Monthly Archives: November 2012

Blood types

What is it that makes blood types different from each other?

The existence of blood types* is down to the presence of antigens (“antibody generators”) on the surface of red blood cells and antibodies in the blood’s plasma. Someone with Type A blood has A-type antigens on their red blood cells and anti-B antibodies in their plasma. Someone with Type B blood has B-type antigens on their red blood cells and anti-A antibodies in their plasma. Those with Type AB blood have both A- and B-type antigens on their red blood cells and no antibodies in their plasma; whereas someone with Type O blood has no antigens on their red blood cells but both anti-A and anti-B antibodies in their plasma.

If, for example, someone with Type A blood is given a transfusion of Type B blood the anti-B antibodies in their system will attach themselves to the Type-B red blood cells, labelling them for destruction by white blood cell phagocytes. This can lead to an acute hemolytic reaction in which the red blood cell count drops to a dangerously low level and the blood is no longer able to carry enough oxygen to support life. This reaction can vary between patients, with some patients dying very soon after receiving a small amount of the wrong type of blood and some not dying after receiving relatively large amounts.

Can receive … Someone with Type …
A B AB O
A ✔ ✔
B ✔ ✔
AB ✔
O ✔ ✔ ✔ ✔

People with Type AB blood are universal recipients and can receive blood of any type, as their plasma does not contain anti-A or anti-B antibodies. Those with Type O blood are universal donors and can donate blood to anyone, as their red blood cells do not have any antigens on their surfaces.

Across the world, Type AB blood is rarest with only 5.5% of the population being Type AB. Type O blood is the most common (40.8%) and Type A is more common (31.8%) than Type B (22.0%). That said, blood types vary enormously between different countries and races: all Bororo people are Type O, nearly half (48%) of Norwegians are Type A and 32% of Indians are Type B.

* For the purposes of simplicity, this post ignores the effect of the Rh (Rhesus) factor that leads to, for example, the difference between A+ or A− blood.

Norman Borlaug

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Norman Borlaug probably saved more lives than anyone who has ever lived (some estimates put the number of lives saved at over one billion) but chances are you’ve never heard of him, despite the fact that he won the Nobel Peace Prize for his work and is one of only six people ever to have won the Nobel Prize, the Presidential Medal of Freedom and the Congressional Gold Medal. Borlaug was an agronomist (that is, he studied the use of plants for food and fuel) who is often referred to as the Father of the Green Revolution; a period of time from the 1940s to 1970s in which the production of food by agriculture increased markedly.

Borlaug worked with wheat, and developed high-yield disease-resistant varieties and led the introduction of these varieties, coupled with modern production methods like irrigation and the use of pesticides, into Mexico, Pakistan and India. In India alone wheat yield went from nine million tonnes in the 1960s to seventy million tonnes in the 1990s. Similar efforts with rice followed (in some cases increasing the yield tenfold) and these efforts are thought to have saved more than one billion people from starvation, with the average person in the developing world now receiving 25% more energy from food than before the Green Revolution.

Osteoporosis

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Osteoporosis is a disease that causes the density of bones to decrease. Normally bones are constantly being remodelled – some of the bone is broken down (resorped) and new bone grows in its place. In a normal person about ten percent of bone at any one time is undergoing this process. If there is a different in the rate of the two processes, with resorption occurring faster than growth, then osteoporosis will develop.

The two micrograph images below, from the Wellcome Collection, demonstrate the difference very clearly.

Normal Bone

Osteoporotic Bone

The holes in bones are required so that nutrients can get to the bones and also to give bones some “give” so that they are not too brittle; it’s important for bones to be able to bend a small amount to absorb shocks.

Solved games

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It might seem odd to describe a game like Draughts (US: Checkers) as being solved, but mathematically and scientifically it makes perfect sense.

A screenshot showing the Thinking Machine 4 chess engine deciding on a move.

A game is described as solved if it is possible for a player with knowledge of the solution to play a perfect game – to win (or at least draw) every time, no matter what moves their opponent makes. Theorists describe a game as being solved in two ways: a weak solution provides a fail-safe method from the game’s standard starting positions (e.g. in chess with all pieces on their “home” squares) and a strong solution provides a fail-safe method given any starting point.

The largest game solved so far is Draughts. It was weakly solved in April 2007 by a team led by Jonathan Schaeffer*, and their solution was implemented in a computer Draughts program called Chinook. It is mathematically impossible to play Chinook at Draughts and win – the only possible options are to lose or draw (if you don’t believe me, you can play against Chinook online).

Not all solved games result in a draw. In Connect Four the first player can force a win, whereas the second player will always win if playing Sim/Hexi or Chopsticks.

There are many important games that remain unsolved. Chess is only partially solved (for three to six piece endgames) and Go, perhaps one of the most computationally complex games, is only solved for board sizes up to five-by-five (standard games take place on a nineteen-by-nineteen board). It is estimated that with current technology it is impossible to solve either of these games.

This post was inspired by the excellent Relatively Prime podcast’s episode about Chinook.

* Jonathan Schaeffer et al, “Checkers is Solved,” Science 317 (2007): 1518-1522. DOI: 10.1126/science.1144079.

Earthquake cloak

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Metamaterial cloaking, the idea of hiding an object using special materials, has become a popular area of research in recent years. Optical cloaks attempt to hide objects from visible light, thus making them invisible. Audible cloaks attempt to hide objects from sound waves, thus making them undetectable by (for example) sonar. Attempts at cloaking also exist for other waves; for example trying to make objects invisible to radar, which has obvious military applications.

If cloaking can work for electromagnetic and sound waves then it may also be possible to make it work for seismic earthquake waves.

The metamaterials used in cloaking have negative refractive indices and so waves do not travel through them in the normal way. All metamaterial cloaking methods work by bending waves around an object and returning them to their original paths, so that it appears that the object was never there. If the same thing could be made to happen for seismic waves around a building, then it could completely isolate the building from the seismic waves’ destructive effects.

In February of this year Sang-Hoon Kim of Mokpo National Maritime University in South Korea and Mukunda Das of the Australian National University in Canberra proposed* a way of doing this. Their method involves creating sixty metre-wide “shells” of specially constructed concrete pillars in the ground around a building, and unlike previously suggested methods doesn’t involve aiming or deflecting the waves at other buildings in the area. They suggest that their method would be able to absorb the energy of the earthquake waves, essentially stopping the waves in their tracks by transferring their energy into sound and thermal energy. A later paper†, by the same authors suggests using a similar method to create an artificial “shadow zone” in which the earthquake waves are not felt.

* Sang-Hoon Kim and Mukunda P. Das, “Seismic Waveguide of Metamaterials”, arXiv:1202.1586.

† Sang-Hoon Kim and Mukunda P. Das, “Artificial Seismic Shadow Zone Created by Metamaterials”, arXiv:1210.5589.

Thanks to KS for the inspiration for this post.