Heat stress is a known occupational hazard. The purpose of this dissertation was to evaluate industrial hygiene heat exposures in electric utility line workers during work in regions with high ambient temperatures (75-115°F) and low relative humidity (8-37%).

Relationships between accepted heat stress and heat strain variables were examined. New variables, namely a modified version of the Physiological Strain Index, and the differences from baseline for the oral temperature and heart rate were examined as well.

The hypotheses tested in this study are as follows:

(1) Certain tasks and job classes had higher levels of heat stress and heat strain than others;

(2) The measured and derived independent heat stress variables, such as Wet Bulb Globe Temperature levels, metabolic effort levels, exposure levels differences from applicable guidelines and standards, and personal factors (age, weight, body mass index, acclimatization), influence or predict measured and derived dependent heat strain variables (heart rate, body temperature, and Physiological

Strain Index);

(3) The test variable of the modified Physiological Strain Index offered improvement over the unmodified version;

(4) The test variables of the difference in heart rate from baseline measurements, and the difference in body temperature from baseline were significant improvements over using the heart rate or body temperatures alone; and

(5) The level of ambient temperature increase from global warming had an impact on occupational heat stress exposures.

The design of the study was a cross-sectional study. Eighty nine subjects, age 18-64, and 428 individual tasks of one to four hour length were evaluated in two populations.

Resultant data were analyzed using univariate comparisons and mixed effects multiple linear and logistic regressions.

Results indicated that workers conducting certain tasks (digging) and working as certain job classes (groundmen and journeyman linemen) represented exposures to higher heat stress levels than others. Results also showed that workers performing certain tasks (digging) and classes (Groundmen and apprentice linemen) exhibited

higher levels of heat strain. Personal variables (age, past shift work) were significantly predictive of increased heat strain. Race was not correlated to heat strain. The analysis of acclimatization status as a variable was removed from this study due to dissimilar populations. Heat exposure standards (ACGIH and NIOSH) appeared to be conservative and protective to the worker, however, this population (utility workers) is a very healthy population and shouldn't necessarily represent the general working population.

California OSHA's use of 85°F as a trigger temperature did not correlate well with increased heat strain metrics. The 95°F set-point correlated better. Oral temperatures, per se, were not correlated to exposure, but the differences in oral temperature from baseline were better heat strain indicators. Heart rate increases were strong indications of heat strain, but the differences in heart rate from baseline were better indicators, especially for tasks with less metabolic load variance. Heart rate set-points of 110 bpm and 120 bpm correlated well with increased exposures. The modified Physiological Strain Index was not an improvement over the non-modified one.

And applying forecasted global warming by the end of the century to the population in this study would increase worker exposures from 33% to 100% of the population being over the recommended limits.

Colloidal metasurfaces are two-dimensional arrays of subwavelength resonators generally composed of a precious metal substrate and a deposited layer of colloidal metal nanoparticles, ultimately yielding a functional nanomaterial surface with a total thickness on the order of 100 nanometers. Colloidal metasurfaces, as like other metasurfaces, possess the ability to control and manipulate light in ways that

cannot be done using natural materials, yet have the added benefit of much faster, cheaper, and larger scale construction. The precise construction parameters of these colloidal metasurfaces allow for the tuning of an extreme, in-plane electromagnetic coupling phenomenon that is primarily localized within the metasurface “gap.” Placing active materials (such as nanocrystals, fluorophores, and others) into this gap can lead to a variety of interesting effects that are potentially useful for the construction of larger functional devices. Certain types of active materials have very poor absorption capabilities, making them very difficult and/or inefficient to use as sensing agents and light collectors. Here we show that these colloidal metasurface gaps can be use to enhance the single- and multi-photon absorption efficiencies and subsequent emission intensities of an active layer of semiconducting nanocrystals via the integration of these nanocrystals into the metasurface gap during the metasurface construction process. Colloidal metasurfaces used for active layer enhancement can subsequently be tuned to accommodate many different types of absorbing active layers.

Mycobacterium tuberculosis is the causative agent of tuberculosis, a primarily pulmonary disease that is estimated to infect approximately one third of the world population yet the mechanisms by which this bacterium causes disease are poorly understood. A key feature of M. tuberculosis pathogenesis is the parasitism of host macrophages following phagocytic entry, which is facilitated by the bacteria's manipulation of the host cell environment. The secretion of virulence proteins is a common mechanism used by pathogenic bacteria for altering the host environment. One such pathway, present in Mycobacterium and other Gram-positive genera, is ESX-1 (early secretory antigenic target 6 system 1). Although ESX-1 is required for multiple phenotypes related to the pathogenesis of infection, only three substrates of the secretion machine have been identified to date, and the mechanism by which these substrates are exported is not understood. In this work I identify a novel ESX-1 substrate and find that its delivery to the ESX-1 machine requires different protein interactions than previously identified substrates. I probe the role of this novel substrate in virulence and present data that the various ESX-1 substrates contribute additively to virulence. These results expand our understanding of a major virulence mechanism of Mycobacteria as well as mechanisms for the secretion of proteins through thick impermeable bacterial cell walls.

M. tuberculosisone of the world's most prevalent pathogens, infecting one third of humans and contributing to 2 million deaths each year. M. marinum (Mm) has been increasingly studied as a model of M. tuberculosis due to its relative safety and its shared mechanisms of pathogenesis; for example, previous studies have highlighted the importance of the secretion system ESX-1 in pathogenesis of both M. tuberculosis and Mm. In this thesis we show that the host's ubiquitin system, best known for tagging host proteins for degradation, also recognizes Mm that have escaped their original phagosomes via an ESX-1-dependent mechanism and entered into the cytosol. Ubiquitinated bacteria have two distinct fates; ubiquitin tagged Mm can be sequestered into lysosome-like compartments, but they also can shed cell wall, which may allow them to evade sequestration. Lysosomal sequestration is independent of autophagy, a response to starvation or infection that leads to degradation of organelles and certain other intracytosolic pathogens. These experiments reveal ubiquitination as a mechanism of host cell recognition of Mycobacteria and the existence of a new interface between the host and invading microbe that may be amenable to therapeutic intervention.

Mycobacterium tuberculosis, the infectious agent of tuberculosis, remains a leading cause of infectious disease worldwide due to poor control of infection, multidrug-resistant strains, and more recently, co-infection with HIV. To facilitate the study of the pathogenesis of M. tuberculosis and the potential discovery of new drug targets, our laboratory makes use of the Mycobacterium marinum model of tuberculosis infection. M. marinum is a very close relative of M. tuberculosis that causes a chronic, granulomatous disease in fish with many similarities to tuberculosis infection in humans. Of importance to the pathogenesis of Mycobacteria, are several secretion systems responsible for the export of proteins to the cell envelope and the extracellular space. SecA2 is an ATPase that provides energy for the export of a subset of proteins. This dissertation confirms that SecA2 is required for the virulence of Mycobacteria and explores the role of SecA2 in the modulation of host immune responses in vivo. In a zebrafish and a mouse tail model of tuberculosis infection we have shown that the SecA2 of M. marinum is required for the maximal induction of several pro-inflammatory cytokines including TNF-α. Additionally, SecA2 has a role in granuloma formation and/or maintenance. In vitro studies of a ΔsecA2 deletion strain in M. marinum reveals that the mutant has an abnormal cell envelope by cryo-electron tomography, and increased sensitivity to SDS treatment. This work provides additional evidence supporting a role for SecA2 in modulating host immunity, and a novel role in cell wall morphology and function.

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