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March 2007 Archives

I actually didn’t buy an APS t-shirt — or a bumper sticker, slinky or travel mug — but I’m still glad I came to Denver.

Here’s some miscellany I learned today.

• There are no guns allowed in the Colorado Convention Center — but nowhere to “check ‘em at the door”.

• Top basketball coaches at US universities earn in excess of one million dollars a year. Not sure how much a top physicist earns…

• APS editor in chief Gene Sprouse told me that the funny symbol that appears next to articles of interest in Physical Review Letters is a colophon that appeared on the cover of the first issue of PRL.

What’s the best way to determine the structure of a molecule that cannot be integrated within a periodic lattice?

Blow the heck out of it using x-ray pulses from the Linac Coherent Light Source (LCLS) — at least according to SLACs Philip Bucksbaum.

The LCLS will open next year at SLAC in California and will be much brighter than existing x-ray sources and will be capable of producing very short x-ray pulses.

It takes about 200 fs for the molecule to explode and the trick is to collect the diffraction data in the first 10-20 fs — when the molecule is still intact. By blowing up 100,000s of the same molecules, Bucksbaum claims that a 3d image of the molecule can be reconstructed. This technique has already been proven at an x-ray facility in Germany.

In his talk “Ultrafast X-ray Science at SLAC and LCLS” (U19 1), Bucksbaum described several other ways of harnessing the violent reaction between the X-ray pulses and sample.

For example, the pulses could be slammed into a solid such as iron. This would heat the sample and drive structural phase transitions that would propagate through the iron as “shock waves”. Real-time images of this process could be generated from the diffracted x-rays. This could give physicists valuable information about how lattice defects and other material properties affect the dynamics of phase transitions.

IOP Publishing’s reception was a big hit last night, judging by the fact that the buffet had to be replenished several times — you can work up a huge appetite running back and forth between sessions for nearly 10 hours a day.

I spent most of my time talking to IOP referees and journal board members as well as the competition — two editors from Physical Review B (not sure how they got in!).

It seems that paper length — or the lack thereof — is a growing concern in the journals community. Authors are apparently under lots of pressure to summarize their work in four pages (I wonder where that comes from?).

One IOP referee told me that he often asks authors to add clarifying paragraphs to their papers, but the authors are reluctant to do so because they believe that publishers favour shorter papers. The referee was concerned that highly truncated papers are of little pedagogic use to newcomers to a field, and that brief papers are so focused on results that the purpose of the research and the underlying physics is sometimes lost.

On the other hand, longer papers are much more difficult to write and referee — with some folks expressing concerns that quality could slip if papers were longer.

Some of the most interesting condensed matter physics occurs at very low temperatures and physicists need accurate ways of knowing just how cold their samples are. Traditionally, this has meant spending hours building, calibrating and troubleshooting temperature measurement and control systems — instead of actually doing the experiments.

Those days are over in many labs — at least according to Shane Hritz of Lake Shore Cryotronics. Hritz was in town to talk to physicists about the company’s cryogenic sensors, temperature control systems and magnetic measurement systems. He believes that physicists are hesitant to commit valuable resources to building and maintaining laboratory equipment. Instead, they want off-the-shelf kit that works the first time.

The company has just launched a new ruthenium oxide temperature sensor that is said to be the first commercial system calibrated down to 20mK — its last sensor was calibrated down to 50mK. “This doesn’t sound like much,” said Hritz, “but at these temperatures heat transfer through the leads becomes a big problem — any small bit of energy that gets into the sample can affect its temperature.”

Hritz say the company is now working on a sensor that is calibrated down to 10mK.

I was having so much fun with the physicists that I nearly forgot to check out the exhibition before it closed for good this afternoon.

First stop was the IOP Publishing stand where I had a chat with Sharice Collins, who is our senior marketing manager for the Americas. Sharice is based in our Philly office and has organized a proper knees-up tonight for the IOP Journals community (Sharice prefers to call it a reception). I will of course be reporting on the reception in a future entry.

It seems that my initial concerns about the remote location of the exhibition were unfounded. Sharice reported a steady stream of traffic through the IOP stand. She said that delegates were very pleased to hear about our community website strategy — and the IOP flashing badges were a big hit.

Here’s a new recipe from Jeffrey Brinker of the University of New Mexico (P42 1)

Mix together water, alcohol, detergent, silica and a good dollop of single-cell organisms.

Dip in a substrate of your choice.

Remove and let dry.

While you do the washing up, the silica, detergent and cells will be busy organizing themselves on the substrate surface to create a highly ordered solid film. The amazing thing about this film is that cells survive the assembly process — and they remain alive for up to one month by eating the detergent.

Such films become even more interesting if they are made with organisms that act as biosensors — organisms that react to changes in light or the presence of certain chemicals.

What? Not Mott?
Pots not dots, lots per pot
…and hot!

You can only get away with describing your experiment with a poem if you have a Nobel Prize — and JILA’s Eric Cornell has one of them.

The pots are the wells within a two-dimensional optical lattice and they were filled with lots of atoms in the Bose-Einstein condensate state. Atoms can tunnel between wells, so you can also think of this as an array of Josephson junctions (still with me?).

“Buckets of BEC with inter-bucket tunnelling”, is how Cornell described it.

Cornell and his team were looking for a Kosterlitz-Thouless transition in the lattice. This occurs when vortices form in the array above a certain temperature.

The lattice is made up of little triangles that look like this (the “O”s are the wells):


Atoms moving clockwise (or counter-clockwise) from well to well around the triangle create a vortex.

And that’s exactly what they saw.

Purdue University’s Vladimir Shalaev is giving the following paper tomorrow :

“Negative-Index Metamaterials in the Visible Range” (W38 1).

Could this be the first invisibility cloak for visible light?

Shalaev has already worked out a way to make metamaterials that respond magnetically to visible light, and has come tantalizingly close to creating negative index materials in the visible range.

I asked Shalaev if he would be unveiling an invisibility cloak on Thursday — but he just grinned, said “come to my talk”, and then he vanished into thin air!

Graphene guru Pablo Jarillo-Herrero of Columbia University set me straight on the miraculous flakes of carbon.

-There were 180 papers published on graphene in the last year, but less than 10% were experimental.

-If it’s five or more atomic layers thick, then it’s just plain old graphite.

-If it’s 1-2 layers thick, the electrons think they are confined to two dimensions and the fun begins.

-Graphene is compatible with silicon fabrication processes and transistors can be made from graphene.

-Graphene has high electon mobility and is a superb heat conductor, which could allow graphene transistors to operate at vey high frequencies.

- A paper presented here at the APS has claimed that graphene grown on SiC has an electron energy gap of ~250 meV, which Jarillo-Herrero says is enough to make room temperature transistors.

-Graphene is not flat and its undulating surface affects its electronic properties

-The undulations could be a way of damping out thermal vibrations and therefore graphene could become flat below a certain temperature

-Graphene provides a laboratory for studying a range of fascinating phenomena including the quantum Hall effect, Berry’s phase and Dirac fermions

In my entry on “Rock star physicists” I said that there are no commercially viable applications of high Tc superconductors. I have just discovered that this could be wrong — at least according to Alexis Malozemoff of American Superconductor Corporation.

In his talk “Transforming the Grid with Superconductivity” (L1 5), Malozemoff said that the company had sold two “synchronous condensers” to the Tennessee Valley Authority. These are electric motor-like devices that act as “shock absorbers” in an electricity grid and help keep voltage levels steady. The devices are wound with high Tc superconductor wire.

The company is also working on giant electric motors to power US Navy warships, and Malozemoff said that the company is still in the running for a contract to supply motors for next-generation destroyers.

I just came out of a medical physics press conference that presented three very different ways that physics can be put to use saving lives.

The first presentation was from David Nolte of Purdue University who has created a very simple but effective way of measuring motion inside cancer cells. The technique involves splitting a laser beam, reflecting one beam off a tumour and then recombining the two beams at a detector. The two beams interfere and motion within the cancer cells causes the interference to change.

The result is an image of the tumour covered in speckles that change rapidly as the organelles inside the cancer cells move. A moving cell is a healthy cell, so the technique can be used to study how some anti-cancer drugs slow down the movement within cells, ultimately killing them.

Andre Brown of the University of Pennsylvania described his work on fibrin, which are molecular chains that create web-like structures that aid in the clotting of blood. Blood clots cause heart attacks and strokes so it is very important to understand the mechanical properties of fibrin — particulalry how it stretches.

Brown used a technique developed a few years ago whereby the tip of an atomic force microscope (AFM) is used to pick up one end of a fibrin chain and tug on it. He discovered that fibrin was made of a chain of coiled proteins, with each coil unfolding 23nm when pulled hard enough by the AFM. The next step is to work out how this unfolding affects larger fibrin structures.

Finally, Michael Deem of Rice University explained how he has used statistical physics to develop strategies of multiple vaccination to keep the body’s immune system one step ahead of a rapidly mutating virus.

And a big thanks to the APS press office for a fantastic lunch today!

The room was packed to the rafters for Tsuneya Ando’s talk on “Theory of quantum transport in graphene and nanotubes” (H28 1), which kicked off the first of five focus sessions on graphene. Although it may still be too early to call, I’d say that graphene will be THE topic of this year’s meeting.

I left the session with my head spinning in Landau levels, but I think I got the general idea — graphene is like a very thin motorway for electrons with nothing in the way to slow them down. There’s a press conference later today on graphene — including the latest development in negative refraction — which should be more my speed.

Day two beckons

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It’s day two of the March meeting and after cutting my teeth yesterday on some lighter material it’s time to get stuck into some serious physics. The first thing on the agenda is graphene. There are at least a half a dozen sessions on graphene this year, not bad for a material that’s only been around for a few years. Also on my list are a couple talks on spintronics. For some light relief I’ll be popping into a session on nuclear weapons.

The meeting got off to a slow start yesterday and before noon I was wondering where everyone was. But by the end of the day I could easily believe that I was surrounded by 7000 physicists. There will be a total of 6500 talks at the meeting and just over 100 companies are represented at the exhibition.

For the most part, the Colorado Convention Center is easy to navigate and it takes no longer than about five minutes to get from one meeting room to another.

But I don’t think I would be very pleased if I was an exhibitor. The exhibition hall is a good distance from the meeting rooms and areas where delegates tend to congregate. I mentioned this to the folks on our booth, but so far they seem pleased with the traffic they are getting.

What do superconductor expert Paul Chu and Jimi Hendrix have in common?

They were both on stage at the “Woodstock” of their respective professions — at least according to the APS, which today celebrated the 20th anniversary of a special session on high Tc superconductivity that was held at the 1987 March Meeting in New York City.

The 1987 session occurred just months after Georg Bednorz and Alexander Muller announced their discovery of a material that was superconducting up to 35K — a much higher temperature than was thought possible. Within a year Chu had found another material that remained superconducting above liquid nitrogen temperature and the race was on to find a room temperature superconductor.

In true APS style, the 1987 special session was marked today by holding another special session called “20th Anniversary of High Tc Superconductivity ‘Woodstock’ Session” (B1), which featured many of the original lineup.

According to Brian Maple, who chaired the 1987 session, about 2200 people attended and it went on until 3.15 am — leading someone to dub it the “Woodstock Session”. Not quite the half million people that attended the four-day Woodstock music festival in 1969, but impressive for the normally staid March meeting.

The 1987 session was well attended by the media, and the speakers gained celebrity status as the world went high-Tc mad. At a press conference held today, Woodstock speaker Paul Grant produced a poster from a trendy Manhattan nightclub that had devoted an entire week to a high Tc theme. Grant said that the nightclub’s bouncers led him through the queue like a rock star. Grant also produced a high Tc t-shirt that he bought from a vendor on a California beach.

Bednorz and Muller went on to win the Nobel Prize and more than 100 high Tc compounds have since been discovered — the current record temperature being about 160K. However, Grant admits that the first real commercially viable applications of high Tc materials are still about a decade away and that “there is no generally accepted theory for high Tc superconductivity”. The latter has led to divisions within the high Tc community about the way forward.

So have the high Tc rock stars suffered the same fate as Spinal Tap?

“It’s not fair to say the theory is in great chaos”, said Woodstock attendee Douglas Scalapino when I asked him about the shortcomings of current approaches. He is confident that physicists understand the nature of the high Tc superconducting state, which he believes is caused by the “d-wave” pairing of electrons. What is not understood, says Scalapino, is why the electrons pair up in the first place and this is going to need better experimental data.

Here’s two things that you probably don’t know about icicles — they are usually filled with liquid water and their shapes are defined by hot air. So says a theory put forth by Martin Short of the University of California at Los Angeles in his talk “How the icicle got its shape” (B7.00003).

Icicles elongate as water flows down the their sides and eventually freezes - but this is not the whole story. Instead of freezing rapidly, the water stays liquid for longer because the icicle is sheathed in warm rising air. The air is warmed by the latent heat given off when the water eventually freezes. This heating makes the icicle longer and thinner that it would otherwise be. The relatively warm liquid core also seems to help this elongation process.

Short’s theory allowed him to predict the shape of an icicle as a function of its length. He then trawled the Internet for photos of icicles, and sure enough the data agreed with his theory.

The strange thing is that stalactites (those things that grow from the roofs of caves) are exactly the same shape as icicles — but their formation doesn’t involve rising air or liquid cores.

Windmills could someday reduce net global carbon dioxide emissions to zero, says Klaus Lackner of Columbia University. But these aren’t the sort of windmills that generate electricity. Instead, they scrub carbon dioxide from the air passing through them — much like a conventional smokestack scrubber.

In his talk “The future of fossil fuels” (A2.00003), Lackner claimed that 250,000 such windmills could eliminate all of mankind’s carbon dioxide emissions — at a cost equivilent of boosting the price of gasoline by 25 cents per gallon.

The ability to remove carbon from the air is essential, says Lackner, because 50% of all carbon emissions come from cars, airplanes and other small sources. It would be very difficult to collect carbon dioxide from such sources and tough to convert them to run on carbon free fuels.

Lackner is currently working with a company in Arizona to develop the technology, and was hesitant to provide further details. He did show a sketch of the windmill and it wasn’t a pretty sight — picture a giant ventilation grating with fins sitting on top of a pole. “Not in my backyard”, do I hear?

I arrived in Denver on Saturday and had a fantastic Sunday touring the mountains with an old physicist friend of mine who lives just outside of the city. While most of our tour involved taking in the beautiful scenery of the Rocky Mountain foothills, it had a definite physics theme.

Steve’s a bit of an expert on magnetic data storage and Colorado is definitely the place for him, with both Seagate and StorageTek having “campuses” outside of Denver. That magnetic attraction might have something to do with NIST in nearby Boulder, which is home to some world’s leading experts on magnetic devices.

Steve used to work at NIST and was keen to get us up into the mountains — which begin just behind Boulder — for a better view. From a lookout on Flagstaff Mountain we could see NIST, JILA (home to three Nobel laureates) and the NOAA’s Earth System Research Laboratory. Not part of the vista, but also in Boulder is the National Center for Atmospheric Research (NCAR). And of course, there is the University of Colorado — not bad for a place with less than 100,000 people!

A few miles outside of Boulder we travelled across a flat, stoney and desolate plateau aptly named “Rocky Flats”. Until very recently this was home to a US government nuclear weapons production facility, where a friend of Steve’s used to make triggers for hydrogen bombs. Now mostly demolished, the plant was the raided by the FBI in 1989 over allegations of poor safety and the illegal dumping of waste.

But you’ll be relieved to hear that the highlight of the tour had absolutely nothing to do with physics. We went up to the town of Evergreen, which is nestled in a steep valley in the first range of the Rockies. The town has a pretty little lake that was dotted with people ice fishing. Being Canadian, Steve and I couldn’t resist walking out onto the ice (which was at least a foot thick) to see if the fish were biting. The fish were not obliging, but it was a lovely warm sunny day and folks were sitting on the ice in lawn chairs sunning themselves — a fantastic sight. Back at the hoteI I looked at myself in the mirror, and sure enough I had managed to get a sunburn out on the ice!