Jet Propulsion

A method of propulsion by which, in accordance with Isaac Newton's third law of motion 'to every action there is an equal and opposite reaction', an object is propelled forwards by a stream of gas or liquid (the jet) expelled in the opposite direction.

Within the animal kingdom, creatures such as squid or octopuses make use of short bursts of jet propulsion to move quickly. In general, water is taken into a muscular sac and is expelled rapidly through a small opening to provide a rapid acceleration in the opposite direction. The simplest example of jet propulsion in the underwater world is jellyfish. Although not all species of jellyfish use jet propulsion to travel, many species fill the umbrella section with water and then push the water out in a stream of short duration. However, the jellyfish has little control over direction. Squid, on the other hand, are able to control the direction of the jet, allowing them to move in a definite direction. Some squid are able to reach speeds high enough to shoot them out of the water and onto the deck of a ship.

Several shelled animals such as clams or scallops can use a more primitive form of jet propulsion to rapidly escape from enemies. They achieve this by bringing the two halves of their shells together rapidly, although like the jellyfish they have little control over the direction of the expelled liquid, and therefore little control over the direction of their movement.

Outside of the animal kingdom, the most common use of jet propulsion is the widely-known jet engine or turbojet. The turbojet is a kind of gas turbine, in which air passes through a forward-facing intake, is compressed and fed into a combustion chamber. Fuel is sprayed in and ignited, producing a rapidly expanding ball of hot gas which proceeds rearwards, spinning a turbine in the process, which drives the compressor. The hot gas is finally ejected from the rear of the unit, usually a nozzle or some form of tail-pipe, at very high speed. This is the simplest form of gas turbine, used in supersonic aircraft.

The turboprop, used for moderate speeds and altitudes, adds extra stages that absorb most of the energy from the gas stream to drive a propellor shaft. The turbofan is best suited to high subsonic speeds, and features an extra compressor in front. Some of the airflow bypasses the core engine and mixes with the jet exhaust stream, providing a lower temperature and velocity. Compared to the turbojet this modification results in improvements in economy, efficiency and quietness, yet provides a higher speed compared to the turboprop.
The turboshaft is a form of jet engine used to drive the rotors of helicopters, as well as providing propulsion to hovercraft, ships and trains. Essentially a turboprop without a propellor, power from the extra turbine instead being delivered to an output shaft or a reduction gearbox.

The ramjet is used for a variety of missiles. When running at twice the speed of sound (Mach 2), the pressure in the front intake of the ramjet engine is such that no compressor or turbine is required. It is cheap and light, but consumes a high amount of fuel, which is burnt in the widest section of what is essentially an open-ended barrel-shaped tube. The lack of a turbine, however, means that the rocket must be boosted to operational speed before the ramjet engine will function.

Variants of the jet engine include vectored thrust engines, allowing vertical takeoff, reverse thrust, used to slow down a jet plane on landing, and reheat or afterburning, used in military aircraft to provide short-duration increases in thrust.

Soldering Iron

A soldering iron is a simple device for applying heat to a specific point. The intention is to melt solder at this point, joining two materials. This joint is then allowed to cool, thus soldering the two materials together. Generally, soldering is used to create an electrically conductive joint betweenelectrical components and a circuit board. It should be noted that although the term soldering also refers to joining pipes, a plumber would use a blowtorch rather than a soldering iron.

Solder is generally a mixture of tin and lead with a melting point just below 190 degrees Celsius. The tip of the soldering iron, therefore, must reach this temperature, and the most common method of achieving this is with electrical power. Other options include butane powered soldering irons, which have the advantage of being cordless, and there are other devices available which are designed to be heated in a furnace.

Depending on the type of work at hand, differently shaped tips can be fitted to the soldering iron. For working with fine electronics components, a slender and rounded tip is useful, whereas a triangular, flat face is useful for work with sheet metal. The tip itself should be coated with a thin layer of solder, a process known as tinning. This ensures a good transfer of heat from the tip of the iron to the surface being soldered, and keeps the tip in good condition.

The high temperatures at which soldering takes place means that certain safety considerations must be taken into account. The majority of soldering irons feature a hook by which the device can be hung whilst hot, or come with a stand into which the iron should be placed when not in use. Additionally, there is always risk of the solder splashing, and so protective goggles are essential.

Although soldering irons come in a range of sizes, the majority of these are visible with the naked eye. New Scientist, however, recently reported the smallest device in the world. Formed from carbon nanotubes with a diameter of 20 millionths of a millimetre. Gaseous iridium is condensed into solid droplets between one and ten nanometres wide, then electrically forced along the nanotube's surface where they collect as a bubbling liquid. The inventor, Alex Zettl, plans to use them to solder tiny parts together, enhancing current work on a 'nano-structure production line'.

Jet Propulsion

A method of propulsion by which, in accordance with Isaac Newton's third law of motion 'to every action there is an equal and opposite reaction', an object is propelled forwards by a stream of gas or liquid (the jet) expelled in the opposite direction.

Within the animal kingdom, creatures such as squid or octopuses make use of short bursts of jet propulsion to move quickly. In general, water is taken into a muscular sac and is expelled rapidly through a small opening to provide a rapid acceleration in the opposite direction. The simplest example of jet propulsion in the underwater world is jellyfish. Although not all species of jellyfish use jet propulsion to travel, many species fill the umbrella section with water and then push the water out in a stream of short duration. However, the jellyfish has little control over direction. Squid, on the other hand, are able to control the direction of the jet, allowing them to move in a definite direction. Some squid are able to reach speeds high enough to shoot them out of the water and onto the deck of a ship.

Several shelled animals such as clams or scallops can use a more primitive form of jet propulsion to rapidly escape from enemies. They achieve this by bringing the two halves of their shells together rapidly, although like the jellyfish they have little control over the direction of the expelled liquid, and therefore little control over the direction of their movement.

Outside of the animal kingdom, the most common use of jet propulsion is the widely-known jet engine or turbojet. The turbojet is a kind of gas turbine, in which air passes through a forward-facing intake, is compressed and fed into a combustion chamber. Fuel is sprayed in and ignited, producing a rapidly expanding ball of hot gas which proceeds rearwards, spinning a turbine in the process, which drives the compressor. The hot gas is finally ejected from the rear of the unit, usually a nozzle or some form of tail-pipe, at very high speed. This is the simplest form of gas turbine, used in supersonic aircraft.

The turboprop, used for moderate speeds and altitudes, adds extra stages that absorb most of the energy from the gas stream to drive a propellor shaft. The turbofan is best suited to high subsonic speeds, and features an extra compressor in front. Some of the airflow bypasses the core engine and mixes with the jet exhaust stream, providing a lower temperature and velocity. Compared to the turbojet this modification results in improvements in economy, efficiency and quietness, yet provides a higher speed compared to the turboprop.

The turboshaft is a form of jet engine used to drive the rotors of helicopters, as well as providing propulsion to hovercraft, ships and trains. Essentially a turboprop without a propellor, power from the extra turbine instead being delivered to an output shaft or a reduction gearbox.

The ramjet is used for a variety of missiles. When running at twice the speed of sound (Mach 2), the pressure in the front intake of the ramjet engine is such that no compressor or turbine is required. It is cheap and light, but consumes a high amount of fuel, which is burnt in the widest section of what is essentially an open-ended barrel-shaped tube. The lack of a turbine, however, means that the rocket must be boosted to operational speed before the ramjet engine will function.

Variants of the jet engine include vectored thrust engines, allowing vertical takeoff, reverse thrust, used to slow down a jet plane on landing, and reheat or afterburning, used in military aircraft to provide short-duration increases in thrust.

X-ray Astronomy

Astronomy is, essentially, the study of electromagnetic radiation received from the sky. At its most basic, the use of a telescope allows an individual to view the visible part of the electromagnetic spectrum - quite simply gazing at the stars. We've all done it - strictly speaking you don't even need a telescope, though it becomes more interesting with the ability to zoom in. X-ray astronomy, however, is a little more involved and focuses on a separate part of the electromagnetic spectrum, normally invisible to the human eye.
X-rays were first observed in 1895 by Wilhelm Röntgen, a German scientist who stumbled on them quite by accident whilst experimenting with vacuum tubes. A short time later he took an X-ray photograph of his wife's hand, which clearly showed the bones of the hand, along with her wedding ring. The X was initially chosen simply to indicate the unknown nature of the radiation, but became common despite Röntgen's objections.
X-rays simply offer a new way to view objects. Active galaxies, binary star systems, black holes, pulsars and neutron stars all provide far more interesting emissions of X-radiation than everyday visible light. So, in June of 1990, the United States launched a German-built satellite to record these X-rays received from the sky. Referred to as ROSAT, this joint venture was in fact called Röntgen Satellite, for obvious reasons.
Why the need for a dedicated satellite to observe X-rays from space? Simply because although more energetic X-rays can travel through air for a few metres, the earth's atmosphere is more than thick enough to absorb nearly all X-rays from space. So, to view these X-rays from space, the X-ray detectors must be flown above the earth's atmosphere, either by placing the detectors in the nose cone of a rocket (first achieved at the White Sands missile range with a V2 rocket), by elevating a detector with a balloon (a more recent attempt being the High Resolution Gamma-ray and Hard X-ray Spectrometer - HIREGS), or the aforementioned satellite.

Jeans Instability

Jeans Instability, despite its name, has nothing to do with the inherent tendencies of denim-based clothing to split, rend or fail during mission critical applications. This is almost a shame, as the notion of unstable trousers is, to the majority of mankind, far more comprehensible than the following.
Waves and instabilities are often related, and it is in relation to acoustic waves that Jeans Instability arises. When an area of gas is compressed, the pressure increases. This compression is smoothed out by the gas, and in the process acoustic waves are produced - futher areas of compression. Any more compressed areas of gas, however, possess enhanced gravity and thus more gas is pulled into the compressed region.

Normally, this isn't a problem. The minute fluctuations in gravity produced by typical sound waves in the air is negligible, as are the effect. Really - it might as well not have happened for all the effect it has. But transfer this theory to astronomical-sized bodies of gas floating about in deep space, Under such situations the changes in gravity are no longer negligible. More material is pulled to the compressed regions of gas, triggering an instability, and since the nature of this instability was first demonstrated by Jeans in 1902, the instability takes his name.

What form does this instability take? Well, under certain conditions the fluctuations will simply die out; the cloud of gas will disperse and return to its original state. Under other conditions the fluctuations will overpower the pressure of the gas, the perturbation will grow and the gas will continue to contract. It is believed that the stars and galaxies we see around us are the end results of perturbations which initially began as Jeans instabilities.

It should be noted that the instability only occurs for wavelengths greater than a certain size, known as the Jeans length. This length is dependent on density. The Jeans length may, in this case, be directly responsible for the size and distribution of galaxies and other matter in space.