1,951 research outputs found
Effect of preoperative P2Y12 and thrombin platelet receptor inhibition on bleeding after cardiac surgery
BACKGROUND:
Drugs that act on the platelet P2Y12 receptor are responsible for postoperative bleeding in cardiac surgery. However, protease-activated receptor (PAR) that reacts to thrombin stimulation might still be active in patients treated with P2Y12 inhibitors. Preoperative platelet function testing could possibly guide the timing of surgery. We investigated the association between P2Y12 receptor and PAR inhibition and bleeding after cardiac surgery.
METHODS:
A retrospective cohort study of 361 patients undergoing cardiac surgery and treated with P2Y12 anti-platelet agents was undertaken. All patients received a preoperative multiplate electrode aggregometry testing of platelet P2Y12 receptor activity (ADPtest) and PAR reactivity with thrombin receptor-activating peptide (TRAP) stimulation. ADPtest and TRAPtest data measured before surgery were analysed for association with postoperative bleeding (ml per 12 h) and severe postoperative bleeding.
RESULTS:
Both the ADPtest and the TRAPtest were significantly (P=0.001) associated with postoperative bleeding. A threshold of 22 U for the ADPtest yielded a negative predictive value (NPV) of 94% and a positive predictive value (PPV) of 20%, and a threshold of 75 U for the TRAPtest yielded an NPV of 95% and a PPV of 23%. In the subgroup of patients with ADPtest <22 U, TRAPtest ≥75 U was not associated with severe bleeding (NPV of 100% and PPV of 37%).
CONCLUSIONS:
In patients taking P2Y12 receptor inhibitors, residual platelet reactivity to thrombin stimulation limits the risk of severe postoperative bleeding
Cosmological Adaptive Mesh Refinement
We describe a grid-based numerical method for 3D hydrodynamic cosmological
simulations which is adaptive in space and time and combines the best features
of higher order--accurate Godunov schemes for Eulerian hydrodynamics with
adaptive particle--mesh methods for collisionless particles. The basis for our
method is the structured adaptive mesh refinement (AMR) algorithm of Berger &
Collela (1989), which we have extended to cosmological hydro + N-body
simulations. The resulting multiscale hybrid method is a powerful alternative
to particle-based methods in current use. The choices we have made in
constructing this algorithm are discussed, and its performance on the Zeldovich
pancake test problem is given. We present a sample application of our method to
the problem of first structure formation. We have achieved a spatial dynamic
range in a 3D multispecies gas + dark matter
calculation, which is sufficient to resolve the formation of primordial
protostellar cloud cores starting from linear matter fluctuations in an
expanding FRW universe.Comment: 14 pages, 3 figures (incl. one large color PS) to appear in
"Numerical Astrophysics 1998", eds. S. Miyama & K. Tomisaka, Tokyo, March
10-13, 199
An adaptive grid refinement strategy for the simulation of negative streamers
The evolution of negative streamers during electric breakdown of a
non-attaching gas can be described by a two-fluid model for electrons and
positive ions. It consists of continuity equations for the charged particles
including drift, diffusion and reaction in the local electric field, coupled to
the Poisson equation for the electric potential. The model generates field
enhancement and steep propagating ionization fronts at the tip of growing
ionized filaments. An adaptive grid refinement method for the simulation of
these structures is presented. It uses finite volume spatial discretizations
and explicit time stepping, which allows the decoupling of the grids for the
continuity equations from those for the Poisson equation. Standard refinement
methods in which the refinement criterion is based on local error monitors fail
due to the pulled character of the streamer front that propagates into a
linearly unstable state. We present a refinement method which deals with all
these features. Tests on one-dimensional streamer fronts as well as on
three-dimensional streamers with cylindrical symmetry (hence effectively 2D for
numerical purposes) are carried out successfully. Results on fine grids are
presented, they show that such an adaptive grid method is needed to capture the
streamer characteristics well. This refinement strategy enables us to
adequately compute negative streamers in pure gases in the parameter regime
where a physical instability appears: branching streamers.Comment: 46 pages, 19 figures, to appear in J. Comp. Phy
Exact Foldy-Wouthuysen transformation for spin 0 particle in curved space
Up to now, the only known exact Foldy- Wouthuysen transformation (FWT) in
curved space is that concerning Dirac particles coupled to static spacetime
metrics. Here we construct the exact FWT related to a real spin-0 particle for
the aforementioned spacetimes. This exact transformation exists independently
of the value of the coupling between the scalar field and gravity. Moreover,
the gravitational Darwin term written for the conformal coupling is one third
of the relevant term in the fermionic case.Comment: 10 pages, revtex, improved version to appear in Phys. Rev.
Self-consistent modelling of line-driven hot-star winds with Monte Carlo radiation hydrodynamics
Radiative pressure exerted by line interactions is a prominent driver of
outflows in astrophysical systems, being at work in the outflows emerging from
hot stars or from the accretion discs of cataclysmic variables, massive young
stars and active galactic nuclei. In this work, a new radiation hydrodynamical
approach to model line-driven hot-star winds is presented. By coupling a Monte
Carlo radiative transfer scheme with a finite-volume fluid dynamical method,
line-driven mass outflows may be modelled self-consistently, benefiting from
the advantages of Monte Carlo techniques in treating multi-line effects, such
as multiple scatterings, and in dealing with arbitrary multidimensional
configurations. In this work, we introduce our approach in detail by
highlighting the key numerical techniques and verifying their operation in a
number of simplified applications, specifically in a series of self-consistent,
one-dimensional, Sobolev-type, hot-star wind calculations. The utility and
accuracy of our approach is demonstrated by comparing the obtained results with
the predictions of various formulations of the so-called CAK theory and by
confronting the calculations with modern sophisticated techniques of predicting
the wind structure. Using these calculations, we also point out some useful
diagnostic capabilities our approach provides. Finally we discuss some of the
current limitations of our method, some possible extensions and potential
future applications.Comment: 15 pages, 8 figures; accepted for publication in MNRA
The feasibility and applications of non-invasive cardiac monitoring in obese patients undergoing day-case surgery: Results of a prospective observational study
Aims: This prospective observational study evaluates the utility of non-invasive cardiac monitoring in obese patients in the day-surgery case, considering factors, such as Body Mass Index (BMI) and anaesthesia technique. Background: Obese patients are more likely to be admitted to hospital or to get hospitalized because they are more prone to concomitant diseases and obesity itself is not a contraindication to day surgery. Obese patients are a high-risk patient population that may particularly benefit from monitoring perioperative haemodynamic variations. Methods: In this observational study, we compared haemodynamic variations between overweight or obese and normal weight patients undergoing day-case surgery. We adopted NICOM® as a non-invasive cardiac output monitoring. Objective: The aim of the current study was to investigate the haemodynamic impact of BMI and anaesthesia technique during day-case surgery procedures. The other goal was to evaluate the feasibility and applications of non-invasive cardiac output monitoring among the obese population in day-surgery. Results: 74 patients were included in the study. 34 were overweight or obese (weight 84 ± 10 kg, height 160 ± 10 cm, BMI ≈ 30 kg/m2), 40 were normal weight (weight 63 ± 15 kg, height 160 ± 10 cm, BMI ≈ 22 kg/m2). Compared to normal-weight patients, obese patients show an increase in blood pressure with a return to baseline values at the end of surgery (p < 0.05). The Cardiac Output (CO) shows a similar trend, whereas the heart rate is normal. A decrease in the Cardiac Index (CI) during the operation was noticed in both groups, the one in obese patients (p = 0.24) being greater. In the same way, the Stroke Volume Index (SVI) was lower in obese patients during surgery (p < 0.05). In spinal anaesthesia, the Total Peripheral Resistance Index (TPRI) was not statistically different between the groups of study. As for the TPRI in obese patients, we reported values similar to the ones in non-obese patients in spinal anaesthesia. In local anesthesia, TPRI was higher in obese patients than in non-obese. Conclusion: Cardiovascular alterations in relation to obesity include an increase in blood pressure, CO and SV. An inadequate monitoring of haemodynamic parameters is a risk factor for perioperative complications. NICOM® provides a continuous, non-invasive haemodynamic measurement
Does Quantum Mechanics Clash with the Equivalence Principle - and Does it Matter?
With an eye on developing a quantum theory of gravity, many physicists have
recently searched for quantum challenges to the equivalence principle of
general relativity. However, as historians and philosophers of science are well
aware, the principle of equivalence is not so clear. When clarified, we think
quantum tests of the equivalence principle won't yield much. The problem is
that the clash/not-clash is either already evident or guaranteed not to exist.
Nonetheless, this work does help teach us what it means for a theory to be
geometric.Comment: 12 page
Off-Center Collisions between Clusters of Galaxies
We present numerical simulations of off-center collisions between galaxy
clusters made using a new hydrodynamical code based on the piecewise-parabolic
method (PPM) and an isolated multigrid Poisson solver. We have performed three
gas-only high-resolution simulations of collisions between equal-mass clusters
with different values of the impact parameter (0, 5, and 10 times the core
radius). With these simulations we have studied the observational appearance of
the merging clusters and the variation in equilibration time, luminosity
enhancement during the collision, and structure of the merger remnant with
varying impact parameter. Observational evidence of an ongoing collision is
present for 1-2 sound crossing times after the collision, but only for special
viewing angles. The remnant actually requires at least five crossing times to
reach virial equilibrium. Since the sound crossing time can be as large as 1-2
Gyr, the equilibration time can thus be a large fraction of the age of the
universe. The final merger remnant is very similar for impact parameters of
zero and five core radii. It possesses a roughly isothermal core, with central
density and temperature twice the initial values. Outside the core the
temperature drops as r^-1, and the density roughly as r^-3.8. The core radius
shows a small increase due to shock heating during the merger. For an impact
parameter of ten core radii the core of the remnant possesses a more flattened
density profile, with a steeper dropoff outside the core. In both off-center
cases the merger remnant rotates, but only for the ten-core-radius case does
this appear to have an effect on the structure of the remnant.Comment: 26 pages, 15 figures included, submitted to ApJ; for color figures
and movies see http://www.astro.virginia.edu/~pmr7u/paper_offctr.htm
A telephone survey of cancer awareness among frontline staff: informing training needs
Background:
Studies have shown limited awareness about cancer risk factors among hospital-based staff. Less is known about general cancer awareness among community frontline National Health Service and social care staff.
Methods:
A cross-sectional computer-assisted telephone survey of 4664 frontline community-based health and social care staff in North West England.
Results:
A total of 671 out of 4664 (14.4%) potentially eligible subjects agreed to take part. Over 92% of staff recognised most warning signs, except an unexplained pain (88.8%, n=596), cough or hoarseness (86.9%, n=583) and a sore that does not heal (77.3%, n=519). The bowel cancer-screening programme was recognised by 61.8% (n=415) of staff. Most staff agreed that smoking and passive smoking ‘increased the chance of getting cancer.’ Fewer agreed about getting sunburnt more than once as a child (78.0%, n=523), being overweight (73.5%, n=493), drinking more than one unit of alcohol per day (50.2%, n=337) or doing less than 30 min of moderate physical exercise five times a week (41.1%, n=276).
Conclusion:
Cancer awareness is generally good among frontline staff, but important gaps exist, which might be improved by targeted education and training and through developing clearer messages about cancer risk factors
Numerical approximation of the Euler-Poisson-Boltzmann model in the quasineutral limit
This paper analyzes various schemes for the Euler-Poisson-Boltzmann (EPB)
model of plasma physics. This model consists of the pressureless gas dynamics
equations coupled with the Poisson equation and where the Boltzmann relation
relates the potential to the electron density. If the quasi-neutral assumption
is made, the Poisson equation is replaced by the constraint of zero local
charge and the model reduces to the Isothermal Compressible Euler (ICE) model.
We compare a numerical strategy based on the EPB model to a strategy using a
reformulation (called REPB formulation). The REPB scheme captures the
quasi-neutral limit more accurately
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