Surface-bound molecular motors can drive the collective motion of cytoskeletal filaments in the form of nematic bands and polar flocks in reconstituted gliding assays. Although these swarming transitions are an emergent property of active filament collisions, they can be controlled and guided by tuning the surface chemistry or topography of the substrate. To date, the impact of surface topography on collective motion in active nematics is only partially understood, with most experimental studies focusing on the escape of a single filament from etched channels. Since the late 1990s, significant progress has been made to utilize the nonequilibrium properties of active filaments and create a range of functional nanodevices relevant to biosensing and parallel computation; however, the complexity of these swarming transitions presents a challenge when attempting to increase filament surface concentrations. In this work, we etch shallow, linear trenches into glass substrates to induce the formation of swarming nematic bands and investigate the mechanisms by which surface topography regulates the two-dimensional (2D) collective motion of driven filamentous actin (F-actin). We demonstrate that nematic swarms only appear at intermediate trench spacings and vanish if the trenches are made too narrow, wide, or tortuous. To rationalize these results, we simulate the F-actin as self-propelled, semiflexible chains subject to a soft, spatially modulated potential that encodes the energetic cost of bending a filament along the edge of a trench. In our model, we hypothesize that an individual filament experiences a penalty when its projected end-to-end distance is smaller than the trench spacing (bending and turning). However, chains that span the channel width glide above the trenches in a force- and torque-free manner (crowd-surfing). Our simulations demonstrate that collections of filaments form nematic bands only at intermediate trench spacings, consistent with our experimental findings.
Abstract: With the growing recognition of the prevalence and impact of adverse childhood experiences, building trauma-informed service systems is critical. Although there are many online resources to help school systems become more trauma informed, how much they meet the needs of educators is not well understood. To help schools implement trauma-informed practices (TIPS) to support both educators (all school-based certificated staff) and students, a partnership among a California research university, a local foundation, and three school districts was developed at the start of the COVID-19 pandemic. The partnership envisioned a three-phase study to determine the feasibility, acceptability, and outcomes of an intervention supporting TIPS. First, two local districts were engaged in a mixed method needs assessment to explore educators’ wellbeing and use of trauma-informed resources. Input from district-level advisory committees guided a needs assessment that informed the development of trainings to (1) help administrators best support their staff, and (2) teach educators how to best support themselves and their students with traumatic stress and related symptoms. Second, researchers curated freely available resources to develop a 3-module administrator training and an 8-module teacher training. Finally, university-based psychologists and teacher educators delivered the curricula in two school districts and the university’s teacher education program. Researchers implemented a pretest–posttest evaluation design and gathered in-session feedback after each module. Results indicated that participants found the sessions helpful and relevant and they had greater knowledge of TIPS. Future directions include scaling up implementation, understanding outcomes from multiple perspectives, and integrating follow-up activities to help with skill retention.
We take two approaches to understanding democratically corrosive sentiment (DCS) in the US, which we operationalize in terms of populist attitudes, conspiracy beliefs, and expectation of fraud in the next election. Our first approach is media use, which is not well understood as a correlate of DCS beyond generalities about the harms of social media and partisan news. We distinguish between mainstream news and right-wing media, and between three categories of social media: those facilitating stronger ties among users, those facilitating weaker ties, and extremist Alt-Tech brands. Our second approach to explaining DCS is attitudinal. For this, we introduce a concept called Feelings of Being Devalued (FBD), which we offer as a complement to status threat and sense of material deprivation. Using a survey of our design ( N = 2,000) fielded in the US in 2022, we show that: (1) mainstream news use and attention to right-wing media have opposite relationships with DCS; (2) not only Alt-Tech social media but also stronger-tie media such as Facebook are correlated with DCS, while use of weaker-tie social media such as X are uncorrelated in a model with a rich set of controls; and (3) FBD is strongly associated with DCS—more so than right-wing authoritarianism, social dominance orientation, and ideology.
Topological defects play a central role in the physics of many materials, including magnets, superconductors, and liquid crystals. In active fluids, defects become autonomous particles that spontaneously propel from internal active stresses and drive chaotic flows stirring the fluid. The intimate connection between defect textures and active flow suggests that properties of active materials can be engineered by controlling defects, but design principles for their spatiotemporal control remain elusive. Here, we propose a symmetry-based additive strategy for using elementary activity patterns, as active topological tweezers, to create, move, and braid such defects. By combining theory and simulations, we demonstrate how, at the collective level, spatial activity gradients act like electric fields which, when strong enough, induce an inverted topological polarization of defects, akin to a negative susceptibility dielectric. We harness this feature in a dynamic setting to collectively pattern and transport interacting active defects. Our work establishes an additive framework to sculpt flows and manipulate active defects in both space and time, paving the way to design programmable active and living materials for transport, memory, and logic.
Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton spin orders in WSe2/WS2 moiré superlattices. We find evidence of an in-plane (xy) order of exciton spin-here, valley pseudospin-around exciton filling vex = 1, which strongly suppresses the out-of-plane spin polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the spin polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose-Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices.
The development of new therapeutics targeting enzymes involved in epigenetic pathways such as histone modification and DNA methylation has received a lot of attention, particularly for targeting diverse cancers. Unfortunately, irreversible nucleoside inhibitors (azacytidine and decitabine) have proven highly cytotoxic, and competitive inhibitors are also problematic. This work describes synthetic and structural investigations of a new class of allosteric DNA methyltransferase 3A (DNMT3A) inhibitors, leading to the identification of several critical pharmacophores in the lead structure. Specifically, we find that the tetrazole and phthalazinone moieties are indispensable for the inhibitory activity of DNMT3A and elucidate other modifiable regions in the lead compound.
