A Two-Sector Economic Growth Model with Labor Force Transfer

In this paper, a two\|sector growth model is given. The labor force transfer process from agricultural sector to industrial sector is exogenous determined. By introducing the labor force transferring function, a two\|dimension nonautonomous differential equation is obtained. The results of the model manifest that the labor force transfer delays industrial sector growth and accelerates the agricultural sector growth. It is proved that the solution of the model is asymptotic stable. By the numerical analysis, the economic growth and labor force transfer is presented under the specific parameters.

Impact of Labor Transfer on Agricultural Land Use Conversion at Rural Household Level Based on Logit Model

Since land and labor force are primary resources to be used and controlled by rural households, the allocation of labor forces will influence land uses, and further lead to land use conversion. The present study used the Binary Logit model to investigate the influence of labor force transfer, characteristics of rural households, location, and land market on agricultural land use conversion at rural household level. This study was conducted based on 329 valid questionnaires, which were obtained in Changshu, Rudong, and Tongshan counties, respectively representing the southern, middle and northern areas of Jiangsu Province. The results showed that land market participation, location, zonal difference and labor transfer had strong influences on agricultural land use conversion. The participation of land market had a strong positive effect on land use conversion, especially for the farmland converted to the fishpond. The nearer to the county seat, the more conversion of land use occurred. Particularly, the labor force transfer caused by wage employment decreased this conversion probability, while the labor transfer caused by self-employment led to more conversion; and the increasing of income from labor transfer increased the conversion. Moreover, land use con- versions demonstrated zonal difference, which were more in Rudong and Changshu counties than in Tongshan County, and the factors influencing this conversion were different in the three regions.

Temperature rise of He Ⅱ forced flow and its negative Joule-Thomson effect

The temperature rise of He Ⅱ transfer system due to the negative Joule-Thomson(JT)effect is one of the major problems in the He Ⅱ forced flow system design.Negative Joule-Thomson effect of the He Ⅱ forced flow was analyzed and calculated in this paper.The temperature rise due to the heat leak along the transfer pipeline was calculated by the simplified equation and was modified by considering the negative Joule-Thomson effect.The modified results were compared with the temperature rise obtained by non-linear differential equations with consideration of the pressure gradient.The results show that the pressure gradient has strong effect on the temperature distribution.The modified results are in good agreement with the values calculated by the complicated equation,which verifies the effectiveness of the simplified equation in calculating the temperature rise when the negative JT effect of He Ⅱ is known.

Three‑Dimensional Numerical Study on the Metal Rotating Spray Transfer Process of High‑Current GMAW

A three-dimensional numerical model based on the volume-of-fluid(VOF)method is typically preferred for studying high-current gas metal arc welding(GMAW)metal transfer mechanism and then controlling it.It is informed that the rotating spray transfer is extremely complicated,and some researchers have focused on simplified models without considering the energy conservation to make analysis manageable for the unstable metal transfer process.Using our created numerical model,the metal transfer of high-current GMAW with shielding gas of different conductivities has been studied by analyzing acting forces and fluid flows in the metal liquid column,especially for the contributions of the self-induced electromagnetic force,equivalent volume force of the capillary pressure of the surface tension(Named surface tension force in this work),static arc pressure.It is found that the unbalanced electromagnetic force greatly promotes the metal rotating motion in 500 A metal inert gas(MIG)welding with pure argon shielding gas and it pushes the metal liquid column to rotate.Considering the arc constricting effect in active shielding gas by simply changing the arc conductivity,it is found that the metal liquid column no longer rotates,it turns to swing since the unbalanced electromagnetic force is large enough to break the rotating motion.The calculated results of the metal liquid column deflected angle and rotating/swing frequency agree well with the experiment of high-speed camera observations.

The relationship between rural surplus labor transfer,urbanization and income gap

Based on the time series data of Shandong province from 2001 to 2018,a VAR model consisting of three variables,namely,rural surplus labor transfer,urbanization and urban-rural income gap,was constructed,and the interaction among the three variables and their characteristics were empirically analyzed.The results show that urbanization and rural surplus labor transfer are Granger causation to each other,and there is a positive correlation between urban-rural income gap and rural surplus labor force in long-term equilibrium,while there is a negative correlation between urban-rural income gap and rural surplus labor force transfer.Therefore,it is necessary to fully recognize the relationship between the transfer of rural surplus labor,urbanization and urban-rural income gap,accelerate the urbanization construction,promote the rural surplus labor to gather in cities,and gradually narrow the urban-rural income gap.

压缩空气储能地下储气库热力学改进模型研究

【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过多的不足。本文在全面分析地下储气库热力学模型理论基础合理性的前提下,先分析储气库热量计算偏差的形成根源;再提出改进模型。【结果】研究结果表明:现有的热力学计算解析模型忽略了CAES地下储气库在运行过程中温度分布的不均匀性,这种温度分布的不均匀导致储气室洞壁与压缩空气之间的对流换热模型失真,导致温度计算结果偏差大。考虑混合对流换热的改进模型二可以较好地解决储气阶段温度计算结果与真实结果之间偏差过大的问题。算例分析证明了改进模型二的合理性。【结论】本文的改进模型二可为CAES地下储气库容积优化设计与效率分析提供计算依据。

钢塔-组合塔混合结构结合部承载性能试验研究

针对新型钢塔-组合塔混合结构结合部构造,开展了局部缩尺模型轴压试验,并建立了非线性有限元模型与试验结果进行比较。研究了钢塔-组合塔结合部的极限承载力以及破坏形式,探究了钢板应变分布规律和焊钉受力分布规律,并对传力路径和荷载分担比例进行了变参数分析。研究结果表明:新型钢塔-组合塔混合结构结合部的承载力符合设计要求;结合部的破坏形式表现为承压板下方钢壁板达到屈服并发生鼓曲变形;承压板为结合部的核心传力构件,增大板厚可以提高结合部承载力以及承压板所传递的荷载,其厚度宜与外壁钢板厚度相近;焊钉和开孔板连接件是保证结合部钢和混凝土共同受力的关键构造,在钢壁板屈服前以受竖向剪力为主,在钢壁板屈服后以受拉拔力为主。

考虑传热条件的搅拌摩擦焊主轴力控制研究

针对搅拌摩擦焊接过程中的试件结构和焊缝位置变化,导致主轴力波动、焊接质量不稳定的问题,对焊缝位置改变和试件结构变化两种传热条件下的热-力关系进行研究,提出考虑传热条件变化的主轴力控制方案。采用Deform-3D软件进行搅拌摩擦焊温度场仿真,并与试验测得实际焊接温度和主轴力进行对比分析,得出靠近试件边缘的主轴力的变化趋势。引入焊接力边缘效应修正系数,基于Hammerstein结构建立考虑传热条件的搅拌摩擦焊主轴力模型,并构造广义预测控制主轴力控制器。将控制器集成到西门子840Dsl数控系统中,并在焊接设备上开展工程测试。结果表明,考虑传热条件变化的主轴力控制方案的控制效果较好,在不同传热条件下,可将实际主轴力控制在期望主轴力±5%的范围内。

可滑动钢锚箱组合索塔锚固结构力学性能试验研究

佛山富龙西江特大桥4~26号斜拉索塔上锚固采用可滑动钢锚箱组合索塔锚固结构,为掌握这种新型索塔锚固结构的力学性能,开展1∶2缩尺模型试验,对滑动副的工作性能、钢锚箱和混凝土塔柱应力状态、钢锚箱与混凝土塔柱间竖向相对滑移量、斜拉索索力传递路径及混凝土塔壁裂缝的发展规律进行研究。结果表明:镜面不锈钢与双组份石墨烯改性氟碳漆涂层组成的滑动副摩擦系数为0.055,适合作为可滑动钢锚箱的滑动副;钢锚箱侧拉板在斜拉索索力作用下处于拉、弯、剪复合受力状态,最大应力为150 MPa,应力水平较低,混凝土塔柱顺桥向最大拉应力仅为0.57 MPa,即使不设预应力也无开裂风险;钢锚箱与混凝土塔柱间的竖向相对滑移量很小,二者间连接可靠,能够很好地共同承受竖向索力;滑动端锁定前,竖向索力几乎全部由钢锚箱的固定端通过剪力连接件传递给混凝土塔柱,水平索力几乎全部由钢锚箱承担,滑动端锁定后,斜拉索索力增量由钢锚箱与混凝土塔柱共同承担;加载至2.5倍标准组合索力过程中,结构依次出现竖向裂缝和水平裂缝,所有裂缝宽度均较小,最大宽度仅0.2 mm。

Study on Forced Convective Heat Transfer of Non-Newtonian Nanofluids

This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles （nanofluids） flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge,thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.

考虑信息传递机制的改进社会力模型

为探究多出口房间内出口开放状态未知情况下行人疏散选择策略,并评估信息传递对疏散过程中运动状态和疏散效率的影响,提出基于信息传递机制的出口寻踪社会力模型(SFM)。首先,在SFM中引入竞争机制,使模型仿真效果更加符合实际疏散场景;然后,研究理性策略与非理性策略引导下的疏散过程,探讨信息变更引发的羊群效应对整体疏散的影响;最后,引入信息传递机制,探索信息交流与合作对逃生路径的优化作用。结果表明:在紧急逃生情境中,对于个体行人而言,理性策略更为稳妥;但从群体行为学角度来看,存在一个最优群体策略分布,即当大约25%的行人选择理性策略,而剩余75%的行人选择非理性策略时,整个群体的疏散效果可以达到最优;通过引入信息传递机制,逃生行人能够有效地从周围人群中获得关键逃生信息,从而显著提高疏散效率。该机制的促进作用对实际开放出口较少的场景尤为明显。

纵扭复合型超声波电机的力传递模型

复合型超声波电机是各种超声波电机中最典型的低速大力矩电机,其定转子接触方式是断续面接触,这与行波型电机连续的若干点接触不同,也是实现大力矩的根本原因,因此分析其定转子的力传递模型很重要。该文先简单叙述了以往采用等效电路描述具有的问题,其次,通过电机轴向冲量守恒建立了定转子接触角与电机预压力和摩擦材料物理参数的关系,随后利用振动周期内周向电机负载和驱动力所作的功相同的原理,给出电机负载与定子纵 扭振动和转子参数的关系,并据此确定电机转子参数和预压力,研制的复合型超声波电机(直径80mm)的堵转力矩为13.2 N穖的大力矩,空转转速为12.5 r/min。初步形成了电机转子设计的理论基础。

黑碳气溶胶辐射强迫全球分布的模拟研究

利用一个改进的辐射传输模式,结合全球气溶胶数据集(GADS),计算晴空条件下冬夏两季黑碳气溶胶的直接辐射强迫在对流层顶和地面的全球分布。计算结果表明,与温室气体引起的整层大气都是正的辐射强迫不同,黑碳气溶胶的辐射强迫在对流层顶为正值,而在地面的辐射强迫却是负值。作者从理论上解释了造成这种结果的原因。对北半球冬季和夏季而言,在对流层顶黑碳气溶胶的全球辐射强迫的平均值分别为0.085W/m2和0.155 W/m2,在地面则分别为-0.37 W/m2和-0.63 W/m2。虽然气溶胶的辐射强迫主要依赖于其本身的光学性质和在大气中的浓度,太阳高度角和地表反照率对黑碳气溶胶的辐射强迫会产生很大的影响。研究指出:黑碳气溶胶在对流层顶正的辐射强迫和在地面负的辐射强迫的绝对值都随太阳天顶角的余弦和地表反照率的增加线性增大;地表反照率对黑碳气溶胶辐射强迫的强度和分布都有重要影响。黑碳气溶胶的辐射强迫分布具有明显的纬度变化特征,冬夏两季的大值区都位于30°N^90°N之间,表明人类活动是造成黑碳气溶胶辐射强迫的主要原因。

液体中气泡上浮与传质过程的耦合模型

针对液体中气泡上浮与传质这一非稳态、强耦合过程,分析气泡的受力情况,考虑到非恒定Basset力的影响,得出了气泡瞬态加速度模型;利用绕球流动传质边界层模型,并引入非平衡传质理论,构建了气泡的瞬态非平衡传质模型;进而依据气泡质量变化率将两模型耦合,以此构建了完整描述这一过程的耦合模型。计算实例表明,Basset力对难溶性气泡的运动过程无明显影响,但对易溶性气泡影响显著;传质条件则对两类气泡都具有重要影响,且该模型中引入非平衡传质理论后,计算值与难溶性气泡的实验结果吻合更好。

苹果切片干燥收缩变形的孔道网络模拟及试验

为揭示果蔬干燥收缩变形的传热传质与应力应变的机理,确定果蔬微孔结构特性及内部毛细力等因素对其干燥过程的影响,该研究运用孔道网络方法、热质传递原理和细观力学理论等交叉学科知识,构建了孔隙尺度下果蔬切片干燥收缩变形的孔道网络模型,采用VC++开发孔道网络求解程序,模拟分析了果蔬切片的湿分场、温度场以及应力应变场等情况,并以苹果切片作为果蔬典型代表进行了热风干燥试验及模型验证。结果表明:湿含量、温度和收缩变形率的模拟值与试验值的相对误差小于10%,模型可有效模拟果蔬干燥热质传递与应力应变的收缩变形真实过程,再现了干燥过程中的“非规则收缩变形”现象;孔道网络模拟的湿分场、温度场及应力应变场均呈现为不规则非对称变化规律,产生了明显的干斑、湿斑、非规则干燥前沿等;毛细应力和湿应力对果蔬干燥收缩变形影响较大,其中毛细应力是引起非规则收缩变形的主导因素;孔隙结构参数对果蔬干燥过程影响显著;孔隙率越大,干燥时间越长,毛细应力越小;配位数越大,毛细应力越大,干燥时间越长;孔隙直径分布呈现均一直径分布规律的物料产生的毛细应力大,其次为孔隙直径分布呈现正态分布规律的物料和试验物料分布。研究结果为果蔬干燥品质及工艺优化分析提供了一定的理论基础。

我国农村劳动力转移数量测算及影响因素分解研究

本研究首先科学构建了农村劳动力转移数量测算体系并测算了我国1991～2009年农村劳动力转移数量,发现总体呈现"上升一下降—再上升"的三阶段变化特征。进一步,基于LMDI模型对农村劳动力转移的影响因素进行分解,结果表明,产业结构因素、农业经济水平因素对农村劳动力转移具有较强的推动作用,与基期相比,分别累计推动了165.52%、147.21%的农村劳动力向城市转移;而效率因素与人口规模因素对农村劳动力转移具有一定的抑制作用,与基期相比,分别累计抑制了192.95%、27.49%的农村劳动力流向城市。

红壤丘陵区典型小流域侵蚀景观时空变化分析——以福建长汀县朱溪河小流域为例

基于1999年和2007年2期数字化侵蚀景观类型图,在ArcGIS 9.0的支持下,提取朱溪河小流域侵蚀景观类型转移矩阵,并结合重心模型,从时间和空间上对侵蚀景观动态变化进行定量分析,结果表明:1)1999年、2007年朱溪河小流域侵蚀景观基质均为微度侵蚀,轻度、中度、强度、极强度和剧烈侵蚀作为斑块单元镶嵌其中;2)1999—2007年,微度和轻度侵蚀的面积均有显著增加,其中微度侵蚀面积增加量最大,主要由轻度转化而来,且主要分布于小流域东部;中度、强度、极强度和剧烈侵蚀面积均有减少,其中剧烈侵蚀面积减少率最大,主要向轻度转化,且高度聚集于小流域上游的游屋圳和高陂次一级小流域;3)1999—2007年期间,剧烈侵蚀重心迁移距离最大,轻度、中度和极强度的重心向西南偏移,微度重心向东北偏移,强度重心向东南偏移。人类活动是该流域侵蚀景观时空变化的主要驱动因素。

低流速过冷沸腾净蒸汽产生点计算模型

已有的过冷沸腾净蒸汽产生点计算方法以高质量流速为主。对于低流速工况,到目前还未见普遍认同的净蒸汽产生点计算模型。本文通过加热壁面汽相蒸发与汽液界面冷凝传热的分析,建立了适用于低流速强迫循环及自然循环工况净蒸汽产生点的蒸发冷凝模型,在较宽广的工况范围内与已有实验数据进行了比较。研究表明,低流速工况下,该模型可以得出满意的预测结果,比目前广泛应用的Saha-Zuber模型以及Levy模型具有更高的预测精度。

基于RS和GIS的绕阳河湿地时空演变及其驱动力分析

基于1975-2007年丰水期TM、ETM+、CBERS遥感数据资料,利用RS和GIS软件提取湿地类型转移矩阵,结合重心模型,分析了自1975年以来绕阳河沼泽湿地的时空演变过程及其驱动力。结果表明:1975-2007年绕阳河沼泽湿地面积占研究区总面积百分比由1.908%下降到0.068%,沼泽湿地主要转出类型为水稻田、裸地;1975-1988年绕阳河沼泽湿地重心向东北方向偏移了1.58km,1988-2007年向西南方向偏移了3.21km,32a间整体向西南方向迁移2.36km,距河流垂直距离缩短了1.79km;水稻田的时空变化是沼泽湿地时空演变的直接驱动因子,人口是其最根本的驱动因子,地下水水位埋深、经济活动与沼泽湿地面积呈显著的负相关关系,河流面积与沼泽湿地面积则呈显著的正相关关系。概括来说,人类活动是绕阳河沼泽湿地时空演变的主要驱动力。

铁路混合梁斜拉桥钢-混结合段传力及疲劳性能试验研究

为了解大跨度铁路混合梁斜拉桥钢-混结合段的传力和疲劳性能,根据应力等效原则设计制作了结合段局部足尺模型,进行了疲劳验证加载和疲劳破坏加载,测试了疲劳加载过程中结合段钢箱梁及剪力钉的应力变化情况。同时,通过考虑钢和混凝土之间不同的摩擦系数,对摩擦力在结构剪力传递中的影响进行了研究。试验研究结果表明:利用接触分析,摩擦系数分别取0.1和0.6时,钢梁纵向应力计算值偏差在0.5%以内,说明在疲劳荷载作用下结构弹性受力时,钢和混凝土之间的摩擦力对剪力传递贡献较小;200万次疲劳验证试验过程中,结合段整体应力水平较低,各测点应力基本保持不变,结构传力安全可靠,具有良好的疲劳性能;100万次的疲劳破坏试验后,钢结构和剪力钉部分测点应力明显增大,结合段钢和混凝土出现黏结滑移现象,尤其在顶板位置,但结构整体稳定性良好,仍具有一定的疲劳安全储备。