Design for suburban houses in Thailand

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1998.Includes bibliographical references (p. 93-95).Natural Ventilation is the most effective passive cooling design strategy for architecture in hot and humid climates. In Thailand, natural ventilation has been the most essential element in the vernacular architecture such as the traditional house, but has become unused nowadays because of the urbanized conditions in big cities like Bangkok. This thesis explores the potential of using natural ventilation for modern houses by using a Computational Fluid Dynamics (CFD) program. The research investigates the characteristics of Thai houses from the past to the present that climate, culture and technology have influenced. The analysis of the climate data concludes that natural ventilation can be used approximately four months a year to create conditions within the zone of thermal comfort. In a suburban housing project, site planning has a significant impact on the wind pattern and velocity. The simulation results indicate that the wind has better characteristics in the houses with square shapes than those with rectangular shapes. The vegetation around the houses also has some effect on the wind by slightly reducing its speed. Lastly, the prevailing winds from the north and north-northeast have similar wind patterns in a large housing project. The final stage is to design a prototype by using some climatic characteristics from the traditional Thai house. The air movement is inadequate in a house with regular size windows. Therefore, the study tests three more cases with larger windows. The results demonstrate that the maximum size window provides better thermal comfort. Finally, the study finds that the stack effect is negligible. The study shows the possibility to use natural ventilation for the houses in this region. The investigation has developed comprehensive design guidelines for architects. Necessary further research is presented in the end to find more solutions for climate-responsive architecture in today's physical conditions.by Chalermwat Tantasavasdi.M.S

A Rigid Image Registration Based on the Nonsubsampled Contourlet Transform and Genetic Algorithms

Image registration is a fundamental task used in image processing to match two or more images taken at different times, from different sensors or from different viewpoints. The objective is to find in a huge search space of geometric transformations, an acceptable accurate solution in a reasonable time to provide better registered images. Exhaustive search is computationally expensive and the computational cost increases exponentially with the number of transformation parameters and the size of the data set. In this work, we present an efficient image registration algorithm that uses genetic algorithms within a multi-resolution framework based on the Non-Subsampled Contourlet Transform (NSCT). An adaptable genetic algorithm for registration is adopted in order to minimize the search space. This approach is used within a hybrid scheme applying the two techniques fitness sharing and elitism. Two NSCT based methods are proposed for registration. A comparative study is established between these methods and a wavelet based one. Because the NSCT is a shift-invariant multidirectional transform, the second method is adopted for its search speeding up property. Simulation results clearly show that both proposed techniques are really promising methods for image registration compared to the wavelet approach, while the second technique has led to the best performance results of all. Moreover, to demonstrate the effectiveness of these methods, these registration techniques have been successfully applied to register SPOT, IKONOS and Synthetic Aperture Radar (SAR) images. The algorithm has been shown to work perfectly well for multi-temporal satellite images as well, even in the presence of noise

Precision plasma etching of Si, Ge, and Ge:P by SF6 with added O2

The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of silicon (Si), germanium (Ge), and phosphorous doped germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile are greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates is found compared to that of Si, but for O2 content above 50% the etch rates follow relatively the same trend. Lightly doped Ge shows the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity is possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge, and Ge:P is possible

Precision plasma etching of Si, Ge, and Ge:P by SF6 with added O2

The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of silicon (Si), germanium (Ge), and phosphorous doped germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile are greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates is found compared to that of Si, but for O2 content above 50% the etch rates follow relatively the same trend. Lightly doped Ge shows the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity is possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge, and Ge:P is possible

Low thermal conductance platforms for mK tunnelling coolers

The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of Silicon (Si), Germanium (Ge) and phosphorous doped Germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile were greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates was found compared to that of Si, but for O2 content above 50% the etch rates followed relatively the same trend. Lightly doped Ge showed the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity was possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge and Ge:P was possible. Suspended Ge structures were fabricated: micro wires, spiderweb and the van der Pauw Greek-cross. The micro wires’size could be reduced to fabricate suspended Ge nanowires devices. The suspended spiderweb could be fabricated for bolometers. The van der Pauw Greek-cross structure could reveal the electrical properties of thin expitaxial layer such as resistivity and mobility via hall measurement as a function of temperature. Removal of dislocations was shown to enhance the electrical isolation. Thermal properties of germanium doped with phosphorus (4x1019 cm-3) were investigated in this study. At lowest Tbath of 312 mK , the results indicate that heat flow from hot electrons to phonons was proportional to T7 and the electron-phonon coupling constant is 1.31x109 W/m3 K7 . The temperature dependence of doped Ge was higher than doped Si (which has a T6 temperature dependence) because the band structure was different. Moreover, the heat flow between electrons and phonon that is proportional to T7 could possibly be explained by a combination of strong disorder and surface modes

Impact of design features on natural ventilation of open-air malls in Thailand

Abstract In recent times, retail buildings in tropical areas have started to evolve from fully enclosed air-conditioned designs towards designs featuring open-air naturally ventilated malls. This paper discusses influential factors that can be used to help achieve thermal comfort conditions in the semi-outdoor spaces of open-air malls within the Bangkok Metropolitan Area in Thailand. The researchers surveyed 23 buildings and categorised them into three groups according to their configurations. Six representative projects were selected and assessed using a computational fluid dynamics program. The results revealed that the percentages of thermal comfort hours varied from 34.7% to 80.8% of the annual occupation time and were highly dependent on the design decisions taken for individual projects. The study found that among five important design factors, which are position of openings in accordance to the prevailing wind, distribution of openings, window-to-wall ratio, building shape, and openings that encourage cross-ventilation, the first factor was the most influential. Buildings that have their position of openings in good accordance to the prevailing winds can achieve the number of hours 2.0 times greater than those that do not.</jats:p