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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Template Synthesis and Mesostructural characterization of Ordered Mesoporous Silica, Titania and Carbon Materials

Kao, Li-Heng 03 January 2008 (has links)
Template synthesis and mesostructural characterization of ordered mesoporous silica, titania and carbon materials have been systematically investigated in this study. In order to obtain a better understanding of the template-precursor relationship, there are two templates adopted in this research. One is the ¡§liquid crystal template (LCT)¡¨, composed of surfactants via self-assembly pathway; the other is the ¡§ordered silica spheres template¡¨, composed of monodispersed SiO2 spheres (~40 nm) via gravity sedimentation. This work was carried out in four related directions: (1) Synthesis and functionalization of ordered mesoporous silicate (MCM-41 and MCM-48) via cationic surfactant template; (2) Using anionic surfactant template-assisted via urea treatment to control the morphology of the TiO2; (3) Synthesis of ordered mesoporous anatase TiO2 via cationic surfactant template; (4) Synthesis of ordered mesoporous carbon from mesophase pitch solution via silica spheres template. Mesoporous silica materials MCM-41 and MCM-48 have been synthesized and identified. The MCM-41 has a hexagonal phase (p6m) with surface area of 1006.90 m2/g and pore size of 37.65 Å, The MCM-48 has cubic phase ( ) with surface area of 1093.34 m2/g and pore size of 29.20 Å. The calcined MCM-41was rehydrated by heating in water and functionalized with 3-amino propyltrimethoxysilane; this functionalized mesoporous silica is targeted as a template of metal oxides, such as TiO2. appears the same tendency of parent MCM-41 in the N2 sorption isotherm measurements. Nanocrystalline TiO2 rods and hollow-tubes with an engraved pattern on the surface have been prepared by the anionic template-assisted sol-gel synthesis via urea treatment and under hydrothermal condition. X-ray diffractometry (XRD) results indicate that these nanocrystallines consist predominantly of anatase TiO2, with minor amounts of rutile and brookite. The crystallographic facetting found from SEM and TEM further reveals the polymorphic nature of the nanocrystalline TiO2 thus prepared. A ¡§reverse micelle¡¨ formation mechanism taking into account the hydrothermal temperature, the pH effect of the sol-gel system, the isoelectric point, the formation of micelles, and the electrostatic interaction between the anionic surfactant and the growing TiO2 particulates is proposed to illustrate the competition between the physical micelle assembly of the ionic surfactants and the chemical hydrolysis and condensation reactions of the Ti precursors. Ordered mesoporous TiO2 materials with an anatase framework have been synthesized by using a cationic surfactant template and soluble peroxytitanates as Ti precursor through an S+I− self-assembly pathway. The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO2 materials indicates a hexagonal mesostructure. XRD and TEM results and N2 sorption isotherms measurements indicate the calcined mesoporous TiO2 possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum BET specific surface area of 284 m2/g. This ordered mesoporous TiO2 also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation. Under a lower carbonization temperature and with a mesophase pitch solution as the carbon precursor, ordered mesoporous carbon thick films with 35-nm pore size have been synthesized using SiO2 spheres as the template. The pore size of the mesoporous carbon thus fabricated was the smallest one ever reported using silica templates. SEM and TEM patterns show a discernible morphology of an ordered cubic close-packing of the mesopores interconnected via holes of 6 nm in diameter. From this study, the template synthesis has been proven to be an effective method to fabricate mesoporous silica, polymorphic titania, ordered mesoporous TiO2, and ordered mesoporous carbon materials. Further utilization of this template synthesis is expected to offer a variety of porous networks with a wide range of pore sizes, well-defined morphologies on controllable length scales, and various chemical functionalities to match the needs of different applications.
2

Robust Classification of Head Pose from Low Resolution Images Under Various Lighting Condition

Khaki, Mohammad January 2017 (has links)
Companies have long been interested in gauging the customer’s level of interest in their advertisements. By analyzing the gaze direction of individuals viewing a public advertisement, we can infer their level of engagement. Head pose detection allows us to deduce pertinent information about gaze direction. Using video sensors, machine learning methods, and image processing techniques, information pertaining to the head pose of people viewing advertisements can be automatically collected and mined. We propose a method for the coarse classification of head pose from low-resolution images in crowded scenes captured through a single camera and under different lighting conditions. Our method improves on the technique described in [1]; we introduce several modifications to the latter scheme to improve classification accuracy. First, we devise a mechanism that uses a cascade of three binary Support Vector Machines (SVM) classifiers instead of a single multi-class classifier. Second, we employ a bigger dataset for training by combining eight publicly available databases. Third, we use two sets of appearance features, Similarity Distance Map (SDM) and Gabor Wavelet (GW), to train the SVM classifiers. The scheme is tested with cross validation using the dataset and on videos we collected in a lab experiment. We found a significant improvement in the results achieved by the proposed method over existing schemes, especially for video pose classification. The results show that the proposed method is more robust under varying light conditions and facial expressions and in the presences of facial accessories compared to [1].
3

Keramické porézní materiály - příprava, struktura a vlastnosti / Ceramic porous materials - preparation, structure and properties

Šenk, Vít January 2011 (has links)
The thesis targets to preparation a foam ceramics suitable for supporting, catalytic and biological applications. Theoretical part deals with methods of preparation, properties and applications of foam ceramics. Experimental part of work is focused on preparation foams by template method using polymer foam. Properties of ceramic slurry were evaluated according to discharge time of Ford cup. Foam structure is assessed using images and mechanical properties are judged by compressive tests.

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