| 11. |
- Barza, Sorina
(författare)
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Weighted multidimensional integral inequalities and applications
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis some new weighted integral inequalities for monotone functions in higher dimensions are proved. These results extend previous results in one dimension, and also those in higher dimensions for particular choices of the weights (power weights, etc.). All inequalities are sharp. A new duality principle (of Sawyer type) over the cone of multidimensional monotone functions is proved and applied. Weighted Chebyshev type inequalities for monotone functions and modular inequalities in higher dimensions are proved. A new type of weighted function spaces are introduced. In particular these spaces generalize the classical Lebesgue spaces. The weights such that they become quasi-Banach spaces are completely characterized. A multidimensional multiplicative inequality (of Carlson type) for weighted Lebesgue spaces with homogeneous weights is proved and applied. The inequality is sharp and all cases of equality are pointed out.
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| 12. |
- Bergman, Greger
(författare)
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Modelling and simulation of simultaneous forming and quenching
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this thesis is to develop and evaluate numerical methods for modelling and simulation of simultaneous forming and quenching within an integrated product development environment. Simultaneous forming and quenching, also referred to as hot-stamping, is a manufacturing process for high strength automotive components such as side impact protection beams. A concept for integrated product and process development is proposed. The prototype system consists of a CAD system, a relational database management system, program interfaces, and nonlinear finite element programs. A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to solve coupled thermomechanical problems. The implementation includes a linear-quadratic thermal shell element, and contact heat transfer. The material behaviour is described by a thermo-elastic-plastic material model. The effective-stress-function algorithm is used to update the stresses. The implemented methods are evaluated by comparison with corresponding experimental results. In one of the developed experiments, pre-heated steel plates are simultaneously formed and quenched by a cold tool. The analyses show good agreement during the initial stage, followed by an overestimation of the tool force at sequential times. It is shown that the computed tool force is very sensitive to the sequence of cooling in different parts of the plate.
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| 13. |
- Boström, Staffan
(författare)
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Crack location in steel structures using acoustic emission techniques
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Denna avhandling utvärderar möjligheten att använda akustisk emission (AE) för att detektera och lokalisera sprickor i stora stålkonstruktioner med ett långt avstånd mellan givarna. De industriella/ekonomiska motivet för projektet är att en noggrannare undersökning av befintliga konstruktioners tillstånd medför att utbyte av dessa konstruktioner kan skjutas på framtiden med bibehållen säkerhet, vilket i sin tur medför besparingar för till exempel broägare. Motiv för långt avstånd mellan givarna är att hålla kostnaden förundersökningen nere. Fältförsöken omfattade mätningar på fyra broar och en kranbana. I korthet var resultaten att det ofta gick att detektera sprickor men att säkerheten i metoden behövde förbättras och att mättiderna behövde reduceras. MAE utvecklades och den baseras på digital signalbehandling samt användandet en ny detektor för att upptäcka AE signaler. Den största fördelen med den nya tekniken är att bruset reduceras, vilket innebär att även svaga signaler går att detektera. Resultat från laboratorieförsök och försök ute i fält visar att MAE kan användas för sprickdetektering och lokalisering med ett avstånd mellan givarna på upp till 20m. Det är dock viktigt att den verkliga våghastigheten för konstruktionen bestäms. I jämförelse med traditionell AE kan mättiderna med MAE kortas, vilket leder till enklare och billigare kontroller/undersökningar av konstruktioners tillstånd.
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| 14. |
- Carlsson, Britta
(författare)
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Ecological understanding : a space of variation
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims at increasing the knowledge of ecological understanding. For this purpose a phenomenographic approach, founded on the theory of variation, is adopted. As a means of expanding the outcome space, a Vygotskian approach to learning is also applied. In line with this, the respondents´ thinking has been deliberately challenged by interventions. these changes of views, and the situations in which they occured are described on both a collective and an induvidual level of awareness. Ten teacher students, chosen by theoretical sampling, has been interviewed on three occasions. The aim of the first interview was to reveal the respondents´ experiences of their relationship to nature. In doing this, photos, taken by respondents, served as concrete, shared objects of attention. In the second and third interview scientific, rather than experential aspects were focused on. To explore ways of understanding the function of the ecosystem two problem solving situations were arranged. Using a systems approach the functional aspects of the ecosystem have been explored, with photosynthesis, recycling and energy as units of analysis. In the third interview also an explanatory text was used as a research tool. The results indicate that the idea of transformation is crucial to a development of ecological understanding. This idea divides the categories into a consumptional and a transformational group. The structure of ecological understanding was also found to be hierarchical in terms of inclusion of critical aspects in more complex ways of thinking. For example, in the most complex form of thinking, a time frame was included. The investigation has shown that the relationship to nature could be described in two qualitatively different ways, Self in nature, and Self and nature. In the former, the respondent sees him- or herself as an integrated, mutually dependent part of nature, while in the latter, humans were separated from nature. No obvious coupling seems to exist between ways of relating to nature and ways of understanding the ecosystem’s function. The identified categories and their critical aspects indicate fruitful paths for learning and crucial dimensions to open up in teaching. Thus, the results concern teachers´ professional object, i.e., an emphasis on what to achieve in teaching and learning.
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| 15. |
- Czmoch, Ireneusz
(författare)
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Influence of structural timber variability on reliability and damage tolerance of timber beams
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis addresses two main problems: 1) Probablistic modelling of lengthwise variability in structural timber, 2) Reliability and damage tolerance analysis of beams made of structural timber. Timber is considered as an elastic-brittle material. Dependence of timber properties on time and environment conditions is neglected. The presented statistical analysis of MOE is based on experimental data. An original method for determination of the MOE function on the basis of a measured deflection curve has been developed. The Log-normal, Gumbel or Normal distributions can be recommended as the probability distribution model of the homogeneous random field of MOE with the scale of fluctuation equal to 1.5-2.5 m. The variability of bending strength of timber beams has been studied with help of a weak-zone model. Assuming a marked Poisson random field as a probabilistic model of bending strength, analytical solutions have been derived for a number of particular problems. The influence of the correlation between strengths of weak zones has been studied with help of the Monte Carlo simulation. Time invariant reliability indices and damage tolerance indices have been computed for the weak-zone model and the corresponding homogeneous modelof a timber beam. The difference in reliability indices between the homogeneous and weak-zone models depends more on the probability model of the weak-zone strength than on the mean distance between the weak zones. There is no significant difference in the damage tolerance indices computed for the two considered models of a timber beam.
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| 16. |
- Degermark, Mikael
(författare)
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Three aspects of packet forwarding in the Internet
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses packet forwarding in packet-switching networks such as the Internet. The interconnection points tying transmission links together in such networks are called routers, computers that may be specialized for the task. Routers need to decide where, when, and in what form each packet should be forwarded. This thesis concerns aspects of these three decisions. A router has to decide where an incoming packet is to be sent. Routers need to determine which outgoing link to use and in the case of multi-access links where on the link the packet should go. Packet headers contain addressing information that specifies the destination of the packet. For IP that information has to be matched with topological information, gathered by routing protocols that operate between routers, to determine the next hop in a viable path through the network. A fast algorithm for this matching operation, the IP routing lookup, is presented. When realized in software running on commercially available general-purpose processors such as the Pentium Pro or the DEC Alpha 21164, the algorithm can perform a few million matching operations per second. This is sufficient to support packet streams arriving at speeds of gigabits per second. In contrast, previous solutions to this problem have used special hardware support and/or have relied on traffic locality by caching the results of recent matching operations. Routers also need to determine when to forward each packet. When an outgoing link is busy, packets must be stored temporarily in the router until they can be forwarded. Modern routers use various queuing schemes to change the order in which packets are forwarded relative to the order in which they arrived. This is done to provide bounds on the latency through the network, and/or to guarantee certain transfer capacities to certain network users. Reservation protocols provide the parameters to these queuing schemes and thus allow network users to reserve network capacity for their traffic. The thesis explores mechanisms for advance reservations; resource reservations made potentially weeks or months before the traffic enters the network. It appears possible to keep the high link utilization of services using measurement based admission control algorithms, such as predictive service, even when resource reservations are made in advance. Finally, routers have to decide what form packets should have when forwarded. A problem with today's Internet Protocol is that headers are relatively large. When payloads are small, header overhead can become prohibitive. This thesis presents ways to reduce header sizes significantly, from 28-100 bytes down to 2-6 bytes. The disadvantage of large headers is thereby eliminated. The methods can be used for all IP packet streams and are, in contrast to previous solutions, usable over links with significant packet-loss rates such as wireless links. The techniques are useful for applications such as Internet telephony where voice samples are carried in a stream of many small packets, and for file transfers over highly asymmetrical (satellite) links where the back channel carrying acknowledgements is the bottleneck.
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| 17. |
- Deleryd, Mats
(författare)
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Enhancing the industrial use of process capability studies
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this thesis is focused on how the industrial use of process capability studies can be improved. This aim is achieved by using two different approaches. As a first approach the gap between the theoretical frontier and practitioners use of process capability studies is identified, quantified, and explained. This is accomplished by using a series of questionnaire surveys within Swedish industry. Based on some retrospective case studies among nine Swedish organisations, a model how to implement process capability studies successfully, has been developed. A strategy to master variation by using several improvement methods together is presented using process capability studies as a framework within this strategy. The first four appended papers present the results of the first approach. As a second approach, the theoretical frontier of process capability studies has been developed to cover practical situations while also enhancing the possibilities of making proper decisions. Within the second approach a method how to use process capability studies when production runs are short has been developed and studied. Furthermore, the effect of skewness on estimates of process capability indices, which are numerical measures of process capability, has been studied. FFinally, since practitioners often seem to use process capability indices in inappropriate ways, a graphic approach for assessing, monitoring and improving the capability of processes has been put forward. The concept of process capability plots is introduced and two process capability plots are studied from both a theoretical and practical point of view in order to find out when each plot is most useful. The last three appended papers, which mainly are based on simulation studies, present the results of the second approach.
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| 18. |
- Du, Qing
(författare)
-
Surface complexation in natural particle suspensions
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is a summary of our studies on (i) the proton and copper adsorption at aqueous illite surfaces, (ii) the proton and copper complexation of humic substances (fulvic acid FA and humic acid HA), (iii) the interaction between illite and fulvic acid, and (iv) the copper complexation behaviors in illite-FA bi-complexant systems. These particular studies were designed to help us develop a framework for modelling heavy metal complexation/adsorption mechanisms at natural particle surfaces. Our data were mainly generated from potentiometric titration, batch adsorption and FI-IR experiments; the model calculations and simulations were accomplished using computer programs FITEQL and SOLGASWATER. To account for the complexation behavior in illite/water suspensions, we analyzed the experimental data using the constant capacitance surface complexation model. Our analysis showed that (i) the proton reactions in the supernatants of illite suspensions can be represented by those of Al(H20)6 3+ and Si(OH)4 in water solutions, (ii) the acid-base properties of illite surfaces can be illustrated using only deprotonation reactions, which suggests that the surface acidic behavior of illite is similar to that of amorphous SiO2, and (iii) the uptake of copper in illite suspensions can be interpreted by the surface adsorption of different Cu(II) aqueous species, followed by the formation of copper precipitates, which were found to be hydroxide precipitates in carbonate-free illite suspensions and hydroxylcarbonate precipitates in carbonate-containing illite suspensions. To account for the complexation properties of humic substances, we used a nonelectrostatic, discrete site distribution model. Model analysis showed that (i) the acid-base properties of FA and HA can be modelled as those of a mixture of three monoprotic acids (R1H, R2H and R3H), (ii) the complexation of copper can be explained by assuming that copper binds mainly with the strongest and weakest acid sites (R1H and R3H) to form monodentate complexes, and (iii) FA has a stronger acid strength, but a weaker copperbinding potential, than HA. As to the adsorption of FA by illite, we found that it decreases with increases in pH values and its pH adsorption edge resembles those of SiO2-FA and montmorillonite-FA systems. The adsorption mechanism might be explained by assuming that the functional groups of FA react with the water molecules held by electrostatic forces near the illite surfaces to form H-bonds. In FA-illite bi-complexant systems, the complexation of Cu2+ ions can be effectively simulated by taking it to be a combination of individual bindings by the illite surfaces and the FA functional groups. This suggests that in natural water systems, fulvic acid can inhibit the retention of heavy metals at solid surfaces by forming soluble complexes with metal ions.
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| 19. |
- Edlund, Ove
(författare)
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Solution of linear programming and non-linear regression problems using linear M-estimation methods
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to algorithms for solving two optimization problems, using linear M-estimation methods, and their implementation. First, an algorithm for the non-linear M-estimation problem is considered. The main idea of the algorithm is to linearize the residual function in each iteration and thus calculate the iteration step by solving a linear M- estimation problem. A 2-norm bound on the variables restricts the step size, to guarantee convergence. The other algorithm solves the dual linear programming problem by making a ``smooth'' approximation of edges and inequality constraints using quadratic functions, thus making it possible to use Newton's method to find the optimal solution. The quadratic approximation of the inequality constraint makes it a penalty function algorithm. The implementation uses sparse matrix techniques. Since it is an active set method, it is possible to reuse the old factor when calculating the new step, by up- and downdating the old factor. It is only occasionally, when the downdating fails, that the factor instead has to be found with a sparse multifrontal LQ-factorization.
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| 20. |
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