Dynamics of self-organizing single-line particle trains in the channel flow of a power-law fluid

The formation of self-organizing single-line particle train in a channel flow of a power-law fluid is studied using the lattice Boltzmann method with power-law index 0.6≤n≤1.2,particle volume concentration 0.8%≤Φ≤6.4%,Reynolds number 10≤Re≤100,and blockage ratio 0.2≤k≤0.4.The numerical method is validated by comparing the present results with the previous ones.The effect n,Φ,Re and k on the interparticle spacing and parallelism of particle train is discussed.The results showed that the randomly distributed particles would migrate towards the vicinity of the equilibrium position and form the ordered particle train in the power-law fluid.The equilibrium position of particles is closer to the channel centerline in the shear-thickening fluid than that in the Newtonian fluid and shear-thinning fluid.The particles are not perfectly parallel in the equilibrium position,hence IH is used to describe the inclination of the line linking the equilibrium position of each particle.When self-organizing single-line particle train is formed,the particle train has a better parallelism and hence benefit for particle focusing in the shearthickening fluid at highΦ,low Re and small k.Meanwhile,the interparticle spacing is the largest and hence benefit for particle separation in the shear-thinning fluid at lowΦ,low Re and small k.

Large eddy simulation of a planar jet flow with nanoparticle coagulation

Coagulation and growth of nanoparticles subject to large coherent structures in a planar jet has been explored by using large eddy simulation. The particle field is obtained by employing a moment method to approximate the nanoparticle general dynamic equa- tion. An incompressible fluid containing particles of 1 nm in diameter is projected into a particle-free ambient. The results show that the coherent structures dominate the evolution of the nanoparticle number intensity, diameter and polydispersity distributions as the jet develops. In addition, the coherent structures act to increase the diffusion of particles, and the vortex rolling-up makes the particles distributing more irregularly while the vortex pairing causes particle distributions to become uniform. As the jet travels downstream, the time-averaged particle number concentration becomes lower in the jet core and higher in the outskirts, whereas the time- averaged particle mass over the entire flow field maintains unaltered, and the time-averaged particle diameter and geometric standard deviations grow and reach their maximum on the interface of the jet region and the ambient.

Estimated biomass carbon in thinned Cunninghamia lanceolate plantations at different stand-ages

Chinese fir(Cunninghamia lanceolate[Lamb.]Hook.)is a fast-growing species which is not only important as a timber-supplier,but also as an available sink for carbon(C)storage in biomass.Stand age and density are two critical factors that can determine tree C sequestration as interrelated drivers through natural self-thinning.C.lanceolate were planted using 1-year-old bare-root seedlings at the initial density of 1800 stems ha^(-1)in a 15-ha montane area of Hunan Province,China in 1987.The plantation was thinned twice 10 and 20 years after planting to leave trees of437.5±26.6,675.0±155.2 and 895.8±60.1 stems ha^(-1)as low,medium,and high densities,respectively.Tree height and diameter at breast height(DBH)were measured every2 years beginning from 23 years(2009)to 31 years(2018)after establishment,timber volume(TV)and biomass C were estimated accordingly.We did not find any interactive effect of age and density on any variables except for height.Both TV and biomass C increased with stand age or decreased in higher densities.The allometric heightDBH relationship can be fitted by an exponential risingto-maximum model with higher maximum value over time.The decline of biomass C along density fit with the inverse first-order polynomial model which indicated that at least1300-1500 stems ha^(-1)may be needed to maximize TV and biomass C for a longer term over 20 years.Therefore,to control the density to a reasonable level,over 1300 stems ha^(-1)in a rotation over 20 years old will be practical for tree biomass C in Chinese fir plantations.

Solution of general dynamic equation for nanoparticles in turbulent flow considering fluctuating coagulation

A new averaged general dynamic equation （GDE） for nanoparticles in the turbulent flow is derived by considering the combined effect of convection, Brownian diffusion, turbulent diffusion, turbulent coagulation, and fluctuating coagulation. The equation is solved with the Taylor-series expansion moment method in a turbulent pipe flow. The experiments are performed. The numerical results of particle size distribu- tion correlate well with the experimental data. The results show that, for a turbulent nanoparticulate flow, a fluctuating coagulation term should be included in the averaged particle GDE. The larger the Schmidt number is and the lower the Reynolds number is, the smaller the value of ratio of particle diameter at the outlet to that at the inlet is. At the outlet, the particle number concentration increases from the near-wall region to the near-center region. The larger the Schmidt number is and the higher the Reynolds num- ber is, the larger the difference in particle number concentration between the near-wall region and near-center region is. Particle polydispersity increases from the near-center region to the near-wall region. The particles with a smaller Schmidt number and the flow with a higher Reynolds number show a higher polydispersity. The degree of particle polydispersity is higher considering fluctuating coagulation than that without considering fluctuating coagulation.

The osmolyte-producing endophyte Streptomyces albidoflavus OsiLf-2 induces drought and salt tolerance in rice via a multi-level mechanism

Drought and salinity are major environmental stresses that impair crop growth and productivity worldwide. Improving drought and salt tolerance of crops with microbial mutualists is an effective and environmentally sound strategy to meet the demands of the ever-growing world population. In the present study, we found that the Streptomyces albidoflavus Osi Lf-2, a moderately salt-tolerant endophytic actinomycete, produced abundant osmolytes, including proline, polysaccharides, and ectoine. Inoculation with Osi Lf-2 increased the osmotic-adjustment ability of the rice host by increasing the proline content(by250.3% and 49.4%) and soluble sugar(by 20.9% and 49.4%) in rice under drought and salt conditions, relative to the uninoculated control. Osi Lf-2 increased stress responses in the rice host at the physiological and biochemical levels(photosynthesis efficiency, osmolytes and antioxidant content), and the gene level(osmolytes synthesis, stress-responsive and ion-transport related genes), raising rice yields under both greenhouse and saline–alkaline soil conditions. The use of endophytic actinomycetes offers a promising biotechnological approach to developing stress-tolerant plants.

Numerical prediction of fiber motion in a branching channel flow of fiber suspensions

Fiber orientation and dispersion in the dilute fiber suspension that flows through a T-shaped branching channel are simulated numerically based on the slender-body theory. The simulated results are consistent qualitatively with the experimental data available in the literature. The results show that the spatial distribution of fibers is dependent on the fiber aspect ratio, but has no relation with the volume fraction of fiber. The content ratio of fibers near the upper wall increases monotonically with an increasing Re number, and the situation is reverse for the region near the bottom wall. The orientation of fibers depends on Re number, however, the function of fiber volume fraction and aspect ratio is negligible. The fibers near the wall and in the central region of the channel align along the flow direction at all times, but the fibers in the other parts of the channel tend to align along the flow direction only in the downstream region.

A review on the flow instability of nanofluids

Nanofluid flow occurs in extensive applications, and hence has received widespread attention. The transition of nanofluids from laminar to turbulent flow is an important issue because of the differences in pressure drop and heat transfer between laminar and turbulent flow. Nanofluids will become unstable when they depart from the thermal equilibrium or dynamic equilibrium state. This paper conducts a brief review of research on the flow instability of nanofluids, including hydrodynamic instability and thermal instability. Some open questions on the subject are also identified.

Distribution of non-spherical nanoparticles in turbulent flow of ventilation chamber considering fluctuating particle number density

The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration.Some results are compared with the experimental data.The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable,and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow.The changes of the particle number concentration M_(0) and the geometric mean diameter dg are more obvious in the core area of the jet,but less obvious in other areas.With the increase in the initial particle number concentration m00,the values of M_(0) and the standard deviation of the particle sizeσdecrease,but the value of d_(g) increases.The decrease in the initial particle diameter leads to the reduction of M_(0) andσand the increase in d_(g).With the increase in the Reynolds number,particles have few chances of collision,and hence the coagulation rate is reduced,leading to the increase in M_(0) andσand the decrease in d_(g).

Mixture flow of particles and power-law fluid in round peristaltic tube

The erythrocyte and blood flowing in the blood vessel can be treated as the two-phase flow of the mixture of particles and a power-law fluid in a peristaltic tube.In the present work, the peristaltic transport of a power-law fluid and the suspension of particles in a tube is investigated by a perturbation method using the long wavelength approximation. The influence of different parameters on the velocity profile and streamlines is explored. Results show that there is a deflection of the flow field when the power-law index n = 0.5 or 1.5 compared with the Newtonian fluid where the trapping zone is symmetric to a certain cross section. The flux rate and reflux of the material are identified,and the conditions under which the reflux appears are determined. Moreover, a reflux phenomenon occurs near the wall. The trapping zone is related to not only the tube geometry and the flow flux but also the fluid properties. Both the length and width of the trapping zone increase with an increase in θ or φ. The trapping zone is more difficult to produce in the shear-thinning fluid than the shear-thickening fluid.

Flow instability of nanofuilds in jet

The flow instability of nanofluids in a jet is studied numerically under various shape factors of the velocity profile, Reynolds numbers, nanoparticle mass loadings,Knudsen numbers, and Stokes numbers. The numerical results are compared with the available theoretical results for validation. The results show that the presence of nanoparticles enhances the flow stability, and there exists a critical particle mass loading beyond which the flow is stable. As the shape factor of the velocity profile and the Reynolds number increase, the flow becomes more unstable. However, the flow becomes more stable with the increase of the particle mass loading. The wavenumber corresponding to the maximum of wave amplification becomes large with the increase of the shape factor of the velocity profile, and with the decrease of the particle mass loading and the Reynolds number. The variations of wave amplification with the Stokes number and the Knudsen number are not monotonic increasing or decreasing, and there exists a critical Stokes number and a Knudsen number with which the flow is relatively stable and most unstable,respectively, when other parameters remain unchanged. The perturbation with the first azimuthal mode makes the flow unstable more easily than that with the axisymmetric azimuthal mode. The wavenumbers corresponding to the maximum of wave amplification are more concentrated for the perturbation with the axisymmetric azimuthal mode.

A review of research on nanoparticulate flow undergoing coagulation

Nanoparticulate flows occur in a wide range of natural phenomena and engineering applications and, hence, have attracted much attention. The purpose of the present paper is to provide a review of the research conducted over the last decade. The research covered relates to the Brownian coagulation of monodisperse and polydisperse particles, the Taylor-series expansion method of moment, and nanoparticle distributions due to coagulation in pipe and channel flow, jet flow, and the mixing layer and in the process of flame synthesis and deposition.

Transcriptome-wide profiling of RNA N^(4)-cytidine acetylation in Arabidopsis thaliana and Oryza sativa

Acetylation of N^(4)-cytidine(ac^(4)C)has recently been discovered as a novel modification of mRNA.RNA ac^(4)C modification has been shown to be a key regulator of RNA stability,RNA translation,and the thermal stress response.However,its existence in eukaryotic mRNAs is still controversial.In plants,the existence,distribution pattern,and potential function of RNA ac^(4)C modification are largely unknown.Here we report the presence of ac^(4)C in the mRNAs of both Arabidopsis thaliana and rice(Oryza sativa).By comparing two ac^(4)C sequencing methods,we found that RNA immunoprecipitation and sequencing(acRIP-seq),but not ac^(4)C sequencing,was suitable for plant RNA ac^(4)C sequencing.We present transcriptome-wide atlases of RNA ac^(4)C modification in A.thaliana and rice mRNAs obtained by acRIP-seq.Analysis of the distribution of RNA ac^(4)C modifications showed that ac^(4)C is enriched near translation start sites in rice mRNAs and near translation start sites and translation end sites in Arabidopsis mRNAs.The RNA ac^(4)C modification level is positively correlated with RNA half-life and the number of splicing variants.Similar to that in mammals,the translation efficiency of ac^(4)C target genes is significantly higher than that of other genes.Our in vitro translation results confirmed that RNA ac^(4)C modification enhances translation efficiency.We also found that RNA ac^(4)C modification is negatively correlated with RNA structure.These results suggest that ac^(4)C is a conserved mRNA modification in plants that contributes to RNA stability,splicing,translation,and secondary structure formation.

New formula for drag coefficient of cylindrical particles

The drag force on a cylindrical particle is calculated using lattice Boltzmann method. The results show that the drag coefficient of a particle with different orientation angles decreases with increasing Reynolds number. When the principal axis of the particle is parallel to flow, the drag coefficient is much larger than that of others and decreases fastest with increasing Reynolds number, which becomes more obvious with increasing particle aspect ratio. When the principal axis of the particle is inclined to flow, the drag coefficient is nearly the same for different particle aspect ratios. In the case of flow with small Reynolds number （Re〈 100）, the drag coefficient decreases with increasing orientation angle at different aspect ratios and Reynolds numbers. The drag coefficient is more sensitive to particle orientation angle when the particle orientation angle is small and the aspect ratio is large. Finally, a new correlation formula for the drag coefficient of cylindrical particle is established, with which the drag force on a cylindrical particle can be directly calculated based on the Reynolds number, particle aspect ratio and orientation angle.

Applications of toxin-antitoxin systems in synthetic biology

Toxin-antitoxin(TA)systems are ubiquitous in bacteria and archaea.Most are composed of two neighboring genetic elements,a stable toxin capable of inhibiting crucial cellular processes,including replication,transcrip-tion,translation,cell division and membrane integrity,and an unstable antitoxin to counteract the toxicity of the toxin.Many new discoveries regarding the biochemical properties of the toxin and antitoxin components have been made since the first TA system was reported nearly four decades ago.The physiological functions of TA systems have been hotly debated in recent decades,and it is now increasingly clear that TA systems are important immune systems in prokaryotes.In addition to being involved in biofilm formation and persister cell formation,these modules are antiphage defense systems and provide host defenses against various phage infec-tions via abortive infection.In this review,we explore the potential applications of TA systems based on the recent progress made in elucidating TA functions.We first describe the most recent classification of TA systems and then introduce the biochemical functions of toxins and antitoxins,respectively.Finally,we primarily focus on and devote considerable space to the application of TA complexes in synthetic biology.

FKF1 F-box protein promotes flowering in part by negatively regulating DELLA protein stability under long-day photoperiod in Arabidopsis^FA

FLAVIN-BINDING KELCH REPEAT F-BOX 1(FKF1)encodes an F-box protein that regulates photoperiod flowering in Arabidopsis under long-day conditions(LDs).Gibberellin(GA)is also important for regulating flowering under LDs.However,how FKF1 and the GA pathway work in concert in regulating flowering is not fully understood.Here,we showed that the mutation of FKF1 could cause accumulation of DELLA proteins,which are crucial repressors in GA signaling pathway,thereby reducing plant sensitivity to GA in flowering.Both in vitro and in vivo biochemical analyses demonstrated that FKF1 directly interacted with DELLA proteins.Furthermore,we showed that FKF1 promoted ubiquitination and degradation of DELLA proteins.Analysis of genetic data revealed that FKF1 acted partially through DELLAs to regulate flowering under LDs.In addition,DELLAs exerted a negative feedback on FKF1 expression.Collectively,these findings demonstrate that FKF1 promotes flowering partially by negatively regulating DELLA protein stability under LDs,and suggesting a potential mechanism linking the FKF1 to the GA signaling DELLA proteins.

An analytical solution for the population balance equation using a moment method

Brownian coagulation is the most important inter-particle mechanism affecting the size distribution of aerosols. Analytical solutions to the governing population balance equation （PBE） remain a challenging issue. In this work, we develop an analytical model to solve the PBE under Brownian coagulation based on the Taylor-expansion method of moments. The proposed model has a clear advantage over conventional asymptotic models in both precision and efficiency. We first analyze the geometric standard deviation （GSD） of aerosol size distribution. The new model is then implemented to determine two analytic solu- tions, one with a varying GSD and the other with a constant GSD, The varying solution traces the evolution of the size distribution, whereas the constant case admits a decoupled solution for the zero and second moments, Both solutions are confirmed to have the same precision as the highly reliable numerical model, implemented by the fourth-order Runge-Kutta algorithm, and the analytic model requires significantly less computational time than the numerical approach. Our results suggest that the proposed model has great potential to replace the existing numerical model, and is thus recommended for the study of physical aerosol characteristics, especially for rapid predictions of haze formation and evolution,

A LB-DF/FD Method for Particle Suspensions

In this paper, we propose a lattice Boltzmann (LB) method coupled with adirect-forcing fictitious domain (DF/FD) method for the simulation of particle suspensions. This method combines the good features of the LB and the DF/FD methodsby using two unrelated meshes, namely, an Eulerian mesh for the flow domain and aLagrangian mesh for the solid domain, which avoids the re-meshing procedure anddoes not need to calculate the hydrodynamic forces at each time step. The non-slipboundary condition is enforced by introducing a forcing term into the lattice Boltzmann equation, which preserves all remarkable advantages of the LBM in simulatingfluid flows. The present LB-DF/FD method has been validated by comparing its results with analytical results and previous numerical results for a single circular particleand two circular particles settling under gravity. The interaction between particle andwall, the process of drafting-kissing-tumbling (DKT) of two settling particles will bedemonstrated. As a manifestation of the efficiency of the present method, the settlingof a large number (128) of circular particles is simulated in an enclosure.

Direct Numerical Simulation of Multiple Particles Sedimentation at an Intermediate Reynolds Number

In this work the previously developed Lattice Boltzmann-Direct Forcing/Fictitious Domain(LB-DF/FD)method is adopted to simulate the sedimentation of eight circular particles under gravity at an intermediate Reynolds number of about 248.The particle clustering and the resulting Drafting-Kissing-Tumbling(DKT)motion which takes place for the first time are explored.The effects of initial particleparticle gap on the DKT motion are found significant.In addition,the trajectories of particles are presented under different initial particle-particle gaps,which display totally three kinds of falling patterns provided that no DKT motion takes place,i.e.the concave-down shape,the shape of letter“M”and“in-line”shape.Furthermore,the lateral and vertical hydrodynamic forces on the particles are investigated.It has been found that the value of Strouhal number for all particles is the same which is about 0.157 when initial particle-particle gap is relatively large.The wall effects on falling patterns and particle expansions are examined in the final.

Ectopic expression of fungal EcGDH improves nitrogen assimilation and grain yield in rice

NADP（H）-dependent glutamate dehydrogenases（GDH） in lower organisms have stronger ammonium affinity than those in higher plants. Here we report that transgenic rice overexpressing the EcGDH from Eurotium cheralieri exhibited significantly enhanced aminating activities. Hydroponic and field tests showed that nitrogen assimilation efficiency and grain yields were markedly increased in these transgenic plants, especially at the low nitrogen conditions.These results suggest that EcGDH may have potential to be used to improve nitrogen assimilation and grain yield in rice.

Asymptotic behavior of the Taylor-expansion method of moments for solving a coagulation equation for Brownian particles

The evolution equations of moments for the Brownian coagulation of nanoparticles in both continuum and free molecule regimes are analytically studied. These equations are derived using a Taylor-expansion technique. The self-preserving size distribution is investigated using a newly defined dimensionless parameter, and the asymptotic values for this parameter are theoretically determined. The dimensionless time required for an initial size distribution to achieve self-preservation is also derived in both regimes. Once the size distribution becomes self-preserving, the time evolution of the zeroth and second moments can be theoretically obtained, and it is found that the second moment varies linearly with time in the continuum regime. Equivalent equations, rather than the original ones from which they are derived, can be employed to improve the accuracy of the results and reduce the computational cost for Brownian coagulation in the continuum regime as well as the free molecule regime.