## #365 papers, part 2!

I’ve joined a group of folks on Twitter who have vowed to read roughly a paper a day, and will summarize my reading here occasionally.  Part 1 can be read here.  Links are provided for those with university access who are interested in reading more.

1/12: Shadow effects in spiral phase contrast microscopy, A. Jesacher, S. Fürhapter, S. Bernet, and M. Ritsch-Marte (2005).  It turns out that filtering an image through an optical vortex phase mask performs excellent edge enhancement of the image!  In this paper, the authors demonstrate that this enhancement can be tweaked to provide directional “shadow effects,” allowing different edges to be selectively highlighted.

1/13: Radial Hilbert transform with Laguerre-Gaussian spatial filters, C-S. Guo, Y-J. Han, J-B. Xu, and J. Ding (2006). Obviously I’m working on the section of my book discussing using vortex masks for edge enhancement!  In this paper, the authors look at using Laguerre-Gaussian filters, which represent very “pure” vortex states, for this filtering.

1/14: Image processing with the radial Hilbert transform: theory and experiments, J.A. Davis, D.E. McNamara, D.M. Cottrell, and J. Campos (2000).  This was the first paper about using vortex filters for edge enhancement.

## So what’s up with that “slower than light” light?

Over the years, there has been a lot of hype about the possibility of “superluminal” light: namely, light than can travel faster than the vacuum speed of light $c = 3\times 10^8$ meters/second, which is overwhelmingly considered the absolute speed limit of the universe.  I’ve talked about superluminal light before, and the related discoveries always turn out to be somewhat less spectacular than they sound, though they always provide some strange insights into the physics of light.

Recently, though, an even stranger discovery has been making the rounds in the press*: an experiment performed by researchers in Glasgow and Edinburgh** shows that appropriately-prepared light particles (photons) can travel even slower than the vacuum speed of light — in vacuum!

Kind of like its superluminal siblings before it, this discovery has caused a bit of confusion.  In this post I’ll try and shed some light on the phenomenon, showing why it is both less and more than it appears.

Posted in Optics | 2 Comments

## Null-field radiationless sources: even more invisible than invisible?

I spend a lot of time talking about invisibility on this blog, as it is a subject near and dear to me: I did my PhD work, completed in 2001, on early historical forms of invisibility.  I like to tell people that I’m an invisibility hipster, and that I worked on invisibility “before it was cool.”

The field has progressed dramatically since I first did my work, and in recent years I’ve been playing a bit of “catch up” with my own invisibility work, trying both to build on the newest insights as well as apply knowledge from the old theories.

This past fall, my student Elisa and I used this approach to ask and answer a curious question: can something be more invisible than invisible?

Our answer was published in a paper titled “Null-field radiationless sources,” that appeared in November in Optics Letters.*  Ordinary invisible objects, including cloaking devices, are objects that don’t scatter any light outside the domain of the object; a potential null-field object will potentially not scatter light inside, as well!

## #365papers, part 1!

At the beginning of this year, my friend Jacquelyn Gill (who blogs over at The Contemplative Mammoth) suggested an interesting resolution for academics like us: read at least one scientific paper a day for the entire year.  This has been hashtagged on twitter as #365papers and, as I am always up for the latest fad, I decided to join in.  I seem to be too unfocused to actually tweet details about each paper I read, so I thought I would summarize my reading every week or so right here, with a short description of what each paper is about!

So, without further ado… here’s part 1 of 365 papers!*

Posted in Physics | 3 Comments

## John Blackburn’s Dead Man’s Handle

This post marks a minor personal milestone: with the book featured in it, I have now read all of John Blackburn‘s published works.  I put off reading this one for quite some time for a reason that I’ll explain at the end of the post.  The novel, Dead Man’s Handle (1978), was written near the end of what I might call Blackburn’s “original” writing career.

Though Blackburn would publish four more books in his lifetime, the last two — A Book of the Dead (1984) and The Bad Penny (1985) are reworkings of his earlier novels, Blue Octavo (1967) and A Sour Apple Tree (1958), respectively.  After Dead Man’s Handle, his last truly new books were Sins of the Father (1979) and A Beastly Business (1982).

I mention this because there is a bit of a decline in the quality of his work near the end of his career, and this is one reason that I was somewhat slow to read this particular book.  However, it is a rather unique mixture of mystery and horror, with a truly ghastly twist at the end.

## The Burnaby Experiments, by Stephen Gilbert

I really should be writing about novels other than those published by Valancourt Books, and I will, but they have released so many eye-catching books in recent years that I’ve had a hard time staying away.  Most recently, I read their edition of The Burnaby Experiments (1952), by Stephen Gilbert.

The goal of the titular experiments is likely familiar to those who have experienced a lot of horror and science fiction: to find out what lies beyond death.  You may have seen the movie Flatliners in 1990, for instance, or read the 1993 novel The Terminal Experiment by Robert Sawyer.  Or, like me, you may have independently written a story based on the same theme years earlier.

Gilbert’s novel offers a unique and very personal take on the concept, however.  In fact it is semi-autobiographical, and the implications of that subtext are perhaps more disturbing than the actual story at times.

## The mystery of the magnetic train

This past week, thanks to Laughing Squid and other sources, a lot of people watched and were amazed by this simple demonstration of electromagnetism in action.

It is billed as the “world’s simplest electric train,” and it is almost certainly the case.  Using only a battery, some strong magnets and some (bare) coiled copper wire, one can make the “train” travel numerous circuits through the copper “track,” until the battery is completely drained.

This caught my attention because it is a very clever twist on one of Michael Faraday’s original discoveries!  Not electromagnetic induction, as I reflexively thought, but a homopolar motor.  Below is an animation of such a motor that I whipped up in my office.

A simple homopolar motor.  Just in case you don’t believe it actually works, a longer video is here.

This particular homopolar motor design is ridiculously simple: a pair of neodymium magnets are stuck (by magnetic force only) to the bottom of an AA battery. A wire loop is balanced on the top of the battery, bent so that it touches the magnets on the bottom.  When the connection is made, the wire will start to spin immediately, and will in general start spinning so fast that it will flip itself off of its perch.  More sophisticated and stable designs exist, but this one is quick and showy.

So how does the homopolar motor work, and the “magneto-electric” train shown in the video?  Both of them depend on the relationship between moving electric charges and magnetism, albeit in somewhat different ways.

Posted in Physics, Physics demos | 7 Comments