CHARACTERIZATION OF ZIRCONIA POWDER SYNTHESIZED VIA REVERSE MICROEMULSION PRECIPITATION

A two-reverse-microemulsion precipitation technique was applied to synthesize nanocrystalline tetragonal zirconia using H₂O solution/CTAB/hexanol as the microemulsion system. Two solutions of reverse microemulsion, one containing Zr⁴⁺ aqueous droplets and the other aqueous ammonia droplets with the same water/surfactant ratio, were prepared separately and mixed together to form a slurry of nanosized ZrO₂ precursors, which filled the matrix of the surfactant, CTAB. The precursors were recovered, calcined to form nanocrystalline zirconia powder, and then characterized by using a transmission electron microscope to determine the particle size, a scanning electron microscope to examine the microstructure of the zirconia powder, and an X-ray diffractometer to determine the crystal phase and crystallite size. It is concluded that the primary particle size of the precursor determines the transformation temperature of the precursor and the crystal structure of the calcined zirconia.     

Influence of Fluorine Content in Apatite–Mullite Glass-Ceramics

The nucleation and crystallization of a series of glasses based on 4.5SiO₂·3Al₂O₃·1.5P₂O₅·(5 − z )CaO · z CaF₂ with a Ca:P ratio corresponding to apatite were studied. In these glasses, the objective was to investigate the influence of fluorine content and z was varied from 3 to 0. All the glasses studied crystallized to fluorapatite (FAP) and mullite with the exception of the glass containing no fluorine, which crystallized to β-tricalcium phosphate (Ca₃(PO₄)₂) and anorthite (CaAl₂Si₂O₈). Glasses that contained sufficient fluorine to form FAP bulk nucleated to give FAP without a nucleation hold. Thermal gravimetric analysis demonstrated a significant weight loss corresponding to the crystallization of mullite, which increased with the fluorine content of the glass and also with decreased particle size. The loss was attributed to volatile SiF₄. The glass transition temperature decreased with increased fluorine content of the glass.     

Plug-in Selection of the Number of Frequencies in Regression Estimates of the Memory Parameter of a Long-memory Time Series

We consider the problem of selecting the number of frequencies, m , in a log-periodogram regression estimator of the memory parameter d of a Gaussian long-memory time series. It is known that under certain conditions the optimal m , minimizing the mean squared error of the corresponding estimator of d , is given by m ^(opt)= Cn ^4/5, where n is the sample size and C is a constant. In practice, C would be unknown since it depends on the properties of the spectral density near zero frequency. In this paper, we propose an estimator of C based again on a log-periodogram regression and derive its consistency. We also derive an asymptotically valid confidence interval for d when the number of frequencies used in the regression is deterministic and proportional to n ^4/5. In this case, squared bias cannot be neglected since it is of the same order as the variance. In a Monte Carlo study, we examine the performance of the plug-in estimator of d , in which m is obtained by using the estimator of C in the formula for m ^(opt) above. We also study the performance of a bias-corrected version of the plug-in estimator of d . Comparisons with the choice m = n ^1/2 frequencies, as originally suggested by Geweke and Porter-Hudak (The estimation and application of long memory time series models. Journal of Time Ser. Anal. 4 (1983), 221–37), are provided.     

KINETICS OF SUPERCRITICAL FLUID EXTRACTION OF ETHANOL FROM AQUEOUS SOLUTION

A 1.3 dm³ high-pressure vessel was used to extract ethanol from aqueous solution of 10 wt% using supercritical carbon dioxide as a solvent. Experiments were carried out in a semibatch mode. A mathematical model based on the two-film theory was derived for estimating the over all mass transfer coefficient. The effects of operating variables, including pressure, CO₂ superficial velocity, and agitation rate, on the mass transfer coefficient were investigated. In general, the mass transfer coefficient increased with increasing pressure, CO₂ superficial velocity, and agitation rate. The concentration of ethanol recovered in the collector after 180 minutes reached 50 wt%, starting with a feed of 10 wt% ethanol.     

Evolution of soluble carbohydrates during the development of pea, faba bean and lupin seeds

Seeds of pea (Pisum sativum L. cv. Ergo), faba bean (Vicia faba ssp. minor Harz., cv. Tibo) and yellow pea lupin (Lupinus luteus L. cv. Juno) were sampled at different days after flowering (DAF) and their content of soluble carbohydrates was determined: Analysis of samples showed thatmyo-inositol, fructose, glucose, galactose and sucrose were found in high abundance early in development and their content decreased gradually during maturation. -Galactosides, which includes the content of raffinose, stachyose and verbascose, started to appear later in seed development, at 37 DAF in peas, 40 DAF in faba beans and 45 DAF in lupins. Their accumulation increased considerably during seed growth, and the maximum content was obtained in mature seeds; 3.8% in peas, 4.5% in faba beans and 10.4% in lupins. Results obtained for these sugars during seed development were fitted to modelling curves in order to predict sugar content at different development stages.     

The effects of bleached and unbleached rosemary oleoresins on light-sensitized oxidation of soybean oil

Bleached and unbleached forms of a rosemary oleoresin (RO) in stripped and nonstripped soybean oil behave both as antioxidant and prooxidant in a light-induced oxidative system. At 0.02 and 0.05% levels, RO had the greatest antioxidant activity, while at 0.01 and 0.5% levels it had the highest prooxidant activity in both stripped and nonstripped soybean oil. Treatment of both soybean oil systems with tertiary butylhydroquinone controlled light-induced oxidation of the oil better than did the oleoresin treatments. The prooxidant activity of the 0.5% RO level was probably due to an excess of prooxidant components being carried into the oil at that level, whereas the reduced antioxidant activity at 0.01% was probably due to the low initial level of active antioxidant components being added to the oil. Published as Journal Series No. 10072, Nebraska Agricultural Research Division, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-0919.     

Build as you earn and learn: informal urbanism and incremental housing financing in Kumasi,Ghana

The continuous evolution, proliferation and resilience of informal housing in cities of developing countries defy all attempts by their formal planning processes to marginalise and relegate them to the periphery. In most instances, their rapid and uncontrolled growth has overwhelmed city planning authorities. More importantly, strategies for financing these informal housing units present complex networks of sources not clearly discussed in the housing literature. Using two informal communities—Ayigya-Zongo and Dakodwom—in Kumasi, Ghana, this paper explores the nature and characteristics of these non-conventional housing financing strategies. The study reveals an evolving and enduring non-conventional informal housing financing system effective for providing convenient and affordable housing for the urban poor; but this system is continuously sidelined by the conventional urban planning and housing financing systems. We argue against these attitudes of formal institutions towards these non-conventional housing financing strategies, and submit that these strategies are the gradual, incremental, and collective responses of residents in informal communities to a hostile formal urban planning and housing environment. Hence the dynamics of these non-conventional housing financing schemes point to a complex and fluid network of informal housing financial sources and structures, which are co-evolving with the processes of informal urbanisation and social learning among residents in informal settlements.     

Biochemical changes occurring during the manufacture of budu

The changes that occur during the commercial production of budu, a Malaysian fish sauce were examined. It was shown that the maximum volume of liquid was produced after 140 days and that proteolysis continued to occur until 200 days when 56% of the insoluble fish protein had been hydrolysed into soluble form. The colour was produced early during the fermentation. The aroma constituents, ammonia and trimethylamine, were produced early in the fermentation process, but the volatile fatty acids did not appear when fresh fish (Stolephorus) was used for the fermentation. In the commercial production, n-butanoic acid concentration remained constant during the fermentation but ethanoic acid did increase during the period. The salt concentration and the pH were approximately constant throughout, at 26% and 5.65, respectively.