Effects of hot deformation parameters on flow stress and establishment of constitutive relationship system of BT20 titanium alloy

The hot compression experiments were performed to investigate the effects of hot deformation parameters on the flow stress of BT20(Ti-6Al-2Zr-1Mo-1V) titanium alloy. The results show that the flow stress decreases with the increment of deformation temperature and increases with the growth of strain rate. The peak stress moves toward the direction of strain reducing and the strain rate sensitivity increases with the rising deformation temperature. There is obvious deformation heating created during hot deformation under relatively higher strain rate and lower deformation temperature. The improved back propagation(BP) neural network with 3-20-16-1 architecture has been employed to establish the prediction model of flow stress using deformation degree, deformation temperature and strain rate as input variables. The predicted values obtained by BP network agree well with the measured values, the relative error is within 6.5% for the sample data and not bigger than 9% for the non-sample data, which indicates that the ANNs adopted can predict the flow stress of BT20 alloy effectively and can be used as constitutive relationship system applied to FEM simulation of plastic deformation.

High gene flows promote close genetic relationship among finewool sheep populations(Ovis aries) in China

The aim of our present study was to construct genetic structure and relationships among Chinese fine-wool sheep breeds. 46 individuals from 25 breeds or strains were genotyped based on the Illumina Ovine 50K SNP array. Meanwhile, genetic variations among 482 individuals from 9 populations were genotyped with 10 microsatellites. In this study, we found high genetic polymorphisms for the microsatellites, while 7 loci in the Chinese superfine Merino strain （Xinjiang types） （CMS） and 5 loci in Gansu alpine superfine-wool sheep strain （GSS） groups were found deviated from Hardy-Weinberg equilibrium （HWE）. Genetic drift FsT=0.019 （P〈0.001） and high gene flows were detected in all the 7 fine-wool sheep populations. Phylogenetic analysis showed fine-wool sheep populations were clustered in a group independent from the Chinese indigenous breeds such that the 7 fine-wool sheep clustered distinct from Liangshan semifine-wool sheep （LS） and Hu sheep （HY） reflected by different population differentiation analyses. Overall, our findings suggested that all fine-wool sheep populations have close genetic relationship, which is consistent with their breeding progress. These populations, therefore, can be regarded as open-breeding populations with high levels of gene flows. Furthermore, the two superfine-wool strains, viz., CMS and GSS, might be formed by strong artificial selection and with frequent introduction of Australian Merino. Our results can assist in breeding of superfine-wool sheep and provide guidance for the cultivation of new fine-wool sheep breeds with different breeding objectives.

Mass transfer mechanism and relationship of gas–liquid annular flow in a microfluidic cross-junction device

Mass transfer performance of gas–liquid two-phase flow at microscale is the basis of application of microreactor in gas–liquid reaction systems.At present,few researches on the mass transfer property of annular flow have been reported.Therefore,the mass transfer mechanism and relationship of gas–liquid annular flow in a microfluidic cross-junction device are studied in the present study.We find that the main factors,i.e.,flow pattern,liquid film thickness,liquid hydraulic retention time,phase interface fluctuation,and gas flow vorticity,which influence the flow mass transfer property,are directly affected both by gas and liquid flow velocities.But the influences of gas and liquid velocities on different mass transfer influencing factors are different.Thereout,the fitting relationships between gas and liquid flow velocities and mass transfer influencing factors are established.By comparing the results from calculations using fitting equations and simulations,it shows that the fitting equations have relatively high degrees of accuracy.Finally,the Pareto front,namely the Pareto optimal solution set,of gas and liquid velocity conditions for the best flow mass transfer property is obtained using the method of multi-objective particle swarm optimization.It is proved that the mass transfer property of the gas–liquid two-phase flow can be obviously enhanced under the guidance of the obtained Pareto optimal solution set through experimental verification.

Strongly nonlinear long interfacial waves in uniform basic flows and their dispersion relationship

In this paper, long interfacial waves of finite amplitude in uniform basic flows are considered with the assumption that the aspect ratio between wavelength and water depth is small. A new model is derived using the velocities at arbitrary distances from the still water level as the velocity variables instead of the commonly used depth-averaged velocities. This significantly improves the dispersion properties and makes them applicable to a wider range of water depths. Since its derivation requires no assumption on wave amplitude, the model thus can be used to describe waves with arbitrary amplitude.

Railway Passenger Flow Forecasting by Integrating Passenger Flow Relationship and Spatiotemporal Similarity

Railway passenger flow forecasting can help to develop sensible railway schedules,make full use of railway resources,and meet the travel demand of passengers.The structure of passenger flow in railway networks and the spatiotemporal relationship of passenger flow among stations are two distinctive features of railway passenger flow.Most of the previous studies used only a single feature for prediction and lacked correlations,resulting in suboptimal performance.To address the above-mentioned problem,we proposed the railway passenger flow prediction model called Flow-Similarity Attention Graph Convolutional Network(F-SAGCN).First,we constructed the passenger flow relations graph(RG)based on the Origin-Destination(OD).Second,the Passenger Flow Fluctuation Similarity(PFFS)algorithm is used to measure the similarity of passenger flow between stations,which helps construct the spatiotemporal similarity graph(SG).Then,we determine the weights of the mutual influence of different stations at different times through an attention mechanism and extract spatiotemporal features through graph convolution on the RG and SG.Finally,we fused the spatiotemporal features and the original temporal features of stations for prediction.The comparison experiments on a railway bureau’s accurate railway passenger flow data show that the proposed F-SAGCN method improved the prediction accuracy and reduced the mean absolute percentage error(MAPE)of 46 stations to 7.93%.

Relationship between the Interannual Variations of Total Ozone in the Northern Hemisphere and the QBO of Basic Flow in the Tropical Stratosphere

The harmonic analyses of monthly mean total ozone in the atmosphere over the Northern Hemisphere for 26 years (1960-1985) are made by using the Fourier expansion. The analysed results show that there is obviously a quasi-biennial oscillation (QBO) in the interannual variations of the amplitudes of total ozone. Generally, the amplitudes of wavenumber 1 and 2 during the westerly of the equatorial QBO are larger than those during the easterly. In the early winter, the amplitude of wavenumber 1 during the easterly phase is larger, and in the late winter, it is larger during the westerly phase. These are in good agreement with the observational distributions.

The relationship of tension and blood flow of the expanded pedicled fasciocutaneous flap in pig

Objective To evaluate the effect of wound closure tension on the blood flow of the expanded pedicled fasciocutaneous flap,so as to find the best tension for the blood supply of the flap.Methods 8 piglets,aged 9-12 months,were used.On

一种高效的OpenFlow流表拆分压缩算法

在软件定义网络中,OpenFlow通过丰富的匹配字段提供了网络流的细粒度管理,同时也带来了流表规模庞大的问题,给OpenFlow交换机的TCAM存储资源提出了严峻的挑战.为此,本文基于匹配域间关系,提出一种高效的OpenFlow流表拆分压缩算法.该算法首先分析了流表匹配字段之间的共存和互斥关系,并据此将流表划分出多个规模较小的子流表,进而针对每个字段建立判定条件,对子流表做进一步压缩,以实现OpenFlow流表的高效存储.最后,借助实际网络流量样本,对本文所提算法的流表压缩性能进行了实验评估.实验结果表明:本文所提算法的流表压缩率明显高于现有压缩算法,可有效节省流表存储资源.

基于GSFLOW的青土湖生态输水量-湖水面积关系研究

西北地区水资源匮乏,生态环境脆弱,如何科学处理生产用水与生态用水的关系一直是西北干旱区水资源开发利用中关注和研究的热点难点课题之一。关于流域中上游生态输水与尾闾湖水域面积(或湿地面积)关系的定量化研究较少。以我国西北干旱区河西走廊石羊河流域的尾闾湖—青土湖为例,利用GSFLOW建立了区域地表水-地下水耦合模型,其中采用LAK模块及SFR2模块分别处理湖泊和输水渠道,在此基础上预测了不同生态输水方案下湖泊湖面面积的变化情况,分析了青土湖生态输水量-湖水面积关系,确定了青土湖生态输水的合理范围。研究结果显示:当前3100×10^(4) m^(3)/a的生态输水量可以保证青土湖维持年内最高湖水水位1212.23 m(平均水位1211.68 m),稳定最大面积可达16.27 km^(2);当输水量为2000×10^(4)~3700×10^(4) m^(3)/a时,随输水量增大水面面积线性增加,面积变化率相对稳定;当输水量为3700×10^(4)~4500×10^(4) m^(3)/a时,水面面积随生态输水量增多,面积增大率逐渐减小;当输水量大于4500×10^(4) m^(3)/a时,水面面积随生态输水增多增大幅度很小,特别是当生态输水量大于5500×10^(4) m^(3)/a时,面积变化率趋近于0。从维持当前青土湖水面面积和向青土湖生态输水的效益考虑,红崖山水库向青土湖的生态输水量应保持在3100×10^(4)~4500×10^(4) m^(3)/a。研究成果对于确定西北干旱区合理生态需水,协调生态、经济、社会用水可持续发展具有一定的参考价值。

A REACTIVE DYNAMIC CONTINUUM USER EQUILIBRIUM MODEL FOR BI-DIRECTIONAL PEDESTRIAN FLOWS

In this paper, a reactive dynamic user equilibrium model is extended to simulate two groups of pedestrians traveling on crossing paths in a continuous walking facility. Each group makes path choices to minimize the travel cost to its destination in a reactive manner based on instantaneous information. The model consists of a conservation law equation coupled with an Eikonal-type equation for each group. The velocity-density relationship of pedestrian movement is obtained via an experimental method. The model is solved using a finite volume method for the conservation law equation and a fast-marching method for the Eikonal-type equation on unstructured grids. The numerical results verify the rationality of the model and the validity of the numerical method. Based on this continuum model, a number of results, e.g., the formation of strips or moving clusters composed of pedestrians walking to the same destination, are also observed.

Numerical Study of the Intensity Correlation between Secondary Flow and Heat Transfer of Circle Tube-Finned Heat Exchanger with Vortex Generators

The application of vortex generators in tube-finned heat exchangers is very universal.The vortex generators can generate secondary flow,and as we all know secondary flow can obviously strengthen heat transfer.To use vortex generators much more efficiently in the circle tube-finned heat exchangers,the intensity correlation study between secondary flow and heat transfer is needed.22 different structures of circle tube-finned heat exchangers were numerically studied,including the plain fin cases and the cases with vortex generators.In addition,the influence of fin spacing,transverse and longitudinal tube pitch,heights and attack angle of vortex generators,positions of vortex generators and shape of vortex generators on heat transfer and fluid flow are studied,too.The non-dimensional parameter Se is applied to quantify the secondary flow intensity.The results show that Se can describe the secondary flow intensity very well.There is very close corresponding relationship between overall averaged Nu and volumetrically averaged Se for all the researched cases and the relational expression is obtained.However,there is no one-to-one correlation not only between Re and f but also between volumetrically averaged Se and f for all the studied cases.

Parameterizations of the Daytime Friction Velocity, Temperature Scale, and Upslope Flow over Gently Inclined Terrain in Calm Synoptic Conditions

A set of new parameterizations for the friction velocity and temperature scale over gently sloped terrain and in calm synoptic conditions are theoretically derived. The friction velocity is found to be proportional to the product of the square root of the total accumulated heating in the boundary layer and the sinusoidal function of the slope angle, while the temperature scale is proportional to the product of the boundary layer depth, the sinusoidal function of the slope angle and the potential temperature gradient in the free atmosphere. Using the new friction velocity parameterization, together with a parameterization of eddy diffusivity and an initial potential temperature profile around sunrise, an improved parameterization for the thermally induced upslope flow profile is derived by solving the Prandtl equations. The upslope flow profile is found to be simply proportional to the friction velocity.

ARTIFICIAL NEURAL NETWORK MODEL OF CONSTITUTIVE RELATIONSHIP FOR 2A70 ALUMINUM ALLOY

The hat deformation behavior of 2A70 aluminum alloy was investigated by means of isothermal compression tests performed on a Gleeble-1500 thermal simulator over a wide range of temperatures 360-480℃ with strain rates of 0.01-1s^-1 and the largest deformation of 60%, and the true stress of the material was obtained under the above-mentioned conditions. The experimental results shows that 2A70 aluminum alloy is a kind of aluminum alloy with the property of dynamic recovery; its flow stress declines with the increase of temperature, while its flow stress increases with the increase of strain rates. On the basis of experiments, the constitutive relationship of the 2A70 aluminum alloy was constructed using a BP artificial neural network. Comparison of the predicted values with the experimental data shows that the relative error of the trained model is less than ±3% for the sampled data while it is less than ±6% for the nonsampled data. It is evident that the model constructed by BP ANN can accurately predict the flow stress of the 2A70 alloy.

CONSTITUTIVE RELATIONSHIP OF SUPERALLOY IN718

Isothermal constant speed compression tests of superalloy IN718 were conducted using a computer-controlled MTS machine at temperatures from 960 to 1040℃, with initial strain rates from 0.001 s￣(1) to 1.0 s￣(1) and engineering strain from 0.1 to 0. 7.The variations of flow stress with deformation temperature, initial strain rate and engineering strain were analyzed in the paper. It was found that there was an obvious power-law relationship between flow stress and initial strain rate, which showed the behavior of strain rate hardening of superalloy IN718 at elevated temperatures.The relationship between flow stress and temperature could be described by an inverse trigonometric function.And the turning point on the curve may be related to the behavior of δ phase at 1000℃. Meanwhile, it was found that there was a complicated relationship between flow stress and strain,which was indicative of the comprehensive effect of work hardening and dynamic softening on flow stress during hot deformation. From the results of these tests, a constitutive equation of superalloy IN718 was developed.

Development of Risk Index of Uninterrupted Traffic Flow According to the Occurrence of Fog

The driver’s visibility is degraded when weather conditions deteriorate, which affects the traffic flow and induces traffic congestion or accidents. In particular, traffic accidents can be?led to chain reaction collisions, with high rate of fatality, when fog occurs in contrast to other weather factors that may restrict visibility. For the development of a traffic risk index, a deviation of the vehicle’s speed was set for the traffic risk index by referring to previous study results. In addition, factors that affected the deviation in a vehicle’s speed were selected as independent variables based on the traffic flow analysis during occurrences of fog. The visible distance, traffic volume, and speed were selected as the independent variables to estimate the optimal parameters in the regression model. The traffic risk index model during occurrences of fog proposed in this study is an exponential model, with the visible distance and the traffic volume defined as independent variables. According to the study model, traffic risk increased as the visible distance decreased and the traffic volume was lower. Thus, the visible distance that can affect traffic flow during occurrences of fog can be determined in the future based on the results of this study. The study results will be expected to contribute to not only traffic safety improvements, but also the facilitation of traffic flow as drivers and traffic operation managers intuitively recognize the level of risk.

Exploring Application Layer Protocol Relationships in SoftSwitch

Relationships between application layer protocols in softswitch are explored in this paper.Two notions, i.e.protocol relationship and protocol grouping, are proposed, which are not clearly defined and even not paid much attention to before.On the basis of a well known protocol relationship named protocol conversion, three novel protocol relationships including protocol collaboration relationship, protocol cooperation relationship and protocol independent relationship are presented, so that protocol relationships are classified into four types.According to the functionality and purpose of each protocol, main protocols related to softswitch are divided into five groups.As to protocol conversion in softswitch, information flow trail(IFT) is utilized to facilitate problem solving.A decision rule for protocol conversion mode is proposed to guide how to choose between direct conversion and indirect conversion.A property of protocol relationships in softswitch is induced from all kinds of service scenarios of softswitch.This property summarizes protocol relationships within each protocol group or between two specific protocol groups.A merit of protocol grouping together with classification of protocol relationship is also presented.The effort of this paper pushes the protocol engineering to go ahead.

要素流动对城乡融合发展的影响机理与空间分异研究

城乡要素双向自由流动有利于提高要素配置效率和优化城乡关系,促进城乡融合发展。现有关于要素流动对城乡融合发展的研究主要围绕传统生产要素对城乡融合发展的研究展开讨论,鲜有文献将数据这一新型生产要素纳入城乡要素流动范围并探索其对城乡融合发展的影响机理。基于2010—2021年中国31个省份的面板数据,在测算要素流动、城乡融合发展水平的基础上,构建双向固定效应模型、地理加权回归模型和中介效应模型实证检验要素流动对城乡融合发展的影响效应及作用机制。研究发现:第一,全国要素流动总指数呈现出小幅度增长的态势,位于均值之上的地区中64%是城乡融合发展试验区,说明城乡融合发展政策实施具有重要的引导作用;第二,要素流动显著促进城乡融合发展,这一结论在引入城乡之间距离作为工具变量进行内生性检验、采用删除4个直辖市和缩短时间窗口的方法进行稳健性检验之后仍然成立;第三,空间异质性分析中,劳动力、土地和数据要素始终表现出促进城乡融合发展的作用,随着时间的推移,土地要素对不同地区城乡融合发展影响程度逐渐增强、影响范围逐步扩大,技术要素对城乡融合发展的促进逐渐凸现,由华东和华南地区向东北和西南地区转移;第四,在要素流动影响城乡融合发展的过程中,电商销售是要素流动影响城乡融合发展的重要途径,农业机械化和产业结构变迁并未发挥出中介变量的作用,不同于已有的研究结果。因此,今后持续深化城乡融合发展的内涵与外延、拓展深度与广度;始终以习近平新时代中国特色社会主义思想为指导,运用科学的世界观和方法论,坚持整体推进与试点示范相统一的指导原则,推广实践中形成的典型经验。研究结论为城乡要素双向合理流动的机制建立、城乡融合发展体制机制的健全提供了理论和经验上的参考。

基于跌坎压力自相似分布的明渠水深−流量关系推求

明渠流量计量是高效灌溉、合理分配水资源和进行用水有效管理的重要手段。跌水是常见的明渠水流上下游衔接的水利设施。当跌落水流不受跌坎下游水流影响时形成自由跌流,可用于明渠流量的精确计量。受自由跌流影响,跌坎断面水流由缓流向急流转变,压力分布显著偏离静水压力分布规律。而获得跌坎压力分布及其准确描述方程则正是明渠自由跌流流量公式推求的关键,其准确与否决定了利用跌流进行流量计量的精度。本文首先通过模型试验和数值计算对矩形明渠自由跌流的断面压力分布特征进行研究,而后利用理论推导建立了明渠跌流的水深−流量关系公式。研究发现,明渠跌水跌坎断面压力呈典型自相似分布规律,其无量纲压力值分布倾向于一条曲线,压力最大值为0.238he(he为跌坎水深),出现在竖向距跌坎0.209he水深处,并且压力自相似分布规律与明渠流量、渠道底坡和边壁糙率无关。在此基础上,结合幂函数和尾迹函数提出了描述跌坎断面压力分布的函数方程,并给出了最大压力和最大压力位置的计算公式,然后根据动量方程和流量连续方程推求了明渠自由跌流的流量计算公式。最后,对本文和其他研究者提出的流量计算公式采用试验数据进行了对比分析,结果表明:本文提出的流量公式在明渠流量为5~100 L/s,底坡为–0.0112~0.0534、糙率为0.0930~0.0193的研究范围内,具有更高的精度和适用性,计算误差在±5%之内,可适用于该流量、底坡和边壁糙率范围内矩形明渠自由跌流的流量精确计算。本文研究结果对于利用自由跌流进行明渠流量计量提供了理论与技术支撑,具有重要的工程应用价值。

从同步数据分析乔木树干液流与气象因子的关系

[目的]树干液流是研究植物蒸腾耗水的重要生理指标,树种和气象因子均是其关键影响因素。本文旨在消除树种因素限制,探讨树干液流与气象因子之间的关系。[方法]以哈尼梯田水源区3种林分中10种乔木树种为研究对象,采用Granier热扩散探针技术测定其树干液流速率,将其同步数据与气象因子进行关联分析。[结果]从次生落叶阔叶林和原生常绿阔叶林的7779条乔木树干液流速率数据中发现7条异常数据,且这些异常数据在各个树种中都表现出同步一致性;进一步关联分析表明,太阳辐射的突然增加是产生乔木树干液流数据同步上升的主要原因,而降雨则是产生树干液流数据同步下降的主要原因,两者的变化可导致其他气象因子发生变化,从而影响树干液流速率;树干液流与气象因子存在一定的时滞效应,在发生同步异常数据的气候条件下,树干液流滞后太阳辐射0~30 min,提前于饱和水汽压差、气温和湿度0~60 min,滞后或提前时间远小于正常气候条件下各树种的时滞时间。[结论]乔木树干液流受到太阳辐射和降雨等气象因子的综合调节,其中太阳辐射的影响最为显著。研究结果可为从生理生态角度探究乔木的蒸腾作用与气象因子的关系提供科学依据。

深圳市轨道交通车站与土地利用互动性研究

城市轨道交通与土地利用发展相互影响,两者协调发展有助于缓解城市交通拥堵,是城市可持续发展的关键问题之一.利用中国深圳市1999年与2015年的建筑普查、土地利用以及轨道交通车站刷卡数据,从开发强度、用地信息熵、车站类型及早晚高峰客流量等多个指标精细化分析轨道交通车站运能与周边土地利用之间的内在联系,并引入“节点-场所”模型构建指标体系评价轨道交通车站与土地利用间的发展协调程度,利用k-means聚类分析将二者协调状态划分为从属状态、平衡状态及失衡状态.结果表明,随着轨道交通车站开发建设,深圳市轨道交通车站周边土地集约利用水平提高;车站客流量与周边土地利用指标的相关性显著,全天客流量与容积率和商办建筑面积显著正相关,早高峰客流量与居住建筑面积和建筑密度显著正相关,而与容积率显著负相关,晚高峰客流量则与商办建筑面积和道路网密度显著正相关.深圳市轨道交通车站与站点周边土地利用协调发展水平偏低,站点类型以节点和场所价值低度均衡发展的从属状态为主,而协调状态则较少且集中分布在中心区圈层.未来应进一步对失衡节点地区采取针对性的开发策略,提升集聚效应与服务水平.