Surface Encapsulation for Low-Loss Silicon Photonics

Encapsulation layers are explored for passivating the surfaces of silicon to reduce optical absorption in the 1500-nm wavelength band. Surface-sensitive test structures consisting of microdisk resonators are fabricated for this purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and SiO2 are applied under varying deposition and annealing conditions. A short dry thermal oxidation followed by a long high-temperature N2 anneal is found to be most effective at long-term encapsulation and reduction of interface absorption. Minimization of the optical loss is attributed to simultaneous reduction in sub-bandgap silicon surface states and hydrogen in the capping material.Comment: 4 pages, 3 figure

ELSA: An Integrated, Semi-Automated Nebular Abundance Package

We present ELSA, a new modular software package, written in C, to analyze and manage spectroscopic data from emission-line objects. In addition to calculating plasma diagnostics and abundances from nebular emission lines, the software provides a number of convenient features including the ability to ingest logs produced by IRAF's splot task, to semi-automatically merge spectra in different wavelength ranges, and to automatically generate various data tables in machine-readable or LaTeX format. ELSA features a highly sophisticated interstellar reddening correction scheme that takes into account temperature and density effects as well as He II contamination of the hydrogen Balmer lines. Abundance calculations are performed using a 5-level atom approximation with recent atomic data, based on R. Henry's ABUN program. Improvements planned in the near future include use of a three-region ionization model, similar to IRAF's nebular package, error propagation, and the addition of ultraviolet and infrared line analysis capability. Detailed documentation for all aspects of ELSA are available at http://www.williams.edu/Astronomy/research/PN .Comment: 2 pages, contributed paper, IAU Symp. 234, Planetary Nebulae in Our Galaxy and Beyon

Qualitative Indicators of Social Resilience in Small-Scale Fishing Communities: An Emphasis on Perceptions and Practice

This paper reports on ethnographic research aimed at understanding what resilience means to those living within fishery-dependent communities. We draw on semi-structured and oral history interviews, focus groups, and household and business interviews in four Maine fishing communities to examine the reflections of fishermen and other community members on the past, present, and future of their communities, including the threats they face and how they are able to respond to them. Based on our analysis, we identify broad qualitative indicators of resilience: survival, social identity, diversification, getting by, and optimism. The indicators of resilience that we identify are difficult to fully understand using secondary data and, therefore, we argue that understanding them also requires an ethnographic research approach that focuses on the practices of fishermen and the context in which those fishermen live

Nonlocalized modulation of periodic reaction diffusion waves: The Whitham equation

In a companion paper, we established nonlinear stability with detailed diffusive rates of decay of spectrally stable periodic traveling-wave solutions of reaction diffusion systems under small perturbations consisting of a nonlocalized modulation plus a localized perturbation. Here, we determine time-asymptotic behavior under such perturbations, showing that solutions consist to leading order of a modulation whose parameter evolution is governed by an associated Whitham averaged equation

Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars

We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass subgiants (1.5 < M*/Msun < 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26 (+9,-8)%, which is significantly higher than the ~5-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} MJup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around intermediate-mass stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ~ M^{alpha}P^{beta} dlnM dlnP, the observed planet frequency, and the detection limits we derived. We find that the values of alpha and beta for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4 sigma level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~ 50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.Comment: Accepted by the Astrophysical Journal; 15 pages, 15 figure

Song Analysis Reveals a Permanent Population of the Mediterranean Lacewing Chrysoperla agilis (Neuroptera: Chrysopidae) Living in Central Alaska

Chrysoperla agilis Henry et al. (Neuroptera: Chrysopidae) is a widespread, nomadic lacewing in the carnea group of cryptic species. C. agilis has previously been found only in the warm parts of Europe, western Asia, and a few oceanic islands. Like others of the carnea group, C. agilis is identifiable only by its unique courtship song. Recently, a population with by the C. agilis song was discovered in central Alaska; based on its persistence over several years and its distribution over a wide area near Fairbanks, it seems to be permanent rather than transitory. To assess the relationship of this Western Hemisphere population to C. agilis in the Eastern Hemisphere, we 1) analyzed its courtship song, comparing it to the Eurasian song; 2) compared larval and adult morphology of Alaskan and Eurasian specimens; 3) inferred phylogenetic relationships of Alaskan and Eurasian specimens, by using sequences from the cox2 gene; and 4) crossed Alaskan with European individuals, raising their progeny and analyzing their "hybrid” songs. Alaskan C. agilis generally fell within the range of variation of Eurasian individuals for all acoustic and morphological traits, and their hybrid progeny were also acoustically indistinguishable. Phylogenetically, and despite current geographical isolation, Alaskan individuals clustered with Eurasian C. agilis rather than with Western Hemisphere taxa of the carnea group. We conclude that the Alaskan population is a bona fide member of C. agilis. Examination of the geographical pattern of song variation suggests that dispersal to Alaska took place quite recently in a west to east direction, via eastern Asia and the Bering Strai

Children's understanding of food and its functions: A preliminary study of the development of concepts of nutrition

Children's developing conceptions of how the body functions nutritionally were examined. Two different tasks provided converging findings. One task asked children to judge the causes of certain end states (e.g., why X is fat). The second task asked children to judge the result of certain contrasting diets (e.g., twin-1 eats twice as much candy as twin-2). The results evidenced; (a) systematic misconceptions on the part of kindergarteners that were overcome by sixth grade; and (b) other fairly sophisticated conceptions present even at the youngest ages tested. The research provides a needed first step toward describing the naive theories of nutrition possessed by children at different ages. Knowledge of childrens' theories of nutrition are essential for optimal planning of curricula and methods in nutrition education.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24015/1/0000264.pd

Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10

VLA radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in the central 5" starburst region of the blue compact galaxy Henize 2-10. We interpret these radio knots as extremely young, ultra-dense HII regions. We model their luminosities and spectral energy distributions, finding that they are consistent with unusually dense HII regions having electron densities, 1500 cm^-3 < n_e < 5000 cm^-3, and sizes of 3-8 pc. Since these H II regions are not visible in optical images, we propose that the radio data preferentially reveal the youngest, densest, and most highly obscured starforming events. Energy considerations imply that each of the five \HII regions contains ~750 O7V equivalent stars, greater than the number found in 30 Doradus in the LMC. The high densities imply an over-pressure compared to the typical interstellar medium so that such objects must be short-lived (<0.5 Myr expansion timescales). We conclude that the radio continuum maps reveal the very young (<0.5 Myr) precursors of ``super starclusters'' or ``proto globular clusters'' which are prominent at optical and UV wavelengths in He 2-10. If the ultra-dense HII regions are typical of those which we predict will be found in other starbursting systems, then super starclusters spend 15% of their lifetime in heavily-obscured environments, similar to Galactic ultra-compact HII regions. This body of work leads us to propose that massive extragalactic star clusters (i.e. proto globular clusters) with ages <10^6 yr may be most easily identified by finding compact radio sources with optically-thick thermal bremsstrahlung spectral signatures.Comment: AASTeX, 8 figures 2 included with psfig in text; other 6 in jpeg format; Postscript versions of figures may be found at http://zem.ucolick.org/chip/Research/young_clusters.html -- Accepted for publication in the Astrophysical Journa