Gas cooling in simulations of the formation of the galaxy population

We compare two techniques for following the cooling of gas and its condensation into galaxies within high resolution simulations of cosmologically representative regions. Both techniques treat the dark matter using N-body methods. One follows the gas using smoothed particle hydrodynamics (SPH) while the other uses simplified recipes from semi-analytic (SA) models. We compare the masses and locations predicted for dense knots of cold gas (the `galaxies') when the two techniques are applied to evolution from the same initial conditions and when the additional complications of star formation and feedback are ignored. We find that above the effective resolution limit of the two techniques, they give very similar results both for global quantities such as the total amount of cooled gas and for the properties of individual `galaxies'. The SA technique has systematic uncertainties arising from the simplified cooling model adopted, while details of the SPH implementation can produce substantial systematic variations in the galaxy masses it predicts. Nevertheless, for the best current SPH methods and the standard assumptions of the SA model, systematic differences between the two techniques are remarkably small. The SA technique gives adequate predictions for the condensation of gas into `galaxies' at less than one percent of the computational cost of obtaining similar results at comparable resolution using SPH.Comment: Revised, Figure 7 added. To appear in MNRA

Dark matter annihilation in the halo of the Milky Way

If the dark matter in the Universe is made of weakly self-interacting particles, they may self-annihilate and emit gamma-rays. We use high resolution numerical simulations to estimate directly the annihilation flux from the central regions of the Milky Way and from dark matter substructures in its halo. Although such estimates remain uncertain because of their strong dependence on the structure of the densest regions, our numerical experiments suggest that less direct calculations have overestimated the emission both from the centre and from halo substructure. We estimate a maximal enhancement of at most a factor of a few with respect to a smooth spherical halo of standard Navarro-Frenk-White (NFW) structure. We discuss detection strategies for the next generation of gamma-ray detectors and find that the annihilation flux may be detectable, regardless of uncertainties about the densest regions, for the annihilation cross-sections predicted by currently popular elementary particle models for the dark matter.Comment: 10 pages, 8 figures, replaced with version accepted by MNRAS (very minor changes

Can I teach mathematics? A study of preservice teachers’ self-efficacy and mathematics anxiety

This paper presents two studies (qualitative and quantitative) with the shared goal of exploring preservice teachers’ (PSTs’) experiences of mathematics anxiety and self-efficacy for mathematics teaching. Findings indicate that PSTs experience high levels of mathematics anxiety, impacting current learning and preference for teaching the content, as well as the development of self-efficacy for teaching mathematics and conceptions of ideal teaching. Findings regarding anxiety (fear) of evaluation and concern about being able to inspire students in their future classrooms converged across studies

From numbers to narratives: Preservice teachers experiences’ with mathematics anxiety and mathematics teaching anxiety

This paper presents qualitative and quantitative approaches to exploring teachers’ experiences of mathematics anxiety (for learning and doing mathematics) and mathematics teaching anxiety (for instructing others in mathematics), the relationship between these types of anxiety and test/evaluation anxiety, and the impacts of anxiety on experiences in teacher education. Findings indicate that mathematics anxiety and mathematics teaching anxiety may be similar (i.e., that preservice teachers perceive a logical continuity and cumulative effect of their experiences of mathematics anxiety as learners in K–12 classrooms that impacts their work as teachers in future K–12 classrooms). Further, anxiety is not limited to occurring in evaluative settings, but when anxiety is triggered by thoughts of evaluation, preservice teachers may be affected by worrying about their own as well as their students\u27 performances. The implications for preservice experiences within a teacher education program and for impacting future students are discussed

Elementary prospective teachers’ visions of moving beyond mathematics anxiety

Previous studies of prospective elementary mathematics teachers’ mathematics anxiety have documented that many prospective teachers often worry about managing their repeated experiences of anxiety while developing their pedagogical and content knowledge to teach mathematics. The literature further indicates the importance of developing learning opportunities for prospective teachers to confront their past experiences while they (re)learn and learn to teach mathematics during methods courses. This study is situated within one such learning opportunity and seeks to analyze potential mathematics anxiety coping strategies generated by forty-eight prospective elementary teachers enrolled in a mathematical methods course. Written responses generated by the prospective teachers were subjected to qualitative thematic analysis to identify patterns of key ideas related to lesson planning for content they felt anxious and/or not confident about teaching and patterns focused on episodes of mathematics anxiety they might experience in the moment of teaching mathematics. Findings indicate that prospective teachers envision using between two and seven strategies grouped across eight coping strategy themes when given the opportunity to reflect on how they might deal with future instances of anxiety when they are tasked with teaching mathematics to their students. We highlight how some of the coping strategies that the prospective teachers envisioned as a means to cope with mathematics anxiety may have more potential to be helpful than others and present implications of our research for mathematics teacher educators

The Hubble Legacy Archive NICMOS Grism Data

The Hubble Legacy Archive (HLA) aims to create calibrated science data from the Hubble Space Telescope archive and make them accessible via user-friendly and Virtual Observatory (VO) compatible interfaces. It is a collaboration between the Space Telescope Science Institute (STScI), the Canadian Astronomy Data Centre (CADC) and the Space Telescope - European Coordinating Facility (ST-ECF). Data produced by the Hubble Space Telescope (HST) instruments with slitless spectroscopy modes are among the most difficult to extract and exploit. As part of the HLA project, the ST-ECF aims to provide calibrated spectra for objects observed with these HST slitless modes. In this paper, we present the HLA NICMOS G141 grism spectra. We describe in detail the calibration, data reduction and spectrum extraction methods used to produce the extracted spectra. The quality of the extracted spectra and associated direct images is demonstrated through comparison with near-IR imaging catalogues and existing near-IR spectroscopy. The output data products and their associated metadata are publicly available through a web form at http://hla.stecf.org and via VO interfaces. In total, 2470 spectra of 1923 unique targets are included in the current release.Comment: 18 pages, 21 figures, accepted for publication in Astronomy & Astrophysic

A SILAC-based Approach Identifies Substrates of Caspase-dependent Cleavage upon TRAIL-induced Apoptosis

The extracellular ligand-induced extrinsic pathway of apoptosis is executed via caspase protease cascades that activate downstream effectors by means of site-directed proteolysis. Here we identify proteome changes upon the induction of apoptosis by the cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in a Jurkat T cell line. We detected caspase-dependent cleavage substrates by quantifying protein intensities before and after TRAIL induction in SDS gel slices. Apoptotic protein cleavage events are identified by a characteristic stable isotope labeling with amino acids in cell culture (SILAC) ratio pattern across gel slices that results from differential migration of the cleaved and uncleaved proteins. We applied a statistical test to define apoptotic substrates in the proteome. Our approach identified more than 650 of these cleaved proteins in response to TRAIL-induced apoptosis, including many previously unknown substrates and cleavage sites. Inhibitor treatment combined with triple SILAC demonstrated that the detected cleavage events were caspase dependent. Proteins located in the lumina of organelles such as mitochondria and endoplasmic reticulum were significantly underrepresented in the substrate population. Interestingly, caspase cleavage is generally observed in not only one but several members of stable complexes, but often with lower stoichiometry. For instance, all five proteins of the condensin I complex were cleaved upon TRAIL treatment. The apoptotic substrate proteome data can be accessed and visualized in the MaxQB database and might prove useful for basic and clinical research into TRAIL-induced apoptosis. The technology described here is extensible to a wide range of other proteolytic cleavage events

Simulating IGM Reionization

We have studied the IGM reionization process in its full cosmological context including structure evolution and a realistic galaxy population. We have used a combination of high-resolution N-body simulations (to describe the dark matter and diffuse gas component), a semi-analytic model of galaxy formation (to track the evolution of the sources of ionizing radiation) and the Monte Carlo radiative transfer code CRASH (to follow the propagation of ionizing photons into the IGM). The process has been followed in the largest volume ever used for this kind of study, a field region of the universe with a comoving length of L~20/h Mpc, embedded in a much larger cosmological simulation. To assess the effect of environment on the reionization process, the same radiative transfer simulations have been performed on a 10/h Mpc comoving box, centered on a clustered region. We find that, to account for the all ionizing radiation, objects with total masses of M~10^9 Msun must be resolved. In this case, the simulated stellar population produces a volume averaged ionization fraction x_v=0.999 by z~8, consistent with observations without requiring any additional sources of ionization. We also find that environment substantially affects the reionization process. In fact, although the simulated proto-cluster occupies a smaller volume and produces a higher number of ionizing photons, it gets totally ionized later. This is because high density regions, which are more common in the proto-cluster, are difficult to ionize because of their high recombination rates.Comment: 10 pages, 9 figures, minor revisions, in press, MNRAS 343 (2003) 1101-110

When is Foreign Exchange Intervention Effective? Evidence from 33 Countries

This paper examines foreign exchange intervention based on novel daily data covering 33 countries from 1995 to 2011. We find that intervention is widely used and an effective policy tool, with a success rate in excess of 80 percent under some criteria. The policy works well in terms of smoothing the path of exchange rates, and in stabilizing the exchange rate in countries with narrow band regimes. Moving the level of the exchange rate in flexible regimes requires that some conditions are met, including the use of large volumes and that intervention is made public and supported via communication