Theoretical Problems in High Resolution Solar Physics, 2

The Science Working Group for the High Resolution Solar Observatory (HRSO) laid plans beginning in 1984 for a series of workshops designed to stimulate a broadbased input from the scientific community to the HRSO mission. These workshops have the dual objectives of encouraging an early start on the difficult theoretical problems in radiative transfer, magnetohydrodynamics, and plasma physics that will be posed by the HRSO data, and maintaining current discussions of results in high resolution solar studies. This workshop was the second in the series. The workshop format presented invited review papers during the formal sessions and contributed poster papers for discussions during open periods. Both are presented

MedLAN: Compact mobile computing system for wireless information access in emergency hospital wards

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A&E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec

Probability of breaking waves in random seas

SIGLEAvailable from British Library Document Supply Centre- DSC:D94941 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Impact of aortic acceleration on haemodynamics

The aortic valve apparatus (AVA) is a complicated structure continuously moving throughout the cardiac cycle such that it may be regarded as a live organ. Different studies previously focused on analysing the dynamism or local deformations of the AVA; however, the effect of the axial movement of the AVA on blood flow or aortic valve loading remains uncharted. In this study we propose analysing the axial acceleration of the AVA and its effect on blood flow. After mathematically decomposing the deformations of healthy AVA’s from CT image tracking, it was deduced that the dominant component is the axial movement towards and away from the left ventricle. Using the 1D water hammer approximation we hypothesised a theory tying the previously inexplicable dicrotic notch seen on the arterial pressure waveform to the AVA acceleration during valve closure. The next intermediate step was to use an idealised model replicating the anatomy of the AVA in order to study the effect of axial acceleration on blood flow combined with steady inflow conditions. A series of non-dimensional parameters describing the underlying physics were derived in order to enable an appropriate comparison with a patient specific anatomy. The final step was to analyse a stationary and an accelerating patient specific AVA using high fidelity Fluid-Structure Interaction (FSI) simulations. The results showed qualitative and quantitative differences between both cases especially in valvular dynamics and loading. Moreover, the FSI simulation results confirmed the presence of a sudden reactive force on the aortic valve in the accelerating AVA case at the time of peak acceleration during valve closure; where the same phenomenon was not present in the stationary AVA case. The calculated force of 0.6 N along with the aortic valve wetted area of 0.0013 m2 yield ≈ 3.5 mmHg which is in the same ball park as previously measured dicrotic notch pressure rises. As a result, we propose that the axial acceleration of the AVA may be a crucial parameter in diagnosing aortic or ventricular disease since it has a significant effect on aortic valve function. We also propose a future plan of investigation in order to strengthen our hypothesis and enable the use of the acceleration of the AVA as a non-invasive diagnostic parameter.Open Acces

Microstructure and Phase Behavior in Colloids and Liquid Crystals

This thesis describes our investigation of microstructure and phase behavior in colloids and liquid crystals. The first set of experiments explores the phase behavior of helical packings of thermoresponsive microspheres inside glass capillaries as a function of volume fraction. Stable helical packings are observed with long-range orientational order. Some of these packings evolve abruptly to disordered states as the volume fraction is reduced. We quantify these transitions using correlation functions and susceptibilities of an orientational order parameter. The emergence of coexisting metastable packings, as well as coexisting ordered and disordered states, is also observed. These findings support the notion of phase-transition-like behavior in quasi-one-dimensional systems. The second set of experiments investigates cross-over behavior from glasses with attractive interactions to sparse gel-like states. In particular, the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions are measured as a function of packing fraction. A crossover from glassy to sparse gel-like states is indicated by an excess of low-frequency phonon modes. This change in vibrational mode distribution appears to arise from highly localized vibrations that tend to involve individual and/or small clusters of particles with few local bonds. These mode behaviors and corresponding structural insights may serve as a useful signature for glass-gel transitions in wider classes of attractive packings. A third set of experiments explores the director structures of aqueous lyotropic chromonic liquid crystal (LCLC) films created on square lattice cylindrical-micropost substrates. The structures are manipulated by modulating of the concentration-dependent elastic properties of LCLC s via drying. Nematic LCLC films exhibit preferred bistable alignment along the diagonals of the micropost lattice. Columnar LCLC films form two distinct director and defect configurations: a diagonally aligned director pattern with local squares of defects, and an off-diagonal configuration with zig-zag defects. The formation of these patterns appears to be tied to the relative free energy costs of splay and bend deformations in the precursor nematic films. The observed nematic and columnar configurations are understood numerically using a Landau-de Gennes free energy model. This work provides first examples of quasi-2D micropatterning of LC films in the columnar phase and the first micropatterning of lyotropic LC films in general, as well as demonstrating alignment and configuration switching of typically difficult-to-align LCLC films via bulk elastic properties

High Harmonic Generation Using Multicolour Fields

This thesis describes the phenomenon of high harmonic generation from atoms irradiated by intense, ultrashort laser pulses. Particular attention is paid to the benefits achieved by using multicolour driving fields. A theoretical description of few-cycle laser pulses is presented, together with their interaction with free-electrons and the role they play in various nonlinear optical processes. A number of numerical models are presented to simulate high harmonic generation from atomic systems. These are used to analyse and explain the temporal structure of the emitted high-frequency dipole radiation. Propagation of the macroscopic harmonic response through a gaseous volume is modelled and the role of phase-matching explained in detail. We consider focussing geometry in optimising the yield of particular harmonics, together with the effects of free-electrons within the interaction region. We discuss means by which multicolour fields may overcome some of the constraints of single-colour high harmonic generation. Using two delayed pulses of the same frequency and parallel polarisation we demonstrate significant cut-off extension without increasing total ionisation throughout the pulse, crucial for maintaining harmonic yield close to the saturation limit. We also explain the significant yield enhancements observed in recent experiments using two parallel colours of incommensurate frequency. Finally, we describe the use of a second, perpendicularly polarised colour in trajectory selection, allowing for a temporal filtering of harmonic emission. Using an ω + 1.5ω frequency ratio also allows for a reduction in the periodicity of emitted attosecond pulse trains, permitting the production of isolated attosecond pulses with longer driving fields. Furthermore, by controlling the relative phase between the two colours, the ellipticity of these attosecond pulses may also be controlled

MedLAN : compact mobile computing system for wireless information access in emergency hospital wards

As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A;E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec.EThOS - Electronic Theses Online ServiceGBUnited Kingdo