Researchers at Lawrence Livermore National Laboratory in Livermore, Calif., have developed a method of using a 100-watt green laser to remove spray-painted graffiti, leaving a clean, undamaged wall. When the laser beam hits the surface layer of paint, it is converted into a sound wave that travels through the paint and strikes the surface below. The sound wave rebounds and collides with the incoming beam, creating a tiny explosion near the paint that pulverizes it into fine dust. The laser has been able to remove paint from hard surfaces like marble and porous ones such as concrete. According to researchers, the technique is more efficient than earlier removal methods such as soda blasting, a procedure that is slower than laser use and requires hazardous chemicals. The next step for developers is to design a laser device that fits in a truck or van for street use.

In the first commercial-scale demonstration of propellant-containing explosives, Sandia National Laboratories in Livermore, Calif.—with Global Environmental Solutions in Magna, Utah, and Universal Tech Corp. in Riverton, Kan.—used 11,000 pounds of the product to move more than 25,000 tons of rock at a Prairie, Okla., quarry last September. Earlier this year, the U.S. Department of Transportation approved shipping the explosive, a key step for wider availability.

The solid propellant, a hazardous waste, is reclaimed from old rocket motors. For the demonstration, 200 excess rocket motors, used at Sandia’s rocket-powered-sled test track in New Mexico, were taken apart to get at the solid propellant.

An essential element of reuse was converting the bulky material into manageable pieces. Even small motors require 20- to 30-pound blocks that are likely to detonate and too large for mining purposes, said Joel Lipkin, who manages the program at Sandia/California’s Technology Applications Department. Researchers developed a cryocycling process that repeatedly freezes and thaws the propellant in liquid nitrogen to break it into smaller chunks. Universal Tech then added the pieces, less than 1/2 inch across, to a water gel explosive.

Cryocycling cut the large blocks down to size efficiently, with no waste stream nor any dangerous mechanical grinding of materials. “If you cut the propellant with a water jet or use solvent to extract it, you’d lose quite a bit of explosive power,” Lipkin said. With nitrogen, he added, the propellant isn’t solvated, so its full explosive properties remain.

Explosives containing recycled propellant have 10- to 15-percent higher blast energy and detonation velocity than traditional destruction methods, Lipkin said. The operations needed to get at the material may make the explosive somewhat more expensive, he added, but those costs could be offset by greater efficiency and by eliminating disposal costs for the former fuel.

Explosives may not be the only use for the propellant. Global Environmental is looking for a partner to market sporting powder that includes the reclaimed material for shotgun shells.

The technique, developed by Deborah D. L. Chung, a professor of mechanical and aerospace engineering at the State University of New York at Buffalo, involves placing small electrical probes that can be permanently mounted or introduced during inspections on or near areas of stress on composite parts, such as those used in aircraft wings, ship hulls, automotive panels, and sporting goods. These probes detect increases in electrical resistivity caused by carbon fibers breaking within the polymer matrix of the composite. This breaking reflects the damage caused by tensile stress. In addition, these probes detect changes in resistivity caused by straining the composite.

Chung developed her technology as a less costly, more efficient alternative to the current method of embedding optical fibers in the composite to monitor damage and strain. Besides reducing cost, the smart-composite technique eliminates the loss of mechanical properties that embedding can cause.

“The most critical aspect of the smart composites is that they are capable of real-time sensing of both damage and reversible deformations, which are particularly difficult to monitor,” said Chung. By sensing both phenomena, the technique allows control of deformation, recording of deformation and damage histories, and lifetime prediction, all in real time.

The $15 antiscald valves use a nickel-titanium shape-memory alloy that brings the water flow down to a trickle 3 seconds after the water temperature reaches 116 degreesF. The hot water causes a shape-memory element to change shape in a way that closes off the valve except for a 0.25-gallon-per-minute flow that later permits colder water to reset the safety device.

Tap-water scald injuries are the second most common cause of serious burns among all age groups, though young children, retired people, and handicapped people are most at risk. Scalding burns are most frequent in the kitchen, but the most severe scalding is caused by hot water flowing into the tub or shower, according to the Consumer Product Safety Commission.

The shower safety device, which is about the size and shape of a roll of quarters, is inserted between the shower pipe and the shower head. Antiscald valves for sinks and tubs are installed directly in the piping system.

A typical home water heater delivers hot water at temperatures that range from 140 degrees F to 160 degrees F. A comfortable water temperature for a shower is about 100 degrees F.

Developed in cooperation with Van Doorne’s Transmissie B.V. of Tilburg, The Netherlands, Honda’s stepless transmission system eliminates all gears, providing for smooth acceleration. This latest incarnation of CVT technology combines the convenience of an automatic transmission with the fuel economy of a manual unit. It entails minor (and, to many drivers, hardly noticeable) sacrifices in acceleration performance.

The ultraviolet light kills bacteria, viruses, molds, and other pathogens (though not giardia) by inactivating their DNA. While the use of ultraviolet light to kill germs has been known since the turn of the century, only recently has the technology become sufficiently inexpensive and reliable for widespread use.

The water to be treated enters a stainless-steel chamber, where it is bathed in ultraviolet light at 254 nanometers, the optimum frequency for killing germs. Conveniently, this frequency is also given off by standard mercury-vapor lamps when, as in this situation, the usual fluorescent phosphor coating is left off and the ultraviolet transport glass is used. The light is positioned above a shallow column of water that moves through the unit. The lid is screwed on to prevent exposure of users to harmful rays, but a safety viewing window is provided so users can see that the device is operating properly.

Because gravity is used to move water through the unit, electricity is needed only to power the lamp, which draws only 40 watts. The system can also be hooked up to a car battery in places where electricity is not available.

Last year the developers, led by physicist and ASME member Ashok Gadgil, field-tested a model in India that was designed to handle a flow rate of 30 liters per minute, only to discover that such a rate exceeded most local requirements; generally the devices would be attached to hand pumps, which generate a maximum flow of 12 liters per minute. The units have accordingly been redesigned to be smaller and cheaper, handling a maximum flow of 15 liters per minute.

The device is capable of providing everyone in a 1,000-member community 10 liters of clean water a day each for a cost of 7 cents a year per person, which is affordable by third-world standards.

The resonant snubber inverter (RSI) also virtually eliminates the electromagnetic interference found in typical inverters, according to Jason Lai of the Oak Ridge National Laboratory, one of eight inventors from the lab and the University of Tennessee working on the project. Without the interference, conversion efficiency improves to 80 percent at low speeds and 98 percent at high, compared with 60 to 70 percent and 94 percent from conventional designs at the same velocities.

The RSI design has three small auxiliary switches in addition to the six main switches normally found in other inverters. Current is diverted through the small switches for just a few microseconds, then routed back to the main switches. This diversion via “soft switching” produces zero voltage across the switch, significantly reducing switching power spikes and the associated electromagnetic interference that can hamper electronic performance.

With no voltage lost across the switch, the RSI generates less heat and uses silicon area more effectively than earlier designs, according to Lai. The total silicon area in the RSI is about five to 10 percent less than the earlier half-switch and pulse-wave modulated inverters.

Less silicon, greater conversion efficiency, and virtually no electromagnetic interference result in greater output from a smaller device. A 100-kilowatt inverter built at Oak Ridge measures just 9 inches by 1 foot by 1 foot and weighs 20 pounds; even the most recent conventional inverters weigh two to three times more. The amount of silicon in the RSI and its output should also make the new device less expensive to use than other models, according to Lai.

Electric vehicles are not the only potential application for the RSI; adjustable-speed motors, heat pumps, fans, and compressors may also benefit from its development. In 1997, the inverter will be tested in advanced air conditioners on electric buses, replacing propane-fueled auxiliary power units.

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© 1996 by The American Society of Mechanical Engineers