Archive for January 17th, 2012

January 17, 2012



plug computer

FreedomBox is a community project to develop, design and promote personal servers running free software for distributed social networking, email and audio/video communications. The project was announced by Columbia Law professor Eben Moglen at an ISOC (Internet Society) meeting in 2010.

The project currently describes a FreedomBox as, ‘a personal server running a free software operating system, with free applications designed to create and preserve personal privacy.’ The project aims to develop a software stack that can run on plug computers (small computers the size of a wall wart) that can easily be located in individual residences or offices. By promoting a decentralized deployment of hardware, the project hopes that FreedomBoxes will ‘provide privacy in normal life, and safe communications for people seeking to preserve their freedom in oppressive regimes.’

January 17, 2012


Tollmanns hypothetical bolide

The word ‘bolide‘ [boh-lahyd] comes from the Greek ‘bolis,’ which can mean ‘missile’ or ‘to flash.’ The International Astronomical Union (IAU) has no official definition of ‘bolide,’ and generally considers the term synonymous with ‘fireball,’ a brighter-than-usual meteor. The IAU defines a fireball as ‘a meteor brighter than any of the planets’ (magnitude −4 or greater). Astronomers tend to use ‘bolide’ to identify an exceptionally bright fireball (magnitude −14 or brighter), particularly one that explodes (sometimes called a detonating fireball).

It may also be used to mean a fireball which creates audible sounds. If the magnitude of a bolide reaches −17 or brighter it is known as a ‘superbolide.’ Geologists use the term ‘bolide’ more often than astronomers do: in geology it indicates a very large impactor. For example, the U.S. Geological Survey uses the term to mean a generic large crater-forming projectile ‘to imply that we do not know the precise nature of the impacting body … whether it is a rocky or metallic asteroid, or an icy comet, for example.’

January 17, 2012

Green Wave

green wave by Jay Harel

A green wave is an intentionally induced phenomenon in which a series of traffic lights (usually three or more) are coordinated to allow continuous traffic flow over several intersections in one main direction. Any vehicle travelling along with the green wave (at an approximate speed decided upon by the traffic engineers) will see a progressive cascade of green lights, and not have to stop at intersections. This allows higher traffic loads, and reduces noise and energy use (because less acceleration and braking is needed).

In practical use, only a group of cars (known as a ‘platoon,’ the size of which is defined by the signal times) can use the green wave before the time band is interrupted to give way to other traffic flows. The coordination of the signals is sometimes done dynamically, according to sensor data of currently existing traffic flows – otherwise it is done statically, by the use of timers.

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January 17, 2012

Traffic Wave

traffic wave

Traffic waves, also called stop waves or traffic shocks, are travelling disturbances in the distribution of cars on a highway. Traffic waves usually travel backwards in relation to the motion of the cars themselves, or ‘upstream.’ The waves can also travel downstream, however, more commonly become ‘pinned’ to a single spot on the road, as a soliton (solitary wave). Traffic waves are a type of traffic jam. A deeper understanding of traffic waves is a goal of the physical study of traffic flow, in which traffic itself can often be seen using techniques similar to those used in fluid dynamics.

It has been said that by knowing how traffic waves are created, drivers can sometimes reduce their effects by increasing vehicle headways and reducing the use of brakes, ultimately alleviating traffic congestion for everyone in the area.