Reference values and improvement of aerodynamic drag in professional cyclists   总被引：4，自引：1，他引：3  

García-López J  Rodríguez-Marroyo JA  Juneau CE  Peleteiro J  Martínez AC  Villa JG 《Journal of sports sciences》2008,26(3):277-286

The aims of this study were to measure the aerodynamic drag in professional cyclists, to obtain aerodynamic drag reference values in static and effort positions, to improve the cyclists' aerodynamic drag by modifying their position and cycle equipment, and to evaluate the advantages and disadvantages of these modifications. The study was performed in a wind tunnel with five professional cyclists. Four positions were assessed with a time-trial bike and one position with a standard racing bike. In all positions, aerodynamic drag and kinematic variables were recorded. The drag area for the time-trial bike was 31% higher in the effort than static position, and lower than for the standard racing bike. Changes in the cyclists' position decreased the aerodynamic drag by 14%. The aero-helmet was not favourable for all cyclists. The reliability of aerodynamic drag measures in the wind tunnel was high (r > 0.96, coefficient of variation < 2%). In conclusion, we measured and improved the aerodynamic drag in professional cyclists. Our results were better than those of other researchers who did not assess aerodynamic drag during effort at race pace and who employed different wheels. The efficiency of the aero-helmet, and the validity, reliability, and sensitivity of the wind tunnel and aerodynamic field testing were addressed.  相似文献   

Brief Report of the Granada,Spain Workshop,Biblioteca de Andalucia,Granada     

Javier Álvarez García  Pilar Tassara  Cristóbal Pasadas 《International Information and Library Review》2009,41(4):286-291

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Influence of different sports on bone mass in growing girls     

Esther Ubago-Guisado  Alba Gómez-Cabello  Javier Sánchez-Sánchez  Jorge García-Unanue  Leonor Gallardo 《Journal of sports sciences》2015,33(16):1710-1718

The aim of this study was to analyse whether there are differences in bone mass in girls playing different sports. Two hundred girls (10.6 ± 1.5 years old, Tanner stages I–III) participated in the study and were divided into groups of 40 (swimmers, soccer players, basketball players, handball players and controls). Bone mineral content and bone mineral density (BMD) (whole body and hip) were measured using dual-energy X-ray absorptiometry. The degree of sexual development was determined using Tanner test, and physical activity habits were recorded through a questionnaire designed ad hoc for this research. Girls were divided by pubertal stage and the type of sport. In the prepubertal group, intertrochanteric BMD was significantly higher in both handball and soccer players compared with the control group (P < 0.05). Furthermore, in the pubertal group, total BMD, mean arms BMD, pelvis BMD, femoral neck BMD, intertrochanteric BMD and Ward’s triangle BMD were significantly higher in soccer and handball players compared with the control group (P < 0.05), and the swimmers showed significantly higher values in the mean arms BMD compared with the control group (P < 0.01). Our data suggest that sport practice during puberty, especially in activities that support the body weight, may be an important factor in achieving a high peak bone mass and improving bone health in girls.  相似文献   

Secure chaotic communication based on extreme multistability     

AN Pisarchik  R Jaimes-Reátegui  C Rodríguez-Flores  JH García-López  G Huerta-Cuellar  FJ Martín-Pasquín 《Journal of The Franklin Institute》2021,358(4):2561-2575

Extreme multistability is the coexistence of a large number of attractors which can be reached by varying initial conditions. In this paper we show how this fascinating phenomenon can be used for secure communication. The main advantage of the communication system based on extreme multistability over a conventional chaos-based communication system is its exceptionally high security. The proposed system consists of two identical six-order oscillators; one in the transmitter and another one in the receiver, each exhibiting the coexistence of a large number of chaotic attractors. The oscillators are synchronized using a private channel through one of the system variables, while the information is transmitted via a public channel through another variable. The information is encrypted by varying the initial condition of one of the state variables in the transmitter using a chaotic map, adhering message packages in a staggered form to the coexisting attractors within the same time series of another state variable, which leads to switching among the coexisting chaotic attractors. To ensure communication security, the duration of the packages is shorter than synchronization time, so that synchronization attacks are ineffective.  相似文献   

Determinants of the Web accessibility of European banks     

Ana B. Martínez  Javier De Andrés  Julita García 《Information processing & management》2014

This paper aims at identifying the factors influencing the implementation of Web accessibility (WA) by European banks. We studied a database made up of 49 European banks whose shares are included in the Dow Jones EURO STOXX® TMI Banks [8300] Index. Regarding the factors for the implementation, we considered three feasible reasons. Firstly, WA adoption can be motivated by operational factors, as WA can aid in increasing operational efficiency. Secondly, we expect large banks to have higher WA levels, as small firms face competitive disadvantages with regard to technology adoption. Lastly, WA can also be understood as a part of the Corporate Social Responsibility (CSR) strategy, so, the more committed a bank is to CSR, the more prone it will be to implement WA. Our results indicate that neither the operational factors nor the firm size seem to have exerted a significant influence on WA adoption. Regarding CSR commitment, results indicate a significant influence on WA adoption. However, the effect of the influence is contrary to that hypothesized, since more CSR-committed banks have less accessible Web sites. A possible reason for this result is that banks not included in the CSR indexes try to overcome this drawback by engaging in alternative CSR activities such as WA.  相似文献   

Knowledge asset similarity and business relational capital gains: evidence from European manufacturing firms     

Andrés Barreneche García  Ahmed Bounfour 《知识管理研究与实践》2014,12(3):246-260

This paper leverages the concept of absorptive capacity to explore whether similar configurations of intellectual capital (IC) are associated with the performance of relational capital in firms. It proposes a novel implementation of graph theory to analyse similarities in knowledge assets. We use Community Innovation Survey data to examine 5813 manufacturing firms in 13 business sectors and 13 European countries. While firms rely on external relations to compensate for a lack of internal assets, we find that a company’s propensity to cooperate in innovation is associated with its own IC profile. In particular, firms with common knowledge assets are more likely to benefit from business relational capital. The main contribution of this study lies in a holistic approach to understanding how similarities in knowledge assets are linked to gains in business relational capital.  相似文献   

Assessment of muscle fatigue after an ultra-endurance triathlon using tensiomyography (TMG)     

García-Manso JM  Rodríguez-Ruiz D  Rodríguez-Matoso D  de Saa Y  Sarmiento S  Quiroga M 《Journal of sports sciences》2011,29(6):619-625

In this study, we used tensiomyography (TMG) to assess muscle status immediately after an ultra-endurance triathlon. Maximal radial displacement or deformation of the muscle belly, contraction time, delay time, sustain time, and relaxation time were measured for both legs, and dependent t-tests were used to compare means between the beginning and end of the race. The 19 men assessed (age 37.9 ± 7.1 years; height 177.5 ± 4.6 cm; weight: 73.6 ± 6.5 kg) participated in the 2009 edition of the Lanzarote Ironman. Deterioration in the neural response was observed for contraction time (P = 0.008) and relaxation time (P = 0.011), with a moderate decrease in the response time (sustain time) and a loss in muscle stiffness (deformation of the muscle belly). The effect of muscle fatigue on the rectus femoris and biceps femoris was different. Barely any changes in contraction time, relaxation time, sustain time, and deformation of the muscle belly were observed, while only the contraction response time decreased to a significant extent (reduction in delay time; P = 0.003). The considerable loss in contractile capacity induced by a long-distance race was reflected in changes in the neuromuscular response and fluctuations in the contractile capacity of the muscle. These modifications, derived from a prolonged, exhausting effort, can be assessed in a simple, non-aggressive, non-invasive way using tensiomyography.  相似文献   

What do K-12 students feel when dealing with technology and engineering issues? Gardner's multiple intelligence theory implications in technology lessons for motivating engineering vocations at Spanish Secondary School     

Jesús Sánchez-Martín  García J. Álvarez-Gragera  M. Antonia Dávila-Acedo  Vicente Mellado 《European Journal of Engineering Education》2017,42(6):1330-1343

The interest on engineering and scientific studies can be raised up even from the early years of academic instructional process. This vocation may be linked to emotions and aptitudes towards technological education. Particularly, students get in touch with these technological issues (namely STEM) during the Compulsory Secondary Education in Spain (12–16 years old).This work presents a preliminary evaluation of how relevant is Gardner's multiple intelligence theory (MIT) in the teaching–learning process within the Technology Lessons. In this sense, MIT was considered as an explanation variable of the emotional response within the different educational parts (so-called syllabus units, SU) in the Technology spanish curriculum. Different intelligence style (IS) will orient the student to a vision of the engineering and technology. This work tries to identify which relationships can be established between IS and specific technology and engineering learning. This research involved up to 135 students were subsequently tested about their predominant (IS) and on the emotions that arouse in them when working with each SU. The results were statistically significant and only those with a Logic-arithmetic or Environmental IS were not affected by the SU.Best teaching and learning practicesare required for encouraging further engineering studies.  相似文献   

PISA as a Political Tool in Spain: Assessment Instrument,Academic Discourse and Political Reform     

Leoncio Vega Gil  Juan Carlos Hernández Beltrán  Eva García Redondo 《欧洲教育》2016,48(2):89-103

This study examines to what extent there is a sort of “political appropiation” by political parties when they seek to set a discourse about the Spanish PISA outcomes. We have consistently found that programs for assessing the competencies of students, especially PISA, have become tools of rationalization and the legitimization of education policies in both the national and territorial contexts. Furthermore, each regional government focuses its discourse on what it feels to be its strong points, that is, a clear “self-justifying reading” of PISA outcomes.  相似文献   

Outreach initiatives operated by universities for increasing interest in science and technology     

Lena Gumaelius  Monica Almqvist  Anna Árnadóttir  Anders Axelsson  J. Alberto Conejero  José P. García-Sabater 《European Journal of Engineering Education》2016,41(6):589-622

ABSTRACT

Since the 1990s, the low number of students choosing to study science and technology in higher education has been on the societal agenda and many initiatives have been launched to promote awareness regarding career options. The initiatives particularly focus on increasing enrolment in the engineering programmes. This article describes and compares eight European initiatives that have been established and operated by universities (and in some cases through collaboration with other actors in society). Each initiative is summarised in a short essay that discusses motivation, organisation, pedagogical approach, and activities. The initiatives are characterised by comparing the driving forces behind their creation, how the initiative activities relate to the activities at the university, size based on the number of participants and cost per participant and pedagogical framework. There seem to be two main tracks for building outreach activities, one where outreach activities are based on the university's normal activities, and one where outreach activities are designed specifically for the visiting students.  相似文献