Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers

We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers

Ultralow threshold graded-index separate-confinement heterostructure single quantum well (Al,Ga)As lasers

Broad area graded‐index separate‐confinement heterostructure single quantum well lasers grown by molecular‐beam epitaxy (MBE) with threshold current density as low as 93 A/cm^2 (520 μm long) have been fabricated. Buried lasers formed from similarly structured MBE material with liquid phase epitaxy regrowth had threshold currents at submilliampere levels when high reflectivity coatings were applied to the end facets. A cw threshold current of 0.55 mA was obtained for a laser with facet reflectivities of ∼80%, a cavity length of 120 μm, and an active region stripe width of 1 μm. These devices driven directly with logic level signals have switch‐on delays <50 ps without any current prebias. Such lasers permit fully on–off switching while at the same time obviating the need for bias monitoring and feedback control

Contrasting soil organic matter properties of a Hawaiian Andosol revealed by fractionations procedures

Volcanic Andosols are recognized by their strong capacity to accumulate soil organic carbon (SOC), and for presenting a singular aggregation pattern. However, the factors that govern their SOC storage and aggregation hierarchy are still poorly understood. In this way, the objective of this study was to evaluate the soil organic matter (SOM) properties of an Andosol through CN analysis, NMR spectroscopy, and scanning electron microscopy (SEM) with subsequent nano scale secondary ion mass spectrometry (NanoSIMS) analysis in the soil mineral fraction testing different fractionation methods. We tested three Andosol samples from two sites of the Kohala region – Hawaii with contrasting precipitation levels. The samples tested were as follow: 1784-60, 1784-80 and 2286-50 (precipitation - average depth in cm). We performed the SOM fractionation using ultrasonic dispersion at 1500 J ml-1, wet sieving and sedimentation. The procedure was carried out in three sets: in deionized water, in 1M NaCL solution, and in polytungstate solution (SPT) 1.8 g cm-3. Six fractions were obtained as follow: free particulate organic matter (fPOM), occluded particulate organic matter (oPOM), 4000-63, 63-20, 20-2 and &lt; 2µm, respectively. Overall, the pre-dispersion treatment with NaCL saturation did not influence the C content and its distribution, as well as the SOM composition observed by NMR and NanoSIMS analysis. The oPOM fraction revealed great differences between the contrasting samples 1784-60 and 2286-50 in C content and SOM composition. More than 90% of the soil mass was concentrated in the fractions below 20 µm. The &lt;2µm fraction was the most representative for the evaluated Andosol, accounting with 83% of the C content and 74% of the soil mass for the three samples evaluated overall. The 2286-50 presented a higher C content than the other samples especially for fPOM and the &lt; 2 µm fraction. The 2286-50 sample presented overall a dominance of alkyl-C, while 1784-60 showed higher amounts of carboxyl-C and O/N alkyl groups, which can be explained by differences in the mineral composition of each sample. In addition, the NanoSIMS analysis demonstrated distinct spatial differences in the distribution of 12C- and 12C14N- in organo-mineral associations at the micro scale between the two sites. The results of this study suggest that mineral interactions in the smaller size-fractions (&lt;2µm) can be the key to explain the mechanisms of C storage in Andosols

Spin-echo small-angle neutron scattering (SESANS) studies of diblock copolymer nanoparticles

Poly(glycerol monomethacrylate)–poly(benzyl methacrylate) (PGMA–PBzMA) diblock copolymer nanoparticles were synthesized via polymerization-induced self-assembly (PISA) using reversible addition–fragmentation chain-transfer (RAFT) aqueous emulsion polymerization in D2O. Such PISA syntheses produce sterically-stabilized nanoparticles in situ and can be performed at relatively high copolymer concentrations (up to 50 wt%). This PGMA–PBzMA formulation is known to form only spherical nanoparticles in water using aqueous emulsion polymerization (Macromolecules, 2014, 47, 5613–5623), which makes it an ideal model system for exploring new characterization methods. The polymer micelles were characterized using small-angle X-ray scattering (SAXS) and a recently developed form of neutron scattering, spin-echo small-angle neutron scattering (SESANS). As far as we are aware, this is the first report of a study of polymer micelles by SESANS, and the data agree well with reciprocal-space scattering. Using this technique enables characterization of the concentrated, as synthesized dispersions directly without dilution, and this will provide a method to study self-assembled polymer systems that have concentration dependent morphologies, while still maintaining the advantages of scattering techniques

Time-Resolved SAXS Studies of the Kinetics of Thermally Triggered Release of Encapsulated Silica Nanoparticles from Block Copolymer Vesicles

Silica-loaded poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles are prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). As the concentration of silica nanoparticles present during the PISA synthesis is increased up to 35% w/w, higher degrees of encapsulation of this component within the vesicles can be achieved. After centrifugal purification to remove excess non-encapsulated silica nanoparticles, SAXS, DCP, and TGA analysis indicates encapsulation of up to hundreds of silica nanoparticles per vesicle. In the present study, the thermally triggered release of these encapsulated silica nanoparticles is examined by cooling to 0 °C for 30 min, which causes in situ vesicle dissociation. Transmission electron microscopy studies confirm the change in diblock copolymer morphology and also enable direct visualization of the released silica nanoparticles. Time-resolved small-angle X-ray scattering is used to quantify the extent of silica release over time. For an initial silica concentration of 5% w/w, cooling induces a vesicle-to-sphere transition with subsequent nanoparticle release. For higher silica concentrations (20 or 30% w/w) cooling only leads to perforation of the vesicle membranes, but silica nanoparticles are nevertheless released through the pores. For vesicles prepared in the presence of 30% w/w silica, the purified silica-loaded vesicles were cooled to 0 °C for 30 min, and SAXS patterns were collected every 15 s. A new SAXS model has been developed to determine both the mean volume fraction of encapsulated silica within the vesicles and the scattering length density. Satisfactory data fits to the experimental SAXS patterns were obtained using this model

Raising children with high self-esteem (but not narcissism)

With the rise of individualism since the 1960s, Western parents have become increasingly concerned with raising children’s self-esteem. This is understandable, given the benefits of self-esteem for children’s psychological health. However, parents’ well-intentioned attempts to raise self-esteem, such as inflated praise, may inadvertently breed narcissism. How, then, can parents raise self-esteem without breeding narcissism? Here, we propose a tripartite model of self-regard, which holds that the development of self-esteem without narcissism can be cultivated through realistic feedback (rather than inflated praise), focus on growth (rather than on outperforming others), and unconditional regard (rather than regard that is conditional). We review evidence in support of these practices and outline promising research directions. The tripartite model integrates existing research, stimulates theory development, and identifies leverage points for intervention concurrently to raise self-esteem and curtail narcissism from a young age

Acinar Cell Apoptosis in Serpini2-Deficient Mice Models Pancreatic Insufficiency

Pancreatic insufficiency (PI) when left untreated results in a state of malnutrition due to an inability to absorb nutrients. Frequently, PI is diagnosed as part of a larger clinical presentation in cystic fibrosis or Shwachman–Diamond syndrome. In this study, a mouse model for isolated exocrine PI was identified in a mouse line generated by a transgene insertion. The trait is inherited in an autosomal recessive pattern, and homozygous animals are growth retarded, have abnormal immunity, and have reduced life span. Mice with the disease locus, named pequeño (pq), exhibit progressive apoptosis of pancreatic acinar cells with severe exocrine acinar cell loss by 8 wk of age, while the islets and ductal tissue persist. The mutation in pq/pq mice results from a random transgene insertion. Molecular characterization of the transgene insertion site by fluorescent in situ hybridization and genomic deletion mapping identified an approximately 210-kb deletion on Chromosome 3, deleting two genes. One of these genes, Serpini2, encodes a protein that is a member of the serpin family of protease inhibitors. Reintroduction of only the Serpini2 gene by bacterial artificial chromosome transgenic complementation corrected the acinar cell defect as well as body weight and immune phenotypes, showing that deletion of Serpini2 causes the pequeño phenotype. Dietary supplementation of pancreatic enzymes also corrected body size, body weight, and immunodeficiency, and increased the life span of Serpini2-deficient mice, despite continued acinar cell loss. To our knowledge, this study describes the first characterized genetic animal model for isolated PI. Genetic complementation of the transgene insertion mutant demonstrates that Serpini2 deficiency directly results in the acinar cell apoptosis, malabsorption, and malnutrition observed in pq/pq mice. The rescue of growth retardation, immunodeficiency, and mortality by either Serpini2 bacterial artificial chromosome transgenic expression or by pancreatic enzyme supplementation demonstrates that these phenotypes are secondary to malnutrition in pq/pq mice

Collaboration scripts - a conceptual analysis

This article presents a conceptual analysis of collaboration scripts used in face-to-face and computer-mediated collaborative learning. Collaboration scripts are scaffolds that aim to improve collaboration through structuring the interactive processes between two or more learning partners. Collaboration scripts consist of at least five components: (a) learning objectives, (b) type of activities, (c) sequencing, (d) role distribution, and (e) type of representation. These components serve as a basis for comparing prototypical collaboration script approaches for face-to-face vs. computer-mediated learning. As our analysis reveals, collaboration scripts for face-to-face learning often focus on supporting collaborators in engaging in activities that are specifically related to individual knowledge acquisition. Scripts for computer-mediated collaboration are typically concerned with facilitating communicative-coordinative processes that occur among group members. The two lines of research can be consolidated to facilitate the design of collaboration scripts, which both support participation and coordination, as well as induce learning activities closely related to individual knowledge acquisition and metacognition. In addition, research on collaboration scripts needs to consider the learners’ internal collaboration scripts as a further determinant of collaboration behavior. The article closes with the presentation of a conceptual framework incorporating both external and internal collaboration scripts

In Situ Small-Angle X-ray Scattering Studies During Reversible Addition–Fragmentation Chain Transfer Aqueous Emulsion Polymerization

Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci. 2016, 7, 5078–5090). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aqueous emulsion polymerization

The close limit from a null point of view: the advanced solution

We present a characteristic algorithm for computing the perturbation of a Schwarzschild spacetime by means of solving the Teukolsky equation. We implement the algorithm as a characteristic evolution code and apply it to compute the advanced solution to a black hole collision in the close approximation. The code successfully tracks the initial burst and quasinormal decay of a black hole perturbation through 10 orders of magnitude and tracks the final power law decay through an additional 6 orders of magnitude. Determination of the advanced solution, in which ingoing radiation is absorbed by the black hole but no outgoing radiation is emitted, is the first stage of a two stage approach to determining the retarded solution, which provides the close approximation waveform with the physically appropriate boundary condition of no ingoing radiation.Comment: Revised version, published in Phys. Rev. D, 34 pages, 13 figures, RevTe