Econstudentlog

Wikipedia articles of interest

i. Song Dynasty. [featured, great article with lots of links)

“The Song Dynasty (Chinese: 宋朝; pinyin: Sòng Cháo; Wade-Giles: Sung Ch’ao; IPA: [sʊ̂ŋ tʂʰɑ̌ʊ̯]) was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a permanent standing navy. This dynasty also saw the first known use of gunpowder, as well as first discernment of true north using a compass. […]

The population of China doubled in size during the 10th and 11th centuries. This growth came through expanded rice cultivation in central and southern China, the use of early-ripening rice from southeast and southern Asia, and the production of abundant food surpluses.[4][5] […]

The Song Dynasty was an era of administrative sophistication and complex social organization. Some of the largest cities in the world were found in China during this period (Kaifeng and Hangzhou had populations of over a million).[1][48] People enjoyed various social clubs and entertainment in the cities, and there were many schools and temples to provide the people with education and religious services.[1] The Song government supported multiple forms of social welfare programs, including the establishment of retirement homes, public clinics, and pauper‘s graveyards.[1] The Song Dynasty supported a widespread postal service that was modeled on the earlier Han Dynasty (202 BC – AD 220) postal system to provide swift communication throughout the empire.[49] The central government employed thousands of postal workers of various ranks and responsibilities to provide service for post offices and larger postal stations.[50] […]

The Song military was chiefly organized to ensure that the army could not threaten Imperial control, often at the expense of effectiveness in war. Northern Song’s Military Council operated under a Chancellor, who had no control over the imperial army. The imperial army was divided among three marshals, each independently responsible to the Emperor. Since the Emperor rarely led campaigns personally, Song forces lacked unity of command.[89] The imperial court often believed that successful generals endangered royal authority, and relieved or even executed them (notably Li Gang,[90] Yue Fei, and Han Shizhong.[91])

Although the scholar-officials viewed military soldiers as lower members in the hierarchic social order,[92] a person could gain status and prestige in society by becoming a high ranking military officer with a record of victorious battles.[93] At its height, the Song military had one million soldiers[22] divided into platoons of 50 troops, companies made of two platoons, and one battalion composed of 500 soldiers.[94][95] Crossbowmen were separated from the regular infantry and placed in their own units as they were prized combatants, providing effective missile fire against cavalry charges.[95] The government was eager to sponsor new crossbow designs that could shoot at longer ranges, while crossbowmen were also valuable when employed as long-range snipers.[96] Song cavalry employed a slew of different weapons, including halberds, swords, bows, spears, and ‘fire lances‘ that discharged a gunpowder blast of flame and shrapnel.[97]

Military strategy and military training were treated as science that could be studied and perfected; soldiers were tested in their skills of using weaponry and in their athletic ability.[98] The troops were trained to follow signal standards to advance at the waving of banners and to halt at the sound of bells and drums.[95] […]

The economy of the Song Dynasty was one of the most prosperous and advanced economies in the medieval world. […] The Song economy was stable enough to produce over a hundred million kilograms (over two hundred million pounds) of iron product a year.[133] […] The annual output of minted copper currency in 1085 alone reached roughly six billion coins.[4] The most notable advancement in the Song economy was the establishment of the world’s first government issued paper-printed money, known as Jiaozi […] The size of the workforce employed in paper money factories was large; it was recorded in 1175 that the factory at Hangzhou employed more than a thousand workers a day.[135] […]

The innovation of movable type printing was made by the artisan Bi Sheng (990–1051), first described by the scientist and statesman Shen Kuo in his Dream Pool Essays of 1088.[179][180] The collection of Bi Sheng’s original clay-fired typeface was passed on to one of Shen Kuo’s nephews, and was carefully preserved.[180][181] Movable type enhanced the already widespread use of woodblock methods of printing thousands of documents and volumes of written literature, consumed eagerly by an increasingly literate public. The advancement of printing had a deep impact on education and the scholar-official class, since more books could be made faster while mass-produced, printed books were cheaper in comparison to laborious handwritten copies.[67][71] The enhancement of widespread printing and print culture in the Song period was thus a direct catalyst in the rise of social mobility and expansion of the educated class of scholar elites, the latter which expanded dramatically in size from the 11th to 13th centuries.[67][182]

ii. Tidal flexing.

“Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon), and the primary planet that it orbits (e.g. the Earth). The acceleration is usually negative, as it causes a gradual slowing and recession of a satellite in a prograde orbit away from the primary, and a corresponding slowdown of the primary’s rotation. The process eventually leads to tidal locking of first the smaller, and later the larger body. The Earth-Moon system is the best studied case.

The similar process of tidal deceleration occurs for satellites that have an orbital period that is shorter than the primary’s rotational period, or that orbit in a retrograde direction. […]

Because the Moon‘s mass is a considerable fraction of that of the Earth (about 1:81), the two bodies can be regarded as a double planet system, rather than as a planet with a satellite. The plane of the Moon’s orbit around the Earth lies close to the plane of the Earth’s orbit around the Sun (the ecliptic), rather than in the plane perpendicular to the axis of rotation of the Earth (the equator) as is usually the case with planetary satellites. The mass of the Moon is sufficiently large, and it is sufficiently close, to raise tides in the matter of the Earth. In particular, the water of the oceans bulges out along both ends of an axis passing through the centers of the Earth and Moon. The average tidal bulge closely follows the Moon in its orbit, and the Earth rotates under this tidal bulge in just over a day. However, the rotation drags the position of the tidal bulge ahead of the position directly under the Moon. As a consequence, there exists a substantial amount of mass in the bulge that is offset from the line through the centers of the Earth and Moon. Because of this offset, a portion of the gravitational pull between Earth’s tidal bulges and the Moon is perpendicular to the Earth-Moon line, i.e. there exists a torque between the Earth and the Moon. This boosts the Moon in its orbit, and decelerates the rotation of the Earth.

As a result of this process, the mean solar day, which is nominally 86400 seconds long, is actually getting longer when measured in SI seconds with stable atomic clocks. (The SI second, when adopted, was already a little shorter than the current value of the second of mean solar time.[9]) The small difference accumulates every day, which leads to an increasing difference between our clock time (Universal Time) on the one hand, and Atomic Time and Ephemeris Time on the other hand: see ΔT. This makes it necessary to insert a leap second at irregular intervals. […]

Tidal acceleration is one of the few examples in the dynamics of the Solar System of a so-called secular perturbation of an orbit, i.e. a perturbation that continuously increases with time and is not periodic. Up to a high order of approximation, mutual gravitational perturbations between major or minor planets only cause periodic variations in their orbits, that is, parameters oscillate between maximum and minimum values. The tidal effect gives rise to a quadratic term in the equations, which leads to unbounded growth. In the mathematical theories of the planetary orbits that form the basis of ephemerides, quadratic and higher order secular terms do occur, but these are mostly Taylor expansions of very long time periodic terms. The reason that tidal effects are different is that unlike distant gravitational perturbations, friction is an essential part of tidal acceleration, and leads to permanent loss of energy from the dynamical system in the form of heat.”

iii. Error function. Somewhat technical, but interesting (the article has a lot more):

“In mathematics, the error function (also called the Gauss error function) is a special function (non-elementary) of sigmoid shape which occurs in probability, statistics and partial differential equations. It is defined as:[1][2]

\operatorname{erf}(x) = \frac{2}{\sqrt{\pi}}\int_{0}^x e^{-t^2} dt.

(When x is negative, the integral is interpreted as the negative of the integral from x to zero.) […]

The error function is used in measurement theory (using probability and statistics), and although its use in other branches of mathematics has nothing to do with the characterization of measurement errors, the name has stuck.

The error function is related to the cumulative distribution \Phi, the integral of the standard normal distribution (the “bell curve”), by[2]

\Phi (x) = \frac{1}{2}+ \frac{1}{2} \operatorname{erf} \left(x/ \sqrt{2}\right)

The error function, evaluated at  \frac{x}{\sigma \sqrt{2}}  for positive x values, gives the probability that a measurement, under the influence of normally distributed errors with standard deviation \sigma, has a distance less than x from the mean value.[3] This function is used in statistics to predict behavior of any sample with respect to the population mean. This usage is similar to the Q-function, which in fact can be written in terms of the error function.”

iv. Lake Vostok

Lake Vostok (Russian: озеро Восток, lit. “Lake East”) is the largest of more than 140 sub-glacial lakes and was recently drilled into by Russian scientists. The overlying ice provides a continuous paleoclimatic record of 400,000 years, although the lake water itself may have been isolated for 15[3][4] to 25 million years.[5]

Lake Vostok is located at the southern Pole of Cold, beneath Russia‘s Vostok Station under the surface of the central East Antarctic Ice Sheet, which is at 3,488 metres (11,444 ft) above mean sea level. The surface of this fresh water lake is approximately 4,000 m (13,100 ft) under the surface of the ice, which places it at approximately 500 m (1,600 ft) below sea level. Measuring 250 km (160 mi) long by 50 km (30 mi) wide at its widest point, and covering an area of 15,690 km2 (6,060 sq mi), it is similar in area to Lake Ontario, but with over three times the volume. The average depth is 344 m (1,129 ft). It has an estimated volume of 5,400 km3 (1,300 cu mi).[2] The lake is divided into two deep basins by a ridge. The liquid water over the ridge is about 200 m (700 ft), compared to roughly 400 m (1,300 ft) deep in the northern basin and 800 m (2,600 ft) deep in the southern. […]

The coldest temperature ever observed on Earth, −89 °C (−128 °F), was recorded at Vostok Station on 21 July 1983.[3] The average water temperature is calculated to be around −3 °C (27 °F); it remains liquid below the normal freezing point because of high pressure from the weight of the ice above it.[30] Geothermal heat from the Earth’s interior may warm the bottom of the lake.[31][32][33] The ice sheet itself insulates the lake from cold temperatures on the surface. […]

The lake is under complete darkness, under 350 atmospheres (5143 psi) of pressure and expected to be rich in oxygen, so there is speculation that any organisms inhabiting the lake could have evolved in a manner unique to this environment.[19][36] These adaptations to an oxygen-rich environment might include high concentrations of protective oxidative enzymes.

Living Hydrogenophilus thermoluteolus micro-organisms have been found in Lake Vostok’s deep ice core drillings; they are an extant surface-dwelling species.[35][40] This suggests the presence of a deep biosphere utilizing a geothermal system of the bedrock encircling the subglacial lake. There is optimism that microbial life in the lake may be possible despite high pressure, constant cold, low nutrient input, potentially high oxygen concentration and an absence of sunlight.[35][41][42]

Jupiter‘s moon Europa and Saturn‘s moon Enceladus may also harbor lakes or oceans below a thick crust of ice. Any confirmation of life in Lake Vostok could strengthen the prospect for the presence of life on icy moons.[35][43]

v. Nicosia

Nicosia (/ˌnɪkəˈsə/ NIK-ə-SEE), known locally as Lefkosia (Greek: Λευκωσία, Turkish: Lefkoşa), is the capital and largest city in Cyprus, as well as its main business center.[2] After the collapse of the Berlin Wall, Nicosia remained the only divided capital in the world,[3] with the southern and the northern portions divided by a Green Line.[4] It is located near the center of the island, on the banks of the Pedieos River.

Nicosia is the capital and seat of government of the Republic of Cyprus. The northern part of the city functions as the capital of the self-proclaimed Turkish Republic of Northern Cyprus, a disputed breakaway region whose independence is recognized only by Turkey, and which the rest of the international community considers as occupied territory of the Republic of Cyprus since the Turkish Invasionin 1974. […]

The Turkish invasion, the continuous occupation of Cyprus as well as the self-declaration of independence of the TRNC have been condemned by several United Nations Resolutions adopted by the General Assembly and the Security Council. The Security Council is reaffirming their condemnation every year.[40]

vi. Perennial plant

“A perennial plant or simply perennial (Latin per, “through”, annus, “year”) is a plant that lives for more than two years.[1] The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials. More correctly, woody plants like shrubs and trees are also perennials.

Perennials, especially small flowering plants, grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring from their root-stock, in addition to seeding themselves as an annual plant does. These are known as herbaceous perennials. However, depending on the rigors of local climate, a plant that is a perennial in its native habitat, or in a milder garden, may be treated by a gardener as an annual and planted out every year, from seed, from cuttings or from divisions. […]

Although most of humanity is fed by seeds from annual grain crops, perennial crops provide numerous benefits.[3] Perennial plants often have deep, extensive root systems which can hold soil to prevent erosion, capture dissolved nitrogen before it can contaminate ground and surface water, and outcompete weeds (reducing the need for herbicides). These potential benefits of perennials have resulted in new attempts to increase the seed yield of perennial species,[4] which could result in the creation of new perennial grain crops.[5] Some examples of new perennial crops being developed are perennial rice and intermediate wheatgrass.”

vii. Anaconda Plan.

“The Anaconda Plan or Scott’s Great Snake is the name widely applied to an outline strategy for subduing the seceding states in the American Civil War. Proposed by General-in-Chief Winfield Scott, the plan emphasized the blockade of the Southern ports, and called for an advance down the Mississippi River to cut the South in two. Because the blockade would be rather passive, it was widely derided by the vociferous faction who wanted a more vigorous prosecution of the war, and who likened it to the coils of an anaconda suffocating its victim. The snake image caught on, giving the proposal its popular name.”

viii. Caesar cipher (featured).

“In cryptography, a Caesar cipher, also known as Caesar’s cipher, the shift cipher, Caesar’s code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a shift of 3, A would be replaced by D, B would become E, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

The encryption step performed by a Caesar cipher is often incorporated as part of more complex schemes, such as the Vigenère cipher, and still has modern application in the ROT13 system. As with all single alphabet substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communication security.”

If you don’t really know much about cryptography but would like a quick and accessible introduction to the subject matter, I recommend Brit Cruise’ videos on the subject at Khan Academy.

ix. Water purification. From the article:

“It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 19th century – must now be tested before determining what kind of treatment, if any, is needed. Chemical and microbiological analysis, while expensive, are the only way to obtain the information necessary for deciding on the appropriate method of purification.

According to a 2007 World Health Organization (WHO) report, 1.1 billion people lack access to an improved drinking water supply, 88 percent of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, and 1.8 million people die from diarrheal diseases each year. The WHO estimates that 94 percent of these diarrheal cases are preventable through modifications to the environment, including access to safe water.[1] Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year.[2] Reducing deaths from waterborne diseases is a major public health goal in developing countries.”

Here’s a related paper on ‘Global Distribution of Outbreaks of Water-Associated Infectious Diseases‘ which I’ve previously blogged here.

June 6, 2012 - Posted by | astronomy, biology, Cryptography, Geography, health, history, mathematics, medicine, Physics, wikipedia

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