Sedimentary pyrite formed in the water column, or during diagenesis in organic muds, provides an accessible proxy for seawater chemistry in the marine rock record. Except for Mo, U, Ni and Cr, ...surprisingly little is known about trace element trends in the deep time oceans, even though they are critical to developing better models for the evolution of the Earthʼs atmosphere and evolutionary pathways of life. Here we introduce a novel approach to simultaneously quantify a suite of trace elements in sedimentary pyrite from marine black shales. These trace element concentrations, at least in a first-order sense, track the primary elemental abundances in coeval seawater. In general, the trace element patterns show significant variation of several orders of magnitude in the Archaean and Phanerozoic, but less variation on longer wavelengths in the Proterozoic. Certain trace elements (e.g., Ni, Co, As, Cr) have generally decreased in the oceans through the Precambrian, other elements (e.g., Mo, Zn, Mn) have generally increased, and a further group initially increased and then decreased (e.g., Se and U). These changes appear to be controlled by many factors, in particular: 1) oxygenation cycles of the Earthʼs ocean–atmosphere system, 2) the composition of exposed crustal rocks, 3) long term rates of continental erosion, and 4) cycles of ocean anoxia. We show that Ni and Co content of seawater is affected by global Large Igneous Province events, whereas redox sensitive trace elements such as Se and Mo are affected by atmosphere oxygenation. Positive jumps in Mo and Se concentrations prior to the Great Oxidation Event (GOE1, c. 2500 Ma) suggest pulses of oxygenation may have occurred as early as 2950 Ma. A flat to declining pattern of many biologically important nutrient elements through the mid to late Proterozoic may relate to declining atmosphere O2, and supports previous models of nutrient deficiency inhibiting marine evolution during this period. These trace elements (Mo, Se, U, Cu and Ni) reach a minimum in the mid Cryogenian and rise abruptly toward the end of the Cryogenian marking the position of a second Great Oxidation Event (GOE2).
•Sedimentary pyrite provides a record of the trace element history of oceans.•Many trace elements show extreme first order variations through time.•Ni and Co content of seawater partly reflects the time distribution of LIP events.•Se content of sedimentary pyrite is proposed as a proxy for ocean–atmosphere O2.•O2 in atmosphere declined in Late Proterozoic to reach a minimum in the Cryogenian.
This study examines concurrent teacher-student interaction quality and 5th graders' (n = 387) engagement in mathematics classrooms (n = 63) and considers how teacher-student interaction quality ...relates to engagement differently for boys and girls. Three approaches were used to measure student engagement in mathematics: Research assistants observed engaged behavior, teachers reported on students' engagement, and students completed questionnaires. Engagement data were conducted 3 times per year concurrent with measures of teacher-student interaction quality. Results showed small but statistically significant associations among the 3 methods. Results of multilevel models showed only 1 significant finding linking quality of teacher-student interactions to observed or teacher-reported behavioral engagement; higher classroom organization related to higher levels of observed behavioral engagement. However, the multilevel models produced a rich set of findings for student-reported engagement. Students in classrooms with higher emotional support reported higher cognitive, emotional, and social engagement. Students in classrooms higher in classroom organization reported more cognitive, emotional, and social engagement. Interaction effects (Gender × Teacher-student interaction quality) were present for student-reported engagement outcomes but not in observed or teacher-reported engagement. Boys (but not girls) in classrooms with higher observed classroom organization reported more cognitive and emotional engagement. In classrooms with higher instructional support, boys reported higher but girls reported lower social engagement. The discussion explores implications of varied approaches to measuring engagement, interprets teacher-student interaction quality and gender findings, and considers the usefulness of student report in understanding students' math experiences.
ABSTRACT
We present BVRI and unfiltered light curves of 93 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search (LOSS) follow-up program conducted between 2005 and 2018. Our sample ...consists of 78 spectroscopically normal SNe Ia, with the remainder divided between distinct subclasses (3 SN 1991bg-like, 3 SN 1991T-like, 4 SNe Iax, 2 peculiar, and 3 super-Chandrasekhar events), and has a median redshift of 0.0192. The SNe in our sample have a median coverage of 16 photometric epochs at a cadence of 5.4 d, and the median first observed epoch is ∼4.6 d before maximum B-band light. We describe how the SNe in our sample are discovered, observed, and processed, and we compare the results from our newly developed automated photometry pipeline to those from the previous processing pipeline used by LOSS. After investigating potential biases, we derive a final systematic uncertainty of 0.03 mag in BVRI for our data set. We perform an analysis of our light curves with particular focus on using template fitting to measure the parameters that are useful in standardizing SNe Ia as distance indicators. All of the data are available to the community, and we encourage future studies to incorporate our light curves in their analyses.
The concentration of atmospheric oxygen (pO2) is thought to have increased throughout Earth history, punctuated by rapid increases ca. 2.4 and 0.8 billion years ago near the beginning and end of the ...Proterozoic Eon. As photosynthesis is the largest source of free O2, the reigning paradigm of rising O2 levels centres around biologic metabolism. Here we show that the phosphorus content of igneous rocks correlates, in a first-order sense, with secular increases in O2 through time, suggesting that rising O2 levels are affected by long-term mantle cooling and its effect on the continental phosphorus inventory. Because phosphorus is the limiting nutrient for primary productivity, its availability has fundamental control over the efficiency of oxygenic photosynthesis, pointing to a previously unrecognized role of the solid Earth in biologic and atmospheric evolution. Furthermore, as many bio-essential elements are effectively incompatible in the mantle, this relationship has implications for any terrestrial planet. All planets will cool, and those with efficient plate tectonic convection will cool more rapidly. We are left concluding that the speed of such cooling may affect pattern of biological evolution on any habitable planet.
•Increases in O2 are affected by mantle cooling and its effect on phosphorus supply.•Periods of dominant mafic or felsic magmatism can in part explain dynamic pO2.•The rate of mantle cooling can affect the speed of biological evolution.
A galaxy cluster acts as a cosmic telescope over background galaxies but also as a cosmic microscope magnifying the imperfections of the lens. The diverging magnification of lensing caustics enhances ...the microlensing effect of substructure present within the lensing mass. Fine-scale structure can be accessed as a moving background source brightens and disappears when crossing these caustics. The recent discovery of a distant lensed star near the Einstein radius of the galaxy cluster MACSJ1149.5+2223 allows a rare opportunity to reach subsolar-mass microlensing through a supercritical column of cluster matter. Here we compare these observations with high-resolution ray-tracing simulations that include stellar microlensing set by the observed intracluster starlight and also primordial black holes that may be responsible for the recently observed LIGO events. We explore different scenarios with microlenses from the intracluster medium and black holes, including primordial ones, and examine strategies to exploit these unique alignments. We find that the best constraints on the fraction of compact dark matter (DM) in the small-mass regime can be obtained in regions of the cluster where the intracluster medium plays a negligible role. This new lensing phenomenon should be widespread and can be detected within modest-redshift lensed galaxies so that the luminosity distance is not prohibitive for detecting individual magnified stars. High-cadence Hubble Space Telescope monitoring of several such optimal arcs will be rewarded by an unprecedented mass spectrum of compact objects that can contribute to uncovering the nature of DM.
Mismatch negativity (MMN) is a scalp-recorded electrical potential that occurs in humans in response to an auditory stimulus that defies previously established patterns of regularity. MMN amplitude ...is reduced in people with schizophrenia. In this study, we aimed to develop a robust and replicable rat model of MMN, as a platform for a more thorough understanding of the neurobiology underlying MMN. One of the major concerns for animal models of MMN is whether the rodent brain is capable of producing a human-like MMN, which is not a consequence of neural adaptation to repetitive stimuli. We therefore tested several methods that have been used to control for adaptation and differential exogenous responses to stimuli within the oddball paradigm. Epidural electroencephalographic electrodes were surgically implanted over different cortical locations in adult rats. Encephalographic data were recorded using wireless telemetry while the freely-moving rats were presented with auditory oddball stimuli to assess mismatch responses. Three control sequences were utilized: the flip-flop control was used to control for differential responses to the physical characteristics of standards and deviants; the many standards control was used to control for differential adaptation, as was the cascade control. Both adaptation and adaptation-independent deviance detection were observed for high frequency (pitch), but not low frequency deviants. In addition, the many standards control method was found to be the optimal method for observing both adaptation effects and adaptation-independent mismatch responses in rats. Inconclusive results arose from the cascade control design as it is not yet clear whether rats can encode the complex pattern present in the control sequence. These data contribute to a growing body of evidence supporting the hypothesis that rat brain is indeed capable of exhibiting human-like MMN, and that the rat model is a viable platform for the further investigation of the MMN and its associated neurobiology.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Molybdenum (Mo) is a popular paleoproxy for tracking the spatiotemporal pattern of euxinic (anoxic and sulfidic) conditions in the ancient ocean, yet surprisingly little is known about the processes ...leading to its fixation under sulfidic conditions. Pyrite has been proposed to be the main host phase for Mo sequestration. To clarify the role played by pyrite, and thus to refine the utility of this paleoproxy, modern and ancient samples from six different study sites were analyzed, all representing euxinic conditions, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Although pyrite often shows substantial enrichments relative to average crust and even matrix samples of similar size, our results show that most of the Mo in euxinic muds and shales is found in the non-pyrite matrix (80–100%) and not in the pyrite grains (0–20%)—simply because the volume of matrix dominates the bulk sediments/rocks. A relationship between the percent of Mo hosted by pyrite and the sulfur isotope composition of that pyrite is observed and can be linked to post-depositional alteration. Specifically, the oldest, typically most altered samples, show the highest δ34S values because of limited sulfate availability at the time of their formation in the early ocean. In these old samples, the relatively small amount of Mo sequestered initially within pyrite is more likely to have been released to the matrix during the strong recrystallization overprints that these rocks have disproportionately suffered. Despite the universal importance of appreciable H2S availability during Mo uptake, we conclude that pyrite should be viewed as a nontrivial sink for Mo but clearly not the primary host in most euxinic shales and rather suggest that other burial pathways should be emphasized in future studies of the mechanisms of Mo sequestration in such settings.
We present extensive optical photometric and spectroscopic observations, from 4 to 482 days after explosion, of the Type II-plateau (II-P) supernova (SN) 2017eaw in NGC 6946. SN 2017eaw is a normal ...SN II-P intermediate in properties between, for example, SN 1999em and SN 2012aw and the more luminous SN 2004et, also in NGC 6946. We have determined that the extinction to SN 2017eaw is primarily due to the Galactic foreground and that the SN site metallicity is likely subsolar. We have also independently confirmed a tip-of-the-red-giant-branch (TRGB) distance to NGC 6946 of 7.73 0.78 Mpc. The distances to the SN that we have also estimated via both the standardized candle method and expanding photosphere method corroborate the TRGB distance. We confirm the SN progenitor identity in pre-explosion archival Hubble Space Telescope (HST) and Spitzer Space Telescope images, via imaging of the SN through our HST Target of Opportunity program. Detailed modeling of the progenitor's spectral energy distribution indicates that the star was a dusty, luminous red supergiant consistent with an initial mass of ∼15 M .
Purpose This study compares retrospective functional and magnetic resonance imaging (MRI) outcomes after arthroscopic bone marrow stimulation (BMS) with and without concentrated bone marrow aspirate ...(cBMA) as a biological adjunct to the surgical treatment of osteochondral lesions (OCLs) of the talus. Methods Twenty-two patients who underwent arthroscopic BMS with cBMA (cBMA/BMS group) for an osteochondral lesion (OCL) of the talus and 12 patients who underwent arthroscopic BMS (BMS alone) for an OCL of the talus were retrospectively reviewed. The Foot and Ankle Outcome Score (FAOS) pain subscale and Short Form 12 general health questionnaire physical component summary score (SF-12 PCS) provided patient-reported outcome scores pre- and postoperatively. MRI scans were assessed postoperatively using the magnetic resonance observation of cartilage repair tissue (MOCART) score. All patients had postoperative MRI performed at the 2-year postoperative visit, and quantitative T2 mapping relaxation time values were assessed in a subset of the cBMA/BMS group. Results The mean FAOS and SF-12 PCS scores improved significantly pre- to post-operatively ( P < .01) at a mean follow-up of 48.3 months (range, 34 to 82 months) for the cBMA/BMS group and 77.3 months (range, 46 to 100 months) for the BMS-alone group. The MOCART score in the cBMA/BMS group was significantly higher than that in the BMS-alone group ( P = .023). Superficial and deep T2 relaxation values in cBMA/BMS patients were higher in repair tissue compared with measurements in adjacent native articular cartilage ( P = .030 and P < .001, respectively). Conclusions BMS is an effective treatment strategy for treatment of OCLs of the talus and results in good medium-term functional outcomes. Arthroscopic BMS with cBMA also results in similar functional outcomes and improved border repair tissue integration, with less evidence of fissuring and fibrillation on MRI. Level of Evidence Level III, retrospective comparative study.
PDF
