Econstudentlog

Wikipedia articles of interest

i. Shannon–Hartley theorem. Muller talked a little bit about this one in one of the lectures, I don’t remember which, but it’s probably one of the wave-lectures. His coverage is less technical than wikipedia’s. I was considering not including this link because I previously linked to wikipedia’s closely-related article about the Noisy-channel coding theorem, but I decided to do it anyway. From the article:

“In information theory, the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. It is an application of the noisy channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes Shannon’s channel capacity for such a communication link, a bound on the maximum amount of error-free digital data (that is, information) that can be transmitted with a specified bandwidth in the presence of the noise interference, assuming that the signal power is bounded, and that the Gaussian noise process is characterized by a known power or power spectral density. […]

Considering all possible multi-level and multi-phase encoding techniques, the Shannon–Hartley theorem states the channel capacity C, meaning the theoretical tightest upper bound on the information rate (excluding error correcting codes) of clean (or arbitrarily low bit error rate) data that can be sent with a given average signal power S through an analog communication channel subject to additive white Gaussian noise of power N, is:

 C =  B \log_2 \left( 1+\frac{S}{N} \right)

where

C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watts (or volts squared);
N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and
S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels).”

ii. Expansion joint. Also covered by Muller, this is important stuff that people don’t think about:

“An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, to hold certain parts together, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of sidewalks, bridges, railway tracks, piping systems, ships, and other structures.

Throughout the year, building faces, concrete slabs, and pipelines will expand and contract due to the warming and cooling through seasonal variation, or due to other heat sources. Before expansion joint gaps were built into these structures, they would crack under the stress induced.”

If you have any kind of construction of a significant size/length, thermal expansion will cause problems unless you try to deal with it somehow. To use expansion joints to deal with this problem is another one of those hidden ‘good ideas’ people don’t think about, because they probably weren’t even aware there was a problem to be solved.

iii. Beaufort scale.

iv. Belle Gunness. Not all serial killers are/were male:

“Personal – comely widow who owns a large farm in one of the finest districts in La Porte County, Indiana, desires to make the acquaintance of a gentleman equally well provided, with view of joining fortunes. No replies by letter considered unless sender is willing to follow answer with personal visit. Triflers need not apply.[2]” […]

“The suitors kept coming, but none, except for Anderson, ever left the Gunness farm. By this time, she had begun ordering huge trunks to be delivered to her home. Hack driver Clyde Sturgis delivered many such trunks to her from La Porte and later remarked how the heavyset woman would lift these enormous trunks “like boxes of marshmallows”, tossing them onto her wide shoulders and carrying them into the house. She kept the shutters of her house closed day and night; farmers traveling past the dwelling at night saw her digging in the hog pen.” Guess what they found buried in the hog pen later?

v. English garden.

“The English garden, also called English landscape park (French: Jardin anglais, Italian: Giardino all’inglese, German: Englischer Landschaftsgarten, Portuguese: Jardim inglês), is a style of Landscape garden which emerged in England in the early 18th century, and spread across Europe, replacing the more formal, symmetrical Garden à la française of the 17th century as the principal gardening style of Europe.[1] The English garden presented an idealized view of nature. They were often inspired by paintings of landscapes by Claude Lorraine and Nicolas Poussin, and some were Influenced by the classic Chinese gardens of the East,[2] which had recently been described by European travelers.[2] The English garden usually included a lake, sweeps of gently rolling lawns set against groves of trees, and recreations of classical temples, Gothic ruins, bridges, and other picturesque architecture, designed to recreate an idyllic pastoral landscape. By the end of the 18th century the English garden was being imitated by the French landscape garden, and as far away as St. Petersburg, Russia, in Pavlovsk, the gardens of the future Emperor Paul. It also had a major influence on the form of the public parks and gardens which appeared around the world in the 19th century.[3]

A few images from the article (click to view full size):

vi. Aquifer.

“An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer,[1] and aquiclude (or aquifuge), which is a solid, impermeable area underlying or overlying an aquifer. If the impermeable area overlies the aquifer pressure could cause it to become a confined aquifer.” The article has much more.

vii. Great Tit.

“The Great Tit (Parus major) is a passerine bird in the tit family Paridae. It is a widespread and common species throughout Europe, the Middle East, Central and Northern Asia, and parts of North Africa in any sort of woodland. It is generally resident, and most Great Tits do not migrate except in extremely harsh winters. Until 2005 this species was lumped with numerous other subspecies. DNA studies have shown these other subspecies to be distinctive from the Great Tit and these have now been separated as two separate species, the Cinereous Tit of southern Asia, and the Japanese Tit of East Asia. The Great Tit remains the most widespread species in the genus Parus.

The Great Tit is a distinctive bird, with a black head and neck, prominent white cheeks, olive upperparts and yellow underparts, with some variation amongst the numerous subspecies. It is predominantly insectivorous in the summer, but will consume a wider range of food items in the winter months, including small hibernating bats.[2] Like all tits it is a cavity nester, usually nesting in a hole in a tree. The female lays around 12 eggs and incubates them alone, although both parents raise the chicks. In most years the pair will raise two broods. The nests may be raided by woodpeckers, squirrels and weasels and infested with fleas, and adults may be hunted by Sparrowhawks. The Great Tit has adapted well to human changes in the environment and is a common and familiar bird in urban parks and gardens. The Great Tit is also an important study species in ornithology. […]

Great Tits combine dietary versatility with a considerable amount of intelligence and the ability to solve problems with insight learning, that is to solve a problem through insight rather than trial and error.[9] In England, Great Tits learned to break the foil caps of milk bottles delivered at the doorstep of homes to obtain the cream at the top.[24] This behaviour, first noted in 1921, spread rapidly in the next two decades.[25] In 2009, Great Tits were reported killing and eating pipistrelle bats. This is the first time a songbird has been seen to hunt bats. The tits only do this during winter when the bats are hibernating and other food is scarce.[26] They have also been recorded using tools, using a conifer needle in the bill to extract larvae from a hole in a tree.[9] […]

The Great Tit has generally adjusted to human modifications of the environment. It is more common and has better breeding success in areas with undisturbed forest cover, but it has adapted to human modified habitats. It can be very common in urban areas.[9] For example, the breeding population in the city of Sheffield (a city of half a million people) has been estimated at 17,164 individuals.[45] In adapting to human environments its song has been observed to change in noise-polluted urban environments. In areas with low frequency background noise pollution, the song has a higher frequency than in quieter areas.[46]

July 10, 2012 - Posted by | biology, Computer science, Geology, history, wikipedia

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