by Ng Chiu-king. / Title also in Chinese characters. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 189-195). / ACKNOWLEDGEMENTS --- p.v / ABSTRACT --- p.vi / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter CHAPTER 2 --- STANDARD MIE SCATTERING AND MORPHOLOGY DEPENDENT RESONANCES --- p.5 / Chapter 2.1 --- General Descriptions --- p.6 / Chapter 2.1.1 --- Nonresonant Scattering --- p.13 / Chapter 2.1.1.1 --- Internal Intensity --- p.13 / Chapter 2.1.1.2 --- Understanding in Terms of Geometric Optics --- p.14 / Chapter 2.1.2 --- Resonances --- p.19 / Chapter 2.1.2.1 --- Q-factor --- p.23 / Chapter 2.1.2.2 --- Internal Intensity --- p.25 / Chapter 2.1.2.3 --- Understanding in Terms of Geometric Optics --- p.28 / Chapter 2.2 --- Theories --- p.31 / Chapter 2.2.1 --- Nonresonances --- p.31 / Chapter 2.2.2 --- Resonances --- p.32 / Chapter 2.2.2.1 --- TE Mode in Lorentzian Form --- p.32 / Chapter 2.2.2.2 --- Degradation due to Absorption --- p.35 / Chapter 2.2.3 --- Response to a Pulse --- p.37 / Chapter 2.2.3.1 --- Nonresonant Modes --- p.38 / Chapter 2.2.3.2 --- Resonant Modes --- p.39 / Chapter CHAPTER 3 --- NONLINEAR MIE SCATTERING AND THE PROPOSED MECHANISMS --- p.42 / Chapter 3.1 --- NRL Experiment --- p.42 / Chapter 3.1.1 --- Observations --- p.42 / Chapter 3.1.2 --- Parameters --- p.43 / Chapter 3.1.3 --- Evidence of Q Degradation --- p.45 / Chapter 3.2 --- Proposed Mechanisms --- p.49 / Chapter 3.2.1 --- Volume Perturbation due to electrostrictively Generated Acoustic Waves --- p.50 / Chapter 3.2.2 --- Surface Perturbation due to Shape Distortion --- p.50 / Chapter 3.2.3 --- Stimulated Brillouin Scattering --- p.51 / Chapter 3.2.4 --- Bubbles Formation --- p.52 / Chapter 3.3 --- Envelope Fluctuation --- p.53 / Chapter CHAPTER 4 --- ELECTROSTRICTION AND THE PERTURBATION THEORY OF THE LINEWIDTH --- p.55 / Chapter 4.1 --- Electrostriction --- p.55 / Chapter 4.2 --- Perturbation of the Linewidth --- p.42 / Chapter 4.2.1 --- Theory --- p.58 / Chapter 4.2.2 --- Remarks --- p.60 / Chapter CHAPTER 5 --- ELECTROSTRICTIVELY GENERATED ACOUSTIC VIBRATIONS --- p.64 / Chapter 5.1 --- Estimate of Density Change --- p.64 / Chapter 5.2 --- Pressure Disturbances --- p.65 / Chapter 5.3 --- Electrostrictively Coupled Coefficients --- p.67 / Chapter 5.4 --- Validity of Impulse Approach --- p.70 / Chapter 5.5 --- An Expedient Model --- p.71 / Chapter 5.5.1 --- Fractional Change in Density --- p.73 / Chapter 5.5.2 --- Q Degradation --- p.81 / Chapter 5.6 --- Exact Result --- p.88 / Chapter 5.7 --- Nonimpulse Approach to Resonant Mode --- p.89 / Chapter 5.7.1 --- Results --- p.91 / Chapter 5.8 --- Chapter Conclusion --- p.93 / Chapter CHAPTER 6 --- LOW-FREQUENCY SURFACE OSCILLATIONS --- p.94 / Chapter 6.1 --- Surface Bulging --- p.95 / Chapter 6.1.1 --- Equation of Motion --- p.97 / Chapter 6.1.2 --- Results --- p.100 / Chapter 6.1.3 --- Justification of Incompressibi1ity --- p.109 / Chapter 6.2 --- Q Degradation --- p.110 / Chapter 6.2.1 --- Experimental Situation --- p.111 / Chapter 6.2.1.1 --- Single Pulse --- p.114 / Chapter 6.2.1.2 --- Pulse Train --- p.116 / Chapter 6.2.2 --- Hypothetical Bulging --- p.119 / Chapter 6.3 --- Further Investigations --- p.123 / Chapter 6.4 --- Chapter Conclusion --- p.130 / Chapter CHAPTER 7 --- STIMULATED BRILLOUIN SCATTERING --- p.131 / Chapter 7.1 --- General Descriptions --- p.132 / Chapter 7.1.1 --- Resonant SBS --- p.133 / Chapter 7.1.2 --- One Gain Mode --- p.136 / Chapter 7.2 --- SBS Pressure Disturbances --- p.137 / Chapter 7.3 --- Pulse Train --- p.140 / Chapter 7.3.1 --- Necessity of Projection --- p.141 / Chapter 7.3.2 --- Amplitude of Projected Mode --- p.143 / Chapter 7.4 --- Results --- p.145 / Chapter 7.5 --- Remarks --- p.150 / Chapter 7.6 --- Chapter Conclusion --- p.155 / Chapter CHAPTER 8 --- BUBBLE FORMATION --- p.156 / Chapter 8.1 --- Degradation due to Cavitations --- p.157 / Chapter 8.2 --- Coalescence of Gas Bubbles --- p.159 / Chapter 8.3 --- Acoustic Cavitation --- p.161 / Chapter 8.4 --- Chapter Conclusion --- p.165 / Chapter CHAPTER 9 --- CONCLUSION AND DISCUSSION --- p.166 / APPENDIX A --- p.170 / APPENDIX B --- p.175 / APPENDIX C --- p.180 / APPENDIX D --- p.184 / APPENDIX E --- p.187 / REFERENCES --- p.189

Deng, Xiaomao. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 98-104). / Chapter 1 --- Introduction to Inverse Scattering Problems --- p.6 / Chapter 1.1 --- Direct Problems --- p.6 / Chapter 1.1.1 --- Far-field Patterns --- p.10 / Chapter 1.2 --- Inverse Problems --- p.16 / Chapter 1.2.1 --- Introduction --- p.16 / Chapter 2 --- Numerical Methods in Inverse Obstacle Scattering --- p.19 / Chapter 2.1 --- Linear Sampling Method --- p.19 / Chapter 2.1.1 --- History Review --- p.19 / Chapter 2.1.2 --- Numerical Scheme of LSM --- p.21 / Chapter 2.1.3 --- Theoretic Justification --- p.25 / Chapter 2.1.4 --- Summarize --- p.38 / Chapter 2.2 --- Point Source Method --- p.38 / Chapter 2.2.1 --- Historical Review --- p.38 / Chapter 2.2.2 --- Superposition of Plane Waves --- p.40 / Chapter 2.2.3 --- Approximation of Domains --- p.42 / Chapter 2.2.4 --- Algorithm --- p.44 / Chapter 2.2.5 --- Summarize --- p.49 / Chapter 2.3 --- Singular Source Method --- p.49 / Chapter 2.3.1 --- Historical Review --- p.49 / Chapter 2.3.2 --- Algorithm --- p.51 / Chapter 2.3.3 --- Far-field Data --- p.54 / Chapter 2.3.4 --- Summarize --- p.55 / Chapter 2.4 --- Probe Method --- p.57 / Chapter 2.4.1 --- Historical Review --- p.57 / Chapter 2.4.2 --- Needle --- p.58 / Chapter 2.4.3 --- Algorithm --- p.59 / Chapter 3 --- Numerical Experiments --- p.61 / Chapter 3.1 --- Discussions on Linear Sampling Method --- p.61 / Chapter 3.1.1 --- Regularization Strategy --- p.61 / Chapter 3.1.2 --- Cut off Value --- p.70 / Chapter 3.1.3 --- Far-field data --- p.76 / Chapter 3.2 --- Numerical Verification of PSM and SSM --- p.80 / Chapter 3.3 --- Inverse Medium Scattering --- p.83 / Bibliography --- p.98

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published_or_final_version / Physics / Master / Master of Philosophy

No description available.

No description available.

No description available.

In his programmatic article More Is Different (1972), Nobel laureate P. W. Anderson captured the fundamental interest in quantum matter in a nutshell. The central motive in this field is emergence. In the inaugural volume of the homonymous journal, J. Goldstein defined this as "the arising of novel and coherent structures, patterns and properties during the process of self-organization in complex systems". Famously, the idea that the "the whole is greater than the sum of its parts" goes back to Aristotle's metaphysics, and it has served as a stimulating concept in 19th century biology, economics and philosophy. The study of emergence in condensed matter physics is unique in that the underlying complex systems are sufficiently "simple" to be modelled from first principles. Notably, the emergent phenomena discovered in this field, such as high-temperature superconductivity, giant magnetoresistance, and strong permanent magnetism have had an enormous impact on technology, and thus, society. Historically, there has been a distinction between materials with localized, strongly interacting (or correlated) electrons - and non-interacting, itinerant electronic states. In the last decade, several new states of matter have been discovered, which emerge not from correlations, but from peculiar symmetries (or topology) of itinerant electronic states. The term quantum materials has therefore become popular to subsume these two strands of condensed matter physics: Electronic correlations and topology. In this thesis, I report investigations of four quantum materials which each illustrate present key interests in the field: The mechanism of high temperature superconductivity, the search for materials that combine both electronic correlations and non-trivial topology and novel emergent phenomena that arise from the synergy of electronic correlations and a strong coupling of spin- and orbital degrees of freedom. The common factor and potential key to understanding these materials is magnetism. My experimental work is focused on neutron and x-ray scattering techniques, which are able to determine both order and dynamics of magnetic states at the atomic scale. I illustrate the full scope of these methods with experimental studies at neutron and synchrotron radiation facilities. This includes both diffraction and spectroscopy, of either single- or polycrystalline samples. My in-depth analysis of each dataset is aided by structural, magnetic and charge transport experiments. Thus, I provide a quantitative characterization of magnetic fluctuations in an iron-based superconductor and in two Dirac materials, and determine the magnetic order in a Dirac semimetal candidate and a complex oxide. As a whole, these results demonstrate the elegant complementarity of modern scattering techniques. Although such methods have a venerable history, they are presently developing at a rapid pace. Several results of this thesis have only been enabled by very recent instrumental advances.

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Measurements of the angular distribution and total reaction rate in neutron-proton scattering are described. The emphasis of this work has been to obtain an accurate normalization of the distribution, which is difficult to achieve with neutral beams. Nearly monoenergetic neutrons from the d(p,n)pp reaction were scattered from a liquid hydrogen target. The neutron beam energy was determined from the time of flight with respect to the radio frequency signal of the TRIUMF cyclotron. The differential cross section was measured at 319 and 493 MeV from 10 to 180 degrees in the centre of mass (CM.). Calibrated neutron beam monitors upstream of the scattering target provided an absolute normalization over the whole angular range. Between 10 and 100 degrees CM. a neutron detector consisting of a charged particle veto, a carbon convertor and two trigger scintillators sandwiching 7 multiwire proportional chambers was used to select elastic neutrons by time of flight techniques. The neutron angular distribution was measured with an average precision of 5% and an uncertainty on the normalization of 1.3%. An associated particle experiment (neutrons and recoil protons detected in coincidence) determined the efficiency of the neutron detector and the monitors were calibrated by measuring the incident neutron flux with the neutron detector in the beam, i.e. at zero degrees. The recoil protons were detected in the angular range between 60 and 180 degrees CM. with a precision of 1% to 2% and an error on the normalization of 2.8% at 319 MeV and 3.7% at 493 MeV. Elastic events were selected by time of flight and by either a measurement of magnetic rigidity (momentum) or total energy. The absolute normalization of the two experimental techniques is verified by the overlap of the two measurements and by comparing the integrated differential cross section with the measured total cross section. The neutron-proton total cross section was measured at six energies between 200 and 500 MeV by a transmission type experiment to a precision of 1% to 3%. The systematic corrections were small, of the order of 1%, and the statistical errors were increased to include monitor and beam instabilities. The measurements show a smooth quadratic energy dependence. The data was included in a phase shift analysis and a dispersion relation analysis along with the previous world data. Agreement between the real part of the forward scattering amplitude predicted by the phase shift analysis and by the dispersion relation analysis is improved. The errors on the 1=0 (isoscalar) phase shifts are decreased and to a lesser extent on the 1=1 phase shifts. There is a marked improvement in the smooth variation with energy of the 1=0 phase shifts and a better agreement of the higher partial waves with the theoretical predictions of the Paris potential. / Science, Faculty of / Physics and Astronomy, Department of / Graduate