8,823 research outputs found
Cygnus X-2, super-Eddington mass transfer, and pulsar binaries
We consider the unusual evolutionary state of the secondary star in Cygnus
X-2. Spectroscopic data give a low mass (M_2 \simeq 0.5 - 0.7\msun) and yet a
large radius (R_2 \simeq 7\rsun) and high luminosity (L_2 \simeq 150\lsun).
We show that this star closely resembles a remnant of early massive Case B
evolution, during which the neutron star ejected most of the \sim 3\msun
transferred from the donor (initial mass M_{\rm 2i}\sim 3.6\msun) on its
thermal time-scale yr. As the system is far too wide to result from
common-envelope evolution, this strongly supports the idea that a neutron star
efficiently ejects the excess inflow during super--Eddington mass transfer.
Cygnus X-2 is unusual in having had an initial mass ratio in a narrow critical range near . Smaller lead to long-period systems with the former donor near the Hayashi line,
and larger to pulsar binaries with shorter periods and relatively
massive white dwarf companions. The latter naturally explain the surprisingly
large companion masses in several millisecond pulsar binaries. Systems like
Cygnus X-2 may thus be an important channel for forming pulsar binaries.Comment: 9 pages, 4 encapsulated figures, LaTeX, revised version with a few
typos corrected and an appendix added, accepted by MNRA
Indirect (source-free) integration method. II. Self-force consistent radial fall
We apply our method of indirect integration, described in Part I, at fourth
order, to the radial fall affected by the self-force. The Mode-Sum
regularisation is performed in the Regge-Wheeler gauge using the equivalence
with the harmonic gauge for this orbit. We consider also the motion subjected
to a self-consistent and iterative correction determined by the self-force
through osculating stretches of geodesics. The convergence of the results
confirms the validity of the integration method. This work complements and
justifies the analysis and the results appeared in Int. J. Geom. Meth. Mod.
Phys., 11, 1450090 (2014).Comment: To appear in Int. J. Geom. Meth. Mod. Phy
On equivariant characteristic ideals of real classes
Let be an odd prime, an abelian totally real number field,
its cyclotomic -extension,
We give an explicit description of the equivariant characteristic ideal of
over for all odd by applying M. Witte's formulation of an equivariant main conjecture (or
"limit theorem") due to Burns and Greither. This could shed some light on
Greenberg's conjecture on the vanishing of the -invariant of
$F_\infty/F.
Lie Algebras and Suppression of Decoherence in Open Quantum Systems
Since there are many examples in which no decoherence-free subsystems exist
(among them all cases where the error generators act irreducibly on the system
Hilbert space), it is of interest to search for novel mechanisms which suppress
decoherence in these more general cases. Drawing on recent work
(quant-ph/0502153) we present three results which indicate decoherence
suppression without the need for noiseless subsystems. There is a certain
trade-off; our results do not necessarily apply to an arbitrary initial density
matrix, or for completely generic noise parameters. On the other hand, our
computational methods are novel and the result--suppression of decoherence in
the error-algebra approach without noiseless subsystems--is an interesting new
direction.Comment: 7 page
Characteristics of medication overdose presentations to the ED: how do they differ from illicit drug overdose and self-harm cases?
Background Medication overdose accounts for >80% of hospital presentations for self-harm. Previous research has identified typical characteristics of medication overdose cases; however, these cases have not been well differentiated from other similar presentations, namely (1) illicit drug overdose and (2) self-harm by means other than overdose. Method A 12-month audit of medication overdose cases (both intentional and unintentional) attending the emergency department (ED) of a major metropolitan public hospital in Melbourne, Australia was conducted. Comparison was made with patients attending for illicit drug overdose or for self-harm by means other than overdose.Results Medication overdose cases (n=453) showed a broadly comparable profile with those found in earlier studies (predominantly female gender, aged in their 30s and referred for psychosocial assessment). A similar though not identical profile was noted for self-harm cases (n=545). In contrast, patients attending for illicit drug overdose (n=409) could be characterised as male, in their 20s and not referred for psychosocial assessment. Illicit drug overdose cases were more likely than either the medication overdose or self-harm cases to be triaged in the most urgent category (19.3, 3.8 and 3.9% respectively), suggesting a high level of acuity in this group. However, the illicit drug overdose group on average spent less time in the ED than medication overdose patients, and were less likely to require hospital admission. Conclusion On both demographic and treatment variables, patients attending the ED following a medication overdose more closely resemble those attending for self-harm by means other than overdose than those attending for illicit drug overdose
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