33 research outputs found
Electronically--implemented coupled logistic maps
The logistic map is a paradigmatic dynamical system originally conceived to
model the discrete-time demographic growth of a population, which shockingly,
shows that discrete chaos can emerge from trivial low-dimensional non-linear
dynamics. In this work, we design and characterize a simple, low-cost,
easy-to-handle, electronic implementation of the logistic map. In particular,
our implementation allows for straightforward circuit-modifications to behave
as different one-dimensional discrete-time systems. Also, we design a coupling
block in order to address the behavior of two coupled maps, although, our
design is unrestricted to the discrete-time system implementation and it can be
generalized to handle coupling between many dynamical systems, as in a complex
system. Our findings show that the isolated and coupled maps' behavior has a
remarkable agreement between the experiments and the simulations, even when
fine-tuning the parameters with a resolution of . We support
these conclusions by comparing the Lyapunov exponents, periodicity of the
orbits, and phase portraits of the numerical and experimental data for a wide
range of coupling strengths and map's parameters.Comment: 8 pages, 10 figure
Vortex dynamics under pulsatile flow in axisymmetric constricted tubes
An improved understanding of how vortices develop and propagate under
pulsatile flow can shed important light on the mixing and transport processes
including the transition to turbulent regime occurring in such systems. For
example, the characterization of pulsatile flows in obstructed artery models
serves to encourage research into flow-induced phenomena associated with
changes in morphology, blood viscosity, wall elasticity and flow rate. In this
work, an axisymmetric rigid model was used to study the behaviour of the flow
pattern with varying constriction degree (), mean Reynolds number
() and Womersley number (). Velocity fields were acquired
experimentally using Digital Particle Image Velocimetry and generated
numerically. For the acquisition of data, was varied from 385 to
2044, was 1.0 cm and 1.6 cm, and was varied from 17 to 33 in the
experiments and from 24 to 50 in the numerical simulations. Results for the
considered Reynolds number, showed that the flow pattern consisted of two main
structures: a central jet around the tube axis and a recirculation zone
adjacent to the inner wall of the tube, where vortices shed. Using the
vorticity fields, the trajectory of vortices was tracked and their displacement
over their lifetime calculated. The analysis led to a scaling law equation for
the maximum vortex displacement as a function of a dimensionless variable
dependent on the system parameters Re and
Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.
RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Eddy formation in the bays of Kamchatka and fluxes to the open ocean
International audienceThe Eastern Kamchatka Current (EKC) is the western boundary current of the North Pacific subpolar gyre. Southeast of the Kamchatka Peninsula lies a large anticyclonic eddy, the Kamchatka Eddy (KE). This eddy is quasi-stationary. More generally, the oceanic region east of the EKC contains many eddies, several of them large and long lasting. Using surface currents derived from altimetry, particle tracking and a simple two-dimensional numerical model of fluid flow, we investigate the variability of this eddy field, the generation of eddies in the bays of Kamchatka by the EKC and fluxes of water to and from these bays. Firstly, we recover in our analysis of long-lasting eddies, the main eddies of the region. Among strong eddies, the parity bias favors anticyclones. Our numerical simulations give a possible explanation for the process of eddy creation in the bays of the peninsula and show that the northernmost bay produces most anticyclones. Then, we track forward the water particles from these bays and we determine their fate in the open ocean; southeastward and southwestward trajectories are the most frequent. We also track water particles backward from the KE site; they often drift near the Kamchatka coast, but others drift south of this site and remain there, a priori trapped in other eddies. This study confirms the complexity of mesoscale motions and water exchanges in this region
Canonical correlation analysis as a statistical method to relate underwater acoustic propagation and ocean fluctuations
International audienc
Bolaamphiphilic liquid crystals based on bis-imidazolium cations
Rare examples of bolaform ionic materials containing cyanometallates and their lamellar mesomorphic supramolecular architectures are characterized.</p
Etude de l'influence des petites échelles océaniques sur la propagation acoustique : application à la campagne ALMA2017
International audienceLa fluctuation océanique est présente à de nombreuses échelles spatio - temporelles. Nous nous intéressons aux fluctuations produites par les ondes internes et les vagues de surface, qui ont une variabilité temporelle allant de la minute aux heures. Les ondes internes créent des fluctuations verticales qui provoquent des variations de la vitesse du son, et donc impactent fortement la réception acoustique d'une manière difficile à prévoir. Il est alors nécessaire de considérer des méthodes stochastiques pour lier la propagation acoustique et la dynamique du milieu de propagation dans les régions de forte activité d'ondes internes. Dans ce travail, nous proposons d'appliquer des méthodes statistiques aux données acoustiques et océanographiques de la campagne ALMA2017 de la DGA. En particulier, nous utilisons l'analyse canonique des corrélations (CCA) qui nous permet d'établir des corrélations entre deux groupes de variables. Par cette analyse nous pouvons construire des variables explicatives plus pertinentes que les variables d'origine afin d'aider à orienter la réflexion vers la recherche de causalité. Ici nous considérons d'un côté les mesures de température, leurs modes empiriques (EOF) et le niveau de bruit ambiant, et de l'autre l'intensité acoustique moyenne, les angles d'arrivée et la fonction de cohérence mutuelle verticale sur l'antenne. De cette manière, nous mettons en évidence des relations entre certaines de ces variables, ouvrant la voie à une meilleure compréhension de l'impact des ondes internes sur des signaux acoustiques reçus
Automatic versus manual oxygen administration in the emergency department
International audienc
Clinical relevance of classification according to weaning difficulty.
International audienceOBJECTIVE: To evaluate the clinical relevance of the weaning from mechanical ventilation classification system derived from the 2005 international consensus conference, in patients who receive mechanical ventilation for more than 48 hours, and evaluate its correlation with prognosis. METHODS: We conducted a retrospective cohort study in a 12-bed intensive care unit (ICU) in a teaching hospital. We included patients who required > 48 hours of mechanical ventilation and who passed a spontaneous breathing trial (SBT). Weaning and sedation were monitored according to standardized protocol-directed procedures. We collected data on physiological characteristics, mechanical ventilation duration, ICU and hospital stay, and mortality from the medical records database. We assessed one-year mortality with a prospective, standardized method. Multivariate logistic regression was performed to evaluate the association between weaning categories and outcome. RESULTS: We included 329 ventilation episodes, in which 115 patients passed at least one SBT. Thirty-four patients (30%) succeeded in their first SBT (simple weaning group), 47 patients (40%) succeeded in their 2nd or 3rd SBT or in less than 7 days of weaning (the difficult weaning group), and 34 patients (30%) required more than 3 SBTs or more than 7 days of weaning (the prolonged weaning group). There were significant differences in ICU and hospital mortality between the simple, difficult, and prolonged-weaning groups. Prolonged weaning was an independent risk factor for longer ICU stay (odds ratio 15.11, 95% CI 1.61-141.91, P = .01) and hospital mortality (odds ratio 3.66, 95% CI 0.99-13.51). However, the weaning process did not impact one-year mortality (odds ratio 2.61, 95% CI 0.82-8.35). CONCLUSIONS: The new weaning classification system is clinically relevant and correlates to ICU and hospital mortality, but not to one-year mortality