Tuesday, February 20, 2007

Fraternal twins

Fraternal twins usually occur when two fertilized eggs are implanted in the uterine wall at the same time. The two eggs form two zygotes, and these twins are therefore also known as dizygotic as well as "biovular" twins. When two eggs are independently fertilized by two different sperm cells, fraternal twins result.

Dizygotic twins, like any other siblings, have a very small chance of having the exact same chromosome profile, but most likely have a number of different chromosomes that distinguish them. Like any other siblings, fraternal twins may look very similar, particularly given that they are the same age. However, fraternal twins may also look very different from each other. They may be a different sex or the same sex. Mixed-race twins, or twins born to parents of mixed racial origin, can vary considerably in their skin colouration and other features.

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Wednesday, February 14, 2007


Economic analysis is fundamentally about the maximization of something subject to constraints. These constraints - or scarcity - inevitably define a trade-off. For example, one can have more money by working harder, but less time . One can have more radishes only at the expense of, for example, fewer carrots .All economies in the world face scarcity.Scarcity is defined as: when the price is zero, the quantity demanded exceeds the quantity supplied.

Price is a measure of relative scarcity. If all other market variables are held constant; When the price is rising, this indicates the commodity is becoming relatively more scarce. When the price is falling, this indicates the commodity is becoming relatively less scarce.Adam Smith considered, for example, the trade-off between time, or convenience, and money. He discussed how a person could live near town, and pay more for rent of his home, or live farther away and pay less, "paying the difference out of his convenience".

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Sunday, February 04, 2007

Super volcano

A super volcano it refers to a volcano that produces the largest and most voluminous kinds of eruption on Earth. The actual explosivity of these eruptions varies, but the sheer volume of extruded magma is enough to radically alter the landscape and severely impact global climate for years, with a cataclysmic effect on life.

The term was originally coined by the producers of the BBC popular science program, Horizon, in 2000 to refer to these types of eruption. That investigation brought the subject more into the public eye, leading to further studies of the possible effects. At first, super volcano was not a technical term used in volcanology, but more recently, in 2003 and 2004, the term has been used in articles. Though there is no well-defined minimum size for a "super volcano", there are at least two types of volcanic eruption that have been identified as super volcanoes: massive eruptions and large igneous provinces.

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