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Search for third generation vector-like leptons with the ATLAS detector
Get PDFThe Standard Model of particle physics provides a concise description of the building blocks of our universe in terms of fundamental particles and their interactions. It is an extremely successful theory, providing a plethora of predictions that precisely match experimental observation. In 2012, the Higgs boson was observed at CERN and was the last particle predicted by the Standard Model that had yet-to-be discovered. While this added further credibility to the theory, the Standard Model appears incomplete. Notably, it only accounts for 5% of the energy density of the universe (the rest being ``dark matter'' and ``dark energy''), it cannot resolve the gravitational force with quantum theory, it does not explain the origin of neutrino masses and cannot account for matter/anti-matter asymmetry. The most plausible explanation is that the theory is an approximation and new physics remains.
Vector-like leptons are well-motivated by a number of theories that seek to provide closure on the Standard Model. They are a simple addition to the Standard Model and can help to resolve a number of discrepancies without disturbing precisely measured observables. This thesis presents a search for vector-like leptons that preferentially couple to tau leptons. The search was performed using proton-proton collision data from the Large Hadron Collider collected by the ATLAS experiment from 2015 to 2018 at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 139 inverse femtobarns. Final states of various lepton multiplicities were considered to isolate the vector-like lepton signal against Standard Model and instrumental background. The major backgrounds mimicking the signal are from WZ, ZZ, tt+Z production and from mis-identified leptons. A number of boosted decision trees were used to improve rejection power against background where the signal was measured using a binned-likelihood estimator. No excess relative to the Standard Model was observed. Exclusion limits were placed on vector-like leptons in the mass range of 130 to 898 GeV
Bear Beta or Speculative Beta?—Reconciling the Evidence on Downside Risk Premium
Get PDFThis article develops a new approach to explain why risk factors constructed from index option returns are priced in the stock market. We decompose an option-based factor into three main components and identify the one responsible for the beta–return relationship. Applying this method to the bear risk factor proposed by Lu and Murray reveals that the negative correlation between bear betas and stock returns does not reflect systematic risk premia. Instead, it represents an anomaly closely related to the betting-against-beta puzzle. We trace the root of this anomaly to disagreement concerning the aggregate stock market. Our work reconciles the conflicting evidence concerning downside risk by showing that neither ex-post nor ex-ante downside risk is priced in the cross-section of stocks while making a methodological contribution that facilitates more accurate interpretation of option-based risk factors in future research.Ye
Strategies For Overcoming the Grand Challenges of Implementing Environmental Flows: A Coupled Human and Natural Systems Perspective
Get PDFGlobal declines in freshwater biodiversity and the ecosystem services freshwater ecosystems provide have prompted a call for accelerated and expanded implementation of conservation interventions to bend the curve on these losses. Environmental flows are recognized as a powerful freshwater conservation tool to boost biodiversity and ecosystem services through targeted water releases from dams, however widespread implementation is lacking. Because implementing environmental flows requires careful planning and consideration of both humans and nature, there are many challenges conservation planners face as they attempt to boost implementation. The research presented in this dissertation aims to provide strategies to overcome the challenges facing environmental flows implementation by conceptualizing and modeling environmental flows as a coupled human and natural system. The first project presented a conceptual framework to identify locations with both high biodiversity value and conservation feasibility to target for e-flows implementation across future climate uncertainty. Despite climate uncertainty, some locations were identified as high conservation priority. This research suggests that despite significant conservation planning challenges, environmental flows can still be implemented, and offers a conservation planning framework that can be used in other settings. The second project tested different simulated scenarios in an incentive-based Payment for Ecosystem Services (PES) water conservation initiative to identify tradeoffs between equity and conservation outcomes. This research found that aiming for an equitable distribution of payments to reduce water consumption and reallocate that water to environmental flows does not result in large tradeoffs to conservation outcomes. This research suggests that prioritizing equity does not sacrifice conservation outcomes and provides a framework for testing equity tradeoffs in PES schemes. The third project surveyed water decision-makers to identify their perspectives on the barriers and data needs to implementing environmental flows. This research found that despite decision makers’ different perspectives on future water conditions, they identified the same barriers and data needs. This research suggests that cooperation on complex human-environmental problems could happen despite strongly held values and beliefs that might otherwise inhibit implementation. The fourth project tested whether targeting influential individuals in conservation networks as early adopters of an environmental flows initiative would boost overall adoption. This research found robust results that targeting influential individuals boosted overall adoption across spatial scales and information diffusion models. This research suggests that to help accelerate and expand environmental flows initiative adoption, influential individuals should be targeted as early adopters. The results presented in this dissertation contribute to current high-priority research efforts in conservation science that aim to help bend the curve on freshwater biodiversity loss by accelerating and expanding the implementation of environmental flows. Overall, considering the needs of both people and nature is key to successful environmental flows implementation
Accelerating Distributed Synthetic Aperture Radar Data Simulations Via CUDA
Get PDFA general simulation of distributed synthetic aperture radar (DSAR) data is useful to evaluate the theoretical performance of a DSAR system and its underlying algorithms without a deployed system in place. Simulating DSAR is a computationally intensive task due to the size and complexity of the resultant data, but a simulation must complete within a reasonable amount of time to be a useful tool in practice. Through the use of both MATLAB and CUDA, a DSAR simulation can be flexible and modifiable while benefiting from efficiently implemented GPU acceleration. Multiple simulation programs have been developed using these programming languages to explore techniques of parallelizing and optimizing the performance of DSAR data simulation
Development of ecological engineering solutions to mine water biogeochemistry and hydrology challenges
No full textAbandoned underground mines can cause a variety of environmental problems, including mine drainage (MD) that negatively impacts thousands of kilometers of streams worldwide. Underground mines accumulate water after pumping operations cease that can discharge to the surface as MD via hydraulically connected mine features such as mine shafts, drill holes, and mining fractures. Aquatic ecosystems receiving MD show signs of impairment such as decreased dissolved oxygen and increased metals concentrations, acidity, and turbidity which can result in habitat alterations and decreases in biological diversity. However, passive treatment can effectively remediate MD.
The study site is the abandoned Picher mining field, located in northeast Oklahoma and southeast Kansas in the central United States, which is part of the Tri-State Lead-Zinc Mining District, Tar Creek Superfund Site (TCSS) and Cherokee County Superfund Site. In the Picher field, mining operations occurred from the early 1900s through the 1970s, producing over 1.5 million metric tons (m-tons) of Pb and 8.0 million m-tons of Zn. The Picher field covers approximately 145 km2, with an estimated underground void volume of at least 9,870 hectare-meters (80,000 ac-ft). After mining ceased and the last pumps were stopped, the mine voids refilled. The first identified MD discharges occurred in 1979 and contained elevated concentrations of Cd, Fe, Pb, and Zn. Today, there are multiple sources of MD throughout the TCSS, two of which continue to be successfully remediated following the implementation of passive treatment systems (PTSs). However, the largest sources of MD, located near the abandoned town of Douthat, OK, remain untreated.
The first objective of this research was to evaluate the effects of implementing PTS on the fish communities of the receiving stream, an unnamed tributary (UT) to Tar Creek that was historically impacted by two sources of MD (Chapter Two). Fish collections were periodically conducted over sixteen years: before the implementation of PTS (2005-2007), after the implementation of the first PTS (Mayer Ranch PTS (MRPTS), 2009-2016), and after the implementation of the second PTS (Southeast Commerce (SECPTS),2017-2021). It was hypothesized that the species richness and diversity of the fish communities would significantly increase following the implementation of PTS. The fish communities in the UT were negatively impacted by the elevated metals concentrations before the implementation of PTS. Both PTSs were shown to significantly decrease Cd, Fe, Pb, and Zn total metals concentrations of the MD discharges (p < 0.05). Fish communities downstream of Mayer Ranch showed a significant increase in species richness and diversity following the implementation of MRPTS (p < 0.05). The mean species richness and Shannon diversity at one site increased from 2.22 to 5.83 and 0.26 to 1.04, respectively. Similarly, after the implementation of SECPTS, the site immediately downstream of the system effluent showed an increase in mean species richness and Shannon diversity of 1.83 to 6.83 and 0.20 to 1.21, respectively. Overall, the findings of this study showed the implementation of PTS to remediate MD can result in a significant increase in the fish species richness and diversity in the receiving stream.
The next study focused on the evaluation of the biological communities in Tar Creek. Rapid bioassessment protocols (RBPs) for fish, benthic macroinvertebrates, and habitat were conducted at six sites along an 11-km reach of Tar Creek to determine if the contamination from the abandoned mining operations in the Picher field were negatively impacting the biological communities and to examine the longitudinal extent of these impacts downstream (Chapter Three). It was hypothesized that biological indices for fish and benthic macroinvertebrate communities in a MD impacted stream would improve with distance from the mining-impacted area and that the sites furthest from the mining-impacted area would have statistically similar metric scores when compared to reference conditions from the same ecoregion. The two most upstream locations (TC1 and TC2) were within the mining-impacted area. TC1 was impacted by waste material from the mining operations which generate elevated aqueous metals concentrations and highly erodible streambeds. TC2, located immediately downstream, received additional contamination from approximately 3,000 liters per minute (lpm) of untreated MD from the Douthat discharges that entered the stream between TC1 and TC2, resulting in increased aqueous iron concentrations that formed iron hydroxide precipitates coating the stream channel bottom. The benthic macroinvertebrate and fish communities at TC1 and TC2 were substantially impaired with significantly lower taxa richness, Shannon diversity, and total RBP metric scores compared to regional reference conditions (p < 0.05). However, the RBP metric scores increased with increasing distance from the mining impacts, and the RBP metric scores at the most downstream site (11 km from the mining impacts) were not significantly different than the regional reference conditions. The study concluded that contamination from abandoned mining operations caused substantial impairments on biological communities in the receiving stream, but high-quality communities downstream are a potential source for upstream recolonization if the contamination were to be remediated.
The remainder of this dissertation focused on untreated MD discharges at Douthat, including mapping the underground mine workings to better understand mine pool hydrology and connectivity (Chapter Four), characterizing the water quality and quantity of untreated discharges (chapter Five), proposing conceptual PTS designs to remediate untreated MD (Chapter Six), and characterizing the mine pool to identify possible mine pool recharge sources (Chapter Seven). The nominal head elevations of the mine pool intersect ground elevations at Douthat, resulting in multiple artesian MD discharges from open boreholes, collapse features, and mine shafts. Five discharges were regularly sampled for water quality from 2018 to 2021, and weirs were installed at three locations with pressure sensors that logged measurements every fifteen minutes to collect continuous flow measurements (Chapter Five). Flow data were plotted against corresponding mine pool elevations to develop trendlines to estimate MD flow rates at any mine pool elevation. It was hypothesized that MD water quality and quantity at Douthat was treatable via PTS. Water quality data showed that the Douthat discharges were treatable via PTS because metals concentrations were less than values for discharges at Southeast Commerce and Mayer Ranch that have been successfully remediated by MRPTS and SECPTS since 2008 and 2017, respectively. The flow weighted average total metals concentrations of the five discharges at Douthat were 0.022 mg/L Cd, 22.6 mg/L Fe, 0.045 mg/L Pb, and 5.76 mg/L Zn. The calculated flow rates that corresponded with the median and maximum mine pool elevations measured from 2009 to 2021 at a USGS monitoring station were 4,046 lpm and 154,000 lpm, respectively. The maximum flow rates were short duration, often less than 37 hours, that corresponded with substantial increases in mine pool elevations that correlated with elevated streamflow-associated flooding events. Multiple open mine shafts near streams were field located and were verified to take-on substantial amounts of water from the stream during elevated streamflow events and were referred to as known inflow locations. The mapped underground mined voids showed these known inflow locations were connected via open void space to the Douthat discharge locations (Chapters Four and Five). The study concluded that the water quantity of the Douthat discharges was treatable via PTS, despite the elevated flow rates, because other treatment wetlands with design flowrates exceeding the maximum flow rate calculated at the Douthat discharges have been designed, constructed, and continue to successfully operate.
The findings from Chapter five were used to design two conceptual PTSs capable of remediating MD at Douthat. PTS-1 was designed based on the median flow rate, assuming elevated flow events would be eliminated following the closure of known inflow locations. PTS-2 was designed to remove 90% of the metals contamination from the discharges based on the current flow rates, which included the elevated flow events. An 11-year simulation based on mine pool elevations and streamflow measurements from USGS stations was then performed to compare the metals loading to Tar Creek from MD and downstream metals concentrations for three scenarios: 1) untreated MD, 2) implementation of PTS-1, and 3) implementation of PTS-2. It was hypothesized that without the implementation of a passive treatment system to treat net-alkaline MD discharges, Tar Creek water quality would not meet state-designated beneficial use classifications more than 50% of the time, even if all other sources of metals contamination upstream of the discharges (e.g., waste piles) were addressed (Chapter Six). The simulation showed that the annual average metals loading from untreated MD to Tar Creek was approximately 46 kg Cd, 65,900 kg Fe, 137 kg Pb, and 15,454 kg Zn, resulting in downstream Zn concentrations not meeting hardness adjusted acute Zn criteria 82% of the time and downstream Cd concentrations not meeting the hardness adjusted chronic Cd criteria 90% of the time. However, the implementation of either conceptual PTS significantly decreased metals loading of Cd, Fe, Pb, and Zn to the receiving stream. The simulation showed PTS-1 treated 66% of the MD volume, and the downstream concentrations met the state-designated beneficial use criteria for fish and wildlife propagation for all metals 95% of the time. PTS-2, which treated 90% of the MD volume during the simulation period, met the state-designated beneficial use criteria for all metals 99.997% of the time. The study concluded that even if all other sources of contamination to Tar Creek were remediated, the stream would not meet the state-designated beneficial use criteria for fish and wildlife propagation a majority of the time. However, the conceptual PTS designs showed that PTS can be implemented to remediate the Douthat MD discharges, and the downstream water quality would substantially improve.
The final study of this dissertation characterized water chemistry of the mine pool to determine if stable isotope ratios of 2H and 18O in water and selected water quality parameters could be used to identify individual mine pool recharge sources (Chapter Seven). The three potential recharges sources included: 1) precipitation, 2) the unconfined aquifer where the mining occurred, and 3) a confined aquifer located below the unconfined aquifer and the underground mine workings. It was hypothesized that aqueous isotope ratios 2H and 18O measured in each potential recharge source would be significantly different, and the differences in the isotopic signatures of each potential recharge source could be used to identify distinct sources of water contributing to the mine pool. The study found that there was no significant difference in deuterium between the three sources (p > 0.05), and only the confined aquifer had significantly different 18O values (p < 0.05). However, conservative ions that were present in elevated concentrations in the groundwater compared to rainfall, such as sodium and chloride, may be an effective tool to differentiate between mine pool recharge sources. The unconfined aquifer had mean chloride and sodium concentrations of 23.7 mg/L and 45.4 mg/L, respectively, while rainfall measured <0.15 mg/L for both ions. Comparatively, mean chloride and sodium concentrations measured in the mine pool were 11.4 mg/L and 30.3 mg/L, respectively. These findings suggest that the unconfined aquifer and rainfall are substantial recharges sources. Mass balances of mean concentrations of Na and Cl indicate rainfall accounts for 30% to 50% of mine pool recharge. Therefore, the study concluded that limiting surface water interactions with the mine pool could substantially decrease mine pool recharge and flow rates at Douthat