Building Merger Trees from Cosmological N-body Simulations

Although a fair amount of work has been devoted to growing Monte-Carlo merger trees which resemble those built from an N-body simulation, comparatively little effort has been invested in quantifying the caveats one necessarily encounters when one extracts trees directly from such a simulation. To somewhat revert the tide, this paper seeks to provide its reader with a comprehensive study of the problems one faces when following this route. The first step to building merger histories of dark matter haloes and their subhaloes is to identify these structures in each of the time outputs (snapshots) produced by the simulation. Even though we discuss a particular implementation of such an algorithm (called AdaptaHOP) in this paper, we believe that our results do not depend on the exact details of the implementation but extend to most if not all (sub)structure finders. We then highlight different ways to build merger histories from AdaptaHOP haloes and subhaloes, contrasting their various advantages and drawbacks. We find that the best approach to (sub)halo merging histories is through an analysis that goes back and forth between identification and tree building rather than one which conducts a straightforward sequential treatment of these two steps. This is rooted in the complexity of the merging trees which have to depict an inherently dynamical process from the partial temporal information contained in the collection of instantaneous snapshots available from the N-body simulation.Comment: 19 pages, 28 figure

Toy Models for Galaxy Formation versus Simulations

We describe simple useful toy models for key processes of galaxy formation in its most active phase, at z > 1, and test the approximate expressions against the typical behaviour in a suite of high-resolution hydro-cosmological simulations of massive galaxies at z = 4-1. We address in particular the evolution of (a) the total mass inflow rate from the cosmic web into galactic haloes based on the EPS approximation, (b) the penetration of baryonic streams into the inner galaxy, (c) the disc size, (d) the implied steady-state gas content and star-formation rate (SFR) in the galaxy subject to mass conservation and a universal star-formation law, (e) the inflow rate within the disc to a central bulge and black hole as derived using energy conservation and self-regulated Q ~ 1 violent disc instability (VDI), and (f) the implied steady state in the disc and bulge. The toy models provide useful approximations for the behaviour of the simulated galaxies. We find that (a) the inflow rate is proportional to mass and to (1+z)^5/2, (b) the penetration to the inner halo is ~50% at z = 4-2, (c) the disc radius is ~5% of the virial radius, (d) the galaxies reach a steady state with the SFR following the accretion rate into the galaxy, (e) there is an intense gas inflow through the disc, comparable to the SFR, following the predictions of VDI, and (f) the galaxies approach a steady state with the bulge mass comparable to the disc mass, where the draining of gas by SFR, outflows and disc inflows is replenished by fresh accretion. Given the agreement with simulations, these toy models are useful for understanding the complex phenomena in simple terms and for back-of-the-envelope predictions.Comment: Resubmitted to MNRAS after responding to referee's comments; Revised figure

Obtaining tissue diagnosis in lung cancer patients with poor performance status and its influence on treatment and survival

Introduction: 25% of patients with lung cancer have performance status 3 or 4. A pragmatic approach to investigative procedures is often adopted based on the risks and benefits in these patients and whether tissue diagnosis is necessary for anticipated future treatment. This cohort study investigated factors influencing a clinician's decision to pursue a tissue diagnosis in patients with lung cancer and performance status 3 and 4 and to examine the association of tissue diagnosis with subsequent management and survival. Methods: All patients with lung cancer diagnosed in North Glasgow from 2009 to 2012 were prospectively recorded in a registry. We investigated the relationships between achieving a tissue diagnosis, treatment and survival. Results: Of 2493 patients diagnosed with lung cancer, 490 patients (20%) were PS 3 and 122 patients (5%) were PS 4. Tissue diagnosis was attempted in 60% and 35% patients with PS 3 and PS 4 respectively. Younger age, better performance status and having stage 4 disease were independently associated with a diagnostic procedure being performed. Only 5% of patients with poor performance status received treatment conventionally requiring a tissue diagnosis. Age, stage and performance status were independent predictors of mortality. Achieving a tissue diagnosis was not associated with mortality. Receiving treatment requiring tissue diagnosis is associated with survival benefit. Conclusions: The majority of patients with poor fitness undergo a diagnostic procedure which does not influence further treatment or affect survival. However, the cohort of patients who do undergo therapy determined by tissue diagnosis have improved survival

Preface

Technology integration is one of the most important issues facing schools in the 1990s

Educational Considerations, vol. 23 (2) Full Issue

Educational Considerations, vol. 23 (2) Spring 1996 - Full issu

Table of contents and editorial information for Vol. 23, no. 2, Spring 1996

Table of contents and editorial information for Vol. 23, no. 2, Spring 199

Do glucosamine and chondroitin worsen blood sugar control in diabetes?

Despite theoretical risks based on animal models given high intravenous doses, glucosamine/chondroitin (1500 mg/1200 mg daily) does not adversely affect short-term glycemic control for patients whose diabetes is well-controlled, or for those without diabetes or glucose intolerance (SOR: A, consistent, good-quality patient-oriented evidence). Some preliminary evidence suggests that glucosamine may worsen glucose intolerance for patients with untreated or undiagnosed glucose intolerance or diabetes (SOR: C, extrapolation from disease-oriented evidence)

Barriers to Curriculum Technology Integration in Education

Many barriers have been placed in the path of school curriculum reform involving technology

How do dwarf galaxies acquire their mass & when do they form their stars?

We apply a simple, one-equation, galaxy formation model on top of the halos and subhalos of a high-resolution dark matter cosmological simulation to study how dwarf galaxies acquire their mass and, for better mass resolution, on over 10^5 halo merger trees, to predict when they form their stars. With the first approach, we show that the large majority of galaxies within group- and cluster-mass halos have acquired the bulk of their stellar mass through gas accretion and not via galaxy mergers. We deduce that most dwarf ellipticals are not built up by galaxy mergers. With the second approach, we constrain the star formation histories of dwarfs by requiring that star formation must occur within halos of a minimum circular velocity set by the evolution of the temperature of the IGM, starting before the epoch of reionization. We qualitatively reproduce the downsizing trend of greater ages at greater masses and predict an upsizing trend of greater ages as one proceeds to masses lower than m_crit. We find that the fraction of galaxies with very young stellar populations (more than half the mass formed within the last 1.5 Gyr) is a function of present-day mass in stars and cold gas, which peaks at 0.5% at m_crit=10^6-8 M_Sun, corresponding to blue compact dwarfs such as I Zw 18. We predict that the baryonic mass function of galaxies should not show a maximum at masses above 10^5.5, M_Sun, and we speculate on the nature of the lowest mass galaxies.Comment: 6 pages, to appear in "A Universe of Dwarf Galaxies: Observations, Theories, Simulations", ed. M. Koleva, P. Prugniel & I. Vauglin, EAS Series (Paris: EDP

The NHS visitor and migrant cost recovery programme - a threat to health?

BACKGROUND: In April 2014 the UK government launched the 'NHS Visitor and Migrant Cost Recovery Programme Implementation Plan' which set out a series of policy changes to recoup costs from 'chargeable' (largely non-UK born) patients. In England, approximately 75% of tuberculosis (TB) cases occur in people born abroad. Delays in TB treatment increase risk of morbidity, mortality and transmission in the community. We investigated whether diagnostic delay has increased since the Cost Recovery Programme (CRP) was introduced. METHODS: There were 3342 adult TB cases notified on the London TB Register across Barts Health NHS Trust between 1st January 2011 and 31st December 2016. Cases with missing relevant information were excluded. The median time between symptom onset and treatment initiation before and after the CRP was calculated according to birthplace and compared using the Mann Whitney test. Delayed diagnosis was considered greater or equal to median time to treatment for all patients (79 days). Univariable logistic regression was used to manually select exposure variables for inclusion in a multivariable model to test the association between diagnostic delay and the implementation of the CRP. RESULTS: We included 2237 TB cases. Among non-UK born patients, median time-to-treatment increased from 69 days to 89 days following introduction of CRP (p < 0.001). Median time-to-treatment also increased for the UK-born population from 75.5 days to 89.5 days (p = 0.307). The multivariable logistic regression model showed non-UK born patients were more likely to have a delay in diagnosis after the CRP (adjOR 1.37, 95% CI 1.13-1.66, p value 0.001). CONCLUSION: Since the introduction of the CRP there has been a significant delay for TB treatment among non-UK born patients. Further research exploring the effect of policies restricting access to healthcare for migrants is urgently needed if we wish to eliminate TB nationally