Figure rotation of dark halos in CDM simulations

We investigate the figure rotation of dark matter halos identified in Lambda CDM simulations. We find that when strict criteria are used to select suitable halos for study, 5 of the 222 halos identified in our z=0 simulation output undergo coherent figure rotation over a 5h^{-1}Gyr period. We discuss the effects of varying the selection criteria and find that pattern speeds for a much larger fraction of the halos can be measured when the criteria are relaxed. Pattern speeds measured over a 1h^{-1}Gyr period follow a log-normal distribution, centred at Omega_p = 0.25h rad/Gyr with a maximum value of 0.94h rad/Gyr. Over a 5h^{-1}Gyr period, the average pattern speed of a halo is about 0.1h rad/Gyr and the largest pattern speed found is 0.24h rad/Gyr. Less than half of the selected halos showed alignment between their figure rotation axis and minor axis, the exact fraction being somewhat dependent on how one defines a halo. While the pattern speeds observed are lower than those generally thought capable of causing spiral structure, we note that coherent figure rotation is found over very long periods and argue that further simulations would be required before strong conclusions about spiral structure in all galaxies could be drawn. We find no correlation between halo properties such as total mass and the pattern speed.Comment: accepted to MNRAS, 8 page

Identifications of FIRST radio sources in the NOAO Deep-Wide Field Survey

In this paper we present the results of an optical and near infrared identification of 514 radio sources from the FIRST survey (Faint Images of the Radio Sky Survey at Twenty centimeters) with a flux-density limit of 1 mJy in the NOAO Deep-Wide Field Survey (NDWFS) Bootes field. Using optical (Bw, R, I) and K band data with approximate limits of Bw ~ 25.5mag, R ~ 25.8 mag, I ~25.5 mag and K~19.4 mag, optical counterparts have been identified for 378 of 514 FIRST radio sources. This corresponds to an identification rate of 34% in four bands (BwRIK), 60% in optical bands (BwRI) and 74% in I band. Photometric redshifts for these sources have been computed using the hyperz code. The inclusion of quasar template spectra in hyperz is investigated. We note that the photometric data are, in many cases, best matched to templates with very short star-formation timescales and the inferred ages of identified galaxies depend strongly on the assumptions about the star-formation timescale. The redshifts obtained are fairly consistent with those expected from the K-z relation for brighter radio sources but there is more scatter in the K-z diagram at z<1.Comment: 9 pages, 7 figures. Accepted for publication in Astronomische Nachrichten; will appear in the issue 5/32

Computer-supported collaborative inquiry learning and classroom scripts

This study examined the influence of classroom-script structure (high vs. low) during computer-supported collaborative inquiry learning on help-seeking processes and learning gains in 54 student pairs in secondary science education. Screen- and audio-capturing videos were analysed according to a model of the help-seeking process. Results show that the structure of the classroom script substantially affects patterns of student help seeking and learning gain in the classroom. Overall, students in the high-structured classroom-script condition sought less help but learnt more than those in the low-structured classroom-script condition

Luminous Red Galaxies in Simulations: Cosmic Chronometers?

There have been a number of attempts to measure the expansion rate of the universe at high redshift using Luminous Red Galaxies (LRGs) as "chronometers". The method generally assumes that stars in LRGs are all formed at the same time. In this paper, we quantify the uncertainties on the measurement of H(z) which arise when one considers more realistic, extended star formation histories. In selecting galaxies from the Millennium Simulation for this study, we show that using rest-frame criteria significantly improves the homogeneity of the sample and that H(z) can be recovered to within 3% at z~0.42 even when extended star formation histories are considered. We demonstrate explicitly that using Single Stellar Populations to age-date galaxies from the semi-analytical simulations provides insufficient accuracy for this experiment but accurate ages are obtainable if the complex star formation histories extracted from the simulation are used. We note, however, that problems with SSP-fitting might be overestimated since the semi-analytical models tend to over predict the late-time star-formation in LRGs. Finally, we optimize an observational program to carry out this experiment.Comment: 11 pages, 10 figures. Accepted to MNRAS

The physiological mechanism behind the talk test

The Talk Test (TT) is a very simple marker of exercise intensity, which has been shown to be a useful surrogate of the ventilatory (VT) and respiratory compensation (RCT) thresholds. The purpose of this study was to evaluate a potential mechanism behind the TT. Healthy, college-aged subjects (n=20) performed a maximal and two sub-maximal cycle ergometer tests. The two submaximal tests were performed: with the Talk Test (EXP) and without speaking (the control trial – CON). Oxygen uptake (VO2), CO2 output (VCO2), minute ventilation (VE), breathing frequency (BF), end-tidal CO2 pressure (PETCO2) and TT times were recorded. VO2, VCO2 and VE were reduced during the TT and increased immediately after it. BF was reduced during the TT. PETCO2 values (a surrogate of PaCO2) were highest during the TT and lowest before the TT. The time to complete the TT increased across progressive stages. This study supports the hypothesis that talking causes CO2 retention, which may cause ventilatory drive to increase. Since the ventilatory drive is already high above the VT, the apparent CO2 retention associated with speech may cause talking to become uncomfortable

Evolution in the bias of faint radio sources to z ~ 2.2

Quantifying how the baryonic matter traces the underlying dark matter distribution is key to both understanding galaxy formation and our ability to constrain the cosmological model. Using the cross-correlation function of radio and near-infrared galaxies, we present a large-scale clustering analysis of radio galaxies to z ~ 2.2. We measure the angular auto-correlation function of Ks90μJy to infer linear bias of radio galaxies in four redshift bins. We find that the bias evolves from b = 0.57 ± 0.06 at z ~ 0.3 to 8.55 ± 3.11 at z ~ 2.2. Furthermore, we separate the radio sources into subsamples to determine how the bias is dependent on the radio luminosity, and find a bias which is significantly higher than predicted by the simulations of Wilman et al., and consistent with the lower luminosity but more abundant FR-I population having a similar bias to the highly luminous but rare FR-IIs. Our results are suggestive of a higher mass, particularly for FR-I sources than assumed in simulations, especially towards higher redshift.Peer reviewe

A model for the cosmological evolution of low frequency radio sources

We present a new evolutionary model that describes the population properties of radio sources at frequencies <5 GHz, thus complementing the De Zotti et al. (2005) model, holding at higher frequencies. We find that simple analytic luminosity evolution is still sufficient to fit the wealth of available data on local luminosity functions, multi-frequency source counts, and redshift distributions. However, the fit requires a luminosity-dependent decline of source luminosities at high redshifts, at least for steep-spectrum sources, thus confirming earlier indications of a "downsizing" also for radio sources. The upturn of source counts at sub-mJy levels is accounted for by a straightforward extrapolation, using the empirical far-IR/radio correlation, of evolutionary models matching the far-IR counts and redshift distributions of star-forming galaxies. We also discuss the implications of the new model for the interpretation of data on large-scale clustering of radio sources and on the Integrated Sachs-Wolfe (ISW) effect, and for the investigation of the contribution of discrete sources to the extragalactic background. As for the ISW effect, a new analysis exploiting a very clean CMB map, yields at a substantially higher significance than reported before.Comment: 14 pages, 11 figures, accepted for publication on MNRA

Scientific discovery and its role in sports science

Scientific discovery is about a search for the Truth, for the consistent and predictable in how the universe works. Using a particular method of inquiry, the scientific method, and with acknowledgement of the inherently self-correcting nature of science, scientific inquiry moves forward incrementally to ever closer approximations of the Truth. This paper reviews the history of scientific inquiry, the methodology of the scientific method, including the necessity for hypothesis testing and development of the probability that a particular answer is a closer approximation of the Truth than previous answers have been. It also discusses some of the pitfalls of scientific inquiry, and areas in which the search for Truth may be corrupted

Doing quantitative research in the learning sciences and CSCL:current developments and applications

While quantitative methods are continuously developed in various fields of origin,such as psychology, the specific applications in the core field of learning sciences and CSCL are less well advanced. In this workshop, we explore and discuss current methodological topics in three relevant fields of empirical research: (1) obtaining data, (2) analyzing data, and (3) sharing data, replicating and integrating findings. Outcomes of the discussions are planned to be published in short guidelines facilitating the application of latest developments in quantitative methods in the learning sciences and CSCL research.<br/

Doing quantitative research in the learning sciences and CSCL:current developments and applications

While quantitative methods are continuously developed in various fields of origin,such as psychology, the specific applications in the core field of learning sciences and CSCL are less well advanced. In this workshop, we explore and discuss current methodological topics in three relevant fields of empirical research: (1) obtaining data, (2) analyzing data, and (3) sharing data, replicating and integrating findings. Outcomes of the discussions are planned to be published in short guidelines facilitating the application of latest developments in quantitative methods in the learning sciences and CSCL research.<br/