Rhodri Evans

Radiative transfer in disc galaxies — III. The observed kinematics of dusty disc galaxies

We present skirt (Stellar Kinematics Including Radiative Transfer), a new Monte Carlo radiative transfer code that allows the calculation of the observed stellar kinematics of a dusty galaxy. The code incorporates the effects of both absorption and scattering by interstellar dust grains, and calculates the Doppler shift of the emerging radiation exactly by taking into account the velocities of the emitting stars and the individual scattering dust grains. The code supports arbitrary distributions of dust through a cellular approach, whereby the integration through the dust is optimized by means of a novel efficient trilinear interpolation technique. We apply our modelling technique to calculate the observed kinematics of realistic models for dusty disc galaxies. We find that the effects of dust on the mean projected velocity and projected velocity dispersion are severe for edge-on galaxies. For galaxies which deviate more than a few degrees from exactly edge-on, the effects are already strongly reduced. As a consequence, dust attenuation cannot serve as a possible way to reconcile the discrepancy between the observed shallow slopes of the inner rotation curves of low surface brightness galaxies and the predictions of cold dark matter cosmological models. For face-on galaxies, the velocity dispersion increases with increasing dust mass owing to scattering, but the effects are limited, even for extended dust distributions. Finally, we show that serious errors can be made when the individual velocities of the dust grains are neglected in the calculations.

Supporting informed decision making for prostate specific antigen (PSA) testing on the web: an online randomized controlled trial.

Background Men considering the prostate specific antigen (PSA) test for prostate cancer, an increasingly common male cancer, are encouraged to make informed decisions, as the test is limited in its accuracy and the natural history of the condition is poorly understood. The Web-based PSA decision aid, Prosdex, was developed as part of the UK Prostate Cancer Risk Management Programme in order to help men make such informed decisions. Objectives The aim of this study was to evaluate the effect of the Web-based PSA decision aid, Prosdex, on informed decision making. Methods A Web-based randomized controlled trial was conducted in South Wales, United Kingdom. Men aged 50 to 75 who had not previously had a PSA test were randomly allocated to two intervention and two control groups. Participants in the intervention groups either viewed Prosdex or were given a paper version of the text. The main outcome measures were the three components of informed decision making: (1) knowledge of prostate cancer and PSA, (2) attitude toward PSA testing, (3) behavior using a proxy measure, intention to undergo PSA testing. Decisional conflict and anxiety were also measured as was uptake of the PSA test. Outcomes were measured by means of an online questionnaire for the Prosdex group, the paper version group, and one of two control groups. Six months later, PSA test uptake was ascertained from general practitioners’ records, and the online questionnaire was repeated. Results are reported in terms of the Mann-Whitney U-statistic divided by the product of the two sample sizes (U/mm), line of no effect 0.50. Results Participants were 514 men. Compared with the control group that completed the initial online questionnaire, men in the Prosdex group had increased knowledge about the PSA test and prostate cancer (U/mn 0.70; 95% CI 0.62 - 0.76); less favourable attitudes to PSA testing (U/mn 0.39, 95% CI 0.31 - 0.47); were less likely to undergo PSA testing (U/mn 0.40, 95% CI 0.32 - 0.48); and had less decisional conflict (U/mn 0.32, 95% CI 0.25 - 0.40); while anxiety level did not differ (U/mn 0.50, 95% CI 0.42 - 0.58). For these outcomes there were no significant differences between men in the Prosdex group and the paper version group. However, in the Prosdex group, increased knowledge was associated with a less favourable attitude toward testing (Spearman rank correlation [ρ] = -0.49, P < .001) and lower intention to undergo testing (ρ = -0.27, P = .02). After six months, PSA test uptake was lower in the Prosdex group than in the paper version and the questionnaire control group (P = .014). Test uptake was also lower in the control group that did not complete a questionnaire than in the control group that did, suggesting a possible Hawthorne effect of the questionnaire in favour of PSA testing. Conclusions Exposure to Prosdex was associated with improved knowledge about the PSA test and prostate cancer. Men who had a high level of knowledge had a less favourable attitude toward and were less likely to undergo PSA testing. Prosdex appears to promote informed decision making regarding the PSA test. Trial Registration ISRCTN48473735; http://www.controlled-trials.com/ISRCTN48473735 (Archived by WebCite at http://www.webcitation.org/5r1TLQ5nK)

Anion—surface interactions: Part I. Perchlorate decomposition and sulphate adsorption hysteresis studied by voltammetry

Cyclic voltammetry has been used to investigate the behaviour of sulphate and perchlorate anions adsorbed on Ir{111} and polycrystalline rhodium. In 0.1 M HClO4, perchlorate anions decompose on polycrystalline rhodium to give a surface intermediate which inhibits hydrogen adsorption. This is in agreement with a previous study by Wieckowski and coworkers, who showed that the surface intermediate was, in fact, adsorbed chloride. The voltammetry of the same electrode in sulphate containing electrolytes depends critically on the concentration of sulphate and the potential sweep rate. We conclude that hydrogen adsorption can only occur after significant desorption of sulphate. Hysteresis in the adsorption and desorption of sulphate results in an asymmetric hydrogen adsorption region with respect to the potential axis. Ir{111} is shown also to cause decomposition of perchlorate anions, although, contrary to the case of rhodium, the process is very much a chemical one in which electric currents, arising from perchlorate decomposition, were not detected. In sulphuric acid, a strong interaction between anions and the Ir{111} surface is observed, which precludes oxide formation at potentials less than 1 V (PdH), behaviour characteristic of a Pt{111} surface in the same electrolyte.

Radiative equilibrium in Monte Carlo radiative transfer using frequency distribution adjustment

The Monte Carlo method is a powerful tool for performing radiative equilibrium calculations, even in complex geometries. The main drawback of the standard Monte Carlo radiative equilibrium methods is that they require iteration, which makes them numerically very demanding. Bjorkman and Wood recently proposed a frequency distribution adjustment scheme, which allows radiative equilibrium Monte Carlo calculations to be performed without iteration, by choosing the frequency of each re-emitted photon such that it corrects for the incorrect spectrum of the previously re-emitted photons. Though, the method appears to yield correct results, we argue that its theoretical basis is not completely transparent, and that it is not completely clear whether this technique is an exact rigorous method, or whether it is just a good and convenient approximation. We critically study the general problem of how an already sampled distribution can be adjusted to a new distribution by adding data points sampled from an adjustment distribution. We show that this adjustment is not always possible, and that it depends on the shape of the original and desired distributions, as well as on the relative number of data points that can be added. Applying this theorem to radiative equilibrium Monte Carlo calculations, we provide a firm theoretical basis for the frequency distribution adjustment method of Bjorkman and Wood, and we demonstrate that this method provides the correct frequency distribution through the additional requirement of radiative equilibrium. We discuss the advantages and limitations of this approach, and show that it can easily be combined with the presence of additional heating sources and the concept of photon weighting. However, the method may fail if small dust grains are included, or if the absorption rate is estimated from the mean intensity of the radiation field.

Anion-surface interactions: Part II. Nitrous oxide reduction as a probe of anion adsorption on transition metal surfaces

The reduction of nitrous oxide on several transition metal surfaces in aqueous sulphuric and perchloric acids has been studied using cyclic voltammetry. It is proposed that the rate-limiting step is the decomposition of N2O(ads) to gaseous dinitrogen and adsorbed oxygen. Adsorbed hydrogen appears not to play an essential, catalytic role in this irreversible process. The electroreduction current itself is believed to arise solely from rapid reduction of the adsorbed oxygen intermediate, i.e. O(ads) + 2H+ + 2e− → H2O, and the rate of the reaction is greatest when the number of tree metal sites is maximised. A strong correlation between anion adsorption-desorption and hysteresis in the N2O reduction current as a function of the potential has been used to demonstrate that perchlorate may be reduced to chloride (as described recently by Wieckowski and coworkers) on a variety of metal electrode surfaces. These include polycrystalline palladium, rhodium, Ir{111} and Pt{110}. As a result of our investigations, we re-examine the assertion made by Parsons and coworkers that strongly adsorbed hydrogen must be invoked to explain the voltammetry of nitrous oxide reduction on Pt{111}.

Supporting Informed Decision Making Online in 20 Minutes: An Observational Web-log Study of a PSA Test Decision Aid

Background Web-based decision aids are known to have an effect on knowledge, attitude, and behavior; important components of informed decision making. We know what decision aids achieve in randomized controlled trials (RCTs), but we still know very little about how they are used and how this relates to the informed decision making outcome measures. Objective To examine mens use of an online decision aid for prostate cancer screening using website transaction log files (web-logs), and to examine associations between usage and components of informed decision making. Methods We conducted an observational web-log analysis of users of an online decision aid, Prosdex. Men between 50 and 75 years of age were recruited for an associated RCT from 26 general practices across South Wales, United Kingdom. Men allocated to one arm of the RCT were included in the current study. Time and usage data were derived from website log files. Components of informed decision making were measured by an online questionnaire. Results Available for analysis were 82 web-logs. Overall, there was large variation in the use of Prosdex. The mean total time spent on the site was 20 minutes. The mean number of pages accessed was 32 (SD 21) out of a possible 60 pages. Significant associations were found between increased usage and increased knowledge (Spearman rank correlation [ρ] = 0.69, P < .01), between increased usage and less favorable attitude towards PSA testing (ρ = -0.52, P < .01), and between increased usage and reduced intention to undergo PSA testing (ρ = -0.44, P < .01). A bimodal distribution identified two types of user: low access and high access users. Conclusions Increased usage of Prosdex leads to more informed decision making, the key aim of the UK Prostate Cancer Risk Management Programme. However, developers realistically have roughly 20 minutes to provide useful information that will support informed decision making when the patient uses a web-based interface. Future decision aids need to be developed with this limitation in mind. We recommend that web-log analysis should be an integral part of online decision aid development and analysis. Trial Registration ISRCTN48473735; http://www.controlled-trials.com/ISRCTN48473735 (Archived by WebCite at http://www.webcitation.org/5pqeF89tS)

A search for low surface brightness dwarf galaxies in different environments

According to the cold dark matter (CDM) hierarchical clustering theory of galaxy and large-scale structure formation, there should be numerous low-mass dark matter haloes present in the Universe today. If these haloes contain sufficient stars, they should be detectable as low-luminosity stellar systems or dwarf galaxies. We have previously described a new detection method for faint low surface brightness objects and we have shown that there are relatively large numbers of very faint dwarf galaxies in the nearby Virgo cluster. In this paper, we present results from a similar survey carried out on the Millennium Galaxy strip, which runs along the celestial equator and samples a very different galaxy environment. We show that the dwarf-to-giant galaxy number ratio along this strip ranges from 0.7 : 1 to, at most, 6 : 1, corresponding to a flat luminosity function (α≈−0.8 to −1.0). This is very different to our value of 20 : 1 for the Virgo cluster. There is no population of low surface brightness dwarf galaxies in the field that have gone undetected by the redshift surveys. This result is exactly opposite to what CDM models predict for the environmental dependence of the dark matter mass function, which is that there are proportionally more small dark matter haloes in lower-density environments.

The NIKA2 large-field-of-view millimetre continuum camera for the 30 m IRAM telescope

Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. CMB - cosmic microwave background and high-redshift galaxies). General purpose, large-field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-ofview of 6.5 arcminutes in diameter, and configurable to map the linear polarisation at 260 GHz. Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors (KID), and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an ad-hoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-meter IRAM (Institut of Millimetric Radio Astronomy) telescope at Pico Veleta, near Granada (Spain). Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper. Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum (FWHM) angular resolutions of around 11 and 17.5 arc-seconds at respectively 260 and 150 GHz. The noise equivalent flux densities (NEFD) are, at these two respective frequencies, 33±2 and 8±1 mJy ·s 1/2. A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years.

A randomised controlled trial of the effects of a web-based PSA decision aid, Prosdex. Protocol

BackgroundInformed decision making is the theoretical basis in the UK for mens decisions about Prostate Specific Antigen (PSA) testing for prostate cancer testing. The aim of this study is to evaluate the effect of a web-based PSA decision-aid, Prosdex, on informed decision making in men. The objective is to assess the effect of Prosdex on six specific outcomes: (i) knowledge of PSA and prostate cancer-related issues – the principal outcome of the study; (ii) attitudes to testing; (iii) decision conflict; (iv) anxiety; (v) intention to undergo PSA testing; (vi) uptake of PSA testing. In addition, a mathematical simulation model of the effects of Prosdex will be developed.MethodsA randomised controlled trial with four groups: two intervention groups, one viewing Prosdex and the other receiving a paper version of the site; two control groups, the second controlling for the potential Hawthorn effect of the questionnaire used with the first control group. Men between the ages of 50 and 75, who have not previously had a PSA test, will be recruited from General Practitioners (GPs) in Wales, UK. The principal outcome, knowledge, and four other outcome measures – attitudes to testing, decision conflict, anxiety and intention to undergo testing – will be measured with an online questionnaire, used by men in three of the study groups. Six months later, PSA test uptake will be ascertained from GP records; the online questionnaire will then be repeated. These outcomes, and particularly PSA test uptake, will be used to develop a mathematical simulation model, specifically to consider the impact on health service resources.Trial registrationCurrent Controlled Trial: ISRCTN48473735.

Development of the HAWC Far-Infrared Camera for SOFIA

HAWC (High-resolution Airborne Wideband Camera) is a facility science instrument for SOFIA (Stratospheric Observatory for Infrared Astronomy). It is a far-infrared camera designed for diffraction-limited imaging in four spectral passbands centered at wavelengths of 53, 89, 155, and 216 μm. Its detector is a 12x32 array of bolometers cooled to 0.2 K by an adiabatic demagnetization refrigerator. In this paper, we report on the development and testing of the instrument and its subsystems.