17,301 research outputs found
SWIFT J1749.4-2807: A neutron or quark star?
We investigate an unique accreting millisecond pulsar with X-ray eclipses,
SWIFT J1749.42807 (hereafter J1749), and try to limit the binary system by
various methods including that of the Roche lobe, the mass-radius relations of
both a main sequence (MS) and a white dwarf (WD) companion stars, as well as
the measured mass function of the pulsar. The calculations are based on the
assumption that the radius of the companion star has reached its Roche radius
(or at 90%), but the pulsar's mass has not been assumed to be a certain value.
Our results are as follows. The companion star should be a MS. For the case
that the radius equals to its Roche one, we have a companion star with mass
and radius , and the
inclination angle is ; for the case that the radius
reaches 90% of its Roche one, we have , and . We also obtain the mass of J1749,
, and conclude that the pulsar could be a quark star
if the ratio of the critical frequency of rotation-mode instability to the
Keplerian one is higher than . The relatively low pulsar mass (about
) may also challenge the conventional recycling scenario for the
origin and evolution of millisecond pulsars. The results presented in this
paper are expected to be tested by future observations.Comment: RAA accepte
Roche tomography of the secondary stars in CVs
The secondary stars in cataclysmic variables (CVs) are key to our
understanding of the origin, evolution and behaviour of this class of
interacting binary. In seeking a fuller understanding of these objects, the
challenge for observers is to obtain images of the secondary star. This goal
can be achieved through Roche tomography, an indirect imaging technique that
can be used to map the Roche-lobe-filling secondary. The review begins with a
description of the basic principles that underpin Roche tomography, including
methods for determining the system parameters. Finally, we conclude with a look
at the main scientific highlights to date, including the first unambiguous
detection of starspots on AE Aqr B, and consider the future prospects of this
technique.Comment: 4 pages, 4 figures. Accepted for publication in A
The Roche problem: some analytics
Some exact analytical formulas are derived for the potential and mass ratio
as a function of Lagrangian points position, in the classical Roche model of
the close binary stars.Comment: aastex, 4 pp. ApJ accepte
Preoperative predictors of knee range of motion during stair walking after total knee replacement
This paper discusses the preoperative predictors of knee range of motion during stair walking after total knee replacement. It was presented at the 17th Annual Meeting of the European Society of Movement Analysis for Adults and Children (ESMAC) in 2008
The Practical Life, the Contemplative Life, and the Perfect Eudaimonia in Aristotle’s Nicomachean Ethics 10.7-8
Two views continue to be defended today. One is that the account of eudaimonia in EN 10 is inconsistent with claims made about it in other books of the work. The other view is that the account in EN 10 is consistent with other claims made in the other books because Aristotle presents one account of perfect eudaimonia by portraying it as consisting solely in contemplative activity. I call this view the intellectualist interpretation. I then argue that neither view is correct because although Aristotle’s position is consistent, he does not hold that the perfect eudaimonia for a human being involves nothing but excellent theoretical activity. His philosopher possesses and exercises the moral excellences and practical wisdom and so some portion of his happiness consists in these activities as well as contemplative activity
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