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1
Content available Progression of clock DBD changes over time
Maciuk Kamil, Varna Inese, Kudrys Jacek
Metrology and Measurement Systems
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2023
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Vol. 30, nr 3
499--505
EN
Day-boundary discontinuity (DBD) is an effect present in precise GNSS satellite orbit and clock products originating from the method used for orbit and clock determination. The non-Gaussian measurement noise and data processing in 24 h batches are responsible for DBDs. In the case of the clock product, DBD is a time jump in the boundary epochs of two adjacent batches of processed data and its magnitude might reach a couple of ns. This article presents the four GNSS (Global Navigation Satellite System) systems DBD analysis in terms of change over an 8 year period. For each of 118 satellites available in this period, the yearly value of DBD was subject to analysis including standard deviation and frequency of outliers. Results show that the smallest DBDs appear in the GPS system, the biggest - for the BeiDou space segment. Moreover, the phenomenon of changes in DBDs over time is clearly seen at the beginning of the analysed period when the magnitude and number of the DBDs were larger than for current, newest clock products.
2
Content available How to teach safe landing after the jump? The use of biofeedback to minimize the shock forces generated in elements of modern dance
Gorwa Joanna, Michnik Robert, Nowakowska-Lipiec Katarzyna
Acta of Bioengineering and Biomechanics
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2021
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Vol. 23, no. 3
47--59
EN
Purpose: The aim of the study was to assess the possible use of biofeedback (information on the course and values of ground reaction forces (GRF) during landing following the performance of a dance evolution) for training minimising impact loads after a jump in modern dance. Methods: The tests involved the analysis of a total of 60 expressive elements of modern dance performed by 5 soloists. The tests involved the recording of the vertical component of GRF (GRFz) vector using Kistler platform in the landing phase following the performance of modern dance jumps. The dancers performed the above-named jumps three times in successive tests: a reference test (without biofeedback) and the next two tests with biofeedback, after the obtainment of information about the vertical value of GRF. After each performance, the dancers watched a course of GRF and films showing the recorded landing phase. Results: Applying of a proposed didactic laboratory session led to: extension of contact time and of time preceding the obtainment of the maximum value of GRFz, reduction of the maximum values of the vertical components of the GRF, reduction of the loading rate of the ground reaction force, increase of an impulse of the vertical component of GRF in the entire stance phase and in the shock absorption phase. Conclusions: Proposed didactic laboratory session with biofeedback may result in the change of the post-jump shock absorption technique.
3
Content available Concurrent validity and reliability of proprietary and open-source jump mat systems for the assessment of vertical jumps in sport sciences
Pueo B., Jimeney-Olmedo J. M., Lipińska P., Buśko K., Penichet-Tomas A.
Acta of Bioengineering and Biomechanics
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2018
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Vol. 20, no. 3
51--57
EN
Vertical jump tests are used to assess lower-limb power of athletes in sport sciences. Flight time measurement with jump-mat systems is the most common procedure for this purpose. The aim of this study was to analyze the concurrent validity and reliability of two proprietary systems (Globus and Axon) and an open-source system (Chronojump). Methods: A conditioning electric circuit governed by a controlled wave generator is designed to substitute athletes jumping on a physical mat. In order to look for possible differences associated to timekeeping by each microcontroller device, all three systems are fed by the circuit simultaneously. Results: Concurrent validity was high for the three systems. Standarized typical error of estimate (TEE) was trivial, according to MBI interpretation, as well as perfect Pearson correlation coefficient. Reliability was assessed using coefficient of variation of flight time measure, resulting in 0.17–0.63% (0.05–0.12 cm) for Globus, 0.01% (0.09 cm) for Chronojump and 5.65–9.38% (2.15–3.53 cm) for Axon. These results show that all jump-mat system produced nearly identical measures of flight time so they can be considered valid and reliable for practical purposes. In comparison, Chronojump showed the best performance whereas Axon showed enough variability and disagreement to pose a problem in testing elite athletes. Conclusions: These experiments show that open-source jump mats are as valid and reliable as their proprietary counterparts at a lower cost. Therefore, practitioners can be confident in using Globus or Chronojump systems to test athletes’ jump height because of their negligible errors and Axon system to monitor general population.
4
Content available Determination of a ground reaction force affecting human body during jump
Karpiński R., Jaworski Ł.
Journal of Technology and Exploitation in Mechanical Engineering
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2016
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Vol. 2, nr 1
32--35
EN
The article presents a study on calculating the ground reaction force, which affects the human body during landing after the jump. A basic, one mass model of human body and an equation of movement are presented in the paper. The model for the studies was created in Adams software and the study on a change of the ground reaction force was performed by using different values of height and mass.
PL
Artykuł opisuje metodę wyznaczania siły reakcji podłoża oddziałującej na ciało człowieka podczas zeskoku. W pracy przedstawiono prosty, jednomasowy model ciała człowieka wraz z opisującym go równaniem ruchu. Zbudowano model ciała w środowisku Adams, a następnie przeprowadzono obliczenia siły reakcji podłoża dla różnych wysokości i mas.
5
Content available A simple tridimensional processing of acceleration measurements for dynamic movements monitoring of sportsmen
Neneman K., Łuczyk A. W., Szostak S., Pleskacz W. A.
International Journal of Microelectronics and Computer Science
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2016
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Vol. 7, nr 2
47--53
EN
Measuring, monitoring and analysis of dynamic movements in sports is becoming more important than ever. Many methods used currently may only be applied in the artificial environment of a laboratory. Other methods require too much processing to be used during a real-time competition. To overcome these difficulties acceleration measurements and a simple method to process them have been proposed. Data processing is based on search and recognition of the characteristic points in the tridimensional representation of acceleration measurements. Three different dynamic movements have been measured: run, jump and punch. The presented results show that the measurements of acceleration and proposed processing may be used to extract movement parameters of a sportsman and monitor the level of his tiredness.
6
Content available Biomechanics of figure skating jump double axel performed in on ice and off ice conditions
Mazurkiewicz A., Iwańska D.
Aktualne Problemy Biomechaniki
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2015
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z. 9
83--88
EN
Figure skating is considered a highly technical discipline. Coaches and researchers are constantly looking for the most effective and safest movement model for jumps, especially Axel Paulsen, which is the hardest kind of all jumps. This research was taken to verify the usefulness of performing double Axel under off- ice conditions as a part of general figure skating training. Research was based on video analysis made in APAS 2000 programme. Parameters taken into account were: joints and take off angle, displacement of centre body mass, horizontal and vertical velocity. Results helped in finding out parameters which are trained during off-ice session.
7
Content available Somatotype : variables related to muscle torque and power output in female volleyball players
Buśko K., Lewandowska J., Lipińska M., Michalski R., Pastuszak A.
Acta of Bioengineering and Biomechanics
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2013
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Vol. 15, no. 2
119--126
EN
The purpose of this study was to investigate the relationship between somatotype, muscle torque, maximal power output and height of rise of the body mass centre measured in akimbo counter movement jump (ACMJ), counter movement jump (CMJ) and spike jump (SPJ), and power output measured in maximal cycle ergometer exercise bouts in female volleyball players. Fourteen players participated in the study. Somatotype was determined using the Heath–Carter method. Maximal muscle torque was measured under static conditions. Power output was measured in 5 maximal cycle ergometer exercise bouts, 10 s each, at increasing external loads equal to 2.5, 5.0, 7.5, 10.0 and 12.5% of body weight (BW). All jump trials (ACMJ, SPJ and CMJ) were performed on a force plate. The mean somatotype of volleyball players was: 4.9-3.5-2.5. The value of the sum of muscle torque of the left upper extremities was significantly correlated only with mesomorphic component. Mesomorphic and ectomorphic components correlated significantly with values of maximal power measured during ACMJ and CMJ. Power output measured in maximal cycle ergometer exercise bouts at increasing external loads equal to 2.5, 5.0 and 7.5% of BW was significantly correlated with endomorphy, mesomorphy and ectomorphy.
8
Content available remote Problemy z praktyki kopalnianej w zakresie określenia wpływu uskoków na budynki znajdujące się na powierzchni terenu
Celmer M., Lubryka M., Kutkowski J.
Górnictwo i Geologia
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2012
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T. 7, z. 1
27-36
PL
Artykuł przedstawia przykłady przypuszczalnego, negatywnego wpływu uskoków zlokalizowanych na obszarach górniczych Rybnickiego Okręgu Węglowego. Przedstawione materiały są próbą nakreślenia problemu prawdopodobieństwa negatywnego wpływu uaktywnionych i nieaktywnych uskoków na budynki znajdujące się na powierzchni. W artykule przedstawiono wybrane przykłady z lat 2008-2011 uszkodzeń budynków, zlokalizowanych w rejonach uskoków, na podstawie istniejących materiałów archiwalnych wybranych kopalń.
EN
Paper presents the examples of negative impact of faults located in mining areas Rybnik Coal District. The material is an attempt to draw the problem of the likelihood of negative impact of activated and inactive fault on buildings located on ground surface. The paper presents examples of damaged buildings located in area of geological fault on the basis of the archival materials from chosen mines from the years 2008 - 2011.
9
Content available remote Thermo-electrodynamics of rigid superconductors
Cimmelli V. A., Oliveri F., Pace A. R.
Archives of Mechanics
|
2004
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Vol. 56, nr 5
377-389
EN
This paper deals with a continuum model of rigid superconductors. It is assumed that their property of shifting to the superconductive state for suitable values of temperature and magnetic field is due to a vectorial internal variable, related to the superelectron current by a linear constitutive law. The compatibility of the model with the second law of thermodynamics is investigated. The propagation of thermo-electromagnetic waves through a one-dimensional conductor is analyzed as well. Comparison is made with different continuum approaches which may be found in the literature.
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