Crossing of stent graft limbs during endovascular aneurysm repair (EVAR) is often used to assist cannulation and prevent graft kinking when the aortic bifurcation is widely splayed. Little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Using computational fluid dynamics, this work numerically examines the hemodynamic differences between these two out-of-plane stent graft configurations against a planar configuration commonly found in literature. Predicted values of displacement force, wall shear stress, and oscillatory shear index were similar between the out-of-plane configurations. The planar configuration predicted similar wall shear stress values, but significantly lower displacement forces than the out-of-plane configurations. These results suggest that the hemodynamic safety of cross-limb EVAR is comparable to conventional EVAR. However, a study of clinical outcomes may reveal reduced thrombosis incidence and long-term structural implications for the stent graft in cross-limb EVAR.

Crossing of stent graft limbs during endovascular aneurysm repair (EVAR) is often used to assist cannulation and prevent graft kinking when the aortic bifurcation is widely splayed. Little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Using computational fluid dynamics, this work numerically examines the hemodynamic differences between these two out-of-plane stent graft configurations against a planar configuration commonly found in literature. Predicted values of displacement force, wall shear stress, and oscillatory shear index were similar between the out-of-plane configurations. The planar configuration predicted similar wall shear stress values, but significantly lower displacement forces than the out-of-plane configurations. These results suggest that the hemodynamic safety of cross-limb EVAR is comparable to conventional EVAR. However, a study of clinical outcomes may reveal reduced thrombosis incidence and long-term structural implications for the stent graft in cross-limb EVAR.

In an effort to achieve lighter and more economical space structures, a new patented steel composite member has been suggested and used in the construction of some steel roof structures. This special element has a sandwich construction composed of some strips of steel plates placed longitudinally along a helical wire core. The function of the helical core is to transfer the shear between the flange plates and increase the sectional inertia of the resulting composite member by keeping the flange plates at a desired distance from each other. Because of the lack of research, design engineers usually treat such elements as a solid member as if it has a full shear transfer between the flanges. However, a detailed analysis shows that this is not a valid assumption and leads to very unsafe results. In this context, the purpose of this study is to investigate the behavior of such members under axial compression and determine their effective sectional flexural rigidity by taking into account the shear deformations. This study applies an analytical investigation to a specific form of such elements with four flange plates placed symmetrically around a helical wire core. Five independent parameters of such a member are selected for this purpose. These are the spiral core and core wire diameters, the pitch of the spiral core, and the flange plate dimensions. Elements with varying combinations of the selected parameters are first analyzed in detail by finite element method, and some design charts are generated for the determination of the effective sectional properties to be used in the structural analysis and the buckling loads. For this purpose, an alternative closed-form approximate analytical solution is also suggested.

Novel antennas attractive to fit in the internal space of a PDA (Personal Digital Assistant) for WLAN (Wireless Local Area Network) operations are presented in this dissertation. The proposed antennas have in common good impedance bandwidth (defined by 10 dB return loss), covering the dual-band WLAN operation in the 2.4/5.2 GHz bands. Two novel designs of foam-base surface-mount antennas are proposed in Chapters 2 and 3. Surface-mountable antennas, compared with ceramic antennas, are generally low cost in fabrication and rigid in nature. Low-profile and good dual-band operation of the proposed surface-mountable antennas can be observed in Chapters 2 and 3, and in addition, a few present-day WLAN bands at 5 GHz are covered in the operating bandwidths of the proposed foam-base surface-mountable shorted monopole antenna, shown in Chapter 3. Finally, in Chapter 4, a novel planar helical antenna printed on both surfaces of a dielectric substrate is demonstrated. This patent-pending helical antenna is very suitable to print and integrate on a circuit board of a PDA device for 2.4/5.2 GHz WLAN operation.

The present study describes the flow characteristics of swirling flows induced by twisted tape inserts in circular pipes. The study is focused on the secondary flow which is investigated experimentally and with numerical models. The results are expected to improve the paper manufacturing process by identifying and removing the detrimental secondary flow. Experimental tests show for the first time the existence of two co-rotating helical vortices superimposed over the main swirling flow, downstream of twisted tapes. The close proximity of the two co-rotating vortices creates a local counter-rotating flow at the pipe centerline. The flow is analyzed using LDV measurements and high speed camera visualization with fine air bubbles seeding which confirm that the helical vortices are stable. After extracting the characteristic tangential velocity profiles of the main vortex and of the two secondary vortices, it was observed that the maximum tangential velocity of all three vortices is the same, approximately half of the bulk velocity. The winding of the helical vortices is in the swirl direction and the pitch of the helical vortices is found to be independent of the inlet velocity. The experimental findings are confirmed by numerical simulations. The numerical results show that the helical vortices originate inside the swirler and evolve from single co-rotating vortices on each side of the tape. The flow characteristics are analyzed in detail. Swirlers with multiple twists and multiple chambers are shown to have less stable secondary motion and could be employed in applications were the secondary motion is detrimental.

The present study investigates experimentally the laminar mixing and heat transfer of a range of helical ribbon and anchor impellers for both Newtonian and inelastic non-Newtonian fluids. The work also correlates the experimental data empirically in the form of dimensionless groups. In order to estimate the relative importance and the effect of all the geometrical parameters on the mixing power and heat transfer, data from the published literature sources will be utilized and combined with the results from this study. Thus, reliable empirical correlations will be obtained which are applicable over the widest range of operating conditions. The study also investigates the ablity of the various impellers to level out temerature distributions. The measurement of these temperature gradients and the impeller power requirements gives a measure of the mixing efficiency of the impeller used.

Palladium-catalyzed olefin dioxygenation is a powerful tool in the generation of complex and valuable substrates, one which may become complimentary to the well known Sharpless dihydroxylation. In this work the mechanism of this transformation is examined via reaction kinetics and Hammett studies, which corroborate a PdII/IV catalytic cycle and suggest that the rate determining step is the oxidation of PdII to PdIV. Olefin dioxygenation was also found to proceed in the presence of catalytic quantities of BF3•OEt2 or triflic acid, with stoichiometric hypervalent iodine oxidant and an acetic acid solvent. Furthermore, asymmetric variants of intramolecular palladium-catalyzed olefin dioxygenation were also investigated, which resulted in the formation of tetrahydrofuran products in up to 36% ee. Next, chelate-assisted C–H bond functionalization of indoles at the C7 position and of carbazoles at the C1 position was investigated with a variety of arylation, halogenation and oxygenation techniques. Lastly, our efforts towards the synthesis of a mono-phosphine based [5]helicene ligand via olefin metathesis and photocyclization strategies will be discussed.

Palladium-catalyzed olefin dioxygenation is a powerful tool in the generation of complex and valuable substrates, one which may become complimentary to the well known Sharpless dihydroxylation. In this work the mechanism of this transformation is examined via reaction kinetics and Hammett studies, which corroborate a PdII/IV catalytic cycle and suggest that the rate determining step is the oxidation of PdII to PdIV. Olefin dioxygenation was also found to proceed in the presence of catalytic quantities of BF3•OEt2 or triflic acid, with stoichiometric hypervalent iodine oxidant and an acetic acid solvent. Furthermore, asymmetric variants of intramolecular palladium-catalyzed olefin dioxygenation were also investigated, which resulted in the formation of tetrahydrofuran products in up to 36% ee. Next, chelate-assisted C–H bond functionalization of indoles at the C7 position and of carbazoles at the C1 position was investigated with a variety of arylation, halogenation and oxygenation techniques. Lastly, our efforts towards the synthesis of a mono-phosphine based [5]helicene ligand via olefin metathesis and photocyclization strategies will be discussed.

Three-dimensional movement analysis was used to evaluate head and neck movement in patients with neck pain and matched controls. The aims were to further develop biomechanical models of head and neck kinematics, to investigate differences between subjects with non-specific neck pain and whiplash associated disorders (WAD), and to evaluate the potential of objective movement analysis as a decision support during diagnosis and follow-up of patients with neck pain. Fast, repetitive head movements (flexion, extension, rotation to the side) were studied in a group of 59 subjects with WAD and 56 controls. A back propagation artificial neural network classified vectors of collected movement variables from each individual according to group membership with a predictivity of 89%. The helical axis for head movement were analyzed in two groups of neck pain patients (21 with non-specific neck pain and 22 with WAD) and 24 matched controls. A moving time window with a cut-off angle of 4° was used to calculate finite helical axes. The centre of rotation of the finite axes (CR) was derived as the 3D intersection point of the finite axes. A downward migration of the axis during flexion/extension and a change of axis direction towards the end of the movements were observed. CR was at its most superior position during side rotations and at its most inferior during ball catching. This could relate to that side rotation was mainly done in the upper spine, while all cervical vertebrae were recruited to stabilize the head in the more complex catching task. Changes in movement strategy were observed in the neck pain groups: Neck pain subjects had lower mean velocities and ranges of movements as compared with controls during ball catching, which could relate to a stiffer body position in neck pain patients in order to stabilize the neck. In addition, the WAD group had a displaced axis position during head repositioning after flexion, while CR was displaced during fast side rotations in the non-specific neck pain group. Pain intensity correlated with axis and CR position, and may be one reason for the movement strategy changes. Increased amount of irregularities in the trajectory of the axis was found in the WAD group during head repositioning, fast repetitive head movements and catching. This together with an increased constant repositioning error during repositioning after flexion indicated motor control disturbances. A higher group standard deviation in neck pain groups indicated heterogeneity among subjects in this disturbance. Wireless motion sensors and electro-oculography was used simultaneously, as an initial step towards a portable system and towards a method to quantify head-eye co-ordination deficits in individuals with WAD. Twenty asymptomatic control subjects and six WAD subjects with eye disturbances (e.g. dizziness and double vision) were studied. The trial-to-trial repeatability was moderate to high for all evaluated variables (single intraclass correlation coefficients >0.4 in 28 of 32 variables). The WAD subjects demonstrated decreased head velocity, decreased range of head movement during gaze fixation and lowered head stability during head-eye co-ordination as possible deficits. In conclusion, kinematical analyses have a potential to be used as a support for physicians and physiotherapists for diagnosis and follow-up of neck pain patients. Specifically, the helical axis method gives information about how the movement is performed. However, a flexible motion capture system (for example based on wireless motion sensors) is needed. Combined analysis of several variables is preferable, as patients with different neck pain disorders seem to be a heterogeneous group.

1 Title Helical symmetry and the non-existence of asymptotically flat periodic solutions in general relativity Author Martin Scholtz Department Institute of theoretical physics Faculty of Mathematics and Physics Charles University in Prague Supervisor Prof. RNDr. Jiří Bičák, DrSc., dr. h.c. Abstract. No exact helically symmetric solution in general relativity is known today. There are reasons, however, to expect that such solutions, if they exist, cannot be asymptotically flat. In the thesis presented we investigate a more general question whether there exist periodic asymptotically flat solutions of Einstein's equations. We follow the work of Gibbons and Stewart [3] who have shown that there are no periodic vacuum asymptotically flat solutions an- alytic near null infinity I. We discuss necessary corrections of Gibbons and Stewart proof and generalize their results for the system of Einstein-Maxwell, Einstein-Klein-Gordon and Einstein-conformal-scalar field equations. Thus, we show that there are no asymptotically flat periodic space-times analytic near I if as the source of gravity we take electromagnetic, Klein-Gordon or conformally invariant scalar field. The auxilliary results consist of corresponding confor- mal field equations, the Bondi mass and the Bondi massloss formula for scalar fields. We also...