801 research outputs found
Spectroscopy of the enigmatic short-period cataclysmic variable IR Com in an extended low state
We report the occurrence of a deep low state in the eclipsing short-period
cataclysmic variable IR Com, lasting more than two years. Spectroscopy obtained
in this state shows the system as a detached white dwarf plus low-mass
companion, indicating that accretion has practically ceased. The spectral type
of the companion derived from the SDSS spectrum is M6-7, somewhat later than
expected for the orbital period of IR Com. Its radial velocity amplitude,
K_2=419.6+-3.4 km/s, together with the inclination of 75-90deg implies
0.8Msun<Mwd<1.0Msun. We estimate the white dwarf temperature to be ~15000K, and
the absence of Zeeman splitting in the Balmer lines rules out magnetic fields
in excess of ~5 MG. IR Com still defies an unambiguous classification, in
particular the occurrence of a deep, long low state is so far unique among
short-period CVs that are not strongly magnetic.Comment: Revised version, MNRAS Letters in pres
Do team processes really have an effect on clinical performance? A systematic literature review
Summary There is a growing literature on the relationship between team processes and clinical performance. The purpose of this review is to summarize these articles and examine the impact of team process behaviours on clinical performance. We conducted a literature search in five major databases. Inclusion criteria were: English peer-reviewed papers published between January 2001 and May 2012, which showed or tried to show (i) a statistical relationship of a team process variable and clinical performance or (ii) an improvement of a performance variable through a team process intervention. Study quality was assessed using predefined quality indicators. For every study, we calculated the relevant effect sizes. We included 28 studies in the review, seven of which were intervention studies. Every study reported at least one significant relationship between team processes or an intervention and performance. Also, some non-significant effects were reported. Most of the reported effect sizes were large or medium. The study quality ranged from medium to high. The studies are highly diverse regarding the specific team process behaviours investigated and also regarding the methods used. However, they suggest that team process behaviours do influence clinical performance and that training results in increased performance. Future research should rely on existing theoretical frameworks, valid, and reliable methods to assess processes such as teamwork or coordination and focus on the development of adequate tools to assess process performance, linking them with outcomes in the clinical settin
Estimating flexibility preferences to resolve temporal scheduling conflicts in activity-based modelling
This paper presents a novel activity-based demand model that combines an optimisation framework for continuous temporal scheduling decisions (i.e. activity timings and durations) with traditional discrete choice models for non-temporal choice dimensions (i.e. activity participation, number and type of tours, and destinations). The central idea of our approach is that individuals resolve temporal scheduling conflicts that arise from overlapping activities, e.g. needing to work and desiring to shop at the same time, in order to maximise their daily utility. Flexibility parameters capture behavioural preferences that penalise deviations from desired timings. This framework has three advantages over existing activity-based modelling approaches: (i) the time conflicts between different temporal scheduling decisions including the activity sequence are treated jointly; (ii) flexibility parameters follow a utility maximisation approach; and (iii) the framework can be used to estimate and simulate a city-scale case study in reasonable time. We introduce an estimation routine that allows flexibility parameters to be estimated using real-world observations as well as a simulation routine to efficiently resolve temporal conflicts using an optimisation model. The framework is applied to the full-time workers of a synthetic population for the city of Lausanne, Switzerland. We validate the model results against reported schedules. The results demonstrate the capabilities of our approach to reproduce empirical observations in a real-world case study
Adaptation in anaesthesia team coordination in response to a simulated critical event and its relationship to clinical performance
Background Recent studies in anaesthesia and intensive care indicate that a team's ability to adapt its coordination activities to changing situational demands is crucial for effective teamwork and thus, safe patient care. This study addresses the relationship between adaptation of team coordination and markers of clinical performance in response to a critical event, particularly regarding which types of coordination activities are used and which team member engages in those coordination activities. Methods Video recordings of 15 two-person anaesthesia teams (anaesthesia trainee plus anaesthesia nurse) performing a simulated induction of general anaesthesia were coded, using a structured observation system for coordination activities. The simulation involved a critical event—asystole during laryngoscopy. Clinical performance was assessed using two separate reaction times related to the critical event. Results Analyses of variance revealed a significant effect of the critical event on team coordination: after the occurrence of the asystole, team members adapted their coordination activities by spending more time on information management—a specific type of coordination activity (F1,28=15.17, P=0.001). No significant effect was found for task management. The increase in information management was related to faster decisions regarding how to respond to the critical event, but only for trainees and not for nurses. Conclusions Our findings support the claim that adaptation of coordination activities is related to improved team performance in healthcare. Moreover, adaptation and its relationship to team performance were found to vary with regard to type of coordination activities and team membe
A mixed malaria infection: is Plasmodium vivax good for you?
We describe a case of mixed malaria infection in a returning traveller. We suggest that our patient had a chronic infection with Plasmodium vivax, which reduced the severity of an acute infection with P. falciparum-an example of cross-species immunity
Doppler imaging of the planetary debris disc at the white dwarf SDSS J122859.93+104032.9
Debris discs which orbit white dwarfs are signatures of remnant planetary systems. We present 12 yr of optical spectroscopy of the metal-polluted white dwarf SDSS J1228+1040, which shows a steady variation in the morphology of the 8600 Å Ca II triplet line profiles from the gaseous component of its debris disc. We identify additional emission lines of O I, Mg I, Mg II, Fe II and Ca II in the deep co-added spectra. These emission features (including Ca H & K) exhibit a wide range in strength and morphology with respect to each other and to the Ca II triplet, indicating different intensity distributions of these ionic species within the disc. Using Doppler tomography, we show that the evolution of the Ca II triplet profile can be interpreted as the precession of a fixed emission pattern with a period in the range 24–30 yr. The Ca II line profiles vary on time-scales that are broadly consistent with general relativistic precession of the debris disc
Accretion of a giant planet onto a white dwarf star
The detection of a dust disc around G29-38 and transits from debris orbiting
WD1145+017 confirmed that the photospheric trace metals found in many white
dwarfs arise from the accretion of tidally disrupted planetesimals. The
composition of these planetesimals is similar to that of rocky bodies in the
inner solar system. Gravitationally scattering planetesimals towards the white
dwarf requires the presence of more massive bodies, yet no planet has so far
been detected at a white dwarf. Here we report optical spectroscopy of a
K hot white dwarf that is accreting from a circumstellar gaseous
disc composed of hydrogen, oxygen, and sulphur at a rate of
. The composition of this disc is
unlike all other known planetary debris around white dwarfs, but resembles
predictions for the makeup of deeper atmospheric layers of icy giant planets,
with HO and HS being major constituents. A giant planet orbiting a hot
white dwarf with a semi-major axis of solar radii will undergo
significant evaporation with expected mass loss rates comparable to the
accretion rate onto the white dwarf. The orbit of the planet is most likely the
result of gravitational interactions, indicating the presence of additional
planets in the system. We infer an occurrence rate of spectroscopically
detectable giant planets in close orbits around white dwarfs of
.Comment: Nature, December 5 issu
Different epitope structures select distinct mutant forms of an antibody variable region for expression during the immune response.
The frequency of gaseous debris discs around white dwarfs
1-3 per cent of white dwarfs are orbited by planetary dusty debris detectable
as infrared emission in excess above the white dwarf flux. In a rare subset of
these systems, a gaseous disc component is also detected via emission lines of
the Ca II 8600\r{A} triplet, broadened by the Keplerian velocity of the disc.
We present the first statistical study of the fraction of debris discs
containing detectable amounts of gas in emission at white dwarfs within a
magnitude and signal-to-noise limited sample. We select 7705 single white
dwarfs spectroscopically observed by the Sloan Digital Sky Survey (SDSS) and
with magnitudes 19. We identify five gaseous disc hosts, all
of which have been previously discovered. We calculate the occurrence rate of a
white dwarf hosting a debris disc detectable via Ca II emission lines as
0.067 per cent. This corresponds to an occurrence rate
for a dusty debris disc to have an observable gaseous component in emission as
4 per cent. Given that variability is a common feature of the
emission profiles of gaseous debris discs, and the recent detection of a
planetesimal orbiting within the disc of SDSSJ122859.93+104032.9, we propose
that gaseous components are tracers for the presence of planetesimals embedded
in the discs and outline a qualitative model. We also present spectroscopy of
the Ca II triplet 8600\r{A} region for 20 white dwarfs hosting dusty debris
discs in an attempt to identify gaseous emission. We do not detect any gaseous
components in these 20 systems, consistent with the occurrence rate that we
calculated.Comment: 13 pages, 6 Figures, accepted for publication in MNRA
Stellar archaeology with Gaia: the Galactic white dwarf population
Gaia will identify several 1e5 white dwarfs, most of which will be in the
solar neighborhood at distances of a few hundred parsecs. Ground-based optical
follow-up spectroscopy of this sample of stellar remnants is essential to
unlock the enormous scientific potential it holds for our understanding of
stellar evolution, and the Galactic formation history of both stars and
planets.Comment: Summary of a talk at the 'Multi-Object Spectroscopy in the Next
Decade' conference in La Palma, March 2015, to be published in ASP Conference
Series (editors Ian Skillen & Scott Trager
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