A semi-explicit multi-step method for solving incompressible navier-stokes equations

The fractional step method is a technique that results in a computationally-efficient implementation of Navier–Stokes solvers. In the finite element-based models, it is often applied in conjunction with implicit time integration schemes. On the other hand, in the framework of finite difference and finite volume methods, the fractional step method had been successfully applied to obtain predictor-corrector semi-explicit methods. In the present work, we derive a scheme based on using the fractional step technique in conjunction with explicit multi-step time integration within the framework of Galerkin-type stabilized finite element methods. We show that under certain assumptions, a Runge–Kutta scheme equipped with the fractional step leads to an efficient semi-explicit method, where the pressure Poisson equation is solved only once per time step. Thus, the computational cost of the implicit step of the scheme is minimized. The numerical example solved validates the resulting scheme and provides the insights regarding its accuracy and computational efficiency.Peer ReviewedPostprint (published version

An explicit/implicit Runge–Kutta-based PFEM model for the simulation of thermally coupled incompressible flows

The final publication is available at Springer via http://dx.doi.org/10.1007/s40571-019-00229-0A semi-explicit Lagrangian scheme for the simulation of thermally coupled incompressible flow problems is presented. The model relies on combining an explicit multi-step solver for the momentum equation with an implicit heat equation solver. Computational cost of the model is reduced via application of an efficient strategy adopted for the solution of momentum/continuity system by the authors in their previous work. The applicability of the method to solving thermo-mechanical problems is studied via various numerical examples.Peer ReviewedPostprint (author's final draft

Evolution of atmospheric connectivity in the 20th century

We aim to study the evolution of the upper atmosphere connectivity over the 20th century as well as to distinguish the oceanically forced component from the atmospheric internal variability. For this purpose we build networks from two different reanalysis data sets using both linear and nonlinear statistical similarity measures to determine the existence of links between different regions of the world in the two halves of the last century. We furthermore use symbolic analysis to emphasize intra-seasonal, intra-annual and inter-annual timescales. Both linear and nonlinear networks have similar structures and evolution, showing that the most connected regions are in the tropics over the Pacific Ocean. Also, the Southern Hemisphere extratropics have more connectivity in the first half of the 20th century, particularly on intra-annual and intra-seasonal timescales. Changes over the Pacific main connectivity regions are analyzed in more detail. Both linear and nonlinear networks show that the central and western Pacific regions have decreasing connectivity from early 1900 up to about 1940, when it starts increasing again until the present. The inter-annual network shows a similar behavior. However, this is not true of other timescales. On intra-annual timescales the minimum connectivity is around 1956, with a negative (positive) trend before (after) that date for both the central and western Pacific. While this is also true of the central Pacific on intra-seasonal timescales, the western Pacific shows a positive trend during the entire 20th century. In order to separate the internal and forced connectivity networks and to study their evolution through time, an ensemble of atmospheric general circulation model outputs is used. The results suggest that the main connectivity patterns captured in the reanalysis networks are due to the oceanically forced component, particularly on inter-annual timescales. Moreover, the atmospheric internal variability seems to play an important role in determining the intra-seasonal timescale networks

A Unified arbitrary lagrangian-eulerian model for fluid-structure interaction problems involving flows in flexible channels

In this work a finite element-based model for analyzing incompressible flows in flexible channels is presented. The model treats the fluid-solid interaction problem in a monolithic way, where the governing equations for both sub-domains are solved on a single moving grid taking advantage of an arbitrary Lagrangian/Eulerian framework (ALE). The unified implementation of the governing equations for both sub-domains is developed, where these are distinguished only in terms of the mesh-moving strategy and the constitutive equation coefficients. The unified formulation is derived considering a Newtonian incompressible fluid and a hypoelastic solid. Hypoelastic constitutive law is based on the strain rate and thus naturally facilitates employing velocity as a kinematic variable in the solid. Unifying the form of the governing equations and defining a semi-Lagrangian interface mesh-motion algorithm , one obtains the coupled problem formulated in terms of a unique kinematic variable. Resulting monolithic system is characterized by reduced variable heterogeneity resembling that of a single-media problem. The model used in conjunction with algebraic multigrid linear solver exhibits attractive convergence rates. The model is tested using a 2D and a 3D example.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The authors acknowledge financial support from the Ministerio de Ciencia, Innovacion e Universidades of Spain via the “Severo Ochoa” Programme for Centres of Excellence in R&D (Referece: CEX2018-000797-S) as well as via AMADEUS Project Grant (Reference: PGC2018-101655-B-I00).Peer ReviewedPostprint (published version

Steady-state stabilization due to random delays in maps with self-feedback loops and in globally delayed-coupled maps

We study the stability of the fixed-point solution of an array of mutually coupled logistic maps, focusing on the influence of the delay times, $\tau_{ij}$, of the interaction between the $i$th and $j$th maps. Two of us recently reported [Phys. Rev. Lett. {\bf 94}, 134102 (2005)] that if $\tau_{ij}$ are random enough the array synchronizes in a spatially homogeneous steady state. Here we study this behavior by comparing the dynamics of a map of an array of $N$ delayed-coupled maps with the dynamics of a map with $N$ self-feedback delayed loops. If $N$ is sufficiently large, the dynamics of a map of the array is similar to the dynamics of a map with self-feedback loops with the same delay times. Several delayed loops stabilize the fixed point, when the delays are not the same; however, the distribution of delays plays a key role: if the delays are all odd a periodic orbit (and not the fixed point) is stabilized. We present a linear stability analysis and apply some mathematical theorems that explain the numerical results.Comment: 14 pages, 13 figures, important changes (title changed, discussion, figures, and references added

High heat resistance can be deceiving: dripping behavior of polyamide 4.6 in fire

Polyamide 4.6 (PA46) is a high-heat-resistant polymer, but it has no dripping resistance under fire. Three commercial grades of PA46 are investigated under UL 94 vertical fire test conditions. Their performances are discussed based on the materials' structural, thermal, and rheological properties. PA46 presents flaming drops, whereas dripping is prevented in the flame-retarded PA46. Friction-modified PA46 has increased flaming dripping. Temperature profiles of the specimens under fire and the temperature of the drops are measured by thermocouples. A UL 94 vertical test configuration consisting of two flame applications is designed to assess the quantitative dripping behavior of the set of materials by the particle finite element method (PFEM). Polymer properties (activation energy and Arrhenius coefficient of decomposition, char yield, density, effective heat of combustion, heat of decomposition, specific heat capacity, and thermal conductivity) in addition to rheological responses in high temperatures are estimated and measured as input parameters for the simulations. The dripping behavior obtained by simulated materials corresponds with the experimental results in terms of time and drop size. A consistent picture of the interplay of the different phenomena controlling dripping under fire appears to deliver a better understanding of the role of different materials’ properties.The authors thank the National Council of Technological and Scientific Development from Brazil (CNPq) for its financial support (205385/2014-1). A.T.S.D. thanks the TU Berlin for the support with a STIBET degree completion grant.Peer ReviewedPostprint (published version

The implementation of mindfulness in healthcare Systems: a theoretical analysis

Objective: Evidence regarding the efficacy of mindfulness-based interventions (MBIs) is increasing exponentially; however, there are still challenges to their integration in healthcare systems. Our goal is to provide a conceptual framework that addresses these challenges in order to bring about scholarly dialog and support healthmanagers and practitioners with the implementation of MBIs in healthcare. Method: This is an opinative narrative review based on theoretical and empirical data that address key issues in the implementation ofmindfulness in healthcare systems, such as the training of professionals, funding and costs of interventions, cost effectiveness and innovative delivery models. Results: Weshowthat even in the United Kingdom,where mindfulness has a high level of implementation, there is a high variability in the access toMBIs. In addition,we discuss innovative approaches based on 'complex interventions,' 'stepped-care' and 'low intensity-high volume' concepts that may prove fruitful in the development and implementation of MBIs in national healthcare systems, particularly in Primary Care. Conclusion: In order to better understand barriers and opportunities for mindfulness implementation in healthcare systems, it is necessary to be aware that MBIs are 'complex interventions,' which require innovative approaches and delivery models to implement these interventions in a cost-effective and accessible way

The structure of Synechococcus elongatus enolase reveals key aspects of phosphoenolpyruvate binding

A structure-function characterization of Synechococcus elongatus enolase (SeEN) is presented, representing the first structural report on a cyanobacterial enolase. X-ray crystal structures of SeEN in its apoenzyme form and in complex with phosphoenolpyruvate are reported at 2.05 and 2.30 Å resolution, respectively. SeEN displays the typical fold of enolases, with a conformationally flexible loop that closes the active site upon substrate binding, assisted by two metal ions that stabilize the negatively charged groups. The enzyme exhibits a catalytic efficiency of 1.2 × 105 M -1s-1for the dehydration of 2-phospho-d-glycerate, which is comparable to the kinetic parameters of related enzymes. These results expand the understanding of the biophysical features of these enzymes, broadening the toolbox for metabolic engineering applications.Fil: Gonzalez, Javier Marcelo. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Martí Arbona, Ricardo. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Chen, Julian C. H.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Unkefer, Clifford. Los Alamos National High Magnetic Field Laboratory; Estados Unido

Conformational changes on substrate binding revealed by structures of Methylobacterium extorquens malate dehydrogenase

Three high-resolution X-ray crystal structures of malate dehydrogenase (MDH; EC 1.1.1.37) from the methylotroph Methylobacterium extorquens AM1 are presented. By comparing the structures of apo MDH, a binary complex of MDH and NAD+, and a ternary complex of MDH and oxaloacetate with ADP-ribose occupying the pyridine nucleotide-binding site, conformational changes associated with the formation of the catalytic complex were characterized. While the substrate-binding site is accessible in the enzyme resting state or NAD+-bound forms, the substrate-bound form exhibits a closed conformation. This conformational change involves the transition of an α-helix to a 310-helix, which causes the adjacent loop to close the active site following coenzyme and substrate binding. In the ternary complex, His284 forms a hydrogen bond to the C2 carbonyl of oxaloacetate, placing it in a position to donate a proton in the formation of (2S)-malate.Crystal structures of apo malate dehydrogenase (MDH) from Methylobacterium extorquens, MDH bound to NAD+, and MDH with oxaloacetate and ADP-ribose revealed conformational changes, closing the active site upon coenzyme and substrate binding. In the ternary complex, His284 is in position to donate a proton in the formation of (2S)-malate.Fil: Gonzalez, Javier Marcelo. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Marti Arbona, R.. Bioscience Division, Los Alamos National Laboratory; Estados UnidosFil: Chen, J. C. H.. Bioscience Division, Los Alamos National Laboratory; Estados UnidosFil: Broom Peltz, B.. Bioscience Division, Los Alamos National Laboratory; Estados UnidosFil: Unkefer, C. J.. Bioscience Division, Los Alamos National Laboratory; Estados Unido

Fast fluid–structure interaction simulations using a displacement-based finite element model equipped with an explicit streamline integration prediction

We propose here a displacement-based updated Lagrangian fluid model developed to facilitate a monolithic coupling with a wide range of structural elements described in terms of displacements. The novelty of the model consists in the use of the explicit streamline integration for predicting the end-of-step configuration of the fluid domain. It is shown that this prediction considerably alleviates the time step size restrictions faced by the former Lagrangian models due to the possibility of an element inversion within one time step. The method is validated and compared with conventional approaches using three numerical examples. Time step size and corresponding Courant numbers leading to optimal behavior in terms of computational efficiency are identified.This work has been supported under the auspices of the FPDI-2013-18471 grant of the Spanish Ministerio de Economia y Competitividad as well as partially funded by the COMETAD project of the National RTD Plan (ref. MAT2014-60435-C2-1-R) of the mentioned ministry.Peer ReviewedPostprint (author's final draft