Physics of the ‘Bends’:

New Study Helps Explain

Decompression Sickness

Science(June 28, 2010) — As you go about your day-to-day activities, tiny bubbles of nitrogen come and go inside your tissues. This is not a problem unless you happen to experience large changes in ambient pressure, such as those encountered by scuba divers and astronauts. During large, fast pressure drops, these bubbles can grow and lead to decompression sickness, popularly known as “the bends.”

A study in the Journal of Chemical Physics, which is published by the American Institute of Physics (AIP), may provide a physical basis for the existence of these bubbles, and could be useful in understanding decompression sickness.

A physiological model that accounts for these bubbles is needed both to protect against and to treat decompression sickness. There is a problem though. “These bubbles should not exist,” says author Saul Goldman of the University of Guelph in Ontario, Canada.

Because they are believed to be composed mostly of nitrogen, while the surrounding atmosphere consists of both nitrogen and oxygen, the pressure of the bubbles should be less than that of the surrounding atmosphere. But if this were so, they would collapse.

“We need to account for their apparent continuous existence in tissues in spite of this putative pressure imbalance,” says Goldman.

If, as is widely believed, decompression sickness is the result of the growth of pre-existing gas bubbles in tissues, those bubbles must be sufficiently stable to have non-negligible half-lives. The proposed explanation involves modeling body tissues as soft elastic materials that have some degree of rigidity. Previous models have focused on bubble formation in simple liquids, which differ from elastic materials in having no rigidity.

Using the soft-elastic tissue model, Goldman finds pockets of reduced pressure in which nitrogen bubbles can form and have enough stability to account for a continuous presence of tiny bubbles that can expand when the ambient pressure drops. Tribonucleation, the phenomenon of formation of new gas bubbles when submerged surfaces separate rapidly, provides the physical mechanism for formation of new gas bubbles in solution. The rapid separation of adhering surfaces results in momentary negative pressures at the plane of separation. Therefore, while these tiny bubbles in elastic media are metastable, and do not last indefinitely, they are replaced periodically. According to this picture, tribonucleation is the source, and finite half-lives the sink, for the continuous generation and loss small gas bubbles in tissues.

Sourced & published by Henry Sapiecha

[HK Fair] Chinese Firm Exhibits ‘

World’s Smallest’ Video Camera

Shenzhen AEE Wireless Technology Co Ltd of China exhibits what it claims is the world’s smallest video camera at the Hong Kong Electronics Fair (Spring Edition).

The fair, which is organized by the Hong Kong Trade Development Council, is taking place in Hong Kong from April 13 to 16, 2009.

The dimensions of the camera, “Mini DV,” are 55 x 20 x 18mm. Its volume is 20cm3 and weight is 50g.

“Only an ultra-small camcorder like this can enable people cycling or skiing, pet animals and radio control toys to shoot video,” AEE said. “We developed this product to have more flexability and to allow people to shoot a wider variety of scenes.”

The company reduced the size by focusing on image recording function. The Mini DV is not equipped with a monitor for checking images, and recorded images can be viewed only after they are transferred to a PC.

The camcorder employs a 2-Mpixel CMOS sensor. It shoots 640 x 480-pixel images at 30fps, compresses the images with the JPEG format and stores them in the AVI format by using a microSD memory card of up to 8 Gbytes.

The interface for PC connection is USB 2.0. When the camcorder is connected to a PC, images can be output to a PC in real time. Its Li-ion secondary battery has a capacity of 260mAh, allowing two hours of continuous shooting.

The Mini DV is equipped with a clip for attaching the camera to clothing or accessories like belts etc..  AEE offers a version including a mount that allows users to attach the camera to a helmet, etc, and is intended for filming while playing sports.

Sourced and published by Henry Sapiecha 22nd April 2009