1,543 research outputs found
On the binary nature of 1RXS J162848.1-415241
We present spectroscopy of the optical counterpart to 1RXS J162848.1-41524,
also known as the microquasar candidate MCQC J162847-4152. All the data
indicate that this X-ray source is not a microquasar, and that it is a
single-lined chromospherically active binary system with a likely orbital
period of 4.9 days. Our analysis supports a K3IV spectral classification for
the star, which is dominant at optical wavelengths. The unseen binary component
is most likely a late-type (K7-M) dwarf or a white dwarf. Using the high
resolution spectra we have measured the K3 star's rotational broadening to be
vsini = 43 +/- 3 km/s and determined a lower limit to the binary mass ratio of
q(=M2/M1)>2.0. The high rotational broadening together with the strong CaII H &
K / Halpha emission and high-amplitude photometric variations indicate that the
evolved star is very chromospherically active and responsible for the
X-ray/radio emission.Comment: 15 pages, 5 figures, accepted for publication in Ap
Exotic spacetimes, superconducting strings with linear momentum, and (not quite) all that
We derive the general exact vacuum metrics associated with a stationary (non
static), non rotating, cylindrically symmetric source. An analysis of the
geometry described by these vacuum metrics shows that they contain a subfamily
of metrics that, although admitting a consistent time orientation, display
"exotic" properties, such as "trapping" of geodesics and closed causal curves
through every point. The possibility that such spacetimes could be generated by
a superconducting string, endowed with a neutral current and momentum, has
recently been considered by Thatcher and Morgan. Our results, however, differ
from those found by Thatcher and Morgan, and the discrepancy is explained. We
also analyze the general possibility of constructing physical sources for the
exotic metrics, and find that, under certain restrictions, they must always
violate the dominant energy condition (DEC). We illustrate our results by
explicitly analyzing the case of concentric shells, where we find that in all
cases the external vacuum metric is non exotic if the matter in the shells
satisfies the DEC.Comment: 13 pages with no figures. Accepted in PR
The transformative potential of reflective diaries for elite English cricketers
The sport of cricket has a history of its players suffering from mental health issues. The psychological study of cricket and, in particular, the attendant demands of participating at an elite level has not previously received rigorous academic attention. This study explored ten elite male cricketers’ experiences of keeping a daily reflective diary for one month during the competitive season. The aim was to assess how valuable qualitative diaries are in this field. Participants were interviewed regarding their appraisal of the methodology as a self‐help tool that could assist coping with performance pressures and wider life challenges. Three outcomes were revealed: first, that diary keeping was an effective opportunity to reflect upon the past and enhance one’s self (both as an individual and a performer); second, that diary keeping acted as a form of release that allowed participants to progress; and third, that diary keeping allowed participants to discover personal patterns of success that increased the likeliness of optimum performance
The emergence of international food safety standards and guidelines: understanding the current landscape through a historical approach
Following the Second World War, the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) teamed up to construct an International Codex Alimentarius (or 'food code') which emerged in 1963. The Codex Committee on Food Hygiene (CCFH) was charged with the task of developing microbial hygiene standards, although it found itself embroiled in debate with the WHO over the nature these standards should take. The WHO was increasingly relying upon the input of biometricians and especially the International Commission on Microbial Specifications for Foods (ICMSF) which had developed statistical sampling plans for determining the microbial counts in the final end products. The CCFH, however, was initially more focused on a qualitative approach which looked at the entire food production system and developed codes of practice as well as more descriptive end-product specifications which the WHO argued were 'not scientifically correct'. Drawing upon historical archival material (correspondence and reports) from the WHO and FAO, this article examines this debate over microbial hygiene standards and suggests that there are many lessons from history which could shed light upon current debates and efforts in international food safety management systems and approaches
Fluxes in H\alpha and Ca II H and K for a sample of Southern stars
The main chromospheric activity indicator is the S index, which is esentially
the ratio of the flux in the core of the Ca II H and K lines to the continuum
nearby, and is well studied basically for stars from F to K. Another usual
chromospheric proxy is the H\alpha line, which is beleived to be tightly
correlated with the Ca II index. In this work we characterize both
chromospheric activity indicators, one associated with the H and K Ca II lines
and the other with H\alpha, for the whole range of late type stars, from F to
M. We present periodical medium-resolution echelle observations covering the
complete visual range, which were taken at the CASLEO Argentinean Observatory.
These observations are distributed along 7 years. We use a total of 917
flux-calibrated spectra for 109 stars which range from F6 to M5. We
statistically study these two indicators for stars of different activity levels
and spectral types. We directly derive the conversion factor which translate
the known S index to flux in the Ca II cores, and extend its calibration to a
wider spectral range. We investigate the relation between the activity
measurements in the calcium and hydrogen lines, and found that the usual
correlation observed is basically the product of the dependence of each flux
with stellar colour, and not the product of similar activity phenomena.Comment: 12 pages, including 11 figures and 2 tables. Accepted for publication
in Astronomy and Astrophysic
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