The First Stars

We review recent theoretical results on the formation of the first stars in the universe, and emphasize related open questions. In particular, we discuss the initial conditions for Population III star formation, as given by variants of the cold dark matter cosmology. Numerical simulations have investigated the collapse and the fragmentation of metal-free gas, showing that the first stars were predominantly very massive. The exact determination of the stellar masses, and the precise form of the primordial initial mass function, is still hampered by our limited understanding of the accretion physics and the protostellar feedback effects. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times. We show how complementary observations, both at high redshifts and in our local cosmic neighborhood, can be utilized to probe the first epoch of star formation.Comment: 38 pages, 10 figures, draft version for 2004 Annual Reviews of Astronomy and Astrophysics, high-resolution version available at http://cfa-www.harvard.edu/~vbromm

Brief cognitive assessment in a UK population sample – distributional properties and the relationship between the MMSE and an extended mental state examination

BACKGROUND: Despite the MMSE's known flaws, it is still used extensively as both a screening instrument for dementia and a population measure of cognitive ability. The aim of this paper is to provide data on the distribution of MMSE scores in a representative sample from the UK population and to compare it with an extended cognitive assessment (EMSE) which covers a wider range of cognitive domains and provides a wider range of difficulty levels. METHODS: The MMSE and the EMSE were administered to over 12,000 participants at the screening stage of the MRC Cognitive Function and Ageing Study (MRC CFAS). MRC CFAS is a multi-centre population-based study in England and Wales with respondents aged 65 years and older. RESULTS: Normative values on the MMSE and EMSE are presented by age group, sex and level of education. There are very large differences between age groups, with smaller differences seen between the sexes and by level of education. The EMSE extends the scores at the high end of the ability range, but is no better than the MMSE at differentiating between dementia and non-dementia. CONCLUSION: Population-derived norms are valuable for comparing an individual's score to the score that would be expected among the general population, given the individual's specific demographic characteristics

The First Stars

The first stars to form in the Universe -- the so-called Population III stars -- bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.Comment: 72 pages, 4 figures. Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklin

THE WAVEFUNCTION OF THE ELECTRON IN A HOMOGENEOUS MAGNETIC-FIELD AND THE PLANE-WAVE STATE - ADIABATIC AND SUDDEN APPROXIMATIONS

ZARCONE M, MCDOWELL MRC, Faisal F. THE WAVEFUNCTION OF THE ELECTRON IN A HOMOGENEOUS MAGNETIC-FIELD AND THE PLANE-WAVE STATE - ADIABATIC AND SUDDEN APPROXIMATIONS. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. 1983;16(21):4005-4014

Self-management: a systematic review of outcome measures adopted in self-management interventions for stroke

Purpose: To systematically review the psychometric properties of outcome measures used in stroke self-management interventions (SMIs) to (1) inform researchers, clinicians and commissioners about the properties of the measures in use and (2) make recommendations for the future development of self-management measurement in stroke. Methods: Electronic databases, government websites, generic internet search engines and hand searches of reference lists. Abstracts were selected against inclusion criteria and retrieved for appraisal and systematically scored, using the COSMIN checklist. Results: Thirteen studies of stroke self-management originating from six countries were identified. Forty-three different measures (mean 5.08/study, SD 2.19) were adopted to evaluate self-SMIs. No studies measured self-management as a discreet concept. Six (46%) studies included untested measures. Eleven (85%) studies included at least one measure without reported reliability and validity in stroke populations. Conclusions: The use of outcome measures which are related, indirect or proxy indicators of self-management and that have questionable reliability and validity, contributes to an inability to sensitively evaluate the effectiveness of stroke self-SMIs. Further enquiry into how the concept of self-management in stroke operates, would help to clarify the nature and range of specific self-management activities to be targeted and aid the selection of existing appropriate measures or the development of new measures

Methylenetetrahydrofolate reductase 677C-->T genotype modulates homocysteine responses to a folate-rich diet or a low-dose folic acid supplement: a randomized controlled trial

Background: Low folate status and elevated plasma homocysteine are associated with increased risk of neural tube defects and cardiovascular disease. Homocysteine responses to folate may be influenced by genetic variants in folate metabolism. Objective: We determined the effect of folate-enhancing dietary interventions on plasma folate and plasma total homocysteine (tHcy) with respect to the methylenetetrahydrofolate reductase 677C→T genotype. Design: A total of 126 healthy subjects (42 TT, 42 CT, and 42 CC genotypes) completed 3 dietary interventions (4 mo each) in random order: 1) exclusion diet (avoidance of folic acid–fortified foods and ingestion of a placebo daily), 2) folate-rich diet (increased intake of fortified and naturally folate-rich foods to achieve 400 μg folate/d), and 3) supplement (exclusion diet plus a folate supplement of 400 μg/d). Results: Plasma folate was higher (P ≤ 0.001) and plasma tHcy lower (P ≤ 0.001) after the folate-rich and supplement interventions than after the exclusion diet. Plasma folate was significantly greater after supplementation than after the folate-rich diet, but there was no significant difference in tHcy concentration (P = 0.72). TT homozygotes had higher plasma tHcy (14.5 compared with 8.9 μmol/L, P ≤ 0.001) and lower plasma folate (14.8 compared with 19.0 nmol/L, P ≤ 0.01) than did subjects with the CC genotype after the exclusion diet. CT heterozygotes had intermediate concentrations. The trend toward higher tHcy in TT homozygotes persisted throughout the study but was less marked with increasing folate intake (TT compared with CC after supplementation, P = 0.097). Conclusions: A folate-rich diet including folic acid–fortified foods or low-dose supplements effectively increases folate status. TT homozygotes require higher folate intakes than do individuals with the CT or CC genotype to achieve similar tHcy concentrations but are responsive to folate intervention