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Accurate flash point and flammability limit data are needed to design safe chemical processes. Unfortunately, improper data storage and reporting policies that disregard the temperature dependence of the flammability limit and the fundamental relationship between the flash point and the lower flammability limit have resulted in compilations filled with erroneous values. To establish a database of consistent flammability data, critical analysis of reported data, experimental investigation of the temperature dependence of the lower flammability limit, and theoretical and empirical exploration of the relationship between flash points and temperature limits are undertaken. Lower flammability limit measurements in a 12-L ASHRAE style apparatus were performed at temperatures between 300 K and 500 K. Analysis of these measurements showed that the adiabatic flame temperature at the lower flammability limit is not constant as previously thought, rather decreases with increasing temperature. Consequently the well-known modified Burgess-Wheeler law underestimates the effect of initial temperature on the lower flammability limit. Flash point and lower temperature limit measurements indicate that the flash point is greater than the lower temperature limit, the difference increasing with increasing lower temperature limit. Flash point values determined in a Pensky-Martens apparatus typically exceed values determined using a small-scale apparatus above 350 K. Data stored in the DIPPR® 801 database and more than 3600 points found in the literature were critically reviewed and the most probable value recommended, creating a database of consistent flammability data. This dataset was then used to develop a method of estimating the lower flammability limit, including dependence on initial temperature, and the upper flammability limit. Three methods of estimating the flash point, with one based entirely on structural contributions, were also developed. The proposed lower flammability limit and flash point methods appear to predict close to, if not within, experimental error.

Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.

Discoveries revolving around false hellebore (Veratrum californicum Durand) have caused a paradigm shift in treatment from eradication to harvest and preservation. Test plots set in place 18 years ago to analyze the effectiveness of eradication treatments (tilling, herbicide, mow, and remow) give us a better idea of how false hellebore communities might respond to disturbances caused by harvest. We focused mainly on the tilling, mow, and remow treatments because of similarities to harvest techniques.We found that mow and remow treatments have little effect on the population of false hellebore in the wild. Tilling treatments were effective in reducing the population dramatically; however some recovery in numbers has taken place. Tilled plots showed a significant decrease in mid seral plant populations, and a significant increase in early seral populations. Tilled treatments were also opened up to intermediately desirable and undesirable plants. Mow and remow treatments reacted similarly to each other, with mow treatments showing decreases in mid seral species and with both treatments showing neither an increase nor a decrease in the other seral stages. Mow and remow plots showed a decrease in desirable plants, but an increase in intermediately desirable plants and no increase in undesirable plants. Greenhouse experiments were unsuccessful due to phenological disruptions caused by removal from the native habitat as well as climate and temperature differences.

The possibility of polarization diversity using left and right hand circular polarization (LHCP and RHCP) in the presence of multipath propagation is examined. We show that there are differences in the received signal for LHCP and RHCP for a number of realistic scenarios. Because multipath propagation can produce different LHCP and RCHP signals, there exists the possibility for diversity improvement involving the two polarizations.

[pt] Este trabalho se propõe a desenvolver um estudo de propagação na faixa VHF, visando determinar os efeitos de construções e irregularidades do terreno na atenuação dos sinais. Com este objetivo foi feito um levantamento dos sinais emitidos pelas estações de televisão da cidade do Rio de Janeiro (canais 4 e 13) em um número de pontos suficientes para caracterizar o comportamento da intensidade de campo nas diversas áreas da cidade. Na análise dos resultados foi dada ênfase especial a três aspectos distintos: distribuição estatística do sinal recebido, efeito da variação da altura da antena receptora e efeito da freqüência. Os resultados obtidos apresentam interesse prático para o dimensionamento de sistemas móveis na faixa VHF. / [en] The purpose of this work is to study the effect of constructions and terrain irregularities on the attenuation of VHF signals. To this end, television signals have been measured in the city of Rio de Janeiro (channels 4 and 13). In order to characterize the behavior of field intensity in different city areas, measurements were made in a sufficiently large number of points. In the analysis of the results, three distinct aspects have been given special emphasis: statistical distribution of the received signal, effect of receiving antenna height and effect of frequency. The results obtained show practical usefulness in the VHF mobile system projects.

[pt] Esse trabalho trata da determinação da atenuação de um enlace radioelétrico em microondas que utiliza um sistema duplo-passivo em região Fresnel de uma antena parabólica adjacente. Com esse objetivo são apresentados os valores do ganho diferencial da configuração para dois casos distintos: a) Repetidores passivos planos com abertura regulares iguais. b) Repetidores passivos planos com abertura quadradas desiguais. Com base nos resultados obtidos para esses dois casos são apresentadas também as curvas do ganho diferencial para a situação em que o sistema duplo-passivo se encontra em região de Fraunhofer da antena parabólica, podendo as mesmas, para uma situações tratadas, ser comparadas com aquelas obtidas por Yang2. Considerou-se campo elétrico sobre a abertura da antena parabólica excitadora polarizado linearmente e da forma 4,5,7 Ea = EO (1 - ar 2) onde r = p /R é a variável radial normalizada e, para uma atenuação de bordas de 10 dB, o parâmetro (alfa) é igual a 0,684. / [en] This theoretical study gives the propagation loss through a microwave radio relay system using doublé-passive configuration in the Fresnel zone of the exciting parabolic antenna. Two cases are treated separately: a) Plane passive repeaters with equal rectangular apertures. b) Plane passive repeaters with nonequal square apertures. Based on the results obtained for the two above cases the curves for the relative gain of a doublé-passive in the Fraunhofer region of the exciting antenna are derived and, for case b, can be checked with those by Yang2.. assuming a constant-phase, symmetrical illumination of the exciter aperture, the source field can be expressed as a function only of the radial variable: Ea = EO (1 - ar 2) where r = p/R is the normalized radial variable and (alfa) = 6.864 to produce the common 10 dB taper.

In an attempt to mitigate the effects of the atmosphere on the coherence of an optical (laser) beam, interest has recently been shown in changing the beam shape to determine if a different power distribution at the transmitter will reduce the effects of the random fluctuations in the refractive index. Here, a model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects upon the scintillation of the beam and upon beam wander are determined. A comparison of these results is made with the like effects on a standard TEM00 Gaussian beam. The theoretical results are verified by comparison with a computer simulation model for the flattened Gaussian beam. Further, a determination of the probability of fade and of mean fade time under weak fluctuation conditions is determined using the widely accepted lognormal model. Although this model has been shown to be somewhat optimistic when compared to results obtained in field tests, it has value here in allowing us to compare the effects of atmospheric conditions on the fade statistics of the FGB with those of the lowest order Gaussian beam. The effective spot size of the beam, as it compares to the spot size of the lowest order Gaussian beam, is also analyzed using Carter's definition of spot size for higher order Gaussian beams.

Spatially discrete Nagumo equations have widespread physical applications, including modeling electrical impulses traveling through a demyelinated axon, an environment typical in multiple scle- rosis. We construct steady-state, single front solutions by employing a piecewise linear reaction term. Using a combination of Jacobi-Operator theory and the Sherman-Morrison formula we de- rive exact solutions in the cases of homogeneous and inhomogeneous diffusion. Solutions exist only under certain conditions outlined in their construction. The range of parameter values that satisfy these conditions constitutes the interval of propagation failure, determining under what circumstances a front becomes pinned in the media. Our exact solutions represent a very specific solution to the spatially discrete Nagumo equation. For example, we only consider inhomogeneous media with one defect present. We created an original script in MATLAB which algorithmically solves more general cases of the equation, including the case for multiple defects. The algorithmic solutions are then compared to known exact solutions to determine their validity.

The aim of this thesis is to introduce my work which has generally been focused on optical wavefronts that have the unusual property of resisting commonplace phenomena such as diffraction and dispersion. Interestingly, these special beams are found both in linear and nonlinear situations. For example, in the linear regime, localized spatio-temporal waves which resemble the spherical harmonic symmetries of the hydrogen quantum orbitals can simultaneously negotiate both diffractive and dispersive effects. In the nonlinear regime, dressed optical filaments can be arranged to propagate multi-photon produced plasma channels orders of magnitude longer than expected. The first portion of this dissertation will begin by surveying the history of diffraction-free beams and introducing some of their mathematical treatments. Interjected throughout this discussion will be several relevant concepts which I explored during my first years a CREOL. The discussion will then be steered into a detailed account of diffraction/dispersion free wavefronts which display hydrogen-like symmetries. The second segment of the document will cover the highly nonlinear process of optical filamentation. This chapter will almost entirely investigate the idea of the dressed filament, an entity which allows for substantial prolongation of this light string. I will then conclude by delving into the topic of supercontinuum generation in parabolic multimode fibers which, in the upcoming years, has great potential of becoming important in optics.