Examining the model dependence of the determination of kinetic freeze-out temperature and transverse flow velocity in small collision system

The transverse momentum distributions of the identified particles produced in small collision systems at the Relativistic Heavy Ion Collider(RHIC) and Large Hadron Collider(LHC) have been analyzed by four models. The first two models utilize the blast-wave model with different statistics. The last two models employ certain linear correspondences based on different distributions.The four models describe the experimental data measured by the Pioneering High Energy Nuclear Interaction eXperiment, Solenoidal Tracker at RHIC, and A Large Ion Collider Experiment collaborations equally well. It is found that both the kinetic freeze-out temperature and transverse flow velocity in the central collisions are comparable with those in the peripheral collisions. With the increase of collision energy from that of the RHIC to that of the LHC,the considered quantities typically do not decrease. Comparing with the central collisions, the proton–proton collisions are closer to the peripheral collisions.

Exploring the epidemic transmission network of SARS in-out flow in China's Mainland

The changing spatiotemporal patterns of the individual susceptible-infected-symptomatic-treated-recovered epidemic process and the interactions of information/material flows between regions,along with the 2002-2003 Severe Acute Respiratory Syndrome(SARS) epidemiological investigation data in China's Mainland,including three typical locations of individuals(working unit/home address,onset location and reporting unit),are used to define the in-out flow of the SARS epidemic spread.Moreover,the input/output transmission networks of the SARS epidemic are built according to the definition of in-out flow.The spatiotemporal distribution of the SARS in-out flow,spatial distribution and temporal change of node characteristic parameters,and the structural characteristics of the SARS transmission networks are comprehensively and systematically explored.The results show that(1) Beijing and Guangdong had the highest risk of self-spread and output cases,and prevention/control measures directed toward self-spread cases in Beijing should have focused on the later period of the SARS epidemic;(2) the SARS transmission networks in China's Mainland had significant clustering characteristics,with two clustering areas of output cases centered in Beijing and Guangdong;(3) Guangdong was the original source of the SARS epidemic,and while the infected cases of most other provinces occurred mainly during the early period,there was no significant spread to the surrounding provinces;in contrast,although the input/output interactions between Beijing and the other provinces countrywide began during the mid-late epidemic period,SARS in Beijing showed a significant capacity for spatial spreading;(4) Guangdong had a significant range of spatial spreading throughout the entire epidemic period,while Beijing and its surrounding provinces formed a separate,significant range of high-risk spreading during the mid-late period;especially in late period,the influence range of Beijing's neighboring provinces,such as Hebei,was even slightly larger than that of Beijing;and(5) the input network had a low-intensity spread capacity and middle-level influence range,while the output network had an extensive high-intensity spread capacity and influence range that covered almost the entire country,and this spread and influence indicated that significant clustering characteristics increased gradually.This analysis of the epidemic in-out flow and its corresponding transmission network helps reveal the potential spatiotemporal characteristics and evolvement mechanism of the SARS epidemic and provides more effective theoretical support for prevention and control measures.

Spatial-temporal characteristics of epidemic spread in-out flow——Using SARS epidemic in Beijing as a case study

For better detecting the spatial-temporal change mode of individual susceptible-infected-symptomatic-treated-recovered epidemic progress and the characteristics of information/material flow in the epidemic spread network between regions,the epidemic spread mechanism of virus input and output was explored based on individuals and spatial regions.Three typical spatial information parameters including working unit/address,onset location and reporting unit were selected and SARS epidemic spread in-out flow in Beijing was defined based on the SARS epidemiological investigation data in China from 2002 to 2003 while its epidemiological characteristics were discussed.Furthermore,by the methods of spatial-temporal statistical analysis and network characteristic analysis,spatial-temporal high-risk hotspots and network structure characteristics of Beijing outer in-out flow were explored,and spatial autocorrelation/heterogeneity,spatial-temporal evolutive rules and structure characteristics of the spread network of Beijing inner in-out flow were comprehensively analyzed.The results show that(1)The outer input flow of SARS epidemic in Beijing concentrated on Shanxi and Guangdong provinces,but the outer output flow was disperse and mainly includes several north provinces such as Guangdong and Shandong.And the control measurement should focus on the early and interim progress of SARS breakout.(2)The inner output cases had significant positive autocorrelative characteristics in the whole studied region,and the high-risk population was young and middle-aged people with ages from 20 to 60 and occupations of medicine and civilian labourer.(3)The downtown districts were main high-risk hotspots of SARS epidemic in Beijing,the northwest suburban districts/counties were secondary high-risk hotspots,and northeast suburban areas were relatively safe.(4)The district/county nodes in inner spread network showed small-world characteristics and information/material flow had notable heterogeneity.The suburban Tongzhou and Changping districts were the underlying high-risk regions,and several suburban districts such as Shunyi and Huairou were the relatively low-risk safe regions as they carried out minority information/material flow.The exploration and analysis based on epidemic spread in-out flow help better detect and discover the potential spatial-temporal evolutive rules and characteristics of SARS epidemic,and provide a more effective theoretical basis for emergency/control measurements and decision-making.

Numerical Modelling and Simulation of Sand Dune Formation in an Incompressible Out-Flow

In this paper, we are concerned with computation of a mathematical model of sand dune formation in a water of surface to incompressible out-flows in two space dimensions by using Chebyshev projection scheme. The mathematical model is formulate by coupling Navier-Stokes equations for the incompressible out-flows in 2D fluid domain and Prigozhin’s equation which describes the dynamic of sand dune in strong parameterized domain in such a way which is a subset of the fluid domain. In order to verify consistency of our approach, a relevant test problem is considered which will be compared with the numerical results given by our method.

Out-of-plane shear flow effects on fast magnetic reconnection in a two-dimensional hybrid simulation model

The effects of out-of-plane shear flows on fast magnetic reconnection are numerically investigated by a two- dimensional （2D） hybrid model in an initial Harris sheet equilibrium with flows. The equilibrium and driven shear flows out of the 2D reconnection plane with symmetric and antisymmetric profiles respectively are used in the simulation. It is found that the out-of-plane flows with shears in-plane can change the quadrupolar structure of the out-of-plane magnetic field and, therefore, modify the growth rate of magnetic reconnection. Furthermore, the driven flow varying along the anti-parallel magnetic field can either enhance or reduce the reconnection rate as the direction of flow changes. Secondary islands are also generated in the process with converting the initial X-point into an O-point.

资金流对乡村产业振兴的影响

基于2006—2019年全国722个脱贫县和1058个非贫困县的非平衡面板数据,构建乡村产业振兴指数,实证检验了金融资金流动对乡村产业振兴的影响效果及作用机制。研究发现:金融资金流入能显著促进乡村产业振兴,且对脱贫县的促进效果强于非贫困县;金融资金流动主要通过带动“实物流”“技术流”和“人才流”发挥促进作用,实现乡村生产体系、经营体系及产业体系的现代化,进而推动乡村产业振兴;新产业新业态发展的需求端、普惠金融发展的供给端和精准扶贫政策实施的政策端均能对促进作用产生正向效应。

不同船体破口对水流出流特性影响研究

利用冲击动力学仿真,构建多种类型的船体破口,将冲击仿真所得的船体破口形状耦合进构建的多相流计算模型中,按照069型和067型登陆艇面临的实际堵漏环境,分析不同形状船体破口、不同尺寸船体破口、不同翻边船体破口的水流出流特性。研究表明,翻边撕裂较深的破口形状出流距离要远;外翻边破口的水流出流距离呈现先小于后大于内翻边破口的规律;400 mm、300 mm和200 mm破口相比同时刻下的出流距离相差较小,但冲击压强的稳定值相差较大,400 mm破口为34700 Pa,比300 mm破口大1300 Pa,比200 mm破口大5700 Pa。研究可为船体破损后的堵漏密封作业提供精准的数据支撑,也可为新型堵漏器材的设计提供技术指导。

黏聚力随机场波动范围的各向异性对流态性滑坡滑动距离的影响

流态性滑坡的大变形运动过程受到诸多因素的影响,其中一个重要因素便是岩土体的强度参数。由于现场测试和室内试验的局限性,强度参数往往呈现出明显的空间变异性,同时在不同方向上具有不同的波动范围,即随机场波动范围具有各向异性。针对黏聚力随机场波动范围的各向异性对流态性滑坡滑动距离的影响问题,引入基于乔列斯基分解的中心点法实现了各向异性随机场的离散,采用摩尔-库仑破坏准则和非牛顿流体模型相结合的光滑粒子流体动力学(smoothed particl ehydrodynamtcs,SPH)分析方法模拟了流态性滑坡的滑动距离,在蒙特卡洛模拟框架上提出了流态性滑坡的随机分析方法。然后,通过羊宝地滑坡和水平地层模型的模拟,验证了流态性滑坡确定性分析方法和随机场离散方法的适用性。最后,根据汶川地震中王家岩滑坡的地形资料构建了概念性的滑坡分析算例,讨论了黏聚力随机场中各向异性波动范围影响下滑坡运动过程的变化,分析了滑动距离的概率分布规律。结果表明:竖直波动范围的增加会增大滑坡滑动距离的分布范围,使其表现出更强的离散性;在黏聚力参数符合对数正态分布的前提下,滑动距离的分布也符合对数正态分布,说明流态性滑坡滑动距离的概率分布与强度参数的不确定性具有一定的联系。

基于均压理论的寺河煤矿采空区瓦斯防治技术研究

寺河煤矿53032巷与5303采空区相邻,目前巷道变形严重,瓦斯抽采能力不足,具有严重的瓦斯安全隐患。本文基于均压原理,研究通风系统调控方案,以此对瓦斯抽采系统进行改造。结果表明:采空区两侧压差点大幅降低,瓦斯扰动减少,流场汇流点发生改变;瓦斯抽采系统改造当月53032巷内平均瓦斯浓度及风排瓦斯涌出量降幅达50%,7个月后降幅达78%。可见本文所得的均压调控措施有效解决了53032巷的瓦斯问题,可为类似条件矿井或区域提供瓦斯问题解决思路。

铁路疆煤外运运输通过能力提升对策

在我国深入实施碳达峰、碳中和的大背景下,随着煤炭行业供给侧结构性改革的纵深推进,全国煤炭生产基地向新疆集中,疆煤产能得到进一步释放,在满足当地市场需求的前提下,将持续大幅度提高疆煤外运量,填补国内市场的煤炭缺口。综合分析当前铁路疆煤外运运输通过能力现状及存在问题,针对主要站点及部分区段运输通过能力不足、机车机班运用相对紧张、施工作业组织待优化等多重因素影响,结合疆煤外运主要流量、流向,从系统提升点-线-网运输通过能力、补充机车机班及优化机车运用、提高货物列车编组质量、优化施工组织、提升调度精细化指挥水平5个方面提出改进建议,以进一步提升铁路疆煤外运运输通过能力,为满足疆煤外运需求提供运力支撑。

Damming of Large River by Debris Flow: Dynamic Process and Particle Composition

The frequency and extent of debris flows have increased tremendously due to the extreme weather and the Wenchuan earthquake on May 12, 2008. Previous studies focused on the debris flow from gullies damming the mountain streams. In this paper, an equation for the run-out distance of debris flow in the main river is proposed based on the dynamic equation of debris flow at different slopes given by Takahashi. By undertaking field investigations and flume experiments, a new calculation method of the volume of debris flow damming large river is obtained. Using the percolation theory and the renormalization group theory it was deduced that the large particles should comprise more than 50% for forming a stable debris flow dam. Hence, the criteria of damming large river by debris flow is presented in terms of run-out distance and grain composition which was then validated through the event of damming river by debris flow at Gaojia gully, the upper reaches of the Minjiang River, Sichuan, China, on July 3, 2011.

Investigating Earth Reaction to Pull-Out Process of Frictional Rock Bolts Using Distinct Element Method

The reaction of earth to pull-out process of frictional rock bolts was here modeled by the distinct element method (DEM). Ten frictional bolts were prepared;the expanding shells of five bolts included convex edges and the others had the shells with concave bits. The strength of bolts was measured by applying a standard pull-out test;the results confirmed that the strength of shells with convex edges was remarkably more than the strength of other shells. Furthermore, a two-dimensional DEM model of the test was developed by a particle flow code;the obtained results showed that the reaction of rock particles to the contacts occurring between the convex edges and earth was considerably more than those of the concave bits. In the other words, the convex edges transferred the pull-out force into a large area of the surrounded rock, causing these bolts to have the highest resistance against earth movements.

储气库干化盐析效应量化表征及干化扩展范围预测方法

储气库注采过程中存在近井地带干化盐析的问题,不仅影响储气库的注采能力,甚至影响储气库稳定运行及运行年限。文中基于BL经典分流理论及气水渗流规律,建立了储气库干化盐析效应量化表征数学模型及盐堵损伤量化评估方法,解决了储气库干化问题关键参数的量化表征及干化扩展范围的预测难题。研究结果表明:理论推导的盐饱和度、盐析出量是评估储层盐堵的重要表征参数,与储层温压条件、流体性质及气水相对渗透率等有密切的关系;储气库注采循环过程会导致干化扩展范围逐渐由近井向远井发展,仅依靠注入端短时间注水来解除近井堵塞,可能无法有效恢复地层孔隙度、渗透率及天然气注采能力;基于文中建立的数学模型得到的研究结论与前人实验研究结论具有较好的一致性。文中研究成果不仅具有较好的现场应用价值,而且对干化盐析现象的理论研究以及干化盐析机理的认识具有指导意义。

砂尘对压气机叶片的侵蚀及性能影响

为了应对飞机在起飞和降落的过程中会面临多砂环境,尘土、砂粒等异物颗粒会随空气被吸入航空发动机内的情况,明确压气机部件的磨损和砂粒的吸入对压气机特性产生的影响,以航空发动机吞砂作为研究背景,以跨声速轴流压气机转子NASA Rotor 37为研究对象,采用两相流动数值模拟的方法对砂粒的运行轨迹、侵蚀分布和特性变化开展仿真研究。获得了不同的吞砂条件和转速工况对颗粒运动轨迹、侵蚀分布和侵蚀量的影响,并分析了砂粒在不同吞砂条件和不同转速下引起的压气机性能和内部流场分布的变化规律。结果表明:大部分颗粒进入压气机后,随气流进入叶栅通道,在叶栅通道内与叶片压力面发生碰撞;吞砂导致压气机的增压能力减弱,对于直径为20、150、300μm的吞砂工况,其增压范围分别缩小了3.83%、2.13%和1.01%。

荒漠区平原水库多目标生态调度能力与潜力分析

针对干旱荒漠区水资源匮乏、区域水资源分配不均等问题,提出一种优化调度方案。本文以塔里木河为例,建立水库多目标生态调度模型,采用融入人工经验的自迭代模拟优化算法求解。通过水库多目标生态调度能力与优化潜力的对比分析,最大程度地满足了枯水期河道内、河道外生态流量以及补湖水量,挖掘了荒漠区平原水库显著的生态调度潜力。结果表明:①优化后大西海子水库多年下泄水量变化较实测值更加均匀;②实测的大西海子下游3年断流,优化后仅有1年断流,枯水期断流天数大幅减少;③在胡杨漂种的关键生态期,河道外可供生态水量较实测值提高了66%;④补湖水量较实测值减少了289.5万m 3,有效控制了台特玛湖补湖水量及其变化过程。研究结果优化了季节性河流的河道内、河道外以及入湖等多要素生态供水过程,对于干旱荒漠区内陆河水资源的集约利用、河岸植被的生态保护与修复具有重要的理论意义和应用价值。

考虑堆积区宽度影响的滑坡碎屑流运动与堆积过程物理模型试验研究

堆积区宽度会显著影响滑坡碎屑流运动与堆积过程,而目前该方面研究却相对较少。本文设计了一种水平滑段宽度可变的物理模型试验装置,在此基础上开展了一系列物理模型试验。试验获取了不同宽度水平滑段条件下颗粒流运动与堆积过程的图像和数据,分析了颗粒流速度分布和堆积特征,进一步结合数值模拟探讨了颗粒流运动机制与堆积特征成因。结果表明:颗粒流在倾斜滑段随运动距离增加逐渐离散且离散范围也逐渐增大;颗粒流在水平滑段的运动速度随水平滑段宽度增加逐渐减小,运动速度方向发生偏移且随水平滑段宽度增加更加显著;颗粒流在水平滑段的堆积长度随水平滑段宽度增加逐渐减小,堆积宽度逐渐增加,堆积面积先减小后增加;数值模拟结果表明:碰撞是颗粒间主要能量传递形式,摩擦是主要耗能形式,随着水平滑段宽度增加,颗粒流在水平滑段颗粒间的碰撞次数逐渐减少,颗粒向两侧滑动展布,摩擦耗能使得颗粒流堆积宽度增加而堆积长度减小。

基于DEM的复杂地形流域特征提取

利用流域数字高程模型(DEM)构建数字水系模型并提取流域水系特征是分布式水文过程模拟的重要前提。提出了面向分布式水文过程模拟和流域特征提取的数字水系模型,并针对现有方法对复杂地形DEM中含有的平地、洼地及其嵌套情形的处理不足,提出了栅格水流分类、填洼分类与归并及有效填平处理、河谷平地的出流代价法构建栅格流向和流序等新的处理方法,并在开发的软件系统得到实现。使用该方法创建的黄土岭流域数字水系模型和提取的水系等流域特征结果表明:本文方法可有效应对复杂地形流域的处理,提取的流域水系特征与实际自然水系比较吻合,能够有效地消除现有方法在地形平坦区域容易产生的平行河道、奇异河道、河道变形等不足。

崩塌土流动化机理的实验研究

作者利用可调坡水槽进行了松散崩塌土与水流掺混并形成泥石流的实验 ,观测了崩塌土运动距离及泥石流的形成过程 ,建立了崩塌土流高比的计算公式。讨论了松散崩塌土流动化形成泥石流的临界条件 ,提出松散崩塌土在一定纵坡下形成泥石流的水流掺混机理。实验中发现了一定形状的块状崩塌土与饱和度较高的下垫层之间存在超载孔隙水压力 ,超载孔隙水压力减轻了块体自重达到减阻的作用。从而 。

分级燃烧室预燃级旋流组织对点熄火性能影响的试验研究

为了有效拓宽多级旋流分级燃烧室的稳定工作边界,在模型燃烧室上开展了分级燃烧室点火和熄火特性试验研究,采用平面激光测量技术获得了燃烧室冷态流场结构和燃油浓度分布,分析了双级旋流预膜式空气雾化预燃级设计参数(两级旋流旋向、旋流强度)对流场结构、燃油浓度分布和燃烧稳定性的影响,并阐明了燃烧室点火和熄火特性与流场结构和燃油浓度分布的内在关联机制。结果表明,预燃级两级旋流反旋、适当减小内级旋流强度和增大外级旋流强度有利于改善这类分级燃烧室的点火和熄火特性。相关研究结论能够应用于分级燃烧室预膜式空气雾化预燃级设计。

基于故障分量综合阻抗的T接线路纵联保护新原理

提出了一种适用于T接线路的基于故障分量综合阻抗的纵联保护新原理,利用故障时线路三端电压故障分量相量之和与电流故障分量相量之和的比值来判断线路上是否发生了故障。外部故障时,该比值反映线路的容抗,其模值较大;内部故障时,该比值反映系统电源阻抗和线路阻抗,其模值相对较小,据此可以区分线路上的内部和外部故障。根据新原理构成的保护不需要对电容电流进行补偿,可用于带或不带电抗器补偿的线路,在原理上不受过渡电阻的影响,而且当T接线路内部发生故障而有汲出电流时,保护的灵敏度也不受影响。EMTP仿真验证了新原理的有效性。