Structured Linearization of Discrete Mechanical Systems for Analysis and Optimal Control

Variational integrators are well-suited for simulation of mechanical systems because they preserve mechanical quantities about a system such as momentum, or its change if external forcing is involved, and holonomic constraints. While they are not energy-preserving they do exhibit long-time stable energy behavior. However, variational integrators often simulate mechanical system dynamics by solving an implicit difference equation at each time step, one that is moreover expressed purely in terms of configurations at different time steps. This paper formulates the first- and second-order linearizations of a variational integrator in a manner that is amenable to control analysis and synthesis, creating a bridge between existing analysis and optimal control tools for discrete dynamic systems and variational integrators for mechanical systems in generalized coordinates with forcing and holonomic constraints. The forced pendulum is used to illustrate the technique. A second example solves the discrete LQR problem to find a locally stabilizing controller for a 40 DOF system with 6 constraints.Comment: 13 page

Polymorphic Students

Objective: In an effort to break away from the stale classifications of community college students that stem from the hegemonic perspective of previous literature, this work utilizes the perceptions of community college practitioners to demonstrate new ways of understanding the identities of community college students. Method: By utilizing Gee’s identity theory and Grillo’s theory of intersectionality, we analyze interviews with community college practitioners from three different community colleges on the West coast of the United States to answer these questions: What identities (i.e., natural, institutional, and discursive) do faculty and administrators recognize in community college students? In what ways do community college faculty and administrators describe and conceptualize community college students? Findings: First, community college student identities are intricate and have changed with time; there are two different institutional views held by organizational members—the educational view and the managerial view—which both shape the construction of student identities and play a prominent role in determining which students are disadvantaged. Second, organizational members constructed meanings of student achievement and value (i.e., attributes or outcomes of the ideal student, or what policy makers and institutions refer to as success) according to organizational priorities and perspectives. Conclusion: This investigation encapsulates and elucidates the portrayals and understandings of community college students held by community college administrators and faculty as a means to acknowledge the diverse identities among these students. Scholars and practitioners are encouraged to acknowledge the polymorphic identities of this diverse population to improve scholarship and practice

Study of the stress intensity factors in the bulk of the material with synchrotron diffraction

Artículo de Proceedings de Congreso Internacional Fatigue2017In this work we present the results of a hybrid experimental and analytical approach for estimating the stress intensity factor. It uses the elastic strains within the bulk obtained by synchrotron X-ray diffraction data. The stress intensity factor is calculated using a multi-point overdeterministic method where the number of experimental data points is higher than the number of unknowns describing the elastic field surrounding the crack-tip. The tool is tested on X-ray strain measurements collected on a bainitic steel. In contrast to surface techniques the approach provides insights into the crack tip mechanics deep within the sample.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors are grateful to the ESRF for ID15 beamtime awarded under MA-1483. Financial support of Universidad de Malaga through Plan Propio, Junta de Andalucía through Proyectos de Excelencia grant reference TEP-3244, Campus de Excelencia Internacional del Mar (CEIMAR) and Ministerio de Economia y Competitividad through grant reference MAT2016-76951-C2-2-P is also acknowledged. PJW acknowledges an ERC advanced grant

COVID-19 lung lesion treated with pirfenidone and effective rehabilitation: A Case Report

SARS-CoV-2 leads to an inflammatory and fibrotic state in the lungs which can be the cause of death and even in those who survive cause a functional limitation. A male patient of 28 years with COVID-19 was treated with nitazoxanide 500 mg 6 hourly, ibuprofen 500 mg 8 hourly, levofloxacin 500 mg and vitamin D 4,000 IU 24 hourly, and pirfenidone (K-LP) 1,200 mg 12 hourly. The patient was ventilated and extubated after 13 days in the intensive care unit. He was then immersed in a strict rehabilitation programme based on re-teaching the diaphragmatic respiratory pattern. Pirfenidone at a dose of 1,200 mg twice a day could be considered as a valid option to reduce lung fibrosis caused by the SARS-CoV-2 virus. To ensure optimal recovery, pulmonary rehabilitation therapy should be added to the management

Inventario sobre el deseo de tener un hijo: una aproximación desde la teoría de acción razonada

El presente estudio tuvo por objetivo la construcción y validación de un instrumento capaz de identificar el deseo de tener un hijo en mujeres adolescentes, basado en los elementos de la teoría de acción razonada. Participaron 200 adolescentes de 12 a 15 años de edad, habitantes del Estado de México (México). La versión final del instrumento tuvo una estructura mixta (diferencial semántico y escala Likert) con un total de 72 reactivos. La confiabilidad y validez mostraron que los reactivos discriminaron con un valor de p 0.007, obteniéndose un alfa de Cronbach de 0.92, KMO de 0.778 y varianza explicada de 71.79%, siendo la actitud hacia el embarazo el elemento de la mencionada teoría que mejor predice el deseo de tener un hijo. Los autores concluyen que el instrumento es válido y confiable en cuanto a su objetivo se refiere

QoSatAr: a cross-layer architecture for E2E QoS provisioning over DVB-S2 broadband satellite systems

This article presents QoSatAr, a cross-layer architecture developed to provide end-to-end quality of service (QoS) guarantees for Internet protocol (IP) traffic over the Digital Video Broadcasting-Second generation (DVB-S2) satellite systems. The architecture design is based on a cross-layer optimization between the physical layer and the network layer to provide QoS provisioning based on the bandwidth availability present in the DVB-S2 satellite channel. Our design is developed at the satellite-independent layers, being in compliance with the ETSI-BSM-QoS standards. The architecture is set up inside the gateway, it includes a Re-Queuing Mechanism (RQM) to enhance the goodput of the EF and AF traffic classes and an adaptive IP scheduler to guarantee the high-priority traffic classes taking into account the channel conditions affected by rain events. One of the most important aspect of the architecture design is that QoSatAr is able to guarantee the QoS requirements for specific traffic flows considering a single parameter: the bandwidth availability which is set at the physical layer (considering adaptive code and modulation adaptation) and sent to the network layer by means of a cross-layer optimization. The architecture has been evaluated using the NS-2 simulator. In this article, we present evaluation metrics, extensive simulations results and conclusions about the performance of the proposed QoSatAr when it is evaluated over a DVB-S2 satellite scenario. The key results show that the implementation of this architecture enables to keep control of the satellite system load while guaranteeing the QoS levels for the high-priority traffic classes even when bandwidth variations due to rain events are experienced. Moreover, using the RQM mechanism the user’s quality of experience is improved while keeping lower delay and jitter values for the high-priority traffic classes. In particular, the AF goodput is enhanced around 33% over the drop tail scheme (on average)

Estudio florístico de la parte central de la barranca nenetzingo, municipio de Ixtapan de la sal, Estado de México

No se cuenta todavía con un inventario completo de plantas que existen en el territorio mexicano. Aún quedan grupos por conocer y zonas del país sin explorar. En tal situación se encuentra la barranca Nenetzingo, Ixtapán de la Sal, Estado de México. Con el objetivo de contribuir con el conocimiento de la fl ora se elaboró un listado de las especies, donde se incluyen algunos aspectos como: forma biológica, fenología reproductiva y abundancia. El trabajo consistió en colectar, secar y prensar todas las especies del área de estudio durante 21 meses, para su posterior identifi cación y con ello se elaboró el listado. Como resultados se reportan 362 especies distribuidas en 89 familias y 248 géneros, se reportan 17 especies por primera vez para el estado. Las familias más importantes a nivel de género son: Asteraceae, Poaceae y Fabaceae con 12.9, 10.6 y 5.2% de géneros cada una; de igual forma en especies 14.1, 9.4 y 6.4% respectivamente. La mayoría de las plantas son hierbas y arbustos representando el 82.6% del total de las especies identifi cadas. Los periodos de fl oración y fructifi cación de la fl ora son verano y otoño sumando 67.6% y 69.4% respectivamente. Gran parte de las plantas son abundantes (47.8%), seguida por frecuentes (29.3%) y escasas (22.9%). Finalmente se observa que la zona de estudio tiene un número considerable de diversidad refl ejada en el número de especies; sin embargo, de acuerdo al análisis de la fl ora se detecta que es un lugar perturbado requiriendo acciones para su conservación