School Leadership Interventions Under the Every Student Succeeds Act: Evidence Review - Updated and Expanded

This RAND analysis offers guidance to states and districts on how they can choose to use the Every Student Succeeds Act to help achieve their school improvement goals by supporting principals and other school leaders

Processing and characterisation of II-VI ZnCdMgSe thin film gain structures

Lattice-matched II-VI selenide quantum well (QW) structures grown on InP substrates can be designed for emission throughout the visible spectrum. InP has, however, strong visible-light absorption, so that a method for epitaxial lift-off and transfer to transparent substrates is desirable for vertically-integrated devices. We have designed and grown, via molecular beam epitaxy, ZnCdSe/ZnCdMgSe multi-QW gain regions for vertical emission, with the QWs positioned for resonant periodic gain. The release of the 2.7 μm-thick ZnCdSe/ZnCdMgSe multi-QW film is achieved via selective wet etching of the substrate and buffer layers leaving only the epitaxial layers, which are subsequently transferred to transparent substrates, including glass and thermally-conductive diamond. Post-transfer properties are investigated, with power and temperature-dependent surface and edge-emitting photoluminescence measurements demonstrating no observable strain relaxation effects or significant shift in comparison to unprocessed samples. The temperature dependant quantum well emission shift is found experimentally to be 0.13 nm/K. Samples capillary-bonded epitaxial-side to glass exhibited a 6 nm redshift under optical pumping of up to 35 mW at 405 nm, corresponding to a 46 K temperature increase in the pumped region; whereas those bonded to diamond exhibited no shift in quantum well emission, and thus efficient transfer of the heat from the pumped region. Atomic force microscopy analysis of the etched surface reveals a root-mean-square roughness of 3.6 nm. High quality optical interfaces are required to establish a good thermal and optical contact for high power optically pumped laser applications

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors reduce the risk of perioperative stroke and mortality after carotid endarterectomy

ObjectiveThere is increasing evidence that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) reduce cardiovascular and cerebrovascular events through anti-inflammatory, plaque stabilization, and neuroprotective effects independent of lipid lowering. This study was designed to investigate whether statin use reduces the incidence of perioperative stroke and mortality among patients undergoing carotid endarterectomy (CEA).MethodsAll patients undergoing CEA from 1994 to 2004 at a large academic medical center were retrospectively reviewed. The independent association of statin use and perioperative morbidity was assessed via multivariate logistic regression analysis.ResultsCEA was performed by 13 surgeons on 1566 patients (987 men and 579 women; mean age, 72 ± 10 years), including 1440 (92%) isolated and 126 (8%) combined CEA/coronary artery bypass grafting procedures. The indication for CEA was symptomatic disease in 660 (42%) cases. Six hundred fifty-seven (42%) patients received a statin medication for at least 1 week before surgery. Statin use was associated with a reduction in perioperative strokes (1.2% vs 4.5%; P < .01), transient ischemic attacks (1.5% vs 3.6%; P < .01), all-cause mortality (0.3% vs 2.1%; P < .01), and median (interquartile range) length of hospitalization (2 days [2-5 days] vs 3 days [2-7 days]; P < .05). Adjusting for all demographics and comorbidities in multivariate analysis, statin use independently reduced the odds of stroke threefold (odds ratio [95% confidence interval], 0.35 [0.15-0.85]; P < .05) and death fivefold (odds ratio [95% confidence interval], 0.20 [0.04-0.99]; P < .05).ConclusionsThese data suggest that perioperative statin use may reduce the incidence of cerebrovascular events and mortality among patients undergoing CEA

Hybrid GaN LED with capillary-bonded II–VI MQW color-converting membrane for visible light communications

The rapid emergence of gallium-nitride (GaN) light-emitting diodes (LEDs) for solid-state lighting has created a timely opportunity for optical communications using visible light. One important challenge to address this opportunity is to extend the wavelength coverage of GaN LEDs without compromising their modulation properties. Here, a hybrid source for emission at 540 nm consisting of a 450 nm GaN micro-sized LED (micro-LED) with a micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well color-converting membrane is reported. The membrane is liquid-capillary-bonded directly onto the sapphire window of the micro-LED for full hybridization. At an injection current of 100 mA, the color-converted power was found to be 37 μW. At this same current, the −3 dB optical modulation bandwidth of the bare GaN and hybrid micro-LEDs were 79 and 51 MHz, respectively. The intrinsic bandwidth of the color-converting membrane was found to be power-density independent over the range of the micro-LED operation at 145 MHz, which corresponds to a mean carrier lifetime of 1.9 ns

Growth and characterization of ZnCdMgSe-based green light emitters and distributed Bragg reflectors towards II–VI based semiconductor disk lasers

We report the structural and optical properties of molecular beam epitaxy grown II–VI semiconductor multiple quantum well (MQW) structures and distributed Bragg reflector (DBR) on InP substrates for application in developing optically-pumped semiconductor disk lasers (SDLs) operating in the green spectral range. One sample was grown directly on an InP substrate with an InGaAs buffer layer, while another had a 5-period ZnCdMgSe-based DBR grown on the InGaAs/InP substrate. X-ray diffraction and scanning electron microscopy measurements revealed sharp superlattice peaks and abrupt layer interfaces, while steady-state photoluminescence measurements demonstrated surface emission between 540–570 nm. Under pulsed excitation both samples exhibited features of amplified spontaneous emission (ASE) or stimulated emission, accompanied by luminescence lifetime shortening. The sample with the DBR showed higher surface luminescence and the onset of ASE at lower pump power. To further explore the design and performance of a ZnCdMgSe-based DBR, a 20-period DBR was grown and a reflectivity of 83% was obtained at ∼560 nm. We estimate that a DBR with ∼40 periods would be needed for optimal performance in a SDL using these materials. These results show the potential of II–VI MQW structures on InP substrates for the development of SDLs operational in the green–yellow wavelength range

Suspension and transfer printing of ZnCdMgSe membranes from an InP substrate

Wide bandgap II-VI semiconductors, lattice-matched to InP substrates, show promise for use in novel, visible wavelength photonic devices; however, release layers for substrate removal are still under development. An under-etch method is reported which uses an InP substrate as an effective release layer for the epitaxial lift-off of lattice-matched ZnCdMgSe membranes. An array of 100-pm-square membranes is defined on a ZnCdMgSe surface using dry etching and suspended from the InP substrate using a three-step wet etch. The ZnCdMgSe membranes are transfer-printed onto a diamond heatspreader and have an RMS surface roughness < 2 nm over 400 |jm 2, similar to the epitaxial surface. Membranes on diamond show a photoluminescence peak at ∼520 nm and a thermal redshift of 4 nm with ∼3.6 MWm −2 continuous optical pumping at 447 nm. Effective strain management during the process is demonstrated by the absence of cracks or visible membrane bowing and the high brightness photoluminescence indicates a minimal non-radiative defect introduction. The methodology presented will enable the heterogeneous integration and miniaturization of II-VI membrane devices