Quantum dot formation on a strain-patterned epitaxial thin film

We model the effect of substrate strain patterning on the self-assembly of quantum dots (QDs). When the surface energy is isotropic, we demonstrate that strain patterning via embedded substrate inclusions may result in ordered, self-organized QD arrays. However, for systems with strong cubic surface energy anisotropy, the same patterning does not readily lead to an ordered array of pyramids at long times. We conclude that the form of the surface energy anisotropy strongly influences the manner in which QDs self-assemble into regular arrays.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87827/2/133102_1.pd

Coarsening in Solid-liquid Mixtures: Overview of Experiments on Shuttle and ISS

The microgravity environment on the Shuttle and the International Space Station (ISS) provides the ideal condition to perform experiments on Coarsening in Solid-Liquid Mixtures (CSLM) as deleterious effects such as particle sedimentation and buoyancy-induced convection are suppressed. For an ideal system such as Lead-Tin in which all the thermophysical properties are known, the initial condition in microgravity of randomly dispersed particles with local clustering of solid Tin in eutectic liquid Lead-Tin matrix, permitted kinetic studies of competitive particle growth for a range of volume fractions. Verification that the quenching phase of the experiment had negligible effect of the spatial distribution of particles is shown through the computational solution of the dynamical equations of motion, thus insuring quench-free effects from the coarsened microstructure measurements. The low volume fraction experiments conducted on the Shuttle showed agreement with transient Ostwald ripening theory, and the steady-state requirement of LSW theory was not achieved. More recent experiments conducted on ISS with higher volume fractions have achieved steady-state condition and show that the kinetics follows the classical diffusion limited particle coarsening prediction and the measured 3D particle size distribution becomes broader as predicted from theory

Scale Development for Perceived School Climate for Girls’ Physical Activity

Objectives: To test an original scale assessing perceived school climate for girls\u27 physical activity in middle school girls. Methods: Confirmatory factor analysis (CFA) and structural equation modeling (SEM). Results: CFA retained 5 of 14 original items. A model with 2 correlated factors, perceptions about teachers\u27 and boys\u27 behaviors, respectively, fit the data well in both sixth and eighth-graders. SEM detected a positive, significant direct association of the teacher factor, but not the boy factor, with girls\u27 self-reported physical activity. Conclusions:School climate for girls\u27 physical activity is a measurable construct, and preliminary evidence suggests a relationship with physical activity

Scale Development for Perceived School Climate for Girls’ Physical Activity

Objectives: To test an original scale assessing perceived school climate for girls\u27 physical activity in middle school girls. Methods: Confirmatory factor analysis (CFA) and structural equation modeling (SEM). Results: CFA retained 5 of 14 original items. A model with 2 correlated factors, perceptions about teachers\u27 and boys\u27 behaviors, respectively, fit the data well in both sixth and eighth-graders. SEM detected a positive, significant direct association of the teacher factor, but not the boy factor, with girls\u27 self-reported physical activity. Conclusions: School climate for girls\u27 physical activity is a measurable construct, and preliminary evidence suggests a relationship with physical activity

Relativistic Static Thin Disks: The Counter-Rotating Model

A detailed study of the Counter-Rotating Model (CRM) for generic finite static axially symmetric thin disks with nonzero radial pressure is presented. We find a general constraint over the counter-rotating tangential velocities needed to cast the surface energy-momentum tensor of the disk as the superposition of two counter-rotating perfect fluids. We also found expressions for the energy density and pressure of the counter-rotating fluids. Then we shown that, in general, there is not possible to take the two counter-rotating fluids as circulating along geodesics neither take the two counter-rotating tangential velocities as equal and opposite. An specific example is studied where we obtain some CRM with well defined counter-rotating tangential velocities and stable against radial perturbations. The CRM obtained are in agree with the strong energy condition, but there are regions of the disks with negative energy density, in violation of the weak energy condition.Comment: 19 pages, 6 figures. Submitted to Physical Review

The development of spatial correlations during Ostwald ripening: a test of theory

AbstractÐThe coarsening of solid-Sn particles in a Pb±Sn liquid was studied under microgravity conditions. Spatial correlation functions were measured on plane sections in a low-volume fraction system undergoing Ostwald ripening. The correlation functions changed with time in a way that indicated that the microstructure initially consisted of clusters of particles and evolved into one which was more dispersed. The model by Akaiwa and Voorhees (AV) was used to study the eect of spatial correlations on the ripening process. We found that the initially highly correlated structure had no observable eect on the evolution of particle size distributions, but did have an eect on the coarsening rate of the system. Speci®cally, we determined that a structure consisting of clusters of particles coarsened faster than a system with a random, spatial arrangement of non-overlapping particles. We also found that the approach of the microstructure towards the steady-state regime could be monitored more sensitively using spatial correlations rather than using particle size distributions. The spatial correlations and the particle size distributions measured from the experiment agreed well with those calculated from the AV simulations using the initial experimental correlations and size distribution.

Open-Retrieval Conversational Question Answering

Conversational search is one of the ultimate goals of information retrieval. Recent research approaches conversational search by simplified settings of response ranking and conversational question answering, where an answer is either selected from a given candidate set or extracted from a given passage. These simplifications neglect the fundamental role of retrieval in conversational search. To address this limitation, we introduce an open-retrieval conversational question answering (ORConvQA) setting, where we learn to retrieve evidence from a large collection before extracting answers, as a further step towards building functional conversational search systems. We create a dataset, OR-QuAC, to facilitate research on ORConvQA. We build an end-to-end system for ORConvQA, featuring a retriever, a reranker, and a reader that are all based on Transformers. Our extensive experiments on OR-QuAC demonstrate that a learnable retriever is crucial for ORConvQA. We further show that our system can make a substantial improvement when we enable history modeling in all system components. Moreover, we show that the reranker component contributes to the model performance by providing a regularization effect. Finally, further in-depth analyses are performed to provide new insights into ORConvQA.Comment: Accepted to SIGIR'2