Test Environmental Research Collection

Permanent URI for this collection

https://hdl.handle.net/1911/118256

This is a test collection created as part of a Fondren Fellows project (2024-2025). This collection is intended to serve as a proof of concept for a permanent collection that showcases environmental research conducted by Rice researchers. All items currently in this collection have been mapped from other collections in R-3.

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Protracted carbon burial following the Early Jurassic Toarcian Oceanic Anoxic Event (Posidonia Shale, Lower Saxony Basin, Germany)
(Springer Nature, 2024) Celestino, R. F. S.; Ruhl, M.; Dickson, A. J.; Idiz, E.; Jenkyns, H. C.; Leng, M. J.; Mattioli, E.; Minisini, D.; Hesselbo, S. P.
Lower Jurassic marine basins across the northwest European epicontinental shelf were commonly marked by deposition of organic-rich black shales. Organic-carbon burial was particularly widespread during the Toarcian Oceanic Anoxic Event (T-OAE: also known as the Jenkyns Event) with its accompanying negative carbon-isotope excursion (nCIE). Lower Toarcian black shales in central and southern Germany are known as the Posidonia Shale Formation (Posidonienschiefer) and are thought to have formed during the T-OAE nCIE. Here, we present stratigraphic (carbon-isotope, Rock–Eval, calcareous nannofossil) data from the upper Pliensbachian and lower Toarcian strata from a core drilled on the northern flank of the Lower Saxony Basin, north–west Germany. The bio- and chemostratigraphic framework presented demonstrates that (i) the rock record of the T-OAE at the studied locality registered highly condensed sedimentation and/or multiple hiatuses and (ii) the deposition of organic-rich black shale extended significantly beyond the level of the T-OAE, thereby contrasting with well-studied sections of the Posidonia Shale in southern Germany but showing similarities with geographically nearby basins such as the Paris Basin (France). Prolonged and enhanced organic-carbon burial represents a negative feedback mechanism in the Earth system, with locally continued environmental perturbance accelerating the recovery of the global climate from T-OAE-associated hyperthermal conditions, whilst also accelerating a return to more positive δ13C values in global exogenic carbon pools.
A global Data Assimilation of Moisture Patterns from 21 000–0 BP (DAMP-21ka) using lake level proxy records
(Copernicus Publications, 2024) Hancock, Christopher L.; Erb, Michael P.; McKay, Nicholas P.; Dee, Sylvia G.; Ivanovic, Ruza F.
Global hydroclimate significantly differed from modern climate during the mid-Holocene (6 ka) and Last Glacial Maximum (21 ka). Consequently, both periods have been described as either a partial or reverse analogue for current climate change. To reconstruct past hydroclimate, an offline paleoclimate data assimilation methodology is applied to a dataset of 216 lake status records which provide relative estimates of water level change. The proxy observations are integrated with the climate dynamics of two transient simulations (TraCE-21ka and HadCM3) using a multivariate proxy system model (PSM) which estimates relative lake status from available climate simulation variables. The resulting DAMP-21ka (Data Assimilation of Moisture Patterns 21 000–0 BP) reanalysis reconstructs annual lake status and precipitation values at 500-year resolution and represents the first application of the methodology to global hydroclimate on timescales spanning the Holocene and longer. Validation using Pearson's correlation coefficients indicates that the reconstruction (0.24) is more skillful, on average, than model simulations (0.09), particularly in portions of North America and east Africa, where data density is high and proxy–model disagreement is prominent during the Holocene. Results of the PSM and assimilation are used to evaluate climatic controls on lake status, spatiotemporal patterns of moisture variability, and proxy–model disagreement. During the mid-Holocene, wetter conditions are reconstructed for northern and eastern Africa, Asia, and southern Australia, but in contrast to the model prior, negative anomalies are observed in North America, resulting in drier-than-modern conditions throughout the Northern Hemisphere midlatitudes. Proxy–model disagreement in western North America may reflect a bias in model simulations to stronger sea level pressure gradients in the North Pacific during the mid-Holocene. The data assimilation framework is able to reconcile these differences by integrating the constraints of proxy observations with the dynamics of the model prior to produce a more robust estimation of hydroclimate variability during the past 21 000 years.
Defaunation Increases Clustering and Fine-Scale Spatial Genetic Structure in a Small-Seeded Palm Despite Remaining Small-Bodied Frugivores
(Wiley, 2025) Lamperty, Therese; Diaz-Martin, Zoe; Swamy, Varun; Karubian, Jordan; Choo, Juanita; Dunham, Amy E.
Anthropogenic pressures such as hunting are increasingly driving the localised functional extinctions of large- and medium-sized wildlife in tropical forests, a phenomenon broadly termed ‘defaunation’. Concurrently in these areas, smaller-bodied species benefit from factors such as competitive release and increase in numbers. This transformation of the wildlife community can impact species interactions and ecosystem services such as seed dispersal and seed-mediated geneflow with far-reaching consequences. Evidence for negative genetic effects following defaunation is well-documented in large-seeded plants that require large frugivores for long-distance seed dispersal. However, how defaunation affects plants with small or medium-small seeds (< 1.5 cm), which tend to be consumed and dispersed by frugivorous mutualists of a range of body sizes and responses to anthropogenic threats, is not well understood. To better understand defaunation's impacts on tropical plant communities, we investigated spatial and genetic patterns in a hyperabundant medium-to-small-seeded palm, Euterpe precatoria in three sites with different defaunation levels. Results indicate that defaunation is associated with higher fine-scale spatial genetic structure among seedlings and increased spatial clustering within seedling cohorts and between seedlings and conspecific adults, as well as a reduction in nearest-neighbour distances between seedlings and conspecific adults. There were no clear effects on inbreeding or genetic diversity. However, we caution these trends may indicate that defaunation reduces seed dispersal services for species previously presumed to be robust to deleterious effects of losing large frugivores by virtue of having smaller seeds and broad suites of dispersal agents, and negative downstream effects on genetic diversity could occur.
Big Data, Big Insights: Leveraging Data Analytics to Unravel Cardiovascular Exposome Complexities
(Houston Methodist DeBakey Heart & Vascular Center, 2024) Ibrahim, Ramzi; Pham, Hoang Nhat; Nasir, Khurram; Hahad, Omar; Sabharwal, Ashutosh; Al-Kindi, Sadeer
The exposome encompasses the full range of environmental exposures throughout a person’s lifetime and plays an important role in cardiovascular health. Interactions with the social, natural, and built components of the exposome significantly impact cardiovascular disease prevalence and mortality. Robust data analytics, including machine learning and geospatial analysis, have advanced our understanding of how these factors converge to influence cardiovascular disease risk. The integration of multiomics platforms and advanced computational approaches enhances our ability to characterize the exposome, leading to targeted public health interventions and innovative risk reduction strategies aimed at improving cardiovascular health globally. These multiomics platforms that integrate factors such as genomics, epigenomics, clinical data, social factors, environmental factors, and wearable technology will characterize the exposome in greater detail concerning cardiovascular health. In this review, we aimed to elucidate the components of the exposome and discuss recent literature regarding their relationship to cardiovascular health.
Interplay Between Residential Nature Exposure and Walkability and Their Association with Cardiovascular Health
(Elsevier, 2025) Makram, Omar M.; Nwana, Nwabunie; Pan, Alan; Nicolas, Juan C.; Gullapelli, Rakesh; Bose, Budhaditya; Sabharwal, Ashutosh; Chang, Jenny; Javed, Zulqarnain; Kash, Bita; Maddock, Jay E.; Nasir, Khurram; Al-Kindi, Sadeer
Background Green space has been linked with cardiovascular (CV) health. Nature access and quality may have significant impact on CV risk factors and health. Objectives The authors aimed to investigate the relationship between NatureScore, a composite score for natural environment exposure and quality of green spaces, with CV risk factors and atherosclerotic cardiovascular diseases (ASCVD). Methods A cross-sectional study including one million adult patients from the Houston Methodist Learning Health System Outpatient Registry (2016-2022). NatureScore is a composite measure of natural environment exposure and quality (0-100) calculated for each patient based on residential address. NatureScores was divided into 4 categories: nature deficient/light (0-39), nature adequate (40-59), nature rich (60-79), and nature utopia (80-100). CV risk factors included hypertension, diabetes, dyslipidemia, and obesity. Results Among 1.07 million included patients (mean age 52 years, female 59%, Hispanic 16%, Non-Hispanic Black 14%), median NatureScore was 69.4. After adjusting for neighborhood walkability, patients living in highest NatureScore neighborhoods had lower prevalence of CV risk factors (OR: 0.91, 95% CI: 0.90-0.93) and ASCVD (OR: 0.96, 95% CI: 0.93-0.98) than those in lowest NatureScore neighborhoods. A significant interaction existed between NatureScore and Walkability (P < 0.001), where those in high NatureScore (≥60) high walkability (≥40) areas had lower prevalence of CV risk factors (OR: 0.93, 95% CI: 0.90-0.97, P < 0.001) and were more likely to have optimal CV risk profile (relative risk ratio: 1.09, 95% CI: 1.04-1.14, P = 0.001). Conclusions These findings suggest that while green spaces benefit health, their accessibility through walkable environments is crucial for cardiovascular disease protection.
Climate Reality On-Screen: The Climate Crisis in Popular Films, 2013-22
(Buck Lab for Climate and Environment at Colby College and Good Energy, 2024) Schneider-Mayerson, Matthew; Lim, Jerald; Bellido, Dominic; Stringer, Moya; Wilson, Adria Zheng; Zhou, Zoky
Most research that has examined climate change in film has focused on anomalous climate-focused films such as The Day After Tomorrow and Don’t Look Up, but fictional narratives have their greatest impact in the aggregate, through repetition of common settings, themes, and actions. Is the film industry as a whole helping us face and respond to the climate crisis—or avoid it? To answer this question, Matthew Schneider-Mayerson worked with five current and former students (Dominic Bellido, Moya Stringer, Adria Zheng Wilson, and Zoky Zhou) to apply a communication studies methodology to the 250 most popular films of the last decade (2013 to 2022), identifying the presence of climate c hange in a film’s story world; climate awareness; scenes with climate mentions; common climate impacts; and climate-positive and climate-negative behaviors in each film. The result is “Climate Change On-screen,” a groundbreaking systematic analysis of climate change in popular films, published by the Buck Lab for Climate & Energy at Colby College and Good Energy, a leading climate consultancy.
RoadsTaken: The history of highway displacement in Houston
(Rice University, 2024-10-31) Drwenski, Matt; Franco, Uilvim Ettore Gardin; Sousa, Bruno; Baker Institute for Public Policy, Center for Energy Studies; Center for Research Computing's Spatial Studies Lab
roadsTaken is an interactive map and geospatial database of buildings removed and people displaced that supports research on highway construction in Houston, Texas. Accompanying this map is a time slider that shows the progression of highway displacement and construction year by year. Displayed alongside the interactive database are historical maps of Houston, aerial photography before and after highway construction, freeway plans and proposals, and details about each of the more than 11,000 structures in our database of buildings removed for urban freeways.
The Sensitivity of the Spatial Pattern of Sea Level Changes to the Depth of Antarctic Meltwater Fluxes
(Wiley, 2024) Eisenman, Ian; Basinski-Ferris, Aurora; Beer, Emma; Zanna, Laure
Regional patterns of sea level rise are affected by a range of factors including glacial melting, which has occurred in recent decades and is projected to increase in the future, perhaps dramatically. Previous modeling studies have typically included fluxes from melting glacial ice only as a surface forcing of the ocean or as an offline addition to the sea surface height fields produced by climate models. However, observational estimates suggest that the majority of the meltwater from the Antarctic Ice Sheet actually enters the ocean at depth through ice shelf basal melt. Here we use simulations with an ocean general circulation model in an idealized configuration. The results show that the simulated global sea level change pattern is sensitive to the depth at which Antarctic meltwater enters the ocean. Further analysis suggests that the response is dictated primarily by the steric response to the depth of the meltwater flux.
Unveiling 4500 years of environmental dynamics and human activity at Songo Mnara, Tanzania
(Elsevier, 2024) Englong, Apichaya; Punwong, Paramita; Seelanan, Tosak; Marchant, Rob; Wynne-Jones, Stephanie; Jirapinyakul, Akkaneewut; Fleisher, Jeffrey
Coastal East Africa has undergone massive transformations through the Late Holocene, with a combination of changes in sea level, increasing human settlement, and ensuing use of coastal resources. A comprehensive multi-proxy analysis, including pollen, phytolith, charcoal, stratigraphy, particle size, and geochemical data from sedimentary cores extracted from mangrove ecosystems combined with soils from archaeological contexts, provided valuable insights into vegetation dynamics, environmental changes, and human interactions within the mangrove ecosystem of Songo Mnara Island, Tanzania over the last 2590 BCE (4540 cal yr BP). The bottommost layers indicate a lack of vegetation, as deduced from the presence of coral rags and high calcium and carbonate content, possibly due to high mid-Holocene sea-level. Evidence of mangrove taxa suggests a decrease in sea level, enabling the establishment of mangroves from around 2590 BCE. A brief period of sea-level rise occurred between 90 BCE and 320 CE before sea-level fell until 1570 CE. Significant evidence of human activity is recorded from around 1400 CE indicated by increased charcoal, crop phytoliths, and evidence of marine resource utilisation. The timing of this human-environment interaction is also linked to the time of lower sea level. However, there was evidence suggesting human abandonment of the island from around 1500 CE. This coincided with a subsequent rise in sea levels and potentially prolonged drought conditions spanning from 1570 to 1700 CE. These factors likely contributed to a shortage of food resources in the area, impacting both agricultural practices due to the scarcity of natural freshwater and the accessibility of marine food resources. From 1700 CE to the present, fluctuations in sea level have been observed, with a signal of recent sea-level rise in tandem with shifts in mangrove, terrestrial herbaceous taxa and fire activity. The low sedimentation rates within mangrove areas suggest that the mangroves on Songo Mnara Island may not keep pace with the current rate of sea-level rise.
Species delimitation, discovery and conservation in a tiger beetle species complex despite discordant genetic data
(Springer Nature, 2024) Duran, Daniel P.; Laroche, Robert A.; Roman, Stephen J.; Godwin, William; Herrmann, David P.; Bull, Ethan; Egan, Scott P.
In an age of species declines, delineating and discovering biodiversity is critical for both taxonomic accuracy and conservation. In recent years, there has been a movement away from using exclusively morphological characters to delineate and describe taxa and an increase in the use of molecular markers to describe diversity or through integrative taxonomy, which employs traditional morphological characters, as well as genetic or other data. Tiger beetles are charismatic, of conservation concern, and much work has been done on the morphological delineation of species and subspecies, but few of these taxa have been tested with genetic analyses. In this study, we tested morphologically based taxonomic hypotheses of polymorphic tiger beetles in the Eunota circumpicta (LaFerté-Sénectère, 1841) species complex using multilocus genomic and mtDNA analyses. We find multiple cryptic species within the previous taxonomic concept of Eunota circumpicta, some of which were historically recognized as subspecies. We found that the mtDNA and genomic datasets did not identify the same taxonomic units and that the mtDNA was most at odds with all other genetic and morphological patterns. Overall, we describe new cryptic diversity, which raises important conservation concerns, and provide a working example for testing species and subspecies validity despite discordant data.
Static Analysis for Checking the Disambiguation Robustness of Regular Expressions
(Association for Computing Machinery, 2024) Mamouras, Konstantinos; Le Glaunec, Alexis; Li, Wu Angela; Chattopadhyay, Agnishom
Regular expressions are commonly used for finding and extracting matches from sequence data. Due to the inherent ambiguity of regular expressions, a disambiguation policy must be considered for the match extraction problem, in order to uniquely determine the desired match out of the possibly many matches. The most common disambiguation policies are the POSIX policy and the greedy (PCRE) policy. The POSIX policy chooses the longest match out of the leftmost ones. The greedy policy chooses a leftmost match and further disambiguates using a greedy interpretation of Kleene iteration to match as many times as possible. The choice of disambiguation policy can affect the output of match extraction, which can be an issue for reusing regular expressions across regex engines. In this paper, we introduce and study the notion of disambiguation robustness for regular expressions. A regular expression is robust if its extraction semantics is indifferent to whether the POSIX or greedy disambiguation policy is chosen. This gives rise to a decision problem for regular expressions, which we prove to be PSPACE-complete. We propose a static analysis algorithm for checking the (non-)robustness of regular expressions and two performance optimizations. We have implemented the proposed algorithms and we have shown experimentally that they are practical for analyzing large datasets of regular expressions derived from various application domains.
Cross-National Variations in Scientific Ethics: Exploring Ethical Perspectives Among Scientists in China, the US, and the UK
(Springer Nature, 2024) Di, Di; Ecklund, Elaine Howard
This research explores the perspectives of academic physicists from three national contexts concerning their roles and responsibilities within the realm of science. Using a dataset comprised of 211 interviews with scientists working in China, the United States, and the United Kingdom, the study seeks to explain whether and in what manner physicists conceptualize scientific ethics within a global or national framework. The empirical findings bring to light disparities across nations in the physicists’ perceptions of what constitutes responsible mentorship and engagement in public service. These cross-national variations underscore the moral agency of physicists as they navigate the ethical standards embraced by the global scientific community vis-à-vis those that are specific to their respective national contexts. The study’s empirical insights may carry significant implications for both policymakers and ethicists, underscoring the imperative of soliciting and acknowledging the perspectives of academic scientists working and living in disparate national contexts when formulating comprehensive science ethics frameworks. Such inclusive and context-aware approaches to shaping ethics in science can contribute to the cultivation of a more robust and universally relevant ethical foundation for the scientific community.
Neighborhood Opportunity Mapping
(Rice University Kinder Institute for Urban Research, 2024) Sherman, Stephen Averill; Rhodes, Anna; Njeh, Joy; Banerjee, Debolina; Kim, Andrew
In December 2023, the Houston Housing Authority (HHA) received a $5 million grant from the U.S. Department of Housing and Urban Development (HUD) to fund a household mobility program that would expand the number of affordable housing options for people who rely on housing choice vouchers. Specifically, the grant aims to move voucher families to “opportunity neighborhoods” or “opportunity areas,” which have high-performing schools, low crime rates, access to jobs, and other characteristics that promote the broader goal of upward mobility for low-income residents. Kinder Institute for Urban Research staff assisted in data collection and analysis, measuring key indicators on poverty, education, crime, jobs, and transportation to identify high-opportunity areas within HHA’s jurisdiction.
Responsible Collaboration Through Appropriate Research Security: A Workshop To Discuss and Study the Emergent Discipline of Research on Research Security
(James A. Baker III Institute for Public Policy of Rice University, 2024) Dao, Tam K.; Evans, Kenneth M.; Shannon, Michael D.; Bronk, Christopher; Neuhauser, Claudia; Roberts, Evan; Haselkorn, Mark P.; Ribes, David; Shih, Tommy; Baker Institute Science and Technology Policy Program
This workshop report offers a summary of "Responsible Collaboration Through Appropriate Research Security" held at Rice University's Baker Institute for Public Policy in May 2024. The report discusses challenges and opportunities to the field of research on research security (RoRS), and provides recommendations to guide the National Science Foundation's new RoRS program.
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Unnatural Disasters: Healing Epistemic Invisibility Through Digital Archiving
(2024-08-06) Graham, Lindsay Diane; Ostherr, Kirsten; Michie, Helena; Howe, Cymene
Unnatural Disasters: Healing Epistemic Invisibility Through Digital Archiving identifies the emerging genre of the digital disaster archive and argues that this genre exposes the concept of disaster as deeply entangled with and produced by epistemological erasure. Invested in the concept of “disaster” as unnatural and unequivocally social, political, and temporal, I connect a growing awareness of environmental precarity to this new kind of digital memory practice to examine how the archive’s methodology and infrastructure engender a vital politics of accountability. I argue that the digital archive is uniquely suited to address epistemologically produced invisibility by challenging the historical processes and systems that lead to disaster; in so doing, the archive proffers an expanded understanding of health, healing, and care from the margins. This project considers collections from disparate geographies, cultures, and languages that respond to the 2010 Haitian earthquake, the 1989 Exxon Valdez oil spill (digitized in 2010), Japan’s triple disaster (2011), and the SARS-CoV-2 pandemic (2020) to explore how the digital archive is both an open encounter and an exchange of knowledge and power. To specifically reflect on the healing affordances of this increasingly popular form of cultural production, I critically approach the archive through the concepts of digital witnessing, archival methodology as recovery, healing nostalgia, digital self-help, and digitality as care, while grappling with the ways that digital tools can exacerbate or expose the unevenness of vulnerability. By delineating the socio-political processes that lead to disaster and by demonstrating how the digital archive is a potential site of activism that de-naturalizes and thus re-politicizes disaster, Unnatural Disasters charts new paths for critical disaster studies and global digital humanities and ultimately argues for a translational digital humanities approach to global disaster response and humanitarian aid.
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Evolutionary History, Extinction, and Environmental Variability Shape the Tropical and Subtropical Diversity Disparity of Terrestrial Mammals
(2024-08-01) Hsieh, Chia; Beaudrot, Lydia
Tropical and subtropical moist forests are home to over half of all extant vertebrate species worldwide, yet they face increasing anthropogenic pressures that are degrading multiple facets of their diversity. High tropical species diversity has been hypothesized to have resulted from an evolutionary history of high species diversification in stable environments relative to temperate regions. However, recent studies have found that varying degrees of environmental variability and historical extinction of large-bodied vertebrates likely lead to the uneven distribution of species richness and body sizes among tropical regions (i.e., tropical diversity disparity) on different continents. However, little is known about how evolutionary history, historical extinction, and environmental variability have shaped the geographic differences among tropical regions in other facets of their diversity. This limited knowledge not only hinders our ability to unravel fundamental questions about drivers of biodiversity distributions but also to assess biodiversity changes that have implications for conservation given ongoing anthropogenetic pressure and environmental change. Hence, to address this research gap, I tested the relative effects of evolutionary and macroecological drivers on 1) community structure, 2) predator-prey interactions, and 3) functional diversity of vertebrate assemblages in tropical and subtropical moist forests globally. I focused on mammals because this well-studied vertebrate class has species-level functional trait data, a well-resolved phylogeny, and community composition data available from both in-situ observations and the reconstructed ranges of extinct species. First, using in-situ observations from 15 protected tropical forests worldwide, I found that the coupled phylogenetic and functional community structure of ground-dwelling mammals has been shaped by slow niche evolution, and phylogenetic clustering tendencies were predicted by colonization time. Second, I found geographic differences in the dietary breadth of carnivoran predators among 380 large mammal communities in the Neotropical, Afrotropical, and Indomalayan realms, for which speciation rates and present temperature seasonality supported dietary niche generalization while historical extinction led to dietary niche specialization. Thirdly, I found geographic differences in the vulnerability to functional diversity loss of tropical and subtropical moist forest mammals from historical and predicted future extinctions. Functional vulnerability to loss increased in mammal assemblages with slower niche evolution but decreased under greater present environmental variability. By integrating evolutionary and macroecological approaches, this dissertation has unraveled the essential roles of evolutionary history, extinction, and present environmental variability in shaping multiple facets of the diversity of extant forest mammals in the global tropics and subtropics.
Embargo
Innovative Materials for Energy Applications and Environmental Impact
(2024-07-31) Saju, Sreehari; Pulickel , Ajayan M
Innovative materials for energy storage devices and energy efficiency are crucial for advancing sustainable technology. This thesis investigates innovative approaches using advanced polymer blends to enhance the performance and sustainability of thermochromic windows and electrochemical energy storage systems. The primary focus is on a mixed polymer system composed of poly(dimethyl siloxane), poly(ethylene oxide), and an alkali salt. The development of a three component thermochromic polymer blend capable of dynamically adjusting transparency in response to external temperatures significantly improves the energy efficiency of HVAC systems in buildings by controlling solar radiation influx. This material presents a promising solution for reducing energy consumption in architectural applications. The thermochromic properties are characterized by the blend's ability to switch between transparent and light-blocking states at specific temperature thresholds. The blend's stability, durability, and responsiveness are tested under various environmental conditions to ensure long-term performance and reliability. In addition to the thermochromic applications, the ionic conduction properties of lithium, sodium, and magnesium ions within the polymer matrix are explored. Enhanced room-temperature ionic conductivity is achieved, leading to the development of safer and more efficient solid-state electrolytes for ion batteries. The thesis also introduces a novel hydrothermal method for the low-temperature transformation of amorphous fused silica into crystalline α-quartz. Facilitated by sodalime glass and sodium ion migration, this process offers a sustainable and energy-efficient approach to material synthesis, significantly reducing the energy requirements compared to traditional high-temperature methods. The potential of advanced polymer blends, particularly in thermochromic smart windows, to contribute to energy-efficient buildings and electrochemical applications is significant. The findings have broad implications for industries such as electronics, optics, and materials engineering, underscoring the importance of innovative materials and methods in advancing sustainable technology.
Characterizing the El Niño-Southern Oscillation and its North American Teleconnections over the Last Millennium
(2024-08-05) Luo, Xinyue; Dee, Sylvia
The El Niño-Southern Oscillation (ENSO) dominates interannual climate variability in the tropical Pacific, with sea surface temperatures (SSTs) oscillating between cooler (La Niña) and warmer (El Niño) conditions. ENSO affects midlatitude weather and climate through reorganizing winds and circulation, shifts known as teleconnections for their far-reaching impacts. ENSO-induced teleconnections were once considered stationary and predictable, but observations show they differ widely between individual events. Internal climate variability produces distinct ENSO events with diverse amplitudes, SST patterns, and ocean-atmosphere feedbacks, causing large uncertainties in ENSO rainfall prediction. Moreover, limited instrumental observations, based on fewer than 50 ENSO events in the 20th century, are insufficient to characterize ENSO complexity and its teleconnections. This thesis uses highly-resolved paleoclimate data spanning the Last Millennium (LM), including climate models and paleoclimate data assimilation (DA) techniques, to expand 20th-century data by thousands of years. We examine the changes in ENSO characteristics and North American hydroclimate teleconnections over the LM, investigating rainfall shifts due to background temperature changes and ENSO teleconnection variability on decadal-to-centennial timescales. We first evaluate ENSO diversity and North American teleconnections over the LM. DA products show intensified Eastern Pacific El Niño in the 20th century, but no change in Central Pacific El Niño frequency. Shifts in El Niño hydroclimate teleconnections over North America are variable in magnitude but consistent in sign over the LM. Then, we present a regional focus on Mississippi River basin hydroclimate extremes, revealing that strong El Niño-like warming over the tropical Pacific and North Atlantic SST patterns jointly contribute to wet extremes across the basin and its major tributaries. Finally, we assess the stationarity of North American hydroclimate responses to various climate modes, finding that teleconnections vary on multi-decadal and multi-centennial timescales throughout the LM, driven partly by predictable SST patterns. Natural variability in rainfall patterns characterized in this work will compound with global warming to shape 21st-century conditions. This research provides new insights from paleoclimate data, expanding statistical constraints on the stationarity and predictability of ENSO impacts, and serves as a last-millennium benchmark for climate prediction and water risk assessments under the 21st-century anthropogenic warming.
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Applications of Mixed Integer Programming to Cloud Computing: Modeling and Computation
(2024-05-10) Alfant, Rachael M; Perez-Salazar, Sebastian; Schaefer, Andrew J
Demand for computing capacity in the cloud is generally not easily forecast; however, sub-optimal pricing and mis-allocation of cloud computing resources both have negative consequences for users and providers of cloud computing. This thesis approaches pricing and capacity allocation in cloud computing through the lens of stochastic mixed integer programming (SMIP), which provides a particularly useful framework for solving large, complex decision-making problems under uncertainty. Often, the uncertainty inherent to SMIPs manifests in the right-hand side (demand) vector. Thus, it is important to have a framework by which to assess a mixed integer programming (MIP) model’s quality over unknown or stochastic right-hand sides. As such, this thesis explores both theoretical and practical applications of SMIPs and MIPs with unknown right-hand sides. In particular, this thesis develops theoretical evaluative metrics for MIPs over multiple right-hand sides via gap functions, presents several stochastic optimization approaches to optimal pricing in the cloud, and formulates waste-minimizing (revenue-maximizing) SMIP models that optimize capacity allocation in the cloud.
Stochastic Scheduling: Strategies for Abandonment Management
(2024-06-23) Xu, Yihua; Perez-Salazar, Sebastian
Motivated by applications where impatience is pervasive and resources are limited, we study a job scheduling model where jobs may depart at an unknown point in time. Initially, we have access to a single server and n jobs with known non-negative values. These jobs also have unknown stochastic service and departure times with known distributional information, which we assume to be independent. When the server is free, we can run a job that has neither been run nor departed and collect its value. This occupies the server for an unknown amount of time, and we aim to design a policy that maximizes the expected total value obtained from jobs run on the server. Natural formulations of this problem suffer from the curse of dimensionality. Furthermore we show that even when the service and departure times are deterministic, our problem is NP-hard to solve. Hence, we focus on policies that can provide high expected reward compared to the optimal value. We demonstrate a polynomial-time Linear Program (LP) based approximation algorithm with guaranteed performance under mild assumptions on service times. Our methodology is flexible, allowing additional constraints to be incorporated. We develop efficient approximation algorithms with provable guarantees for extensions like job release times, deadlines, and knapsack constraints. We further extend our analysis to the setting where all jobs have independent and identically distributed (i.i.d.) service times. In this case, we show that the greedy policy that always runs the highest-valued job whenever the server is free guarantees a factor of 1/2 compared to the optimal expected value. We evaluate our LP-based policies and the greedy policy empirically on synthetic and real datasets.

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