High-quality 3D shape measurement with binarized dual phase-shifting method

ABSTRACT 3-D technology is commonplace in today\u27s world. They are used in many dierent aspects of life. Researchers have been keen on 3-D shape measurement and 3-D reconstruction techniques in past decades as a result of inspirations from dierent applications ranging from manufacturing, medicine to entertainment. The techniques can be broadly divided into contact and non-contact techniques. The contact techniques like coordinate measuring machine (CMM) dates way back to 1950s. It has been used extensively in the industries since then. It becomes predominant in industrial inspections owing to its high accuracy in the order of m. As we know that quality control is an important part of modern industries hence the technology is enjoying great popularity. However, the main disadvantage of this method is its slow speeds due to its requirement of point-by-point touch. Also, since this is a contact process, it might deform a soft object while performing measurements. Such limitations led the researchers to explore non-contact measurement technologies (optical metrology techniques). There are a variety of optical techniques developed till now. Some of the well-known technologies include laser scanners, stereo vision, and structured light systems. The main limitation of laser scanners is its limited speed due to its point-by-point or line-by-line scanning process. The stereo vision uses two cameras which take pictures of the object at two dierent angles. Then epipolar geometry is used to determine the 3-D coordinates of points in real-world. Such technology imitates human vision, but it had a few limitations too like the diculty of correspondence detection for uniform or periodic textures. Hence structured light systems were introduced which addresses the aforementioned limitations. There are various techniques developed including 2-D pseudo-random codication, binary codication, N-ary codication and digital fringe projection (DFP). The limitation of 2-D pseudo-random codication technique is its inability to achieve high spatial resolution since any uniquely generated and projected feature requires a span of several projector pixels. The binary codication techniques reduce the requirement of 2-D features to 1-D ones. However, since there are only two intensities, it is dicult to differentiate between the individual pixels within each black or white stripe. The other disadvantage is that n patterns are required to encode 2n pixels, meaning that the measurement speeds will be severely affected if a scene is to be coded with high-resolution. Dierently, DFP uses continuous sinusoidal patterns. The usage of continuous patterns addresses the main disadvantage of binary codication (i.e. the inability of this technique to differentiate between pixels was resolved by using sinusoid patterns). Thus, the spatial resolution is increased up to camera-pixel-level. On the other hand, since the DFP technique used 8-bit sinusoid patterns, the speed of measurement is limited to the maximum refreshing rate of 8-bit images for many video projectors (e.g. 120 Hz). This made it inapplicable for measurements of highly dynamic scenes. In order to overcome this speed limitation, the binary defocussing technique was proposed which uses 1-bit patterns to produce sinusoidal prole by projector defocusing. Although this technique has signicantly boosted the measurement speed up to kHz-level, if the patterns are not properly defocused (nearly focused or overly defocused), increased phase noise or harmonic errors will deteriorate the reconstructed surface quality. In this thesis research, two techniques are proposed to overcome the limitations of both DFP and binary defocusing technique: binarized dual phase shifting (BDPS) technique and Hilbert binarized dual phase shifting technique (HBDPS). Both techniques were able to achieve high-quality 3-D shape measurements even when the projector is not sufficiently defocused. The harmonic error was reduced by 47% by the BDPS method, and 74% by the HBDPS method. Moreover, both methods use binary patterns which preserve the speed advantage of the binary technology, hence it is potentially applicable to simultaneous high-speed and high-accuracy 3D shape measurements

Some Aspects of Incentive-Based Optimal Pricing and Environmental Regulation with Asymmetric Information.

The paper aims to analyze the problem of regulating a pollution-generating single product monopolistic firm in the presence of information asymmetry about the firm?s cost performance. Following Boyer and Laffont (1999), incentive-based optimal regulation of the firm?s price/ output and the environmental performance is characterized when costs are increasing in output and declining in pollution generated during production. Further, the regulatory agency/ legislator may or may not be politically motivated. When he/ she is politically inclined, the process of lobbying assumes that interest groups offer monetary contributions to the regulatory agency or the legislator. These contributions from the lobby help fund election campaigns. Thus, he/ she no longer behaves as a benevolent maximizer of social welfare, but instead maximizes a weighted average of social welfare and welfare of the lobby. Two alternative cases are considered: one, where the lobby represents environmental interests alone, and another, where the lobby stands solely for firm?s/ industry?s interests. The analysis derives interesting implications for incentive-based regulation of the firm. In general, pricing and environmental performance are distorted for the inefficient firm type under asymmetric information to restrict rents accruing to the efficient firm type. In the presence of the environmental lobby, the politically inclined regulator imposes more stringent environmental regulation under both full information and incomplete information as compared to the no-lobbying case. Interestingly, lobbying by the firm/ industry group also induces the politically motivated regulator to have more restrictive environmental regulation, albeit it now combines it with a higher regulated output for the inefficient firm type under incomplete information vis-…-vis the case of no-lobbying activity.

Thermally induced secondary atomization of droplet in an acoustic field

We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization

Insight into morphology changes of nanoparticle laden droplets in acoustic field

Hollow structures with unique morphologies form due to particle agglomeration in acoustically levitated nanofluid functional droplets when subjected to external heating. The final diameter of the structure depends only on the ratio of agglomeration to evaporation time scales for various nanoparticle laden droplets, and not on the type of the suspended particles. These time scales depend only on nanoparticle concentration. This valuable information may be exploited to form microstructures with desired properties from ceramic compounds. Phase diagrams for alumina and silica droplets indicate the transition from a bowl to ring structure depending on concentration