, rúbricas de evaluación y entrevistas, con el objetivo de analizar la pertinencia y efectividad de implementar metodologías activas en la enseñanza del "Prácticum" de investigación. Los autores buscan demostrar cómo el uso de estrategias como el aprendizaje basado en problemas, el análisis de estudios de caso, los debates y las actividades prácticas, pueden contribuir a una formación más sólida y contextualizada de las habilidades investigativas en los futuros trabajadores sociales. En resumen, este trabajo se enfoca en explorar las posibilidades que ofrecen las metodologías activas para mejorar la enseñanza-aprendizaje en el ámbito de la investigación social dentro de la carrera de Trabajo Social
Subtypes of suicidal ideation among university students – An ecological momentary assessment study
No full textBackground: Suicide is a leading cause of death among youth ages 15 to 29. This study identifies suicidal ideation (SI) subtypes among university students based on daily reports of SI, assesses how stress sensitivity may affect SI variability within these subtypes, and how they differ in terms of past and future self-injurious thoughts and behaviors (SITB).
Methods: 756 students participated in a 14-day ecological momentary assessment and web-based survey at baseline and 12-month follow-up. Latent Profile Analysis identified SI subtypes using indicators of intensity, variability and frequency. Multinomial regressions evaluated the associations between SITB and SI subtypes, as well between SI subtypes and future SITB. Linear models assessed how stress sensitivity was associated to SI variability within the subtypes.
Results: Three SI subtypes were identified: sporadic and low intensity/variability (S1), frequent and medium intensity/variability (S2), and frequent and high intensity/variability (S3). Stress sensitivity was highest in S2 and S3, in S3 higher stress sensitivity was associated with lower day-to-day variability. Nearly all aORs for SITB significantly increased from S1 to S3 compared to controls, with each subtype showing higher aORs compared to the previous subtype (S3 vs, S2 vs S1). S3 students showed higher persistence of suicidal thoughts and behaviors at follow-up (aOR = 20.6; 95 % CI = 8.3–51.2), with 4 of the 7 attempts occurring among students in this subtype.
Conclusions: Daily SI severity predicts future active SI and attempts, with stress sensitivity contributing to more extreme, rigid suicidal thinking. Targeting stress sensitivity could be effective for suicide prevention among university students
Revisiting secondary model features for describing the shoulder and lag parameters of microbial inactivation and growth models
No full textThe Baranyi and Geeraerd models are two of the most reliable models for the description of, respectively, microbial growth and inactivation. They are defined as a system of differential equations, whose algebraic solution can describe the microbial response during isothermal conditions, especially when combined with suitable secondary models. However, there are still large uncertainties regarding the best functions to use as secondary models for the lag phase duration (λ) and the shoulder length (Sl).
In this article, we revisit these models, focusing on the implications related to the assumption of an ideal substance whose dynamics define bacterial adaptation. We demonstrate that their link with the isothermal lag and shoulder leads to unique secondary models for the effect of temperature changes on λ and Sl. Namely, a log-linear relationship for Sl and a reverse cuadratic relationship for λ (considering a Ratkowsky model for μ). Furthermore, we observe a coupling between both secondary models (k and Sl for Geeraerd; λ and μ for Baranyi), reducing the number of unknown model parameters from four to three. Using data from the scientific literature, we illustrate the applicability of these results, being able to improve the robustness of parameter estimates.
The identification of these links are of great relevance for the field of predictive microbiology, as they resolve the uncertainty regarding the functional form of secondary models. Our results also provide a way to assess the validity of those dynamic hypotheses using data gathered under isothermal conditions, something that was hardly possible using data gathered under dynamic conditions. Although this study is limited to the effect of temperature, the general approach and methodology are also applicable to other type of secondary models, so this article can be a blueprint for future studies
Phenolic compounds and epigenetic mechanisms regulating gene expression: effects on human health
No full textAbstract
Phenolic compounds are a large class of phytochemicals with relevant physiological effects that are naturally found in plant-origin foods and derived products. Beneficial effects associated with polyphenol consumption are related to their ability to prevent and/or counteract disease features: they exert anti-inflammatory, antioxidant and anticancer effects, as well as protective actions against metabolic diseases. Phenolic compounds and their metabolites can modulate cell function by regulating gene expression. These effects are partially mediated through specific changes in epigenetic mechanisms such as DNA methylation, histone modifications and microRNA (miRNA) expression. Some polyphenols affect DNA methylation and are effective in counteracting deleterious actions induced by inflammatory/pro-oxidant factors, both in in vitro and in vivo settings. Specific mechanisms include modulation of methyl-transferases, whose levels are inhibited upon polyphenols treatment. Some polyphenols are histone deacetylase inhibitors, which prevent transcriptional repression and suppress tumor and inflammation genes by affecting selective regulation of miRNA expression. Their mostly recognized actions as anti-inflammatory and antioxidants seem to be partially mediated through regulation of individual miRNAs. Due to these actions, polyphenols and polyphenol-derived metabolites are under study in clinical and interventional trials for their benefits on inflammation and/or metabolic disorders. In conclusion, phenolic compounds might be an interesting approach to contribute to human homeostasis given their capacity to dynamically regulate epigenetic factors at cellular and systemic level. The present review aims to study available evidence regarding regulatory effects of polyphenols on gene expression, specifically mediated through epigenetic mechanisms