744 research outputs found
Two-dimensional simulations of internal gravity waves in a 5 Zero-Age-Main-Sequence model
Main-sequence intermediate-mass stars present a radiative envelope that
supports internal gravity waves (IGWs). Excited at the boundary with the
convective core, IGWs propagate towards the stellar surface and are suspected
to impact physical processes such as rotation and chemical mixing. Using the
fully compressible time-implicit code MUSIC, we study IGWs in two-dimensional
simulations of a zero-age-main-sequence 5 solar mass star model up to 91\% of
the stellar radius with different luminosity and radiative diffusivity
enhancements. Our results show that low frequency waves excited by core
convection are strongly impacted by radiative effects as they propagate. This
impact depends on the radial profile of radiative diffusivity which increases
by almost 5 orders of magnitude between the centre of the star and the top of
the simulation domain. In the upper layers of the simulation domain, we observe
an increase of the temperature. Our study suggests that this is due to heat
added in these layers by IGWs damped by radiative diffusion. We show that
non-linear effects linked to large amplitude IGWs may be relevant just above
the convective core. Both these effects are intensified by the artificial
enhancement of the luminosity and radiative diffusivity, with enhancement
factors up to times the realistic values. Our results also highlight
that direct comparison between numerical simulations with enhanced luminosity
and observations must be made with caution. Finally, our work suggests that
thermal effects linked to the damping of IGWs could have a non-negligible
impact on stellar structure.Comment: 15 pages, 10 figures, accepted for publication in MNRA
A blind HI survey of the M81 group
Results are presented of the first blind HI survey of the M81 group of
galaxies. The data were taken as part of the HI Jodrell All Sky Survey
(HIJASS). The survey reveals several new aspects to the complex morphology of
the HI distribution in the group. All four of the known dwarf irregular (dIrr)
galaxies close to M81 can be unambiguously seen in the HIJASS data. Each forms
part of the complex tidal structure in the area. We suggest that at least three
of these galaxies may have formed recently from the tidal debris in which they
are embedded. The structure connecting M81 to NGC2976 is revealed as a single
tidal bridge of mass approx. 2.1 x 10^8 Msol and projected spatial extent
approx. 80 kpc. Two `spurs' of HI projecting from the M81 complex to lower
declinations are traced over a considerably larger spatial and velocity extent
than by previous surveys. The dwarf elliptical (dE) galaxies BK5N and Kar 64
lie at the spatial extremity of one of these features and appear to be
associated with it. We suggest that these may be the remnants of dIrrs which
has been stripped of gas and transmuted into dEs by close gravitational
encounters with NGC3077. The nucleated dE galaxy Kar 61 is unambiguously
detected in HI for the first time and has an HI mass of approx.10^8 Msol,
further confirming it as a dE/dIrr transitional object. HIJASS has revealed one
new possible group member, HIJASS J1021+6842. This object contains approx. 2 x
10^7 Msol of HI and lies approx.105arcmin from IC2574. It has no optical
counterpart on the Digital Sky Survey.Comment: To be published in Astrophysical Journal Letters 9 pages, including 3
figure
Profiling Sea Ice with a Multiple Altimeter Beam Experimental Lidar (MABEL)
The sole instrument on the upcoming ICESat-2 altimetry mission is a micropulse lidar that measures the time-of-flight of individual photons from laser pulses transmitted at 532 nm. Prior to launch, MABEL serves as an airborne implementation for testing and development. In this paper, we provide a first examination of MABEL data acquired on two flights over sea ice in April 2012: one north of the Arctic coast of Greenland, and the other in the East Greenland Sea.We investigate the phenomenology of photon distributions in the sea ice returns. An approach to locate the surface and estimate its elevation in the distributions is described, and its achievable precision assessed. Retrieved surface elevations over relatively flat leads in the ice cover suggest that precisions of several centimeters are attainable. Restricting the width of the elevation window used in the surface analysis can mitigate potential biases in the elevation estimates due to subsurface returns at 532 nm. Comparisons of nearly coincident elevation profiles from MABEL with those acquired by an analog lidar show good agreement.Discrimination of ice and open water, a crucial step in the determination of sea ice free board and the estimation of ice thickness, is facilitated by contrasts in the observed signal background photon statistics. Future flight lines will sample a broader range of seasonal ice conditions for further evaluation of the year-round profiling capabilities and limitations of the MABEL instrument
Playing with the Rules: Influences on the Development of Regulation in Sport
Sport today is a rule-governed practice: constitutive rules, both prescriptive and proscriptive, define required equipment and facilities as well as setting the formal rules of play; auxiliary rules specify and control eligibility: and regulatory rules place restraints on behaviour independent of the sport itself. This article offers a broad sweep examination of the historical process of rule development in sport including an assessment of the influence over time of gambling, fair play ideology, economic pressures, technological developments and legal intervention. En route a seven-stage scheme of constitutive rule development is postulated which it is hoped will set a research agenda for sports historians to test with case studies of particular sports
Genetic aetiologies for childhood speech disorder: Novel pathways co-expressed during brain development
Childhood apraxia of speech (CAS), the prototypic severe childhood speech disorder, is characterized by motor programming and planning deficits. Genetic factors make substantive contributions to CAS aetiology, with a monogenic pathogenic variant identified in a third of cases, implicating around 20 single genes to date. Here we aimed to identify molecular causation in 70 unrelated probands ascertained with CAS. We performed trio genome sequencing. Our bioinformatic analysis examined single nucleotide, indel, copy number, structural and short tandem repeat variants. We prioritised appropriate variants arising de novo or inherited that were expected to be damaging based on in silico predictions. We identified high confidence variants in 18/70 (26%) probands, almost doubling the current number of candidate genes for CAS. Three of the 18 variants affected SETBP1, SETD1A and DDX3X, thus confirming their roles in CAS, while the remaining 15 occurred in genes not previously associated with this disorder. Fifteen variants arose de novo and three were inherited. We provide further novel insights into the biology of child speech disorder, highlighting the roles of chromatin organization and gene regulation in CAS, and confirm that genes involved in CAS are co-expressed during brain development. Our findings confirm a diagnostic yield comparable to, or even higher, than other neurodevelopmental disorders with substantial de novo variant burden. Data also support the increasingly recognised overlaps between genes conferring risk for a range of neurodevelopmental disorders. Understanding the aetiological basis of CAS is critical to end the diagnostic odyssey and ensure affected individuals are poised for precision medicine trials
Introduction to special section on Recent Advances in the Study of Optical Variability in the Near-Surface and Upper Ocean
Optical variability occurs in the near-surface and upper ocean on very short time and space scales (e.g., milliseconds and millimeters and less) as well as greater scales. This variability is caused by solar, meteorological, and other physical forcing as well as biological and chemical processes that affect optical properties and their distributions, which in turn control the propagation of light across the air-sea interface and within the upper ocean. Recent developments in several technologies and modeling capabilities have enabled the investigation of a variety of fundamental and applied problems related to upper ocean physics, chemistry, and light propagation and utilization in the dynamic near-surface ocean. The purpose here is to provide background for and an introduction to a collection of papers devoted to new technologies and observational results as well as model simulations, which are facilitating new insights into optical variability and light propagation in the ocean as they are affected by changing atmospheric and oceanic conditions
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Sensitivity of simulated regional Arctic climate to the choice of coupled model domain
The climate over the Arctic has undergone changes in recent decades. In order to evaluate the coupled response of the Arctic system to external and internal forcing, our study focuses on the estimation of regional climate variability and its dependence on large-scale atmospheric and regional ocean circulations. A global oceanâsea ice model with regionally high horizontal resolution is coupled to an atmospheric regional model and global terrestrial hydrology model. This way of coupling divides the global ocean model setup into two different domains: one coupled, where the ocean and the atmosphere are interacting, and one uncoupled, where the ocean model is driven by prescribed atmospheric forcing and runs in a so-called stand-alone mode. Therefore, selecting a specific area for the regional atmosphere implies that the oceanâatmosphere system can develop âfreelyâ in that area, whereas for the rest of the global ocean, the circulation is driven by prescribed atmospheric forcing without any feedbacks. Five different coupled setups are chosen for ensemble simulations. The choice of the coupled domains was done to estimate the influences of the Subtropical Atlantic, Eurasian and North Pacific regions on northern North Atlantic and Arctic climate. Our simulations show that the regional coupled oceanâatmosphere model is sensitive to the choice of the modelled area. The different model configurations reproduce differently both the mean climate and its variability. Only two out of five model setups were able to reproduce the Arctic climate as observed under recent climate conditions (ERA-40 Reanalysis). Evidence is found that the main source of uncertainty for Arctic climate variability and its predictability is the North Pacific. The prescription of North Pacific conditions in the regional model leads to significant correlation with observations, even if the whole North Atlantic is within the coupled model domain. However, the inclusion of the North Pacific area into the coupled system drastically changes the Arctic climate variability to a point where the Arctic Oscillation becomes an âinternal modeâ of variability and correlations of year-to-year variability with observational data vanish. In line with previous studies, our simulations provide evidence that Arctic sea ice export is mainly due to âinternal variabilityâ within the Arctic region. We conclude that the choice of model domains should be based on physical knowledge of the atmospheric and oceanic processes and not on âgeographicâ reasons. This is particularly the case for areas like the Arctic, which has very complex feedbacks between components of the regional climate system
The Future of Qualitative Research in Psychology: Accentuating the Positive.
In this paper we reflect on current trends and anticipate future prospects regarding qualitative research in Psychology. We highlight various institutional and disciplinary obstacles to qualitative research diversity, complexity and quality. At the same time, we note some causes for optimism, including publication breakthroughs and vitality within the field. The paper is structured into three main sections which consider: 1) the positioning of qualitative research within Psychology; 2) celebrating the different kinds of knowledge produced by qualitative research; and 3) implementing high quality qualitative research. In general we accentuate the positive, recognising and illustrating innovative qualitative research practices which generate new insights and propel the field forward. We conclude by emphasising the importance of research training: for qualitative research to flourish within Psychology (and beyond), students and early career researchers require more sophisticated, in-depth instruction than is currently offered
The College News, 1923-01-24, Vol. 09, No. 13
Bryn Mawr College student newspaper. Merged with The Haverford News in 1968 to form the Bi-college News (with various titles from 1968 on). Published weekly (except holidays) during the academic year
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