In the interest of exploiting natural forces for propellant-less spacecraft missions, this investigation proposes an adaptive control strategy to account for unknown parameters in the dynamic ...modeling of a reflectivity-controlled solar sail spacecraft. A Lyapunov-based control law along with integral concurrent learning is suggested to accomplish and prove global exponential tracking of the estimated parameters and states of interest, without satisfying the common persistence of excitation condition, which in most nonlinear systems cannot be guaranteed a priori. This involves estimating the solar flux or irradiance from the Sun to account for uncertainty and variation over time in this value. To illustrate potential applications, two missions are considered: (1) a geostationary debris removal case and (2) an Earth–Mars interplanetary transfer orbit following a logarithmic spiral reference trajectory. The proposed formulation demonstrates the benefit of estimating the solar flux using integral concurrent learning. The results are compared to trajectories with no estimation to illustrate the need to account for the actual solar flux.
•Integral concurrent learning is proposed to estimate the solar flux.•A gradient-based control law using Gauss’ variational equations is developed.•Global tracking of the solar flux is proved given a Lyapunov-based update law.•The persistence of excitation condition is relaxed to a finite excitation condition.
The sole method available for the photocycloaddition of unconjugated aliphatic alkenes is the Cu‐catalyzed Salomon–Kochi reaction. The Cu(OTf)2⋅benzene catalyst that has been standard in this ...reaction for many decades, however, is air‐sensitive, prone to photodecomposition, and poorly reactive towards sterically bulky alkene substrates. Using bench‐stable precursors, an improved catalyst system with superior reactivity and photostability has been designed, and it offers significantly expanded substrate scope. The utility of this new catalyst for the preparation of sterically crowded cyclobutane structures is highlighted through the preparation of the cores of the natural products sulcatine G and perforatol.
Described here is a new catalytic method for the 2+2 photocycloaddition of simple aliphatic alkenes. The CuI catalyst features a weakly coordinating anion that enables the formation of a long‐lived Cu bis(alkene) complex and supporting olefin ligands that stabilize the cationic CuI center without disrupting its photochemistry. This catalyst enjoys increased reaction rates and substrate scope compared to previous Cu‐templated photocycloaddition methods.
Currently, one of the main challenges faced in large metropolitan areas is traffic congestion. To address this problem, adequate traffic control could produce many benefits, including reduced ...pollutant emissions and reduced travel times. If it were possible to characterize the state of traffic by predicting future traffic conditions for optimizing the route of automated vehicles, and if these measures could be taken to preventively mitigate the effects of congestion with its related problems, the overall traffic flow could be improved. This paper performs an experimental study of the traffic distribution in the city of Valencia, Spain, characterizing the different streets of the city in terms of vehicle load with respect to the travel time during rush hour traffic conditions. Experimental results based on realistic vehicular traffic traces from the city of Valencia show that only some street segments fall under the general theory of vehicular flow, offering a good fit using quadratic regression, while a great number of street segments fall under other categories. Although in some cases such discrepancies are related to lack of traffic, injecting additional vehicles shows that significant mismatches still persist. Thus, in this paper we propose an equation to characterize travel times over a segment belonging to the sigmoid family; specifically, we apply logistic regression, being able to significantly improve the curve fitting results for most of the street segments under analysis. Based on our regression results, we performed a clustering analysis of the different street segments, showing that they can be classified into three well-defined categories, which evidences a predictable traffic distribution using the logistic regression throughout the city during rush hours, and allows optimizing the traffic for automated vehicles.
The main objective of the present study is to determine the kinetics, thermodynamics, and adsorption mechanism of the oxytetracycline (OTC) on rice husk ash (RHA). The adsorbent was characterized by ...scanning electronic microscopy, Fourier transform infrared spectroscopy, and nitrogen physisorption. Batch studies were carried out to evaluate the influence of the adsorbent dose, initial concentration, contact time, temperature, and initial pH. RHA was characterized as having heterogeneous, fibrous, and porous particles, consisting predominantly of silica. The removal of OTC depends on the pH of the medium, which is favored at acid pH values. The kinetic data followed the Bangham model, which indicated an OTC diffusion in the pores of RHA, although this was not the only process, as demonstrated through the use of the Weber-Morris model (IPD model). The Sips isotherm best represents the experimental results of the equilibrium study. It was found that the adsorption process was spontaneous and endothermic. The highest adsorption capacity was found at a pH in the range of 4–6, when the OTC is in its zwitterion form and the surface of the RHA is positively charged, thus permitting electrostatic interactions and the formation of hydrogen bonds between the adsorbent and adsorbate molecules. These findings demonstrate the potential of rice husk ash to remove oxytetracycline from water.
Traffic congestion is an important problem faced by Intelligent Transportation Systems (ITS), requiring models that allow predicting the impact of different solutions on urban traffic flow. Such an ...approach typically requires the use of simulations, which should be as realistic as possible. However, achieving high degrees of realism can be complex when the actual traffic patterns, defined through an Origin/Destination (O-D) matrix for the vehicles in a city, remain unknown. Thus, the main contribution of this paper is a heuristic for improving traffic congestion modeling. In particular, we propose a procedure that, starting from real induction loop measurements made available by traffic authorities, iteratively refines the output of DFROUTER, which is a module provided by the SUMO (Simulation of Urban MObility) tool. This way, it is able to generate an O-D matrix for traffic that resembles the real traffic distribution and that can be directly imported by SUMO. We apply our technique to the city of Valencia, and we then compare the obtained results against other existing traffic mobility data for the cities of Cologne (Germany) and Bologna (Italy), thereby validating our approach. We also use our technique to determine what degree of congestion is expectable if certain conditions cause additional traffic to circulate in the city, adopting both a uniform pattern and a hotspot-based pattern for traffic injection to demonstrate how to regulate the overall number of vehicles in the city. This study allows evaluating the impact of vehicle flow changes on the overall traffic congestion levels.
Lacustrine blue spaces provide benefits to the urbanites and wildlife habitat. Their availability varies depending on the city in which they are established and intra-urban social interactions. We ...analyzed the presence, distribution, and size of lentic water bodies in Mexico’s 145 most populated cities. We searched for patterns in their distribution concerning demographic, socioeconomic, and geographic data, aiming to understand their socio-ecological interactions in cities. We digitized lacustrine spaces to obtain their number per city, total surface, area of blue space per inhabitant, and surface as a percentage of the city’s total area. We tested for relationships between their number and surface and city population, hydrological regions, and urban marginalization index through linear and generalized linear models. We delimited 1834 lacustrine blue spaces, finding almost two-thirds of them artificial. Their presence and surface in Mexican cities were generally low, except for hydrological regions close to the Gulf of Mexico. Their number and surface decreased as the urban marginalization index increased. The lack of equitable provision of lacustrine space at the national level has implications for urban planning and land management. Blue spaces should maximize their ecosystem services’ provision for the whole society to promote cities’ sustainability and resilience.
La educación en escuelas rurales multigrado presenta diversos desafíos debido a la naturaleza del contexto y la limitada disponibilidad de recursos. En el caso específico de Ecuador, un país ...latinoamericano con una considerable cantidad de población rural, existen grandes deficiencias en cuanto a la calidad de los servicios educativos, especialmente en escuelas de Educación General Básica. Como respuesta a lo mencionado, surge el libro titulado Estrategias didácticas para la escuela rural multigrado, coordinado por Miguel Ángel Herrera-Pavo y María Gladys Cochancela Patiño, como parte de un proyecto de colaboración entre la escuela y la universidad. El propósito de este libro es ayudar al profesorado a desarrollar sus clases de manera más práctica y eficaz, optimizando mejor el tiempo y los recursos. Texto que proporciona una variedad de estrategias didácticas que pueden ser implementadas de forma transversal y específica en cada área curricular.
This paper proposes a framework for a satellite mission with the goal to perform Lunar Occultations within the context of the circular restricted three-body problem (CR3BP) of the Earth-Moon system. ...This is achieved by exploiting the geometrical relationships between the Earth, Moon, and a spacecraft orbiting around L4. Additionally, it examines the viability of a linear state-feedback control policy to stabilize short-period orbits under the presence of the gravitational effect of the Sun, Solar radiation pressure, and the Lunar orbital eccentricity, which is not accounted for in the CR3BP dynamics. Given the unprecedented NUV angular resolution achieved by a spacecraft at L4, this research proposes a framework for a remote sensing observatory for Solar activity, thereby enabling the monitoring of the entire hemisphere of Solar radiation, and to study different astrophysical issues via Lunar Occultations.
•Lunar Occultations are studied by leveraging short-period orbits about L4.•Short-period orbits (SPO) are selected to increase observation time of the Solar corona.•A linear controller is used to account for unmodeled orbital perturbations.•SPO with lower angular velocity is preferred to observe LO and Kordylewski clouds.•LO from L4 offer unprecedented NUV angular resolution.
Rice husk ash and rice husk are waste materials generated in the rice agro-industries. This study focuses on the possibility of using these materials as adsorbents for the removal of reactive blue ...dye 19. The adsorbents were characterized by employing the point of zero charge technique, scanning electron microscopy, X-ray microanalysis, and Fourier-transform infrared spectroscopy. The adsorption study was performed in a static system and by determining the influence of the initial concentration, adsorbent dose, initial pH, contact time, and temperature effect. The conditions of the removal process were established as being an initial pH 2, an adsorbent dose of 1 g/100 mL, and an equilibrium time of 120 min. A kinetic study was performed, and the data obtained for rice husk ash as regards blue dye 19 adsorption fitted best to the Bangham model, while those obtained for RH fitted best to the pseudo-second order and Bangham models. The equilibrium isotherms were analyzed by employing the Langmuir, Freundlich, Toth, and Sips models, and the Langmuir and Toth models proved to be the best representatives of blue dye 19 adsorption for both rice husk ash and rice husk. The thermodynamics of the adsorption process was studied, showing that the rice husk/blue dye 19 and rice husk ash/blue dye 19 removal systems were spontaneous and exothermic.
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