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  1. Asymmetric cell division (ACD) allows stem cells to generate differentiating progeny while simultaneously maintaining their own pluripotent state. ACD involves coupling mitotic spindle orientation with cortical polarity cues to direct unequal segregation of cell fate determinants. InDrosophilaneural stem cells (neuroblasts; NBs), spindles orient along an apical-basal polarity axis through a conserved complex of Partner of Inscuteable (Pins; human LGN) and Mushroom body defect (Mud; human NuMA). While many details of its function are well known, the molecular mechanics that drive assembly of the cortical Pins/Mud complex remain unclear, particularly with respect to the mutually exclusive Pins complex formed with the apical scaffold protein Inscuteable (Insc). Here we identify Hu li tai shao (Hts; human Adducin) as a direct Mud-binding protein, using an aldolase fold within its head domain (HtsHEAD) to bind a short Mud coiled-coil domain (MudCC) that is adjacent to the Pins-binding domain (MudPBD). Hts is expressed throughout the larval central brain and apically polarizes in mitotic NBs where it is required for Mud-dependent spindle orientation.In vitroanalyses reveal that Pins undergoes liquid-liquid phase separation with Mud, but not with Insc, suggesting a potential molecular basis for differential assembly mechanics between these two competing apical protein complexes. Furthermore, we find that Hts binds an intact Pins/Mud complex, reduces the concentration threshold for its phase separation, and alters the liquid-like property of the resulting phase separated droplets. Domain mapping and mutational analyses implicate critical roles for both multivalent interactions (via MudCColigomerization) and protein disorder (via an intrinsically disordered region in Hts; HtsIDR) in phase separation of the Hts/Mud/Pins complex. Our study identifies a new component of the spindle positioning machinery in NBs and suggests that phase separation of specific protein complexes might regulate ordered assembly within the apical domain to ensure proper signaling output.

     
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    Free, publicly-accessible full text available August 16, 2024
  2. Group-based educational disparities are smaller in classrooms where teachers express a belief that students can improve their abilities. However, a scalable method for motivating teachers to adopt such growth mindset–supportive teaching practices has remained elusive. In part, this is because teachers often already face overwhelming demands on their time and attention and have reason to be skeptical of the professional development advice they receive from researchers and other experts. We designed an intervention that overcame these obstacles and successfully motivated high-school teachers to adopt specific practices that support students’ growth mindsets. The intervention used the values-alignment approach. This approach motivates behavioral change by framing a desired behavior as aligned with a core value—one that is an important criterion for status and admiration in the relevant social reference group. First, using qualitative interviews and a nationally representative survey of teachers, we identified a relevant core value: inspiring students’ enthusiastic engagement with learning. Next, we designed a ~45-min, self-administered, online intervention that persuaded teachers to view growth mindset–supportive practices as a way to foster such student engagement and thus live up to that value. We randomly assigned 155 teachers (5,393 students) to receive the intervention and 164 teachers (6,167 students) to receive a control module. The growth mindset–supportive teaching intervention successfully promoted teachers’ adoption of the suggested practices, overcoming major barriers to changing teachers’ classroom practices that other scalable approaches have failed to surmount. The intervention also substantially improved student achievement in socioeconomically disadvantaged classes, reducing inequality in educational outcomes. 
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    Free, publicly-accessible full text available June 20, 2024
  3. Insects perform feats of strength and endurance that belie their small stature. Insect-scale robots—although subject to the same scaling laws—demonstrate reduced performance because existing microactuator technologies are driven by low–energy density power sources and produce small forces and/or displacements. The use of high–energy density chemical fuels to power small, soft actuators represents a possible solution. We demonstrate a 325-milligram soft combustion microactuator that can achieve displacements of 140%, operate at frequencies >100 hertz, and generate forces >9.5 newtons. With these actuators, we powered an insect-scale quadrupedal robot, which demonstrated a variety of gait patterns, directional control, and a payload capacity 22 times its body weight. These features enabled locomotion through uneven terrain and over obstacles.

     
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    Free, publicly-accessible full text available September 15, 2024
  4. Abstract

    TheGila robustaspecies complex in the lower reaches of the Colorado River includes three nominal and contested species (G. robusta, G. intermedia,andG. nigra) originally defined by morphological and meristic characters. In subsequent investigations, none of these characters proved diagnostic, and species assignments were based on capture location. Two recent studies applied conservation genomics to assess species boundaries and reached contrasting conclusions: an ezRAD phylogenetic study resolved 5 lineages with poor alignment to species categories and proposed a single species with multiple population partitions. In contrast, a dd-RAD coalescent study concluded that the three nominal species are well-supported evolutionarily lineages. Here we developed a draft genome (~ 1.229 Gbp) to apply genome-wide coverage (10,246 SNPs) with nearly range-wide sampling of specimens (G. robustaN = 266,G. intermediaN = 241, andG. nigraN = 117) to resolve this debate. All three nominal species were polyphyletic, whereas 5 of 8 watersheds were monophyletic. AMOVA partitioned 23.1% of genetic variance among nominal species, 30.9% among watersheds, and the Little Colorado River was highly distinct (FSTranged from 0.79 to 0.88 across analyses). Likewise, DAPC identified watersheds as more distinct than species, with the Little Colorado River having 297 fixed nucleotide differences compared to zero fixed differences among the three nominal species. In every analysis, geography explains more of the observed variance than putative taxonomy, and there are no diagnostic molecular or morphological characters to justify species designation. Our analysis reconciles previous work by showing that species identities based on type location are supported by significant divergence, but natural geographic partitions show consistently greater divergence. Thus, our data confirmGila robustaas a single polytypic species with roughly a dozen highly isolated geographic populations, providing a strong scientific basis for watershed-based future conservation.

     
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  5. Introduction In Midwestern maize ( Zea-mays L.)-based systems, planting an over-wintering cover crop such as rye ( Secale cereale L.) following fall harvests of summer crops maintains continuous soil cover, offering numerous environmental advantages. However, while adoption of cover crops has increased over the past decade, on a landscape-scale it remains low. Identifying where agronomic research could be most impactful in increasing adoption is therefore a useful exercise. Decision analysis (DA) is a tool for clarifying decision trade-offs, quantifying risk, and identifying optimal decisions. Several fields regularly utilize DA frameworks including the military, industrial engineering, business strategy, and economics, but it is not yet widely applied in agriculture. Methods Here we apply DA to a maize-soybean [ Glycine max (L.) Merr.] rotation using publicly available weather, management, and economic data from central Iowa. Results In this region, planting a cover crop following maize (preceding soybean) poses less risk to the producer compared to planting following soybean, meaning it may be a more palatable entry point for producers. Furthermore, the risk of reduced maize yields when planting less than 14 days following rye termination substantially contributes to the overall risk cover crops pose to producers, but also has significant potential to be addressed through agronomic research. Discussion In addition to identifying research priorities, DA provided clarity to a complex problem, was performed using publicly available data, and by incorporating risk it better estimated true costs to the producer compared to using input costs alone. We believe DA is a valuable and underutilized tool in agronomy and could aid in increasing adoption of cover crops in the Midwest. 
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  6. Abstract

    Educational outcomes remain highly unequal within and across nations. Students’ mindsets—their beliefs about whether intellectual abilities can be developed—have been identified as a potential lever for making adolescents’ academic outcomes more equitable. Recent research, however, suggests that intervention programs aimed at changing students’ mindsets should be supplemented by programs aimed at the changing the mindsetculture, which is defined as the shared set of beliefs about learning in a school or classroom. This paper reviews the theoretical and empirical origin of the mindset culture and examines its potential to reduce group-based inequalities in education. In particular, experiments have identified two broad ways the mindset culture is communicated by teachers: via informalmessagesabout growth (e.g., that all students will be helped to learn and succeed), and formalopportunitiesto improve (e.g., learning-focused grading policies and opportunities to revise and earn credit). New field experiments, applying techniques from behavioral science, have also revealed effective ways to influence teachers’ culture-creating behaviors. This paper describes recent breakthroughs in the U.S. educational context and discusses how lessons from these studies might be applied in future, global collaborations with researchers and practitioners.

     
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  7. Behavioral science interventions have the potential to address longstanding policy problems, but their effects are typically heterogeneous across contexts (e.g., teachers, schools, and geographic regions). This contextual heterogeneity is poorly understood, however, which reduces the field’s impact and its understanding of mechanisms. Here, we present an efficient way to interrogate heterogeneity and address these gaps in knowledge. This method a) presents scenarios that vividly represent different moderating contexts, b) measures a short-term behavioral outcome (e.g., an academic choice) that is known to relate to typical intervention outcomes (e.g., academic achievement), and c) assesses the causal effect of the moderating context on the link between the psychological variable typically targeted by interventions and this short-term outcome. We illustrated the utility of this approach across four experiments (total n = 3,235) that directly tested contextual moderators of the links between growth mindset, which is the belief that ability can be developed, and students’ academic choices. The present results showed that teachers’ growth mindset-supportive messages and the structural opportunities they provide moderated the link between students’ mindsets and their choices (studies 1 to 3). This pattern was replicated in a nationally representative sample of adolescents and did not vary across demographic subgroups (study 2), nor was this pattern the result of several possible confounds (studies 3 to 4). Discussion centers on how this method of interrogating contextual heterogeneity can be applied to other behavioral science interventions and broaden their impact in other policy domains. 
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  8. Dolan, Erin L. (Ed.)
    Mindset interventions, which shift students’ beliefs about classroom experiences, have shown promise for promoting diversity in science, technology, engineering, and mathematics (STEM). Psychologists have emphasized the importance of customizing these interventions to specific courses, but there is not yet a protocol for doing so. We developed a protocol for creating customized “peer-modeled” mindset interventions that elicit advice from former students in videotaped interviews. In intervention activities, clips from these interviews, in which the former students’ stories model the changes in thinking about challenge and struggle that helped them succeed in a specific course, are provided to incoming life sciences students. Using this protocol, we developed a customized intervention for three sections of Introductory Biology I at a large university and tested it in a randomized controlled trial ( N = 917). The intervention shifted students’ attributions for struggle in the class away from a lack of potential to succeed and toward the need to develop a better approach to studying. The intervention also improved students’ approaches to studying and sense of belonging and had promising effects on performance and persistence in biology. Effects were pronounced among first-generation college students and underrepresented racial/ethnic minority students, who have been historically underrepresented in the STEM fields. 
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  9. ABSTRACT

    PSR J1757−1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of $P_\text{b}=4.4\, \text{h}$ and an orbital eccentricity of e = 0.61. As such, it has promised to be an outstanding laboratory for conducting tests of relativistic gravity. We present the results of a 6-yr campaign with the 100-m Green Bank and 64-m Parkes radio telescopes, designed to capitalize on this potential. We identify secular changes in the profile morphology and polarization of PSR J1757−1854, confirming the presence of geodetic precession and allowing the constraint of viewing geometry solutions consistent with General Relativity. We also update PSR J1757−1854’s timing, including new constraints of the pulsar’s proper motion, post-Keplerian parameters, and component masses. We conclude that the radiative test of gravity provided by PSR J1757−1854 is fundamentally limited to a precision of 0.3 per cent due to the pulsar’s unknown distance. A search for pulsations from the companion neutron star is also described, with negative results. We provide an updated evaluation of the system’s evolutionary history, finding strong support for a large kick velocity of $w\ge 280\, \rm{km\,s}^{-1}$ following the second progenitor supernova. Finally, we reassess PSR J1757−1854’s potential to provide new relativistic tests of gravity. We conclude that a 3-σ constraint of the change in the projected semimajor axis ($\dot{x}$) associated with Lense–Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-σ measurement of the relativistic orbital deformation parameter δθ as soon as 2026.

     
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