Elastic scattering and inelastic excitation of the second, unbound, state 9Be (5/2ˉ, 2.43 MeV) for the identical-particle fermionic system 9Be + 9Be have been measured at the highest incident beam energy presently available ELab(9Be) = 25 MeV. A 9Be beam, produced by the General Ionex Corporation model 860C sputter ion-source, was accelerated by the EN Tandem Van de Graaff accelerator of the iThemba LABS (Gauteng) and was used to bombard a thin 9Be target. The experimental equipment associated with the C-line includes a high resolution ΔE-E gas-ionisation detector coupled to a small scattering chamber. Energy loss and residual energy signals were processed using a CAMAC-based plus OS/2 WIMPS2 data acquisition system running on an online computer. The ΔE-E plots were used to identify the reaction products and their kinematic energies, thereby determining the elastic and inelastic scattering cross-sections. The elastic and inelastic scattering data were analysed in terms of the optical model and Distorted Wave Born Approximation, respectively. Angular distribution data for the elastic scattering for 9Be + 9Be conformed well to the optical model predictions using an energy-independent optical model potential. Inelastic scattering cross-sections were determined up to θc.m.  135° and symmetry effects were investigated. As such, excitation of the second, unbound, state 9Be (5/2ˉ, 2.43 MeV) via a strong E2 one-step two-body interaction from the 9Be (3/2ˉ, g.s.) did not show effects due to symmetry in the entrance channel. These results were consistent with a previous study at ELab(9Be) = 16 MeV.

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

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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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