A challenge in Underwater Acoustics is identifying the independent variables associated with an environment’s ambient noise. A strict definition of ambient noise would focus on non-transient signatures and exclude transient impacts from marine mammals, pelagic fish species, man-made sources, or weather events such as precipitation or wind speeds. Recognizing transient signatures in acoustic spectra is an essential element for providing environmental intelligence to the U.S. Navy, specifically the acoustic signatures from meteorological events. While weather event detection in acoustic spectra has been shown in previous studies, leveraging these concepts via U.S. Navy assets is largely an unknown. Environmental intelligence collection can be improved by detecting precipitation events and establishing wind velocities with acoustic signatures. This will further improve meteorological models by enabling validation from both manned and unmanned sub-surface assets.

Data on monthly precipitation for three areas of Southern Utah--Beaver, Cedar City and Ephraim--and three areas of Northern Utah--Salt Lake City, Ogden and Logan--where a series of measuring stations were arranged as traverses from the valleys to the mountain tops; were assembled and analyzed. The relationships between elevation and precipitation amounts were shown. The Southern Utah stations were drier at the same elevations than the Northern Utah stations and the differences became greater as the elevations increased. There was a close correlation between the high elevation and low elevation stations in the same traverse even with the above divergence. A higher percentage of the annual precipitation fell during the winter months at the Northern Utah stations than at the Southern Utah stations. These differences were also greater at the high elevations. There appears to be an elevation of maximum precipitation between 9000 and 10,000 feet. The annual precipitation decreases both above and below these elevations. A higher percentage of the years in Southern Utah are near the mean showing more uniformity than the stations in Northern Utah. These difference in not reflected in the numbers of consecutive dry years except when the consecutive years extend beyond 8 wherein the Northern Utah stations have had as many as 14 consecutive years of subnormal precipitation. The Northern Utah stations show the same trend in consecutive wet years, with the Logan record showing as many as 14 consecutive years with above normal precipitation. The Beaver precipitation record shoed a continually decreasing 5-year mean, while Salt Lake City and Logan records showed the opposite trend.

Occult deposition is the direct uptake of cloudwater by vegetation that comes into physical contact with wind-driven cloud droplets. This can be a significant pathway for hydrological and chemical fluxes from the atmosphere to some forests. Methods for estimating cloudwater fluxes to forests are reviewed. Previous studies have neglected the fact that cloudwater is not a conservative atmospheric quantity. This invalidates traditional micrometeorological approaches for estimation of cloudwater fluxes to forests. A theory is developed to predict the change in the cloudwater flux with height due to condensation in the updrafts of orographic cloud, allowing estimation of surface uptake via eddy correlation measurements while accounting for condensation. The performances of three microphysical instruments are examined. From collocated measurements, errors in cloud liquid water content are determined for a Particulate Volume Monitor (PVM) and a Forward Scattering Spectrometer Probe (FSSP) to be less than 0.01 g m⁻³ and 0.035 g m⁻³ respectively. Similarly, the error bounds for surface-normal cloud liquid water fluxes are found to be 2 mg m⁻² s⁻¹ for the PVM and 3.5 mg m⁻² s⁻¹ for the FSSP. Smaller errors are found to be associated with the uncertainty in the direction of the flux relevant to surface uptake. The FSSP is seen to have larger errors when droplet concentrations exceed 600 cm⁻³. A vertical divergence is detected in the cloudwater flux; the downward flux decreases with increasing distance from the surface, usually changing sign by 15 m above ground. Five candidate processes are identified as possible explanations for this measured flux divergence. A scale analysis shows that the liquid water source (condensation due to pseudoadiabatic ascent) is largely responsible for the change in flux with height. Accounting for the change in flux with height results in a near doubling of the estimated surface flux relative to the flux measured at a height of 10 m in the surface layer for this silver fir forest. This factor applies to chemical as well as liquid water fluxes. This source of liquid water also is seen to be important in developing a simple model for cloudwater deposition. / Graduation date: 1997

Low phosphate fertilizer efficiency in high pH soils is primarily due to the retardation of P movement in the soil-P fertilizer reaction zone. The objective of this study was to obtain fundamental information on the influence of multi-ionic interactions on the solubility and diffusion of P in columns containing a model soil system and two soil types. The study also aimed to identify the salt combinations and factors that have the potential to enhance the solubility and movement of P in calcareous soil condition. The results showed that the interaction of NH4+ and SO42- was consistent at enhancing the water solubility and movement of P under a high soil pH condition. This effect was attributed to the combination of various mechanistic factors associated with (NH4)2SO4 compound including significant pH reduction, cation exchange reaction of NH4+ with the exchangeable Ca2+, and anionic competition of SO42- with P for precipitation with Ca2+. / October 2006

Microstructural evolution during heat treatment and the precipitation hardening response of Mg-Ca-Zn alloys were investigated. The binary Mg-2.5Ca alloy was chosen as the base alloy and the effects of adding one and two wt% zinc on the microstructural characteristics and precipitation hardening of the alloy system were studied. The as-cast microstructure of all three alloys showed dendritic solidification of α-Mg and the formation of the eutectic mixtures and/or multiple phases within the interdendritic regions. Homogenization heat treatment of the binary alloy removed the dendritic structure of α-Mg and spherodized the lamellar eutectic of α-Mg+Mg2Ca. Homogenization heat treatment in the ternary Mg-Ca-Zn alloys resulted in the formation of α-Mg grains with Mg2Ca and zinc-containing particles mainly dispersed along the grain boundaries. The EDS analysis suggested that zinc is incorporated in Mg2Ca particles. To study the precipitation hardening response of the alloys, homogenized alloys were aged at 175°C, 200°C and 220°C. At all three isothermal aging temperatures, the binary alloy showed only a slight increase in hardness, i.e. from 50 VHN in the homogenized state to approximately 53 VHN when peak aged. On the other hand, adding zinc was found to promote the age hardening response of the ternary alloys and caused the hardness to increase up to 70 VHN at the peak-aged condition. To further study the precipitation hardening behavior of the alloys, DSC and IC studies were conducted on the homogenized, as–quenched, alloys. The DSC result of the binary alloy showed only one exothermic heat effect, while the ternary alloys showed multiple exothermic peaks. Analysis of the DSC and IC traces, along with the evaluation of the slight increase in microhardness, suggested that non-coherent equilibrium precipitates formed in the aged binary alloy. In addition, it was suggested that the formation of coherent precipitates during aging can be the cause of the pronounced increase in hardness in the aged ternary alloys. The IC traces of the alloys were used to evaluate the kinetics of precipitation in the ternary alloys. It was concluded that increasing aging temperature from 175°C to 220°C greatly increased the precipitation rate. Finally the JMAK model was fit to the experimentally analyzed data for the evolution of the relative volume fraction of precipitates. It was found that the experimentally analyzed data was reasonably well described by the JMAK model. The corresponding JMAK kinetic parameters k and n were relatively close for the two ternary alloys at any aging temperature. The temperature dependence of k was modeled using the Arrhenius-type rate relationship. This analysis resulted in a smaller value for the apparent activation energy in the ternary alloy containing the higher zinc level, i.e. in Mg-2Ca-2Zn alloy.

The microstructural evolution and mechanical properties at elevated temperatures of a recently fabricated fine-grained AA6xxx aluminium sheet were evaluated and compared to the commercially fabricated sheet of the same alloy in the T4P condition. The behaviour of the fine-grained and T4P sheets was compared at elevated temperatures between 350°C and 550°C, as well as room temperature. Static exposure to elevated temperatures revealed that the precipitate structure of the fine-grained material did not change extensively. The T4P material, however, underwent extensive growth of precipitates, including a large amount of grain boundary precipitation. At room temperature, the T4P material deformed at much higher stresses than the FG material, but achieved lower elongations. Deformation at elevated temperatures revealed that the fine-grained material achieved significantly larger elongations to failure than the T4P material in the temperature range of 350°C-450°C. Both materials behaved similarly at 500°C and 550°C. Above 500°C, the grain size was greatly reduced in the T4P material, and only a slightly increased in the fine-grained material. At temperatures above 450°C, the elongation to failure in both materials generally increased with increasing strain-rate. The poor performance of the T4P material at low temperatures was attributed to the precipitate characteristics of the sheet, which lead to elevated stresses and increased cavitation. The deformation mechanism of both materials was found to be controlled by dislocation climb, accommodated by the self diffusion of aluminium at 500°C and 550°C. The deformation mechanism in the fine-grained material transitioned to power law breakdown at lower temperatures. At 350°C to 450°C, the T4P material behaved similarly to a particle hardened material with an internal stress created by the precipitates. The reduction in grain size of the T4P material after deformation at 500°C and 550°C was suggested to be caused by dynamic recovery/recrystallization. The role of a finer grain-size in the deformation behaviour at elevated temperatures was mainly related to enhanced diffusion through grain boundaries. The differences in the behaviour of the two materials were mainly attributed to the difference in the precipitation characteristics of the materials.

Microstructural evolution during heat treatment and the precipitation hardening response of Mg-Ca-Zn alloys were investigated. The binary Mg-2.5Ca alloy was chosen as the base alloy and the effects of adding one and two wt% zinc on the microstructural characteristics and precipitation hardening of the alloy system were studied. The as-cast microstructure of all three alloys showed dendritic solidification of α-Mg and the formation of the eutectic mixtures and/or multiple phases within the interdendritic regions. Homogenization heat treatment of the binary alloy removed the dendritic structure of α-Mg and spherodized the lamellar eutectic of α-Mg+Mg2Ca. Homogenization heat treatment in the ternary Mg-Ca-Zn alloys resulted in the formation of α-Mg grains with Mg2Ca and zinc-containing particles mainly dispersed along the grain boundaries. The EDS analysis suggested that zinc is incorporated in Mg2Ca particles. To study the precipitation hardening response of the alloys, homogenized alloys were aged at 175°C, 200°C and 220°C. At all three isothermal aging temperatures, the binary alloy showed only a slight increase in hardness, i.e. from 50 VHN in the homogenized state to approximately 53 VHN when peak aged. On the other hand, adding zinc was found to promote the age hardening response of the ternary alloys and caused the hardness to increase up to 70 VHN at the peak-aged condition. To further study the precipitation hardening behavior of the alloys, DSC and IC studies were conducted on the homogenized, as–quenched, alloys. The DSC result of the binary alloy showed only one exothermic heat effect, while the ternary alloys showed multiple exothermic peaks. Analysis of the DSC and IC traces, along with the evaluation of the slight increase in microhardness, suggested that non-coherent equilibrium precipitates formed in the aged binary alloy. In addition, it was suggested that the formation of coherent precipitates during aging can be the cause of the pronounced increase in hardness in the aged ternary alloys. The IC traces of the alloys were used to evaluate the kinetics of precipitation in the ternary alloys. It was concluded that increasing aging temperature from 175°C to 220°C greatly increased the precipitation rate. Finally the JMAK model was fit to the experimentally analyzed data for the evolution of the relative volume fraction of precipitates. It was found that the experimentally analyzed data was reasonably well described by the JMAK model. The corresponding JMAK kinetic parameters k and n were relatively close for the two ternary alloys at any aging temperature. The temperature dependence of k was modeled using the Arrhenius-type rate relationship. This analysis resulted in a smaller value for the apparent activation energy in the ternary alloy containing the higher zinc level, i.e. in Mg-2Ca-2Zn alloy.

The microstructural evolution and mechanical properties at elevated temperatures of a recently fabricated fine-grained AA6xxx aluminium sheet were evaluated and compared to the commercially fabricated sheet of the same alloy in the T4P condition. The behaviour of the fine-grained and T4P sheets was compared at elevated temperatures between 350°C and 550°C, as well as room temperature. Static exposure to elevated temperatures revealed that the precipitate structure of the fine-grained material did not change extensively. The T4P material, however, underwent extensive growth of precipitates, including a large amount of grain boundary precipitation. At room temperature, the T4P material deformed at much higher stresses than the FG material, but achieved lower elongations. Deformation at elevated temperatures revealed that the fine-grained material achieved significantly larger elongations to failure than the T4P material in the temperature range of 350°C-450°C. Both materials behaved similarly at 500°C and 550°C. Above 500°C, the grain size was greatly reduced in the T4P material, and only a slightly increased in the fine-grained material. At temperatures above 450°C, the elongation to failure in both materials generally increased with increasing strain-rate. The poor performance of the T4P material at low temperatures was attributed to the precipitate characteristics of the sheet, which lead to elevated stresses and increased cavitation. The deformation mechanism of both materials was found to be controlled by dislocation climb, accommodated by the self diffusion of aluminium at 500°C and 550°C. The deformation mechanism in the fine-grained material transitioned to power law breakdown at lower temperatures. At 350°C to 450°C, the T4P material behaved similarly to a particle hardened material with an internal stress created by the precipitates. The reduction in grain size of the T4P material after deformation at 500°C and 550°C was suggested to be caused by dynamic recovery/recrystallization. The role of a finer grain-size in the deformation behaviour at elevated temperatures was mainly related to enhanced diffusion through grain boundaries. The differences in the behaviour of the two materials were mainly attributed to the difference in the precipitation characteristics of the materials.

The purpose of this dissertation is to enhance the applicability and the accuracy of the Poisson cluster stochastic rainfall generators. Firstly, the 6 parameters of the Modified Bartlett-Lewis Rectangular Pulse (MBLRP) stochastic rainfall simulation model were regionalized across the contiguous United States. Each of the parameters of MBLRP model estimated at 3,444 National Climate Data Center (NCDC) rain gages was spatially interpolated based on the Ordinary Kriging technique to produce the parameter surface map for each of the 12 months of the year. Cross-validation was used to assess the validity of the parameter maps. The results indicate that the suggested maps reproduce well the statistics of the observed rainfall for different accumulation intervals, except for the lag-1 autocorrelation coefficient. The estimated parameter values were also used to produce the maps of storm and rain cell characteristics. Secondly, the relative importance of the rainfall statistics in the generation of watershed response characteristics was estimated based on regression analyses using the rainfall time series observed at 1099 NCDC rain gages. The result of the analyses was used to weigh the rainfall statistics differently in the parameter calibration process of MBLRP model. It was observed that synthetic rainfall time series generated weighing the precipitation statistics according to their relative importance outperformed those generated weighing all statistics equally in predicting watershed runoff depths and peak flows. When all statistics were given the same weight, runoff depths and peak flows were underestimated by 20 percent and 14 percent, respectively; while, when the statistics were weighed proportionally to their relative importance, the underestimation was reduced to 4 percent and 3 percent, which confirms the advantage of weighing the statistics differently. In general, the value of the weights depends on the hydrologic process being modeled. Lastly, a stochastic rainfall generation model that can integrate year-to-year variability of rainfall statistics is suggested. The new framework consists of two parts. The first part generates the short-term rainfall statistics based on the correlation between the observed rainfall statistics. The second part generates the rainfall time series using the modified Bartlett-Lewis rectangular pulse model based on the simulated rainfall statistics. The new approach was validated at 104 NCDC gages across the United States in its ability to reproduce rainfall and watershed response characteristics. The result indicates that the new framework outperformed the traditional approach in reproducing the distribution of monthly maximum rainfall depths, monthly runoff volumes and monthly peak flows.

This thesis aims to fabricate the high performance Magnesium/Carbon-Fiber/PEEK five-layer hybrid nanocomposite laminates. The adopted Mg thin sheets are 0.5mm thick. The Carbon-Fiber/PEEK prepregs were stacked into two lay-ups, such as cross-ply [0/90]s and quasi-isotropic [0/45/90/-45], with the adding of nanoparticles SiO2 spreaded among the laminates. After etching of Mg foils by CrO3-base etchants, a five-layered Mg/Carbon-Fiber/PEEK nanocomposite laminate was made according to the modified diaphragm curing process. Then, the mechanical properties, such as stress-strain curve, strength and stiffness were obtained by tensile test at room temperature (25¢J), 50, 75, 100, 125 and 150¢J and the fatigue properties were also obtained under constant stress amplitude tension-tension cyclic loading elevated at room and elevated temperatures 25, 75, 100, 125 and 150¢J. Finally, the Mg sheets and fractured laminates were observed by the SEM and OM. The results according to the experiments were summarized as follows: 1.The slope of stress-strain curve dropped at strain¡Ü0.0015. It can be inferred that fracture occurred in the laminates at this time. Stiffness approached the theoretical value by curve fitting with the strain range of 0 to 0.0015. 2.The mechanical properties decreased with the environmental temperature rise. 3.The resistance to the temperature effect of the quasi-isotropic Magnesium/Carbon-Fiber/PEEK laminate is superior to that of the cross-ply Magnesium/Carbon-Fiber/PEEK laminate. 4.The cross-ply Magnesium/Carbon-Fiber/PEEK laminate is brittler than that of the quasi-isotropic laminate generally. 5.The irregular bright lines were found in the third etched Mg sheet and that resulted in the delamination of Mg sheet after treatment. The unetched part maybe the defect of Mg sheet. 6. It was found that AZ31 has the precipitation hardening effect at 50¢J and 75¢J.