Vavilov, Cherenkov, and credit for discoveries

We all know that accelerated charged particles emit light - that's how modern high-intensity light sources, synchrotrons, function. Interestingly, uniformly moving particles can emit light too.

The idea goes back to the 1904 Sommerfeld's paper, where he studied the motion of charged particles in a vacuum, and demonstrated that particles flying faster than the speed of light emit radiation even when moving uniformly [1]. Of course, the special relativity theory that appeared next year, rendered Sommerfeld's discovery just a funny mathematical result that has nothing to do with reality, since according to the special relativity no particle can move faster than light in a vacuum.

It's worth noting that the velocity restrictions imposed by the special relativity apply only to a single particle (a group velocity of a bunch of particles can be anything) moving in a vacuum (the speed of light in a medium is much smaller than in a vacuum and particles can move faster than that). However, it took more than 30 years to generalize the Sommerfeld idea to the case of charged particles propagating through a material.

Pavel Cherenkov was pursuing a PhD under Sergey Vavilov, a brother of a famous geneticist Nikolai Vavilov (who was imprisoned and eventually killed by the Soviet regime). Cherenkov was studying the luminescence of uranium salts in solutions irradiated by gamma-rays, and was quite surprised to see the "luminescence" of a pure liquid (sulfuric acid it was), with no salts added. Actually, he was convinced that his PhD work was completely ruined [2].

And it was Vavilov who suggested that this radiation was not luminescence but something completely new, and encouraged Cherenkov to continue the measurements. Indeed, very soon Igor Tamm and Ilya Frank developed a theory for the effect, showing that the radiation is emitted by electrons propagating faster than the speed of light in this particular solution. In 1958 Cherenkov, Tamm, and Frank shared a Nobel Prize for this discovery (unfortunately, without Vavilov who deceased in 1951).

Although Russians call it the "Vavilov-Cherenkov effect", it seems that the name of Vavilov is omitted in the rest of the world where people simply refer to the "Cherenkov Radiation". Why do they?

The funny thing is that immediately after the discovery Vavilov (himself) wrote a paper and submitted it to Nature, where it was rejected (!), and then to Physical Review. This paper had a single author - Cherenkov [3].

I wonder whether such an extreme academic generosity would be possible nowadays :-)

Take care,

Misha

[1] A. Sommerfeld, Göttingen Nachrichten 9, 363 (1904); 201 (1905)

[2] V. L. Ginsburg "About science and about myself" (2001)

[3] P. A. Čerenkov, Phys. Rev. 52, 378 (1937)

Hell for scientists

First Circle: Limbo

"The uppermost circle is not a place of punishment, so much as regret. Those who have committed no scientific sins as such, but who turned a blind eye to it, and encouraged it by their awarding of grants and publications, spend eternity on top of this barren mountain, watching the carnage below and reflecting on how they are partially responsible..."

Second Circle: Overselling

"This circle is reserved for those who exaggerated the importantance of their work in order to get grants or write better papers. Sinners are trapped in a huge pit, neck-deep in horrible sludge. Each sinner is provided with the single rung of a ladder, labelled 'The Way Out - Scientists Crack Problem of Second Circle of Hell"

Third Circle: Post-Hoc Storytelling

"Sinners condemned to this circle must constantly dodge the attacks of demons armed with bows and arrows, firing more or less at random. Every time someone is hit in some part of their body, the demon proceeds to explain at enormous length how they were aiming for that exact spot all along."

Fourth Circle: P-Value Fishing

"Those who tried every statistical test in the book until they got a p value less than 0.05 find themselves here, an enormous lake of murky water. Sinners sit on boats and must fish for their food. Fortunately, they have a huge selection of different fishing rods and nets (brandnames include Bayes, Student, Spearman and many more). Unfortunately, only one in 20 fish are edible, so they are constantly hungry."

Fifth Circle: Creative Use of Outliers

"Those who 'cleaned up' their results by excluding inconvenient data-points are condemned here. Demons pluck out their hairs one by one, every time explaining that they are better off without that hair because there was something wrong with it."

Sixth Circle: Plagiarism

"This circle is entirely empty because as soon as a sinner arrives, a winged demon carries them to another circle and forces them to suffer the punishment meted out to the people there. After their 3 year "post" is up, they are carried to another circle, and so on..."

Seventh Circle: Non-Publication of Data

"Here sinners are chained to burning chairs in front of desks covered with broken typewriters. Only if they can write an article describing their predicament, will they be set free. Each desk has a file-drawer stuffed full of these, but the drawers are locked.

Eighth Circle: Partial Publication of Data

"At any one time exactly half of the sinners here are chased around by demons prodding them with spears. The demons choose who to chase at random after ensuring that the groups are matched for age, gender, height and weight. Howling desert winds blow a constant torrent of articles announcing the success of a new program to enhance participation in physical exercise - but with no mention of the side effects."

Ninth Circle: Inventing Data

"Here Satan himself lies trapped forever in a block of solid ice alongside the worst sinners of all. Frozen in front of their eyes is a paper explaining very convincingly that water cannot freeze in the environmental conditions of this part of Hell. Unfortunately, the data were made up."

via 

Take care,

Misha

Misconduct or not?

Imagine such a hypothetical situation. Someone is working in a research institution as a PhD student or a postdoc. She/he is very lazy and hires university students to analyze her/his experimental data, paying them as low-class workers. No one knows about that including the group leader, and names of these students never appear in articles neither among the authors nor in acknowledgements.

As for me, I think that this situation would make a case of misconduct, since it goes against such basic principles of research as openness and confidence.

What do you think?

Misha 

That's all about the blood, the sweat, the tears

Yesterday Amy Bishop, a Harvard PhD and a faculty member of University of Alabama in Huntsville unfolded a shooting in the biology department over there. Three faculty members were killed and many more were injured as a result of her shooting spree.

The most possible reason is that Dr. Amy Bishop was denied tenure at the University of Alabama at Huntsville last year.

The Hirsch-bar index: leave your boss' name out of the authors list

I think you know what the Hirsch-index is: if you have n papers cited at least n times – then your h-index is n. For instance, if out of your 10 papers two were cited 4 times, and the rest three times, then your h-index is 3. The index was introduced by Jorge Hirsch in 2005, and became an accepted tool to rank scientists within about one year: community found it useful that a scientist's productivity may be described by a single number. However, the h-index does not take into account such important things as the number of co-authors and the self-citations.

Recently Jorge Hirsch himself wrote a preprint, where he proposed a new, ħ (hbar) - index, that is aimed to solve at least one of these problems, multiple co-athorship. Indeed, the "mass graves" (sorry), published by high-energy physicists and the institute policies to include everyone's name to any article, can unreasonably increase the Hirsch-index, with no extra work.

Some of the h-index terminology before describing the ħ-index. You have the h-index n, if n of your papers belong to the "h core". The paper belongs to the h-core if it was cited n times or more. Your co-authors will probably have other h cores, and a given paper may belong there or not.

The ħ - index is defined in a similar way: you have the ħ - index m if m of your papers belong to the ħ-core. But, the paper belongs to the ħ-core if it was cited m times or more and it also belongs to the h-core of your co-authors. (Actually, the latter h should be also ħ, but since the index would be extremely difficult to compute in this case, Hirsch decided to relax the condition a bit)

In other words, only if the paper improves the h-index of all the authors, it will contribute to your ħ-index. Imagine that you have the h-index of 20, and you have a paper cited 25 times, co-authored by a student with a h-index of 5. Then, it will be included in your and the student's ħ-index, because it belongs to the h-cores of both of you. But, if you add a third author to this paper, say, a director of your institute with a h-index of 45, the paper will not count for any of you, because it doesn't belong to the director's h-core.

So, if you have 200 papers, cited 44 times each and co-authored by your director, who has the h-index of 45, none of them will count, and your ħ-index will be zero. Hirsch expects this to stimulate young scientists to work independently. However, he mentions, that the ħ-index will be definitely useless for postdocs, since they are used to include senior scientists in their papers.

I wonder whether it will be possible to eliminate self-citations at some point.

Who cites you is important: a new approach to ranking scientists

We are used to such metrics of a scientist's impact in a field like the number of papers published, how many times they are cited, and the h-index that the scientist has. These parameters are expected to rely on credit given to the researcher by the rest of community. However, they don't account for the important thing, namely who cites the published work.

In a paper recently published in Phys. Rev. E, Filippo Radicchi with colleagues propose a new ranking technique that captures this "who" issue: the citations coming from renowned scientists have more weight than those from less known researchers. The authors focused on physics and used the PROLA journal archive (1983-2006) as a testing ground for the methodology. The results show that the probability to win a major physics prize is more accurately predicted by their new method, than by the other metrics, such as citations count.

The only thing is probably missing here – the "negative" citations. The results may be cited as "doubtful" or "wrong" even by famous scientists, and the trustless paper will be scored higher. However, in the case of a scientist's rank, averaging over all his papers will probably make this contribution negligible.

Here is a website where you may figure out a rank of any scientist, based on his articles in physical review journals published before 2006. This piece of work was also highlighted in Physics.

An application

Today I've got an application for a PhD position by e-mail. Well, this is probably not the best idea to send those to PhD students...

How far can you go to get cited?

That's amazing how hard some authors work on promoting their own papers.

Here is a number of submissions to the astro-ph section of the arXive, by time of day, in 10 minute bins:

I took it from the recent investigation by Haque and Ginsparg.

The thing is that 16:00 (US eastern time) is the deadline for the daily submission to the arxive. So, the papers submitted at 16:01 will be the first for the next day and will appear on the top of the daily mailing. You are probably wondering why is that important? Recent research by Dietrich and also the preprint I cited above show that articles appearing the first are more visible and far better cited than others.

No matter how good your work is, just put it on the top of the list.

Links for 11.01.09

1) The Fine Line Between Plagiarism and Necessary Repetition by Chad Orzel.

2) Next generation search engines could rank sites by “talent” - in the physics arXiv blog.

3) Think atheist - a social network for those who has no shame being an atheist.

4) A Staged Scene in a Gaza Hospital? - a CNN video of a twelve year old boy, dying in the hospital, with remarks of a specialist. The (most likely) fake video, was later withdrew from the CNN website with no further comments.

What to do with deleted sections?

When we write an article, we almost always have to omit some material, which has a lot of work behind it. There may be some restrictions to the article length, as in the case of letters to the editor. Also, a referee may ask to shorten appendices and skip insignificant details. An he/she will be right - a short paper is most likely to be read.

So, one usually has a choice: on the one hand an article should describe new and interesting results, without technical stuff interesting for 5% of readers or less. On the other hand, It might be a good idea to keep all the relevant material in the same place. This may be useful for further work of authors, or also for somebody else, who wants to learn from the paper or to work out something similar.

Recently there was a post by "How many deleted sections do you write?", where Daniel Lemire proposes a good idea what to do with deleted pages. Daniel suggests to put them in the article's supplementary material, with a reference in the article. In such a way, one can expect the article to be easily read with an access to all necessary details.

Another way might be to keep all the omitted material in the arXiv preprint, and cite it in the forthcoming paper.

Why one needs peer review?

A few days ago Michael Nielsen published an excellent post "Three myths about scientific peer review". Briefly, in the nonscientific (and sometimes in the scientific) community it is usually supposed that:

i) Peer review system was used since very long time ago. Actually, it was not. For instance, Albert Einstein, while living in Germany, was not used to "independent referees" - in such journals as Zeitschrift für Physik the decision "whether to publish a paper or not" was always made by editors. And, as far as I know, before WWII this journal was considered as much better place to publish than Physical Review. After moving to the US, Einstein had withdrew one of his contributions from the Physical Review, because he "has not authorized the editor to show it to specialists before it is printed". I wrote a little post about this story before.

ii) It is reliable, in other words "it nearly always picks up errors, is a very accurate gauge of quality, and rarely suppresses innovation". Of course, no one can predict the future, and say which piece of work will be a "citation classic" in ten years. Furthermore, there is probably no way to discuss the reliability of peer review since we simply don't know how many revolutionary papers were never published (or were, but in some obscure journals) due to negative referee reports.

and

iii) It can show what is right and what is wrong in science. This is also not true, because it is impossible to check all math in the manusript, redo computations, not to mention repeating experimental results.

The post of Michael was followed by interesting comments of Daniel Lemire, "The purpose of peer review", induced by another comment of Peter Turney to Michael's post: "I’m sympathetic to much of what you’re saying, but, on the other hand, I know that peer review has immensely improved many of my own papers."

Being nothing but graduate student, I absolutely agree with Daniel and Peter: at least two from three papers, written during the first year of my PhD, were substantially improved after referee's comments. Apart from submitting  the papers, we have always sent preprints to some good friends from our field - always getting positive feedback (some of them may be the referees in the same time, but this we don't know).

In my opinion, the fact of peer review doesn't mean that the article is reliable, correct or "interesting to a wide community of scientists" (as it should be e.g. for Nature and Phys. Rev. Lett.). But, the review process is some kind of necessary (but not the sufficient!) condition for paper to be read and cited in the long-time future. After publication the scientific community will make it clear, whether such a condition was actually sufficient - there will be a lot of readers  and time for it, much more than two referees having three weeks to submit a report.

Of course, no one can read all journals in his field, even if the field is small enough. Let alone that articles show what was done about one year ago, but not now. Almost no one is actually reading journals - conferences and arXive give a perfect taste of what is going on. But if we come across an arXive preprint dated back to 2007 without any journal reference - this looks strange, doesn't it?

And last, but not least, it seems that reviewing good papers is an excellent way to learn how to write good papers.

Mendeley - some suggestions

As I mentioned before, I signed up to Mendeley, here is a link to my profile. In this post I just want to mention some improvements, that (I believe) will make Mendeley even more useful than it is now:

1) As I wrote earlier, the metadata transfer for arXiv preprints doesn't work properly.

2) On the one hand, all of us are used to publish arXiv preprints prior to publications, but one should not mix preprints and peer-review journal articles in the CV. Therefore, it will be great if the "preprint" option will be added as an article type.

3) Also, one may want to distinguish "conference proceedings" from "conference abstracts" (which may be also presented as posters).

4) A useful thing might be to add a list of conferences, visited by scientist, with a type of contribution (invited talk/oral presentation/poster) as an option.

5) Looks like a little bug: when I type my location, the list of suggestions appears. But, If I ignore this list and type "Berlin, Germany" by myself (which is exactly the same thing as given in the list), the following message occurs: "Sorry, we don't have details for the location you have entered. Please select one from the drop down list."

6) If I see a green cross near "add entry", I immediately want to click it. But it doesn't work, one has to click "add entry" itself.

I hope these issues may be fixed...

Mendeley

In comments to my recent post Jan Reichelt brought my attention to another academic collaboration tool, called Mendeley. The idea is a bit different from those of 2collab, and therefore one cannot directly compare these two things. While 2collab is a bookmarking tool, dealing with articles somewhere in the web, the heart of Mendeley is an online library, where you can upload and organize your .pdf files. You can also create your profile with CV and publication list, as well as join different groups. The online library can be synchronized with files on your computer using the offline tool, Mendeley desktop.

Surprisingly enough, Mendeley correctly reads almost all the metadata from .pdf's. However, it doesn't work correctly with arXiv preprints: what I had is the arXiv link read as an article title (e.g. arXiv:0809.3331), and the blank field of publication name (where the journal title should be). Hope that the authors can fix it soon.

Another point is that at the moment there are only very few users of such services as Mendeley and 2collab are. However, I believe that in the nearest future using "academic social networks" will be as usual as, for instance, having a personal webpage at institute website nowadays.

2collab

I came across an interesting service - 2collab, a tool for scientific bookmarking, sharing and collaborating. It looks like an academic analogue of delicious. This project was started by Elsevier, and therefore any article from Elsevier journal may be immediately bookmarked using an "add 2collab" button at the journal website - and all the bibliographic data will be automatically transferred.  Unfortunately, at the moment no other journals have such buttons. Of course, one can bookmark absolutely any webpage, but in this case one should write up the bookmark description (title, etc.) by hands, which can take a while.

For this day, 2collab seems to be not very popular among the researchers, but I hope it will change soon.

Links for 28.09.08

• Sergey Brin's blog
• Survivor: theoretical physics - some thoughts about career.
• How long should an astronomical paper be to increase its Impact? - an interesting preprint.

Ten Lessons I wish I had been Taught

I came across these advices of Gian-Carlo Rota in the blog of Alexandre Borovik. Among them there is the following one:

"6) Do not worry about your mistakes.
Once more let me begin with Hilbert. When the Germans were planning to publish Hilbert’s collected papers and to present him with a set on the occasion of one of his later birthdays, they realized that they could not publish the papers in their original versions because they were full of errors, some of them quite serious. Thereupon they hired a young unemployed mathematician, Olga Taussky-Todd, to go over Hilbert’s papers and correct all mistakes. Olga labored for three years; it turned out that all mistake scould be corrected without any major changes in the statement of the theorems. There was one exception, a paper Hilbert wrote in his old age, which could not be fixed; it was a purported proof of the continuum hypothesis, you will find it in a volume of the Mathematische Annalen of the early thirties. At last, on Hilbert’s birthday, a freshly printed set of Hilbert’s collected papers was presented to the Geheimrat. Hilbert leafed through them carefully and did not notice anything."

Terence Tao

A 33 years old professor of math from University of California, 2006 Fields medal winner Terence Tao has a blog. It is extremely interesting as a whole, but here are some links to Terry's advices: Advices on career, On writing papers, Talk to your advisor, Take the initiative, and tons of references to older posts therein.

Why the h-index is little use

Two interesting posts by Michael Nilsen about the Hirsch index: the first and the second. Michael notes that the h-index can be calculated to a good approximation from the formula:

h ~ sqrt(T) / 2,

where T is the total number of citations. Therefore it provides no new information beyond the total number of citations, and can not be properly regarded as a new measure of impact at all. Earlier I wrote a little post about Hirsch index (in Russian).

"Work. Finish. Publish."

This was an advice of Michael Faraday to his younger colleague William Crookes. The second statement, "finish", is probably the most difficult part. Here it does not mean "stop collecting the experimental data", or "switch off the computer and do no extra calculations" (...since we have enough for a paper). It is really hard to came up with some closed-form investigation, with an exciting story you have nothing to add to. Most likely, if this is done, the third step, "to publish", needs only a bit of routine work...

О мелочах, влияющих на цитирования

Наткнулся на два интересных препринта J. P. Dietrich, о том, как влияет позиция препринта в ежедневной рассылке arxiv.org на количестыо цитирований, полученных статьей:

1) The Importance of Being First: Position Dependent Citation Rates on arXiv:astro-ph

2) Disentangling Visibility and Self-Promotion Bias in the arXiv:astro-ph Positional Citation Effect

Автор выяснил, что препринты, находящиеся в конце ежедневной рассылки в среднем получают в два раза меньше ссылок, чем работы из первых строчек. В первом препринте Дитриха этот факт был обнородован, но было еще не понятно, в чем причина такой разницы, в "случайном попадании в топ" или намеренной отправкой препринта в течение короткого времени после дедлайна, чтобы статья появилась в верхних строчках рассылки. Дело в том, что опытные авторы, которые много публикуются и цитируются, часто поступают именно таким образом. Во втором препринте Dietrich (проанализировав log - файлы сервера arxiv.org, которые ему любезно предоставили) приходит к выводу, что играют роль оба фактора.