No description available.

Call number: LD2668 .T4 1979 H364 / Master of Science / Mechanical and Nuclear Engineering

This thesis presents the findings of the investigation into the Monte Carlo simulation of superficial cancer treatments of the head and neck region. The EGSnrc system of codes for the Monte Carlo simulation of the transport of electrons and photons through a phantom representative of either a water phantom or treatment site in a patient is utilised. Two clinical treatment units are simulated using the BEAMnrc system of codes: the Varian Medical Systems Clinac® 2100C accelerator for 6MeV electron fields and the Pantak Therapax SXT 150 X-ray unit for 80kV and 100kV photon fields. Depth dose, profile and isodose curves are compared against those measured from a PTW MP3 water phantom with good agreement being achieved. Quantitative dose distributions are determined for both MeV electron and kV photon fields with treatment sites containing high atomic number materials, rapidly sloping surfaces and different density interfaces. This highlights the relatively high level of dose deposition of dose in tissue-bone and tissue-cartilage interfaces in the kV photon fields. From these dose distributions DVH and dose comparators are used to assess the simulated treatment fields.

No description available.

No description available.

No description available.

No description available.

Fluorescence lifetime sensing using time correlated single photon counting (TCSPC) is a key analytical tool for molecular and cell biology research, medical diagnosis and pharmacological development. However, commercially available TCSPC equipment is bulky, expensive and power hungry, typically requiring iterative software post-processing to calculate the fluorescence lifetime. Furthermore, the technique is restrictively slow due to a low photon throughput limit which is necessary to avoid distortions caused by TCSPC pile-up. An investigation into CMOS compatible multimodule architectures to miniaturise the standard TCSPC set up, allow an increase in photon throughput by overcoming the TCSPC pile-up limit, and provide fluorescence lifetime calculations in real-time is presented. The investigation verifies the operation of the architectures and leads to the selection of optimal parameters for the number of detectors and timing channels required to overcome the TCSPC pile-up limit by at least an order of magnitude. The parameters are used to implement a low power miniaturised sensor in a 130 nm CMOS process, combining single photon detection, multiple channel timing and embedded pre-processing of the fluorescence lifetime, all within a silicon area of < 2 mm2. Single photon detection is achieved using an array of single photon avalanche diodes (SPADs) arranged in a digital silicon photomultiplier (SiPM) architecture with a 10 % fill-factor and a compressed 250 ps output pulse, which provides a photon throughput of > 700 MHz. An array of time-interleaved time-to-digital converters (TI-TDCs) with 50 ps resolution and no processing dead-time records up to eight photon events during each excitation period, significantly reducing the effect of TCSPC pile-up. The TCSPC data is then processed using an embedded centre-of-mass method (CMM) pre-calculation to produce single exponential fluorescence lifetime estimations in real-time. The combination of high photon throughput and real-time calculation enables advances in applications such as fluorescence lifetime imaging microscopy (FLIM) and time domain fluorescence lifetime activated cell sorting. To demonstrate this, the device is validated in practical bulk sample fluorescence lifetime, FLIM and simulated flow based experiments. Photon throughputs in excess of the excitation frequency are demonstrated for a range of organic and inorganic fluorophores for minimal error in lifetime calculation by CMM (< 5 %).

Lee Wai Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 177-181). / List of Figures and Tables --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Photonic Band Gap materials --- p.1 / Chapter 1.2 --- Theoretical Calculation on PBG materials --- p.5 / Chapter 2 --- Plane Wave Expansion --- p.13 / Chapter 2.1 --- Plane Wave Expansion within Scalar Wave Approximation --- p.14 / Chapter 2.2 --- Plane Wave Expansion to Scalar I and II Equations --- p.21 / Chapter 3 --- Formalism of Photonic k.p Theory --- p.33 / Chapter 3.1 --- Vectorial k.p formulation --- p.33 / Chapter 3.2 --- Scalar k. p formulations --- p.36 / Chapter 4 --- Implementation and k.p Band Structures --- p.38 / Chapter 4.1 --- Evaluation of Integrals plj and qlj --- p.38 / Chapter 4.2 --- k.p Band Models --- p.47 / Chapter 5 --- Dependence of k .p Parameters on Dielectric Contrast and Fill- ing Ratio --- p.57 / Chapter 5.1 --- Accuracy of Integrals plj and qlj --- p.57 / Chapter 5.2 --- Sensitivity of k.p Parameters to System Parameters --- p.71 / Chapter 6 --- Empirical Tight-binding Scheme --- p.99 / Chapter 6.1 --- Electronic Tight Binding Approximation --- p.99 / Chapter 6.2 --- Empirical Tight-binding Scheme --- p.101 / Chapter 7 --- Summary --- p.137 / Chapter A --- Preprint of Ref. [36] --- p.144 / Chapter B --- The Coefficients in Eq. (2.22) --- p.161 / Chapter C --- Formalism of Photonic k.p Theory --- p.163 / Chapter D --- The Coefficients in Eq. (5.2) --- p.166 / Chapter E --- The Coefficients in Eq. (5.3) --- p.168 / Chapter F --- The Coefficients in Eq. (6.15) --- p.170

One of the daunting challenges in wave physics is to accurately control the flow of light at the subwavelength scale. By patterning the optical medium one can design anisotropic artificial medium, this engineering method is commonly known as photonic crystals or metamaterials. Negative or zero index of refraction, slow-light propagation, cloaking with transformation optics material, and beam collimation are only a few such unique functionalities that can be achieved in engineered media at the subwavelength scale. Another interesting phenomenon in wave physics, Anderson localization, which suggests electron localization inside a semiconductor, has been intensely investigated over the past years, including transverse localization in bulk and waveguide arrays periodic in one and two dimensions. Here we report the photon transport and collimation enhanced by transverse Anderson localization in chip-scale anisotropic artificial medium, a similar physical model to doping the impurity in insulator and turning it into a semiconductor. First, by engineering the photonic crystal, we demonstrate a new type of anisotropic artificial medium for diffraction-free transport through cascaded tunneling of guided resonances. High-resolution near-field measurements demonstrate the coupling of transverse guided resonances, supported by large-scale numerical modeling. Second, with the disordered scattering sites in this superlattices, we uncover the mechanism of disorder-induced transverse localization in chip-scale. Arrested spatial divergence is captured in the power-law scaling, along with the exponential asymmetric mode profiles and enhanced collimation bandwidth for increasing disorder, over 4,000 scattering sites. With increasing disorder, we observe the crossover from cascaded guided resonances into transverse localization regimes, beyond the ballistic and diffusive transport of photons. As disorder is ubiquitous in natural and artificial materials, the transport through random media is of great importance. It also leads to various interesting optical phenomena, of which the most surprising one is Anderson localization of light. However, not all the states in disordered system are localized. Nonlocalized modes that extend over the whole sample via coupling between multiple local cavities with similar resonance frequencies are also present in disordered systems. These extended modes are called necklace states. Here, we also show that long-distance beam collimation can be witnessed in millimeter-scale photonic crystals that were fabricated lithographically with ultrahigh resolutions. By precisely controlling the disorder level of three million scattering sites in photonic crystals, we uncovered the transformation of light flows from the propagation of regular Bloch modes to necklace states.