Tuesday, February 20, 2007

Identical twins
Identical twins occur when a single egg is fertilized to form one zygote which then divides into two separate embryos. This is not considered to be a hereditary trait, but rather an anomaly that occurs in birthing at a rate of about 1:150 births worldwide, regardless of ethnic background. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. Depending on the stage at which the zygote divides, identical twins may share the same amnion, which can cause complications in pregnancy.

For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. About 50% of mono-mono twins die from umbilical cord entanglement. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. These twins may develop such that blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome.

Wednesday, February 14, 2007

In marginalist economic theory, the price level is determined by the marginal cost and marginal utility. The price of all goods will be the cost of making the last one that people will purchase, and the price of all the employees in a company will be the cost of hiring the last one the business needs. Marginalism looks at decisions based on "the margins", what the cost to produce the next unit is, versus how much it is expected to return in profit. When the marginal return of an action reaches zero, the action stops. Marginal utility is how much more happiness or use a person receives from a purchase in contrast with buying less. Marginal rewards are often subject to diminishing returns: Less reward is obtained from more production or consumption. For example, the 10th bar of chocolate that a person consumes does not taste as good as the first, and so brings less marginal utility.

Marginalism became increasingly important in economic theory in the late 19th century, and is a tool which is used to analyze how economic systems will react. Marginal cost of production divides costs into "fixed" costs which must be paid regardless of how many of a commodity are produced, and "variable costs". The marginal cost is the variable cost of the last unit. Marginalism states that when the profit from the next unit will be zero, that unit will not be produced. This is often termed the marginal revolution in economic thought.

Sunday, February 04, 2007

Mega tsunami
Mega tsunami often hyphenated as mega-tsunami, also known as iminami or "wave of purification" is an informal term used by popular media and popular science to describe a very large tsunami-like wave significantly beyond the size reached by tsunamis. For this reason, there is no scientific definition of a mega tsunami. Informally, the term generally refers to waves beyond the norm for tsunamis, ranging from over 40 meters to giants over 100 meters tall. Note that mega tsunamis often reach higher than their wave height when they meet land, as the water often floods upwards from the force of impact.

Mega tsunamis are related to tsunamis in name only: they do not usually have the same cause or appearance, the only connection being that both are very large scale water movements caused by point events.[citation needed] They are also not the same as freak waves which appear in ocean waters and are often up to 30 meters tall.