Red, green and blue lasing enabled by single-exciton gain in colloidal quantum dot films

Colloidal quantum dots exhibit efficient photoluminescence with widely tunable bandgaps as a result of quantum confinement effects. Such quantum dots are emerging as an appealing complement to epitaxial semiconductor laser materials, which are ubiquitous and technologically mature, but unable to cover the full visible spectrum (red, green and blue; RGB). However, the requirement for high colloidal-quantum-dot packing density, and losses due to non-radiative multiexcitonic Auger recombination, have hindered the development of lasers based on colloidal quantum dots. Here, we engineer CdSe/ZnCdS core/shell colloidal quantum dots with aromatic ligands, which form densely packed films exhibiting optical gain across the visible spectrum with less than one exciton per colloidal quantum dot on average. This single-exciton gain allows the films to reach the threshold of amplified spontaneous emission at very low optical pump energy densities of 90?μJ?cm(-2), more than one order of magnitude better than previously reported values. We leverage the low-threshold gain of these nanocomposite films to produce the first colloidal-quantum-dot vertical-cavity surface-emitting lasers (CQD-VCSEL). Our results represent a significant step towards full-colour single-material lasers.     

Single-site and nanosized Fe-Co electrocatalysts for oxygen reduction: Synthesis, characterization and catalytic performance

The impregnation of Ketjen Black (C) with iron and cobalt phthalocyanines (MPc) taken one by one or as a 1:1 stoichiometric mixture, followed by heat treatment at 600 °C under inert atmosphere, gave materials containing arrays of single metal ions coordinated by four nitrogen atoms (M-N₄ units). Increasing the pyrolysis temperature to 800° resulted in the formation of carbon-supported, nanosized metal particles. A key role of the carbon support in determining the material structure at either temperature investigated was demonstrated by TPD, EXAFS, XANES and XRPD studies. These also showed that a Fe-Co alloy is obtained at 800 °C when the impregnation of Ketjen Black involves a mixture of FePc and CoPc. Electrodes coated with the different Fe, Co and Fe-Co materials, containing ca. 3 wt% metal loadings, were scrutinized for the oxygen reduction reaction (ORR) in alkaline media by linear sweep voltammetry. For comparative purposes, two Pt electrocatalysts containing 3 and 20 wt% metal were investigated. The electrochemical activity of all materials was analyzed by Tafel and Koutecky-Levich plots as well as chronopotentiometry. The Fe-containing electrocatalysts have been found to be highly active for the ORR in alkaline media with convective limiting currents as high as 600 A g Fe⁻¹ at room temperature and onset potentials as high as 1.02 V vs. RHE. It has been found that (i) the ORR mass activity of the Pc-derived electrocatalysts is superior to that of the Pt catalysts investigated; (ii) the activity of FePc and FePc-CoPc/C, heat treated at either 600 or 800 °C, is superior to that of the corresponding Co materials; (iii) the electrocatalysts obtained at 600 °C are fairly more active than those obtained at 800 °C.     

Validated Simulation Models for Lateral Response of Bridge Abutments with Typical Backfills

Abutment-backfill soil interaction can significantly influence the seismic response of bridges. In the present study, we provide numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. Those tests involve well-compacted clayey silt and silty sand backfill materials. The simulation methods considered include a method of slices approach for the backfill materials with an assumed log-spiral failure surface coupled with hyperbolic soil stress-strain relationships [referred to as “log-spiral hyperbolic (LSH) model”] as well as detailed finite-element models, both of which were found to compare well with test data. Through parametric studies on the validated LSH model, we develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall deflection and are amendable to practical application in seismic response simulations of bridge systems.     

Mechanisms of Seismically Induced Settlement of Buildings with Shallow Foundations on Liquefiable Soil

Seismically induced settlement of buildings with shallow foundations on liquefiable soils has resulted in significant damage in recent earthquakes. Engineers still largely estimate seismic building settlement using procedures developed to calculate postliquefaction reconsolidation settlement in the free-field. A series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction-induced building settlement. Previous studies of this problem have identified important factors including shaking intensity, the liquefiable soil’s relative density and thickness, and the building’s weight and width. Centrifuge test results indicate that building settlement is not proportional to the thickness of the liquefiable layer and that most of this settlement occurs during earthquake strong shaking. Building-induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms. The development of high excess pore pressures, localized drainage in response to the high transient hydraulic gradients, and earthquake-induced ratcheting of the buildings into the softened soil are important effects that should be captured in design procedures that estimate liquefaction-induced building settlement.     

A joke is just a joke (except when it isn't): Cavalier humor beliefs facilitate the expression of group dominance motives.

[Correction Notice: An erratum for this article was reported in Vol 100(2) of Journal of Personality and Social Psychology (see record 2011-01042-001). In the article “A Joke Is Just a Joke (Except When It Isn’t): Cavalier Humor Beliefs Facilitate the Expression of Group Dominance Motives,” by Gordon Hodson, Jonathan Rush, and Cara C. MacInnis (Journal of Personality and Social Psychology, 2010, Vol. 99, No. 4, pp. 660–682), there was an error in Table 6. The last row of data should have read “Obese”, not “Mexican”.] Past research reveals preferences for disparaging humor directed toward disliked others. The group-dominance model of humor appreciation introduces the hypothesis that beyond initial outgroup attitudes, social dominance motives predict favorable reactions toward jokes targeting low-status outgroups through a subtle hierarchy-enhancing legitimizing myth: cavalier humor beliefs (CHB). CHB characterizes a lighthearted, less serious, uncritical, and nonchalant approach toward humor that dismisses potential harm to others. As expected, CHB incorporates both positive (affiliative) and negative (aggressive) humor functions that together mask biases, correlating positively with prejudices and prejudice-correlates (including social dominance orientation [SDO]; Study 1). Across 3 studies in Canada, SDO and CHB predicted favorable reactions toward jokes disparaging Mexicans (low-status outgroup). Neither individual difference predicted neutral (nonintergroup) joke reactions, despite the jokes being equally amusing and more inoffensive overall. In Study 2, joke content targeting Mexicans, Americans (high-status outgroup), and Canadians (high-status ingroup) was systematically controlled. Although Canadians preferred jokes labeled as anti-American overall, an underlying subtle pattern emerged at the individual-difference level: Only those higher in SDO appreciated those jokes labeled as anti-Mexican (reflecting social dominance motives). In all studies, SDO predicted favorable reactions toward low-status outgroup jokes almost entirely through heightened CHB, a subtle yet potent legitimatizing myth that “justifies” expressions of group dominance motives. In Study 3, a pretest–posttest design revealed the implications of this justification process: CHB contributes to trivializing outgroup jokes as inoffensive (harmless), subsequently contributing to postjoke prejudice. The implications for humor in intergroup contexts are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrospinning of nanomaterials and applications in electronic components and devices

Electrospinning of nanomaterial composites are gaining increased interest in the fabrication of electronic components and devices. Performance improvement of electrospun components results from the unique properties associated with nanometer-scaled features, high specific surface areas, and light-weight designs. Electrospun nanofiber membrane-containing polymer electrolytes show improved ionic conductivity, electrochemical stability, low interfacial resistance, and improved charge-discharge performance than those prepared from conventional membranes. Batteries with non-woven electrospun separators have increased cycle life and higher rate capabilities than ones with conventional separators. Electrospun nanofibers may also be used as working electrodes in lithium-ion batteries, where they exhibit excellent rate capability, high reversible capacity, and good cycling performance. Moreover, the high surface area of electrospun activated carbon nanofibers improves supercapacitor energy density. Similarly, nanowires having quasi-one-dimensional structures prepared by electrospinning show high conductivity and have been used in ultra-sensitive chemical sensors, optoelectronics, and catalysts. Electrospun conductive polymers can also perform as flexible electrodes. Finally, the thin, porous structure of electrospun nanofibers provides for the high strain and fast response required for improved actuator performance. The current review examines recent advances in the application of electrospinning in fabricating electronic components and devices.     

Synthesis and screening of thin films in the CeCl3-CeBr3 system for scintillator applications

Thin film samples of CeCl₃, CeBr₃, and combinatorial compositions along the CeCl₃-CeBr₃ join were produced using thermal evaporation, which is being evaluated as a method for rapid screening of scintillator materials. The combinatorial thin films were shown to be compositionally reproducible from run-to-run within reasonable limitations. Analytical results suggest a continuous variation in the combinatorial samples in terms of their compositions, crystal structures, and luminescence characteristics.     

Evaluation of the overload effect on fatigue crack growth with the help of synchrotron XRD strain mapping

The overload retardation effect on fatigue crack growth rate (FCGR) in titanium alloy Ti-6Al-4V is studied. Synchrotron X-ray diffraction strain mapping of near-crack tip regions of pre-cracked fatigued samples is used to determine the effective stress intensity factors experienced by the crack tip. The effective stress intensity factor values are computed by finding the best match between the experimental strain maps and linear elastic fracture mechanics (LEFM) predictions. The dependence of the effective stress intensity factor, K, on the applied load is plotted, and an interpretation of the overload retardation effect is proposed. The present approach permits to reconcile the traditional LEFM fatigue crack propagation prediction and the experimental measurement of strain fields.     

Soft X-ray spectroscopy of oxide-embedded and functionalized silicon nanocrystals

An X-ray absorption spectroscopic investigation into the electronic and optical properties of silicon nanocrystals (Si-NCs) derived from the thermal processing of hydrogen silsesquioxane (HSQ) is presented. Hydrofluoric (HF) acid etching and subsequent photochemical hydrosilylation with styrene liberates the as-synthesized oxide-embedded Si-NCs from their matrix and renders them solution dispersible through the formation of surface Si–C bonds. The impact of this process on the photoluminescence behavior exhibited by these materials has been studied through near edge X-ray absorption fine structure (NEXAFS) and X-ray excited optical luminescence (XEOL) spectroscopies.