20 research outputs found
Thermodynamics of trajectories of the one-dimensional Ising model
We present a numerical study of the dynamics of the one-dimensional Ising
model by applying the large-deviation method to describe ensembles of dynamical
trajectories. In this approach trajectories are classified according to a
dynamical order parameter and the structure of ensembles of trajectories can be
understood from the properties of large-deviation functions, which play the
role of dynamical free-energies. We consider both Glauber and Kawasaki
dynamics, and also the presence of a magnetic field. For Glauber dynamics in
the absence of a field we confirm the analytic predictions of Jack and Sollich
about the existence of critical dynamical, or space-time, phase transitions at
critical values of the "counting" field . In the presence of a magnetic
field the dynamical phase diagram also displays first order transition
surfaces. We discuss how these non-equilibrium transitions in the 1 Ising
model relate to the equilibrium ones of the 2 Ising model. For Kawasaki
dynamics we find a much simple dynamical phase structure, with transitions
reminiscent of those seen in kinetically constrained models.Comment: 23 pages, 10 figure
On the fluctuations of jamming coverage upon random sequential adsorption on homogeneous and heterogeneous media
The fluctuations of the jamming coverage upon Random Sequential Adsorption
(RSA) are studied using both analytical and numerical techniques. Our main
result shows that these fluctuations (characterized by )
decay with the lattice size according to the power-law . The exponent depends on the dimensionality of
the substrate and the fractal dimension of the set where the RSA process
actually takes place () according to .This
theoretical result is confirmed by means of extensive numerical simulations
applied to the RSA of dimers on homogeneous and stochastic fractal substrates.
Furthermore, our predictions are in excellent agreement with different previous
numerical results.
It is also shown that, studying correlated stochastic processes, one can
define various fluctuating quantities designed to capture either the underlying
physics of individual processes or that of the whole system. So, subtle
differences in the definitions may lead to dramatically different physical
interpretations of the results. Here, this statement is demonstrated for the
case of RSA of dimers on binary alloys.Comment: 20 pages, 8 figure
Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model
The first-order irreversible phase transitions (IPT) of the Yaldran-Khan
model (Yaldran-Khan, J. Catal. 131, 369, 1991) for the CO+NO reaction is
studied using the constant coverage (CC) ensemble and performing epidemic
simulations. The CC method allows the study of hysteretic effects close to
coexistence as well as the location of both the upper spinodal point and the
coexistence point. Epidemic studies show that at coexistence the number of
active sites decreases according to a (short-time) power law followed by a
(long-time) exponential decay. It is concluded that first-order IPT's share
many characteristic of their reversible counterparts, such as the development
of short ranged correlations, hysteretic effects, metastabilities, etc.Comment: 17 pages, 10 figure
Non-equilibrium Characterization of Spinodal Points using Short Time Dynamics
Though intuitively appealing, the concept of spinodal is rigourously defined
only in systems with infinite range interactions (mean field systems). In
short-range systems, a pseudo-spinodal can be defined by extrapolation of
metastable measurements, but the point itself is not reachable because it lies
beyond the metastability limit. In this work we show that a sensible definition
of spinodal points can be obtained through the short time dynamical behavior of
the system deep inside the metastable phase, by looking for a point where the
system shows critical behavior. We show that spinodal points obtained by this
method agree both with the thermodynamical spinodal point in mean field systems
and with the pseudo-spinodal point obtained by extrapolation of
meta-equilibrium behavior in short range systems. With this definition, a
practical determination can be achieved without regard for equilibration
issues.Comment: 10 pages, 12 figure
Recovery index, attentiveness and state of memory after xenon or isoflurane anaesthesia: a randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>Performance of patients immediately after anaesthesia is an area of special interest and so a clinical trial was conducted to compare Xenon with Isoflurane anaesthesia. In order to assess the early cognitive recovery the syndrome short test (SST) according to Erzigkeit (Geromed GmbH) was applied.</p> <p>Methods</p> <p>ASA I and II patients undergoing long and short surgical interventions were randomised to receive either general anaesthesia with Xenon or Isoflurane. The primary endpoint was the validated SST which covering memory disturbances and attentiveness. The test was used on the day prior to intervention, one and three hours post extubation. The secondary endpoint was the recovery index (RI) measured after the end of the inhalation of Xenon or Isoflurane. In addition the Aldrete score was evaluated up to 180 min. On the first post-operative day the patients rated the quality of the anaesthetic using a scoring system from 1-6.</p> <p>Results</p> <p>The demographics of the groups were similar. The sum score of the SST delivered a clear trend one hour post extubation and a statistically significant superiority for Xenon three hours post extubation (p < 0.01). The RI likewise revealed a statistically significant superiority of Xenon 5 minutes post extubation (p < 0.01). The Aldrete score was significantly higher for 45 min. The scoring system results were also better after Xenon anaesthesia (p < 0.001).</p> <p>Conclusions</p> <p>The results show that recovery from anaesthesia and the early return of post-operative cognitive functions are significantly better after Xenon anaesthesia compared to Isoflurane. The results of the RI for Xenon are similar with the previously published results.</p> <p>Trial Registration</p> <p>The trial was registered with the number ISRCTN01110844 <url>http://www.controlled-trials.com/isrctn/pf/01110844</url>.</p
Reliability of the volatile agent consumption display in the Draeger Primus™ anesthesia machine
Knowledge of the consumed amount of volatile anesthetic (VA) expressed in liquid agent is necessary to enable agent sparing dosing measures and for billing purposes. The widespread Draeger Primus™ anesthesia machine displays in its logbook the amount of consumed VA at the end of each anesthesia, but the reliability of this parameter is yet unknown. The objective was to evaluate the precision and reliability of the inbuilt VA consumption display in Draeger Primus™ anesthesia machines as compared with the gold standard of weighing the vaporizer before and after anesthesia. In this prospective laboratory investigation we compared the VA consumption displayed by the Draeger Primus™ anesthesia machine with measured vaporizer weight differences before and after 10 sevoflurane and 10 desflurane anesthesias. We assessed the average difference and spread of values between the predicted (displayed) and measured (control) values for VA consumption. The displayed sevoflurane consumption overestimated the measured values by 4.3 ± 5.4 ml (7.6 %). The displayed desflurane consumption underestimated the measured values by -3.5 ± 6.3 ml (6.2 %). Nine from 10 sevoflurane pairs of values and all desflurane pairs of values were within ±1.96 SD. The displayed VA consumption calculations for sevoflurane and desflurane in the Draeger Primus™ are sufficiently reliable to estimate the pharmacoeconomic impact of VA delivery during inhalational anesthesia