Cocktail Party Physics

through rose-colored glasses

Last year a close friend of mine lost his elderly father to complications from Parkinson's Disease. This was a once-vibrant, keenly intelligent, accomplished man who'd been ravaged by a steady decline in neural and motor function, plus the unpleasant side effects that accompanied some of the medications to treat his condition. The decline occurred over the course of 15 long years, and while losing his father was devastating for my friend -- as losing a loved one always is -- I suspect that his father's passing was also something of a relief, since it was tough to watch that slow inevitable decline, knowing the man his father had once been. [UPDATE: We join our Spousal Unit and countless others in the physics community who mourn the passing of Harvard physicist Sidney Coleman, who suffered from Parkinson's for several years, and was a truly incomparable human and scientist.]

It's safe to say that most people have heard of Parkinson's Disease, at least in passing, if only because actor Michael J. Fox (Family Ties, Spin City, the Back to the Future film franchise) suffers from it, and established an eponymous Foundation for Parkinson's Research to promote R&D to treat and hopefully one day cure the disease. To his credit, Fox hasn't shirked from going public with his condition, or from occasionally displaying the terrible impact it has had on his motor functions. Sure, for a guest TV stint, while he was still in the early stages, he kept his hands in his pockets to hide their shaking, but his controversial TV ad espousing stem cell research last year was a poignant reminder of just how debilitating the disease can be.

Sadly, people lost no time politicizing the personal, using as an excuse the fact that the ad was, technically, associated with a Missouri Democratic effort to pass a bill on stem cell funding. That belligerent blowhard, Rush Limbaugh, predictably wasted no time denouncing Fox's on-camera behavior as "exaggerated," concluding that either he hadn't been taking his medications, or he was "acting" to gain the sympathy vote. To which one can only respond (and many people did): oh, please. Wherever you stand on the issue of stem cell research (we are heartily in favor, for the record, and pleased that the state of California supports it, too), accusing someone who has such a debilitating disease of "faking it" to further your own political agenda is ethically beyond the pale. Because Parkinson's Disease is first and foremost a personal tragedy, not just for the sufferer, but for his/her loved ones as well. It's a bit like Alzheimer's in that respect -- another degenerative disease that could benefit from increased stem cell research.

Parkinson's is officially defined as a progressive, degenerative neurological disorder of the central nervous system that afflicts somewhere between .5 and 1.5 million people in the US alone, and as many as 6 million people worldwide. The name derives from the British physician, James Parkinson, who was the first to formally characterize the disease (then known as paralysis agitans) and its symptoms in 1817 in his treatise, An Essay on the Shaking Palsy.

There's a region of the brain called the substantia nigra, whose cells produce the chemical neurotransmitter, dopamine, which is responsible for transmitting signals within the brain that allow for coordination of movement. Without enough dopamine, neurons fire without the usual level of control, so sufferers are less able over time to direct or control their movements. Nobody knows what causes the loss of dopamine and, hence, the disease, exactly, but studies point to a combination of genetic and environmental factors. Early signs include the onset of tremor: a telltale slight shaking in the hand, sometimes even in the legs. There may also be some cognitive or speech impairment: mild memory loss, perhaps, or soft, mumbling speech.

One of the most common symptoms of advancing Parkinson's is that as the disease progresses, the sufferer experiences greater difficulty walking. Specifically, they tend to take small little stutter steps, exhibiting a shuffling walk, an unsteady gait, and a stooped posture. There's a medical term for it: akinesia (or bradykinesia, if you're referring to the whole range of slowed motion that accompanies the progression of the disease).

Usually this is treated with a drug called Levadopa, or L-dopa, a chemical precursor of dopamine that can be found naturally in plants and animals. The brain's nerve cells convert L-Dopa into dopamine, often reversing many of the more disabling symptoms of Parkinson's. (One cannot, alas, just administer dopamine directly, because it can't cross the protective blood-brain barrier -- that meshwork of tightly packed cells in the walls of the brain's capillaries that serve to screen out certain substances. L-dopa can penetrate that barrier, although it diffuses so much that only a small amount actually gets to the brain. Combining L-dopa with another drug, carbidopa, makes it a bit more effective, and also reduces some of the unpleasant side effects, which include involuntary movements, hallucinations, a drop in blood pressure when standing, and nausea.)

Then there's physical and/or occupational therapies, to retard the degradation of motor function. Along with akinesia, there's also an intriguing counter-phenomenon called kinesia paradoxa, in which Parkinson's patients begin to walk normally when triggered by the placement of physical obstacles at their feet. Walking up regularly spaced stairs, for example, can "unfreeze" someone who otherwise has difficulty walking with a normal gait. The same effect can be achieved with black and white tiles spaced evenly on a floor. The black tiles appear as objects to avoid, or as guides, thereby triggering a reflexive landing of the feet between the black spaces.

In general, though, most "normal" or "natural" environments are sadly lacking in these critical visual cues. This is where a California podiatrist named Tom Reiss comes in. He was diagnosed with Parkinson's at the age of 33 -- like Fox, struck down in his prime -- and wasn't content to merely accept the associated reduced motor functions. Instead, he spent 16 years working in his garage, using himself as the  main test subject, trying to figure out adaptive methods for countering his impaired walking abilities. He noticed the kinesia paradoxia effect while shopping at Safeway, because the floors were lined with evenly-spaced black and white tiles, and also noticed the same thing happened when walking up the stairs. Reiss compares the visual cues to an array of ordinary playing cards, displayed like the rungs of a ladder, with the subject landing his feet between the rungs.

He built several prototype cueing devices over the years, some of them owing more than a little to quirky inventor Rube Goldberg's influence. He used coat hangers to attach playing cards to the tips of his tennis shoes, for example, because the cards appeared to be evenly spaced objects as he walked -- an approach he describes as "not too socially acceptable, but it worked!" Then he heard about an off-the-shelf Virtual Vision Sport Personal Viewing system, essentially a pair of "augmented reality" goggles that superimpose a virtual TV screen image onto the real world a few feet ahead of the wearer, in such a way that both were visible at the same time. So the wearer could watch TV while mowing the lawn, for example.

For Reiss, the system offered the perfect solution for his impaired walking abilities, and he ended up working with the University of Washington's Human Interface Technology lab to demonstrate the effectiveness of his glasses concept. The first time he donned the prototype goggles, he saw the real world augmented by a series of small, colored moving squares, projected into space at regular intervals in front of him. Wearing them, he could walk normally. So he founded his own tiny start-up company, HMD Therapeutics, to further develop his invention, which he called Central Field Cueing Device Glasses.

The glasses have an array of light-emitting diodes (LEDs) working in conjunction with a computer chip embedded in the sidebar of what would otherwise be a fairly typical pair of wraparound sunglasses. The LEDs produce a pattern of thin, horizontal virtual lines projected onto a transparent screen across the wearer's entire field of view. The lines appear to scroll towards the wearer in an even flow when s/he is stationary, but appears stationary when s/he is walking. Should the user look up, the lines disappear entirely. There are also built-in mercury switches to track head movements so the glasses can "choreograph" the appropriate visual cues.

The glasses are light, portable, relatively inexpensive, easily scaled up for commercial manufacture and offer hands-free control to the user. Most importantly, they're pretty stylin'. These are not the visual equivalent of orthopedic shoes, or some bizarre cyber-punk apparatus (although I suspect there might be a market for that, too); Reiss recognizes the need to make his product attractive. Parkinson's sufferers don't need to feel any more like outsiders than they already are.

Reiss's invention may soon be available to the public at large, thanks to a company called Enhanced Vision, which has licensed his patented technology to refine and perfect the prototypes into a viable commercial product. And he's continued making improvements to the original design, thanks to a Small Business Innovative Research (SBIR) grant. A more recent version, called Virtual Vection Glasses, uses LEDs to generate peripheral cues to not only promote a "normal" walking gait, but also to help suppress another complication of Parkinson's, dyskinesia -- the jerky, uncontrolled movements so painfully evident in Fox's televised plea on behalf of stem cell research, resulting from the body's attempts to process "apparently irrational peripheral movements," and from the excessive build-up of L-dopa in the body.

It's an inspiring story, and Reiss has deservedly received his proverbial 15 minutes of media exposure because of it. But ultimately, it's about reclaiming the life that Parkinson's Disease gradually takes away from sufferers. We fully expect one day soon to see Reiss, Fox and any other sufferers happily strolling along city streets and parks with fully normal gaits, outfitted with stylish sunglasses that only they know serve more purpose than merely blocking out the sun's blinding rays.

they do it with mirrors

Flipping through channels a couple of weeks ago, in a rare (these days) moment of TV-viewing leisure, I caught Texas Instruments' latest commercial for its Digital Light Processing (DLP) technology. You know the one: an adorable little girl is strolling along with an elephant -- willing suspension of disbelief, people! Work with me! -- holding a very small box. She opens it to reveal a beam of pretty light shining upwards, and the little girl says in awestruck sotto voce: "It's amazing. It's the mirrors."

Most people viewing that commercial probably have only the vaguest idea what it's about, other than describing a key enabling feature of high-definition TV. (They're probably distracted by wondering, "What's with the elephant? Why an elephant?") But TI's Larry Hornbeck must feel a special frisson of satisfaction every time he sees it, since he's the guy who invented that enabling technology in the first place. All those HDTVs, digital movie projectors, and the digital displays used by so many schools and businesses? Hornbeck's research gave us that. And last week the American Institute of Physics rewarded him with its 2007 Prize for Industrial Applications of Physics, "for his invention and pioneering innovations in both the design and manufacturing of Digital Micromirror Devices (DMDs) integrated into metal-oxide semiconductor (MOS) technology." He can add that award to the Emmy he snagged in 1998 for the same technology, and his 33 (and counting!) US patents.

Just what are these miraculous mirrors? It just so happens I wrote a feature article back in June 1997 on the DMD technology. (You can read items from Physics News Update about DMDs here and here.) At heart, it is a complex, rectangular array of as many as 2 million microscopic mirrors nestled on an integrated circuit. Each mirror measures less than one-fifth the width of a human hair, if you need a comparison point to get a handle on the tiny scale we're talking about. The DMD acts like a light switch: each mirror is hinge-mounted so it can tilt on its, regardless of what the other mirrors are doing. This enables a digital image to be processed from a digital signal, because each mirror acts as a single pixel and can be switched on and off thousands of time per second, reflecting light onto a screen.

It all started back in 1997, when Hornbeck was working on building an analog light modulator for optical processing. He based the device -- which appeared four years later -- on a deformable mirror mounted on a metallic membrane. Then he got the idea for replacing that with an array of tilting mirrors connected by hinges, and the DMD concept was born. It was admittedly rudimentary, and too limited in how much light it produced to be immediately implemented into display applications, but Hornbeck and his TI colleagues did manage to develop a useful product: a ticket printer for commercial airlines. At the time, the airline industry was looking for a way to move past carbon-copy ticketing (older readers may remember those pre-e-ticket artifacts) with high-speed, high-resolution printing. The DMD proved ideal for that purpose.

The real breakthrough occurred in 1989, when DARPA awarded the company a $10 million grant to develop cutting-edge projection display systems. By then the DMD technology had sufficiently advanced optically that the notion was perfectly feasible. A year later, Hornbeck came up with the current design, and the first 640-by-480 pixel projection display using DMD appeared in 1992. Further improvements came fast and furious: the earliest devices had thousands of the tiny mirrors, but today's version boasts millions.

By 1997, when I wrote my article, TI was integrating the DMD technology with DLP, which proved to be the winning combination for the commercial marketplace. Thanks to the incorporation of DMD technology, the DLP chip is frequently described as "the world's most sophisticated light switch." Feed a digital or graphic signal to the chip, combine it with a light source and projection lens, and voila! All those tiny mirrors reflect a fully digital image onto your surface of choice (screens are nice).

Inside the DLP chip, the hinge-mounted mirrors tilt towards the light source for the "ON" position, and away from it to indicate the "OFF" position. "ON" corresponds to a light pixel on the screen, while "OFF" corresponds to a dark pixel. Various shades of gray (up to 1,024 -- I didn't know there were that many) can be achieved by switching on and off several thousand times per second. If a mirror is "ON" more than "OFF", it reflects a light gray pixel, and if it's "OFF" more than "ON", it reflects a dark gray pixel. The result is a high-resolution gray scale image.

But we don't live in a gray scale world, so the DLP system passes the white light generated by the lamp serving as an illumination source through a color wheel (or a prism) as it travels to the surface of the DLP chip, filtering the light into red, green and blue. The  "ON" and "OFF" positions for each micromirror are coordinated with those basic color building blocks, such that a mirror responsible for projecting purple (one purple pixel) will only reflect red and blue light to the projection surface. Our perception blends the rapidly alternating flashes of color and will "see" the intended color (purple) in the projected image. TVs, home theater systems and business projectors are 1-chip systems capable of producing at least 16.7 million different colors, while the more advanced 3-chip systems can produce a whopping 35 trillion colors. The mind boggles. Truly it does.

Is DLP perfect? Probably not -- nothing is. Its main competitors in the HDTV marketplace are LCDs and plasma flat panel displays, and each probably has its benefits and drawbacks. The closest competitor is Liquid Crystal on Silicon (LCoS), which uses a stationary mirror mounted onto a chip and relies on a liquid crystal matrix -- similar to those used in LCDs -- to control the reflected light. Thus far, DLP is holding its own quite well. More than 13 million DLP subsystems have been sold to date, with more than 50 manufacturers offering various models in late 2004. TI is reaping the economic benefits: DLP chips constitute a good 5% of the company's total sales.

Innovations are still being made, too. Early in September, TI showcased its high-definition 3D DLP technology at a major home theater and entertainment industry expo (CEDIA), which gives 3D stereoscopic capability to existing HDTVs for a truly immersive viewing experience. Now you can truly feel like you're in the midst of the action if you're watching a spectacular chase scene or action sequence -- and it's designed for easy adaption of existing 3D computer games, which should give all hardcore gamers a warm, happy feeling. This latest innovation builds upon DLP Cinema, launched a few years ago and now in use on more than 4500 movie screens globally. This was a boon to films like Meet the Robinsons, Harry Potter and the Order of the Phoenix, and Beowulf, all of which were shot in 3D. Industry buzz has it that Hollywood intends to expand the number of 3D theatrical releases in the future.

And to think, it all started with one small deformable mirror and the fertile imagination of a gifted , creative physicist. The next time you're at a cocktail party and someone wonders aloud how all this high-falutin' digital TV and 3D cinematic technology is possible, you can bask in the warm glow of superior knowledge, lean over, and whisper the industry's secret: they do it with mirrors. Be sure to mention Hornbeck -- a.k.a. The Founding Father -- by name.

REPOST: wonder woman and the invisible man

[Original posting at Cocktail Party Physics is on hiatus, due to a temporary absence due to honeymoon. In the interim, we are offering a few leftovers. A few minutes in the microwave and you'll hardly notice they weren't made fresh this morning. For today's offering, we were reminded of one of our earliest posts in March 2006 on plasmons, by this recent item in Physics News Update describing a plasmon version of Thomas Young's seminal two-slit experiment to investigate whether light is a particle or wave.]

True confession time: I idolized Wonder Woman growing up. Strong female role models were in short supply for die-hard tomboys like me. It's been said that nine-tenths of the law of chivalry is the desire to have all the fun, and that certainly seemed to be the case to my young-yet-jaundiced eye. So I thrilled to the sight of live-action Lynda Carter defying the girlie stereotypes and kicking bad guy butt on TV, and rejoiced when the character later emerged as a proud member of the Justice League. For many little girls like me, Wonder Woman was the epitome of female empowerment in the pre-Buffy era.

(Needless to say, ultra-fangrrrl Jen-Luc Piquant is beside herself with excitement that none other than Joss Whedon -- known to her simply as "Joss the Great," the creative genius behind Buffy the Vampire Slayer and Angel -- will be writing and directing a new Wonder Woman movie.)

Wonder Woman had all the usual super-powers -- uber-strength, the ability to fly -- plus an uncanny knack for accessorizing her skimpy All-American outfit with all manner of nifty gadgets, including the lasso of truth, unbreakable silver bracelets, and a razor-sharp golden tiara that doubled as a deadly weapon. She could also create invisible vehicles at will, most notably her signature invisible plane. In fact, she could stretch any such invisible vehicle to construct a complete transparent fortress, dubbed the Wonderdome.

Sometimes science fiction intrudes on the real world in surprising ways. It turns out that there is a bizarre physical phenomenon (electrical waves that travel along the surface of some metals) that could one day lead to a kind of "cloaking" technology capable of making airplanes "invisible" -- at least to radar detection systems.

When light strikes a metallic surface -- silver, gold, or whatever strange metallic material is native to Wonder Woman's Amazonian homeland and used to make her spiffy plane -- it generates electron waves, called plasmons. Last year scientists at the University of Pennsylvania discovered they could potentially use plasmon coatings as a cloaking device to render objects invisible by creating a kind of "shell" around the object. Yes -- just like Wonder Woman's plane. It's risky to indulge in unfounded scientific conjecture, especially about a fictional heroine, but it seems like the Amazon princess could generate those same electron waves at will. Now that's what I call a super power.

Plasmon waves limit light scattering off an object because they resonate at the same frequency as the light striking them -- the two are literally on the same wavelength, so they cancel each other out. This makes the object in question very difficult to detect, since we see things in our environment by detecting the light that bounces off those objects.

Sadly, we won't be riding around in Wonder Woman's invisible jet any time soon, in part because the cloaking effect only works with wavelengths of light that are about the same size as whatever object one is trying to render "invisible." Anything bigger would have to be visible because it would disturb the light, causing it to scatter. An airplane is many, many times larger than the range of wavelengths for visible light, so it would still be visible even with a plasmon cloaking shell, although it might be undetectable to radar systems, which rely on radio waves with much longer wavelengths. Shape is equally critical: to date the effect has only been observed in small, perfectly cylindrical or spherical shapes. Only really tiny objects that cancel out scattering from visible light would be rendered "invisible" to the naked human eye.

Metaphorically speaking, however, plasmons seem to have rendered one scientist invisible, at least in terms of broad recognition: Robert W. Wood, a physics professor at Johns Hopkins University who first observed so-called "field emissions" -- charged particles emitted from a conductor in an electric field -- in 1897. (This effect became the basis for field-emission microscopes, used to study atomic structure.) Wood was also the first person to unwittingly record the energy lost as heat by plasmons skimming along the surface of metals in 1902, although he couldn't explain the effect at the time. It took 40 years for Italian physicist Ugo Fano to provide an explanation: metals are not perfect conductors, as had been previously believed. Fano found that a conducting surface could guide light as a 2D surface wave (which is why plasmons are also known as two-dimensional light). Those waves absorb energy, which explains Wood's anomalous observations of energy loss in the light reflected from metallic surfaces.

So technically, Wood "discovered" plasmons; he just didn't realize it. And while he was internationally known at the time for his many achievements in optics and spectroscopy, nowadays, his name is hardly a household word, even within the physics community. He's more of a historical curiosity, a footnote to the many scientific papers now being published on plasmon-related research; Wikipedia only has him listed as a "stub." Personally, I blame those mischievous little plasmons. They have cunningly shielded him from the recognition he so richly deserves. To me, Wood is physics' Invisible Man.

That's a shame, because he certainly had an interesting and varied career. Black lights are sometimes known as "Wood lights" in his honor, since he is considered the father of infrared and ultraviolet photography. Using a glass filter that would transmit only UV light, he photographed the moon, demonstrating that the darkest area in UV light is the Aristarchus Plateau. The Wood crater on the far side of the moon is named after him. He was the first to publish infrared photographs of landscapes in 1910, which were later exhibited at the Royal Photographic Society. And in 1919 he published the first ultraviolet photographs of the human body. 

Unlike most modern physicists, Wood's research involved almost no mathematics; he thought math was boring, and preferred to focus on pictures and showy demonstrations during his class lectures, sometimes involving small explosions or flames. He never earned a bona fide PhD, and funded his early post-undergraduate studies by working part-time as a bottle-washer. His well-known fondness for pranks paid off around 1906, when he famously debunked Henri Blondlot's claim to have discovered a new form of invisible radiation, "N-rays."  (This was just a few years after Wilhelm Roentgen discovered X-rays, so the public was inclined to be a bit more credulous about the existence of invisible radiation.) Blondlot claimed the N-rays could only be detected with his own machine. Wood secretly removed the inner workings of the machine -- specifically, a prism -- and when Blondlot repeated the demonstration, he still claimed to see his N-rays, unaware his "detector" no longer worked. Wood was highly amused; one assumes Blondlot was not.

As if those accomplishments weren't enough, Wood also invented the method for thawing frozen street water mains by passing an electric current them; the frosted glass bulb; even a method for detecting forged documents that was very cutting edge in his day. He experimented with aerial photography by attaching a camera to a kite. And during a trip to Germany in August 1896, Wood photographed a few test flights by famed aviator Otto Lilienthal -- literally one week before Lilienthal plunged to his death during another test flight when his glider stalled out. He even published a children's book of nonsense verse in 1907, How To Tell the Birds from the Flowers.

Plasmons are back in the science news this year, thanks to several papers presented at the APS March meeting in Baltimore last week on the emerging field of plasmonics. To date, it's proven difficult to combine photonic components -- such as fiber optic cables -- with electronic components like wires and transistors because of their mismatched capabilities and size scales. Photonic components can carry a lot of data -- witness the explosion in broadband data transmission rates -- but are bulkier than electronic components, which in turn can carry less data. The Holy Grail is to be able to combine the best features of both onto a single chip. Plasmons might be the key to achieving it, since they operate at optical frequencies -- typically 100,000 times greater than the frequency of even the most cutting-edge microprocessors -- and the higher the frequency of the wave, the more information you can transport over it. Yet they take up much less space because their wavelengths are much smaller than the light used to create them.

This makes plasmons extremely promising for a wide range of applications -- not just to make things "invisible," but also to enable scientists to see fine details that were previously undetectable. For instance, a team of scientists at the University of Maryland are developing a two-dimensional plasmon microscope, ideal for imaging living cells, that could operate much like a point-and-shoot camera and reveal much more detail that currently available with existing imaging techniques. Other researchers are exploiting plasmons to create "super lenses," relying on tiny nanoparticles to amplify and focus the light shining on a given sample. Scientists at the University of Texas, for example, have built a "super lens" and used it in a device to take pictures just below the surface of thin material substrates.

And at Rice University, researchers have created rice-shaped particles of gold and iron oxide, called "nanorice," that they hope to attach to the probe tips of scanning microscopes to map out the surfaces of biological cells. To my eye, the Rice University nanoparticles (pictured below) look as much like worms or maggots as grains of rice, but "nanomaggots" doesn't have quite the same ring to it, and also lacks the handy institutional tie-in. As group leader Naomi Halas says, "How often do you get the chance to name a nanoparticle after your university?"

So people are talking about plasmons a lot these days. What they aren't talking about is Robert W. Wood, the physicist who first observed plasmons over a century ago. It reminds me of the classic film, "My Man Godfrey," in which spoiled Bright Young Things in socialite New York go on a scavenger hunt and must bring back a "forgotten man." Carole Lombard's character happens upon a vagrant named Godfrey (played by the incomparable William Powell) and ends up employing him as a butler. He turns out to be a bit more than he appears. Wood, too, is an unjustly forgotten man. Perhaps, as plasmons begin to shed light on the fine details of living cells, some of that light will spill over and illuminate the once-living man who first noticed their existence.

search lights in the sky

We are now well into Day 13 of the search for missing millionaire-cum-adventurer Steve Fossett, whose plane disappeared off the radar -- literally -- somewhere over the vast expanse of the Nevada wilderness. A planned three-hour private excursion turned into a immense manhunt to rescue the missing man. Dozens of aircraft have scoured a whopping 20,000 square miles, with a small army of online volunteers poring over satellite imagery, courtesy of Google and Amazon, and yet Fossett and his single-engine plane remain missing. Searchers have found wreckage from seven prior unrecorded crash sites, however -- a testament to just how difficult it can be to locate small planes in that region, a task made even more difficult by (a) an apparent malfunction in the plane's transponder/emergency locater, and (b) Fossett's failure to file a flight plan. (In fairness, it was supposed to be a very short, routine flight, and Fossett is/was a highly experienced pilot who has survived plenty of harrowing crash landings in the past.)

I don't know if the airborne searchers are employing just conventional  aerial and satellite imaging, or whether they're also making use of more innovative techniques, notably Light Detection and Ranging (LIDAR), but I hope they'll at least consider doing so, just to improve the odds that much more. LIDAR is an optical remote sensing technology that exploits the same basic principle as radar and sonar -- sending out pulses that bounce off objects and analyzing the returning signals to determine an object's distance from the source -- except it uses light wave pulses instead of radio waves. (Yes, I know, radio waves are technically just another form of electromagnetic radiation; in this instance, "light" refers to the visible and near-infrared frequencies in the spectrum.) It's not so much a replacement technology, as a complementary one -- just one more tool in our growing arsenal for remote sensing and mapping, and for finding things like Fossett's downed plane.

A LIDAR instrument transmits pulses of light to a target, and the parts of the spectra that are not absorbed by the target are reflected back (known as backscatter) to the system, which then are detected, stored and analyzed. It's the changes in the properties of the light when it scatters back that enable scientists to measure specific properties of the target.  Bats use ultrasonic pulses to hunt for their prey, emitting a series of pulses that become more frequent the closer it gets to its target, climaxing in a kind of "feeding buzz" as it locks in for the kill. Similarly, the more frequent the light pulses emitted in a LIDAR system, the more information is gathered, and the more accurately a target area can be mapped. For airborne topographical mapping, as many as 33,000 laser pulses can be transmitted every second.

LIDAR has been around for quite a long time, having been invented shortly after the first lasers appeared in 1958. But the technology was a bit ahead of its time, and languished for several decades until a whole bunch of other enabling technologies emerged. Early lasers were too expensive, frankly, and too heavy, too big, and required too much power, to make them practical for airborne applications. When the solid-state diode pumped laser emerged, that changed: they were cheap, rugged, and compact, with comparably low power requirements. Computing technology also needed to advance to the point where it was fast enough, and cheap enough, to perform the kind of advanced data analysis required by a LIDAR system.

Most notably, early LIDAR systems could make accurate measurements in the centimeter range, but only for lasers fixed on the ground. This strictly limited its useful deployment, since once anyone placed a laser on a moving platform, all bets were off. Then came the Global Positioning System (GPS), and suddenly it became perfectly feasible to figure out exactly where a moving object might be in relation to a ground-based coordinate system. And LIDAR was finally dusted off and brought into the marketplace.

For remote sensing applications, the LIDAR system is mounted onto an aircraft equipped with a GPS receiver (de rigeur these days in just about any vehicle) to track its exact location and altitude. It also needs a high-accuracy inertial measurement unit (IMU) to track the pitch and roll of the airplane so that movement can be accounted for in the final analysis.  Basic physics tells us that objects spinning at a very high rate tend to maintain their relative position in space, so an IMU incorporates several spinning gyroscopes. By measuring the angle of tilt as each spins a spherical mass within a gimbal (or cage), and coupling that with an accelerometer to keep track of shifts in velocity, the system can tell us how far, how fast and in what direction a target is moving relative to a given starting point. Usually, all the data collected from the various instruments, when combined, can give an elevation that is accurate to within 6 inches.

Generally speaking, we can usually only image a feature or object roughly the same size as the wavelength of the EM radiation being used, or larger. Radio waves used in typical radar systems are great at detecting things like metallic objects -- which is why they're so useful for military and aviation applications -- but rocks or raindrops might not produce much in the way of detectable reflections at all, making them well nigh invisible to radar. But because the wavelengths used are much shorter than radio waves, LIDAR systems are much better at detecting very small objects, like particles in the atmosphere. In fact, they are already used to study atmospheric conditions, notably the densities of various particles, not to mention all kinds of emerging applications in geology, seismology, and even archeology. Also, lasers use a very narrow beam, so LIDAR allows for mapping of physical features with much higher resolution than conventional radar. It can have a "footprint" of less than 1 meter, making it possible to map the floor underneath a forest canopy, or the urban canyons between tall buildings.

There's more than one kind of LIDAR system, each suited to a specific kind of application. If you just want to measure the distance from your instrument to a solid target, range-finder LIDAR should suit your purposes just fine. If it's a moving target, and you want to figure out how fast it's moving, you'll probably want to use Doppler LIDAR, which -- as its name clearly implies -- relies on the Doppler shift effect  to determine an object's velocity. If you're a meteorologist interested in measuring the specific concentrations of chemicals and such in the atmosphere -- ozone, water vapor, and pollutants -- or if you want to map a shallow river bed underwater, you're better off using differential absorption LIDAR. Underwater imaging in particular can be difficult using infrared  and near-infrared preferred for terrestrial mapping, since water absorbs those wavelengths; only the blue-green end of the visible spectrum can penetrate water, for the most part.

Small wonder so many applications have emerged in the past decade for LIDAR systems. In geology and seismology, they're used to detect faults -- most famously, to locate the fault in Seattle, Washington -- and to measure "uplift"  at Mount St. Helen's in Oregon. (I assume this refers to plumes of ashes that the mountain occasionally burps out from time to time, which is an indication of whether its internal distress is reaching a critical eruption point.) Airborne LIDAR is used to monitor glacial melting and other coastal changes, while in forestry, LIDAR is used to study canopy heights and measure biomass, not to mention making the surveying process that much faster. On a more mundane scale, there are now handheld LIDAR systems for traffic enforcement. Whereas radar relies on Doppler shifts to directly measure speed, LIDAR actually calculates the speed, making it easier to isolate particular vehicles from a heavy stream of traffic. Remember that next time you're tempted to weave in and out of lanes at high speeds.

LIDAR has been used for search and rescue before, most notably in the wake of the terrorist attacks of September 11, 2001. For several days after the World Trade Center fell, a small plane made several passes over Ground Zero in Manhattan (and also over the damaged Pentagon in Washington, DC) taking LIDAR readings of the debris -- courtesy of a company called EarthData, which used the collected data to produce topographical images of the sites. This in turn helped rescue workers navigate the often-treacherous terrain by identifying unstable areas likely to shift or collapse. The maps also enabled building and utility workers to locate foundation-support structures, elevator shafts, basement storage areas, and so forth. As workers moved deeper into the WTC's basement wreckage, LIDAR mapping showed where the integrity of the underground walls might have been compromised, thus making those areas more at risk of flooding. The maps were even able to measure the volume of the debris and how much reach the cranes would need to efficiently remove it.   

In the realm of atmospheric studies, LIDAR systems could bring some relief to frequent fliers who have spent way too many wasted hours in airports with chronic delays (*cough* O'Hare *cough*) because our flights were grounded. Scientists at RL Associates in Pennsylvania presented a paper at the recent meeting of the Optical Society of America on their new near-infrared LIDAR system, now in its prototype phase and slated for testing in about 18 months. According to Mary Ludwig, one of the leading scientists on the project, the system will provide better images in foggy, rainy, or extremely hazy conditions, thereby making it a whole lot easier for pilots to take off an land in those conditions, as well as giving more advance warning of potentially hazardous atmospheric conditions, such as icing. This in turn could help reduce weather-related flight delays .

There are other experimental LIDAR systems for similar purposes, using visible green light to detect different kinds of particles in the atmosphere, but most commercial planes aren't equipped with such systems. Ludwig's team has developed a system that uses a polarized laser light beam, i.e., its electric field points in a specific direction. The system beams this polarized infrared light outwards, and then records the amount of polarization that returns to the sensors. The data is then processed to form an image of the ground. If need it be, it can also be translated into verbal commands. This is especially useful for atmospheric applications because ice crystals, for example, are highly depolarizing, while mere water droplets are not. Hard, manmade objects will depolarize the returning signal less than natural objects, so it's possible to get enhanced images of targets in a obscured or camouflaged environment -- say a small, crashed aircraft hidden in dense underbrush. Ergo, Ludwig et al.'s system is better at detecting different types of atmospheric particles, such as ice, supercooled liquid, or water vapor, plus it can also tell the different between water vapor and other substances (metal, or the human body, for example).

The system also incorporates something called a "range-gated detector" that is only turned on for very short periods of time, rather than continuously -- namely, whenever the return signal is expected. The detector is turned off when the laser pulse is first emitted from the system, so it doesn't pick up all the near-field backscatter from things that might be in the pulse's path to the target -- usually the major source of noise for such a system. This means there's a lot less noise in the resulting data so you get better images, particularly in foggy or hazy conditions. All of which spells welcome news for frequent airline travelers.

Perhaps the niftiest new application of LIDAR is in archeology. In England, Cambridge University is collaborating with the UK Environment Agency in the use of LIDAR imaging to produce terrain maps for large swathes of the countryside. It started out as a way of assessing flood risks, but then an organization called English Heritage contracted with the EA to conduct a LIDAR survey of Stonehenge -- one of the most studied landscapes in all of Europe, and a certified World Heritage Site. See the nifty LIDAR image of Stonehenge below, courtesy of English Heritage? How cool is that? It turns out that LIDAR is terrific for recording terrestrial features that have been leveled by many years of ploughing: the WHS survey revealed several previously unrecorded banks in and around the Stonehenge site.

LIDAR mapping isn't just about mapping positions and elevations anymore (although that's definitely the primary focus); newer systems seek to integrate other aspects of feature recognition to make map production ever more automated. A few years ago, scientists from Sweden and Italy teamed up to use LIDAR to image the various types of stone used in the construction of Lund Cathedral. Located in Sweden, the cathedral is an impressive 12-century edifice that ranks as the largest Romanesque building in northern Europe. (Whether you're impressed probably depends on your fondness for the Romanesque period.) Not only could they "see" the differences between the stone used, but they could also tell, from a distance, which of the walls had moss and lichen growing on them.

As intensity recording is incorporated into LIDAR systems, scientists should be able to improve even further on this type of analysis. Intensity recording not only measures the distance between the LIDAR and the target, but it can determine the features of a landscape based on the strength of returning signals. That's because every reflective surface will absorb some wavelengths and reflect others. A concrete block, for instance, reflects almost every wavelength and absorbs very little, so the returning signal is very strong. Leafy vegetation, however, absorbs quite a bit more of the light, and hence returns a weaker signal. These data can also be turned into a visual image.

So light and lasers are an increasingly important tool in archaeological mapping. And the innovations just keep coming. An article a couple of months ago in the San Francisco Chronicle profiled a retired civil engineer named Ben Kacyra, who invented "a camera-like device that uses lasers to scan three-dimensional objects -- such as archaeological ruins -- to create digital blueprints accurate to within a few millimeters." (You can see many such images taken with the instrument here.) At the heart of his device is a laser that emits light with sufficient power to bounce off a distant object and return to a sensor, capable of timing the intervals between signal and response. In this way, "the laser maps the surface of objects by taking millions of measurements at different angles." Sounds like a LIDAR system to me.

Kacyra's system -- which he sold to Swiss company Leica Geosystems in 2001 -- has been used to study pre-Incan Peruvian ruins, the buried Roman city of Pompeii, and the cliff dwellings of the extinct Anasazi people in southwest Colorado. And once these digital blueprints are created and stored, it becomes so much easier to recreate portions of those sites and edifices in a virtual framework -- perhaps, one day, in Second Life. Kacyra has already created a small reproduction of an ancient frieze that he scanned, using his mapping tool. As the Chronicle article put it, "Think of the archaeological equivalent of a reprint of a famous painting, a chance to hold a piece of history." Indeed. There lies the future of LIDAR.

honey, i shrunk the camera

Every writer needs both encouragement and constructive input during the long, painful process of producing a manuscript. I owe a great debt of gratitude to the various members of my former writer's group in Washington DC, who provided both of those things for my two books. One of those members was fellow science writer (and blogger) James Riordon (a.k.a., Buzz Skyline), who was working on his first science fiction novel during the same time period. I'm thrilled to announce that the novel is now finished, and available for your purchasing pleasure via Lulu. It's called The Dark Net -- tag line: "You can log out any time you like, but you can never leave" -- and features not just a "hero" who is epileptic and rendered pretty much impotent by the drugs to control his condition, but also an adorable pair of virtual penguins named Linus and Minus, the subjects of an experiment in neural network behavioral conditioning. In true science fiction fashion, it all goes horribly wrong, and the hero is compelled to ponder the question of what makes something "real."

James was inspired to write the novel after reading that as much as 5% of the Internet is "dark," i.e., inaccessible to the average user Googling around Cyberspace. That portion is most likely home to, say, high-level government classified information, and probably quite a few hackers as well, so it's a natural fodder source for science fiction. The Dark Net takes us into the not-so-distant future, where the trappings of everyday life are still familiar, but with advanced technological gadgetry having now become commonplace, including biometrics and wearable computers with those nifty headset/eyewear display screens. You know you're just itching to read it. Go! Order The Dark Net now! We'll wait...

Are you back? Good. I love the fact that The Dark Net's main character has a physical disability -- reminds me a bit of Ben Elton's Gridlock, which features a wheelchair-bound protagonist with cerebral palsy -- and that for all the technological developments, he still had to rely on imperfect pharmaceutical solutions to keep seizures at bay. It might have been easier (albeit less interesting) if James had made his protagonist blind, because scientists have made great strides over the last 10 years in developing artificial retinas that can restore some semblance of sight to the blind. One of the key enabling components to our visual system is a bunch of cells that lie at the base of the retina, which send electrical pulses to the optic nerve when they detect light; the brain then interprets these signals into images.

Not all blindness is created equal, particularly when it comes to the causes of losing one's eyesight, but artificial retinas will soon be a viable solution for people who lost their eyesight due to retinitis pigmentosa or age-related macular degeneration –- two of the most common causes of vision loss. In both these conditions, the photoreceptor layer of the retina is destroyed, but the inner layers remain intact, still capable of integrating incoming signals and transmitting output signals to the brain's visual cortex via the optic nerve.

Sometime around 1985, a neuro-opthalmologist named Joseph Rizzo III was working retinal transplants and had an epiphany as he was removing a lab animal's retina: even though the light-sensing cells had died off, the nerve connections were still intact and could still transmit signals from those cells to the brain. Rizzo concluded that it should be possible to create a retinal prosthesis capable of gathering wireless video signals from an external camera and feeding those signals directly to the brain, bypassing the damaged cells altogether. He lost no time demonstrating proof of principle with experiments showing that direct electrical stimulation of the retinal ganglion cells in blind test subjects produced some sense of vision. And he launched the Boston Retinal Implant Project with MIT electrical engineer John Wyatt Jr., which now boasts more than 27 researchers at eight institutions.

There's lots of different options when it comes to finding substitutes for the mangled photoreceptor layer. One of my favorites can be found in the work of Oak Ridge National Laboratory's Elias Greenbaum, who works with the protein centers of spinach leaves. He's got a lot of fancy, complicated equipment in his lab, like most scientists, but he's also got a common kitchen blender. That's what he uses to puree spinach leaves to a pulp, after which the pulp is put into a centrifuge to separate the various molecules. Greenbaum's particular interest is in one particular reaction center (Photosynthesis I, or PSI), which is basically a tiny photosensitive battery, converting light into energy by absorbing sunlight and emitting electrons. Spinach PSIs can't generate a lot of current, it's true, but there's enough that Greenbaum thinks it might produce enough electricity to one day run minuscule molecular machines. PSIs also behave like simple diodes, passing current in one direction but not the other, which means they could eventually be used to construct logic gates for molecular computers, connecting them into functioning circuits using wires made of carbon nanotubes, for instance.

While we're all waiting for molecular machines to become a reality, however, Greenbaum's found another use for PSIs: as a raw material for constructing artificial retinas.  This is biomimicry in its purest form: the PSIs perform a similar function to the retina's photoreceptor cells, turning light into electrical signals, so why not use them to replace damaged photoreceptor cells? To do this, the PSIs are embedded into tiny fatty spheres (liposomes) and injected into the membranes of retinal cells, so when light falls on them, they produce a voltage in response strong enough to trigger electrical impulses along the optic nerve to brain. Whether or not these constitute "neural events" that the brain can then accurately interpret has yet to be determined.

Fascinating though Greenbaum's work may be, even he emphasizes that there's a long way to go before this is ready for any kind of real-world clinical application -- last time I checked, he hadn't yet started experimenting with animals, never mind human trials. So people suffering from damaged photoreceptor layers should really be looking to Rizzo and his growing army of collaborators for a short-term solution. As he'd envisioned, his breakthrough insight and subsequent proof of principle did indeed lead to the development of the first retinal prosthesis.

In such a system, an array of electrically activated microelectrodes fabricated onto a flexible substrate is implanted close to the retinal ganglion cell layer from the front of the retina. A small commercial video camera mounted on a pair of glasses takes the place of the damaged retinal photoreceptor layer, providing images of the outside world as the user "looks" around. These are transmitted wirelessly via a transmitter coil to a corresponding 'receiver coil" sitting on an implant on the surface of the eye -- basically a very thin electrode array placed just under the retina. The electrodes stimulate any surviving nerve cells in response to incoming images from the camera, providing a small patch of vision. The camera's signals are designed to be transformed into a format suitable for directly stimulating the retinal ganglion cells, and then sent wirelessly to the array.

Ideally, they would have liked to have a fully implantable prosthetic retina, but, as Wyatt told Technology Review, "The eye doesn't like stuff inside; that's why it doesn't have a zipper." Considering the discomfort a single eyelash can cause if it falls onto the surface of the eye, I can't image anyone being able to endure a full-scale implant. So they developed the outer device. They attach the plant to the surface of the eye with tiny sutures and the only part that penetrates the eye is that electrode array, which is only 10 micrometers thick, two millimeter wide, and three millimeters long. In 2005, Wired reported that an artificial retina could be clinically available as early as 2008, thanks to a system developed by researchers at the University of Southern California and the Doheney Eye Institute. The system is called Argus, after the mythological Greek god who had 100 eyes, and it wouldn't be cheap: it would probably cost between $30,000 to $50,000 -- still a small price to pay, I'd think, for the gift of restored sight.

Yet scientists haven't quite given up hope that it might be possible to come up with a fully implantable device. The extraocular camera approach is not without its limitations. For instance, subjects must move their heads in order to scan the environment. This conflicts with natural eye movements, which can be confusing since the only information the retina receives is from the camera. Even something as simple as shaking one's head "yes" or "no" can be uncomfortable and disorienting.

To address that problem, researchers at the University of Southern California's National Science Foundation Engineering Research (ERC) for Biomimetic MicroElectronic Systems (BMES) are developing a tiny "intraocular" camera for retinal prosthetic systems that can be implanted directly into the crystalline lens sac of the human eye. (Full disclosure: I helped write the linked press release, so if you hear echoes of the same wording in this post, that's why. There's a very nice writeup in Popular Science on the research, too. I had nothing to do with that.) The operation is similar to the techniques used in cataract surgery. The prototype being developed by USC/BMES team leader Armand Tanguay and his colleagues' would allow for natural eye and head movements.

Any camera that small has to meet all kinds of stringent requirements to make it suitable for implantation into a human eye, not least of which is a certain degree of biocompatibility. But it also has to be very, very small, extremely lightweight, and not require too much power to operate (batteries are so very bulky). The researchers needed to include only the bare minimum of functioning components. In order to optimize the design constraints for their ultra-miniature camera, Tanguay's group performed a series of psychophysical studies to determine the minimum requirements for several important characteristics of human visual perception: object recognition, face recognition, navigation, and mobility. They did this by pixellating high-resolution images at increasing lower resolutions to emulate the number of electrodes in the microstimulator array, with each electrode representing one "pixel," or picture element. They then tested both the accuracy and speed of image (object) recognition in human subjects.

(Interesting side note: one of Tanguay's team members, Noelle Stiles, worked extensively on the psychophysical aspects of the project, but she's not a PhD: she is still an undergraduate at USC. Yet she's been working with the group since her junior year in high school, after she met Tanguay at a science fair awards ceremony. When I asked him about it, Tanguay admitted in an email exchange that even he forgets sometimes that Noelle is still an undergraduate: ""She really understands what research is all about, and what it means when we really know something is true as opposed o think (or even hope) it is. Many PhD students aren't this far along even when they graduate." At the Annual Meeting of the Association for Research in Vision and Opthalmology (ARVO) in 2005, she became the only high school student ever to present a conference paper as a full member of USC's Optical Materials and Device Laboratory. You go, girl! At this rate, she'll win the Nobel Prize before she's 30. Suddenly I feel like a total slacker.)

Tanguay's team found that surprisingly few pixels were required to achieve good results for many of those tasks: approximately 625 pixels in total, compared to more than a million for a typical computer display. They also found that pre- and post-pixellation blurring of images resulted in significantly improved object recognition and tracking – even better for moving objects as with static ones. Those findings have made it possible to substantially relax the design of key components of the intraocular camera, thereby reducing the prototype intraocular camera's size and weight from an object the size of a Tylenol tablet down to an object that is now about one-third the size of a Tic-Tac. Tanguay and ERC Director Mark S. Humayun (who was instrumental in developing Argus) predict that the next generation prototype will be pretty much fully implantable -- and that includes things like support arms for the device. Early prototypes have been highly successful in initial tests, although human FDA trials are still at least two years in the future.

Tanguay and his collaborators' work will be well represented at the upcoming meeting of the Optical Society of America, should you wish to hear more about their latest progress. And in between talks you can read your shiny new copy of The Dark Net. Go on, you know you want to!

a walk in the park: part II

Gracing the downtown Los Angeles skyline at 111 South Grand Avenue is the Walt Disney Concert Hall, whose structure bears the unmistakable imprint of its designer, Frank Gehry. As we saw in the Part I post on Gehry's design for Chicago's Pritzer Pavilion, he's quite fond of using stainless steel curved surfaces, and the Disney Hall is no exception. But his choice to polish those surfaces to a mirror-like shine for the Los Angeles performance venue had an unexpected consequence when it finally opened in 2003: downtown LA is far more residential these days, and people living in nearby condo and apartment buildings were plagued by chronic, blinding glare as the perennial sunshine was reflected off those shiny surfaces. The effect was similar to that of a parabolic mirror, concentrating the reflected light so effectively that certain "hot spots" were created on nearby sidewalks, reaching temperatures as high as 140 degrees F. Residents experienced their own "hot spots," in the form of rooms directly exposed to the reflections, which in turn caused A/C costs to skyrocket for the affected units. It proved to be a fairly easy fix: after identifying the offending surfaces using computer analysis, they simply sanded them down to reduce the glare to reasonable levels. Ad the Disney Hall has co-habitated peacefully with downtown's residents ever since.

I mostly bring it up because another distinguishing feature of Chicago's Millennium Park is the modern art sculpture officially titled "Cloud Gate," although locals quickly dubbed it "the Bean" because of its kidney-bean shape. It rises three stories and weighs 110 tons, and is the creation of the artist Anish Kapoor (who initially resisted the moniker of "the Bean" for his masterpiece, but has since come to embrace it). The Bean is another highly polished, reflective steel structure, intended to resemble a drop of mercury hovering just at the point of landing, but in this case, the structure was sanded to a smooth polish to enhance the reflections by getting rid of the visible seams between the 168 steel plates that make up the sculpture. The result is strikingly warped reflections of people, the city buildings, even the sky, captured within the curved, mirror-like surface.  

The Bean has proved tremendously popular with both locals and tourists, perhaps because we all love shiny things, or perhaps because deep down, we all have an element of Narcissus in us. Witness the enduring popularity of fun house mirrors, and our fascination with the way they reflect skewed images of our selves. That's why most science museums have some kind of exhibit element that incorporates the basic optics behind mirrors. And it's probably a big reason why the Bean is so immensely popular.

You sometimes get ghostly partial reflections in glass windows -- an effect that Richard Feynman explained eloquently in his QED lectures as arising from the way photons interact with the glassy matter (the vast majority of photons hitting a pane of glass are either absorbed or pass right through, but a small number are reflected back, producing a partial reflection). Unlike window panes, however, mirrors are "silvered" on one side with tin or mercury, making the reflections that much stronger (because more photons are reflected back).

We all learned the basic maxim of mirrors and light in science class: the angle of incidence is equal to the angle of reflection. And we know from personal experience that a concave mirror will make you seem taller, while a convex mirror makes you seem shorter, because instead of hitting your eyes in a normal perpendicular line, the reflected light hits your eyes slightly above or below that perpendicular line. (There was one particular mirror in my former Brooklyn dojo that we all swore took off 10 pounds: all the older guys wanted to do their forms in front of it.)

Curved glass surfaces are the principle behind lenses, and curved mirrors can be used to concentrate light in, say, telescopes or solar cookers -- or chic condos in downtown Los Angeles. The San Francisco Exploratorium has a very nice online set of activities examining the science behind parabolic and spherical reflections. (The latter ingeniously employs silver Christmas tree balls packed in a box to create an array of spherical reflectors.) It's worth checking out, especially if you're planning on visiting the Bean: the most striking is the parabolic effect of the sculpture is seen in the Bean's underbelly, which Kapoor calls the "omphalos" or navel of the sculpture: there, in addition to being warped, people's reflections are multiplied -- another popular fun house effect. 

Reflecting pools are another popular feature of many parks, and Millennium Park boasts one, too: a black granite one, measuring 232 feet in length, part of the interactive public fountain called Crown Fountain, designed by Spanish sculptor Jaume Plensa. It's shallow water, a mere eighth of an inch deep, but it's enough to refresh the crowds scampering around the fountain on a hot summer day. (The water feature is only active from mid-spring through mid-fall, given Chicago's notoriously cold winters.) It looks a bit like one is walking on water, a boon to those with a Messiah complex.

On either side of the reflecting pool are two 50-foot glass block towers, facing each other. Underneath those glass bricks are cutting-edge LED video screens that, when illuminated, showcase videos of the faces of nearly 1000 Chicago residents, in random rotation, all smiling out at the world while a stream of water cascades over their visages. Every so often, the person in the video will open his or her mouth, and carefully placed nozzles will spray water into the center of the pond -- as if the faces were spewing the water directly onto the populace, much like the gargoyles found in older historical fountains. Needless to say, kids love it.

A great deal of science went into making the Crown Fountain the artistic and technological wonder that it is, well worth the $17 million price tag. The hydraulics must have been the easy part: you just pump the water and recirculate it through the fountain, as with any other such structure. Crown Fountain just needs dual pump rooms below each tower, drawing water from a reservoir beneath the reflecting pool. The towers are built around a special stainless steel T-frame, strong enough to bear the load of the 50-foot walls made of glass bricks, and to withstand the Chicago winds. Those glass bricks were custom-made by hand at a factory in Pittsburgh: white glass, not the usual green glass (which is the result of iron impurities). The glass had to be thin enough to avoid image distortion, and only one of the six faces of the block is polished; the rest are textured. 

But the most central technology that makes the Crown Fountain possible is the light-emitting diode (LED). We take LED screens for granted these days, forgetting that they really are somewhat wondrous.  LEDS are basically solid state devices mounted on a substrate of clear plastic, glass or foil. Typically, there is a transparent anode layer that injects "holes," and a cathode layer that injects electrons when a current is applied across the device. Sandwiched between those two layers are hole- and electron-transporting layers, separated by an emissive layer. It's the emissive layer that (duh) emits light when a voltage is applied. The color of the light depends on the type of  semiconducting material is used.

So at heart, LEDS are tiny light bulbs that fit easily into an electrical circuit, except the illumination comes solely from the movement of electrons in the semiconductor material. There is no need for a filament, so they don't burn out, nor do they get especially hot (unless there are large arrays of them housed inside a glass tower, like the Crown Fountain). Less heat means less energy is wasted, leaving more electrical energy devoted to illumination. LEDs used to be quite pricey, but as semiconducting materials costs have lowered, the technology has become more affordable. Crown Fountain uses approximately 70 units per tower of color-changing LED lighting fixtures. The natural advantages and disadvantages of LEDs had to be taken into account when designing Crown Fountain. The advantages are obvious: LEDs are efficient, cost-effective and long-lasting, and Plensa intends his piece to last a century or more.

The disadvantages might be less obvious to someone unfamiliar with the technology. Not only did the structure need to be robust enough to support the weight of the LED arrays, but the displays had to be legible even in daylight (which can be quite bright in Chicago on a clear day), and steps had to be taken to combat heat buildup. The latter was easily address by adding fans to cool the air at the bottom before it works its way through the chimney-like tower, and we've already seen how the T-frame structure was chosen for its load-bearing properties. (Side note: the individual glass blocks are actually removable for cleaning and repair, without disrupting the overall display.) For optimal viewing, Plensa chose low- rather than high-resolution images, which were also less expensive. Black fins were placed in the screens to keep direct sunlight from hitting the LEDs -- anyone who's tried to use their laptop in direct sunlight knows why this is so important.

LED technology is constantly evolving, and a subclass known as organic light-emitting diodes (OLEDs) are now blazing their own path to commercial glory. It's already big business: the market for OLEDs is estimated at around $1.4 billion, expected to increase to $10.9 billion by 2012. You see OLEDs around you all the time: they're used in the small screens in cell phones, PDAs, digital cameras, and portable music players, although they have yet to break into full-sized display or TV applications, despite the best efforts to date of corporate giants like Kodak, Sony, Dupont and Universal Display Corporation.

OLEDs are organic, so they degrade over time and are easily damaged by exposure to water, making them unsuitable for long-life watery applications like, say, the Crown Fountain. But polymer OLEDs bring the advantage of a thin, flexible substrate that can be printed with just standard inkjet printer technology instead of expensive lithographic etching, for example. They're more easily integrated with other electronic components, too, and that flexibility could one day lead to roll-up displays or even displays embedded in clothing. OLEDs also show a great deal of promise as eventual cheap, disposable microarrays of chemical and biological sensors which light up in the presence of toxic compounds or gases.

Plensa chose to use LED technology in his Crown Fountain piece because he was familiar and comfortable with the technology -- it had become commonplace enough that he was able to use LED fixtures in several earlier projects. I can't wait to see how modern artists choose to use OLEDs as they become more broadly available commercially -- especially the flexible polymer versions. One can imagine a Crown Fountain that bends with the winds, or displays of fabric embedded with OLED sensors to create constantly changing images on cloth. Science begets technology, and more and more these days, cutting-edge technology is giving rise to fascinating and innovative new forms of art. Who knows what the future will bring?

nothing like the sun

It was a stunning afternoon here in DC, weather-wise, and since my DSL wasn't working, Jen-Luc Piquant and I played hooky and went on a 30-mile bike ride along the Mount Vernon trail. That's one of the perks of being self-employed: the ability to take advantage of the first 82-degree day of the year by strapping on my iPod Shuffle, donning my spiffy new biking togs, and pedaling off towards the Potomac. If only I'd remembered to slather sunblock on my sadly melanin-deprived skin before setting out. I am now sporting odd patches of sunburned epidermis, which will no doubt fade into an equally unattractive patchwork tan in a day or two. (Jen-Luc never goes out without her trademark beret and black turtleneck sweater -- she's a hipster, through and through, and guards her natural pallor vigilantly. She wouldn't be caught dead in a fuscia, orange and lime green paisley biking skort.)

The exposure to all that ultraviolet radiation not only perked up my mood (DSL detox ain't pretty), it prepared me for tomorrow's journey south to Dallas for the APS April Meeting. Dallas has been experiencing a record-breaking heat wave, although temperatures should settle down to the comfy mid-80s by the time I arrive. At least I've gotten the first sunburn of the season out of the way, and can look forward to basking in the sun's warm, welcoming rays when I'm not trapped in a darkened conference room looking at grainy overheads of random physics data.

There's not a lot to see in Dallas, frankly, which might explain the proliferation of drive-through liquor stores. But five hundred miles southwest is the tiny town of Marfa, with an estimated population of 2500. The town has two claims to fame. It's the site where Giant, James Dean's last movie, was filmed, making it a popular tourist attraction for film buffs. The famed El Paisano Hotel featured in the movie is still open for business, and you can still see the roadside ruins of Reata, some 40+ years later. Marfa is also home to the mysterious "Marfa Lights."

Those lights are nothing like the sun. They only appear at night, some nine miles east of town, flitting about the night sky, splitting apart, melting together, disappearing and then reappearing with no observable patterns. It sounds suspiciously like an X-Files episode, but it's a genuine, well-documented natural phenomenon. In fact, similar optical effects have been seen elsewhere, like the Hessdalen lights of Norway, or northeastern Australia's Min Min lights.

Such sightings make for colorful tales. In Marfa, town legend holds that in 1883, a cowhand named Robert Reed Ellison noticed a flickering light while driving cattle though the Paisano Pass. He assumed they marked the campfires of Apache Indians, but other settlers reported no evidence of ashes of those supposed fires. Periodic sightings were reported from then on, and the "Marfa Lights" gradually developed their own sort of notoriety; they were even featured in a 1991 episode of NBC's "Unsolved Mysteries." Everyone has their own ideas of what the mysterious lights might be, including the usual UFO contingent. My personal favorite is that the lights are the ghosts of accursed Spanishh conquistadors looking for gold -- a much cooler notion than alien spaceships.

Naturally, wherever one finds an entertaining legend about a supposedly unexplained phenomenon, those curmudgeonly skeptics are lurking not far behind with their own scientific theories. Some of those are pretty wacky in their own right: really, phosphorescent jackrabbits? Fans of the piezoelectric effect discovered by Pierre Curie in 1883 contend that the quartz rocks that are typical of that mountainous region expand during the day and contract at night from thermal expansion. The stress this creates on the crystals converts into voltages that accumulate over time before discharging into the atmosphere.

Most, however, think the lights are a mirage created by the sharp temperature differentials -- often as much as a 50-60 degree difference -- between cold and warm layers of air, which serve to bend light, whether it be from cars or stars. If nothing else, this would explain why the lights can only be viewed from a distance, not up close. Those who have viewed the Marfa Lights through high-powered binoculars (skeptics always have nifty science toys on hand) claim it's little more than an optical illusion created by the reflections of the headlights and taillights of cars on US-67.

The binocular-wielding killjoys, it turns out, are probably right. Last year a few enterprising members of the University of Texas, Dallas, chapter of the Society of Physics Students published the results of their official study of the Marfa Lights phenomenon. Their conclusion, based on a series of experiments between May 10-14, 2004: "All the lights reliably observed during the experiment were car headlights."

Okay, so the Marfa Lights aren't so mysterious after all. I doubt any number of scientific studies will convince the true believers. If people want to believe, they believe, and nothing we can say will change that, so no doubt the legend will continue to thrive. And sometimes even the skeptics can be momentarily fooled. I recall a terrific anecdote that University of Maryland physicist (and staunch debunker of pseudoscience) Bob Park relates in his 2000 book, Voodoo Science. During his earliest years in science, he was driving down a desert road late one night in -- yes! -- Texas, when he saw a mysterious light hovering in the sky, looking for all the world like a flying saucer. His heart skipped a beat, and it took a couple of seconds for him to realize it was just an optical illusion created by the reflection of his headlights off the power lines. But he tries to remember that experience whenever he becomes exasperated with people's superstitions, when, for a split second, "I believed in flying saucers."

Just in case interest in weird lights and James Dean start to wane, the town has one more tourist fallback: according to a recent item in the Los Angeles Times, Marfa is becoming "a center of Minimalist art and earth sculpture." Earthworks are "sculptures that erode or degrade over time." Physicists call this entropy, but to some people, I guess it's art. Among the "installations" is a 15-by-25 foot mock store, "Prada Marfa," filled with genuine Prada shoes and handbags, sealed shut and supposedly left to rot.

I predict a crime wave will soon hit the tiny town of Marfa. A few locks, chains and industrial-grade sealant would never stop true fashionistas from breaking in and making off with designer inventory that would otherwise just go to waste. Jen-Luc Piquant is so there already... and she's already dressed for stealth.

ocular proof

In one of my favorite episodes of Numb3rs, Charlie -- the mathematical genius -- faces off against his old grad school rival, who is publicly challenging the revolutionary (fictional) proof that made Charlie the youngest tenured professor at his university. Said rival claims to have found a fatal error in the proof that renders it just plain wrong. Tensions run high, and what should have been a civilized, albeit heated, academic debate quickly escalates to the acerbic, and then to outright acrimony, ending with a crude, mean-spirited barb from the usually good-natured Charlie regarding his rival's lack of manly endowment. Two fascinated FBI agents are watching the exchange; one murmurs to the other, "Oooh... math fight!"

That scene captures a fundamental reality: academic debates aren't always pretty. Or polite. And sometimes they get downright nasty. I once likened academic warfare to being slashed quickly with a very sharp scalpel; you don't even feel the cuts until you look down and realize you're bleeding out. Personally, I prefer a direct stab in the back.

Take the debate currently -- still! five years later! -- raging in the art world over David Hockney's controversial thesis that some Renaissance painters, including Jan van Eyck, used optical devices to achieve certain "realistic" effects. The so-called "Hockney-Falco Thesis" was the subject of the artist's 2001 book, Secret Knowledge. Art historians, to put it mildly, were far from universally pleased; to many, it seemed like Hockney was accusing the Old Masters of "cheating." But the ugliest skirmish has revolved not around the art, but the science.

In one corner, we have Hockney's scientific collaborator, Charles Falco, a professor of optical sciences at the University of Arizona with more than 250 scientific papers to his name. In the other corner, we have the challenger, David Stork, chief scientist at Ricoh Innovations, who can trot out his own long list of publications. What started out as genteel sparring has escalated over the past two years into a gloves-off, below-the-belt, bloodied, brawling free-for-all. (Okay, the metaphor is over-ripe, but you must admit, it's colorful.) The latest development was reported last week by Nature: Falco has publicly accused Stork of "fabrications and manipulations" that are "at significant variance with accepted standards of scientific publication." In other words, "Who's a cheater now?" Stork, in turn, calls the accusation "insane."

Ooh... art fight. Or optics fight. Take your pick.

(I won't even try to summarize the details of the debate here, which I've been following off and on since 2001. Interested parties can look up my original 2001 review of Hockney's book in Discover, or a short update I wrote in 2004, or just Google the damn thing and peruse the millions of hits you'll get. If you want to go straight to the source material and weigh all the evidence yourself, Falco's FAQ and Stork's FAQ both contain more than you probably ever wanted to know about the details of the controversy.)

Falco was on hand this morning at the APS March meeting in Baltimore for a press conference, being a featured speaker at an invited session called "Physics for Everyone" (my kind of topic!). Naturally the "Stork affair" came up -- in the context of Falco's ruminations on what he's learned about being a scientist in the midst of a very public storm. Falco's association with Hockney catapulted him to sudden fame -- some might say notoriety. It is not without its perks. Falco has given more than 60 invited talks and public lectures in nine countries, and been featured in an hour-long BBC special and a segment on "60 Minutes." He's had the rare privilege of sitting for a portrait with Hockney. (I forgot to ask whether Hockney used an optical device -- a camera lucida, perhaps? -- for the initial sketching.) And after all those years as a condensed matter physicist -- his optics specialty is the characterization of thin film materials -- Falco jokes, "I get a theory in art history named after me."

But being in the spotlight also casts a shadow, and over the last five years Falco has discovered just how long, and how dark, that shadow can get. It might result in minor inconvenience; Falco advises fellow physicists contemplating similar national media exposure on controversial topics to get an unlisted phone number before the excrement really hits the fan. It might make you a lightning rod for harmless crackpots, like the person who sent Falco a thick sheaf of diagrams and excerpts from old books, asking that he analyze the materials to help the sender prove that aliens from outer space used optics to design Mayan temples. And it's bound to draw attention from detractors, some of whom can be quite impassioned and vocal about their displeasure.

Still, for the most part, Falco has found both the public and private discourse -- even with those who rabidly disagree with his findings -- to be "reasoned and thoughtful." But one group became so upset that it circulated a petition on the Internet and picketed the Metropolitan Museum of Art in New York, denouncing Hockney and Falco for supposedly "defaming" the Old Masters. And when Falco spoke at a meeting of the Optical Society of America, the organization placed plainclothes bodyguards in the audience as a precaution.

Things got really ugly in 2004, when Stork bounded onto the scene with his public refutation of the Hockney-Falco Thesis, providing the nay saying art historians with their own scientific champion.  January 2005 brought an especially acrimonious confrontation and Falco decided he'd had enough. He carefully analyzed and dissected Stork's various arguments -- sifting through a daunting pile of articles and lecture notes in the process -- and concluded there was evidence of misconduct in several of them. (You can see one of Falco's examples here.) He alerted the publishers to his conclusions. Most of the questionable articles had appeared in conference proceedings. But last December, Nature published a review by Stork once again attacking the Hockney-Falco Thesis. When Falco confronted the editor about the review, it turned into a major story.

Last week's Nature article is a fascinating artifact in its own right, if only for the reporter's strangely loaded choice of wording in odd places -- though he's clearly bending over backwards to be even-handed. Anyone who doesn't think a reporter's tone and choice of wording can create bias has never watched Fox News. Even when it's unintentional and we're just trying to be clever, biases can sneak in. For instance, Falco is described as an "optics scientist." Fair enough, that is his academic title. But Stork merits the moniker "optics expert" -- even though his research specialty, as stated on his corporate bio, is pattern recognition and neural networks. The wording of a later paragraph, in turn, seems to imply that Stork deliberately exploited a past association with Stanford to beef up his academic credentials. (Shrugs Jen-Luc, "At least they're being smeared equally.")

One bit of wording in particular I found interesting: the Nature article stated that Falco "decided to go public" with his accusations after they ran the December book review. I asked Falco about this "decision" at the press conference, since it seemed out of character. (Full disclosure: I've interviewed him repeatedly over the years, on several optics-related subjects, although today was the first time I'd actually met him.) His reply was carefully circumspect: "Well, if writing to the editor of Nature about my objections and concerns [about Stork] constitutes 'going public,' I suppose I did." Implication: he didn't intend to have the dirty laundry aired quite so publicly. Perhaps he was just a wee bit peeved that his private email communication with an editor was treated as "on the record," although that's just speculation on my part. If so, he didn't figure on the rapacious journalistic instinct for scandal: Nature caught whiff of a scoop and pounced on it. (Jen-Luc Piquant thinks we should be more cautious in the future whenever we communicate delicate matters to our own editors... just in case.)

The jury is still out on Stork's alleged guilt -- or innocence, since Stork "categorically denies" any wrongdoing. But Stanford, for one, has opted for prudent withdrawal. The university removed Stork's Web page and email from its server last November, and even Stork acknowledges that the dean of research has asked him not to represent himself as being affiliated with that institution.

Shakespeare's Othello demanded "ocular proof" of his beloved wife's alleged infidelity, but he forgot about the necessity of corroborating evidence, with tragic results. For similar reasons, the debate over the Hockney-Falco Thesis will likely rage on, even if Stork leaves the stage. After all, you can point to all the internal optical evidence you like, on either side of the debate. Barring any supporting textual evidence from other sources (say, a handwritten note by van Eyck mentioning his use of a "mirror lens"), it basically comes down to arguing over artistic intent -- something that is notoriously difficult to prove, especially when said artists are dead. I personally favor the Hockney-Falco Thesis; I'm just not prepared to call it "proven."