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July 31, 2007

Oil and Water Don't Mix

Alan Turing, who is arguably the world's first computer scientist [1], was interested not only in artificial automata, but in autonomous natural processes also. He proposed what is called the Turing hypothesis of pattern formation in nature to explain such things as a zebra's stripes and a leopard's spots. The hypothesis is built on the physical principles of reaction and diffusion, and it explains many natural patterns.

One such pattern occurs in a surface reaction of a mixture of oil and detergent on the surface of water that evolves through time in a peculiar way. "Spreading oil on the waters" as a way to calm the surface was studied by Benjamin Franklin as early as 1774. His account, published in the Transaction of the American Philosophical Society, recalls how he had observed spear fishermen putting oil on the water's surface to dampen small surface waves to make it easier to see the fish. An interesting experiment involving oil on water can be performed by mixing a little detergent with mineral oil, and then placing a drop of the mixture onto water. The oil layer will expand and contract in a regular fashion, and it will eventually reach a static state. What is curious about this reaction, and a key to the mechanism, is that the expansion and contraction will stop if the water vessel is capped.

A group of scientists from the Massachusetts Institute of Technology have studied this reaction and their results will appear in a future issue of the Journal of Fluid Mechanics [2]. The actor in this effect is changes in surface tension mediated by evaporation. The detergent, a surfactant, reduces surface tension, and it would rather be at the interface between the water and oil, rather than in solution with the oil. As the detergent diffuses to the interface, the decreased surface tension causes the oil droplet to expand. Since the center of the oil droplet is thicker than the edges, there's a differential surface tension (a shear) that causes the generation of waves from the center to the edge of the droplet. This causes the detergent to be expelled from the droplet, so the surface tension of the surrounding water is reduced, and the oil droplet contracts. Evaporation of the surfactant from the water is needed to reset the reaction, so preventing evaporation by capping the vessel will stop the cycle.

1. OK, there's Babbage and Ada Lovelace, but that's why I say, "arguably."
2. Denise Brehm, "Case closed: MIT gumshoes solve "throbbing" oil mystery" (MIT Press Release, July 17, 2007).

July 30, 2007

Carbon Paper

In the dark days, before Xerox machines and digital printing, the only way to make copies of typewritten documents was to use carbon paper. I used a lot of it in high school and college, but when the time came to write my dissertation, Xerography had developed as a reasonably inexpensive way to produce copies. This was fortunate, since a scientific dissertation is not just words, but a lot of graphs and figures. Now, after a many year's retirement, carbon paper has emerged in a new material form [1, 2]. In a spin-off of previous research on graphene, single atom sheets of graphitic carbon, researchers at Northwestern University have produced stacked layers of graphene oxide to make free-standing, mechanically strong, sheets of graphene "paper." [3]

The bonds in graphene are very strong, but unless graphene sheets are anchored at the edges, they will roll-up into three-dimensional structures and will not remain as sheets. The Northwestern research team, led by Rod Ruoff, made graphene oxide paper by the following process. They oxidized graphite to form graphite oxide. The graphite oxide breaks apart in water to form graphene oxide sheets, and the water acts as a glue in which hydrogen bonds form between the graphene oxide planes. Using what is likely a Langmuir-Blodgett trough process to collect micrometer-sized sheets of graphene oxide into thicker layers, they were able to make graphene oxide paper in sheets about five inches in diameter and thickness of up to 100 micrometers.

Bucky paper is another carbon-based paper formed from C60. Ruoff's graphene oxide paper has higher tensile strength and stiffness than bucky paper. The graphene oxide paper is stiff in the plane, but it has the useful feature that it can be folded. This compliance will make it useful as a gasket material, since the graphene oxide is a chemical resistivity, high temperature, impermeable material. Completely oxidized graphene is an insulator, and pure graphene is a conductor, which opens the possibility of semiconducting graphene, which may be a useful electronic material. Controlled-permeability membranes are another possibility, as well as the dielectric layer in capacitors. The graphene oxide paper would be a good candidate as a component of hybrid materials when combined with metals, polymers, or ceramics.

1. Katharine Sanderson, "Carbon makes super-tough paper" Nature Online (July 25, 2007).
2. Megan Fellman, "Graphene oxide paper could spawn a new class of materials" (Northwestern University Press Release, July 25, 2007).
3. Dmitriy A. Dikin, Sasha Stankovich, Eric J. Zimney, Richard D. Piner, Geoffrey H. B. Dommett, Guennadi Evmenenko, SonBinh T. Nguyen and Rodney S. Ruoff, "Preparation and characterization of graphene oxide paper," Nature, vol. 448 (July 26, 2007), pp. 457-460.

July 27, 2007

The End is Nigh (Maybe)

Ever since Cassandra, various prophets have claimed that the world will soon end. This has always been a cartoon cliche, with men in togas carrying signs that the end was near. In early history, such predictions were based on religious or philosophical arguments, but science entered the fray late in the last century. In 1947, the Bulletin of the Atomic Scientists introduced the Doomsday Clock showing the minutes before midnight, where midnight represented nuclear war. Later, the Union of Concerned Scientists was formed to highlight other global issues, such as environmental pollution, and possible technological solutions. The doomsday theme re-emerged around the time of the Y2K bug, when all computers were predicted to cease functioning, thereby throwing civilization into turmoil.

By far, the most "scientific" argument was produced by Richard Gott, a professor of astrophysics at MIT. His Doomsday argument gives a probable end of the world based on a simple statistical argument. He merely calculates how many people might be born into the world based on the idea that the number of people who have been born to date is somewhere within 2.5% to 97.5% of that range. This 95% confidence level is the usual standard for statistical likelihood. Using reasonable estimates for life expectancy, etc., Gott calculates that humans will exist for only another 9,000 years, maximum.

Gott's argument gives an end point, but it doesn't postulate any mechanism. Sir Martin Rees, formally, Baron Rees of Ludlow, Astronomer Royal, and current President of the Royal Society, not only gives some mechanisms, but he reduces Gott's estimate considerably [1]. His latest book, "Our Final Century," [2] predicts that humans have only a fifty-fifty chance of making it through the 21st century. He lists eight possible world-altering events:

• Major Strike by an Asteroid or Comet (It's happened before)

• Earth is Swallowed by a Man-Made Black Hole (Our larger and larger particle accelerators may create one, but this seems unlikely)

• Global Warming (I think we'll adapt, rather than be wiped-out)

• Worldwide Pandemic (Perhaps by a virus created by terrorists or a rogue state. This is my front-runner)

• Robots Take Over The World (we may still be around, but we'll be irrelevant, perhaps kept as pets)

• Gamma Ray Burst (As an astrophysicist, Rees sees danger in objects with which he's most familiar)

• Nuclear Holocaust (Actually, less likely today than fifty years ago)

• Overpopulation (As Malthus pointed out, population increases at a geometrical rate, whereas food supply grows arithmetically. However, there's a feedback mechanism here (famine) that limits population).

I'm an optimist, so I trust that my children will thrive in our technological world. Then again, their jobs may be outsourced to Mars.

1. Robert Blevins, "Eight Likely and Unlikely Ways Life on Earth Could End" (Adventure Books of Seattle).
2. Martin Ress, "OUR FINAL HOUR: A Scientist's warning," Basic Books (ISBN-10: 0465068634, ISBN-13: 978-0465068630).

July 26, 2007

Attack of the Giant Rhombicosidodecahedron

The Ancient Greeks had no real knowledge of algebra, but they made many advances in geometry (e.g., Euclid). The idea of "proof" in Euclid's Elements is probably a consequence of Greek philosophical interest in rationality. Plato, described the regular solids in his dialogue, Timaeus, so they are often called the Platonic Solids. The Platonic Solids are those polyhedra you can make using just one type of regular polygon. There are only five such solids,

• icosahedron, made from triangles
• octahedron, made from triangles
• tetrahedron, made from triangles
• cube (hexahedron), made from squares
• dodecahedron, made from pentagons

Plato, who was always trying to divine the true nature of the universe, set up an equivalence between these five solids and the five classical elements,

• cube = earth
• octahedron= air
• tetrahedron = fire
• icosahedron = water
• dodecahedron = aether

We now know more than a hundred elements, and our knowledge of geometry has transcended the three classical dimensions. In four dimensions, there are six regular polyhedra (formally called "regular polytopes"). Surprisingly, there are only three regular polytopes in five dimensions and all higher dimensions. Johannes Kepler published an astronomical version of Plato's idea in his explanation of the orbits of the planets in his Mysterium Cosmographicum (1596). His model of the solar system was a nested array of the five solids with inscribed and circumscribed spheres. For a particular order of the solids, Kepler was able to match the orbits of the six known planets at the time (Mercury, Venus, Earth, Mars, Jupiter, and Saturn). Kepler himself disproved his concept with his discovery that planetary orbits are elliptical, rather than spherical.

If we relax the requirement that all sides must be the same polygon, we can generate other polyhedra. There are thirteen such polyhedra, called the Archimedean Solids. Most are made by truncating the regular polyhedra; that is, slicing off the vertices.

• cuboctahedron
• great rhombicosidodecahedron
• great rhombicuboctahedron
• icosidodecahedron
• small rhombicosidodecahedron
• small rhombicuboctahedron
• snub cube
• snub dodecahedron
• truncated cube
• truncated dodecahedron
• truncated icosahedron
• truncated octahedron
• truncated tetrahedron

Attack of the Giant Leeches (1959, Directed by Bernard L. Kowalski; Roger Corman, Executive Producer) was one of Roger Corman's "B" movie productions. A "B" movie, for the uninitiated, was the second feature of double feature in the days when theaters screened two films for a single admission price. It was typically a poorly done, low budget, film. Roger Corman, who initially studied engineering, was the B-Movie King. He once shot an entire film in two and a half days. Corman said that his engineering education gave him experience in making low-budget films on a tight schedule. All this, before Microsoft Project!

1. Platonic Solids (Math World).
2. Archimedean Solids (Math World)

July 25, 2007


The X-15 was an experimental rocket plane funded in a joint USAF/NASA/USN program initiated in 1954. It was manufactured by North American Aviation (now part of Boeing). There were three aircraft in the series, the maiden flight was on June 8, 1959, and the X-15 was retired from service in December, 1968. The X-15 set many altitude records in the early 1960s, and since it was the closest thing the US had to a space ship, it was covered extensively in the media of that period. It could be considered the first suborbital spacecraft. In the early days of space flight, the "aeropause," the putative boundary of the Earth's atmosphere at 19 miles (30 km) altitude was considered to be "space." Eventually, fifty miles (80 km) was adopted by the US as a convenient standard, although the international community thought the boundary between Earth and space should be 100 km (62.1 miles).

Two X-15 flights, both piloted by Joe Walker, went beyond the international 100 km standard for spaceflight, thus making Walker the first internationally sanctioned astronaut. These were Flight 90 (19 July 1963, 106,010 m) and Flight 91 (22 August 1963, 107,960 m). Walker flew a P-38 in World War II, and he became a test pilot after the war. He flew the original plane in the "X" series, the Bell X-1. Unfortunately, Walker died in 1966 when an F-104 he was piloting collided with a prototype XB-70 Valkyrie bomber, so he didn't see the first men walk on the moon.

Almost six years to the day after Flight 90, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin landed on the moon (July 20, 1969). Aldrin has an Sc.D. from MIT. His graduate thesis was "Line-of-sight guidance techniques for manned orbital rendezvous."

The "X" in the "X" series aircraft signified "experimental," but "x" symbolizes the unknown, both in mathematics and in popular culture. X: The Unknown (1956, Leslie Norman, Director) was a British movie about an army drilling operation that unleashed a creature from the depths of the Earth. This plot was redone in 1970 in a Doctor Who serial, Inferno

1. Tony Long, "July 19, 1963: Cracking the 100-Kilometer-High Barrier ... in a Plane" (Wired).
2. Edwin Eugene Aldrin, Jr., "Line-of-sight guidance techniques for manned orbital rendezvous" (Sc.D. Thesis, MIT, PDF FIle).

July 24, 2007

Sticky Gecko

Geckos (Reptilia-Squamata-Lacertilia-Gekkonidae) are small lizards. They are known to the public because of an advertising campaign by GEICO, a subsidiary of Berkshire Hathaway that provides automobile insurance to about seven million motorists. Scientists have taken note of the gecko since their toes adhere to most surfaces without excretion of an adhesive substance. Scientists have discovered that this property arises from van der Waals forces between fine structures on the gecko toe and surfaces. These 200 nanometer spatula-like structures (about a quarter billion on each foot) allow intimate contact between the gecko toe and uneven surfaces to maximize this force. Now, scientists from Northwestern Northwestern University, as reported in a paper in Nature [1], have merged the sticking power of a gecko with a natural adhesive from the mussel [2,3].

The gecko effect has been replicated in some nanoscale materials, but the effect diminishes after many application cycles, presumably from wear on the gecko material, and it doesn't work well under water. The Northwestern scientists have overcome these problems by coating nanoscale polymer pillars with a thin polymer that mimics the mussel protein responsible for their adhesion to wet surfaces, an amino acid called 3,4-L-dihydroxyphenylalanine. The wet adhesion of the synthetic gecko material was increased fifteen-fold by the addition of the mussel-like adhesive. More importantly, the adhesive effect remained after a thousand contact cycles on wet and dry surfaces. Quantitatively, about 85% of adhesion remained after a thousand contacts on wet surfaces, and about 95% of adhesion remained after a thousand contacts with dry surfaces. Since their research was funded by the US National Institutes of Health, their targeted application is bandages, drug-delivery patches, and surgical materials; but that won't stop mundane applications, such as improved Post-It Notes.

1. Haeshin Lee, Bruce P. Lee and Phillip B. Messersmith, "A reversible wet/dry adhesive inspired by mussels and geckos," Nature, vol. 448 (19 July 2007), pp. 338-341.
2. Bob Kuska, "Nature's secrets yield new adhesive material" (NIH Press Release, July 18, 2007).
Public release date: 18-Jul-2007
3. Charles Loebbaka, "Synthetic adhesive mimics sticking powers of gecko and mussel" (Northwestern University Press Release, July 18, 2007).

July 23, 2007

Computer Checkers

The game, checkers, which is called draughts in much of the world, is a favorite among children, since it has very simple rules. While much effort has gone into programming chess, probably because of its popular tournament structure and the existence of Grandmasters, there has been a background effort on programming computers to play checkers. Much of this effort has been by Jonathan Schaeffer, a professor of computer science at the University of Alberta, Canada, who has been working on checkers programs since 1989. Since checkers has about 5 x 1020 possible positions, this is not a small problem. There are just nineteen possible opening moves in checkers, but endgames of fewer than ten pieces have 39 trillion positions. After many years of effort, Schaeffer announced [1] that he had "solved" checkers; that is, he has a computer program that will win or tie a checkers game, but it will not lose.

Schaeffer enlisted the aid of a large network of desktop computers, at times as many as 200, to examine every one of the huge number of possible positions for play pieces. Error checking was an important part of these two decades of computation, since an error at an early stage would invalidate many subsequent computations. As the analysis advanced, Schaeffer would include the information into a checkers program called Chinook. Although Chinook was in a constant state of development, it did have some early successes. It won the World Checkers Championship in 1994, but it did not always win or draw games, since much of the play relied on artificial intelligence principles. However, as more positions were analyzed, more games were played by rote, and now all possible piece positions are available to the program. The artificial intelligence has been removed, since the problem is now a "no brainer." The object of this work is not just the checkers game. Schaeffer says that the programming principles developed in Chinook can be applied to program management. So, next time you're working on Microsoft project, remember that it's just a game.

Chinook is also a warm, dry wind at the base of the Rocky Mountains; or, Oncorhynchus tshawytscha, a type of salmon; or, a twin engine, twin rotor, heavy-lift helicopter. Checkers was Richard Nixon's family dog. Checkers was made famous in a speech, subsequently called the "Checkers speech," by Richard Nixon on September 23, 1952. Nixon had been accused of campaign finance impropriety, and he appealed to the public to keep him as the Republican Vice Presidential candidate. I think the world would be a different place if Checkers had been a cat.

1. Jonathan Schaeffer, Neil Burch, Yngvi Björnsson, Akihiro Kishimoto, Martin Müller, Robert Lake, Paul Lu, and Steve Sutphen, "Checkers Is Solved" (Science Magazine, published online July 19, 2007, DOI: 10.1126/science.1144079).
2. Computers crack famous board game (BBC News, July 19, 2007).
3. Justin Mullins, "Checkers 'solved' after years of number crunching" (New Scientist Online, July 19, 2007).
4. Jonathan Schaeffer, "One Jump Ahead: Challenging Human Supremacy in Checkers" (Springer, ISBN 0-387-94930-5, Hardcover, 504 pp., $34.95).
5. Online Chinook.
6. The Checkers Speech (YouTube).

July 20, 2007

The Axis of Evil

The principle of uniformity states that the universe is everywhere the same; that is, the laws of physics discovered on the earth are the same laws that rule the heavens. Astronomers have been pushing back the limits of the known universe, and they may have found unexpected order in what has been considered to be a random array of galaxies speeding away from each other in a universal expansion. First, there appear to be huge voids in which there are very few galaxies, and these are separated by long filaments of galaxies, such as the Great Wall. The great wall is a collection of galaxies about 500 million light years long, by 300 million light years wide, but only 15 million light years thick.

Preliminary observations of 1660 spiral galaxies, the same type of galaxy as our own Milky Way, seem to indicate that they are aligned on a axis, dubbed the "axis of evil" [1,2]. Spiral galaxies look like pin wheels, and like pin wheels, they are known to spin, albeit very slowly. Some spin clockwise, and others, counter-clockwise, and it just may be that they all spin predominantly in one direction on this axis. It's just our vantage point that have some appear to spin clockwise, and others counter-clockwise. Astronomers at the University of Oxford have launched a web site to have the public help to decide this issue. The web site, Galaxy Zoo, has about a million images from the Sloan Digital Sky Survey, and interested members of the public can receive a short online training course to help categorize the images as spiral galaxies (clockwise and counter-clockwise), elliptical galaxies, or stars and other objects. These images are generally too fuzzy to allow for computer image analysis, so human eyes are needed for this study, and the public gets to view galaxies that have never before been seen by humans.

Cosmologist Kate Land, one of the project leaders, is excited about the outcome, but she admits that finding a random distribution would please most astronomers, since it won't need further explanation. I would have preferred using "Lathe of Heaven," rather than "axis of evil," as a name for the conjectured phenomenon. The Lathe of Heaven is a 1971 science fiction novel by Ursula K. Le Guin. The plot revolves around a character whose dreams alter reality.

Margaret Geller and John Huchra discovered the Great Wall [3]. Margaret Geller is the daughter of Seymour Geller, who authored several papers with Alten Gilleo [4]. I authored several papers with Gilleo [5]. It looks as if the six degrees of separation principle is at work.

1. Michael Hopkin, "See new galaxies without leaving your chair" (Nature Online, 11 July 2007.
2. Public to join search for cosmic 'axis of evil' (New Scientist News Service, 11 July 2007).
3. Margaret J. Geller and John P. Huchra, "Mapping the Universe," Science, vol. 246, no. 4932 (17 November 1989), pp. 897-903.
4. M. A. Gilleo and S. Geller, "Magnetic and Crystallographic Properties of Substituted Yttrium-Iron Garnet," Phys. Rev., vol. 110 (1958), pp. 73-78.
5. D. M. Gualtieri, P. F. Tumelty, and M. A. Gilleo, "Influence of flux composition and growth temperature on the octahedral incorporation of rare-earth cations in rare-earth iron garnet," Journal of Applied Physics, vol. 52, no. 3 (March 1981), pp. 2335-2337.

July 19, 2007

Mining Elementary Particles

The 1885 novel, The Time Machine, by H. G. Wells was released as the movie, The Time Machine (1960, George Pal, Director), when I was still in elementary school. The essential plot is that mankind has evolved into two species in the far-distant future. One species, the Eloi, was docile and non-working. The other species, the Morlocks, toil in maintaining the underground machinery that maintains the lifestyle of the Eloi. The Morlocks' remuneration has evolved into feasting on the Eloi. There will soon be a group of physicists toiling with their machinery 2,250 meters (1.4 miles) underground looking for elementary particles.

The Homestake Mine, an abandoned gold mine near Lead, South Dakota, has been chosen by the National Science Foundation for the Deep Underground Science and Engineering Laboratory. This is no small enterprise, since it will take about a quarter of a billion dollars to create this laboratory for studies in physics, microbiology and geology.

Although scientists agree that Homestake will be an excellent site, the choice of South Dakota may have been influenced by some incentives. South Dakota will provide $46 million for the project. T. Denny Sanford, a billionaire residing in South Dakota, contributed another $70 million. Sanford has now become a member of the growing group of billionaires who have funded scientific projects recently.

The biologists are interested in studies of extremophiles, organisms that live in hostile environments. There are types of bacteria that live in rock miles below the surface of the earth, and these may be related to the earliest life forms. They don't need oxygen to thrive, and their nutrient supply is limited, so their living conditions are much like the early earth, and perhaps other planets. Physicists are interested in the underground location, since the earth provides shielding from all but the most energetic elementary particles. One experiment planned is a search for double-beta decay, a supposed process for the decay of neutrons that might explain why matter predominates over antimatter in the universe.

1. Geoff Brumfiel, "Underground lab set for South Dakota" (Nature Online, 11 July 2007).
2. The Time Machine (1960) on the Internet Movie Database.

July 18, 2007

Energy Harvesting

Michael Faraday had little formal education, but he's recognized as one of the best experimentalists in the history of physics. His experimental technique may have been aided by the fact that he knew little mathematics, so he wasn't distracted by any theory. One of his most important discoveries is his law of induction. Faraday's law, simply stated, is that the voltage in a coil is proportional to the rate of change of magnetic flux through the coil. This effect is easily demonstrated by dropping a magnet through a coil of wire and viewing the voltage across the coil on a voltmeter. Faraday's law was put into a mathematical framework by James Clerk Maxwell in Maxwell's equations.

The Faraday effect is an easy was to convert vibration into electricity, and a micro energy harvester using this principle has been produced by engineers at the University of Southampton. Their approximately cube-shaped microgenerator, called Mk2, measures 7 x 7 x 8.5 mm. It contains four tiny neodymium iron boron magnets attached to a cantilever. Neodymium iron boron is an extremely powerful magnet, having a maximum energy product of up to 54 mega-Gauss-Oersteds (MGO). The equivalent energy content of one MGO is 7,958 J/m3. The cantilever is forked, and two magnets at one side of the fork are at the top of a small coil, and two at the other side of the fork are at the bottom. As the cube vibrates, the cantilever moves, and the magnets generate a small voltage in the coil.

While the Mk2 converts about 30% of applied vibration energy into electricity, the supplied power is still extremely small. In a typical application, it produces less than 50 microwatts of electrical power, but this is enough power for remote wireless sensors, or an implanted pacemaker powered by the vibration of a beating heart. A coffee-cup sized version of this generator is being sold by Perpetuum, a spin-off company which bills itself as "the global leader in vibration energy harvesting." Energy harvesting will be an important technology for deployment of wireless sensor networks. The European Union is ahead of the game on energy harvesting devices because of a program called Vibration Energy Scavenging (VIBES). The Mk2 was developed with VIBES funding.

1. Will Knight, "Micro-generator feeds on good vibrations" (New Scientist Online, July 4, 2007).
2. VIBES Web Site.

July 17, 2007


Electricity produced by rubbing substances together was known to the ancient greeks, and the first written record is by Thales of Miletus. The combination of two natural substances, rabbit fur and amber, generates considerable static charge. Our word for the negative charge carrier, electron, comes from the Greek word for amber, ηλεκτρον. The rubbing process pulls electrons from the surface of one material onto the other. An ampere of current is a flow of electrons of one coulomb per second. A coulomb is about 6.2 x 1018 electrons, which is a millionth the number of atoms in a mole, so the actual fraction of electrons transferred is small, but it has a big effect, since humans feel electrical sparks at the 5 milliamp level.

This transfer of charge from rubbings is called the triboelectric effect. This process of generating electricity from rubbing surfaces was mechanized in the Wimshurst machine, which was developed in the later part of the nineteenth century by the British engineer, James Wimshurst (1832-1903). The Wimshurst machine has two disks that are rubbed together in a contrary circular motion by a hand crank, along with metal patches to transfer the charge to outer electrodes. This rubbing process was improved by American physicist Robert Van de Graaff(1901-1967), a professor at Princeton University, who developed the eponymous Van de Graaff generator for producing high voltages. These generators, which are a relatively inexpensive means of generating millions of volts, were used for early studies in nuclear physics.

The word triboelectric comes from the Greek verb for rubbing, tribo (τριβω), but the triboelectric effect does not really involve friction or rubbing. It's only necessary for the materials to contact each other, although rubbing increases the contact area. Surface chemical bonds form between the materials, and charge in transferred in order to equalize the electrochemical potential. The charge is diffused away from the surface, leaving an opportunity to repeat the process. Today, the emphasis is on studies of the really small (a.k.a., nano), so it's not surprising that scientists at nearby Rutgers University would investigate the interaction of small rubbing particles.

The result of their investigation (to be published in Physical Review Letters) is surprising [1,2]. When two populations of sand grains ("art sand," available in various colors at craft stores - the Rutgers scientist used red and blue) are mixed in a hopper and poured into a beaker, they will spontaneously segregate. In effect, they will "unmix" because of the triboelectric effect. The Rutgers scientists discovered that the grains are all positively charged, having lost electrons to the hopper, but one population is charged to a greater extent than the other. The mutual repulsion of the particles is enough to propel some two meters into the air. Needless to say, there may be industrial applications for the "unmixing" process.

1. Phil Schewe and Ben Stein, "Spontaneous Separation of Charged Grains," Physics News Update, Number 832 (July 12, 2007).
2. Troy Shinbrot, "Tribocharging of Identical Materials" Rutgers University, Biomedical Engineering.

July 16, 2007

Robert W. Cahn

When I made the transition from physics to materials science between my undergraduate and graduate years, I spent many days in the library reviewing the literature of my newly chosen field. One name that I saw repeatedly as both author and in citations was Robert W. Cahn, one of the founders of modern materials science and a prolific author. Robert Wolfgang Cahn died on April 9, 2007, at age 82 [1, 2].

Cahn wrote an autobiography [3], so the details of his life are well known. His family, a prosperous Jewish family from Fürth, fled Nazi Germany in 1933, and he eventually started his Ph. D. research under Egon Orowan at the Cavendish Laboratory. While at Cavendish, Cahn met his future wife, whose father, Daniel Hanson, connected him with Alan Cottrell. Cahn and Cottrell performed experiments that provided the first evidence for dislocations.

Cahn completed his Ph. D. at the British Atomic Energy Research Establishment (Harwell) under Bruce Chalmers. At Harwell, Cahn studied the plastic flow of uranium. Cahn eventually became the first professor of Materials Science in the UK, at the University of Sussex. His main research focus was on metallurgy, on topics such as creep, recrystallization, ordering in alloys, rapid solidification, and metallic glasses. While in supposed retirement, he did research at the General Electric Central Research Laboratory (Schenectady, NY) on ductility in Ni3Al-Fe alloys.

Cahn was the first materials science correspondent for Nature. Cahn had a column also in Materials Today, and he was the inaugural editor of the Journal of Materials Research. His most notable editorial achievement was the multi-author textbook, Physical Metallurgy. Cahn was a fellow of the Royal Society.

1. A. Lindsay Greer, "Obituary: Robert Wolfgang Cahn (1924–2007)," Nature Materials, vol. 6 (2007), p. 477.
2. Roger Doherty, "Robert W. Cahn (1924-2007) and David Turnbull (1915-2007)," Science, vol. 317, no. 5834 (2007), pp. 56-57.
3. R. W. Cahn, "The Art of Belonging," Book Guild Publishing (Sussex, UK, 2005).

July 13, 2007

The Big Bang Theory

No, this article isn't about the cosmological Big Bang that spawned the universe. It's about a bigger bomb, the impending television series, "The Big Bang Theory," scheduled to air on CBS this Fall. I've viewed the trailer for the series [1], and my opinion is that it will not last more than three episodes. After three episodes, anyone can do a linear regression to zero viewers with a good confidence value.

The story is about two physicists who share an apartment, their cadre of physics friends, and a beautiful young woman who moves into an apartment across the hall. Sure, we physics types are not well polished, but these guys are Nerds with a capital "N." They are nothing like the scientists I know, including the extremely introverted engineers I encountered during my brief stay at RPI. This is quite a contrast to "Numb3rs," a television drama that quite accurately portrays the lives of academic scientists, including backroom university politics, although it exaggerates their depth of knowledge and speed of action.

Since the "The Big Bang Theory" is a comedy, shouldn't some exaggeration be expected? It may not even be an exaggeration that it takes two physicist's salaries to afford an apartment in the same building as a young woman who works "at the cheesecake factory." The show apparently has a good technical advisor, since a white board in a living room scene had some Feynman diagrams and some equations that seem to be an expectation value calculation. However, the trailer contained a very inappropriate joke about Stephen Hawking, and the towel-clad young woman needs to use the physicist's shower, which has a Periodic Table shower curtain. I don't foresee my watching even the first episode.

1. The Big Bang Theory trailer (YouTube).
2. The Big Bang Theory on the Internet Movie Database
3. The Big Bang Theory cast photograph with Leonard (Johnny Galecki), Sheldon (Jim Parsons), and Penny (Kaley Cuoco).

July 12, 2007

All Things Being Equal

Carl Jung, along with Sigmund Freud, was a founder of modern psychoanalysis. He introduced the concepts of introversion and extraversion, and the Myers-Briggs Type Indicator test is based on his work. His last psychological book, "Man and His Symbols," written in collaboration with several colleagues, was published posthumously in 1964, three years after his death [1]. This book was profusely illustrated and written in an accessible style, so I enjoyed reading it even though I was just a high school student. I still have a copy on my bookshelf. Surprisingly, there are no mathematical symbols in this book. This omission may be an example of the cultural divide between the "Technorati" and Literati.

The equal sign (=) is ubiquitous in algebra, and it would seem that it has existed forever, but it was introduced in 1557. Most algebraic equations up to that time were written as word problems, Diophantine equations being a prime example. Robert Recorde, a Welsh mathematician, introduced the equal sign in florid fashion:

"To auoide the tediouse repetition of these woordes: is equalle to : I will sette as I doe often in woorke use, a paire of paralleles, or Gemowe [i.e. "twin"] lines of one lengthe, thus: =, bicause noe .2. thynges, can be moare equalle. [2, 3]"

In short, Recorde thought that parallel lines gave a good image of equality. His equal sign, however, was five times longer than present usage, in keeping with his parallel lines idea, so it didn't catch on immediately. Some rotated Recorde's lines and used "||" as the equal sign. The symbol "ae," which is an abbreviation of the Latin word for equals, "aequalis," was used into the eighteenth century. Cajori, an influential historian of mathematics, wrote [4] that the modern equal sign might have been used first in Bologna, Italy, sometime between 1550 and 1568, about the same time as Recorde's use. Recorde published his work, so he gets priority according to our scientific norm.

1. C. G. Jung, M. -L, Franz, et al., "Man and His Symbols" (Doubleday, Garden City, N. Y.), 1964. ISBN 0-440-35183-9
2. Equal Sign.
3. Equals sign (Wikipedia).
4. Florian Cajori, "A History of Mathematical Notations," (Dover, New York), 1993. ISBN 0-486-67766-4.

July 11, 2007

Chameleon Iron

Displays are so important in the modern world that an attempt has been made to transform every physical effect leading to a change in color or contrast into a display. These efforts are not yet exhausted, since new effects are discovered every day. The latest display technology involves the current darling of materials science, nanoscale materials, and magnetism. Scientists at the University of California, Riverside, have created significant color changes in solutions of iron oxide nanoparticles by subjecting them to magnetic fields [1]. This research, led by Yadong Yin, an Assistant Professor of Chemistry, will be featured on the inside cover of a future issue of Angewandte Chemie (Volume 46, Issue 34).

Their display material is a colloid of iron oxide (Fe3O4 nanoparticles that self-assemble into an ordered structure in a magnetic field. The ordered structure is a photonic crystal in which the spacing of the iron oxide nanoparticles determines what color of light will be reflected. By varying the magnetic field, the color is changed over the entire visible spectrum of light, since the spacing of the iron oxide nanoparticles is changed. The iron oxide nanoparticles are superparamagnetic; that is, they respond to a magnetic field, but they are not in themselves magnetic, so they don't keep a memory of their previous state. Yin says that the display response is rapid and reversible, and this is a "green" technology. Iron oxide is non-toxic, and it's also inexpensive. Their paper is not yet published, but I'm curious to read the power requirement. The generation of magnetic fields typically takes a lot of power.

1. Iqbal Pittalwala, "A simple magnet can control the color of a liquid, making new technologies possible" (UCR Press Release).

July 10, 2007

Preserving Plastic

There's much talk about using biodegradable plastics to solve a large fraction of our waste disposal problem. Degradable plastic for six-pack packaging is commendable, but what about all those items you want to keep? Even plastics that are not formulated as being biodegradable still undergo degradation by ultraviolet insolation, wheathering, and other chemical effects. There may be no archaeological record of our present "plastic" civilization. Museums have lead goblets from the Roman Empire, but there may be no trace of our beverage holders after a few hundred years. As a result, there's a concerted effort to develop traetments to preserve some plastic items, and to develop plastics that will not degrade.

Among the earliest plastics were cellulose acetate, which has been used since 1865, and cellulose nitrate, more commonly known as nitrocellulose, discovered in 1832 as the product of the reaction between nitric acid and cellulosic materials, such as cotton. The transitory nature of these plastics is realized when you consider that nitrocellulose was called "gun cotton," and it's the major component in smokeless gunpowder. That didn't deter the artist Naum Gabo (1890-1977) from making cellulose acetate sculptures, and early plastic dolls were made from cellulose nitrate. Aside from the explosive potential, these chemicals will spontaneously disintegrate when exposed to ultraviolet light.

Polyvinylchloride (a.k.a., Polychloroethene and PVC) is one of the most common plastics used today, but the plasticizing additives added to it are a problem. Phthalates are typical plasticizers for PVC, but they are not strongly bonded to the polychloroethene molecules. As a consequence, they diffuse to the surface to change the appearance of an object. When exposed to an acidic environment, white crystals of phthalic acid form at the surface, spoiling the object's original appearance. Of course, as any chemist knows, diffusion and other chemical reactions are slow at low temperatures, so keep your Bratz dolls in the freezer.

1. Katharine Sanderson, "Plastics for posterity" (Nature Online, 25 May 2007).

July 09, 2007

Perpetual Postponement

Many months ago, I reported on the perpetual motion machine developed by the Irish company, Steorn [1]. The Steorn machine, which operates on a principle they call "Orbo Technology," is said to operate by a precise arrangement of permanant magnets. Of course, physicists has always been skeptical about perpetual motion machines, so much so that the American Physical Society has issued a statement about the impossibility of such devices.Thermodynamics, which has been confirmed by hundreds of years of experimental evidence, invalidates the concept of perpetual motion.

Well, Steorn could delay no further, so it announced a demonstration at the Kinetica Museum in London. The demonstration did not proceed as planned, and Steorn has postponed the demonstration until further notice [2, 3]. Steorn claimed that "technical problems arose during the installation of the demonstration unit in the display case... These problems were primarily due to excessive heat from the lighting in the main display area. Attempts to replace those parts affected by the heat led to further failures and as a result we have to postpone the public demonstration until a future date."

Perhaps the only think perpetual here will be delays in the demonstration.

1. John Borland, Perpetual Motion Claim Probed, Wired News (August 21, 2006)
2. Charlie Sorrel, "Surprise! Perpetual Machine Demo Cancelled" (Wired News).
3. Steorn announcement: Kinetica Demonstration.

July 06, 2007

Musical Computers

In the early days of the personal computer, there were so few of them around that the US Federal Communications Commission had not yet set any standards for acceptable radio interference from computers. In my house, we were early adopters of computing, and many of my computers were hand-built. By hand-built, I don't mean plugging in circuit cards and screwing things together, which is today's definition; I mean integrated circuits and a soldering iron. Needless to say, when a computer was on, we would get television interference, so I would work late at night when everyone was asleep. This radio interference effect was known since the mid-1960s, but it allowed an unintended application for early computers - the creation of music.

When I was in high school in the early 1960s, the math club took a field trip to the computer center at Colgate University. The center had one of IBM's first transistorized computers, the IBM 1401. One reason they had it was that the computer, originally priced at several million dollars by today's standards, was at the end of its life-cycle. IBM introduced its System/360 in the mid-1960s. We played Tic-Tac-Toe and some of the other simple demonstration programs available at the time, then the operators brought out an AM radio and played some computer music. What they were doing was using the radio frequency interference from the computer to generate music by means of some carefully timed program loops. As I learned recently, this technique was pioneered by Johann Gunnarsson, an Icelandic engineer who worked with the 1401 in the early 1960s.

Johann's son, Johann Johannsson, is an avant-garde musician. He discovered recordings his father had made of his computer music, and in 2006 he released an album, called "IBM 1401, A User's Manual," incorporating the sounds [1]. This effort has been expanded into a song and dance performance piece that incorporates readings from the 1401 user manual [2]. When the performance played in Geneva, many in the audience were retirees from CERN who remembered the machine.

While we're on the topic of musical recordings, June was a special month in recording history. Handel's Oratorio, "Israel in Egypt," became the first musical recording on June 29, 1888 [3]. It was recorded on a paraffin cylinder by George Gourand, the foreign sales agent for Edison's phonograph, in London's Crystal Palace.

1. Art Inspired by IBM 1401 (Wikipedia).
2. Robert Andrews, "IBM 1401 Mainframe, the Musical" (Wired Online, June 29, 2007).
3. Tony Long, "June 29, 1888: Handel Oratorio Becomes First Musical Recording" (Wired Online, June 29, 2007).

July 05, 2007

Recycling Plastics

Much of the world's oil becomes feedstock for the production of plastics. In traditional recycling, the plastic is shredded to become filler for other articles, such as plastic wood, or it is burned to reclaim its energy value. It would be nice to turn plastic back into oil, and one company is attempting just this using microwave energy. Their technique is a variation of something that spectroscopists have known for quite a while, that electrons in chemical bonds absorb radiation at certain discrete wavelengths. Chemists use infrared radiation for analysis of most molecular substances, but molecules absorb radiation in the microwave spectrum, also. For example, the simple molecule, methane, has 38 absorption lines between 6.895204 and 19.28863 GHz [1].

Global Resource Corporation (GRC), located in West Berlin, New Jersey, near Philadelphia, has developed a process that decomposes plastic to more basic hydrocarbons by bombarding it with intense microwave radiation [2]. They use 1200 different microwave frequencies tuned to specific bonds in hydrocarbons. As an example of their process, they converted twenty pounds of shredded tires into 1.2 gallons of diesel oil, 160 cubic feet of combustible gas, 7.5 lbs. of carbon black, and 2.2 lbs. of steel. There are nearly thirty million tons of tires discarded each year. A quick calculation shows that their conversion would result in 3.6 billion gallons of diesel oil per year, or more than a hundred million barrels. For conversion of plastic, a cleaner material than tires, GRC claims the following:

• Kerosene 12.5%
• Diesel Oil 21.5%
• Lubricating Oil 66%

One intended application is the conversion of "autofluff," which is the remains of an automobile after all the metal has been removed. The metal in automobiles is mostly steel, but for every ton of steel, about 600 pounds of autofluff remains. Autofluff contains a multitude of materials, including fabrics, glass, wood, plastic, and dirt. The GRC process is able to extract enough energy-laden hydrocarbons to at least pay its own electric bill, and reduce landfill volume at the same time.

1. NIST Molecular Spectra Web Site.
2. Catherine Brahic, "Giant microwave turns plastic back to oil" (New Scientist Online, 26 June 2007).
3. Global Resource Corporation Plastic Recycling.

July 04, 2007

Independence Day

July Fourth is Independence Day in the United States. This national holiday celebrates The Declaration of Independence, the document published on July 4, 1776, that asserted our independence from Great Britain. After more than two hundred years of change in the world, it's hard to believe that we were once at war with Great Britain. The holiday is celebrated by traditional summer activities, such as baseball games and picnics. Fireworks are associated with this holiday, but personal use of fireworks is highly discouraged for safety reasons. What celebration in an obese country would be complete without a hot dog eating contest?

Aside from this holiday observance, is there anything special about the date, variously 7/4/07, 7/04/07, 7/4/2007, 7/04/2007, and 2007/07/04? I checked these number sequences, without the slashes, for primality [1], and they are all composite numbers.

• 7407 = 3*2469
• 70407 = 3*23469
• 742007 = 7*106001
• 7042007 = 7*1006001
• 20070704 = 2*10035352

The last one, of course, is a no-brainer, since all even numbers are divisible by two. There's no sense in trying variations on July 4, 1776, since they're all even numbers.

Prime numbers are the basis for secure transactions on the internet, so it's important to be able to test numbers quickly for primality to develop the necessary encryption keys. The numbers above are small, so a brute-force approach works well. When the numbers are large, brute-force does not work, and that's why internet transactions are secure from brute-force decryption. The necessary mathematics to test whether a number is prime to a high probability was developed hundreds of years ago.

Pierre de Fermat proved what is now called "Fermat's Little Theorem," the core of which can be used as a probabilistic test to determine whether a number is prime. In 1736, Euler developed a generalized version of the theorem, which is known as Euler's Totient Theorem (a great phrase to drop into casual conversation on your July Fourth picnic). Fermat's test, called the "Fermat Primality Test," is very easy to program. If n is the number to be tested as prime, choose a random number r in the range 1 to (n-1). Then compute

rn-1 mod n

If the result is one, then n is probably prime. You do this calculation many times with different random numbers, and each time, you're more and more certain that the number is prime. Most encryption programs loop through the calculation quite a few times to ensure that the number has only a 10-50 chance of not being prime. This is enough for practical purposes.

1. Online Prime Test.
2. Fermat's little theorem (Wikipedia).
3. Fermat primality test (Wikipedia).
4. Euler's theorem (Wikipedia).

July 03, 2007

Genome Replacement

In yesterday's post, I described how scientists from the J. Craig Venter Institute have filed a patent application on the essential genome kit for the basic elements of life. They believe that less than four hundred and fifty genes are required. Of course, such a synthetic genome would need to be inserted into a cell, since a synthetic genome is not alive in itself. It needs all the cellular mechanisms to thrive and reproduce. Venter's people have quickly gone on to the next step by demonstrating that they can replace the genome in one bacterium with that of another [1-3].

The Venter team, led by John Glass, removed the DNA from cells of the bacterium, Mycoplasma mycoides, and inserted it into cells of another bacterium, Mycoplasma capricolum. This transplant worked, since the new bacteria produced proteins characteristic of Mycoplasma mycoides. Their technique is surprisingly simple. They suspended Mycoplasma mycoides bacteria in a gel and lysed (broke apart) the cells with enzymes to leave the bare nuclear DNA. This DNA was added to colonies of Mycoplasma capricolum along with chemicals that allow incorporation of the DNA into bacterial cells. The resultant cellular hybrids divided to produce equal numbers of Mycoplasma capricolum and Mycoplasma mycoides, the later produced solely from its genome. An antibiotic, tetracycline, was added to remove the Mycoplasma capricolum, leaving only the synthetically created Mycoplasma mycoides. The process is successful in only about one in every 150,000 cells, but bacteria reproduce so quickly that large colonies are produced in just a short time. This work is described in a paper in Science [4].

1. Philip Ball, "Genome transplant makes species switch" (Nature Online, 28 June 2007, doi:10.1038/news070625-9).
2. Peter Aldhous, "Tycoon succeeds in 'genome transplant'" (NewScientist.com news service, 28 June 2007).
3. Matthew Herper, "Venter Takes Step Toward Synthetic Cells" (Forbes, June 28, 2007).
4. Carole Lartigue, John I. Glass, Nina Alperovich, Rembert Pieper, Prashanth P. Parmar, Clyde A. Hutchison III, Hamilton O. Smith, and J. Craig Venter, "Genome Transplantation in Bacteria: Changing One Species to Another" (Science Online, June 28, 2007, doi: 10.1126/science.1144622)

July 02, 2007

Bare Bones

Actually, bare genome. How few genes are needed for a bacterial cell to be alive? A group of scientists from the J. Craig Venter Institute think it's less than four hundred and fifty. They're so sure that they've filed a US patent application on this hypothetical bare-bones life form [1]. In order to create this life-form, a bacterial cell would be stripped of its own DNA, and it would be replaced with a synthetic genome of these 450 essential genes. Of course, this isn't producing a new life-form from scratch, since the essential cell machinery of the original cell is used for replication, energy conversion, etc. Of course, a utility patent application must present a useful invention, and in this case the utility claimed is the production of ethanol or hydrogen. Another useful feature is that this synthetic cell could be used as the fruit fly of bacterial genetics, since none of its functions would interfere with other genetic modifications.

Although he is not listed as an inventor, this work was encouraged by Craig Venter, founder of Celera Genomics, and one of the principals in the successful government-funded effort sequence the human genome. This patent has some unusual wording, since much of the basic research on this idea was published in 1999, and there have been other publications since that time [2,3]. Some groups are upset about the idea of patenting this basic life-form, but practicing geneticists are not worried. Stuffing the genome with a few more genes to put the total number over 450 is all that's needed to get around this patent. There are rumors that this bacterium has been created already in the laboratory, and it will be unveiled soon by the Venter Institute [4].

It's surprising that such a small number of genes is required for the basic functions of life; but more surprising is the finding that the human genome contains less than 24,500 functional genes [5]. During the course of the Human Genome Project, some geneticists believed that the number might top 100,000. The present estimate of less than 24,500 genes means that humans have only a third more genes than Caenorhabditis elegans, a simple worm. There was actually a betting pool on the number of human genes (GeneSweep). As it turned out, Lee Rowen of the Institute of Systems Biology, Seattle, Washington, had the lowest bet (25,947) and was declared the winner.

1. Glass; John I.,et al.,"Minimal bacterial genome," United States Patent Application 20070122826 (May 31, 2007).
2. Glass JI, Assad-Garcia N, Alperovich N, Yooseph S, Lewis MR, Maruf M, Hutchison CA, Smith HO, and Venter JC, "Essential genes of a minimal bacterium," Proc Natl Acad Sci U S A. vol. 103, no. 2 (Jan 10, 2006), 425-430.
3. Koonin EV, "How many genes can make a cell: the minimal-gene-set concept," Annu. Rev. Genomics Hum. Genet. vol. 1 (2000), pp. 99-116.
4. Peter Aldhous, "Tycoon seeks patent for 'minimal genome'" (NewScientist.com, 8 June 2007).
5. Genome FAQ (Oak Ridge National Laboratory).
6. Bob Holmes, "Alive! The race to create life from scratch" (NewScientist.com, 12 February 2005).