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Groundwater supplies are threatened by the pervasiveness of dense non-aqueous phase liquid wastes in the subsurface. Most studies treat these wastes as pure solvents, rather than as the mixtures they actually are. To predict the distribution and migration of these wastes in the subsurface, the waste's interfacial properties must be understood. The interfacial tension and contact angle on quartz were studied in tetrachloroethylene (PCE)/water systems containing selected combinations of octanoic acid (OA), dodecylamine (DDA), Aerosol OT (AOT), and alkyl polyoxyethylene glycols (C 12E6, C12E9, and C14E 6). In the OA/DDA mixtures, the interfacial tension was lower than simple addition prediction and the contact angle was increased around neutral pH despite OA itself does not change contact angle. Speciation distribution modeling suggested that the protonated DDA and deprotonated OA formed a neutral complex, whose formation as a function of pH was almost in phase with the synergistic surface activity. This suggested that this complex could be responsible for the positive synergistic interfacial behaviors. In the mixed AOT/C12Ex and mixed nonionic surfactant systems, interfacial tension was higher than the prediction based on simple addition. This negative synergism was attributed to the steric repulsion and repulsive interaction between the hydrophobic tails. The contact angle increases with increasing C12E6 concentration and decreasing aqueous pH and showed a negative synergism upon the addition of AOT, which by itself does not change wettability. The addition of a second nonionic surfactant either had little impact or increased the contact angle. These results can be explained by the variation of surfactant adsorption on quartz and at the PCE/water interface. Different values of contact angle associated with the order of exposure were observed in the nonionic surfactant system and were attributed to irreversible adsorption on quartz. Characterization of the interfacial properties of two real wastes showed that the dry cleaning PCE waste behaved like the model system containing nonionic surfactants and the degreasing TCE waste behaved like the system containing anionic surfactants, a supposition which was substantiated by analysis of the chemical composition of the two wastes.

The computational constitutive Modified Cam Clay Model (MCCM) was developed at Cambridge to study the behavior of clays and has been proven to be effective. In this study, this model is extended to the case of dense sands to analyze the accuracy of the stress-strain behavior. This analysis is based on triaxial test data applied to remolded and compacted sand samples under drained conditions. The laboratory triaxial tests were performed by the Florida Department of Transportation to research the permeability effect in sandy soils compacted up to 95% of maximum unit weight at the optimum moisture content. Each soil sample was tested using different stress paths. In addition, these data were also used to obtain the soil parameters. These soil parameters are used as input data for the Modified Cam Clay Model. Moreover, a computer program in MATLAB was developed based on the MCCM constitutive theory and application in order to predict the stress-strain response for overconsolidated soils under drained condition. Based on observations of the qualitative behavior of these soils, a modification is proposed in this thesis to the original constitutive model to improve the predicted stress-strain behavior. The results of the computer program are typically presented in the deviatoric stress versus shear strain and the stress path plane (deviatoric stress versus mean effective stress). These are the principal plots used for the behavior prediction of soil specimens. Furthermore, the results of the computer program were compared to the laboratory triaxial test data. In general, it is may be concluded that, MCCM with some modification, is applicable to dense sands.

The field of forward laser-accelerated ions and protons is relatively new, existing only since 2000. This work reports on research done at the Center for Ultrafast Optical Science on proton and ion generation from intense terawatt laser interactions with up to 1019 W/cm2 on target. The source of these protons and ions is still of considerable interest, and as such we have conducted several experiments that have shown the front-side and rear-side nature of these sources for our laser conditions. The proton beam quality as a function of target conductivity is discussed, as well as beam profile manipulation via target geometry. The proton beam has also been used to create radioactive isotopes, which have great applications for nuclear medicine.

Considerable attention has been focused on issues relating to groundwater protection and remediation. As a result, significant research has explored on the processes governing dense nonaqueous phase liquid (DNAPL) contaminant migration and entrapment following its release to the subsurface environment. Much of this work has assumed that subsurface materials are completely water-wet even though variations in wettability are likely in the contaminated subsurface. In this work a series of one and two-dimensional experiments was conducted to quantify the effects of solid wettability on DNAPL migration and entrapment in saturated porous media. In the two-dimensional infiltration study the organic-wet sands acted as a very effective capillary barrier, retaining the DNAPL and inhibiting its downward migration. Numerical simulations of this sand box infiltration experiment employing the wettability modified van Genuchten and Brooks-Corey retention functions, in conjunction with the Burdine model, were able to bracket observed DNAPL migration and entrapment behavior. This infiltration study also highlighted the need for a simple predictive retention function model for the broad range of wettabilities that may be encountered in the contaminated subsurface. Such a model, based upon the Leverett and Cassie equations, was developed to predict drainage and imbibition retention functions in fractional water, intermediate and organic-wet systems. This Leverett-Cassie equation was validated with data from number of water/intermediate and water/organic fractional wettability DNAPL/water systems measured in this study, as well as data from two published studies. A series of multistep outflow experiments was also conducted to determine the effects of wettability on fluid flow. A sensitivity analysis found that outflow predictions were very sensitive to the retention function, but fairly insensitive to the selected relative permeability model. In addition simulation results, based upon traditional multiphase flow equations, failed to adequately fit observed outflow rates. To improve the outflow fit, the multiphase flow governing equations were modified to incorporate dynamic capillary pressure effects. Inclusion of a saturation-dependent dynamic capillary pressure effect that significantly improved water outflow and outflow rate fits. Endpoint permeability measurements from these outflow experiments indicate that endpoint relative permeabilities do not approach a value of one at residual saturations, as is typically assumed.

This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescence of ytterbium-doped crystals and glasses. The main results are the observation of intrinsically bistable luminescence at room temperature and chromatic switching at low temperature, reported here for the first time. The nonlinear dynamics responsible for these optical phenomena are shown to arise from ion-ion interactions controlled by the application of resonant electromagnetic fields. On the theoretical side, the classical Lorentz local field correction is shown to be the lowest order term of radiation-driven correlation contributions to local polarization which arise from inter-ion coherences and cooperative relaxation and frequency shifts beyond the dynamic shift are predicted. The nonlinear Maxwell-Bloch equations are extended to describe energy transfer between different species of ions predicting bistability in excited state populations which then emit bistable luminescence as a consequence, and an intensity dependent transfer rate is predicted. Diffusive excitation migration in space is also explored as a possible mechanism for generating multiple instabilities, but is not predicted to give rise to hysteresis loops by itself. On the experimental side, original observations of intrinsic optical switching and hysteresis are reported in the luminescence of Yb:CsCdBr 3 and Yb, Tm:glass. Evidence of cross-coupling between different impurities is also presented, together with spectroscopic details of intrinsic chromatic switching between different luminescent transitions of the acceptor species in Yb, Er:CsCdBr3 excited at the infrared Yb resonance wavelength. Conclusive spectroscopic evidence that excludes thermal effects as responsible for low temperature intrinsic switching is also presented. Room temperature intrinsic optical switching and hysteresis are reported for the first time in bulk Yb,Tm:glass samples. Switching, hysteresis, and clamping of laser output from waveguide channels fabricated in the glass material are also reported and indicate fundamental design limitations for compact optical amplifiers and oscillators.

The evaporation of cold dense objects in relatively hot tenuous plasmas is a subject of interest to several groups of scientists, including astrophysicists, researchers in magnetic fusion energy (MFE), and researchers in inertial confinement fusion (ICF). Analytic models based upon the steady-state hydrodynamic conservation equations are routinely used to estimate the characteristics of the evaporating material. We have developed a computer code that solves the time-dependent hydrodynamic conservation equations. In our simulations, we apply the code to examine the validity of the steady-state models, and to examine the effect of flux-limited thermal conduction in pellet injected tokamak plasmas. We find that the steady-state model examined (Cowie, McKee, Astrophys. J., 211: 135-146, 1977) is reproduced by the time dependent calculations only when assumptions made by the model are included in the simulations. The most significant assumption is found to be the neglect of the cooling wave launched into the hot plasma as energy is conducted to the cloud. Neglecting the cooling wave results in overestimating the mass ablation rate and underestimating the cloud lifetime. Thus, the applicability of the model in astrophysical and MFE environments is compromised. The cooling wave has less of an effect in ICF experiments since the plasma is steadily reheated by the laser pulse. We have simulated the evaporation of fuel pellets injected into tokamak plasmas and compared our results to data from experiments. By matching the calculated and measured excitation radiation emitted by the ablating pellet, we are able to estimate the flux-limit parameter (f) in the flux-limited conduction expression (q = fnv$\sb{\rm t}$kT). We obtain good agreement with the data by using a flux-limit parameter f = 0.2. This is one order of magnitude larger than those typically required in ICF simulations, and is near a maximum value (f $\simeq$ 0.32) estimated by distribution function and zero current arguments. Our calculations reproduce the data without the need to invoke any shielding mechanism to protect the pellet from the plasma. It is common in MFE calculations to require that a neutral gas surround the pellet as it penetrates the plasma so as to reduce the energy flux to the pellet. We find that this neutral gas shield is not present. Finally, the steady-state model of Cowie and McKee does not reproduce our pellet injection results. A steady-state does appear to develop but the density decays spatially as 1/r$\sp{3}$, and the expanding ablatant is sonic (M = 1), scalings which are quite different from those of Cowie and McKee.

Demand for higher speed and higher capacity communication systems continues to grow and to stretch the limits of our current technologies. All of the recent demonstrations of terabit per second or higher transmission rates have used wavelength division multiplexing to multiply the transmission capacity by using multiple wavelengths on the same fiber. In order to translate these incredible advances in capacity from the controlled laboratory environment into practical use, wavelength-stabilized laser arrays will need to be available at reasonable cost. This is the goal of the integration of an optical phase-locked loop (OPLL). In this thesis, a high-speed p-i-n/HBT (heterojunction bipolar transistor) process is used as the basis for integration. Individual component circuits were designed in LIBRA using HBT models derived from measured HBT characteristics. The OPLL circuits and components include Gilbert cell phase detectors, high-gain photoreceivers, a waveguide Y-branch coupler, waveguide photodiodes, high-gain waveguide photoreceivers, and an HBT oscillator. A Gilbert cell/high-gain photoreceiver combination and a Gilbert cell/oscillator/high-gain photoreceiver/waveguide coupler combination were also designed and fabricated. A novel hybrid fiber-based OPLL using semiconductor lasers without external linewidth-narrowing was designed. Components were individually tested and the system demonstrated phase-lock with the use of monolithically integrated photoreceivers and phase detector. These OPLLs exhibited record performance in terms of operating frequency range and hold-in range. The hold-in range, operating frequency range, and highest locking frequency demonstrated in this work represent the best values reported for any OPLL with semiconductor lasers without external line-narrowing. The operating range of these OPLLs extended from 1 GHz to over 27.11 GHz, while the maximum hold-in range measured was 1.558 GHz. Several monolithically integrated components were included in the OPLL designs. These included Gilbert cells, which demonstrated a phase detector gain $K\sb{d}=5.2$mV/degree 10 GHz, high gain photoreceivers with $f\sb{-3dB}=10.2$ GHz, and waveguide photodiodes with $f\sb{-3dB}=16$ GHz.

In most previous theoretical investigations, the effect of binary collisions between particles, in a fully-ionized plasma, on the shape of the scattered radiation spectrum, was neglected. The common result of these investigations was that, for low-density plasmas, interparticle collisions are negligible and therefore a Vlasov description is valid. The shape of the spectrum depends on the ratio a of the scale length for scattering to the plasma Debye length. When a is much smaller than unity, the scattered spectrum reflects the shape of the electron velocity distribution. In this case, the scattering is done by randomly distributed electrons. The total scattered power is just the sum of the independent contributions of each electron. However, when a is greater than unity, the electrons can no longer be considered as independent in evaluating the scattering from a plasma and correlations between them must be taken into account. Such correlations can of course be expected because the electrons interact with the ions and with other electrons via the Coulomb force, giving the Debye shielding effect. In the Vlasov description however, interparticle collisions are ignored, and the Landau damping is the only damping mechanism included. While this approach is valid for low-density plasmas in which collisions between particles are negligible, it is not applicable to high-density, low-temperature and hence collision-dominated plasmas, as many investigations showed. One such investigation used a BGK approach to modeling collisions between particles in a fully-ionized plasma, but it failed to incorporate collisions between unlike-charged particles. In this work, we show, using a BGK model for collisions between like-charged and unlike-charged particles, along with a stochastic approach for the calculation of the scattering function, that for a highly-density, low-temperature plasma (N (GREATERTHEQ) 10('19)cm('-3)), collisions between electrons and ions are important, and therefore cannot be neglected. The model used allows for an analytic solution from which numerical results are readily obtained.

This thesis comprises three major components: (1) development of polarimetric millimeter-wave (MMW) scatterometer system and the associated calibration and measurement procedure, (2) development of a hybrid experimental/theoretical scattering model for bare soil surfaces, and (3) development of a novel approach for experimental characterization of the effective propagation constant in dense random media. The polarimetric MMW scatterometer system consists of network analyzer-based coherent-on-receive radars capable of measuring directly the Mueller matrix of a target. An accurate calibration technique for coherent-on-receive radars is developed which requires measuring the backscatter response of two targets: a metallic sphere and any depolarizing target (unknown scattering matrix) for four and two transmitted polarizations respectively. The study of MMW interactions with bare soil surfaces is of importance since soil surfaces contribute to the backscatter response from different types of terrain. The MMW backscatter response of bare-soil is examined by conducting polarimetric measurements for different soil surfaces. The measured data indicate that in general the backscatter response comprises a surface scattering component and a volume scattering component. A semi-empirical surface scattering model is developed that relates the surface scattering component to the surface roughness, and the dielectric constant of the soil. The volume scattering component is modeled using radiative transfer theory. Accurate characterization of the effective propagation constant (K) of the mean-field in a random medium is essential for predicting volume scattering from a layered random medium. Due to deficiencies in present measurement techniques, the region of validity of the analytical models used to compute K has not been examined for dense random media with fractional volumes beyond 10%. A new technique for measuring K of a dense random media is presented. In this technique, the mean bistatic scattered fields of a spherical cluster of the random medium is measured using a monostatic radar and ground plane. By searching for an effective dielectric constant, the measured response is fitted to the bistatic scattering pattern of a homogeneous sphere having an identical radius. Measurements of K at 9.5 GHz for different dense random media comprising spherical particles of different fractional volumes have shown that none of the existing models are able to predict the extinction accurately for volume fractions beyond 10%.

This dissertation addresses the important problem of electromagnetic field propagation through and scattering from random media. The mathematical parameter that characterizes the coherent interaction of an electromagnetic field with a random medium is embodied in the fundamental constant of effective permittivity. Effective permittivity relates the small scale interaction of fields in an inhomogeneous medium to the macroscopic behavior of the aggregate. In granular or aerosol media, these inhomogeneities are represented as discontinuities or inclusions, separate from a homogeneous background such as free space. The ability to relate the theoretically understood microscopic behavior of fields in random media to the observed macroscopic behavior is a fundamental problem of applied physics and remote sensing. This dissertation is the culmination of a thorough investigation into this phenomenon and presents a unique, rigorous and consistent method of determining the fundamental parameter of effective permittivity for both two- and three-dimensional random media. In the development of this work, a number of new tools were implemented to model electromagnetic fields in random media. These were (i) a packing algorithm to simulate particle arrangements in gravity-deposited random media such as sand, snow or soils, and (ii) a numerical method for determining effective permittivity independent of particle density, shape, dielectric contrast and arrangement method. The packing algorithm referenced to here, provides essential unknowns such as the correlation function and/or the pair distribution function for use with commonly applied theoretical methods like the Born approximation and the quasi-crystalline approximation. Additionally, the packing algorithm may be used as the first step in the full numerical method for determining effective permittivity. This numerical method surpasses existing theoretical techniques by directly solving the integral form of Maxwell's equations, thereby eliminating approximations employed by theoretical methods to make them tractable. Thus, the numerical method is capable of modeling complex problems often found in nature. As a result, this work represents a solid step forward in our basic understanding of how electromagnetic fields propagate through, and scatter from, random media.

In order to substantiate the observation that the fraction of blue galaxies in the cores of dense clusters increases with redshift (the Butcher-Oemler effect), spectra were obtained for 61 galaxies in 7 dense clusters over the redshift range 0.195 $

Sieve methods have been developed as tools for establishing the existence of prime numbers, or else numbers with a bounded number of prime factors, in certain naturally occurring sets of integers. The underlying philosophy is that unless the set of integers is chosen with a preexisting multiplicative constraint which would preclude the presence of primes, it should contain a representative number of primes. One example is the set of all primitive roots to a fixed modulus, which is simply a union of arithmetic progressions. We use sieve methods to derive an upper bound for the least primitive root to a given modulus with a bounded number of prime factors, and show that if a certain analytic phenomenon (a Siegel zero) occurs, then an upper bound for the least prime primitive root can be established. We also improve existing bounds for the least prime primitive root for all but a very thin set of moduli and show how the same methods lead to an existing bound on the least prime primitive root under the assumption of the generalized Riemann hypothesis. Finally, we generalize these results to any integer modulus, where the analogue of a primitive root is an element of maximal multiplicative order. Every positive rational number has representations as Egyptian fractions (sums of reciprocals of distinct positive integers) with arbitrarily many terms and with arbitrarily large denominators. However, such representations normally use a very sparse subset of the positive integers up to the largest denominator. We show that for every positive rational there exist, for sufficiently large N, Egyptian fractions whose largest denominator is at most N and whose denominators form a positive proportion of the integers up to N; furthermore, the proportion is within a small factor of best possible. Although sieve methods are not directly applied, the construction involves results on the distribution of smooth numbers (numbers without large prime factors), which are related to results in sieve theory.