Wednesday, July 06, 2005

Metallic hydrogen
Metallic hydrogen results when hydrogen is sufficiently compressed and undergoes a phase change, and it is an example of degenerate matter. Metallic hydrogen consists of a lattice of atomic nuclei (namely protons) with a spacing that is significantly smaller than a Bohr radius; indeed, the spacing is more comparable with an electron wavelength (see De Broglie wavelength). The electrons are unbound and behave like the conduction electrons in a metal.
Though topping the periodic table's alkali metal column, hydrogen is not, under ordinary conditions, an alkali metal itself. In 1935, however, Nobel Prize-winning physicist Eugene Wigner predicted that under immense pressure, hydrogen atoms would indeed join their first group kin, relinquishing their proprietary hold over their electrons.
The pressures required made experimental verification elusive. In March 1996, however, a group of scientists at Lawrence Livermore National Laboratory reported that they had serendipitously produced - for about a microsecond, and at temperatures of thousands of kelvins and pressures of over a million atmospheres - the first identifiably metallic hydrogen, ending the 60-year search.
The Lawrence Livermore team did not expect to produce metallic hydrogen, as they were not using solid hydrogen, thought to be necessary, and were working above the temperatures specified by metallization theory; furthermore, in previous studies in which solid hydrogen was compressed inside diamond anvils to pressures of up to 2.5 million atmospheres, detectable metallization did not occur. The team sought simply to measure the less extreme conductivity changes that they expected to take place.
The researchers used a 1960s-era light gas gun originally used in guided missile studies to shoot an impactor plate into a sealed container containing a half-millimetre-thick sample of liquid hydrogen. First, at one end of the gun, the hydrogen was cooled to about 20 K inside a container that included a battery connected by wires to a Rogowski coil and an oscilloscope; the wires also touched the surface of the hydrogen in several places, so the apparatus could be used to measure and record its electrical conductivity. At the opposite end, up to 3 kg (7 lb) of gunpowder was ignited, and the resulting explosion pushed a piston through a pump tube, compressing the gas inside. Eventually the gas reached a pressure high enough to throw a valve at the far end of the chamber. Entering the thin "barrel", it propelled the plastic-covered metal impactor plate into the container at up to 8 km/s (18,000 mph), compressing the hydrogen inside.
The scientists were stunned to find that as pressure rose to 1.4 million atmospheres, the electronic energy band gap (a measure of electrical resistivity) fell to almost zero.
The electronic energy band gap of hydrogen in its uncompressed state is about 15 eV, making it an insulator, but as pressure rises to almost unimaginable heights, the band gap gradually falls to 0.3 eV. Because 0.3 eV are provided by the thermal energy of the fluid (the temperature became about 3000 K due to compression of the sample), the hydrogen can at this point be considered fully metallic.
Metallic hydrogen is present in tremendous amounts in the gravitationally compressed interiors of Jupiter, Saturn, and some of the newly discovered extrasolar planets. Because previous predictions of the nature of those interiors had taken for granted metallization at a higher pressure than the one at which we now know it to happen, those predictions must be adjusted. The new data indicate that much more metallic hydrogen exists inside Jupiter than thought, that it comes closer to the surface, and therefore that Jupiter's tremendous magnetic field, the strongest of any planet in the solar system, is, in turn, produced closer to the surface.
Metal detector
Metal detectors use electromagnetic induction to detect metal.
In 1881, Alexander Graham Bell constructed a crude metal detector in an attempt to find an assassin's bullet in President James Garfield. Gerhard Fischar patented a portable version in 1931.
Upright "archway" detectors are used at entrances to secured buildings, such as courthouses or airports, to detect metallic weapons which may be brought in. Small portable "wand" detectors are used by security staff to frisk persons for the same. Larger portable metal detectors are used by treasure hunters to locate metallic items, such as jewelry or coins, buried shallowly underground.
There are three types of metal detectors: beat frequency oscillator, induction balance, and pulse induction.
In a beat frequency oscillator detector, a coil is used as an inductor in an oscillator, whose frequency changes when metal causes its inductance to change. Another oscillator produces a close frequency, and audible beats between them signal metal. In an induction balance detector, there are two coils, usually gibbous with about 10% overlap, and a sine wave is transmitted with one coil and received with the other. The coils are adjusted so that there is no signal in the receive coil when there is no metal nearby. In a pulse induction detector, a pulse is generated (usually by cutting off an inductor) and sent through a coil and the detector listens for echoes. [edit]Metal detectors and archaeologyThe use of metal detectors to search for archaeological finds is practised both by archaeologists and hobbyists. In some European countries including France and Sweden the use of a metal detector is forbidden by law, unless one has special permission. This is intended to protect archaeological sites but rarely means that illicit metal detecting ('nighthawking') does not take place and has the effect that new sites found by metal detector are never publicised or investigated fully. Instead they are slowly plundered for their metal items, disturbing the stratigraphy and forcing the artefacts on to the Black Market, never to be seen again. In the United Kingdom metal detecting is generally permitted provided certain criteria are met and efforts are made to record finds through the Portable Antiquities Scheme. The scheme has critics however, including some archaeologists and some metal detectorists themselves.
Countries with no restrictions or methods to deal with new finds in place are in danger of sites being regularly raided and their contents sold on without the information they provide ever being known. However, there are some responsible metal detectorists in unrestricted nations who contact archeologists when they find artifacts, and who never dig. They benefit archeology by finding artifacts for scientists.
Archaeologists use metal detectors to scan their spoil heaps and also to examine wide areas such as battlefield sites where surface scatters of metal objects may be all that survives. New metal detectors have small screens near the handle.
Glam Metal Detectives
Glam Metal Detectives was a comedy show combining both sketch and sitcom elements, produced by the BBC in 1995. It was heavily promoted by the BBC but, possibly due to its attempts to innovate and combine genres, failed to catch the public imagination and only lasted one series of six episodes.
It starred Gary Beadle, Phil Cornwell, Doon Mackichan (playing most of the female roles), Sara Stockbridge, George Yiasoumi, and Mark Craven.
The show was designed to appear as if the viewer was channel surfing through a multi-channel wasteland, happening upon spoof adverts, short sketches, and recurring show elements. Like other BBC content of the mid-1990s (most notably KYTV), it often lampooned the harsh and low-quality satellite television available in the UK at the time.
Show segments included:
The Glam Metal Detectives themselves. A rock group charged with the mission of "saving the planet's ecology with your top-selling records", they would fight the evil media mogul Royston Brockade in between gigs.This segment, combined elements of the cultish, kitsch and televisual trash in what was intended as an innovative manner. Betty's Mad Dash - a supposed 1950s adventure serials, set in the 1930s, about two flappers, Betty and Maisie on the run from the police. Each episode involved hiding from the police in some period location and robbing from people at gunpoint. Bloodsports - a short segment portraying violent UK topics such as ram raiding as if they were recognised sports, complete with commentators. The Big Me - a chat show parody featuring Morag, who was extremely self-obsessed and egomanaical, ignoring her guests and instead talking about herself. Colin Corleone - a nondescript Londoner who acted as if he was as a mafia godfather, complete with henchmen; for example, when his dole is cut off because he refuses to work in Do It All, he arranges a 'hit' on the DSS office worker, shooting him with a water pistol while he has his lunch.