Contamination of groundwater by petroleum-hydrocarbons is a serious environmental problem. Monitored natural attenuation (MNA) is a passive remedial approach to degrade and dissipate contaminants in groundwater. In this study, a full-scale natural bioremediation investigation was conducted at a gasoline spill site. Results show that the concentrations of major contaminants [benzene, toluene, ethylbenzene, and xylenes (BTEX)] dropped to below detection limit before they reached the downgradient monitor well. This indicates that natural biodegradation process was the major cause of the contaminant reduction. In this study, 1,2,4-trimethylbenzene (1,2,4-TMB) was used as tracer to calculate the biological decay rates of BTEX. The calculated biological first-order decay rates for ethylbenzene, m+p-xylene, toluene, benzene, and o-xylene were 1.5¡Ñ10-3, 1.2¡Ñ10-3, 7.0¡Ñ10-4, 6.7¡Ñ10-4, and 1.2¡Ñ10-4, respectively. Mann-Kendall test was applied to analyze the trend of contaminant variations. Results show that the S-value of four monitor wells (CT-4, CT-41, CT-42, and CT-7) were -0.52, -1.57, -0.52, and -1.22, respectively. The negative S values reveal that the all contaminants tended to decrease. This indicates that the hydrocarbon plume at this site is not expanding, and has been contained effectively by the natural attenuation mechanisms. Evidences for the occurrence of natural attenuation include the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial species; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Results also show that the biodegradation capacity (46.02 mg/L) for BTEX and 1,2,4-TMB was much higher than the detected contaminants within the plume. Results indicate that natural attenuation can effectively contain the plume, and biodegradation processes played an important role on contaminant removal.

The CISPR of IEC in European and the ANSI in American use the model of site attenuation to evaluate and quantify the quality of OATS. The ANSI also uses the concept of Normalized Site Attenuation (NSA) to eliminate the effects brought about by different antennas, which may cause the inaccuracy of site attenuation. To stringently require the quality of OATS, the measured values of NSA have to be compared with the theoretical ones. If their differences are within (+/-)4 dB at all frequencies, the test environment of the OATS can be accepted. At present, the theoretical values of NSA are used as a standard for verifying the OATS in the world. However, many non-ideal factors derived from certain assumptions and simplifications of the NSA may cause the measured NSA to deviate from the theoretical values. To understand the manner and extent of the effects, in this thesis we find out the non-ideal factors by studying the NSA by numerically simulating the effects of each factor on NSA measurement by the method of moment (MoM), and the results are analyzed and discussed. We find that there is a difference of 6 dB on the NSA when the impedance of the receive antenna is mismatched. Meanwhile, we also study the relationship between the conductivity of non-perfect electrical conductor and the ideal value of NSA. We conclude that a ground plane made by metal can be regarded as a PEC one. However, the values of NSA will increase if the conductivity of ground plane is below 1000 S/m. Besides, considering the humid Taiwan climate in particular, we investigate the condition of a thin layer of water covering the ground plane after rain and the results show that the effect of the water plane will decrease the values of NSA. As for the measurement at a distance of 3 m, a deviation of 2 dB at low frequencies arises from the effect of near field for the case of horizontal polarization. Finally as for the non-conducting table in OATS, our results show that the larger values of relative permittivity and conductivity of table result in the larger change of NSA value. The difference can be 3 dB for the case with a wooden table. With results of our research, the effects of non-ideal factors on NSA measurement can be comprehended clearly. The comparison of the differences also can be used as a reference for the modification of the NSA measurement in the future.

This thesis first discusses the ground plane effects of a test site on the antenna factors (AFs) of hybrid antenna (biconical log-periodic dipole array). Meanwhile, the effects of mutual coupling between antenna and its image, and the variation of active phase center are also discussed. From these analyses, a hybrid method, based on the modified SSM (Standard Site Method) and the PCPM (Phase Center and Pattern Matching) applied to the hybrid antenna for NSA (Normalized Site Attenuation) measurement is proposed. By this method, the low geometry- dependent AFs of hybrid antenna can be obtained to produce more reasonable NSA values for a test site. Secondly, this thesis proposes a simple, fast, and accurate method to calibrate the free-space AFs of broadband EMC (Electromagnetic Compatibility) antennas. This method adopts a fixed-height configuration and a MUSIC (MUltiple SIgnal Classification) algorithm. This configuration significantly shortens measurement time and removes height-dependent calibration errors. Meanwhile, the MUSIC algorithm can remove unexpected reflections from the ground plane or any other reflecting objects, by which the free-space AFs can be calculated. In addition, this method can also automatically compensate for the phase center shift, which makes measurement easier and more convenient. To verify this method, the calibrated results are compared with other published standard methods: the mean differences can be as low as 0.25 dB for the LPDA (log-periodic dipole array), 0.42 dB for the hybrid antennas, and 0.36 dB for the horn antennas. Finally, this thesis provides a method of using two equivalent negative inductances from two terminals of three coupled inductors to reduce the parasitic inductances of a typical three-capacitor EMI (Electromagnetic Interference) filter. Theoretical analysis and formula deduction for the design of two equivalent negative inductances are demonstrated. The experimental results show that the insertion losses of a three-capacitor EMI filter at 50 MHz can be reduced by 16.8 dB for the DM (differential-mode) and by 19.2 dB for the CM (common-mode). In Appendix A of this thesis, an extended study of the effect of ground plane on antenna¡¦s radiation is described. A simple V-shape edge-groove design for a finite ground plane can effectively reduce the pattern ripples of a monopole. The optimal design of proposed structure can reduce the peak-to-peak pattern ripples from 26 to 4.5 dB.

Site characterization methods for measuring the occurrence, magnitude, and rate of microbial mediated transformation processes were evaluated to assess the implementation of monitored natural attenuation (MNA) at chlorinated ethenes contaminated sites. A model site in Arizona, the Park-Euclid WQARF site in Tucson, was selected for the study. Field, geochemical, and compound specific carbon isotope fractionation (CSI) data confirm intrinsic biodegradation is occurring in the perched aquifer. Use of the BIOCHLOR model and a screening protocol support the potential for reductive dehalogenation found in the perched aquifer. Biotransformation of tetrachloroethene to cis-1,2-dichloroethene (cis-DCE) was achieved in microcosm studies. Transformation of cis-DCE to vinyl chloride and to ethene is, at the moment, the laboratory rate limiting step. PCR analysis established that the aquifer contains Dehalococcoides sp. and other dechlorinating microorganisms, though genes that encode for enzymes capable of achieving complete dehalogenation of the chlorinated contaminants were confirmed only in one monitoring well. The regional aquifer shows little evidence of intrinsic biodegradation. This study corroborates that CSI analysis can be used as an additional line of evidence to evaluate and verify MNA. Microbial analysis provides relevant information about the capabilities of native microbial communities to carry out reductive dehalogenation and thus, to naturally attenuate chlorinated compounds at a contaminated site. The combination of microcosm studies, CSI analysis, and bacterial DNA identification is becoming a convincing line of evidence for the assessment of MNA application to chloroethenes contaminated sites.

Using a specially constructed Gas Hydrate Resonant Column (GHRC), the University of Southampton explored different methods of hydrate synthesis and measured the properties of the resulting sediments, such as shear wave velocity (Vs), compressional wave velocity (Vp) and their respective attenuation measurements (Qs -1 and Qp -1). Two approaches were considered. The first utilises an excess gas technique, where known water volume in the pore space dictates the quantity of hydrate. The second approach uses a known quantity of methane gas within the water saturated pore space to constrain the volume of hydrate. Results from the two techniques show that hydrates formed in excess gas environments cause stiffening of the sediment structure at low concentrations (3%), whereas, even at high concentrations of hydrate (40%) in excess water environments, only moderate increase in stiffness was observed. Additionally, attenuation results show a peak in damping at approximately 5% hydrate in excess gas tests, whereas in excess water tests, damping continues to increase with increasing hydrate content in the pore space. By considering the results from the two approaches, it becomes apparent that formation method has an influence on the properties of the hydrate bearing sand, and must therefore influence the morphology of the hydrate in the pore space.

Astrophysical models that address stellar energy generation and nucleosynthesis require a considerable amount of input from nuclear physics and are very sensitive to the detailed structure of nuclei, both stable and unstable. Radioactive nuclei play a dominant role in several stellar environments such as supernovae, X-ray bursts, novae etc. and nuclear data are important in the interpretation of these phenomena. When carbon, nitrogen and oxygen isotopes are present in substantial quantities in a star of sufficient mass, the fusion of four hydrogen nuclei to form a helium nucleus proceeds via the CNO cycles. Energy release in the CNO cycles is limited by the long lifetimes of 14O and 15O. In explosive stellar scenarios such as X-ray bursts, the energy output is very large, suggesting a breakout from the CNO cycles. 15O(α,γ)19Ne is the first reaction that breaks out of the CNO cycle. Nuclear structure information on high lying states in 19Ne is required to calculate the rate of the 15O(α,γ)19Ne reaction. This work focuses on the study of states in 19Ne above 3.53 MeV. The lifetimes of five states in 19Ne above 3.53 MeV were measured in this work. The states in 19Ne were populated via the 3He(20Ne,α)19Ne reaction at a beam energy of 34 MeV. The lifetimes were measured using the Doppler Shift Attenuation Method. The lifetimes of five states were measured and an upper limit was set on the lifetime of a sixth state. Three of the measurements are the most precise thus far. The lifetimes of the other three states agree with the values of the only other measurement of the lifetimes of these states. An upper limit on the rate of the 15O(α,γ)19Ne reaction was calculated at the 90% confidence level using the measured lifetimes. The contributions to the 15O(α,γ)19Ne reaction rate from several states in 19Ne at different stellar temperatures are discussed.

It is well known that surface water waves interact with fluid mud on the sea bed. Wave mud interaction results in high wave energy dissipation and mud mass transport. This kind of wave energy dissipation, which generally is much more significant than wave dissipation due to bottom friction, should be considered in the simulation of wave evolution and transformation in muddy coastal environments. In this research, a two-dimensional horizontal wave propagation and morphodynamic model for muddy coasts was developed. The model can be applied on a general three dimensional bathymetry of a soft muddy coast to calculate wave damping, fluid mud transport and resulting bathymetry change under wave action. In addition to the effect of wave-mud interaction on wave propagation, the dissipation due to wave-mud interaction was also implemented in SWAN (a third generation numerical model for Simulating WAves Nearshore) using a multilayered wave mud interaction model. These two models combined can be used for generation and propagation of waves in muddy coastal areas. The nonlinear constitutive equations of the visco-elastic-plastic model are adopted for the rheological behavior of fluid mud in this research. The results of the numerical model are compared against a series of wave-basin experiments, wave flume experiments and field observations. Comparisons between the simulated results with the both field and laboratory data reveal the capability of the proposed model to predict the wave transformation and mud mass transport. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-07-24 11:18:18.622

No description available.

Advances in today’s fast growing communication systems have resulted in congestion in the lower frequency bands and the need for higher capacity broadband services. This has made it inevitable for service providers to migrate to higher frequency bands so as to accommodate the ever increasing demands on radio communication systems. However, the reliability of such systems at these frequency bands tend to be severely degraded due to some natural atmospheric phenomena of which rain is the dominant factor. This is not to say that other factors have become unimportant; however, if attenuation by rain is so severe that a radio link is unavailable for use, then other factors become secondary. Therefore, it is paramount to establish a model capable of predicting the behaviour of these systems in the presence of rain. This study employs a semi-empirical approach for the formulation of rain attenuation models using the knowledge of rain rate, raindrop size distribution, and a signal level measurement recorded at 19.5 GHz on a horizontally polarized terrestrial radio link. The semi-empirical approach was developed by considering the scattering effect of an electromagnetic wave propagating through a medium containing raindrops. The complex forward scattering amplitudes for the raindrops are determined for all raindrop sizes at different frequencies, utilizing the Mie scattering theory on spherical dielectric raindrops. From these scattering amplitudes, the extinction cross-sections for the spherical raindrops are calculated. Applying the power-law regression to the real part of the calculated extinction cross-section, power-law coefficients are determined at different frequencies. The power-law model generated from the extinction crosssection is integrated over different raindrop-size distribution models to formulate theoretical rain attenuation models. The developed rain attenuation models are used with 0.01 R rain rate statistics determined for four locations in different rain climatic zones in South Africa to calculate the specific rain attenuation. From a horizontally polarized 6.73 km terrestrial line-of-sight link in Durban, South Africa,experimental rain attenuation measurements were recorded at 19.5 GHz. These rain attenuation measurements are compared with the results obtained from the developed attenuation models with the same propagation parameters to establish the most appropriate attenuation models that describe the behaviour of radio link performance in the presence of rain. For the purpose of validating the results, it is compared with the ITU-R rain attenuation model. This study also considers the characteristics and variations associated with rain attenuation for terrestrial communication systems. This is achieved by utilizing the ITU-R power-law rain attenuation model on 5-year rain rate data obtained from the four different climatic rain zones in South Africa to estimate the cumulative distributions of rain attenuation. From the raindrop size and 1-minute rain rate measurement recorded in Durban with a distrometer over six months, rain events over the six months are classified into drizzle, widespread, shower and thunderstorm rain types and the mean rain rate statistics determined for each class of rain. Drop-size distribution for all the rain types is estimated. This research has shown a statistical analysis of rain fade data and proposed an empirical rain attenuation model for South Africa localities. This work has also drawn out theoretical rain attenuation prediction models based on the assumption that the shapes of raindrops are spherical. The results predicted from these theoretical attenuation models have shown that it is not the raindrop shapes that determine the attenuation due to rain, but the raindrop size distribution and the rain rate content in the drops. This thesis also provides a good interpretation of cumulative rain attenuation distribution on seasonal and monthly basis. From these distributions, appropriate figures of fade margin are derived for various percentages of link availability in South Africa. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2010.

In today's rapidly expanding communications industry, there is an ever-increasing demand for greater bandwidth, higher data rates and better spectral efficiency. As a result current and future communication systems will need to employ advanced spatial, temporal and frequency diversity techniques in order to meet these demands. Even with the utilisation of such techniques, the congestion of the lower frequency bands, will inevitably lead to the increased usage of the millimetre-wave frequencies in terrestrial communication systems. Before such systems can be deployed, radio system designers require realistic and readily useable channel and propagation models at their disposal to predict the behaviour of such communication links and ensure that reliable and efficient data transmission is achieved The scattering and attenuation of electromagnetic waves by rain is a serious problem for microwave and millimetre-wave frequencies. The conversion of rain rate to specific attenuation is a crucial step in the analysis of the total path attenuation and hence radio-link availability. It is now common practice to relate the specific attenuation and the rain rate using the simple power law relationship. The power-law parameters are then used in the path attenuation model, where the spatial variations of rainfall are estimated by a path-integration of the rain rate. These power law parameters are strongly influenced by the drop-size-distribution (DSD). Thus an examination of the various DSDs and their influence on the specific attenuation and link availability is warranted. Several models for the DSD have been suggested in literature, from the traditional exponential, to the gamma, log normal and Weibull distributions. The type of DSD varies depending on the geographical location and rainfall type. An important requirement of the DSD is that it is consistent with rain rate (i.e. the DSD must satisfy the rain-rate integral equation). Thus before application in the specific attenuation calculations, normalisation needs to be performed to ensure the consistency, as done in this study. Once the specific attenuation has been evaluated for necessary frequency and rain-rate range, path averaging is performed to predict the rain attenuation over the communication link. The final step in this dissertation is the estimation of the percentage of time of such occurrences. For this, cumulative time statistics of surface point rain rates are needed. The resulting cumulative distribution model of the fade depth and duration due to rain is a valuable tool for system designers. With such models the system designer can then determine the appropriate fade margin for the communication system and resulting period of unavailability for the link / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.