An improved method of retarding and stopping railway trains     

Alexander Allen 《Journal of The Franklin Institute》1860,69(2):78-80

  相似文献   

Modelling error distribution in the ground reaction force during an induced-acceleration analysis of running in rear-foot strikers     

Sekiya Koike  Seigo Nakaya  Hiroto Mori  Tatsuya Ishikawa  Alexander P. Willmott 《Journal of sports sciences》2019,37(9):968-979

The objective of this study was to develop and evaluate a methodology for quantifying the contributions of modelling error terms, as well as individual joint torque, gravitational force and motion-dependent terms, to the generation of ground reaction force (GRF), whose true value can be measured with high accuracy using a force platform. Dynamic contributions to the GRF were derived from the combination of (1) the equations of motion for the individual segments, (2) the equations for constraint conditions arising from the connection of adjacent segments at joints, and (3) the equations for anatomical constraint axes at certain joints. The contribution of the error term was divided into four components caused by fluctuation of segment lengths, geometric variation in the constraint joint axes, and residual joint force and moment errors. The proposed methodology was applied to the running motion of thirteen rear-foot strikers at a constant speed of 3.3?m/s. Modelling errors arose primarily from fluctuations in support leg segment lengths and rapid movement of the virtual joint between the foot and ground during the first 20% of stance phase. The magnitudes of these error contributions to the vertical and anterior/posterior components of the GRF are presented alongside the non-error contributions, of which the joint torque term was the largest.  相似文献   

Validity of the Blast Athletic Performance Monitor for Assessing Vertical Jump Height in Female Volleyball Players     

Alexander H.K. Montoye  Joe Mitrzyk 《Measurement in physical education and exercise science》2019,23(2):99-109

Introduction: Wearable activity monitors have been developed for jump height assessment, but the Blast Athletic Performance monitor has not yet been validated, and it remains unclear if the Blast can track changes across a sports season. Methods: Collegiate women’s volleyball players (n = 20) wore the Blast monitor (waistband) while performing standing vertical jumps (SVJs) and one-step vertical jumps (OSJs) weekly during and after a 9-week season. Jump heights from the Blast were compared to a Vertec (criterion). Results: Correlations of Blast and Vertec were moderately high (r = 0.67–0.69), but the Blast underestimated SVJ and OSJ (9.2–10.0 cm), with mean absolute percent errors 19.8–21.0%. A + 23% correction factor reduced errors to 10.5–11.3%. The Blast did not detect small decreases (2–4 cm) in criterion-measured jump height in the postseason. Conclusion: The Blast underestimated jump height and had limited ability to detect changes of up to 5.0 cm following a volleyball season. A relative correction lowered, but did not eliminate, measurement error.  相似文献   

Validation of Accelerometer-Based Energy Expenditure Prediction Models in Structured and Simulated Free-Living Settings     

Alexander H. K. Montoye  Scott A. Conger  Christopher P. Connolly  Mary T. Imboden  M. Benjamin Nelson  Josh M. Bock 《Measurement in physical education and exercise science》2017,21(4):223-234

This study compared accuracy of energy expenditure (EE) prediction models from accelerometer data collected in structured and simulated free-living settings. Twenty-four adults (mean age 45.8 years, 50% female) performed two sessions of 11 to 21 activities, wearing four ActiGraph GT9X Link activity monitors (right hip, ankle, both wrists) and a metabolic analyzer (EE criterion). Visit 1 (V1) involved structured, 5-min activities dictated by researchers; Visit 2 (V2) allowed participants activity choice and duration (simulated free-living). EE prediction models were developed incorporating data from one setting (V1/V2; V2/V2) or both settings (V1V2/V2). The V1V2/V2 method had the lowest root mean square error (RMSE) for EE prediction (1.04–1.23 vs. 1.10–1.34 METs for V1/V2, V2/V2), and the ankle-worn accelerometer had the lowest RMSE of all accelerometers (1.04–1.18 vs. 1.17–1.34 METs for other placements). The ankle-worn accelerometer and associated EE prediction models developed using data from both structured and simulated free-living settings should be considered for optimal EE prediction accuracy.  相似文献   

The relationship between physical activity,fitness, physical complaints and BMI in German adults – results of a longitudinal study     

Susanne A. Tittlbach  Darko Jekauc  Steffen C. E. Schmidt  Alexander Woll  Klaus Bös 《European Journal of Sport Science》2017,17(8):1090-1099

Objectives: This study’s aims were to describe the development of physical activity, physical fitness (PF), subjective (physical complaints (PC)) and objective (Body mass index (BMI)) health measures and to examine the relationship between the development trajectories. In addition, the study also aimed to assess the influence of sociodemographic determinants (age, sex, socioeconomic status (SES)) in German adults over a period of 18 years. Methods: The longitudinal study population comprises of 721 men and women, aged 33–76 years over the study period. There was self-report of physical activity and PC and testing of physical fitness and BMI in each study year (1992, 1997, 2002 and 2010). Latent growth curve models were used to analyse the development. Results: Physical activity slightly increased while fitness, PC and BMI worsened over the course of 18 years. Sex, age and SES play important roles concerning physical activity, fitness and health. Several integrative associations could be detected between physical activity, fitness, PC and BMI as well as their trajectories. In particular, high initial levels of physical activity and fitness protect from high PC and BMI.The slope of physical activity was not significantly associated with slopes of fitness, PC and BMI. However, increase of fitness resulted in decrease of PC. Conclusions: A general positive development regarding the amount of physical activity could be detected. However, if it is only an unsystematic increase of physical activity, this is not in itself enough to achieve health benefits. The strengthening of fitness should be focused when increasing physical activity, since only then a health benefit is possible.  相似文献   

Performance and age of African and non-African runners in World Marathon Majors races 2000–2014     

Beat Knechtle  André Aschmann  Vincent Onywera  Pantelis T. Nikolaidis  Thomas Rosemann  Christoph Alexander Rüst 《Journal of sports sciences》2017,35(10):1012-1024

The age for the fastest marathoners is well investigated, but not the age and nationality of the fastest. We investigated the age of peak marathon performance for the annual top 100 women and men competing in four races of the “World Marathon Majors” (Boston, Berlin, Chicago and New York) and the “Stockholm Marathon” between 2000 and 2014 using mixed-effects regression analyses and one-way ANOVA. Race times of Ethiopian men decreased to 2:14 h:min, but remained unchanged for Kenyan (2:14 h:min), Moroccan (2:15 h:min) and South African (2:18 h:min) men. Race times in Ethiopian (2:34 h:min), Kenyan (2:29 h:min) and South African (2:49 h:min) women showed no changes. Age increased in Ethiopian and South African men to 29.0 ± 5.0 and 32.0 ± 1.0 years, respectively. Age for Kenyan (29.9 ± 2.0 years) and Moroccan (34.9 ± 3.9 years) men remained unchanged. Age remained unchanged for Ethiopian (26.5 ± 2.0 years), Kenyan (30.0 ± 0.8 years) and South African (36.3 ± 7.0 years) women. In summary, Ethiopian men improved marathon race times, but not Ethiopian women. Age increased in Ethiopian men, but not in Ethiopian women. For practical applications, female and male marathoners from Ethiopia were the youngest and the fastest.  相似文献   

Muslim Rulers Visiting the Imperial City: Building Alliances and Personal Networks between Constantinople and the Eastern Borderlands (Fourth/Tenth–Fifth/Eleventh Century)     

Alexander D. Beihammer 《Al-Masaq: Islam & the Medieval Mediterranean》2012,24(2):157-177

This essay explores one of the main tools of Byzantine diplomatic techniques: inviting foreign rulers to Constantinople and establishing bonds of alliance through the bestowal of titles and stipends, with respect to the empire's Muslim neighbours in the fourth/tenth and fifth/eleventh centuries. In particular, it will be explained how and under what circumstances the traditional lines of communication between Constantinople and the caliphal court of Baghdad were gradually transformed into a multilayered network of personal contacts between the emperor and a number of Muslim frontier lords, who partly took on the role of representatives and dignitaries of the Byzantine Empire. Furthermore, I will try to examine the development of these newly established networks with respect to the emirates of Aleppo and Edessa, the Jarrā?id clan in Syria and the Marwānid dynasty in the Upper Euphrates and Lake Van region.  相似文献   

Forgeries of Fossils in “Amber”: History,Identification and Case Studies     

David A. Grimaldi  Alexander Shedrinsky  Andrew Ross  Norbert S. Baer 《Curator: The Museum Journal》1994,37(4):251-274

The appeal of ancient fossilized tree resin, or amber, has made pieces with animal and plant inclusions particularly prized. Unfortunately, amber forgeries are more convincingly and routinely made than most other kinds of fossils, by embedding organisms in natural resins (e.g., copal) or synthetic resins (especially polyester) or by filling a carved niche in a natural piece of amber with resin and a modern inclusion. The confusion of organisms in copal (forged and natural) for ones in amber has a long history. Reviewed here are simple tests for discerning forgeries and natural inclusions in both substances. We discuss an old but sophisticated technique for crafting amber forgeries from authentic amber and present several new examples from old collections in two large museum collections. Also discussed is the widespread use of polyester resin forgeries in the Dominican Republic and Mexico.  相似文献   

Drivers and barriers to the utilisation of gamification and game-based learning in universities: A systematic review of educators' perspectives     

Danielle Lester  Gregory J. Skulmoski  Darren P. Fisher  Vishal Mehrotra  Iris Lim  Alexander Lang  Justin W. L. Keogh 《British journal of educational technology : journal of the Council for Educational Technology》2023,54(6):1748-1770

While gamification and game-based learning have both been demonstrated to have a host of educational benefits for university students, many university educators do not routinely use these approaches in their teaching. Therefore, this systematic review, conducted using the PRISMA guidelines, sought to identify the primary drivers and barriers to the use of gamification and game-based learning by university educators. A search of multiple databases (Web of Science, Scopus and EBSCO (Business Source Complete; ERIC; Library, Information Science & Technology Abstracts)) identified 1330 articles, with 1096 retained after duplicates were removed. Seventeen articles (11 quantitative, two mixed-methods and four qualitative) were included in the systematic review. The primary drivers described by the educators that positively influenced their gamification and game-based learning usage were their beliefs that it encourages student interactions and collaborative learning; provides fun and improves engagement; and can easily be used by students. Alternatively, the university educators' major barriers included a lack of time to develop gamification approaches, lack of proven benefits and classroom setting issues. Many of these and other less commonly reported drivers and barriers can be categorised as attitudinal, design-related or administrative in nature. Such categorisations may assist university educators, teaching support staff and administrators in better understanding the primary factors influencing the utilisation of gamification and game-based learning and develop more effective strategies to overcome these barriers to its successful implementation.

Practitioner notes

What is already known about this topic

• Gamification and game-based learning may have many benefits for university students.
• The majority of university educators do not routinely use gamification and game-based learning in their teaching.

What this paper adds

• University educators' major drivers that positively influence the use of gamification and game-based learning include their perceptions that it encourages student interactions and collaborative learning, provides fun and improves engagement and can easily be used by students.
• University educators' major barriers that negatively influence the use of gamification and game-based learning include their perceptions of a lack of time to develop gamification approaches, lack of proven benefits and classroom setting issues.
• These drivers and barriers may be classified as attitudinal, design-related and administrative, with these categories providing a useful way for universities to develop strategies to better support educators who wish to use these approaches in their teaching.

Implications for practice and policy

• Attitudinal factors such as university educators' intention to use gamification and game-based learning are influenced by a host of their perceptions including attitude, perceived usefulness and ease of use.
• A range of design-related and administrative barriers may need to be overcome to increase the use of gamification and game-based learning in the university sector.

  相似文献   

Leadership Styles of Russian Enterprise Managers: The Effect of Transactional and Transformational Behaviors on Employees' Evaluation of Managerial Performance     

Alexander Ardichvili 《Performance Improvement Quarterly》2001,14(1):96-117

The purpose of this research was to identify leadership styles of today's Russian enterprise managers and to determine how these styles are related to employees' subjective evaluation of managerial performance. The survey was based on Bass and Avolio's MLQ5x leadership styles instrument. Valid responses were received from 1,216 managers and employees at three large manufacturing enterprises located in Moscow. The study results suggest that Russian managers used three well‐known leadership styles—transactional, transformational, and laissez‐faire. However, the laissez‐faire style was not prevalent. Overall, transactional leadership was used more often than transformational leadership. Transactional contingent ceward leadership was used more often than any other approaches. Charisma and Individualized Consideration have received the lowest scores among the transformational leadership style dimensions. Tests of the relationship between leadership styles and managerial performance measures indicate that transformational leadership‐and one of its components, Charisma‐had the strongest relationship with positive outcomes. Implications for developing leadership training programs in Russia and for the transfer of Western training and development approaches are discussed.  相似文献