Econstudentlog

Wikipedia articles of interest

i. Alternation of generations. It’s a bit technical, but I thought the article was interesting:

Alternation of generations (also known as alternation of phases or metagenesis) is a term primarily used to describe the life cycle of plants (taken here to mean the Archaeplastida). A multicellular sporophyte, which is diploid with 2N paired chromosomes (i.e. N pairs), alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes. A mature sporophyte produces spores by meiosis, a process which results in a reduction of the number of chromosomes by a half. Spores germinate and grow into a gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a zygote, which develops into a diploid sporophyte. This cycle, from sporophyte to sporophyte (or equally from gametophyte to gametophyte), is the way in which all land plants and many algae undergo sexual reproduction.

The relationship between the sporophyte and gametophyte varies among different groups of plants. In those algae which have alternation of generations, the sporophyte and gametophyte are separate independent organisms, which may or may not have a similar appearance. In liverworts, mosses and hornworts, the sporophyte is less well developed than the gametophyte, being entirely dependent on it in the first two groups. By contrast, the fern gametophyte is less well developed than the sporophyte, forming a small flattened thallus. In flowering plants, the reduction of the gametophyte is even more extreme; it consists of just a few cells which grow entirely inside the sporophyte.

All animals develop differently. A mature animal is diploid and so is, in one sense, equivalent to a sporophyte. However, an animal directly produces haploid gametes by meiosis. No haploid spores capable of dividing are produced, so neither is a haploid gametophyte. There is no alternation between diploid and haploid forms. […] Life cycles, such as those of plants, with alternating haploid and diploid phases can be referred to as diplohaplontic (the equivalent terms haplodiplontic, diplobiontic or dibiontic are also in use). Life cycles, such as those of animals, in which there is only a diploid phase are referred to as diplontic. (Life cycles in which there is only a haploid phase are referred to as haplontic.)

ii. Lightning. Long article, lots of stuff and links:

Lightning is an atmospheric electrical discharge (spark) accompanied by thunder, usually associated with and produced by cumulonimbus clouds, but also occurring during volcanic eruptions or in dust storms.[1] From this discharge of atmospheric electricity, a leader of a bolt of lightning can travel at speeds of 220,000 km/h (140,000 mph), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse silica sand into glass channels known as fulgurites, which are normally hollow and can extend as much as several meters into the ground.[2][3]

There are some 16 million lightning storms in the world every year.[4] Lightning causes ionisation in the air through which it travels, leading to the formation of nitric oxide and ultimately, nitric acid, of benefit to plant life below.

Lightning can also occur within the ash clouds from volcanic eruptions,[5] or can be caused by violent forest fires which generate sufficient dust to create a static charge.[1][6]

How lightning initially forms is still a matter of debate.[7] Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, friction, and atmospheric pressure) to the impact of solar wind and accumulation of charged solar particles.[4] Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning.[4]

The irrational fear of lightning (and thunder) is astraphobia. The study or science of lightning is called fulminology, and someone who studies lightning is referred to as a fulminologist.[8] [I had no idea there was a name for this!] […]

An old estimate of the frequency of lightning on Earth was 100 times a second. Now that there are satellites that can detect lightning, including in places where there is nobody to observe it, it is known to occur on average 44 ± 5 times a second, for a total of nearly 1.4 billion flashes per year;[101][102] 75% of these flashes are either cloud-to-cloud or intra-cloud and 25% are cloud-to-ground.[103]

Approximately 70% of lightning occurs in the tropics where the majority of thunderstorms occur. The place where lightning occurs most often (according to the data from 2004–2005) is near the small village of Kifuka in the mountains of eastern Democratic Republic of the Congo,[105] where the elevation is around 975 metres (3,200 ft). On average this region receives 158 lightning strikes per 1 square kilometer (0.39 sq mi) a year.[102]

Above the Catatumbo river, which feeds Lake Maracaibo in Venezuela, Catatumbo lightning flashes several times per minute, 140 to 160 nights per year, accounting for 25% of the world’s production of upper-atmospheric ozone. Singapore has one of the highest rates of lightning activity in the world.[106] The city of Teresina in northern Brazil has the third-highest rate of occurrences of lightning strikes in the world.”

iii. Dreadnought (featured).

“The dreadnought was the predominant type of battleship in the early 20th-century. The first of the kind, the Royal Navy‘s Dreadnought, had such an impact when launched in 1906 that similar battleships built after her were referred to as “dreadnoughts”, and earlier battleships became known as pre-dreadnoughts. Her design had two revolutionary features: an “all-big-gun” armament scheme and steam turbine propulsion. The arrival of the dreadnoughts renewed the naval arms race, principally between the United Kingdom and Germany but reflected worldwide, as the new class of warships became a crucial symbol of national power. […]

While dreadnought-building consumed vast resources in the early 20th century, there was only one battle between large dreadnought fleets. At the Battle of Jutland, the British and German navies clashed with no decisive result. The term “dreadnought” gradually dropped from use after World War I, especially after the Washington Naval Treaty, as all remaining battleships shared dreadnought characteristics; it can also be used to describe battlecruisers, the other type of ship resulting from the dreadnought revolution.[1] […]

The building of Dreadnought coincided with increasing tension between the United Kingdom and Germany. Germany had begun to build a large battlefleet in the 1890s, as part of a deliberate policy to challenge British naval supremacy. With the conclusion of the Entente Cordiale between the United Kingdom and France in April 1904, it became increasingly clear that the United Kingdom’s principal naval enemy would be Germany, which was building up a large, modern fleet under the ‘Tirpitz’ laws. This rivalry gave rise to the two largest dreadnought fleets of the pre-war period.[93]

The first German response to Dreadnought came with the Nassau class, laid down in 1907. This was followed by the Helgoland class in 1909. Together with two battlecruisers—a type for which the Germans had less admiration than Fisher, but which could be built under authorization for armored cruisers, rather than capital ships—these classes gave Germany a total of ten modern capital ships built or building in 1909. While the British ships were somewhat faster and more powerful than their German equivalents, a 12:10 ratio fell far short of the 2:1 ratio that the Royal Navy wanted to maintain.[94]

In 1909, the British Parliament authorized an additional four capital ships, holding out hope Germany would be willing to negotiate a treaty about battleship numbers. If no such solution could be found, an additional four ships would be laid down in 1910. Even this compromise solution meant (when taken together with some social reforms) raising taxes enough to prompt a constitutional crisis in the United Kingdom in 1909–10. In 1910, the British eight-ship construction plan went ahead, including four Orion (1910)-class super-dreadnoughts, and augmented by battlecruisers purchased by Australia and New Zealand. In the same period of time, Germany laid down only three ships, giving the United Kingdom a superiority of 22 ships to 13. […]

The dreadnought race stepped up in 1910 and 1911, with Germany laying down four capital ships each year and the United Kingdom five. Tension came to a head following the German Naval Law of 1912. This proposed a fleet of 33 German battleships and battlecruisers, outnumbering the Royal Navy in home waters. To make matters worse for the United Kingdom, the Imperial Austro-Hungarian Navy was building four dreadnoughts, while the Italians had four and were building two more. Against such threats, the Royal Navy could no longer guarantee vital British interests. The United Kingdom was faced with a choice of building more battleships, withdrawing from the Mediterranean, or seeking an alliance with France. Further naval construction was unacceptably expensive at a time when social welfare provision was making calls on the budget. Withdrawing from the Mediterranean would mean a huge loss of influence, weakening British diplomacy in the Mediterranean and shaking the stability of the British Empire. The only acceptable option, and the one recommended by First Lord of the Admiralty Winston Churchill, was to break with the policies of the past and make an arrangement with France. The French would assume responsibility for checking Italy and Austria-Hungary in the Mediterranean, while the British would protect the north coast of France. In spite of some opposition from British politicians, the Royal Navy organised itself on this basis in 1912.[96]

In spite of these important strategic consequences, the 1912 Naval Law had little bearing on the battleship force ratios. The United Kingdom responded by laying down ten new super-dreadnoughts in her 1912 and 1913 budgets—ships of the Queen Elizabeth and Revenge classes, which introduced a further step change in armament, speed and protection—while Germany laid down only five, focusing resources on the Army.[97]

iv. Travelling salesman problem.

“The travelling salesman problem (TSP) is an NP-hard problem in combinatorial optimization studied in operations research and theoretical computer science. Given a list of cities and their pairwise distances, the task is to find the shortest possible route that visits each city exactly once and returns to the origin city. It is a special case of the travelling purchaser problem.

The problem was first formulated as a mathematical problem in 1930 and is one of the most intensively studied problems in optimization. It is used as a benchmark for many optimization methods. Even though the problem is computationally difficult, a large number of heuristics and exact methods are known, so that some instances with tens of thousands of cities can be solved.

The TSP has several applications even in its purest formulation, such as planning, logistics, and the manufacture of microchips. Slightly modified, it appears as a sub-problem in many areas, such as DNA sequencing. In these applications, the concept city represents, for example, customers, soldering points, or DNA fragments, and the concept distance represents travelling times or cost, or a similarity measure between DNA fragments. In many applications, additional constraints such as limited resources or time windows make the problem considerably harder. […]

The most direct solution would be to try all permutations (ordered combinations) and see which one is cheapest (using brute force search). The running time for this approach lies within a polynomial factor of O(n!), the factorial of the number of cities, so this solution becomes impractical even for only 20 cities. One of the earliest applications of dynamic programming is the Held–Karp algorithm that solves the problem in time O(n22n).[13] […]

An exact solution for 15,112 German towns from TSPLIB was found in 2001 using the cutting-plane method proposed by George Dantzig, Ray Fulkerson, and Selmer M. Johnson in 1954, based on linear programming. The computations were performed on a network of 110 processors located at Rice University and Princeton University (see the Princeton external link). The total computation time was equivalent to 22.6 years on a single 500 MHz Alpha processor. In May 2004, the travelling salesman problem of visiting all 24,978 towns in Sweden was solved: a tour of length approximately 72,500 kilometers was found and it was proven that no shorter tour exists.[16]

In March 2005, the travelling salesman problem of visiting all 33,810 points in a circuit board was solved using Concorde TSP Solver: a tour of length 66,048,945 units was found and it was proven that no shorter tour exists. The computation took approximately 15.7 CPU-years (Cook et al. 2006). In April 2006 an instance with 85,900 points was solved using Concorde TSP Solver, taking over 136 CPU-years […]

Various heuristics and approximation algorithms, which quickly yield good solutions have been devised. Modern methods can find solutions for extremely large problems (millions of cities) within a reasonable time which are with a high probability just 2–3% away from the optimal solution.”

v. Ediacara biota (featured).

“The Ediacara (play /ˌdiˈækərə/; formerly Vendian) biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period (ca. 635–542 Ma). Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.[note 1] The Ediacara biota radiated in an event called the Avalon Explosion, 575 million years ago,[1][2] after the Earth had thawed from the Cryogenian period’s extensive glaciation, and largely disappeared contemporaneously with the rapid appearance of biodiversity known as the Cambrian explosion. Most of the currently existing body-plans of animals first appeared only in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota completely replaced the organisms that populated the Ediacaran fossil record.

The organisms of the Ediacaran Period first appeared around 585 million years ago and flourished until the cusp of the Cambrian 542 million years ago when the characteristic communities of fossils vanished. The earliest reasonably diverse Ediacaran community was discovered in 1995 in Sonora, Mexico, and is approximately 585 million years in age, roughly synchronous with the Gaskiers glaciation.[3] While rare fossils that may represent survivors have been found as late as the Middle Cambrian (510 to 500 million years ago) the earlier fossil communities disappear from the record at the end of the Ediacaran leaving only curious fragments of once-thriving ecosystems.[4] Multiple hypotheses exist to explain the disappearance of this biota, including preservation bias, a changing environment, the advent of predators and competition from other life-forms.

Determining where Ediacaran organisms fit in the tree of life has proven challenging; it is not even established that they were animals, with suggestions that they were lichens (fungus-alga symbionts), algae, protists known as foraminifera, fungi or microbial colonies, to hypothetical intermediates between plants and animals. The morphology and habit of some taxa (e.g. Funisia dorothea) suggest relationships to Porifera or Cnidaria.[5] Kimberella may show a similarity to molluscs, and other organisms have been thought to possess bilateral symmetry, although this is controversial. Most macroscopic fossils are morphologically distinct from later life-forms: they resemble discs, tubes, mud-filled bags or quilted mattresses. Due to the difficulty of deducing evolutionary relationships among these organisms some paleontologists have suggested that these represent completely extinct lineages that do not resemble any living organism. One paleontologist proposed a separate kingdom level category Vendozoa (now renamed Vendobionta)[6] in the Linnaean hierarchy for the Ediacaran biota. If these enigmatic organisms left no descendants their strange forms might be seen as a “failed experiment” in multicellular life with later multicellular life independently evolving from unrelated single-celled organisms.[7]

Terms like ‘may have’ (9), ‘perhaps’ (3) and ‘probably’ (3) are abundant in the article, but think about how long time ago this was. I think it’s frankly just incredibly awesome that we even know anything at all.

vi. Three Emperors Dinner. Yes, there’s a Wikipedia article about a dinner that happened more than 100 years ago. Wikipedia is awesome!

“The Dîner des trois empereurs or Three Emperors Dinner was a banquet held at Café Anglais in Paris, France on 7 June 1867.

It was prepared by chef Adolphe Dugléré at the request of King William I of Prussia who frequented the cafe during the Exposition Universelle. He requested a meal to be remembered and at which no expense was to be spared for himself and his guests, Tsar Alexander II of Russia, plus his son the tsarevitch (who later became Tsar Alexander III), and Prince Otto von Bismarck. The cellar master, Claudius Burdel, was instructed to accompany the dishes with the greatest wines in the world, including a Roederer champagne in a special lead glass bottle, so Tsar Alexander could admire the bubbles and golden colour.[1]

The banquet consisted of 16 courses with eight wines served over eight hours. The cost of the meal was 400 francs per person[2] (about 8,800 in 2012 prices).”

June 17, 2012 - Posted by | biology, genetics, history, mathematics, Paleontology, wikipedia

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