Growth of InGaN quantum dots with AlGaN barrier layers via modified droplet epitaxy

The growth of c-plane InGaN quantum dots via modified droplet epitaxy with AlGaN barrier layers is reported. The growth of the AlGaN layer underlying the InGaN quantum dot layer was carried out under H₂ at 1050 °C, while the capping AlGaN layer was grown at the same temperature (710 °C) and using the same carrier gas (N₂) as that used to grow the InGaN quantum dot layer to prevent decomposition of the InGaN. Atomic force microscopy of InGaN epilayers grown and annealed on high temperature AlGaN using identical growth conditions used for the quantum dot samples highlighted a narrower distribution of nanostructure heights than that obtained for similar growth on GaN. Scanning transmission electron microscopy (STEM) imaging combined with energy dispersive X-ray (EDX) analysis revealed the presence of a thin high aluminium content layer at the surface of both AlGaN layers, which is believed to be related to loss of Ga during temperature ramping processes. Micro-photoluminescence studies carried out at low temperature revealed near resolution-limited peaks while time-resolved measurements on these peaks demonstrated mono-exponential decay times between 1 and 4 ns, showing that quantum dots had successfully been formed between the AlGaN barriers. Temperature-dependant measurement of the emission lines revealed that quenching of the peak often occurred at ∼60–70 K, with some of the peaks exhibiting significant line broadening whilst others remained narrow.     

The mechanism of pleural inflammation by long carbon nanotubes: interaction of long fibres with macrophages stimulates them to amplify pro-inflammatory responses in mesothelial cells

Background

Little is known of how the toxicity of nanoparticles is affected by the incorporation in complex matrices. We compared the toxic effects of the titanium dioxide nanoparticle UV-Titan L181 (NanoTiO₂), pure or embedded in a paint matrix. We also compared the effects of the same paint with and without NanoTiO₂.

Methods

Mice received a single intratracheal instillation of 18, 54 and 162 μg of NanoTiO₂ or 54, 162 and 486 μg of the sanding dust from paint with and without NanoTiO₂. DNA damage in broncheoalveolar lavage cells and liver, lung inflammation and liver histology were evaluated 1, 3 and 28 days after intratracheal instillation. Printex 90 was included as positive control.

Results

There was no additive effect of adding NanoTiO₂ to paints: Therefore the toxicity of NanoTiO₂ was reduced by inclusion into a paint matrix. NanoTiO₂ induced inflammation in mice with severity similar to Printex 90. The inflammatory response of NanoTiO₂ and Printex 90 correlated with the instilled surface area. None of the materials, except of Printex 90, induced DNA damage in lung lining fluid cells. The highest dose of NanoTiO₂ caused DNA damage in hepatic tissue 1 day after intratracheal instillation. Exposure of mice to the dust from paints with and without TiO₂ was not associated with hepatic histopathological changes. Exposure to NanoTiO₂ or to Printex 90 caused slight histopathological changes in the liver in some of the mice at different time points.

Conclusions

Pulmonary inflammation and DNA damage and hepatic histopathology were not changed in mice instilled with sanding dust from NanoTiO₂ paint compared to paint without NanoTiO₂. However, pure NanoTiO₂ caused greater inflammation than NanoTiO₂ embedded in the paint matrix.     

Microbial quality assessment of household greywater

A monitoring program was undertaken to assess the microbial quality of greywater collected from 93 typical households in Melbourne, Australia. A total of 185 samples, comprising 75 washing machine wash, 74 washing machine rinse and 36 bathroom samples were analysed for the faecal indicator Escherichia coli. Of these, 104 were also analysed for genetic markers of pathogenic E coli and 111 for norovirus (genogroups GI and GII), enterovirus and rotavirus using RT-PCR. Enteric viruses were detected in 20 out of the 111 (18%) samples comprising 16 washing machine wash water and 4 bathroom samples. Eight (7%) samples were positive for enterovirus, twelve (11%) for norovirus genogroup GI, one (1%) for norovirus genogroup GII and another (1%) for rotavirus. Two washing machine samples contained more than one virus. Typical pathogenic E. coli were detected in 3 out of 104 (3%) samples and atypical enteropathogenic E. coli in 11 (11%) of samples. Levels of indicator E. coli were highly variable and the presence of E. coli was not associated with the presence of human enteric viruses in greywater. There was also little correlation between reported gastrointestinal illness in households and detection of pathogens in greywater.     

Evaluation of stable isotope tracing for ZnO nanomaterials--new constraints from high precision isotope analyses and modeling

This contribution evaluates two possible routes of stable isotope tracing for ZnO nanomaterials. For this we carried out the first high precision Zn isotope analyses of commercially available ZnO nanomaterials, to investigate whether such materials exhibit isotope fractionations that can be exploited for tracing purposes. These measurements revealed Zn isotopic compositions (of δ(66/64)Zn = +0.28 to -0.31‰ relative to JMC Lyon Zn) that are indistinguishable from "normal" natural and anthropogenic Zn in environmental samples. Stable isotope tracing therefore requires the application of purpose-made isotopically enriched ZnO nanoparticles. A detailed evaluation identified the most suitable and cost-effective labeling isotopes for different analytical requirements and techniques. It is shown that, using relatively inexpensive (68)Zn for labeling, ZnO nanoparticles can be reliably detected in natural samples with a Zn background of 100 μg/g at concentrations as low as about 5 ng/g, if the isotopic tracing analyses are carried out by high precision mass spectrometry. Stable isotope tracing may also be able to differentiate between the uptake by organisms of particulate ZnO and Zn(2+) ions from the dissolution of nanoparticles.     

Enhanced light trapping in solar cells using snow globe coating

A novel method, snow globe coating, is found to show significant enhancement of the short circuit current J_SC (35%) when applied as a scattering back reflector for polycrystalline silicon thin‐film solar cells. The coating is formed from high refractive index titania particles without containing binder and gives close to 100% reflectance for wavelengths above 400 nm. Snow globe coating is a physicochemical coating method executable in pH neutral media. The mild conditions of this process make this method applicable to many different types of solar cells. Copyright © 2012 John Wiley & Sons, Ltd.     

A communication-based intervention for nonverbal children with autism: What changes? Who benefits?

Objective: This article examines the form and function of spontaneous communication and outcome predictors in nonverbal children with autism following classroom-based intervention (Picture Exchange Communication System [PECS] training). Method: 84 children from 15 schools participated in a randomized controlled trial (RCT) of PECS (P. Howlin, R. K. Gordon, G. Pasco, A. Wade, & T. Charman, 2007). They were aged 4–10 years (73 boys). Primary outcome measure was naturalistic observation of communication in the classroom. Multilevel Poisson regression was used to test for intervention effects and outcome predictors. Results: Spontaneous communication using picture cards, speech, or both increased significantly following training (rate ratio [RR] =1.90, 95% CI [1.46, 2.48], p     

An artificial biomineral formed by incorporation of copolymer micelles in calcite crystals

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.     

The validity and incremental validity of knowledge tests, low-fidelity simulations, and high-fidelity simulations for predicting job performance in advanced-level high-stakes selection.

In high-stakes selection among candidates with considerable domain-specific knowledge and experience, investigations of whether high-fidelity simulations (assessment centers; ACs) have incremental validity over low-fidelity simulations (situational judgment tests; SJTs) are lacking. Therefore, this article integrates research on the validity of knowledge tests, low-fidelity simulations, and high-fidelity simulations in advanced-level high-stakes settings. A model and hypotheses of how these 3 predictors work in combination to predict job performance were developed. In a sample of 196 applicants, all 3 predictors were significantly related to job performance. Both the SJT and the AC had incremental validity over the knowledge test. Moreover, the AC had incremental validity over the SJT. Model tests showed that the SJT fully mediated the effects of declarative knowledge on job performance, whereas the AC partially mediated the effects of the SJT. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Intraphase Microstructure–Understanding the Impact on Organic Solar Cell Performance

A comprehensive study of the effect of intraphase microstructure on organic photovoltaic (OPV) device performance is undertaken. Utilizing a bilayer device architecture, a small molecule donor (TIPS‐DBC) is deposited by both spin‐coating and by thermal evaporation in vacuum. The devices are then completed by thermal evaporation of C₆₀, an exciton blocking layer and the cathode. This bilayer approach enables a direct comparison of device performance for donor layers in which the same material exhibits subtle differences in microstructure. The electrical performance is shown to differ considerably for the two devices. The bulk and interfacial properties of the donor layers are compared by examination with photoelectron spectroscopy in air (PESA), optical absorption spectroscopy, charge extraction of photo‐generated charge carriers by linearly increasing voltage (photo‐CELIV), time‐resolved photoluminescence measurements, X‐ray reflectometry (XR), and analysis of dark current behavior. The observed differences in device performance are shown to be influenced by changes to energy levels and charge transport properties resulting from differences in the microstructure of the donor layers. Importantly, this work demonstrates that in addition to the donor/acceptor microstructure, the intraphase microstructure can influence critical parameters and can therefore have a significant impact on OPV performance.