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Ham

Ham is pork from a leg cut that has been preserved by wet or dry curing, with or without smoking. As a processed meat, the term ham includes both whole cuts of meat and ones that have been mechanically formed.

Ham is made around the world, including a number of regional specialties. In addition, numerous ham products have specific geographical naming protection.

History
The preserving of pork leg as ham has a long history, with traces of production of cured ham among the Etruscan civilization known in the 6th and 5th century BC.

Cato the Elder wrote about the "salting of hams" in his De agri cultura tome around 160 BC.

There are claims that the Chinese were the first people to mention the production of cured ham. Larousse Gastronomique claims an origin from Gaul. It was certainly well established by the Roman period, as evidenced by an import trade from Gaul mentioned by Marcus Terentius Varro in his writings.

The modern word ham is derived from the Old English ham or hom meaning the hollow or bend of the knee, from a Germanic base where it meant 'crooked'. It began to refer to the cut of pork derived from the hind leg of a pig around the 15th century.

Because of the preservation process, ham is a compound foodstuff or ingredient, being made up of the original meat, as well as the remnants of the preserving agent(s), such as salt, but it is still recognised as a food in its own right.

Methods
Ham is produced by curing raw pork by salting, also known as dry curing, or brining, also known as wet curing. Additionally, smoking may be employed, and seasonings may be added.

Dry-cured
Traditional dry cure hams may use only salt as the curative agent, although this is comparatively rare. This process involves cleaning the raw meat, covering it in salt while it is gradually pressed to squeeze out fluid. Specific herbs and spices may be used to add flavour during this step. The hams are then washed and hung in a dark, temperature-regulated place until dry. It is then hung to air for another period of time.

The duration of the curing process varies by the type of ham. For example, Jinhua ham takes approximately 8 to 10 months to complete, jamón serrano cures in 9–12 months, prosciutto di Parma takes more than 12 months, and Iberian ham can take up to 2 years to reach the desired flavor characteristics. Many dry-cured hams, such as prosciutto, are eaten without being cooked.

Most modern dry cure hams also use nitrites (either sodium nitrite or potassium nitrite), which are added along with the salt. Nitrites are used because they prevent bacterial growth and, in a reaction with the meat's myoglobin, give the product a desirable dark red color. The amount and mixture of salt and nitrites used have an effect on the shrinkage of the meat. Because of the toxicity of nitrite, some areas specify a maximum allowable content of nitrite in the final product. Under certain conditions, especially during cooking, nitrites in meat can react with degradation products of amino acids, forming nitrosamines, which are known carcinogens.

The dry curing of ham involves a number of enzymatic reactions. The enzymes involved are proteinases (cathepsins – B, D, H & L, and calpains) and exopeptidases (peptidase and aminopeptidase). These enzymes cause proteolysis of muscle tissue, which creates large numbers of small peptides and free amino acids, while the adipose tissue undergoes lipolysis to create free fatty acids. Salt and phosphates act as strong inhibitors of proteolytic activity. Animal factors influencing enzymatic activity include age, weight, and breed. During the process itself, conditions such as temperature, duration, water content, redox potential, and salt content all have an effect on the meat.

The salt content in dry-cured ham varies throughout a piece of meat, with gradients determinable through sampling and testing or non-invasively through CT scanning.

Wet-cured
Wet-cured hams are brined, which involves the immersion of the meat in a brine, sometimes with other ingredients such as sugar also added for flavour. The meat is typically kept in the brine for around 3 to 14 days. Wet curing also has the effect of increasing volume and weight of the finished product, by about 4%.

The wet curing process can also be achieved by pumping the curing solution into the meat. This can be quicker, increase the weight of the finished product by more than immersion, and ensure a more even distribution of salt through the meat. This process is quicker than traditional brining, normally being completed in a few days.

Wet-cured ham is usually cooked, either during processing, or after ageing. It is first brined, then cooked in a container and finally surface pasteurized. Italian regulations allow it to contain salt, nitrites, sugar, dextrose, fructose, lactose, maltodextrin, milk protein, soy protein, natural or modified starches, spices, gelatin, and flavorings.

Smoking
Ham can also be additionally preserved through smoking, in which the meat is placed in a smokehouse (or equivalent) to be cured by the action of smoke.

The main flavor compounds of smoked ham are guaiacol, and its 4-, 5-, and 6-methyl derivatives as well as 2,6-dimethylphenol. These compounds are produced by combustion of lignin, a major constituent of wood used in the smokehouse.

Labeling
In many countries the term is now protected by statute, with a specific definition. For instance, in the United States, the Code of Federal Regulations (CFR) says that "the word 'ham', without any prefix indicating the species of animal from which derived, shall be used in labeling only in connection with the hind legs of swine".

In addition to the main categories, some processing choices can affect legal labeling. For instance, in the United States, a "smoked" ham must have been smoked by hanging over burning wood chips in a smokehouse or an atomized spray of liquid smoke such that the product appearance is equivalent; a "hickory-smoked" ham must have been smoked using only hickory. However, injecting "smoke flavor" is not legal grounds for claiming the ham was "smoked"; these are labeled "smoke flavor added". Hams can only be labeled "honey-cured" if honey was at least 50% of the sweetener used, is at least 3% of the formula, and has a discernible effect on flavor. So-called "lean" and "extra lean" hams must adhere to maximum levels of fat and cholesterol per 100 grams of product.

Whole fresh pork leg can be labeled as fresh ham in the United States.

Protected designations
A number of hams worldwide have some level of protection of their unique characteristics, usually relating to their method of preservation or location of production or processing. Dependent on jurisdiction, rules may prevent any other product being sold with the particular appellation, such as through the European protected geographical indication.

 * Belgium
 * Jambon d'Ardenne – Wallonia

 * Bulgaria
 * Elenski but – Elena

 * China
 * Anfu ham- Jiangxi
 * Jinhua ham – Jinhua
 * Rugao ham – Rugao
 * Xuanwei ham – Xuanwei

 * Czech Republic
 * Pražká Šunka ("Prague Ham") – Prague

 * Croatia
 * Pršut

 * France
 * Jambon noir de Bigorre (PDO), made from black gascon pigs
 * Jambon de kintoa (PDO), made from basque pigs
 * Jambon de Corse (PDO), made from black nustrale pigs
 * Jambon de Bayonne (PGI)
 * Jambon d'Auvergne (PGI)
 * Jambon de l'Ardèche (PGI)
 * Jambon de Lacaune (PGI)
 * Jambon de Vendée (PGI)
 * Jambon sec des Ardennes (PGI)
 * Jambon de Luxeuil
 * Jambon du Limousin, made from black cul-noir pigs
 * Jambon de Savoie
 * Jambon du Périgord
 * Jambon des Pyrénées

 * Germany
 * Ammerländer Schinken – Ammerland
 * Schwarzwälder Schinken – Black Forest
 * Westfälischer Schinken – Westphalia

 * Italy
 * Prosciutto di Parma – Parma
 * Prosciutto di San Daniele – San Daniele del Friuli
 * Speck Alto Adige – South Tyrol
 * Vallée d’Aoste Jambon de Bosses – Saint-Rhémy-en-Bosses, Aosta Valley

 * Luxembourg
 * Éisleker ham – Oesling region

 * Montenegro
 * Njeguška pršuta – Njeguši, Montenegro

 * Portugal
 * Portuguese Fiambre (not to be confused with Guatemalan fiambre)
 * Presunto
 * Jamón Ibérico

 * Slovenia
 * Kraški pršut

 * Spain
 * Jamón serrano
 * Jamón Ibérico, made from the Black Iberian pig breeds
 * Lacón Gallego, from Galicia

 * United Kingdom
 * Wiltshire cure ham

 * United States
 * Smithfield ham – Smithfield, Virginia

Uses
Ham is typically used in its sliced form, often as a filling for sandwiches and similar foods, such as in the ham sandwich and ham and cheese sandwich. Other variations include toasted sandwiches such as the croque-monsieur and the Cubano. It is also a popular topping for pizza in the United States.

In the United Kingdom, a pork leg cut, either whole or sliced, that has been cured but requires additional cooking is known as gammon. Gammons were traditionally cured before being cut from a side of pork along with bacon. When cooked, gammon is ham. Cooked ham joints are a popular dish around Christmas time, particularly in the Anglosphere and Northern Europe. Gammon can also served as gammon steaks, which are fried or grilled, and served in a similar manner to bacon.

<!--== Health effects == As a processed meat, there has been concern over the health effects of ham consumption. A meta-analysis study from 2012 has shown a statistically relevant correlation between processed meat consumption and the risk of pancreatic cancer, with an increase in consumption of 50 g per day leading to a 19% increase in risk.

This supported earlier studies, including the 2007 study "Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective", by the World Cancer Research Fund and the American Institute for Cancer Research, which reviewed more than 7,000 studies published worldwide. Among the recommendations was that, except for very rare occasions, people should avoid eating ham or other processed meats – cured, smoked, salted or chemically preserved meat products such as bacon, hot dogs, sausage, salami, and pastrami. The report states that once an individual reaches the 510 g weekly limit for red meat, every 48 g of processed meat consumed a day increases cancer risk by 21%.

A European cohort study from 2013 also positively correlated processed meat consumption with higher all-cause mortality, with an estimation that 3.3% of the deaths amongst participants could have been prevented by consuming an average of less than 20 g of processed meat per day over the course of the study. -->

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Henry Laurens

Henry Laurens ( – December 8, 1792) was an American Founding Father,  merchant, slave trader, and rice planter from South Carolina who became a political leader during the Revolutionary War. A delegate to the Second Continental Congress, Laurens succeeded John Hancock as its president. He was a signatory to the Articles of Confederation and, as president, presided over its passage.

Laurens had earned great wealth as a partner in the largest slave-trading house in North America, Austin and Laurens. In the 1750s alone, this Charleston firm oversaw the sale of more than 8,000 enslaved Africans. Laurens served for a time as vice president of South Carolina and as the United States minister to the Netherlands during the Revolutionary War. He was captured at sea by the British and imprisoned for a little more than a year in the Tower of London. His oldest son, John Laurens, was an aide-de-camp to George Washington and a colonel in the Continental Army.

Early life and education
Laurens' forebears were Huguenots who fled France after the Edict of Nantes was revoked in 1685. His grandfather Andre Laurens left earlier, in 1682, and eventually made his way to America, settling first in New York City and then Charleston, South Carolina. Andre's son John married Hester (or Esther) Grasset, also a Huguenot refugee. Henry was their third child and eldest son. John Laurens became a saddler, and his business eventually grew to be the largest of its kind in the colonies.

In 1744, Laurens was sent to London to augment his business training. This took place in the company of Richard Oswald. His father died in 1747, bequeathing a considerable estate to 23-year-old Henry.

Marriage and family
Laurens married Eleanor Ball, also of a South Carolina rice planter family, on June 25, 1750. They had thirteen children, many of whom died in infancy or childhood. Eleanor died in 1770, one month after giving birth to their last child. Laurens took their three sons to England for their education, encouraging their oldest, John Laurens, to study law. Instead of completing his studies, John Laurens returned to the United States in 1776 to serve in the American Revolutionary War.

Political career
Laurens served in the militia, as did most able-bodied men in his time. He rose to the rank of lieutenant colonel in the campaigns against the Cherokee Indians in 1757–1761, during the French and Indian War (also known as the Seven Years' War). In 1757, he was elected to South Carolina's colonial assembly. Laurens was elected again every year but one until the Revolution replaced the assembly with a state convention as an interim government. The year he missed was 1773, when he visited England to arrange for his sons' educations. He was named to the colony's council in 1764 and 1768 but declined both times. In 1772, he joined the American Philosophical Society of Philadelphia and carried on extensive correspondence with other members.

As the American Revolution neared, Laurens was at first inclined to support reconciliation with the British Crown. But as conditions deteriorated, he came to fully support the American position. When Carolina began to create a revolutionary government, Laurens was elected to the Provincial Congress, which first met on January 9, 1775. He was president of the Committee of Safety and presiding officer of that congress from June until March 1776. When South Carolina installed a fully independent government, he served as the vice president of South Carolina from March 1776 to June 27, 1777. Laurens was first named a delegate to the Continental Congress on January 10, 1777. He served in the Congress until 1780. He was the president of the Continental Congress from November 1, 1777, to December 9, 1778.

In the fall of 1779, the Congress named Laurens their minister to the Netherlands. In early 1780, he took up that post and successfully negotiated Dutch support for the war. But on his return voyage to Amsterdam that fall, the British frigate HMS Vestal (1779) intercepted his ship, the continental packet Mercury, off the banks of Newfoundland. Although his dispatches were tossed in the water, they were retrieved by the British, who discovered the draft of a possible U.S.-Dutch treaty prepared in Aix-la-Chapelle in 1778 by William Lee and the Amsterdam banker Jean de Neufville. This prompted Britain to declare war on the Dutch Republic, becoming known as the Fourth Anglo-Dutch War.

The British charged Laurens with treason, transported him to England, and imprisoned him in the Tower of London (he is the only American to have been held prisoner in the tower). His imprisonment was protested by the Americans. In the field, most captives were regarded as prisoners of war, and while conditions were frequently appalling, prisoner exchanges and mail privileges were accepted practice. During his imprisonment, Laurens was assisted by Richard Oswald, his former business partner and the principal owner of Bunce Island, a slave-trading island base in the Sierra Leone River. Oswald argued on Laurens' behalf to the British government. Finally, on December 31, 1781, he was released in exchange for General Lord Cornwallis and completed his voyage to Amsterdam. He helped raise funds for the American effort.

Laurens' oldest son, Colonel John Laurens, was killed in 1782 in the Battle of the Combahee River, as one of the last casualties of the Revolutionary War. He had supported enlisting and freeing slaves for the war effort and suggested to his father that he begin with the 40 he stood to inherit. He had urged his father to free the family's slaves, but although conflicted, Henry Laurens never manumitted his 260 slaves.

In 1783, Laurens was sent to Paris as one of the peace commissioners for the negotiations leading to the Treaty of Paris. While he was not a signatory of the primary treaty, he was instrumental in reaching the secondary accords that resolved issues related to the Netherlands and Spain. Richard Oswald, a former partner of Laurens in the slave trade, was the principal negotiator for the British during the Paris peace talks.

Laurens generally retired from public life in 1784. He was sought for a return to the Continental Congress, the Constitutional Convention in 1787 and the state assembly, but he declined all of these positions. He did serve in the state convention of 1788, where he voted to ratify the United States Constitution.

British forces, during their occupation of Charleston, had burned the Laurens home at Mepkin during the war. When Laurens and his family returned in 1784, they lived in an outbuilding while the great house was rebuilt. He lived on the estate the rest of his life, working to recover the estimated £40,000 that the revolution had cost him (equivalent to about $ in ).

Death and legacy
Laurens suffered from gout starting in his 40s and the affliction plagued him throughout the rest of his life. Laurens died on December 8, 1792, at his estate, Mepkin, in South Carolina. In his will he stated he wished to be cremated and his ashes be interred at his estate. It is reported that he was the first Caucasian cremation in the United States, which he chose because of a fear of being buried alive. Afterward, the estate passed through several hands. Large portions of the estate still exist. Part of the original estate was donated to the Roman Catholic Church in 1949 and is now the location of Mepkin Abbey, a monastery of the Order of Cistercians of the Strict Observance (Trappist monks).

The city of Laurens, South Carolina, and its county are named for him. The town and the village of Laurens, New York, are named for him. Laurens County, Georgia, is named for his son John. General Lachlan McIntosh, who worked for Laurens as a clerk and became close friends with him, named Fort Laurens in Ohio after him.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Henry Laurens


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British Aerospace HOTOL

HOTOL, for Horizontal Take-Off and Landing, was a 1980s British design for a single-stage-to-orbit (SSTO) spaceplane that was to be powered by an airbreathing jet engine. Development was being conducted by a consortium led by Rolls-Royce and British Aerospace (BAe).

Designed as a single-stage-to-orbit (SSTO) reusable winged launch vehicle, HOTOL was to be fitted with a unique air-breathing engine, the RB545 or Swallow, that was under development by British engine manufacturer Rolls-Royce. The propellant for the engine technically consisted of a combination of liquid hydrogen/liquid oxygen; however, it was to employ a new means of dramatically reducing the amount of oxidizer needed to be carried on board by utilising atmospheric oxygen as the spacecraft climbed through the lower atmosphere. Since the oxidizer typically represents the majority of the takeoff weight of a rocket, HOTOL was to be considerably smaller than normal pure-rocket designs, roughly the size of a medium-haul airliner such as the McDonnell Douglas DC-9/MD-80.

While HOTOL's proof-of-concept design study was being carried out, attempts were made by both industry and the British government to establish international cooperation to develop, produce, and deploy the spacecraft. In spite of American interest in the programme, there was little appetite amongst the members of the European Space Agency (ESA), and the British government was not prepared to depart from ESA cooperation. Additionally, technical issues were encountered, and there were allegations that comparisons with alternative launch systems such as conventional rocket vehicle using similar construction techniques failed to show much advantage to HOTOL. In 1989, funding for the project ended. The termination of development work on HOTOL led to the formation of Reaction Engines Limited (REL) to develop and produce Skylon, a proposed spacecraft based on HOTOL technologies, including its air-breathing engine.

Origins
The ideas behind HOTOL originated from work done by British engineer Alan Bond in the field of pre-cooled jet engines. Bond had specifically performed this research with the intention of producing a viable engine for powering a space launch system. In 1982, British Aerospace (BAe), which was Europe's principal satellite-builder, began studying a prospective new launch system with the aim of providing launch costs that were 20 per cent of the American Space Shuttle operated by NASA. BAe became aware of work by British engine manufacturer Rolls-Royce on a suitable engine, and soon conceived of an unmanned, fully reusable single-stage-to-orbit (SSTO) winged spaceplane as a launch vehicle.

Thus, the project had soon become a joint venture between BAe and Rolls-Royce, led by John Scott-Scott and Bob Parkinson. Early on, there was an ambition to 'Europeanise' the project and to involve other nations in its development and manufacture as it was recognised that an estimated £4 billion would be needed to fund full-scale development. In August 1984, BAe unveiled a public display of the HOTOL satellite launcher project and released details on its proposed operations.

In December 1984, a Department of Trade and Industry (DTI) memorandum noted that West Germany was interested in the programme, while France had adopted a critical attitude towards HOTOL, which the ministry viewed as potentially due to it being seen as a competitor to French-led projects. According to Minister of Trade and Industry Geoffrey Pattie, French diplomatic pressure to gather support for its own proposed Hermes space vehicle had inadvertently generated support and interest amongst European Space Agency (ESA) members in the HOTOL project. Despite this climate of tentative interest and possible European support, there was a general attitude of reluctance within the British government to take the lead on a new space launcher.

American interest and design study
In March 1985, there were claims that Rolls-Royce was in the process of conducting licensing talks for HOTOL engine technology with American propulsion company Rocketdyne. In April 1985, Pattie wrote to Secretary of State for Defence Michael Heseltine to propose a two-year £3 million proof of concept study be performed under a public-private partnership arrangement, consisting of £1 million provided by the UK government and the remainder being financed by Rolls-Royce and BAe themselves. Pattie reasoned that the project would serve Britain's "strategic capability", and that tests of key technologies could foster international collaboration. According to aerospace publication Flight International, the support of the Ministry of Defense (MoD) was critical as the design of HOTOL's engine had been classified.

In July 1985, Rolls-Royce's technical director Gordon Lewis stated that the firm sought the involvement of the Royal Aircraft Establishment's (RAE) propulsion group, and that Rolls-Royce was not prepared to invest its own funds into engine development for HOTOL. By the second half of 1985, work had commenced on the two-year concept-of-proof study. Early on, there was considerable pressure to demonstrate the project's feasibility and credibility in advance of final decisions being taken by ESA on the Hermes and what would become the Ariane 5 launch system, thus the work concentrated on the validation of critical technologies involved.

By November 1985, DTI and RAE discussions noted that Rolls-Royce were seeking American data on ramjet technology to support their work on the engine, which it referred to by the name Swallow. Reportedly, the United States Air Force were interested in the technology used in the Swallow engine for its own purposes. In November 1985, discussions between Prime Minister Margaret Thatcher, Minister without portfolio David Young and US President Ronald Reagan's scientific advisor George Keyworth noted American interest in collaboration on developing hypersonic vehicles such as HOTOL, and that a prototype could be flying as early as 1990.

According to British government files, neither BAe nor the MoD were enthusiastic for the prospects of American involvement in the programme, expressing reluctance out of a belief that the outcome of such a move could result in the UK becoming a junior member in a project that it once led. There was also a belief that if Britain chose to pair up with the United States, it would find itself frozen out of work on future European launchers. However, Rolls-Royce viewed transatlantic cooperation as necessary. BAe's head of future business, Peter Conchie, stated that, if possible, HOTOL should become a part of the European space framework. In early 1986, the British government formally approved the two-year study.

Problems and criticism
In December 1984, project management consultant David Andrews issued an eight-page critique of the programme, noting that the design was optimised for the ascent while exposing itself to extended thermal loads during descent due to a low level of drag. He also claimed that the vehicle offered no capability that was not already available; BAe responded that the criticisms made had been answered. In April 1985, the Ministry of Defence's research and development department deputy controller James Barnes claimed that HOTOL lacked a justification, and that there was no defence requirement for such vehicles. He also noted that the "engineering problems are considerable" and that it was unlikely to enter service until the 2020s; Barnes also observed the HOTOL engine to be "ingenious".

In November 1985, the RAE issued an assessment of HOTOL's study proposal; the organisation believed that HOTOL would take up to 20 years to develop, rather than the 12-year timetable that had been envisioned by industry. The RAE also projected that the project would have an estimated total cost of £5 billion (as of its value in 1985), £750 million of which would be required in a six-year definition phase and an estimated £25 million in a pre-definition feasibility study.

During development, it was found that the comparatively heavy rear-mounted engine moved the centre of mass of the vehicle rearwards. This meant that the vehicle had to be designed to push the centre of drag as far rearward as possible to ensure stability during the entire flight regime. Redesign of the vehicle to do this required a large mass of hydraulic systems, which cost a significant proportion of the payload, and made the economics unclear. In particular, some of the analysis seemed to indicate that similar technology applied to a pure rocket approach would give approximately the same performance at less cost.

Shutdown
By 1989, the outlook for HOTOL had become bleak; from the onset of the project, support between the British government and industrial partners had been uneven, while the United States had emerged as the only foreign nation that showed willingness to contribute to the programme, in part because of the secrecy surrounding it. There was little prospect for European involvement, ESA having elected to pursue development of what would become the Ariane 5, a conventional space launch system. Rolls-Royce withdrew from the project, judging the eventual market for the engine was unlikely to be large enough to repay the development costs. The British government declined to offer further funding for HOTOL. The project was almost at the end of its design phase while much of the plans remained in a speculative state; the craft was reportedly still dogged with aerodynamic problems and operational disadvantages at this point.

Successors
A cheaper redesign, Interim HOTOL or HOTOL 2, which was to be launched from the back of a modified Antonov An-225 transport aircraft, specifically was promoted by BAe in 1991; however, this proposal was rejected as well. The design for Interim HOTOL was to have dispensed with an air-breathing engine cycle and was designed to use a more conventional mix of LOX and liquid hydrogen as fuel instead.

In 1989, HOTOL co-creator Alan Bond and engineers John Scott-Scott and Richard Varvill formed Reaction Engines Limited (REL) which has since been working on a new air-breathing engine, SABRE, which used alternative designs to work around (and improve upon) the Rolls-Royce patents, and the Skylon vehicle intended to solve the problems of HOTOL. They first published these engine and spacecraft concepts in 1993, and have since been developing the core technologies, particularly the engine and its frost-controlled pre-cooler; initially supported by private funding, but latterly with support from the European Space Agency, the British National Space Centre, the United Kingdom Space Agency, BAe, and the Air Force Research Laboratory. REL plan to demonstrate a flight-ready pre-cooler operating under simulated flight conditions in 2018, and statically test a demonstration engine core in 2020.

Overview
HOTOL was envisioned as an unmanned, fully reusable single-stage-to-orbit (SSTO) winged spaceplane. The unmanned craft was intended to put a payload of around 7 to 8 tonnes in orbit, at 300 km altitude. It was intended to take off from a runway, mounted on the back of a large rocket-boosted trolley that would help get the craft up to "working speed". The engine was intended to switch from jet propulsion to pure rocket propulsion at 26–32 km high, by which time the craft would be travelling at Mach 5 to 7. After reaching low Earth orbit (LEO), HOTOL was intended to re-enter the atmosphere and glide down to land on a conventional runway (approx 1,500 metres minimum). Only a single payload would have been carried at a time as BAe had judged this to be more economic as it removed any need for satellite interfacing and allowed for missions to be tailored to individual requirements.

During its high-altitude phase, its flight control system would have been linked to ground stations and to space-based global navigation system navigation, while radar would have been used during the take-off and landing phases. In addition to the placing of satellites into geosynchronous orbit or LOE, HOTOL was also projected as being able to also perform the retrieval of satellites and hardware from LOE. BAe promotional material depicts HOTOL docking with the International Space Station (ISS), a feat that the company claimed would have required manned operation as automated systems were not capable of performing such docking manoeuvres at that time. HOTOL was designed to conduct fully automated unmanned flights; however, it had been intended at a later stage to potentially re-introduce a pilot. Manned operations would have required the installation of a dedicated pressurised module within the payload bay.

As designed, HOTOL would have been 62 metres long, 12.8 metres high, a fuselage diameter of 5.7 metres and a wingspan of 19.7 metres. It featured a wing design that had been derived from that of Concorde; its large area resulted in relatively low wing loading, which would have resulted in lower reentry temperatures (never rising above 1,400 °C). Built out of carbon composite materials, there would have been no need for the use of insulating tiles akin to those that comprised the Space Shuttle thermal protection system. The internally stowed landing gear would have been too small to carry the weight of the fully fuelled rocket, so emergency landings would have required the fuel to be dumped.

Engine
The RB545, which was given the name "Swallow" by its manufacturer, British engine maker Rolls-Royce, was an air-breathing rocket engine. It would have functioned as an integrated dual-role powerplant, having been capable of air-breathing while operating within the atmosphere and operating in a similar manner to that of a rocket when having attained close to and within LEO. This engine would have also been capable of powering the spacecraft to hypersonic speeds. It was a crucial element of the programme, having been publicly attributed as "the heart of Hotol's very low launch costs".

The exact details of this engine were covered by the Official Secrets Act of the United Kingdom; consequently, there is relatively little public information about its development and on its operation. However, material was later declassified when government policy changed to prevent the keeping of secret patents without an attributed justification.

Within the atmosphere, air is taken in through two vertically mounted intake ramps, then the flow would be split, passing the correct amount to the pre-coolers, and the excess to spill ducts. Hydrogen from the fuel tanks would be passed through two heat exchangers to pre-cool the air prior to entering a high overall pressure-ratio turbojet-like engine cycle — the heated hydrogen driving a turbine to compress and feed the cooled air into the rocket engine, where it was combusted with some of the hydrogen used to cool the air. The majority of the remaining hot hydrogen was released from the back of the engine, with a small amount drawn off to reheat the air in the spill ducts in a ramjet arrangement to produce "negative intake momentum drag".

To prevent the pre-coolers from icing up, the first pre-cooler cooled the air to around 10 degrees above freezing point, to liquefy the water vapour in the air. Then liquid oxygen (LOX) would have been injected into the airflow to drop the temperature to -50 C flash freezing the water into microscopic ice crystals, sufficiently cold that they wouldn't melt due to kinetic heating if they struck the second pre-cooler elements. A water trap could have been added after the first pre-cooler if operating conditions resulted in an excess of moisture.

When it was no longer possible to use the atmosphere for combustion, the RB545 would switch to using on-board LOX to burn with the hydrogen as a high-efficiency hydrogen/oxygen rocket.

title: British Aerospace HOTOL


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Talk:Human/Archive 1

Remark on A Look at Modern Human Origins reference:

Isn't there a better site available? I would like to see a site referenced which is more explicit about the various fossiles found. Not just a list, but as well a tree diagram with time info. -- HJH

Another site is http://www.talkorigins.org/. I'm not sure if it meets your requirements. I think there's no general agreement at present on how to draw such a tree -- Hagedis

Thanks. The site is nicely done and contains useful information. However it is not the thing I'm looking for. -- HJH

I changed "dominant" to "among the most generalized." If anything is "dominant," I think it is bacteria, not us! But I take issue with the notion of "dominant," I suspect it is a species-centric term. Darwinian models of evolution lead away from hierarchies like "the great chain of being," which this echoes. -- SR

 * I agree with you, but I don't know what "most generalized" means. And I think one intent of "dominant" was "top of all food chains". Certainly we are the most powerful and advanced species by some measures, or the most intelligent. Surely that should be made clear. --Dmerrill

 * "most generalized" means adapted to the widest variety of environments; the relationship between the organism and its environment is a fundamental issue in Darwinian models of evolution. And as I said, Darwinian approaches (which certainly are "dominant" today!) really are anti-hierarchical.  The notion of the "food chain" is itself a remnant of the 19th century Victorian myth of the "great chain of being," and really anti-ecological (since ecology is a complex interactive and dynamic system that does not lend itself to linear models (except in very very local senses).  There is NO scientific basis for saying one species is more "advanced" than another -- there are always differences, but any species that survives does so because it is adapted to its niche; there are many niches in which we cannot survive (I have even heard that a cockroach can survive a nuclear explosion; maybe they are more advanced than us?)  We are definitely NOT at the top of the food chain -- when we get sick (well, if it is because of a parasite, virus, or bacteria) we are being eaten.  I do not think there is an objective standard by which we can say we are the "most intelligent" -- intelligence is at best a species-specific concept (when we say that another species is very intelligent, we are really saying that its intelligence approximates our own); some people have even questioned whether there is a universal criteria for intelligence WITHIN our own species (see the section on race and intelligence in race).  Are we the most powerful?  Perhaps -- depending on how you measure it.  We certainly are destructive and have managed to kill a lot of other species off.  But I suspect that we will become extinct long before all other species become extinct.  In the meantime, although we have wrecked havoc with this planet, we are still pretty afraid of some of those critters "higher" up on the food chain, like the bubonic plague or even influenza.  So personally, I will wait and see before asserting that we are th most powerful. -- SR

Your term "most generalized" is not self-explanatory however. And I'm not even sure that we are adapted to the widest range of environments. How about the cockroaches, or soil bacteria? Why not simply say "inhabits almost all landmasses on Earth and has modified environments extensively"? --AxelBoldt

 * Good points, all. I tried to npov the text with your criticism in mind. Removed "food chain" reference entirely, since as you point out it is really more of a "food cycle". We all get eaten sooner or later! --Dmerrill

 * I put in a definition of "generalized" -- I hope it is clear and sensible. I also appreciate Dmerrill's modifications.  Personally, I do not think there is a need for "In terms of population size or diversity of species, smaller and simpler animals such as bacteria and insects dominate the Earth's species, however." -- although it certainly gives us something to think about.  My point really was to question the whole validity of the word "dominant."  I won't cut the sentence myself because I do not want to be too nit-picky.  Personally I would rather excise the word dominant, perhaps pursue the thread in this section.  But if others believe that the word belongs in the article, I think it requires some discussion.  So I included a few more sentences.  I worry about NPOV issues either way, and hope others can improve upon this.  One good thing about my addition, I think, is that if provided an opportunity for more links, because it is in those other articles that a full discussion of "dominant" really belongs. -- SR

 * I think one can make a good argument that pointing out the general belief that we are dominant (and I do think it is the, ahem, dominant belief among people) gives the opportunity to discuss the less homo-centric findings of science. You can't have one without the other. I think we can still improve the way it's all worded, though. --Dmerrill

 * sure -- a point well-taken. Perhaps as others contribute we can eventually create a subsection within the article? -- SR

 * I started a section along those lines, mentioning the general belief followed by scientific viewpoints. More scientific viewpoints need to be added. Toolmaking is certainly an important one, so I added the bit I know about it. I'm not a biologist, so I can only do my best. Please correct anything wrong. --Dmerrill

 * I think your reorganization is GREAT -- I just put some provisional section headings in. My sense is that tool-use and language are closely related; one physical anthropologist has argued that they both express our capacity for symbolic thought, which is what distinguishes us from other animals.  If I can figure out a clear way to express this without being too partisan, I will work it in.  Anyway, I like your recent revision very much. -- SR

I also expanded the second half of the article to provide more detail. I also think most anthropologists agree that although hominenes diverged from australopithecines, and neanderthals diverged from modern humans, H. habilus, erectus, and sapiens all form one lineage. Also, all three species used tools, not just H. sapiens. I think this addition can be edited a bit to make it more elegant (also I need to fix some of the text) --SR

I added a few comments about the whole question of "distinguishing characteristic: it's not a question normally asked about a species. (I suspect--and left this out because I'm not sure it's NPOV) that the distinguishing characteristic of H. sapiens is that we're the only species that asks that question.)

Also, those molecular genetic numbers seem low--I've seen 2% for human/chimp difference. Anyone have a cite? Vicki Rosenzweig

 * I got these numbers from a physical anthropology textbook that is over ten years old. I can find the proper citation if you like, but the real point is that the figures might be out of date, given the nature of scientific research.  So if anyone has anything authoriative from the last five years, put them in!  SR

 * Another clarification I'd like to see about that figure is whether the difference is measured between the entire chromosomal sequences, or just the gene-encoding regions? Non-coding regions tend to mutate faster than coding regions, since mutations there are usually neutral. Bryan Derksen

 * This does need to be updated in light of recent research (c.f. New Scientist and Proceedings of the National Academy of Sciences). I'd love to do it myself but I am so not-qualified. You'd have to reconcile it with the number given for gorillas too. -- Nate

I modified the section on physical traits with two ends in mind -- to replace the language of "distinguishing features" with "evolutionary trends," and to refine the list (e.g. adding canine reduction, making a point about brain structure). Also, I pointed out that height and weight are heavily influenced by environment and culture (which makes them pretty hard to use to "define" a species). I also cut the word "designed" (e.g. bipedal locomotion was designed to permit tool-use) as the general tenor of the article is scientific rather than creationist.

I also did some general tweaking to make the article read better. SR

Unless somebody can give me a very good reason not to, I am going to move this article to simply Human so that it conforms to our well established naming conventions on the use of English and simple titles of articles. Homo sapiens can be introduced in the first line and then used throughout if need be. --maveric149

 * Not sure if it's "reason not to", but Homo sapiens is a species and other species have the scientific name as the main page, right? I'd have 'human' be a redirect. -- OlofE

 * Other species do but that is either because it is wrong or there isn't a common name. I'm making good on my threat now. --mav

 * Page moved with it's complete history. --mav

The entry for "Human" is listed under Requested pictures. I'd like to put the picture of a man and a woman from the Pioneer 11 spacecraft onto this page as an example of a "picture of humans," though I suspect some folks would complain because the man and the woman are...NAKED. Would there be any objections, do you think? -- Modemac 15:41 Feb 15, 2003 (UTC)

 * Do it. If they have a problem with it then they have big issues. I've seen far racier stuff in my anatomy textbook than the Pioneer 11 drawing. --mav

 * I appreciate your support. Picture now added. -- Modemac 17:22 Feb 15, 2003 (UTC)

 * Ironically, Sagan and the team who prepared the plaque were accused of "sending pornography into space" at the time they made it. I'm not too happy with having the picture here, though, as I would much prefer an actual photograph. The Pioneer image is also a bit problematic because, in order to represent all humans, different "racial" features have been merged together, giving an overall image that is hardly found in reality. Also, the version presented here suffers from JPEG artifacts.

 * Sagan et al. selected a photo of humans for the Voyager Golden Record, I have a copy in his book "Murmurs of Earth". It shows a naked man and woman holding hands and looking at each other, the woman is pregnant. NASA blocked the image, again for fears of being accused of sending porn to space, and it was replaced with a boring silhouette (probably revealing more about human nature to potential alien recipients than intended). Unfortunately my scanner is currently defective, but I will try to get it digitized ASAP. --Eloquence 17:34 Feb 15, 2003 (UTC)

 * Please do! Properly downsized that image could go in the table per WikiProject Tree of Life guidelines. --mav 18:02 Feb 15, 2003 (UTC)

 * I looked at the images of the Voyager, and unfortunately the NASA web site hosting these images says the photos are still copyrighted. This means that we can't use those images here, alas.  That's one reason why I chose the Pioneer 11 image -- as far as I can tell, it's public domain.  -- Modemac 17:50 Feb 15, 2003 (UTC)

 * Copyright shouldn't be an issue in this case because of fair use. --mav

 * Yeah, most of the Voyager stuff is copyrighted, however, in the case of the photo in question, no source is given in the book, unlike for most other photos, so it may well be PD. Aside from that, as Mav points out, we have taken the position that photos do not necessarily need to be in the public domain or under the FDL for us to use them, although this is a somewhat shaky tenet (fair use is an American doctrine, and possibly incompatible with the FDL). --Eloquence

 * "sending pornography into space"! egad! That deserves a mention on the Pioneer 11 article! -- Tarquin 18:47 Feb 15, 2003 (UTC)

Creationists are useful for something. I found out where our ultra-low figures for human-gorilla and human-chimp difference come from. According to http://www.apologeticspress.org/docsdis/2002/dc-02-07.htm the two figures given are probably the earliest estimates in existence -- they date back to the early 1960s - the chimp one to the famous duo Watson & Crick. They are far out of date and misleading. The creationist article does its best to distort the figures in the downwards direction, arguing that the similarity is insignificant, but I'm happy to revise the article to use the previously cited and recent estimate of 5% without equivocation. -- Tim Starling 11:11 Mar 17, 2003 (UTC)

Will the photo of the human, when uploaded and placed? have to be naked? :-s -fonzy

My Latin is weak; does anyone know the plural of homo sapiens? I fear that the way it appears on this page will further the illiterate back-formation "homo sapien". -- Mike Hardy

The plural of homo is homines (both vocative and nominative forms). --Roger 15 Aug 2003

That's true, but it's not relevant (if you'll pardon my bluntness) in this context. Species names don't have or need plurals. Every species is unique, by definition. A human is not "a Homo sapiens", but a member of the species Homo sapiens. Perhaps we need to state explicitly, for the benefit of those who might try to write *sapien, that the s at the end of sapiens does not make it a plural. I'll have a go. -- Heron

Oh, and I removed this bit:

 * The lived body (Maurice Merleau-Ponty) is posited as a way out of the trap of Rationalism vs. Empirism. It points outward as well as inward.

which probably belongs in an article on consciousness rather than here, and anyway needs more explanation. -- Heron (again)

--

"The mean height of an American adult female is 162 centimetres and the mean weight is 62 kg" < could someone change this to either a worldwide statistic, or one for each major continent? We are not a US encyclopedia -- Tarquin 18:01, 6 Dec 2003 (UTC)

I think that hte image DOES portray caucasians: The term caucasian includes arabs, indians, and basically everyone with a certain hair/bone structure. Just based on the guy's hair it is evident that the people in the drawing are most definately not of sub-saharan, aboriginal australian, or east asian origin. --Mishac 20:01, 23 Feb 2004 (UTC)

bad bullet list
Under "Physical Characteristics", the list-tags aren't displaying properly under IE6---that is, the bullet marks don't display at all, and the text seems to simply be broken into short lines randomly. Though I can't imagine why this'd be (the UL and LI tags are in the generated HTML), it does make the page look funny to a lot of users. Any ideas? Grendelkhan 16:43, 29 Mar 2004 (UTC)

 * It's the skeleton thumbnail image. I've moved it lower so that it doesn't interfere with the bullets. - UtherSRG 21:17, 29 Mar 2004 (UTC)

race vs. species
"Subspecies" is not the same as "race". It's deceptive to equate the two terms. Here is one definition for "race" from my dictionary:

2 a : a family, tribe, people, or nation belonging to the same stock b : a class or kind of people unified by community of interests, habits, or characteristics

 * You are correct, although in other taxonomic classes, you would not be: bird subspecies are often called races. - UtherSRG 11:50, 14 Apr 2004 (UTC)

Habitats
No offence, but I think that a discussion of habitats along the lines of "about 3 humans at a time live on space, of the remaining 6.3 billion Earthbound humans, blah blah" is amusing (to put it politely). I have changed it around. As a biological species, Humans are adapted to the savannah where they evolved, then colonized all continents and climates through cultural, not biological evolution. Just my 2 Euro cents. — Miguel 04:45, 2004 Apr 29 (UTC)

Stub notices?
Why are there some stub messages in the middle of this article?? 66.32.141.227 21:46, 23 May 2004 (UTC)

 * Well, it's a non-standard usage, but it indicates that those sections of the article are underdeveloped. Yours, Meelar 21:50, 23 May 2004 (UTC)

Page move
Neumannkun - you copy-paste moved this page to human being. First, page moves should be done with the "Move this page" option to preserve page histories. Second, the disambiguation page you replaced it had two terms - the article you moved, and a dictionary definition which should not be here -- see Wikipedia is not a dictionary. Third, human is much more intuitive than human being as an article title -- Naming conventions: Generally, article naming should give priority to what the majority of English speakers would most easily recognize with a reasonable minimum of ambiguity, while at the same time making linking to those articles easy and second nature.. That's why I reverted. →Raul654 01:50, May 28, 2004 (UTC)

Spiritual characteristics
IMHO, the spiritual characteristics section fails to distinguish between spiritual and supernatural. I am non-theistic but I don't deny a spiritual dimension, just the supernatural basis for it. Humans have engaged in funeral rites for tens of thousands, if not hundreds of thousands, of years. Whether or not there is a theistic basis for this, it is spiritual. Other mammals grieve, and some (like elephants) go to particular places to die, but no other animal has --- to our knowledge --- a universal, cross-cultural concern with death. I don't feel qualified to repair this section, though. Miguel 17:40, 7 Jul 2004 (UTC)

"Human" vs "Homo sapiens"
This article seems to be entirely about the biological "Homo sapiens". I think a little bit of disambiguation (rather than simple forwarding) would be in order: If you ask me, I would say "Homo sapiens" and "human" should be two separate articles, with a section "biology" in "human" pointing to "Homo sapiens"... Dbachmann 07:21, 12 Aug 2004 (UTC)
 * is "Human" really equivalent to "Homo sapiens"? This is not a political issue, since no other "Homo" have survived, but I am not sure whether Homo neanderthalensis should really be classified as non-human
 * besides being a biological term, the word human is also used in a cultural/ethical sense: human vs. inhuman, humanism, humanitarian etc. Maybe there should at least be a paragraph addressing this (adjectival) use.
 * how about some etymology and history of the term (latin "earthling", etc.) rather than stark biology? What was the meaning of "human" in antiquity? In the middle ages? During Colonialism?

 * is Human equivalent to Homo sapiens -- Some scientists like to call everything in the Homo genus human, while for everybody else, human means Homo sapiens sapiens and nothing else. I think we should stick with the second view.

 * As for the article focusing on the biological side, well, go ahead and fix it. A section including a summary and link to culture might be nice. There is a lot that could be done with the article. But disambiguation is not in order. --Yath 08:22, 12 Aug 2004 (UTC)

 * well, it would be an encyclopedia's job to detail the different views, rather than "sticking" with one. As for "fixing" human (cultural)/human (adjective), it's a tall order I cannot pull off in a coffee-break. I maintain that there is ambiguity in the term 'human', while I won't insist that it be disambiguated here. Rather, there can be articles like human condition, human nature or similar dealing with the other aspects. The only thing I'd impose on this article would be a "this article is about your biological species, see also bla bla" header. Although this article could do with a History of the term section, showing views that predate the modern/biologist one endorsed in the rest of the article (which I also endorse, but that's because I'm a 21st century human) -- maybe starting with Plato's "non feathered bipedals" definition, progressing through christian notions of "capable of sin" and what not. But here's my original point: such a section would make sense in an article titled "Human" but not in one titled "Homo sapiens" where the subject treated is immediately clear. Dbachmann 11:38, 12 Aug 2004 (UTC)

 * I don't see your problem. Are human condition and human nature aspects of Homo sapiens sapiens or some less specific group of organisms? Homo neanderthalensis and other proto-humans are not included in culture (except possibly as a mention that humans are interested in their origin). We also don't know what culture the proto-humans have, and comments on what we can surmise from paleoarcheological findings belongs on the appropriate proto-human pages. Everything else are just items that should be added to this article, or summarized in this article with pointers to other articles on those subjects (philosophy, religion, etc). I'm going to add a "to do" list at the top of this talk. Feel free to add any pertinent items you feel are missing from the article. - UtherSRG 13:27, 12 Aug 2004 (UTC)

title: Talk:Human/Archive 1


text:
Hammerhead shark

The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a cephalofoil (a T-shape or "hammer"). The shark's eyes are placed one on either end of this T-shaped structure, with their small mouths directly centered and underneath. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many different— but not necessarily mutually exclusive—functions have been postulated for the cephalofoil, including sensory reception, manoeuvering, and prey manipulation. The cephalofoil gives the shark superior binocular vision and depth perception.

Hammerheads are found worldwide, preferring life in warmer waters along coastlines and continental shelves. Unlike most sharks, some hammerhead species will congregate and swim in large schools during the day, becoming solitary hunters at night.

Description
The known species range from 0.9 to 6.0 m in length and weigh 3 –. One specimen caught off the Florida coast in 1906 weighed over 680 kg. They are usually light gray and have a greenish tint. Their bellies are white, which allows them to blend into the background when viewed from below and sneak up to their prey. Their heads have lateral projections that give them a hammer-like shape. While overall similar, this shape differs somewhat between species; examples are: a distinct T-shape in the great hammerhead, a rounded head with a central notch in the scalloped hammerhead, and an unnotched rounded head in the smooth hammerhead.

Hammerheads have disproportionately small mouths compared to other shark species. Some species are also known to form schools. In the evening, like most other sharks, they become solitary hunters. National Geographic explained that hammerheads can be found in warm, tropical waters, but during the summer, they begin a mass migration period in search of colder waters.

Taxonomy and evolution
Since sharks do not have mineralized bones and rarely fossilize, only their teeth are commonly found as fossils. Their closest relatives are the requiem sharks (Carcharinidae). Based on DNA studies and fossils, the ancestor of the hammerheads probably lived in the Early Miocene epoch about 20 million years ago.

Using mitochondrial DNA, a phylogenetic tree of the hammerhead sharks showed the winghead shark as sister to the rest of the hammerhead sharks. As the winghead shark has proportionately the largest "hammer" of the hammerhead sharks, this suggests that the first ancestral hammerhead sharks also had large hammers.

Cephalofoil
The hammer-like shape of the head may have evolved at least in part to enhance the animal's vision. The positioning of the eyes, mounted on the sides of the shark's distinctive hammer head, allows 360° of vision in the vertical plane, meaning the animals can see above and below them at all times. They also have an increased binocular vision and depth of visual field as a result of the cephalofoil. The shape of the head was previously thought to help the shark find food, aiding in close-quarters maneuverability, and allowing sharp turning movement without losing stability. The unusual structure of its vertebrae, though, has been found to be instrumental in making the turns correctly, more often than the shape of its head, though it would also shift and provide lift. From what is known about the winghead shark, the shape of the hammerhead apparently has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. The pores on the shark's head lead to sensory tubes, which detect electric fields generated by other living creatures. By distributing the receptors over a wider area, like a larger radio antenna, hammerheads can sweep for prey more effectively.

Reproduction
Reproduction occurs only once a year for hammerhead sharks, and usually occurs with the male shark biting the female shark violently until she agrees to mate with him. The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal, with the male transferring sperm to the female through one of two intromittent organs called claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. Usually, a litter consists of 12 to 15 pups, except for the great hammerhead, which gives birth to litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water until they are old enough and large enough to survive on their own.

In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female's ovum fuses with a polar body to form a zygote without the need for a male. This was the first shark known to do this.

Diet
Hammerhead sharks eat a large range of prey such as fish (including other sharks), squid, octopus, and crustaceans. Stingrays are a particular favorite, with the positioning of their (comparatively) smaller, crescent-shaped mouths underneath their T-shaped heads allowing for skilled skate, ray, and flounder hunting, among other seafloor-dwellers. These sharks will often be found swimming above the sand along the bottom of the ocean, stalking their prey. Their unique heads are further utilized as a tool (or weapon) if hunting rays and flatfishes; the shark uses its head to pin down and briefly stun the prey, and only eats once their quarry is clearly weakened and in shock. The great hammerhead, tending to be larger and more aggressive to its own kind than other hammerheads, occasionally engages in cannibalism, eating other hammerhead sharks, including mothers consuming their own young. In addition to the typical animal prey, bonnetheads have been found to feed on seagrass, which sometimes makes up as much as half their stomach contents. They may swallow it unintentionally, but they are able to partially digest it. At the time of discovery, this was the only known case of a potentially omnivorous species of shark (since then, whale sharks were also found to be omnivorous).

Species
There are nine distinct species of Hammerhead shark in the wild:

Relationship with humans

According to the International Shark Attack File, humans have been subjects of 17 documented, unprovoked attacks by hammerhead sharks within the genus Sphyrna since AD 1580. No human fatalities have been recorded. Most hammerhead shark species are too small to inflict serious damage to humans. The great and the scalloped hammerheads are listed on the World Conservation Union's (IUCN) 2008 Red List as endangered, whereas the smalleye hammerhead is listed as vulnerable. The status given to these sharks is as a result of overfishing and demand for their fins, an expensive delicacy. Among others, scientists expressed their concern about the plight of the scalloped hammerhead at the American Association for the Advancement of Science annual meeting in Boston. The young swim mostly in shallow waters along shores all over the world to avoid predators.

Shark fins are prized as a delicacy in certain countries in Asia (such as China), and overfishing is putting many hammerhead sharks at risk of extinction. Fishermen who harvest the animals typically cut off the fins and toss the remainder of the fish, which is often still alive, back into the sea. This practice, known as finning, is lethal to the shark.

In captivity
The relatively small bonnethead is regular at public aquariums, as it has proven easier to keep in captivity than the larger hammerhead species, and it has been bred at a handful of facilities. Nevertheless, at up to 1.5 m in length and with highly specialized requirements, very few private aquarists have the experience and resources necessary to maintain a bonnethead in captivity. The larger hammerhead species can reach more than twice that size and are considered difficult, even compared to most other similar-sized sharks (such as Carcharhinus species, lemon shark, and sand tiger shark) regularly kept by public aquariums. They are particularly vulnerable during transport between facilities, may rub on surfaces in tanks, and may collide with rocks, causing injuries to their heads, so they require very large, specially adapted tanks. As a consequence, relatively few public aquaria have kept them for long periods. The scalloped hammerhead is the most frequently maintained large species, and it has been kept long term at public aquaria in most continents, but primarily in North America, Europe, and Asia. In 2014, fewer than 15 public aquaria in the world kept scalloped hammerheads. Great hammerheads have been kept at a few facilities in North America, including Atlantis Paradise Island Resort (Bahamas), Adventure Aquarium (New Jersey), Georgia Aquarium (Atlanta), Mote Marine Laboratory (Florida), and the Shark Reef at Mandalay Bay (Las Vegas). Smooth hammerheads have also been kept in the past.

Protection
Humans are the number one threat to hammerhead sharks. Although they are not usually the primary target, hammerhead sharks are caught in fisheries all over the world. Tropical fisheries are the most common place for hammerheads to be caught because of their preference to reside in warm waters. The total number of hammerheads caught in fisheries is recorded in the Food and Agriculture Organization of the United Nations Global Capture Production dataset. The number steadily increased from 75 metric tons in 1990, to 6,313 metric tons by 2010.

Shark fin traders say that hammerheads have some of the best quality fin needles which makes them good to eat when prepared properly. Hong Kong is the world's largest fin trade market and accounts for about 1.5% of the total annual amount of fins traded. It is estimated that around 375,000 great hammerhead sharks alone are traded per year which is equivalent to 21,000 metric tons of biomass. However, most sharks that are caught are only used for their fins and then discarded. The actual meat of hammerheads is generally unwanted. Consumption of regular hammerhead meat has been recorded in countries such as Trinidad and Tobago, Venezuela, Kenya, and Japan.

In March 2013, three endangered, commercially valuable sharks, the hammerheads, the oceanic whitetip, and porbeagle, were added to Appendix II of CITES, bringing shark fishing and commerce of these species under licensing and regulation.

Cultural significance
Among Torres Strait Islanders, the hammerhead shark, known as the beizam, is a common family totem and often represented in cultural artefacts such as the elaborate headdresses worn for ceremonial dances, known as dhari (dari). They are associated with law and order. Renowned artist Ken Thaiday Snr is known for his representations of beizam in his sculptural dari and other works.

In native Hawaiian culture, sharks are considered to be gods of the sea, protectors of humans, and cleaners of excessive ocean life. Some of these sharks are believed to be family members who died and have been reincarnated into shark form, but others are considered man-eaters, also known as niuhi. These sharks include great white sharks, tiger sharks, and bull sharks. The hammerhead shark, also known as mano kihikihi, is not considered a man-eater or niuhi; it is considered to be one of the most respected sharks of the ocean, an aumakua. Many Hawaiian families believe that they have an aumakua watching over them and protecting them from the niuhi. The hammerhead shark is thought to be the birth animal of some children. Hawaiian children who are born with the hammerhead shark as an animal sign are believed to be warriors and are meant to sail the oceans. Hammerhead sharks rarely pass through the waters of Maui, but many Maui natives believe that their swimming by is a sign that the gods are watching over the families, and the oceans are clean and balanced.

title: Hammerhead shark


text:
Hall effect

[[File:Hall effect.png|thumb|upright=1.4|In diagram A, the flat conductor possesses a negative charge on the top (symbolized by the blue color) and a positive charge on the bottom (red color). In B and C, the direction of the electrical and the magnetic fields are changed respectively which switches the polarity of the charges around. In D, both fields change direction simultaneously which results in the same polarity as in diagram A. 1. electrons

2. flat conductor, which serves as a hall element (hall effect sensor)

3. magnet

4. magnetic field

5. power source]]

The Hall effect is the production of a potential difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879.

The Hall coefficient is defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field. It is a characteristic of the material from which the conductor is made, since its value depends on the type, number, and properties of the charge carriers that constitute the current.

Discovery
Wires carrying current in a magnetic field experience a mechanical force perpendicular to both the current and magnetic field. André-Marie Ampère in the 1820s observed this underlying mechanism that led to the discovery of the Hall effect. However it was not until a solid mathematical basis for electromagnetism was systematized by James Clerk Maxwell's "On Physical Lines of Force" (published in 1861–1862) that details of the interaction between magnets and electric current could be understood.

Edwin Hall then explored the question of whether magnetic fields interacted with the conductors or the electric current, and reasoned that if the force was specifically acting on the current, it should crowd current to one side of the wire, producing a small measurable voltage. In 1879, he discovered this Hall effect while he was working on his doctoral degree at Johns Hopkins University in Baltimore, Maryland. Eighteen years before the electron was discovered, his measurements of the tiny effect produced in the apparatus he used were an experimental tour de force, published under the name "On a New Action of the Magnet on Electric Currents".

Hall effect within voids
The term ordinary Hall effect can be used to distinguish the effect described in the introduction from a related effect which occurs across a void or hole in a semiconductor or metal plate when current is injected via contacts that lie on the boundary or edge of the void. The charge then flows outside the void, within the metal or semiconductor material. The effect becomes observable, in a perpendicular applied magnetic field, as a Hall voltage appearing on either side of a line connecting the current-contacts. It exhibits apparent sign reversal in comparison to the "ordinary" effect occurring in the simply connected specimen. It depends only on the current injected from within the void.

Hall effect superposition
Superposition of these two forms of the effect, the ordinary and void effects, can also be realized. First imagine the "ordinary" configuration, a simply connected (void-less) thin rectangular homogeneous element with current-contacts on the (external) boundary. This develops a Hall voltage, in a perpendicular magnetic field. Next, imagine placing a rectangular void within this ordinary configuration, with current-contacts, as mentioned above, on the interior boundary of the void. (For simplicity, imagine the contacts on the boundary of the void lined up with the ordinary-configuration contacts on the exterior boundary.) In such a combined configuration, the two Hall effects may be realized and observed simultaneously in the same doubly connected device: A Hall effect on the external boundary that is proportional to the current injected only via the outer boundary, and an apparently sign-reversed Hall effect on the interior boundary that is proportional to the current injected only via the interior boundary. The superposition of multiple Hall effects may be realized by placing multiple voids within the Hall element, with current and voltage contacts on the boundary of each void.

Further "Hall effects" may have additional physical mechanisms but are built on these basics.

Theory
The Hall effect is due to the nature of the current in a conductor. Current consists of the movement of many small charge carriers, typically electrons, holes, ions (see Electromigration) or all three. When a magnetic field is present, these charges experience a force, called the Lorentz force. When such a magnetic field is absent, the charges follow approximately straight paths between collisions with impurities, phonons, etc. However, when a magnetic field with a perpendicular component is applied, their paths between collisions are curved; thus, moving charges accumulate on one face of the material. This leaves equal and opposite charges exposed on the other face, where there is a scarcity of mobile charges. The result is an asymmetric distribution of charge density across the Hall element, arising from a force that is perpendicular to both the straight path and the applied magnetic field. The separation of charge establishes an electric field that opposes the migration of further charge, so a steady electric potential is established for as long as the charge is flowing.

In classical electromagnetism electrons move in the opposite direction of the current $I$ (by convention "current" describes a theoretical "hole flow"). In some metals and semiconductors it appears "holes" are actually flowing because the direction of the voltage is opposite to the derivation below.

For a simple metal where there is only one type of charge carrier (electrons), the Hall voltage $ξ_{y}$ can be derived by using the Lorentz force and seeing that, in the steady-state condition, charges are not moving in the $V_{H}$-axis direction. Thus, the magnetic force on each electron in the $V_{H}$-axis direction is cancelled by a $ξ_{y}$-axis electrical force due to the buildup of charges. The $V_{H}$ term is the drift velocity of the current which is assumed at this point to be holes by convention. The $y$ term is negative in the $y$-axis direction by the right hand rule.

$$\mathbf{F} = q\bigl(\mathbf{E} + \mathbf{v} \times \mathbf{B}\bigl)$$

In steady state, $y$, so $v_{x}$, where $v_{x}B_{z}$ is assigned in the direction of the $y$-axis, (and not with the arrow of the induced electric field $F = 0$ as in the image (pointing in the $0 = E_{y} − v_{x}B_{z}$ direction), which tells you where the field caused by the electrons is pointing).

In wires, electrons instead of holes are flowing, so $E_{y}$ and $y$. Also $ξ_{y}$. Substituting these changes gives

$$V_\mathrm{H}= v_x B_z w$$

The conventional "hole" current is in the negative direction of the electron current and the negative of the electrical charge which gives $−y$ where $v_{x} → −v_{x}$ is charge carrier density, $q → −q$ is the cross-sectional area, and $E_{y} = −V_{H}⁄w$ is the charge of each electron. Solving for $$w$$ and plugging into the above gives the Hall voltage:

$$V_\mathrm{H} = \frac{I_x B_z}{n t e}$$

If the charge build up had been positive (as it appears in some metals and semiconductors), then the $I_{x} = ntw(−v_{x})(−e)$ assigned in the image would have been negative (positive charge would have built up on the left side).

The Hall coefficient is defined as $$R_\mathrm{H} = \frac{E_y}{j_x B_z}$$ or $$\mathbf{E} = -R_\mathrm{H}(\mathbf{J}_c \times \mathbf{B})$$ where $j$ is the current density of the carrier electrons, and $n$ is the induced electric field. In SI units, this becomes $$R_\mathrm{H} =\frac{E_y}{j_x B}= \frac{V_\mathrm{H} t}{IB}=\frac{1}{ne}.$$

(The units of $tw$ are usually expressed as m3/C, or Ω·cm/G, or other variants.) As a result, the Hall effect is very useful as a means to measure either the carrier density or the magnetic field.

One very important feature of the Hall effect is that it differentiates between positive charges moving in one direction and negative charges moving in the opposite. In the diagram above, the Hall effect with a negative charge carrier (the electron) is presented. But consider the same magnetic field and current are applied but the current is carried inside the Hall effect device by a positive particle. The particle would of course have to be moving in the opposite direction of the electron in order for the current to be the same—down in the diagram, not up like the electron is. And thus, mnemonically speaking, your thumb in the Lorentz force law, representing (conventional) current, would be pointing the same direction as before, because current is the same—an electron moving up is the same current as a positive charge moving down. And with the fingers (magnetic field) also being the same, interestingly the charge carrier gets deflected to the left in the diagram regardless of whether it is positive or negative. But if positive carriers are deflected to the left, they would build a relatively positive voltage on the left whereas if negative carriers (namely electrons) are, they build up a negative voltage on the left as shown in the diagram. Thus for the same current and magnetic field, the electric polarity of the Hall voltage is dependent on the internal nature of the conductor and is useful to elucidate its inner workings.

This property of the Hall effect offered the first real proof that electric currents in most metals are carried by moving electrons, not by protons. It also showed that in some substances (especially p-type semiconductors), it is contrarily more appropriate to think of the current as positive "holes" moving rather than negative electrons. A common source of confusion with the Hall effect in such materials is that holes moving one way are really electrons moving the opposite way, so one expects the Hall voltage polarity to be the same as if electrons were the charge carriers as in most metals and n-type semiconductors. Yet we observe the opposite polarity of Hall voltage, indicating positive charge carriers. However, of course there are no actual positrons or other positive elementary particles carrying the charge in p-type semiconductors, hence the name "holes". In the same way as the oversimplistic picture of light in glass as photons being absorbed and re-emitted to explain refraction breaks down upon closer scrutiny, this apparent contradiction too can only be resolved by the modern quantum mechanical theory of quasiparticles wherein the collective quantized motion of multiple particles can, in a real physical sense, be considered to be a particle in its own right (albeit not an elementary one).

Unrelatedly, inhomogeneity in the conductive sample can result in a spurious sign of the Hall effect, even in ideal van der Pauw configuration of electrodes. For example, a Hall effect consistent with positive carriers was observed in evidently n-type semiconductors. Another source of artefact, in uniform materials, occurs when the sample's aspect ratio is not long enough: the full Hall voltage only develops far away from the current-introducing contacts, since at the contacts the transverse voltage is shorted out to zero.

Hall effect in semiconductors
When a current-carrying semiconductor is kept in a magnetic field, the charge carriers of the semiconductor experience a force in a direction perpendicular to both the magnetic field and the current. At equilibrium, a voltage appears at the semiconductor edges.

The simple formula for the Hall coefficient given above is usually a good explanation when conduction is dominated by a single charge carrier. However, in semiconductors and many metals the theory is more complex, because in these materials conduction can involve significant, simultaneous contributions from both electrons and holes, which may be present in different concentrations and have different mobilities. For moderate magnetic fields the Hall coefficient is

$$R_\mathrm{H}=\frac{p\mu_\mathrm{h}^2 - n\mu_\mathrm{e}^2}{e(p\mu_\mathrm{h} + n\mu_\mathrm{e})^2}$$ or equivalently $$R_\mathrm{H}=\frac{p-nb^2}{e(p+nb)^2}$$ with $$b=\frac{\mu_\mathrm{e}}{\mu_\mathrm{h}}.$$ Here $−e$ is the electron concentration, $V_{H}$ the hole concentration, $E_{y}$ the electron mobility, $R_{H}$ the hole mobility and $n$ the elementary charge.

For large applied fields the simpler expression analogous to that for a single carrier type holds.

Relationship with star formation
Although it is well known that magnetic fields play an important role in star formation, research models  indicate that Hall diffusion critically influences the dynamics of gravitational collapse that forms protostars.

Quantum Hall effect
For a two-dimensional electron system which can be produced in a MOSFET, in the presence of large magnetic field strength and low temperature, one can observe the quantum Hall effect, in which the Hall conductance $σ$ undergoes quantum Hall transitions to take on the quantized values.

Spin Hall effect
The spin Hall effect consists in the spin accumulation on the lateral boundaries of a current-carrying sample. No magnetic field is needed. It was predicted by Mikhail Dyakonov and V. I. Perel in 1971 and observed experimentally more than 30 years later, both in semiconductors and in metals, at cryogenic as well as at room temperatures.

The quantity describing the strength of the Spin Hall effect is known as Spin Hall angle, and it is defined as:

$$\theta_{SH}=\frac{2e}{\hbar}\frac{|j_s|}{|j_e|}$$

Where $$j_s$$ is the spin current generated by the applied current density $$j_e$$.

Quantum spin Hall effect
For mercury telluride two dimensional quantum wells with strong spin-orbit coupling, in zero magnetic field, at low temperature, the quantum spin Hall effect has been observed in 2007.

Anomalous Hall effect
In ferromagnetic materials (and paramagnetic materials in a magnetic field), the Hall resistivity includes an additional contribution, known as the anomalous Hall effect (or the extraordinary Hall effect), which depends directly on the magnetization of the material, and is often much larger than the ordinary Hall effect. (Note that this effect is not due to the contribution of the magnetization to the total magnetic field.) For example, in nickel, the anomalous Hall coefficient is about 100 times larger than the ordinary Hall coefficient near the Curie temperature, but the two are similar at very low temperatures. Although a well-recognized phenomenon, there is still debate about its origins in the various materials. The anomalous Hall effect can be either an extrinsic (disorder-related) effect due to spin-dependent scattering of the charge carriers, or an intrinsic effect which can be described in terms of the Berry phase effect in the crystal momentum space ($p$-space).

Hall effect in ionized gases
The Hall effect in an ionized gas (plasma) is significantly different from the Hall effect in solids (where the Hall parameter is always much less than unity). In a plasma, the Hall parameter can take any value. The Hall parameter, $μ_{e}$, in a plasma is the ratio between the electron gyrofrequency, $μ_{h}$, and the electron-heavy particle collision frequency, $ν$: $$\beta=\frac {\Omega_\mathrm{e}}{\nu}=\frac {eB}{m_\mathrm{e}\nu}$$ where
 * $e$ is the elementary charge (approximately $0 C$)
 * $k$ is the magnetic field (in teslas)
 * $β$ is the electron mass (approximately $0 kg$).

The Hall parameter value increases with the magnetic field strength.

Physically, the trajectories of electrons are curved by the Lorentz force. Nevertheless, when the Hall parameter is low, their motion between two encounters with heavy particles (neutral or ion) is almost linear. But if the Hall parameter is high, the electron movements are highly curved. The current density vector, $Ω_{e}$, is no longer collinear with the electric field vector, $e$. The two vectors $B$ and $m_{e}$ make the Hall angle, $θ$, which also gives the Hall parameter: $$\beta = \tan(\theta).$$

Other Hall effects
The Hall Effects family has expanded to encompass other quasi-particles in semiconductor nanostructures. Specifically, a set of Hall Effects has emerged based on excitons and exciton-polaritons n 2D materials and quantum wells.

Applications
Hall sensors amplify and use the Hall effect for a variety of sensing applications.

Corbino effect

The Corbino effect, named after its discoverer Orso Mario Corbino, is a phenomenon involving the Hall effect, but a disc-shaped metal sample is used in place of a rectangular one. Because of its shape the Corbino disc allows the observation of Hall effect–based magnetoresistance without the associated Hall voltage.

A radial current through a circular disc, subjected to a magnetic field perpendicular to the plane of the disc, produces a "circular" current through the disc.

The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect.

title: Hall effect