Diel Patterns in the Composition and Activity of Planktonic Microbes in a Subtropical Bay

Planktonic microbes play a crucial role in the matter transformation and energy transfer of marine ecosystems.Marine microbial communities are profoundly influenced by various environmental factors,and their variations are typically investigated in a time-dependent manner.However,studies conducted on a monthly or annual basis do not offer sufficient temporal resolution to reveal changes that can occur on an hourly basis.We conducted a high-resolution time-series study using amplicon sequencing on seawater samples taken at 2-h intervals over a 3-d period from the subtropical Daya Bay to investigate changes in the microbial community composition and activity.The results showed that 46.8%of the microbial rRNA sequences exhibited circadian rhythms,including phytoplankton(e.g.,Bacillariophyta,Cryptophyta,and Dinophyceae),heterotrophic bacteria(e.g.,Actinomarinaceae,Flavobacteriaceae,and SAR11_clade),and zooplankton(e.g.,Bestiolina and Phyllopharyngea).The genera of Bacillariophyta(e.g.,Chaetoceros and Pseudo-nitzschia)exhibited higher activity than those of Chlorophyta(e.g.,Micromonas).A similar trend was observed for zooplankton,where Choanozoa(e.g.,Copepoda)showed a strong circadian rhythm in abundance whereas Ciliophora(e.g.,Pithites)were more active.Light intensity and tides were identified as the driving factors behind the periodic succession and activity of the heterotrophic bacteria and phytoplankton with the exception of picocyanobacteria,which were mainly influenced by fluctuations in temperature,nutrients,and salinity.These high-resolution time-dependent observations showed that,despite the dynamic coastal environment,the periodic changes in the microbial community and activity were distinct and phylogenetically conserved.The findings may help in the development of ecosystem models for predicting microbial abundance and activity in rapidly changing coastal and estuary environments.

A unified implicit scheme for kinetic model equations. Part I. Memory reduction technique

A memory reduction technique is proposed for solving stationary kinetic model equations. As implied by an integral solution of the stationary kinetic equation, a velocity distribution function can be reconstructed from given macroscopic variables. Based on this fact, we propose a technique to reconstruct distribution function at discrete level, and employ it to develop an implicit numerical method for kinetic equations. The new implicit method only stores the macroscopic quantities which appear in the collision term, and does not store the distribution functions. As a result, enormous memory requirement for solving kinetic equations is totally relieved. Several boundary conditions, such as, inlet, outlet and isothermal boundaries, are discussed. Some numerical tests demonstrate the validity and efficiency of the technique.The new implicit solver provides nearly identical solution as the explicit kinetic solver, while the memory requirement is on the same order as the Navier–Stokes solver.

A Comparison and Unification of Ellipsoidal Statistical and Shakhov BGK Models

The Ellipsoidal Statistical model(ES-model)and the Shakhov model(S-model)were constructed to correct the Prandtl number of the original BGK model through the modification of stress and heatflux.With the introduction of a new pa-rameter to combine the ES-model and S-model,a generalized kinetic model can be developed.This new model can give the correct Navier-Stokes equations in the con-tinuumflow regime.Through the adjustment of the new parameter,it provides abun-dant dynamic effect beyond the ES-model and S-model.Changing the free parameter,the physical performance of the new model has been tested numerically.The unified gas kinetic scheme(UGKS)is employed for the study of the new model.In transitionflow regime,many physical problems,i.e.,the shock structure and micro-flows,have been studied using the generalized model.With a careful choice of the free parameter,good results can be achieved for most test cases.Due to the property of the Boltz-mann collision integral,the new parameter in the generalized kinetic model cannot be fully determined.It depends on the specific problem.Generally speaking,the S-model predicts more accurate numerical solutions in most test cases presented in this paper than the ES-model,while ES-model performs better in the cases where theflow is mostly driven by temperature gradient,such as a channelflow with large boundary temperature variation at high Knudsen number.

核糖体RNA测序技术在海洋微生物多样性研究中的应用

海洋微生物总数高达10^30个,在海洋生态系统中发挥着驱动能量物质循环和维持生态平衡的重要作用。深入研究海洋微生物多样性有助于理解海洋生态系统运行机理、应对全球海洋生态危机,以及开发海洋微生物资源。由于目前可培养分离的海洋微生物种类极少,极大限制了对海洋微生物群落、丰度和生理生态特征的研究。核糖体RNA测序技术以较低的成本,根据遗传信息差异对微生物快速准确地进行分类鉴定,揭示群落结构、评估进化和生态学关系。近年来基于核糖体RNA序列测序分析的海洋微生物学研究随着测序技术本身的快速优化,在发现海洋微生物新类群,揭示海洋微生物生态规律,分析海洋微生物进化关系,以及与海洋微生物相关的代谢产物开发和海洋生态治理等研究中取得显著进展。本综述详细介绍了核糖体RNA序列测序技术的原理,各代测序技术在海洋微生物多样性研究中的应用,以及多种建库和测序技术的有机结合。最后对研究不同海洋微生物多样性问题提供了测序方案的建议和展望,以期为核糖体RNA测序技术在海洋微生物多样性研究中的应用提供参考。

A Well-Balanced Kinetic Scheme for Gas Dynamic Equations under Gravitational Field

In this paper,a well-balanced kinetic scheme for the gas dynamic equations under gravitational field is developed.In order to construct such a scheme,the physical process of particles transport through a potential barrier at a cell interface is considered,where the amount of particle penetration and reflection is evaluated according to the incident particle velocity.This work extends the approach of Perthame and Simeoni for the shallow water equations[Calcolo,38(2001),pp.201-231]to the Euler equations under gravitational field.For an isolated system,this scheme is probably the only well-balanced method which can precisely preserve an isothermal steady state solution under time-independent gravitational potential.A few numerical examples are used to validate the above approach.

A Three Dimensional Gas-Kinetic Scheme with Moving Mesh for Low-Speed Viscous Flow Computations

The paper introduces the gas-kinetic scheme for three-dimensional(3D)flow simulation.First,under a unified coordinate transformation,the 3D gaskinetic BGK equation is transformed into a computational space with arbitrary mesh moving velocity.Second,based on the Chapman-Enskog expansion of the kinetic equation,a local solution of gas distribution function is constructed and used in a finite volume scheme.As a result,a Navier-Stokes flow solver is developed for the low speed flow computation with dynamical mesh movement.Several test cases are used to validate the 3D gas-kinetic method.The first example is a 3D cavity flow with up-moving boundary at Reynolds number 3200,where the periodic solutions are compared with the experimental measurements.Then,the flow evolution inside a rotating 3D cavity is simulated with the moving mesh method,where the solution differences between 2D and 3D simulation are explicitly presented.Finally,the scheme is applied to the falling plate study,where the unsteady plate tumbling motion inside water tank has been studied and compared with the experimental measurements.