‘Dancing’ algae discovered

From New Scientist:

‘Dancing’ algae can waltz and minuet

* 17:35 20 April 2009 by Michael Marshall and Sandrine Ceurstemont

Freshwater algae can dance around each other in stable groups, held together only by fluid flows in the surrounding water.

Raymond Goldstein of the University of Cambridge and colleagues studied a well-known alga called Volvox. This species lives in colonies of cells around a thousand strong: the individual cells live on the surfaces of spheres of jelly.

Each cell has a pair of flagella: thin flexible rods that extend out into the surrounding water and function as outboard motors, propelling the colonies around – as well as causing them to spin like tops.

When the colonies swim near the surface of the water, they can get together in one of two formations.

The first is called the “waltz”: the two colonies orbit around each other, like a planet circling the sun. The second is the “minuet”, in which the colonies oscillate back and forth, as if held together by an elastic band.

Goldstein’s team have developed a mathematical analysis that explains the two dances – they are caused by the unusual behaviour of the water near its surface.

Journal reference: Physical Review Letters, in press (pdf)

These videos are about human waltzing and minuet.

Coralline Algae In The Mediterranean Lost Their Tropical Element Between 5 And 7 Million Years Ago: here.

Vampire Algae Suck on Salad: here.

Vanishing Marine Algae Can Be Monitored From a Boat With Your Smartphone: here.

Spring Rain, Then Foul Algae in Ailing Lake Erie: here.


Chinese Wall longer than thought

From Associated Press:

Apr 20, 3:06 AM EDT

Study: China’s Great Wall is longer than thought

Associated Press Writer

BEIJING — The Great Wall of China is even greater than once thought.

A two-year government mapping study has uncovered new sections of the ancient Chinese monument that total about 180 miles (290 kilometers), according to a report posted on the State Bureau of Surveying and Mapping Web site.

Using mapping technologies such as infrared range finders and GPS devices, experts discovered portions of the wall – concealed by hills, trenches and rivers – that stretch from Hu Mountain in northern Liaoning province to Jiayu Pass in western Gansu province, the official China Daily reported Monday.

The newly mapped parts of the wall were built during the Ming Dynasy [sic; Dynasty] (1368-1644) to protect against northern invaders and were submerged over time by sandstorms that moved across the arid region, the study said.

The additional parts mean the Great Wall – which Chinese emperors began constructing 2,000 years ago to keep out Monguls [sic; Mongols] and invaders – spans about 3,900 miles (6,300 kilometers) through the northern part of the country.

The joint project, conducted by the State Administration of Cultural Heritage and State Bureau of Surveying and Mapping, will continue for another year in order to map sections of the wall built during the Qin (221 B.C.-206 B.C.) and Han (206 B.C.-9 A.D.) Dynasties, the report said. …

The wall’s modern sections around the Chinese capital date from the Ming Dynasty, including those restored since the Communist Party took power in 1949, and several areas – including the most popular, Badaling, just north of Beijing – draw hundreds of thousands of visitors each year.

Tourist encroachment also has been a problem in recent years, with state media saying that near Badaling almost every brick on a popular section of the wall has been carved with people’s names or other graffiti.