56,533 research outputs found
Possible Explanation to Low CMB Quadrupole
The universe might experience many cycles with different vacua. The slow-roll
inflation may be preceded by kinetic-dominated contraction occurring in
"adjacent" vacua during some cycles. In this report we briefly show this
phenomenon may lead to a cutoff of primordial power spectrum. Thus in some
sense the CMB at large angular scale might encode the information of other
vacua.Comment: 10 pages, 3 eps figures, accepted for publication in PRD, v2 revised
with published versio
The correlations between the twin kHz QPO frequencies of LMXBs
We analyzed the recently published kHz QPO data in the neutron star low-mass
X-ray binaries (LMXBs), in order to investigate the different correlations of
the twin peak kilohertz quasi-eriodic oscillations (kHz QPOs) in bright Z
sources and in the less luminous Atoll sources. We find that a power-law
relation \no\sim\nt^{b} between the upper and the lower kHz QPOs with
different indices: 1.5 for the Atoll source 4U 1728-34 and
1.9 for the Z source Sco X-1. The implications of our results for
the theoretical models for kHz QPOs are discussed.Comment: 6 pages, accepted by MNRA
Massive star evolution in close binaries:conditions for homogeneous chemical evolution
We investigate the impact of tidal interactions, before any mass transfer, on
various properties of the stellar models. We study the conditions for obtaining
homogeneous evolution triggered by tidal interactions, and for avoiding any
Roche lobe overflow during the Main-Sequence phase. We consider the case of
rotating stars computed with a strong coupling mediated by an interior magnetic
field. In models without any tidal interaction (single stars and wide
binaries), homogeneous evolution in solid body rotating models is obtained when
two conditions are realized: the initial rotation must be high enough, the loss
of angular momentum by stellar winds should be modest. This last point favors
metal-poor fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is high enough
(typically a time-averaged surface velocities during the Main-Sequence phase
above 250 km s), whatever the mass losses. In close binaries, mixing is
stronger at higher than at lower metallicities. Homogeneous evolution is thus
favored at higher metallicities. Roche lobe overflow avoidance is favored at
lower metallicities due to the fact that stars with less metals remain more
compact. We study also the impact of different processes for the angular
momentum transport on the surface abundances and velocities in single and close
binaries. In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in binary or
single star models. In contrast, models computed with mild coupling may produce
strong surface enrichments associated to low surface velocities. Close binary
models may be of interest for explaining homogeneous massive stars, fast
rotating Wolf-Rayet stars, and progenitors of long soft gamma ray bursts, even
at high metallicities.Comment: 21 pages, 13 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Using handheld pocket computers in a wireless telemedicine system
Objectives: To see if senior emergency nurse practitioners can provide support to
inexperienced ones in a Minor Injuries Unit by using a wireless LAN system of
telemedicine transmitting images to a PDA when they were on duty. In addition,
whether such a system could be sufficiently accurate to make clinical diagnoses with
a high level of diagnostic confidence. This would permit an overall lower grade of
nurse to be employed to manage most of the cases as they arrive with a proportionate
lowering of costs.
Methods: The wireless LAN equipment could roam in the Minor Injuries Unit and
the experienced emergency Nurse practitioners could be at home, shopping or even
at a considerable distance from the centre.
Thirty pictorial images of patients who had been sent to the Review Clinic were
transmitted to a PDA various distances of one to sixteen miles from the centre. Two
senior emergency nurse practitioners viewed the images and opined on the diagnosis,
their degree of confidence in the diagnosis and their opinion of the quality of the
image.
Results: the images of patients were sharp, clear, and of diagnostic quality. The
image quality was only uncertain, as was the level of confidence of the diagnosis if
the patient was very dark skinned.
Conclusions: The wireless LAN system works with a remote PDA in this clinical
situation. However there are question marks over the availability of enough
experienced emergency nurse practitioners to staff a service that provides senior
cover for longer parts of the day and at weekends
Close binary evolution I. The tidally induced shear mixing in rotating binaries
We study how tides in a binary system induce some specific internal shear
mixing, able to substantially modify the evolution of close binaries prior to
mass transfer. We construct numerical models accounting for tidal interactions,
meridional circulation, transport of angular momentum, shears and horizontal
turbulence and consider a variety of orbital periods and initial rotation
velocities. Depending on orbital periods and rotation velocities, tidal effects
may spin down (spin down Case) or spin up (spin up Case) the axial rotation. In
both cases, tides may induce a large internal differential rotation. The
resulting tidally induced shear mixing (TISM) is so efficient that the internal
distributions of angular velocity and chemical elements are greatly influenced.
The evolutionary tracks are modified, and in both cases of spin down and spin
up, large amounts of nitrogen can be transported to the stellar surfaces before
any binary mass transfer. Meridional circulation, when properly treated as an
advection, always tends to counteract the tidal interaction, tending to spin up
the surface when it is braked down and vice versa. As a consequence, the times
needed for the axial angular velocity to become equal to the orbital angular
velocity may be larger than given by typical synchronization timescales. Also,
due to meridional circulation some differential rotation remains in tidally
locked binary systems.Comment: 10 pages, 18 figures, Accepted for publication in Astronomy and
Astrophysic
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