Non-equilibrium turbulent phenomena in the ?ow over a backward-facing ramp

Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.

Description of inverse energy cascade in homogeneous isotropic turbulence using an eigenvalue method

A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue method.We show a special isotropic turbulence,in which the initial condition is constructed by reversing the velocity field in space,i.e.,the time-reversed turbulence.It is shown that the product of eigenvalues of the rate-of-strain tensor can quantitatively describe the backward energy transfer process.This description is consistent to the velocity derivative skewness Sk.However,compared with Sk,it is easier to be obtained,and it is expected to be extended to anisotropic turbulence.Furthermore,this description also works for the resolved velocity field,which means that it can be used in engineering turbulent flows.The description presented here is desired to inspire future investigation for the modeling of the backward energy transfer process and lay the foundation for the accurate prediction of complex flows.

APOE-mediated suppression of the lncRNA MEG3 protects human cardiovascular cells from chronic inflammation

Dear Editor,Cardiovascular diseases(CVDs)are the leading cause of death world-wide.Thus,diagnosing and treating CVD remains at the forefront for clinicians while identifying targetable disease mechanisms in preclinical models are focus areas for researchers and drug developers(Cai et al.,2022a).The polymorphic protein apolipoprotein E(APOE),central to lipid transport and metabolism,is well-recognized for the role of its isoforms as important predictors for human cardiovascular disorders and neurodegenerative diseases(Tudorache et al.,2017).Plasma APOE is generated primarily from liver hepatocytes,accounting for around 75%of the APOE production from the whole body(Getz and Reardon,2009),and plays important functional roles in monocytes/macrophages,adipocytes,and the central nervous system(Kockx et al.,2018).However,despite the fact that APOE is widely expressed in different mammalian cells,studies on the functional roles of APOE mostly focus on its extracellular secreted form,and the specific effects of APOE,particularly intracellular form in cell types closely related to human cardiovascular diseases are therefore still poorly understood.

PARALLEL IMPLEMENTATIONS OF THE FAST SWEEPING METHOD

The fast sweeping method is an efficient iterative method for hyperbolic problems. It combines Gauss-Seidel iterations with alternating sweeping orderings. In this paper several parallel implementations of the fast sweeping method are presented. These parallel algorithms are simple and efficient due to the causality of the underlying partial different equations. Numerical examples are used to verify our algorithms.

Controlled synthesis of silver nanoparticles from polyoxometalates-immobilized poly(4-vinylpyridine) brushes

This contribution reports the immobilization of polyoxometalate(POM)into poly(4-vinyl pyridine)(P4 VP)brushes and the controlled reduction of silver ions,in-situ generating metal nanoparticles in the brushes.P4 VP brushes were straightforwardly created by UV-assisted photopolymerization of 4-vinyl pyridine(4VP)on silicon or glass substrates.Phosphotungstic acid(H3 PW12 O40),one of the most widely used Keggin-type POM was anchored onto these pyridine moieties through electrostatic interaction,leading to the P4 VP/POM hybrid brushes.The immobilized POM was further reduced to heteropolyblue,which could be used to generate silver nanoparticles in a controlled fashion.AFM,UV-vis and IR characterization indicate that P4 VP brushes not only provide an efficient platform in the controlled preparation of Ag nanoparticles,but also efficiently disperse and stabilize POM,thus preventing the aggregation of the generated Ag nanoparticles.

A COMPACT UPWIND SECOND ORDER SCHEME FOR THE EIKONAL EQUATION

We present a compact upwind second order scheme for computing the viscosity solution of the Eikonal equation. This new scheme is based on： 1. the numerical observation that classical first order monotone upwind schemes for the Eikonal equation yield numerical upwind gradient which is also first order accurate up to singularities; 2. a remark that partial information on the second derivatives of the solution is known and given in the structure of the Eikonal equation and can be used to reduce the size of the stencil. We implement the second order scheme as a correction to the well known sweeping method but it should be applicable to any first order monotone upwind scheme. Care is needed to choose the appropriate stencils to avoid instabilities.

ROBUST INEXACT ALTERNATING OPTIMIZATION FOR MATRIX COMPLETION WITH OUTLIERS

We investigate the problem of robust matrix completion with a fraction of observation corrupted by sparsity outlier noise.We propose an algorithmic framework based on the ADMM algorithm for a non-convex optimization,whose objective function consists of an l1 norm data fidelity and a rank constraint.To reduce the computational cost per iteration,two inexact schemes are developed to replace the most time-consuming step in the generic ADMM algorithm.The resulting algorithms remarkably outperform the existing solvers for robust matrix completion with outlier noise.When the noise is severe and the underlying matrix is ill-conditioned,the proposed algorithms are faster and give more accurate solutions than state-of-the-art robust matrix completion approaches.

Shipborne oceanic high-spectral-resolution lidar for accurate estimation of seawater depth-resolved optical properties

Lidar techniques present a distinctive ability to resolve vertical structure of optical properties within the upper water column at both day-and night-time.However,accuracy challenges remain for existing lidar instruments due to the ill-posed nature of elastic backscatter lidar retrievals and multiple scattering.Here we demonstrate the high performance of,to the best of our knowledge,the first shipborne oceanic high-spectral-resolution lidar(HSRL)and illustrate a multiple scattering correction algorithm to rigorously address the above challenges in estimating the depth-resolved diffuse attenuation coefficient Kd and the particulate backscattering coefficient bbp at 532 nm.HSRL data were collected during day-and night-time within the coastal areas of East China Sea and South China Sea,which are connected by the Taiwan Strait.Results include vertical profiles from open ocean waters to moderate turbid waters and first lidar continuous observation of diel vertical distribution of thin layers at a fixed station.The root-mean-square relative differences between the HSRL and coincident in situ measurements are 5.6%and 9.1%for Kd and bbp,respectively,corresponding to an improvement of 2.7-13.5 and 4.9-44.1 times,respectively,with respect to elastic backscatter lidar methods.Shipborne oceanic HSRLs with high performance are expected to be of paramount importance for the construction of 3D map of ocean ecosystem.

Preface--Special issue on“Modern Optimization and Applications 2018”

This special issue contains eight selected papers from the International Workshop on Modern Optimization and Applications,which was held over the three days,16-18 June 2018 at Academy of Mathematics and Systems Science,Chinese Academy of Sciences,Beijing.This conference brought together leading scientists,researchers,and practitioners from the world to exchange and shared ideas and approaches in using modern optimization techniques to model and solve real-world application problems from engineering,industry,and management.A prominent feature of this conference is the mixture of optimization theory,optimization methods,and practice of mathematical optimization.This conference provided a forum for researchers from academia to present their latest theoretical results and for practitioners from industry to describe their real-world applications,and discuss with participants the best way to construct suitable optimization models and how to find algorithms capable of solving these models.

Numerical Study of Surfactant-Laden Drop-Drop Interactions

In this paper,we numerically investigate the effects of surfactant on dropdrop interactions in a 2D shear flow using a coupled level-set and immersed interface approach proposed in(Xu et al.,J.Comput.Phys.,212(2006),590–616).We find that surfactant plays a critical and nontrivial role in drop-drop interactions.In particular,we find that the minimum distance between the drops is a non-monotone function of the surfactant coverage and Capillary number.This non-monotonic behavior,which does not occur for clean drops,is found to be due to the presence of Marangoni forces along the drop interfaces.This suggests that there are non-monotonic conditions for coalescence of surfactant-laden drops,as observed in recent experiments of Leal and co-workers.Although our study is two-dimensional,we believe that drop-drop interactions in three-dimensional flows should be qualitatively similar as the Maragoni forces in the near contact region in 3D should have a similar effect.

Gaussian Beam Summation for Diffraction in Inhomogeneous Media Based on the Grid Based Particle Method

We develop an efficient numerical method to compute single slit or double slit diffraction patterns from high frequency wave in inhomogeneous media.We approximate the high frequency asymptotic solution to the Helmholtz equation using the Eulerian Gaussian beam summation proposed in[20,21].The emitted rays from a slit are embedded in the phase space using an open segment.The evolution of this open curve is accurately computed using the recently developed Grid Based Particle Method[24]which results in a very efficient computational algorithm.Following the grid based particle method we proposed in[23,24],we represent the open curve or the open surface by meshless Lagrangian particles sampled according to an underlying fixed Eulerian mesh.The end-points of the open curve are tracked explicitly and consistently with interior particles.To construct the overall wavefield,each of these sampling particles also carry necessary quantities that are obtained by solving advection-reaction equations.Numerical experiments show that the resulting method can model diffraction patterns in inhomogeneous media accurately,even in the occurrence of caustics.