title: Stress (mechanics)

paragraphs: Stress is the force per unit area on a body that tends to cause it to change shape.

paragraphs: Stress is a measure of the internal forces in a body between its particles. These internal forces are a reaction to the external forces applied on the body that cause it to separate, compress or slide. External forces are either surface forces or body forces. Stress is the average force per unit area that a particle of a body exerts on an adjacent particle, across an imaginary surface that separates them.

paragraphs: The formula for uniaxial normal stress is:

paragraphs: where σ is the stress, F is the force and A is the surface area.

paragraphs: In SI units, force is measured in newtons and area in square metres. This means stress is newtons per square meter, or N/m. However, stress has its own SI unit, called the pascal. 1 pascal (symbol Pa) is equal to 1 N/m. In Imperial units, stress is measured in pound-force per square inch, which is often shortened to "psi". The dimension of stress is the same as that of pressure.

paragraphs: In continuum mechanics, the loaded deformable body behaves as a continuum. So, these internal forces are distributed continually within the volume of the material body. (This means that the stress distribution in the body is expressed as a piecewise continuous function of space and time.) The forces cause deformation of the body's shape. The deformation can lead to a permanent shape change or structural failure if the material is not strong enough.

paragraphs: Some models of continuum mechanics treat force as something that can change. Other models look at the deformation of matter and solid bodies, because the characteristics of matter and solids are three dimensional. Each approach can give different results. Classical models of continuum mechanics assume an average force and do not properly include "geometrical factors". (The geometry of the body can be important to how stress is shared out and how energy builds up during the application of the external force.)

paragraphs: In some situations, the stress within an object can be described by a single number, or by a single vector (a number and a direction). Three such simple stress situations are the "uniaxial normal stress", the "simple shear stress", and the "isotropic normal stress".

paragraphs: Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress.

paragraphs: Therefore in a uniaxial material the length increases in the tensile stress direction and the other two directions will decrease in size. In the uniaxial manner of tension, tensile stress is induced by pulling forces. Tensile stress is the opposite of compressive stress.

paragraphs: Structural members in direct tension are ropes, soil anchors and nails, bolts, etc. Beams subjected to bending moments may include tensile stress as well as compressive stress and/or shear stress.

paragraphs: Tensile stress may be increased until the reach of tensile strength, namely the "limit state" of stress.

paragraphs: All real objects occupy three-dimensional space. However, if two dimensions are very large or very small compared to the others, the object may be modelled as one-dimensional. This simplifies the mathematical modelling of the object. One-dimensional objects include a piece of wire loaded at the ends and viewed from the side, and a metal sheet loaded on the face and viewed up close and through the cross section.


title: Pericyclic reaction

paragraphs: In organic chemistry, a pericyclic reaction is a type of chemical reaction between organic compounds. In the case of pericyclic reactions, the transition state of the molecule is a ring (has a cyclic geometry), and the reaction goes forward in a concerted way. Pericyclic reactions are usually rearrangement reactions. The most important groups of pericyclic reactions are:

paragraphs: In general, pericyclic reactions are equilibrium processes. However, it is possible to push the reaction in one direction if the product is at a significantly lower energy level. This is applying Le Chatelier's principle to a reaction involving a single molecule.

paragraphs: Many pericyclic reactions have similar stepwise radical processes connected with them. Chemists disagree whether some reactions are pericyclic reactions. For example, it is not definitively known whether the [2+2] cycloaddition mechanism is concerted (or may depend on the reactive system). Many pericyclic reactions have similar reactions that are metal-catalyzed. But these metal-catalyzed reactions are also not really pericyclic. The metal catalysts stabilize the reaction intermediates. So the reaction is not concerted, but rather metal-stabilized.

paragraphs: A large photoinduced hydrogen sigmatropic shift was utilized in a corrin synthesis performed by Albert Eschenmoser containing a 16π system.

paragraphs: Due to the principle of microscopic reversibility, there is a parallel set of "retro" pericyclic reactions, which perform the reverse reaction.

paragraphs: Pericyclic reactions also happen in several biological processes:


title: 2011–12 Manchester United F.C. season

paragraphs: The 2011–12 season is Manchester United's 20th season in the Premier League.

paragraphs: Manchester United signed a £40 million four-year deal with DHL.

paragraphs: On November, Sir Alex Ferguson celebrated 25 years in charge of the club.

paragraphs: Manchester United started their season with a tour in the United States. United finishing the tour with a game against Barcelona in Washington on 30 July.

paragraphs: Manchester United will face Benfica, Basel and Otelul Galati in Group C.

paragraphs: Manchester United were drawn against Crystal Palace in the quarter-finals of the League Cup.


title: The Annoying Orange

paragraphs: The Annoying Orange is a comedy web series created by Dane Boedigheimer. The main character is an orange who annoys other fruits. The episodes are uploaded to the YouTube channel "realannoyingorange" weekly, with now over 200 videos. , The channel had almost 3 million subcribers. At that time, it was 43rd in terms of how many people are subscribed to it.

paragraphs: Orange is the main character. He is described as really annoying, but sometimes funny. He warns others about a knife and other items ready to kill them.

paragraphs: Pear is described as a normal/bad/lying/negative/abusive character. He was Orange (Annoying Orange)'s best friend and normally tells Orange to stop being annoying and shut up, but it is discovered in the episode "Wishful Thinking" that Pear would not be friends without Grapefruit. Pear is in Grapefruit's gang and was making fun of Orange.

paragraphs: Midget Apple is a small apple in the series. He does not like being called "Midget Apple", prefering the term "Little Apple".

paragraphs: Apple is Orange's former best friend and current rival (bully). Apple is in Grapefruit's bullying gang.

paragraphs: In 2012, Cartoon Network made a 2012-2014 high fructose adventures TV show based on the YouTube series.


title: Cycloaddition

paragraphs: A cycloaddition is a chemical reaction between reactants with double bonds that get replaced by a ring structure. It is a pericyclic chemical reaction where "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." It is a cyclization reaction: it makes new ring of atoms.

paragraphs: Cycloadditions are named by the basic size of the molecules that are being brought together. This would make the Diels–Alder reaction a [4 + 2]cycloaddition, and the 1,3-dipolar cycloaddition a [3 + 2]cycloaddition. This type of reaction is a non-polar addition reaction.

paragraphs: Heat can cause the double bonds to form a ring. Thermal cycloadditions usually have (4n + 2) π electrons participating in the starting material, for some whole number "n". Because of orbital symmetry, most cycloadditions are suprafacial-suprafacial. Rarely, they are antarafacial-antarafacial. There are a few examples of thermal cycloadditions which have 4n π electrons (for example the [2 + 2] cycloaddition). These proceed in a suprafacial-antarafacial sense. For example, the dimerisation of ketene has a orthogonal set of p orbitals. Those p orbitals allow the reaction to proceed using a crossed transition state.

paragraphs: Light can also cause the double bonds to form a ring. Cycloadditions in which 4n π electrons participate can also occur as a result of photochemical activation. Here, one component makes an electron move from the highest occupied molecular orbital (HOMO) (π bonding) to the lowest unoccupied molecular orbital (LUMO) (π* antibonding). After the electron is promoted to the higher orbital, orbital symmetry allows the reaction to proceed in a suprafacial-suprafacial manner. An example is the DeMayo reaction. Another example is shown below, the photochemical dimerization of cinnamic acid.

paragraphs: Note that not all photochemical (2+2) cyclizations are cycloadditions; some are known to operate by radical mechanisms.

paragraphs: Some cycloadditions instead of π bonds operate through strained cyclopropane rings; as these have significant π character. For example, an analog for the Diels–Alder reaction is the quadricyclane-DMAD reaction:

paragraphs: In the (i+j+...) cycloaddition notation i and j refer to the number of atoms involved in the cycloaddition. In this notation a Diels-Alder reaction is a (4+2)cycloaddition and a 1,3-dipolar addition such as the first step in ozonolysis is a (3+2)cycloaddition. This notation uses parenthesis. The IUPAC preferred notation however, with [i+j+...] counts electrons and not atoms. It uses square brackets. In this notation, the Diels–Alder reaction and the dipolar reaction both become a [4+2]cycloaddition. The reaction between norbornadiene and an activated alkyne is a [2+2+2]cycloaddition.

paragraphs: The Diels–Alder reaction is a [4+2]cycloaddition reaction.

paragraphs: The Huisgen cycloaddition reaction is a [2+3]cycloaddition.

paragraphs: The Nitrone-olefin cycloaddition is a [3+2]cycloaddition.

paragraphs: Cycloadditions often have metal-catalyzed and stepwise radical analogs, however these are not strictly speaking pericyclic reactions. When charged or radical intermediates are involved in a cycloaddition, or when the cycloaddition result is found in a series of reaction steps, they are sometimes called formal cycloadditions to make a difference from true pericyclic cycloadditions.

paragraphs: One example of a formal [3+3]cycloaddition between a cyclic enone and an enamine catalyzed by "n"-butyllithium is a Stork enamine / 1,2-addition cascade reaction:


title: Cheletropic reaction

paragraphs: Cheletropic reactions are a type of pericyclic reaction where one atom on one of the reagents gets two new bonds. A pericyclic reaction is one that involves a transition state with a cyclic array of atoms and an associated cyclic array of interacting orbitals. A reorganization of σ and π bonds occurs in this cyclic array.

paragraphs: Cheletropic reactions are a subclass of cycloadditions. What sets cheletropic reactions apart is that on one of the reagents, both new bonds are being made to the same atom. A few examples are shown to the right in Figure 1. In the first case, the single atom is the carbon atom in the carbonyl group. That carbon atom ends up in carbon monoxide. The end result is making two new bonds to one atom. The first two examples are known as "cheletropic extrusions" because a small stable molecule is given off in the reaction. The driving force for these reactions is often the entropic benefit of releasing a gas (e.g. CO or N).

paragraphs: Because of the geometry of the molecules involved in cheletropic reactions, they confirm a number of predictions made by theoretical chemists. Cheletropic reactions confirm the conservation of molecular orbital symmetry.

paragraphs: In the pericyclic transition state, a small molecule donates two electrons to the ring. Two possible geometries can explain the reaction. The small molecule can approach in either a linear or non-linear way. In the linear approach, the electrons in the orbital of the small molecule are pointed directly at the π system of the big molecule. In the non-linear approach, the orbital approaches at a slightly off angle. The π-systems ability to rotate as the small molecule approaches is crucial in forming new bonds. The direction of rotation will be different depending on how many π-electrons are in the system. A diagram of a two-electron fragment approaching a four-electron π-system using frontier molecular orbitals is shown below. The rotation will be disrotatory if the small molecule approaches linearly and conrotatory if the molecule approaches non-linearly. Disrotatory and conrotatory tell how the bonds in the π-system are rotating. Disrotatory means opposite directions while conrotatory means the same direction. This is also shown in the diagram below.

paragraphs: Using Huckel's Rule, one can tell if the π-system is aromatic or anti-aromatic. If aromatic, linear approaches use disrotatory motion while non-linear approaches use conrotatory motion. The opposite goes with an anti-aromatic system. Linear approaches will have conrotatory motion while non-linear approaches will have disrotatory motion.

paragraphs: When sulfur dioxide reacts with butadiene and isoprene, two different products result. The reaction mechanism will control what gets made. A kinetic product and a thermodynamic product are both possible. More of the thermodynamic product gets made than the kinetic product. The kinetic product comes from a Diels–Alder reaction, while a cheletropic reaction makes a more thermodynamically stable product. The cheletropic pathway is used more because it makes to a more stable five-membered ring adduct. The scheme below shows the difference between the two products. The path to the left shows the thermodynamic product, while the path to the right shows the kinetic product. Suarez and Sordo showed this in 1995. They showed this both with experiments and using Gaussian calculations.

paragraphs: One example of this is the cheletropic reactions of 1,3-dienes with sulfur dioxide. Chemists have carefully looked at the kinetics of this reaction. In 1976, Isaacs and Laila measured the kenetic factors for the addition of sulfur dioxide to butadiene derivatives. Rates of addition were monitored in benzene at 30 °C with an initial twentyfold excess of diene. They used a spectrophotometer to study light at 320 nm to measure the disappearance of SO. The reaction showed "pseudo first-order kinetics". The chemists found that electron-withdrawing groups on the diene decreased the rate of reaction. Also, the reaction rate was affected considerably by steric effects of 2-substituents, with more bulky groups increasing the rate of reaction. (In other words, the larger the group of atoms hanging from the second carbon atom, the quicker the reaction ran.) The authors attribute this to the tendency of bulky groups to favor the cisoid conformation of the diene which is essential to the reaction (see table below). In addition, the rates at four temperatures were measured for seven of the dienes. From these measurements, chemists used the Arrhenius equation to calculate the enthalpy of activation (ΔH) and entropy of activation (ΔS) for each reaction. This was one of the first important efforts to study the kenetics of a cheletropic reaction.

paragraphs: Monnat, Vogel, and Sordo, in 2002, measured the kinetics of addition of sulfur dioxide to 1,2-dimethylidenecycloalkanes. They wrote that the reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide can give two different products depending on reaction conditions. The reaction makes the corresponding sultine through a hetero-Diels-Alder reaction under kinetic control (≤ -60 °C), but, under thermodynamic control (≥ -40 °C), the reaction makes the corresponding sulfolene through a cheletropic reaction. The activation enthalpy for the hetero-Diels-Alder reaction is about 2 kcal/mol smaller than that for the corresponding cheletropic reaction. The sulfolene is about 10 kcal/mol more stable than the isometric sultine in CHCl/SO solution.

paragraphs: The authors were able to experimentally work out a rate law at 261.2 K for the reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide to give the corresponding sulfolene. The reaction was first order in 1,2-dimethylidenecyclohexane but second order in sulfur dioxide (see below). This confirmed a prediction of theoretical chemists based on high-level "ab initio" quantum calculations. Using computational methods, the authors proposed a transition structure for the cheletropic reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide (see figure at right). The reaction is second order in sulfur dioxide because another molecule of sulfur dioxide likely binds to the transition state to help stabilize it. Similar results were found in an 1995 study by Suarez, Sordo, and Sordo which used "ab initio" calculations to study the kinetic and thermodynamic control of the reaction of sulfur dioxide with 1,3-dienes.

paragraphs: The effect of the solvent of the cheletropic reaction of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide (shown at right) was kinetically investigated in 14 solvents. The reaction rate constants of the forward and reverse reaction in addition to the equilibrium constants were found to be linearly correlated with the E(30) solvent polarity scale.

paragraphs: Reactions were done at 120 °C and were studied by 1H-NMR spectroscopy of the reaction mixture. The forward rate k was found to decrease by a factor of 4.5 going from cyclohexane to methanol. The reverse rate k was found to increase by a factor of 53 going from cyclohexane to methanol, while the equilibrium constant K decreased by a factor of 140. It is suggested that there is a change of the polarity during the activation process as evidenced by relationships between the equilibrium and kinetic data. The authors say that the reaction appears to be influenced by the polarity of the solvent, and this can be shown by the change in the dipole moments when going from reactant to transition state to product. The authors also state that the cheletropic reaction doesn’t seem to be influenced by either solvent acidity or basicity.

paragraphs: The results of this study lead the authors to expect the following behaviors:

paragraphs: 1. The change in the solvent polarity will influence the rate less than the equilibrium.

paragraphs: 2. The rate constants will be characterized by opposite effect on the polarity: k will slightly decrease with the increase of E(30), and k will increase under the same conditions.

paragraphs: 3. The effect on k will be larger than on k.

paragraphs: One of the most synthetically important cheletropic reactions is the addition of a singlet carbene to an alkene to make a cyclopropane (see figure at left). A carbene is a neutral molecule containing a divalent carbon with six electrons in its valence shell. Because of this, carbenes are highly reactive electrophiles and generated as reaction intermediates. A singlet carbene contains an empty "p" orbital and a roughly "sp" hybrid orbital that has two electrons. Singlet carbenes add stereospecifically to alkenes, and alkene stereochemistry is retained in the cyclopropane product. The mechanism for addition of a carbene to an alkene is a concerted [2+1] cycloaddition (see figure). Carbenes derived from chloroform or bromoform can be used to add CX to an alkene to give a dihalocyclopropane, while the Simmons-Smith reagent adds CH.

paragraphs: Interaction of the filled carbene orbital with the alkene π system creates a four-electron system and favors a non-linear approach. It is also favorable to mix the carbene empty "p" orbital with the filled alkene π orbital. Favorable mixing occurs through a non-linear approach (see figure 2 at right). However, while theory clearly favors a non-linear approach, there are no obvious experimental implications for a linear vs. non-linear approach.


title: Sigmatropic reaction

paragraphs: A sigmatropic reaction in organic chemistry is a pericyclic reaction. A sigmatropic reaction does not use a catalyst and involves a single molecule (an uncatalyzed intramolecular process). It changes one σ-bond into a different σ-bond. The name "sigmatropic" is the result of a compounding of the long-established "sigma" name for single carbon-carbon bonds and the Greek word "tropos", meaning turn. This is a rearrangement reaction which means that the bonds in a molecule shift between atoms without any atoms leaving or new atoms added to the molecule. In a sigmatropic reaction, a substituent moves from one part of a π-bonded system to another part in an intramolecular reaction with simultaneous rearrangement of the π system. True sigmatropic reactions usually do not need a catalyst. Some sigmatropic reactions are catalyzed by a Lewis acid. Sigmatropic reactions often have transition-metal catalysts that form intermediates in analogous reactions. The most well-known of the sigmatropic rearrangements are the [3,3] Cope rearrangement, Claisen rearrangement, Carroll rearrangement and the Fischer indole synthesis.

paragraphs: A special notation is used to describe sigmatropic shifts. Each of the carbon atoms on the backbone of the molecule are assigned a position number. Sigmatropic rearrangements are described by an order term [i,j]. This means the migration of a σ-bond adjacent to one or more π systems to a new position (i-1) and (j-1) atoms removed from the original location of the σ-bond. When the sum of i and j is an even number, this is an indication of the involvement of a neutral, all C atom chain. An odd number suggests that there is a charged C atom or of a heteroatom lone pair replacing a carbon-carbon double bond. Thus, [1,5] and [3,3] shifts become [1,4] and [2,3] shifts with heteroatoms, while preserving symmetry considerations. Hydrogens are omitted in the third example for clarity.

paragraphs: Here is a way to find the order of a given sigmatropic rearrangement. The first step is to give numbers to each atom starting with the atoms of the bond being broken as atom 1. Chemists count the atoms in each direction from the broken bond to the atoms that form the new σ-bond in the product. The numbers that correspond to the atoms forming the new bond are then separated by a comma and placed within brackets. This creates the sigmatropic reaction order descriptor.

paragraphs: Chemists also count atoms when naming a sigmatropic shift where a hydrogen atom moves. The carbon chain does not break in a hydrogen atom migration. So, chemists count across all atoms involved in the reaction rather than only across the closest atoms. For example, the following hydrogen atom migration is of order [1,5], attained by counting counterclockwise through the π system, rather than the [1,3] order through the ring CH group that would mistakenly result if counted clockwise.

paragraphs: Chemists have studied sigmatropic reactions where the migrating group has a sterocenter. In principle, all sigmatropic shifts can occur with either the same (retention) or the opposite (inversion) geometry of the migrating group. This depends on whether the original bonding lobe of the migrating atom or its other lobe is used to form the new bond.

paragraphs: In cases of stereochemical retention, the migrating group translates without rotation into the bonding position. In the case of stereochemical inversion the migrating group both rotates and translates to reach its bonded conformation.

paragraphs: There is another way that a sigmatropic reaction can produce products with different sterochemistry. The migrating group can stay on the original face of the π system after rebonding. Or, it can go to the opposite face of the π system. If the migrating group remains on the same face of the π system, the shift is known as suprafacial. If the migrating group transfers to the opposite face is called an antarafacial shift. Transformations that occur within small- or medium-sized rings cannot make antarafacial shifts.

paragraphs: In a thermal [1,3] hydride shift, a hydride moves three atoms. The Woodward-Hoffmann rules dictate that it would proceed in an antarafacial shift. Although such a shift is symmetry allowed, the Mobius topology required in the transition state prohibits such a shift. It is geometrically impossible. This is why enols do not isomerize without an acid or base catalyst.

paragraphs: Thermal alkyl [1,3] shifts, similar to [1,3] hydride shifts, must proceed antarafacially. The geometry of the transition state is prohibitive. But an alkyl group, due to the nature of its orbitals, can invert its geometry and form a new bond with the back lobe of its sp orbital. This reaction will result a suprafacial shift. These reactions are still not common in open chain systems because of the highly ordered nature of the transition state. So, the reactions work better in cyclic molecules.

paragraphs: Photochemical [1,3] shifts should be suprafacial shifts; however, most are non-concerted because they proceed through a triplet state (that is, they have a diradical mechanism, to which the Woodward-Hoffmann rules do not apply).

paragraphs: A [1,5] shift involves the shift of 1 substituent (-H, -R or -Ar) down 5 atoms of a π system. Hydrogen has been shown to shift in both cyclic and open chain systems at temperatures at or above 200 ˚C. These reactions are predicted to proceed suprafacially, by a Huckel-topology transition state.

paragraphs: Photoirradiation would require an antarafacial shift of hydrogen. Although such reactions are rare, there are examples where antarafacial shifts are favored:

paragraphs: In contrast to hydrogen [1,5] shifts, there have never been any observed [1,5] alky shifts in an open-chain system. Chemists have determined rate preferences for [1,5] alkyl shifts in cyclic systems: carbonyl and carboxyl> hydride> phenyl and vinyl» alkyl.

paragraphs: Alkyl groups undergo [1,5] shifts very poorly and usually require high temperatures. However, for cyclohexadienes, the temperature for alkyl shifts is not much higher than that for carbonyls, the best migratory group. A study showed that this is because alkyl shifts on cyclohexadienes proceed through a different mechanism. First the ring opens, followed by a [1,7] shift, and then the ring reforms electrocyclically:

paragraphs: This same mechanistic process is seen below, without the final electrocyclic ring-closing reaction, in the interconversion of lumisterol to vitamin D.

paragraphs: [1,7] sigmatropic shifts are predicted by the Woodward-Hoffmann rules to proceed in an antarafacial fashion, by a Mobius topology transition state. An antarafacial [1,7] shift is observed in the conversion of lumisterol to vitamin D, where following an electrocyclic ring opening to previtamin D, a methyl hydrogen shifts.

paragraphs: Bicyclic nonatrienes also undergo [1,7] shifts in a so called walk rearrangement, which is the shift of divalent group, as part of a three-membered ring, in a bicyclic molecule.

paragraphs: [3,3] sigmatropic shifts are well studied sigmatropic rearrangements. The Woodward-Hoffman rules predict that these six electron reactions would proceed suprafacially, using a Huckel topology transition state.

paragraphs: Discovered in 1912 by Rainer Ludwig Claisen, the Claisen rearrangement is the first recorded example of a [3,3]-sigmatropic rearrangement. This rearrangement is a useful carbon-carbon bond-forming reaction. An example of Claisen rearrangement is the [3,3] rearrangement of an allyl vinyl ether, which upon heating yields a γ,δ-unsaturated carbonyl. The formation of a carbonyl group makes this reaction, unlike other sigmatropic rearrangements, inherently irreversible.

paragraphs: The ortho-Claisen rearrangement involves the [3,3] shift of an allyl phenyl ether to an intermediate which quickly tautomerizes to an ortho-substituted phenol.

paragraphs: When both the ortho positions on the benzene ring are blocked, a second ortho-Claisen rearrangement will occur. This para-Claisen rearrangement ends with the tautomerization to a tri-substituted phenol.

paragraphs: The Cope rearrangement is an extensively studied organic reaction involving the [3,3] sigmatropic rearrangement of 1,5-dienes. It was developed by Arthur C. Cope. For example 3,4-dimethyl-1,5-hexadiene heated to 300 °C yields 2,6-octadiene.

paragraphs: The Oxy-Cope rearrangement a hydroxyl group is added at C3 forming an enal or enone after Keto-enol tautomerism of the intermediate enol:

paragraphs: The Carroll rearrangement is a rearrangement reaction in organic chemistry and involves the transformation of a β-keto allyl ester into a α-allyl-β-ketocarboxylic acid. This organic reaction can be followed by decarboxylation and the final product is a γ,δ-allylketone. The Carroll rearrangement is an adaptation of the Claisen rearrangement and effectively a decarboxylative allylation.

paragraphs: The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by Hermann Emil Fischer.

paragraphs: The choice of acid catalyst is very important. Successful acid catalysts include: Bronsted acids such as HCl, HSO, polyphosphoric acid and p-toluenesulfonic acid. Lewis acids such as boron trifluoride, zinc chloride, iron chloride, and aluminium chloride are also useful catalysts.

paragraphs: Similar to [3,3] shifts, the Woodward-Hoffman rules predict that [5,5] sigmatropic shifts would proceed suprafacially, Huckel topology transition state. These reactions are rarer than [3,3] sigmatropic shifts, but this is mainly a function of the fact that molecules that can undergo [5,5] shifts are rarer than molecules that can undergo [3,3] shifts.

paragraphs: The migration of a divalent group, such as O, S, NR or CR, which is part of a three-membered ring in a bicyclic molecule, is commonly referred to as a walk rearrangement. This can be formally characterized according to the Woodward-Hofmann rules as being a (1, n) sigmatropic shift. An example of such a rearrangement is the shift of substituents on tropilidenes (1,3,5-cycloheptatrienes). When heated, the pi-system goes through an electrocyclic ring closing to form bicycle[4,1,0]heptadiene (norcaradiene). Thereafter follows a [1,5] alkyl shift and an electrocyclic ring opening.

paragraphs: Proceeding through a [1,5] shift, the walk rearrangement of norcaradienes is expected to proceed suprafacially with a retention of stereochemistry. Experimental observations, however, show that the 1,5-shifts of norcaradienes proceed antarafacially. Theoretical calculations found the [1,5] shift to be a diradical process, but without involving any diradical minima on the potential energy surface.


title: Group transfer reaction

paragraphs: A Group transfer reaction is pericyclic reaction where one pi bond is converted to one sigma bond, at the same time that a sigma bond migrates.

paragraphs: The best known group transfer reaction is the ene reaction.


title: Mercedes-Benz W201

paragraphs: The Mercedes-Benz W201 is an automobile produced by Mercedes-Benz. It was introduced in 1982 and came before the C-Class, that replaced the W201 in 1993.


title: Cadel Evans

paragraphs: Cadel Evans (born 14 February 1977 in Katherine, Northern Territory) is an Australian professional bicycle race driver. In 2011, he is the first Australian to win the Tour de France.

paragraphs: Cadel Evans was born on 14 February 1977 at the Katherine Hospital, Katherine, Northern Territory, Australia. He is the son of Helen Cocks, a bank manager and Paul Evans, a council foreman. He spent his early childhood in the small aboriginal community of Barunga, 80 km east of Katherine. At the age of seven, he was hit in the head by a horse and spent seven days in an induced coma. In 1986, his parents got divorced and he moved with his mother to Armidale, New South Wales. Later they moved to the state of Victoria. Skateboarding was one of his interests when he was a teenager. His father describes him as a good student, but otherwise just an ordinary kid who would leave his toys around. "Not in [my] wildest dreams" would he imagine that his son would become a top world athlete.

paragraphs: Evans attended Newling Public School in Armidale, and Eltham High School in Melbourne.


title: Grand Army Plaza (Manhattan)

paragraphs: Grand Army Plaza is at 59th Street and Fifth Avenue in Manhattan, New York. It is in front of the Plaza Hotel. It is opposite the southeast corner of Central Park. The sculptor Karl Bitter first had the idea for the Plaza in 1898. It is named after the Grand Army of the Potomac. The Carrère and Hastings architecture firm designed it. Construction was finished in 1916.

paragraphs: The Plaza is oval. 59th street divides it into northern and southern parts. The northern part has a golden statue of William Tecumseh Sherman designed by Augustus Saint-Gaudens. The statue features Sherman on a horse with the goddess "Victory" in front of him. There are often temporary sculpture exhibits at the north side of the plaza.

paragraphs: The southern part is the Plaza of the Pulitzer Fountain of Abundance. This fountain was designed by Bitter and paid for by Joseph Pulitzer. A bronze statue of the Roman goddess Pomona is at the top of the fountain. The statue of Pomona was the last one that Bitter designed.

paragraphs: The plaza was renovated in 1990 at a cost of $3.7 million. The Plaza Hotel is named for the Plaza, and is at its southwest corner.


title: USS Enterprise (CV-6)

paragraphs: USS "Enterprise" (CV-6), often called the "Big E," was the sixth aircraft carrier of the United States Navy. She was also the seventh U.S. Navy ship to use the name. She was launched in 1936 and was a "Yorktown" class aircraft carrier. She was one of three American carriers brought into service before World War II which survived the war. She took part in more fights against Japan than any other U.S. ship. These fights included the Battle of Midway, the Battle of the Eastern Solomons, the Battle of the Santa Cruz Islands, many other fights during the Guadalcanal campaign, the Battle of the Philippine Sea, and the Battle of Leyte Gulf. At three different times during the Pacific War, the Japanese said that she had been sunk in battle. This lead her to be nicknamed "The Grey Ghost".

paragraphs: "Enterprise" earned 20 battle stars. This was more than any other U.S. warship in World War II. Some have said that she is the most glorious and honored ship in the history of the United States Navy. However, the 18th century frigate USS "Constitution" could perhaps rival that.

paragraphs: "Enterprise" was launched on 3 October 1936 at Newport News Shipbuilding. She was sponsored by Lulie Swanson, who was the wife of the Secretary of the Navy Claude A. Swanson. "Enterprise" was commissioned on 12 May 1938. "Enterprise" sailed south so that her performance could be tested. This took her to Rio de Janeiro. After she returned, she was used along the east coast and in the Caribbean until April 1939. This is when she was ordered to serve in the Pacific.

paragraphs: "Enterprise" was one of fourteen ships to be fitted with the RCA CXAM-1 RADAR. She was first based in San Diego (where she was used in the movie "Dive Bomber") and then at Pearl Harbor after President Roosevelt ordered the Fleet to be based far forward. "Enterprise" and the aircraft squads she carries trained a lot and moved aircraft among the island bases of the Pacific. "Enterprise" left Pearl Harbor on 28 November 1941. "Enterprise" was completing a transport mission, returning to Hawaii after moving Marine Fighter Squadron 211 (VMF-211) to Wake Island on 7 December 1941. This was when the Japanese attacked Pearl Harbor.

paragraphs: "Enterprise" was returning to Oahu on the morning of 7 December 1941. 18 SBD Dauntlesses from "Enterprise" squadrons Scouting Squadron Six (VS-6) and Bombing Squadron Six (VB-6) arrived at Pearl Harbor while the Japanese were attacking it. Even though they were surprised, they quickly went into action to defend Pearl Harbor. VS-6 lost six planes during the attack. VB-6 lost one. Many of these planes were shot down by the Japanese. However, at least one plane was lost to anti-aircraft (AA) fire, and many more were damaged. During the battle, one radio report was heard: "Do not attack me, this is Six Baker Three an American plane". Later, the same pilot (Ensign Manuel Gonzales from VB-6) was heard telling his radioman/gunner to get ready to land on the water. Lieutenant C. E. Dickinson and his crewmate William C. Miller, from VS-6, shot down one Japanese plane before they had to jump out after their plane caught fire. Dickinson later went to Ford Island to fly another plane. He took part when the United States were searching for the Japanese fleet.

paragraphs: "Enterprise" also sent up six F4F Wildcats from Fighting Squadron Six (VF-6) during the attack. All of these aircraft except two were shot down by shellshocked AA gunners when they tried to land on Ford Island later that night. "Enterprise" got her aircraft ready to go on a large search for the Japanese force that attacked Pearl Harbor. They search was to the south and west of Oahu. However, the Japanese had started moving northwest. "Enterprise" went into Pearl Harbor for fuel and supplies on the night of 8 December. Early the next morning, she went to patrol the rest of the Hawaiian Islands to make sure there were no more attacks. Even though the group did not find any ships, "Enterprise" aircraft sank Japanese submarine . "I-70" was sunk at on 10 December 1941.

paragraphs: During the last two weeks of December 1941, "Enterprise" and her group moved to the west of Hawaii to make sure those islands were not attacked. Two other groups tried to help at Wake Island at the same time. After the "Enterprise" group had a short rest at Pearl Harbor, they left on 11 January. They were protecting ships sending help to Samoa. On 1 February, "Enterprise"'s Task Force 8 raided Kwajalein, Wotje, and Maloelap in the Marshall Islands. They sank three ships, damaged eight and destroyed many aircraft.

paragraphs: Five days later, "Enterprise" sailed for the South Pacific to help other U.S. carriers in the Coral Sea. However, the Battle of the Coral Sea was over before "Enterprise" got there.

paragraphs: On 28 May, "Enterprise" moved, as Rear Admiral Raymond A. Spruance's flagship, to Midway. She was ordered to hold Midway and do as much damage to the enemy as possible. USS "Hornet", six cruisers and 10 destroyers were with "Enterprise" on that day.

paragraphs: Both the Americans and Japanese launched air attacks. Even though the fighting went on until 7 June, by the end of 4 June the result had been decided. The Battle of Midway began on the morning of 4 June 1942, when four Japanese carriers attacked on Midway Island. The Japanese did not know that the U.S. Navy was in the area. Just three hours after the first bomb hit Midway, planes from the U.S. carriers attacked. "Enterprise" launched an attack using torpedo bombers, but this failed. Soon after this, "Enterprise" dive bombers attacked and sank the Japanese carriers and . Later in the afternoon, bombers from "Enterprise" and USS "Yorktown" sank (aircraft from "Yorktown" also sank ). "Yorktown" and USS "Hammann" were the only American ships sunk, but 113 planes were lost. 61 of these were lost during the attacks. Japanese losses were much bigger. They lost four carriers, one cruiser and 272 planes. Even though she lost many planes, "Enterprise" returned to Pearl Harbor on 13 June 1942 undamaged.

paragraphs: After a month of rest, "Enterprise" headed on 15 July 1942 for the South Pacific. There, she helped support the attack on the Solomon Islands on 8 August. During the Battle of the Eastern Solomons, the Japanese light carrier "Ryūjō" was sunk. The Japanese troops that were supposed to land on Guadalcanal was forced back. "Enterprise" was hit three times. 77 sailors were killed and 91 were hurt. "Enterprise" was damaged badly.

paragraphs: "Enterprise" was fixed at Pearl Harbor from 10 September-16 October 1942.

paragraphs: On 13 November, pilots from "Enterprise" helped to sink . When the Naval Battle of Guadalcanal ended on 15 November 1942, "Enterprise" had helped to sink 16 ships and damage eight more.

paragraphs: On July 20 1943, "Enterprise" started being upgraded. These happened over several months. She was given an anti-torpedo blister. This meant that the carrier would be protected more against torpedoes.

paragraphs: "Enterprise" was back by November 1943. She helped the U.S. soldiers landing on Makin Atoll from 19–21 November 1943.

paragraphs: "Enterprise" launched planes to strike the Marshall Islands and helped U.S. soldiers land on Kwajalein from 29 January-3 February 1944. Then she went to strike the Japanese base in Truk Lagoon in the Caroline Islands on 17 February.

paragraphs: "Enterprise" launched planes to hit Jaluit Atoll on 20 February. She helped troops who were landing on Emirau Island (19–25 March). On 14 April she helped troops to land in Hollandia (currently known as Jayapura), in New Guinea.

paragraphs: On 19 June 1944, "Enterprise" took part in the Battle of the Philippine Sea. For over eight hours, American and Japanese pilots fought. Over two days, six American ships were damaged. 130 planes and 76 pilots and aircrew were lost. American aircraft and U.S. submarines sank three Japanese carriers (, , and ). The Japanese lost 426 planes.

paragraphs: "Enterprise" helped to defend the U.S. ships and to strike the Japanese ships. After the battle, "Enterprise" helped with the invasion of Saipan until 5 July. She then went back to Pearl Harbor for a month of rest. She came back on 24 August and attacked the Bonin Islands from 31 August – 2 September.

paragraphs: In the Battle of Leyte Gulf (23–26 October), "Enterprise" planes attacked battleships and destroyers. During November, planes from "Enterprise" hit Manila and Yap. She returned to Pearl Harbor on 6 December 1944.

paragraphs: "Enterprise" sailed to Pearl Harbor with 1,100 soldiers. She then started sailing to Europe. She brought 10,000 soldiers home. During the Enterprise’s last trip, the ship was caught in very high winds in the Atlantic. The crew almost abandoned ship. "Enterprise" had to go back to New York.

paragraphs: "Enterprise" got a British Admiralty Pennant. The pennant was given to "Enterprise" as a gift from an ally. "Enterprise" is the only non-Royal Navy ship to get the award in more than 400 years.

paragraphs: "Enterprise" went into the New York Naval Shipyard on 18 January 1946 to be deactivated. In 1946, she was going to be given to the state of New York to be a memorial. However, this plan was cancelled in 1949. The "Big E" was sold on 1 July 1958 to the Lipsett Corporation to be scrapped. Scrapping was done in May 1960.

paragraphs: In November 1961, USS "Enterprise" (CVA(N)-65) was brought into service. This was the world's first nuclear-powered aircraft carrier. The was decommissioned on 1 December 2012. Another "Enterprise" would be a , CVN-80.

paragraphs: "Enterprise" was awarded a Presidential Unit Citation for her service during World War II. The citation says:

paragraphs: "Enterprise" also got the Navy Unit Commendation and 20 battle stars for World War II service. This means that she is the highest decorated US ship ever.


title: Pentagon Force Protection Agency

paragraphs: The Pentagon Force Protection Agency (PFPA) protects and keeps safe the occupants, visitors, and infrastructure of the Pentagon, Navy Annex and other assigned Pentagon facilities. PFPA is a civilian Defense Agency within the United States Department of Defense. PFPA does its job using law enforcement officers (Pentagon Police), criminal investigative and protective services agents; threat management agents; chemical, biological, radiological, nuclear and explosives technicians; and anti-terrorism/force protection and physical security personnel.

paragraphs: The mission of the Pentagon Police Department (PPD) is to promote high quality law enforcement and security services, in order to provide a safe and orderly work environment for Department of Defense workers in the Washington, DC area.

paragraphs: Formerly The Defense Protective Service (DPS), The Pentagon Police have exclusive jurisdiction within the Pentagon Reservation and share concurrent jurisdiction with other police agencies in an area of approximately around the complex. Arlington County, Virginia also gave the Pentagon Police officers conditional police authority throughout Arlington County. The United States Pentagon Police is also charged with the protection of certain Department of Defense executive officers.

paragraphs: Pentagon Police officers are Federal law enforcement officers, appointed under Title 10 Section 2674 of the United States Code. They receive their initial training at the Federal Law Enforcement Training Center in Glynco, Georgia.

paragraphs: The mission of the Anti-Terrorism / Force Protection Directorate (AT/FP) is to provide Office of the Secretary of Defense (OSD) interests throughout the National Capital Region with a total AT/FP program designed to protect lives, facilities, information and equipment. The AT/FP Division advises Pentagon leaders on AT/FP matters; conducts anti-terrorism training for all OSD workers; gathers, analyzes and disseminates threat information as it relates to AT/FP; develops AT/FP plans and programs, conducts threat/vulnerability assessments and performs other duties pursuant to the protection and security of the Pentagon.

paragraphs: The AT/FP Directorate is composed of highly trained anti-terrorism and security specialists responsible for deterring, detecting, and responding against terrorist activity particularly when the Secretary of Defense or other Department of Defense employees are the target. They are leaders in this effort even when top Defense officials are away from the Pentagon.

paragraphs: The Criminal Investigations & Protective Directorate investigates violations of the United States Code within the jurisdiction of PFPA and provide executive protection to DoD High Risk Personnel (HRP) in the Washington area.

paragraphs: PFPA Special Agent's (1811) investigate violations of federal criminal laws. The agents also provide protection during visits by foreign Ministers of Defense to the 48 contiguous United States. They also protect other visits designated by the Office of the Secretary of Defense. CIPD's Operations Section is responsible for coordinating protection missions and providing around-the-clock ("24/7") support for field agents.

paragraphs: The Protective Services Unit (PSU) is responsible for providing protective support for the Office of the Secretary of Defense and the Chairman and Vice Chairman of the Joint Chiefs of Staff at the Pentagon Building. They handle visits to the Pentagon by foreign and domestic dignitaries, as well as cover protection for special events on the Pentagon Reservation, most recently noted the dedication of the 9/11 memorial. The police officers assigned to PSU provide residence security in hotels while traveling with HRP's both inside and outside of the United States.

paragraphs: This unit guards the Pentagon and other nearby Department of Defense facilities against possible attacks. It checks all mail and deliveries. CBRNE also monitors the environment at the Pentagon and DOD installations to make sure that they do not have these hazards. When a suspicious item is found, bomb experts are sent to examine and sometimes to destroy the item.

paragraphs: This group manages PFPA's computers and networks. It maintains security alarms and sensoring systems. It operates the computerized locks that control building access.

paragraphs: This group issues Pentagon building passes. It operates all barriers and gates that control access on the Pentagon campus. It reviews all requests from people to take pictures of the Pentagon.


title: Linaceae

paragraphs: The Linaceae is a family of flowering plants. The family is cosmopolitan, and includes exactly 250 species. There are 14 genera, classified into two subfamilies: Linoideae and Hugonioideae (often recognized as a distinct family, the Hugoniaceae). Leaves of Linaceae are always simple. Their arrangement varies from alternate (most species) to opposite (in "Sclerolinon" and some "Linum") or whorled (in some "Hesperolinon" and "Linum").


title: National Museum of the Marine Corps

paragraphs: The National Museum of the Marine Corps is the historical museum of the United States Marine Corps. It is located in Quantico, Virginia. It is open to the public with free admission. The museum had its grand opening on November 10, 2006. Over 500,000 people visit the museum each year.

paragraphs: The museum is a public-private venture, a cooperative effort of the United States Marine Corps and the Marine Corps Heritage Foundation. The Foundation manages the museum operation, while the museum building will be donated to the Marine Corps. The Foundation raised $60 million to build the building. The Marine Corps spent $30 million to build the museum's exhibits and displays.

paragraphs: On the day the museum opened, President George W. Bush gave a dedication speech and also presented the Medal of Honor to the family of fallen Marine Jason Dunham.

paragraphs: President Bush said, "These walls remind all who visit here that honor, courage, and commitment are not just words. They are core values for a way of life that puts service above self. And these walls will keep the history of the Marine Corps alive for generations of Americans to come."

paragraphs: Curtis W. Fentress, FAIA, RIBA of Fentress Architects, designed the museum building. The exterior design is meant to "evoke the image of the flag raisers of Iwo Jima," an image that is also preserved by the USMC War Memorial. The 210 ft steel spire is like the Iwo Jima flagpole. The museum is a tribute to the U.S. Marines who have served their country since 1775.

paragraphs: The new museum replaces the Marine Corps Historical Center, in the Washington Navy Yard, which closed 1 July 2005, and the Marine Corps Air-Ground Museum, in Quantico, Virginia, which closed on 15 November 2002.

paragraphs: The museum building was designed for expansion. New galleries can be added around the circular lobby. On June 5, 2010, 12,000 square feet of additional galleries were added. They cost $12 million.

paragraphs: In October 2010, skylights in the museum lobby were shot on two different evenings as a part of the Northern Virginia military shootings. On April 14, 2011, the Semper Fidelis Memorial Park was dedicated. It covers 23.2 acres and includes 1.07 miles of new walking trails.

paragraphs: The Marine Corps Heritage Foundation, established in 1979, is a private, non-profit organization which was established in support of historical programs of the Marine Corps. The MCHF programs initially included "education, awards, publications, special projects, preservation..." In 1999, the Foundation expanded its mission to include the creation of the National Museum of the Marine Corps.

paragraphs: The National Museum of the Marine Corps is designed to be the centerpiece of a complex of facilities called the Marine Corps Heritage Center. This multi-use, campus includes the Semper Fidelis Memorial Park and Semper Fidelis Chapel; a demonstration area with parade grounds; hiking trails and other outdoor recreational offerings; a conference center and hotel; and an archive facility to restore and preserve Marine artifacts.

paragraphs: The chapel, designed by Fentress Architects, was completed in 2009 with a donation of $5 million from a retired Marine.

paragraphs: The museum features the following permanent exhibits, which were designed by Christopher Chadbourne and Associates, Inc.:

paragraphs: On 5 June 2010 the following three exhibits were opened.

paragraphs: The historical exhibits including displays of artifacts, multimedia, and full immersion experiences. For example, the exhibit on wintertime in the Korean War is in a room cooled to a lower temperature. The museum building also include class rooms, a theater, a gift shop, bar and a restaurant.

paragraphs: The museum hosts lectures by historians and military experts. The Marine Corps Band performs a summer concert series. The Arts Mentorship Program has interships for student artists attending the Prince William County schools.


title: Celastrales

paragraphs: Celastrales is an order of flowering plants. They are found throughout the tropics and subtropics, with only a few species extending far into the temperate regions. There are about 1200 to 1350 species in about 100 genera. All but 7 of these genera are in the large family Celastraceae. Until recently, the composition of the order and its division into families varied greatly from one author to another.


title: Celastraceae

paragraphs: Celastraceae the staff-tree family, in the order Celastrales, comprising about 55 genera of woody vines, shrubs, and trees, native in tropical and temperate zones but best known for ornamental forms of the genera "Euonymus" and "Celastrus" (bittersweet). Fruit of the family is often colourful. Leaves are frequently leathery and flowers are small, with four to five sepals and petals; alternating between the petals, stamens rise from a usually conspicuous nectar disk.


title: Arlington National Cemetery

paragraphs: Arlington National Cemetery is a cemetery in Arlington County, Virginia. People who served in the United States military are buried here. The cemetery started during the American Civil War. It is on a big farm called Arlington House. Arlington House was the home of Mary Anna Custis Lee. Mary Anna Custis Lee was a great-granddaughter of Martha Washington. She was also the wife of Confederate general Robert E. Lee. Although most of the farm now has graves, the old farmhouse still stands in the middle of the cemetery. The cemetery is across the Potomac River from the Lincoln Memorial in Washington, D.C..

paragraphs: The cemetery covers . People who died serving the United States in a war, and military veterans are allowed to be buried in the cemetery. People are buried here who fought in wars from American Civil War to the military actions in Afghanistan and Iraq. People who were buried here before the Civil War were reburied after 1900.

paragraphs: Arlington National Cemetery is taken care of by the United States Army. Arlington House (Custis-Lee Mansion) and its land are taken care of by the National Park Service as a memorial to Lee. Recently, the way the cemetery is managed caused controversy.

paragraphs: George Washington Parke Custis was the grandson of Martha Washington, and grew up with Martha and George Washington. He got the land that now is Arlington National Cemetery in 1802. He began building Arlington House, where he lived with his wife Mary Lee Fitzhugh Custis. The land and house was given to their only child that lived to be an adult, Mary Anna Custis Lee. She was married to Robert E. Lee, a West Point graduate and United States Army officer. When Fort Sumter was forced to surrender at the beginning of the American Civil War, President Abraham Lincoln asked Lee to be the general of the federal army. Lee did not give an answer right away, but waited to see if his home state of Virginia would leave the Union.

paragraphs: Lee left the federal army when Virginia said it was leaving the United States. He decided he could not fight against his home state. He became the leader of the armed forces of the Commonwealth of Virginia. He then became commander of the Army of Northern Virginia. Lee was a great commander and won several battles against the Union forces. Most Union officers thought Lee had broken his promises to the Union because he chose to fight against them. Part of Arlington was taken away from the Lee family and became a graveyard. Mostly Union dead are buried there.

paragraphs: Before the Civil War, the United States did not have large military-only cemeteries. Important generals were buried in the Congressional Cemetery with other important leaders. American military cemeteries were needed on distant frontiers, and near battles and hospitals where many soldiers died. When dead Civil War soldiers filled the burial grounds near Washington, D.C., Quartermaster General Montgomery C. Meigs proposed in 1864 that of the Robert E. Lee family property at Arlington be taken for a cemetery.

paragraphs: During the Civil War, people invented tricks to capture or to make life hard for Americans that fought on the other side of the war. The government assessed taxes on properties and insisted that the owners appear in person to pay them. If the plantation owner did not come, the government would sell the land. The government bought Arlington at tax sale in 1864 for $26,800. Mrs. Lee did not show up in person, but rather had sent an agent to pay the $92.07 in property taxes that were owed for the land. The government turned away her agent, refusing to accept the tax payment. In 1874, Custis Lee, heir under his grandfather's will passing the estate in trust to his mother, sued the United States claiming ownership of Arlington. After the U.S. Supreme Court ruled 5-4 in Lee's favor in "United States v. Lee", deciding that Arlington had been taken illegally, Congress returned the land to him. The next year, Custis Lee sold it back to the government for $150,000. Custis Lee and Robert Todd Lincoln, Secretary of War and son of President Lincoln, were both present when the property was officially turned over to the government.

paragraphs: In 2011, Hurricane Irene killed six large trees at the cemetery. The 220-year-old "Arlington Oak" fell down near the grave of John F. Kennedy.

paragraphs: Arlington National Cemetery is divided into 70 sections, with some sections in the southeast part of the cemetery saved for future use. Section 60, in the southeast part of the cemetery, is the burial ground for military personnel killed in the Iraq War and the War in Afghanistan. In 2005, Arlington National Cemetery bought another from the National Park Service, along with from the Department of Defense that was part of Fort Myer and that is the site of the Navy Annex.

paragraphs: Section 21, also known as the Nurses Section, is the area of Arlington National Cemetery where many nurses are buried. The Nurses Memorial is there. In the cemetery, there is a Confederate section with graves of soldiers of the Confederate States of America and a Confederate Memorial. All Confederate headstones are peaked rather than rounded. In Section 27, there are buried more than 3,800 former slaves, called "Contrabands" during the Civil War. Their headstones are designated with the word "Civilian" or "Citizen".

paragraphs: The United States Department of Veterans Affairs takes care of the National Cemetery Administration's requests for the words and faith emblems (a cross, Jewish star, etc.) at no charge to the family of the dead put on upright marble headstones or columbarium niche covers. There are 39 authorized faith emblems available for placement to represent the deceased's faith. See also, the United States Department of Veterans Affairs webpage "Available Emblems of Belief for Placement on Government Headstones" and "Markers" Markers

paragraphs: The cemetery had allowed privately-purchased markers in certain burial areas. Since 2001, the areas that the cemetery permitted such markers in are filled. The older sections of the cemetery have many different private markers, including artillery pieces.

paragraphs: The Tomb of the Unknowns at Arlington National Cemetery is also called the "Tomb of the Unknown Soldier". It stands on top of a hill overlooking Washington, D.C. It honors soldiers who died without their bodies being identified.

paragraphs: The Tomb is one of the more popular sites at the Cemetery. The tomb is made from Yule marble quarried in Colorado. It consists of seven pieces, with a total weight of 79 short tons (72 metric tons). The tomb was completed and opened to the public April 9, 1932, at a cost of $48,000.

paragraphs: U.S. Army guards have stood watch at the Tomb of the Unknowns at all times since July 2, 1937. The 3rd U.S. Infantry Regiment ("The Old Guard") began guarding the Tomb April 6, 1948.

paragraphs: The Tomb of the Unknowns is part of the Arlington Memorial Amphitheater. The Memorial Amphitheater has hosted state funerals and Memorial Day and Veterans Day ceremonies. Ceremonies are also held for Easter. About 5,000 people attend these holiday ceremonies each year. The structure is mostly built of Imperial Danby marble from Vermont. The Memorial Display room, between the amphitheater and the Tomb of the Unknowns, uses Botticino stone, imported from Italy. The amphitheater was the result of a campaign by Ivory Kimball to construct a place to honor America's soldiers. Congress authorized the structure March 4, 1913. Woodrow Wilson laid the cornerstone for the building on October 15, 1915. The cornerstone contained 15 items including a Bible and a copy of the Constitution.

paragraphs: The Netherlands Carillon is a carillon (bell tower) that was a gift from the Netherlands to the people of the United States in 1954, in thanks for their efforts during World War II. The bells are played by people with special training. This happens regularly during the summer and on special days. Recorded tunes are played on the hour and during the day. It is next to Arlington National Cemetery, on the north side.

paragraphs: It is now hard to find space to build new memorials at the cemetery. The army worries that new memorials take up space that could otherwise be used for graves. The army requires a joint or concurrent resolution from Congress before it will place new memorials onto the cemetery grounds. Still, there are several memorials on the cemetery grounds, and groups regularly ask for space for new memorials.

paragraphs: The Space Shuttle "Challenger" Memorial was dedicated on May 20, 1986, in memory of the crew of flight STS-51-L, who died during launch on January 28, 1986. Written on the back of the stone is the text of the John Gillespie Magee, Jr. poem "High Flight". Although many remains were identified and returned to the families for private burial, some were not, and were laid to rest under the marker. Two of the crew members, Scobee and Smith, are buried in Arlington, as well. There is a similar memorial to those who died when the Shuttle "Columbia" broke apart during reentry on February 1, 2003. It was dedicated on the first anniversary of the disaster. Astronauts Laurel Clark, David Brown and Michael Anderson are also buried in Arlington.

paragraphs: The Cairn, the Lockerbie memorial is a memorial to the 270 killed in the bombing of Pan Am Flight 103 over Lockerbie, Scotland. The memorial is made up of 270 stones, one for each person killed in the disaster. In section 64, there is a memorial to the 184 victims of the September 11 attacks on the Pentagon. The memorial takes the shape of a pentagon, and lists the names of all the victims that were killed.

paragraphs: There are only two mausoleums located within the confines of the cemetery. One is for the family of General Nelson Appleton Miles in Section 3 and the other one belongs to the family of General Thomas Crook Sullivan and it is in Section 1.

paragraphs: There is a Commonwealth Cross of Sacrifice with the names of all the citizens of the USA who lost their lives fighting in the Canadian forces during the Korean War and the two world wars.

paragraphs: The "Women in Military Service for America Memorial" is at the Ceremonial Entrance to Arlington National Cemetery.

paragraphs: The first soldier to be buried in Arlington was Private William Henry Christman of Pennsylvania on May 13, 1864.

paragraphs: Whether or not they were wartime service members, U.S. presidents are eligible to be buried at Arlington, since they oversaw the armed forces as commanders-in-chief.

paragraphs: Four state funerals have been held at Arlington: those of Presidents William Howard Taft and John F. Kennedy, that of General John J. Pershing, and that of U.S. Senator Edward M. Kennedy.

paragraphs: As of May 2006, there were 367 Medal of Honor recipients buried in Arlington National Cemetery. Nine of these recipients are Canadians.

paragraphs: Warrant Officer Gregory S. Crandall's helicopter was shot down over Savannakhet province, Laos, on February 18, 1971. In May of that year the military listed him KIA. According to Arlington National cemetery records John Manning, chief of the Army's Mortuary Affairs Branch stated that witnesses to the crash reported that the ..."helicopter burst into flames and exploded when it hit the ground.". It was also reported that there were a series of seven explosions. The remains of Crandall and two other soldiers were recovered in February 1991 and on September 17, 1993, with full military honors, a full sized steel casket, and at the protest of the family, the remains of Warrant Officer Gregory S. Crandall, a single No. 4 maxillary premolar tooth, was buried.


title: Torquoselectivity

paragraphs: In organic chemistry, torquoselectivity describes electrocyclic reactions that produce one isomer more than the other. An official definition is "the preference for inward or outward rotation of substituents in conrotatory

paragraphs: or disrotatory electrocyclic reactions." In other words, a chemical reaction is torquoselective if the groups of atoms that hang from a ring of atoms are more likely to have rotated in a particular direction during the reaction (instead of being equally likely to rotate in both possible directions.) Torquoselectivity is different from the normal diastereoselectivity of pericyclic reactions. Instead it is more selectivity beyond the Woodward–Hoffmann rules. The name comes from the idea that the substituents in an electrocyclization appear to rotate during the reaction. The reaction produces a single product because only one direction of rotation was allowed (that is, the direction of rotation on the substituents was favored). The concept was originally developed by Kendall N. Houk.

paragraphs: When a chemical reaction closes a ring, its torquoselectivity is the same as enantioselectivity. A single enantiomer of a cyclization product is formed from the selective ring closure of the starting material. In a typical electrocyclic ring closing, selection for either conrotatory or disrotatory reactions modes still produces two enantiomers. Torquoselectivity is a discrimination "between" these possible enantiomers that requires asymmetric induction.

paragraphs: Torquoselectivity also happens in selective electrocyclic reactions that break open rings. The different directions of rotation produce distinct structural isomers. In these cases, steric strain is often the driving force for the selectivity. Studies have shown that the selectivity can also be changed by the presence of electron donating and electron withdrawing groups.

paragraphs: Torquoselectivity can also apply to other mechanisms, including chiral Lewis acid catalysts, induction by neighboring stereocenters (in which case the torquoselectivity is a case of diastereoselectivity), and axial-to-tetrahedral chirality transfer. An example of axial-to-tetrahedral chirality transfer is shown below for the torquoselective Nazarov cyclization reaction of a chiral allenyl vinyl ketone.


title: 2011 Pan American Games

paragraphs: The 16th Pan American Games were held in 2011 in Guadalajara, Mexico. Over 6,000 athletes from 42 countries competed in 36 sports.


title: William Kidd

paragraphs: Captain Kidd, or, by his real name, "William Kidd", (c. 1645 – 23 May 1701) was a Scottish pirate and sailor. It is heard that he buried a treasure chest on a deserted island. The chest had a lot of gold and jewels in it. He was found guilty of murder and was executed by hanging at 'Execution Dock', Wapping, in London on 23 May 1701.


title: Gripper

paragraphs: A gripper is something that grips things or makes it easier to grip things. It may refer to:


title: Jeff Kent

paragraphs: Jeffrey Franklin Kent (born March 7, 1968) was an American baseball player. He played second base. He played for six different teams, including the New York Mets, San Francisco Giants, and Los Angeles Dodgers. He was a five-time All-Star, and the 2000 National League MVP. In his career, he batted .290, with 2,461 hits, 377 home runs and 1,518 RBIs. He has more home runs than any other second baseman. He also drove in 90 or more batters in nine straight seasons.

paragraphs: Kent was from Bellflower, California and went to high school in Huntington Beach.


title: Angelshark

paragraphs: An angelshark is a species of cartilaginous fish in the genus Squatina. They have flattened bodies and wide pectoral fins, which make them look similar to rays. Twenty-three species are known.

paragraphs: The genus is the only one in its family, Squatinidae, and order Squatiniformes. They are worldwide in temperate and tropical seas. Most species are in shallow temperate or tropical seas, but one species is found in deeper water, down to 1,300 metres. Angelsharks are specialised for a kind of predation which is unusual for sharks.

paragraphs: They are ambush predators. They have extensible jaws with long, needle-like teeth. They quickly snap upwards to capture prey. They bury themselves in sand or mud lying in wait for their prey, which includes fish, crustaceans, and many different types of mollusks.

paragraphs: The front part of the angel sharks' bodies are wide and flattened, but the back part is more muscular. The eyes and spiracles are on the top, and the five gill slits are on its back. Both the pectoral fins and the pelvic fins are large and are held horizontally. There are two dorsal fins, no anal fin. Unusually for sharks, the lower lobe of the caudal fin is longer than the upper lobe. Most types of angel sharks grow to a length of about 1.5 metres: the Japanese angelshark reaches two metres. They are ovoviviparous, and can have up to 13 pups at a time.

paragraphs: Although angelsharks are bottom dwellers and appear harmless, they can give painful bites if provoked, due to their powerful jaws and sharp teeth. Angelsharks may bite if a diver approaches the head or grabs the tail.


title: Goblin shark

paragraphs: The Goblin shark ("Mitsukurina owstoni") is a rare, poorly-known species of deep-sea shark. Sometimes called a "living fossil", it is the only living species in the family Mitsukurinidae.

paragraphs: The Goblin shark can be easily identified by its long, flattened snout. Males can reach up to lengths of 12.6 feet (3.8 meters), and females can reach up to lengths of 12.2 feet (3.7 meters). The heaviest Goblin shark found weighed 210 kg (460 pounds).

paragraphs: The Goblin shark is a bottom-dwelling shark, being found in waters as deep as 4265 feet (1,300 meters). It has been found in the Atlantic, Indian, and Pacific Ocean.

paragraphs: The Goblin shark can be easily identified by its long, flattened snout. It has a noticeably long head, tiny eyes and five short gill openings. The mouth is large and parabolic in shape. Its body is soft and flabby. This shark has a long caudal fin without a ventral lobe. The pectoral fins are short and wide, and the two dorsal fins are small, round and equal in size. The anal fin is round and smaller than the dorsal fins, while the pelvic fins are larger than the dorsals. The Goblin shark has a long extendable jaw, with long, thin teeth. The shape of its body shows that the Goblin shark is a slow moving species of shark.

paragraphs: Living Goblin sharks are a pinkish-white color with bluish fins. Specimens fade and become a brownish color when preserved in alcohol.

paragraphs: Goblin sharks have 26 long, thin, spike-like teeth on their upper jaw and 24 on their lower jaw. They have three rows of front teeth on each side of both jaws. The teeth in the front upper jaw are separated from the smaller upper side teeth by a gap.

paragraphs: Mature male Goblin sharks have been found to reach lengths ranching from 8.66 to 12.6 feet (2.6 to 3.8 meters) long. Mature females have been found to reach lengths ranging from 11 to 12.2 feet (3.4 to 3.7 meters). The size at birth is not known, but the smallest specimen found was 3.51 feet (1.07 meters) long. The heaviest Goblin shark found weighed 210 kg (460 pounds), and was 3.8 metres (12 feet) long.

paragraphs: This species of deep-sea shark is thought to be widely distributed. Specimens have been seen in the Atlantic, off the coast of Guyana, Surinam, French Guiana, France, Madeira, Senegal, Portugal, and the Gulf of Guinea. It has also been reported in the western Pacific off Japan, Australia and New Zealand. In the Indian Ocean it is found off South Africa and Mozambique. It was recently recorded in the U.S.A near San Clemente Island off the coast of California, as well as in the northern Gulf of Mexico, south of Pascagoula, Mississippi.

paragraphs: The Goblin shark is a bottom-dwelling shark that is rarely seen at the surface or in shallow coastal waters. This species is found along the outer continental shelves, upper slopes, and off seamounts. Most specimens have been observed near continental slopes, between 885 and 3149 feet (270 and 960 meters) deep. It has been found in waters up to 4265 feet (1,300 meters) deep, and in waters as shallow as 311 to 449 feet (95 to 137 meters). Records show that the Goblin shark could also be an oceanic species.

paragraphs: The Goblin shark senses its prey with the help of electro-sensitive organs. The jaws are made for rapid projection to help in the capture of prey. The jaw is thrust forward by a double set of ligaments at the mandibular (lower jaw) joints. When the jaws are withdrawn, the ligaments are stretched and they become relaxed when the jaw is projected forward. The jaws are usually held tightly while swimming, and have a function like a catapult when the Goblin shark wants to feed. The front teeth are made for crushing. The Goblin shark feeds on shrimps, pelagic octopuses, fish, and squids. It is also thought to feed on crabs, and deep-sea rockfish.

paragraphs: There is no proper information about the reproduction habits of the Goblin shark. No pregnant female has been found or captured. It is believed that they are ovoviviparous, meaning that the young are born live, but there is no placental connection, instead the embryos are nourished by egg yolk. There is no real information of when the Goblin shark matures, when and how it mates, and how long the gestation period lasts.

paragraphs: The Goblin shark is fished commercially off Japan, and is sometimes caught along with cutlassfish off Portugal. Elsewhere, they are taken mainly as bycatch of deep-water trawls and occasionally with deep-water longlines, deep-set gillnets, and possibly purse seines.

paragraphs: The Goblin shark is probably harmless, but since it has rarely been encountered by humans it is not yet possible to tell. Although probably common, this species of shark is rarely seen and is therefore poorly known.


title: Blue shark

paragraphs: The blue shark ("Prionace glauca") is a species of requiem shark. It has a slim, smooth-looking body with large eyes, and a long, cone-shaped snout. The dorsal surface is a dark blue colour, and the belly is white.

paragraphs: The largest blue sharks can reach lengths of up to 3.8 metres, and weigh as much as 206 kg. The shark is found worldwide in temperate and tropical waters. They range from the surface to as deep as 350 metres, and prefer water with the temperature of 7 to 16 °C.

paragraphs: The blue shark has a slim, smooth-looking body with large eyes, and a long, cone-shaped snout that is longer than the width of its mouth. It has extremely long, pointed pectoral fins, which are usually as long as the distance from its snout to the front of its gill slit. The dorsal fin is moderate in size. It is located closer to the pelvic fins than to the pectoral fins. The blue shark's name comes from its distinct dark blue dorsal surface, and bright blue sides. The belly is white. The colours of the blue shark help it to camouflage in the open ocean. The largest blue shark on record measured 3.8 metres (12.5 feet), but they are rumored to get as large as 6.1 metres (20 feet). Males reach maturity at the ages of 4–5 years, when they are at the lengths of between 1.8-2.8 metres (6-9.2 feet). Females mature at slightly older ages from 5–6 years, when they are at the lengths of between 2.2-3.2 metres (7.2-10.5 feet). The largest blue sharks range in weights from 204–206 kg (450-454 pounds).

paragraphs: Blue sharks are found worldwide, in temperate and tropical waters. They are a pelagic species that rarely comes near shore. They have been known to frequently swim to inshore areas around oceanic islands, and locations where the continental shelf is narrow. In the western Atlantic they can be found from Newfoundland, Canada to Argentina. In the eastern Atlantic they range from Norway to South Africa, including the Mediterranean. In the Indian Ocean, they range from South Africa to Indonesia. In the western Pacific they are found from Japan to New Zealand. In the eastern Pacific, Blue sharks range from the Gulf of Alaska to Chile.

paragraphs: Being a pelagic species, the shark's habitat consists of open ocean areas, from the surface to 350 metres (1,148 feet) in depth. They prefer cooler water ranging from 7 to 16 °C (45-61 °F) in temperature. They are known to swim in water with the temperature of 21 °C (70 °F) or greater. When in the tropics, the shark usually swims to deeper water with cooler temperatures. This is common in the tropical Indian Ocean, where the majority of Blue sharks are found at depths of 80–220 metres (263–722 feet), where water temperatures range from 12-25 °C (54-77 °F). In the Pacific, at latitudes between 20°N and 50°N, they are known to migrate to higher latitudes during the summer and lower latitudes during the winter. Their populations remain constant throughout the year between 20°N and 20°S latitude.

paragraphs: The blue shark has one of the largest ranges in terms of depths of the water. They can be found from the surface to the bottom. This type of adaption makes it easy for them to be able to find food. Blue sharks are known to migrate thousands of miles for food and for mating. This species of shark often is not found alone. Instead, they form groups based on their gender and on their size. They are often referred to as the "Wolves of the Sea" due to the complex levels of hierarchy that they form within their groups which highly reflects the behaviour of wolves. Due to their territorial instincts and their aggressive behaviours, divers have to be very careful around them. Many of the filmings of these sharks have been done with the divers in cages for the divers' own personal safety.

paragraphs: The majority of the blue shark's diet consists of invertebrates such as squid, cuttlefish, and pelagic octopus, and bony fish such as herring and sardines. They also feed on various types of sea birds, crustaceans such as lobster, crab, and shrimp, and they also feed on carrion.

paragraphs: They are very opportunistic when it comes to hunting. They have been known to feed on almost anything that they can find, including prey items which they can find in large numbers such as shrimp. They have been known to feed until they actually can not eat any more. Since they feed on almost anything that they can find, they have been known to feed on garbage and rubbish such as plastic and rubber tires. This can result in the shark falling ill, and even dying.

paragraphs: Blue sharks are viviparous, with the males maturing at the age of 4-5, and females reaching maturity at the age of 5-6. The gestation period lasts from 9 to 12 months. During mating, the males have been known to bite the females, but their thick skin is believed to stop any pain. Pups are 41 to 50 cm (16 to 20 inches) long at birth, with females giving birth to 4-135 pups at a time, but the number of pups depend on the size of the female, with larger females giving birth to more pups. Blue sharks live to up to 20 years.

paragraphs: Predators of the blue shark include the California sea lion and larger sharks such as the Shortfin mako shark, and the Great white shark.

paragraphs: Recreationally, blue sharks are considered a sport fish, and large individuals provide a challenge for fishermen. Most commercially caught blue sharks are considered bycatch. It is estimated that 10 to 20 million are killed each year, possibly having a negative impact on world populations. The salmon, mackerel, and sardine fisheries are affected by Blue shark predation on catches, and entanglement in nets. The fins of blue sharks are sold to Asian markets and are used to make shark-fin soup.

paragraphs: Having been known to attack humans and boats, blue sharks are considered to be a dangerous species. Twelve unprovoked attacks and four boat attacks have been documented by the International Shark Attack File (ISAF). Three documented attacks resulted from air or sea disasters. There are several accounts where Blue sharks attacked shipwrecked sailors floating in the open ocean. The blue shark sometimes circles swimmers or divers for up to fifteen minutes or more. While not overly aggressive, it is not a timid shark, and needs to be approached with caution, especially if it has been circling, since it may attempt to bite.

paragraphs: Although blue sharks are among the most abundant, widespread, and fast growing shark, they are one of the most heavily fished sharks in the world. With an estimated 10 to 20 million individuals caught and killed each year, there is concern not only about what this is doing to Blue shark populations, but also about the effect the removal of such an important predator might have on the oceanic ecosystem. Blue sharks are one of the most important species in the international shark-fin trade. However, their meat, while eaten in a few countries, is not very popular. The blue shark is listed as Near Threatened by the IUCN.


title: Let's Kill Hitler

paragraphs: "Let's Kill Hitler" is the eighth episode of the sixth series of the British science fiction television series "Doctor Who". The episode was broadcast on BBC One, Space and BBC America on 27 August 2011. It is the second episode of a two-part story. The story began with "A Good Man Goes To War" (episode seven). It is the 778th episode.

paragraphs: The episode centers around River Song and the history of Amy Pond.


title: Romano Mattè

paragraphs: Romano Mattè (Trento, January 17 1939) is an Italian former association football player, who coached the national teams of Mali and Indonesia.


title: Mental breakdown

paragraphs: Mental breakdown (also known as a nervous breakdown) is a non-medical term used to describe an acute, temporary, short phase of a disorder with features of depression or anxiety.

paragraphs: The terms 'nervous breakdown' and 'mental breakdown' are not formally defined in a diagnostic system such as the DSM-IV or ICD-10. The terms are not often used in the scientific literature on mental illness.

paragraphs: Specific cases are sometimes described as a 'breakdown' only after a person cannot function in day-to-day life. It is a temporary condition.

paragraphs: Different things can cause a mental breakdown. A study found that problems with intimate relationships, such as divorce or separation, contributed to 24% of nervous breakdowns. Problems at work and school accounted for 17% of cases, and financial problems for 11%. Surveys suggest that in the United States, health problems have decreased in importance as a contributor to nervous breakdowns, as these accounted for 28% of nervous breakdowns in 1957, 12% in 1976, and only 5.6% in 1996.

paragraphs: In themselves, nervous breakdowns are considered a 'health problem' by most professionals.


title: Javier Hernández Balcázar

paragraphs: Javier Hernández Balcázar (born 1 June 1988 in Guadalajara, Mexico), also known as Chicharito, is a Mexican footballer. He plays for the English club, West Ham United and the Mexican national team.

paragraphs: Hernández was born in 1988 in Guadalajara, Mexico. His father Javier Hernández Gutiérrez is a retired footballer.

paragraphs: Includes the InterLiga, FA Cup and DFB-Pokal.

paragraphs: Includes the Copa Libertadores, Copa Sudamericana, North American SuperLiga, UEFA Champions League and the UEFA Europa League.

paragraphs: Includes other competitive competitions, including the Primera División playoffs, FA Community Shield, UEFA Super Cup and the FIFA Club World Cup.


title: Booster seat

paragraphs: A booster seat is a seat cushion that is used to elevate children in cars. Children have to use booster seats so that the seat belt fits better.

paragraphs: In general most booster seats can be used for children who are between four and twelve years of age and between 40 and 59 inches (100–150 cm) tall. Children under 40 inches are usually too small to use booster seats and have to use a car seat (a child safety seat with an own seat belt system, used for children under the age of 4-6).

paragraphs: Many countries have laws that require the use of booster seats. In the United States of America children under 57 inches (145 cm) and younger than 9 years old have to use a booster seat. Many European countries require a booster seat until the child is either twelve years old or 59 inches tall. There are some exceptions. In the United Kingdom for example children are allowed to ride without a booster seat when they are 53 inches tall and in Austria children who are not 59 inches tall have to use a booster seat until their 14th birthday. However booster seats are used to keep children safe, not because of a law. In general no child can ride safely in a car without booster seat when he is not 57 inches tall. It is proved that children under 57 inches who do not use a booster seat are more likely to suffer serious injuries or even death in the event of an accident.


title: Arthur Rubinstein

paragraphs: Arthur Rubinstein (January 28, 1887 – December 20, 1982) was a Polish-American pianist. He got praise from around the world for his playing of the music of a selection of composers (many call him the greatest Chopin player of the century).

paragraphs: Rubinstein was born in Łódź, Poland to a family of Jews. He was the youngest child of the family. His father was a rich owner of a factory.

paragraphs: Although his given name is Artur Rubinstein, in English-speaking countries he wanted to be known as Arthur Rubinstein. However, his United States impresario Sol Hurok wanted him to still be billed as "Artur", and his recordings were released in the West under both names.

paragraphs: Rubinstein learned the piano at the age of two in Warsaw, before beginning study in Berlin at the age of eight. His debut in Berlin was made in 1898 followed by a debut at Carnegie Hall in the United States in 1906.

paragraphs: Throughout his life, Rubinstein was famous as a solo pianist, a soloist in piano concertos, and even as a chamber musician. He retired from the stage at age eighty-nine, and died in Geneva, Switzerland, on 20 December 1982, at the age of ninety-five, and his body was cremated. On the first anniversary of his death, his ashes were buried in Jerusalem – as specified in his will – in a plot now nicknamed the "Rubinstein Forest" overlooking the Jerusalem Forest.


title: U.S. Defense Department firefighters

paragraphs: The United States Department of Defense employs civilian firefighters. They are stationed at military bases to work as firefighters. These workers have their own uniforms and equipment. They are not a part of any military unit. They will work alongside military units if needed. Many times, they are the only firefighters at a military facility. The civilian firefighters wear special uniforms, usually a dark blue suit with a badge and with a shoulder patch indicating their firefighting organization.

paragraphs: Firefighters go to special classes to learn firefighting skills. They earn certificates after taking the classes. One major class is called "DoD Fire & Emergency Services Training."


title: Bongo (antelope)

paragraphs: The Bongo (tragelaphus eurycerus) is a nocturnal antelope. It has two subspecies: the western or lowland bongo, and the eastern or mountain bongo. The western bongo is near threatened and the mountain bongo is critically endangered. Bongos eat plants. They live in forests in Africa. Kenya is the only place eastern bongos live in the wild. Like the west African giraffe, the eastern or mountain bongo is one of the most threatened animals in Africa. Bongos live in both captivity and the wild.

paragraphs: As bongos grow their horns appear. Both male and female bongos have horns.


title: Dyotropic reaction

paragraphs: A dyotropic reaction is a type of chemical reaction. It is when an organic compound changes its structure. Two substituents jump from one place on the molecule to another. It is a pericyclic valence isomerization when two sigma bonds move at the same time to a new place on the same molecule. Dyotropic reactions are important in organic chemistry. They can explain how certain reactions work. Dyotropic reactions can be a useful step in making large and complicated molecules. Dyotropic reactions were first described by Manfred T. Reetz in 1971. The name "dyotropic reaction" comes from the Greek word "dyo" meaning "two." "Rearrangement" means that the reaction changes the bonds between atoms on a single molecule.

paragraphs: In a type I reaction, two migrating groups trade their relative positions. A type II reaction involves migration to new bonding sites without positional interchange.

paragraphs: In type I rearrangements (Y-A-B-X conversion to X-A-B-Y), the two migrating groups are oriented trans to each other. The reaction leaves both groups on the opposite sides. The first example of a dyotropic rearrangement involving a carbon-carbon bond was reported by Cyril A. Grob and Saul Winstein. They saw the exchange of two bromine atoms in a certain steroid.

paragraphs: In a simple example, the two bromine atoms in 3-tert-butyl-trans-1,2-dibromohexane mutarotate by heating. In the transition state both bromine atoms connect symmetrically two both carbon atoms on opposite sides and the reaction is concerted. Chemists have also investigated stepwise mechanisms in dyotropic reactions.

paragraphs: In organic synthesis, an important dyotropic reaction is the conversion of 4-substituted-gamma-lactones to butyrolactones. Type I dyotropic rearrangements also occur around carbon-oxygen bonds. One example is using heat to change RRSiRC-O-SiR to RRSiRC-O-SiR. (This reaction can go in both directions depending on temperature.) Another example is the 1,2-Wittig rearrangement. Dyotropic reactions can also happen with N-O bonds or N-N bonds.

paragraphs: Type II rearrangements often involve two hydrogen atoms moving along a carbon skeleton. This reaction type can be found in certain transfer hydrogenations. An example is hydrogen transfer in syn-sesquinorbornene


title: Diels–Alder reaction

paragraphs: The Diels–Alder reaction (DA) is a chemical reaction between organic compounds. The reaction causes the compounds to form a new six-sided compound. This is called a cyclohexene. A conjugated diene joins with an alkene to make the cyclohexene. This compound looks like a ring.

paragraphs: This reaction was discovered by Otto Diels and Kurt Alder in 1928. In 1950, they were given the Nobel Prize in Chemistry for their work on this reaction. The DA reaction is very useful as it means cyclohexenes can be made with very little energy. Cyclohexenes are used to make complex organic molecules. One of the first uses of the DA reaction was to make insecticides.

paragraphs: The DA reaction makes a new hexagonal ring-shaped compound. A compound with two double bonds which are one carbon atom apart from each other is joined to another compound with at least one double bond. A DA reaction can also happen if some of the atoms in the newly formed ring are not carbon. Some of the DA reactions are reversible. The reaction caused during this breaking up of the cyclic system is called the retro-Diels–Alder. These retro-Diels–Alder compounds are often seen when they are analyzed by mass spectrometry.

paragraphs: Some chemists call the Diels–Alder reaction the 'Mona Lisa' of organic reactions. Like the simple smile on the painting, the reaction may be far more complex than chemists have so far discovered.

paragraphs: Lewis acids (AlCl, ZnCl, and others) act as catalysts to the reaction.


title: Dagestan

paragraphs: Dagestan is a federal subject of the Russian Federation in the Caucasus region. The name comes from two Persian words, "dag" which means mountain, and "stan" which means land. Dagestan has a population of nearly 3 million, and its people are known as "Dagestani". Its capital city is Makhachkala.

paragraphs: Dagestan has the status of "republic" in Russia and has its own constitution and official languages. Republics in Russia are the home of its ethnic minorities (those who are not Russians), and usually one or two nationalities have a majority of the population in each republic. But in Dagestan, there are over 30 different nationalities (the largest of which are the Avar, Lak, Dargwa, Lezgian, and Tabasaran), and none of these form a majority. This is because the mountains in the region make it hard for people to move around. These people speak 30 different languages, but use Russian as their lingua franca to communicate between each other.

paragraphs: Most people of Dagestan are Muslims and belong to the Shafi`i school of Sunni Islam.


title: Theoretical chemistry

paragraphs: Theoretical chemistry tries to explain data from chemistry experiments. It uses mathematics and computers. Theoretical chemistry predicts what happens when atoms combine to form molecules. It also predicts chemical properties (characteristics) of molecules. An important part of theoretical chemistry is quantum chemistry. This is using quantum mechanics to understand valency (the number of bonds formed by an atom of an element). Other important parts include molecular dynamics, statistical thermodynamics and theories of electrolyte solutions, reaction networks, polymerization and catalysis.

paragraphs: Theoretical chemists use a wide range of tools. These tools include analytical models (for example, LCAO-MOs to approximate the behaviors of electrons in molecules) and computational and numerical simulations.

paragraphs: Theorists in chemistry create theoretical models. Then, they find things that experimental chemists can measure from those models. This helps chemists to look for data that can prove a model not true. The data helps to chose between several different or opposite models.

paragraphs: Theorists also try to generate or modify models to fit any new data, If the data can not fit the model, chemists try to make the smallest change to the model to fit the data. In some cases, chemists throw out a model if a lot of data will not fit, over time.

paragraphs: Theoretical chemistry uses physics to explain or predict chemical observations. In recent years, it has been mainly about quantum chemistry (the application of quantum mechanics to problems in chemistry). The main parts of theoretical chemistry are electronic structure, dynamics, and statistical mechanics.

paragraphs: All of these areas are used in the process of predicting chemical reactivities. Other less central research areas include the mathematical description of bulk chemistry in various phases. Theoretical chemists want to explain chemical kinetics (the pathway that molecules combine).

paragraphs: Scientists call a lot of this work "computational chemistry". Computational chemistry usually uses theoretical chemistry to work on industrial and practical problems. Examples of computational chemistry are projects to approximate chemical measurements such as certain types of post Hartree-Fock, Density Functional Theory, semiempirical methods (such as PM3) or force field methods. Some chemical theorists use statistical mechanics to create a link between the microscopic phenomena of the quantum world and the macroscopic bulk properties of systems.

paragraphs: Historically, researchers use theoretical chemistry to study:


title: Pebble

paragraphs: A pebble is a piece of rock with a particle size of 4 to 64 millimetres. They are often made of flint.

paragraphs: Pebbles are larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter). A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.

paragraphs: A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach resists wave erosion, and has ecological niches which can provide habitat for animals and plants.


title: MESSENGER

paragraphs: MESSENGER, MErcury Surface, Space ENvironment, GEochemistry and Ranging, was an unmanned NASA and APL spacecraft. It was orbiting and studying the planet Mercury. Its mission lasted 10 years, 8 months and 28 days.

paragraphs: It was launched on August 3, 2004 at Cape Canaveral Air Force Station. It was aboard a Boeing Delta II rocket. After launch, the probe did several fly-bys and deep space manoeuvres to gain the right trajectory and speed.

paragraphs: It completed 30% mapping of Mercury on January 14, 2008. MESSENGER made one more pass by Mercury in 2009, and on March 18, 2011 began to orbit Mercury. 100% mapping was completed in March 2013 and the probe continued its studies. On April 30, 2015, it crashed into Mercury. It crashed near the crater Janáček.