| 1. |
- Berbyuk, Viktor, 1953
(författare)
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Dynamics and optimal control of biotechnical systems "Man-Prosthesis"
- 1997
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Ingår i: IUTAM Symposium on Interaction Between Dynamics and Control in Advanced Mechanical Systems, Ed. D. van Campen, Kluwer Academic Publishers, 1997. - Dordrecht : Springer Netherlands. ; , s. 35-42
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Konferensbidrag (refereegranskat)abstract
- In the paper, a mathematical model is proposed for investigating the controlled motion of human locomotion system (HLS) with an above-knee prosthesis. To provide insight into the interaction between dynamics and control in biotechnical system Man-Prosthesis the energy optimal control problem of the HLS wearing a lower limb prosthesis has been considered. The algorithm is based on special conversion of the optimal control problem for a nonlinear dynamical system which models HLS into a standard nonlinear programming problem. A number of energy-optimal control problems of human locomotion with an artificial leg, and optimization problems for the constructive parameters of the prostheses under different boundary conditions and constraints have been solved. The numerical results obtained were compared with experimental data for normal human locomotion. The energy-optimal elastic and viscoelastic characteristics of the ankle and knee joints of the prostheses have been determined.
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| 2. |
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| 3. |
- Thunberg, Hans, 1956-
(författare)
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A recycled characterization of kneading sequences
- 1999
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Ingår i: International Journal of Bifurcation and Chaos in Applied Sciences and Engineering. - : World Scientific. - 0218-1274. ; 9:9, s. 1883-1887
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Tidskriftsartikel (refereegranskat)abstract
- For any infinite sequence E on two symbols one can define two sequences of positive integers S(E) (the splitting times) and T(E) (the cosplitting times), which each describe the self-replicative structure of E. If E is the kneading sequence of a unimodal map, it is known that S(E) and T(E) carry a lot of information on the dynamics, and that they are disjoint. We show the reverse implication: A nonperiodic sequence E is the kneading sequence of some unimodal map if the sequences S(E) and T(E) are disjoint.
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| 4. |
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| 5. |
- Berbyuk, Viktor, 1953
(författare)
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Energy-optimal control of human leg in swing phase
- 1995
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Ingår i: Biomechanics Seminar. - 1100-2247. ; 9, s. 32-49
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Konferensbidrag (refereegranskat)abstract
- The mathematical model and efficient algorithm for designing the energy-optimal controlled processes of a human leg in the swing phase are proposed. This algorithm is based on special conversion of the optimal control problem for nonlinear dynamical system modeled a human leg into a standard nonlinear programming problem. The objective function for the optimization algorithm is the integral over swing phase's time from the sum of the mechanical power absolute values for all controlling stimuli. A number of the energy-optimal controlled processes of a human leg under different boundary conditions and restrictions on phase coordinates have been obtained. The kinematical and dynamical characteristics of obtained optimal controlled processes are compared with respective characteristics of a human leg's swing phase during normal gait.
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| 6. |
- Berbyuk, Viktor, 1953
(författare)
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On complete controllability of linear nonstationary systems
- 1993
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Ingår i: Journal of Soviet Mathematics. - 0090-4104. ; 67:2, s. 2973-2975
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Tidskriftsartikel (refereegranskat)abstract
- The concept of controllability is connected with the transfer of a dynamic system from one state to another by means of a control. An important problem in the theory of control systems is the search for necessary and sufficient conditions for complete controllability of dynamic systems. By using of the first integrals of the equations of unperturbed motion the necessary and sufficient conditions for complete controllability of linear nonstationary dynamic systems have been proposed.
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| 7. |
- Berbyuk, Viktor, 1953
(författare)
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The use of first integrals to synthesize the energetically optimal control of a nonlinear system
- 1997
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Ingår i: Journal of Mathematical Sciences. - 1573-8795 .- 1072-3374. ; 86:2, s. 2642-2645
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Tidskriftsartikel (refereegranskat)abstract
- In the paper a method of solving problems of optimal control of the motion of nonlinear dynamical systemswith respect to energy expenditure given a fixed time and fixed ends of the phase trajectory has been proposed. The method is based on the use of first integrals of the equations of free motion. The application of the method isillustrated by examples.
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| 8. |
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| 9. |
- Lindgren, Kristian, 1960
(författare)
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Evolutionary dynamics in game-theoretic models
- 1997
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Ingår i: The Economy as an Evolving Complex System II. ; , s. 337-368
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Konferensbidrag (refereegranskat)abstract
- A number of evolutionary models based on the iterated Prisoner's Dilemma with noise are discussed. Different aspects of the evolutionary behaviour are illustrated (i) by varying the trickiness of the game (iterated game, mistakes, misunderstandings, choice of payoff matrix), (ii) by introducing spatial dimensions, and (iii) by modifying the strategy space and the representation of strategies. One of the variations involves the finitely iterated game, that has a unique Nash equilibrium of only defecting strategies, and it is illustrated that when a spatial dimension is added, evolution usually avoids this state. The finite automaton representation of strategies is also revisited, and one model shows an evolution of a very robust error-correcting strategy for the Prisoner's Dilemma game.
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| 10. |
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| 11. |
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| 12. |
- Wistedt, Inger, 1943-
(författare)
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Matematiska samtal
- 1993
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Ingår i: Nämnaren. - Göteborg. - 0348-2723. ; 20:3, s. 21-23
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- I den pedagogiska debatten framhålls ofta kommunikationens betydekse för kunskapsbildningen. Genom matematisks samtal får barnen en möjlighet att uttryck och reflektera över sina tankar och de får också chans att pröva och ompröva dem i samspel med andra. I artikeln diskuteras kommunikationen som både ett överskattat och ett underskattat verktyg i lärprocessen, utifrån exempel hjämtade från projektet "Att använda barn informella kunskaper i matematikundervisningen".
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| 13. |
- Axelsson, B.O.M., et al.
(författare)
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Studies of the main cutting force at and near a cutting edge
- 1993
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Ingår i: European Journal of Wood and Wood Products. - 0018-3768 .- 1436-736X. ; 51:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- The present work is a study of how various parameters affect the cutting forces at, and near a cutting edge when cutting wood at full speed and with all cutting edges of the tool. Statistical methods from experimental results are used to develop a model
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| 14. |
- Lundberg, Staffan, et al.
(författare)
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Cutting forces at and near a cutting edge
- 1992
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Ingår i: Better wood products through science : All-Division 5 conference "Forest Products". - Nancy : ENGREF. - 2907086030
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Konferensbidrag (refereegranskat)
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| 15. |
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| 16. |
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| 17. |
- Wik, Torsten, 1968, et al.
(författare)
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Transfer functions for series of continuously stirred biofilm reactors
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There is an increasing interest in modeling and applications of biofilm reactors. Commonly, biofilm reactors are modeled as a single continuously stirred biofilm reactor (CSBR), or as a series of such. The models can be used to extract information about the reactor, for design and to predict reactor effluent characteristics as a function of influent characteristics. A CSBR consists of a stirred tank, which the bulk water flows through, and from which substrates diffuse into a biofilm where they may be transformed into new substances by bacteria living in the biofilm. Here, standard assumptions are used to derive a general and flexible dynamic model of CSBR-systems, where the reaction kinetics are of zero or first order. An exact, and an approximate transfer function, which enables easy simulations, analysis, and implementation in real-time softwares, is derived. Particular focus is on pulse responses, which is an important experimental procedure in control and reactor design. Explicit equations for the pulse responses are presented, and parameter dependancy is discussed. Experimental data from a pilot plant nitrifying trickling filter are used to illustrate the use of transfer functions for identification of reactor and biofilm parameters.
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| 18. |
- Jeppsson, Ulf, et al.
(författare)
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An evaluation of a dynamic model of the secondary clarifier
- 1996
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of the paper is to support and illustrate recent theoretical results on the mathematical modelling of the secondary clarifier. A new settler model is compared with a traditional layer model by means of numerical simulations. Emphasis is put on the numerical solution's ability to approximate the analytical solution of the conservation law written as a non-linear partial differential equation. The new settler model is consistent in this respect. Another important conclusion is that a layer model dividing the settler into only ten layers (normally used in settler models) is too crude an approximation to capture the detailed dynamic behaviour of the settler. All simulations presented are performed with the settler models coupled to the IAWQ Activated Sludge Model No. 1.
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| 19. |
- Jeppsson, Ulf, et al.
(författare)
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On the modelling of the dynamic propagation of biological components in the secondary clarifier
- 1996
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 85-92
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Tidskriftsartikel (refereegranskat)abstract
- When coupling a model of the biological reactor to a model of the settler, difficulties appear because of the different representations used for the particulate material. A combined model of the entire activated sludge process needs to include an algorithm for the dynamic propagation of the biological components of the particulate material through the secondary clarifier. In particular, this is of importance for an accurate description of the sludge that is recycled to the biological reactor. Two one-dimensional algorithms have been evaluated by means of numerical simulations. The first algorithm investigated is the one by Otterpohl and Freund in 1992 and some inherent problems of this method are discussed. For example, it will produce oscillating solutions as the number of layers in the settler model increases. Therefore, an alternative algorithm is proposed. It is based on a percentage vector that describes the different particulate biological components as fractions of the total suspended solids concentration. The vector is updated for every layer in the settler model by a robust numerical method. The algorithm is derived analytically, is computationally efficient and does not exhibit any oscillatory behaviour.
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| 20. |
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| 21. |
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| 22. |
- Carey, Alan L., et al.
(författare)
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Loop groups, anyons and the Calogero-Sutherland model
- 1999
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Ingår i: Communications in Mathematical Physics. - : Springer Science and Business Media LLC. - 0010-3616 .- 1432-0916. ; 201, s. 1-34
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Tidskriftsartikel (refereegranskat)
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| 23. |
- Grosse, Harald, et al.
(författare)
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The geometric phase and the Schwinger term in some models
- 1992
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Ingår i: International Journal of Modern Physics A. - : World Scientific. - 0217-751X .- 1793-656X. ; 7:21, s. 5045-5083
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Forskningsöversikt (refereegranskat)abstract
- We discuss the quantization of fermions interacting with external fields and observe the occurrence of equivalent as well as inequivalent representations of the canonical anticommutation relations. Implementability of gauge and axial gauge transformations leads to generators which fulfil an algebra of current with a Schwinger term. This term can be written as a cocycle and leads to the boson-fermion correspondence.Transport of a quantum-mechanical system along a closed loop of parameter space may yield a geometric phase. We discuss models for which nonintegrable phase factors are obtained from the adiabatic parallel transport. After second quantization, one obtains, in addition, a Schwinger term. Depending on the type of transformation, a subtle relationship between these two obstructions can occur. We indicate finally how we may transport density matrices along closed loops in parameter space.
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| 24. |
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| 25. |
- Lehto, Niklas, et al.
(författare)
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Effects of dislocation interactions : application to the period-doubled core of the 90° partial in silicon
- 1998
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 80:25, s. 5568-5571
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Tidskriftsartikel (refereegranskat)abstract
- The elastic strain field of a dislocation is highly affected by nearby dislocations. The effects of dislocation-dislocation interactions on elastic energy and core structure are analyzed using a new and self-consistent method to apply periodic boundary conditions on unit cells containing dislocations. Local density functional theory on hydrogen terminated clusters is used to gauge the effects of long-range elastic fields on the core structure of the 90° partial in silicon. It is shown that the single and double period structures of this core are very close in energy, and that the structure adopted probably depends on the environment in which the dislocation is located
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| 26. |
- Lehto, Niklas, et al.
(författare)
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Interaction of vacancies with partial dislocations in silicon
- 1997
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 56:20, s. R12706-R12709
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of vacancies with 30° and 90° partial dislocations in silicon is examined. In particular, the structures and binding energies are calculated using hydrogen-terminated clusters and local density-functional theory. Moreover the electronic structure is determined using supercells containing dislocation dipoles. Vacancies are found to have binding energies of approximately 2.0 eV and 0.9 eV to 90° and 30° partials, respectively. The elastic strain field of the partials makes the fourfold vacancy reconstruct, which essentially clears the fundamental gap
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| 27. |
- Yang, Jikuang, 1948, et al.
(författare)
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Computer Simulation of Impact Response of the Human Knee Joint in Car-pedestrian Accidents
- 1996
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Ingår i: SAE Special Publication PT-56, USA. ; , s. 567-581
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Tidskriftsartikel (refereegranskat)abstract
- A 3D pedestrian knee joint model was deve-loped as a first step in a new description of the whole pedestrian body for computer simulations. The model was made to achieve better correlation with the results from previous tests with biological material. The model of the knee joint includes the articular surfaces, ligaments and capsule repre-sented by the ellipsoid and plane elements as well as the spring-damping elements, respectively. The mechanical properties of the knee joint were based on available biomechanical data.To verify the new developed model with results from tests with biological material previously performed at the Department of Injury Prevention, Chalmers University of Technology, the computer simulations were carried out with the model of the knee joint using the MADYMO 3D program. To simulate different test conditions, which correspond to previous tests with biomechanical system, the following parameters were varied in our simulations: bumper height and bumper compliance. Four com-puter simulations were performed and compared with four test series with biological material with five tests in each series. The impact force, the condyle interface forces, the ligament forces and the ligament relative elongations were calculated and verified with the results of the tests with biological material. The output parameters calculated from the knee joint model correspond in general to what was observed in the studies with biological material.Complementary two computer simulations were performed to study the influence of the upper body mass to the distribution of the forces in the simulated knee structures. These simulations appear that body mass has an influence on the impact and condyle forces, the ligament strain and on the trajectory of the lower extremities.
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| 28. |
- Yang, Jikuang, 1948, et al.
(författare)
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Development and Validation of a Human-Body Mathematical Model for Simulation of Car-Pedestrian Impacts
- 1997
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Ingår i: Proc. of the Int. IRCOBI Conference on the Biomechanics of Impacts. Hannover, Germany. ; , s. 133-149. SAE paper no. 1997-13-0008-
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to develop a 3D mathematical model of the human body to simulateresponses of pedestrians in car impacts with emphasis on the lower extremities and the head. Themodel, implemented by using MADYMO-GEBOD program, consists of fifteen body segmentsconnected by fourteen joints, including two human-like knee joints and two breakable leg segmentswhich allow to simulate the knee responses associated with leg fracture.The model was verified by using published sled impact tests with cadavers in terms of kinematicsof the pedestrian substitutes, accelerations of the body segments, and failure description fromanatomical investigations of the pedestrian substitutes. The sensitivity of the model to input variableswas studied at impact speeds of 15 and 40 km/h with the following parameters: bumper height,bumper stiffness, bumper lead distance, height of hood-edge, hood-edge stiffness, and impact speed.The validated model demonstrated its capability in simulations of car-pedestrian impacts to predict riskof pedestrian injuries and to develop safety countermeasures for pedestrian protection.
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| 29. |
- Yang, Jikuang, 1948
(författare)
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Mathematical Simulation of Knee Responses Associated with Leg Fracture in Car-Pedestrian Accidents
- 1997
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Ingår i: International Journal of Crashworthiness. - 1358-8265 .- 1754-2111. ; 2:3, s. 259-271
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Tidskriftsartikel (refereegranskat)abstract
- A new mathematical model of a pedestrian with a breakable leg and a human-like knee was developed to simulate the fracture of the leg in a car-pedestrian impact, and knee responses associated with leg fracture in such an impact to the leg. The leg model consists of two elements connected by a frangible joint. The characteristics of the frangible joint are described by a moment-rotation function; this is based on the leg fracture tolerance data from tests with leg specimens. The knee model origin was based on the anatomical structure of the knee; it represents a femoral condyle-ligament-tibial condyle complex. The pedestrian mathematical model was implemented using the MADYMO 3D program and verified against previous impact tests with biological specimens at a speed of 31 km/h. In the simulation of leg fracture, calculated ligament strain was 9% for MCL (medial collateral ligament), and 25% in the simulation without leg fracture. Contact forces between the lateral articular surfaces in the case of no leg fracture were about 85% higher than in the case of leg fracture. Results from computer simulations confirmed that the impact response and injury mechanism of the knee joint are dependent on whether or not the leg is fractured. The breakable leg model gave a higher biofidelity than did the original one-legged pedestrian model with an undeformable representation of the leg segment.
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| 30. |
- Yang, Jikuang, 1948, et al.
(författare)
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Modeling of adaptive passenger airbag systems in car frontal crashes
- 1997
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Ingår i: Proc. of the 15th Int. Technical Conf. on the Enhanced Safety Vehicles, Melbourne, Australia, May 13-16, 1996. ; , s. 486-501. SAE paper no. 976041
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Konferensbidrag (refereegranskat)abstract
- The objective of this study was to evaluate whether the effectiveness of a passenger airbag can be increased by making the passenger airbag adaptive to crash conditions, such as severity and type of impact, belt use, and passenger size. Such an adaptive passenger airbag will better cover a wider range of crash situations than a conventional airbag system. In this study, mathematical modeling was performed for the optimization of an existing passenger airbag restraint system. The final solution can be used as reference for the design of an adaptive airbag system. The present study was divided into four steps: (1) a FEM airbag model was developed by using the MADYMO 3D program based on an existing prototype of a passenger airbag; (2) the airbag model was validated against airbag static deployment tests, airbag drop tests, and sled tests; (3) the performance of passenger airbag systems of different volumes was evaluated in terms of injury criteria for front seat occupants of different sizes; (4) a parameter study with different impact conditions and varying levels of variables was carried out to find an optimized design of an adaptive passenger airbag restraint system.Three variables selected for passenger airbag optimization are the airbag volume, the bag pressure, and the size of the ventilation hole. Four input factors that varied in different crash conditions are the dummy size, belted/unbelted, impact speed, and rigid/deformable barrier. The HIC, chest acceleration, chest deflection, neck moment, and axial femur force were calculated in each simulation. The effectiveness of the passenger airbag models was evaluated in terms of the injury criteria of FMVSS 208 and other relevant injury parameters. The influence of the airbag variables on the dummy response was analyzed and discussed. The size of the ventilation hole was found to have the dominating influence on the performance of the airbag. The best effect of the passenger airbag system could be obtained either by using a small airbag with high initial pressure or by using a big airbag with low initial pressure. The findings in the present study indicate that a midsize volume (120-liter) airbag with variable venthole can give front seat occupants of different sizes better protection over a range of crash severities than a conventional big (150-liter) airbag with only one size of venthole. The results from this study can be used for the development of a future adaptive passenger airbag system.
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| 31. |
- Dodunekova, Rossitza, 1948, et al.
(författare)
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Almost-MDS and near-MDS codes for error detection
- 1997
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Ingår i: IEEE Transactions in Information Theory. ; 43:1, s. 285-290
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Tidskriftsartikel (refereegranskat)abstract
- The error detection capability of AMDS and NMDS codes is studied. Necessary and sufficient conditions for the codes to be proper or good for error detection are given.
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| 32. |
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| 33. |
- Dodunekova, Rossitza, 1948
(författare)
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Intermediate St. Petersburg sums
- 1996
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Ingår i: Studia Sci. mathe. Hungar.. ; 31:1-3, s. 93-119
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Tidskriftsartikel (refereegranskat)
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| 34. |
- Dodunekova, Rossitza, 1948
(författare)
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Limit theorems for the Petersburg game
- 1991
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Ingår i: Sums, trimmed sums, and extremes. Progr. Prob.. ; 23, s. 285-315
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Tidskriftsartikel (refereegranskat)
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| 35. |
- Dodunekova, Rossitza, 1948, et al.
(författare)
-
Sufficient conditions for good and proper error detecting codes
- 1997
-
Ingår i: IEEE Transactions in Information Theory. ; 43:6, s. 2023-2026
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Tidskriftsartikel (refereegranskat)abstract
- The performance of linear block codes over a finite field is investigated when they are used for pure error detection. Sufficient conditions for a code to be good or proper for error detection are derived.
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| 36. |
- Dodunekova, Rossitza, 1948, et al.
(författare)
-
Sufficient conditions for good and proper error detecting codes via their duals
- 1997
-
Ingår i: Math. Balkanica (N.S.). ; 11:3-4, s. 357-381
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Tidskriftsartikel (refereegranskat)abstract
- We have found earlier in [1] sufficient conditions for a linear block code to be good or proper for error detection. These conditions are expressed in terms of the weight distribution of the code. However, for codes with small co-dimension or with small number of nonzero weights in their dual codes the conditions would be technically easier to check if they were presented in terms of the dual weight distribution. This alternative representation is the purpose of the present paper.
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Dybjer, Peter, 1953, et al.
(författare)
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Inductive definitions and type theory an introduction (preliminary version)
- 1994
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Ingår i: Foundation of Software Technology and Theoretical Computer Science: 14th Conference Madras, India; (Lecture Notes in Computer Science; 880). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 3540587152 ; 880, s. 60-76
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Konferensbidrag (refereegranskat)abstract
- We give a short introduction to Martin-Löf's Type Theory, seen as a theory of inductive definitions. The first part contains historical remarks that motivate this approach. The second part presents a computational semantics, which explains how proof trees can be represented using the notations of functional programming.
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| 44. |
- Dybjer, Peter, 1953
(författare)
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Inductive Families
- 1994
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Ingår i: Formal Aspects of Computing. ; 6, s. 440-465
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Tidskriftsartikel (refereegranskat)
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| 45. |
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| 46. |
- Dybjer, Peter, 1953
(författare)
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Internal type theory
- 1996
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Ingår i: TYPES '95, LNCS. ; 1158, s. 120-134
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Tidskriftsartikel (refereegranskat)
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Dybjer, Peter, 1953, et al.
(författare)
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Normalization and the Yoneda embedding
- 1998
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Ingår i: Mathematical Structures in Computer Science. ; 8, s. 153-192
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Tidskriftsartikel (refereegranskat)
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