85 °C error-free operation at 38 Gb/s of oxide-confined 980-nm vertical-cavity surface-emitting lasers

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 100, 081103 (2012) and may be found at https://doi.org/10.1063/1.3688040.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP7/224211/EU/VISIT - Vertically Integrated Systems for Information Transfer/VISI

Templated Synthesis of Peptide Nucleic Acids via Sequence-Selective Base-Filling Reactions

The templated synthesis of nucleic acids has previously been achieved through the backbone ligation of preformed nucleotide monomers or oligomers. In contrast, here we demonstrate templated nucleic acid synthesis using a base-filling approach in which individual bases are added to abasic sites of a peptide nucleic acid (PNA). Because nucleobase substrates in this approach are not self-reactive, a base-filling approach may reduce the formation of nontemplated reaction products. Using either reductive amination or amine acylation chemistries, we observed efficient and selective addition of each of the four nucleobases to an abasic site in the middle of the PNA strand. We also describe the addition of single nucleobases to the end of a PNA strand through base filling, as well as the tandem addition of two bases to the middle of the PNA strand. These findings represent an experimental foundation for nonenzymatic information transfer through base filling.Chemistry and Chemical Biolog

Parton-Hadron Duality: Resonances and Higher Twists

We explore the physics of the parton-hadron duality in the nucleon structure functions appearing in lepton-nucleon scattering. We stress that the duality allows one to extract the higher-twist matrix elements from data in the resonance region, and learn about the properties of resonances if these matrix elements are known. As an example, we construct the moments of $F_2(x, Q^2)$ for the low and medium $Q^2$ region, and from which we study the interplay between higher twists and the resonance contributions.Comment: 7 pages with 4 figures and 1 table, REVTeX, MIT-CTP-234

Evaluation of a learner-designed course for teaching health research skills in Ghana

<p>Abstract</p> <p>Background</p> <p>In developing countries the ability to conduct locally-relevant health research and high quality education are key tools in the fight against poverty. The objective of our study was to evaluate the effectiveness of a novel UK accredited, learner-designed research skills course delivered in a teaching hospital in Ghana.</p> <p>Methods</p> <p>Study participants were 15 mixed speciality health professionals from Komfo Anokye Teaching Hospital, Kumasi, Ghana. Effectiveness measures included process, content and outcome indicators to evaluate changes in learners' confidence and competence in research, and assessment of the impact of the course on changing research-related thinking and behaviour. Results were verified using two independent methods.</p> <p>Results</p> <p>14/15 learners gained research competence assessed against UK Quality Assurance Agency criteria. After the course there was a 36% increase in the groups' positive responses to statements concerning confidence in research-related attitudes, intentions and actions. The greatest improvement (45% increase) was in learners' actions, which focused on strengthening institutional research capacity. 79% of paired before/after responses indicated positive changes in individual learners' research-related attitudes (n = 53), 81% in intention (n = 52) and 85% in action (n = 52). The course had increased learners' confidence to start and manage research, and enhanced life-long skills such as reflective practice and self-confidence. Doing their own research within the work environment, reflecting on personal research experiences and utilising peer support and pooled knowledge were critical elements that promoted learning.</p> <p>Conclusion</p> <p>Learners in Ghana were able to design and undertake a novel course that developed individual and institutional research capacity and met international standards. Learning by doing and a supportive peer community at work were critical elements in promoting learning in this environment where tutors were scarce. Our study provides a model for delivering and evaluating innovative educational interventions in developing countries to assess whether they meet external quality criteria and achieve their objectives.</p

Foster Care Placement, Poor Parenting, and Negative Outcomes Among Homeless Young Adults

Although homeless youth with and without foster care histories both face adverse life circumstances, little is known about how these two groups compare in terms of their early histories and whether they face similar outcomes. As such, we compared those with and without a history of foster care placement to determine if the associations between a history of poor parenting and negative outcomes including depression, delinquency, physical and sexual victimization, and substance use, are similar for these two groups. The sample consisted of 172 homeless young adults from the Midwestern United States. Multivariate results revealed that among those previously in foster care, a history of physical abuse and neglect were positively associated with more depressive symptoms whereas sexual abuse and neglect were related to delinquency and physical victimization. Additionally, lower caretaker monitoring was linked to greater delinquent participation. Among those without a history of foster care, physical abuse was related to more depressive symptoms whereas sexual abuse was positively correlated with delinquency, sexual victimization, and substance use. Furthermore, lower monitoring was related to more substance use. Our findings are discussed in terms of a social stress framework and we review the implications of foster care placement for homeless young adults

Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources