楼主: Rojer

[项目新闻] [独立平台] [人工协作类] [天文类] Stardust@home

 楼主| 发表于 2007-9-24 10:02:56 | 显示全部楼层
September 21, 2007

New Blog!!

We have added a new feature to our website in the news section, a blog. Through the blog you will be able to find out what is happening behind the scenes of Stardust@home directly from the team members themselves. Our first blog entry is from the project director, Andrew Westphal. You need to be logged in to read the blog and all questions or comments you have about anything in the blog should be directed to the forums.

我们在网站的新闻部分添加了一个新东西,Blog。通过该Blog诸位可以从小组成员那里直接找出 Stardust@home 幕后正在发生着什么。我们首篇Blog来自项目主管 Andrew Westphal (安德鲁 维斯特法尔)。需要登陆后才能看到,你对blog任何的问题和评论都将被定向到论坛。

我把 Andrew 的贴过来吧

Thursday, September 20, 2007
Picokeystoning this week
This is our first blog entry. In order to do this expeditiously, these will be stream-of-conciousness blogs, with little or no wordsmithing, so please forgive spelling mistakes, ungrammatical sentences, and so on. I'm just writing this as if I'm writing an e-mail to a colleague. Which, effectively, I am.

We're doing picokeystoning practice here at SSL in preparation for another trip to JSC the week of Oct. 8 to practice picokeystoning in the Stardust flight spare. We set up a picokeystone in the cleanroom on Monday afternoon on a practice tile of aerogel, but when we came in on Tuesday morning, it looked strange. After scratching our heads for a bit, we realized that the undercutting needle was trying to do the vertical cut, and the result was a strange-looking keystone that had the vertical cuts backwards. We realized that it was a port configuration problem, and fixed it. We set up a new picokeystone on Tuesday afternoon, and on Wednesday morning realized that the vertical cut was not quite deep enough, so Dave (Frank) restarted it with a deeper vertical cut. This cut turned out to be too deep -- the picokeystone popped out and was lost! Obviously we can't tolerate this kind of problem with the real interstellar grains. We're busy today preparing a cometary sample for FTIR analysis at the ALS. After we finish that, by tomorrow morning, we'll set up a new practice picokeystone, going back to a technique that we used before the return of Stardust. We'll do most of the keystoning procedure, up but not including the final cut that separates it from the tile. We'll remove the undercutting needle and replace it with a micropicklefork, and place the fork gently on the keystone to hold it in place. Then we'll do the final cut, put the fork into its final place, and lift it out. This is a good reminder that this is really as much art as science.

Stay tuned!

-- Andrew


参与人数 1基本分 +20 维基拼图 +10 收起 理由
霊烏路 空 + 20 + 10


 楼主| 发表于 2007-12-13 08:53:41 | 显示全部楼层
 楼主| 发表于 2008-2-14 09:22:40 | 显示全部楼层
2008年2月13日   竟然在我生日这天
早上我们从“星尘”收集器的 I1017,2 提取出第一个轨迹。见下图,由于比例关系最终颗粒位于表面200微米之下。

http://stardustathome.ssl.berkel ... e=1&coords=?299,20&firstclicker=mhershberg&TheName=No%20name%20specified%20yet

[ 本帖最后由 Rojer 于 2008-2-14 10:19 编辑 ]


参与人数 1基本分 +20 维基拼图 +10 收起 理由
霊烏路 空 + 20 + 10


发表于 2008-2-14 10:35:46 | 显示全部楼层

回复 #33 Rojer 的帖子


发表于 2008-2-14 10:41:03 | 显示全部楼层

回复 #33 Rojer 的帖子


发表于 2008-2-14 11:51:48 | 显示全部楼层
Rojer 生日快乐~~
发表于 2008-2-14 14:08:21 | 显示全部楼层
发表于 2008-2-14 14:48:09 | 显示全部楼层
发表于 2008-2-14 14:59:19 | 显示全部楼层
 楼主| 发表于 2008-3-17 16:08:36 | 显示全部楼层
The Alpha List
Thu, 28 Feb 2008 00:47:00 +0000

We have recently added a new feature to the Stardust@home website to help make our candidate selection process more transparent, called the Alpha List.
我们已在 Stardust@home 的网页上添加了一个称为“Alhpa List”新的东西,它有助于使我们的候选者筛选过程更透明。

The Alpha list is a list of focus movies that show the most promise in being a candidate stardust particle track. The alpha list movies are chosen from the top scoring focus movies as determined by all of the Stardust@home Dusters. The alpha list also contains some movies that were mentioned in the forums and promoted by the Stardust@home team as being promising. Other alpha list movies have been promoted to the list by members of our Red Team.
Alpha 名单是一份最有希望成为星际尘埃轨迹候选者的影片名单。alpha名单中的影片是从全体搜尘者打分最高的影片中选出的。Alpha名单同样包含了一些论坛中提到并由Stardust@home小组提升进来的一些有希望的影片。Alpha名单中其他的影片是由“红组”的成员提升进来的。

We have recently formed a so-called "Red Team" for Stardust@home, consisting of 29 of the most experienced Dusters. Red Teams at NASA are used to evaluate and improve projects. Our Red Team evaluates the top candidates by rating the alpha list movies and making comments about them. The Red Team members were selected based on their experience in the project, they are some of the highest scorers from Phases 1 and 2 as well as some of our Dustmods from the forums. You, too, can join the Red Team. You qualify to join by scoring in the top 23 of the Phase 2 rankings.

The Red Team and the Stardust@home team have been reviewing the alpha list and giving each movie on the list a rating on a 10-point scale where 0 is not likely at all to be an interstellar dust impact, and 10 is the highest likelihood. The ratings you see on the alpha list page are the average of the ratings given to each movie by the Red Team and the Stardust@home team.

We start off with millions of movies. Dusters are the only technology we have to identify movies of interest. Once enough Dusters have identified a movie, it is then promoted to the alpha list. The alpha list is then refined by the Red Team. Finally, the Science Team prioritizes the alpha list for extraction and analysis.

Now that we are extracting candidates from the collector, we will be learning a tremendous amount about the features that the Stardust@home "dusters" have identified. The contrast between the images taken while the track is still in the aerogel tile in the collector, and in the keystone extracted from the collector, (see the blog) shows how important it is to do extractions. We will all be learning together!

[ 本帖最后由 Rojer 于 2008-3-17 16:11 编辑 ]


参与人数 1基本分 +50 维基拼图 +25 收起 理由
霊烏路 空 + 50 + 25


 楼主| 发表于 2008-3-18 12:59:47 | 显示全部楼层
Friday, February 29, 2008

Synchrotron x-ray fluorescence analysis of the first track Last week, Frank Brenker and his colleagues Bart Vekemans, Laszlo Vincze, and Manfred Burghammer analyzed the first track to be extracted from the Stardust Interstellar Collector. We suspected that this is a particle that was ejected from an impact of a high-velocity particle (either an interplanetary dust particle or an interstellar dust particle) on the port (left-side) aft solar panel. We thought that this would be the case for two reasons. We mainly based this expectation on the trajectory -- it appears to be pointing back to the aft solar panel -- but also on the track shape -- it does not show the shock-induced flaring that one usually sees with hypervelocity impacts. Dr. Brenker and colleagues used a highly focussed x-ray beam at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. ESRF is essentially an x-ray microscope the size of a shopping mall. The incredibly tight focus of this beam (about a tenth of a micron!) is ideal for the analysis of these very tiny samples. The use of x-ray fluorescence is also ideal for the analysis of these particles, because you can analyze particles while they are still in the aerogel keystones -- there is no need to extract them.
上周 Frank Brenker 和他的同事们 Bart Vekemans, Laszlo Vincze, Manfred Burghammer 对从“星尘”收集器中取出的第一个轨迹进行了同步X射线荧光分析。我们怀疑这个颗粒来自于一个高速粒子(可能是太阳系内尘埃也可能是星际尘埃)与船左后部太阳能板撞击产生的溅射。我们认为可能有两种原因导致这一情形。我们的这种期望主要基于它的弹道看上去是指向后部的太阳板,但它同样有轨迹的外形,没有显示出高速撞击通常出现的冲击引起的开口。Brenker 博士及其同事们使用的是在法国 Grenoble 市的欧洲同步辐射装置(ESRF)产生的高度聚焦的X射线。ESRF 本质上来说是一台购物中心大小的X射线显微镜。射线焦点小的难以置信(大约十分之一微米)对于分析这些非常微小的样本非常合适。使用X射线荧光对分析这些颗粒同样十分理想,因为它们还在凝胶楔块里的时候你就可以对其分析,没有必要把它们弄出来。

Dr. Brenker found that the captured particle was very rich in the elements cerium and zinc. This is consistent with the glass covering over the solar panels. But there was also a surprise: there was a substantial amount of iron and nickel. These are not expected to be present in the solar panel glass, but are very commonly found in extraterrestrial materials. (Iron-56 is the most tightly bound nucleus in Nature, is made in prodigious quantities in supernovae, and is very commonly found in extraterrestrial materials.) So it appears that not only do we have materials from the spacecraft, which we expected, we also have our first sample of extraterrestrial material capture in the interstellar collector, which we did not! The next steps are to do more detailed, non-destructive analysis on this track, and the other two tracks that have been extracted. Eventually, these tracks will be made available to the scientific community to request to for doing destructive analyses. For example, these particles couldbe extracted from their keystones, sliced into extremely thin slices using a diamond knife, and analyzed by Transmission Electron Microscopy, or they could be analyzed for their isotopic abundances in very sensitive mass spectrometers, like the Cameca nanoSIMS.
Brenker博士发现捕获到的颗粒中铈、锌元素的丰度很高。这与覆盖太阳能板的玻璃相一致。但也有令人惊异的:大量的铁和镍。不认为这些来自太阳能板玻璃,而在地球之外物质中经常见到。(铁-56是自然界中最稳固原子核的上界,大量产生于超新星,在地外物质中十分常见。)看起来我们既得到了预期来自飞船的物质,同时还得到了星际尘埃收集器捕获的第一个地外物质样本!接下来要做的更为细致,对这个轨迹进行非破坏性的分析,同时另外两个轨迹也取出来了。最终这些轨迹将提供给科学界作破坏性的分析。比如,这些颗粒将从各自的楔块中被取出,用钻石刀切成极其微小的小块儿由透射电镜(Transmission Electron Microscopy)分析,或者用于非常灵敏的光谱仪(象Cameca nanoSIMS之类的)分析它们的同位素丰度。


参与人数 1基本分 +50 维基拼图 +25 收起 理由
霊烏路 空 + 50 + 25


 楼主| 发表于 2008-4-20 13:51:39 | 显示全部楼层
Monday, March 31, 2008
Houston Trip
Whew! That was a great trip! The teamwork approach of having one fellow in the cleanroom during an extraction, and others available via conference call has been very workable. This week we pulled out a blank, and a high angle track first found by playingthru. The particle is as yet unnamed.
啊、真是这趟旅行真不错!在提取期间小组差不多只剩一个人在洁净室了,其他人都受到不同会议的召唤。本周取出了一个空白块,以及由 playingthru 发现的一个高角度轨迹。该颗粒还没有命名。

The blank picokeystone served a couple purposes. First, it acted as a control, and as a test for the new experimental setups. Second, it allowed us another practice shot at pulling picokeystones from the collector without risking a live particle. As you know, pulling particles from the interstellar side is vastly more difficult than it was for the cometary side.

The first blank went well, but I had to babysit it -- we had some trouble with the needles getting caught on the corners while cutting. The resulting keystone is a beauty. Here it is:

The needle catching problem is an old issue that we have ameliorated with stiffer needles and an improved corner cutting procedure, but it hasn’t been fully solved, apparently. We had ideas in the queue about how to solve this problem should it arise again, but we hadn’t implemented them because we thought they wouldn’t be needed.

Well, now they are needed. And they are the essence of simplicity. Andrew’s idea from some time ago is that instead of cutting a “U” shape, we will cut criss-cross lines -- like this:
现在用的上了,最主要的是简单。Andrew 的办法是取代切出“U”形,转而使用十字交叉线,就像这样:

This is a great improvement because it means that the needle never turns corners. So we shouldn’t have the problem at all. In addition, I appended the idea that we change the sequence of the cuts to leave the pico portion until last. This would reduce the amount of strain on the aerogel in the vicinity of the track and minimize chances of gremlins getting access to the keystone.

So, while I was at Houston, Dave and Andrew threw together all the ingredients and tried this out on our system in Berkeley -- to champion results! We’ll soon be trying this on the flight spare collector (not the real thing) in Houston again, to make sure that it is risk free, and then we’ll move back to the flight collector (real thing) for some particle extractions!
所以当我在休斯顿时,Dave 和 Andrew 将这两个因素投入到我们伯克利的系统上实验,为结果而奋斗!我们很快会在休斯顿的备用收集器(不是真正的)上再次实验,以确保没有风险,然后再回到真正的收集器上做一些颗粒的提取。

Meanwhile, I went on to cut another high angle track -- this one was originally found by playingthru and he hasn’t given it a name yet. So, until we get an official name, this is the playingthru track. And here she is (100X, 200X, 500X):
此间,我会继续切割别的高角度轨迹——这是由playingthru最先发现的,尚未命名。所以在得到名字之前就叫playingthru轨迹。见图(100X, 200X, 500X):

This track has similar angle to the other tracks, so our best guess is that it is a fragment from the spacecraft solar panel that was splattered into our collector after something impacted the panel. That would be called a secondary particle. However, we also know that in such an impact, there is a chance that a fragment of the impactor may fly into the collector, so until we get to look at it with x-rays in the synchrotron we won’t know for sure whether this is space dust, or Earth dust in space. :-) But in the interests of not giving false hope, the chances are, probably, it is solar panel.
这个轨迹同其他的轨迹有着相似的角度,于是最佳的假设是有什么东西撞上了太阳能电池板之后溅射出的碎片进入了收集器。可以称为二次颗粒。我们知道在这样的撞击中,撞击体的碎片有机会飞入收集器,所以直到用同步加速器中的X射线检查过后才能确切的知道这是宇宙尘埃还是宇宙中的地球尘埃。:-) 有可能它是来自电池板。



参与人数 1基本分 +60 维基拼图 +30 收起 理由
霊烏路 空 + 60 + 30


 楼主| 发表于 2008-5-30 11:28:51 | 显示全部楼层
Friday, May 23, 2008
2008年5月23 星期五

Here is an update on where we are on extractions.
We were extracting in Houston the week before last, and progress was very slow-we had to abort two overnight extractions because of problems with the needle wandering and in both cases endangering the targets.  This was mysterious behavior, and we were quite puzzled about it. We only just understood the cause of this on Thursday–it is because of large temperature varations (around 10 degrees F) in the Cosmic Dust Lab.  This causes differential contraction in the extraction equipment–we don't know yet whether it is in the micromanipulator, the long arm, the arm holder, or a combination–but it is just not acceptable to put the samples at risk. The temperature variations are new, without a doubt, but we didn't know whether this is because it is become summer in Houston or because of some failure in the laboratory temperature control, or something else entirely. We found out this week that it was the "something else entirely":  it was a combination of a failure of the steam heating system, and also setting the thermostat lower in the neighboring Meteorite Lab, where they were processing frozen meteorites from Antarctica.

We had planned to go back this week to continue, but we postponed in order to give JSC time  to diagnose and correct the problem–which they did!  Zack is going back to Houston next week, and we will resume extractions. Dave is taking a well-deserved break, and will be moving to Houston permanently in June.
我们原计划这星期回去继续,不过我们推迟了以给JSC时间诊断并纠正问题——就是他们造成的!Zack 将在下周回休斯顿,我们将继续提取工作。Dave 正在享受应得的休息,将在六月回休斯顿。

Here's where we are:

38843 First IS candidate–looks consistent with a IS track when viewed in the picokeystone. Waiting for analysis from ESRF.
48469 Successfully extracted in a picokeystone, analyzed at the ALS by STXM, turned out to be a small disk-like piece of alumina
16490 Aborted in the middle of the extraction because it became clear that it was an inclusion. It looked like an extended feature in a little "valley" in a region of complex topography, but after we started the extraction and some aerogel debris was  generated by the cutting, we realized that there was a substantial amount of water-clear aerogel above it, so it became clear that it was not a track.  The aerogel is totally invisible in the VM and in the microscope before extraction.
834150 Successfully extracted–will go to the nanoprobe at ESRF in June
129070 This target was reminiscent of 38843.  Aborted in the middle because it became obvious that it was not a track–it moved!
38843 首个IS候选者——透过楔块儿观察有着与IS相符的轨迹。等待来自ESRF的分析结果。
48469 成功的提取出来已经在ALS用STXM分析过,证实是一小片盘状氧化铝。
16490 在提取过程中中止了,因为事情变得明确了它是一个内含物。它看起来像是一片复杂地形的一处“小山谷”中的结构,但是在我们开始提取以及切割过程中产生的一些凝胶碎片后,我们意识到这地方有大量的水色透明的凝胶在它上面,事情清楚了它不是一个轨迹。在提取前这些凝胶在VM和显微镜中完全看不到。
834150 成功的取出——将在六月送到ESRF用纳米探针探查。
129070 就像是38843的回顾。中途停止了它明显不是一个轨迹——它移动了!

We have chosen another target similar to 38843, now officially named "Nairbus" by its discoverer. This is 134954.  We are about half-way through its extraction, and will resume on


参与人数 1基本分 +50 维基拼图 +25 收起 理由
霊烏路 空 + 50 + 25


 楼主| 发表于 2008-7-18 13:56:30 | 显示全部楼层
Thursday, July 10, 2008
Update on ESRF run on five interstellar candidates
2008年7月10日 星期四

We've analyzed five of our interstellar candidates on beamline ID22 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Our colleagues there are Alexandre Simionovici (University of Grenoble), Laurence Lemelle (University of Lyon), Pierre Bleuet (ESRF), and Romain Basset (University of Lyon).  This is a highly sophisticated synchrotron beamline called the x-ray nanoprobe. It uses Kirkpatrick-Baez mirrors to focus the intense x-ray photons from the synchrotron to a spot only 150nm by 90nm in size. (1 nm -- a nanometer -- is a billionth of a meter). This beamline is very well-suited for the analysis of the expected interstellar dust particles.
我们用位于法国 Grenoble 的欧洲同步辐射设备(ESRF)对5个星际尘埃候选者进行了分析。我们的同事 Alexandre Simionovici(Grenoble 大学)、Laurence Lemelle(里昂大学)、Pierre Bleuet(ESRF)和 Romain Basset(里昂大学)在那里。这是种高度复杂的叫做X射线纳米探针的同步光线。它是使用Kirkpatrick-Baez镜将来自同步加速器的强烈X射线聚焦到仅有150-90纳米范围内的一点(1纳米等于10亿分之一米)。这种光线非常适于分析期望中的星际尘埃颗粒。

This analysis was challenging technically. We used two different kinds of sample mounting techniques, each of which has its advantages and disadvantages.

The first is a silicon nitride window sandwich (picture below). The picokeystone is trapped between the two silicon nitride windows. The silicon window frames are each 200 microns thick, so the total sandwich thickness is 400 microns. The window frames are 5mm x 5mm and the windows are 1500 microns wide and 70nm (!) thick. This is a really nice mounting technique for numerous reasons -- one of which is critical: the keystone cannot be easily lost because it is trapped in the sandwich. The windows are very clean and have undetectable levels of trace elements.  We can place the picokeystone essentially anywhere in the window to help with any geometrical issues.  The advantage of this method is that it is very easily to see the sample and to navigate, and the silicon nitride is quite robust. The disadvantage is that this precludes fluorescence-tomography.
第一种是氮化硅夹心窗(下图)。小楔块儿陷于两个氮化硅窗体中间。每一个硅窗框有200微米厚,所以整个夹窗的厚度是400微米。窗框是5mm x 5mm,窗口是1500微米宽厚度只有70纳米。这是种非常好的固定技术,有诸多原因——其中一个很重要的是陷在夹层中的楔快不容易丢失。窗体很干净痕迹元素水平低到无法觉察。本质上我们可以把小楔块儿放置在窗中的任何位置,没有任何几何问题。该方法的优点是可以很容易的对样品进行观察和定位,氮化硅也相当的结实。缺点是不能做X射线荧光层析。


The second is an ultralene bubble -- the picokeystone is sandwiched between two 4-micron ultralene plastic sheets, then sealed in with a soldering iron with a Nb wire tip. The advantage is that one has no geometrical issues with seeing the sample through the side. The disadvantage is that we found that is very difficult to navigate -- the plastic is hard to see through, and there are interesting optical effects that offset the optical image with respect to the actual position. We never could converge on a suitable fiducial. Fine (10-micron) chromel wire produced too much Ni background in the fluorescence detector. For scale, the Al holder in the image is the same size as the one in the image with the silicon nitride window sandwich.
第二种是ultralene bubble,小楔块儿夹在两个4微米的 ultralene 塑料薄片中,然后用铌线尖端做的烙铁封闭。优点是从边上观察样品没有几何障碍,缺点是我们发现它很难定位——很难透过塑料观察,并且存在有趣的光学效应——会使实际位置的光学影像发生偏移。我们从没能就一个合适的基准达成一致。细小的镍铬合金线在荧光探测器中产生了过高的镍背景。

Experience has shown that it is not wise to speculate about what we have until we've really digested the data.  We expected from the beginning that at least some of our candidates would not turn out to be real -- comparing the number of candidates and the number of expected events in the same area, we anticipate that at most 40% of our candidates would be real. The candidates that we looked are: 9471219V1, 5637295V1, 404198V1, 3602277V1, and 9267050V1. You can look at these on the alpha list.
经验表明在我们真正消化掉数据前对结果进行推测是不明智的。我们从一开始就认为至少部分候选者不会是真的——对比一下在同一区域中的候选者数量和预期的数量,我们估计最多有40%是真的。我们看过的候选者是:9471219V1, 5637295V1, 404198V1, 3602277V1, 和 9267050V1。你可以在Alpha表中看到这些。

This was a successful synchrotron run at one of the most sophisticated beamlines at one of the three most powerful synchrotrons in the world. It will tell us a lot about how to recognize real tracks as we continue our search. Stay tuned!


参与人数 1基本分 +70 维基拼图 +35 收起 理由
霊烏路 空 + 70 + 35


 楼主| 发表于 2008-8-12 16:07:27 | 显示全部楼层
Thursday, July 31, 2008
Status report on six interstellar candidates

We have finished the analysis now of six of our interstellar candidates -- one by Scanning Transmission X-ray Microscopy (STXM) at the Advanced Light Source (ALS) synchrotron at Lawrence Berkeley National Laboratory, and five by high-resolution Synchrotron X-ray Fluorescence (SXRF) Microscopy at the European Synchrotron Radiation Facility (ESRF). All candidates have also been analyzed using Fourier-Transform Infrared (FTIR) spectroscopy at the ALS. The STXM work was done in collaboration with Tolek Tyliszczak and Anna Butterworth; the SXRF work was done with Alexandre Simionovici, Laurence Lemelle, Pierre Bleuet, Peter Cloetens, and Romain Basset. The FTIR work was done in collaboration with Hans Bechtel and Sasa Bajt.

First, the mildly disappointing but unsurprising news -- it does not appear that any of our candidates are likely to be interstellar. The one that we looked at by STXM (4589365V1) was a water-clear alumina inclusion near the surface of the aerogel. Of the five that we analyzed at the ESRF, three (9471219V1, 9267050V1, 404198V1) show high Zn/Fe, one (5637295V1) shows Si, S and Ni but no Fe , and one (3602277V1) shows nothing at all in x-ray fluorescence.
首先是稍微有些失望但并不奇怪的消息——看起来没有一个候选者像是星际尘埃。我们用STXM观察的那个(4589365V1)是一个靠近凝胶表面的透明氧化铝内含物。在ESRF分析的那5个,三个(9471219V1, 9267050V1, 404198V1)表现出高Zn/Fe值,一个(5637295V1)显示出Si、S和Ni但没有Fe,另一个(3602277V1)在X射线荧光反应中什么也没显示出来。

The reason that we conclude that these are unlikely to be interstellar candidates is because Zn is a relatively rare element in the universe, while Fe is one of the most common. A high Zn/Fe ratio is most likely an indication of terrestrial material. Similarly, it is unexpected to find Ni without Fe. Lastly, it is possible that an impact could show no detectable material using these techniques if it is purely made of H, C, N and O ("organic" material), but feature 3602277V1 appears to be crater-like rather than track-like, which is unexpected.

While our assessment is that none of these features are likely to be interstellar, these samples will be available to investigators for more detailed analyses in the near future, and we could be surprised.

But there is also good news. We have successfully demonstrated the critical techniques that will be important for this project.

First, identification of candidates through the Stardust@home collaboration:
We know from two lines of evidence that the detection efficiency for tracks with the expected size and morphology of interstellar dust tracks is high -- first, because we have measured duster efficiency using calibration images and found the efficiency to be very high, and second, because many very thin (2 micron diameter) bona-fide off-normal tracks have been identified by Stardust@home dusters --- typically >300 dusters have identified each of these. Because of their weaker contrast, these should be more difficult to identify than high-velocity interstellar tracks.

Second, we can now reliably extract tracks directly from the tray with low (but not zero) risk, although the process is slow and tedious (and fortunately mostly automated), and must be tailored to each extraction since the local topography is often complex. Dave Frank has now completed the move from Berkeley to JSC and is working hard at extractions on the interstellar tray. We now permanently preserve trajectory information right in the picokeystone using a thin artificial track.
其次,现在我们可以以低风险(但不是零)从盘中直接取出轨迹,虽然过程慢且枯燥(幸运的是几乎是自动的),并且由于局部地形总是很复杂每一个提取物都要经过裁剪。Dave Frank 现在完成了伯克利给JSC的影片,正埋头于星际尘埃盘上的提取工作。我们现在用一条细小的人造轨迹永久的保存微楔形块中弹道信息。

Third, we can analyze these candidates on at least four different synchrotron beamlines (ALS/1.4.3 FTIR, ALS/11.0.2 STXM, ESRF/ID13 SXRF, ESRF/ID22 SXRF) and next week we expect to have an analysis at the 2-ID SXRF beamline at the Advanced Photon Source (APS) at Argonne National Laboratory with Steve Sutton and George Flynn on at least two more IS candidates. We can do synchrotron fluorescence mapping with ~100nm resolution, map abundances of many major elements (including Mg and Si) and do X-ray Absorption Near-Edge Spectroscopy (XANES) using x-ray absorption mapping with ~25nm resolution, and search for organic materials with ~0.1% sensitivity in micron-scale particles using FTIR, all essentially non-destructively and in situ in the aerogel picokeystones. We expect to have a fluorescence tomography analysis done on one of the IS candidates by Alexandre Simionovici and colleagues at ESRF in the next month or so.
第三,我们可以用至少四种不同的同步光(ALS/1.4.3 FTIR, ALS/11.0.2 STXM, ESRF/ID13 SXRF, ESRF/ID22 SXRF)来分析这些候选者,下周我们期待用阿冈国家实验室先进光子源的2-ID SXRF光线来分析至少两个IS候选者。我们可以做到分辨率约100纳米的同步荧光图,绘制多种主要元素(包括Mg和Si)图;还能做近缘X射线吸收光谱(XANES),分辨率~25纳米;使用FTIR在微米尺度粒子上以~0.1%的灵敏度寻找有机物质,所有都是本质上非破坏性的对微楔形凝胶块的分析。我们期待下月在ESRF的 Alexandre Simionovici 及其同事对一颗IS候选者做的荧光断层分析。

Finally, an important point is that although none of our first candidates appear to be interstellar, it is quite amazing that we are able to say that at all. The fact that we are able to do detailed characterizations and make sensible assessments of these tiny candidates is very important. A lesson from the cometary side of Stardust is how critical but difficult it is to adequately characterize samples before they are sent out to investigators.

Although this is mildly disappointing, it is not unexpected. We are just starting to look at our candidates, and we knew from the beginning that our signal to noise was low. These are still early days -- these candidates comprise about 6% of our current list of candidates. Statistically we could have expected to find perhaps one real interstellar track among these first candidates, so finding none is not at all surprising. We are not at all discouraged by these early results, but even more determined to press on to identify and analyze the first contemporary interstellar dust particles ever returned to earth for analysis.


参与人数 1基本分 +100 维基拼图 +60 收起 理由
霊烏路 空 + 100 + 60


您需要登录后才可以回帖 登录 | 新注册用户



小黑屋|手机版|Archiver|中国分布式计算总站 ( 沪ICP备05042587号 )

GMT+8, 2023-12-6 09:51

Powered by Discuz! X3.4

© 2001-2017 Comsenz Inc.

快速回复 返回顶部 返回列表