31,524 research outputs found
Concentration of the distance between points in the unit ball
No full textWe prove that in every finite dimensional normed space, for “most” pairs (x, y) of points in the unit ball, ║x − y║ is more than √2(1 − ε). As a consequence, we obtain a result proved by Bourgain, using QS-decomposition, that guarantees an exponentially large number of points in the unit ball any two of which are separated by more than √2(1 − ε)
Generating ball trajectory in soccer video sequences
No full textThis paper demonstrates innovative techniques for estimating the trajectory of a soccer ball, using fixed cameras with constant calibration parameters. In contrast with broadcast coverage, for fixed camera data, the ball is often rendered with poor resolution away from the image centre. The rapidly moving ball is subject to motion-blur, caused by finite shutter speeds and interlaced fields, resulting in variable shape, size and colour. The velocity estimated from Kalman tracking is used in both normalising ball size and filtering the ball from false alarms. Furthermore, occlusion-reasoning and tracking-back methods are utilized to estimate its position when it is occluded, and also to remove false alarms. Finally, temporal hysteresis based thresholding of the ball likelihood is applied for trajectory filtering to improve the robustness and continuity of the tracked ball. Promising experimental results from several long sequences are reported
The Development and Assessment of Core Strength Clinical Measures: Validity and Reliability of Medicine Ball Toss Tests
No full textCore strengthening has become a significant focus in physical fitness, performance training, injury prevention, and rehabilitation. Core strength is theorized to optimize athletic performance, reduce risk of injury, and facilitate return from injury. Reliable and valid measures of core strength are necessary to track progress and determine effectiveness of human performance training. The purpose of this study was to determine the reliability and validity of three medicine ball toss tests. A total of 20 healthy physically active males and females (Age: 22.7±7.8 years, Height: 164.79±25.70 cm, Weight: 70.95±12.34 kg) participated. Testing occurred in two sessions separated by one to seven days. During session one, isokinetic testing was performed followed by medicine ball toss tests. Isokinetic strength testing included torso flexion, extension, and rotation, standardized according to manufacturer’s recommendations. Medicine ball toss tests were performed in four directions: forwards, backward, and rotational (right/left). Subjects performed five practice trials of each throw, followed by a five-minute rest period. Following the rest period, subjects performed five measured medicine ball toss tests. Subjects performed only the medicine ball toss tests in session two. Average peak torque was utilized for analysis of isokinetic strength. The average distance of the first three medicine ball toss tests in each direction was utilized for analysis. Pearson correlations were calculated to assess validity between medicine ball toss tests in session one and the corresponding isokinetic strength. Intraclass correlation coefficients were calculated to determine the reliability of the medicine ball toss tests between sessions. No significant Pearson correlations were observed between the forward, backward, and rotational medicine ball toss tests and corresponding measures of isokinetic strength (r=-0.047, p=0.845; r=-0.074, p=0.756; r=-0.051, p=0.832 (right); r=0.18, p=0.447 (left), respectively). Significant intraclass correlations were observed between session one and two medicine ball toss tests (ICC=0.835; ICC=0.835; ICC=0.870 (right); ICC=0.909 (left); p<0.001, respectively). These results illustrate that medicine ball toss tests have excellent reliability but are not valid against isokinetic strength, indicating that modifications to these medicine ball toss tests may be necessary. Future research should focus on preserving reliability while establishing validity of these medicine ball toss tests through appropriate modifications
Shear-band formation in a non-Newtonian fluid model with a constitutive instability
No full textWe examine the behaviour in shear of a viscoelastic fluid model (Johnson-Segalman fluid plus a Newtonian contribution) which exhibits a constitutive instability with respect to shear banding. Because there is a range of stress values at which shear bands can coexist, it is not clear which value of the stress is attained at a given, nominal shear rate, nor whether a selection of some particular value for the stress throughout the unstable range of shear rates exists or not. In this paper, at least for the specific fluid considered, we show that (i) a phase-separated flow actually occurs, and (ii) a selection mechanism for the stress in the shear-banded regime does exist. To obtain these clear-cut results, we used the Couette concentric cylinder geometry, where a ‘seed’ for the phase separation is automatically provided by the curvature: the portion of the material which is near to the inner (moving) cylinder is more strongly sheared than any other portion, and can induce the formation of a high shear rate band. At steady state, the existence of a selection mechanism for the stress implies that the ‘volume fraction’ of the high shear rate phase (not its shear rate) increases by increasing the velocity of the moving cylinder. These and other features of our computed solutions resemble experimental observations. We conclude the paper by showing how a simple variational reasoning can help in locating the selected stress
The Influence of Co-designers on the Generation and Evaluation of Solution Alternatives.
No full textAdelson B, Soloway A (1986) A model of software design. International Journal of Intelligent Systems 1: 195-213 Ball LJ, Evans JStBT, Dennis I (1994) Cognitive processes in engineering design: A longitudinal study. Ergonomics 37: 1753-1786 Ball LJ, Lambell NJ, Ormerod TC, Slavin S, Mariani JA (2000) Representing design rationale to support innovative design re-use: A minimalist approach. Automation in Construction, in press Ball LJ, Maskill L, Ormerod TC (1998) Satisficing in engineering design: Causes, consequences and implications for design support. Automation in Construction 7: 213-227 Ball LJ, Ormerod TC (2000) Putting ethnography to work: The case for a cognitive ethnography of design. International Journal of Human-Computer Studies, in press Cross N (1994) Engineering design methods: Strategies for product design, 2nd edn. Wiley, Chichester Gero JS (1990) Design prototypes: A knowledge representation schema for design. AI Magazine 11: 26-36 Jeffries R, Turner AA, Polson PG, Atwood ME (1981) The processes involved in designing software. In: Anderson JR (ed.) Cognitive skills and their acquisition. Erlbaum, Hillsdale, NJ, pp 255-283 Kant E (1985) Understanding and automating the algorithm design process. In: Proceedings of the International Joint Conference on Artificial Intelligence. Morgan Kaufmann, Los Altos, CA, pp 211-219 MacLean A, Young RM, Bellotti VME, Moran TP (1991) Questions, Options, and Criteria: Elements of design space analysis. Human-Computer Interaction 6: 201-250 Olson GM. Olson JS, Carter MR, Storrøsten M (1992) Small group design meetings: An analysis of collaboration. Human-Computer Interaction 7: 347-374 Olson GM, Olson JS, Storrøsten M, Carter MR, Herbsleb J, Rueter H (1996) The structure of activity during design meetings. In: Moran TP, Carroll, JM (eds.) Design rationale: Concepts, techniques, and use. Lawrence Erlbaum Associates, Mahwah, NJ pp 217-239 Ormerod TC, Mariani JA, Ball LJ, Lambell NJ (1999) Desperado: Three-in-one indexing for innovative design. In: Sasse MA, Johnson, C (eds.) Proceedings of the Seventh IFIP Conference on Human-Computer Interaction—INTERACT ’99. IOS Press, London, pp 336-343 Pahl G, Beitz W (1984) Engineering design. The Design Council, London [Original German text, 1977, Springer-Verlag, Berlin]. Pugh S (1991) Total design: Integrated methods for successful product engineering. Addison-Wesley, London Simon HA (1981) The sciences of the artificial, 2nd edn. MIT Press, Cambridge, MA Ullman DG, Dietterich TG, Stauffer LA (1988) A model of the mechanical design process based on empirical data. Artificial Intelligence for Engineering Design, Analysis and Manufacturing 2: 33-5
Parametric impact characterisation of a solid sports ball, WITH a view to developing a standard core for the GAA Sliotar
No full textThe main aim of this research was to characterise the dynamic impact behaviour of the sliotar core. Viscoelastic characterisation of the balls was conducted for a range of impact speeds. Modern polymer balls exhibited strain and strain-rate sensitivity while traditional multi-compositional balls exhibited strain dependency. The non-linear viscoelastic response was defined by two values of stiffness, initial and bulk stiffness.
Traditional balls were up to 2.5 times stiffer than the modern types, with this magnitude being rate-dependent. The greater rate of increase of traditional ball stiffness produced a more non-linear COR velocity-dependence compared to modern balls. The dynamic stiffness results demonstrated limited applicability of quasi-static testing and springtheory equations. Analysis of ball deformation behaviour demonstrated that centre-of mass displacement and diameter compression values were not consistently equivalent for all ball types. The contribution of manufacturing conditions to ball performance was investigated by conducting extensive prototyping experiments. Manufacturing parameters of temperature, pressure and material composition were varied to produce a range of balls. Polymer hardness affected stiffness but not energy dissipation, with increased hardness increasing ball stiffness. The nucleating additive influenced ball COR, with increased additive tending to reduce ball COR, but this effect was sensitive to polymer grade. The impact response of the ball was simulated using three mathematical models. The first model was shown to replicate ball behaviour to only a limited degree, despite being used previously with reported success for other ball types. The second model exhibited a reasonable representation of ball impact response that was universally applicable to all tested ball types; however, the accuracy in terms of predicting force-displacement response was not as high as required for broad range implementation. The third model exhibited significantly better accuracy in simulating ball response. The force values generated from this model exhibited up to 95% agreement with experimental data
Fatou and Korányi-Vági type theorems on the minimal ball
No full textIn this paper we develop the Hp (p [greater than or equal] 1) theory on the minimal ball. After identifying the admissible approach regions, we establish theorems of Fatou and Korányi-Vági type on this ball
Stability of a spherical flame ball in a porous medium
No full textGaseous flame balls and their stability to symmetric disturbances are studied numerically and asymptotically, for large activation temperature, within a porous medium that serves only to exchange heat with the gas. Heat losses to a distant ambient environment, affecting only the gas, are taken to be radiative in nature and are represented using two alternative models. One of these treats the heat loss as being constant in the burnt gases and linearizes the radiative law in the unburnt gas (as has been studied elsewhere without the presence of a solid). The other does not distinguish between burnt and unburnt gas and is a continuous dimensionless form of Stefan's law, having a linear part that dominates close to ambient temperatures and a fourth power that dominates at higher temperatures.Numerical results are found to require unusually large activation temperatures in order to approach the asymptotic results. The latter involve two branches of solution, a smaller and a larger flame ball, provided heat losses are not too high. The two radiative heat loss models give completely analogous steady asymptotic solutions, to leading order, that are also unaffected by the presence of the solid which therefore only influences their stability. For moderate values of the dimensionless heat-transfer time between the solid and gas all flame balls are unstable for Lewis numbers greater than unity. At Lewis numbers less than unity, part of the branch of larger flame balls becomes stable, solutions with the continuous radiative law being stable over a narrower range of parameters. In both cases, for moderate heat-transfer times, the stable region is increased by the heat capacity of the solid in a way that amounts, simply, to decreasing an effective Lewis number for determining stability, just as if the heat-transfer time was zero
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