MIGRANT FARM WORKERS ON VIRGINIA'S EASTERN SHORE: AN ANALYSIS OF ECONOMIC IMPACTS

The economic impact of migrant farmworkers on an agriculture-dependent region is investigated. The direct effects of inflows of state and federal dollars for migrant services, and production of high-valued commodities are computed. Indirect and induced effects are modelled through the use of the IMPLAN input output model. Various alternatives to migrant labor are investigated, including production of less labor-intensive crops, acreage retirement, and contract H2A workers. Migrants are found to create substantial economic activity on the Eastern Shore of Virginia.Economic impact, Input-output, Migrant labor, Labor and Human Capital,

The influence of operational sex ratio on the mating behaviour of reindeer (Rangifer tarandus L.) during an experimental rut: the effect of male age

The operational sex ratio (OSR), the ratio of sexually active males to sexually receptive females, is one of the main measures used to predict the intensity and direction of mating competition, influencing the opportunity for sexual selection. Here we conducted the first experimental study to investigate how OSR and male age impacts the intensity of mating competition and the male activity budget in a large mammalian species, reindeer (Rangifer tarandus), under semi-natural conditions. We manipulated OSR on two levels in two enclosures, a female biased treatment (3♂:6♀ = OSR 0.5) and a sex balanced treatment (3♂:3♀ = OSR 1), over two years with males from two age groups (1.5 or 2.5-years-old), and with females of various ages. We found some support for prevailing OSR theory, notably with female intrasexual competition occurring at lower frequencies in OSR = 1. An emerging trend was noted for male intrasexual competition, with higher frequencies of occurrence in OSR = 1 for our 2.5-year-old males. Courtship behaviour was also found to occur at higher frequencies of occurrence among the 2.5-year-old males, however, there was no effect of OSR. Regarding the male activity budget, we found that 1.5-year-old males followed a more income breeding strategy, with no difference in foraging behaviour between OSR treatments. In contrast, our 2.5-year-old males had a significantly lower frequency of foraging behaviour in OSR = 1, presumably resulting from a higher occurrence of intrasexual competition. Vigilance behaviour was also found to occur at higher frequencies in OSR=1 for the 2.5-year-old males, likely due to females being more limiting. Our results suggest that age is an important factor with respect to how male reindeer respond to differing OSR values. Future research aiming to expand the generalizability of experimental OSR theory to a wider range of taxa and ecological conditions need to consider other factors that will impact competition for mates, such as prime reproductive age

Silicon Photonics: All-Optical Devices for Linear and Nonlinear Applications

Silicon photonics has grown rapidly since the first Si electro-optic switch was demonstrated in 1987, and the field has never grown more quickly than it has over the past decade, fueled by milestone achievements in semiconductor processing technologies for low loss waveguides, high-speed Si modulators, Si lasers, Si detectors, and an enormous toolbox of passive and active integrated devices. Silicon photonics is now on the verge of major commercialization breakthroughs, and optical communication links remain the force driving integrated and Si photonics towards the first commercial telecom and datacom transceivers; however other potential and future applications are becoming uncovered and refined as researchers reveal the benefits of manipulating photons on the nanoscale. This thesis documents an exploration into the unique guided-wave and nonlinear properties of deeply-scaled high-index-contrast sub-wavelength Si waveguides. It is found that the tight confinement inherent to single-mode channel waveguides on the silicon-on-insulator platform lead to a rich physics, which can be leveraged for new devices extending well beyond simple passive interconnects and electro-optic devices. The following chapters will concentrate, in detail, on a number of unique physical features of Si waveguides and extend these attributes towards new and interesting devices. Linear optical properties and nonlinear optical properties are investigated, both of which are strongly affected by tight optical confinement of the guided waveguide modes. As will be shown, tight optical confinement directly results in strongly vectoral modal components, where the electric and magnetic fields of the guided modes extend into all spatial dimensions, even along the axis of propagation. In fact, the longitudinal electric and magnetic field components can be just as strong as the transverse fields, directly affecting the modal group velocity and energy transport properties since the longitudinal fields are shown to contribute no time-averaged momentum. Furthermore, the vectoral modal components, in conjunction with the tensoral nature of the third-order susceptibility of Si, lead to nonlinear properties which are dependent on waveguide orientation with respect to the Si parent crystal and the construction of the modal electric field components. This consideration is used to maximize effective nonlinearity and realize nonlinear Kerr gratings along specific waveguide trajectories. Tight optical confinement leads to a natural enhancement of the intrinsically large effective nonlinearty of Si waveguides, and in fact, the effective nonlinearty can be made to be almost 10^6 times greater in Si waveguides than that of standard single-mode fiber. Such a large nonlinearity motivates chip-scale all-optical signal processing techniques. Wavelength conversion by both four-wave-mixing (FWM) and cross-phase-modulation (XPM) will be discussed, including a technique that allows for enhanced broadband discrete FWM over arbitrary spectral spans by modulating both the linear and nonlinear waveguide properties through periodic changes in waveguide geometry. This quasi-phase-matching approach has very real applications towards connecting mature telecom sources detectors and components to other spectral regimes, including the mid-IR. Other signal processing techniques such as all-optical modulation format conversion via XPM will also be discussed. This thesis will conclude by looking at ways to extend the bandwidth capacity of Si waveguide interconnects on chip. As the number of processing cores continues to scale as a means for computational performance gains, on-chip link capacity will become an increasingly important issue. Metallic traces have severe limitations and are envisioned to eventually bow to integrated photonic links. The aggregate bandwidth supported by a single waveguide link will therefore become a crucial consideration as integrated photonics approaches the CPU. One way to increase aggregate bandwidth is to utilize different eigen-modes of a multimode waveguide, and integrated waveguide mode-muxes and demuxes for achieving simultaneous mode-division-multiplexing and wavelength-division-multiplexing will be demonstrated

Blowout and liftoff limits of a hydrogen jet flame in a supersonic, heated, coflowing air stream

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76310/1/AIAA-1993-446-753.pd

Simultaneous CH planar laser-induced fluorescence and particle imaging velocimetry in turbulent flames

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77055/1/AIAA-1998-151-822.pd

The study of the turbulent burning velocity by imaging the wrinkled flame surface

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76129/1/AIAA-2002-482-348.pd

Genotyping Analyses of Tuberculosis Cases in U.S.- and Foreign-Born Massachusetts Residents

We used molecular genotyping to further understand the epidemiology and transmission patterns of tuberculosis (TB) in Massachusetts. The study population included 983 TB patients whose cases were verified by the Massachusetts Department of Public Health between July 1, 1996, and December 31, 2000, and for whom genotyping results and information on country of origin were available. Two hundred seventy-two (28%) of TB patients were in genetic clusters, and isolates from U.S-born were twice as likely to cluster as those of foreign-born (odds ratio [OR] 2.29, 95% confidence interval [CI] 1.69, 3.12). Our results suggest that restriction fragment length polymorphism analysis has limited capacity to differentiate TB strains when the isolate contains six or fewer copies of IS6110, even with spoligotyping. Clusters of TB patients with more than six copies of IS6110 were more likely to have epidemiologic connections than were clusters of TB patients with isolates with few copies of IS6110 (OR 8.01, 95%; CI 3.45,18.93)