Emergence of spatio-temporal dynamics from exact coherent solutions in pipe flow

Turbulent-laminar patterns are ubiquitous near transition in wall-bounded shear flows. Despite recent progress in describing their dynamics in analogy to non-equilibrium phase transitions, there is no theory explaining their emergence. Dynamical-system approaches suggest that invariant solutions to the Navier–Stokes equations, such as traveling waves and relative periodic orbits in pipe flow, act as building blocks of the disordered dynamics. While recent studies have shown how transient chaos arises from such solutions, the ensuing dynamics lacks the strong fluctuations in size, shape and speed of the turbulent spots observed in experiments. We here show that chaotic spots with distinct dynamical and kinematic properties merge in phase space and give rise to the enhanced spatio-temporal patterns observed in pipe flow. This paves the way for a dynamical-system foundation to the phenomenology of turbulent-laminar patterns in wall-bounded extended shear flows.Peer ReviewedPostprint (published version

Against Sonderholm: still committed to expressivism

Jorn Sonderholm (2005) has argued that Simon Blackburn's commitment semantics for evaluative discourse is unable to explain the validity of simple inferences involving disjunction. This is true insofar as the basic rules which Blackburn suggests are not strong enough, but it is relatively simple to augment those rules so as to meet Sonderholm's challenge, whilst respecting the spirit of commitment semantics. One way of doing this is to add a reduction rule such that if accepting p commits one to inconsistent commitments, one is committed to accepting ¬p. Thus Sonderholm has not provided any reason to doubt the adequacy of commitment semantics to explain validity in evaluative discourse

Histeretical behaviour of two-dimensional vortex shedding past the NACA0012 airfoil at ultra-low Reynolds number

We unfold the complex transition route from steady to chaotic dynamics of the two-dimensional flow past the NACA0012 airfoil upon increasing the angle of attack a at the ultra-low Reynolds number Re = 5300. Hopf, forward and backward period-doubling cascades, Neimark-Sacker and saddlenode bifurcations are found along the way, the latter producing hysteretical regions where two distinct two-dimensional vortex-shedding modes coexist. Although the advent of three-dimensionality obliterates the two-dimensional path here addressed and deteriorates aerodynamic performances shortly after the advent of time-dependence at the first Hopf bifurcation, active flow control might assist in postponing the disruption of spanwise invariance to some extent, thus partially recovering the two-dimensional scenario.Peer ReviewedPostprint (published version

Review of the safety and efficacy of imiglucerase treatment of Gaucher disease

Most patients who suffer from symptomatic Gaucher disease will benefit from enzyme replacement therapy (ERT) with imiglucerase. The safety profile is excellent, only a small percentage of those exposed developing antibodies; similarly, very few patients require pre-medication for allergic reactions. Within 3 to 5 years of imiglucerase therapy, best documented at doses of 30 to 60 units/kg/infusion, hepatosplenomegaly can be expected to be reduced so that the liver volume will be maintained at 1 to 1.5 times normal (30% to 40% reduction from advent of ERT) and spleen volume to ≤ 2 to 8 times normal (50% to 60% reduction from advent of ERT). For anemic and thrombocytopenic patients, with 2 to 5 years of imiglucerase, hemoglobin levels are expected to be ≥ 11 g/dL for women and children and ≥ 12 g/dL for men; and platelet counts in patients with an intact spleen, depending on the baseline value, should approximately be doubled. Bone crises and bone pain but not irreversible skeletal damage will improve in most patients. Nonetheless, some features and some symptomatic patients apparently do not respond equally well and/or perhaps inadequately. The benefit for patients with the neuronopathic forms is primarily in improved visceral and hematological signs and symptoms. There are still several unresolved issues, the high per-unit cost being an important one, which have spurred the development of biosimilar enzymes as well as chaperone therapies currently in clinical trials

Symmetry-breaking waves and space-time modulation mechanisms in two-dimensional plane Poiseuille flow

We investigate two distinct scenarios of spatial modulation that are candidate mechanisms for streamwise localization of waves in two-dimensional plane Poiseuille flow. The first one stems from a symmetry-breaking bifurcation that disrupts the half-shift and reflect equivariance of Tollmien-Schlichting waves (TSW). A new state, an asymmetric TSW (ATSW), emerges from unstable lower-branch TSWs at subcritical Reynolds number and undergoes subharmonic Hopf bifurcations that lead to branches of asymmetric time-periodic space-modulated waves (MATSW). Streamwise modulation does not evolve into localization within the range of parameters explored. In breaking the last standing remnants of the reflectional symmetry about the channel midplane, ATSW and MATSW admit a bias toward either one of the channel walls, thus bearing a potential for explaining near-wall structures that are typical of developed turbulence. The second scenario follows the fate of a branch of time-periodic space-modulated TSWs (MTSW) initially discovered by Mellibovsky and Meseguer [J. Fluid Mech. 779, R1 (2015)]. We find that these waves can lead to localization but the mechanism is not new, as they do so through their connection, by means of a codimension-2 bifurcation point, with other known localizing MTSWs. The codimension-2 point is, however, responsible for the appearance of MTSWs that exclusively bridge upper-branch TSW-trains of different number of replicas. In this respect, these MTSWs possess all required properties that single them out as possible constituents of the strange saddle that governs domain-filling turbulent dynamics at high Reynolds numbers.Postprint (author's final draft

How Classical Economic Theory Fails to Explain the Gender Wage Gap, and How Sociology Fills That Gap

Why do economic models miss the mark in their analysis of the gender wage gap? This paper argues that conventional interpretation of the wage equation and that economic models typically overlook critical factors of social life that substantially affect the gender wage gap, and answers the question: What is the impact of certain social factors such as pay secrecy, and percent of women in legislation on wages? This paper aims to evaluate the differences in a model’s effectiveness if social measures are added. Through regression analysis of family level data on household heads and wives aggregated with state level social data, it was found that social variables positively impact men while negatively impacting women; however, results for women are not statistically significant

Transition to periodic behaviour of flow past a circular cylinder under the action of fluidic actuation in the transitional regime

This study focuses on the numerical investigation of the underlying mechanism of transition from chaotic to periodic dynamics of circular cylinder wake under the action of time-dependent fluidic actuation at the Reynolds number = 2000. The forcing is realized by blowing and suction from the slits located at ±90° on the top and bottom surfaces of the cylinder. The inverse period-doubling cascade is the underlying physical mechanism underpinning the wake transition from mild chaos to perfectly periodic dynamics in the spanwise-independent, time-dependent forcing at twice the natural vortex-shedding frequency.This work has been financed by the Spanish and Catalan Governments under grants FIS2016-77849-R and 2017-SGR-00785, respectively. The authors also thankfully acknowledge the computer resources at MareNostrum and Calendula accessed through grants RES-FI-2017-2-0020 and RES-FI-2017-3-0009, respectivelyPostprint (published version

Fold-pitchfork bifurcation for maps with Z(2) symmetry in pipe flow

This study aims to provide a better understanding of recently identified transition scenarios exhibited by traveling wave solutions in pipe flow. This particular family of solutions are invariant under certain reflectional symmetry transformations and they emerge from saddle-node bifurcations within a two-dimensional parameter space characterized by the length of the pipe and the Reynolds number. The present work precisely provides a detailed analysis of a codimension-two saddle-node bifurcation arising in discrete dynamical systems (maps) with Z2 symmetry. Normal form standard techniques are applied in order to obtain the reduced map up to cubic order. All possible bifurcation scenarios exhibited by this normal form are analyzed in detail. Finally, a qualitative comparison of these scenarios with the ones observed in the aforementioned hydrodynamic problem is provided.Postprint (published version