22 research outputs found
A model for the collapse of the edge when two transitions routes compete
The transition to turbulence in many shear flows proceeds along two competing
routes, one linked with finite-amplitude disturbances and the other one
originating from a linear instability, as in e.g. boundary layer flows. The
dynamical systems concept of edge manifold has been suggested in the
subcritical case to explain the partition of the state space of the system.
This investigation is devoted to the evolution of the edge manifold when a
linear stability is added in such subcritical systems, a situation poorly
studied despite its prevalence in realistic fluid flows. In particular the fate
of the edge state as a mediator of transition is unclear. A deterministic
three-dimensional model is suggested, parametrised by the linear instability
growth rate. The edge manifold evolves topologically, via a global saddle-loop
bifurcation, from the separatrix between two attraction basins to the mediator
between two transition routes. For larger instability rates, the stable
manifold of the saddle point increases in codimension from 1 to 2 after an
additional local saddle node bifurcation, causing the collapse of the edge
manifold. As the growth rate is increased, three different regimes of this
model are identified, each one associated with a flow case from the recent
hydrodynamic literature. A simple nonautonomous generalisation of the model is
also suggested in order to capture the complexity of spatially developing
flows.Comment: 12 pages, 10 figures, under review in Phys. Rev.
Multistability of elasto-inertial two-dimensional channel flow
Elasto-inertial turbulence (EIT) is a recently discovered two-dimensional
chaotic flow state observed in dilute polymer solutions. It has been
hypothesised that the dynamical origins of EIT are linked to a center-mode
instability, whose nonlinear evolution leads to a travelling wave with an
'arrowhead' structure in the polymer conformation, a structure also observed
instantaneously in simulations of EIT. In this work we conduct a suite of
two-dimensional direct numerical simulations spanning a wide range of polymeric
flow parameters to examine the possible dynamical connection between the
arrowhead and EIT. Our calculations reveal (up to) four co-existent attractors:
the laminar state and a steady arrowhead, along with EIT and a 'chaotic
arrowhead'. The steady arrowhead is stable for all parameters considered here,
while the final pair of (chaotic) flow states are visually very similar and can
be distinguished only by the presence of a weak polymer arrowhead structure in
the 'chaotic arrowhead' regime. Analysis of energy transfers between the flow
and the polymer indicates that both chaotic regimes are maintained by an
identical near-wall mechanism and that the weak arrowhead does not play a role.
Our results suggest that the arrowhead is a benign flow structure that is
disconnected from the self-sustaining mechanics of EIT.Comment: 17 pages, 10 figure
The edge as a Lagrangian Coherent Structure in a high-dimensional state space
Dissipative dynamical systems characterised by two basins of attraction are
found in many physical systems, notably in hydrodynamics where laminar and
turbulent regimes can coexist. The state space of such systems is structured
around a dividing manifold called the edge, which separates trajectories
attracted by the laminar state from those reaching the turbulent state. We
apply here concepts and tools from Lagrangian data analysis to investigate this
edge manifold. This approach is carried out in the state space of automous
arbitrarily high-dimensional dissipative systems, in which the edge manifold is
re-interpreted as a Lagrangian Coherent Structure (LCS). Two different
diagnostics, finite-time Lyapunov exponents and Lagrangian Descriptors, are
used and compared with respect to their ability to identify the edge and to
their scalability. Their properties are illustrated on several low-order models
of subcritical transition of increasing dimension and complexity, as well on
well-resolved simulations of the Navier-Stokes equations in the case of plane
Couette flow. They allow for a mapping of the global structure of both the
state space and the edge manifold based on quantitative information. Both
diagnostics can also be used to generate efficient bisection algorithms to
approach asymptotic edge states, which outperform classical edge tracking.Comment: 16 pages, 10 figures, Accepted in Phys. Rev. Researc
Inertial enhancement of the polymer diffusive instability
Beneitez et al. (2023b) have recently discovered a new linear "polymer
diffusive instability" (PDI) in inertialess viscoelastic rectilinear shear flow
of a FENE-P fluid with polymer stress diffusion. Here, we examine the impact of
inertia on the PDI, which we delineate for both plane Couette and channel
configurations under varying Weissenberg number , polymer stress diffusivity
, solvent-to-total viscosity and Reynolds number ,
considering Oldroyd-B and FENE-P constitutive relations. Both the prevalence of
the instability in parameter space and the associated growth rates are found to
significantly increase with . For instance, as increases with
fixed, the instability emerges at progressively lower values of and
than in the inertialess limit, and the associated growth rates
increase linearly with when all other parameters are fixed. This
strengthening of PDI with inertia and the fact that stress diffusion is always
present in time-stepping algorithms, either implicitly as part of the scheme or
explicitly as a stabiliser, implies that the instability is likely operative in
computational work using the popular Oldroyd-B and FENE-P constitutive models.
The fundamental question now is whether PDI is physical and observable in
experiments, or is instead an artifact of the constitutive models that must be
suppressed.Comment: 10 pages, 3 figure
La Pena de Privación de Libertad en la Legislación Militar.
Este trabajo de fin de grado tiene por finalidad analizar la actual regulación de la pena privativa de libertad en el Código Penal Militar de 2015, así como las particularidades que presenta dicha pena en cuanto a su cumplimiento. Se revisará brevemente el antiguo CPM de 1985, determinando el ámbito y los antecedentes históricos de la jurisdicción militar, hasta llegar al análisis de la pena privativa de libertad que se encuentra recogida en la Ley Orgánica 14/2015 de 14 de octubre mediante la cual se aprueba el nuevo Código Penal Militar
Effectiveness of an intervention for improving drug prescription in primary care patients with multimorbidity and polypharmacy:Study protocol of a cluster randomized clinical trial (Multi-PAP project)
This study was funded by the Fondo de Investigaciones Sanitarias ISCIII (Grant Numbers PI15/00276, PI15/00572, PI15/00996), REDISSEC (Project Numbers RD12/0001/0012, RD16/0001/0005), and the European Regional Development Fund ("A way to build Europe").Background: Multimorbidity is associated with negative effects both on people's health and on healthcare systems. A key problem linked to multimorbidity is polypharmacy, which in turn is associated with increased risk of partly preventable adverse effects, including mortality. The Ariadne principles describe a model of care based on a thorough assessment of diseases, treatments (and potential interactions), clinical status, context and preferences of patients with multimorbidity, with the aim of prioritizing and sharing realistic treatment goals that guide an individualized management. The aim of this study is to evaluate the effectiveness of a complex intervention that implements the Ariadne principles in a population of young-old patients with multimorbidity and polypharmacy. The intervention seeks to improve the appropriateness of prescribing in primary care (PC), as measured by the medication appropriateness index (MAI) score at 6 and 12months, as compared with usual care. Methods/Design: Design:pragmatic cluster randomized clinical trial. Unit of randomization: family physician (FP). Unit of analysis: patient. Scope: PC health centres in three autonomous communities: Aragon, Madrid, and Andalusia (Spain). Population: patients aged 65-74years with multimorbidity (≥3 chronic diseases) and polypharmacy (≥5 drugs prescribed in ≥3months). Sample size: n=400 (200 per study arm). Intervention: complex intervention based on the implementation of the Ariadne principles with two components: (1) FP training and (2) FP-patient interview. Outcomes: MAI score, health services use, quality of life (Euroqol 5D-5L), pharmacotherapy and adherence to treatment (Morisky-Green, Haynes-Sackett), and clinical and socio-demographic variables. Statistical analysis: primary outcome is the difference in MAI score between T0 and T1 and corresponding 95% confidence interval. Adjustment for confounding factors will be performed by multilevel analysis. All analyses will be carried out in accordance with the intention-to-treat principle. Discussion: It is essential to provide evidence concerning interventions on PC patients with polypharmacy and multimorbidity, conducted in the context of routine clinical practice, and involving young-old patients with significant potential for preventing negative health outcomes. Trial registration: Clinicaltrials.gov, NCT02866799Publisher PDFPeer reviewe