Abstract
We study the effect of tidal forcing on gravitational wave signals from tidally relaxed white dwarf pairs in the LISA, DECIGO and BBO frequency band (0.1 − 100 mHz). We show that for stars ...not in hydrostatic equilibrium (in their own rotating frames), tidal forcing will result in energy and angular momentum exchange between the orbit and the stars, thereby deforming the orbit and producing gravitational wave power in harmonics not excited in perfectly circular synchronous binaries. This effect is not present in the usual orbit-averaged treatment of the equilibrium tide, and is analogous to transit timing variations in multiplanet systems. It should be present for all LISA white dwarf pairs since gravitational waves carry away angular momentum faster than tidal torques can act to synchronize the spins, and when mass transfer occurs as it does for at least eight LISA verification binaries. With the strain amplitudes of the excited harmonics depending directly on the density profiles of the stars, gravitational wave astronomy offers the possibility of studying the internal structure of white dwarfs, complimenting information obtained from asteroseismology of pulsating white dwarfs. Since the vast majority of white-dwarf pairs in this frequency band are expected to be in the quasi-circular state, we focus here on these binaries, providing general analytic expressions for the dependence of the induced eccentricity and strain amplitudes on the stellar apsidal motion constants and their radius and mass ratios. Tidal dissipation and gravitation wave damping will affect the results presented here and will be considered elsewhere.
Whole-class discussion is a common instructional approach used by secondary science teachers. When orchestrated well, such an approach can provide students with opportunities to engage in extensive ...science talk with the benefit of teacher guidance and feedback. Our study investigated teachers' approaches to discussion during the piloting of an urban ecology curriculum designed to support student participation in science discourse as well as teachers' beliefs about science talk. Participants included five secondary science teachers and their students (n = 116). Our analysis focused on transcripts of whole-class discussions and interviews with teachers about their beliefs regarding talk. We found that the students' contributions during discussions were typically limited to simple phrases or short sentence responses that did not voluntarily include reasoning. The teachers' framing of the lessons and the moves the teachers made during the discussions seemed to reinforce the limited nature of the students' responses. Furthermore, we found that teachers rarely used probing questions or tossed back students' ideas. The beliefs teachers expressed about their students, themselves, and external factors provided insight into why teachers continued to take an authoritative stance even though they believed teacher-driven discussion was not the ideal.
The role of the teacher is essential for students' successful engagement in scientific inquiry practices. This study focuses on teachers' use of an 8-week chemistry curriculum that explicitly ...supports students in one particular inquiry practice, the construction of scientific arguments to explain phenomena in which students justify their claims using evidence and reasoning. Participants included 6 teachers and 568 students. Videotapes, teacher questionnaires, and student pre- and posttests were analyzed to develop case studies that characterized the support the teachers provided their students for scientific argumentation and subsequent student learning. Patterns from the case studies suggest that one particular instructional practice, the way teachers defined scientific argumentation, characterized teachers' support and influenced the other practices they used in their classrooms. In some cases, the teachers' definitions of scientific argumentation did not align with the intended learning goal in the curriculum materials. These teachers' greater simplification of this complex inquiry practice resulted in decreased learning gains in terms of students' ability to write scientific arguments to explain phenomena using appropriate evidence and reasoning. Educative curriculum materials can have a positive impact on teachers' classroom support for scientific argumentation, but how the teachers use these materials influences student learning.
A mesocosm experiment was conducted to quantify the effects of reduced pH and elevated temperature on an intact marine invertebrate community. Standardised faunal communities, collected from the ...extreme low intertidal zone using artificial substrate units, were exposed to one of eight nominal treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16°C). After 60 days exposure communities showed significant changes in structure and lower diversity in response to reduced pH. The response to temperature was more complex. At higher pH levels (8.0 and 7.7) elevated temperature treatments contained higher species abundances and diversity than the lower temperature treatments. In contrast, at lower pH levels (7.3 and 6.7), elevated temperature treatments had lower species abundances and diversity than lower temperature treatments. The species losses responsible for these changes in community structure and diversity were not randomly distributed across the different phyla examined. Molluscs showed the greatest reduction in abundance and diversity in response to low pH and elevated temperature, whilst annelid abundance and diversity was mostly unaffected by low pH and was higher at the elevated temperature. The arthropod response was between these two extremes with moderately reduced abundance and diversity at low pH and elevated temperature. Nematode abundance increased in response to low pH and elevated temperature, probably due to the reduction of ecological constraints, such as predation and competition, caused by a decrease in macrofaunal abundance. This community-based mesocosm study supports previous suggestions, based on observations of direct physiological impacts, that ocean acidification induced changes in marine biodiversity will be driven by differential vulnerability within and between different taxonomical groups. This study also illustrates the importance of considering indirect effects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidification and global warming on marine communities.
In early placental development, progenitor cytotrophoblasts (CTB) differentiate along one of two cellular trajectories: the villous or extravillous pathways. CTB committed to the villous pathway fuse ...with neighboring CTB to form the outer multinucleated syncytiotrophoblast (SCT), whereas CTB committed to the extravillous pathway differentiate into invasive extravillous trophoblasts (EVT). Unfortunately, little is known about the processes controlling human CTB progenitor maintenance and differentiation. To address this, we established a single cell RNA sequencing (scRNA-seq) dataset from first trimester placentas to identify cell states important in trophoblast progenitor establishment, renewal and differentiation. Multiple distinct trophoblast states were identified, representing progenitor CTB, column CTB, SCT precursors and EVT. Lineage trajectory analysis identified a progenitor origin that was reproduced in human trophoblast stem cell organoids. Heightened expression of basal cell adhesion molecule (BCAM) defined this primitive state, where BCAM enrichment or gene silencing resulted in enhanced or diminished organoid growth, respectively. Together, this work describes at high-resolution trophoblast heterogeneity within the first trimester, resolves gene networks within human CTB progenitors and identifies BCAM as a primitive progenitor marker and possible regulator.
African American and Hispanic women report less physical activity (PA) than non-Hispanic White women. As such, a digitally-enhanced 16-week social support pilot intervention was conducted to promote ...PA among African American and Hispanic women dyads. This study quantitatively and qualitatively examined the engagement and satisfaction of participants (N = 30; 15 dyads) assigned to the intervention. Intervention participants received telephone counseling calls based on motivational interviewing and a Jawbone UP activity monitor. Intervention engagement and satisfaction data were collected from the Jawbone UP, call logs, self-report questionnaires conducted at the 16-week follow-up, and two post-intervention focus groups. Nonparametric tests assessed group differences across engagement and satisfaction measures, and a manually-driven coding scheme was used to evaluate emerging themes from qualitative text. Participants demonstrated high engagement in the telephone counseling sessions and moderate engagement with the Jawbone UP. Friend/co-worker dyads and participants who were 45 years and older were more likely to use the device. Qualitative results emphasized participants’ appreciation for the counseling calls, the Jawbone UP, and the overall dyadic framework of the study to collectively nurture social support and accountability for PA. Overall, the intervention group reacted positively to study components. Additional research is needed to understand the role of technology in facilitating long-lasting PA change via social support in minority populations.
The southern Hikurangi subduction zone exhibits significant along‐strike variation in convergence rate and obliquity, sediment thickness and, uniquely, the increasing proximity of southern Hikurangi ...to, and impingement on, the incoming continental Chatham Rise, an ancient Gondwana accretionary complex. There are corresponding changes in the morphology and structure of the Hikurangi accretionary prism. We combine widely spaced multichannel seismic reflection profiles with high resolution bathymetry and previous interpretations to characterize the structure and the history of the accretionary prism since 2 Ma. The southern Hikurangi margin can be divided into three segments. A northeastern segment (A) characterized by a moderately wide (∼70 km), low taper (∼5°) prism recording uninhibited outward growth in the last ∼1 Myr. Deformation resolvable in seismic reflection data accounts for ∼20 % of plate convergence, comparable with the central Hikurangi margin further North. A central segment (B) characterized by a narrow (∼30 km), moderate taper (∼8°) prism, with earlier (∼2‐∼1 Ma) shortening than segment A. Outward prism growth ceased coincidentally with development of major strike‐slip faults in the prism interior, reduced margin‐normal convergence rate, and the onset of impingement on the incoming Chatham Rise to the south. A southwestern segment (C) marks the approximate southern termination of subduction but widens to ∼50 km due to rapid outward migration of the deformation front via fault reactivation within the now‐underthrusting corner of the Chatham Rise. Segment C exhibits minimal shortening as margin‐normal subduction velocity decreases and plate motion is increasingly taken up by interior thrusts and strike‐slip faults.
Plain Language Summary
Between the North and South Islands of New Zealand, the interaction of the Pacific and Australian tectonic plates is highly complex. Beneath the North Island, the Pacific plate moves westward and slides underneath the Australian plate at the Hikurangi subduction zone, but through the South Island, the two plates slide past each other along the Alpine Fault. The transition between these two zones affects tectonic patterns to the north and south, and the resulting earthquake and tsunami hazard. Using marine seismic reflection technology, we have built detailed cross‐sectional images of the shallowest ∼20 km of the structure of the Earth beneath the seabed, which record the history of plate interactions. By studying how the structure changes from northeast to southwest off the east coast of New Zealand, we can link these changes to tectonic processes. We suggest that changes in fault structure and activity relate to relatively low‐density rocks off the east coast of New Zealand. These lower density rocks were formed during a now extinct phase of tectonic activity, but in the present day they are impinging on the Hikurangi subduction zone. This changes the relative buoyancy of the two tectonic plates and inhibits subduction.
Key Points
The southern Hikurangi subduction margin lies within a subduction to transform transition
We divide the region into three segments based on prism morphology, structure and tectonic shortening
Margin properties vary due to proximity of buoyant rocks on the incoming plate, decreasing subduction velocities, and strike‐slip faults
Scientific argumentation and explanation are essential practices of science that have been highlighted as equally important for K-12 science education. However, as Osborne and Patterson (2011) have ...recently argued, both the term "argument" and "explanation" have multiple, overlapping, meanings, and uses in science education. In this article, the authors explore two possible educational strategies for responding to the overlapping meanings of these two key practices, in K-12 science classrooms.
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