Five different combinations of Hydraulic Retention Times (HRT) and temperatures were used in a two stage (feed and test reactor) Autothermal Thermophilic Aerobic Digestion System to assess the impact of these parameters on the production of odorous gases. The gases monitored were hydrogen sulphide, dimethyl sulphide, methyl mercaptan, ammonia, and amines. Other liquid parameters were also monitored in order to better understand the impacts of temperature and HRT. These parameters are total solids content, volatile solids content, volatile solids destruction, specific oxygen uptake rate, alkalinity, ammonia concentration, and pH. In order to assess the character of the sludge and understand the digestion process the carbohydrate, fat, and protein content were also measured in the inputs and in the test reactor. It was found that all of the odorous compounds measured were affected by stage of digestion and temperature more than by HRT. Of the five compounds monitored, none were affected by changes in the HRT of the test reactor. However, the concentrations measured in the feed and test reactors were often a degree of magnitude apart. The reduced sulphur compounds (hydrogen sulphide, methyl mercaptan, and dimethyl sulphide) were found in higher concentrations in the feed reactor than in the test reactor; whereas ammonia and amines were found in much higher concentrations in the test reactor than in the feed reactor. Also, ammonia concentrations were significantly higher in both reactors when the temperature was higher; and amine concentration was higher in the test reactor when the temperature was higher. One set of tests for volatile fatty acid concentration was also undertaken. While breakdown of the carbohydrates and fats occurred throughout the process, proteins were broken down into their amino acids, releasing reduced sulphur compounds in the feed reactor and then deaminated, releasing ammonia and amines in the test reactor. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Field studies were conducted at Lincoln University of Missouri (USA) and Hokkaido University (Japan) to: (i) study the relationships between greenhouse gases emissions and soil properties, (ii) assess the influence of agricultural practices on greenhouse gas fluxes and soil properties and (iii) improve the quantification of greenhouse gases from soil in agricultural fields using geospatial technologies. Results showed that besides soil temperature (T), soil thermal properties such as thermal conductivity (K), resistivity (R) and diffusivity (D) and soil pore spaces indices such as the pore tortuosity factor and the relative gas diffusion coefficient (Ds/Do) are controlling factors for greenhouse gases emissions. Soil thermal properties correlated with greenhouse gases emissions when soil temperature could not. The study has found that predicted Ds/Do and correlate with greenhouse gas fluxes even when the air-filled porosity and the total porosity from which they are predicted did not. We have also showed that Ds/Do and can be predicted quickly from routine measurements of soil water and air and existing diffusivity models found in the literature. Agricultural practices do seriously impact greenhouse gases emissions as showed by the effect of mechanized tillage operations on soil physical properties and greenhouse gas fluxes in a corn and soybean fields. In fact, our results showed that tractor compaction increased soil resistance to penetration, water, bulk density and pore tortuosity while reducing air-filled porosity, total pore space and the soil gas diffusion coefficient. Changes in soil properties resulted in increased CO2, NO and N2O emissions. Finally, our results also confirmed that greenhouse gas fluxes vary tremendously in space and time. As estimates of greenhouse gas emissions are influenced by the data processing approach, differences between the different calculation approaches leads to uncertainty. Thus, techniques for developing better estimates are needed. We have showed that Geographic Information Systems (GIS), Global Positioning System (GPS), computer mapping and geo-statistics are technologies that can be used to better understand systems containing large amounts of spatial and temporal variability. Our GIS-based approach for quantifying CO2, CH4 and N2O fluxes from soil in agricultural fields showed that estimating (extrapolating) total greenhouse gas fluxes using the “standard” approach – multiplying the average flux value by the total field area – results in biased predictions of field total greenhouse gases emissions. In contrast, the GIS-based approach we developed produces an interpolated map portraying the spatial distribution of gas fluxes across the field from point measurements and later process the interpolated map produced to determine flux zones. Furthermore, processing, classification and modeling enables the computation of field total fluxes as the sum of fluxes in different zones, therefore taking into account the spatial variability of greenhouse gas fluxes.

No description available.

No description available.

The preionization of a shock tube's gas before the shock passes through it is called the precursor effect. An experimental and theoretical study has been carried out on precursor ionization in an electromagnetic shock tube. The precursor ionization was detected with different types of electric probes and also with photoraaltipliers. Extensive experiments indicated that the ionization was not due to diffusion of particles from the discharge in the shock tube driver. The ionization is primarily caused by radiation from the discharge of wavelengths less than 2000 Å. Radiation from the shock front makes a negligible contribution to the ionization. Langmuir double probe measurements indicated that the gas was about 0.1% ionized and that the electrons in the precursor were not in thermal equilibrium with the gas atoms and ions. The time interval between detection of ionization at two stations was independent of the shock tube gas (air, argon, helium), and corresponded to a propagation speed greater than 1/20 the speed of light. The precursor had a main component lasting about 50 microseconds with ionization proportional to the square of the discharge current. There was also a weaker component which lasted for about 500 microseconds. The experimental results can be understood in terms of a theoretical model based on black body radiation. Considering the driver to act as an infinite slab radiator, whose temperature is a function of the discharge parameters, an expression is derived for the number of photons emitted in some frequency interval. Assuming the electron density to be proportional to radiation absorption from such a radiator, the electron density variation with distance from the driver can be adequately understood. When the shock tube is considered to behave as a transmission line, whose resistance per unit length is proportional to the electron density, one can explain the variation of the shock tube's gas potential both with distance from the driver and with time. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A superheterodyne Dicke type radiometer suitable for the measurement of radiation from a high temperature plasma in the 35 GHz range has been developed. The radiometer employs a balanced mixer at the radiometer frequency, a 3.5 GHz parametric amplifier using a varactor diode as the first IF amplifier, a broad-band transistor amplifier at the second IF of 7Q MHz and a commutator detector. The performance of the radiometer has been measured by conducting hot load tests and by using an S-band argon noise source. The minimum detectable temperature change was found from the hot load tests to be 11 deg K for an output bandwidth of 0.32 Hz. However, from argon noise source measurements, a minimum detectable temperature change of 1.4 x 10³ deg K was determined for an output bandwidth of 6.4 KHz and 9.5 x 10³ deg K for an output bandwidth of 160 KHz. The equation for the minimum detectable temperature change for the Dicke radiometer has been deduced following conventional analysis. It has been found that there are two errors in Goldstein's derivation the effects of which cancel out and his final formula is correct. Thus, the change suggested by Ring does not appear to be valid. For the two channel subtraction radiometer it has been found that the expression given by Graham should be multiplied by √2. The d.c. radiometer has also been analysed and it has been found that its minimum detectable signal power is independent of both the radiometer bandwidth and the output bandwidth. The effect of noise at the radiometer input before the modulating switch has been investigated and it is shown that this noise could produce a cutoff condition in the Dicke radiometer and the two channel subtraction radiometer. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The spin relaxation time, T₁, has been measured at low densities in normal H₂ at 77°K, 196°K, 298°K and 392°K as a function of density using a 96 mHz pulsed N.M.R. spectrometer and a T₁ minimum obtained. The data at 77°K, where only the J=1 rotational state is populated, is fit by the conventional theories, but the results at higher temperatures are not explained by the generalization of the Bloom-Oppenheim⁽⁶⁾ theory. T₁ was also measured as a function of density for a mixture of 54.5% He in at 298°K in an effort to investigate the role of transitions between J states in the relaxation process. The spin relaxation time T₁ was also measured in HD as a function of density in the region of the T₁ minimum at 196°K and 298°K. Since the most recent theory has not been extended to a system of several populated J levels the results are rather inconclusive. T₁ was also measured in CH₄ as a function of density in the region of the T₁ minimum at 196°K and 298°K and information about the rotational coupling constants obtained. From these results it is concluded that measurements of T₁ as a function of density is very useful in testing theories of relaxation and obtaining information on the rotational coupling constants for polyatomic molecules. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Part I An efficient ionizer designed for the ionization of a low intensity molecular beam has been developed. The ionizer will have an efficiency for an argon beam at room temperature and 0.8 amperes plate electron current of greater than 5.3% and for an helium 4 beam at room temperature and 0.8 amperes plate electron current of greater than 0.12%. The electron bombardment ionization occurs between two flat plates both of which are at 200 volts potential with respect to the cathode. The two plates are at a 2.5° angle to each other so that the ions once formed experience a field gradient produced by this angle which accelerates them out the open side of the ionizer 90° to the direction of the incident neutral beam. The electrons were emitted from 6, 0.030 x 0.004 inches, thoriated tungsten ribbon filaments heated by d.c. power. Successful activation of the filaments, however, was not achieved and so they were used as pure tungsten filaments. The ionizer ran at between 1900° Kelvin and 2600°Kelvin for about 8 hours without significant distortion, filament sag, or appreciable outgassing. Part II The design of a source of doubly charged helium ions was carried out to provide an helium beam of twice the terminal energy of the Van de Graafe Accelerator. The unit, to be installed in the top terminal of the Van de Graaffe, employs a radio frequency ion source followed by a double focusing magnet. The magnet has plane parallel pole pieces with a fringing field that produces focusing in a vertical plane. The unit is designed so that at 2.5 kilovolts extraction voltage a magnetic field of 3060 gauss is required to bend the He⁺⁺ through an angle of 90° and bring them to a focus at 5.8 cm. from the exit face of the magnet. The beam acceptance angle of the magnet is 10° at a source distance from the entrance face of 5 cm. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A Rogowski coil has been used for the measurement of a pulsed discharge current. The frequency response of the coil is discussed, and a method which extends this response to higher frequencies (100 Mc/s) is described. It has been found that the noise signals associated with the measurement of a pulsed discharge current are due principally to the electromagnetic radiation from the spark gap switches which are required in such a circuit. The radiation depends upon the breakdown mechanism of the spark gap, and its effect upon the measuring circuit can be minimized by making use of damping, resistors in series with the triggering sparks, shielded cables in the measuring circuit, and careful grounding of the discharge circuit. The noise signal on the current wave form can be completely eliminated by altering the spark gap geometry of the open air spark gap switch. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The spin-lattice relaxation time has been studied in normal H₂ as a function of density and temperature in the range 293°K - 700°K. The measurements were made in the region where T₁ α [formula omitted]. The H₂ results have been interpreted using the Bloom-Oppenheim theory in which the transitions between different J states were taken into account. The analysis indicates that the resonant transitions (1,3↔3,1) and quasi-resonant transitions (1,2↔3,0) and (1,4↔3,2) contribute significantly to the relaxation mechanism. The anisotropic inter-molecular potential between the two H₂ molecules which depends on the orientation of both the molecules could be given by quadrupole-quadrupole interaction while the part that depends on the orientation of one of the molecules alone was found to be adequately represented by a Lennard-Jones potential. T₁ was measured in H₂ - He and H₂ - CO₂ mixtures as a function of density and composition in the temperature range 293°K - 700°K. The analysis indicates that the interaction potential for H₂ - He could be adequately described by a Lennard-Jones potential while the dominant interaction for H₂ - CO₂ could be given by quadrupole-quadrupole interaction. There were indications that the dependence of T₁/[formula omitted] in H₂ - He mixture on the percentage of He is non-linear above 150°K. However, this was not found to be the case in H₂ - CO₂ mixtures. T₁ was also measured in CH₄ and CH₄ - He mixture as a function of density and composition in the same temperature range. The data can be fitted by T₁/[formula omitted] = AT⁻ⁿ where n takes the value of 1.5 for pure CH₄ and 0.79 for CH₄ gas infinitely diluted in He. The analysis based on the existing theory for polyatomic gases shows that the intermolecular potential for CH₄ - CH₄ and CH₄ - He could be described by medium range potentials. The results indicate that the dependence of T₁/[formula omitted] on the percentage of He is not linear below 4OO°K. / Science, Faculty of / Physics and Astronomy, Department of / Graduate