Month: May 2019

Artificial noses and beyond

While out for a walk in my neighborhood, I caught a whiff of something that instantly made me think of my grandmother’s house. I haven’t experienced that smell—either from its original source or elsewhere—in maybe 25 years, but the memory of being back at my grandmother’s house was immediate and striking. On the other hand, I can’t really remember or recreate that smell in my mind; either it’s there or it isn’t. I have convenient analog and digital methods of recording images and sounds so that I can see and hear them later, but no way to capture the scent of a dish at a restaurant, a favorite vacation spot, or any other smell that moves me in some way.

I don’t normally think of smelling as being something within the province of machines. I understand, of course, that devices like smoke detectors and breathalyzers perform what amounts to mechanical olfaction of sorts, but I was still sort of surprised to learn that increasingly sophisticated artificial noses are being incorporated into robots and other devices. What intrigues me more than anything is how such sensors might work. How does one go about measuring and quantifying something as broad and seemingly subjective as smell?

Name That Smell

All smells result from molecules of various chemicals floating through the air. Not all substances have a smell—only those containing chemicals that are volatile (meaning they evaporate easily). Our nasal cavities contain millions of neural receptors, of about 350 different types—all of which respond to different chemicals. Depending on which chemicals are present and in what quantities, different sets of odorant receptor neurons are activated; the brain decodes each pattern and assigns a meaning to it: “floral,” “putrid,” “Grandma’s house,” or whatever. Therefore, getting a machine to do the same thing involves two challenges: detecting individual chemical components, and figuring out what a specific combination of components in a given proportion represents.

One way to detect chemicals in the air is to use large, expensive laboratory machines such as gas chromatographs and time-of-flight mass spectrometers. These devices can very accurately detect minuscule amounts of volatile chemicals in air samples—but they also detect substances that have nothing to do with smell, so determining just which parts of their output are relevant adds more complexity to the problem. They are also, so far at least, not very portable. But other, more direct—and more compact—methods of artificial smell detection have been developed. Here are just a few of many examples:

• Aromyx’s EssenceChip has a grid containing hundreds of individual receptors that, like those in the human nose, respond to different chemicals. After a chip has been exposed to a scent, it can be read by a special machine. (Unfortunately, these appear to be disposable, single-use chips—not a real-time smelling apparatus.)
• A quartz crystal microbalance (QCM) sensor is a tiny device that can detect a single, arbitrary chemical. This sensor consists of a quartz crystal vibrating at a known frequency. It’s coated with a material that can absorb molecules only of a very specific size and shape. When it does, its mass increases slightly, changing the frequency of the crystal’s vibration. A simple circuit detects the change and signals that the chemical in question is present. Given an array of QCM sensors, each with a coating that responds to a different chemical, you can detect a wide range of smells.
• A variation on this idea developed by IBM in Zürich is the cantilever sensor: a series of flexible, microscopic silicon beams—each coated with a different polymer. When one of the beams absorbs a specific chemical, it bends slightly; the chip to which the beams are attached detects this change. A similar approach is being studied at Caltech.
• An entirely different approach involves using vapor-sensitive dyes called metalloporphyrins that change color when exposed to certain chemicals. By examining the “before” and “after” states of an array of these dyes, a computer can essentially “see” smells.

Decoding output from an array of sensors (of whatever sort) is an interesting challenge, because substances that are very similar chemically sometimes smell much different from each other; conversely, substances that smell nearly the same can be completely different at the molecular level. For this task, researchers often rely on neural networks, software that can be trained to identify patterns and make educated guesses about new combinations based on their similarities to patterns that have already been verified.

So where is all this technology going to be put to use? And what about those robots?

Follow Your Nose

Artificial noses show the most promise in applications where the human nose is insufficiently sensitive or discriminating. For example, sensors could detect when food is spoiled long before a human nose could—an artificial nose may be built into your refrigerator one day. Just as the bacteria that cause spoilage produce distinctive odors, so do some disease-causing bacteria. Devices have been developed that can diagnose numerous illnesses by smelling a patient’s breath.

But it’s one thing to be able to identify an odor in a test tube; it’s another to be able to trace the source of an airborne scent. This is where robots come in: a mobile platform with an artificial nose can continuously sample the air, reorienting itself dynamically to move in the direction where an odor is strongest. This makes robots that can smell ideal for locating gas leaks, explosives, drugs, and other dangerous stuff—since robots can go places where it would be unsafe to send a human or a dog. One rather gruesome use for sniffing robots is locating buried bodies; this is but one of many possible forensic applications. A mechanical bloodhound may be years in the future, but it’s not at all far-fetched.

If You Could Bottle This Smell…

Many years ago a company called DigiScents made headlines with its iSmell device, a desktop computer peripheral that could synthesize thousands of scents. Their idea was that games could be enhanced with smells (presumably lots of smoke and burnt rubber), email from that special someone could be scented with perfume, and so on. When DigiScents went out of business in 2001 before the iSmell became commercially available, no one was particularly surprised—why do we need to smell computer games, anyway? But I think the real problem was that they only had half of the solution ready: the output but no input. I suspect that if someone created a pocket-sized gadget that could record the scent of a bakery, garden, or any other smell you encounter and play it back accurately on command, it would be a huge success. I, for one, would gladly pay for a machine that could make scents of my childhood.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on July 9, 2004.

Image credit: Genia Brodsky and Noam Sobel (The Weizmann Institute) [CC BY 2.5], via Wikimedia Commons

Reinventing the two-wheeler

When I first learned to drive, I learned on a car with a manual transmission. It never seemed especially difficult because that was what I got used to. In fact, the first time I had to drive an automatic, I remember being very confused. What was I supposed to do with my left foot? Do I not have to shift at all? And if it’s automatic, then what’s with all these different choices on the gearshift lever? I quickly got the idea, of course, but still preferred the increased control and responsiveness I got from making my own decisions about when to shift. It would therefore seem that I should have the same attitude about bicycles, which not only require manual shifting but typically have many more than four or five gears. But manual bicycle transmissions have always given me trouble, and I’ve frequently wished I could have the convenience of an automatic transmission on a multi-speed bike.

Yanking My Chain

For the record, I am not what you’d call an avid cyclist. Indeed, I’m somewhat embarrassed to say I don’t even own a bike right now, because I work at home, I walk most places I need to go, and on the occasions when I have to travel beyond walking distance, I nearly always need to be transporting more people and/or goods than a bike could accommodate. Nevertheless, I like the idea of bike ownership very much—good exercise, good for the environment, and so on.

But even when my bike was my sole form of transportation a number of years ago, I never fully grasped the way bicycle gears worked. That is to say, I understood the mechanics, but actually using them was another story—the logic of how one must manipulate those levers to reach the desired balance between torque and speed always seemed a bit like a black art. It was not a simple linear progression of lower to higher as on a car, but a function of the ratio of the front gear size to the rear gear size, both of which are variable. My usual practice was just to fiddle with the controls until pedaling felt about right, then leave them where they were until I couldn’t stand it any longer.

Another problem with shifting gears on bicycles is that the derailleur—the mechanism that moves the chain between gears of different sizes—is by nature imprecise. Although some designs are better than others, over- or undershooting your desired gear is common, and if you’re pedaling too fast or under too heavy a load, the chain can easily slip off the gears entirely, requiring a greasy manual adjustment. Wouldn’t it be nice if bikes could figure out how to change their own gears as painlessly and accurately as cars with automatic transmissions?

Gearing Up for a Change

Sure enough, automatic bicycle transmissions of various kinds have been in development for nearly 50 years, though they’re still quite rare (and often expensive). Mechanically, the main thing needed for a basic automatic bike transmission is a motor or piston that moves the chain between gears in place of the standard lever-operated cable. This is a relatively straightforward engineering problem, but the slightly trickier thing is working out how and when to tell the gears to shift. That computation requires the use of a tiny, battery-operated computer along with sensors that determine the current gear and the speeds at which wheels, pedals, and sprockets are moving. The computer constantly recalculates the optimal combination of front and rear gears to keep the rider at a consistent pedaling cadence, automatically signaling the gears to shift lower when going uphill or higher when going downhill. Using a controller on the handlebars, riders can, if they want, adjust the gearing to provide a more intense workout or a gentler ride; they can also override the automatic shifting entirely and use it as a power-assisted manual transmission.

The first automatic bicycle transmission was designed by the Browning family, whose main claim to fame had been gun design. For a while, Browning Components, Inc. was an independent company based near Seattle that focused solely on bicycles and bike transmissions. (It is now entirely defunct, as far as I can tell.) Their most interesting innovation was a special gear with a hinged section (somewhat like a pizza slice) that swung in and out to guide the chain from one gear to the next. It kept the chain engaged in sprockets at all times, rather than simply dropping onto the next gear, virtually eliminating the possibility of the chain slipping; it also made it possible to shift smoothly and almost silently regardless of speed or load. You can still find used Browning bikes or transmissions with some effort and luck.

Shifting More Than Gears

Shimano, the largest manufacturer of bicycle components such as brakes and shifters, also got into the automatic transmission business for a while. One of their designs used a seven-speed, internally geared hub; another used a power-assisted derailleur system, but added an automatic, powered suspension to adjust the comfort of the ride to fit current conditions. But Shimano, too, stopped making their automatic bike transmissions, presumably because they were unable to find enough people willing to pay a premium for them.

But a number of manufacturers are still developing and selling automatic bike transmissions of various kinds. For example, ProShift offers automatic transmissions that can be retrofitted onto racing bikes. SRAM, which makes wireless manual electronic shifting systems for conventional bikes and an automatic transmission for electric bikes, also sells the Automatix, a purely mechanical two-speed transmission built into a hub. And NuVinci offers continuously variable automatic transmissions for electric bikes, as well as manually adjustable, continuously variable transmissions for non-electric bikes, such as Priority Bicycles’ Continuum.

Adding an automatic transmission to a bicycle seems—in the abstract at least—like a wonderful step forward in user interface. It replaces something awkward with something invisible, which is the way good technology should be. But as numerous manufacturers have seen, cycling enthusiasts aren’t warming to the idea very quickly. Some are put off by the extra weight; some feel it’s not worth the money just to avoid having to move a lever; and some just think automatic transmissions are for wimps. Having never used one of these bikes myself, I can’t say whether the performance would be improved enough to make me want to ride my bike more often, but at least I would no longer view gear shifting as the annoyance I do now.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on June 26, 2003, and again in a slightly revised form on October 5, 2004.

Image credit: Keanu @ no:wp [CC BY-SA 3.0], via Wikimedia Commons

Triumph of His Majesty’s Bathtub Navy

Stories of war—whether modern or historical—are not usually of much interest to me. I don’t like to dwell on tragedy, and war is always tragic, for every side, regardless of the motivations or outcome. Occasionally, however, in the midst of tragedy is a story of hope that is worth retelling. I told such a story here back in 2005, back when the Battle of Dunkirk (which has always been well known in Britain and France), was little known in North America. Then Christopher Nolan had to go and make an Oscar-winning movie about it. So the story is much better known now in outside Europe, but no less interesting, unique, or inspiring.

The year was 1940, and World War II was raging. Hitler’s army had overtaken Belgium and advanced into France. Britain sent over 300,000 troops to assist the French army, but in spite of those sizable numbers, the German force was winning, due to their superior armaments, training, and organization. By late May, German troops had the bulk of the allied forces surrounded, trapped in Dunkirk (Dunkerque in French), in the northernmost corner of France across the English Channel from Dover. To the east was occupied Belgium; to the south and west, the advancing German army; to the north, the sea.

Operation Dynamo

Britain had already suffered severe casualties in France, and they knew this battle could not be won. Retreat was the only option, but all escape routes had been blocked. Vice Admiral Bertram Ramsay, headquartered in the reinforced tunnels beneath Dover Castle, was put in charge of evacuating the troops. The rescue plan was code-named Operation Dynamo.

Unfortunately, there were several major problems. Time was quickly running out for the cornered British troops. Ramsay believed he had a week at most to rescue the soldiers, who were packed onto the beaches and being shelled mercilessly. An exodus by sea was the only possibility, but German planes had sunk so many ships in Dunkirk harbor that it was nearly impossible to navigate, and U-boats posed a constant threat. Farther to the west, where the beaches were, the water was so shallow that British destroyers and transport ships could not get any closer than about a mile (1.6km). As if that weren’t enough, Britain had far too few vessels available to transport the hundreds of thousands of soldiers trapped on the beach, even under the best conditions.

Ramsay was deliberate and methodical in his preparations. He arranged transportation, food, and medical care for the troops that would soon be arriving in Dover. He sought out every available ship, and established a complex and efficient communications network. Logistics in place, Operation Dynamo was put into motion on May 26. But after the first day, the outlook was grim. Fewer than 8,000 troops had been rescued, and the most optimistic estimate was that a total of 45,000 might escape before Germany overtook the beaches—at the rate the operation was progressing, it would take 40 days to rescue all the remaining troops. Ramsay faced the possibility that the core of the British army would be wiped out. At that time, conventional wisdom held that Britain would inevitably be invaded as soon as France fell, and with so much of its army gone, Britain’s defenses would be in ruins.

The Bathtub Navy Saves the Day

In desperation, Ramsay put out a public call for help: everyone with a boat—any kind of boat—was asked to help rescue the troops. The response was instantaneous and overwhelming. A makeshift flotilla of 850 “Little Ships”—yachts, lifeboats, fishing boats, and anything else that could float—rushed to the scene. Most of the boats were manned by British sailors, but in many cases the civilian owners themselves risked gunfire and mines to make the 22-mile (35km) crossing. When possible, the small craft were used just to ferry troops to the larger vessels offshore, but thousands of troops used them for transport all the way back to England. By the morning of May 29, officials estimated that 2,000 troops per hour were being evacuated. Nine days after Operation Dynamo began, a total of 338,226 people—including about 95,000 French troops—had been rescued.

Churchill called it a “miracle of deliverance,” and the “Dunkirk spirit” quickly became the stuff of legend. In retrospect, the eventual allied victory might well have been thwarted had Britain lost hundreds of thousands of troops at Dunkirk. Nevertheless, the massive rescue could hardly be considered a victory. There was more to the story than the heartwarming tale of heroism.

The Other Side of the Story

For one thing, the escape was not as clean as the media made it sound. While swarms of small boats were shuttling soldiers off the beach, more than four hundred Luftwaffe fighters attacked, dropping bombs and inflicting heavy casualties. Soldiers returning to England described the beaches as littered with dead bodies. In all, tens of thousands of people lost their lives at Dunkirk.

In addition, the highly publicized rescue obscured the fact that thousands of British troops were still trapped elsewhere in France. Two weeks later, the British ship Lancastria was returning from a rescue mission when it was sunk off the coast of Brittany. Half of the 6,000 passengers lost their lives, but nothing was mentioned in the press about the incident for weeks, lest it dampen the spirits that had been uplifted by the Dunkirk miracle.

Meanwhile, France felt deeply betrayed. The British troops had ostensibly come to their rescue, but then fled the German army. Without any hope left from across the Channel, France surrendered to Hitler within three weeks. Notwithstanding the many French soldiers rescued at Dunkirk, many in France resented what they regarded as British cowardice. It wasn’t until 1944 that Britain redeemed itself, when British and American forces collaborated in the D-Day operation, leading to France’s liberation.

Dunkirk Redux

In June of 2000, on the 60th anniversary of the Battle of Dunkirk, Britain commemorated the event with a massive celebration. A large number of small boats reenacted the Channel crossing to Dunkirk. Although there weren’t nearly as many boats as there had been in 1940, some of the original craft had been restored specifically so that they could make the journey again. While British television crews lined the Dunkirk shore to relay the landings to exuberant crowds back home, the French media—as might be expected—gave little coverage to the event.

About 800 British and French veterans who had been rescued at Dunkirk attended a massive parade past the town hall. Prince Charles gave a speech at the Dunkirk Memorial in both English and French, praising the courage of all those who had helped in the miraculous rescue. The remaining members of the Dunkirk veterans’ associations—many in their 80s and 90s—chose that occasion to officially disband their organizations.

Politics and media spin aside, the story of the Battle of Dunkirk inspires me for one simple reason: it shows ordinary people lifting the veil of war—the impersonal propaganda of numbers—and seeing each other as human beings. Fisherman didn’t row across the English channel to transport “troops”; they risked their lives to rescue people with names and faces. That the public could, however briefly, set aside their habit of detached reliance on the machinery of government and take personal responsibility for other lives—especially in a time of war—is to me an immensely hopeful sign. It’s a step toward understanding that the soldiers wearing different uniforms are human beings too.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on April 16, 2003, and again in a slightly revised form on January 21, 2005.

Image credit: Frank Capra (film) [Public domain], via Wikimedia Commons