Structural disjoining potential for grain boundary premelting and grain coalescence from molecular-dynamics simulations

We describe a molecular dynamics framework for the direct calculation of the short-ranged structural forces underlying grain-boundary premelting and grain-coalescence in solidification. The method is applied in a comparative study of (i) a Sigma 9 120 degress twist and (ii) a Sigma 9 {411} symmetric tilt boundary in a classical embedded-atom model of elemental Ni. Although both boundaries feature highly disordered structures near the melting point, the nature of the temperature dependence of the width of the disordered regions in these boundaries is qualitatively different. The former boundary displays behavior consistent with a logarithmically diverging premelted layer thickness as the melting temperature is approached from below, while the latter displays behavior featuring a finite grain-boundary width at the melting point. It is demonstrated that both types of behavior can be quantitatively described within a sharp-interface thermodynamic formalism involving a width-dependent interfacial free energy, referred to as the disjoining potential. The disjoining potential for boundary (i) is calculated to display a monotonic exponential dependence on width, while that of boundary (ii) features a weak attractive minimum. The results of this work are discussed in relation to recent simulation and theoretical studies of the thermodynamic forces underlying grain-boundary premelting.Comment: 24 pages, 8 figures, 1 tabl

Ginzburg-Landau theory of crystalline anisotropy for bcc-liquid interfaces

The weak anisotropy of the interfacial free-energy $\gamma$ is a crucial parameter influencing dendritic crystal growth morphologies in systems with atomically rough solid-liquid interfaces. The physical origin and quantitative prediction of this anisotropy are investigated for body-centered-cubic (bcc) forming systems using a Ginzburg-Landau theory where the order parameters are the amplitudes of density waves corresponding to principal reciprocal lattice vectors. We find that this theory predicts the correct sign, $\gamma_{100}>\gamma_{110}$, and magnitude, $(\gamma_{100}-\gamma_{110}) / (\gamma_{100}+\gamma_{110})\approx 1$, of this anisotropy in good agreement with the results of MD simulations for Fe. The results show that the directional dependence of the rate of spatial decay of solid density waves into the liquid, imposed by the crystal structure, is a main determinant of anisotropy. This directional dependence is validated by MD computations of density wave profiles for different reciprocal lattice vectors for $\{110\}$ crystal faces. Our results are contrasted with the prediction of the reverse ordering $\gamma_{100}<\gamma_{110}$ from an earlier formulation of Ginzburg-Landau theory [Shih \emph{et al.}, Phys. Rev. A {\bf 35}, 2611 (1987)].Comment: 9 pages, 5 figure

Task l Report: Summary and Evaluation of Water Supply Studies for the Kentucky River Basin

This report provides a review and critique of previous water supply studies for the Kentucky River Basin. The main focus of the review is on the 1990 Harza study, entitled Phase 1 Report: Water Demands and Water Supply Yield and Deficit

Capillary force-induced structural instability in liquid infiltrated elastic circular tubes

The capillary-induced structural instability of an elastic circular tube partially filled by a liquid is studied by combining theoretical analysis and molecular dynamics simulations. The analysis shows that, associated with the instability, there is a well-defined length scale (elasto-capillary length), which exhibits a scaling relationship with the characteristic length of the tube, regardless of the interaction details. We validate this scaling relationship for a carbon nanotube partially filled by liquid iron. The capillary-induced structural transformation could have potential applications for nano-devices

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

We report direct single-laser excitation of the strictly forbidden (6s^2)^1S_0 -(6s6p)^3P_0 clock transition in the even 174Yb isotope confined to a 1D optical lattice. A small (~1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FHWM) with high contrast were observed, demonstrating a record neutral-atom resonance quality factor of 2.6x10^13. The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35+/-0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks, and can create new clock possibilities in other alkaline earth-like atoms such as Mg and Ca.Comment: Submitted to Physics Review Letter

An Online Growth Mindset Intervention in a Sample of Rural Adolescent Girls

Background. Students living in rural areas of the United States exhibit lower levels of educational attainment than their suburban counterparts. Innovative interventions are needed to close this educational gap. Aims. We investigated whether an online growth mindset intervention could be leveraged to promote academic outcomes. Sample. We tested the mindset intervention in a sample of 222 10th-grade adolescent girls (M age=15.2; 38% White, 25% Black, 29% Hispanic) from four rural, low-income high schools in Southeastern United States. Methods. We conducted a randomized controlled trial to test the efficacy of the growth mindset intervention, relative to a sexual health programme. We used random sampling and allocation procedures to assign girls to either the mindset intervention (n-115) or an attention-matched control programme (n-107). We assessed participants at pre-test, immediate post-test, and 4-month follow up. Results. Relative to the control condition, students assigned to the mindset intervention reported stronger growth mindsets at immediate post-test and 4-month follow up. Although the intervention did not have a total effect on academic attitudes or grades, it indirectly increased motivation to learn, learning efficacy and grades via the shifts in growth mindsets. Conclusions. Results indicate that this intervention is a promising method to encourage growth mindsets in rural adolescent girls

Randomized Trial of a Single-Session Growth Mind-Set Intervention for Rural Adolescents’ Internalizing and Externalizing Problems

Objective. Adolescents living in rural regions of the United States face substantial barriers to accessing mental health services, creating needs for more accessible, non-stigmatizing, briefer interventions. Research suggests that single-session “growth mindset” interventions (GM-SSIs)—which teach the belief that personal traits are malleable through effort—may reduce internalizing and externalizing problems in adolescents. However, GM-SSIs have not been evaluated among rural youth, and their effects on internalizing and externalizing problems have not been assessed within a single trial, rendering their relative benefits for different problem types unclear. We examined whether a computerized GM-SSI could reduce depressive symptoms, social anxiety symptoms, and conduct problems in adolescent girls from rural areas of the U.S. Method. Tenth-grade girls (N=222, M age=15.2, 38% white, 25% Black, 29% Hispanic) from four rural, low-income high schools in the Southeastern United States were randomized to receive a 45-minute GM-SSI or a computer-based, active control program, teaching healthy sexual behaviors. Girls self-reported depression symptoms, social anxiety symptoms, and conduct problem behaviors at baseline and four-month follow-up. Results. Relative to girls in the control group, girls receiving the GM-SSI reported modest but significantly greater reductions in depressive symptoms (d=.23) and likelihood of reporting elevated depressive symptoms (d=.29) from baseline to follow-up. GM-SSI effects were nonsignificant for social anxiety symptoms, although a small effect size emerged in the hypothesized direction (d=.21), and nonsignificant for change in conduct problems (d=.01). Conclusions. A free-of-charge, 45-minute GM-SSI may help reduce internalizing distress, especially depression—but not conduct problems—in rural adolescent girls