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Detrital Zircon Record of Magmatism and Sediment Dispersal Across the North American Cordilleran Arc System (28–48°N)
Get PDFAs zircon U-Pb geochronology has become a leading method in sediment provenance studies and basin analysis over the past 20 years, the volume of detrital zircon data made available in published literature has enabled researchers to go beyond source-to-sink provenance studies to explore increasingly complex geologic problems. In this review, we utilize the growing body of detrital zircon data acquired from Jurassic-Paleocene forearc and foreland basin strata of the North American Cordillera to investigate the Mesozoic to earliest Cenozoic evolution of the arc and its associated basins between 28°N and 48°N. Our compilation includes 830 detrital zircon samples (101,898 individual ages) from 70 studies published between 2000 and 2020. For comparative purposes, we also compile 1307 igneous zircon U-Pb ages that characterize the magmatic history of the arc. We place primary emphasis on detrital zircon ages between 251 and 56 Ma that we infer to be uniquely derived from magmatic sources in the arc. Informed by existing knowledge of magmatic, structural, and sedimentological processes that acted on the orogen, we investigate spatial and temporal trends in these “arc-derived zircon” to establish a detrital record of arc magmatism, investigate source-to-sink relationships between the arc and adjacent basins, and discuss controls on sediment dispersal across the orogen. Our review shows that compilations of detrital zircon data from the Cordilleran forearc and foreland basin systems are excellent proxies for arc magmatism because the basins are enriched in arc-derived zircon and compilations provide space- and time-integrated records of crystallization ages. The compiled detrital zircon data support a history of continuous arc magmatism throughout Mesozoic and earliest Cenozoic time, characterized by low-volume magmatism from Triassic-Early Jurassic time (~251–174 Ma) and episodic higher-volume magmatism from Middle Jurassic-Late Cretaceous time (~174–66 Ma). These trends elucidate the initiation and timing of magmatic events at the orogen-scale and corroborate our understanding of cyclic arc behavior. Detrital zircon distributions are spatially and temporally variable both within and across basins, which we discuss relative to topographic development of the orogen and attendant responses of sediment dispersal systems. Detrital zircon distributions in the forearc signal rapid transfer of sediment from the arc to basins dominantly via fluvial processes. In contrast, detrital zircon distributions across the foreland reflect the presence of topographic barriers in the hinterland region of the arc that effectively isolated parts of the foreland. The presence of hinterland topography in turn highlights the important role of ash-fall events in delivering arc-derived zircon to the foreland, underscoring the need to consider ash-fall processes in paleodrainage reconstructions. These broad regional trends, and in general the close linkage between orogenic process and sediment dispersal, emerge from our compilation because it averages out much of the local variability observed in studies of more limited geographic or temporal extent
Formula SAE: Final Design Report
Get PDFThe primary objectives of this year’s senior design team were to deliver a fully functional FSAE race car that would be competition-ready by June 2021. Prior to this year, the chassis had been fully constructed, the suspension had been fully installed, and the engine had been fully mounted into the car. In addition, our team’s objectives are to complete the subsystems of the car which includes the following: body panels, engine wiring, electronic control unit (ECU) hardware and software, cockpit, brakes, steering, and wheels.
This year, the team finished many sectors on the car such as the headrest, body panels, brakes, internal wiring, ECU wiring, the seat, and wheel alignment. Along with finishing the subsystems, this year’s team was also tasked with designing and manufacturing the car body that would fulfill all of the FSAE guidelines and requirements. This includes maintaining driver visibility, offering adequate protection to subsystems, and being clear and free from interacting with other moving components of the car. In the Fall semester in 2020, the team designed CAD models of the body in Fusion360 and selected fiberglass as the material of choice based on multiple criteria. In the spring semester of 2021, the team fully manufactured and mounted the fiberglass body panels onto the car. This year’s FSAE team has not completed the vinyl wrap and due to the failure of some electronic components, the car is not currently running.
The mechanical issues that arose this year were all resolved, however the main difficulties were with the electrical subsystems. Future teams will need to troubleshoot the relay systems to ensure adequate voltage is reaching all engine and ECU components. Seeing as the relay systems have not been in use in over four years, it may be necessary to order some new electronic systems. Similarly, the team feels that it is important that each team fully understands the importance of the tuning process. The team recommends that each future team use TunerStudio to tune the car to their specifications. As of May 1, 2021, the ECU communication with the software needs to be improved, and needs to be returned to include upgrades to the daughter board. The team has already placed an order for these components and plans on installing them in an attempt for one last engine test. If the team does not successfully complete this last test, future teams should look to the ECU and engine relay systems
Life History and Environment Predict Variation in Testosterone Across Vertebrates
No full textEndocrine systems act as key intermediaries between organisms and their environments. This interaction leads to high variability in hormone levels, but we know little about the ecological factors that influence this variation within and across major vertebrate groups. We study this topic by assessing how various social and environmental dynamics influence testosterone levels across the entire vertebrate tree of life. Our analyses show that breeding season length and mating system are the strongest predictors of average testosterone concentrations, whereas breeding season length, environmental temperature, and variability in precipitation are the strongest predictors of within-population variation in testosterone. Principles from small-scale comparative studies that stress the importance of mating opportunity and competition on the evolution of species differences in testosterone levels, therefore, likely apply to the entire vertebrate lineage. Meanwhile, climatic factors associated with rainfall and ambient temperature appear to influence variability in plasma testosterone, within a given species. These results, therefore, reveal how unique suites of ecological factors differentially explain scales of variation in circulating testosterone across mammals, birds, reptiles, amphibians, and fishes
Uncovering Internalized Whiteness Through Critical Race Counterstories: Navigating Our Experiences in the State of Texas
No full textThis chapter illustrates that critical theories can function as methods and that critical scholars should continue to take them up as legitimate forms of research. Critical Race counterstories function as a way to center the narratives of the multiply marginalized. Counterstories also function to connect communities together who share similar experiences with oppression as a means of providing support and validation – recognizing that their experiences are shared. Counterstories traditionally provide a format for which to convert the lived realities of People of Color into narratives that can be used to understand the intricacies of white supremacy and whiteness in different contexts. The removal and detachment from cultural and ethnic identity in schools for communities of color has a clear history, not only nationally, but specifically in Texas. As Critical Race scholars people argue that the seductiveness of whiteness remains highly intact, even when living in contexts that are predominantly of color
Implications of Giant Ooids for the Carbonate Chemistry of Early Triassic Seawater
No full textLower Triassic limestones contain giant ooids (\u3e2 mm) along with other precipitated carbonate textures more typical of Precambrian strata. These features appear to have resulted from changes in seawater chemistry associated with the end-Permian mass extinction, but quantifying the carbonate chemistry of Early Triassic seawater has remained challenging. To constrain seawater carbonate saturation state, dissolved inorganic carbon, alkalinity, and pH, we applied a physicochemical model of ooid formation constrained by new size data on Lower Triassic ooids from south China, finding that the Triassic giant ooids require a higher carbonate saturation state than typifies modern sites of ooid formation. Model calculations indicate that Early Triassic oceans were at least seven times supersaturated with respect to aragonite and calcite. When combined with independent constraints on atmospheric pCO2 and oceanic [Ca2+], these findings require that Early Triassic oceans had more than twice the modern levels of dissolved inorganic carbon and alkalinity and a pH near 7.6. Such conditions may have played a role in inhibiting the recovery of skeletal animals and algae during Early Triassic tim
“Two Schools Within a School”: Elitism, Divisiveness, and Intra-Racial Gentrification in a Dual Language Strand
No full textWith most elementary dual language bilingual education (DLBE) programs being implemented as strands within schools, tensions related to inequities, unequal distribution of resources, and academic quality and demographic differences often arise. Based on a longitudinal ethnographic study and two interview phases with DLBE and mainstream teachers, this study analyzes teachers’ perceptions and discourses regarding tensions related to the Spanish-English two-way bilingual education program at their urban elementary school. Findings from a thematic analysis approach pointed to teachers’ discourses of elitism and divisiveness in relation to the DLBE strand based on racial tensions and school inequities, including what we call intra-racial DLBE gentrification. These findings are based on how educators experienced tensions regarding this bilingual program related to (a) the composition of the student body in terms of perceived quality and quantity, (b) cognitive and academic benefits, (c) resources provided by a university partnership, and (d) parental involvement. Implications for administrators and teacher preparation programs toward equity and school integration with DLBE strands are discussed
Improving Quantitative Abilities and Attitudes in Clinical Psychology Courses: Longitudinal Assessment of a Blended Learning Intervention
No full textBackground: Many students report negative attitudes toward research methods and statistics (RMS), and these attitudes are associated with impaired performance. Student interest in clinical psychology suggests that clinical courses may provide a promising venue for integrating RMS instruction. This approach may be particularly valuable for students from underrepresented groups in psychology.
Objective: We evaluated whether integrating core RMS concepts into undergraduate clinical psychology courses using a blended learning intervention improved students’ quantitative knowledge and attitudes. Exploratory analyses assessed whether the intervention had differential efficacy for students from underrepresented groups.
Method: Students completed pre- and post-course assessments of content knowledge, perceived RMS competence, implicit theories of quantitative skills, and statistics anxiety. We compared changes in student outcomes before (n = 101) and after (n = 91) implementing the blended learning intervention.
Results: Overall, the intervention did not result in greater improvements in content knowledge, perceived RMS competence, or statistics anxiety. However, exploratory analyses suggested that the intervention was more effective for first-generation and racial/ethnic minority students. Change in endorsement of a growth-oriented mindset for quantitative skills was marginally stronger among students in courses implementing the blended learning intervention.
Conclusion: These findings suggest that integrating RMS content in clinical psychology courses may confer modest benefits for students’ knowledge and attitudes toward quantitative skills, especially among students from underrepresented groups
Influence of Mechanical Layering and Natural Fractures on Undercutting and Rapid Headward Erosion (Recession) at Canyon Lake Spillway, Texas, U.S.A
Get PDFThis study investigates the role of mechanical layering and fractures on flood-related erosional undercutting and resulting rapid spillway recession. In the summer of 2002, 86 cm of rain fell in an 8-day period across the Guadalupe River drainage basin in central Texas, causing Canyon Lake reservoir to completely fill and overtop the emergency spillway for the first time. The resulting flood incised a gorge into the mechanically layered Glen Rose Formation and caused headward erosion (recession) at the downstream edge of the emergency spillway. Comparison of pre- and post-flood imagery and assessment of flood records indicates that maximum recession localized at the northern end of the emergency spillway where 28 m recession occurred. This recession occurred at an estimated rate of up to 10 m/day during the first ~3 days of the flood, which is among the highest rates of recorded bedrock recession. Analysis of historical photographs, field observations and measurement of erosional undercutting, along with measurements of fracture orientation, fracture spacing, and mechanical rebound are used to understand rock mass characteristics that influenced erosional undercutting and rapid recession of the spillway. Evidence of significant undercutting was observed where incompetent argillaceous wackestone (marl) underlies competent limestone. These results reveal that the greatest amount and rate of recession of the spillway was associated with undercutting and toppling collapse of fracture-bounded limestone blocks. Block size may be a factor in continuation of the process, in that large blocks may accumulate at the base of the scarp and inhibit continued erosional undercutting, whereas in other areas smaller eroded blocks can be carried away by the floodwaters and undercutting may continue, facilitating recession. The combination of mechanical contrast between layers and natural fractures in competent layers together contributed to exceptionally high rates of headward erosion. Observed rock mass erodibility behavior was in the range of medium to high erodibility in limestone with widely spaced fractures that would normally be expected to have very low erodibility. Bulk rock mass erodibility in this situation was similar to the most erodibile layer, specifically, the marl at base of spillway pour-off cliff
The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)-Oxo Complex
No full textIn this paper, we report the preparation, spectroscopic and theoretical characterization, and reactivity studies of a Co(IV)–oxo complex bearing an N4-macrocyclic coligand, 12-TBC (12-TBC = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane). On the basis of the ligand and the structure of the Co(II) precursor, [CoII(12-TBC)(CF3SO3)2], one would assume that this species corresponds to a tetragonal Co(IV)–oxo complex, but the spectroscopic data do not support this notion. Co K-edge XAS data show that the treatment of the Co(II) precursor with iodosylbenzene (PhIO) as an oxidant at −40 °C in the presence of a proton source leads to a distinct shift in the Co K-edge, in agreement with the formation of a Co(IV) intermediate. The presence of the oxo group is further demonstrated by resonance Raman (rRaman) spectroscopy. Interestingly, the EPR data of this complex show a high degree of rhombicity, indicating structural distortion. This is further supported by the EXAFS data. Using DFT calculations, a structural model is developed for this complex with a ligand-protonated structure that features a Co═O···HN hydrogen bond and a four-coordinate Co center in a seesaw-shaped coordination geometry. Magnetic circular dichroism (MCD) spectroscopy further supports this finding. The hydrogen bond leads to an interesting polarization of the Co–oxo π-bonds, where one O(p) lone-pair is stabilized and leads to a regular Co(d) interaction, whereas the other π-bond shows an inverted ligand field. The reactivity of this complex in hydrogen atom and oxygen atom transfer reactions is discussed as well
Legitimacy in Public Recreation: Examining Rhetorical Shifts in Institutional Creation and Maintenance
Get PDFThis paper uncovers the rhetorical strategies used by the National Recreation and Park Association (NRPA) to affect institutional discourse and field logics during the first 25 years of its existence (1965-1990). Analyzing editorials featured in the organization’s flagship publication, Parks & Recreation, we describe how the NRPA sought to establish itself as the legitimate steward of public recreation, sport, and leisure in the U.S. by utilizing five rhetorical approaches: normalization, rationalization, moralization, authorization, and anti-authorization. Furthermore, we identify discrete patterns and combinations of strategies that have thus far not been described in the literature. Our research adds to prior sport-related institutional work scholarship, which has examined the importance of legitimacy in attempting to establish alternative modes of organizing and functioning in a field dominated by powerful incumbents, by offering an alternative look at the ‘starting-from-scratch’ establishment of a unified field logic