juno-labs/simple_wikipedia huggingface dataset:
Nuclear reaction

A **nuclear reaction** is a process involving an atomic nucleus or more than one nucleus. The most common kinds are
1. Nuclear fusion, a reaction in which two or more particles collide. The results are new particles which are different from the first ones.
1. Nuclear fission, a nucleus breaking into pieces.
1. Radioactive decay, in which a nucleus spits something out, changing itself into a different kind of nucleus.

In the case of radioactivity the reaction is spontaneous. Fission and fusion can be done on purpose, to release energy. This energy can then be used for different things, for example to make steam (as in a nuclear power plant). It can also be used as energy for a bomb.

In the example figure <sup>6</sup>Li fuses with deuterium. This makes Beryllium which then decays into two alpha particles.

Nuclear reactions occur in the sun, in nuclear reactors, in particle accelerators, and in outer space.  Other than radioactive decay, very few nuclear reactions occur on earth except in these special places.  Nuclear reactors use nuclear reactions to make heat and electricity.  Accelerators sometimes cause nuclear reactions to make radioactive materials.  Particles from outer space cause nuclear reactions in earth's atmosphere that make air slightly radioactive.

Nuclear reactions differ from chemical reactions in that they do not need a catalyst.  Radioactive decay also cannot be stopped, sped up or slowed down.

## Related pages

- Chemical reaction

## Other websites

- Images for nuclear reaction
- Videos for nuclear reaction
St Paul's Cathedral

**St Paul's Cathedral** is an Anglican church in the City of London. The original version was built by Mellitus in 604 AD. He was Bishop of the East Saxons.

In 962 and 1087, the cathedral burnt down and was built again. Before today's version of the cathedral, there were four others. The earlier ones burnt down.

Today's cathedral is made of limestone. It was built after the Great Fire of London in 1666 had destroyed the "Old St Paul's". Its architect was Sir Christopher Wren, who designed a further 50 churches. Wren designed it in the Renaissance style. St Paul's is a popular tourist attraction and is still used as a church today. It is the cathedral of the Church of England Diocese of London.
It is 365 feet (111 meters) high to the cross on top.
Greenhouse

A **greenhouse** (also called a glass-house or hothouse) is a building where plants such as flowers and vegetables are grown. It usually has a glass or translucent plastic roof. Many greenhouses also have glass or plastic walls. Greenhouses warm up during the day via penetration of the sun's rays which heat the plants, soil and structure. This heat is given up gradually throughout the night.

## Types of greenhouses

Greenhouses come in many shapes and sizes, with different functions. Some people have small greenhouses in their backyard, or as a lean-to attached to their home, called mini greenhouses, or tomato houses. They want to start off their seeds and seedlings in a protected environment as well as those growing plants that need warmer conditions. Others, wishing to extend their living space, have house extensions in the form of mini-conservatories. Commercial companies usually have larger greenhouses for horticultural purposes, but have more substantial structures for plant displays where the public is admitted. For the same reason, botanic gardens usually have a high proportion of greenhouses with substantial structures.

## Role of greenhouses

Many vegetables and flowers are grown in greenhouses in late winter and early spring, when it is still too cold to grow plants outside. Then these plants move into the soil outside as the weather warms up. Greenhouses are used to grow crops in cold countries such as Canada. The largest group of greenhouses in the world is in Leamington, Ontario (in Canada), where about 200 acres (0.8 km²) of tomatoes are grown in glass greenhouses.

## Gardening in greenhouses

Gardening and growing plants in greenhouses is different from growing plants outside as no rain can get inside a greenhouse, so gardeners have to water plants. Also, greenhouses can get very hot from the sun's heat, so gardeners have to make sure that it does not get too hot for the plants. Greenhouses usually have vents that can be opened to let excess heat out. Some greenhouses have electric exhaust fans that automatically turn on if it gets too hot in the greenhouse. A greenhouse is the place for tender plants such as tomatoes, cucumbers, and aubergines.

## History

Roman gardeners grew cucumbers in frames covered with oiled cloth or with sheets of mica. In the 1500s, Italian gardeners built structures for the tropical plants that explorers brought back to Italy. Jules Charles built the first modern greenhouse in Holland. In the 1800s, large greenhouses were built in England. The greenhouse concept also appeared in the Netherlands and then England in the 17th century

## Further reading

- Woods, May (1988) _Glass houses: history of greenhouses, orangeries and conservatories_. Aurum Press, London, .
- Mini Greenhouse nhà kính mini
Apprenticeship

**Apprenticeship** is a system of training people who are learning how to do a job which needs special skill.  Someone who is learning in this way is called an "apprentice".  An apprentice will learn by working with someone who is already skilled at a job.  They are like a teacher and pupil.

## Development

The system of apprenticeship has been used for many hundreds of years.  In the late Middle Ages the craft guilds and town governments used to watch and control the system.  A master craftsman had the right to employ young people to work for them and pay them a small salary.  In return the apprentice would be learning the trade.  Most apprentices were males, but female apprentices are more common nowadays, especially in crafts such as embroidery, silk-weaving etc..

## Related pages

- Education

## Further reading

- _Modern Apprenticeships: the way to work_, The Report of the Modern Apprenticeship Advisory Committee, 2001 http://www.dfes.gov.uk/ma.consultation
- _Apprenticeship in the British "Training Market"_, Paul Ryan and Lorna Unwin, University of Cambridge and University of Leicester, 2001 http://ner.sagepub.com/cgi/content/abstract/178/1/99
- _Creating a ‘Modern Apprenticeship’: a critique of the UK’s multi-sector, social inclusion approach_ Alison Fuller and Lorna Unwin, 2003 (pdf)
- _Apprenticeship systems in England and Germany: decline and survival._ Thomas Deissinger in: _Towards a history of vocational education and training (VET) in Europe in a comparative perspective_, 2002 (pdf)

## Other websites

- The School of Applied Arts Apprentice program
- Facts about Germany: Apprenticeships, Federal Foreign Office
- Apprenticeships - a great idea (UK)
- _L'Apprenti_, in French
- Article on the history of apprenticeship in the U.S.  from EH.NET
- Academic Apprentices: Still an Ideal?, Barry Yeoman, _Duke Magazine_
Battle droid

In the _Star Wars_ fictional universe, **battle droids** are robots that are made for fighting. They are seen in the prequel trilogy of the _Star Wars_ movies. Battle droids are used by the Confederacy of Independent Systems to fight the Galactic Republic.Clones of the Republic could easily overcome these droids.The battle droids are controlled by a central droid control ship. If the control ship is destroyed, the droids shut off.

## Types of battle droids

|style="width:25%;"|<div style="text-align:center;">**<span style="color:#fff;">Name(s)</span>**</div>|width=""|<div style="text-align:center;">**<span style="color:#fff;">Appearance</span>**</div>|width=""|<div style="text-align:center;">**<span style="color:#fff;">Function</span>**</div>|
| --- | --- | --- | --- | --- | --- |
|**B-1 (Standard) battle droids**|tall, use blaster rifles, with added backpack|soldiers||||
|**Pilot droid**, **Engineer droid**|looks like standard battle droid, with blue shoulders and chest with no backpack|flies starships and drives vehicles||||
|**Security battle droid**|looks like standard battle droid, with maroon shoulders and chest with no backpack|move in groups to remove intruders and guard prisoners||||
|**Battle droid commander**|looks like standard battle droid, with yellow forehead and shoulders; circular symbol on chest with small backpack|gets orders from controlships and leaders and commands soldiers and security battle droids||||
|**Assault droid**|looks like standard battle droid, with Blue shoulders|uses missile launchers||||
|**Droid Sniper (also known as assassin droids)**|red shoulders|uses sniper rifles||||
|**B-2 Super battle droid (also known as Super Battle Droids)**|large chested, blue, shiny bodies|advanced soldiers, built-in wrist blasters and wrist rocket launcher||||
|**Geonosis battle droid**|same look as standard battle droid, with reddish body|soldiers for desert areas; used only during Battle of Geonosis||||
|**Droideka**|Cobra-like body on three legs with two arms; with blasters, metallic body; transforms|heavyily armed soldier with two cannons and deflector shield; rolls into wheel for fast travel||||
|**IG Lancer droid**|tall, black, pointed cylindrical head|cuts through heavy armor with lances and pilots Speeder bikes (Closely resembles IG-88 from The Empire Strikes Back and Star Wars Droids: The Lost Prince)||||

## Other websites

- Star Wars Databank |Battle droid
Western long-beaked echidna

The **western long-beaked echidna** (_Zaglossus bruijni_) is one of the echidnas which live in New Guinea. Fossils of this species have also been found in Australia. It is one of the four living echidnas, three of which are species of _Zaglossus_.

This echidna lives from 1300m to 4000m above sea level. It lives in alpine meadow and humid forests in the mountains. Unlike the short-beaked echidna which eats ants and termites, the long-beaked species eats earthworms. It is also larger that the short-beaked species. It can be told apart from the other _Zaglossus_ species by the number of claws on the front and back feet. It has three (rarely four) claws.

It is an endangered species. Its population has been reduced by habitat loss and hunting. The long-beaked Echidna is good to eat. Although hunting the species has been banned by the Indonesian and Papua New Guinea governments, traditional hunting is permitted.

In February 2006, an expedition led by Conservation International found a population of them in what they described as a "lost world" of wildlife in the Foja Mountains of Papua Province, Indonesia.

The echidnas and Platypus are monotremes, the only mammals to lay eggs.

## References

- Augee M and Gooden B. 1993. _Echidnas of Australia and New Guinea_. Australian National History Press
- Flannery T.F. and Groves C.P. 1998 A revision of the genus _Zaglossus_ (Monotremata, Tachyglossidae), with description of new species and subspecies. _Mammalia_, **62**(3): 367-396
Eastern long-beaked echidna

The **eastern long-beaked echidna** (_Zaglossus bartoni_), also known as **Barton's long-beaked echidna**, is one of three species from the genus _Zaglossus_. All of them occur in New Guinea. It is found mainly in Papua New Guinea between 2000 and 3000 meters above sea level.

It can be distinguished from other members of the genus by the number of claws on the fore and hind feet. It has five claws on its fore feet and four on its hind feet. The adult animal weights between 5 kg (11 lb) and 10 kg (22 lb). Its body length ranges from 60 to 100 cm (23.5-39 inches). It has no tail. It has dense black fur. The species is the largest monotreme and is slow moving. It rolls into a spiny ball for defense.

There are four recognised subspecies:
- _Z. bartoni bartoni_
- _Z. bartoni clunius_
- _Z. bartoni smeenki_
- _Z. bartoni diamondi_
The population of each subspecies is geographically isolated and they can be distinguished primarily by differences in body size.

## References

- Flannery, T.F. and Groves, C.P. 1998 A revision of the genus _Zaglossus_ (Monotremata, Tachyglossidae), with description of new species and subspecies. _Mammalia_, 62(3): 367-396
Long-beaked echidna

The **long-beaked echidnas** make up one of the two genera (Genus ***Zaglossus***) of echidna. Echidna is a spiny monotreme that lives in New Guinea. There are three living species, and two extinct ones.

Echidnas are one of only two types of living mammals that lay eggs.

### _Zaglossus attenboroughi_

- Habitat: regions of New Guinea at higher elevation than highland forests
- Era: the present
- Status: Endangered

Remarks: Species described from one sample only. May be endangered, or locally extinct. See Sir David's Long-beaked Echidna

### _Zaglossus bartoni_

- Habitat:on the central cordillera between the Paniai Lakes and the Nanneau Range, as well as the Huon Peninsula
- Era: the present
- Status: Endangered

Remarks: see Eastern Long-beaked Echidna

### _Zaglossus bruijni_

- Habitat: highland forests of New Guinea
- Era: the present
- Status: Endangered

Remarks: see Western Long-beaked Echidna

### _Zaglossus hacketti_

- Habitat: Western Australia
- Era: Upper Pleistocene

Remarks: This species is known only from a few bones. At a metre long, it was huge for an echidna and for monotremes in general.

### _Zaglossus robustus_

- Habitat: Tasmania
- Era: Pleistocene

Remarks: This species is known from a fossil skull about 65 cm long.

## References

- Flannery, T.F. and Groves, C.P. 1998 A revision of the genus _Zaglossus_ (Monotremata, Tachyglossidae), with description of new species and subspecies. _Mammalia_, 62(3): 367-396

## Other websites

- EDGE of Existence _(Zaglossus spp.)_  - Saving the World's most Evolutionarily Distinct and Globally Endangered (EDGE) species
- A pretty good summary, including references on animalinfo.org
Sir David's long-beaked echidna

**Sir David's long-beaked echidna** (_Zaglossus  attenboroughi_), also known as the **cyclops long-beaked echidna**, is one of three species of the genus _Zaglossus_. All of them are found in New Guinea. It is named after Sir David Attenborough. It lives in the Cyclops mountains in Papua province of Indonesia near the cities of Sentani, Jayapura.

The species was described from a single damaged animal, which was collected in the Dutch colonial era (c. 1961). It has not been collected since that time. The Cyclops mountain forest habitat has been disturbed recently. This has raised concern that _Z. attenboroughi_ populations may already be endangered or even locally extinct. However, many parts of the mountains are covered in thick jungle and have not been searched since 1961. It is possible that the animal still exists there or in nearby mountain ranges. In 2007 scientists found holes which they believe were made by the echidna poking its nose into the dirt while looking for earthworms.

It is the smallest member of the genus. It is closer in size to the short-beaked echidna than other members of the genus. It has five claws on its fore and hind feet. It has dense short fur.
Whittier, Alaska

**Whittier** is a small town in Alaska on the Kenai Peninsula. Whittier has 272 people always living in it. The Whittier Glacier near Whittier was named for the American poet John Greenleaf Whittier in the year 1915.

During World War II the United States Army built a port and railroad near the glacier and named the port Whittier. The two big buildings that are very easy to notice in Whittier were built after World War II. The Hodge Building (now called Begich Towers) was built for housing soldiers and the Buckner Building, finish being built in 1953, was called the "city under one roof". It was once the biggest building in Alaska. The Begich Building is now a condominium (or houst that has many rooms that people live in), and almost all of the people that live in Whittier's live here.

The town was badly damaged by tsunamis (or very big waves) started by the 1964 Good Friday Earthquake; thirteen people died because of the waves that were 13 m (43 ft) tall.

Whittier is a popular port for cruise ships, because people can go to Anchorage and the inside of Alaska by both car and train. Whittier is also popular with visitors and fishermen.

Whittier is the wettest city in Alaska and the United States. The city receives at least  of rain a year.

## Other websites

- City of Whittier
- Whittier Chamber of Commerce

## Infobox (settlement)

- **name**: Whittier, Alaska
- **settlement type**: City
- **image skyline**: File:Whittier, Alaska (2006).jpg
- **image caption**: Whittier in July 2006
- **pushpin map**: USA Alaska
- **pushpin map caption**: Location in Alaska
- **subdivision type**: Country
- **subdivision name**: United States
- **subdivision type1**: U.S. state, State
- **subdivision type2**: List of boroughs and census areas in Alaska, Census Area
- **subdivision name1**: Alaska
- **subdivision name2**: Chugach Census Area, Alaska, Chugach
- **established title**: Founded
- **established title2**: Municipal corporation, Incorporated
- **established date2**: July 15, 1969
- **government type**: Council–manager
- **area total km2**: 50.86
- **area total sq mi**: 19.64
- **area land km2**: 31.73
- **area land sq mi**: 12.25
- **area water km2**: 19.13
- **area water sq mi**: 7.39
- **elevation m**: 13
- **elevation ft**: 43
- **population total**: 272
- **population as of**: 2020 United States census, 2020
- **population density km2**: 8.57
- **population density sq mi**: 22.20
- **postal code type**: ZIP Code
- **postal code**: 99693
- **area code**: Area code 907, 907
- **area code type**: North American Numbering Plan, Area code
- **timezone**: Alaska Time Zone, Alaska (AKST)
- **utc offset**: −09:00
- **timezone dst**: AKDT
- **utc offset dst**: −08:00
- **blank name**: Federal Information Processing Standard, FIPS code
- **blank info**: 02-84510
- **blank1 name**: Geographic Names Information System, GNIS feature ID
- **unit pref**: Imperial
Kate Winslet

**Kate Elizabeth Winslet**,  (born 5 October 1975) is an English actress. She is best known for her starring role in the American movie, _Titanic_.

She made her movie debut as Juliet Hulme in Peter Jackson's _Heavenly Creatures_ (1994). Winslet is the second of four children, her sisters are the actresses Anna and Beth Winslet and her brother is Joss Winslet, her mother Sally Anne is a barmaid and her father Roger John Winslet is a swimming pool contractor. Her maternal grandparents Linda and Oliver Bridges founded the Reading Repertory Theatre and her uncle is the actor Robert Bridges, Her maternal great-grandmother Florence Theodelinda Lidman, was the daughter of a Swedish immigrant.

Kate Winslet was married to director Jim Threapleton; they had a daughter, Mia. She married director Sam Mendes; they had a son, Joe. In 2012, she married Ned Rocknroll, nephew of billionaire Richard Branson. She had his first son in December 2013.

## Films

- _Heavenly Creatures_ (1994) _Juliet Hulme_
- _A Kid in King Arthur's Court_ (1995) _Princess Sarah_
- _Sense and Sensibility_ (1995) _Marianne Dashwood_
- _Jude_ (1996) _Sue Bridehead_
- _Hamlet_ (1996) _Ophelia_
- _Titanic_ (1997) _Rose DeWitt Bukater_
- _Hideous Kinky_ (1998) _Julie_
- _Faeries_ (1999) _Brigid_
- _Holy Smoke!_ (1999) _Ruth Barron_
- _Quills_ (2000) _Madeleine LeClerc_
- _Enigma_ (2001) _Hester Wallace_
- _Christmas Carol: The Movie_ (2001) Belle
- _Iris_ (2001) _Young Iris Murdoch_
- _The Life of David Gale_ (2003) _Bitsey Bloom_
- _Eternal Sunshine of the Spotless Mind_ (2004) _Clementine Kruczynski_
- _Finding Neverland_ (2004) _Sylvia Llewelyn Davies_
- _Romance & Cigarettes_ (2005) _Tula_
- _All the King's Men_ (2006) _Anne Station_
- _Little Children_ (2006) _Sarah Pierce_
- _Flushed Away_ (2006) _Rita Malone_
- _The Holiday_ (2006) _Iris Simpkins_
- _The Reader_ (2008) Hanna Schmitz
- _Revolutionary Road_ (2008) April Wheeler
- _Carnage_ (2011) Nancy Cowan
- _Contagion_ (2011) Dr. Erin Mears
- _Movie 43 _(2013) Beth
- _Labor Day_ (2013) Adele Wheeler
- _A Little Chaos_ (2014) Sabine De Barra
- _Divergent_ (2014) Jeanine Matthews
- The Dressmaker (2014) Myrtle 'Tilly' Dunnage

## Infobox (person)

- **name**: Kate Winslet
- **image**: Kate Winslet at the 2017 Toronto International Film Festival (cropped).jpg
- **caption**: Winslet at the 2017 Toronto International Film Festival
- **alt**: A close-up shot of Kate Winslet's face in 2017
- **birth name**: Kate Elizabeth Winslet
- **birth place**: Reading, Berkshire, England
- **nationality**: English national identity, English
- **alma mater**: Redroofs Theatre School
- **occupation**: Actress
- **years active**: 1991present
- **children**: 3
Joe DiMaggio

**Joseph Paul DiMaggio** (November 25, 1914 - March 8, 1999) was an American Major League Baseball center fielder who played his whole career for the New York Yankees.  His nicknames were **Joltin' Joe** and **The Yankee Clipper**.  He played from 1936 to 1942 and then joined the army in 1943 because of World War II. He came back and began playing again in 1946 until his retirement in 1951 at the age of 36. By the time he retired he had hit 361 home runs.  He hit almost one home run for every strikeout.  DiMaggio died on the 8th of March, 1999, of lung cancer. He is widely regarded as one of the best baseball players of all time.  DiMaggio was also well known for his marriage and lifelong devotion to Marilyn Monroe.
Parthia

|Languages||
| --- | --- |
|colspan="2" style="font-size: x-small; text-align: center; font-style: italic;"|Parthian Empire at its greatest extent, c. 60 BCE.|
|Parthian language||
|Zoroastrianism||
|Ctesiphon, Hecatompylus||
|Middle East||
|238 BCE–228 CE||
**Parthia** was an ancient Parthian empire in Asia that included what are now Iran, part of Armenia, Iraq, Georgia, eastern Turkey, eastern Syria, Azerbaijan, Turkmenistan, Afghanistan, Tajikistan, Pakistan, Kuwait, the Persian Gulf coast of Saudi Arabia, Bahrain, Qatar and the United Arab Emirates.

The Parthians were excellent horsemen and archers. In battle, mounted Parthians often discharged their arrows back towards the enemy and pretended to flee.

In 250 BC, the Parthians succeeded in founding an independent kingdom, which in the 1st century BC grew into an empire extending from the Euphrates to the Indus and from the Amu Darya to the Indian Ocean. They expanded by successfully expelling the Seleucids from Persia and establishing the second great Persian Empire.

- See Crassus for an account of the Parthians' defeat of a Roman army.

## Other websites

- Parthia.com - with an extensive bibliography

- History of Parthia
- The Establishment and Development of Christianity in the Parthian Empire in Transoxiana 6.
- Parthia (Old Persian Parthava)
238 BC

## Events

- In the Battle of Utica, the loyal Carthaginian troops of Hamilcar Barca defeat rebels.
- Tiberius Sempronius Gracchus attacks Carthaginian rebels on the island of Sardinia, and he makes it into a Roman province.
- The Parthian kingdom breaks away to become independent of the Seleucid Empire.
Hydrolysis

**Hydrolysis** is a chemical reaction or process where a chemical compound reacts with water. This is the type of reaction that is used to break down polymers into many smaller units. In this reaction, water is always added to the chemical compound.

## Hydrolysis of metal salts

Hydrolysis of metal salts is more commonly known as hydration.  Many metal ions are strong Lewis acids, and in water they may undergo hydrolysis to form _basic salts_.  Such salts contain a hydroxyl group that is directly bound to the metal ion in place of a water ligand. The positive charge on metal ions creates an attraction to water, a Lewis base with a non-binding electron pair on the oxygen atom, and alters the water molecule's electron density. This in turn increases the polarity of the O-H bond, which now acts as a proton donor under Brønsted-Lowry acid-base theory to release the hydrogen as a H+ ion, increasing the acidity of the solution. For example, aluminium chloride undergoes extensive hydrolysis in water with the solution being very acidic.
- <chem title="Hydrolysis of a hydrated Al3+ ion">[Al(H2O)6]^3+ + H2O <=> [Al(OH)(H2O)5]^2+ + H3O+</chem>

This implies that hydrogen chloride is lost in the evaporation of AlCl<sub>3</sub> solutions and the residue is a basic salt (in this case an _oxychloride_) in place of AlCl<sub>3</sub>. This type of reaction is also seen with other metal chlorides such as ZnCl<sub>2</sub>, SnCl<sub>2</sub>, FeCl<sub>3</sub> and lanthanide halides such as DyCl<sub>3</sub>. With some compounds such as TiCl<sub>4</sub>, the hydrolysis may go to completion and form the pure hydroxide or oxide, in this case TiO<sub>2</sub>.
Lymphatic system

The **lymphatic system** is a network of thin vessels that branch, like blood vessels, into tissues throughout the body, in mammals. It is part of the immune system. It is a one-way system which carries cells and fluid back to the blood system.

Lymphatic vessels carry lymph, a colorless, watery fluid, and white blood cells. It comes from interstitial fluid in the tissues which is squeezed out of the blood vessels. The lymphatic system transports infection-fighting cells called lymphocytes, and is involved in the removal of foreign matter and cell debris by phagocytes. A second function is to transport fats from the small intestine to the blood.

Lymphatic fluid gathers from the tissues and enters the valved lymphatic ducts. These valves make sure the lymph flows the right way. On its way back to the blood system, the lymph passes through glands called lymph nodes, in places like the back of the neck, the armpits and the groin. Lymph nodes swell in the region of an infected body part. This acts to keep the infection from spreading. It prevents or reduces the pathogens getting into the general blood circulation and reaching other parts of the body.

Lymph ends up back in the blood system. In mammals under normal conditions, most of the lymph is returned to the blood stream via veins through lymph-vein communications at the base of the neck. Some vertebrates have more complex lymphatic systems. Amphibian<nowiki/>s for example have multiple "lymph hearts" to control the flow of lymph.
Chastity

**Chastity** is the sexual behavior of a man or woman which is right and proper according to the moral rules of a culture or religion. It has recently begun to mean sexual abstinence (not having sex at all), especially before marriage. However, it can also be used for all kinds of people (even married people) with more meaning than simply not having sex. The word chastity came from the Latin word _castitatem_, meaning "purity".

## Related pages

- Virginity
- Sexual abstinence
Metallic bond

A **metallic bond** is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding.
Metals have low ionization energy.  Therefore, the valence electrons can be delocalized throughout the metals. Delocalized electrons are not associated with a particular nucleus of metal, instead, they are free to move throughout the whole crystalline structure forming a "sea" of electrons.

The electrons and the positive ions in the metal have a strong attractive force between them.  Therefore, metals often have high melting or boiling points. The principle is similar to that of ionic bonds.

Metallic bonds causes many of the traits of metals, such as strength, malleability, ductility, luster, conduction of heat and electricity.

Because the electrons move freely, the metal has some electrical conductivity. It allows the energy to pass quickly through the electrons, generating an electric current. Metals conduct heat for the same reason: the free electrons can transfer the energy at a faster rate than other substances with electrons that are fixed into position. There also are few non-metals that conduct electricity: graphite (because, like metals, it has free electrons), and ionic compounds that are molten or dissolved in water, which have free moving ions.

Metal atoms have at least one valence electron which they do not share with neighboring atoms, and they do not lose electrons to form ions. Instead, the outer energy levels (atomic orbitals) of the metal atoms overlap. They are similar to covalent bonds. Not all metals exhibit metallic bonding. For example, mercury ions () form covalent metal-metal bonds.

An alloy is a solution of metals. Most alloys are shiny like pure metals are.

## Related pages

- Chemical bond
- Covalent bond
- Ionic bond
- Coordination complex
- Alloy
Heat conduction

**Heat conduction** (or **thermal conduction**) is the movement of heat from one object to another one that has different temperature when they are touching each other.  For example, we can warm our hands by touching hot-water bottles. When the cold hands touch the hot-water bottle, heat flows from the hotter object (hot-water bottle) to the colder one (hand). People make things with different thermal conductivity, for example cookware to heat things or insulated containers to keep hot things hot or cold things cold.

Other ways to transfer heat are by thermal radiation and/or convection. Usually more than one of these processes happen at the same time.

## Microscopic explanation

In the atomic theory solids, liquids and gases are made of tiny particles called "atoms". The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.

Conduction can happen when one part of a material is heated. The atoms in this part vibrate faster and are more likely to hit  their neighbors. The collisions cause those atoms also to move faster, passing the heat energy to them. In this way the energy travels through the solid. (Rather like the way energy passes along a set of tumbling domino<nowiki/>s).

The atomic picture also helps explain why conduction is more important in solids: in solids the atoms are close together and unable to move around. In liquids and gases the particles can move past each other, so the collisions are less common.

## Law of heat conduction

The **law of heat conduction**, also known as **Fourier's law**, means that the rate, in time, of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing:

where:
- _Q_ is the amount of heat transferred, and
- _t_ is the time taken, and
- _k_ is the material's thermal conductivity' and
- _S_ is the area through which the heat is flowing, and
- _T_ is the temperature.

Thermal conductivity usually varies with temperature, but the variation can be small, over a significant range of temperatures, for some common materials.

## Related pages

- Heat transfer
- Convection
- Thermal radiation
Judith Weir

**Judith Weir CBE** (born 11 May 1954) is a British composer. She is well known for her theatre works, choral music, orchestral music and chamber music.

## Early life

Weir was born in Cambridge, England to Scottish parents. While she was still at school she trained with the composer John Tavener. She played the oboe in the National Youth Orchestra of Great Britain. She then studied at the University of Cambridge where her teacher was Robin Holloway.

## Career

Judith Weir’s music has harmonies which are very exciting and original. Her Christmas carol _Illuminare_ has become very popular, but it is quite difficult and needs a good choir to pitch the notes of the dissonant chords. She often uses medieval history as inspiration for her music, as well as music from her native Scotland, e.g. piobaireachd, which is a kind of variation form using small intervals. Her music often tells stories. Her operas include _A Night at the Chinese Opera_, _The Vanishing Bridegroom_, _Blond Eckbert_, and _Armida_, an opera for television.

From 1995 to 2000, she was the artistic director of the Spitalfields Festival in London. She has composed works for the City of Birmingham Symphony Orchestra. She has received many honours, including the CBE in 1995.

## Other websites

- Judith Weir's homepage at Chester Music (music publishers)
- Judith Weir (b 1954) (BBC)
Chorus

**Chorus** can mean several things:

- Greek chorus, a feature of ancient Greek theatre
- Choir, a group of singers
- Refrain, the part of a song that is repeated
    - Bridge (music), The verse before the refrain
Vassal

A **vassal** during the feudalism of medieval Europe, was someone who had shared duties  with a lord. Usually the vassal provided soldiers to the lord. The lord used his army of soldiers from all of his vassals to protect those vassals. The lord also gave him the piece of land that he held as a fief. By analogy the term _vassal_ is used also for similar systems in other feudal societies.

## Western vassalage

The development of the _vassal_, in a society that was increasingly organised around the concept of "lordship"– in French the _seigneur_– is one sign that Antiquity ended and the Early Middle Ages began. Lordship is the basic social institution as Tacitus described them in his book _Germania_. The Roman West experienced them for the first time in the Migration Period.

As the system developed in the seventh century, the vassals were gangs of freemen who subjected themselves, in some degree of formality, to the authority of a leader, from whom they could expect to be fed, clothed and armed. The quality of a vassal was only in his fighting ability and the strength of his loyalty. The etymology (where the word came from) of "vassal" is from a Celtic word _gwas_ "boy" that meant a young male slave, with a Latinised form, _vassus_ that appeared in Salic Law (Rouche 1987 p 429), like the way  "knight" came from the from  Old English word _cniht_ and similar words in Frisian and Dutch, all meaning "lad" http://www.etymonline.com/index.php?l=k&p=3.

## Related pages

- Gokenin, vassals of the shogunate in Japan

## References

- Cantor, Norman, _The Civilization of the Middle Ages_ 1993
- Ganshof, François Louis, _Feudalism_ translated 1964
- Rouche, Michel, "Private life conquers state and society," in _A History of Private Life_ vol I, Paul Veyne, editor, Harvard University Press 1987
Migration period

The **migration period**, or **barbarian invasions** or **Völkerwanderung** happened in 300–700 AD in Europe, at the end of ancient history and during the Early Middle Ages.

The migrations included the Goths, Vandals, Franks, and other Germanic tribes; the Bulgars; and Slavic tribes. They may have been influenced by attacks of the Huns in the East and may also be connected to the Turkic migrations in Central Asia, overpopulation, or climate change. The migration period also included groups of Angles, Saxons, Frisians, and some Jutes to Britain.

The migrations would continue well into the Middle Ages, beyond 1000 AD, with successive waves of Slavs, Roma, Avars, Bulgars, Hungarians, Pechenegs, Cumans, and Tatars, which changed the ethnic makeup of Eastern Europe. Historians in Western Europe, however, tend to stress the migrations that were most relevant to that area.

## Related pages

- Human migration

## Other websites

- J.B. Bury (1923). _History of the Later Roman Empire_
San Francisco Bay

**San Francisco Bay** is a shallow bay in northern California, along the Pacific Ocean. It is an estuary because salt water from the ocean mixes with fresh water from rivers, especially the Sacramento and San Joaquin rivers. These rivers carry water from the Sierra Nevada mountains through the Central Valley. Water from about forty percent of California enters the bay.

The Sacramento and San Joaquin rivers enter the Suisun Bay. There water flows through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay. This connects at its south end to the San Francisco Bay. The San Francisco Bay is connected to the Pacific by a strait called the Golden Gate. However, this entire group of interconnected bays is often called "the San Francisco Bay".

San Francisco Bay lies in the US state of California and is surrounded by a region known as the San Francisco Bay Area, that includes the big cities of San Francisco, Oakland, and San Jose.

The Bay covers somewhere between 400 http://www.sfmuseum.org/hist9/mcgloin.html and 1,600 http://response.restoration.noaa.gov/cpr/watershed/sanfrancisco/sfb_html/sfbenv.html square miles (1,040 to 4,160 square kilometres), depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement.

## References

- 1999 Grolier Multimedia Encyclopedia.
- 1988 Encyclopædia Britannica.

## Other websites

- _San Francisco Bay: Portrait of an Estuary_, David Sanger and John Hart, University of California Press
- Barging In - A Short History of Liveaboards on the Bay
- Army Corps of Engineers Bay Model: Working scale model of the Bay
- BoatingSF.com: Photos of SF Bay and its boats, plus online cruising guide
- SF Estuary Institute: San Francisco Bay Historical View Maps
Ahmed Yassin

**Ahmed Yassin** (Arabic: الشيخُ أَحْمَدُ إِسْمَاعِيلُ)  (June 1936 – March 22, 2004) was a spiritual leader of the militant Palestinian group Hamas.

## Life

Ahmed Yassin was born on June 1936 in al-Jura, British Mandate of Palestine. He helped create Hamas and became its spiritual leader in 1987. To other members of Hamas he was a hero but he was blamed by the Israeli government for planning suicide bombings and other attacks against Israel. He claimed that was the only way of fighting occupation. He was confined to a wheelchair because he was paralyzed since age 12, he was also nearly blind and could barely hear. He was very powerful and influential.

Yassin's birth date is in dispute. He claimed he was born 1/1/1938, however, his passport indicated 1/1/1937. To some he was a hero, to some he was a well known member of a terrorist organization. He was also a symbolic figure for Palestinians to fight against Israel.

## Death

Yassin was killed in an airstrike in Gaza City by the Israeli Army after he left a mosque in Gaza in the early morning hours. He was 67 years old.

## Other websites

- Israel Bombing of Refugee Camp
- Yassin killed, Ahmed Yassin biography
- Yassin's letter and kids named after him

## Infobox (person)

- **honorific prefix**: Sheikh
- **name**: Ahmed Yassin
- **image**: Military trial of Ahmed Yassin, March 1990 I (colorized).jpg
- **caption**: Picture of Yassin on trial
- **native name**: الشيخُ أَحْمَدُ إِسْمَاعِيلُ
- **native name lang**: ar
- **birth date**: June 1936
- **birth place**: Al-Jura
- **death place**: Gaza City, Gaza Strip, State of Palestine, Palestine
- **death cause**: Killed by Israeli airstrike
- **nationality**: Palestinian
Field strength

In physics, the **field strength** of a field is the magnitude (size) of its (vector) value. This means that the force exerted by the field on a given object is proportional to the field strength.

In differential geometry, the field strength is another name for the curvature form.  For the electromagnetic field, the curvature form is an antisymmetric matrix whose elements are the electric field and magnetic field: the electromagnetic tensor.

In radio engineering, field strength is the strength of radio waves in a particular location.
Field (physics)

In physics, a **field** means that a physical quantity is assigned to every point in space (or, more generally, spacetime). A field is seen as extending throughout a large region of space so that it influences everything. The strength of a field usually varies over a region. Michael Faraday became the first to coin the term "field", in 1849.

For some fields, there is a number for each point in space. They are called _scalar fields_. For more complicated fields, there are more than one number for each point in space. They are called _vector fields_ or _tensor fields_. For example, one can model a gravitational field by a vector field where a vector indicates the acceleration a mass would experience at each point in space. Other examples are temperature fields or air pressure fields, which are often illustrated on weather reports by isotherms and isobars by joining up the points of equal temperature or pressure respectively.

### Classical fields

- Newtonian gravitation: describes the gravitational force as a mutual interaction between two masses.
- Electromagnetism:  electric and magnetic fields are not only fields of force which dictate the motion of particles, but also have an independent physical reality because they carry energy.
- Gravitation in general relativity: this is Einstein's theory of gravity.
- Waves as fields

### Quantum fields

It is now believed that quantum mechanics should underlie all physical phenomena.

### Field theory

A field theory is a physical theory that describes how one or more physical fields interact with matter.

## Related pages

- Elasticity
- Fluid dynamics
- General relativity
- Maxwell's equations
- Particle physics

## References

- Landau, Lev D. and Lifshitz, Evgeny M. 1971. _Classical theory of fields_. 3rd ed, London: Pergamon.  Vol. 2 of the _Course of Theoretical Physics_.
Gradient

In vector calculus, the **gradient** of a multivariate function measures how steep a curve is. On a graph of the function, it is the slope of the tangent of that curve. More generally, it is a vector that points in the direction in which the function grows the fastest. Its coordinates are partial derivatives of that function. The gradient of a function _f_ is often written as  or .

## Related pages

- Laplace operator
Gradient (disambiguation)

**Gradient** could mean:

- Gradient of a function, in vector calculus
- Slope or grade, referring to the inclination of a road or other geographic features
- Image gradient, a gradual change or blending of color

- In biology
    - Concentration gradient, the ratio of solute concentration between two regions next to each other
    - Electric gradient, the difference in electric charge between two regions next to each other
    - Pressure gradient, the difference in the exerted force per unit area in two regions next to each other
Archery

**Archery** is the practice of using a bow to shoot arrows. Archery has historically been used in hunting and combat and has become a precision sport. A person practicing archery is called an _archer_, and one who enjoys or is an expert at archery is sometimes called an toxophilite.

## History

The earliest evidence of archery dates back more than 9,000 years. The bow probably was used in hunting first and later adopted as a tool of warfare. It was one of the earliest forms of artillery.

Classical civilizations, notably the Persians, Macedonians, Nubians, Greeks, Parthians, Indians, Japanese, Chinese, and Koreans, had large numbers of archers in their armies. Archers in chariots were especially important in armies of ancient Egypt. Arrows were very destructive against massed formations, and the use of archers helped win battles.

One of the primary sub-genres of archery is mounted archery. Japanese Samurai, North American tribes, Turkish nomadic groups, Persian armies and more honed the skill of hunting and warfare through mounted archery. The army of the Mongol Empire was mostly archers on horseback.

Though archery fell out of practical use, it never fully went away as a sport. As early as the 1480s in Britain, societies like the Ancient Society of Kilwinning Archers were having archery competitions.

## Other websites

- Archery Interchange UK  The UK's largest online archery community.
- The Great Northwood Bowmen  Medieval Longbow Archery and re-enactment Society, re-enacting the 15th century, based in London.
- Bowhunting Basics
- Archery Information
- Archery Pictures
Signal transduction

A **signal transduction** in biology is a  cellular mechanism. It converts a stimulus into a response in the cell. There are two stages in this process:
1. A signalling molecule attaches to a receptor protein on the cell membrane.
1. A second messenger transmits the signal into the cell, and a change takes place in the cell.
So, signal transduction starts with a signal to a cell receptor, and ends with a change in cell function. In either step, the signal can be amplified. Thus, one signalling molecule can cause many responses.

Receptors are in the cell membrane, with part of the receptor outside and part inside the cell.  The  chemical signal binds to the outer portion of the receptor, changing its shape. This causes another signal inside the cell.  Some chemical messengers, such as testosterone, can pass through the cell membrane, and bind directly to receptors in the cytoplasm or nucleus.

Sometimes there is a cascade of signals within the cell. With each step of the cascade, the signal can be amplified, so a small signal can result in a large response. Eventually, the signal creates a change in the cell, either in the expression of the DNA in the nucleus or in the activity of enzymes in the cytoplasm.

Most often, ordered sequences of biochemical reactions inside the cell are involved. These are carried out by enzymes and linked through second messengers. So a "second messenger pathway" is produced. These things usually happen quickly, sometimes very quickly. They may last from milliseconds (in the case of ion flux) to days for gene expression.

The number of proteins and other molecules that take part increases during the process. So a 'signal cascade' develops and _a relatively small stimulus may cause a large response_.

In bacteria and other single-cell organisms, the transduction processes a cell has limits the number of ways it can respond to its environment. In multicellular organisms, lots of different signal transduction processes are used to coordinate the behavior of individual cells. By this means the function of the organism as a whole is organized. The more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess.

Thus, sensing of both the external and internal environment at the cellular level, relies on signal transduction. Many disease processes such as diabetes, heart disease, autoimmunity and cancer arise from defects in signal transduction pathways. This highlights the critical importance of signal transduction to biology and medicine.

These systems of communication between cells are extremely ancient, and are found in all metazoa.

## Related pages

- Transduction (physiology)
- Ligand
- Cytokine
    - Cytokine storm
- Neuroscience

## Other websites

- _Science_'s STKE - Signal transduction knowledge environment, from _Science_, published by AAAS.
- Cosma Shalizi's Signal transduction notebook