Ken's Blog

Yesterday I learned about the Halbach array, a wonderful way of arranging magnets that was first discovered by John Mallinson in 1973, and then rediscovered by Klaus Halbach a decade later. Why it’s not called a Mallinson array is beyond me.

To make a Halbach array you can arrange magnets in a line, rotating each successive magnet’s orientation by 90^o, as in the picture below:

 

When you do this, it turns out that there is very little magnetic field above the array, and a very strong magnetic field below it. It’s not too hard to see why this happens, and I encourage you to read the Wikipedia page, which explains it quite well.

This “magnetic on one side but non-magnetic on the other side” property has many uses. One of those uses is ordinary refrigerator magnets — in case you’ve ever wondered why refrigerator magnets are only magnetic on one side. Another use is as a component in levitated trains, which is extremely cool.

It occurred to me today that rolling a cylindrical magnet on a table — if the magnet is magnetized across its diameter — should produce the same effect as a Halbach array, since the magnetic orientation will rotate in just the right way as the magnet rolls along.

As it happens, I had such a magnet, so I decided to test this hypothesis.

I suspended a steel spring precariously between two Nespresso packets (since they happened to be just the right height): 

 

As you can see below, if the magnet — which was quite powerful — got anywhere near the spring, the spring would jump off its Nespresso packet supports and snap to the magnet: 

 

Then I tried rolling the magnet under my delicate little suspension bridge. Sure enough, the spring would stay on the bridge while the powerful magnet rolled right under it:

 

I suspect that this only works because of hysteresis in the steel. The spring takes a little time to change its magnetic orientation in response to the rolling magnet, and so the reaction of the spring to the magnet is smeared out over time. To the spring, the magnet appears like a continuous Halbach array, which has a reduced magnetic field above it.

If this theory is correct, then when the spring is below the table the opposite would occur: The rolling magnet would very strongly attract the spring. Maybe I should try that next.

In Washington Square
Students flutter in, like leaves.
A season begins

My post the other day showed a way to use an interactive text narrative as a guide to a visual explanation.

But I’m not yet satisfied with it. The narrative itself should also be able to change, as the visual explanation evolves.

In order to build up to that capability, I’m starting to play with mutable text narratives. A simple (and very fun) kind of mutable text narrative is the MadLib, so I thought I would begin with one of those.

If you click on the image below, you can see my first take on narrative as MadLib. As before, you change things by clicking on the orange words and phrases:

So now it seems that Apple did not, in 2005, invent the “pinch to zoom” gesture that Myron Krueger had already implemented in 1983.

According to a recent US Patent and Trademark Office ruling, in fact it was Bran Ferren and Danny Hillis who in 2005 invented the pinch to zoom gesture that Mr. Krueger created thirty years ago.

So my apologies to those of you who read my earlier post congratulating Apple on its brilliant invention of Krueger’s technique. It turns out that Ferren and Hillis deserve all of the credit for this bold innovation.

I can imagine that some of you might be confused by this turn of events. You may, for example, be thinking of some sort of bizarre alternate universe in which the first to conceive of an innovation, to reduce that innovation to practice, to publicly demonstrate that achievement, has perhaps some vague claim on said invention.

But no, we do not live in such a world. We live here in the real world, where objective truth, proper credit, and true authorship are determined the old fashioned way: Through the sheer hard work and persistent efforts of a highly paid legal team.

So as you watch this video made in 1988, which documents the system that Krueger had first implemented five years earlier, pay particular attention to what happens at 4:30.

It may look for all the world as though you are seeing a two finger pinch to zoom gesture. But in fact that is impossible, since as any good lawyer will tell you, pinch to zoom was not invented until 2005.

Which means that you must be hallucinating. You really need to stop using those drugs.

In Joseph Heller’s seminal novel “Catch 22”, the reluctant WWII bombardier Yossarian is concerned that people are trying to kill him. Given the fact that he is continually being ordered to go up in an airplane to be shot at by the enemy, he has a point.

Yossarian’s alienation truly begins after Snowden, a member of his flight crew, dies in his arms, mortally wounded by antiaircraft fire. From that point on, whenever Yossarian is asked whether he has any questions, he merely replies “Where are the Snowdens of yesteryear?”

Here Heller is paraphrasing “Ballade des dames du temps jadis” by the great fifteenth century french poet François Villon, whose haunting refrain “Où sont les neiges d’antan?” was later translated by Rosetti as “Where are the snows of yesteryear?”

Interestingly, Villon spent much of his short and colorful life speaking out for the rights of the people — the great unwashed citizenry — in defiance of his government.

This theme ties in curiously to another battle of perception being fought today, with the rights of citizens on one side, and the powers of government on the other.

This new battle centers on an outspoken rebel named Snowden. Mere coincidence?

One of my interests is mixing narrative and computer graphics to tell stories that teach. It’s an interest I share with my Ph.D. student Adam Gashlin, and with some other people too.

I thought it might be a good idea to use the go game as an excuse to explore that space a bit — to teach something through a narrative text that interacts with computer graphics.

I’m going to start with something simple: An explanation of how I make the stones look rounded and three dimensional. I would love some feedback!

Click on the image below to try it:

Today I received two packages at home: The book “Go: A Complete Introduction to the Game” by Chikun Cho, and a one pound spool of 32 gauge magnet wire. That last comes out to 7860 feet of 1/125 inch thick wire. I’m guessing it will be enough.

Each of these two objects will be put to use in projects I’m working on, and I am very happy to have them.

Yet getting these two things on the same day, and thinking about all the ways they contrast with each other, creates its own jumble of thoughts and possible directions. The Go book is, in a sense, a thing of pure thought — a physical object dedicated to an abstract idea. The spool of wire bends matter into a thing of pure possibility. When used in the right way, it is a way to connect the physical and the intentional.

 

Here you can see them lying on a Go board. Its regular grid seems to connect these two very different objects in some strange yet logical way.

What sort of project would make use of both a mile and a half of magnet wire and a book about the history and strategy of the most elegant of board games? Maybe I will end up with a robot that plays Go.

Yesterday I made the basic Go board. Today I tried my hand at making a board that automatically cleans up after a battle.

For those of you who don’t know, the basic idea of Go is to amass territory by strategically placing stones so that they surround your opponent’s stones. When groups of stones are completely surrounded — cut off from any empty spaces that would let them “breathe” — then those stones die, and are removed from the board.

My programming task today was to figure out when a group of stones has died, and then automatically remove them from the board.

Just for fun, I’ve turned this into a little puzzle. When you click on the image below, a page will pop up containing a Go board. Your task is to click twice: Your first click should add a black stone that finishes surrounding a group of white stones. Your second click should add a white stone that finishes surrounding a group of white stones.

If you get it right, then after each click a group of surrounded stones will automatically disappear from the board.

Because this is all Javascript, you can see the program using “View Source” in your browser.

A long time ago I learned the basics of the ancient Chinese game of Go, or 圍棋 (wéiqí) as it is called in Mandarin. I hadn’t played in years, but recently a good friend has reintroduced me to the game, and now I want to understand it better.

As I learn about gameplay and strategy, I thought it would be an interesting exercise to write little computer programs that reflect the concepts I’m learning, mostly because I’m curious to see what sorts of things I end up making.

I thought I would start with an interactive computer graphic rendering of the Go board and basic game play (no strategy yet). Partly this is also an excuse for me to start writing 2D graphics entirely in Javascript.

If you click on the image below, you’ll jump to a page with my first results. After you get there, click on the board and see what happens:

Today, after weeks of hard work, Kyle Rosenbluth and I managed to look around a four dimensional shape called a “24 cell”, through an Oculus Rift VR display.

Kyle is a brilliant high school student visiting our lab, and he is amazing to collaborate with. We’ve actually been very fortunate this summer in having a whole bunch of incredible students visiting our lab and doing great work. It’s great how the energy builds when a whole bunch of really smart people do research together. There is definitely a kind of multiplier effect, as the collective ideas and energy bounce off one another.

By the way, I think the 24 cell is, in some ways, the most beautiful of all mathematical shapes. So it was a thrill to finally get to meet it in person. Well, as close as I might ever get to meeting a four dimensional shape in person.