Elimination of cracks in self-assembled photonic band gap crystals

Thin colloidal crystals (or synthetic opals) composed of Stober silica spheres typically develop cracks when they are utilized to obtain photonic band gap crystals (or inverted opals). We find that by sintering the silica spheres prior to assembly of the opal these cracks can be avoided. We report the effects of temperature and duration of the heat treatment on 850 nm silica spheres using electron microscopy, thermogravimetry, and light scattering. We also find a large dependence of the refractive index of the silica on the temperature of the heat treatment. This may allow tuning of the refractive index of silica spheres.Comment: REvTex: 4 pages, 3 figure

Coping with speaker-related variation via abstract phonemic categories

Listeners can cope with considerable variation in the way that different speakers talk. We argue here that they can do so because of a process of phonological abstraction in the speech-recognition system. We review evidence that listeners adjust the bounds of phonemic categories after only very limited exposure to a deviant realisation of a given phoneme. This learning can be talker-specific and is stable over time; further, the learning generalizes to previously unheard words containing the deviant phoneme. Together these results suggest that the learning involves adjustment of prelexical phonemic representations which mediate between the speech signal and the mental lexicon during word recognition. We argue that such an abstraction process is inconsistent with claims made by some recent models of language processing that the mental lexicon consists solely of multiple detailed traces of acoustic episodes. Simulations with a purely episodic model without functional prelexical abstraction confirm that such a model cannot account for the evidence on lexical generalization of perceptual learning. We conclude that abstract phonemic categories form a necessary part of lexical access, and that the ability to store talker-specific knowledge about those categories provides listeners with the means to deal with cross-talker variation

A Review of Generalist and Specialist Community Health Workers for Delivering Adolescent Health Services in sub-Saharan Africa.

The health of adolescents is increasingly seen as an important international priority because the world's one point eight billion young people (aged 10 to 24 years) accounts for 15.5% of the global burden of disease and are disproportionately located in low- and middle-income countries (LMICs). Furthermore, an estimated 70% of premature adult deaths are attributable to unhealthy behaviors often initiated in adolescence (such as smoking, obesity, and physical inactivity). In order for health services to reach adolescents in LMICs, innovative service delivery models need to be explored and tested. This paper reviews the literature on generalist and specialist community health workers (CHWs) to assess their potential for strengthening the delivery of adolescent health services. We reviewed the literature on CHWs using Medline (PubMed), EBSCO Global Health, and Global Health Archive. Search terms (n = 19) were sourced from various review articles and combined with subject heading 'sub-Saharan Africa' to identify English language abstracts of original research articles on generalist and specialist CHWs. A total of 106 articles, from 1985 to 2012, and representing 24 African countries, matched our search criteria. A single study in sub-Saharan Africa used CHWs to deliver adolescent health services with promising results. Though few comprehensive evaluations of large-scale CHW programs exist, we found mixed evidence to support the use of either generalist or specialist CHW models for delivering adolescent health services. This review found that innovative service delivery approaches, such as those potentially offered by CHWs, for adolescents in sub-Saharan Africa are lacking, CHW programs have proliferated despite the absence of high quality evaluations, rigorous studies to establish the comparative effectiveness of generalist versus specialist CHW programs are needed, and further investigation of the role of CHWs in providing adolescent health services in sub-Saharan Africa is warranted

Language-universal constraints on the segmentation of English

Two word-spotting experiments are reported that examine whether the Possible-Word Constraint (PWC) [1] is a language-specific or language-universal strategy for the segmentation of continuous speech. The PWC disfavours parses which leave an impossible residue between the end of a candidate word and a known boundary. The experiments examined cases where the residue was either a CV syllable with a lax vowel, or a CVC syllable with a schwa. Although neither syllable context is a possible word in English, word-spotting in both contexts was easier than with a context consisting of a single consonant. The PWC appears to be language-universal rather than language-specific

Identification and control of structures in space

The derivation of the equations of motion for the Spacecraft Control Laboratory Experiment (SCOLE) is reported and the equations of motion of a similar structure orbiting the earth are also derived. The structure is assumed to undergo large rigid-body maneuvers and small elastic deformations. A perturbation approach is proposed whereby the quantities defining the rigid-body maneuver are assumed to be relatively large, with the elastic deformations and deviations from the rigid-body maneuver being relatively small. The perturbation equations have the form of linear equations with time-dependent coefficients. An active control technique can then be formulated to permit maneuvering of the spacecraft and simultaneously suppressing the elastic vibration