The long term impact of a coherence based model for mathematics intervention

This article presents a large-scale longitudinal study of hundreds of students across the state of Kentucky that participated in a dual-focus mathematics intervention initiative when they were in the third grade. Rather than an exclusive focus on intervention, this initiative focused on both (i) high quality pull-out intervention and (ii) coherence between pull-out intervention and classroom instruction. The study found that over half of the third grade intervention students that participated in this initiative were classified as “novice” (the lowest possible performance category) on state standardized mathematics assessments at the end of the third grade. However, over the course of the following four years, the novice reduction rate of these students was significantly (p < .01) greater than other novices in Kentucky that did not participate in the initiative. These findings indicate that when implementing intervention initiatives to help students that are struggling with mathematics, it may be important to establish coherence between pull-out intervention and classroom instruction. The long term impact of this approach among traditionally underrepresented minorities suggest that this publication may provide insight into important equity issues where long-term analyses may sometimes be needed to capture the full impact of intervention initiatives.     

Intertwined electronic and structural phase transitions in the In/Si(111) interface

The structural (4 x 1) to (8 x 2) transition and the electronic metal to semimetal transition at the In/Si interface are studied with scanning tunneling microscopy and spectroscopy. Both transitions are gradual, resulting in a complex domain structure in the transition temperature regime. At these intermediate temperatures, the metallic (4 x 1) and semimetallic (8 x 2) domains coexist with each other and with new nanophases. By probing the two intertwined but distinguishable transitions at the atomic level, the interaction between different phases is visualized directly.     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Generation and propagation of a picosecond acoustic pulse at a buried interface: time-resolved x-ray diffraction measurements

We report on the propagation of coherent acoustic wave packets in (001) surface oriented Al0.3Ga0.7As/GaAs heterostructure, generated through localized femtosecond photoexcitation of the GaAs. Transient structural changes in both the substrate and film are measured with picosecond time-resolved x-ray diffraction. The data indicate an elastic response consisting of unipolar compression pulses of a few hundred picosecond duration traveling along [001] and [001] directions that are produced by predominately impulsive stress. The transmission and reflection of the strain pulses are in agreement with an acoustic mismatch model of the heterostructure and free-space interfaces.     

Melting temperature and enthalpy variations of phase change materials (PCMs): a differential scanning calorimetry (DSC) analysis

Differential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.     

Atom probe tomography analysis of radiation-induced solute clustering in austenite stainless steels

Various types of defects are produced by the irradiation of energetic particles onto a structural material. The large number of mobile vacancies and self-interstitial atoms during irradiation induce defect fluxes and the diffusion of solute atoms in the matrix. The preferential interaction between the solute atoms and radiation-induced defects leads to the enrichment/depletion or clustering of the solutes at defect sinks. In the current work, atom probe tomography (APT) was used for the analysis of radiation-induced solute clustering in ion-irradiated austenite stainless steel 316. Quantitative analysis of the localised clustering of chemical elements was implemented and a parameter selection procedure was proposed. The number density and size distribution of Si clusters in APT specimens irradiated at various temperatures were examined. At high temperature, the number density of the clusters decreased and their size increased. The localized Si atoms in variously shaped defects were clearly identified. The APT method was demonstrated to be suitable for identifying defect structures and for the quantitative analysis of clustering in irradiated specimens.     

Spin-orbit interaction in symmetric wells with two subbands

We investigate the spin-orbit (SO) interaction in two-dimensional electron gases in quantum wells with two subbands. From the 8x8 Kane model, we derive a new intersubband-induced SO term which resembles the functional form of the Rashba SO but is nonzero even in symmetric structures. This follows from the distinct parity of the confined states (even or odd) which obliterates the need for asymmetric potentials. We self-consistently calculate the new SO coupling strength for realistic wells and find it comparable to the usual Rashba constant. Our new SO term gives rise to a nonzero ballistic spin-Hall conductivity, which changes sign as a function of the Fermi energy (epsilonF) and can induce an unusual Zitterbewegung with cycloidal trajectories without magnetic fields.     

Gyrocenter shift of low-temperature plasmas and the retrograde motion of cathode spots in arc discharges

The gyrocenter shift phenomenon explained the mechanism of radial electric field formation at the high confinement mode transition in fusion devices. This Letter reports that the theory of gyrocenter shift is also applicable to low temperature high collisional plasmas such as arc discharges by the generalization of the theory resulting from a short mean free path compared with the gyroradius. The retrograde motion of cathode spots in the arc discharge is investigated through a model with the expanded formula of gyrocenter shift. It is found that a reversed electric field is formed in front of the cathode spots when they are under a magnetic field, and this reversed electric field generates a rotation of cathode spots opposite to the Amperian direction. The ion drift velocity profiles calculated from the model are in agreement with the experimental results as functions of magnetic flux density and gas pressure.     

Incoherent one beam recording in LiNbO3

We find a way to record and retrieve images in a photorefractive LiNbO₃ crystal using a single white light source instead of a coherent light source. According to the experimental results, we think this recording is not due to the recording of fanning gratings, but a variation of refractive index responding to the non-uniform illumination. We have also simulated the recording using the band transport model taking into account the photovoltaic effect. The simulation result agrees with the experimental results.     

Cone-shaped structures of GeO2 fabricated by a thermal evaporation process

We have synthesized cone-like GeO₂ structures via thermal heating of Ge powders. We have investigated the effects of substrate temperature on the sample morphology, revealing that cone-shaped structures are preferentially obtained at higher temperature. The cone-shaped structures, which gradually become thinner to form a sharp tip, appear to be a single-crystalline, hexagonal structure of GeO₂. Room-temperature photoluminescence measurement revealed two emission peaks, at about 2.78 and 3.04 eV.