UMD Theses and Dissertations
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Item Unmasking risk variability in a changing climate: acute effects from exposure to outdoor heat and air pollution among patients with end-stage renal disease(2021) Remigio, Richard V; Sapkota, Amir; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)End-stage renal disease (ESRD) is a chronic condition that disproportionately affects communities of color and diabetics. Hallmark burdens include the lack of essential renal functions and routine life-saving dialysis treatments to filter and remove toxic wastes from the body. Given their compromised survival advantage, the ESRD population is vulnerable to adverse complications associated with acute environmental exposures. However, little is known about the effect of extreme heat events (EHE), air pollution, and ambient temperature on this targeted population. This dissertation focused on ESRD patients receiving hemodialysis treatments at Fresenius Medical Care facilities within the Northeastern United States region (n=60,717). Using longitudinal study design methods, we investigated the association between acute environmental exposures and the risk of all-cause mortality (ACM) and all-cause hospital admissions (ACHA).We applied case-crossover methods to estimate acute EHE effects on mortality and hospital admissions stratified by latitude, race/ethnicity, and comorbidities. Overall, risks varied, but same-day ACM and ACHA risks were most pronounced. ESRD patients with cardiovascular disease (rate ratio [RR], 2.14; 95% CI:1.91-2.40) and cerebrovascular disease (RR, 1.47; 95% CI:1.26-1.71) had notably increased risks of same-day EHE-related mortality. We furthered our investigation by studying PM2.5 and O3 effects using a similar study design but considered the role of EHE as a modifier and incorporated distributed lag nonlinear modeling to account for cumulative lag structures. Pooled same-day EHE-adjusted models estimated an 8% ACM rate increase when O3 concentrations exceeded air quality standards during warmer months. Our data suggest that EHE can act as a modifier between O3 and ACM. Though, no effect modification by EHE was observed for acute air pollutant exposures and ACHA. Lastly, this dissertation explored the mediating role of selected thermoregulatory responses to increased temperature on ACM or ACHA outcomes using traditional mediation analyses. Systolic blood pressure before dialysis treatment (preSBP) and interdialytic weight gain change (IDWG) were identified as significant pathways. However, we observed inconsistent mediation in the IDWG pathway for ACM (-6.26%) and ACHA (-2.67%). Concomitant physiological changes in preSBP and IDWG may have little intermediary effect in combined pathway models. Overall, this research provided additional lines of evidence for enhancing patient response protocols and early warning systems to improve healthcare delivery in an era of a changing climate specific to subpopulations living with ESRD.Item Imaging Pyrometry of Smoldering Wood Embers(2019) Kim, Dennis Kgangyon; Sunderland, Peter B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The wild fire problem in U.S. and across the world has caused the losses of human lives and property. Firebrands can dramatically increase the hazards of wildland fires. While embers have been extensively studied (e.g. firebrand generation, transport, ignition, size, mass, and moisture contents etc.), little is known about their temperatures. Also, all past works failed to measure firebrand temperature relying on thermocouple and IR camera, which are not accurate and have many drawbacks. Therefore, in this dissertation, to address this an imaging stationary ember and airborne firebrand pyrometer was developed using an inexpensive digital color camera. The camera response was calibrated with a blackbody furnace at 600 – 1200 °C. The embers were 6.4 mm maple rods with lengths of 2 cm. Temperatures were obtained from ratios of green/red pixel values and from grayscale pixel values. Ratio pyrometry is more accurate when ember emissivity times ash transmittance is not unity, but grayscale pyrometry has signal-to-noise ratios 18 times as high. Thus, a hybrid pyrometer was developed that has the advantages of both, providing a spatial resolution of 17 µm, a signal-to-noise ratio of 530, and an estimated uncertainty of 20 C. The measured ember temperatures were between 750 – 1070 °C with a mean of 930 °C. Comparing the ratio and grayscale temperatures indicates the mean visible emissivity times transmittance was 0.73. Temperatures were also measured with fine bare-wire thermocouples, which were found to quench smolder reactions, make imperfect thermal contact, and underpredict the mean ember temperature by more than 200 °C. The pyrometry was also performed on a pendulum firebrand with different velocities imitating airborne firebrands in real fire scenario. The temperature increases as the velocity of pendulum firebrands increases. Ratio pyrometry determined mean temperatures of pendulum firebrand between 878 – 1064 C. Grayscale pyrometry temperatures were lower. The relationship between velocities and temperatures were quantified. The pyrometry was additionally performed on smoldering fuels such as a rolled paper, incense, maple rod, ashless filter paper, and rattan sticks with different air jet velocities to explore the smoldering extinction at high air velocity. To summarize, the main achievement of my Ph. D researches was to develop a new diagnostic of ember and firebrand temperature and emissivity and was successfully completed. The results would be a stepping stone to nearby future exploration of wildfire. The hazards of various firebrand materials and moisture contents could be better assessed in different wind velocities. Computational fire models could be improved. The firebrand size could be simultaneously measured with the same device, both key firebrand attributes could be determined in near real time.Item FAILURE MECHANISMS OF ULTRA HIGH MOLAR MASS POLYETHYLENE SINGLE FIBERS AT EXTREME TEMPERATURES AND STRAIN-RATES(2017) Jenket II, Donald Robert; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of temperature and strain-rate on the mechanical properties of Ultra High Molar Mass Polyethylene (UHMMPE) single fibers was investigated at eleven temperatures from room temperature (20 °C) to the orthorhombic-hexagonal phase transition (148 °C) and at six strain-rates from quasi-static (10-3 s-1) to dynamic (103 s-1). Dimensional analysis of ballistic limit tests using has shown an underperformance of materials comprised of UHMMPE fibers. A possible explanation is the relatively low melting temperature of UHMMPE fibers (~150 °C) in comparison to other fiber materials, such as poly-aramids (~450 °C). The mechanical properties of UHMMPE single fibers were investigated through a series of 437 tensile tests at 66 temperature-strain-rate combinations. Changes in stress-strain curve shapes were observed with respect to temperature and strain-rate. The transition of stress-curve shape with increasing temperature was observed to be pseudo-brittle, plateauing, necking, and non-failure and transitions between these phases were observed within a strain-rate dependent temperature range. For low and intermediate strain rates, a temperature and strain-rate equivalence is observed: a decadal increase of strain-rate is mechanically equivalent to a ~20 °C decrease in temperature. Strain to failure for dynamic strain rates was invariant over the temperature range of this study. Strength and modulus properties were observed to decrease with increasing temperature and increase with increasing strain-rate. An orthorhombic to hexagonal phase transition occurs between 145 °C and 148 °C and a sudden decrease in strength and moduli was observed. The change in dominant stress-relieving mechanism is proposed. Chain slippage is dominant for the majority of conditions in this study except where scission and straightening are the dominant mechanism. At high temperatures for constrained fibers in the hexagonal phase, chain slippage occurs more frequently due to the trans to gauche conformation. Chain scission is only dominant moments before fiber failure and near the failure surface. Chain straightening is dominant at low strain (0 % to 0.5 %) and at temperatures greater than or equal to the necking temperatures for the quasi-static and intermediate strain-rates and at all temperatures for the dynamic strain-rates.Item Water Mist Suppression in a Turbulent Line Burner(2016) Keller, Elizabeth; Marshall, Andre W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental study of water mist fire suppression in a buoyant, turbulent diffusion flame is presented. An existing turbulent line burner facility was modified to allow for water mist suppression. These modifications include streamlining the oxidizer delivery system, facility improvements to increase mist generation efficiency, as well as the addition of a mist containment system and an enhanced exhaust flow to homogenize the water mist in the flame region and reduce secondary flows. Following these improvements, the capabilities of the water mist generation system were characterized both using a classical mass balance approach and using more modern advanced diagnostic techniques. The turbulent line burner facility fitted with the water mist improvements were applied to suppress a 50 kW methane flame. Species-based calorimetry was used to evaluate the global heat release rate and combustion efficiency to evaluate suppression behavior. Detailed local measurements of flame temperature were also performed and provide a useful data set for the evaluation of flame suppression response and for the validation of CFD fire models.Item UNDERSTANDING THE RELATIONSHIP BETWEEN THE BROWN MARMORATED STINK BUG, HALYOMORPHA HALYS (STÅL), AND ITS SYMBIONT, PANTOEA CARBEKII, WITH IMPLICATIONS FOR STINK BUG MANAGEMENT(2016) Taylor, Christopher Michael; Mitter, Charles; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Symbiotic relationships between insects and beneficial microbes are very common in nature, especially within the Hemiptera. The brown marmorated stink bug, Halyomorpha halys Stål, harbors a symbiont, Pantoea carbekii, within the fourth region of the midgut in specialized crypts. In this dissertation, I explored this insect- microbe relationship. I determined that the brown marmorated stink bug is heavily reliant on its symbiont, and that experimental removal of the symbiont from the egg mass surface prior to nymphal acquisition led to lower survival, longer development, lower fecundity, and aberrant nymphal behavior. Additionally, I determined that even when the symbiont is acquired and housed in the midgut crypts, it is susceptible to stressors. Stink bugs reared at a higher temperature showed lower survival, longer development, and a cease in egg mass production, and when bugs were screened for their symbiont, fewer had successfully retained it while under heat stress. Finally, with the knowledge that the stink bug suffers decreases in fitness when its symbiont is missing or stressed, I wanted to determine if targeting the symbiont was a possible management technique for the stink bug. I tested the efficacy of a number of different insecticidal and antimicrobial products to determine whether prevention of symbiont acquisition from the egg mass was possible, and results indicated that transmission of the symbiont from the egg mass to the newly hatched nymph was negatively impacted when certain products were applied (namely surfactants or products containing surfactants). Additionally, direct effects on hatch rate and survival were reported for certain products, namely the insect growth regulator azadirachtin, which suggests that nymphs can pick up residues from the egg mass surface while probing for the symbiont. I conclude that P. carbekii plays a critically important role in the survival of its host, the brown marmorated stink bug, and its presence on the egg mass surface before nymphal hatch makes it targetable as a potential management technique.Item The Effects of CO2 and Temperature on the Soil Microbial Carbon and Nitrogen of Urban and Rural Forests(2015) Kulka, Elizabeth; McIntosh, Marla S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigated and compared the effects of elevated temperature and elevated CO2 on the microbial biomass carbon (MBC) and nitrogen (MBN) of urban and rural forest soils. Soils analyzed from Baltimore Long-Term Ecological Research forests in June and October, 2014 had greater MBC and MBN quantities in rural than urban forests. A controlled environmental chamber study was conducted where June-collected soils were planted with hybrid poplars and exposed to ambient and elevated temperature and CO2 levels. After exposure for 49 days, MBC and MBN quantities were again greater in rural than urban soils. Soil MBC was greater under elevated than ambient CO2, while soil MBN was greater under elevated than ambient CO2 and temperature. Results suggest that if temperature and CO2 levels increase in the Baltimore area as predicted, microbial C and N pools in the studied forests will increase, and will remain greater in rural than urban soils.Item EVALUATION OF PLANT SPECIES FOR SURVIVAL, GROWTH AND CONTRIBUTION TO GREEN ROOF FUNCTION(2013) DeLong, Clark; Lea-Cox, John; Cohan, Steven M; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The evaluation of plant species for use in green roof systems is an important step in providing recommendations to the industry. In this study we investigated the ability of five species to grow and survive on a green roof in the Mid-Atlantic, and how they contributed to the performance of a green roof system. One species, Tradescantia ohiensis was found to retain more storm water than other species and an unplanted control. Three of the plants evaluated were found to reduce substrate temperatures when compared to unplanted controls during the summer months. One species, Chielanthes lanosa, was unable to survive the summer. While another, Asclepias verticillata, lost biomass over the study. Indicating both are unsuitable for use on green roofs in the Mid-Atlantic. The other species: Sedum album, Sedum kamtschaticum and Tradescantia ohiensis all survived and exhibited a positive growth rate.Item Algorithmic Approaches to Reducing Resource Costs in Data Centers(2013) Mukherjee, Koyel; Khuller, Samir; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A substantial portion of resource costs incurred by data centers relate to energy costs, with cooling energy and equipment powering energy accounting for a major fraction. Other major costs incurred by data centers, is due to huge data transmission volume and resultant network bandwidth consumption. In this dissertation, we study problems inspired by the needs to reduce energy consumption and network bandwidth billing costs in data centers. A significant amount of data center cooling energy is wasted due to thermal imbalance and hot spots. In order to prevent this, the workload should be scheduled in a thermally aware manner based on the overall thermal profile, since machine temperatures depend on local load as well as on neighboring machines' load. We define `effective load' that captures this spatial cross-interference and analyze different models for: 1) maximizing the profit of scheduled jobs under a cooling energy budget, for which we give 1/2 - O(epsilon) approximation algorithms; 2) minimizing the maximum temperature when all jobs have to be scheduled, for which we give a 2-approximation algorithm and a 3-competitive online algorithm for a single rack of machines, where the factors approach 4/3 and 2 respectively as the cross-interference decays. Servers consume energy while running; hence, shutting down some will reduce the costs. We consider two problems which study this in literature: active time and busy time, the goal being minimizing the total `on' time of machines. In active time, we have access to a single machine whereas in busy time, number of machines allowed is unlimited. Machines have bounded capacity and jobs have release times, deadlines and lengths. For active time, we show a minimal feasible solution is 3-approximate and give a 2-approximation algorithm via LP rounding. For busy time, we give a 3-approximation algorithm which improves the 4-approximation, and analyze the preemptive problem also. Data centers need to transmit a huge volume of data daily which results in high network bandwidth costs. Frequently, ISP's charge for Internet use either based on the peak bandwidth usage in any slot in the billing cycle, or according to some percentile cost. We provide an optimal offline algorithm for the percentile problem when jobs can have variable delay. For the online problem of minimizing peak bandwidth, we study small values of delay in a discrete time setting and give much better lower and upper bounds than the best known bound of e that holds when delay allowed is arbitrarily large and time is continuous.Item Electro-Thermal Codesign in Liquid Cooled 3D ICs: Pushing the Power-Performance Limits(2013) Shi, Bing; Srivastava, Ankur; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The performance improvement of today's computer systems is usually accompanied by increased chip power consumption and system temperature. Modern CPUs dissipate an average of 70-100W power while spatial and temporal power variations result in hotspots with even higher power density (up to 300W/cm^2). The coming years will continue to witness a significant increase in CPU power dissipation due to advanced multi-core architectures and 3D integration technologies. Nowadays the problems of increased chip power density, leakage power and system temperatures have become major obstacles for further improvement in chip performance. The conventional air cooling based heat sink has been proved to be insufficient for three dimensional integrated circuits (3D-ICs). Hence better cooling solutions are necessary. Micro-fluidic cooling, which integrates micro-channel heat sinks into silicon substrates of the chip and uses liquid flow to remove heat inside the chip, is an effective active cooling scheme for 3D-ICs. While the micro-fluidic cooling provides excellent cooling to 3D-ICs, the associated overhead (cooling power consumed by the pump to inject the coolant through micro-channels) is significant. Moreover, the 3D-IC structure also imposes constraints on micro-channel locations (basically resource conflict with through-silicon-vias TSVs or other structures). In this work, we investigate optimized micro-channel configurations that address the aforementioned considerations. We develop three micro-channel structures (hotspot optimized cooling configuration, bended micro-channel and hybrid cooling network) that can provide sufficient cooling to 3D-IC with minimum cooling power overhead, while at the same time, compatible with the existing electrical structure such as TSVs. These configurations can achieve up to 70% cooling power savings compared with the configuration without any optimization. Based on these configurations, we then develop a micro-fluidic cooling based dynamic thermal management approach that maintains the chip temperature through controlling the fluid flow rate (pressure drop) through micro-channels. These cooling configurations are designed after the electrical parts, and therefore, compatible with the current standard IC design flow. Furthermore, the electrical, thermal, cooling and mechanical aspects of 3D-IC are interdependent. Hence the conventional design flow that designs the cooling configuration after electrical aspect is finished will result in inefficiencies. In order to overcome this problem, we then investigate electrical-thermal co-design methodology for 3D-ICs. Two co-design problems are explored: TSV assignment and micro-channel placement co-design, and gate sizing and fluidic cooling co-design. The experimental results show that the co-design enables a fundamental power-performance improvement over the conventional design flow which separates the electrical and cooling design. For example, the gate sizing and fluidic cooling co-design achieves 12% power savings under the same circuit timing constraint and 16% circuit speedup under the same power budget.Item Bioenergetic responses of Chesapeake Bay white perch to nursery conditions of temperature, salinity, and dissolved oxygen(2009) Hanks, Deanna McQuarrie; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Changes in the physical and chemical structure of estuaries affect the habitat availability for anadromous species. White perch, an estuarine species, are among the most abundant and important fishes in the Chesapeake Bay. Here, I evaluate nursery quality for juvenile white perch by measuring metabolic and growth responses over a range of environmental conditions such as salinity, temperature, and dissolved oxygen. Rearing white perch in 10-d trials varying in temperature, salinity and dissolved oxygen conditions, I estimated growth rates, feeding rates, gross growth efficiency, and routine metabolism. Juveniles experienced higher feeding and growth rates in warmer, more oxygenated waters. In hypoxic environments (<40% saturation), metabolic rates increased as much as 4-fold while growth decreased 3-fold and feeding decreased 2-fold. My results indicate that while white perch are well suited to the saline and thermal conditions present in the Bay, nursery habitat value can be substantially curtailed by hypoxia.