Velocity observer design for the consensus in delayed robot networks     

Marco A. Arteaga–Pérez  Emmanuel Nuño 《Journal of The Franklin Institute》2018,355(14):6810-6829

The consensus problem for networks of multiple agents consists in reaching an agreement between certain coordinates of interest using a distributed controller. It may be desirable that all the agents find a consensus at a given desired leader coordinate (Leader Follower Consensus Problem LFCP), or it may be only necessary that they agree at a certain coordinates value (Leaderless Consensus Problem LCP). Consensus has many practical applications in robot networks systems, where the interconnection of the agents may present variable time delays, hence rendering the stability analysis and control design more complex. Another problem that may arise is the possible lack of velocity measurements. In this work, a Proportional plus damping injection (P + d) controller together with a linear velocity observer is introduced. Our approach is able to solve both the LFCP and the LCP in networks of robots modeled as undirected weighted graphs with unknown asymmetric (bounded) variable time delays. Local (semi global) asymptotic stability is proven and simulation results are provided to test the performance of the proposed scheme.  相似文献   

Superintendent’s leadership: the cultural aspects of the role enactment     

Juan Manuel Niño 《International Journal of Leadership in Education》2018,21(3):267-283

This qualitative study seeks to create a better understanding of the work of school superintendents. This study was conducted using ethnographic techniques as a way to describe the practice of a Latino superintendent in a borderland community in south Texas. Guiding questions for this study were: What goes on in the workday life of a superintendent? and how does the superintendent enact his role as superintendent? Field study for this qualitative inquiry occurred over a period of seven months. Data for this study, including transgressive data, were collected primarily through participant observations, semi-structured ethnographic interviews, from artefacts and journal notes.  相似文献   

Effects of weightlifting exercise,traditional resistance and plyometric training on countermovement jump performance: a meta-analysis     

Ricardo Berton  Manoel E. Lixandrão  Claudio M. Pinto e Silva 《Journal of sports sciences》2018,36(18):2038-2044

Jump performance is considered an important factor in many sports. Thus, strategies such as weightlifting (WL) exercises, traditional resistance training (TRT) and plyometric training (PT) are effective at improving jump performance. However, it is not entirely clear which of these strategies can enable greater improvements on jump height. Thus, the purpose of the meta-analysis was to compare the improvements on countermovement jump (CMJ) performance between training methods which focus on WL exercises, TRT, and PT. Seven studies were included, of which one study performed both comparison. Therefore, four studies comparing WL exercises vs. TRT (total n = 78) and four studies comparing WL exercises vs. PT (total n = 76). The results showed greater improvements on CMJ performance for WL exercises compared to TRT (ES_diff: 0.72 ± 0.23; _95%CI: 0.26, 1.19; P = 0.002; Δ % = 7.5 and 2.1, respectively). The comparison between WL exercises vs. PT revealed no significant difference between protocols (ES_diff: 0.15 ± 0.23; _95%CI: ?0.30, 0.60; P = 0.518; Δ % = 8.8 and 8.1, respectively). In conclusion, WL exercises are superior to promote positive changes on CMJ performance compared to TRT; however, WL exercises and PT are equally effective at improving CMJ performance.  相似文献   

Exploring the perspectives of physically active and inactive adolescents: how does physical education influence their lifestyles?     

João Martins  Adilson Marques  António Rodrigues  Hugo Sarmento  Marcos Onofre  Francisco Carreiro da Costa 《Sport, Education and Society》2018,23(5):505-519

Based on a socio-ecological framework for physical education (PE), this study explored and analysed the perspectives of physically active and inactive adolescent boys and girls with different socioeconomic status (SES), regarding the meanings that PE had on their physical activity (PA) lifestyles throughout childhood and adolescence. An interpretative and qualitative design was adopted and operationalised through an individual two-hours in-depth interview. Thematic analysis identified five main themes that distinguish active from inactive adolescents: ‘Early experiences of PE at primary school’; ‘PE experiences in middle and secondary school’; ‘Friendly, professional and pedagogue. That’s what I want from my PE teacher’; ‘Friends in PE and PA’; ‘Active lifestyles? Are schools and PE ready for making a difference?…’. Regardless of the lifestyle, girls revealed more PE negative experiences, related to uninteresting and competitive activities, groups’ constitution and logistic factors. SES played a major role on their PA and PE experiences, with low SES adolescents having limited opportunities inclusively within the primary school PE context. This study provides evidence for the importance of promoting positive PE and PA experiences in early years. Based on adolescents’ voices, several recommendations are discussed that can be considered for improving PE professionals’ effectiveness in promoting active lifestyles.  相似文献   

Effect of wetted surface area on friction,pressure, wave and total drag of a kayak     

Beatriz B. Gomes  Leandro Machado  Nuno V. Ramos  Filipe A. V. Conceição  Ross H. Sanders  Mário A. P. Vaz 《Sports biomechanics / International Society of Biomechanics in Sports》2018,17(4):453-461

Using theoretical principles, the components of drag (friction D _F, pressure D _PR and wave D _W) of a single-seat kayak were analysed. The purpose was to examine the effect of changes in wetted surface area due to changes in kayaker’s weight and the relative contribution of D _F, D _PR and D _W to the total passive drag as function of velocity. The total passive drag values were based on experimental data collected in a single-seat kayak. Three different kayaker simulated weights were tested – 65, 75 and 85 kg. D _F was the drag component that contributed the greatest percentage (between 60 and 68% at 5.56 m/s the top velocity tested) to the total passive drag for all the velocities tested and simulated weights. D _W was the most affected by the increase in kayaker’s simulated weight, mainly when comparing 65/75 to 85 kg. Results support the importance of a kayak design selection that minimises the kayak’s drag for the individual weight of the kayaker. Also, the results suggest that the path for better hydrodynamic kayak performance should seek changes that can reduce D _F, D _PR and D _W with D _F offering the most potential to reduce passive drag.  相似文献   

Sodium bicarbonate ingestion increases glycolytic contribution and improves performance during simulated taekwondo combat     

João Paulo Lopes-Silva  Jonatas Ferreira Da Silva Santos  Guilherme Giannini Artioli  Irineu Loturco  Chris Abbiss  Emerson Franchini 《European Journal of Sport Science》2018,18(3):431-440

Purpose: To investigate the effect of sodium bicarbonate (NaHCO₃) on performance and estimated energy system contribution during simulated taekwondo combat. Methods: Nine taekwondo athletes completed two experimental sessions separated by at least 48?h. Athletes consumed 300?mg/kg body mass of NaHCO₃ or placebo (CaCO₃) 90?min before the combat simulation (three rounds of 2 min separated by 1 min passive recovery), in a double-blind, randomized, repeated-measures crossover design. All simulated combat was filmed to quantify the time spent fighting in each round. Lactate concentration [La^?] and rating of perceived exertion (RPE) were measured before and after each round, whereas heart rate (HR) and the estimated contribution of the oxidative (W_OXI), ATP (adenosine triphosphate)-phosphocreatine (PCr) (W_PCR), and glycolytic (W_{[ La^? ]}) systems were calculated during the combat simulation. Results: [La^?] increased significantly after NaHCO₃ ingestion, when compared with the placebo condition (+14%, P?=?0.04, d?=?3.70). NaHCO₃ ingestion resulted in greater estimated glycolytic energy contribution in the first round when compared with the placebo condition (+31%, P?=?0.01, d?=?3.48). Total attack time was significantly greater after NaHCO₃ when compared with placebo (+13%, P?=?0.05, d?=?1.15). W_OXI, W_PCR, VO₂, HR and RPE were not different between conditions (P?>?0.05). Conclusion: NaHCO₃ ingestion was able to increase the contribution of glycolytic metabolism and, therefore, improve performance during simulated taekwondo combat.  相似文献   

Teacher and school determinants of perceived classroom discipline: a multilevel analysis of TALIS 2013     

Lopes  João A.  Oliveira  Célia 《Learning Environments Research》2022,25(1):41-58

Learning Environments Research - Classroom discipline is a significant concern in most educational systems and a critical element of an effective learning environment. In this article, we present a...  相似文献   

University entrepreneurial performance: A Fuzzy Set Qualitative Comparative Analysis     

Lurdes D. Patrício  João J. Ferreira 《Higher Education Quarterly》2023,77(4):602-622

As key players in innovation and entrepreneurial ecosystems, Higher Education Institutions (HEI) assume a position as catalysts in creating and disseminating knowledge with repercussions in the societal, economic, political and innovation environments. In this scenario, HEI are facing the need to balance the performance of their traditional missions—teaching and research—with the pursuit of entrepreneurial performance. This brings awareness of the need to pay particular attention to HEI entrepreneurial performance (HEIEP) and how to measure it. Based on HEInnovate, a self-assessment tool resulting from a joint effort of the European Community and the OECD, this study aims to explore the benefits of university entrepreneurial metrics, analysing HEIEP as a discriminant function of the HEInnovate dimensions complemented with a qualitative approach using Fuzzy Set Qualitative Comparative Analysis (fsQCA). The analysis provides valuable details, presenting recipes based on the HEInnovate dimensions or combinations of dimensions to achieve a mission legitimation. This research brings awareness to the use of the HEInnovate scale, where it is possible to highlight the importance of the digital transformation and capability dimension to entrepreneurial performance (EP) and university mission legitimation.  相似文献