Non-photochemical laser-induced nucleation

Non-photochemical laser-induced nucleation (NPLIN) is the formation of a new phase from a metastable phase by the action of light on matter. Using millijoule, nanosecond laser pulses at visible and near-infrared wavelengths, it is possible to form the new phase localized in the volume of the beam. In the case of nucleating molecular solids, the laser polarization may have an effect on the particular polymorph that is formed. Despite the huge potential for applications of NPLIN, there is uncertainty regarding the molecular-scale mechanism, and various possible scenarios may well be relevant to nucleation in general and not just NPLIN. In this Perspective, the discovery and phenomenology of NPLIN are described, putative mechanisms are outlined, and some observations on the broader class of nucleation phenomena are given. © 2019 Author(s).The authors acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC) through funding for some of the work described in this Perspective (Nos. EP/G067546/1, EP/I033459/1, and EP/L022397/1). P.J.C. acknowledges support from the Ministry of Education and Science of the Russian Federation (Agreement No. 02.A03.21.0006 and Project No. 3.1438.2017/4.6). We are grateful to our colleagues, collaborators, reviewers, and editors for their encouragement and suggestions over the years

Determinants of Ethnic Differences in School Modality Choices during the COVID-19 Crisis

A growing body of research and popular reporting shows racial differences in school modality choices during the COVID-19 crisis, with white students more likely to attend school in person. This in-person learning gap raises serious equity concerns. We use unique panel survey data to explore possible explanations. We find that a combination of factors may explain these differences. School districts’ offerings, political partisanship, and local COVID-19 outbreaks are all meaningfully associated with and plausibly explain the in-person learning racial gap. As schools start offering more in-person learning, significant efforts may be necessary to ensure that families and students attend those in-person learning opportunities

Rapid and Accurate Pressure Sensing Device for Direct Measurement of Intraocular Pressure.

PurposeIntraocular pressure (IOP) is the primary modifiable risk factor for glaucoma. Current devices measure IOP via the dynamic response of the healthy cornea and do not provide the accurate IOP measurements for patients with altered corneal biomechanics. We seek to develop and test an accurate needle-based IOP measurement device that is not cornea dependent.MethodsOur device combines a high-resolution pressure microsensor with 30- and 33-gauge Luer lock needles to provide IOP measurements via a microcontroller and USB interface to a computer. The device was calibrated in a membrane chamber and then tested and validated in the anterior chamber and post-vitrectomy vitreous chamber of rabbit eyes. The results were compared to Tonopen readings across a pressure range of 0 to 100 mm Hg, imposed in increments of 10 mm Hg.ResultsBoth the needle based sensor device and the Tonopen demonstrated a linear relationship with changes in imposed pressure. The Tonopen was found to consistently underestimate the IOP both in the anterior and vitreous chambers. The Tonopen exhibited a significantly greater error than our needle-based sensor device. With increased pressure (>30 mm Hg), the error of the Tonopen increased, whereas the error of our device did not. The 30-gauge needle produces an insignificant improvement in accuracy over the 33-gauge needle.ConclusionsA needle-based sensor device enables accurate IOP measurements over a broad range of induced IOP.Translational relevanceDirect measurement of IOP in the anterior chamber circumvents the influence of corneal parameters on IOP measurement

Revisiting Ethnic Differences in In-Person Learning During 2021-2022

In the spring of 2020, the COVID-19 pandemic closed schools throughout the United States, forcing a shift to remote learning that lasted the rest of the academic year. In the fall of 2020, schools reopened using combinations of in-person, hybrid, and remote learning models with great geographic variability in access to in-person learning. A growing body of research shows important racial differences in the use of in-person learning during the 2020-2021 school year, with Black and Hispanic students returning to in-person learning at lower rates than white students (Camp and Zamarro, 2021; Kurmann and Lalé, 2022). This in-person learning gap raises serious equity concerns as emerging research illustrates how remote learning was associated with both larger decreases in academic performance during the pandemic and a widening racial achievement gap (Goldhaber et al., 2022)

Movers, Switchers, and Exiters: Teacher Turnover during COVID-19

In this brief, we examine teacher turnover in the state of Arkansas both before and during the COVID-19 pandemic. In line with available reports from Washington State, North Carolina, and South Carolina, we find evidence of increased teacher turnover in Arkansas entering the current school year. However, a large proportion of this turnover can be explained not by teachers leaving the education sector but switching to non-instructional roles such as principals or instructional coaches. The use of Elementary and Secondary School Emergency Relief (ESSER) funds may be driving these transitions. A survey of schools conducted by the National Center for Education Statistics in January of 2022 found that 30% of vacancies were newly created positions. We additionally find that many of those teachers who did leave the education sector did not find immediate employment in other sectors which may indicate that these teachers might be more likely to return to the teaching profession if their concerns are addressed

Teacher Turnover During the COVID-19 Pandemic

Teachers\u27 levels of stress and burnout have been high throughout the COVID-19 pandemic, raising concerns about a potential increase in teacher turnover and future teacher shortages. We examine how the COVID-19 pandemic affected teacher turnover in Arkansas from 2018-19 to 2022-23 using administrative data. We find no major changes in turnover entering the first two pandemic years, but a large increase of 5.3 percentage points (26%) entering the third year, with variation by teacher and student characteristics. We also find that increases in teacher turnover are related to instructional mode and that this turnover may partially be explained by the use of COVID-19 relief funds. Additionally, we find evidence that more effective teachers became more likely to leave the education sector after the pandemic as compared to before the pandemic. Our results suggest increased strain and reduced diversity and quality in the Arkansas teacher workforce and raise concerns about the long-term impacts that COVID-19 may have on its stability and quality

Tooth enamel microstructure in North American Phytosauria (Diapsida:Archosauriformes): Implications for biogeography and ecology of a Late Triassic clade of crocodylian-like predators

Teeth can provide important insight into diet and evolution of extinct vertebrates. Tooth enamel microstructure records functional and phylogenetic signals beyond the gross morphology of the dentition. Here, we provide the first systematic sampling of phytosaur tooth enamel to address questions of intra- and interspecific variation, and thus taxonomic identification, biogeographic connectivity, and heterodonty. We sampled 23 phytosaur teeth from five localities throughout the American Southwest and one locality from the Newark Supergroup of North Carolina. These teeth probably represent five heterodont genera and are tentatively assigned to Angistorhinus, Smilosuchus, Machaeroprosopus, Redondasaurus, and “Rutiodon”. We used scanning electron microscopy to examine their enamel microstructure from transverse, longitudinal, and tangential cross-sections. All sampled teeth are composed of columnar enamel ranging in thickness from 20 to 150 µm, typically 50–100 µm, across all genera. In phytosaurs from the western US, lines of incremental growth (LIGs) are rare, whereas in the Newark Supergroup phytosaur “Rutiodon”, LIGs are abundant and welldeveloped. Although phytosaur tooth enamel microstructure is not useful for the taxonomic assignment of isolated teeth, it can be used to differentiate phytosaurs from different basins and lends support to the hypothesis that western and eastern North American phytosaurs are taxonomically distinct. The posterior blade-like teeth of heterodont phytosaurs are consistently composed of proportionately thicker enamel (10– 14 µm thicker than anterior teeth of comparable size in heterodont phytosaurs), implying a greater degree of force on these teeth during food processing. Combined with independent measures of diet, enamel microstructure can help refine dietary hypotheses during the Triassic archosauriform radiation

SWITCHABLE OLEFIN ISOMERIZATION IN IRIDIUM COMPLEXES

The structure-reactivity relationships in iridium-pincer crown ether complexes is expanded in this work. These frameworks contain a strongly donating pincer scaffold with a flexible, weakly donating aza-crown ether moiety that can reversibly bind the metal center. The iridium pincer-crown ether complexes can access tridentate, tetradentate, or pentadentate coordination modes reversibly using discrete chemical steps. Careful NMR characterization of representative complexes in each coordination mode revealed a correlation between the difference in chemical shift between geminal diastereotopic protons of the crown and coordination mode of the complex, allowing characterization of the binding modes of the complexes in solution using routine and time efficient NMR experiments. Binding studies demonstrate the modulation of affinity of the crownether for cations with organometallic fragments. Adding transition metal centers changes 1-aza-crown ether host-guest properties: the selectivity of the 1-aza-15-crown-5 ethers for Li+ over Na+ is increased; the binding affinity for Li+ and Na+ salts is reduced, though increasing the ring size of the crown ether mitigates the decrease; distinct proton-dependent reactivity is observed; and the ion binding properties shift fundamentally to enable heteroditopic binding of ion pairs. The observation that moving to larger crowns increases the binding affinity of pincer-crown ether complexes towards cations motivated the synthesis of new cationic complex, [k5- (18c6NCOPiPr)Ir(H)]+, featuring a larger 1-aza-18-crown-6 crown ether to improve salt rate enhancement of olefin isomerization to access switchable regioselectivity. Without cation in solution, the complex is selective for the one bond isomerization product, with a strong preference for the E stereoisomer. Upon the addition of cation, the selectivity is observed to favor thermodynamic olefinic products, with complete inversion in regioselectivity observed across diverse functionalized substrates. Despite the impressive shifts in regioselectivity in the studied substrate, isomerizations with Lewis basic substituted olefins were unable to be “switched” to favor thermodynamic regioisomers. Explorations of these substrates revealed Lewis basic olefins can form chelated species which significantly inhibit the rate of isomerization with these substrates. Using the aquated iridium complex, [k4-(18c6NCOPiPr)Ir(H)(OH2)]+, >30% conversion to thermodynamic products were observed after 216 hours, representing an improvement to the activity seen in [k5- (18c6NCOPiPr)Ir(H)]+. Explorations with long chain olefins revealed selectivity for internal olefins in the presence of cation, while preserving preference for the one-bond isomerization product in the absence of cation. While high yielding switchable catalysis to thermodynamic products and internal olefins is elusive, this work lays the foundation for continuing efforts to increase the scope of switchable olefin isomerization to functionalized olefins.Doctor of Philosoph

Teacher Turnover During the COVID-19 Pandemic

Teachers\u27 levels of stress and burnout have been high throughout the COVID-19 pandemic, raising concerns about a potential increase in teacher turnover and future teacher shortages. We examine how the COVID-19 pandemic affected teacher turnover in Arkansas from 2018-19 to 2022-23 using administrative data. We find no major changes in turnover entering the first two pandemic years, but a large increase of 5.3 percentage points (26%) entering the third year, with variation by teacher and student characteristics. We also find that increases in teacher turnover are related to instructional mode and that this turnover may partially be explained by the use of COVID-19 relief funds. Additionally, we find evidence that more effective teachers became more likely to leave the education sector after the pandemic as compared to before the pandemic. Our results suggest increased strain and reduced diversity and quality in the Arkansas teacher workforce and raise concerns about the long-term impacts that COVID-19 may have on its stability and quality

Movers, Switchers, and Exiters: Teacher Turnover during COVID-19

In this brief, we examine teacher turnover in the state of Arkansas both before and during the COVID-19 pandemic. In line with available reports from Washington State, North Carolina, and South Carolina, we find evidence of increased teacher turnover in Arkansas entering the current school year. However, a large proportion of this turnover can be explained not by teachers leaving the education sector but switching to non-instructional roles such as principals or instructional coaches. The use of Elementary and Secondary School Emergency Relief (ESSER) funds may be driving these transitions. A survey of schools conducted by the National Center for Education Statistics in January of 2022 found that 30% of vacancies were newly created positions. We additionally find that many of those teachers who did leave the education sector did not find immediate employment in other sectors which may indicate that these teachers might be more likely to return to the teaching profession if their concerns are addressed