Diss. (sammanfattning) Linköping : Univ. / Härtill 6 uppsatser.

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Detonation waves are supersonic combustion waves that have a complex three-dimensional cellular structure. There is growing experimental evidence that the cellular structure of detonations promotes their propagation in the presence of losses. In spite of that, the conventional model for the detonation structure, known as the Zeldovich - Von Neumann - Doring (ZND) model, neglects the existence of cellular structure for detonations and assumes the wave to consist of a strong leading planar shock coupled with trailing chemical reactions. Therefore, the influence of cellular structure on the dynamics and extinction limits of detonation waves has been of particular interest. Previous studies have investigated the influence of cellular structure on the dynamics of detonations with mass divergence in the framework of narrow tubes, porous-walled tubes and weak confinement. However, precise quantification of the loss mechanism in these frameworks has been associated with some difficulties. Complex flow in the boundary layers, inherent in thin tubes, or attenuation of the transverse waves in the porous-walled tubes has made the evaluation of the loss mechanism more difficult in such geometries. In this thesis, a novel well-posed problem is formulated for detonations with mass divergence. It is shown that detonations propagating in a channel with a cross-section area increasing exponentially have a constant mass divergence. The detonations were found to propagate at a quasi-steady speed below the ideal Chapman-Jouguet velocity. This permitted to make meaningful comparison with the theoretical models and simulations. The experiments were performed in two mixtures, one displaying characteristic weakly unstable detonations (2C2H2 + 5O2 + 21Ar), and the other displaying highly unstable detonations (C3H8 + 5O2). The dependence of the velocity deficits and limits on the amount of mass divergence for the two mixtures were compared with the predictions of the quasi-one-dimensional ZND model with lateral mass divergence. Since the ZND model neglects the cellular structure of the detonations, such comparison permitted to asses the influence of cellular structure on the dynamics of detonations with mass divergence. Comparisons were also made with the results of simulations of inviscid cellular detonations. These comparisons showed that the velocity deficits and critical rate of mass divergence in the weakly unstable mixture were reasonably well predicted by the quasi-one-dimensional model. For smaller values of mass divergence rate, a good agreement between the experiments and the predictions of the two-dimensional cellular simulations was observed for the weakly unstable mixture. For the highly unstable detonations, the quasi-one-dimensional model significantly over-predicted the effect of mass divergence.Detonations were observed for rates of mass divergence 93% higher than the critical predicted value, displaying more substantial velocity deficits than predicted. Such observations show conclusively that the ZND model cannot capture the dynamics of highly unstable detonations on large scales.

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Considered in this thesis is multi-input multi-output (MIMO) systems with non-minimum phase (NMP) zeros and unstable poles where some of the unstable poles are located to the right of the NMP zeros. In the single-input single-output (SISO) case such systems pose serious difficulties in controller synthesis for performance and stability. In spite of the added degrees of freedom the MIMO case also poses difficulties as has been shown in the stabilization of the X-29 aircraft. When using the MIMO QFT technique the synthesis starts by considering a set of equivalent SISO plants derived from the plant transfer function matrix that are used to develop a controller. In effect the design problem is reduced to several MISO designs with the diagonal entries of as the equivalent SISO plants. Developed is a transformation scheme that can be used to condition the resulting equivalent SISO plants so that the difficult problem of NMP zeros lying to the left of unstable poles is avoided. Examples illustrate the use of the proposed transformation.

No description available.

Considered in this thesis is multi-input multi-output (MIMO) systems with non-minimum phase (NMP) zeros and unstable poles where some of the unstable poles are located to the right of the NMP zeros. In the single-input single-output (SISO) case such systems pose serious difficulties in controller synthesis for performance and stability. In spite of the added degrees of freedom the MIMO case also poses difficulties as has been shown in the stabilization of the X-29 aircraft. When using the MIMO QFT technique the synthesis starts by considering a set of equivalent SISO plants derived from the plant transfer function matrix that are used to develop a controller. In effect the design problem is reduced to several MISO designs with the diagonal entries of as the equivalent SISO plants. Developed is a transformation scheme that can be used to condition the resulting equivalent SISO plants so that the difficult problem of NMP zeros lying to the left of unstable poles is avoided. Examples illustrate the use of the proposed transformation.

This study explored the risk factors for homelessness in single men, the largest group of people experiencing homelessness and a group about which little is known regarding their risks for homelessness. A case control design was used to differentiate risk factors between men who were homeless and men who were unstably housed. Risk factors included cumulative risk, negative life events, and demographic factors. Two models were tested using discriminant function analysis (DFA). The Cumulative Risk Model did not significantly differentiate between the two groups. However, the Negative Life Events Model yielded one discriminant function that significantly differentiated between the groups and correctly classified approximately 72.4% of the overall cases. Negative life events regarding the loss of housing, unstable housing, and family conflict/disruption were the most important discriminating variables. Furthermore, homeless men were associated with more experiences of loss of housing and family conflict/disruption, and with fewer experiences of housing instability. Implications for policy, social work practice, and research are discussed.

Magister Scientiae - MSc / The aim of nuclear structure physics is to study the interplay between singleparticle and collective degrees of freedom in nuclei and to explain how nuclei get excited and decay under di erent external conditions, such as strong electric and magnetic elds. If nuclei absorb a large amount of energy and angular momentum, like in a scattering reaction when you bombard a target that is in the ground state with a projectile at high bombarding energies, the energy from the projectile gets transfered to the target and vice versa, hence both projectile and target may get excited. During the de-excitation process nuclei may release the energy in a form of electromagnetic radiation (gamma rays) which carries angular momentum. The atomic nucleus is a many-body system, whose structure is de ned in terms of interactions between protons and neutrons. In nature there are only around 300 stable isotopes [1]. They are all in their ground states (although some are in a low-energy excited isomeric state with a long lifetime). To study excited states in these nuclei one needs to provide energy to the system. In addition, there are some 3000 unstable nuclei, most of which do not exist in nature. Many have been produced and studied in research laboratories, and there could be more than 3000 other unstable nuclei that can in principle exist in astrophysical environments, but have not yet been synthesized on Earth [1].