Bochum, Univ., Diss., 2005. / Computerdatei im Fernzugriff.

Bochum, University, Diss., 2005.

Ruhr-Universität Bochum, Universitätsbibliothek, Fakultät für Chemie, Diss., 2005. / Computerdatei im Fernzugriff.

Ruhr-Universität Bochum, Universitätsbibliothek, Fakultät für Chemie, Diss., 2005.

No description available.

No description available.

Discrete Fourier Transform (DFT) and Finite Impulse Response (FIR) filters are extensively used in Digital Signal Processing (DSP) and Image Processing. As a result, there is a strong motivation to come up with area- and delay-efficient hardware realizations of DFT and FIR filters. In this thesis, we propose an arithmetic Sum-of-Product (SOP) based approach to implement area- and delay-efficient Discrete Fourier Transform (DFT) and FIR filter circuits. Our SOP based engine uses an improved column compression algorithm, and handles the sign of the input efficiently. The partial products of the computation are compressed down to 2 operands, which are then added using a single hybrid adder (which is comprised of a ripple carry adder for the early-arriving lower-order bits, a Kogge-Stone adder for the slower middle bits, and a carry-select adder for the early-arriving higher order bits). The DFT and FIR filters can also be cast as instances of the Multiple Constant Multiplication (MCM) problem. RAG-n is one of the best known algorithms for realizing an MCM block with the minimum number of adders. We compare our SOP-based implementations with the RAG-n algorithm. We implement both approaches using a 45 nm cell library, and demonstrate that our approach yields a faster DFT circuit (by about 12-13%), with a small (about 5%) area penalty and a significantly better algorithmic runtime. We also demonstrate that our approach realizes FIR filters with hard-to-implement coefficients with a 4.4× speedup and 1.38× area penalty as compared to two recent adder cascade based approaches. For a set of symmetric and asymmetric filters, we compare the area-delay curves of the circuits generated by using our SOP based approach with that of the circuits generated by using a Common Sub-expression Elimination (CSE) based algorithm, which tries to minimize the number of adders utilized under a maximum adder cascade length constraint. We show that for a large range of delays, the circuits generated by using our approach have the smallest area. Finally, we propose a new hybrid form realization for FIR filters. The hybrid form realization attempts to perform the computation using both the Direct and Transposed Direct form realization styles. We discuss conditions under which it would improve on both the Direct and Transposed Direct form realizations, in terms of circuit area and delay.

Bochum, Universiẗat, Diss., 1999.

Orientadores: Ulf F. Schuchardt, Heloise de Oliveira Pastore / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-05T04:44:02Z (GMT). No. of bitstreams: 1 Gallo_JeanMarcelRibeiro_M.pdf: 5237424 bytes, checksum: 618c52e79b92842d0ef0d9e910c1ebc8 (MD5) Previous issue date: 2005 / Resumo: Otimizamos a síntese da Nb-MCM-41 à temperatura ambiente, variando a base, as fontes de sílica e nióbio e a ordem de adição da fonte de nióbio. Os materiais, antes e após a calcínação, foram caracterizados por difração de raios-X e reflectância difusa na região do UV-Vis. A Nb-MCM-41 com o melhor resultado foi silanizada e caracterizada por espectroscopia de emissão atômica por plasma indutivamente acoplado (ICP-OES), análise termogravimétrica (TGA), adsorção-dessorção de nitrogênio, ressonância magnética nuclear no ângulo mágico (RMN-MAS) de Si, análise elementar de carbono, hidrogênio e nitrogênio (CHN) e espectroscopia na região do infravermelho (IV). As Nb-MCM-41 calcinada e a silanizada foram testadas na epoxidação de cis-cicloocteno com terc-butilhidroperóxido (TBHP) 69,4 % em cicloexano obtendo após 48 h, 46,6 e 62,2 % de conversão e 77 e 94 % de seletividade, respectivamente. Usando peróxido de hidrogênio 70 % em água obtivemos após 5 h, 8 % de conversão e 80% de seletividade para a amostra calcinada e 13 % de conversão e 70 % de seletividade para a silanizada. Nas reações usando peróxido de hidrogênio aquoso. este foi todo consumido nas 10 primeiras horas. mostrando que o nióbio decompõe facilmente o peróxido de hidrogênio. Montmorilonita K-10 foi trocada com polihidroxi-nióbio e caracterizada por difração de raios-X, TGA, adsorção-desorção de nitrogênio e ICP-OES. O material foi então calcinado a 300. 500 e 900°C para se obter a montmorilonita pilarizada com nióbio que foi caracterizada por difração de raios-X. Observando que mesmo quando a argila é calcinada a 900°C mantém-se a microporosidade, o que é surpreendente, pois a maioria das argilas pilarizadas com óxidos metálicos perde sua microporosidade a cerca de 600°C. A montmorilonita K10 pura, a trocada com nióbio e a pilarizada foram testadas como catalisadores ácidos nas reações de abertura do anel oxirano do oleato de metila epoxidado, usando metanol como nucleófilo, para se obter o b-hidroxiéter correspondente. A argila trocada com nióbio foi mais ativa que as demais. mostrando que a incorporação de nióbio realmente aumenta a acidez de Bronsted. As amostras calcinadas eram menos ativas quanto maior a temperatura de calcinação / Abstract: Nb-MCM-41 synthesis was optimized at room temperature varying the hydroxide, the silica and niobium sources and the order of addition of the niobium source. The materials, before and after the calcinations, were characterized by XRD and UV-Vis diffuse reflectance. The Nb-MCM-41 with best results was silylated and characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify the niobium, thermogravimetric analysis (TGA) , adsorption-desorption of nitrogen, magic angle spinning nuclear magnetic resonance (RMN-MAS) of Si, elementary analysis of carbon, hydrogen and nitrogen (CHN) and infrared spectroscopy (FTIR). The calcined and the silylated Nb-MCM-41 were used in the epoxidation of ciclooctene with feributylhydroperoxide (TBHP) 69,4 % in ciclohexane obtaining after 48 h, 46,6 and 62,2 % of conversion and 77 and 94 % of selectivity, respectively. Using hydrogen peroxide 70 % in water it was obtained after 5 h, 8% of conversion and 80 % of selectivity for the calcinated sample and 13 % of conversion and 70 % of selectivity for the silylated. When using hydrogen peroxide all the peroxide was decomposed after 10 h, showing that niobium decompose easily hydrogen peroxide Montmorillonite K10 was ion-exchanged with polyhydroxyniobium characterized by XRD, TGA, adsorption-desorption of nitrogen and ICP. Then the material was calcined at 300, 500 e 900°C to obtain the Nb-pillared montmorillonite. These materials were characterized by XRD, and even when calcined at 900°C the microporosity is maintained, which is surprising since most of metal oxide pillared clays lose the microporosity at temperatures around 600°C. The montmorillonite K10 pure, niobium exchanged and Nb-pillared were used as acid catalysts in the oxirane ring-oppening reactions of the epoxidazed methyl oleate with methanol as nucleophile, to obtain the correspondent b-hydroxyether. The ion-exchanged clay was more active that the pure clay, proving than niobium incorporation improves Bronsted acidity. The calcined samples were less active the higher was the calcination temperature / Mestrado / Quimica Inorganica / Mestre em Química

The purpose of this thesis was to conduct preliminary research into the feasibility of using MCM-41 as a catalyst support material in the treatment of organochloride contaminated water. Specifically, the stability of MCM-41 in water and its efficiency as a Pd metal catalyst support in the degradation of trichloroethylene (TCE) was examined. MCM-41 is a mesoporous siliceous material that was developed by scientists with the Mobile Corporation in 1992. Since its development, MCM-41 has been the subject of a great deal of research into its potential application in catalytic sciences. The material possesses two especially notable characteristics. First, the diameter of its pores can be adjusted between 2 and 10 nm depending on the reagents and procedure used in its synthesis. Second, MCM-41 has an exceptionally high surface area, often in excess of 1 000 m2/g in well-formed samples. Other researchers have succeeded in grafting a variety of different catalytic materials to the surfaces and pores of MCM-41 and reported dehalogenation reactions proceeding in the presence of hydrogen. Thus, MCM-41 shows promise in treating a variety of chlorinated volatile organic compounds (cVOCs), such as chlorinated benzenes, trichloroethylene (TCE), perchloroethylene (PCE) and some polychlorinated biphenyls (PCBs). Preliminary stages of this research were devoted to synthesising a well-formed sample of MCM-41. The method of Mansour et al. (2002) was found to be a reliable and repeatable procedure, producing samples with characteristic hexagonal crystallinity and high surface areas. Crystallinity of all materials was characterized by small angle X-ray powder diffraction (XRD). Samples of MCM-41 prepared for this research exhibited a minimum of three distinct peaks in their XRD traces. These peaks are labelled 100, 110, and 200 according to a hexagonal unit cell. The 100 peak indicates that the sample is mesoporous. The 100, 110, and 200 peaks together indicate a hexagonal arrangement of the mesopores. An additional peak, labelled 210, was also observed in materials prepared for this research, reflecting a high degree of crystallinity. The position of the 100 peak was used to calculate the unit cell parameter - ???a??? - of the samples according to Bragg???s Law. The value of the unit cell parameter corresponds to the centre to centre distance of the material???s pores and thus the relative diameter of the pores themselves. The unit cell parameter of samples prepared for this research ranged from 4.6 nm to 5.3 nm with an average value of 4.8 nm. Surface areas of prepared samples were determined by BET nitrogen adsorption analysis and ranged from 1 052 to 1 571 m2/g with an average value of 1 304 m2/g. Field emission scanning electron microscope (SEM) images of a representative sample of MCM-41 revealed a particle morphology referred to as ???wormy MCM-41??? by other researchers. A sample of aluminum-substituted MCM-41 (Al-MCM-41) was also synthesized. The crystallinity of Al-MCM-41 was characterized by small angle XRD. The XRD trace of the material showed only one distinct peak centred at 2.1 degrees 2??. The 110 and 200 peaks seen in MCM-41 were replaced by a shoulder on the right hand side of the 100 peak. The shape of this trace is typical of Al-MCM-41 prepared by other researchers and is indicative of the lower structural quality of the material, i.e. a less-ordered atomic arrangement in Al-MCM-41 compared to that of regular MCM-41. The unit cell parameter of the Al-MCM-41 sample was 4.9 nm. The surface area of the sample was determined through BET nitrogen adsorption analysis and found to be 1 304 m2/g. Attempts were made to synthesize an MCM-41 sample with enlarged pores. Difficulties were encountered in the procedure, specifically with regards to maintaining high pressures during the crystallization stage. Higher temperatures used during these procedures caused failure of the O-ring used in sealing the autoclave, allowing water to be lost from the reaction gel. Samples generated in these attempts were amorphous in character and were subsequently discarded. A solubility study involving MCM-41 was undertaken to determine the stability of the material in water at ambient temperature and pressure. The experiment included several different solid/water ratios for the dissolution experiments: 1/200, 1/100, 1/75, 1/25. Results indicated that MCM-41 is metastable at ambient temperatures and more soluble than amorphous silica in water. The maximum silica concentration observed during the experiment was used to calculate a minimum Gibbs free energy of formation for MCM-41 of - 819.5 kJ/mol. The higher free energy value compared to quartz (- 856.288 kJ/mol) is indicative of the metastability of the material in water. Supersaturation with respect to amorphous silica was observed in samples prepared with relatively high concentrations of MCM-41. A subsequent decrease in dissolved silica concentration with time in these samples represented precipitation of amorphous silica, driving the concentration downward towards saturation with respect to this phase (120 ppm). The equilibrium concentration of 120 ppm recorded in these samples represented 4.8 mg out of 200, 400, 500, and 1 600 mg of initial MCM-41 dissolving into solution in the solid/liquid ratios of 1/200, 1/100, 175, and 1/25, respectively. Supersaturation with respect to amorphous silica did not occur in experiments with very low solid/water ratios. It also did not occur in higher solid/water experiments from which the SiO2 saturated supernatant was decanted and replaced with fresh deionized water after two weeks of reaction. The difference in dissolution behaviour is believed to result from deposition of a protective layer of amorphous silica from solution onto the MCM-41 surfaces, which reduces their dissolution rate. Thus, supersaturation with respect to amorphous silica is only manifested at early time and only when relatively large amounts of fresh MCM-41 are added to water. The solubility experiment was repeated using samples of Al-MCM-41 to determine the effect of Al substitution on the stability of the MCM-41. Dissolution curves for the Al-MCM-41 samples revealed behaviour that was analogous to that of the silica-based MCM-41 at similar solid/water ratios. Substitution of Al into the structure of MCM-41 appeared to have no positive or negative effects on the stability of the material in water. Solid MCM-41 material was recovered on days 28 and 79 of the solubility experiment and dried under vacuum. Solid material was also recovered from the Al-MCM-41 solubility experiment on day 79. These recovered samples were characterized by XRD and BET nitrogen adsorption analysis. An increase in background noise in the XRD plot of MCM-41 from the fresh to the 79 d sample indicated an increased proportion of an amorphous phase in the sample. The XRD plot of the 79 d sample of Al-MCM-41 also showed increased background noise corresponding to an increased proportion of an amorphous phase. The increased amorphous phase would have resulted from the continuous dissolution of the crystalline MCM-41 and reprecipitation as amorphous silica in the samples. BET surface area analysis of recovered MCM-41 compared to the freshly prepared material showed no significant change in surface area after 28 and 79 days in water. Analysis of the 79 d Al-MCM-41 indicated a 10% decrease in surface area relative to the as-prepared material. A set of SEM images were taken of the day 28 and 79 MCM-41 samples and compared to a sample of freshly prepared material. No substantial change in morphology was observed in the day 28 sample when compared to the fresh material. Some change was noted in the day 79 sample particle morphology, with worm-like structures appearing to be better developed than in the as-synthesized material. A series of palladized MCM-41 (Pd/MCM-41) samples with varying mass percent loadings of Pd was prepared to investigate the dehalogenation efficiency of Pd/MCM-41 in contact with TCE. TCE degradation was investigated in batch experiments. MCM-41 samples were prepared with calculated Pd loadings of 0.1, 1, and 5 mass %. The actual palladium content of the materials was determined using an EDAX-equipped SEM. The success of the loading technique was better at lower mass loadings of Pd, i.e. there was a greater deviation of actual Pd content from targeted or calculated contents at higher loadings of Pd. It was found that a procedure designed to yield 1% by mass Pd/MCM-41 produced an average loading of 0.95% Pd by mass. A procedure designed to produce a 5% Pd/MCM-41 sample resulted in an average loading of 2.6 mass %. These deviations were attributed to error inherent in the EDAX analysis and reduced effectiveness of the loading technique at higher Pd concentrations. All batch experiment reaction bottles were prepared with solid/liquid ratios of 1/800. The various Pd/MCM-41 samples induced rapid dehalogenation reactions, with the maximum extent of TCE degradation occurring before the first sample was taken at 7 to 12 min and within 35 min in the case of 0.1% Pd/MCM-41. The 0.1% Pd/MCM-41 sample degraded 70% of total TCE in solution with an estimated degradation half-life of 14 min. The 1% Pd/MCM-41 sample degraded 92% of total TCE in solution with an estimated half life of between 3 and 6 min. The 5% Pd/MCM-41 sample degraded only 22% of total TCE in solution; degradation half-life could not be determined. The seemingly paradoxical result of lower degradation efficiency at higher Pd loadings is proposed to result from absorption of hydrogen from solution by Pd, which is unreactive relative to the dissolved hydrogen in solution. Production of reaction intermediates and daughter products was also lower in the 1% by mass Pd/MCM-41 experiment compared to the 0.1 and 5% by mass Pd/MCM-41. Analysis of degradation products results from the experiments indicated that TCE degrades to ethane in the presence of Pd/MCM-41 with relatively low concentrations of chlorinated daughter products resulting from a random desorption process. A batch experiment using pure silica MCM-41 was also conducted to determine if there was adsorption of TCE to the support material itself. A lack of change in TCE concentration between the control sample and the MCM-41 sample during the experiment indicated no significant adsorption of TCE onto MCM-41. The conclusion of this research is that although MCM-41 is relatively unstable in water, its high TCE degradation efficiency shows promise for its application in developing water treatment technologies. However, more research needs to be conducted to fully determine the potential use of MCM-41 in water treatment and to investigate ways to improve its long-term stability in water.