Week of October 24, 2005

Portable augmented reality

Computer monitors are by no means an endangered species, but it is becoming increasingly apparent that they will soon be replaced for many uses by floors, walls and table tops.

The latest evidence: a Microsoft Research scientist has developed a projector and computer vision system dubbed PlayAnywhere that projects interactive computer-generated images without the need for specially mounted cameras.

Researchers have been reducing the cost and complexity of the augmented reality systems in recent years. (See PCs augment reality, TRN June 26/July 3, 2002)

The PlayAnywhere system goes further by packaging the components into a single portable unit that doesn't require calibration. The system consists of an NEC tabletop projector, an infrared light source, an infrared camera and a computer. The device projects a 40-inch diagonal image onto the surface it stands on.

Computer vision techniques allow users to use their hands to move, rotate and scale projected virtual objects. The system tracks shadows to determine where fingertips touch the surface; frame-to-frame pixel-level changes determine hand motion. The system also keeps track of sheets of paper in its view and can project images onto them.

The projector system could be used for games, educational software and other interactive graphical computer applications.

(PlayAnywhere: A Compact Interactive Tabletop Projection-Vision System, Symposium on User Interface Software and Technology (UIST 2005), Seattle, October 23-26, 2005)

Bacteria simplifies fuel cells

Most fuel cells run on hydrogen that the cells first extract from hydrocarbons like fossil fuels and plant matter. The extraction process, however, also produces carbon monoxide, which inhibits the chemical reaction that fuel cells use to generate electricity. Removing the carbon monoxide usually requires high temperatures.

Researchers from the University of Oxford in England, Humboldt University of Berlin in Germany and the Technical University of Berlin in Germany have found that an enzyme from an unusual bacteria makes fuel cells immune to the effects of carbon monoxide.

Ralstonia eutropha strain H16 is one of several types of bacteria that survive on hydrogen and live in oxygen-free or oxygen-poor environments. Strain H16, however, can extract energy from hydrogen even in the presence of oxygen.

A fuel cell anode, or positive electrode, coated with the bacterial enzyme makes for a fuel cell that generates electricity even when the fuel is a mix of nine parts carbon monoxide to one part hydrogen. The enzyme's resistance to oxygen also means that the fuel cell does not require the membrane typically used to keep oxygen away from the anode.

The discovery could significantly simplify the design fuel cells.

(Electrocatalytic Hydrogen Oxidation by an Enzyme at High Carbon Monoxide or Oxygen Levels, Proceedings of the National Academy of Sciences, published online October 24, 2005)

Nano error correction

Molecular-scale manufacturing promises extremely small, fast, cheap devices like computers. Molecular-scale fabrication processes tend to involve chemistry and biology, which are usually simple and inexpensive to carry out, but also error-prone.

This makes it necessary for scientists working on nanofabrication techniques to find ways to minimize errors or to design devices that tolerate errors.

Taking a cue from nature, researchers from the University of Illinois at Urbana-Champaign have developed an error correction technique that uses DNA molecules to proofread assemblies of nanoparticles held together by other DNA molecules and cut loose any nanoparticle that does not belong. Nanoparticles are bits of metal or semiconductor only a few nanometers wide. A nanometer is one millionth of a millimeter.

The researchers tested the method by constructing clumps of 5- and 13-nanometer gold particles held together by DNA and edited out the smaller nanoparticles. The method could work with proteins or similar molecules and could be used to assemble nanotubes and nanowires as well as nanoparticles.

(Proofreading And Error Removal in a Nanomaterial Assembly, Angewandte Chemie International Edition, published online October 17, 2005)

Addressing nanowire arrays

Smaller circuitry means smaller, faster, lower-power computers.

One way to make smaller circuits is to use densely-packed nanowires, which can be as small as a few millionths of a millimeter.

A big challenge in developing nanoelectronics is connecting molecular-scale circuits to today's merely microscopic electronics. The key is being able to control a large number of nanowires with a much smaller number of larger wires. Researchers from the California Institute of Technology have made a nanowire demultiplexer that is easier to fabricate than previous designs.

Several nanowire demultiplexers have been developed in recent years, most notably by teams at Hewlett-Packard Labs and Harvard University (see HP maps molecular memory, TRN July 18, 2001 and Chemicals map nanowire arrays, TRN January 28/February 4, 2004).

The Caltech demultiplexer is simpler than its predecessors because it does not require mapping addresses or chemically modifying specific parts of the nanowires. It uses a binary tree structure that allows 20 wires to address around 1,000 nanowires and 40 wires to address around 1,000,000 nanowires.

The device could also be used to connect arrays of nanoelectrodes to control circuitry that would make biosensors capable of measuring the inner workings of cells.

(Bridging Dimensions: Demultiplexing Ultrahigh-Density Nanowires Circuits, Science, October 21, 2005)

Bits and pieces

A filter brings color to electronic paper, silicon photonic crystal makes for fast, low-power all-optical memory chip; inorganic semiconductor nanocrystals promise cheap, stable solar cells.

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