Introduction: Radiofrequency ablation (RFA) is a popular method of treating unresectable liver tumours by the use of a high frequency, alternating electrical current that heats and destroys tumour cells. The size of the ablation is limited by localised charring of adjacent tissue that prevents further conduction of the radiofrequency current. In the clinical setting, this results in increased rates of local recurrence in tumours that are greater than 3 cm in diameter as multiple, overlapping ablations need to be performed to treat the one tumour. To overcome this problem, a modified form of RFA called Bimodal Electric Tissue Ablation (BETA) has been created. BETA adds a direct electrical current to the alternating radiofrequency current, thus establishing its bimodal character. When direct currents are used in biological tissues, water is transferred from anode to cathode by a process called electro-osmosis. By attaching the cathode to the radiofrequency electrode, water is attracted to the area thus preventing tissue desiccation and charring. The BETA circuit has been constructed and tested using a porcine model. The aims of the studies are to confirm that larger ablations can be produced with the BETA system and that it is safe to use in an animal model. Three studies have been performed to test these aims in porcine liver. Methods: The first study was designed to compare sizes of the ablation produced between standard RFA and the BETA circuit. This was followed by a long-term study to assess associated changes to liver function and pathological changes within the liver as well as identifying any other treatment related morbidity. The third study assessed the difference in ablation size and safety aspects when the positive electrode of the direct current circuitry was moved from small surface area under the skin to a large surface area on the skin. Results: Ablations with significantly larger diameters are created with the BETA circuit using a multi-tine needle (49.55 mm versus 27.78 mm, p<0.001). This finding was confirmed in the third experiment using a straight needle (25 mm versus 15.33 mm, p<0.001). Ablations produced by the BETA circuit induce coagulative necrosis within the treated liver and the injury heals by fibrosis in a manner similar to other thermal therapies. Significant rises in some serum liver enzymes are seen within 24 hours of treatment but these return to normal within 4 days. An electrolytic type injury can be produced at the site of the positive electrode. By increasing the surface area of this electrode, the risk of tissue damage is decreased but ablations are significantly smaller (18 mm versus 25 mm, p<0.001). Conclusions: The BETA circuit consistently produces significantly larger ablations than RFA. The treatment appears safe but positioning of the positive electrode of the direct current requires careful consideration. Injuries produced behave like other thermal therapies with coagulative necrosis followed by fibrotic healing. As larger ablations are consistently produced, it is hypothesised that with further refinements, tumours greater than 3 cm in diameter could be treated with lower rates of recurrence. / Thesis (M.S.) -- University of Adelaide, School of Medicine, 2008

Introduction: Radiofrequency ablation (RFA) is a popular method of treating unresectable liver tumours by the use of a high frequency, alternating electrical current that heats and destroys tumour cells. The size of the ablation is limited by localised charring of adjacent tissue that prevents further conduction of the radiofrequency current. In the clinical setting, this results in increased rates of local recurrence in tumours that are greater than 3 cm in diameter as multiple, overlapping ablations need to be performed to treat the one tumour. To overcome this problem, a modified form of RFA called Bimodal Electric Tissue Ablation (BETA) has been created. BETA adds a direct electrical current to the alternating radiofrequency current, thus establishing its bimodal character. When direct currents are used in biological tissues, water is transferred from anode to cathode by a process called electro-osmosis. By attaching the cathode to the radiofrequency electrode, water is attracted to the area thus preventing tissue desiccation and charring. The BETA circuit has been constructed and tested using a porcine model. The aims of the studies are to confirm that larger ablations can be produced with the BETA system and that it is safe to use in an animal model. Three studies have been performed to test these aims in porcine liver. Methods: The first study was designed to compare sizes of the ablation produced between standard RFA and the BETA circuit. This was followed by a long-term study to assess associated changes to liver function and pathological changes within the liver as well as identifying any other treatment related morbidity. The third study assessed the difference in ablation size and safety aspects when the positive electrode of the direct current circuitry was moved from small surface area under the skin to a large surface area on the skin. Results: Ablations with significantly larger diameters are created with the BETA circuit using a multi-tine needle (49.55 mm versus 27.78 mm, p<0.001). This finding was confirmed in the third experiment using a straight needle (25 mm versus 15.33 mm, p<0.001). Ablations produced by the BETA circuit induce coagulative necrosis within the treated liver and the injury heals by fibrosis in a manner similar to other thermal therapies. Significant rises in some serum liver enzymes are seen within 24 hours of treatment but these return to normal within 4 days. An electrolytic type injury can be produced at the site of the positive electrode. By increasing the surface area of this electrode, the risk of tissue damage is decreased but ablations are significantly smaller (18 mm versus 25 mm, p<0.001). Conclusions: The BETA circuit consistently produces significantly larger ablations than RFA. The treatment appears safe but positioning of the positive electrode of the direct current requires careful consideration. Injuries produced behave like other thermal therapies with coagulative necrosis followed by fibrotic healing. As larger ablations are consistently produced, it is hypothesised that with further refinements, tumours greater than 3 cm in diameter could be treated with lower rates of recurrence. / Thesis (M.S.) -- University of Adelaide, School of Medicine, 2008

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Current research in the field of nano-electronics is directed towards device miniaturization in order to find ways to increase the speed of electronic devices. The work presented in this dissertation is on the electronic transport properties of single walled carbon nanotube (SWNT) ropes synthesized by laser ablation. The measurements were performed on devices with different geometries; namely SWNT mats, metal incorporated (aligned individual and bundled) SWNTs and lastly on aligned pure SWNTs from low temperatures up to room temperature. The work was performed so as to gain an understanding on how best to utilize SWNTs in the semiconductor industry towards miniaturization. Such an understanding would ultimately highlight if SWNTs can be considered as a viable alternative to the current silicon-based technology, which seems to be approaching its physical limit. For a mat of SWNTs, 3D-Variable range hopping is the principal conduction mechanism from 2 K – 300 K. The magneto-resistance was found to be predominantly negative with a parabolic nature which converts to a linear nature as the temperature is increased. The negative MR is a consequence of quantum interference and the positive upturn is attributed to wave function shrinkage at low temperatures as described by the Efros-Shklovskii model. The hopping ranges of the electrons for a SWNT mat increases as the temperature decreases due to manifestation of quantum effects and reduced scattering. It was also found that metal incorporation does not alter the properties of the SWNT significantly. SWNT ropes aligned by di-electrophoresis across a 1 micron gap between gold micro-electrodes, exhibit Tomonaga-Luttinger liquid (TLL) like behaviour, within the 80 K – 300 K temperature range. The effects of confinement and electron-electron interaction unique to one dimension were identified in electronic transport as a non-universal power law dependence of the differential conductance on temperature and source-drain voltage. Ballistic conductance at room temperature was confirmed from the high frequency transport of the SWNT devices. The complex impedance showed some oscillatory behaviour in the frequency range 6 to 30 GHz, as has been predicted theoretically in the Tomonaga-Luttinger Liquid model. The observation of Luttinger Liquid behaviour demonstrates the outstanding nature of these one-dimensional molecular systems. In these devices the charging Coulomb energy of a single particle played a critical role in the overall device performance. This study can be used to understand the nature of dynamics of plasmons which are the charge carriers in a TLL system and how Coulomb interactions can be used to design highly tuneable systems for fabrication of single molecule devices. The incorporation of metal onto individual SWNT ropes does not alter its electronic properties significantly but the properties of the bundled metal incorporated SWNT ropes are altered. This study has found that under optimized conditions SWNTs might be a viable option for incorporation in nano electronics devices. Individual SWNT ropes promise better devices compared to SWNT mats and further work should be done on individual SWNTs.

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Johannesburg, 2015. / In this thesis electron transport properties of silicon nanowires are studied. The devices are synthesized using a laser ablation technique. The catalysts used in the synthesis are nickel nanoparticles. The silicon nanowires are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Dielectrophoresis is used to align and contact nanowires across two electrodes to create two-terminal devices. In addition four-terminal devices are fabricated using PMMA lift-off based electron beam lithography. Electron transport properties of the fabricated devices have been studied using dc measurement techniques. Resistance of the silicon nanowires has been measured as a function of temperature and magnetic field. These measurements have been accomplished using a Cryogenics system at low temperature, and high magnetic field. Temperature dependent studies reveal that Arrhenius type thermally activated transport behavior is the dominant transport mechanism in measurements at zero magnetic field. Magnetic field dependent measurements show a weak positive linear magnetoresistance. There are also strong oscillations in magnetoresistance curves. The temperature and field independence of the oscillations has been attributed to quantum interference effects.

by Fei Yang. / Title also in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 92-96). / ACKNOWLEDGEMENTS --- p.i / ABSTRACT --- p.ii / TABLE OF CONTENT --- p.iii / Chapter CHAPTER I. --- INTRODUCTION --- p.1 / Chapter §1.1 --- The Background of Pulsed Laser Ablation --- p.1 / Chapter §1.2 --- Properties of PZT --- p.3 / Chapter §1.3 --- Objectives of This Thesis --- p.7 / Chapter CHAPTER II. --- INTERACTION OF PULSED LASER RADIATION WITH A SOLID TARGET --- p.8 / Chapter §2.1 --- Introduction --- p.8 / Chapter §2.2 --- Absorption of Laser Radiation by the Target --- p.9 / Chapter §2.3 --- Absorption of Laser Radiation by the Plume --- p.11 / Chapter §2.4 --- Ablation Depth and Ablation Rate --- p.12 / Chapter §2.5 --- Formation and Evolution of the Plume --- p.14 / Chapter (a) --- Small-time Solution (c´Øt ζ) --- p.15 / Chapter (b) --- Large-time Solution (c´Øt ζ) --- p.15 / Chapter §2.6 --- Piezoelectric Signal --- p.17 / Chapter §2.7 --- Angular Distributions --- p.21 / Chapter §2.8 --- Target Surface Temperature --- p.26 / Chapter CHAPTER III. --- EXPERIMENTAL TECHNIQUES --- p.27 / Chapter §3.1 --- Pulsed Laser System --- p.27 / Chapter §3.2 --- Setup for Piezoelectric Detection of Laser Pulse --- p.28 / Chapter §3.3 --- Setup for Optical Measurement of Laser Plasma --- p.30 / Chapter §3.4 --- Setup for Ion Detection --- p.32 / Chapter §3.5 --- Sample Preparation --- p.35 / Chapter CHAPTER IV. --- PIEZOELECTRIC DETECTION OF LASER ABLATION --- p.38 / Chapter §4.1 --- Laser Ablation of a Piezoelectric Target --- p.38 / Chapter §4.1.1 --- Pyroelectric Effect --- p.38 / Chapter §4.1.2 --- Laser-induced Piezoelectric Signal (LIPS) --- p.39 / Chapter §4.2 --- Propagation of LIPS --- p.41 / Chapter §4.3 --- Laser Ablation Threshold --- p.45 / Chapter §4.4 --- Ablation Rate Measurement by LIPS --- p.47 / Chapter §4.5 --- Temperature Dependence of LIPS --- p.53 / Chapter §4.5.1 --- The Polarization Measurement --- p.53 / Chapter §4.5.2 --- The Piezoelectric Coefficient --- p.56 / Chapter CHAPTER V. --- STUDIES OF LASER PLASMA BY FARADAY PROBE METHOD --- p.59 / Chapter §5.1 --- Angular Distribution of The Plume Density --- p.59 / Chapter §5.2 --- The Plume Ionization Fraction --- p.64 / Chapter §5.3 --- The Plume Velocity Distribution and The Plume Temperature --- p.72 / Chapter §5.4 --- The Target Surface Temperature --- p.82 / Chapter §5.5 --- Plume Orientation Determination --- p.85 / Chapter CHAPTER VI. --- OVERALL CONCLUSION --- p.90 / REFERENCES --- p.92

The interaction between the mapping/ablation catheter and left atrial (LA) myocardium potentially affects the LA electrical and mechanical properties and impacts on ablation efficacy. Using catheters able to provide real-time contact force (CF) measurement, it has become possible to explore these relationships in vivo. In 60 persistent atrial fibrillation (AF) patients, ablation CF was higher in the right than left wide area circumferential (WACA) lines and where steerable transseptal sheaths were used. Differences were also apparent in the burden of WACA segment reconnection but did not just reflect differences in ablation CFs, suggesting factors other than CF contribute to ablation efficacy. Relationships between ablation force time integral (FTI), impedance drop and electrogram attenuation were assessed in 15 persistent AF patients. FTI significantly correlated with electrogram attenuation and impedance drop from ablation. The relationship was stronger for the former but in both cases plateaued at 500g.s, suggesting no ablation efficacy gains beyond this. Factors further affecting CF and ablation efficacy, the latter judged by impedance drop, were assessed in 30 patients. The variability of the CF waveform and catheter locational stability were both affected by factors including atrial rhythm and catheter delivery mode. Greater CF variability, catheter drift and perpendicular catheter contact were associated with reduced ablation efficacy. The relationship between CF and the electrogram was assessed in 30 patients. The size of the electrogram complexes was affected by CF increases but only where initial CF was <10g. This was also the case for electrogram fractionation measurements. Increasing CF was associated with an increasing incidence of atrial ~ 3 ~ ectopics during sinus rhythm. Spectral parameters (dominant frequency and organisation index) were unaffected by CF. Various factors affect the contact between the catheter and LA myocardium. In turn, catheter contact significantly affects the electrogram during LA mapping and the efficacy of clinical radiofrequency ablation.

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