Smooth surface fabrication in mask projection based stereolithography

The surface finish is critical for applications such as optics, micro-fluid flow and mechanical assembly, in which optical lenses, fluidic channels and rotating components are all required to be smooth. However, the stair-stepping effect is well known in the layer-based additive manufacturing processes, in which a three-dimensional model is approximated by a set of two-dimensional layers. Consequently the fabricated surfaces have poor surface finishes especially those that are close to the horizontal plane. In this paper, a novel approach for achieving improved surface finish is presented for the mask-image-projection-based stereolithography (MIP-SL) process. Theoretical models and parameter characterization are presented for the developed methods. Accordingly, the process planning and calibration approaches for fabricating smooth up-facing surfaces in the MIP-SL process have been developed. Multiple test cases based on various types of curved surfaces have been performed. A comparison of the build results based on the traditional and the newly developed approaches illustrates the effectiveness of our method.     

Positive polarotaxis in a mayfly that never leaves the water surface: polarotactic water detection in Palingenia longicauda (Ephemeroptera)

Tisza mayflies, Palingenia longicauda (Olivier 1791), swarm exclusively over the river Tisza (from which the name of the mayfly was derived). This river is bordered by a high vertical wall of trees and bushes, which hinder P. longicauda to move away horizontally from the water. During swarming, Tisza mayflies fly immediately above the river in such a way that their cerci touch the water frequently or sweep its surface. This continuous close connection with water and the vertical wall of the shore and riparian vegetation result in that Tisza mayflies never leave the water surface; consequently, they need not search for water. Several Ephemeroptera species move away far from water and return to it guided by the horizontal polarization of water-reflected light. To reveal whether also P. longicauda is or is not polarotactic, we performed a field experiment during the very short swarming period of Tisza mayflies. We show here that also P. longicauda has positive polarotaxis, which, however, can be observed only under unnatural conditions, when the animals are displaced from the water and then released above artificial test surfaces. P. longicauda is the first species in which polarotactic water detection is demonstrated albeit it never leaves the water surface, and thus, a polarotactic water detection seems unnecessary for it. The polarotactic behaviour of Tisza mayflies explains the earlier observation that these insects swarm above wet asphalt roads running next to river Tisza.     

河口潮流和水质数值模拟研究

河口与海岸环境中污染物质的稀释扩散，是环境流体力学研究的重要课题，同时也是城市污水排海工程建设的关键技术之一。该文采用沿水深积分的平面二维非定常流动数学模型，来计算污染物质降解影响的溶解物质输运扩散过程，并以长江口水域为例，对潮汐水流中溶解物质的稀释扩散过程，进行了细致的数值模拟。结果表明，潮型，排放量，污染物质的降解等，对污水排放口的远场水质有明显的影响。     

人类活动影响下的黄河流域水资源演化规律初探

应用分布式流域水文模型WEP-L模型初步分析了人类活动影响下的黄河水资源演化规律。通过2000年现状下垫面条件下的评价结果与历史系列条件下的评价结果比较,以及考虑与不考虑人工取用水条件下的模拟结果比较,初步发现:黄河流域在强烈的人类活动影响下,水资源量及其构成均发生了显著变化,地表水资源量衰减,而不重复地下水量增加;在狭义水资源衰减的同时,伴随着有效蒸散即降水有效利用的增加,流域广义水资源量有一定幅度增加。研究成果对黄河的治理规划和水安全战略具有参考价值。     

跨音速风扇叶片高低转速下混合相积冰的对比研究

目的 获得跨音速风扇转子叶片高、低转速下混合相积冰的影响规律。方法 使用CFX获取风扇叶片空气流场数据,采用FENSAP-ICE获取积冰冰形,通过过冷水滴与冰晶温度、撞击叶片角度等进行混合相积冰高、低转速冰形分析。结果 风扇叶片高、低转速运转时,过冷水滴与冰晶的运动状态变化相对明显。高转速时,流场内的气流为跨音速流动,过冷水滴与冰晶撞击角度相差较大,撞击角度较大的叶根区域更容易收集过冷水滴与冰晶;低转速时,过冷水滴和冰晶与叶片的撞击角度大部分区域低于10°,使过冷水滴与冰晶碰撞到叶片后的捕获难度提升。风扇叶片高、低转速运转时,叶身的温度差异使过冷水滴在低转速下易直接凝结,未凝结的水膜量极少,而冰晶表面未形成水膜,不易被捕获,使得最终的积冰主要为过冷水滴积冰。结论 风扇叶片混合相积冰在高转速时,流道内温度升高更快,水膜不易凝结,冰晶表面易融化,促进了冰晶积冰。     

福建省山区电线积冰候特征及预报模型研究

在福建山区,最易对架空线路造成危害的是雨凇型的电线积冰,其次是雾凇型积冰。电线积冰发生在11月到次年的4月,集中出现在12月到次年的2月。电线积冰的形成与温度、湿度、风速(向)、降水量、前期积冰持续时间等因子密切相关。文章介绍了电线积冰灾害等级预报模型的思路、灾害指数计算方法、等级划分标准。效果检验表明,预报回代值与实际值拟合率较高,在实际业务应用中有一定的参考意义。     

铝氧化物-水界面化学及其在水处理中的应用

天然水体中,铝氧化物矿物表面上的吸附等各种反应在很大程度上影响着金属阳离子、无机阴离子和一些天然有机物的迁移转化和归趋.在水处理等工业领域中,铝氧化物由于其水合表面的吸附能力而被用做离子交换剂和催化剂载体.因此,对铝氧化物表面化学过程的研究具有重要意义.铝氧化物-水界面上的反应十分复杂,对各种无机、有机污染物的吸附结合能力取决于氧化物固相表面性质、溶液条件和吸附质的性质.从对铝氧化物表面荷电特性和吸附活性的认识出发,就各种铝氧化物的结构特征和表面反应活性及其在水处理技术中的应用进行了简要综述.     

普兰店湾水体交换数值模拟研究

采用不规则三角网格和有限体积方法,建立普兰店湾附近海域的潮流数值模型,在验证良好的潮流数学模型的基础上,以溶解态的保守物质作为示踪剂,对普兰店湾水交换状况进行了数值模拟,将普兰店湾划分成6个区域,针对各区域进行了水交换能力研究。结果表明:普兰店湾内不同区域的地形和地理位置变化较大,水体交换能力平面分布不均匀。在普兰店湾的6个子区域中与湾外的水交换速度最快的为A区（湾口处）,连续潮作用10 d后,水体交换率达到45%。水交换速度最慢的为F区,100 d后水体交换速率为14%。普兰店湾内水交换控制机制的区域性差异使得湾内不同区域水交换率相差较大。     

典型下垫面径流系数预测的神经网络方法研究

根据5种典型下垫面的径流系数的实测数据,运用LM(Levenberg-Marquardt)BP算法的神经网络模型,建立了径流系数与影响因素关系间的S型/S型数学模型。用该方法对不同降雨条件下每种下垫面的径流系数进行了预测,并与传统方法进行了比较。结果表明,该模型的预测精度更高。     

镇江市城区降雨径流水质分析

雨水径流污染是城市面源污染的主要形式,通过对镇江市城区2011年10场降雨径流水质监测,分析了镇江市城区降雨径流水质。结果表明,镇江市城区降雨径流存在一定污染,直接排入城市地表水体会对其造成污染。其主要污染指标为COD、BOD5、NH3-N、TP和总悬浮颗粒物,重金属含量较低,基本不存在重金属污染。各种不同类型雨水径流水质污染程度差异较大,天然降雨、屋面径流,大市口路面径流水质相对较好,基本能达到Ⅲ或Ⅳ类水体的水质标准;泵站、排口径流、河道径流污染较重,大多属于超Ⅴ类水体;南门大街路面径流污染最为严重,部分水质指标接近工业废水。     

Acoustic mirror effect increases prey detection distance in trawling bats

Many different and phylogenetically distant species of bats forage for insects above water bodies and take insects from and close to the surface; the so-called trawling behaviour. Detection of surface-based prey by echolocation is facilitated by acoustically smooth backgrounds such as water surfaces that reflect sound impinging at an acute angle away from the bat and thereby render a prey object acoustically conspicuous. Previous measurements had shown that the echo amplitude of a target on a smooth surface is higher than that of the same target in mid-air, due to an acoustic mirror effect. In behavioural experiments with three pond bats (Myotis dasycneme), we tested the hypothesis that the maximum distances at which bats can detect prey are larger for prey on smooth surfaces than for the same prey in an airborne situation. We determined the moment of prey detection from a change in echolocation behaviour and measured the detection distance in 3D space from IR-video recordings using stereo-photogrammetry. The bats showed the predicted increase in detection distance for prey on smooth surfaces. The acoustic mirror effect therefore increases search efficiency and contributes to the acoustic advantages encountered by echolocating bats when foraging at low heights above smooth water surfaces. These acoustic advantages may have favoured the repeated evolution of trawling behaviour.     

抽水对地壳形变观测影响的研究

抽水引起地面沉降问题早已引起世界各国的关注,是目前世界上许多取用地下水的国家共同面临的严重环境保护问题。我国地面沉降研究工作的开展已有10多年的历史,主要方法是利用沉降模型进行模拟推测,其弊端较多。由于缺少地下水水位和地面沉降的实际观测资料,难以进行细致的研究。蓟县地震台进行地形变监测已有十几年的历史,在长期的地形变观测中,不仅能监视到抽水引起地面倾角的地变化(经换算可得地面垂直方向的变化),还能监视地面因抽水引起地面水平方向的变化。为具体研究人工抽水与地壳形变的关系进行抽水实验。     

ACP1000冷却水管道采用超疏水表面湍流流动数值模拟

目的 探索超疏水表面对ACP1000冷却水管道内流体流动的减阻性能和潜在工程应用,对冷却水管道内的湍流流动进行数值模拟计算,研究具有超疏水表面内壁的冷却水圆管管道内湍流的流动特性。方法 对超疏水表面采用交替的气–液、液–固表面进行模拟,湍流流动采用二维轴对称方法进行数值模拟计算。结果 随着超疏水表面气液比的增大,冷却水圆管内湍流流动的摩擦阻力系数随之减小;随着超疏水表面气液比的增大,冷却水圆管内湍流流动的能量损失随之降低。结论 超疏水表面的应用能够优化ACP1000冷却系统冷却水管道的流动性能。此结果对于未来进一步优化核电站冷却水系统设计提供了理论基础。     

Three dimensional path integration in the house mouse (Mus domestica)

 Previous studies have explored two-dimensional path integration in rodents by recording responses to passive rotation on a horizontal plane. This study adds the element of passive rotation in a vertical plane, necessitating the mouse to integrate positional information from three dimensions. Mice were trained to climb a wire mesh joining two horizontal planes. The whole arena was rotated 90° while the mouse was vertically oriented as it moved between planes. Rotation was conducted both clockwise and counter-clockwise, controls being provided by rotation of the arena while the mouse was in its nest-box. All 16 mice tested altered their direction of travel subsequent to rotation in the vertical plane, compensating with a change in their path on the following horizontal plane. Received: 20 April 2000 / Accepted in revised form: 5 September 2000     

Glass buildings on river banks as “polarized light traps” for mass-swarming polarotactic caddis flies

The caddis flies Hydropsyche pellucidula emerge at dusk from the river Danube and swarm around trees and bushes on the river bank. We document here that these aquatic insects can also be attracted en masse to the vertical glass surfaces of buildings on the river bank. The individuals lured to dark, vertical glass panes land, copulate, and remain on the glass for hours. Many of them are trapped by the partly open, tiltable windows. In laboratory choice experiments, we showed that ovipositing H. pellucidula are attracted to highly and horizontally polarized light stimulating their ventral eye region and, thus, have positive polarotaxis. In the field, we documented that highly polarizing vertical black glass surfaces are significantly more attractive to both female and male H. pellucidula than weakly polarizing white ones. Using video polarimetry, we measured the reflection-polarization characteristics of vertical glass surfaces of buildings where caddis flies swarmed. We propose that after its emergence from the river, H. pellucidula is attracted to buildings by their dark silhouettes and the glass-reflected, horizontally polarized light. After sunset, this attraction may be strengthened by positive phototaxis elicited by the buildings' lights. The novelty of this visual-ecological phenomenon is that the attraction of caddis flies to vertical glass surfaces has not been expected because vertical glass panes do not resemble the horizontal surface of waters from which these insects emerge and to which they must return to oviposit.     

水平表面上多机理作用下气溶胶沉积特性数值分析

采用离散随机模型模拟了水平表面上气溶胶粒子沉积的微观过程.基于随机游走方法,求解了微粒在布朗扩散和外场迁移两种输运机制耦合作用下的运动轨迹,分析了沉积物形结构特征与微粒输运机制间的作用关系,并讨论了不同沉积机制和粒径分布下的表面沉积水平.结果表明,低Pe数下沉积物形态呈现疏松的粉尘絮团结构,而在高Pe数下沉积物则表现出较为紧密的堆积结构.不同沉积机制下粒子沉积形态结构的差异取决于微粒运动轨迹的随机强度;水平表面最大沉积微粒数存在一上限值,且与微粒输运机制和粒径分布均有关.     

地表水水质模型综合评价技术体系研究

水环境数学模型开发及应用的不规范会严重影响水环境管理决策的有效性和科学性.为了更好地发挥模型的职能,减少因采用的模型差异而造成差别管理等不公平因素,应当建立科学的模型筛选制度和评价体系.基于模型开发及应用的生命周期全过程,在文献调研和专家咨询基础上,提出了包含目标层、准则层和指标层的地表水水质模型综合评价指标和评价方法,其中指标层包括通用性、可靠性、友好性、先进性和易用性5个准则的29个指标.采用层次分析法和专家打分法确定指标值及指标权重,并以国内外常用的水质模型,即HEC-RAS、MIKE11、CE-QUAL-W2、WASP、EFDC和Delft3D模型为例,进行了水质模型的综合评价.案例应用的模型评价得分高低的排序依次为Delft3D、EFDC、CE-QUAL-W2、MIKE11、WASP和HEC-RAS模型,结果表明建立的水质模型综合评价技术体系科学、可靠、易用,可为我国水环境数学模型的规范化建设提供重要参考.      

模糊数学法在兰州市地表水环境质量评价中的应用分析研究

根据模糊数学理论,建立了水环境质量模糊综合评价数学模型.选取兰州市地表水为研究对象,对兰州市地表水(黄河岸门桥断面)2009年-2014年全年各项水质平均值进行水环境质量评价,更加综合的评价兰州市地表水环境质量变化趋势及主要污染物,科学的分析兰州市地表水环境质量现状和存在的问题.结果表明:兰州市地表水2009年-2014年环境质量呈日益改善的状态,2009年-2010年兰州市地表水环境质量综合评价结果属于V类,2010年-2014年兰州市地表水环境质量综合评价结果属于Ⅰ类,水体中主要污染物为总氮.     

煤层气区域开发环境影响和管理研究

煤层气开发激励政策和规划的实施,使其区域化和商业化开发将逐步展开。煤层气区域开发有别于常规天然气,主要表现为井网密度大、疏水降压排采和加压集输。大量煤层排水可能污染地表水、降低地下水位、影响水生态、土壤侵蚀等;井网密度大意味着要建设更多的井场、道路、管线、集气压缩站等,则单位面积地表扰动大,导致景观生态破碎化和生态退化等;煤层气压缩机增压集输、其它油气田重型机械、增加的交通流量影响区域声环境质量;压缩机燃气废气、煤层气放空、扬尘对区域大气环境质量产生影响。针对煤层气开发环境问题的特殊性,提出煤层气开发应以水平井为主减少地表扰动。我国水资源极度缺乏,对煤层排水应合理处置,淡水应考虑综合利用,高矿化度水应考虑回注地下。     

磁湖水体BOD_5与COD_(cr)相关性分析

根据湖北省磁湖的实测水质数据资料,应用数理统计的方法分析了该水体BOD5和CODcr间的相关关系,同时也指出了一些BOD5和CODcr的相关性在实际应用中应该注意的问题。