Lateral Shear Layer and Its Velocity Distribution of Flow in Rectangular Open Channels

The lateral velocity distribution of flow in the shear layer of open channel is required to many problems in river and eco-environment engineering, e.g. distribution of pollutant dispersion, sediment transport and bank erosion, and aquatic habitat. It is not well understood about how the velocity varies laterally in the wall boundary layer. This paper gives an analytical solution of lateral velocity distribution in a rectangular open channel based on the depth-averaged momentum equation proposed by Shiono & Knight. The obtained lateral velocity distributions in the wall shear layer are related to the two hydraulic parameters of lateral eddy viscosity (λ) and depth-averaged secondary flow (Γ) for given roughened channels. Preliminary relationships between the above two parameters and the aspect ratio of channel, B/H, are obtained from two sets of experimental data. The lateral width (δ) of the shear layer was investigated and found to relate to the λ and the bed friction factor (f), as described by Equation (26). This study indicates that the lateral shear layer near the wall can be very wide (δ/H = 14.6) for the extreme case (λ = 0.6 and f = 0.01).

Effect of Mixed Vegetation of Different Heights on Open Channel Flows

Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .

Overbank Flow in a Multi-Staged Open Channel: Zonal and Overall Discharge Studies

An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the second stage floodplain, fractional contribution of the main channel and first stage floodplain under bankfull height plays a pivotal role in shear layer and momentum distribution. Therefore, a new mathematical model has been suggested for estimating the stage-discharge relationship for staged channels of more than one floodplain using the 1D technique of overall roughness correction. .

Impact of Partially Covered Vegetation on the Lateral Velocity Distribution of Open Channel Flow

The vegetation affects the flow process and water environment, thus drawing increasing attention to river environment management. Previous research is mainly focused on flow through vegetation in a channel with fully covered single-layer vegetation. However, in natural rivers, different heights’ vegetation often co-exists along one or two sides of a river. This paper experimentally studies how the flow velocity distribution is affected by the two different-layered vegetation allocated along two sides of an open-channel. The vegetation was simulated by dowels of two heights, 10 cm and 20 cm, and arranged in a parallel pattern along two sides of a flume under partially submerged conditions. The velocities along a cross-section were measured by Acoustic Doppler Velocimetry (ADV). The results of lateral velocity distribution show that a strong shear layer exists between vegetation and non-vegetation zones, indicating the retarding effect of vegetation. Meanwhile, as the flow depth increases, the relative velocity in the free flow zone decreases compared with that in the vegetated region, indicating that vegetation resistance to the flow decreases as increasing depth under the same vegetation configuration. These ?ndings would help understand the role of multi-layered vegetation in riparian management.

A Computational Study of Interaction of Main Channel and Floodplain: Open Channel Flows

The assumption of steady uniform flow permits the computation of the velocity isoline, secondary current and turbulent statistics in open channel flows. However, it becomes important to choose appropriate turbulence models to capture the length scale of turbulence near the interfacial zone of compound channels. This paper not only focusses on capturing the longitudinal vortex and primary mean velocity but also extrapolates the results of numerical analysis to understand the interaction between the main channel and floodplain in asymmetric compound channels. The results of computational fluid dynamics simulation showed that the velocity isoline bulging near the bed of the floodplain and sidewall at the junction, due to high-momentum transport by secondary current, can be captured with Reynolds stress model. Furthermore, by applying the three different cases of channels with varying geometrical aspects, the maximum velocity simulated showed similar results to the experiments where the structure of primary mean velocity is seen to be influenced by momentum transport due to the secondary current.

CD45RO^(+)记忆T细胞作为非小细胞肺癌患者预后标志物的研究

背景与目的肺癌是世界范围内最常见的恶性肿瘤之一。肿瘤微环境中多种多样的免疫浸润细胞,是肿瘤免疫的重要组成,对患者预后具有临床意义。CD45RO^(+)肿瘤浸润淋巴细胞(tumor infiltrating lymphocytes,TILs),即记忆T细胞,其表达与多种肿瘤预后相关。本研究旨在探讨非小细胞肺癌(non-small cell lung cancer,NSCLC)中评估肿瘤和基质区CD45RO^(+)TILs密度与患者临床特征和预后的关系,及其联合程序性死亡受体配体1(programmed cell deathligand 1,PD-L1)作为预后标志物的临床价值。方法对167例NSCLC患者的组织微阵列进行多重荧光免疫组织化学染色,标记CD45RO、细胞角蛋白(cytokeratin,CK)和PD-L1。利用人工智能图像识别技术和肿瘤细胞特异性CK染色,划分组织中的肿瘤区和基质区,评估肿瘤区和基质区CD45RO^(+)TILs的密度以及肿瘤细胞的PD-L1表达水平。采用非参检验分析CD45RO^(+)TILs与患者临床特征的关系,使用Kaplan-Meier方法和Cox风险比例模型分析CD45RO^(+)TILs独立或与PD-L1联合与肿瘤预后的关系。结果CD45RO^(+)TILs的密度与患者年龄、吸烟、肿瘤分期和病理类型显著相关。在NSCLC和肺腺癌(lung adenocarcinoma,LUAD)患者中,基质区高密度CD45RO^(+)TILs具有更长的总生存期(overall survival,OS)(NSCLC:P=0.007;LUAD:P<0.001),并且是OS的独立预后因素(NSCLC:HR=0.559,95%CI:0.377-0.829,P=0.004;LUAD:HR=0.352,95%CI:0.193-0.641,P=0.001)。联合肿瘤细胞的PD-L1评分以及所有区域CD45RO^(+)TILs的浸润评分将患者分为四组:其中PD-L1^(+)/CD45RO^(+)患者无病生存期(disease-free survival,DFS)最长,PD-L1^(+)/CD45RO-的患者DFS时间最短,并可作为DFS预后的独立因素(HR=2.221,95%CI:1.258-3.919,P=0.006)。结论肿瘤组织中CD45RO^(+)TILs密度以及CD45RO^(+)TILs联合肿瘤区PD-L1,与NSCLC的临床病理特征及预后显著相关,可作为新的生存预后标志物。

Evaluating Two-Layer Models for Velocity Profiles in Open-Channels with Submerged Vegetation

For submerged vegetated flow, the velocity profile has two distinctive distributions in the vegetation layer in the lower region and the surface layer in the upper non-vegetated region. Based on a mixing-layer analogy, different analytical models have been proposed for the velocity profile in the two layers. This paper evaluates the four analytical models of Klopstra et al., Defina & Bixio, Yang et al. and Nepf against a wide range of independent experimental data available in the literature. To test the applicability and robust of the models, the author used the 19 datasets with various relative depths of submergence, different vegetation densities and bed slopes (1.8 × 10?6 - 4.0 × 10?3). This study shows that none of the models can predict the velocity profiles well for all datasets. The three models except Yang’s model performed reasonably well in certain cases, but Yang’s model failed in most the cases studied. It was also found that the Defina model is almost the same as the Klopstra model, if the same mixing length scale of eddies (λ) is used. Finally, close examination of the mixing length scale of eddies (λ) in the Defina model showed that when λ/h = 1/40(H/h)1/2, this model can predict velocity profiles well for all the datasets used.

An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of pollutant and biomass. As a pre-requisite for the analysis of environmental capacity in a channel, the vertical velocity distribution of flows has attracted much research attention;however, there is yet lack of a good prediction model available. For the channel with submerged vegetation, the vertical velocity distribution in the lower vegetation layer will be different from that in the upper flow layer of non-vegetation. In this paper, after review on the most recent two-layer model proposed by Baptist et al., the author has proposed an improved two-layer analytical model by introducing a different mixing length scale (λ). The proposed model is based on the momentum equation of flow with the turbulent eddy viscosity assumed as a linear relationship with the local velocity. The proposed model is compared with the Baptist model for different datasets published in the literature, which shows that the proposed analytical model can improve the vertical velocity distribution prediction well compared with the Baptist model for a range of data. This study reveals that the λ is well related with the submergence of vegetation (H/h), as suggested by . When the constant β is taken as 3/100, the proposed model shows good agreement with a wide range of datasets studied: flow depth (H)/vegetation height (h) in 1.25 to 3.33, different vegetation densities of a in 1.1 to 18.5 m&#8722;1 (a defined as the frontal area of the vegetation per unit volume), and bed slopes in (1.38 - 4.0) × 10&#8722;3.

Electrochemical process of sulfur in carbon materials from electrode thickness to interlayer

Lots of efforts have been done on different porous carbon materials as cathode for Lithium–sulfur(Li–S)battery. However, seldom researches have been done on the relationship between cathode thickness and electrochemical performance. Our work investigates the relation between electrochemical performance and cathode thickness with typical porous carbon materials. We explain the phenomenon that only a modest cathode thickness can have the most adequate electrochemical reaction trend through the aspect of thermodynamics(chemical potential) so that the best electrochemical performance can be obtained.Besides, interlayer can remit the shuttle effect but hinder the lithium ion diffusion process simultaneously. And we verify the effect of interlayer thickness on the shuttle effect and lithium ion diffusion process.

Evaluating Methods for Discharge Prediction of Straight Asymmetric Compound Channels

Accurate prediction of flow discharge in a compound channel is increasingly important in river flood risk management.This paper evaluates four most recently developed 1-D methods for discharge prediction.The four methods,which have considered the impact of momentum exchange,are Interacting Divided Channel Method(IDCM),Momentum-Transfer Divided Channel Method(MTDCM),Modified Divided Channel Method(MDCM)and Apparent Shear Stress Method(ASSM).The four methods are compared with 20 experimental datasets from the author and the literature.These datasets include both homogeneous(8 datasets)and heterogeneous(12 datasets)asymmetric compound channels,which have various width ratios(B/b)of 1.5~5[channel total width B at bankfull/main channel bottom b]and bed slopes of 2.65×10^-4 to 1.3×10^-2.This study shows that the four methods performed reasonably well(in averaged errors<6.5%)against all the datasets except in a very steep channel with high width ratio(e.g.B/b≥5 in So=0.013),particularly with improved discharge predictions of main channels compared with conventional divided channel method(DCM).It appears that the MDCM shows the best overall performance for homogeneous channels whereas all four methods perform similarly for heterogeneous compound channels.Close examination reveals that the error percentage by all four methods increases as increasing width ratio(B/b)for roughened floodplain channels,but it seems in reverse for homogeneous channels.Finally,all four methods have shown improved flow predictions of main channels compared with the DCM.

Secondary Product Inversion of Wind Profile Data and Its Application in Weather Forecast

Using wind field data of boundary-layer wind profile of Changsha national comprehensive meteorological observation test base,the inversion of atmospheric temperature advection was studied.Moreover,four typical heavy precipitation processes in Changsha region during 2018-2019 were analyzed in detail,and low-level jet index product was calculated.The results showed that the retrieved temperature advection can well reflect the change details of atmospheric temperature advection,and there was a good corresponding relationship between change of the cold and warm advection and the heavy precipitation process;low-level jet index generally had an explosion and enhancement process before precipitation,but the time was not consistent with prior research result,and a large number of samples need to be further studied.

Si/C particles on graphene sheet as stable anode for lithium-ion batteries

Silicon is considered as one of the most promising anodes for Li-ion batteries(LIBs), but it is limited for commercial applications by the critical issue of large volume expansion during the lithiation. In this work, the structure of silicon/carbon(Si/C) particles on graphene sheets(Si/C–G) was obtained to solve the issue by using the void space of Si/C particles and graphene. Si/C–G material was from Si/PDA-GO that silicon particles was coated by polydopamine(PDA) and reacted with oxide graphene(GO). The Si/C–G material have good cycling performance as the stability of the structure during the lithiation/dislithiation.The Si/C–G anode materials exhibited high reversible capacity of 1910.5 mA h g^(-1) and 1196.1 mA h g^(-1) after 700 cycles at 357.9 m A g^(-1), and have good rate property of 507.2 mA h g^(-1) at high current density,showing significantly improved commercial viability of silicon electrodes in high-energy-density LIBs.