Design and Fabrication of a Low Power 7.2 Terabit Transmitter for Exascale Computing

Enhanced Coupled Strength (ECS) gratings fabricated into III-V based devices offer high reflected power per unit length and broad band reflectivity as compared to conventional 1st order gratings, desired qualities for short-haul high speed transmitters that can be implemented without the need for chip-level temperature control, contributing to the low power per transmitted bit. For commercial DBR lasers, the grating reflectivity results in an extremely narrow reflectivity spectrum, which is highly desired for most/many applications, but requires a power hungry thermo-electric cooler to maintain a fixed frequency. The proposed LEAM (laser electro-absorption modulator) requires a broad reflectivity spectrum, which, by Fourier Transform theory, means the gratings have to be very short, which only ECS gratings allow. By integrating the ECS gratings, laser, and electro-absorption modulator (EAM) into the same III/V epitaxial layers, the shift in wavelength due to temperature changes of the laser region will be identical to that of the electro-absorption modulator section, therefore eliminating temperature control requirements, contributing significantly to a low power per transmitted bit for data communications systems. A novel laser and integrated electro-optic modulator will be described, that when coupled with CWDM and 12 channel ribbon fiber, can enable a total of 7.2 Tbps connectivity, with calculated operating speeds of \u3e100 Gbps per channel non-return-to-zero (NRZ or PAM2). VCSEL based systems have shown signs of speed limits to significantly exceed 28 GBd (Gigabaud) PAM (4-level pulse amplitude modulation). Additionally, short 2nd order outcoupling gratings can be designed into the transmitter device to efficiently outcouple power into a single mode fiber. From a manufacturability point of view, fabricating the devices with both p and n metal pads on the same side of the wafer as the out-coupler allows wafer level testing, which has been a key advantage of VCSELs (Vertical Cavity Surface Emitting Lasers). VCSEL epitaxial growth can contain on the order of thousands of discrete layers with a thickness of ~10 microns. By contrast, the epitaxy grown for this thesis work contains ~ 30 layers not including doping changes.The transmitter is designed to leverage mostly existing mature semiconductor process methods with a few exceptions. Challenging process development work included methods to fill and planarize a low optical index material in the grating teeth spaces such that a higher index material can be deposited on top of the planarized low index layer and precisely coincide with the top of the grating teeth

An Ultrastructural and Electron Probe X-Ray Microanalytical Study of Sweat Gland Function

This thesis was undertaken to determine the ultrastructure of the rat footpad sweat gland before and after pilocarpine stimulation and to assess whether it undergoes the same morphological changes on activation as have been described for other species. A second objective was to measure, by electron probe X-ray microanalysis (EPXMA), the intracellular concentrations of K, Na and Cl in the human and rat atrichial and the horse epitrichial sweat glands before and after stimulation. The final objective was to determine the site and possible mechanism of action of aluminium-containing antiperspirants in the human sweat gland by comparing the ultrastructural and elemental changes before and after a course of antiperspirant treatment. The ultrastructural changes in the rat footpad sweat gland after pilocarpine stimulation included narrowing of the lumen, dilatation of the intercellular spaces, contraction of the myoepithelial cells, exocytosis and the loss of cytoplasmic material from the secretory cells. In general, these changes are qualitatively the same as have been reported in other species after thermal stimulation and it was concluded that the rat gland conforms to the model suggested by Montgomery et al. (1985). Although a successful method was developed for cutting ultrathin cryosections of biological material this was found to be unsuitable for the EPXMA study of sweat glands in skin samples. Using a method of bulk freeze-drying and resin embedding the results from the glands of the three species studied by EPXMA are shown below in mM/kg total dry weight of specimen analysed i. e. biological tissue and embedding medium. In man and horse stimulation was produced by thermal stress and the samples were obtained by high speed biopsy punch. For the rat the samples were obtained by autopsy after pilocarpine stimulation

Assessing the Density of Vegetation for Wildlife Cover in Regenerating Clearcuts via Analysis of Digital Imagery

Increasing the availability of shrubland habitat is a major conservation priority in the Northeastern United States because many wildlife species require this habitat and its extent has been decreasing in recent decades. Conservation agencies often monitor the number of hectares of shrubland habitat created, but rarely monitor the density of the resulting vegetation because the process is tedious and time-consuming. The current study tested a new approach to assess vegetation density: Digital Imagery Vegetation Analysis (DIVA). We compared the density estimates of DIVA with four other methods (Cover Board, Robel Pole, Height of Obstruction, and Line Intercept), and assessed the advantages and disadvantages of using these five methods in shru- bland studies. We concluded that DIVA offers two main advantages over the other methods: (a) it directly measures the vertical structure of the vegetation and thus better captures the complex wildlife habitat characteristics required by many wildlife, and (b) it does not rely on ocular estimates and thus avoids much of the bias associated with the other methods that estimate vertical structure. Furthermore, DIVA provides a rich documentation that permits quality control and other analyses to be conducted after the fieldwork is completed. However, DIVA is more time consuming than the other methods, thus we recommend either Robel Pole or Cover Board for routine monitoring

A New Model to Estimate Daily Energy Expenditure for Wintering Waterfowl

Current models to estimate daily energy expenditure (DEE) for free-living birds are limited to either those that use fixed thermoregulatory costs or those that more accurately estimate thermoregulatory costs, but require extensive and often logistically difficult measurements. Here, we propose a model based on basal metabolic rate (BMR), activity budgets, and site-specific energetic costs of thermoregulation that requires only simple measures of ambient temperature and wind speed to provide estimates of DEE. We use the model to calculate the DEE of Buffleheads (Bucephala albeola) wintering at six habitats that afford differing degrees of protection from exposure within Narragansett Bay, Rhode Island. Bufflehead activity budget data collected during the winters of 2001–2002 and 2002–2003, along with average temperatures and wind speeds at the sites, were used to calculate DEE that ranged from 46.9 to 52.4 kJ/hr and increased with increasing wind speed. The energetic cost of thermoregulation composed as much as 28% of total DEE and increased with wind speed. Our DEE values were 13.4% higher, and thermoregulatory costs were up to 2× higher than those calculated using an existing model that incorporates fixed thermoregulatory costs. We also saw an increase in feeding activity with increasing wind speed; sensitivity analysis of the effects of wind speed and feeding activity showed that a 1 m/sec increase in wind speed at our sites increased DEE by 2.5%, whereas a corresponding increase in feeding activity increased DEE by 4.5%. This suggests that in temperate winter habitats, increased feeding activity may have a greater impact on Bufflehead DEE than wind exposure. Site-specific model estimates of DEE could also provide additional insight into the relative contribution of environmental conditions and changes in waterfowl behavior to DEE

Energy-Based Carrying Capacities of Bufflehead \u3cem\u3eBucephala albeola\u3c/em\u3e Wintering Habitats

We present a model for calculating energy-based carrying capacities for bufflehead (Bucephala albeola), a small North American sea duck wintering in coastal and estuarine habitats. Our model uses estimates of the seasonal energy expenditures that incorporate site-specific energetic costs of thermoregulation, along with available prey energy densities to calculate carrying capacities in numbers of birds per winter. The model was used to calculate carrying capacities under several foraging scenarios for bufflehead wintering at three urban and three rural sites in the coastal northeast U.S. We found that energy-based carrying capacities varied from 20 – 320 birds per site per winter (0.38 – 6.22 birds per hectare), and showed a trend towards increasing with prey energy density (r = 0.53) and with decreasing average daily energy expenditure (r2 = 0.57, p = 0.08). We found greater prey species richness at rural sites, but similar prey biomass and productivity across all sites. Bufflehead density averaged 1.89 ± 2.34 birds per hectare (range 0.38 – 6.22 birds per hectare) across the sites. Bufflehead abundance at urban sites was reduced by an average of 43.7% from that predicted using the relationship between per-hectare carrying capacity and bufflehead abundance at rural sites. This difference may arise from natural or human induced factors that act to limit sea duck populations on wintering habitats

Using Life History and Ecology as Tools to Manage a Threatened Salamander Species

Selected aspects of the life history and ecology of the small-mouthed salamander (Ambystoma texanum Matthes) relevant to the management of this threatened species in Iowa are presented. The population studied utilizes flooded woodland habitat during courtship, breeding and egg laying, and during the entire larval period. Larval foraging strategies in this habitat included ontogenetic but no diel shifts in prey selection. Synchronous, nocturnal breeding migration allowed effective use of drift fences fur capture of adults used in captive breeding, courtship behavior studies, and the estimation of breeding population size. Large numbers of spennatophores, apparently indiscriminate mate choice, and the relatively large number of eggs produced by females makes captive breeding programs potentially very successful. Because larvae are particularly vulnerable to predation by fish and larval tiger salamanders, ephemeral ponds are required for breeding and larval habitat. The primary management objective should be to preserve ephemeral woodland ponds and adjacent terrestrial habitat favorable for larval and adult survival

Fat Stores and Antioxidant Capacity Affect Stopover Decisions in Three of Four Species of Migratory Passerines With Different Migration Strategies: An Experimental Approach

During migratory stopovers, birds must make decisions about when and where to travel and these decisions are likely contingent on their fuel stores, food availability, and antioxidant capacity as well as seasonal changes in key environmental factors. We conducted a field experiment on an offshore stopover site (Block Island, Rhode Island, United States: 41°130N, 71°330W) during autumn migration to test the hypothesis that birds with greater fuel stores and non-enzymatic antioxidant capacity have shorter stopovers than lean birds with low antioxidant capacity, and to determine the extent to which this depends on migration strategy. We used a 2 × 2 factorial field experiment (two levels each of available food and dietary polyphenols) with four species of songbirds kept in captivity for 3–5 days to produce experimental groups with different fuel stores and antioxidant capacity. We attached digital VHF transmitters to assess stopover duration and departure direction using automated telemetry. Non-enzymatic antioxidant capacity increased during refueling for Red-eyed Vireos (Vireo olivaceus) and Blackpoll Warblers (Setophaga striata) fed ad lib diets, and for ad lib fed Hermit Thrushes (Catharus guttatus) supplemented with polyphenols, but not for Yellow-rumped Warblers (Setophaga coronata coronata). Glutathione peroxidase (GPx) decreased during captivity and was influenced by dietary treatment only in Red-eyed Vireos. Oxidative damage decreased during captivity for all species except Yellow-rumped Warblers. Stopover duration was shorter for Vireos and Blackpolls fed ad lib as compared to those fed maintenance. Ad lib fed Hermit Thrushes supplemented with polyphenols had shorter stopovers than those fed ad lib, as did thrushes fed at maintenance and supplemented with polyphenols compared with those fed at maintenance alone. There was no influence of condition on stopover duration for Yellow-rumped Warblers. Departure direction was not strongly related to condition, and birds primarily reoriented north when departing Block Island. Thus, fat stores and oxidative status interacted to influence the time passerines spent on stopover, and condition-dependent departure decisions were related to a bird’s migration strategy. Therefore, seasonal variation in macro- and micro-nutrient resources available for refueling at stopover sites can affect body condition and antioxidant capacity and in turn influence the timing and success of migration

Diet Quality and Food Limitation Affect the Dynamics of Body Composition and Digestive Organs in a Migratory Songbird (Zonotrichia Albicollis)

Migrating songbirds interrupt their feeding to fly between stopover sites that may vary appreciably in diet quality. We studied the effects of fasting and food restriction on body composition and digestive organs in a migratory songbird and how these effects interacted with diet quality to influence the rate of recovery of nutrient reserves. Food limitation caused whitethroated sparrows to reduce both lean and fat reserves, with about 20% of the decline in lean mass represented by a decline in stomach, small intestine, and liver. During refeeding on diets similar in nutrient composition to either grain or fruit, foodlimited grain-fed birds ate 40% more than did control birds, and they regained body mass, with on average 60% of the increase in body mass composed of lean mass including digestive organs. In contrast, food-limited fruit-fed birds did not eat more than did control birds and did not regain body mass, suggesting that a digestive constraint limited their food intake. The interacting effects of food limitation and diet quality on the dynamics of body composition and digestive organs in sparrows suggest that the adequacy of the diet at stopover sites can directly influence the rate of recovery of body reserves in migrating songbirds and hence the pace of their migration

Metabolic Routing of Dietary Nutrients in Birds: Effects of Diet Quality and Macronutrient Composition Revealed Using Stable Isotopes

During fall migration many songbirds switch from consuming primarily insects to consuming mostly fruit. Fruits with more carbohydrates and less protein may be sufficient to rebuild expended fat stores, but such fruits may be inadequate to replace catabolized protein. We manipulated the concentrations and isotopic signatures of macronutrients in diets fed to birds to study the effects of diet quality on metabolic routing of dietary nutrients. We estimated that approximately 45% and 75%, respectively, of the carbon in proteinaceous tissue of birds switched to high‐ or low‐protein diets came from nonprotein dietary sources. In contrast, we estimated that approximately 100% and 20%–80%, respectively, of the nitrogen in proteinaceous tissues of birds switched to high‐ or low‐protein diets was attributable to dietary protein. Thus, the routing and assimilation of dietary carbon and nitrogen differed depending on diet composition. As a result, δ15N of tissues collected from wild animals that consume high‐quality diets may reliably indicate the dietary protein source, whereas δ13C of these same tissues is likely the product of metabolic routing of carbon from several macronutrients. These results have implications for how isotopic discrimination is best estimated and how we can study macronutrient routing in wild animals