A simulation scheme is proposed to analyze the effects of elliptic-conical lensed fiber parameters on the coupling efficiency between a 980nm laser diode and single-mode fiber(SMF). The variation of fiber tip shapes with different melting zone volumes was investigated in this thesis. The heat-transfer finite element model in MARC package is employed to simulate the temperature distribution during the melting process. The free convection is considered in predicting the melting zone. Due to the surface tension, a round tip may be solidificated. In this study an elliptical tip lens is expected to improve the coupling efficiency. The microlens shapes with different radius of curvature is simulated with the software of Surface Evolver. The coupling efficiency of 980nm laser source and different elliptic-conical lensed fiber is calculated by utilizing the ZEMAX optical analysis software. The Taguchi method is employed to evaluate the effect of tip shape parameters on the coupling efficiency. The optimal elliptic-conical lensed fiber parameters has also been proposed. The efficiency loss introduced from the misalignments in laser module packaging has also been discussed in this study.

A simulation algorithm is proposed in this thesis to investigate the effects of lensed fiber parameters on the variation of radius of curvature of the melted lens and the coupling efficiency of butterfly type laser diode transiver module. Two different endface shapes, i.e. the taper and the conical-wedge type lensed fibers, will be studied. The effect of endface shapes, sizes, and the melting zone volume on the coupling efficiency of lensed fibers are simulated and discussed. In the study on the conical type lensed fiber, the MARC¡¦s elastic-plastic-thermal finite element model is employed to simulate the melting and the solidification processes at the fiber tip endface with different conical angles. The temperature dependent material properties are used to calculate the melting zone and the post-melten deformation during the heating process. The Surface Evolver Software has also been employed to simulate the solidified lens shapes. The variation of radius of curvature of the tip lens is analyzed. The ZEMAX optical analysis software is applied to explore the relation between the coupling efficiency and the distribution of the radius of curvature. The variation of laser signal coupling efficiency introduced from different conical lensed fibers is simulated numerically. A good agreement between the published measured data and the simulated results indicate the proposed simulation model is feasible. The effect of endface shape and molten zone size on the conical wedge type lensed fiber has been studied in a similar way. The coherence between the shape of solidified elliptical lens at fiber tip and the coupling efficiency for the 980nm LD will be explored. Different endface shapes will also be investigated by using the simulation model proposed previously. Different aspect ratio of the conical-wedge type tip will be introduced to compensate the elliptical LD ray model and to recover the coupling efficiency loss. The agreement between the results simulated using the proposed model and the measured data is examined. The simulated results indicate that the coupling efficiency of a butterfly type laser diode transever can be improved significantly by controlling the shape of the lens introduced in this type lensed fiber. The optimal grinding parameters and the melting parameters used to fabricate the lensed fibers will also be studied. The effects of the shape parameters, i.e. the conical taper angle, the wedge angle and the size of molten zones on the curvature variation of the lens will also be studied. A better understanding about the design and fabrication of the lensed fiber of a laser diode based transever module is expected from the results presented in this thesis.

Aim: The primary aim of this study was to find if there is any correlation between the corneal radius of curvature and its eccentricity. Method: 45 subjects participated in this study, 24 emmetropes, 18 myopes and three hyperopes. All subjects were free of ocular abnormalities and had no media opacities. All the subjects had normal ocular health and good visual acuity of 1.0 or better for both distance and near. The values for eccentricity and corneal radius of curvature were obtained by using a Topcon CA-100F Corneal Analyzer. Results: For the 4.5 mm zone the only significant correlation between corneal radius of curvature and eccentricity was obtained for the mean of the meridian (p = 0.007). On the other hand, we found no significant correlation for the average of two meridians or for meridian 1 and meridian 2 separately in the 8.0 mm zone. Conclusions: We found no correlation between the corneal radius of curvature and the eccentricity for both zones. In addition, no correlation could be found between the spherical equivalent of the refractive errors and the corneal eccentricity. The reason for not finding any significant correlation between the two entities could be due to factors such as smaller sample size and poor distribution of refractive errors in the sample. Moreover, there may be other factors that could influence the overall corneal shape like eye shape, axial length and corneal diameter, which was not evaluated in this study.

The semicircular canals detect head rotations and trigger compensatory movements that stabilize gaze and help maintain visual fixation. Mammals with large eyes and high visual acuity presumably require more precise gaze stabilization mechanisms because they experience degradation of spatial resolution at a lower threshold of uncompensated motion. Because semicircular canal radius of curvature is a primary determinant of canal sensitivity, species with large canal radii are expected to be capable of more precise gaze stabilization than species with small canal radii. Here the relationship between semicircular canal radius of curvature, eye size, and visual acuity is examined in a large sample of therian mammals. These results demonstrate that eye size and visual acuity both explain a significant proportion of the variance in mean canal radius of curvature after statistically controlling for the effects of body mass and phylogeny. These findings suggest that interspecific variation in semicircular canal radius of curvature is partly the result of selection for improved gaze stabilization in species with large eyes and acute vision. / text

Conventional interferometry is widely used to measure spherical and flat surfaces with nanometer level precision but is plagued by back reflections. We describe a new method of isolating the measurement surface by controlling spectral properties of the source (Spectrally Controlled Interferometry - SCI). Using spectral modulation of the interferometer's source enables formation of localized fringes where the optical path difference is non-zero. As a consequence it becomes possible to form white-light like fringes in common path interferometers, such as the Fizeau. The proposed setup does not require mechanical phase shifting, resulting in simpler instruments and the ability to upgrade existing interferometers. Furthermore, it allows absolute measurement of distance, including radius of curvature of lenses in a single setup with possibility of improving the throughput and removing some modes of failure.

Thin films have become very important in the past years as there is a tremendous increase in the need for small-scale devices. Thin films are preferred because of their electrical, mechanical, chemical, and other unique properties. They are often used for coatings, and in the fabrication of Microelectronic devices and Micro-electro Mechanical Systems (MEMS). Internal (residual) stress always exists when a thin film is employed in the device design. Residual and thermal stresses cause membrane bow, altering the anticipated dynamic response of a membrane-based MEMS design. The device may even become inoperable under the high stresses conditions. As a result, the stresses that act upon the membrane should be minimized for optimum operation of a MEMS device. In this research, the fabrication process parameters leading to low stress silicon nitride films were investigated. Silicon nitride was deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) and the residual stresses on these films were determined using a wafer curvature technique. By adjusting the silane (SiH4) and nitrogen (N2) gas flow rates, and the radiofrequency (RF) power; high quality silicon nitride films with residual stress as low as 11 MPa were obtained. Furthermore, an analytical study was also conducted to explore the effect of thermal stresses between layers of thin films on the MEMS device operation. In this thesis, we concentrated our efforts on three layers of thin films, as that is the most commonly encountered in a membrane based MEMS device. The results obtained from a parametric study of the membrane center deflection indicate that the deflection can be minimized by the appropriate choice of materials used. In addition, our results indicate that thin films with similar coefficient of thermal expansion should be employed in the design to minimize the deflection of the membrane, leading to anticipated device operation and increased yield. A complete understanding of the thermal and residual stress in MEMS structures can improve survival rate during fabrication, thereby increasing yield and ultimately reducing the device cost. In addition, reliability, durability, and overall performance of membrane-based structures are improved when substrate curvature and membrane deflection caused by stresses are kept at a minimum.

Tooth cusp radius of curvature (RoC) has been hypothesized to play an important role in food item breakdown, but has remained largely unstudied due to difficulties in measuring and modeling RoC in multicusped teeth. We tested these hypotheses using a parametric model of a four cusped, maxillary, bunodont molar in conjunction with finite element analysis. When our data failed to support existing hypotheses, we put forth and tested the Complex Cusp Hypothesis which states that, during brittle food items breakdown, an optimally shaped molar would be maximizing stresses in the food item while minimizing stresses in the enamel. After gaining support for this hypothesis, we tested the effects of relative food item size on optimal molar morphology and found that the optimal set of RoCs changed as relative food item size changed. However, all optimal morphologies were similar, having one dull cusp that produced high stresses in the food item and three cusps that acted to stabilize the food item. We then set out to measure tooth cusp RoC in several species of extant apes to determine if any of the predicted optimal morphologies existed in nature and whether tooth cusp RoC was correlated with diet. While the optimal morphologies were not found in apes, we did find that tooth cusp RoC was correlated with diet and folivores had duller cusps while frugivores had sharper cusps. We hypothesize that, because of wear patterns, tooth cusp RoC is not providing a mechanical advantage during food item breakdown but is instead causing the tooth to wear in a beneficial fashion. Next, we investigate two possible relationships between tooth cusp RoC and enamel thickness, as enamel thickness plays a significant role in the way a tooth wears, using CT scans from hundreds of unworn cusps. There was no relationship between the two variables, indicating that selection may be acting on both variables independently to create an optimally shaped tooth. Finally, we put forth a framework for testing the functional optimality in teeth that takes into account tooth strength, food item breakdown efficiency, and trapability (the ability to trap and stabilize a food item).

Vacuum-assisted toilets make use of a large pressure difference between the ambient pressure and a vacuum tank to transport waste from the toilet bowl to the septic tank. This process requires 98% less water per flush making it an attractive product for transport vehicles such as airplanes, cruise ships, and trains. Unfortunately, the water savings come at the cost of high noise levels. This thesis investigates the acoustic characteristics of a vacuum-assisted toilet flush and several methods to reduce the radiated noise. Some methods include changing rinse parameters such as rinse pressure, rinse length, and rinse timing, adding structural damping of the bowl to reduce re-radiation, inserting a tube between the bowl and valve that utilizes a larger bend radius and longer tube length than what is currently installed, and modifying the valve. The most effective solution without requiring more water per flush was to insert a tube. The initial peak level was reduced by 16 dB and the steady-vacuum noise was reduced by 5 dB. Evidence of evanescent decay and reduced flow velocity as possible mechanisms for the noise reduction are presented and discussed. Rinse variations show a strong impact of the rinse-tube interaction on the noise reduction. In addition to these techniques, a modified flush plate opening and closing velocity profile is suggested which optimizes the sound generated by the opening and closing of the valve. Finally, a promising dual-valve solution that may take extra coordination of vacuum-assisted toilet manufacturers and airplane/cruise ship/train manufacturers is presented. By placing a secondary valve near the septic tank, the main noise from the valve is significantly reduced.

No description available.

The primary aim of this research was to investigate the bending behaviour of helically wound steel cables of various types (i.e. normal spiral strands, sheathed spiral strands and locked coil cables) in the presence of friction and to propose more efficient computational models for their analysis under combined tension and bending. The proposed model fully takes into account interwire contact forces both in the radial direction (point contact between wires in different layers) and hoop direction (line contact within the wires in the same layer). Extensive theoretical parametric studies have been undertaken on a variety of cable constructions covering a wide range of geometrical and material parameters. Explicit formulations have been developed for the smooth transition of the bending stiffness from no-slip to full slip regimes, as a function of cable curvature. Based on these formulations, it is now possible to calculate the relative displacements of the wires, as well as the tensile, bending and hoop stresses in the individual wires of the cable. Furthermore, bending stiffness of the cable is shown to decrease by a factor of 2 to 16, depending upon the friction coefficient between wires and the type of cable construction. Wherever possible, the theoretical results have been compared with experimental results from the available literature and are found in very good agreement with them. A simple method for the determination of the bending stiffness of large diameter multi-layered cable has been developed. The simplified method is further shown to provide estimates of the bending stiffness which are very close to those calculated by the original theory, allowing hand calculations for an easier use in industry. The proposed formulations have been extended to cater for the effects of external hydrostatic pressure on sheathed spiral strands in deep water applications. These forces are shown to have a great influence on the pattern of interwire contact forces and hence the interlayer slippage between the wires in the strand. Numerical results have been obtained and analysed for three different 127 mm diameter strands with lay angles of 12°, 18° and 24° respectively, experiencing a wide range of external hydrostatic pressures of 0 to 2,000 metres. The significant increase in normal contact force between wires is shown to suppress the slippage of wires in the cable. However, the no-slip and full slip values of the effective bending stiffness of the cable is shown to be independent of the level of hydrostatic pressure. A theoretical model is also proposed for estimating wire kinematics, pattern of interwire slippage, contact forces as well as the flexural rigidity of locked coil cables with outer layers made of shaped wires. In order to validate this model, numerical results are reported for two different locked coil cables. It is shown that the shaped wires in the outer layers of locked coil cables play an important role in the distribution of contact forces, slip initiation and cable unwinding.