The authors thank the Deutsches Zentrum f&#252;r Luft- und Raumfahrt (DLR), the Deutsche Forschungsgemeinschaft (DFG), and the TU Braunschweig for continual support of our laboratory activities. The low-velocity drop tower has been established under DLR grant 50WM0936, the high-velocity drop tower has been developed under DFG grant INST 186/959-1 as part of the CRC 963 &#8220;Astrophysical Flow Instabilities and Turbulence&#8221;.

注意：根据所使用的颗粒，它可以在相应的安全数据表中找到的危害性，口腔保护和安全装置必须由具有防尘工作的人佩戴。此外，还建议使用抽气系统，以保持环境空气无尘。 1，制备厘米大小的灰尘聚集样片<ol><li>由米计算所需材料的量=Φρ0 V，其中m是所要求的质量，Φ是所需的体积填充率（体积填充率= 1 -孔隙度），ρ0是材料的密度，V是体积样品。 77克不规则硅酸盐粉尘（ρ0 = 2.6克/厘米3）是必需的，以实现70％的样品的孔隙率（体积填充率= 0.3）为5cm直径和高度的圆柱状样品，分别为。 注：解放军地面形成网开始微米大小的尘埃颗粒的混凝 - 主要由硅酸盐 - 成厘米大小的多孔体。甲充分研究和合适的实验室模拟材料为SiO 2，其可为不规则形状的粉末具有粒度分布范围从0.5到10μm，以及在单分散的球形颗粒获得更好的可比性，以理论模型的形式（见表1和图1）。 </li></ol><table border="0" cellpadding="0" cellspacing="0" width="569"><tbody><tr height="20"><td height="20" style="height:20px;width:161px;"> SiO 2的单体粒型</td><td style="width:96px;">生产厂家</td><td style="width:119px;">粒径</td><td style="width:95px;">颗粒形状</td><td style="width:100px;">例如图</td></tr><tr height="21"><td height="21" style="height:21px;">单分散</td><td> Micromod </td><td> 1.52±0.06＆＃181;米</td><td>球形</td><td> 图1（左） </td></tr><tr height="20"><td height="20" style="height:20px;">多分散</td><td> Sigma-Aldrich公司</td><td> 0.1 - 10微米</td><td>不规​​则</td><td> 图1（右） </td></tr></tbody></table> 表1特性中的灰尘聚集碰撞实验中使用的SiO 2的粒子。 <img alt="图1" fo:content-width="5in" src="/files/ftp_upload/51541/51541fig1highres.jpg" width="500" /> 单分散（左）和多分散（右）二氧化硅用于生产宏观灰尘聚集体颗粒2图1。电子-显微镜图像。 <a href="https://www.jove.com/files/ftp_upload/51541/51541fig1highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <ol开始=“2”&gt; <li>采取与微米尺寸的SiO 2颗粒的容器（ 见表1），其内容为0.5mm的筛目尺寸倒入筛子上。筛材料的足够量和填补计算质量到模具中。通过用手推压在活塞直到样品高度达到压缩该材料在模具中（ 例如，5厘米）。转身对活塞模具，打开底板，轻轻样品推出。 注意：样品可以以多种形状（球形，圆柱形），大小（1毫米至10厘米）和孔隙率（60〜85％）来制备（参见图3）。样品可以被单独使用在碰撞实验或组合成群集，然后撞击其它聚集体或簇。 </li></ol><img alt="图2" src="/files/ftp_upload/51541/51541fig2highres.jpg" fo:content-width="5in" width="500" /> 图2。的照片。灰尘聚集样品的尺寸和形状的变化的下列样品都显示：灰尘气瓶1厘米，2厘米，和直径为5厘米（后排），粉尘球体用1厘米，直径2厘米（中间行），并2-3毫米大小的Al 2 O 3球（正面）。 <a href="https://www.jove.com/files/ftp_upload/51541/51541fig2highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <ol start="3"><li>表征样品相对于孔隙度和均匀性。如果样品落在外面允许的利润，产生新的样本。 <ol><li>为了确定灰尘样品的孔隙率，由一个精确的平衡装置，测量其尺寸和它的质量决定了其体积。 </li><li>使用X-射线断层扫描技术（XRT）12获得的均匀性和所生成的样品的孔隙大小分布的信息。 注：对于5厘米大小的灰尘聚集，我们发现偏离平均体积填充事实R， 即该样品的质量密度的比值和单体的灰尘颗粒，只有约1％的体积的样品体积的范围内，并通过到一个稍大的增加的体积填充率的材料密度朝向外边界12 8％。 图3示出了通过直径为5厘米和5厘米的高度的圆柱形灰尘聚集的切口的XRT重建。我们不使用XRT每个灰尘聚集，但检查随机样本的内部结构和均匀性。 </li></ol></li></ol><img alt="图3" src="/files/ftp_upload/51541/51541fig3highres.jpg" fo:content-width="5in" width="500" /> 为5厘米的高度和XRT分析后的5厘米直径的圆筒状灰尘聚集样品的内部结构的图3。重构。的灰度级表示的体积填充率，这是吨的质量密度的比值他样品和单体的尘埃微粒的物质的密度。从XRT重建，它是清晰可见的，这种高孔隙度样品用毫米大小的尘埃聚集组装。 <a href="https://www.jove.com/files/ftp_upload/51541/51541fig3highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> 落塔安装2。原理<ol><li>释放机制： 在落塔的上部两个释放机制被附接一个在另一个的上面。他们每个人都拥有一个样本，并释放它变成自由落体。上部的释放和较低的颗粒之间的时间差确定碰撞的相对速度。根据形态和粒子的形状，合适的释放机构被选择。如果一个粒子加速机制被使用时，仅需要一个释放机构。 <ol><li>颗粒上的一个字符串释放机制（球形样品，UPP呃颗粒）： 本次发布机构由线性螺线管磁体和固体金属计数器一块。 <ol><li>连接被释放到一个字符串的颗粒。通过螺线管磁体和实心金属计数器片之间的夹紧它保持在字符串中的位置。 </li><li>以释放粒子，施加电流到螺线管磁体（参见电影1）。 </li></ol></li><li>活板门释放机制（球形样品，较低的颗粒）： 本次发布机构由旋转螺线管磁铁，把一个粒子支架连接的。 <ol><li>将微粒成半球形模，这是向下的旋转螺线管，当一个电流施加（见电影1）旋转。 </li><li>这一机制也可用于颗粒簇或聚集团块的释放。在后一种情况下，将两片活板门释放装置上面彼此（见电影2）。 </li></oL&gt; </li><li>剪刀型双释放机制（圆柱试样）： 本次发布机制包括两对旋转螺线管磁体的金属棒连接。每个释放机构的两个电磁体被放置，使得两个金属棒平行。 <ol><li>两个样本放置到所述两个平行的杆。 </li><li>施加电流到两个旋转螺线管的颗粒释放到自由下落。 （见电影3）。 </li></ol></li><li>双翼陷门释放机制（圆柱试样，在与粒子加速机制组合）： 这释放机构包括两个弹簧加载的金属板，它们共同形成一个V形的粒子支架。两个金属板，以代替由一个金属棒，它是连接到一个旋转螺线管磁体保持。 <ol><li>将圆柱形粉尘采样到封闭的活板门。 </li><li>通过应用解锁陷阱门电流给螺线管磁体。为了避免弹跳回门的，涡流制动器阻止他们（见电影4）。 注意：在颗粒释放到自由下落而不初始速度和旋转是非常重要的。出于这个目的，一些发行机制已经发展（2.1.1 - 2.1.4）。 </li></ol></li></ol></li><li>粒子加速机制： 或者通过一个预加载的弹簧或由电磁驱动的直线加速阶段的颗粒。既促进剂可配用于不同形状的粒子的样品架。 </li> <li>电子控制设备： 设置定时器，并释放电子到适当的值，以实现所需的碰撞速度和操作相机在质心的一帧。 注：颗粒释放，粒子加速和照相机释放的时间是由一组电子计时器，其功能在M被解释执行OVIE 5。 </li></ol> 3，进行实验<ol><li>低速碰撞（小降塔）： <ol><li>负载样品放入剪刀型双释放机制，并接近真空的玻璃管。 </li><li>开始疏散，并设置定时器参数。 </li><li>连接相机至其磁脱扣单元。开始连续摄像头录制。 注意：由于LED的亮场照明的高强度，高速相机的足够短的曝光时间，可以选择这样的曝光过程中颗粒的运动可以忽略不计。最重要的是，在光圈的相机目标必须设置为足够高的值，延长深度焦在落塔的整个直径。 </li><li>当达到所需的真空质量，开关照明，按下启动按钮，并下载图像序列。 </li></ol></li><li>高速碰撞（大落塔）： <ol><li>负载样品到双赢克活板门释放机制和加速器，并关闭真空玻璃管。 </li><li>开始疏散，并设置定时器参数。 </li><li>开始连续摄像头录制。当达到所需的真空品质，开启灯光，并按下启动按钮。下载的图像序列。 注意：由于LED的亮场照明的高强度，高速相机的足够短的曝光时间，可以选择这样的曝光过程中颗粒的运动可以忽略不计。最重要的是，在光圈的相机目标必须设置为足够高的值，延长深度焦在落塔的整个直径。 </li></ol></li></ol> 4例实验<ol><li>谨慎地装载样品到适当的释放机制。 <ol><li>低速碰撞（双重释放机制;0.09米/秒）：5公分比5厘米，弹跳。 加载样本分为两个剪刀式释放机制。至实现0.09米/秒的碰撞速度，将粒子7毫米并设置释放机制的时间延迟到9毫秒。 注：在此冲击速度，灰尘样品弹开对方碰撞后。图像序列是由一个自由落体高速摄像机（见电影6）抓获。 </li> <li>高速碰撞（电磁加速器;7.4米/秒）：2厘米比2厘米，碎片。 加载一个样本到双翼陷门释放机制;将其他样品的线性阶段加速器的样品夹持器。 注意：为了实现7.4米/秒的碰撞速度，较低的灰尘聚集体顺利地加速上行用2克，同时上部灰尘聚集降低。在7.4米/秒的相对速度，灰尘样品片段（见电影7）。 </li> <li>对大骨料小聚合高速碰撞：0.5厘米比5厘米，传质。 负载日Ë大样本到一个剪刀式释放机制;将小样品在弹簧加速器的样品夹持器。 注：为了达到所需的质量传递的碰撞速度，较低的灰尘聚集顺利加速上行，同时上聚集的灰尘落入。在这个相对速度，更小的样品碎片和传输少量的质量到更大的样本。由于相机落在沿上（更大规模的）粒子，采取高速摄像机的图像给大颗粒的印象，或多或少在休息（见电影8），从外面看这是不正确的落塔。 </li></ol></li><li>关闭真空玻璃管。 </li><li>小心打开真空阀，泵启动缓慢疏散，并设置定时器参数，为所需的碰撞速度所需的时间差。 </li><li>连接相机至其释放器（如果自由落体摄像机使用）。开始连续摄像头录像并开启照明。 </li><li>当达到所需的真空质量，按下释放按钮启动定时器序列。 </li><li>下载记录的高速摄像机到计算机的图像序列。 </li></ol> 5。数据分析<ol><li>选择的背景和对象的灰度值之间的一个合适的阈值的灰度值。通过设置具有高于阈值灰度值的像素为白色（二进制值1），像素较低的灰度值，以黑色创建基于此阈值的二值图像（二进制值0）。 </li><li>求出质量的粒子的在每个图像的中心的位置。一个很好的近似，以确定质量中心为对称的粒子是投影区域的中心。这是从二值化后的图像来计算。 </li><li>使用质量的物体的中心的相对位置，时间信息从相机中的图像来计算相对速度（见电影9）。位置曲线的斜率显示在电影9的右手边。 <ol><li>如果发生碰撞反弹的，确定前后联系的相对速度。计算恢复系数， 即速度的碰撞和前后的比率。暗算恢复系数的相对速度。这种分析的一个例子示于图4。 </li></ol></li></ol><img alt="图4" fo:content-width="5in" src="/files/ftp_upload/51541/51541fig4highres.jpg" width="500" /> 图4实施例的碰撞反弹的分析。恢复系数， 即回弹速度与冲击速度的比值，被绘制为碰撞速度的函数。圆圈显示的数据为2厘米直径球形聚集的灰尘之三13（参见图2），三角形表示碰撞直径为5厘米和5厘米的高度的圆柱形灰尘聚集体之间（ 见图2），而在0.3和0.4两个不同的体积填充因子，分别为12。数据显示减少恢复原状随着冲击速度的系数的趋势。 <a href="https://www.jove.com/files/ftp_upload/51541/51541fig4highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <ol start="2"><li>如果一个或两个粒子片段，确定尽可能多地通过测量它们各自的投影面积，并假设适当形状的最大片段的大小。 <ol><li>如果出现只有一个粒子的碎片，它通常一定量的质量转移到幸存的颗粒。确定传送质量的量通过测量增生体积，假定适当的形状和孔隙率来量化质量transfe效率较低。 </li></ol></li></ol>

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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+investigation+of+the+nebular+formation+of+chondrule+rims+and+the+formation+of+chondrite+parent+bodies.">Experimental investigation of the nebular formation of chondrule rims and the formation of chondrite parent bodies.</a> Geochimica et Cosmochimica Acta. 116, 41-51 (2013).</li><li>Jankowski, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crossing+barriers+in+planetesimal+formation:+The+growth+of+mm-dust+aggregates+with+large+constituent+grains.">Crossing barriers in planetesimal formation: The growth of mm-dust aggregates with large constituent grains.</a> Astronomy and Astrophysics. 542, (2012).</li><li>Gundlach, B., Kilias, S., Beitz, E., Blum, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micrometer-sized+ice+particles+for+planetary-science+experiments+-+I.+Preparation,+critical+rolling+friction+force,+and+specific+surface+energy.">Micrometer-sized ice particles for planetary-science experiments - I. Preparation, critical rolling friction force, and specific surface energy.</a> Icarus. 214, 717-723 (2011).</li></ol>

We have nothing to disclose.

由于高的机械精度，这两种滴塔的故障率是极低的。这是非常重要的，因为样品制备可能需要最多几个小时，这取决于尺寸，形状和所希望的灰尘聚集体的孔隙率。它应该提到的是大的灰尘聚集具有非常高的孔隙度是极其脆弱的，因此，难以处理。它可能发生的提取过模具或转移到落塔在这些灰尘聚集打破。在这些情况下，一个新的样本已被制备。因此，重要的是，小落塔可实现可靠的（和可预测的）碰撞速度下降到0.01米/秒11,13。最低的冲击速度迄今取得为0.004米/秒。这些小的冲击速度只能为自由粒子在微重力环境下即可到达。该实验室落塔是一种廉价和灵活的实现这样一个微重力设施。 Alternati已经的方法来实现低的冲击速度下利用悬浮技术14,15（通过电磁或气动悬浮EG），但通常引起碰撞粒子，其具有要考虑到在碰撞的分析之间的力。此外，磁悬浮往往引起旋转运动14，如果没人要，不允许旋转无碰撞，但是，在另一方面，甚至可能让冲突的旋转颗粒间逼真的模拟。在壳体的气动悬浮的，在碰撞过程中的气垫效应可能导致不希望的条件不匹配的那些原行星盘。然而，悬浮允许无限的观察时间和重复的实验，以便它必须考虑的替代落塔，如果时间限制是必要的。我们所有的努力，到目前为止，已经集中在SiO 2的硅酸盐在陆地行星的形成为r的代表EGION年轻的太阳能系统。由于大多数原行星盘的质量集中超出水冰的冷凝点，有必要也研究聚集体组成的微米尺寸的H 2 O的冰颗粒的碰撞行为。我们目前正在建立一个低温真空落塔用于此目的。但必须指出的是，温度在这样的模拟实验必须低于〜150 K，这就是所谓的“雪线”在原行星盘（温度的“雪线”划分，其中水是在气相内的区域相位并从那里被发现作为固体水冰）的外部区域。我们已经表明，微米尺寸的水冰颗粒的形成是可行的，其骨料可以生产16，让我们乐观地未来1-2年之内对他们的碰撞行为第一批成果。

人们普遍认为行星的形成始于微观小灰尘颗粒的非引力聚集成较大的灰尘聚集（见审查百隆＆亚龙）1。灰尘颗粒的原行星盘内，由于布朗运动，相对漂移运动，和星云的气体湍流碰撞（见审查约翰森等人 ）2。如果碰撞速度是足够低的，灰尘颗粒粘在一起，形成更大的团聚体。在过去数年丰富的实验室测量，导致了预测，对灰尘聚集任意群众和碰撞速度3的结果产生灰尘聚集碰撞模型。基本的碰撞结果被粘（一般为小骨料质量和低碰撞速度），弹跳，以及碎片（用于高冲击速度）。然而，这些阶段之间的过渡是不尖锐，还有其他结果，像， 如传质或糜烂。这种模式适用于典型的原行星盘预计在数千年的4厘米大小的灰尘聚集体的增长。厘米大小的灰尘聚集物的存在已被广泛地研究由天文观测，在过去几年，现在可以被认为是关系成立（参见审查TESTI 等人 ）5，使我们得出结论，通过该机制原理的第一个宏观体在年轻的行星系统的形式已经确定。 然而，进一步增长到至少千米大小的身体不是那么清楚。对于陆地行星区，两个假设目前讨论（也见约翰森等人在这个问题上，最近的评论2和TESTI 等[5]。）：（一）浓度厘米大小的灰尘聚集所， 如流不稳定6及后续gravit憩崩溃7,8和几个“幸运儿”，以更大的尺寸与后续质量吸积的传质过程9,10,11（II）的增长。在这两种模式，厘米大小的灰尘聚集发生相互碰撞的巨大数目在低到中等的速度。目前还不清楚这些碰撞的（除了弹跳）可能的结果是。 为了提高通过Güttler 等 3灰尘聚集碰撞模型，并更详细地碰撞调查宏观灰尘聚集在相关的速度政权中，我们设置了两个下拉塔在我们的实验室，其中个人总-总能碰撞被研究的很详细真空和微重力条件。既降塔具有1.5米自由落体的高度，这限制了观察时间来〜0.5秒。因此，我们观察到了碰撞的高速摄像机，百万像素格式和高达每秒7,500帧。为了获得最大的对比度和高的记录速度，亮场照明选择。照明是由高强度的LED面板从而提供和由漫射屏幕均匀。因此，高速摄像机查看碰撞的灰尘聚集的黑色物体在照亮屏幕的正前方。为了避免闪烁时，LED是直流供电。 为了实现低碰撞速度，这两个聚集的灰尘都放在上面彼此的双重释放机制。 吨的时间释放上部骨料下部1的结果中的ν= GT的相对速度之前，用克 =9.81米/秒2为地球的重力加速度。两个高速摄像机，它看到从两个方向90°的碰撞，通常在发布两粉尘总量之间（通常为T / 2上粒子后）。摄像机中的连续记录模式，这是由照相机的影响终止运行人成沙桶。在这种操作模式下，最大帧频为每秒1000张图像万像素的分辨率。采用这种设置，速度降低到低于0.01米/秒已经实现。由于双释放机构的机械设置的限制，最大相对碰撞速度为〜3米/秒。涉及灰尘聚集多达5厘米大小的碰撞进行了调查这个落塔。对于更高的碰撞速度高达约10米/秒，第二分出塔时，里面装有一个电磁加速器，其能够平稳地加速灰尘聚集高达5米/秒在垂直向上的方向。其它灰尘聚集是由一个双翼陷阱门释放机构保持，并且可以旋转自由在任何给定时间释放到自由下落。在这里，它没有任何意义用自由落体摄像机。我们宁愿用两个固定的高速摄像机，每秒百万像素分辨率高达7,500帧。由于较大diamet这个落塔的呃灰尘聚集到（并且可能上文）10cm大小都可以使用。

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Monodisperse SiO2 particles</td>
			<td style="width:71px;">Micromod</td>
			<td style="width:119px;">43-00-153</td>
			<td style="width:167px;">Particle diameter 1.52 &#177; 0.06 &#181;m; particle shape spherical</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Polydisperse SiO2 particles</td>
			<td style="width:71px;">Sigma-Aldrich</td>
			<td style="width:119px;">S5631</td>
			<td>Particle diameter 0.1 &#8211; 10 &#181;m; particle shape irregular</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
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laboratory drop towers for the experimental simulation of dust-aggregate collisions in the early solar system

对于调查的灰尘聚集在早期太阳系演化的目的，我们开发了两个真空下降塔中脆弱的灰尘聚集与规模可达约10厘米，孔隙率高达70％，可以发生碰撞。一个下拉塔主要用于非常低的冲击速度降低至低于0.01米/秒，并使用了双释放机构。冲突由两个高速摄像机，沿玻璃真空集热管中的两个灰尘聚集体的质心的框架落在记录在立体视图。另一自由下落塔使得电磁加速器，其能够平缓加速灰尘聚集到长达5米/秒的用途。在与另一个灰尘聚集体的释放，以自由落体组合，碰撞速度高达约10米/秒就可以实现。在这里，两个固定的高速摄影机记录下碰撞事件。在两个降塔，灰尘聚集在自由落体碰撞时，使它们失重和匹配条件在早期太阳系。

使用在协议中描述的充分表征的灰尘聚集的样品（参见图1-3），在实验室中滴塔之一观察到任何碰撞会产生类似的碰撞在原行星盘的结果，科学的有价值的信息。到目前为止，我们已系统地研究了2厘米碰撞结果大小的球形灰尘聚集体（与填充量为0.5因素）之间的0.008和2.02米/秒13和5厘米大小的柱状灰尘聚集在速度范围内（与体积之间的填充因子在速度范围在0.3和0.5）之间的0.004和2米/秒12。我们发现了灰尘聚集体之间弹跳，作为下面速度〜占主导地位的结果0.4米/秒，这两种类型的灰尘聚集体（参见电影6中的示例）。在图4中，显示这些弹跳碰撞的恢复系数。圆圈表示实验2厘米大小的球形样品13和三角形代表之间5厘米大小的灰尘气缸有两个不同的包装从碰撞结果密度12。虽然个别实验归还系数分散广泛，恢复系数的平均值随碰撞速度减小。 兼具防尘通常聚集在冲击片段速度以上〜1米/秒（见电影7的例子）。为之间〜0.4和〜1米/秒的速度，仅两个碰撞灰尘聚集体的1碎裂的发生原因。在这种情况下，无碎片尘埃聚集由传质13获得质量的百分之几。上述速度极限是不清晰，但表示其中约不同的制度之间的界限在于2,11。对于不同大小的灰尘聚集和中等速度之间的碰撞，影响一般不会导致吨<html>邻的两个灰尘聚集体的较大的碎片。在对面，大机构通过较小的撞击（见电影8）质量的一部分转移提高它们的质量。 为的情况下，其中两个灰尘聚集弹开彼此，从平动能传输碰撞之前（介意的灰尘聚集在碰撞之前不旋转）转换成平动能，回转动能，和其他（耗散）的能量通道（灰尘聚集体如压实）可以被确定。我们发现，对于中央碰撞（在该旋转能量可以忽略不计）耗散的能量的相对量的增加速度强烈地增加，并且是更高的灰尘量较低的填充因子聚集体12。这种行为可以通过分子动力学模拟12为蓝本。 TTPS :/ / www.jove.com/files/ftp_upload/51541/string_trapdoor.MP4“目标=”_blank“&gt;电影1。的粒子上的一个字符串（高速动画（回放慢动作）顶部）和陷阱门释放机制（下）。 <a href="https://www.jove.com/files/ftp_upload/51541/mold_cluster_cluster.MP4" target="_blank">电影2</a> 。双活板门释放装置的高速电影（回放慢动作）。这两个样本是直径为2毫米的Al 2 O 3颗粒，这仍然在自由落体由于发布在极低的干扰受限的团块。 <a href="https://www.jove.com/files/ftp_upload/51541/scissor.MP4" target="_blank">电影3</a> 。剪刀型双释放机制的高速电影（回放慢动作）。 <a href="https://www.jove.com/files/ftp_upload/51541/dw-trapdoor.MP4" target="_blank">电影</a>4，高速双翼陷门释放机制的电影（回放慢动作）。 <a href="https://www.jove.com/files/ftp_upload/51541/trigger.wmv" target="_blank">电影5</a> 。计时器电子开关的上部和下部释放机制以及相机释放到自由下落的动画。 <a href="https://www.jove.com/files/ftp_upload/51541/9ms_2.MP4" target="_blank">电影6</a> 。两个5厘米大小的灰尘聚集气缸之间的碰撞弹跳的高速电影（回放慢动作）。这两个聚集的灰尘通过剪刀式双释放机制释放，碰撞0.09米/秒的速度。 <a href="https://www.jove.com/files/ftp_upload/51541/fragmentation.MP4" target="_blank">电影7</a> 。两个2厘米大小的柱状尘埃聚集的高速电影（回放慢动作）collidi纳克在7.4米/秒的相对速度。这两个片段的聚集完全。 <a href="https://www.jove.com/files/ftp_upload/51541/mass-transfer.MP4" target="_blank">电影8</a> 。5毫米大小的灰尘聚集影响有5厘米大小的柱状固体靶的高速电影（回放慢动作）。由于4.3米/秒的冲击速度超过了小灰尘聚集的碎片的速度，这会崩解和转让其质量的一部分的目标，这是在电影中清晰可见。 <a href="https://www.jove.com/files/ftp_upload/51541/tracking_new.mov" target="_blank">电影9</a> 。测定的粒子轨迹由一个半自动粒子跟踪算法。这里，示出了22厘米大小的球形聚集体尘埃之间的碰撞。

Watch this Scientific Journal Video about Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System at JoVE.com

Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System

我们目前的技术来实现低速到脆弱的灰尘聚集在实验室之间的中间速度的碰撞。为了这个目的，两个真空落塔的设置已经开发了允许&lt;0.01和〜10米/秒之间的碰撞速度。在碰撞事件是由高速摄像记录。

实验室落塔的粉尘聚集在碰撞早期太阳系的实验模拟

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust ...

laboratory-drop-towers-for-experimental-simulation-dust-aggregate

Research

Education

JoVE Core

JoVE Journal

Mechanical Engineering

Engineering

Unit 1

Kinetics of a Particle: Impulse and Momentum

SCIENTISTS IN ACTION

12.6K 次观看.  Technische Universität Braunschweig. 我们目前的技术来实现低速到脆弱的灰尘聚集在实验室之间的中间速度的碰撞。为了这个目的，两个真空落塔的设置已经开发了允许

视频: Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.
Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4.
To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO2 films. In this configuration, photoinduced electrons are injected into TiO2 and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer6. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells7.

A general strategy for the development of charge-separating semiconductor nanocrystal composites deployable for solar energy production is presented. We show that assembly of donor-acceptor nanocrystal domains in a single nanoparticle geometry gives rise to a photocatalytic function, while bulk-heterojunctions of donor-acceptor nanocrystal films can be used for photovoltaic energy conversion.

通过电荷分离纳米晶及其固体收获太阳能

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials ...

科研

工程学

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

模拟行星内部分化过程中的实验室

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

快速成像技术来研究非牛顿流体的跌落冲击动力学

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

集成的三重态 - 三重态湮灭上转换系统，提高染料敏化太阳能电池的响应子带隙光

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

Ambient Method for the Production of an Ionically Gated Carbon Nanotube Common Cathode in Tandem Organic Solar Cells

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

A method of fabricating, in ambient conditions, organic photovoltaic tandem devices in a parallel configuration is presented. These devices feature an air-processed, semi-transparent, carbon nanotube common cathode.

对于一个以离子门控碳纳米管共阴极的串联有机太阳能电池的生产环境法

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two ...

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we present a protocol to adjust the properties of solution-processed CH3NH3PbI3 through the incorporation of monovalent cation additives in order to achieve highly efficient perovskite solar cells.

CH的单价阳离子兴奋剂<sub&gt; 3</sub&gt; NH<sub&gt; 3</sub&gt;碘化铅<sub&gt; 3</sub&gt;对钙钛矿型高效太阳能电池

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical ...

Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of electrospun titanium dioxide nanofibers (TiO2-NFs) on top of a blocking layer made of commercially available titanium dioxide nanoparticles (TiO2-NPs). This is achieved by first electrospinning a solution of titanium (IV) butoxide, polyvinylpyrrolidone (PVP), and glacial acetic acid in ethanol to obtain composite PVP/TiO2 nanofibers. These are then calcined at 500 &#176;C to remove the PVP and to obtain pure anatase-phase titania nanofibers. This material is characterized using scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The photoanode is prepared by first creating a blocking layer through the deposition of a TiO2-NPs/terpineol slurry on a fluorine-doped tin oxide (FTO) glass slide using doctor blading techniques. A subsequent thermal treatment is performed at 500 &#176;C. Then, the light-scattering layer is formed by depositing a TiO2-NFs/terpineol slurry on the same slide, using the same technique, and calcinating again at 500 &#176;C. The performance of the photoanode is tested by fabricating a dye-sensitized solar cell and measuring its efficiency through J-V curves under a range of incident light densities, from 0.25-1 Sun.

The overall goal of this project was to use electrospinning to fabricate a photoanode with improved performance for dye-sensitized solar cells.

染料敏化太阳能电池的光催化电极的电纺丝

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of ...

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction of degradation mechanisms and prevention of module field failure can consequently decrease investment risks as well as increase the electricity yield. An improved knowledge level can for these reasons significantly decrease the total costs of PV electricity. 
In order to better understand and minimize the degradation of PV modules, the occurring degradation mechanisms and conditions should be identified. This should preferably happen under combined stresses, since modules in the field are also simultaneously exposed to multiple stress factors. Therefore, two 'Combined Stress test with in situ measurement' setups have been designed and constructed. These setups allow the simultaneous use of humidity, temperature, illumination, and electrical biases as independently controlled stress factors on solar cells and minimodules. The setups also allow real-time monitoring of the electrical properties of these samples. This protocol presents these setups and describes the experimental possibilities. Moreover, results obtained with these setups are also presented: various examples about the influence of both deposition and degradation conditions on the stability of thin film Cu(In,Ga)Se2 (CIGS) as well as Cu2ZnSnSe4 (CZTS) solar cells are described. Results on the temperature dependency of CIGS solar cells are also presented.

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for CuIn,GaSe2 Solar Cells

Two &#39;Combined Stress test with in situ measurement&#39; setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.

就地太阳能电池和模块加速性能退化的监测: 铜 (in, Ga) Se2太阳能电池的实例研究

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction ...

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is composed of two materials, a plastic and an elastomer, whose dispersion characteristics (refractive index variation with wavelength) are different. We first designed the lens geometry and then used ray-tracing simulation, based on the Monte Carlo method, to analyze its performance from the point of view of both optical efficiency and the maximum attainable concentration. Afterwards, ADG Fresnel lens prototypes were manufactured using a simple and reliable method. It consists of a prior injection of plastic parts and a consecutive lamination, together with the elastomer and a glass substrate to fabricate the parquet of ADG Fresnel lenses. The accuracy of the manufactured lens profile is examined using an optical microscope while its optical performance is evaluated using a solar simulator for concentrator photovoltaic systems. The simulator is composed of a xenon flash lamp whose emitted light is reflected by a parabolic mirror. The collimated light has a spectral distribution and an angular aperture similar to the real Sun. We were able to assess the optical performance of the ADG Fresnel lenses by taking photographs of the irradiance spot cast by the lens using a charge-coupled device (CCD) camera and measuring the photocurrent generated by several types of multi junction (MJ) solar cells, which have been previously characterized at a solar simulator for concentrator solar cells. These measurements have demonstrated the achromatic behavior of ADG Fresnel lenses and, as a consequence, the suitability of the modelling and manufacturing methods.

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass ADG Fresnel Lens for Concentrating Photovoltaics

The achromatic doublet on glass (ADG) Fresnel lens makes use of two materials with differing dispersion to reduce chromatic aberration and increase attainable concentration. In this paper, a protocol for the complete characterization of the ADG Fresnel lens is presented.

玻璃 (ADG) 菲涅耳透镜对聚光光伏的效率和辐照点的室内实验评价

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is ...

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued development of nanocrystalline metals. Despite these efforts, the transition of these materials from the lab bench to actual applications has been blocked by the inability to produce large scale parts that retain the desired nanocrystalline microstructures. Following the development of a method proven to stabilize the nanosized grain structure to temperatures approaching that of the melting point for the given metal, the US Army Research Laboratory (ARL) has progressed to the next stage in the development of these materials - namely the production of large scale parts suitable for testing and evaluation in a range of relevant test environments. This report provides a broad overview of the ongoing efforts in the processing, characterization, and consolidation of these materials at ARL. In particular, focus is placed on the methodology used for producing the nanocrystalline metal powders, in both small and large-scale amounts, that are at the center of ongoing research efforts.

This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

美国陆军研究实验室散装纳米晶金属的加工

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued ...