Radiocarbon Dating

a method of dating ORGANIC material up to 8000 years old. There is a small amount of radioactive carbon 14 in the atmosphere which is taken up naturally by plants and animals during life. When the organism dies there is no more uptake of ¹⁴C and it starts to decay, with a HALF-LIFE of 5730 years. A date for the sample is arrived at by comparing the amount of ¹⁴C left with known standards.

Taken from Dictionary of Science

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Radiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (¹⁴C) to determine the age of carbonaceous materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), "Present" being defined as AD 1950. Such raw ages can be calibrated to give calendar dates.

One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites. When plants fix atmospheric carbon dioxide (CO₂) into organic material during photosynthesis they incorporate a quantity of ¹⁴C that approximately matches the level of this isotope in the atmosphere (a small difference occurs because of isotope fractionation, but this is corrected after laboratory analysis). After plants die or they are consumed by other organisms (for example, by humans or other animals) the ¹⁴C fraction of this organic material declines at a fixed exponential rate due to the radioactive decay of ¹⁴C. Comparing the remaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴C allows the age of the sample to be estimated.

The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby in a seminar at Chicago that year. Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, he was awarded the Nobel Prize in chemistry for this work. He first demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from an ancient Egyptian royal barge for which the age was known from historical documents.

Taken from Wikipedia

Magnetic Bubble

a portion of computer memory which consists of a small region in a material such as garnet (a silicate mineral), which is magnetized in one direction. Slices of this material placed on a SUBSTRATE (base material) produce a magnetic chip that under a magnetic field produces magnetic bubbles. Information can be stored on the chip, which may contain up to one million bubbles in 20 square millimetres, in BINARY form, through the presence or absence of a bubble in a specific location.

Taken from Dictionary of Science

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The magnetic bubble apparatus consists of a thin (8-12μm) single crystal film of Ferromagnetic Garnet (FMG) sandwiched between a pair of crossed Polaroids. The FMG crystals are magnetically anisotropic, that is, they have a strong tendency to orient themselves in fixed directions under the influence of an external magnetic field. The preferred or "easy" axis of orientation is perpendicular to (in or out of) the crystal surface. With no external magnetic field, the domains in the crystal orient up or down in roughly equal amounts. Polarized light passing through the crystal will have its plane of polarization rotated by due to interaction with the magnetic field of the domains (an effect called Faraday rotation). For the 'up' domains, the light will be crossed with respect to the exiting Polaroid therefore appearing dark, and for 'down' domains uncrossed (or vice versa) so appearing bright. The domains appear as serpentine patterns of alternating bright and dark (figure 1a.). Application of an external magnetic field (provided by a built-in electromagnet) flips the domains to one preferred orientation. As the field is increased, the serpentine patterns gradually disappear until you are left with one or two strings and isolated "bubbles".

Taken from fas.harvard.edu

Quantum

(plural quanta) a small amount or unit of electromagnetic radiation which can be thought of as a particle of energy.

Taken from Dictionary of Science

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In physics, a quantum (plural: quanta) is the minimum unit of any physical entity involved in an interaction. An example of an entity that is quantized is the energy transfer of elementary particles of matter (called fermions) and of photons and other bosons. The word comes from the Latin "quantus", for "how much." Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number.

A photon, for example, is a single quantum of light, and may thus be referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general.

As incorporated into the theory of quantum mechanics, this is regarded by physicists as part of the fundamental framework for understanding and describing nature at the infinitesimal level, for the very practical reason that it works. It is "in the nature of things", not a more or less arbitrary human preference.

Taken from Wikipedia

Nanometre

a unit of measurement that is used for extremely small objects. One nanometre equals one thousand millionth of a metre (i.e., 10^-9.m).

Taken from Dictionary of Science












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A nanometre (American spelling: nanometer; symbol nm) (Greek: νάνος, nanos, "dwarf"; μέτρον, metrοn, "unit of measurement") is a unit of length in the metric system, equal to one billionth of a meter.

It is one of the more often used units for very small lengths, and equals ten Ångström, an internationally recognized non-SI unit of length. It is often associated with the field of nanotechnology and the wavelength of light. Formerly, millimicron (symbol mµ) was used for the nanometre. The symbol µµ has also been used.

It is also the most common unit used to describe the manufacturing technology used in the semiconductor industry. It is the most common unit to describe the wavelength of light, with visible light falling in the region of 400–700 nm.

Taken from Wikipedia

Y-chromosome

the small chromosome that carries a dominant gene for maleness. All normal males have 22 matched pairs of chromosomes and one unmatched pair, one large X-chromosome and one small Y-chromosome. The X-chromosome, which is inherited from the mother, carries many more genes than the Y-chromosome, which is inherited from the father. During sexual reproduction, the mother must contribute one X-chromosome, but the father can contribute either an X or Y-chromosome. The effect of the Y-chromosome is that a testis develops in the embryo instead of an ovary. Thus the sex of the resulting offspring is dependent on the father's contribution -- female (X,X) or male (X,Y).

Taken from Dictionary of Science

Earth

the Earth is one of a group of nine planets which orbit a star that we call the sun. It occurs in one small part of the galaxy (also called the milky way) which is referred to as the solar system. The Earth is the fifth largest of the planets and the third nearest to the Sun. Most of the Earth's surface is covered by the oceans -- about two-thirds compared to one third which is land. A layer of air, the atmosphere, surrounds the Earth which is sub-divided into a number of different regions according to height above the surface. The Earth, as viewed from space, is like a blue ball or sphere which is flattened at both the poles. At the equator, the radius of the Earth is 6378 km or 3963 miles.

The Earth itself is composed of four main layers; an outer crust overlying a mantle, followed by an outer core and inner core. The rocky crust varies in thickness, being about 40 km thick under the continents and 8 km under the oceans. It 'floats' on the mantle which is made up of extremely hot rock and is about 2900 km thick. The core is so hot that it is part liquid, with a temperature in the region of 6500 km. The outer core is believed to be about 2250 km thick and is thought to be more liquid than the inner core which is solid and composed mainly of iron and nickel.

Taken from Dictionary of Science