Selective Area Growth and Characterization of GaN Nanorods Fabricated by Adjusting the Hydrogen Flow Rate and Growth Temperature with Metal Organic Chemical Vapor Deposition

CaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen （H2）/nitrogen （N2） and growth temperature of the selective area growth （SAG） method with metal organic chemical vapor deposition （MOCVD）. The SAG template is obtained by nanospherical-lens photolithography. It is found that increasing the flow rate of 1-12 will change the CaN crystal shape from pyramid to vertical rod, while increasing the growth temperature will reduce the diameters of GaN rods to nanometer scale. Finally the CaN nanorods with smooth lateral surface and relatively good quality are obtained under the condition that the H2：N2 ratio is 1：1 and the growth temperature is 1030℃. The good crystal quality and orientation of GaN nanorods are confirmed by high resolution transmission electron microscopy. The cathodoluminescence spectrum suggests that the crystal and optical quality is also improved with increasing the temperature.

INFLUENCE OF EXTERNAL MAGNETIC FIELD ON THE FLOW FIELD IN MOLTEN SEMICONDUCTOR OF CZOCHRALSKI CRYSTAL GROWTH——A NUMERICAL SIMULATION

Numerical results show that an external magnetic field may influence significantly the flow pattern in the molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet. ic field with the intensity of several thousands Gauss, while the temperature field is affected only in a less extent by the magnetic field.

Effects of deficit irrigation on daily and seasonal variations of trunk sap flow and its growth in Calligonum arborescens

Water deficit in arid and semiarid regions affects whole-plant sap flow and leaf-level water relations. The objectives of this study were to clarify how sap flow of Calligonum arborescens responds to different drought stress conditions and to understand its acclimation mechanism to drought environments. A field experiment was conducted for C. arborescens during the growing season to evaluate the effects of deficit irrigation on the daily and seasonal variations of trunk sap flow in the shelterbelt along the Tarim Desert Highway, Xinjiang, China. Three dif- ferent water regimes （2,380, 1,960 and 1,225 m3/hm2） were applied at different stages of plant growth. From 1 May to 30 October 2007, a heat-balance stem flow gauge was used to monitor the sap flow dynamics of C. arborescens under different water regimes. Atmospheric evaporation demand and soil moisture conditions for differentially irri- gated C. arborescens were also monitored. The result showed that sap flow exhibited a clear diurnal pattern re- gardless of treatments; the diurnal patterns of sap flow and vapour pressure deficit were very similar under different water regimes and growing seasons, while the slope of the linear regression of this correlation confirmed an in- creasing water regime. The sap flow decreased under reduced water regimes and there was nocturnal sap flow regardless of water regimes, which was mainly contributed to nocturnal transpiration and water recharge. The sap flow peaked before midnight and dropped afterwards with obviously higher values in summer than in other seasons. It is speculated that the water consumption of C. arborescens during the day can be supplemented through the sap flow at night, which increased with increasing irrigation amount. Net radiation was the most significant correlated factor that influenced sap flow velocity and transpiration under different water regimes （R2〉0.719）. Compared with the commonly practiced water regime, the growth of C. arborescens was significantly slower in the stress deficit irrigation, but not significantly different from that in the moderate deficit irrigation. The moderate deficit irrigation would not affect the stability of the shelterbelt and was a more efficient use of water resources compared with the current watering amount.

Relations among Sap Flow, Soil Moisture, Weather, and Soybean Plant Parameters in High Water Demand and Final Growth Stages

The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.

The effect of far field flow on a spherical crystal growth in the undercooled melt

The effect of convective flow on a spherical crystal growth in the undercooled melt with a moderate far field flow is studied. The asymptotic solution of the evolution of the interface of the spherical crystal growth is obtained by the matched asymptotic expansion method. The analytic result shows that the convective flow in the undercooled melt has a strong effect on the evolution of spherical crystal growth. The convective flow induced by the far field flow makes the interface of the growing spherical crystal enhance its growth velocity in the upstream direction of the far field flow and inhibit growth in the downstream direction, and the interface of the decaying spherical crystal further decay in the upstream direction and inhibit decay in the downstream direction. The maximum growth velocity of the interface of the spherical crystal influenced by the far field flow is obtained.

Algorithm for transient growth of perturbations in channel Poiseuille flow

This study develops a direct optimal growth algorithm for three-dimensional transient growth analysis of perturbations in channel flows which are globally stable but locally unstable. Different from traditional non-modal methods based on the Orr- Somrnerfeld and Squire （OSS） equations that assume simple base flows, this algorithm can be applied to arbitrarily complex base flows. In the proposed algorithm, a re- orthogonalization Arnoldi method is used to improve orthogonality of the orthogonal basis of the Krylov subspace generated by solving the linearized forward and adjoint Navier-Stokes （N-S） equations. The linearized adjoint N-S equations with the specific boundary conditions for the channel are derived, and a new convergence criterion is pro- posed. The algorithm is then applied to a one-dimensional base flow （the plane Poiseuille flow） and a two-dimensional base flow （the plane Poiseuille flow with a low-speed streak） in a channel. For one-dimensional cases, the effects of the spanwise width of the chan- nel and the Reynolds number on the transient growth of perturbations are studied. For two-dimensional cases, the effect of strength of initial low-speed streak is discussed. The presence of the streak in the plane Poiseuille flow leads to a larger and quicker growth of the perturbations than that in the one-dimensional case. For both cases, the results show that an optimal flow field leading to the largest growth of perturbations is character- ized by high- and low-speed streaks and the corresponding streamwise vortical structures. The lift-up mechanism that induces the transient growth of perturbations is discussed. The performance of the re-orthogonalization Arnoldi technique in the algorithm for both one- and two-dimensional base flows is demonstrated, and the algorithm is validated by comparing the results with those obtained from the OSS equations method and the cross- check method.

Transient growth in Poiseuille-Rayleigh-Bénard flows of binary fluids with Soret effect

The transient growth due to non-normMity is investigated for the Poiseuille- Rayleigh-Benard problem of binary fluids with the Soret effect. For negative separation factors such as ψ = -0.1, it is found that a large transient growth can be obtained by the non-normal interaction of the two least-stable-modes, i.e., the upstream and downstream modes, which determine the linear critical boundary curves for small Reynolds numbers. The transient growth is so strong that the optimal energy amplification factor G（t） is up to 10^2 - 10^3. While for positive separation factors such as ψ = 0.1, the transient growth is weak with the order O（I） of the amplification factor, which can even be computed by the least-stable-mode. However, for both cases, the least-stable-mode can govern the long-term behavior of the amplification factor for large time. The results also show that large Reynolds numbers have stabilization effects for the maximum amplification within moderate wave number regions. Meanwhile, much small negative or large positive separation factors and large Rayleigh numbers can enlarge the maximum transient growth of the pure streamwise disturbance with the wavenumber α= 3.14. Moreover, the initial and evolutionary two-dimensional spatial patterns of the large transient growth for the pure streamwise disturbance are exhibited with a plot of the velocity vector, spanwise vorticity, temperature, and concentration field. The initial three-layer cell vorticity struc- ture is revealed. When the amplification factor reaches the maximum Gmax, it develops into one cell structure with large amplification for the vorticity strength.

Optimal transient growth in turbulent pipe flow

The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the governing equations onto the sub- space spanned by the radial vorticity and radial velocity. The method is validated by comparing with the previous studies. Two peaks of the maximum transient growth am- plification curve are found at different Reynolds numbers ranging from 20 000 to 250 000. The optimal flow structures are obtained and compared with the experiments and DNS results. The location of the outer peak is at the azimuthal wave number n = 1, while the location of the inner peak is varying with the Reynolds number. It is observed that the velocity streaks in the buffer layer with a spacing of 100δv are the most amplified flow structures. Finally, we consider the optimal transient growth time and its dependence on the azimuthal wave length. It shows a self-similar behavior for perturbations of different scales in the optimal transient growth process.

Simulation of dendritic growth of magnesium al oys with fluid flow

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp(hexagonal closepacked) structure, an extension was made to the formerly established CA(cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.

The Economic Growth with the Flows of Capital ＆ Technology

The difference of regional economy comes from capital dissymmetry, technology dissymmetry, manpower dissymmetry and the information dissymmetry. In the knowledge-based economic ages, globalization and information exceed any age of the history. It provides the new terrace for the balanced development of global economy. The flows of capital and technology improve the regional dissymmetry of production factor. By establishing circulating channels, the flows of the production factor will be enlarged. This will raise the distribution efficiency of global resources and lead to the global economic growth.

Improvement of uniformity in cultivation environment and crop growth rate by hybrid control of air flow devices

A complete control type plant factory has high efficiency in terms of cultivation area by constructing vertical multiple layered cultivation beds.However,it has a problem of irregular crop growth due to temperature deviation at upper and lower beds and increases in energy consumption by a prolonged cultivation period.In this work,air flow rate inside a facility was improved by a hybrid control of air flow devices like air conditioning and air circulation fan with an established wireless sensor network to minimize temperature deviations between upper and lower beds and to promote crop growth.The performance of proposed system was verified with an experimental environment or Case A wherein air conditioning device was operated without a control algorithm and Case B wherein air conditioning and circulation fans were alternatively operated based on the hybrid control algorithm.After planting leafy vegetables under each experimental condition,crops were cultivated for 21 days.As a result,Case B wherein AC(air conditioning) and ACF(air-circulation fan) were alternatively operated based on the hybrid control algorithm showed that fresh mass,number of leaves,and leaf length for the crops grown were increased by 40.6%,41.1%,and 11.1%,respectively,compared to Case A.

Growth Characteristics of <i>Fuirena umbellata</i>in a Surface Flow Constructed Wetland and Its Influence in Nutrients and Faecal Bacteria Removal from Domestic Wastewater in Cameroon

Various configurations of vegetated bed systems with a variety of macrophytes have been tested experimentally in Cameroon, for the treatment of domestic wastewater. The aim of this work was to assess the growth and biomass production of Fuirena umbellata (Cyperaceae) and its potentials in the removal of faecal bacteria and nutrients from primarily treated domestic effluent. A wetland vegetated with this macrophyte and a non-vegetated wetland (control) were continuously fed with primarily treated domestic wastewater at an estimated loading rate of 205 Litres/day in dry and rainy seasons for two consecutive years. Physicochemical and microbiological parameters of the effluent were monitored at the inflow and outflows of the wetlands alongside with the growth and productivity attributes of the young plants during each season. The density of plants ranged in the wetland from 17 - 185 plants/m2 and from 11 - 146 plants/m2 respectively during the first and the second years. More biomasses were instead produced in the dry seasons than in the rainy seasons but with no significant differences observed. As for nutrients removal, higher efficiencies were observed in the vegetated wetland (45% - 73%) compared to the non-vegetated control (17% - 66%). Similar trends were observed for the faecal bacteria but with no significant differences between the seasons. However, the vegetated beds were significantly more efficient than the non-vegetated control in the reduction of many physicochemical parameters and faecal bacteria. This varied with the seasons.

基于FP__Growth算法的路段拥堵分析

笔者从城市交通的历史拥堵数据出发,从时间和空间两个角度去寻找城市内道路的拥堵模式,最终得到城市存在的带时间因子的路段拥堵模式。为了提高算法效率,本文参考频繁模式算法FP-Growth的思想,构建一个三维的FPTree来提高算法效率。最后使用从百度地图获得的上海城市拥堵实时数据作为实验数据,对算法进行了验证,实验证明,该算法可以获得更加实际有效的城市拥堵模式集合。

基于Ebb&Flow灌溉系统的不同营养液组分对朵丽蝶兰生长和开花的影响

采用Ebb&Flow灌溉系统对朵丽蝶兰Doritaenopsis‘Labios’进行了栽培研究,并通过比较3种不同营养液对朵丽蝶兰生物量积累及开花特性的影响,探讨了采用潮汐灌溉系统对朵丽蝶兰进行规模化栽培的可行性。结果显示:循环潮水式Ebb&Flow灌溉系统可用于朵丽蝶兰的规模化栽培。N3营养液(硝态氮115.5 mg·L-1,铵态氮7.0mg·L-1;磷120.0 mg·L-1;钾243.8 mg·L-1;钙200 mg·L-1;镁60.0 mg·L-1)有助于增加朵丽蝶兰地上部分生物量的积累及花梗长度,其中氮和钾的质量浓度为主要因素,且硝态氮更利于朵丽蝶兰的吸收。

Investigation of in situ Growth of SrMoO_4 Nanoplates by Microcalorimetry

SrMoO4 nanoplates were synthesized by a facile reverse microemulsion method at room temperature.Energy evolution of this in situ growth process was monitored by means of a microcalorimeter.A sharp exothermic peak for the initial reaction and two discontinuous relatively weak exothermic peaks for the subsequent crystal growth emerged on the microcalorimetric heat flow curve.Based on the in situ thermokinetic data,the rate constants of the nucleation process and crystallization process at 298.15 K were calculated to be 4.078×10-3 and 5.033×10-4 s-1,respectively.The growth mechanism and energy evolution were investigated.

Multispecies communities:interspecies interactions influence growth on saliva as sole nutritional source

Human oral bacteria live in multispecies communities in the biofilm called dental plaque. This review focuses on the interactions of seven species and the ability of each species individually and together with other species to grow on saliva as the sole source of nutrient. Community formation in biofihns in flow cells is monitored using species-specific fluorophore-conjugated immunoglobulin Gy and images are captured by confocal microscopy. Early colonizing veillonellae emerge from this review of interspecies interactions in saliva as a critical genus that guides the development of multispecies communities. Highly selective interspecies recognition is evident as initial colonizers pair with early and middle colonizers to form multispecies communities that grow on saliva.

A numerical study on pattern selection in crystal growth by using anisotropic lattice Boltzmann-phase field method

Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model.In the model,the phase transition,melt flows,and heat transfer are coupled and mathematically described by using the lattice Boltzmann(LB)scheme.The anisotropic streaming-relaxation operation fitting into the LB framework is implemented to model interface advancing with various preferred orientations.Crystal pattern evolutions are then numerically investigated in the conditions of with and without melt flows.It is found that melt flows can significantly influence heat transfer,crystal growth behavior,and phase distributions.The crystal morphological transition from dendrite,seaweed to cauliflower-like patterns occurs with the increase of undercoolings.The interface normal angles and curvature distributions are proposed to quantitatively characterize crystal patterns.The results demonstrate that the distributions are corresponding to crystal morphological features,and they can be therefore used to describe the evolution of crystal patterns in a quantitative way.

NUMERICAL STUDY OF BUOUNCY- AND THERMOCAPILLARY-DRIVEN FLOWS IN A CAVITY

Thermocapillary-and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical solutions of the two- dimensional Navier-Stokes equations coupled with the energy equation. We studied the thermocapillary and buoyancy convection in the cavities, filled with low-Prandtl- number fluids, with two aspect-ratios A=1 and 4, Grashof number up to 10~5 and Reynolds number |Re|≤10~4. Our results show that thermocapillary can have a quite significant effect on the stability of a primarily buoyancy-driven flow, as well as on the flow structures and dynamic behavior for both additive effect (i.e., positive Re) and opposing effect (i.e., negative Re).

Effect of carrier gas pressure on vapor condensation and mass flow-rate in sonic nozzle

Non-equilibrium vapor condensation of moist gas through a sonic nozzle is a very complicated phenomenon and is related to the measurement accuracy of sonic nozzle.A gas-liquid two-phase model for the moist gas condensation flow was built and validated by moist nitrogen experiment of homogeneous nucleation through a transonic nozzle.The effects of carrier gas pressure on position and status of condensation onset in sonic nozzle were investigated in detail.The results show that condensation process is not easy to occur at lower carrier pressure and throat diameter.The main factors influencing condensation onset are boundary layer thickness,heat capacity of carrier gas and expansion rate.All of results can be used to further analyze the effect of condensation on mass flow-rate of sonic nozzle.

Design of Poiseuille Flow Controllers Using the Method of Inequalities

This paper investigates the use of the method of inequalities （MoI） to design output-feedback compensators for the problem of the control of instabilities in a laminar plane Poiseuille flow. In common with many flows, the dynamics of streamwise vortices in plane Poiseuille flow are very non-normal. Consequently, small perturbations grow rapidly with a large transient that may trigger nonlinearities and lead to turbulence even though such perturbations would, in a linear flow model, eventually decay. Such a system can be described as a conditionally linear system. The sensitivity is measured using the maximum transient energy growth, which is widely used in the fluid dynamics community. The paper considers two approaches. In the first approach, the MoI is used to design low-order proportional and proportional-integral （PI） controllers. In the second one, the MoI is combined with McFarlane and Glover＇s H∞ loop-shaping design procedure in a mixed-optimization approach.