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It has been proposed to use heavy ion beams with energies around 10 MeV/amu, masses around 200, and average charges of 1+ as a driver for inertial fusion reactor. Current designs require the beams to travel through a region where the background gas pressure is several milli-torr. Thus, it is important to assess the rate at which the charge state of an incident beam evolves while passing through the background gas. The first objective of this project is to study the dependence of cross sections for multi-electron loss on target atomic number by using 6 MeV/amu Xe18+ ions and to compare the results with the n-body Classical Trajectory Monte Carlo calculations. A secondary objective of this project is to determine the extent to which the cross sections for molecular targets can be represented as sum of the cross sections for their atomic constituents. Cross sections for loss of one through eight electrons from 6 MeV/amu Xe18+ in single collisions have been measured with noble gas targets. The target Z-dependence of the total loss cross section was found to be well represented by two straight line segments. The cross section for He and Ne define one straight line segment and those for Ar, Kr and Xe define the other, where exhibits a smaller slope. The predictions of n-CTMC calculations are in good agreement with the measured total electron loss cross sections. A semiempirical fitting procedure based on the independent electron approximation provided a reasonably good representation of the individual cross sections for all of the noble gas targets. Additional measurements performed with a variety of molecular targets provided a rigorous test of cross section additivity and showed that the additivity rule works well for electron loss from heavy ions in the present energy and charge regime. A semiempirical calculation based the IEA shows that the average most probable impact parameter for electron loss is much smaller than the target molecular bond length. This result is believed to account for the finding of the insensitivity of the electron loss cross section to molecular structure.

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Disertacijoje nagrinėjami lantano manganitai, pasižymintys faziniu virsmu iš paramagnetinės į feromagnetinę būseną bei milžiniškos neigiamos magnetovar-žos efektu. Tiriami magnetovaržos ir jos anizotropijos efektai silpnuose (iki  0,5 T) magnetiniuose laukuose bei stiprių impulsinių srovių ir magnetinių laukų sukelti efektai plonuose epitaksiniuose manganitų sluoksniuose. Pateikiami pasiūlymai tyrimo rezultatus panaudoti kuriant magnetinio lauko jutiklius, spar-čiųjų elektrinių impulsų formuotuvus bei amplitudės moduliatorius. Tiriant sil-pnų magnetinių laukų poveikį ultraplonųjų La-Sr-MnO3 sluoksnių elektriniam laidumui, buvo nustatyta, kad magnetovaržos anizotropijos ženklas ir vertė šiuo-se laukuose priklauso nuo sluoksnio storio. Pateiktas modelis, paaiškinantis eks-perimentinius rezultatus, paremtas vidutinio lauko artiniu ir įskaitantis sluoksnio struktūros kitimą kintant jo storiui. Aptiktas ir ištirtas grįžtamasis termoelektrinis nestabilumas, išaiškintos šio reiškinio atsiradimo priežastys. Pasiūlytas ir ekspe-rimentiškai realizuotas naujas ns trukmės elektrinių impulsų amplitudės modulia-vimo išoriniu magnetiniu lauku būdas, naudojant epitaksinius La0,87Sr0,17MnO3 sluoksnius. Disertaciją sudaro reziumė lietuvių ir anglų kalbomis, įvadas, šeši skyriai, pagrindiniai rezultatai ir išvados, literatūros sąrašas, publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas bei uždaviniai, aprašomas mokslinis... [toliau žr. visą tekstą] / The objective of this dissertation is to investigate lanthanum manganites, which exhibit colossal negative magnetoresistance and phase transitions from the paramagnetic state to the ferromagnetic state. The magnetoresistance and its ani-zotriopy of thin epitaxial manganite films at low (up to  0.5 T) magnetic fields, as well as effects induced by strong pulsed magnetic and electric fields were in-vestigated. It was demonstrated how it can be used in the development of magne-tic field sensors, short electric pulse forming devices and amplitude modulators. It was found that in the case of ultra-thin La-Sr-MnO3 films, the sign and value of the magnetoresistance anisotropy at low magnetic fields depends on the thickness of the films. An explanation of these results was proposed using the mean field approach and taking into consideration that the structure of the films changes with its thickness. A reversible thermoelectrical switching effect was discovered and investigated. A new method for nanosecond duration electrical pulses amplitude modulation by an external magnetic field using La0.87Sr0.17MnO3 films was suggested and experimentally verified. This dissertation consists of the abstracts in Lithuanian and English, intro-duction, six chapters, the main results and conclusions and list of literature. The introduction contains topicality and problem, the aim of the work, tasks, scientific novelty, practical value, approval of the results, statement to be de-fended and... [to full text]

The objective of this dissertation is to investigate lanthanum manganites, which exhibit colossal negative magnetoresistance and phase transitions from the paramagnetic state to the ferromagnetic state. The magnetoresistance and its ani-zotriopy of thin epitaxial manganite films at low (up to  0.5 T) magnetic fields, as well as effects induced by strong pulsed magnetic and electric fields were in-vestigated. It was demonstrated how it can be used in the development of magne-tic field sensors, short electric pulse forming devices and amplitude modulators. It was found that in the case of ultra-thin La-Sr-MnO3 films, the sign and value of the magnetoresistance anisotropy at low magnetic fields depends on the thickness of the films. An explanation of these results was proposed using the mean field approach and taking into consideration that the structure of the films changes with its thickness. A reversible thermoelectrical switching effect was discovered and investigated. A new method for nanosecond duration electrical pulses amplitude modulation by an external magnetic field using La0.87Sr0.17MnO3 films was suggested and experimentally verified. This dissertation consists of the abstracts in Lithuanian and English, intro-duction, six chapters, the main results and conclusions and list of literature. The introduction contains topicality and problem, the aim of the work, tasks, scientific novelty, practical value, approval of the results, statement to be de-fended and... [to full text] / Disertacijoje nagrinėjami lantano manganitai, pasižymintys faziniu virsmu iš paramagnetinės į feromagnetinę būseną bei milžiniškos neigiamos magnetovar-žos efektu. Tiriami magnetovaržos ir jos anizotropijos efektai silpnuose (iki  0,5 T) magnetiniuose laukuose bei stiprių impulsinių srovių ir magnetinių laukų sukelti efektai plonuose epitaksiniuose manganitų sluoksniuose. Pateikiami pasiūlymai tyrimo rezultatus panaudoti kuriant magnetinio lauko jutiklius, spar-čiųjų elektrinių impulsų formuotuvus bei amplitudės moduliatorius. Tiriant sil-pnų magnetinių laukų poveikį ultraplonųjų La-Sr-MnO3 sluoksnių elektriniam laidumui, buvo nustatyta, kad magnetovaržos anizotropijos ženklas ir vertė šiuo-se laukuose priklauso nuo sluoksnio storio. Pateiktas modelis, paaiškinantis eks-perimentinius rezultatus, paremtas vidutinio lauko artiniu ir įskaitantis sluoksnio struktūros kitimą kintant jo storiui. Aptiktas ir ištirtas grįžtamasis termoelektrinis nestabilumas, išaiškintos šio reiškinio atsiradimo priežastys. Pasiūlytas ir ekspe-rimentiškai realizuotas naujas ns trukmės elektrinių impulsų amplitudės modulia-vimo išoriniu magnetiniu lauku būdas, naudojant epitaksinius La0,87Sr0,17MnO3 sluoksnius. Disertaciją sudaro reziumė lietuvių ir anglų kalbomis, įvadas, šeši skyriai, pagrindiniai rezultatai ir išvados, literatūros sąrašas, publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas bei uždaviniai, aprašomas mokslinis... [toliau žr. visą tekstą]

This thesis presents the design of new integrated charge pumps with high performance. An analysis method is determined to evaluate the voltage gain, the output resistance and the conversion efficiency parameters of integrated charge pumps. An optimization method is developed to improve the performance through capacitor sizing based on area constraints. Several charge pumps structures are optimized and compared including the losses due to devices parasitics. Results show that the Dickson charge pump (voltage doubler) is the best structure for integration. Therefore, techniques to improve per- formance and conversion efficiency of integrated voltage doubler are proposed. Switch bootstrapping technique prevents short-circuit losses, improves driving capability, and enhances the overall efficiency. The application of charge reuse technique reduces the dynamic power losses of integrated voltage doublers and double charge pumps. A pro- totype of the integrated voltage doublers was fabricated in a 0.18-μm CMOS process with the proposed techniques. Measured results have been presented, demonstrating the improvements in performance and conversion efficiency, with a good correlation between measured and predicted results.

This thesis presents the design and implementation of PMOS-based integrated charge pumps with extended voltage range and their regulation circuits in a standard process. The performance of charge pumps are evaluated by their output resistances and power conversion efficiencies. Formulas which describe the charge pump characteristics are developed and presented. Existing charge pumps are analyzed and studied to understand their limitations in generating high voltages and achieving high performance. The proposed charge pump structures are designed to use PMOS switches to alleviate the high voltage stresses across transistors by biasing their bulk independently. The voltages across transistors and capacitors are kept within the suggested voltage rating (VDD)regardless of how high the output voltage is, thus the maximum voltage range is extended and no longer limited by the breakdown voltages of the devices. The charge pump circuits only need low-voltage devices and standard processes, and can be easily integrated in a digital or mixed-signal design. The proposed charge pump regulation circuits include a voltage divider, a voltage controlled ring oscillator and a feedback operational amplifier. The regulation circuits are able to adjust the clock frequency to regulate the charge pump to a steady output voltage (set by the reference voltage) under a large range of current loads. A test chip including the proposed charge pumps and regulation circuits was fabricated in a 0.18 um digital CMOS process provided by Taiwan Semiconductor Manufacturing Company (TSMC). The proposed charge pumps were tested and demonstrated the reliable generation of output voltages up to 11.47 V using only low-voltage devices. The simulation and measurement results have been presented and compared, demonstrating the functionality and performance of the proposed circuits. / Kapik Integration, Mitacs

I investigate the self-force acting on static scalar and electric charges in Schwarzschild-de Sitter and Schwarzschild-Anti-de Sitter spacetimes. The self-force occurs when a charged particle's field interacts with the curvature of spacetime so that the particle interacts with its own field. Because the field of a point particle is singular at the location of the particle, it is necessary to decompose the field into a regular part responsible for the self-force and a singular part that does not contribute to the self-force. To do this, I use the mode-sum regularization scheme introduced by Barack and Ori, in which the field is decomposed into a sum over modes, and the singular part is removed from each mode using so-called regularization parameters. I find that the electrostatic self-force in Schwarzschild-de Sitter and Schwarzschild-Anti-de Sitter behaves similarly to Schwarzschild self-force near the black hole, but can deviate strongly at larger distances. This is especially true in Schwarzschild-Anti-de Sitter, where the self-force is seen to increase linearly with distance. I provide an explanation for this behaviour using conformal transformations. A particular feature evident in Schwarzschild-Anti-de Sitter is that the self-force can become negative (attractive) at small distances when the Schwarzschild radius and the cosmological length scale are of a similar order. I find that the scalar self-force in Schwarzschild-de Sitter can not actually be computed, and in Schwarzschild-Anti-de Sitter the asymptotic behaviour is similar to its electrostatic counterpart.

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