Officials say the two devices which exploded by the finishing line of the marathon were triggered by a remote-controlled detonator, the AP reported on Wednesday.
These devices, which work by combining hydrogen with oxygen from the air to produce electricity, are popular candidates to replace internal-combustion engines in road vehicles.
Each of these power-boosting devices, which operate by forcing more air into an engine than it would draw on its own, has proved effective in making small, fuel-efficient 4- or 6-cylinder power plants deliver V-8 punch.
That in turn could make the materials attractive building blocks for spintronic devices, which compute by manipulating electron spins.
In early days computers are operated by various interface devices, which are developed by the humans to interact with computers.
At the end of the free-living recording period, women returned the monitoring devices, which were downloaded by means of software packages provided by the manufacturers.
The other two devices, which were approved by the F.D.A. in the last year, are made by Cook Inc., a private company in Bloomington, Ind., and by W. L. Gore & Associates, a private company in Newark, Del.
Officers then deployed teargas and about three explosive devices, which were described by some present as flashbang grenades.
The treelike devices, which were created by Klaus Lackner, a Columbia University geophysicist, resemble giant fly swatters in one design.
Medtronic has about half of the market for the devices, which save lives by shocking a racing heartbeat back to normal rhythm.
