In this investigation, the nonlinear swing-up problem associated with the cart-pole system modeled as a multibody dynamical system is solved by developing a deep Reinforcement Learning (RL) ...controller. Furthermore, the sensitivity analysis of the deep RL controller applied to the cart-pole swing-up problem is carried out. To this end, the influence of modifying the physical properties of the system and the presence of dry friction forces are analyzed employing the cumulative reward during the task. Extreme limits for the modifications of the parameters are determined to prove that the neural network architecture employed in this work features enough learning capability to handle the task under modifications as high as 90% on the pendulum mass, as well as a 100% increment on the cart mass. As expected, the presence of dry friction greatly affects the performance of the controller. However, a post-training of the agent in the modified environment takes only thirty-nine episodes to find the optimal control policy, resulting in a promising path for further developments of robust controllers.
In this paper, a literature review on two-wheeled vehicle systems is methodically performed and presented. For this purpose, the principal aspects concerning the kinematic, dynamic, control, and ...identification features of articulated mechanical systems described within the multibody formulation approach are emphasized in this review article. First, the scientific investigations on two-wheeled vehicle modelling are chronologically described employing a historical literature review approach. This is done to set a consistent context for the subsequent developments analyzed in the paper. Then, following the systematic literature review methodology described in this work, a rich corpus of relevant documents in the time span between 2013-present. Moreover, bibliometric methods are used to construct the conceptual structure map of the research field, which also allowed for formulating a thematic classification. Thus, considering the full-texts of the identified corpus of documents, this work presents a synthetic analysis of the fundamental issues about the multibody approaches for modelling two-wheeled vehicles. Finally, future research perspectives are pointed out in this article
In recent years,
-heterocyclic carbenes (NHC) have gained recognition as versatile molecules capable of acting as organocatalysts in various reactions, particularly through the activation of ...aldehydes via Breslow-type adducts. This organocatalytic activation has enabled the production of numerous 3,4-dihydropyran-2-ones and related derivatives. In this review, we provide an overview of the production of 3,4-dihydropyran-2-ones and derivatives via organocatalytic processes involving NHCs over the past eight years. These processes involve the use of a diverse range of substrates, catalysts, and reaction conditions, which can be classified into 4+2-and 3+3-type cycloadditions, primarily aimed at synthesizing this skeleton due to its biological activity and multiple stereocenters. These processes are scaled up to the gram scale, and the resulting products are often directed towards epimerization and functionalization to produce more complex molecules with potential applications in the biological field. Finally, we provide a perspective and the future directions of this topic in organic synthesis.
In this study, a novel technique for multiple damage detection of structures using modal characterization to evaluate the dynamic response of the structure given a damage model is investigated. The ...damage identification problem is seen as an optimization problem to be solved using a firefly optimization algorithm. The objective function is based on a numerical damage model that considers the modal response of the structures. We show some implementation details and discuss the obtained results for a benchmark problem used to assess the performance of the method and its advantages for structural health monitoring.
El presente trabajo tiene por objeto investigar la detección de daños en estructuras como un problema de optimización, utilizando la caracterización modal para evaluar la respuesta dinámica de la estructura ante un modelo de daño. Se llevó a cabo la implementación del algoritmo de optimización de la luciérnaga, tomando como caso de estudio un modelo numérico de daño sencillo, para ver los alcances del método propuesto y sus ventajas dentro del campo de monitoreo estructural (SHM). Se indican detalles de la implementación y los resultados obtenidos con este planteamiento.
In this investigation, a closed-chain kinematic model for two-wheeled vehicles is devised. The kinematic model developed in this work is general and, therefore, it is suitable for describing the ...complex geometry of the motion of both bicycles and motorcycles. Since the proposed kinematic model is systematically developed in the paper by employing a sound multibody system approach, which is grounded on the use of a straightforward closed-chain kinematic description, it allows for readily evaluating the effectiveness of two alternative methods to formulate the wheel-road contact constraints. The methods employed for this purpose are a technique based on the geometry of the vector cross-product and a strategy based on a simple surface parameterization of the front wheel. To this end, considering a kinematically driven vehicle system, a comparative analysis is performed to analyze the geometry of the contact between the front wheel of the vehicle and the ground, which represents a fundamental problem in the study of the motion of two-wheeled vehicles in general. Subsequently, an exhaustive and extensive numerical analysis, based on the systematic multibody approach mentioned before, is carried out in this work to study the system kinematics in detail. Furthermore, the orientation of the front assembly, which includes the frontal fork, the handlebars, and the front wheel in a seamless subsystem, is implicitly formulated through the definition of three successive rotations, and this approach is used to propose an explicit formulation of its inherent set of Euler angles. In general, the numerical results developed in the present work compare favorably with those found in the literature about vehicle kinematics and contact geometry.
This work presents a thermal management strategy for fuel cell hybrid electric vehicles under low-temperature conditions. Protecting the fuel cell system (FCS) and battery pack from such operating ...conditions prevent their degradation and performance decay. Thus, an approach similar to the keep-warm strategy is proposed to avoid the well-known issues related to the thaw-at-start methods, as well as promote a rapid startup after long parking periods. Particularly, the present work proposes a strategic synergy between the battery pack recharging and thermal management during the parking phase, so as to minimize the fuel consumption, while featuring vehicle to grid functionality and rapid startup of the vehicle when resuming driving. Such thermal management strategy was evaluated via simulation analyses, considering the transient thermal dynamics of the FCS and battery pack under low-temperature conditions and the temperature control strategy. The results outlined how proper exploitation of plugin functionalities, beyond introducing innovative vehicle-to-grid (V2G) concepts to suitably link driving to parking phases energy management, also allows for low-temperature safe thermal management of involved electrochemical devices. Finally, an economic analysis demonstrated that the proposed plugin-based vehicle to grid scenario presents a cost-saving potential of up to 56 % with respect to non V2G charge-sustaining one.
•Model based optimization for preliminary design of FCHVs powertrain.•Development of an energy management strategy for an FCHV during a driving cycle.•Advanced keep-warm approach for the thermal management of parked FCHVs under low- temperature conditions.•The vehicle to grid scenario features a 56% cost-saving potential of up to 56 % with respect to the baseline keep-warm approach.
In recent years, N-heterocyclic carbenes (NHC) have gained recognition as versatile molecules capable of acting as organocatalysts in various reactions, particularly through the activation of ...aldehydes via Breslow-type adducts. This organocatalytic activation has enabled the production of numerous 3,4-dihydropyran-2-ones and related derivatives. In this review, we provide an overview of the production of 3,4-dihydropyran-2-ones and derivatives via organocatalytic processes involving NHCs over the past eight years. These processes involve the use of a diverse range of substrates, catalysts, and reaction conditions, which can be classified into 4+2-and 3+3-type cycloadditions, primarily aimed at synthesizing this skeleton due to its biological activity and multiple stereocenters. These processes are scaled up to the gram scale, and the resulting products are often directed towards epimerization and functionalization to produce more complex molecules with potential applications in the biological field. Finally, we provide a perspective and the future directions of this topic in organic synthesis.
Tuberculosis esofágica: informe de un caso Manrique Martínez, Camilo Andrés; Salinas G, Diana Carolina; Martínez Marín, Julián David ...
Revista colombiana de gastroenterología,
12/2014, Letnik:
29, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Informamos el caso de un hombre inmunocompetente que consultó por cuadro de sangrado digestivo alto secundario a una úlcera esofágica de origen tuberculoso. El compromiso gastrointestinal por el ...Mycobacterium tuberculosis es raro aun en pacientes con altas prevalencias de enfermedad pulmonar y extrapulmonar; los sitios de mayor afectación son íleon terminal y el peritoneo, la enfermedad esofágica es exótica y generalmente es secundaria a la extensión proveniente de órganos vecinos infectados, como ganglios mediastinales y/o bronquios.
La clínica, las imágenes endoscópicas y radiológicas de la enfermedad esofágica suele simular una neoplasia maligna. La quimioterapia antituberculosa es la base del tratamiento, rara vez se requiere manejo quirúrgico.
La videocápsula endoscópica (VCE) ha revolucionado el estudio de las patologías de intestino delgado. El objetivo de este estudio es determinar las indicaciones, hallazgos y rendimiento diagnóstico ...de la VCE en un registro nacional.
Se realizó un estudio observacional, de corte transversal analítico, analizando los registros de VCE en siete centros del país, se recolectaron diferentes variables.
Se evaluaron 1.883 estudios de VCE. La edad promedio fue 55,4 años (5,6-94,2). Las indicaciones más frecuentes fueron sospecha de sangrado de intestino delgado (SID) (64,4%), estudio enfermedad de Crohn (15,2%) y diarrea crónica (11,2%). El 54,3% de VCE se prepararon con laxantes. Las lesiones más frecuentes fueron erosiones/úlceras (31,6%), angiectasias (25,7%) y parasitosis (2,7%). El rendimiento diagnóstico (P1+P2, clasificación de Saurin) de VCE en SID fue 60,6%, siendo mayor en SID evidente (66,0%) comparado con SID oculto (56,0%) (P=0,003). Los estudios con mejor preparación presentaban mayor detección de lesiones (93,8% vs. 89,4%) (OR=1,8; IC: 95%: 1,2-2,6; P=0,004). La tasa de complicación de VCE fue 3,1%, con visualización completa del ID en 96,6% y tasa de retención en ID de 0,7%. El 81,5% de VCE se realizaron en forma ambulatoria, y presentaron mayor visualización completa de ID que las hospitalarias (97,1% vs. 94,3%) (OR=2,1; IC: 95%; 1,2-3,5; P=0,008).
Las indicaciones, hallazgos y rendimiento diagnóstico de VCE en Colombia son similares a los reportados en la literatura universal, con alto porcentaje de estudios completos y baja tasa de complicaciones.
The small bowel capsule endoscopy (SBCE) has revolutionised the study of small bowel diseases. The objective of this study is to determine the indications, findings and diagnostic yield of SBCE in a national registry.
An observational, analytical cross-sectional study was carried out, analysing the SBCE records at seven centres in the country, where different variables were collected.
1,883 SBCEs were evaluated. The average age was 55.4 years (5.6-94.2). The most frequent indications were suspicion of small bowel bleeding (SBB) (64.4%), study of Crohn's disease (15.2%) and chronic diarrhoea (11.2%). 54.3% were prepared with laxatives. The most frequent lesions found were erosions/ulcers (31.6%), angioectasias (25.7%) and parasitosis (2.7%). The diagnostic yield (P1+P2, Saurin classification) of SBCE in SBB was 60.6%, being higher in overt SBB (66.0%) compared to occult SBB (56.0%) (P=.003). The studies with better preparation showed higher detection of lesions (93.8% vs. 89.4%) (OR=1.8, CI: 95%: 1.2-2.6; P=.004). The SBCE complication rate was 3.1%, with complete SB visualisation at 96.6% and SB retention rate of 0.7%. 81.5% of SBCEs were performed on an outpatient basis, and presented a greater complete SB visualisation than hospital ones (97.1% vs. 94.3%) (OR=2.1, CI: 95%, 1.2-3.5; P=.008).
The indications, findings and diagnostic performance of SBCEs in Colombia are similar to those reported in the literature, with a high percentage of complete studies and a low rate of complications.
The small bowel capsule endoscopy (SBCE) has revolutionised the study of small bowel diseases. The objective of this study is to determine the indications, findings and diagnostic yield of SBCE in a ...national registry.
An observational, analytical cross-sectional study was carried out, analysing the SBCE records at seven centres in the country, where different variables were collected.
1,883 SBCEs were evaluated. The average age was 55.4 years (5.6-94.2). The most frequent indications were suspicion of small bowel bleeding (SBB) (64.4%), study of Crohn's disease (15.2%) and chronic diarrhoea (11.2%). 54.3% were prepared with laxatives. The most frequent lesions found were erosions/ulcers (31.6%), angioectasias (25.7%) and parasitosis (2.7%). The diagnostic yield (P1+P2, Saurin classification) of SBCE in SBB was 60.6%, being higher in overt SBB (66.0%) compared to occult SBB (56.0%) (P=.003). The studies with better preparation showed higher detection of lesions (93.8% vs. 89.4%) (OR=1.8, CI: 95%: 1.2-2.6; P=.004). The SBCE complication rate was 3.1%, with complete SB visualisation at 96.6% and SB retention rate of 0.7%. 81.5% of SBCEs were performed on an outpatient basis, and presented a greater complete SB visualisation than hospital ones (97.1% vs. 94.3%) (OR=2.1, CI: 95%, 1.2-3.5; P=.008).
The indications, findings and diagnostic performance of SBCEs in Colombia are similar to those reported in the literature, with a high percentage of complete studies and a low rate of complications.
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