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February 29, 2008

The Art of the Periodic Table

The visual arts have always been aided by technology. There's the simple fact that our technological age gives people the time to create and enjoy art; and it often gives people enough money to buy works of art and support the starving artists in our communities. There is also the fact that artists are able to use technology in the creation of their art. In the area of painting alone, there's the development of pigments (which I mentioned in a different context in a previous article), older devices such as the camera obscura, and the newer computer image creation and manipulation programs. The science journal, Nature, regularly contains articles by the noted art historian, Martin Kemp, who writes about the connections between art and science. Kemp has a personal web site with a bibliography of his publications relating to art and science.

The periodic table of the elements is the centerpiece in the practice of chemistry, and it's important to all technical fields, so it's something that invokes the interest of artists and the general public. In one example, a craftsman built a periodic table that's an actual wooden table. He's also stuffed as many samples of elements he could obtain into chambers beneath their chemical symbols.

Another interesting arts project involving the periodic table is the 2007 Periodic Table of the Elements Printmaking Project in which ninety-six printmakers produced 118 prints to populate a periodic table. Each print, produced as a woodcut, linocut, or monotype, or by such techniques as etching, lithography, and screen-printing, represent the element to which they are associated. Sometimes the choice of image is easy. Helium gets a balloon. Sometimes the choice of image is more abstract. Gallium, for example, is represented by a rooster, since the Latin word for rooster is gallus. The discoverer of gallium, the Frenchman Lecoq de Boisbaudran, named the element after the Latin name for France (Gallia), but it's interesting that le coq is rooster in French. Silicon, of course, gets an electronic calculator. High resolution images of many of the elements are available on a Flikr Group. My favorites are


The originator of the project, who goes by the internet name AzureGrackle, says that one inspiration for the project was his mother, who taught high school chemistry and physics for 30 years [2]. He hopes to get the project published as a coffee table book, calendar and a deck of flash cards. He says that the project has made him much more familiar with the elements than he was in high school, and this art project might make learning the elements easier and more enjoyable to students.

1. Art Aids Science (August 21, 2006).
2. Art and Science Converge: The Periodic Table Printmaking Project (Etsy.com, January 10, 2008).
3. Periodic Table Printmaking Project (Flikr.com).

February 28, 2008

Magnetic Sound Recording

Now that music is recorded digitally, the analog magnetic tape recorder is fading from existence. Its most recent home incarnation, the tape cassette recorder, is just the last in a long list of magnetic recording devices. Before the cassette, there were reel-to-reel recorders; and before those, there were wire recorders. Recording music on a wire? Yes, it's possible, but first some background.

The tape in magnetic tape recorders is a polymer (generally acetate) tape coated with a powdered magnetic material. The magnetic material is usually a type of iron oxide, but there was an effort by tape manufacturers to differentiate their products by improving the magnetic properties of the magnetic powder, especially the saturation magnetization. This increased saturation magnetization translated into an improved signal-to-noise ratio for recordings on certain recorders. That's why cassettes are labeled "Type I" and "Type II."

The recording process used an electromagnet, the tape head, to imprint on the moving tape a magnetism that varies with the sound amplitude. On playback, the complementary function of the tape head is used to create a voltage from the varying magnetic field as the tape moves. There are some tricks that have been developed over the years to improve the fidelity of magnetic recording, the most important of which is biasing the magnetic particles at a linear portion of the hysteresis curve of their magnetic response. This is accomplished by adding a high frequency signal, above the range of human hearing and generally above the range of the playback electronics, to the recorded signal.

The idea of magnetic recording was conceived by Oberlin Smith in 1877, and demonstrated in 1898 by Valdemar Poulsen, long before the invention of the vacuum tube. Steel tape was used in the early days of magnetic recording, since it's easy to produce, and it's magnetic; but you can imagine the weight of tape required to record for even a short time. The motors needed to move such a large mass of metal were huge. Soon thereafter, there was the idea of using a steel wire, rather than a tape, but inevitable twisting of the wire led to problems. This is because the magnetic field on the wire was aligned one way during recording, but a slightly different way during playback. This problem was solved by magnetizing the wire longitudinally, that is, along its length, rather than perpendicularly through the wire.

The speed of the wire past the tape head was quite fast, usually 24 inches per second, so a one hour recording required 7,200 feet of wire. The wire, however, was very fine, just a few thousandths of an inch in diameter, so the wire spools were small. This speed is close to the speed of early studio tape recorders (15 and 30 inches per second), but quite a bit faster than a cassette tape (15/32 inches per second). I've seen many tape recorders, including some expensive multi-channel analog studio recorders, but I've never seen a wire recorder. Home tape recorders were introduced at about the time I was born, and they quickly replaced wire recorders. Recently, a wire recording was in the news because it won a Grammy Award, and it owes its existence to some mathematics and computer algorithms [1].

The audio wire recording was made at Rutgers University in 1949 at a Woody Guthrie concert. Woody Guthrie (1912-1967), the American songwriter and folk musician who wrote This Land is Your Land and Hard, Ain't It Hard, stopped giving concert performances during the transition from wire recording to tape recording, and there had been no extant concert recordings of Guthrie. When this wire recording was discovered, the first problem was transfer of the audio information to a modern digital format, but that wasn't all that was required. Wire recordings had acceptable sound quality when recorded and played on the same machine, but since wire recorders lacked the speed-controlling capstan of tape recorders, the actual speed of the wire would vary over the time of the recoding. Furthermore, stretching of the wire would vary the playback speed in a random fashion.

The technique used by the audio engineers to correct the recording speed on this wire recording relied on some internal frequency references. All live recordings have some background noise, and many of these noises, such as those from fan motors, are rhythmic. Also, there's the typical 60 Hz and 120 Hz noise caused by the electrical mains, and the internal high-frequency bias signal on the wire. Through use of these internal frequency standards, the proper speed adjustments were made to the concert audio, and the concert was released on a CD in September, 2007 [2]. The CD was nominated for a 2008 Grammy award, and it won in the "Historical" classification.

1. Julie J. Rehmeyer, "The Grammy in Mathematics" (Science News Online, vol. 173, no. 6, Feb. 9, 2008).
2. The Live Wire - Woody Guthrie In Performance 1949 (Nora Guthrie and Jorge Arvalo Mateus, compilation producers; Jamie Howarth, Steve Rosenthal, Warren Russell-Smith and Dr. Kevin Short, mastering engineers). Available for purchase at http://woodyguthrie.org/mm5/merchant.mvc.
3. "Using Digital Tools to Repair Analog Audio," Robert Siegel interview with Jamie Howarth, February 19, 2007 (NPR).

February 27, 2008

Paint it Black

A common optical metrology instrument is the integrating sphere, a large, hollow sphere coated on the inside with barium sulfate powder. Barium sulfate is a very pure white, so it's an ideal diffuser of light. The total light output of any light source placed in an integrating sphere will bounce around inside. Viewing a calibrated area on the inside of the sphere through a small porthole allows very accurate measurement of the total optical power of the source and its optical spectrum. Scientists have recently created a perfect optical complement of white barium sulfate. It's a nearly ideal black surface that absorbs all the light incident on it from all angles and at all wavelengths [1].

It's not surprising that the starting material for this ideal absorber is carbon, since carbon black is used extensively as a blackening agent. This ideal absorber is prepared by growing an array of vertically aligned carbon nanotubes on a substrate. The array of nanotubes effectively "traps" any incident light. This textured surface has a diffuse reflectance of just 10-7, which is a factor of ten lower than standard low-reflectance carbon surfaces, and the integrated total reflectance of the surface is only 0.045%. The research team from Rensselaer Polytechnic Institute fine-tuned the density of the nanotube array to achieve minimum reflectance. One application of this technology would be an efficient light harvester for solar energy devices. Details of this research have been published in Nano Letters [2].

In a previous article (Black Gold, November 29, 2006), I reported on the creation of extremely black surfaces by treating metal layers with short, intense pulses of laser light from a femtosecond laser. This laser treatment produces a metal surface with a convoluted nanoscale topography of large surface area, rendering it into an optically absorbent light trap much like the carbon nanotube array. Another method of producing an optical absorber is to evaporate gold in the presence of a rarefied inert atmosphere, such as argon or nitrogen at 750 millitorr pressure. In losing energy to the inert gas molecules, the gold atoms cool and cluster before attaching to a substrate, producing a rough surface topography. This roughened gold is a good optical absorber called black gold.

Paint It, Black was the title of a 1966 recording by The Rolling Stones. Black was a popular mantra in 1966, since another musical group, Los Bravos, had the hit recording, Black Is Black that same year.

1. Helen Briggs, "Darkest ever material created" (BBC News, January 16, 2008).
2. Zu-Po Yang, Lijie Ci, James A. Bur, Shawn-Yu Lin, and Pulickel M. Ajayan, "Experimental Observation of an Extremely Dark Material Made By a Low-Density Nanotube Array," Nano Letters, vol. 8, no. 2 (January 9, 2008), pp. 446-451.
3. Ultra-intense laser blast creates true 'black metal'.

February 26, 2008

All Your (Lewis) Base Are Belong To Us

Faithful readers of this blog might remember that I used a similar title for a past article [1-2]. The phrase, "All your base are belong to us," is from the English language version of the opening scene of the 1989 Japanese video game, Zero Wing. The English in this game is poor, and I suspect that the script was just a placeholder for a better translation that was never implemented, which is something programmers do all the time. Since this phrase is particularly humorous, it propagated on the internet quickly. You can read about "AYBABTU" on Wikipedia.

In the early days of chemistry, a base was an ionic species identified by an (OH)- group, and these complemented the ionic acids, which had an H+. This was a nice definition when chemistry dealt with simple compounds, but the prominent American chemist, Gilbert N. Lewis (1975-1946), thought it would be useful to extend the acid-base idea. Lewis defined an acid as an electron acceptor, and a base as an electron donor, and these acid-base units could combine their electrons to form a covalent bond. The electron dot structures that you may have used in your introductory chemistry courses to illustrate valence bond theory were invented by Lewis more than a hundred years ago. Lewis and Merle Randall (1888-1950) wrote an influential physical chemistry textbook [3] that was still useful in my graduate school years. Lewis also coined the term, "photon."

Studies on acid-base reactions have been undertaken for more than a century, so you wouldn't think that there would be any new discoveries, especially in the reaction in which the simple base, ammonia (NH3), reacts with the simple acid, HCl. The interesting thing about this reaction is that if you introduce a single molecule of ammonia to a single molecule of HCl, no reaction takes place. However, when you have a solution of ammonia and HCl in water, the ammonia eagerly bonds to the hydrogen of HCl and attracts the resulting Cl- ion to form an ammonium chloride (NH4Cl) molecule. It was suspected that electron charge from other molecules aids the reaction, and the actual product is [NH4+Cl-]-, and not neutral ammonium chloride.

A team of chemists from Johns Hopkins University, the Universität Karlsruhe, Pacific Northwest National Laboratory, the University of Gdansk, and the Heriot-Watt University, decided to unravel the true nature of this acid-base reaction by the simple technique of running the reaction in reverse [4-5]. Starting with molecules of [NH4+Cl-]-, they used light to remove the extra electron, and the molecules immediately separated into NH3 and HCl. They also solved another mystery, as to whether the interaction between NH3 and HCl was by a weak hydrogen bond, or a strong ionic bond. Their conclusion is that the bond is the weaker hydrogen bond.

Nowadays, every scientist needs to justify his research. The supposed application of all this is the control of reactions to make them environmentally friendly. Gilbert Lewis didn't need to make excuses for his work. He just did chemistry.

1. All your base are belong to us December 8, 2006.
2. All Your Base (Continued) December 11, 2006.
3. G.N. Lewis and Merle Randall, "Thermodynamics and the Free Energy of Chemical Substances," 1923; Gilbert Newton Lewis and Merle Randall (Revised by Kenneth S. Pitzer and Leo Brewer), "Thermodynamics, 2nd Edition," McGraw-Hill Book Co. (New York, 1961).
4. Soren N. Eustis, Dunja Radisic, Kit H. Bowen, Rafa A. Bachorz, Maciej Haranczyk, Gregory K. Schenter, and Maciej Gutowski, "Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia," Science, vol. 319, no. 5865 (February 15, 2008), pp. 936-939.
5. Mary Beckman, "All alone, ammonia and hydrogen chloride use negativity to get attached" (DOE/Pacific Northwest National Laboratory Press Release, February 14, 2008).

February 25, 2008


One of the few things most physics students remember about magnetism is the right-hand rule, an aid for visualizing the force induced by a magnetic field on a charged particle. There is a special case in which the charges (electrons) are hidden, but they are known by their effect (current). In that case, the left-hand rule is used to show the force on the current-carrying conductor in a magnetic field. Since current flow in a wire generates a magnetic field around the wire, a simple application of the left-hand rule to a loop of wire shows that there is a new force acting to expand the loop. Anyone who has discharged a large capacitor through a wire, or has operated a spot welder, has seen this effect - the wires move. A simple leap of imagination to a current loop in which one of its sides is moveable as a sliding conductor on a pair of current carrying rails leads to the concept of a railgun. The force acting on the moveable element allows it to slide on the rails. If the current is sufficiently high, the moveable element will accelerate down the rails and will eject from the rail ends. The theory is simple, but a practical application requires considerable materials technology.

• A current source of millions of amperes is required to accelerate kilogram masses to high velocity.

• The rails, and at least a portion of the payload, must have high electrical conductivity.

• There must be a high electrical conductivity between the sliding payload and the rails, otherwise the current will be limited.

• The current in the rails creates considerable heat that scales with the square of the current.

Friction between the payload and the rails will generate additional heat, and there will be erosion of the rails by the rubbing payload.

• The rails should have a high thermal conductivity to dissipate the heat caused by friction between the payload and the rails.

There are quite a few methods of creating large currents. One, well known to welders, is to charge a large capacitance at a slow rate with a modest current source, and then discharge the capacitor quickly. A homopolar generator is an electrical generator designed to produce large currents at low voltage, a combination that's ideal for railgun power. Another generator type is the compulsator (short for compensated pulsed alternator), which stores energy in a rapidly spinning flywheel. A more exotic method is the explosively-pumped flux compression generator (EPFCG) in which compression of magnetic field lines leads to a high induced current. This is a consequence of Faraday's law of induction, which states that the induced electromotive force in a closed loop is directly proportional to the rate of change of magnetic flux through the loop. In the case of EPFCGs, the rate of change of magnetic field is very large because of the explosive compression of the medium creating the magnetic field. EPFCGs have produced peak currents of nearly a gigaamp. The major disadvantage of an EPFCG is that it's destroyed when used, and in a railgun application we would just be substituting one method of payload launch by explosives for another.

The materials requirements for rail guns are similar to the mutually exclusive requirements that face materials scientists daily. For example, pure metallic elements, such as aluminum and copper, have excellent electrical conductivity and thermal conductivity, but low strength. High strength is required in railguns, since the same forces acting to propel the payload will act on the rails themselves. Strength in metals is generally accomplished by the addition of alloying elements, or by mechanical operations such as forging and drawing. These strengthening processes lead to diminished electrical conductivity. One solution to this problem is to fix a conductive outer layer on an alloy rail, but conductive metals are soft, and they do not wear well. What's left is a series of compromises, but that's what materials science is about.

There may be a physical limitation to the maximum velocity achieved by a railgun payload. This is a consequence of the inductance of the rail loop. Inductance is the property of electrical circuits that limits the rate of change of current. Railgun inductance scales with the length of the rail in a complex fashion. All these problems have not prevented some spectacular test of railguns, although most of these have been single-shot tests, since the rails were severely damaged for the reasons cited above. Just last month [1], a US Navy railgun at the Naval Surface Warfare Center Dahlgren Division fired a payload with an exit velocity of 2,520 meters per second. The projectile had an energy of 10.64 megajoule.

1. "Electromagnetic Railgun: An Innovative Naval Program" (US Navy Press Release, February 8, 2008).
2. Railgun FAQs (US Navy).
3. Frank Jin, "Railguns from the late 1800s to 1980".

February 22, 2008

Nuts and Bolts

My favorite piece of hardware is the 6-32 bolt. For the uninitiated, these bolts have 32 threads per inch on a 0.138-inch outside diameter shaft. Unlike wire sizes, where smaller gauges mean larger diameters, bolts follow a more logical standard in which smaller numbers signify smaller diameters; so my next favorite bolt, the 4-40 is somewhat smaller (0.112-inch diameter). The number six bolt fits nearly every component of the vacuum tube era, including tube sockets, terminal strips and panel knobs. These bolts provided both mechanical attachment and electrical connection. There's a lot of mechanical engineering and materials science in joining with bolts, and all this is essential when you're looking for the most cost-effective way to fasten components at an anticipated load in a particular environment. I'm not qualified to give authoritative advice on bolt selection, but I can give an historical background.

Archytas of Tarentum (428 BC - 350 BC), a contemporary of Plato, is credited with the invention of the screw thread, the first application of which was the olive oil press [1]. It wasn't until the Industrial Revolution, when large quantities of fasteners were needed, that standards developed. In the 1840s, Joseph Whitworth (1803 - 1887) in England devised a standard based on a sampling of screws in use at the time. The Whitworth standard had a uniform thread flank of 55 degrees and a variable number of threads per inch dependent on the bolt diameter. In 1864, William Sellers (1824 - 1905) proposed [2] a simpler thread with a 60 degree flank, and this evolved into two US standards, the American Standard Coarse Series, known simply as NC, and the American Standard Fine Series, or NF, which are still in use today. The principal advantage of the Sellers thread is its ease of manufacture. The Sellers thread has a flat root and crest, while the Whitworth thread has a rounded root and crest.

Sellers patented his screw design, and about ninety other mechanical inventions. He knew what the machine trades needed, since he started his career as an apprentice machinist at age fourteen, eventually owning his own machine shop by the age of twenty-one. He served in various capacities at the Franklin Institute in Philadelphia, and it was at an Institute meeting on April 21, 1864, that he introduced his screw system in a talk entitled, "On a Uniform System of Screw Threads." Sellers' thread system was adopted by the US Navy in 1868 after a technical study, and it became widely used by the US government within a few years [3]. This early adoption by the government hastened its use in commerce.

I mentioned the use of the 6-32 bolt in electronics. I subscribe to Nuts and Volts magazine, which presents simple electronic construction projects.

1. Historical Background on Screw Threads (BoltScience.com).
2. William Sellers, "On a Uniform System of Screw Threads," J. Franklin Inst., vol. 77 (1864), pp. 345-351.
3. James Surowiecki, "Turn of the Century" (Wired News (Issue 10.01, January, 2002).
4. Fastrenal Technical Reference Guide (PDF File).
5. Bolted Joint (Wikipedia).
6. Examples of Bolt Failure (BoltScience.com).

February 21, 2008

Wallace and Gromit Meet the Monads

The clay animation (a.k.a., Claymation®) character, Wallace, of Wallace and Gromit fame, has a definite appeal to technologists. Wallace is the inveterate inventor who finds technological solutions to common, everyday problems. Wallace is made of clay; or, more accurately, the artificial clay called Plasticine. Plasticine is composed mainly of chalk (calcium carbonate), petroleum jelly and stearic acid. It was patented in 1899, but its exact formulation is not published. Plasticine has much to recommend itself, since it is non-toxic, sterile, and will not harden upon exposure to air like water-based Play-Doh.

Plasticine is the primordial material in the Wallace and Gromit world, since the entire world is built from that one substance. One idea of a primordial substance was developed by the philosopher, Gottfried Wilhelm Leibniz, who thought that every material of the universe was composed of individual units called monads. His idea of the nature of monads and how they combine to form material substances is contained in his treatise, Monadology (1714). It's atomism as viewed from the standpoint of a philosopher, not a physicist.

Building more complex objects from identical and simple building blocks has much to recommend itself. Researchers at Carnegie Mellon University (CMU) and elsewhere are using this methodology to build robots [1-3]. At CMU, "claytronic robot atoms," named "catoms," are ringed with electromagnets to bond together to form a "claytronic robot." [1] These robots don't have wheels, but they are able to move by changing shape. Their catoms are macro-sized for now, but the CMU team is experimenting with smaller units. Hardware is one problem, but writing software to have these swarm robots function autonomously is a major problem, since the changeable whole is greater than the sum of its parts.

For software development, some robotocists are taking their cue from the swarm behavior of insects, such as ants. I described a similar strategy for parameter optimization in a previous article (Ants in My Computer, November 8, 2006). A European research team [2] has used swarm intelligence to have smaller robots team together to move heavy objects. The individual robots follow simple rules that allow an intelligent collective behavior. In this case, the rules were allowed to evolve by genetic programming. The robots communicated with each other using colored lights.

Roboticists at the Swiss Federal Institute of Technology in Lausanne and the University of Lausanne used similar evolutionary programming techniques to develop a generation of robots that can "feed" more efficiently from their environment [3]. The robots were placed in an environment that contained both "food" and "poison." Initially, the robots could only differentiate food from poison by touch, but they had the ability to send and receive flashing light signals. At that point, there was no robot "language" to express the words "food" and "poison," but after several hundred generations, inter-robot communication about food and poison was established through natural selection. Of course, a few rogues will always be born, and some robots produced misleading signals, perhaps to hoard the food for themselves. That these rogues will persist after many generations of natural selection possibly tells us a lot about our own human nature.

Fans of the Stargate SG-1 television series may remember the Replicators, a race of self-replicating machines composed of modular blocks. These modules come together into larger forms to accomplish tasks, not unlike the claytronic robots. Now, if they could just assemble themselves into clones of SG-1 team member, Samantha Carter...

1. Tom Simonite, "Shape-shifting robot forms from magnetic swarm" (New Scientist Online, January 29, 2008).
2. Tom Simonite, "Robot swarm works together to shift heavy objects" (New Scientist Online, October 17, 2006).
3. Tom Simonite, "Robot swarms 'evolve' effective communication" (New Scientist Online, February 23, 2007).
4. (Ants in My Computer, November 8, 2006).

February 20, 2008

Cellulosic Ethanol

One criticism of ethanol as a fuel source is that most ethanol production processes use a foodstuff, typically corn, as the starting material. It's a lot like a "guns and butter" scenario in which wealthier individuals, in order to fuel their SUVs, drive up food prices for the poor (Confession - there's an SUV in my family). Butanol, which can be produced by fermentation of biomass, is another alcohol being considered as an alternative fuel. Butanol's energy content is closer to that of gasoline, but it's less volatile than ethanol, which leads to problems with starting a vehicle on cold days.

For comparison, typical unleaded gasoline has an energy content of 115 kBTU/gallon; ethanol has 84 kBTU/gallon; and Butanol has 110 kBTU/gallon. A BTU is a British Thermal Unit, defined logically as the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This is a convenient way to envision heat energy, at least in the US, so this unit has persisted. The problem with this unit, aside from the non-metric units, is that it takes a different quantity of heat to raise the water temperature at different temperatures. That problem notwithstanding, the International Organization for Standardization (ISO) decided to use 1055.056 joules/BTU as a conversion factor. The precision of this conversion factor belies the inaccuracy of the BTU as a unit.

Ethanol derived from non-food sources would be a better fuel source, and that's where cellulosic ethanol enters the arena. Cellulosic ethanol is ethanol produced from lignocellulose, which is abundant in such non-edibles as wood residue, waste paper, corn stover (stalks and straw), and grasses. Turning the annual hundreds of cubic feet of grass clippings and fallen leaves from my property into a useful energy product is an exciting idea, but these materials are more difficult to convert into ethanol than corn. Coskata, an Illinois biofuel startup, claims to have a process for manufacture of cellulosic ethanol for a dollar a gallon [1]. Coskata is backed by General Motors [2], which has an interest in keeping the (outdated) concept of the private passenger vehicle alive.

The Coskata process uses a bacterial strain developed at the University of Oklahoma in a process that involves a prior feedstock gasification step. The resulting synthetic gas, or syngas, is processed by the bacteria to produce 99.7% ethanol, plus water. The Coskata-University of Oklahoma bacteria are said to be extremely efficient at their task, and the Coskata process can convert nearly the entire mass of biomass into ethanol. The Coskata-University of Oklahoma bacteria have a demonstrated resistance to syngas impurities.

The push towards more ethanol comes from the Energy Independence and Security Act of 2007, which legislates an increase in ethanol production with a goal of 36 billion gallons annual production in 2022. The Coskata process can produce five gallons of $1/gallon ethanol from two bales of hay, a savings over corn ethanol produced at $1.40 a gallon. Ethanol would likely be blended with standard fossil fuels to produce a mixture known as E85, which contains up to 85% ethanol. E85 with the Coskata process would be a dollar cheaper per gallon than gasoline. A Coskata pilot plant, scheduled for completion in about a year, will produce about 40,000 gallons of ethanol per year. Environmentally, the Coskata process generates 7.7 times more energy than is required to produce it, while corn ethanol generates only 1.3 times more energy than is used producing it. One major advantage of the process is that ethanol can be made locally from whatever biomass is available.

As in any complex system, there are hidden problems in biofuel production. A recent paper in Science [3] concludes that clearing grassland will release about 93 times the amount of greenhouse gas saved annually by biofuel production from that land; that is, it would take ninety-three years to pay back the initial carbon debt. This "biofuel carbon debt" for biofuel cultivation ranges from 17 to 420 years, depending on the crop. Sugar cane appears to be the most benign biofuel crop in this respect.

1. Chuck Squatriglia, "Startup Says It Can Make Ethanol for $1 a Gallon, and Without Corn" (Wired News Online, January 24, 2008).
2. James R. Healey, "General Motors finances ethanol maker Coskata" (USA Today, January 13, 2008).
3. Joseph Fargione, Jason Hill, David Tilman, Stephen Polasky and Peter Hawthorne, "Land Clearing and the Biofuel Carbon Debt" (Science, Published Online, February 7, 2008).

February 19, 2008

ZIF Zeolite Zaps ZO2 Zelectively

Zeolites are an interesting class of materials whose utility comes not merely from the reactivity of their component molecules, but also from their topology. Prototypical zeolite exists as a hydrated aluminosilicate mineral. It was named zeolite, from the Greek words zeo (ζεω), "to boil," and lithos (λιθος), "stone," by the Swedish mineralogist, Axel Cronstedt, who found that stones of this mineral would move when rapidly heated as their hydrated water was released. There are forty-eight natural zeolite minerals, and many more synthetic zeolites formed mainly by substitution of other cations, such as Na+, K+, Ca2+, Mg2+, into the structure. For example, the mineral, Pollucite, has the chemical formula (Cs,Na)2Al2Si4O12·2H2O. The microporous topology of zeolite can selectively encourage or inhibit chemical reactions, since confinement of reactant molecules in small spaces often changes their conformation, and thereby their reactivity. The ability of the zeolite structure to accept a wide variety of substituent atoms makes zeolite an ideal framework for an engineered material.

Recently, a group of scientists from the University of California at Los Angeles and Arizona State University has developed a synthesis technique for producing large quantities of zeolitic imidazolate frameworks, commonly called ZIFs [1-2]. The advantage of ZIFs is that they incorporate transition metal ions and organic units within their pores as an integral part of the zeolite framework. Incorporation of transition metals opens a much broader spectrum of catalytic materials. The ZIF structures produced by this group incorporate zinc and cobalt, which replace aluminum and silicon. They are stable up to 390oC in the presence of organic and aqueous media, and have surface areas of up to 1970 square meters per gram.

The importance of these newly synthesized ZIFs is that they exhibit a high selectivity for capture of CO2 over CO, and one liter of one of these materials (ZIF-69) was found to hold about eighty liters of CO2 at 0oC and atmospheric pressure. Smokestack scrubbers at power plants now use toxic materials and consume about a quarter of the plant's power output. The ZIF materials bind about five times as much CO2 as these, so they may be candidates for this application. Omar M. Yaghi, a co-author of the paper in Science [1] on this work, says [2]

"Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoir, as we have demonstrated. No carbon dioxide escapes. Nothing escapes, unless you want it to do so. We believe this to be a turning point in capturing carbon dioxide before it reaches the atmosphere."

For those of you who were wondering whatever became of combinatorial chemistry, this work was performed using combinatorial techniques. The team ran 9,600 micro-reactions and discovered twenty-five new structures in their experiments.

1. Rahul Banerjee, Anh Phan, Bo Wang, Carolyn Knobler, Hiroyasu Furukawa, Michael O'Keeffe, and Omar M. Yaghi, "High-Throughput Synthesis of Zeolitic Imidazolate Frameworks and Application to CO2 Capture," Science, vol. 319, no. 5865 (February 15, 2008), pp. 939-943.
2. Stuart Wolpert, "New materials can selectively capture carbon dioxide, UCLA chemists report" (UCLA Press Release, February 14, 2008).

February 18, 2008

The Quasisolar Extrasolar Planetary System

The discovery of extrasolar planets has become so commonplace that it's really not news anymore. It reminds me of the early days of spaceflight, when every satellite launched received front page coverage in newspapers. After several years, news coverage of satellites migrated to the back pages. A star with a confirmed presence of planets was in the news last week because this extrasolar planetary system has a strong resemblance to our own solar system, and it's located at a great distance [1-3]. This discovery was published in the February 15, 2008, issue of Science [4]. The listing of the team of 69 scientists who discovered it is as long as the article abstract, and the list contains the names of some amateur astronomers. Observations were made on eleven different ground-based telescopes in New Zealand, Tasmania, Israel, Chile, the Canary Islands and the United States. What was discovered is a slightly scaled-down version of our solar system.

Nearly all extrasolar planets have been discovered by measurements of the wobble in the position of stars as their planets pull on them as they orbit. This technique works well for large planets circling nearby stars. The discovery of planets circling what is now called OGLE-2006-BLG-109L (Named after the Optical Gravitational Lensing Experiment) was made using gravitational microlensing. In gravitational microlensing, the gravitational field of a star in between the target star and the Earth can bend and magnify the farther star's light. An analysis of the how the intensity of the light varies gives information about the star and its planets. This technique works best for distant stars, and OGLE-2006-BLG-109L is about 26,000 light years away. The star bending and magnifying its light is about 5,000 light years away.

Analysis of the light curves showed that this star has at least two planets with masses of about 225 and 85 times the mass of the Earth, orbiting at about half the distance that our Jupiter (317.8 Earth's mass) and Saturn (95.15 Earth's mass) orbit our Sun. The star they orbit is about half the size of the Sun, so the scaling of this solar system is just slightly smaller than our own.

1. Dennis Overbye, "Scientists Find Solar System Like Ours," New York Times, February 14, 2008.
2. Scott Gaudi, "Astronomers discover scaled-down Jupiter and Saturn in a faraway solar system like our own" (Ohio State University Press Release, February 14, 2008.
3. Anne M. Stark, "International team discovers new solar system with scaled-down versions of Jupiter and Saturn" (Lawrence Livermore National Laboratory Press Release, February 14, 2008.
4. B. S. Gaudi, et al., "Discovery of a Jupiter/Saturn Analog with Gravitational Microlensing," Science, vol. 319, no. 5865 (February 15, 2008), pp. 927-930

February 15, 2008


Bread has been an important human staple; so important, that the word bread is used as a surrogate for money. Most bread is made from wheat, and breads made from other grains usually contain wheat to glue everything together. This wheat glue is a protein called gluten. Unfortunately, a small fraction of people have a subtle allergic reaction to gluten that causes intestinal upset, and I'm a member of that population. Fortunately, there are substitute grain foods made from corn and rice that don't contain gluten, and a cursory look at my waistline confirms the fact that I'm not lacking for nourishment.

There's an analogy between chemistry and cooking. Much of chemistry, especially synthetic chemistry, is like cooking, and the best synthetic chemists devise their own recipes. Analytical chemists tend to use other people's recipes, but their skill lies in what recipe to use for a particular occasion. As in any other industrial process, bread making requires analytical tools. The viscoelastic behavior of gluten in bread dough is a function of its mobility, which depends on its chemical interaction with the local dough environment. Researchers from the Technical University of Denmark have applied near-infrared (NIR) spectroscopy to ascertain the affect of moisture and heat on bread gluten [1-3]. They found peak shifts and peak amplitude changes with moisture content, and they found also that heat exposure causes an increased ratio of signals at 220 and 2167-2182 nm, which is indicative of a helix to sheet transformation of the molecular conformation. They found further that adding salt caused very little change, except at high concentrations where dehydration occurs.

It's not surprising that chemists are interested in cooking, and this explains why a book, "The science of Bakery Products," has been published by no less than the Royal Society of Chemistry (RSC) [4]. This book was reviewed by Peter Martin in the December, 2007, issue of Materials Today. Martin thought the book had much useful information, but it was badly produced by the RSC.

There's a further subtle connection between bread and technology. When I was a young boy, a popular bread was Wonder Bread. Its advertising slogan was, "Wonder Helps Build Strong Bodies 8 Ways." The eight came from the number of vitamin and mineral supplements added to the bread, and the number was increased to twelve in the 1960s. This practice, initiated in the 1940s in a government-sponsored program, reduced the incidence of beriberi (caused by thiamine deficiency) and pellagra (caused by niacin deficiency). Continental Baking, which made Wonder Bread, was owned by the conglomerate, ITT. ITT was also a technology company that made munitions for the Vietnam War, and there were boycotts against Wonder Bread for that reason.

In 1974, the Federal Trade Commission charged ITT with illegal pricing in an attempt to monopolize markets for Wonder bread. According to the FTC, "ITT set profit and market goals for ITT Continental that forced the subsidiary to adopt predatory practices." ITT's problems transcended bread [5]. In March, 2007, ITT was convicted of criminal violation of the Arms Export Control Act for its outsourcing practices and fined $100 million. ITT had sent information about night vision goggles and laser weapon countermeasures to engineers in Singapore and the People's Republic of China [6].

1. Susanne Wrang Bruun, Ib Sndergaard, and Susanne Jacobsen, "Analysis of Protein Structures and Interactions in Complex Food by Near-Infrared Spectroscopy. 1. Gluten Powder," J. Agric. Food Chem., vol. 55, no. 18 (August 3, 2007), pp. 7234-7243.
2. Susanne Wrang Bruun, Ib Sndergaard, and Susanne Jacobsen, "Analysis of Protein Structures and Interactions in Complex Food by Near-Infrared Spectroscopy. 2. Hydrated Gluten," J. Agric. Food Chem., vol. 55, no. 18 (August 3, 2007), pp. 7244-7251.
3. Photonics Spectra, "NIR Spectroscopy in Breadmaking," Photonics Showcase (November 2007), page 13.
4. William P. Edwards, "Science of Bakery Products" (Royal Society of Chemistry, June 21, 2007, ISBN-10: 0854044868, ISBN-13: 978-0854044863).
5. Dividing the Loaf (Time Magazine, December 23, 1974).
6. Drew Cullen, "ITT fined $100m for shipping night vision goggles to China," The Register (March 27, 2007).

February 14, 2008

Piezoelectric Ceramics

Interesting things happen near phase transitions. The phase transition we most often see is the solid-liquid transition of materials, commonly called melting, which involves an unexpected energy, the latent heat of fusion. There are more complex transitions encountered in materials, all with their own surprises, and surprise is what got most of us interested in science in the first place. A technologically important transition is the morphotropic phase transition in ferroelectrics. As the name, "morphotropic," suggests, these materials are seeking a change, but they haven't yet decided to change. At the morphotropic phase transition, ferroelectric materials have a greater number of degrees of freedom in the arrangement of their electrical domains. This leads to larger dielectric constants and an enhanced piezoelectric effect.

The premier example of this group of materials is lead zirconate titanate (Pb[ZrxTi1-x]O3, where x can range between zero and one), commonly called PZT. As a piezoelectric, PZT generates a voltage across its crystal faces when it's strained; or, conversely, will change shape if a voltage is applied. Both of these properties are extremely useful, and they are enhanced at the boundary of a morphotropic phase transition at x = 0.52; that is, at the composition PbZr0.52Ti0.48O3. Often lanthanum replaces some of the lead to improve properties to form lead lanthanum zirconate titanate (PLZT). Common applications of PZT-type ceramics are ultrasound transducers, high capacitance ceramic capacitors, and ferroelectric random-access memory (FRAM, not to be confused with Honeywell's FRAM)

At a materials level, the morphotropic phase transition boundary is obtained from the complex solid-solution mixture of the lead, zirconium, and titanium oxides. A recent project funded by the Office of Naval Research investigated the fundamentals of this phase transition. The Navy, of course, has a keen interest in piezoelectric transducers for sonar applications. A team of scientists from the Carnegie Institution of Washington, the Argonne National Laboratory and its Advanced Photon Source, and the University of California at Berkeley, have found that lead titanate without any alloying elements can display a morphotropic phase transition when subjected to extreme pressures. They demonstrated this using a high intensity x-ray source to monitor the crystal structure of lead titanate as it was subjected to pressure in a diamond anvil cell. A diamond anvil cell uses two flawless diamonds to concentrate a uniaxial force into a high pressure between them. Computer simulations show that the electromechanical coupling of the pressurized lead titanate should be larger than that found in any other material. If these research results can be transitioned to modify ambient pressure materials, there will be a definite advance in piezoelectric applications.

1. Muhtar Ahart, "Squeezed crystals deliver more volts per jolt" (Carnegie Institution Press Release, January 30, 2008).
2. Muhtar Ahart, Maddury Somayazulu, R. E. Cohen, P. Ganesh, Przemyslaw Dera, Ho-kwang Mao, Russell J. Hemley, Yang Ren, Peter Liermann amd Zhigang Wu, "Origin of morphotropic phase boundaries in ferroelectrics," Nature, vol. 451 (31 January 31, 2008), pp. 545-548.
3. B. Noheda, J. A. Gonzalo, R. Guo, S.-E. Park, L.E. Cross, D.E. Cox, and G. Shirane, "The Monoclinic Phase in PZT: New Light on Morphotropic Phase Boundaries" 12th. IEEE International Symposium on Applications of Ferroelectrics (PDF File).
4. Andrew J. Bell, "On the origin of the large piezoelectric effect in morphotropic phase boundary perovskite single crystals," Appl. Phys. Lett., vol. 76 (January 3, 2000), pp. 109 ff.

February 13, 2008

Diversity in Science and the Oxides

During my career, I've worked with scientists of many national origins, including (but I'm certainly forgetting some)

South Africa
Viet Nam

These are just the ones with whom I've worked. I've met scientists from at least a dozen additional countries, as well. This diversity is mirrored in the periodic table of the elements. Perhaps because we are created from these same elements, there seems to be an element for every application we can imagine. There are elements that are gases or liquids at room temperature; but there are elements that won't melt until incredibly high temperatures. For example, rhenium melts at 3186oC. Practically every element bonds with oxygen, but just like the parent elements, these oxides have diverse properties as well.

My two favorite oxides are aluminum oxide (Al2O3, alumina) and zirconium oxide (ZrO2, zirconia). Aluminum oxide is an inexpensive oxide with a very high melting point (2054 oC) and a high dielectric constant. It's a useful electrical insulator. Cubic zirconium oxide, a crystal phase usually stabilized by an 8 mole-% addition of yttrium oxide, has a very low thermal conductivity, so it's useful as a thermal barrier material. Because of its low thermal conductivity, it's especially useful as a pedestal for holding platinum crucibles in high temperature furnaces. Single crystals of cubic zirconia are used as gemstones, since the refractive index is like that of diamond, and these gems are generally indistinguishable from diamonds. An acquaintance of mine who founded a company that makes cubic zirconia made an additional profit selling thermal conductivity instruments to jewelers so they could distinguish cubic zirconia gemstones from the more highly thermally conductive diamonds. Another acquaintance of mine, and a former Honeywell (née Allied Chemical) employee, is growing crystals of gem-quality diamond.

One lowly transition metal, manganese, has an oxide with an unusual property. Manganese (II) oxide, MnO, is an electrical insulator, but application of a megabar hydrostatic pressure converts it to a metallic conductor. Recent computer modeling by a diverse band of physicists at the University of California, Davis, the University of Augsburg, Germany, the Ural State Technical University and the Institute of Metal Physics, Russia, indicates that the reason for this insulator-conductor transition is that electrons that were involved with magnetism are free to be conducting electrons [1, 2]. MnO is an example of a Mott insulator, a material expected to be conducting by the usual electron band structure calculations, but is instead an insulator. In this case, the "missing" electrons are magnetically ordered, and they follow the "usual rules" at high pressures, only. Another manganese oxide, Mn3O4, is a Mott insulator, as are FeO, CoO, NiO, Cr2O3, and Fe2O3. All the elements forming these oxides share the same transition metal row with manganese.

1. Andy Fell, "How Crystal Becomes a Conductor" (UC Davis Press Release, February 5, 2008).
2. Jan Kunes Caron, Alexey V. Lukoyanov, Vladimir I. Anisimov, Richard T. Scalettar, and Warren E. Pickett, "Collapse of magnetic moment drives the Mott transition in MnO," Nature Materials Online (February 3, 2008, doi:10.1038/nmat2115).

February 12, 2008

Sonic Fire Extinguisher

One cartoon and movie cliché is the opera singer breaking a wine glass with the power of his or her voice [1]. This idea may have started with the famed opera singer, Enrico Caruso, who claimed to have done this. Breaking a wine glass became a benchmark for the power of the human voice, although video proof of this feat was lacking until recently [2]. Of course, the scientific basis to all this is acoustic resonance. If you strike a wine glass, you can hear a characteristic ring. If a driving signal is applied at this same frequency, the amplitude affect on the wine glass will be enhanced. Since glass is a brittle material, made more fragile by the presence of surface scratches, strain amplitudes above a certain limit will break the glass. We're assisted, also, by the fact that wine glasses tend to be thin.

Sound has been shown to extinguish flames, but the mechanism for this is unclear [3]. Physicist John Tyndall, who is known best for Tyndall Effect that explains why the sky is blue, reported on this fact in 1857. One theory evokes the fact that sound is just a modulation of pressure. According to the ideal gas law (PV = nRT), a pressure modulation would result in a temperature modulation. A study by students at the University of West Georgia, presented at the 2005 meeting of the Acoustical Society of America and published in abstract form in The Journal of the Acoustical Society of America [4], showed that lower frequencies had the best extinguishing affect. Frequencies between 40-50 Hz were best at extinguishing their particular flame.

One application for this technology is extinguishing fires in space. In weightlessness, conventional techniques, such as a water spray, spray of some chemical agent or a gas, would be messy. A variation of the sonic technique is to use an electric arc to generate an acoustical impulse that could be directed at a flame [3].

1. Long-Haired Hare (1949, Chuck Jones, Director)
2. Mythbusters, Episode 31: Breaking Glass, A Rolling Stone Gathers No Moss, Shop-Vac Jet Engine.
3. Alison Snyder, "When Fire Strikes, Stop, Drop and... Sing?" (Scientific American Online, January 24, 2008).
4. Dmitriy Plaks, Elizabeth Nelson, Nesha Hyatt, James Espinosa, Zade Coley, Cathy Tran, and Ben de Mayo, "Zero-g acoustic fire suppression system," Journal of the Acoustical Society of America, vol. 118, no. 3 (September, 2005), p. 1945.

February 11, 2008

Mathematics on the Web

One advantage of the internet is the variety of quality content in many specialized areas available at no charge. I think that the driving force here is that everyone thinks his specialty is the best, and if he can interest more people in it, it will lead to greater funding and job security. I mentioned in a previous article how astronomers were promoting their specialty on the internet.

Mathematics is not as exciting as astronomy. In fact, it's generally hated by the public, especially students. However, mathematicians have been promoting their art on the internet for some time. The American Mathematical Society has an excellent web site. I particularly recommend the monthly column, "What's New in Mathematics" by Joseph Malkevitch of the City University of New York, as well as the "Notices" feature. Much of the web site is understandable by non-mathematicians, although there is some content that gives you an appreciation of their intellectual prowess.

Plus is a British mathematics web site targeted at the general public. It was started in 1997 as a joint development of Cambridge University and Keele University. Plus is now a part of the Millennium Mathematics Project, a UK effort to bring mathematics to people of all ages and abilities and demonstrate its importance to science and commerce. One of its aims is "to change people's attitudes to maths [1]." The current issue of Plus has an interesting article on tiling [2]. For those of you who haven't heard of Penrose Tiling, this is a good place to start. Penrose tiles are one of the few mathematical objects that have been patented [3].

1. What Americans call "math," the British call "maths." Actually, mathematics is a better term, and it's valid in either dialect.
2. Craig Kaplan, "The trouble with five".
3. Roger Penrose, "Set of tiles for covering a surface," (U.S. Patent No. 4,133,152, January 9, 1979). Available as a PDF file here and here.

February 08, 2008

Harvesting Body Heat

When architects design an auditorium, they have a simple way of estimating the heat load on the air conditioning equipment - Every occupant is a hundred watt light bulb. An auditorium with five hundred seats will have a human heat source of fifty kilowatts when fully occupied! Here's a list of the approximate power generated by a human in various activities (Watts, BTU/hr) [1]:

• Reclining (80, 271.2)
• Seated, quietly (100, 339)
• Sedentary (office) activity (120, 400)
• Standing at ease (120, 400)
• Light laboratory activity (160, 550)
• Light machine work (200, 675)
• Garage work, heavy machine work (300, 1000)

Of course, this heat is used to good advantage in cold weather, since it offsets the heat required from a building HVAC system. In some cases, such as subway and railway stations, there is more heat than required, even in the coldest weather. Sweden, of course, is well known for its cold weather, so it's not surprising that engineers at Jernhusen AB, the company that manages the railway stations of the Swedish railway network and their attached buildings, plan to harvest the waste heat of Stockholm's railway station to heat an adjoining office building [2]. They estimate that for less than $50,000 they can use hot air from the station to heat water that can be used to heat the thirteen story building. About a quarter of a million people use this railway station daily. A quick calculation shows that a residence time of just fifteen minutes per person gives a heat source of more than five megawatt-hours. The engineers estimate that the excess heat from these waiting passengers would provide the building with 5-15% of its heating requirements.

Could body heat be used to power some of the portable electronics, such as cell phones, music players and calculators, we carry with us much of the time? The power demands of electronic circuitry are being reduced at a steady pace, and some university research teams are working on this concept [3], but it will be applicable only to things such as medical sensors. A back-of-the-envelope calculation posted on the internet [4] explains why we won't see a cell phone powered by body heat. The cross-sectional area of a cell phone is only about a half percent of the surface area of a human, so it can intercept only about a half watt of body heat. However, 100% conversion of this power can never be attained. A major principle of the thermodynamics of heat engines is that a temperature difference is needed to obtain useful work. If a human (32 oC) is in a 25 oC environment, the maximum efficiency for conversion of his heat to useful work is less than 2.5%. Under best conditions, only about 10 milliwatts of power can be harvested, whereas a cell phone's battery is rated at more than a watt-hour (>1000 mW-hr). More than a hundred hours of body contact would be required for a full cell phone charge.

Of course, for such stubborn power demands, you could use an elephant. Kleiber's Law is a well-known law in physiology relating metabolic rate to body mass. Metabolic rate, and thereby heat output, scales with the 3/4 power of an animal's mass. A bull elephant (5000 kg) will radiate about 25 times more heat than a human does, or 2.5 kW. That assumes a sedentary (non-charging) bull elephant. Now I'm off to develop my charging-elephant charger.

1. Cornell University Ergonomics Web, DEA350: Ambient Environment: Thermal Conditions.
2. Random Samples: Body Heat, Science, vol. 319, no. 5862 (25 January 2008), p. 391.
3. Alexis Madrigal, "New Super-Efficient Chip Could Run on Body Heat" (Wired News, February 4, 2008).
4. Comment by J. Goodman, Slashdot (January 12, 2008).

February 07, 2008

Cool Sound

People classify some sounds, such as Jazz music, as "cool." Now, sound has been shown to enhance liquid cooling efficiency significantly [1].

Because of the large heat of vaporization of some liquids, boiling is an efficient way to transport heat. For example, water has an extremely high heat of vaporization, 40.65 kJ/mol (2.260 kJ/g), but you need to heat it to 100oC (at one atmosphere of pressure) to have it boil. Methanol has a lower heat of vaporization, 37.4 kJ/mol (1.1 kJ/g), but its boiling point is only 64.7oC, so it's more suited to cooling temperature-sensitive electronics. As anyone who has boiled water knows, there is one problem with this approach. Bubbles tend to nucleate at certain surface locations and stick there for significant periods, so the local cooling at these regions is small. That's where sound becomes important.

Ari Glezer, a Professor of Mechanical Engineering and George W. Woodruff Chair in Thermal Systems at the Georgia Institute of Technology, and his colleagues have been working for many years on liquid cooling. Their first approach to the bubble problem was to use liquid jets to detach bubbles from surfaces. They've now shown that sound waves can increase liquid cooling efficiency by nearly 150%, and they have obtained heat transfer of 338 W/cm2 [2-3].

In their technique, they place an acoustic transducer above the surface to be cooled with the liquid coolant in between. The gap between the acoustic transducer and the cooled surface is only a few millimeters. Both the frequency (1 kHz) and sound pressure are quite low. Although the initial application is cooling of electronics, Satish Kandlikar, a professor at Rochester Institute of Technology and another mechanical engineer interested in cooling, finds application in micro-scale heat exchangers and aerospace cooling applications [1].

1. Jason Palmer, "Bubble-busting sounds could keep chips cool" (New Scientist Online, January 24, 2008).
2. Z. W. Douglas, M. K. Smith, and A. Glezer, "Acoustically Enhanced Boiling Heat Transfer" (Preprint, January 7, 2008). Available as a PDF file here.
3. Steven W. Tillery, Samuel N. Heffington, Marc K. Smith, and Ari Glezer, "Boiling Heat Transfer Enhancement Using a Submerged, Vibration-Induced Jet," Journal of Electronic Packaging, vol. 128, no. 2 (2006). pp. 145-149.

February 06, 2008

A Better Buffer

Chemical processes are temperature-dependent. One rule-of-thumb I use is that reaction rates tend to double for every five degree Centigrade increase in temperature. This is a consequence of the exponential nature of the Arrhenius equation

K = A e (-Ea/RT)

in which K is the reaction rate, A is a constant, Ea is the activation energy, and R is the gas constant. This rule is only true near room temperature for activation energies of about 100 kJ/mole (25 kcal/mole). The rule is usually not far from the truth, although the doubling often occurs at a ten degree increase in temperature, since activation energies for many reactions are as low as 50 kJ/mole (12.5 kcal/mole). In either case, this is a big change for such a small change in temperature. A hundred degree rise in temperature will give more than a thousand-fold (210) increase in reaction rate.

Chemical buffers are chemicals added to solutions to maintain their pH; that is, their relative acidity or alkalinity. Buffering is a chemical reaction involving the production of hydronium (H3O+) or hydroxide (OH-) ions, so the buffering process is temperature dependent. Buffers are less effective as temperature is lowered, and this problem is most acute in freeze-storage of pharmaceuticals.

Now, scientists at the University of Illinois have developed a buffer that's relatively insensitive to temperature [1-3]. It maintains a neutral pH of 7.0 down to -180 oC. In creating this buffer, they were aided by the fact that some buffers become more acidic as the temperature decreases, while others become more alkaline. They decided to combine these, hoping that their affects would cancel, which is something my colleagues and I did to solve a different problem with temperature [4]. In this way, they were able to reduce a pH change over a range of temperatures from 2 to 0.2. Their magic mixture is 60% HEPES (4 - (2 - hydroxyethyl) - 1 - piperazineethanesulfonic acid) and 40% potassium phosphate. They intend to continue research to develop temperature-independent buffers for other pH values and publish these on a web site.

1. Diana Yates, "New buffer resists pH change, even as temperature drops" (University of Illinois Press Release, January 14, 2008).
2. James Mitchell Crow, "Cool solution for sensitive biomolecules" (Royal Society of Chemistry Online, January 14, 2008).
3. Nathan A. Sieracki, Hee Jung Hwang, Michelle K. Lee, Dewain K. Garner and Yi Lu, "A temperature independent pH (TIP) buffer for biomedical biophysical applications at low temperatures," Chem. Commun. (2008), DOI:10.1039/b714446f.
4. Devlin M. Gualtieri, Janpu Hou, William R. Rapoport, and Herman Van de Vaart, U.S. Pat. No. 5,694,205, Birefringent-Biased Sensor Having Temperature Compensation (Dec. 2, 1997).

February 05, 2008

Tragic Tiger Trajectory

Rote memorization is a major part of elementary school education. Some things should be memorized, like the multiplication table, known by the younger students as the Times Table. However, when I was a young student, I was required to memorize poetry, a very distasteful task for which I still can't see any justification. It's not that I didn't like poetry, since several of the Odes of Horace had a special appeal to me. The trouble was that we weren't allowed to choose which poems to memorize.

One poem we memorized was William Blake's The Tiger. Blake is likely best remembered among scientists for his color print, Newton (1795), rendered with pen, ink and watercolor. The Tiger begins as follows:

Tiger, tiger, burning bright
In the forests of the night,
What immortal hand or eye
Could frame thy fearful symmetry?

I happened to remember this poem when I read the news about a teenager who was killed by a 350 pound Siberian Tiger at the San Francisco Zoo late last year. News accounts indicate that this teenager and his friends were taunting the captive tiger, and the tiger was able to jump a barrier wall to exact its revenge. Not only was the teenager killed, but his two friends were badly injured. The tiger enclosure had a 12.5 foot (3.81 meter) wall surrounded by a 15 foot (4.5 meter) moat [1, 2].

The height of the wall is apparently below standard for a tiger enclosure set by The Association of Zoos & Aquariums (And you thought that standards only applied to your specialty!) [2]. A five meter wall is recommended, but is this five meters just a guess, or is there some science behind it?

Raza Syed, a physicist at Northeastern University, and his coauthor, Erica Walker, have posted a calculation that shows that the fatal tiger trajectory was feasible, and their calculation can be used to verify the standard for such enclosures [3, 4]. They calculated the velocity needed to launch a 350 pound object over a 12.5 foot barrier that is 33 feet distant. The answer, 26.7 miles per hour, is less than the maximum reported speed of tigers, 35 miles per hour. Tigers can attain this speed with a running start of only ten yards. So, the 12.5 foot wall is just a little too low, but five meters (16.4 feet) should be more than sufficient.

1. US tiger death zoo a crime scene (BBC News, December 27, 2007).
2. Tiger death zoo walls 'too low' (BBC News, December 28, 2007).
3. Arxive Blog: Feline ballistics (February 1, 2008).
4. Erica Walker and Raza M. Syed, "Tiger Tales: A Critical Examination of the Tiger's Enclosure at the San Francisco Zoo" (Preprint, January 29, 2008).

February 04, 2008

The Honeywell Global Arc

Mathematicians see mathematics in all of nature, since quantities in nature can be expressed by equations. As Galileo, who was arguably the first experimental physicist, wrote in Il Saggiatore (The Assayer) in 1623, "The great book of nature is written in mathematical symbols." [1] One example of mathematics in nature is the Fibonacci Series, which expresses the branching of trees, the arrangement of pine cones, and the breeding of rabbits. Physicists have used the ability of mathematics to model nature to great advantage, but so have artists. The use of mathematics to the advantage of art goes back at least to the Greek sculptor, Phidias (Φειδιας), who proportioned his sculptures according to the Golden Ratio (~1.618014), which can be defined exactly by an equation and is thought to be the most aesthetically pleasing proportion.

Honeywell employees, and the targets of our advertising campaigns, should be familiar with the Global Arc, the graphic that appears at the bottom of our print ads [2]. When I first saw this arc, it reminded me of an inverted catenary curve, which is the shape of a hanging wire supported at its ends with no forces applied except the gravitational pull of its own weight. Derivation of the catenary is a beloved homework problem for mechanical engineers and physicists, but I'll spare you the exercise and just give the result, as follows:

y = a cosh (x/a) = (a/2)[ex/a + e-x/a]

in which cosh is the hyperbolic cosine, expressed in exponentials as shown, and a is a parameter expressing the mechanical properties of the hanging wire.

To compare the arc with the catenary curve, I needed to digitize the arc. Since many electronic versions of the arc are available, I wrote a computer program to extract the (x,y) trajectory of the arc [3]. The fit to an inverse catenary was good, but not perfect. The overlap was excellent near the ends, but the catenary had lower amplitude at the peak than the arc, so there was about a 5% error in y with respect to the entire range of y for the central region of the arc. A quadratic fit (y = x2) was a little better, giving a correlation coefficient of 0.996. A quartic equation (y = x4), however, gave a perfect fit and a correlation coefficient of 0.99995. The Honeywell Global Arc is a quartic function.

How was the arc actually generated? Honeywell's Communications Office wasn't able to tell me. Its origin, and the identity of its creator, are probably lost in the mist of time. However, in reviewing some Honeywell web sites, it appears that QuarkXPress is a popular program among graphic designers, and this includes a Bézier curve generator. This curve generator can likely produce such a quartic function.

1. Quotations of Galileo Galilei (Wikiquote).
2. Honeywell Advertising Guidelines (available only on Honeywell's internal network).
3. I analyzed a *.tga image file to generate 95 (x,y) data points. This file format is the easiest type from which to extract data.

February 01, 2008

It's Alive (Continued)

In a series of previous articles [1-3], I described the efforts of scientists at the J. Craig Venter Institute to create a genome de novo and have it replicated as an organism; that is, create an artificial life form. Although it's fairly easy today to create synthetic DNA, the main problem is that a living cell needs more than just DNA. It needs all the cellular mechanisms to thrive and reproduce. Unless the genome, as expressed in the DNA, can do all this, you don't really have artificial life. Now, scientists from the Venter Institute, led by John Craig Venter, himself, along with Daniel G. Gibson and Hamilton O. Smith, have produced a complete microbial chromosome that they believe will boot up inside a cell and produce the first artificial life form. They've targeted the end of 2008 for completion of this feat. Hamilton O. Smith was awarded the Nobel Prize in Physiology or Medicine in 1978.

One possible reason for the speed at which all this is happening is that the J. Craig Venter Institute is closely managed by Venter. Venter founded this non-profit laboratory with proceeds from the sale of his Celera Genomics stock, valued at much more than a hundred million dollars. The Institute employs more than four hundred people.

The starting point for this research was Mycoplasma genitalium, chosen for the fact that it has a very small genome of just 580,076 base pairs. For comparison, most bacterial genomes have on the order of ten million base pairs, and the human genome has about three billion. In this respect, M. genitalium is 0.02% as complex as a human. The base pairs in M. genitalium express 465 genes, whereas humans have about 20,000 genes, so by this other measure this bacterium is about 2.5% as complex as a human. The first step was to find the precise order of these base pairs in the genome. The team was then able to synthesize another genome that was nearly an identical copy. One important change was deletion of the code that enables the cells to infect other cells. Another was to add "watermarks" of non-functional code to allow identification of their de novo organism.

Although the science itself is interesting, there is an objective to this research. Venter wants to engineer organisms to excrete bio-fuels, hydrogen for energy, and foodstuffs. This would involve large-scale manufacture of artificial bacteria and almost certain release of artificial life forms into the environment. Venter says that his research has been reviewed by the National Academy of Sciences and an independent ethics review board. As any scientist knows, every experiment has risk and unintended consequences, so caution is advised. It's interesting how the title of one news article about this work [4] can be misread as "Mad Scientists Build Bacterial Chromosome."

1. It's Alive! (October 9, 2007).
2. Genome Replacement (July 3, 2007).
3. Bare Bones (July 2, 2007).
4. Rick Weiss, "Md. Scientists Build Bacterial Chromosome" (Washington Post, January 25, 2008).
5. Andrew Pollack, "Researchers Take Step Toward Synthetic Life" (New York Times, January 25, 2008).
6. Jonathan Leake, "The synthetic genome" (The Sunday Times (London), January 27, 2008).