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p2p architecture

Recommended reading.

“[...] A MojoNation user who wanted to keep a file safe from prying eyes could break it into chunks, encrypt the pieces, and store them on the millions of computers belonging to people who, theoretically, would be running the software worldwide.”

“ Cohen realized that chopping up a file and handing out the pieces to several uploaders would really speed things up. He sketched out a protocol: To download that copy of Meet the Fokkers, a user's computer sniffs around for others online who have pieces of the movie. Then it downloads a chunk from several of them simultaneously. Many hands make light work, so the file arrives dozens of times faster than normal. ”

“[...] The more files you're willing to share, the faster any individual torrent downloads to your computer. This prevents people from leeching, a classic P2P problem in which too many people download files and refuse to upload, creating a drain on the system. "Give and ye shall receive" became Cohen's motto, which he printed on T-shirts and sold to supporters.”

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watching and mapping from space

“Kobrick said he would in future like to fly a satellite that continuously mapped the Earth's topography at a higher resolution, in which the satellite could detect objects as small as a car. Germany is planning to launch its one-metre-resolution TerraSAR-X radar satellite in 2006.”

This article is worth a scan.

New Zealand fly-over animation

All manner of related NASA stuff on the project can be accessed here.

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model fuel cell car

car made from model fuel cell kit. Image credit:

“With this unique kit, you can build your own experimental reversible fuel cell car to learn more about this energy source. With more than 30 experiments and demonstrations, provided either in the kit or on our web site, users will learn how a reversible fuel cell works to perform electrolysis as well as to create energy. The electricity required to activate electrolysis is created with a large solar cell included with the kit. During electrolysis, water is separated into hydrogen and oxygen and the resulting energy is stored as a gas. When needed, the gas is fed into the fuel cell, which then serves as the power source.

“The Thames & Kosmos Fuel Cell kit also includes a digital MultiMate which measures currents and voltage, allowing you to learn exactly what a fuel cell is and how it functions. The experiments and demonstrations explain the physics upon which this future technology is based.


“30 Experiments include: How to build a solar-powered car; Effects of direct and indirect radiation; Characteristics of a solar module; Electrolysis and its effect on water; Oxy-hydrogen test; How to construct and load a reversible fuel cell; Decomposition of water in the fuel cell; Qualitative and quantitative analysis of gas in a fuel cell; How efficient is electrolysis?; How light influences electrolysis; Solar electrolysis; Fuel cell-powered car. Add your own experiments!”

A fascinating site where you can also buy astronaut ice cream, your very own working ‘make a volcano’ kit and a ‘pet tornado’ in a bottle.

There are even news stories.

The kit is priced at US$130. has had had no dealings with this company. This report is given as interesting news only.

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huygens probe starts work today at titan

“On 14 January, a series of three alarm clocks will wake the probe as it approaches the very edges of Titan's atmosphere. [1] It will be travelling at 18,000km per hour at this point, but as it encounters the thick upper atmosphere it will be slowed to just 400km per hour in a mere three minutes. As the craft plunges into the atmosphere, it will generate a huge amount of heat. The heat shield will reach temperatures of up to 1800°C as it is exposed to energies 1000 times more intense than the solar constant.

“The probe contains three parachutes. The first, pilot, parachute will slow the craft to less than 300km per hour. The shell of the module will then fall away, exposing the instruments to the atmosphere, and the second parachute, eight metres wide, will deploy. Once the craft reaches an altitude of around 160km, this large parachute will be cut away and a smaller one deployed. This is to ensure that the craft reaches the ground in time to carry out its surface experiments.”

marker at

“It'll have just about three minutes to relay data to the Cassini mothership as part of a three point three (b) billion dollar international mission to study the Saturn system.”[Quoted from 7kplc]

marker at

“Saturn has been a long-term objective of NASA's planetary program at least since the encounter by Pioneer 11 in 1979, and Saturn and Titan were important targets of Voyagers 1 and 2.” ”[Quoted from]

related material
spectacular images of saturn’s rings
saturn fly-past by cassini
cassini homing in on saturn

end notes

  1. One of Saturn’s eighteen or more moons and the second biggest in the solar system. The only larger moon is the slightly larger Ganymede, orbiting Jupiter. Titan is bigger than either Pluto or Neptune. If Titan circled the sun instead of Saturn, it would be classed as a planet.

    The particular interest in Titan is that it is the only moon with an atmosphere, and the only other place besides the Earth with an atmosphere containing mostly nitrogen.

  2. solar constant: the amount of solar radiation that falls on an area above the top level of the Earth’s atmosphere at a vertical angle. The solar constant equals 1.37 kW/m².

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increasing power of computers

Increasing calculating power of computers. Image credit:

A chart of computer power from 1940.

Detailed versions of similar charts are available here, together with charts showing chess computer and AI program progress.

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radar satellites capture tsunami wave images

There are no other observations of a similar nature anywhere in the world [...] ”

“The satellites saw the first two wavefronts produced by the main quake, spaced 500 to 800 kilometres apart. These waves reached a maximum height of 50 centimetres in the open ocean, only reaching their full devastating height when entering the shallow waters of the coast.

“By comparison, wind-driven waves typically reach 10 metres. However, these waves only involve water close to the ocean surface and are separated by at most several hundred metres.

“Tsunami waves have a very deep reach indeed - 4000 metres or more. "These waves involve the entire depth of the ocean. Their energy is thousands of times more than a monster storm," Fu says. And even though tsunamis barely ripple the surface, they speed through the water as fast as jet airliners.”

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  • Humans have a hearing range of roughly 20 to 20,000 Hertz (the lowest note on a piano is around 33Hz). Sounds that fall below the threshold are not audible, but they are felt. This is infrasonic sound, or infrasound. Infrasonics is the study of sound below the range of human hearing.
  • Infrasonics is one of the three basic sub-branches of acoustics (the other two are ultrasonics and acoustics - for audible sound).
  • Low-frequency sounds (infrasound) are produced by a variety of geophysical (natural) processes including earthquakes, severe weather, volcanic activity, geomagnetic activity, ocean waves and waves pounding the shores, avalanches, turbulence aloft, and meteors hitting the atmosphere.
  • Large-scale, manmade sources of infrasound include nuclear explosions, rocket launches, aircraft and explosions.
  • Since infrasound is not absorbed to the same degree as higher frequencies, it can travel great distances.

  • Some birds can hear infrasound. That they sense the low-frequency waves is a suggestion for why they change behaviour before a storm (often described as predicting the storm).
  • Observations of elephant and other large mammal behavior suggests that they respond to the waves through the ground before they hear them in the air. This is plausible since the waves travel faster in solid material.

  • Although infrasonics was used to detect the location of cannons as early as before the World War II, uses for infrasonic detection has only developed in the last 40 years.
    Some applications are:
    • detect the positions, magnitudes and other characteristics of nuclear explosions, rocket launches or typhoons.
    • forecast some disasters. Many disasters such as volcanic eruptions, earthquakes, mountain landslides, typhoons, blowout of oil wells etc. can radiate infrasound in advance of visual or audible detection, thus one can forecast them using the infrasonic waves received.
    • monitor the activities of atmosphere, particularly large-scale meteorological motions.
    • develop high-powered infrasound generators and exploit infrasonic weapons.

[data synthesised from Institute of Acoustics, Chinese Academy of Sciences, Dept of Physics, Georgia State University, NOAA Environmental Technology Laboratory]

Animals probably sense infrasound from great distances. The infrasound travels many time the speed of sound. The infrasound can scare the animals, who then run away.

However, without witness reports from the animals themselves, this is difficult to verify.

related material
Loud music and hearing damage

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