4,166 research outputs found
A study of B-type stars
The effect of rotation on quantities used in classifying B -type
stars is discussed. The tendency for stars with high rotational velocities
to have weaker Balmer lines for the same (U - B)â
has been investigated
using published data. Abt's explanation of the affect in terms of the
change in effective surface gravity due to rotation is confirmed. A
correction term in Crawford's method of determining ages of clusters and
field stars from Balmer line intensities and UBV photometry is derived.
It is shown that errors in age determinations due to rotation are much
smaller when the wavelength λâ of the Balmer discontinuity is used
instead of Balmer line intensities. A colour index sensitive to λâ is
discussed. Methods of determining the inclinations of the axes of rotation
are suggested. It is shown that the "cosmic dispersion" in the relation
between Balmer line intensities and absolute magnitudes is largely caused , by rotation. A scheme of two -dimensional spectral classification using
measurements of the position and size of the Balmer discontinuity on low
dispersion objective prism plates is outlined. Rotational velocities for
18 stars have been derived from slit spectrograms; several lines including five Balmer lines were measured for each star
Rotation and chemical composition of early-type stars
Some early-type stars with abnormal line strengths for their
intrinsic colours are investigated in order to determine their
structure and the chemical composition of their atmospheres. The
abnormal line strengths in several B-type stars (αScl, 36 Lyn,
20 Tau and HD 175156) are shown to be probably due to large ranges
of surface temperature such as would be observed in rapidly rotating
stars of normal chemical composition, if viewed pole-on. These
stars differ from the peculiar A stars, which rotate slowly and have
abnormal chemical composition. Members of the Mn group of peculiar A
stars rotate more slowly than those of the Si-4200 group, although the
mean intrinsic colours of the two groups are similar.Previous work on abundance determination in peculiar A stars
is reviewed. The chemical composition of the manganese star 53 Tau
is studied by a refined differential curve-of-growth method with
αLyr as the comparison star. Groups of lines of similar mean
excitation and ionisation potentials and wavelengths are used so
that the results are independent of the structure of 53 Tau, which
is shown to be abnormal. A new double-line peculiar A spectroscopic
binary HR 4072 was discovered, and it was found that excesses of Sr
and Y are common to both components. Spectral variations in some
peculiar A stars are described.Well established abundance abnormalities in peculiar A stars may
be explained on a modified form of van den Heuvel's theory that peculiar A
stars have been secondaries of binary systems with initial separations in
the range 10 a.u. to 100 a.u. approximately. The primaries, initially
earlier than spectral type B8, have evolved and exploded as type II
supernovae. During the explosions material enriched in heavy elements
by interior nuclear reactions was transferred to the surfaces of the
secondaries, which are now observed as peculiar A stars and are still
on the main sequence. Excesses of Be and Si and deficiencies of 0 are
caused by surface nuclear reactions on the secondaries after the
explosions of the primaries. Ln stars differ from other peculiar A
stars in many respects; the differences may be due to the primaries
expanding beyond the Roche limits before they explode. On the oblique
rotator theory, spectrum variables result from irregular distributions
of surface nuclear reactions and ion migration on the secondaries.
Some other theories of peculiar A stars are reviewed and shown to be
in conflict with observation
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Heterotopic Ossification following Suprapatellar Intramedullary Nailing.
Introduction: Tibial shaft fractures are common fractures seen in trauma and orthopedic practice today. The majority of these fractures are treated with intramedullary nailing (IMN) which is rapidly becoming a gold standard. The procedure itself is performed by either a suprapatellar approach or infrapatellar approach. Suprapatellar approach is gaining popularity due to relative ease of insertion, decreased associated risk of anterior knee pain, and more accurate reduction. We report a case of heterotopic ossification noted in the knee following IMN of tibia performed using a suprapatellar approach. Case Report: A 27-year-old male, having sustained a left, Gustilo IIIB tibial shaft fracture following a motor vehicle accident, underwent a reamed intramedullary nail fixation performed through a suprapatellar approach. Two months later, he presented with intra-articular heterotopic ossification which was limiting his knee movement. He then underwent arthroscopic removal of the bony fragments which resolved his symptoms. Conclusion: An extensive search of literature did not yield any reported incidence of heterotopic ossification associated with IMN performed through a suprapatellar approach. We present this case report to raise awareness that although IMN through a suprapatellar approach is a safe approach, it does have associated risk of heterotopic ossification which needs to be included in the consent process
Modelling the atomic structure of very high-density amorphous ice
The structure of very high-density amorphous (VHDA) ice has been modelled by
positionally disordering three crystalline phases, namely ice IV, VI and XII.
These phases were chosen because only they are stable or metastable in the
region of the ice phase diagram where VHDA ice is formed, and their densities
are comparable to that of VHDA ice. An excellent fit to the medium range of the
experimentally observed pair-correlation function g(r) of VHDA ice was obtained
by introducing disorder into the positions of the H2O molecules, as well as
small amounts of molecular rotational disorder, disorder in the O--H bond
lengths and disorder in the H--O--H bond angles. The low-k behaviour of the
experimental structure factor, S(k), is also very well reproduced by this
disordered-crystal model. The fraction of each phase present in the best-fit
disordered model is very close to that observed in the probable crystallization
products of VHDA ice. In particular, only negligible amounts of ice IV are
predicted, in accordance with experimental observation.Comment: 4 pages, 3 figures, 1 table, v2: changes made in response to
referees' comments, the justification for using certain ice phases is
improved, and ice IV is now disordered as wel
The disastrous 17 February 2006 rockslide-debris avalanche on Leyte Island, Philippines: a catastrophic landslide in tropical mountain terrain
International audienceIn February 2006, a disastrous rockslide-debris avalanche occurred in tropical mountain terrain, on Leyte Island, Central Philippines. Over 1100 people perished when the village of Guinsaugon was overwhelmed directly in the path of the landslide. The landslide was initiated by the failure of a 450 m high rock slope within the damage zone of the Philippine Fault where the rock mass consisted of sheared and brecciated volcanic, sedimentary and volcaniclastic rocks. Tectonic weakening of the failed rock mass had resulted from active strike-slip movements along the Philippine Fault which have been estimated by other workers at 2.5 cm/year. The landslide involved a total volume of 15 Mm3, including significant entrainment from its path, and ran out a horizontal distance of 3800 m over a vertical distance of 810 m, equivalent to a fahrböschung of 12°. Run-out distance was enhanced by friction reduction due to undrained loading when the debris encountered flooded paddy fields in the valley bottom at a path distance of 2600 m. A simulation of the event using the dynamic analysis model DAN indicated a mean velocity of 35 m/s and demonstrated the contribution of the paddy field effect to total run-out distance. There was no direct trigger for the landslide but the landslide did follow a period of very heavy rainfall with a lag time of four days. The rockslide-debris avalanche is one of several disastrous landslides to have occurred in the Philippines in the last twenty years. In terms of loss of life, the Guinsaugon event is the most devastating single-event landslide to have occurred worldwide since the Casita Volcano rock avalanche-debris flow which was triggered by Hurricane Mitch in Nicaragua in 1998
Surviving Communicative Labor: Theoretical Exploration of the (In)Visibility of Gendered Faculty Work/Life Struggle
The work experiences of faculty in higher education often entail being overworked and stressed, and this is particularly true for women faculty and faculty of color. This essay is situated at the intersection of gender, race, axiological, epistemological, and occupational identities. In this metatheoretical argument, we propose a new concept communicative labor by exploring how existing scholarly frameworks regarding workplace emotion, compassionate communication, and gendered work intersect to inform the experiences of critical women scholars and the ways their labor is communicatively manifested across research, teaching, and service. More specifically, we argue that communication itself (i.e., literally listening, speaking, and writing) becomes emotionally-laden work amid the research, teaching, and service performed by critical women scholars. We aim, through our articulation of communication labor, to disrupt dominant narratives of what faculty work lives should be, and we call for a paradigm shift in the way faculty labor is socially constructed so that we can improve critical women facultyâs success and well-being
Chain Galaxies are Edge-On Low Surface Brightness Galaxies
Deep HST WFPC2 images have revealed a population of very narrow blue galaxies
which Cowie et al. (1996) have interpreted as being a new morphological class
of intrinsically linear star forming galaxies at . We show that the
same population exists in large numbers at low redshifts (z=0.03) and are
actually the edge-on manifestation of low surface brightness disk galaxies.Comment: 18 pages + 3 pages of figures. Uuencoded, gzipped, tar file of 1
latex file, 5 figures, and 2 latex style files. To appear in the
Astrophysical Journal Letter
Effective Feedback to Improve Primary Care Prescribing Safety (EFIPPS) a pragmatic three-arm cluster randomised trial:designing the intervention (ClinicalTrials.gov registration NCT01602705)
Peer reviewedPublisher PD
[Editorial] Accounting scholarship and management by numbers
There is a plethora of indices ranking universities, departments, and individual researchers based on a variety of indices. These invariably include a measurement of research, usually based on a combination of quantity and quality of journal publications. Informal discussions with accounting researchers invariably turns to the question of journal rankings and performance management indicators. Why is this so
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