In Clostridium acetobutylicum the three enzymes thiolase, CoA-transferase, and acetoacetate decarboxylase serve to catalyze the formation of acetone from acetyl-CoA. This process is unique to butyric-acid clostridia and has long-term industrial significance. These three enzymes are known to he induced at the onset of solvent production. Both the acetoacetate decarboxylase and CoA-transferase activities are often spontaneously lost in degenerative mutants. To further investigate the regulatory mechanisms governing the expression of these enzymes, the genes encoding each of the three enzymes were cloned and expressed in Escherichia coli. The CoA-transferase is an $\alpha\sb2$,$\beta\sb2$ heterotetramer of 23 and 26 kDa subunits. Cloning revealed the enzyme is encoded by two genes (actA and actB). Genes for both subunits of the CoA-transferase were located in an operon arrangement. DNA sequence analysis suggests that these genes are co-transcribed as part of a larger operon from an upstream promoter. The adc gene, encoding the acetoacetate decarboxylase, was cloned and physically mapped downstream from the CoA-transferase genes. However, it is not part of the actAB operon, being oriented in the opposite direction. DNA sequencing analysis demonstrates transcription of the adc as a monocistronic operon. The 65 bp intergenic region between the C-termini of the adc and actB genes is characterized by a novel stem-loop structure which appears capable of rho-independent transcription termination function in both directions in C. acetobutylticum. The cloned adc gene was successfully reintroduced into a C. acetobutylicum adc$\sp-$ mutant, resulting in wild-type regulation and expression of the gene. The gene encoding the thiolase (thl) was also cloned, although it is not located near the other acetone production genes. The cloned thiolase is transcribed from its own promoter. No other thiolase genes were identified. A profound bias for adenine or thymidine in the third ("wobble") position of each codon was demonstrated in all four genes sequenced. Despite preferential usage of codons rarely used in E. coli, the transcription of the genes, assembly of subunits, and high levels of enzyme activity indicate the genes were well expressed in E. coli.

Agricultural soils in Nova Scotia are usually limed in order to raise soil pH to ensure optimum availability of soil nutrients. Wood ash, produced by burning wood-based fuels, is promoted as a substitute for agricultural lime. This study individually assessed two wood ash sources available to Nova Scotia producers through on-farm sampling as well as greenhouse bioassay and incubation experiments. The variables measured were soil pH, plant-available and total element concentrations in soil, total element concentrations in above ground plant tissue, botanical composition and pasture condition scores (PCS). Soil pH was significantly increased after the application of wood ashes, however the effect was short-lived for one ash (NewPage). Agricultural lime was the most effective at increasing pH. Total soil concentrations of Al, Cr, K and Na remained elevated one year after ash application to NewPage sites. Brooklyn Power ash contained excessive levels of Zn, Cd, Pb and As.

Effects of superheated steam drying were determined for surface properties and pore structure of paper, properties which are important in the end use of paper. Two furnishes were investigated, thermomechanical pulp (TMP) and a TMP/kraft pulp blend. Drying of handsheets under matched conditions in air was used as the basis of comparison. / TMP paper dried in superheated steam has a slightly higher surface roughness, by about 0.5 $ mu$m at a roughness around 8 $ mu$m. This difference decreases with drying fluid temperature. It is also reduced by about half after a very light blade coating. Surface roughness of paper from 50/50 TMP/kraft blend is unaffected. / Superheated steam drying reduces substantially the linting propensity of TMP paper, by about 30%-60% depending on the criteria used. Improved lignin softening by higher web temperature from the beginning of drying in superheated steam drying is believed an important mechanism in improving bonding of surface fines and short fibre fragments. / The Z-direction bond strength of TMP paper after surface treatment with water is about 20% higher for sheets dried in steam. Time for water absorption is 100%-150% longer for superheated steam dried TMP paper and contact angle of water is also substantially increased. / Superheated steam drying substantially reduces the volume of micropores of diameter 0.2-0.6 $ mu$m while having no significant effect on larger pores. Thus superheated steam drying affects only the pore structure of the micronetwork. The decrease of micropore volume in superheated steam drying is associated with an increase of Z-direction bond strength and a decrease of light scattering coefficient.

The fundamental objectives of this research is to produce and study magnetically loaded fibers and magnetic paper. The lumen-loading of commercially available ferrimagnetic (Fe$ sb3$O$ sb4$, $ gamma$-Fe$ sb2$O$ sb3$) and ferromagnetic (CrO$ sb2$) pigments was first performed as a "physical" approach to prepare magnetic paper. Our experiments resulted in the determination of the "kraft pulp/$ gamma$-Fe$ sb2$O$ sb3$ pigment" composite as an optimal combination of optical, mechanical and magnetic properties. / We have also developed a "chemical" process for the preparation of magnetic fibers which consists of using a cellulosic substrate with ion-exchange properties for Fe(II), i.e. Na-carboxymethylcellulose, as a host matrix for the growth of very small iron oxide particles. The in situ oxidation reaction of Fe(OH)$ sb2$ in the fiber cell walls yielded to superparamagnetic ferrite particles of about 100 A. / Because magnetism is a value added property for paper, our specialty fibers allow exploration of new concepts in papermaking (e.g. fiber orientation during paper formation), information storage, paper handling in copiers, magnetographic printing, etc.

A new experimental apparatus for high intensity through drying of paper was constructed and commissioned. The principal direct measurements with this facility are the air flow rate, and on-line measurements from beginning to end of the drying of the air temperature and pressure above and below the sheet, the sheet surface temperature on the flow inlet side and the local moisture content of a 2.5 mm diameter spot of the sheet. The equipment, constructed for the use of either air or superheated steam as the drying fluid, was commissioned with air as the drying medium. This facility was tested using three levels of drying air temperature, 90$ sp circ$, 200$ sp circ$, and 300$ sp circ$C, for through-flow rates up to those for which pressure drop across the sheet did not exceed 40 kPa. Papers from kraft, TMP and blended furnishes of grammage between 44 and 100 g/m$ sp2$, were dried from a range of initial moisture contents. / Sheet moisture content was measured on-line with a custom made, 3-wavelength transmission-type infra-red moisture sensor with optical fibre leads permitting installation inside the dryer. / For the kraft and TMP papers for which satisfactory moisture sensor calibrations were obtained, the moisture content-time drying history curves were processed to yield drying rate curves with the instantaneous drying rate as a function of local sheet moisture content. (Abstract shortened by UMI.)

The effect of drying paper by direct contact with superheated steam was determined with respect to the physical, optical and chemical properties of the dried sheet. The results were compared with those for paper dried in a similar fashion by direct contact with hot air. / It was found that the results depended on the type of pulp from which the sheet was made. For thermomechanical pulp sheets, superheated steam drying resulted in improved strength properties; burst index, tensile index and elastic modulus were 20-30% higher relative to the air dried sheets. The increase in strength was found to be due to an increase in bonded area, especially of the fine fraction, caused by the higher sheet temperatures occurring in the constant rate period of steam drying. As a result of the increased bonding but not due to any color change, brightness of the steam dried sheet decreased by 5 points. Steam drying of TMP sheets results in strength and optical properties more characteristic of paper made from CTMP. / Superheated steam drying of kraft pulp sheets had a smaller and opposite effect, as strength properties decreased and optical properties increased relative to the properties of sheets dried in air. Unlike mechanical pulp, no increase in bonded area was observed because of the already high bonding potential of kraft fibres; a thermally induced drying stress relaxation is thought to be the cause of the decreased strength properties.

No description available.

Pulp fibers can be spouted in a conical vessel if the inlet Reynolds number is above a critical value which varies linearly with mass of pulp in the vessel. Continuous pulp spouting is also feasible in a wedge-like vessel within certain limits of flow rate and inlet pulp consistency. Spouting hydrodynamics and particle separation behavior in both vessels were investigated for pulp fibers and recycled pulp suspensions. / The minimum spouting velocity (MSV), spouting stability and the pressure drop-flow rate relationship were determined for liquid spouting of pulp fibers and of rigid particles. Liquid spouting of rigid particles is similar to gaseous spouting; pulp spouting is different. The liquid flow field in a conical spouted bed of pulp fibers is of a jet expansion type. A model for predicting the MSV for spouting pulp fibers was developed based on visual observation of the transition of the jet flow patterns in the conical vessel. / Small particles including both ink and pulp fines can be elutriated from a spouted bed of a recycled pulp suspension, with little fiber loss, in both semi-batch and continuous modes using conical and wedge-like vessels, respectively. Both processes were studied using on-line measurement of the exit particle concentration. / For the semi-batch process, the first order elutriation coefficient increased with the flow rate, but was about the same for all pulps. Based on the analysis of the flow field around a porous spherical particle in a shear flow, an elutriation model was developed for fine particle removal from a suspension of porous coarse particles. For the continuous operation, the particle separation mechanism and the fractional particle removal were investigated. Separation occurs by excluding fibers from the top stream, while fines are split according to the ratio of top to bottom flow rates.

No description available.

The purpose of this research was to improve and apply to industrial conditions the 3-D computer simulation of the impregnation and pulping of wood developed using large handmade wood blocks by Morin (Ph.D. theses, McGill 1994). The simulation, written in Fortran 77, predicts the convection, diffusion, and reaction mechanisms in CMP and CTMP pulping processes. Chemicals concentration profiles inside the chips can be obtained at any point of time during impregnation and pulping. / The simulation was rendered practical and easy to use by reducing the required input parameters to known operating conditions. Correlations between sapwood and heartwood chips fundamental properties and operating conditions were developed and integrated into the program. Experiments with different combinations of pre-treatments were performed using a mixture of sapwood and heartwood black spruce chips of different thicknesses. The experimental results were used to modify and improve the computer model. / The program was shown to accurately predict the impregnation concentration profiles for all experiments.