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Low-functioning pinhead...
August 24, 2005
Trackbacks and the ArXivs
Ever since hep-th was founded in 1991 (or maybe a couple of years later, when it sprouted a web interface), people have talked about trying to overlay some sort of “discussion” or “commentary” layer. For understandable reasons, Paul Ginsparg has been reluctant to host any such endeavour at arxiv.org itself, wishing to maintain it purely as an e-print server.
Two and a half years ago, I started this blog, in the belief that weblogs (and weblogging software) could provide a distributed mechanism for such an overlay, without the implied endorsement and other drawbacks of a centralized service. Blogs, as you know, provide a wonderful sense of an interwoven, distributed conversation. But the missing ingredient was the ability to ‘plug into’ that conversation from the arXivs. How do you discover that I or some other physicist-blogger, has commented on a given paper?
The obvious answer is, of course … Trackbacks. I’d been intermittently bugging Ginsparg to implement Trackbacks on the arXivs for a couple of years, now. Finally, at Sidneyfest, he sidled up to me and said, “So, about this Trackback thing …”
I’m happy to report that my pestering has finally paid off. The arXiv abstract pages are now Trackback-enabled. At the bottom of every abstract page, you’ll find a link, “N trackbacks” (when N>0). Click on it, and you’ll get a list of weblog entries commenting on that paper.
So does that mean that every crackpot and trackback spammer on the internet can now get linked-to from the arXivs? Well, … no. Just as you need to be a registered author to submit papers, your weblog needs to be on an approved list, in order for your Trackbacks to appear. Going forward, the precise mechanism for getting on that list is yet to be determined. But, in the short term, the list of serious physicist-bloggers is short enough to handle by hand.
You know who you are …
August 23, 2005
PDF Accessibility
We physicists use a lot of PDF.
It’s the primary means of distribution of papers at the arXivs. It’s what we use to distribute class notes to students. The NSF requires our proposals be produced in PDF, … Indeed, pretty much anything with mathematical content is authored in TeX, and turned into a PDF file.
Accessibility is not something we think a lot about. Until, that is, we run into some regulation (either Government or University) that mandates that the documents we produce be accessible to the blind or vision-impared. If you’re Australian or Canadian, you may already have run afoul of these demands.
Sooner or later, we all surely will …
Joe Clark to the rescue.
I won’t repeat all the main points of his article. Instead, what I want to concentrate on is mathematical text, and our PDF content-creation tools.
First of all, everyone is, or should be, using pdftex. There used to be issues with handling figures in pdftex. But that’s a thing of the past. And pdftex offers so many advantages over tex→dvips→ghostscript (hypertext links, bookmarks, alpha-transparency, …) that there’s really no good reason to use the latter.
One important feature for accessibility is “tagged PDF,” which was introduced with PDF 1.4. By default, pdftex outputs PDF 1.4, but it doesn’t produce tags. You can retrofit tags into PDF 1.4 documents using recent versions of Acrobat. But it would be better if pdftex had the ability to generate them natively1.
Accessibility of equations is something Joe didn’t touch upon at all, though he did allude to the shortcomings in the rendering of XHTML+MathML as a reason why they’re not going to replace PDF for mathematical texts anytime soon. But, whatever else you may say about it, MathML is accessible, and there’s at least one tool out there that will read MathML equations aloud. (Design Science received an NSF Grant for this effort, so, US readers, don’t think your Government doesn’t care about the issue.)
What about equations in PDF? Well, that’s the subject of another, more recent NSF Grant. What they plan to do, apparently, is embed MathML in the PDF file, and use the same technology, that allows their MathPlayer plugin to read MathML on the web, to read the MathML embedded in the PDF file.
MathML embedded in PDF … will some future version of pdftex support this? I don’t know. Ask Hàn Thể Thành. If not, there’s a serious possibility that, someday, you will be reduced to using MathType in Microsoft Word to produce accessible mathematical (PDF) documents.
1 There has been sporadic mention of tagged PDF on the pdftex mailing list but, as far as I can tell, no move afoot to implement it.
Designing the 5th Dimension
I’ve just gotten back from a visit to the University of Washington which is, currently, the mecca for applications of AdS/CFT to QCD. I’ve talked a bit about some of the applications to RHIC physics. But there are lots of other interesting recent developments.
I’ll probably talk some more about them in future posts but, for today, I thought I’d summarize a paper by Erlich, Katz, Son & Stephanov.
Rather than trying to find a string background whose near-horizon geometry is holographically dual to QCD, they take a “bottom-up” approach, introducing those fields in AdS5 which couple to the observables they are interested in. To study the low-lying mesons of QCD, they introduce 5D gauge fields, which couple to the corresponding currents, , and a 5D scalar, , in the representation of , which couples to the quark bilinear. The geometry is taken to be that of a slice of AdS5,