Ph.D. / A one-dimensional numerical simulation of photovoltaic (PV) cells has been written, and has been designated RAUPV2. An algorithm for determining the optical generation rate profile, taking into account multiple internal reflections in a multilayer cell has been developed. A method which enables realistic boundary values to be calculated, using RAUPV2 itself, has been developed. This method allows all three boundary values (', Fn and Fp) at each surface, to be determined, without the need to specify any additional input parameters. A comprehensive set of input parameters for aSi:H PV cells has been established, in consultation with the literature. Dangling-bond theory has been described and input parameters for dangling-bond defects have been presented. The effect of surface states in the p-layer on the contact potential at the TCO/p interface has been investigated. It was found that there is an intimate relationship between the contact potential and the parameters pertaining to the surface states. A simple method has been demonstrated, which has allowed RAUPV2 to reproduce the J-V curve of an existing aSi:H PV cell. The method requires that only the dangling-bond concentration in the i-layer and the contact potential at the Sn02/P interface needs to be adjusted. Once the J- V curve had been generated, the simulation results were used to characterise the empirical cell, in both thermodynamic- and steady-state equilibrium. This simulated cell was designated the realistic cell. The effect of asymmetries in the input parameters, under carrier band mobility interchange, on the performance of p-i-n cells has been investigated. The results indicate that, while asymmetries in the gap state distributions do give rise to asymmetrical behaviour in the J- V curve, the effect is slight, and it is the positional asymmetry of the optical generation profile that is mostly responsible for the observed asymmetry in the J- V curve under mobility interchange. An investigation of the limiting carrier effect has led to the conclusion that, in a p-i-n aSi:H cell under forward bias, the electron is the limiting carrier. This has been explained by appealing to the form of the optical generation profile, since most electron-hole pairs (EHPs) are generated near the front of the cell, and it is electrons that must be collected at the back contact. Investigations of the n-i-p aSi:H cell, under forward bias, have shown the hole to be the limiting carrier. It was found that the introduction of positional symmetry into the optical generation rate profile greatly reduced the limiting carrier effect, and it was concluded that the limiting carrier effect arises due to the asymmetries in the material parameters of the cell, particularly the _ positional asymmetry of the optical generation profile. It was observed that the nature of the optical generation profile actually plays an important role in determining the identity of the limiting carrier, in a p-i-n cell. The same effect was not observed in the n-i-p cell. The effective carrier collection length has been defined, and it was seen that the limiting carrier possesses the larger effective collection length. The effect of boron and phosphorous profiling of the i-layer was studied. It was found that boron profiling led to a decrease in cell performance, while phosphorous profiling improved cell performance. It was found that there was a P concentration at which cell performance peaked. The dependence of the spectral response of the realistic cell on device length L, was investigated, showing a general improvement in the spectral response as L was decreased. The spectral response has been interpreted in a novel way. It was assumed that the form of the monochromatic optical generation profiles in the vicinity of the peak in the spectral response represented optimal generation profiles. These profiles were subjected to a linear transformation, such that their form was preserved but that their integrated value was the same as that of the realistic optical generation profile, under global AM1.5 illumination. Using these transformed optical generation profiles, J- V curves were obtained. The maximum power output PM of these J- V curves was seen to exhibit a maximum some 17% greater than that of the realistic cell with a realistic optical generation profile. The spectral response of the phosphorous profiled cell was obtained. In a manner similar to that for the non-P profiled cell, the optimal generation profile was found. The PM for this profile was found to be 7.86mWcm -2 , considerably larger than the 5.60mWcm-2 for the phosphorous profiled cell with a realistic optical generation profile. The effect on the simulation output of variations in numerous dangling-bond defect input parameters has been investigated. It was found that the energy position and concentration of the doped layer defects need not be known to a high degree of precision. On the other hand, it was found that the energy position of the i-layer defects, the standard deviation of the defect distributions, and the defect carrier capture cross-sections, do need to be known with certainty.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Bibliography : leaves 99-101. / M.S.

No description available.

Shadowing of random surfaces is accounted for by multiplying the Kirchhoff electric current density by a shadowing function. The shadow-corrected incoherent intensity is computed in the backscatter direction and is found to be proportional to the probability of a specular point being illuminated from the source. This probability is computed numerically using an infinite series of integrals, developed by Ricciardi and Sato, and by Monte Carlo computer simulations. The results obtained are compared to the analytic approximations of Wagner and Smith, which neglect correlation between the shadowing points and the shadowed point. Assumptions made by Wagner are explained using the infinite series of integrals. Furthermore, comparison is made to Wagner's results which include correlation between the shadowed point and the shadowing point. / Master of Science

Radar altimeters were originally designed to study ocean geodynamics, where the scattering processes are governed entirely by the surface features. These same altimeters have recorded data from over the polar ice sheets, where the scattering processes cannot in general be limited to surface properties. Radar pulse penetration, which gives rise to volume scattering, must also be accounted for in these return waveforms. This pulse penetration affects the altimeter range measurements as well as other information that is derived from the altimeter waveform data. To aid in the study of pulse penetration effects, a waveform model for combining surface and volume scattering effects in the estimation of the radar altimeter returns recorded over continental ice and snow is developed and discussed. The surface scattered waveform model is based on the well-known impulse response method which is capable of accounting for arbitrary altitude, beamwidth, pulsewidth and pointing angle. The newly formulated volume scattered waveform model is also an impulse response based method which differs from previous versions in that it can also be applied to a general altimeter configuration. The two models are time registered and then added together in an arbitrary ratio representing the relative contributions of surface and volume scattering to the overall return power waveform. The combined model can be used to study actual altimeter waveforms by varying the important parameters, including surface roughness and effective extinction coefficient. The capabilities and limitations of this new combined model are also discussed and guidelines for its use are detailed. The combined model is tested by comparing it to the Multimode Aircraft Radar Altimeter (MARA) data which were recorded over and around the Greenland ice sheet in September 1991. Evaluation of this averaged waveform data identified problems that were encountered with the MARA design. A number of techniques are developed in an effort to account for and correct these problems, but none of these attempts were completely successful. The 1991 MARA data are considered usable for waveform analysis, but with the understanding that some error may be present in the final results. The MARA data obtained from the Greenland ice sheet are analyzed for estimates of surface roughness, effective extinction coefficient and ratio of surface to volume scattering strengths. A simple optimization method is employed which achieves a least-squares fit of the combined model to the altimeter data. The result is an estimate of these parameters as a function of location on the ice shelf. To the author's knowledge, this is the first time both surface- and volume-related parameters have been estimated simultaneously from Ka-band radar data. / Ph. D.

by Yeung Wai Lung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 120-122). / Text in English; abstracts in English and Chinese. / by Yeung Wai Lung. / Abstract --- p.i / Abstract (Chinese version) --- p.ii / Acknowledgements --- p.iii / Contents --- p.iv / List of figures --- p.vii / List of tables --- p.xi / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- The El Nino ´ؤ Southern Oscillation Phenomenon --- p.3 / Chapter 2.1 --- Introduction to El Nino - Southern Oscillation --- p.3 / Chapter 2.2 --- The mean conditions of the Tropical Ocean --- p.4 / Chapter 2.3 --- Life Cycle of ENSO --- p.8 / Chapter 2.4 --- Understanding ENSO --- p.12 / Chapter 3 --- ENSO prediction schemes --- p.18 / Chapter 3.1 --- Introduction --- p.18 / Chapter 3.2 --- Statistical prediction models --- p.19 / Chapter 3.2.1 --- Introduction --- p.19 / Chapter 3.2.2 --- Atmospheric models --- p.19 / Chapter 3.2.3 --- Oceanic models --- p.22 / Chapter 3.3 --- Coupled ocean-atmosphere models --- p.24 / Chapter 3.3.1 --- Introduction --- p.24 / Chapter 3.3.2 --- Intermediate coupled models --- p.25 / Chapter 3.3.3 --- Hybrid coupled models --- p.28 / Chapter 3.3.4 --- Coupled general circulation models --- p.30 / Chapter 3.4 --- Skill sensitivities --- p.36 / Chapter 3.4.1 --- Introduction --- p.36 / Chapter 3.4.2 --- Dependence of skill on season --- p.36 / Chapter 3.4.3 --- Dependence of skill on decade --- p.37 / Chapter 3.4.4 --- Dependence of skill on the Phase of the ENSO cycle --- p.38 / Chapter 4 --- The ENSO model --- p.40 / Chapter 4.1 --- Introduction --- p.40 / Chapter 4.2 --- Models formalism --- p.40 / Chapter 4.2.1 --- Oceanic model --- p.40 / Chapter 4.2.2 --- Atmospheric model --- p.43 / Chapter 4.2.3 --- Coupling of atmospheric and oceanic models --- p.44 / Chapter 4.3 --- Numerical implementation --- p.45 / Chapter 4.3.1 --- Oceanic model --- p.45 / Chapter 4.3.2 --- Atmospheric model --- p.49 / Chapter 4.3.3 --- Averaging and interpolation during coupling --- p.52 / Chapter 4.4 --- Standard response of the model --- p.54 / Chapter 4.5 --- Limitation of the model --- p.57 / Chapter 5 --- Behavior of the ENSO model --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.2 --- Numerical results of the model --- p.60 / Chapter 5.3 --- Effects of the parameters --- p.62 / Chapter 5.3.1 --- Introduction --- p.62 / Chapter 5.3.2 --- Coupling constant parameters --- p.62 / Chapter 5.3.3 --- Rayleigh friction --- p.66 / Chapter 5.3.4 --- The oceanic Kelvin wave speed --- p.69 / Chapter 5.3.5 --- The ocean basin length --- p.69 / Chapter 5.3.6 --- Reflections at the western boundary --- p.74 / Chapter 5.4 --- Modification of the model background state --- p.76 / Chapter 5.4.1 --- Introduction --- p.76 / Chapter 5.4.2 --- The results of the modified model --- p.77 / Chapter 5.4.3 --- Sensitivity of the western boundary of the modified model --- p.81 / Chapter 5.4.4 --- Parameters sensitivities of the modified model --- p.83 / Chapter 5.5 --- Conclusion and discussion --- p.87 / Appendix A --- p.91 / Appendix B --- p.112 / Bibliography --- p.120

During the operation of phase-change ink-jet printers a bubble formation phenomenon often occurs. These bubbles are detrimental to the operation of the printer and substantial efforts are made to remove them. The objective of this research was 1: to develop a fundamental understanding of how bubble or void formation occurs during the phase-change process, and, 2: to develop a simple computer model to simulate this behavior which can then be used as a tool for better design of print-head geometries. Preliminary experimental work indicated the void formation to be a result of the density change accompanying the phase-change process. The commercial numerical code, Flow 3-D, was used to model the phase-change process in print-head geometries and substantiate certain simplifying assumptions. These assumptions included the effect of convection on the process and the effect of the varying material properties. For channel sizes less than 0.5 cm the phase-change process was found to be a pure conduction process. Convection effects are thus negligible and can be eliminated from the model. The variability of density, specific heat and thermal conductivity must be included in the model, as they affect the phase-change process dramatically. Specific heat is the most influential of the properties and determines, along with the conductivity, the rate at which the phase change takes place. The density must be included since it is directly linked to the void formation. / Graduation date: 1994

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Fluctuation phenomena are important to many physical systems, such as the fusion plasma. Noise theory is used to study the time and space correlations of stationary Markovian fluctuations that are statistically homogeneous and isotropic. The relaxation of the fluctuations is modeled by the diffusion equation. The spatial correlations are modeled by the exponential decay. Based on these models, the correlation function and the power spectral density of random fluctuations. We also find that the fluctuation-induced transport coefficients may be estimated by the correlation length and the correlation time. The theoretical results are compared with the observed plasma density fluctuations from tokamak and helimak experiments.

We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrödinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A [delta]-function model as a single impurity is very attractive, but it has been known that [delta]-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a [delta]-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also agrees with the classical predictions. We also compute the electron transmission probability through a multi-ripple electron waveguide. We find an effect analogous to the Dicke effect in the multi-ripple electron waveguide. We show that one of the S-matrix poles, that of the super-radiant resonance state, withdraws further from the real axis as each ripple is added. The lifetime of the super-radiant state, for N quantum dots, decreases as [1/N] . This behavior of the lifetime of the super-radiant state is a signature of the Dicke effect. / text