## June 30, 2008

### Random Pi

My Uncle Walter was an interesting character. He served as a Marine in World War II, rolled his own cigarettes, and was into recycling before it became popular. He was high school educated only, as were most of his generation, and when he told people what his nephew did, he described it as "Pi-R-Squared-Physics." He realized in his own way that the mathematical constant, pi, has a special place in physical reality. I was reminded of this when I read a recent news article about a crop circle in Britain that encoded the decimal value of pi to high precision [1]. A crop circle is a geometrical pattern created in an agricultural field by flattening the crop. Although some people believe that these are messages from extraterrestrials, they are generally considered to be school boy pranks, although these must be well educated school boys.

I've discussed pi in several previous articles [2-5]. Pi is a transcendental, irrational number with a number sequence that does not repeat. Pi is part of many fundamental equations of physics, which indicates to me that pi has a physical reality independent of an observer. Pi is considered to be so important to mathematics that it's been calculated to more than a trillion digits. This is definitely overkill for most applications, since only fifty digits of pi are needed to calculate the circumference of the observable universe to within a proton's width. The first few decimal digits of pi are

3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510

A casual glance indicates quite a few more threes and nines after the decimal point than randomness would indicate. There are eight threes and eight nines, but only two zeros. This is only a small statistical sample, so it takes many more digits to discover that pi is indeed random. Interested readers can find listings of many digits of pi on the internet [6] and one approach to random number testing [7].

Testing pi for randomness is an interesting experiment, the results agree with our expectations, but there's no theory that states this must be the case. In fact, we should admit that pi is not random, since it can be calculated. Something that can be calculated is, a priori, not random. This was expressed succinctly by computer pioneer, John von Neumann, when he said, "Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number, there are only methods to produce random numbers; and a strict arithmetic procedure, of course, is not such a method."

Von Neumann was interested in randomness, since he participated in the development of the Monte Carlo method. To speed his computer calculations, von Neumann developed a simple random number generator, called the middle-square method. This generator has its problems, the most important of which is the limit on the number of random numbers you can get from it (its "period"), but it was useful for the small-scale computer models of his time. It works as follows:

• Step 1: Select a ten-digit number.
• Step 2: Square the number.
• Step 3: Select the middle ten digits of the square
• Step 4: This is your random number
• Step 5: Use this as your new ten-digit number and go to Step 2

If you use n-digit numbers, this procedure will give you 10n random numbers, although there are a few cases, involving too many zeros in the middle numbers, in which it fails.

John von Neumann was born on December 28, 1903. The sequence 122803 occurs starting at position 1,600,569 in the digits of pi after the decimal point [8]. The number 12281903 does not occur in the first 200,000,000 digits of pi.

## June 26, 2008

### Magnetic Earth

Physicists love models. A model is an easily understood analogue of a principle or process. The Bohr Model of the atom is one of the more famous pencil and paper models. Sir William Bragg's bubble raft, well known to materials scientists, is a physical model of dislocations in crystal lattices. Our current understanding of the nature of the elementary particles is known as the Standard Model.

William Gilbert (1544-1603) was one of the patriarchs of the field of magnetism and the author of the first topical book on magnetism, De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth, 1600). In this book, Gilbert described his experiments on a model of the Earth constructed from a sphere of magnetite, a magnetic mineral of composition Fe3O4. This physical model, called a terrella, explained not just the direction of compass needles, but also their tendency to point into the Earth. Some theories of the time said that the pole star, Polaris, was responsible for magnetic attraction of compass needles. Advanced versions of Gilbert's terrella were used in the twentieth century to simulate the Earth's magnetosphere.

Dan Lathrop, a geophysicist at the University of Maryland, has been using the terrella concept to investigate how its molten core gives the Earth a magnetic field. Lathrop and his team have been building a succession of larger and larger physical models of the Earth and its liquid metal core [2]. These physical models are huge, rotating metal spheres filled with liquid sodium, the latest of which is three meters in diameter [3]. Sodium is a convenient material to use, since it has a melting point of only 98 oC. Fortunately, liquid sodium does not react with the stainless steel containment spheres, an idea once important to the concept of liquid metal cooled nuclear reactors. The liquid sodium is intended to simulate the liquid iron thought to be the major constituent of the Earth's core. For scaling reasons, the three meter sphere will need to spin with an equatorial speed of eighty miles an hour to simulate the Earth. The motion of the liquid metal will generate a magnetic field by dynamo action.

Lathrop expects that the rotating sphere will induce a regular turbulent flow in the liquid sodium, and there may be other surprises. The geological record has shown that the Earth's magnetic field has flipped directions many times, and data indicate that we may be due for another flip. Lathrop's physical model of the Earth is needed, since computer simulations can't capture the entire complexity of the turbulent system.

## June 25, 2008

### Self-Assembled Nanodielectric

Radiation is bad not just for living things, but for materials as well. Materials used for nuclear reactor containment are a good example [1]. Neutron irradiation leads to embrittlement of steel in the reactor containment vessel. This embrittlement is a consequence of the radiation-induced precipitation of trace elements, such as copper. In a previous article (Fleeting Memory, September 28, 2006), I mentioned the susceptibility of electronic materials to cosmic rays. When a cosmic ray strikes a DRAM memory chip, it will cause the formation of millions of electron-hole pairs, leading to a transient memory error. This is somewhat of a problem on Earth, but it's a major problem in space. The historical approach to radiation-hardened electronics is to limit the amount of active semiconductor material in an integrated circuit to reduce the possibility of formation of the electron-hole pairs. This is achieved by making circuits in a thin layer of silicon laid atop a non-conductive substrate, as in silicon on sapphire (SOS). With shrinking transistor dimensions, even SOS technology is reaching its limits.

Materials scientists at Northwestern University have been developing a gate insulating material for field-effect transistors that's inherently radiation-resistant as a replacement for the traditional silicon dioxide [2]. Aside from the radiation-resistance, the material satisfies the other requirements for a gate dielectric; namely, high insulation resistance and a high dielectric constant. This material, called a self-assembled nanodielectric (SAND), is prepared by either a dipping process, or by vapor-phase deposition of highly polarizable organic molecules that form an ordered, hydrogen-bonded film [3]. Because of polarization, the film offers high dielectric constant. As another benefit, it's flexible, offering an approach to printed and ruggedized electronics. Early tests in nuclear reactor environments confirmed the radiation-resistance. Some SANDs transistors were transported to the International Space Station (ISS) and placed on the ISS outer surface during a spacewalk on March 22, 2008, for long-term exposure of about a year's duration.

The Soviet Union utilized a different type of radiation-resistant electronics in their MIG-25 (Foxbat) fighter aircraft. The Foxbat avionics avoided transistors almost entirely, using vacuum tubes instead.

## June 24, 2008

### Name That Tune

"Name That Tune" was a television game show in which contestants tried to identify a melody based on a small number of starting notes. One "losing" contestant on this show had actually named a different tune with the same few starting notes as the one presented at the competition. As a consequence, the production company was forced to create a one-off episode for his next round competition. Did the composer of "The Bus Stop Song" (the show's tune) copy the tune of "If You Will Marry Me" (the contestant's answer), or is there such a small number of original melodies that this happens often, purely by accident?

The Western chromatic musical scale has twelve notes. For technical reasons, the melodic minor scale can be claimed to have ten notes. These scales are rare, existing in compositions of Arnold Schoenberg, Mozart, and a few others. You won't hear Kelly Clarkson or Madonna singing melodies in either of these scales. Western popular music today is uniformly composed from an eight note major scale.

If you have just eight notes, how many original melodies can you create? This depends on how long a melodic line and number of different durations of the individual notes you want to consider. Note duration may vary over a considerable interval, but in a popular music melody line it's unlikely that more than six durations would be used (eighth, dotted-eighth, quarter, dotted-quarter, half, and dotted-half notes). Thus, each note in a typical melody can have (8 x 6) = 48 different values of pitch and duration. Since melody is independent of key, the value of the first note just sets the tonic, so only its duration is important. Its pitch value can be ignored. Based on these assumptions, we can calculate the possible number of melodies N for n notes

N = 6 x (48)n-1

For a ten note melody (e.g., "How much is that doggy in the window"), this is 8,115,632,763,568,128 possible melodies. In the "Name That Tune" game show, the typical grand challenge was to name a tune based on the first four notes

N = 6 x (48)3 = 663,552

You can see that the odds of two melodies having the same first four notes are not astronomical.

One of the more famous Western melodies is "Happy Birthday to You," a six note melody (N = 1,528,823,808). This song, composed about a hundred years ago, still generates an estimated \$2 million a year in licensing revenue [1]. You rarely hear this song in any movie or television show, since the producers are loath to pay licensing fees, but Igor Stravinsky arranged a variation of the song, the Greeting Prelude, in 1955. There is considerable discussion about whether this song should have copyright protection, but it's not an issue that anyone would pay lawyers to adjudicate [2].

## June 23, 2008

### Speedo Fluid Dynamics

When I work with chemicals, or when I do messy work like machining, I wear a lab coat. There have been a few improvements in lab coats over the years. What was once a bulky cotton coat with buttons is now made from a lightweight nylon-polyester-type material with snaps. The snaps serve an important purpose, since the coat can be removed more easily after a significant chemical spill; or in the unlikely occurrence of an injury or fire. Although the less bulky lab coat makes it easier to move, I wouldn't characterize the new style coats as "performance enhancing." What would a performance-enhancing lab coat be like? Would I be able to perform five experiments in the same time it takes to do four? What would be the price-point for Honeywell to purchase such a lab coat for its employees? Would use of such a lab coat be considered an unfair trade practice?

This seems to be a silly exercise, at least for lab coats, but this issue is being hashed-out presently in the Olympic swimming arena. The "performance enhancing" article in question is the Speedo LZR Racer swimsuit, and the controversy is nicely summarized for the scientific community in an editorial by Jonathan Wood in the current issue of Materials Today [1]. When Wood wrote his editorial, twenty-eight out of twenty-nine swimming records had been broken by swimmers using this new swim suit. As of June 8, 2008, 38 records have been broken by swimmers wearing the Speedo LZR Racer. Indeed, in just the first week after its introduction, three world records were broken by swimmers wearing the Speedo LZR Racer. It appears that it's now necessary to wear a Speedo LZR Racer to compete in the Beijing Olympics. In fact, there have been notable defections of world-class swimmers, such as Kosuke Kitajima, from other manufacturers to Speedo [2-3]. In a recent 200 meter breaststroke competition, LZR Racer-clad Kitajima broke a 2006 record by nearly a second.

How does the Speedo LZR Racer work? The fundamental idea is the reduction of a swimmer's drag in the water. This was accomplished crudely in the past by shaving all body hair. The suit is made from an hydrophobic polyurethane fabric that's not stitched; it's ultrasonically welding. Furthermore, textured patches that mimic sharkskin are placed at high friction points, and the suit compresses the body to prevent muscle vibration that increases drag. The suits reduce drag by about five percent over the next best suit, another Speedo product, the FS Pro. All this was done with a hearty dose of science [4-8]. Speedo worked with the University of Nottingham on computational fluid dynamics (CFD) and with NASA on the fabric. Four hundred swimmers were body scanned for the CFD database. The suits were even wind tunnel tested.

Of course, Speedo's competitors (who haven't invested in as much R&D, so how can they complain?) have protested. Arena sent a letter to FINA, Fédération Internationale de Natation, the ruling body in this case, stating that the Speedo LZR Racer acts also as a buoyancy aid, and such aids are strictly prohibited. FINA has ruled that the Speedo LZR Racer is an acceptable suit. Sport rules further prohibit body-shaping, but the Speedo LZR Racer firms and does not shape. Adidas has issued a statement saying it will not penalize its athletes who wear other, unbranded suits. The Speedo LZR Racer has no branding, but it's distinctive nonetheless.

## June 19, 2008

### Dental Restorations

Because of the processed food time of our youth, most of my generation has had extensive dental work. Earlier generations had their own dental problems, which prompted a memorable editorial by Eric Sevareid on Walter Cronkite's CBS Evening News. Sevareid commented that the reason diplomats in historic photographs never smiled was not because their diplomacy went bad; it was because they all had rotten teeth. In their generation, and mine also, dental restoration involved filling holes with a silver amalgam. Although metallurgists understand "amalgam" to mean any alloy of mercury with another metal, the popular usage is the specific alloy used in dental restoration. This is about 40% mercury and 35% silver combined with some tin, copper and zinc to provide mechanical strength.

Although dental amalgams have been used for more than a century, there's concern about the toxicity of mercury. Mercury is a heavy metal (atomic number 80), and it has a tendency to form some nasty organo-metallic compounds in nature. Despite criticism from some quarters, the US Food and Drug Administration has always claimed that amalgam fillings are safe. The FDA's conundrum, from a scientific standpoint, is that toxic compounds can cause problems when exposure is only at the part-per-billion level for long periods, and there's no simple experiment to test any hypothesis on short time scales. Although mercury itself is a toxic element, it's bound quite tightly to the other elements in the amalgam, so it can do less harm. Thermodynamicists say that its fugacity (a quaint, classical term for activity) is significantly reduced. This is true also for the lead in lead-tin solder, and the beryllium in copper-beryllium electrical contacts.

The FDA has finally cautioned pregnant women and children about amalgam fillings. Although the FDA doesn't recommend removal of existing dental amalgam fillings, it states, somewhat obliquely, that "Dental amalgams contain mercury, which may have neurotoxic effects on the nervous systems of developing children and fetuses." [1] Of course, materials scientists have been ahead of the game in the development of materials to replace dental amalgam, and an article that summarizes these materials appears in the April, 2008, issue of Physics Today, available free online [2]. Dental restorations are done now with a glass-filled polymer. The glass provides mechanical strength and an aesthetic mimicry of dentine material. The material is usually prepared in situ by UV photopolymerization of a methacrylate monomer. This process is aided by the UV light-emitting diodes presently available. The wavelengths used are only as long as 400 nm, so there's no danger from exposure. But things are not completely perfect. About 5 - 10% of the monomer is still unreacted in a typical procedure, and this eventually leaches from the dental filling.

## June 18, 2008

### Super-paper

Although you can claim that plastics are the primary material of this age [1], as I look about my home office where I am composing this article, nearly everything is wood. The walls are wood, the desk is wood, the suspended ceiling is a wood fiber composite, the book shelves are wood, and the books themselves are paper made from wood. Wood, and its principal component, cellulose, are wonderful materials. They are strong, formable into different shapes, aesthetically pleasing, and inexpensive. It's no wonder that research is underway to make improved wood-based materials. Since "nano" is the current materials buzzword, it's not surprising that wood nanoparticles, in the form of cellulose fibers, have been investigated and found to exhibit high strength.

A research team at the Fibre and Polymer Technology Department of the Swedish Royal Institute of Technology in Stockholm, Sweden, has just published an article on "super-paper" in the American Chemical Society journal, Biomacromolecules [2-3]. Normal paper is made from cellulose fibers of about thirty micrometers in diameter, and it has a tensile strength of about 1 MPa. The cellulose fibers in the cell walls of plants, however, are only 20 nanometers in diameter, and it's these fibers that give plants both high strength and fracture toughness. The research team, led by Lars Berglund, developed a process to harvest these nanofibers (a.k.a. "nanofibrils") by treating plant material with enzymes and then using the shear forces of a mechanical beater to separate the fibers from the other plant components. What's left is an aqueous suspension of the cellulose nanofibers that join into a hydrogen-bonded paper sheet when the water is removed.

The tensile strength of this "super-paper" is 214 MPa. For comparison, cast iron has about 130 MPa tensile strength, and structural steels have about 250 MPa tensile strength. What's just as significant is that the paper is resistant to fracture; that is, it has fracture toughness. It exhibits plastic elongation, having a large strain-to-failure, since the cellulose fibers are able to slide against each other to dissipate local stress.

References:
1. Cf., the famous conversation (via Wikiquotes) from the film, The Graduate (1967, Mike Nichols, Director):
Mr. McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics.

2. Jon Evans, "New 'super-paper' is stronger than cast iron" (New Scientist Online, June 6, 2008).
3. Marielle Henriksson, Lars A. Berglund, Per Isaksson, Tom Lindström, and Takashi Nishino, "Cellulose Nanopaper Structures of High Toughness," Biomacromolecules, vol. 9, no. 6 (May 23, 2008), pp. 1579-1585.

## June 17, 2008

### The Coke-Mentos Reaction

This article should begin with a "don't try this at home" caution, but if you're trained in laboratory safety, as many of us are, grab your safety glasses, but don't say I didn't warn you! Coke™ is a much beloved beverage of computer programmers, scientists and engineers, so it's important for us to keep up-to-date on the latest Coke research. For those cloistered few who haven't heard, a violent reaction occurs when the candy, Mentos™, is added to Diet Coke. This reaction is found on many YouTube videos and video at other places on the Internet [1]; and it was the subject of a MythBusters episode [2]. In short, a pack of Mentos candy dropped into a bottle of Diet Coke will result in the forceful ejection of a foamy stream of liquid from the bottle opening. With all this experimental confirmation, it was time for a scientific explanation [3-4].

The Appalachian State University in Boone, North Carolina, may not be a physics hot spot, but a physics professor there, Tonya Coffey, has published a paper in the American Journal of Physics on the Diet Coke-Mentos reaction [4]. The aforementioned MythBusters episode suggested several hypotheses for the reaction, including the presence of various ingredients in the candy and soft drink (gum arabic, gelatin, caffeine, potassium benzoate and aspartame). Although MythBusters does take a scientific approach, its main purpose is entertainment. No controlled experiments were done on this reaction, so no definitive mechanism for the reaction could be ascertained.

To elucidate the reaction mechanism, Coffey did controlled experiments in which she varied the reaction parameters and recorded the distance of liquid ejection from bottles tilted ten degrees from vertical. She found that both fruit and mint Mentos worked, giving a seven meter ejection. Caffeine-free Diet Coke works just as well, eliminating caffeine as an important element. Furthermore, the acidity (pH) of the liquid does not change in the reaction, so this isn't like the baking soda-vinegar experiments we conducted in our youth. The principal reason for the Diet Coke-Mentos reaction is the rough surface of the candy, which allows nucleation of bubbles of the dissolved carbon dioxide in the soft drink.

Since lower surface tension allows more rapid bubble growth, the diet drink, which lacks sugar, performs better than regular Coke, since sugar increases surface tension. The gum arabic coating on the candy aids the reaction, also, since gum arabic is a surfactant; that is, it reduces surface tension. The process for addition of the candy pieces to the liquid is an important factor, also. Since the candy pieces are dense, they fall quickly and generate bubbles as they fall. Smaller candy pieces generate fewer bubbles as they fall.

## June 16, 2008

### Fifty Years of Velcro

Biomimetics, also known as Bionics, is the use of natural forms and processes to engineer solutions to technical problems. Biomimetics seems to be a new technology area, but it's been around for quite some time. One early example is the peristaltic pump, much beloved by wet chemists, process engineers and dialysis patients, which mimics the action of the intestine. Another is Velcro, inspired by the tendency of burdock burrs to stick to clothing. The burrs are the seeds of burdock, and their stickiness is an aid in seed propagation.

As a vindication of the expression, "Chance favors a prepared mind," [1] the Swiss electrical engineer, George de Mestral, noticed on a hunting trip in 1941 how well the burdock burrs stuck to his clothing, and he decided to put the effect to good use. His microscopic analysis showed that the burdock burrs were covered with hooked spines, but it took de Mestral many years to launch a viable product. It was only in 1957 that Velcro manufacture was established in the United States, in Manchester, New Hampshire. Since Velcro is so useful as a fastener, the world market blossomed in 1978 when the Velcro patent expired. Velcro is good not only for clothing fasteners, but for keeping objects in place. The US space shuttle contains hundreds of feet of Teflon-polyester Velcro strips to fix objects that would float away because of weightlessness.

Whence the word, "Velcro?" George de Mestral combined the French words velours (velvet) and crochet (hook) to form Velcro, which is a registered trademark. Velcro makes an important appearance in an episode of Star Trek: Enterprise ( Carbon Creek, Season 2, Episode 2, September 25, 2002), in which T'Mir, T'Pol's ancestor, sells the idea of Velcro to augment a boy's college fund. Yes, even the Vulcans have Velcro (Vulcro?).

## June 13, 2008

### Lazy Days of Summer

Honeywell's Morristown Headquarters, where my office and laboratory are located, is on a summer hours schedule. On this schedule, we work a putative nine hours Monday-Thursday, and four hours on Friday. Many of us, me included, choose to use half vacation days to obtain a four day work week for the summer. It's an energy-saving tactic, both for my own energy, and the two gallons of gasoline I won't burn on my daily commute. As a consequence, this blog is on a summer schedule with four articles, Monday-Thursday, each week.

"Those Lazy Hazy Crazy Days of Summer" was a 1963 recording of Nat King Cole. It wasn't that popular, climbing to just six on the Billboard Hot 100 Chart, but it expressed an idyllic sentiment (Lyrics by Charles Tobias):

Roll out those lazy, hazy, crazy days of summer
You'll wish that summer could always be here

## June 12, 2008

### Indistinguishable from Magic

The Wizard of Id is an enjoyable cartoon serial originated by Brant Parker and Johnny Hart in 1964 and continued by Parker's son, Jeff Parker, and Johnny Hart in 1997. A recent Wizard of Id cartoon has a student explaining his Political Science major - "It's like science fiction, only less relevant." There's a veiled admission here that something about science fiction is "relevant."

It's not difficult to find many examples of inventions before their time in science fiction. Arthur C. Clarke, whom I eulogized in a previous article (Arthur C. Clarke, March 28, 2008), said, "Any sufficiently advanced technology is indistinguishable from magic." We have only to look at the last hundred years to get an idea of what this means.

My favorite prognostic SF novel is the 1933 work, The Shape of Things to Come by H.G. Wells [1], which was made into the 1936 film, Things to Come (William Cameron Menzies, Director) [2]. This novel is especially interesting, since the technocrats save the world from endless war, but they must still battle the Luddites in the new world they've created. You haven't seen a large-screen TV until you've seen the version in the movie. It's interesting how the Luddites in this movie, and those of today, use technology to further their technology-bashing agenda.

In 1870, Jules Verne had an example of the modern submarine in his book, Twenty Thousand Leagues Under the Sea [3]. This idea was updated to the era of actual nuclear submarines in the 1961 movie, Voyage to the Bottom of the Sea (Irwin Allen, Director) that presciently introduced the concept of global warming. The global warming in the movie, however, was induced by meteors setting fire to the Van Allen radiation belt. This movie was spun-off into the enjoyable television series, Voyage to the Bottom of the Sea (1964-1968), which used special effects models, stock footage and props from the movie [4].

Jules Verne didn't write The Time Machine, but you wonder whether he actually had one [5]. Verne's novels predicted not just the submarine, but the helicopter, and such incidental consumer products as the film projector. His novel, Paris in the 20th Century, gives accurate descriptions of air conditioning, automobiles, the Internet, and television. Verne's From the Earth to the Moon [6] contains many details of the Apollo Program; namely, there are three astronauts, launched from Florida, and recovered in an ocean landing.

I don't intend to diminish Verne's prognostic ability, but if a person in Verne's age were asked to develop a "wish list" of things he would like invented, things like air conditioning, powered flight, and television would likely make the list. I think the important step here is the list. What would be on your list? It reminds me of the Underpants Gnomes whose business plan is summarized as

1. Collect underpants
2. ???
3. Profit

No one in the gnome organization knows what's involved in the second step, but everyone assumes that someone does, so they carry on with their important collection task. Our take on this would be the following:

2. Show it to your scientists and engineers
3. Profit

Profit you will, since scientists and engineers do things that are indistinguishable from magic to the general public.

## June 11, 2008

### Fresnel Telescope

Optics is one of the most interesting areas of physics. In the past, it was an area in which you could actually see your results, but the discovery of detectors and emitters for wavelengths from radio through x-rays have expanded optics into a huge playing field. The fact that radiation of any wavelength can be described by both amplitude and phase allows manipulation of radiation in many novel ways. The manipulation of light began with the mirror, used by humans for many millennia, and the lens. The burning lens, a biconvex lens used to concentrate solar radiation, was mentioned in The Clouds (Aristophanes, 424 BC). The most famous use of the lens is Galileo's telescope, which he built just a few years after the invention of the telescope by Hans Lippershey and used it to discover the moons of Jupiter.

A telescope can be formed also from a concave mirror. Such a reflecting telescope was invented a few years after Galileo's refracting telescope and perfected by Newton a short time thereafter. There is another way to image objects that uses not the refractive or reflective, but rather the diffractive, properties of light. This is the Fresnel zone plate named after a founding father of physical optics, Augustin-Jean Fresnel. A research team at the Observatoire Midi Pyrénées (Toulouse, France) has proposed a huge Fresnel telescope for use in space [1]. Since the Fresnel telescope would require two synchronized objects in space, one the Fresnel zone plate, and the other a focal plane detector at a great distance, the team presented their research proposal at the 3rd International Symposium on Formation Flying, Missions and Technologies in Noordwijk, The Netherlands, in April, 2008.

The Fresnel lens space telescope would use a sheet of metal patterned with an array of holes to diffract light to a focal point. The resolution of such a zone plate lens would be the same as for a mirror of the same size, but since the sheet blocks 90% of the light, the sensitivity would be less. There is the further problem that the focal point of such a zone plate lens would be kilometers distant, and the detector would need to hold its position in space to within a millimeter. Not only that, but if you wanted to view more than a single region of the sky, the zone plate lens would need to rotate, and the detector would need to travel a large distance. Not surprisingly, since this is diffractive optics, the system will change focus depending on the wavelength, but there are ways to correct for this using other diffractive elements at the detector. It's estimated that a thirty meter zone plate could detect Earth-sized extrasolar planets and measure their spectrum. The Toulouse team has already performed laboratory experiments using credit card sized pattern sheets of stainless steel to image objects.

## June 10, 2008

### What Falls Up

When he thought his sons were using too many nails to attach a floor, my father, a carpenter, would ask us, "Where's it going to fall, up?" Down is the direction that everything falls, but we're accustomed only to the properties of normal materials. As soon as antimatter was discovered, physicists became interested in the complementarity between the matter and antimatter worlds. The predominant feature of antimatter, and the one that makes it difficult to study, is that it combines with normal matter to produce photons in a mutual annihilation. This is the process that fuels the antimatter drive on many a fictitious spacecraft. However, antimatter has many other unusual properties. The antielectron, also known as the positron, has the same mass as an electron, but an opposite charge of equal magnitude. Forces caused by charge necessarily dominate the world, as I mentioned in a previous article (Gravitation, January 25, 2007). For example, the repulsive electrical force between two electrons is nearly 1043 times stronger than their gravitational attraction. Because of the weakness of gravitation, no definitive experiment has been done to determine the gravitational force between normal matter and antimatter. Could it be that antimatter has a gravitational repulsion against ordinary matter, and antimatter will "fall up?"

One considerable argument against the idea of a gravitational repulsion between matter and antimatter comes from Einstein's theory of General Relativity, and is summarized in what's called the equivalence principle. The equivalence principle states that gravitational mass and inertial mass are the same. In General Relativity, much proven after a century of research, observed gravitational effects are caused by a curvature of space, rather than by some mysterious force. It's very unlikely that antimatter would violate such a fundamental property of space. One argument in favor of a gravitational repulsion between matter and antimatter is the fact that our local region of the universe is composed of normal matter. The dominance of matter over antimatter is one of the fundamental unanswered questions in cosmology. Perhaps matter and antimatter repelled each other early in the history of the universe, and there was a universal phase separation that segregated antimatter somewhere else. Some models of quantum gravity would allow antimatter to violate the equivalence principle [1].

The solid state physicist and materials scientist, Bernd Matthias, once said that one good experiment is worth a hundred theoretical papers. He said this after synthesizing a material and showing that its properties were quite different from those expected in the literature. A very large group of physicists [2-3] has decided that it's time to do an experiment to measure the gravitational force on antimatter, and they've designed an experiment to accomplish this at CERN, where antiparticles are produced in abundance. The experiment, called AEGIS for Antimatter Experiment: Gravity, Interferometry, Spectroscopy, will see how antihydrogen atoms are deflected by Earth's gravity. antiprotons and positrons will be combined to form antihydrogen, a neutral atom that will unaffected by stray electromagnetic fields. Gravitational acceleration will be detected by the vertical deflection of an antihydrogen particle beam traveling a meter distance at a speed of a few hundred meters per second. This beam should be deflected a few micrometers, and the deflection will be detected by an interference effect in a Moiré deflectometer.

The AEGIS proposal was presented at the 2008 Workshop on Cold Antimatter Plasmas and Application to Fundamental Physics, Okinawa, Japan.

## June 09, 2008

### Scientist Programmers

My first introduction to science was the cinema, and there wasn't an early science fiction movie that didn't have a blinking light, spinning tape reel, computer. When I started college in the mid-1960s, my interest in computing waned when I discovered that computer programming for students involved the tedious process of punching a Fortran program onto cards; and then passing your card stack over a counter to some high priests of computerdom. They would run your card stack and give you a printout of your program's mostly error-message output after a day's delay. In those days, computers didn't give you Carpal Tunnel Syndrome. Instead you got "Engineer's Elbow" from carrying huge boxes of punch cards. This process didn't appeal to me, so I resisted learning Fortran until the late 1960s when I had access to a time-share terminal connected to a GE mainframe computer at a local air force base. Later, I learned APL on an IBM 360 in graduate school, and quite a number of languages after that. With the advent of ubiquitous personal computing, programming became so easy that it enhanced nearly every project on which I was involved. It appears that the scientist programmer is an oddity, and not the rule, which is surprising to me, since programming is such as useful tool.

This sentiment was echoed in a recent letter by David Leppinen of the University of Birmingham, in the May, 2008, issue of Physics Today [1]. Leppinen's letter, entitled "What? No code?," is a response to a book review for Introduction to Computational Science by Angela B. Shiflet and George W. Shiflet that appeared in a previous issue [2]. The reviewer of the book, Wouter van Joolingen, wrote the following in praising the book - "Let me reassure those who fear that computational science is not for them because they are not programmers: The book does not contain a single line of programming code." Leppinen comments that the number of programmer-scientists has declined at the same time that computers have become more important to the sciences. Many scientists now use "canned" programs, modern age black boxes, for their analysis tasks. Leppinen's sentiments are similar to those of Robert Lucky's article in the September, 2007, issue of IEEE spectrum [3], which I reviewed in a previous article (Pay No Attention to That Man Behind the Curtain, March 25, 2008).

The spate of articles on this topic apparently precipitated a discussion on Slashdot [4] that was initiated by an anonymous "fairly new physics professor at a well-ranked undergraduate university." He was surprised to find that a programming course wasn't required of his undergraduate students, and the rest of the faculty didn't see any problem with this. He says he would "hang my head in shame if our majors start proudly putting Excel down on their resumes." Excel was designed for finance purposes, but there are enough mathematical and statistical functions in it to convince scientists that it's all they need for numerical analysis. Matlab and Mathematica are much better tools, but they come at a stiff price, both for purchase and in learning curve. The exact language a scientist learns isn't important, but there are extensive analysis libraries available for the two languages currently popular among physicists, Fortran and C. In particular, the GNU Scientific Library (GSL) for C/C++ is free, and it provides most routines required for scientific analysis of data. It may be too late to teach some old dogs new tricks, but secondary school students interested in science should learn a programming language.

## June 06, 2008

### An "L" of a Prize

Before the era of ubiquitous electronic gadgets, the principal use of electricity was for lighting. Even today, lighting is responsible for about 22% of the total electrical usage in the US. Although commercial offices use fluorescent lighting almost exclusively, most home lighting is via inefficient incandescent lamps. Unfortunately, many consumers, me included, have resisted using compact fluorescent lighting in our homes because of their toxic chemical content, cheap design and construction causing a potential fire hazard, and radio frequency interference. The unit of luminous efficiency is lumens per watt. An "ideal" white light source would have a luminous efficiency of 242.5 lumens per watt. An incandescent bulb has an efficiency of 10 - 15 lumens per watt, depending on its wattage rating (e.g., a hundred watt bulb is more efficient than a forty watt bulb). An efficient fluorescent light has a luminous efficiency of a hundred lumens per watt.

As I mentioned in a previous article (Some Like It Hot, February 28, 2007), General Electric has developed an improved incandescent light scheduled for sale in 2010. Technical details are lacking, but this bulb, called the high efficiency incandescent lamp (HEI), has a claimed efficiency of 30 lumens/watt and a possibly higher efficiency with further development. GE claimed in February, 2007, to have invested more than \$200 million in the development of energy efficient lighting. Ceramic discharge metal halide lamps (Plasma Lamps, June 08, 2007) have been made with a luminous efficiency of up to fifteen lumens per watt, and they may reach 30 lumens per watt.

To encourage further development of efficient lighting, the U.S. Department of Energy (DOE) has announced a Bright Tomorrow Lighting Prize competition, also called The L Prize [1]. The L Prize competition will award cash prizes, and the government will be committed to buying lighting from the winners. The general requirement in the category for an incandescent lamp replacement is for a low cost, mass-manufacturable light with a luminous efficiency of about five times that of an incandescent light. The DOE claims that substitution of all sixty watt bulbs with the L Prize light equivalent will save the US about 34.0 terawatt-hours of electricity per year, and it will avoid 5.6 million metric tons of carbon emission. The power savings is enough to service the electrical requirements of 17.4 million U.S. households. More details of the L Prize can be found in the references [1-5].

## June 05, 2008

### Carbon Nanotube Substrates

Silicon is a useful material, not just for electronics, but for mechanics as well. Micromechanical devices, such as resonators and actuators, are displacing traditional macro-sized devices to allow a further miniaturization of systems. One problem inherent in this technology is that the cost of silicon is very sensitive to energy cost. Silicon, as used in electronics and micromechanical devices, is a single-crystal formed by solidification of molten silicon in an orderly fashion onto the face of a "seed" crystal. The usual technique for doing this is the Czochralski process, a process I used to produce single crystals of an oxide material two decades ago. This process requires melting a large quantity of silicon at 1420oC and keeping it molten for an extended period. The term, "large quantity," is an understatement. A commercial silicon crystal for producing 300mm diameter silicon wafers weighs several hundred kilograms [1].

Carbon nanotubes have high mechanical strength, and carbon is an inexpensive material. Carbon nanotubes are typically grown on silicon wafers, but if the nanotubes themselves could be formed into a useful substrate it would be a huge advance in the state-of-the-art. A recent paper in Nature Nanotechnology by scientists from the Nanotube Research Center of the Japanese National Institute of Advanced Industrial Science and Technology (Tsukuba, Japan), along with Robert C. Davis, a physicist from Brigham Young University (Provo, Utah), describes a process for fabrication of substrates from carbon nanotubes [2-3]. These substrates can be processed by traditional silicon etching techniques, and the research team has demonstrated some functional micromechanical elements on them.

The process works as follows. Carbon nanotubes are grown by traditional techniques onto a wafer. These vertically-aligned nanotubes are widely-spaced, but the surface tension of an added alcohol solution causes the nanotubes to draw themselves into a dense assemblage. The assemblage functions as a wafer for subsequent processing.

## June 04, 2008

### Contingency

My son married a lovely woman on May 31, 2008. The reason he married this particular woman, and not another, is because Seton Hall University has a radio station. Of course, all the other obvious reasons apply, but the happy couple would not have met if my son had not been a student at Seton Hall; and he attended Seton Hall since he liked their radio station. The idea that things happen only because other things have happened is the philosophical notion of contingency. Contingency is not the same as randomness or accident; it's an unpredictable sequence of antecedent causal states [1].

The idea of contingency is generally known through its use by Aquinas, who followed Aristotle in thinking that all events have a cause. Aquinas used causality in a proof of the existence of God called The Argument from Contingency [2-3]. However, the modern debate on contingency owes its existence to a scientist, the paleontologist, Stephen Jay Gould. Gould's book [4], "Wonderful Life: The Burgess Shale and the Nature of History," which is an exposition of the fossilized life forms found in the Canadian geological formation known as the Burgess Shale. Gould wondered what would have become of life on Earth if some of these organisms had not existed. Gould wondered what would happen if the "tape of life" was rewound to that period, and then replayed with a few small changes. Contingency is such that any small change is amplified greatly over the course of time, and there's the possibility that I wouldn't be writing this article if some trifling detail was different in the past. For a modern day exposition, see the Simpson's episode, Time and Punishment, in which Homer Simpson builds a time machine, kills a mosquito in the distant past, and then returns to the present to witness horrific change.

This replaying of evolution has been done experimentally on a small scale using bacteria. Scientists at Michigan State University (East Lansing) monitored twelve identical colonies of E. coli bacteria for twenty years, which is 40,000 generations. After about 31,500 generations, one colony of the twelve was able to absorb a nutrient E. coli does not absorb. Further investigation showed that this ability was a result of a mutation at about 20,000 generations, compounded with a later mutation. Says Richard Lenski of the Michigan team, "I would argue that this is a direct empirical demonstration of Gould-like contingency in evolution." [4]

Many writers of science fiction have pondered what the world would be like if certain things were invented before their time. For example, "The Difference Engine" by William Gibson and Bruce Sterling explores the idea of the computer, and complex steam-driven technology, being developed in Victorian England. On a personal level, contingency says that what we technologists do today will have exponential consequences in the future.

References:
1. Michael Shermer, "Glorious Contingency" (Metaviews Views, February 16, 2000).
2. The Argument from Contingency (Philosophy of Religion Web Site)
3. The argument from contingency (Wikipedia).
4. Patrick Barry, "Replaying evolution" (Science News, June 2, 2008).
5. Stephen Jay Gould, "Wonderful Life: Burgess Shale and the Nature of History," ISBN 0-09-927345-4.