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182W and HSE constraints from 2.7 Ga komatiites on the heterogeneous nature of the Archen mantle
(Elsevier, 2018-03-02) Puchtel, I.S.; Blichert-Toft, J.; Touboul, M.; Walker, Richard J.
While the isotopically heterogeneous nature of the terrestrial mantle has long been established, the origin, scale, and longevity of the heterogeneities for different elements and isotopic systems are still debated. Here, we report Nd, Hf, W, and Os isotopic and highly siderophile element (HSE) abundance data for the Boston Creek komatiitic basalt lava flow (BCF) in the 2.7 Ga Abitibi greenstone belt, Canada. This lava flow is characterized by strong depletions in Al and heavy rare earth elements (REE), enrichments in light REE, and initial e143Nd = +2.5 ± 0.2 and initial e176Hf = +4.2 ± 0.9 indicative of derivation from a deep mantle source with time-integrated suprachondritic Sm/Nd and Lu/Hf ratios. The data plot on the terrestrial Nd-Hf array suggesting minimal involvement of early magma ocean processes in the fractionation of lithophile trace elements in the mantle source. This conclusion is supported by a mean mu142Nd = -3.8 ± 2.8 that is unresolvable from terrestrial standards. By contrast, the BCF exhibits a positive 182W anomaly (mu182W = +11.7 ± 4.5), yet is characterized by chondritic initial g187Os = +0.1 ± 0.3 and low inferred source HSE abundances (35 ± 5% of those estimated for the present-day Bulk Silicate Earth, BSE). Collectively, these characteristics are unique among Archean komatiite systems studied so far. The deficit in the HSE, coupled with the chondritic Os isotopic composition, but a positive 182W anomaly, are best explained by derivation of the parental BCF magma from a mantle domain characterized by a predominance of HSE-deficient, differentiated late accreted material. According to the model presented here, the mantle domain that gave rise to the BCF received only ~35% of the present-day HSE complement in the BSE before becoming isolated from the rest of the convecting mantle until the time of komatiite emplacement at 2.72 Ga. These new data provide strong evidence for a highly heterogeneous Archean mantle in terms of absolute HSE abundances and W isotopic composition, and also indicate slow mixing, on a timescale of at least 1.8 billion years. Additionally, the data are consistent with a stagnant-lid plate tectonic regime in the Hadean and Archean, prior to the onset of modern-style plate tectonics.
Adaptive magnetorheological fluid energy absorption systems: a review
(Institute of Physics, 2024-03-01) Bai, Xianxu 'Frank'; Zhang, Xinchi; Choi, Young; Shou, Mengje; Zhu, Guanghong; Wereey, Norman M.; Wereley, Norman
In the last two decades, magnetorheological (MR) fluids have attracted extensive attention since they can rapidly and continuously control their rheological characteristics by adjusting an external magnetic field. Because of this feature, MR fluids have been applied to various engineering systems. This paper specifically investigates the application of MR fluids in shock mitigation control systems from the aspects of three key technical components: the basic structural design of MR fluid-based energy absorbers (MREAs), the analytical and dynamical model of MREAs, and the control method of adaptive MR shock mitigation control systems. The current status of MR technology in shock mitigation control is presented and analyzed. Firstly, the fundamental mechanical analysis of MREAs is carried out, followed by the introduction of typical MREA configurations. Based on mechanical analysis of MREAs, the structural optimization of MREAs used in shock mitigation control is discussed. The optimization methods are given from perspectives of the design of piston structures, the layout of electromagnetic coil, and the MR fluid gap. Secondly, the methods of damper modeling for MREAs are presented with and without consideration of the inertia effect. Then both the modeling methods and their characteristics are introduced for representative parametric dynamic models, semi-empirical dynamic models, and non-parametric dynamic models. Finally, the control objectives and requirements of the shock mitigation control systems are analyzed, and the current competitive methods for the ideal ‘soft-landing’ control objectives are reviewed. The typical control methods of MR shock mitigation control systems are discussed, and based on this the evaluation indicators of the control performance are summarized.
Age, genetics, and crystallization sequence of the group IIIE iron meteorites
(Elsevier, 2023-06-14) Chiappe, Emily M.; Ash, Richard; Walker, Richard J.
Chemical and isotopic data were obtained for ten iron meteorites classified as members of the IIIE group. Nine of the IIIE irons exhibit broadly similar bulk siderophile element characteristics. Modeling of highly siderophile element abundances suggests that they can be related to one another through simple crystal-liquid fractionation of a parent melt. Our preferred model suggests initial S, P, and C concentrations of approximately 12 wt%, 0.8 wt %, and 0.08 wt%, respectively. The modeled IIIE parent melt composition is ~4 times more enriched in highly siderophile elements than a non-carbonaceous (NC) chondrite-like parent body, suggesting a core comprising ~22% of the mass of the parent body. Although chemically distinct from the other IIIE irons, formation of the anomalous IIIE iron Aletai can potentially be accounted for under the conditions of this model through the nonequilibrium mixing of an evolved liquid and early formed solid. Cosmic ray exposure-corrected nucleosynthetic Mo, Ru, and W isotopic compositions of four of the bona fide IIIE irons and Aletai indicate that they originated from the non-carbonaceous (NC) isotopic domain. Tungsten-182 isotopic data for the IIIE irons and Aletai yield similar model metal-silicate segregation ages of 1.6 ± 0.8 Myr and 1.2 ± 0.8 Myr, respectively, after calcium aluminum-rich inclusion (CAI) formation. These ages are consistent with those reported for other NC-type iron meteorite parent bodies. The IIIE irons are chemically and isotopically similar to the much larger IIIAB group. Despite some textural, mineralogical, and chemical differences, such as higher C content, the new results suggest they may have originated from a different crystallization sequence on the same or closely-related parent body.
Anthracite Memories: Semantic Tagging and Coal Mining Oral Histories
(2023) Paul A. Shackel
Oral histories are a critical source of information about lived experiences of past events. They have been analyzed both for their form – linguistically as texts, performances, and expressive accounts – and their content for understanding historic events and personal experiences. Here we focus on sentiment analysis approaches frequently applied to big data research questions, but less often utilized by anthropologists working with oral histories. Oral histories collected half a century ago in the anthracite mining communities of northeastern Pennsylvania are examined by considering methodological and historical questions. This project explores how oral history and data science might be productively combined to understand these now historic communities' everyday lives and working conditions. Bakhtin's (1981) concept of chronotope helps us understand the memory of these anthracite coal mining communities' daily life and working conditions.
Black Sexual Minority Adults’ Avoidance of Professional Mental Health Care
(Psychiatric Services, 2023) Williams, Natasha D.; Turpin, Rodman E.; Boekeloo, Bradley O.; King-Marshall, Evelyn C.; Fish, Jessica N.
Objective: The authors sought to determine whether Black sexual minority individuals were more likely than White sexual minority individuals to postpone or avoid professional mental health care (PMHC) and, if so, to identify the reasons for postponing or avoiding care. Methods: Analyses were conducted with a subsample of cisgender Black (N=78) and White (N=398) sexual minority individuals from a larger survey of U.S. adults administered via MTurk in 2020 (N=1,012). Logistic regression models were used to identify racial differences in overall postponement or avoidance of care as well as differences in the prevalence of each of nine reasons for postponing or avoiding care. Results: Black sexual minority individuals were more likely than their White counterparts to report ever postponing or avoiding PMHC (average marginal effect [AME]=13.7 percentage points, 95% CI=5.4–21.9). Black sexual minority people also were more likely than their White counterparts to cite beliefs that they should work out their problems on their own (AME=13.1 percentage points, 95% CI=1.2–24.9) or with family and friends (AME=17.5 percentage points, 95% CI=6.0–29.1) and to cite providers’ refusal to treat them (AME=17.4 percentage points, 95% CI=7.6–27.1) as reasons for postponing or avoiding care. Conclusions: Black sexual minority individuals were more likely than their White counterparts to report delaying or avoiding PMHC. Personal beliefs about managing mental health and providers’ refusal to offer treatment influenced Black sexual minority individuals’ willingness or ability to seek PMHC.
Characterization of Magnetorheological Impact Foams in Compression
(MDPI, 2024-06-14) Choi, Young; Wereley, Norman M.; Wereley, Norman M.
This study focuses on the development and compressive characteristics of magnetorheo- logical elastomeric foam (MREF) as an adaptive cushioning material designed to protect payloads from a broader spectrum of impact loads. The MREF exhibits softness and flexibility under light compressive loads and low strains, yet it becomes rigid in response to higher impact loads and ele- vated strains. The synthesis of MREF involved suspending micron-sized carbonyl Fe particles in an uncured silicone elastomeric foam. A catalyzed addition crosslinking reaction, facilitated by platinum compounds, was employed to create the rapidly setting silicone foam at room temperature, simplify- ing the synthesis process. Isotropic MREF samples with varying Fe particle volume fractions (0%, 2.5%, 5%, 7.5%, and 10%) were prepared to assess the effect of particle concentrations. Quasi-static and dynamic compressive stress tests on the MREF samples placed between two multipole flexible strip magnets were conducted using an Instron servo-hydraulic test machine. The tests provided measurements of magnetic field-sensitive compressive properties, including compression stress, energy absorption capability, complex modulus, and equivalent viscous damping. Furthermore, the experimental investigation also explored the influence of magnet placement directions (0◦ and 90◦) on the compressive properties of the MREFs.
Connecting Spaces: Gender, Video Games and Computing in the Early Teens
(Sage, 2023-04) Ashlock, Jennifer; Stojnic, Miodrag; Tufekci, Zeynep
Informed by evidence that computing attitudes may be uniquely constructed in informal contexts and that the early teens are a key period for academic decision-making, we investigate lines of practice that connect computing skills, attitudes, and videogames. We compare the relationship between computer skill, computer efficacy, and activities associated with gaming using a data set of 3,868 children in middle school. The time that children spend gaming has very modest association with skill and efficacy. Accounting for the frequency with which children modify games, engage in social gaming activities, and the salience of gamer identity explains the gender gap in computer skill and significantly narrows the gender gap in computer efficacy. We find support for the argument that computer skill and efficacy are dependent on children connecting often isolated social contexts, a socially embedded characteristic of the digital divide.
Disparities in Toxic Chemical Exposures and Associated Neurodevelopmental Outcomes: A Scoping Review and Systematic Evidence Map of the Epidemiological Literature
(2023-09-27) Payne-Sturges, Devon C.; Taiwo, Tanya Khemet; Ellickson, Kristie; Mullen, Haley; Tchangalova, Nedelina ; Anderko, Laura ; Chen, Aimin ; Swanson, Maureen
BACKGROUND: Children are routinely exposed to chemicals known or suspected of harming brain development. Targeting Environmental Neuro-Development Risks (Project TENDR), an alliance of more than 50 leading scientists, health professionals, and advocates, is working to protect children from these toxic chemicals and pollutants, especially the disproportionate exposures experienced by children from families with low incomes and families of color. OBJECTIVE: This scoping review was initiated to map existing literature on disparities in neurodevelopmental outcomes for U.S. children from population groups who have been historically economically/socially marginalized and exposed to seven exemplar neurotoxicants: combustion-related air pollution (AP), lead (Pb), mercury (Hg), organophosphate pesticides (OPs), phthalates (Phth), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs). METHODS: Systematic literature searches for the seven exemplar chemicals, informed by the Population, Exposure, Comparator, Outcome (PECO) framework, were conducted through 18 November 2022, using PubMed, CINAHL Plus (EBSCO), GreenFILE (EBSCO), and Web of Science sources. We examined these studies regarding authors’ conceptualization and operationalization of race, ethnicity, and other indicators of sociodemographic and socioeconomic disadvantage; whether studies presented data on exposure and outcome disparities and the patterns of those disparities; and the evidence of effect modification by or interaction with race and ethnicity. RESULTS: Two hundred twelve individual studies met the search criteria and were reviewed, resulting in 218 studies or investigations being included in this review. AP and Pb were the most commonly studied exposures. The most frequently identified neurodevelopmental outcomes were cognitive and behavioral/psychological. Approximately a third (74 studies) reported investigations of interactions or effect modification with 69% (51 of 74 studies) reporting the presence of interactions or effect modification. However, less than half of the studies presented data on disparities in the outcome or the exposure, and fewer conducted formal tests of heterogeneity. Ninety-two percent of the 165 articles that examined race and ethnicity did not provide an explanation of their constructs for these variables, creating an incomplete picture. DISCUSSION: As a whole, the studies we reviewed indicated a complex story about how racial and ethnic minority and low-income children may be disproportionately harmed by exposures to neurotoxicants, and this has implications for targeting interventions, policy change, and other necessary investments to eliminate these health disparities. We provide recommendations on improving environmental epidemiological studies on environmental health disparities. To achieve environmental justice and health equity, we recommend concomitant strategies to eradicate both neurotoxic chemical exposures and systems that perpetuate social inequities.
Family Rejection and LGBTQ+ Asian Americans’ Psychological Distress and Disordered Eating: The Role of Conflicts in Allegiances and Familial Shame
(2024) Pease, M V.; Le, Thomas P.; Ahn, Lydia HaRim
LGBTQ+ Asian Americans experience unique psychological health concerns at the intersection of multiple forms of marginalization. White supremacist, cisheteronormative, and colonial ideals and their structural and interpersonal manifestations may encourage family rejection of LGBTQ+ identities within Asian American family units. Family shame, conflicts in allegiances, and internalized anti-LGBTQ+ stigma were hypothesized as mediators in the association between family rejection and psychological distress and disordered eating. The current study examined family rejection and its impacts on psychological distress and disordered eating in a sample of LGBTQ+ Asian American adults (N = 155; MAge = 24.26; 30.3% Gender Diverse) using a cross-sectional survey design and path analysis. There was a significant serial mediation such that family rejection was positively associated with conflicts in allegiances, which was positively associated with familial shame, which was positively associated with psychological distress (B = .12, p = .01). The same serial mediation was nonsignificant for disordered eating (B = .04, p = .26). Results indicate the importance of considering conflicts in allegiances, family shame, and the interpersonal dynamics of LGBTQ+ Asian Americans in understanding experiences of psychological distress and disordered eating. Implications are drawn for further research, clinical work, and broader efforts addressing the larger sociocultural environment that encourages familial rejection of LGBTQ+ identity.
Floral traits and their connection with pollinators and climate
(Oxford Academic, 2024-03-19) Basnett, Shweta; Krpan, Julia; Espindola, Anahi
Floral characteristics vary significantly among plant species, and multiple underlying factors govern this diversity. Although it is widely known that spatial variation in pollinator groups can exert selection on floral traits, the relative contribution of pollinators and climate to the variation of floral traits across large geographical areas remains a little-studied area. Besides furthering our conceptual understanding of these processes, gaining insight into the topic is also of conservation relevance: understanding how climate might drive variation in floral traits can serve to protect plant–pollinator interactions in globally change conditions. We used Rhododendron as a model system and collected floral traits (corolla length, nectar volume and concentrations), floral visitors and climatic data on 21 Rhododendron species across two continents (North America, Appalachians and Asia, Himalaya). Based on this, we quantified the influence of climate and pollinators on floral traits using phylogeny-informed analyses. Our results indicate that there is substantial variation in pollinators and morphological traits across Rhododendron species and continents. We came across four pollinator groups: birds, bees, butterflies and flies. Asian species were commonly visited by birds, bees and flies, whereas bees and butterflies were the most common visitors of North American species. The visitor identity explained nectar trait variation, with flowers visited by birds presenting higher volumes of dilute nectar and those visited by insects producing concentrated nectar. Nectar concentration and corolla length exhibited a strong phylogenetic signal across the analysed set of species. We also found that nectar trait variation in the Himalayas could also be explained by climate, which presented significant interactions with pollinator identity. Our results indicate that both pollinators and climate contribute and interact to drive nectar trait variation, suggesting that both can affect pollination interactions and floral (and plant) evolution individually and in interaction with each other.
Geodynamic implications of ophiolitic chromitites in the La Cabaña ultramafic bodies, Central Chile
(Taylor & Francis, 2014-07-18) González-Jiménez, José María; Barra, Fernando; Walker, Richard J.; Reich, Martin; Gervilla, Fernando
Chromitites (>80% volume chromite) hosted in two ultramafic bodies (Lavanderos and Centinela Bajo) from the Palaeozoic metamorphic basement of the Chilean Coastal Cordillera were studied in terms of their chromite composition, platinum group element (PGE) abundances, and Re-Os isotopic systematics. Primary chromite (Cr# = 0.64–0.66; Mg# = 48.71–51.81) is only preserved in some massive chromitites from the Centinela Bajo ultramafic body. This chemical fingerprint is similar to other high-Cr chromitites from ophiolite complexes, suggesting that they crystallized from arc-type melt similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction mantle. The chromitites display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 180 and 347 ppb, as is typical of chromitites hosted in the mantle of supra-subduction zone (SSZ) ophiolites. Laurite (RuS2)-erlichmanite (OsS2) phases are the most abundant inclusions of platinum-group minerals (PGM) in chromite, indicating crystallization from S-undersaturated melts in the subarc mantle. The metamorphism associated with the emplacement of the ultramafic bodies in the La Cabaña has been determined to be ca. 300 Ma, based on K-Ar dating of fuchsite. Initial 187Os/188Os ratios for four chromitite samples, calculated for this age, range from 0.1248 to 0.1271. These isotopic compositions are well within the range of chromitites hosted in the mantle section of other Phanaerozoic ophiolites. Collectively, these mineralogical and geochemical features are interpreted in terms of chromite crystallization in dunite channels beneath a spreading centre that opened a marginal basin above a supra-subduction zone. This implies that chromitite-bearing serpentinites in the metamorphic basement of the Coastal Cordillera are of oceanic-mantle origin and not oceanic crust as previously suggested. We suggest that old subcontinental mantle underlying the hypothetical Chilenia micro-continent was unroofed and later altered during the opening of the marginal basin. This defined the compositional and structural framework in which the protoliths of the meta-igneous and meta-sedimentary rocks of the Eastern and Western Series of the Chilean Coastal Cordillera basement were formed.
Growing Uncertainty in Marriage Expectations among U.S. Youth
(Socius, 2024-03-26) Cohen, Philip N.; Pepin, Joanna R.
Marriage rates are falling in the United States. The authors ask whether today's young adults are likely to continue this trend. Using Monitoring the Future Public-Use Cross-Sectional Datasets (1976-2022), this visualization presents U.S. 12th graders' marriage expectations. It shows declining optimism that they will be "very good" spouses and declining expectations that they will eventually marry. Both trends are prominent in the last 10 years of the survey, and both are more dramatic among young women than among young men. If these trends hold, it may foretell further declines in marriage rates in the coming years.
Hello World! Building Computational Models to Represent Social and Organizational Theory
(2024) Grand, James A.; Braun, Michael T.; Kuljanin, Goran
Computational modeling holds significant promise as a tool for improving how theory is developed, expressed, and used to inform empirical research and evaluation efforts. However, the knowledge and skillsets needed to build computational models are rarely developed in the training received by social and organizational scientists. The purpose of this manuscript is to provide an accessible introduction to and reference for building computational models to represent theory. We first discuss important principles and recommendations for “thinking about” theory and developing explanatory accounts in ways that facilitate translating their core assumptions, specifications, and ideas into a computational model. Next, we address some frequently asked questions related to building computational models that introduce several fundamental tasks/concepts involved in building models to represent theory and demonstrate how they can be implemented in the R programming language to produce executable model code. The accompanying supplemental materials describes additional considerations relevant to building and using computational models, provides multiple examples of complete computational model code written in R, and an interactive application offering guided practice on key model-building tasks/concepts in R.
High-Precision Tungsten Isotopic Analysis by Multicollection Negative Thermal Ionization Mass Spectrometry Based on Simultaneous Measurement of W and 18O/16O Isotope Ratios for Accurate Fractionation Correction
(American Chemical Society, 2016-01-11) Trinquier, Anne; Touboul, Mathieu; Walker, Richard J.
Determination of the 182W/184W ratio to a precision of ±5 ppm (2σ) is desirable for constraining the timing of core formation and other early planetary differentiation processes. However, WO3 − analysis by negative thermal ionization mass spectrometry normally results in a residual correlation between the instrumental-mass-fractionation-corrected 182W/184W and 183W/184W ratios that is attributed to mass-dependent variability of O isotopes over the course of an analysis and between different analyses. A second-order correction using the 183W/184W ratio relies on the assumption that this ratio is constant in nature. This may prove invalid, as has already been realized for other isotope systems. The present study utilizes simultaneous monitoring of the 18O/16O and W isotope ratios to correct oxide interferences on a per-integration basis and thus avoid the need for a double normalization of W isotopes. After normalization of W isotope ratios to a pair of W isotopes, following the exponential law, no residual W−O isotope correlation is observed. However, there is a non-ideal mass bias residual correlation between 182W/iW and 183W/iW with time. Without double normalization of W isotopes and on the basis of three or four duplicate analyses, the external reproducibility per session of 182W/184W and 183W/184W normalized to 186W/183W is 5−6 ppm (2σ, 1−3 μg loads). The combined uncertainty per session is less than 4 ppm for 183W/184W and less than 6 ppm for 182W/184W (2σm) for loads between 3000 and 50 ng.
In Search of Late-Stage Planetary Building Blocks
(Elsevier, 2015-07-03) Walker, Richard J.; Bermingham, Katherine; Liu, Jingao; Puchtel, Igor S.; Touboul, Mathieu; Worsham, Emily A.
Genetic contributions to the final stages of planetary growth, including materials associated with the giant Moon-forming impact, late accretion, and late heavy bombardment are examined using siderophile elements. Isotopic similarities between the Earth and Moon for both lithophile and siderophile elements collectively lead to the suggestion that the genetics of the building blocks for Earth, and the impactor involved in the Moon-forming event were broadly similar, and shared some strong genetic affinities with enstatite chondrites. The bulk genetic fingerprint of materials subsequently added to Earth by late accretion, defined as the addition of ~0.5 wt.% of Earth's mass to the mantle, following cessation of core formation, was characterized by 187Os/188Os and Pd/Ir ratios that were also similar to those in some enstatite chondrites. However, the integrated fingerprint of late accreted matter differs from enstatite chondrites in terms of the relative abundances of certain other HSE, most notably Ru/Ir. The final ≤0.05 wt.% addition of material to the Earth and Moon, believed by some to be part of a late heavy bombardment, included a component with much more fractionated relative HSE abundances than evidenced in the average late accretionary component. Heterogeneous 182W/184Wisotopic compositions of some ancient terrestrial rocks suggest that some very early formed mantle domains remained chemically distinct for long periods of time following primary planetary accretion. This evidence for sluggish mixing of the early mantle suggests that if late accretionary contributions to the mantle were genetically diverse, it may be possible to isotopically identify the disparate primordial components in the terrestrial rock record using the siderophile element tracers Ru and Mo.
Maryland Biology Expectations Survey (MBEX) for characterizing student epistemology in biology courses
(2024) Hall, Kristi L.; Chatzikyriakidou, Kyriaki; Redish, Edward F.; Cooke, Todd J.
The Maryland Biology Expectations Survey (MBEX) is a pre-post survey instrument that was designed by Hall (2013) to evaluate the changes of student epistemology occurring in an introductory biology course (Cooke et al., 2023). The MBEX addresses four epistemic themes: principles vs. facts, independence vs. authority, interdisciplinary reasoning vs. siloed thinking, and connection (= relevance) vs. isolation (Hall, 2013). The major difference between MBEX-1 statements and MBEX-2 statements resides in the interdisciplinary reasoning cluster. MBEX-1 incorporates more chemistry-related statements, whereas MBEX-2 focuses almost exclusively on math and physics. It turns out that biology students showed very favorable attitudes toward chemistry in their pre-course MBEX-1 responses, which reduced the ability of that survey to reveal any post-course changes in student attitudes toward interdisciplinary reasoning. This website includes the following files: • MBEX-1 survey • MBEX-2 survey • Cluster assignments, polarization, and correspondence of MBEX-1 and MBEX-2 statements. For further information, email either Kyriaki Chatzikyriakidou (kchatzikyriak@gmail.com) or Todd Cooke (tjcooke@umd.edu). References Cooke, T. J., Jensen, J. S., Carleton, K. L., Hall, K. L., Jardine, H. E., Kent, B. W., Redish, E.F., and Shultz, J. W. (2023). Group active engagements for facilitating principles-based learning in introductory organismal biology. American Biology Teacher 85 (6): 317–326. https://doi.org/10.1525/abt.2023.85.6.317 Hall, K. L. (2013). Examining the effects of students’ classroom expectations on undergraduate biology course reform. Ph.D. Dissertation in Digital Resources at the University of Maryland. https://drum.lib.umd.edu/items/91d250d1-0890-4adc-a040-6b9c9b5eff40
Oceanic and continental lithospheric mantle in the 1.95 Ga Jormua Ophiolite Complex, Finland: implications for mantle and crustal evolution
(Oxford, 2023-10-31) Finlayson, Valerie; Haller, Mitchell; Day, James M.D.; Ginley, Stephen; O'Driskoll, Brian; Kontinen, Asko; Hanski, Eero; Walker, Richard J.
The ca. 1.95 Ga Jormua Ophiolite Complex (JOC), Finland, is a rare Paleoproterozoic ophiolite that preserves a record of diverse upper mantle materials and melting processes. Meter-scale grid sampling of four JOC outcrops, as well as non-grid samples, permits evaluation of meter- to kilometer-scale mantle heterogeneity within the JOC. Significant heterogeneity is observed between the four grids, and also among a number of the non-grid samples examined. Variations in the concentrations of fluid-mobile elements are particularly large among different samples and locations. New whole-rock major, lithophile trace, and highly siderophile element data (HSE: Os, Ir, Ru, Pt, Pd, Re), including 187Re-187Os isotopic data, for serpentinized harzburgites indicate the presence of two distinct compositional types and probable modes of origin within the JOC. This is consistent with prior findings. Type 1 is similar to modern refractory abyssal-type mantle. Type 2 is more highly refractory than Type 1, and most likely represents samples from sub-continental lithospheric mantle (SCLM). Type 1 mantle is moderately heterogeneous with respect to chemical and Os isotopic compositions at both the meter and kilometer scales. By contrast, Type 2 mantle is considerably more homogeneous than Type 1 grids at the meter scale, but is more heterogeneous at the kilometer scale. The median initial γOs value for Type 1 mantle, calculated for 1.95 Ga, is ~-2.0 (where γOs is the % deviation in 187Os/188Os relative to a chondritic reference calculated for a specified time). This isotopic composition is consistent with a moderate, long-term decrease in Re/Os relative to the estimate for Primitive Mantle, prior to JOC formation. The similarity in this γOs value to the value for the modern abyssal mantle, as well as the initial values for several Phanerozoic ophiolites suggests that the upper mantle achieved a Re/Os ratio similar to the chondritic reference by ~2 Ga, then evolved along a subparallel trajectory to the chondritic reference since then. For this to occur, only limited Re could have been permanently removed from the upper mantle since at least the time the JOC formed. A localized secondary metasomatic event at ~2 Ga, concurrent with the estimated obduction age for the JOC and subsequent Svecofennian Orogeny, affected the HSE systematics of some Type 1 samples. By contrast, late Archean Os TRD model ages for Type 2 rocks indicate a depletion event superimposed upon the long-term Re depletion of the abyssal mantle. This event was established no later than ~2.6 Ga and may have occurred during a period of significant, well-documented crustal production in the Karelia craton at ~2.7 Ga.
Preservation of Earth-forming events in the W isotopic 1 composition of modern flood basalts
(Science Magazine, 2016-05-13) Rizo, Hanika; Walker, Richard J.; Carlson, Richard W.; Horan, Mary F.; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G.
How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth’s primary accretionary period have survived to the present.
Prevention is a Privilege: Black Drug-free Community Leaders Implementing Drug-free Community Coalitions in Black Communities
(Journal of Ethnicity in Substance Abuse, 2024-02-15) Quinton, Sylvia L.; Burgon E; Hicks Harper, P. Thandi; Parker, Rosalind M.; Cunningham, Suzanne Randolph; Boekeloo, Bradley O.
Community-based interventions for youth substance use prevention require high levels of capacity to organize and coordinate community resources to support youth development and create opportunities to prevent youth substance use. This project aimed to better understand what Black prevention practitioners perceive as the requirements for a successful drug-free community coalition. Black prevention practitioners, who were engaged in drug-free community funded coalitions had discussions about coalitions as a strategy for youth substance use prevention in Black communities. These facilitated discussions resulted in consensus over a set of nine core principles regarding successful youth substance use prevention coalition building in these communities.
Quantized topological energy pumping and Weyl points in Floquet synthetic dimensions with a driven-dissipative photonic molecule
(Nature Physics, 2024-02-26) Sridhar, Sashank; Ghosh, Sayan; Dutt, Avik
Topological effects manifest in a wide range of physical systems, such as solid crystals, acoustic waves, photonic materials and cold atoms. These effects are characterized by `topological invariants' which are typically integer-valued, and lead to robust quantized channels of transport in space, time, and other degrees of freedom. The temporal channel, in particular, allows one to achieve higher- dimensional topological effects, by driving the system with multiple incommensurate frequencies. However, dissipation is generally detrimental to such topological effects, particularly when the systems consist of quantum spins or qubits. Here we introduce a photonic molecule subjected to multiple RF/optical drives and dissipation as a promising candidate system to observe quantized transport along Floquet synthetic dimensions. Topological energy pumping in the incommensurately modulated photonic molecule is enhanced by the driven-dissipative nature of our platform. Furthermore, we provide a path to realizing Weyl points and measuring the Berry curvature emanating from these reciprocal-space (k-space) magnetic monopoles, illustrating the capabilities for higher-dimensional topological Hamiltonian simulation in this platform. Our approach enables direct k-space engineering of a wide variety of Hamiltonians using modulation bandwidths that are well below the free-spectral range (FSR) of integrated photonic cavities.