California Institute of Tech nology Engineering & Science Volume LlX, Number 3 1996 In this issue Smelfing Yums and Yucks Feynrnan Redux Turbulence in Flux Richard Feynman entertains a group of students with his safecracking tales. This photo, the last of a set of foul' that first appeared in E&S in June 1964, was captioned: "He's sitting there all this time thumbing through a magazine, with this big fat smile on his face. So I let about 5 minutes go by and then I swing the thing open ••• He is flabbergasted!" Feynman also deliv­ ered a lecture in 1964 that was recently unearthed and made the subject of a book, an excerpt from which begins on page 14. California Institute I of Technology' EngIneering Clen e Volume LlX, Number 3 1996 2 The Caltech Electronic Nose Project - by Nathan S. Lewis Cal(ccb "ciellflsts build all affiJicial llm,e, usiJlg IhHlgS you may already have around the house. 14 Feynman's Lost Lecture: The Motion of Planets Around the Sun­ by Daz1id L. Goodstein andJudith R. Goodstein An onginal geometric proof is resurrected from a few pages of notes and drawings. 22 Turbulence, Fractals, and CCDs - by Paul E. Dimotakis Faster, more powerful computers and high-tech video cameras designed for interplanetary spacecraft are giving us a better look at the complexities of turbulence. 35 What Is Life? A Closer Look - by Robert L. Simheimer Recem DNA sequencing offers insight into cellular organization. Departments 38 Books: Thread of the Silkworm by Iris Chang 41 Oral History: Norman Davidson 43 Random Walk On the cover: This sponge is actually a portrait of the turbu­ lence caused by squirting a dye jet into a tank of standing Engineering & Science (ISSN 0013-7812) is published quarterly Edward M. Lambert water. The cube's at the California Institute of Technology, 1200 East California President of the Alumni Association front face is a S-x-S­ Boulevard, Pasadena, California 91125. Annual subscription centimeter square, $10.00 domestic; $20.00 foreign air mail; single copies $3.00. J. Ernest Nunnally and looking into the Third class postage paid at Pasadena, California. All rights reserved. Vice President for Institute Relations page corresponds to Reproduction of material contained herein forbidden without Robert 1. O'Rourke looking backwards in authorization. © 1996 Alumni Association, California Institute Associate Vice President for Institute Relations of Technology. Published by the California Institute of Technology time. The sponge's and the Alumni Association. Telephone: 818-395-3630. cross section any Postmaster: Send change of address to Cal tech 1-71, Pasadena, CA depth consists of 91125. all the points in the square with a given PICTURE CREDITS: Inside front cover - Kent McCaulley; 4,6, dye concentration at STAFF: Editor - Jane Dietrich 9, 10, 11 - Erik Severin; 5,9 - Brett Doleman; 5,26 - Doug Managing Editor - Douglas Smith that ·instant of time. Smith; 6,10,11,21 - Bob Paz; 7,8 - Mark Lonergan; 12- Copy Editors - Barbara DiPalma, Michael For more on how sci­ Hillary Bhaskaran; 14,17,18,20,39 - Caltech Archives; 16- entists are getting a Igor Bitman; 25,27,28 - Haris Catrakis; 34 - Paul Dimotakis; Farquhar, Danielle Gladding, Julie Hakewill better look at the face 36 - Jean-Paul Revel, Stefan Offermanns, Md Simon; 41,42- B/tSiness Manager - Debbie Bradbury of turbulence, see the James McClanahan; 43 - Herb Shoebridge; 44 - Bill Varie; Circulation Manager - Susan Lee story on page 22. inside back cover - Tom Bida/Judith Cohen Photographer - Robert Paz The Caltech Electronic Nose Project Can we teach a computer to "smell" in the same way that by Nathan S. lewis we can teach it to "see"? Of our five senses-sight, smell, taste, People have since extended that idea to measure hearing, and touch-we understand three well other molecules, such as glucose. In almost every enough to build machines that mimic them. case, the strategy is to design a molecule that has Touch is basically a pressure sensor. There are a hole in it-a lock-such that only the right artificial cochleas-mechanical resonators that key, i.e., glucose, will fit and generate a signal. transmure sounds into signals that our brain, (There are, of course, more generalized sensors or a machine, can recognize. And we can build that measure some physical property of the cameras that are essentially electronic eyes. But molecule, but they don't really "recognize" it­ we know very, very little about the molecular they merely tell you that they've detected a basis of taste and smell, and even less about how molecule with, say, the same charge-to-mass ratio to model them. So my lab is trying to build as the molecule you're looking for.) Nature uses something that will give a value judgment-a the lock-and-key approach very successfully-in number-to a smell, taking design lessons from enzymes, for example-but it takes evolution Although not blessed biology without necessarily mimicking the exact millions of years of work to make the molecules with the keenest noses in the animal way that a human nose works. We can assign a fit just right. You can see the daunting task that kingdom, humans (in visual magnitude, a brightness, to a star; can we a chemist would face in trying to build 700 such this case, the author's teach a computer to "smell" in the same way that locks to detect the 700 odor components in a three·year.old son deffrey) can smell we can teach it to "see"? This project began as a glass of beer. And we'd have to build all 700, the difference be·. crazy idea in January of 1993, but there may be because we don't know which components are tween yum and yuck something to it. critical for identifying the smell of beer, and almost from birth. Photo and subject Smell is a remarkably subtle sense, because determining whether it smells good or stale. courtesy of Dr. Carol most smells are not pure substances, but complex And what would happen when we encountered Lewis, .let Propulsion mixtures of different molecules. There are some the 701st molecule in a different odor, like in Laboratory. 700 different chemical vapors in a glass of beer, another brand of beer? We'd have to build yet somehow we can take a sniff and say it's beer. another sensor. And we'd have to make each The human nose is generalized enough to sense lock specific enough that a very slightly different almost all possible molecules, yet discriminating molecule wouldn't also fit, because even if the enough to tell the difference between strawberries other molecule fits poorly we'd still get a signal. and raspberries. How can we model that? Designing such exact locks from scratch is avery, The way that most chemists have approached very complex problem at the frontiers of chemis­ this problem is epitomized by what Arnold try, and hundreds of groups around the world are Beckman [PhD '28} did when he invented the working on it. pH meter. He built a chemical sensor that We abandoned this approach in favor of a measures the concentration of one thing (protons pattern-recognition strategy. We decided that in water) very selectively and very sensitively. the biological olfactory system must employ a set Engineering & Science/No. 3, 1996 3 The electronic nose, hlgh-sc_1 science­ _Ject style. Two electrode.... t8pee1 When to._.__ I.dry . (top). the eleetrode. Dogs have no rea­ a ... In conblct. com­ pleting the circuit end son to sniff out lighting up the bulb. As the mol.t...... cocaine in the _ swells (bot· tom). the eleetrode. wild, and yet move apart and break they can be the circuit. The light goes out. trained to do so in airports, The dogs must be learning to recog­ of generalized sensors that respond to everything, wonderful to study I because it works for anyone bue in different ways to different stimuli. anywhere." Our sensor is a sponge made of insu­ nize a pattern, Evolution might have developed specific recep­ lating plastic, much like a bathtub sponge, but because one cer­ rors for fruits and wines, for example, but it's containing little conducting particles scattered tainly couldn't unlikely that dogs would have evolved receptors here and there within it. When we pass a current to smell drugs. Dogs have no reason to sniff out through it, rhe electrons have to hop from one train them to cocaine in the wild, and yet they can be trained conductor to the next, so the sponge has a charac­ develop a new to do so in airports. The dogs must be learning teristic, measurable resistance. If we were to to recognize a pattern, because one certainly moisten the sponge, it would swell, and the receptor overnight, couldn't train them to develop a new receptor conduCting particles would move farther apart. or even in a few overnight, or even in a few months. So the [ask It would get harder for the electrons to jump months, facing anyone trying CO develop an artificial nose between the conductors, and the resistance is to develop a generalized sensor whose output would go up, Later, as the sponge dried, it would pacterns will announce the difference between the shrink, and the resistance would go back down. vapors emitted by a rose and a dead fish. Then (If you soak a sponge, it won't shrink all the way we train an eiecrronic circuit to recognize those back to its original size when it dries, but if you patterns, in the same way that signals fired to our jusr add a few droplets, the swelling can be fully brain get recognized as yum or yuck.