Multi-object spectroscopy of the field surrounding PKS 2126-158: Discovery of a z=0.66 galaxy group

The high-redshift radio-loud quasar PKS 2126-158 is found to have a large number of red galaxies in close apparent proximity. We use the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to obtain optical spectra for a large fraction of these sources. We show that there is a group of galaxies at $z\sim0.66$, coincident with a metal-line absorption system seen in the quasar's optical spectrum. The multiplexing capabilities of GMOS also allow us to measure redshifts of many foreground galaxies in the field surrounding the quasar. The galaxy group has five confirmed members, and a further four fainter galaxies are possibly associated. All confirmed members exhibit early-type galaxy spectra, a rare situation for a Mg II absorbing system. We discuss the relationship of this group to the absorbing gas, and the possibility of gravitational lensing of the quasar due to the intervening galaxies.Comment: Monthly Notices of the Royal Astronomical Society, in press. 10 pages, 8 figure

The Optical/Near-IR Colours of Red Quasars

We present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fν ∝ ν0 to Fν, ∝ ν-2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19 · 6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band

Resonance tuning of two-photon absorption microcavities for wavelength-selective pulse monitoring

We show the potential use of a single photodetector for multichannel pulse monitoring. Two-photon absorption in a microcavity structure is used as the nonlinear optical technique for pulse monitoring. Angle tuning of the device allows the resonance to be tuned. For the device studied here that is optimized for 2-ps pulses, a possible tuning range of 55 nm is shown

Optical signal processing via two-photon absorption in a semiconductor microcavity for the next generation of high-speed optical communications network

Due to the introduction of new broadband services, individual line data rates are expected to exceed 100 Gb/s in the near future. To operate at these high speeds, new optical signal processing techniques will have to be developed. This paper will demonstrate that two-photon absorption in a specially designed semiconductor microcavity is an ideal candidate for optical signal processing applications such as autocorrelation, sampling, and demultiplexing in high-speed wavelength-division-multiplexed (WDM) and hybrid WDM/optical time-division-multiplexed networks

When Do People Trust Their Social Groups?

Trust facilitates cooperation and supports positive outcomes in social groups, including member satisfaction, information sharing, and task performance. Extensive prior research has examined individuals' general propensity to trust, as well as the factors that contribute to their trust in specific groups. Here, we build on past work to present a comprehensive framework for predicting trust in groups. By surveying 6,383 Facebook Groups users about their trust attitudes and examining aggregated behavioral and demographic data for these individuals, we show that (1) an individual's propensity to trust is associated with how they trust their groups, (2) smaller, closed, older, more exclusive, or more homogeneous groups are trusted more, and (3) a group's overall friendship-network structure and an individual's position within that structure can also predict trust. Last, we demonstrate how group trust predicts outcomes at both individual and group level such as the formation of new friendship ties.Comment: CHI 201

Uncovering the Neoproterozoic Carbon Cycle

Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter1,2. Neoproterozoic carbonate records contain unusualand large negative isotopic anomalies within long periods (10–100 million years) characterized by d13C in carbonate (d13Ccarb) enriched to more than +5 per mil. Classically, d13Ccarb is interpreted as a metric of the relative fraction of carbon buried as organic matter in marine sediments2–4, which can be linked to oxygen accumulation through the stoichiometry of primary production3,5. If a change in the isotopic composition of marine dissolved inorganic carbon is responsible for these excursions, it is expected that records of d13Ccarb and d13C in organic carbon (d13Corg) will covary, offset by the fractionation imparted by primary production5. The documentation of several Neoproterozoic d13Ccarb excursions that are decoupled from d13Corg, however, indicates that other mechanisms6–8 may account for these excursions. Here we present d13C data from Mongolia, northwest Canada and Namibia that capture multiple large-amplitude (over 10 per mil) negative carbon isotope anomalies, and use these data in a new quantitative mixing model to examine the behaviour of the Neoproterozoic carbon cycle. We find that carbonate and organic carbon isotope data from Mongolia and Canada are tightly coupled through multiple d13Ccarb excursions, quantitatively ruling out previously suggested alternative explanations, such as diagenesis7,8 or the presence and terminal oxidation of a large marine dissolved organic carbon reservoir6. Our data from Namibia, which do not record isotopic covariance, can be explained by simple mixing with a detrital flux of organic matter. We thus interpret d13Ccarb anomalies as recording a primary perturbation to the surface carbon cycle. This interpretation requires the revisiting of models linking drastic isotope excursions to deep ocean oxygenation and the opening of environments capable of supporting animals9–11.Earth and Planetary Science

Dynactin-dependent cortical dynein and spherical spindle shape correlate temporally with meiotic spindle rotation in Caenorhabditis elegans.

Oocyte meiotic spindles orient with one pole juxtaposed to the cortex to facilitate extrusion of chromosomes into polar bodies. In Caenorhabditis elegans, these acentriolar spindles initially orient parallel to the cortex and then rotate to the perpendicular orientation. To understand the mechanism of spindle rotation, we characterized events that correlated temporally with rotation, including shortening of the spindle in the pole-to pole axis, which resulted in a nearly spherical spindle at rotation. By analyzing large spindles of polyploid C. elegans and a related nematode species, we found that spindle rotation initiated at a defined spherical shape rather than at a defined spindle length. In addition, dynein accumulated on the cortex just before rotation, and microtubules grew from the spindle with plus ends outward during rotation. Dynactin depletion prevented accumulation of dynein on the cortex and prevented spindle rotation independently of effects on spindle shape. These results support a cortical pulling model in which spindle shape might facilitate rotation because a sphere can rotate without deforming the adjacent elastic cytoplasm. We also present evidence that activation of spindle rotation is promoted by dephosphorylation of the basic domain of p150 dynactin

Teacher characteristics, classroom instruction, and student literacy and language outcomes in bilingual kindergartners

This study investigated the relation of teacher characteristics, including ratings of teacher quality, to classroom instructional variables and to bilingual students' literacy and oral language outcomes at the end of the kindergarten year. Teacher characteristics included observational measures of oral language proficiency, quality, and classroom activity structure, as well as surveys of knowledge of reading-related skills. Student outcomes in both languages included letter naming, word reading, and phonological awareness and oral language composites. The study involved 141 teachers from a multisite project who were observed up to 3 times at the beginning, middle, and end of the year during their reading/language arts block while teaching English language learners to read in their primary language (Spanish) and/or in English. Teacher quality, but not teacher knowledge, was related positively to student engagement and negatively to time spent in noninstructional activities. Initial student and classroom performance, language of instruction and of outcomes, and teacher oral language proficiency in both Spanish and English predicted outcomes, whereas teacher quality was less related, and teacher content knowledge was consistently not related to student outcomes

The Spectra of Red Quasars

We measure the spectral properties of a representative sub-sample of 187 quasars, drawn from the Parkes Half-Jansky, Flat-radio-spectrum Sample (PHFS). Quasars with a wide range of rest-frame optical/UV continuum slopes are included in the analysis: their colours range from 2 < B-K < 7. The median H-beta and [O III] emission-line equivalent widths of the red quasar sub-sample are a factor of ten weaker than those of the blue quasar sub-sample. Both the colours and the emission-line equivalent widths of the red quasars can be explained by the addition of a featureless red synchrotron continuum component to an otherwise normal blue quasar spectrum. The relative strengths of the blue and red components span two orders of magnitude at rest-frame 500nm. The blue component is weaker relative to the red component in low optical luminosity sources. This suggests that the fraction of accretion energy going into optical emission from the jet is greater in low luminosity quasars. This synchrotron model does not, however, fit around 10% of the quasars, which have both red colours and high equivalent width emission-lines. We hypothesise that these red, strong-lined quasars have intrinsically weak Big Blue Bumps. There is no discontinuity in spectral properties between the BL Lac objects in our sample and the other quasars. The synchrotron emission component only dominates the spectrum at longer wavelengths, so existing BL Lac surveys will be biassed against high redshift objects.Comment: 22 pages, 12 figures, accepted for publication in PASA. Data tables and composite spectra from the paper can be found at http://msowww.anu.edu.au/~pfrancis