Excitation of surface plasmons at a SiO2/Ag interface by silicon quantum dots: Experiment and theory

The excitation of surface plasmons (SPs) by optically excited silicon quantum dots (QDs) located near a Ag interface is studied both experimentally and theoretically for different QD-interface separations. The Si QDs are formed in the near-surface region of an SiO2 substrate by Si ion implantation and thermal annealing. Photoluminescence decay-rate distributions, as derived from an inverse Laplace transform of the measured decay trace, are determined for samples with and without a Ag cover layer. For the smallest, investigated Si-QDs-to-interface distance of 44 nm the average decay rate at lambda=750 nm is enhanced by 80% due to the proximity of the Ag-glass interface, with respect to an air-glass interface. Calculations based on a classical dipole oscillator model show that the observed decay rate enhancement is mainly due to the excitation of surface plasmons that are on the SiO2/Ag interface. By comparing the model calculations to the experimental data, it is determined that Si QDs have a very high internal emission quantum efficiency of (77±17)%. At this distance they can excite surface plasmons at a rate of (1.1±0.2)×104 s¿1. From the model it is also predicted that by using thin metal films the excitation of surface plasmons by Si QDs can be further enhanced. Si QDs are found to preferentially excite symmetric thin-film surface plasmons

Ultrafast optical switching of three-dimensional Si inverse opal photonic band gap crystals

We present ultrafast optical switching experiments on 3D photonic band gap crystals. Switching the Si inverse opal is achieved by optically exciting free carriers by a two-photon process. We probe reflectivity in the frequency range of second order Bragg diffraction where the photonic band gap is predicted. We find good experimental switching conditions for free-carrier plasma frequencies between 0.3 and 0.7 times the optical frequency: we thus observe a large frequency shift of up to D omega/omega= 1.5% of all spectral features including the peak that corresponds to the photonic band gap. We deduce a corresponding large refractive index change of Dn'_Si/n'_Si= 2.0% and an induced absorption length that is longer than the sample thickness. We observe a fast decay time of 21 ps, which implies that switching could potentially be repeated at GHz rates. Such a high switching rate is relevant to future switching and modulation applications

A little hill with big impact: Favelas, art and social relevance

Many forms of artistic expression have stemmed and taken inspiration from favela culture. In this post, Simone Kalkman introduces Morrinho, a grassroots NGO based in Rio de Janeiro, to argue that the distinctiveness of this venture lies in its giving voice to favela dwellers, and in effectively showing that these voices should be taken seriously

Meaning in Animal Communication: Varieties of meaning and their roles in explaining communication

Why explain the communicative behaviours of animals by invoking the information/meaning 'transmitted' by signals? Why not explain communication in purely causal/functional terms? This thesis addresses active controversy regarding the nature and role of concepts of information, content and meaning in the scientific explanation of animal communication. I defend the methodology of explaining animal communication by invoking the 'meaning' of signals, and responds to worries raised by sceptics of this methodology in the scientific and philosophical literature. This task involves: showing what facts about communication non-informational methodology leaves unexplained; constructing a well-defined theory of content (or 'natural meaning') for most animal signals; and getting clearer on what cognitive capacities, if any, attributing natural meaning to signals implies for senders and receivers. Second, it weighs into comparative debates on human-nonhuman continuity, arguing that there are, in fact, different notions of meaning applicable to human communication that have different consequences for how continuous key aspects of human communication are with other species

LAF-Fabric: a data analysis tool for Linguistic Annotation Framework with an application to the Hebrew Bible

The Linguistic Annotation Framework (LAF) provides a general, extensible stand-off markup system for corpora. This paper discusses LAF-Fabric, a new tool to analyse LAF resources in general with an extension to process the Hebrew Bible in particular. We first walk through the history of the Hebrew Bible as text database in decennium-wide steps. Then we describe how LAF-Fabric may serve as an analysis tool for this corpus. Finally, we describe three analytic projects/workflows that benefit from the new LAF representation: 1) the study of linguistic variation: extract cooccurrence data of common nouns between the books of the Bible (Martijn Naaijer); 2) the study of the grammar of Hebrew poetry in the Psalms: extract clause typology (Gino Kalkman); 3) construction of a parser of classical Hebrew by Data Oriented Parsing: generate tree structures from the database (Andreas van Cranenburgh)

Impact of Responsive Classroom and PBIS on Behavior Choices in the Elementary Classroom

Effective teaching encompasses more than instructional strategies, content knowledge, and assessing; effective teachers must be able to manage their classroom and build relationships with the students they work with in order to foster student growth. This study examined what effect Responsive Classroom and Positive Behavioral Interventions & Supports (PBIS) strategies had on reducing negative student behaviors and improving student attitudes towards school. Over a seven-week period Responsive Classroom and PBIS strategies were utilized as the primary classroom management strategies in a suburban first-grade classroom in Minnesota. Student attitudes towards school were surveyed at the beginning and end of the study in addition to daily data collection on Take-A-Breaks (Responsive Classroom), student support center referrals, and a teacher reflection completed every other day. The data showed a correlation between the implemented strategies and improved attitudes towards school as assessed by the student survey. Over the course of the study, the number of breaks taken each day decreased overall as did the number of students that took breaks in a day. The positive results from the study indicate the effectiveness of the strategies used and encourage future use of both programs. Peer to peer relationships was the primary area that did not experience growth or positive results during the programs, so future research or implementation of other programs should be done in order to fill that gap

Purcell factor enhanced scattering efficiency in silicon nanocrystal doped micro-cavities

Scattering induced by nano-particles in a microcavity is investigated for the case of silicon nanocrystal doped microtoroids and a significant enhancement of scattering into the originally doubly-degenerate cavity eigenmodes is found, exceeding >99.42%