Polyphyly is a term in cladistics. It describes a group of organisms whose last common ancestor is not a member of the group. Another way of expressing this is to say that polyphyly includes groups some members of which are descended from ancestral populations.

The diagrams show that birds and mammals are indeed related, but only at the level of the early amniotes. In terms of evolution, there is a vast gulf between them.

More common in traditional taxonomy is to include all descendants (say, living mammals) without the group they evolved from (which would be some clade in the therapsida). This is done for convenience; but it makes the mammals polyphyletic.

Biological classification aims to group species together such that every group is descended from a single common ancestor. A polyphyletic group can be "fixed" either by excluding clades or by adding the common ancestor.

According to cladistics it should be the aim of classification to ensure that all groups are monophyletic. However, other taxonomists argue that there is a valid place for groups that are paraphyletic. These would contain their most recent common ancestor but not all the descendants of that ancestor.

Notes

Cladistics

Polyphyly


A plebiscite or referendum is a type of voting, or of proposing laws. Some definitions of 'plebiscite' suggest that it is a type of vote to change the constitution or government of a country. Others define it as the opposite. Australia defines 'referendum' as a vote to change the constitution and 'plebiscite' as a vote that does not affect the constitution.

There are two types of result
 Mandatory - meaning the government must do what the result says
 Advisory - meaning the result of the vote is only to help the government make the final choice.

It usually depends on the country's history and constitution what sort of referendum/plebiscite is used.  In Switzerland a referendum is usually mandatory, because the people are seen as the source of the government's mandate (power) to govern. For example, during Switzerland's basic income campaign the country utilized a national referendum for the polling.

In the United Kingdom referendums have only been advisory, because the government says that the people elected to Parliament make the decisions. The referendum on the independence of Scotland was an exception. It was legally binding, but it was not a referendum of the UK electorate. It was restricted to present residents of Scotland.

An example of a proposed plebiscite was the 2011 decision by Greek Prime Minister George Papandreou to let the Greek people vote on whether the heavily indebted nation would accept a €130 billion bailout package from the European Union. The idea shocked eurozone nations, as a "no" vote could mean Greece defaulting on its national debt, and leaving the European Union and the eurozone. However, the vote was cancelled.

Another example was the voting on the European Constitution in 2005. The vote took place in some countries. France and The Netherlands had a referendum on the subject. In both states, the voters said no to the proposal and no constitution was made.

The separate simultaneous referendums held on 24 April 2004 in the Turkish Republic of Northern Cyprus and the Republic of Cyprus on the comprehensive settlement plan of the UN Secretary-General provides yet another example of such a vote. The Plan was approved in the Turkish Cypriot referendum by 65%, while it was rejected in the Greek Cypriot referendum by 75%.

Problems with referendums
Many political problems can be solved by asking the people their opinion because the supporters of the argument will be forced to accept the decision of the people. However:

 It is feared that the electorate do not have sufficient political knowledge to truly understand what they are voting for

 Philosophers Plato and Madison thought voters are too easily persuaded by their own internal feelings of a matter instead of focusing on the good of the nation. That is to say they vote selfishly.

References

Voting

Plebiscite


A game is something that people often do for fun. It is different from work. Many sports are games, and there are many professional sports. In those cases, there is money to be made, because it is a type of entertainment.

There are different kinds of games using many kinds of equipment. For example, in video games, people often use controllers or their keyboard to control what happens on a screen, such as a television screens and computers ones too.  In card games, players use playing cards.  There are also games that use your body, such as the Kinect. Most games need equipment, but not always. Children's street games often need no equipment.

In board games, players may move pieces on a flat surface called a board. The object of the game varies. In race-type games like ludo, the object is to reach the end first. In go the object is to surround more space. In soccer it is to score more goals. Some games have complicated rules, some have simple rules.

Definitions

Ludwig Wittgenstein
Ludwig Wittgenstein was probably the first academic philosopher to address the definition of the word game. In his Philosophical Investigations, Wittgenstein demonstrated that the elements (parts) of games, such as play, rules, and competition, all fail to correctly define what games are. He concluded that people apply the term game to a range of different human activities that are related, but not closely related.

Homo Ludens
Homo Ludens (Playing Man) is a book written in 1938 by Dutch historian Johan Huizinga. It discusses the importance of the play element in culture and society. Huizinga suggests that play is a  condition for the generation of culture.

Roger Caillois
French sociologist Roger Caillois, in his book Les jeux et les hommes (Games and Men), said that a game is an activity which is these things:

 free: the activity is voluntary
 separate: the activity cannot happen everywhere or, all the time
uncertain: the people doing the activity do not know how it will end
non-productive: doing the activity does not make or do anything useful
governed by rules: the activity has rules that are different from everyday life
fictitious: the people doing the activity know that the game is not reality

Chris Crawford
Computer game designer Chris Crawford tried to define the word game using a series of comparisons:
Something creative is art if it was made because it is beautiful, and entertainment if it was made for money.
Something that is entertainment is a plaything if it is interactive. Movies and books are entertainment, but not interactive.
If a plaything does not have any goals to complete, it is a 'toy. If a plaything has goals, it is a challenge.
If a challenge does not have an opponent, it is a puzzle. If it has an opponent, it is a conflict.
If the player can do better at something than an opponent but cannot affect the opponent, the conflict is a competition. Racing and figure skating are competitions. However, if attacks are allowed, then the conflict qualifies as a game.

Crawford's definition of a game is: an interactive, goal-oriented activity, with opponents to play against, and where players and opponents can interfere with each other.

 History of Games
The first writer of history was Herodotus, an ancient Greek. He wrote a book called "The Histories" around 440 BC, which is nearly 2500 years ago. Some of the stories he wrote were not true, and we don't know if this is one of those.

Herodotus tells us about king Atys; he ruled about 5,500 [five thousand five hundred] years ago in a country called Lydia. His country was in western Asia Minor, near modern Greece. Atys had a serious problem; his lands had very little food because the climate was not good for agriculture. The people of Lydia demonstrated patience and hoped that the good times of plenty would return.

But when things failed to get better, the people of Lydia thought up a strange solution for their problem. The path they took to fight their natural need to eat – the hungry times caused by the unusually hard climate - was to play games for one entire day so that they would not think about food. On the next day they would eat, so eating occurred every second day. In this way they passed 18 years, and in that time they invented dice, balls, and all the games commonly played today.

Games appear in all cultures all over the world, an ancient custom that brings people together for social opportunities. Games allow people to go beyond the limit of the immediate physical experience, to use their imagination. Common features of games include a finish that you cannot forecast, agreed upon rules, competition, separate place and time, imaginary elements, elements of chance, established goals and personal enjoyment. Games are used to teach, to build friendships, and to indicate status.

In his 1938 history book the Dutch writer Johan Huizinga says that games are older than human culture. He sees games as the beginning of complex human activities such as language, law, war, philosophy and art. Ancient people used bones to make the first games. Dice are very early game pieces. Games began as part of ancient religions. The oldest gaming pieces ever found – 49 [forty nine] small painted stones with pictures cut into them from 5,000 [five thousand] years ago – come from Turkey, so perhaps the history of Herodotus is true. One of the first board games, Senet, appears in ancient Egypt around 3,500 [three thousand five hundred] years ago. The ancient Greeks had a board game similar to checkers, and also many ball games.

The first reference to the game of Go occurs in Chinese records from around 2,400 [two thousand four hundred] years ago. Originally the game Go was used by political leaders to develop skill in strategy and mental skill. Knowing how to play Go was required by a Chinese gentleman, along with the skills of artistic writing or calligraphy, painting and the ability to play a musical instrument. These were regarded as the four most important skills. In ancient China, a gentleman had to pass a test in these four key skills in order to get a good paying job in the government. The Chinese brought Go to Korea, and it entered Japan around 1,500 [one thousand five hundred] years ago, and it has been popular ever since.

In March 2016 a Google computer program beat the best Go players in the world. Go is believed to be the most complex board game ever created. Is this computer program smarter than a person? Well, it did beat the South Korean Go master Lee Se-dol, and Lee was surprised by the result.  He acknowledged defeat after three and a half hours of play. Demis Hassabis, who made the Google program, called it an important moment in history, because a machine beat the best person in the world in an intelligent game.  Such computer programs rely on what is called artificial intelligence. Go is a two-player game of strategy said to have had an origin in China perhaps around 3,000 [three thousand] years ago. Players compete to win more territory by placing black and white "stones" on a board made up of 19 [nineteen] lines by 19 [nineteen] lines.

The first computer game that was ever created was probably the game OXO by Alexander Douglas in 1952.  It was a version of tic-tac-toe. But most people consider the first true computer game where players actually participate to be Tennis for Two developed in 1958 by the physics scientist William Higginbotham. He wanted to teach about gravity, the force of attraction between masses. These men who created the early computer games did not forecast the potential for the popular use of games, because at that period in modern history it took a small room full of computers to make these games work! Another early game was Spacewar! developed in 1961 by MIT university student Steve Russell. In 1972 the company Atari produced the Pong game which was a huge commercial success; being a commercial success means that it made a lot of money. This was the true beginning of computer games that could be played at home.

Today, all around the world people spend more than 3,000,000,000 [three billion] hours a week playing computer games. This is equivalent to more than 342,000 [three hundred and forty two hundred thousand] years!

 Other definitions
 "A game is a system in which players engage in an artificial conflict, defined by rules, that results in a quantifiable outcome".
 "A game is a form of art in which participants, termed players, make decisions in order to manage resources through game tokens in the pursuit of a goal". (Greg Costikyan)
 "A game is an activity among two or more independent decision-makers seeking to achieve their objectives in some limiting context''".
 "At its most elementary level then we can define game as an exercise of voluntary control systems in which there is an opposition between forces, confined by a procedure and rules in order to produce a disequilibrial outcome".
 "A game is a form of play with goals and structure".

Related pages
Video game
Puzzle
Sports
Toy

References

Game


A computer virus is a program that is able to copy itself when it is run. Often, computer viruses are run as a part of other programs. Any program that is affected by the virus is "infected". Biological viruses also work that way, as they copy themselves as part of other organisms. This is how the computer virus got its name.

In addition to copying itself, a computer virus can also execute instructions that cause harm. For this reason, computer viruses affect security. They are part of malware.

Very often, the term is also used for other kinds of malware, such as trojan horses and worms. Even though this is wrong, it may be difficult to tell the difference between different kinds of malware; they often occur together, and only an expert may be able to tell them apart. Such programs also fit more than one category.

Computer viruses are created for a cause, sometimes they are created to spread political messages and they are also created to hack some system files.

Computer viruses are spread through many ways. Some of the common ways of spreading are through downloads, email attachments, removable hardwares, and so on. Most viruses are very dangerous kind of malware.

Kinds of computer viruses
There are different kinds of computer viruses:
 Probably the most common form is the macro-virus or script virus. Such viruses are programmed with the script function which is present in many text processing systems and spreadsheets; or with general "script" functionality of a program.
 Boot sector viruses infect the boot sector of floppy disks, hard drives and other media.
 Executable files and scripts of the operating system; including those that are run automatically when a medium is inserted into a drive.
 Cross-site scripting; scripts in web pages that replicate to other webpages.
 Any computer file; generally buffer overflows, format strings, and race conditions are exploitable.

Limited user rights can limit the spread of a virus
In the beginning, operating systems on personal computers (or PC) did not have the concept of access control. There were no "users", everyone could do everything. Modern operating systems have the concept of access control. There can be more than one user and some users may have more "privileges" than others. Certain users may only have access to certain files and are unable to access others. Other users may be able to modify or delete certain files. These privileges can be specified for each file.

The damage a virus can cause is influenced by the rights the user has; if the user has no rights to write to certain places in the system, the virus will not be able to spread to those places.

Another problem is that sometimes the system for rights management may be available, but that it is not used by default. This is the case with systems such as Windows NT or Windows XP, where by default all users have same rights.

Antivirus software
Antivirus software can protect computers against known viruses. Some antivirus software scan files and compare a hash code for each file with its database of hash codes (or "signature"). If the code matches, it has likely found a virus. This way of doing things has created some problems. It will only protect against viruses whose hash code is known. The companies that wrote the antivirus need to keep the virus signatures up-to-date and need to give this information to the PC to be protected.

There are two possible modes of scanning: Either the file is scanned "on demand" (or "manually"), or it is scanned when the system registers an access to the file called "on access".

Antivirus software cannot offer full protection, even in the case the virus is known. Some viruses use something called polymorphic code to change their signature every time they move. No matter how many signatures the company has, they will not be able to stop these types of viruses.

Another way that antivirus software can protect against viruses is to use heuristics. Instead of knowing each virus by its signature, heuristic antivirus software look at the behavior of other software. If a software does something that seems bad, the antivirus software steps-in to stop it. Since every step needs to be watched, this is a slow way to do things.

"Live system"
The best protection against viruses can be obtained by using a system that boots off a read-only medium, such as a compact disc (called CD), digital versatile disc (called DVD), or USB flash drive (called USB) that does not allow write access to hard disk (or other removable media). This limits the usability of the computer as it is not possible to save documents or install new programs. Only -R media (not -RW) should be used, and the media should be finalized to prevent creating a new session that might possibly contain a virus.

References

Malware

Computer virus


In special relativity, the Minkowski spacetime is a four-dimensional manifold, created by Hermann Minkowski. It has four dimensions: three dimensions of space (x, y, z) and one dimension of time. Minkowski spacetime has a metric signature of (-+++), and describes a flat surface when no mass is present. The convention in this article is to call Minkowski spacetime simply spacetime.

However, Minkowski spacetime only applies in special relativity. General relativity used the notion of curved spacetime to describe the effects of gravity and accelerated motion.

Definition(s)

Mathematical
Spacetime can be thought of as a four-dimensional coordinate system in which the axes are given by

They can also be denoted by

Where  represents . The reason for measuring time in units of the speed of light times the time coordinate is so that the units for time are the same as the units for space. Spacetime has the differential for arc length given by

This implies that spacetime has a metric tensor given by

As before stated, spacetime is flat everywhere; to some extent, it can be thought of as a plane.

Simple
Spacetime can be thought of as the "arena" in which all of the events in the universe take place. All that one needs to specify a point in spacetime is a certain time and a typical spatial orientation. It is hard (virtually impossible) to visualize four dimensions, but some analogy can be made, using the method below.

Spacetime diagrams

Hermann Minkowski introduced a certain method for graphing coordinate systems in Minkowski spacetime. As seen to the right, different coordinate systems will disagree on an object's spatial orientation and/or position in time. As you can see from the diagram, there is only one spatial axis (the x-axis) and one time axis (the ct-axis). If need be, one can introduce an extra spatial dimension, (the y-axis); unfortunately, this is the limit to the number of dimensions: graphing in four dimensions is impossible. The rule for graphing in Minkowski spacetime goes as follows:

1) The angle between the x-axis and the x'-axis is given by  where v is the velocity of the object

2) The speed of light through spacetime always makes an angle of 45 degrees with either axis.

Spacetime in general relativity

In the general theory of relativity, Einstein used the equation

To allow for spacetime to actually curve; the resulting effects are those of gravity.

Related pages
Spacetime
Special relativity
General relativity

Relativity

Minkowski spacetime


A test tube is a kind of laboratory glassware, composed of a fingerlike length of glass tubing, open at the top, usually with a rounded lip at the top, and a rounded 'U' shaped bottom.

They range in size from a couple inches to several inches long, from a few millimeters to a couple centimeters in diameter. They are designed to allow easy heating of samples, to be held in a flame, and often are made of expansion-resistant glasses, such as borosilicate glass (known by brand-names such as Pyrex and Kimax).

Tests tubes are often preferred above beakers when multiple small chemical or biological samples have to be handled and/or stored.

Vacutainers are a type of test tube that can be used for both collection and storage of blood.

Laboratory equipment

Test tube


Substance is the material, or matter, of which something is made. Substances are physical things that can be seen, touched, or measured. They are made up of one or more elemental parts. Iron, aluminium, water and air are examples of substances.

Problems of definition

The main problem of a clear definition of what the substance is that if, for example, to consider not just the universe (cosmos), being and non-being, and in general all, the question arises, what is the constant basic principle (attribute) is the basis of the substance, which generally consists of all (that is, matter, mind, senses, space, soul, and so on).

History of the concept

The Latin word substantia - a translation of the Greek word for the essence (ousia), and in Latin to describe the essence of using the word essentia. In ancient philosophy substance is treated as a substrate, the first principle of all things (for example, "water" of Thales, the "fire" of Heraclitus).

In modern times, the concept of substance is treated and spread widely. The first view is connected with an ontological understanding of substance as ultimate bases being (Francis Bacon, Benedict Spinoza, Gottfried Wilhelm Leibniz). Central category of metaphysics in philosophy substance is identified as with God and with nature and determined as the cause of itself (Latin, causa sui). The main characteristics (attributes) of a substance from Benedict Spinoza are thinking and stretch. By analogy with the philosophy of Benedict Spinoza substance considered in the light of the concept of René Descartes and Leibniz. The first substance is a unity of subject and object, and the second - the same atoms are simple beings who lose their stretch, but receive attribute aspirations (French, appetition) and multiplicity. Thanks Leibniz substance begins to associate with matter.

The second point of view on the substance - an epistemological understanding of the concept, its capabilities and the need for scientific knowledge (John Locke, David Hume). Immanuel Kant believed that the law under which any change in the substance of events and the number of stored it in nature remains the same, can be attributed to the "analogies of experience." Georg Wilhelm Friedrich Hegel defined substance as the integrity of changing, transient side of things, as a "major step in the development of the will." For Arthur Schopenhauer substance - matter for David Hume - a fiction, the coexistence properties.

Related articles
 Chemical substance

Basic English 850 words
Physics

Substance


A video game developer is a person or company who makes games on computers and other game systems. Some developers make games for only one or two types of game systems, others might even make one kind of game. Some games are only for one system. Developers might try and make a copy of such a game to another, different system. Some translate games from one language to another.

Video game developers work in development companies. There are over 1,000 development companies today. A big part of that thousand is very small companies, that usually only have one or two workers - these kind of small companies make games for the Internet or mobile phones. Some development companies are big, too. They have buildings in many places and hundreds of workers.

Types of developers
There are three types of video game developers.

Third-party developer
Third-party developers are video game developers that make deals with big publishers to make one game at a time. The developers are not part of the company: when the game is complete, the developers do not have to make another game for the publisher if they do not want to. Publishers will tell them exactly what they want third-party developers to do, and the developers do not have very much power to do something else.

In-house developers
In-house developers work directly with the publisher. They have more freedom in the making of the game than third-party developers have. Sometimes publishers buy third-party developers, and so they become in-house developers: workers for the publisher. This is an easy way for the publisher because the developers are workers for the publisher and so the publisher has more control.

Independent developers
Independent developers are usually small groups of people that are not owned by any publisher or another company. Because of that, most independent developers publish their games themselves. If they do that, the games usually will not get much attention or money. Still, independent developers can make exactly the game they want, when there is no publisher to tell them what to do. These are also sometimes called indie developers.

Occupations

Video game developer


Ferdinand II the Catholic (, 10 March 1452 – 23 January 1516) was king of Aragon (1479–1516), Castile, Sicily (1468–1516), Naples (1504–1516), Valencia, Sardinia and Navarre and Count of Barcelona. His marriage to Isabella of Castile brought together most of the Iberian Peninsula as Spain and started its move to become a great power.

Biography
Ferdinand was the son of John II of Aragon by his second wife, the Aragonese noblewoman Juana Enriquez.  He married Infanta Isabella, the sister by a different mother of Henry IV of Castile, on 19 October 1469 in Ocaña. He became Ferdinand V of Castile when Isabella succeeded her brother as Queen of Castile in 1474. The two young monarchs had to begin with a civil war against Juana, princess of Castile (also known as Juana la Beltraneja), who claimed to be the daughter of Henry IV. They won. Ferdinand succeeded his father as King of Aragon in 1479. This meant the Crown of Castile and the various territories of the Crown of Aragon were united in a personal union. For the first time since the 8th century this created a single political unit which came to be called Spain, although the various territories were not administered as a single unit until the 18th century.

The first decades of Ferdinand and Isabella's joint rule were taken up with the conquest of the Kingdom of Granada, the last Muslim bit of Al-Andalus. This was completed by 1492 and then the Jews were expelled from both Castile and Aragon. The royal couple sent Christopher Columbus  on his expedition which discover the New World.  By the Treaty of Tordesillas of 1494, the extra-European world was split between the crowns of Portugal and Castile by a north-south line through the Atlantic Ocean.

Ferdinand was busy in the last decades of his life with the so-called Italian Wars. He was fighting with the Kings of France for control of Italy. In 1494, Charles VIII of France invaded Italy and expelled Ferdinand's cousin, Alfonso II, from the throne of Naples.  Ferdinand's alliance with various Italian princes and with Emperor Maximilian I, expelled the French by 1496 and installed Alfonso's son, Ferdinand, on the Neapolitan throne.  In 1501, following the death of Ferdinand II of Naples and his succession by his uncle Frederick, Ferdinand of Aragon signed an agreement with Charles VIII's successor, Louis XII. Louis had just successfully asserted his claims to the Duchy of Milan, and they agreed to partition Naples between them, with Campania and the Abruzzi, including Naples itself, going to the French and Ferdinand taking Apulia and Calabria. The agreement soon fell apart, and over the next several years, Ferdinand's great general Gonzalo Fernández de Córdoba conquered Naples from the French, by 1504. Another less famous "conquest" took place in 1502, when Andreas Paleologus, de jure Emperor of the Eastern Roman Empire, left Ferdinand and Isabella as heirs to the empire, thus Ferdinand became de jure Roman Emperor.

After Isabella's death, her kingdom went to her daughter Joanna. Ferdinand served as the latter's regent during her absence in the Netherlands, ruled by her husband Archduke Philip. Ferdinand attempted to retain the regency permanently, but was rebuffed by the Castilian nobility and replaced with Joanna's husband, who became Philip I of Castile. After Philip's death in 1506, with Joanna mentally unstable, and her and Philip's son Charles of Ghent only six years old, Ferdinand resumed the regency, ruling through Francisco Cardinal Jimenez de Cisneros, the Chancellor of the Kingdom.

In 1508, war resumed in Italy, this time against Venice. All the other powers on the peninsula, including Louis XII, Ferdinand, Maximilian, and Pope Julius II joined together against as the League of Cambrai.  Although the French were victorious against Venice at the Battle of Agnadello, the League soon fell apart, as both the Pope and Ferdinand became suspicious of French intentions.  Instead, the Holy League was formed, in which all the powers now joined together against France.

In November 1511 Ferdinand and his son-in-law Henry VIII of England signed the Treaty of Westminster, pledging mutual aid between the two against France.  Earlier that year, Ferdinand had conquered the southern half of the Kingdom of Navarre, which was ruled by a French nobleman, and annexed it to Spain. At this point to reinforce his claim to the kingdom, Ferdinand remarried with the much younger Germaine of Foix (1490–1538), a granddaughter of Queen Leonor of Navarre. The Holy League was generally successful in Italy, as well, driving the French from Milan, which was restored to its Sforza dukes by the peace treaty in 1513. The French were successful in reconquering Milan two years later, however.

Ferdinand died in 1516 in Madrigalejo, Cáceres, Extremadura. He had made Spain the most powerful country in Europe. The succession of his grandson Charles, who inherited not only the Spanish lands of his maternal grandparents, but the Habsburg and Burgundian lands of his paternal family, would make his heirs the most powerful rulers on the continent.  Charles succeeded him in the Aragonese lands, and was also granted the Castilian crown jointly with his insane mother, bringing about at long last the unification of the Spanish thrones under one head.

Children
Ferdinand and Isabella had 5 children, Isabella of Asturias, Juan of Aragon, Joanna of Castile, Maria of Aragon, and Catherine of Aragon. Joanna and Catherine married with several European dynasties, setting the bases for the huge heritage of their grandson Charles V. His granddaughter was Queen Mary I of England.

Miscellaneous
 Ferdinand is entombed in the Capilla Real of Granada, alongside his wife, his daughter Joanna and her husband Philip, and his grandson Miguel.
 During his joint reign with Queen Isabella, they used the motto "Tanto monta, monta tanto, Isabel como Fernando" ("They amount to the same, Isabel and Ferdinand"). This was used to imply their equal power in both of their domains, as such an arrangement was uncommon in those times.
 Some scholars argue that Ferdinand, and not the unfortunate Cesare Borgia, was the true inspiration for Niccolò Machiavelli's The Prince, in which he is frequently mentioned.

Related pages
 History of Spain

1452 births
1516 deaths
Kings and Queens of Spain
People from Aragon

Ferdinand II of Aragon


Spamming is when one person or company sends an unwanted email to another person. Spam emails are the computer version of unwanted "junk mail" that arrives in a mailbox, such as advertising pamphlets and brochures. Spam emails are usually sent to try to get the person to buy something or do something else that will cause gain for the sender.

Names
The emails sent when someone is spamming is called spam. The person or company who sent the unwanted email is called a spammer. Both of these words came from a brand of canned meat called "Spam", but it was a short sketch created by the British comedy group Monty Python in 1970 that led to the word "Spam" being widely used to mean unwanted email messages.

Uses
Spam emails are usually sent to many people at once trying to get them to buy a product or sign up for a service. The people who receive the email did not ask to receive the email, and do not want to receive it.

One of the reasons there is so much spam emails around is that it costs very little to send millions of spam messages at once.  Spam messages can easily be sent, sometimes even by a special computer program.

How spammers find email addresses
The hardest part about spamming is to get the email addresses to send the spam to. Sometimes the spammers do this by searching for emails on the internet, or by buying emails from people who know a lot of them (for example, someone who runs a site that makes users tell them their email address to signup will have a lot of email addresses to sell to spammers).

Method one
One part of getting e-mail addresses is to find addresses that are still in use. One trick used by spammers is to put a link at the end of a message like this:

If you do not wish to get more of these messages
from us click here to stop getting them.

If the person clicks on the link, it tells the spammers that there is someone at the address.  Then the spammers put that person on a list of people who actually open spam messages. Next, the spammers sell that list to other spammers. The same thing happens if the person sends another email back to the spammer (called replying), which also tells the spammer the message has been opened.

Method two
Another trick that spammers use is to put a picture – even one that cannot be seen – into a spam message.  The picture will have a name that goes with just that one email.  When the email is opened, a request will be sent to the server that has that picture to get the image. If they get this request, then they know that you read their email, which could cause a person to receive even more email spam.

Other meanings
The word "spamming" is also used to describe the act of typing a lot of words or text in Internet chat rooms, so that other people using the chatroom cannot carry on conversations.  Usually this blocks the screen with meaningless words, in order to annoy the other people in the chatroom.  Spamming in Internet chatrooms is usually considered to be rude. This kind of behavior is usually called flooding rather than spamming.

The word "spam" is often (mistakenly) applied to emails containing content that the receiver sees as silly or simply meaningless (e.g. yujhcykgfvylfuv,uyguvgy).

Problems with spam
Computer users at home and in workplaces waste a lot of time opening and deleting spam messages. In some cases, spam emails contain viruses or links to pornography or illegal gambling websites. Spam emails often advertise products or services which are being lied about by the companies sending the spam, such as frauds or scams.

Spam prevention
Some user email programs can automatically delete spam messages when they arrive, or move them to a separate spam folder. Internet service providers also detect them automatically and cooperate to cut off customers who are major spammers.

References

E-mail
Internet communication

Spamming


An estuary is where a river meets the sea. There, saltwater mixes with freshwater. The river becomes wider and wider and flows slowly to the ocean.

Bays, marshes, swamps, and inlets can all have estuaries. A view of an estuary from the air is usually an interesting sight: many estuaries meander (curve and bend) to find their way to the sea. Estuaries come in all sizes and shapes, each according to its location and climate. Where rivers meet the sea and fresh water mixes with salt water, the mixture is called brackish water.

Some estuaries are very large. They may be large ocean bays that have more than one river flowing into them.  For example, Chesapeake Bay is a large estuary, and several different rivers meet the Atlantic Ocean there.
In simple terms it is where a river meets with a large body of water only with ((one)) outlet and not  many like a ((delta)).

Habitat
Estuaries are usually filled with shallow waters, and sunlight reaches all levels of the water. Marsh grasses, algae, and other kinds of plants live in estuaries and provide food for a variety of fish, crabs, oysters, and shrimp. Estuaries are especially important since they act as nurseries for many different types of young fish and other animals before they head out toward the open ocean. Many sea birds also nest in estuaries.

The United States government has a program to study and protect the natural environment in many different estuaries, called the National Estuarine Research Reserve System. One reason that the natural environment in so many estuaries is in danger is because they are also good places for people to live and build cities. Unfortunately, many of world's largest cities are at or near estuaries.

References

Bodies of water
Ecosystems

Estuary


For the second operand of a division, see division (mathematics).

In mathematics, a divisor of an integer n, also called a factor of n, is an integer which divides n without leaving a remainder. The statement "m is a divisor of n" can be written as . Any number is always divisible by 1 and itself, which are two of the divisors. A prime number is a number with no other divisors. The positive divisors of a number n, other than n itself, are the proper divisors of n.

Finding one or more factors of a given number is called factorization.

Explanation

For example, 7 is a divisor of 42 because 42÷7 = 6. We also say that "42 is divisible by 7", "42 is a multiple of 7", "7 divides 42", or "7 is a factor of 42", and we usually write 7 | 42. For example, the positive divisors of 42 are 1, 2, 3, 6, 7, 14, 21, 42.

In general, we say that m divides n for non-zero integers m and n, if and only if there exists an integer k such that n = km.  Thus, divisors can be negative as well as positive, although we often restrict our attention to positive divisors. (For example, there are six divisors of four, 1, 2, 4, -1, -2, -4, but one would usually mention only the positive ones, 1, 2, and 4.)

1 and -1 divide (are divisors of) every integer, every integer is a divisor of itself, and every integer is a divisor of 0, except by convention 0 itself (see also Division by zero). Numbers divisible by 2 are called even, and numbers not divisible by 2 are called odd.

A divisor of n that is not 1, -1, n or -n is known as a non-trivial divisor; numbers with non-trivial divisors are known as composite numbers, while prime numbers have no non-trivial divisors.

The name comes from the arithmetic operation of division: if a÷b = c, then a is the dividend, b the divisor, and c the quotient.

Spotting divisors
There are properties which allow one to recognize certain divisors of a number from the number's digits. Those properties can be used as "math tricks" to quickly spot some divisors of a number.

For example, if the last digit is even (0, 2, 4, 6 or 8), then 2 is a divisor. If the last digit is 0 or 5, then 5 is a divisor. If the digits add up to a multiple of 3, then 3 is a divisor. For the number 340, ending in "0" then both 2 and 5 are divisors, plus 2×5 = 10 is also a divisor. Dividing by 10, 340/10 = 34, as finally 2×17. Combining all the smaller numbers, the 12 divisors of 340 are:
 Divisors of 340:  1, 2, 4, 5, 10, 17, 20, 34, 68, 85, 170, 340.
Note that any number is always evenly divisible by 1 and itself.

Related pages

 Coprime
 Euclid's lemma

References

Other websites

 Online Number Factorizer Instantly factors numbers up to 17 digits long
 Factoring Calculator  -- Factoring calculator that displays the prime factors and the prime and non-prime divisors of a given number.

Arithmetics
Number theory

Divisor


Organizational architecture, also known as organizational design, is a field concerned with the creation of roles, processes, and formal reporting relationships in an organization. It refers to architecture metaphorically, as a structure which fleshes out the organizations. The various features of a business's organizational architecture has to be internally consistent in strategy, architecture and competitive environment.

It provides the framework through which an organization aims to realize its core qualities as specified in its vision statement. It provides the infrastructure into which business processes are deployed and ensures that the organization's core qualities are realized across the business processes deployed within the organization. In this way, organizations aim to consistently realize their core qualities across the services they offer to their clients. This perspective on organizational architecture is elaborated below.

Content
According to most authors organizational architecture is a metaphor. Like traditional architecture, it shapes the organizational (some authors would say the informational) space where life will take place. It also represents a concept which implies a connection between the organizational structure and other systems inside the organization in order to create a unique synergistic system that will be more than just the sum of its parts.

Conventionally organizational architecture consists of the formal organization (organizational structure), informal organization (organizational culture), business processes, strategy and the most important human resources, because what is an organization if not a system of people? The table shows some approaches to organizational architecture.

The goal of organizational architecture is to create an organization that will be able to continuously create value for present and future customers, optimizing and organizing itself.

Some under organizational architecture understand building blocks, which are mandatory for the growth of the organization. To design an organization means to set up a stage where the drama of life will take place.

Design

Design process and approach
Although the process of organization design isn't necessarily linear, a five milestone process has been created to organize the approach. The five milestone design process is as follows:

Business case and discovery
Goal: Build a business case for the change; compare the current state to future state and implications that would be involved.
Milestone: at the end of this phase, the problem to be solved is clear.
Strategic grouping
Goal: Determine what basic grouping of work will create the capabilities necessary to deliver the decided strategy.
Milestone: Decided on a structure change which supports the strategy.

Integration
Goal: The boundaries created by grouping work must be breached to deliver results for customers, partners and shareholders.
Milestone: Pieces have been tied together and defined power relationships.
Talent and leadership
Goal: Determine the number of positions, the profile of a candidate who will fill those positions, and who will report to the leader of the new structure(s).
Milestone: Critical roles have been designed and staffed and defined work for the executive team.
Transition
Goal: Set the transition plan to account for a logical implementation plan.
Milestone: The change is being executed and lead, and closely monitoring the changes to prepare for any adjustments

Reshaping organization structure

Organization design can be defined, narrowly, as the process of reshaping organization structure and roles. It can also be more effectively defined as the alignment of structure, process, rewards, metrics, and talent with the strategy of the business. Jay Galbraith and Amy Kates have made the case persuasively (building on years of work by Galbraith) that attention to all of these organizational elements is necessary to create new capabilities to compete in a given market. This systemic view, often referred to as the "star model" approach, is more likely to lead to better performance.

Organization design may involve strategic decisions, but is properly viewed as a path to effective strategy execution. The design process nearly always entails making trade-offs of one set of structural benefits for another. Many companies fall into the trap of making repeated changes in organization structure, with little benefit to the business. This often occurs because changes in structure are relatively easy to execute while creating the impression that something substantial is happening.  This often leads to cynicism and confusion within the organization. More powerful change happens when there are clear design objectives driven by a new business strategy or forces in the market require a different approach to organize resources.

The organization design process is often explained in phases. Phase one is the definition of a business case, including a clear picture of strategy and design objectives. This step is typically followed by "strategic grouping" decisions, which define the fundamental architecture of the organization - essentially deciding which major roles will report at the top of the organization.  The classic options for strategic grouping are to organize by:

Behavior
Function
Product or category
Customer or market
Geography
Matrix

Each of the basic building block options for strategic grouping brings a set of benefits and drawbacks. However, such generic pros and cons are not the basis for choosing the best strategic grouping. An analysis must be completed relative to a specific business strategy.

Subsequent phases of organization design include operational design of processes, roles, measures, and reward systems, followed by staffing and other implementation tasks.

The field is somewhat specialized in nature and many large and small consulting firms offer organization design assistance to executives. Some companies attempt to establish internal staff resources aimed at supporting organization design initiatives. There is a substantial body of literature in the field, arguably starting with the work of Peter Drucker in his examination of General Motors decades ago.  Other key thinkers built on Drucker's thinking, including Galbraith (1973), Nadler, et al. (1992) and Lawrence and Lorsch (1967).

Organization design can be considered a subset of the broader field of organization effectiveness and organization development, both of which may entail more behaviorally focused solutions to effectiveness, such as leadership behaviors, team effectiveness and other characteristics of that nature. Many organizational experts argue for an integrated approach to these disciplines, including effective talent management practices.

Various approaches
There are various approaches to organizational architecture including

 (1986, 1991, 2004) - Kenneth D. Mackenzie
 (1992, 1993) - David A. Nadler and Michael L. Tushman.
  Organizational Architecture - by David A. Nadler, Marc S. Gerstein and Robert B. Shaw.
 (1993, 1995) - Designing organizations using the STAR Model as developed by Jay Galbraith
 Benjamin's Layered Model of organizations.
 The Organizational Adaption Model by Raymond E. Miles and Charles C. Snow.
 (1995) - Richard M. Burton and Børge Obel
 (2001) - Ralph Kilmann
 (2004) - Richard L. Daft

Five principles of good design

Specialization principle - the primary concern in the specialization principle how to group responsibilities into units. The unit boundaries should be defined to achieve the important benefits available.
Coordination principle - this principle links closely with the specialization principle, to ensure the links are established between the units.
Knowledge and competence principle - the primary concern in this principle is determining which responsibilities to decentralize and what hierarchical levels to create.
Control and commitment principle - the primary concern in this principle is insuring managers have a process to effectively discharge decentralized principles.
Innovation and adaptation principle - the primary concern in this principle is insuring the organization can change and evolve in the future.

Five good design tests
Each tests coincides with the principles previously mentioned.

 Specialist culture test (Specialization Principle)
 Difficult links test (Coordination Principle)
 Redundant hierarchy test (Knowledge and Competence Principle)
 Accountability test (Control and Commitment Principle)
 Flexibility test (Innovation and Adaptation Principle)

Characteristics of effective organizational design
Some systems are effective and efficient whereas others are not. Successful systems may be attributable to the skill exercised in designing the system or to the quality of management practised during operations, or both. Successful systems are characterized by their simplicity, flexibility, reliability, economy, and acceptability. Simplicity, flexibility, and reliability tend to be a function of design, whereas economy and acceptability pertain to both design and operations. Numerous relationships exist among these characteristics; for example, simplicity will affect economy and possibly reliability. Moreover, management must reach a compromise between economy and reliability, and between technical efficiency and organizational climate. The balance reached will determine whether short- or long-run objectives are optimized.

 Simplicity

An effective organizational system need not be complex. On the contrary, simplicity in design is a desirable quality. Consider the task of communicating information about the operation of a system and the allocation of its inputs. The task is not difficult when components are few and the relationships among them are straightforward. However, the problems of communication multiply with each successive stage of complexity.

The proper method for maintaining simplicity is to use precise definitions and to outline the specific task for each subsystem. Total systems often become complex because of the sheer size and nature of operations, but effectiveness and efficiency may still be achieved if each subsystem maintains its simplicity.

 Flexibility

Conditions change and managers should be prepared to adjust operations accordingly. There are two ways to adjust to a changing operating environment: to design new systems or to modify operating systems. An existing system should not be modified to accommodate a change in objectives, but every system should be sufficiently flexible to integrate changes that may occur either in the environment or in the nature of the inputs. For example, a company should not use the same system to build missiles as it uses to build airplanes, nor the same system to sell insurance as the one originally designed to sell magazines. However, it should be possible to modify an existing system to produce different sizes, varieties, or types of the same product or service.

A practical system must be well designed but it cannot be entirely rigid. There will always be minor variations from the general plan, and a system should be able to adapt to such changes without excessive confusion. The advantages associated with having a flexible system will become more apparent when we consider the difficulty of administering change.

 Reliability

System reliability is an important factor in organizations. Reliability is the consistency with which operations are maintained, and may vary from zero output (a complete breakdown or work stoppage) to a constant or predictable output. The typical system operates somewhere between these two extremes. The characteristics of reliability can be designed into the system by carefully selecting and arranging the operating components; the system is no more reliable than its weakest segment. When the requirements for a particular component — such as an operator having unique skills — are critical, it may be worthwhile to maintain a standby operator. In all situations, provisions should be made for quick repair or replacement when failure occurs. One valid approach to the reliability-maintenance relationship is to use a form of construction that permits repair by replacing a complete unit. In some television sets, for example, it is common practice to replace an entire section of the network rather than try to find the faulty component. Reliability is not as critical an issue when prompt repair and recovery can be instituted.

 Economy
An effective system is not necessarily an economical (efficient) system. For example, the postal service may keep on schedule with mail deliveries but only by hiring a large number of additional workers. In this case, the efficiency of the postal system would be reduced. In another example, inventories may be controlled by using a comprehensive system of storekeeping. However, if the cost of the storekeeping were greater than the potential savings from this degree of control, the system would not be efficient. It is often dysfunctional and expensive to develop much greater capacity for one segment of a system than for some other part. Building in redundancy or providing for every contingency usually neutralizes the operating efficiency of the system. When a system's objectives include achieving a particular task at the lowest possible cost, there must be some degree of trade-off between effectiveness and efficiency. When a system's objective is to perform a certain mission regardless of cost, there can be no trade-off.

 Acceptability
Any system, no matter how well designed, will not function properly unless it is accepted by the people who operate it. If the participants do not believe it will benefit them, are opposed to it, are pressured into using it, or think it is not a good system, it will not work properly. If a system is not accepted, two things can happen:(1) the system will be modified gradually by the people who are using it, or (2) the system will be used ineffectively and ultimately fail. Unplanned alterations in an elaborate system can nullify advantages associated with using the system.

Differentiation and integration
A basic consideration in the design of organizations is dividing work into reasonable tasks (differentiation) while giving simultaneous attention to coordinating these activities and unifying their results into a meaningful whole (integration). Two guidelines may be followed in grouping activities:

 Units that have similar orientations and tasks should be grouped together. (They can reinforce each other's common concern and the arrangement will simplify the coordinating task of a common manager).
 Units required to integrate their activities closely should be grouped together. (The common manager can coordinate them through the formal hierarchy).

When units neither have similar orientations nor share their activities, the task of grouping becomes more difficult. For example, when units are similar in nature and function but are also relatively independent, the manager must base their decision on the most appropriate way to group activities according to their past experience.

A difficult task associated with system-subsystem determination is to establish proper boundaries of operations. The more specific and distinct the goals of the operation, the easier it is to set boundaries. Other factors such as the influence of the environment, the availability of men and machines, the time schedule for design and operation, the cost of alternative designs, and the particular biases of the designers must be considered when establishing boundaries.

The role of management
Designers with imagination have the best chance to group people and machines into workable combinations having the greatest efficiency and effectiveness within the recognized constraints. Certain characteristics should be designed into an effective and efficient system — simplicity, flexibility, reliability, economy, and acceptability.

At this point, the designer must determine what has to be done to achieve the stated objective(s) and how the total task can be divided into meaningful units. Of the many possible combinations, one must be selected as that which satisfies the decision criteria better than the other alternatives. Of course, the balance between technical efficiency and the human factors that determine organizational climate should be included in making this decision. The eventual success or failure of the project is somewhat predetermined by management's attitude and the relationship between the designers and those who must implement the process.

The systems approach suggests a new role for management. In the traditional view, the manager operated in a highly structured, rigid system having well-defined goals, clear-cut relationships, tight controls, and hierarchical information flows. In the flexible (or open) systems view, the organization is not static but is continually evolving to meet both external and internal changes. The manager's role is to develop a viable organization, cope with change, and help participants establish a dynamic equilibrium. Leonard Sayles has expressed the manager's problem as follows:

"The one enduring objective is the effort to build and maintain a predictable, reciprocating system of relationships, the behavioral patterns of which stay within reasonable physical limits. But this is seeking a moving equilibrium, since the parameters of the system (the division of labor and the controls) are evolving and changing. Thus, the manager endeavors to introduce regularity in a world that will never allow him to achieve the ideal".

The systems approach does not offer a prescription for making a manager's difficult and complex job easier. Rather it helps him understand and operate more effectively within the reality of complex systems. The systems approach suggests that operations cannot be neatly departmentalized but must be viewed as overlapping subsystems. In addition, it suggests that leadership patterns must be modified, particularly when dealing with professionals and highly trained specialists, and motivation must take the form of active, willing participation rather than forceful subjugation.

Systems design involves establishing projects and facilitating subsystems to accomplish certain tasks or programs. In this approach, the network of human independence required to accomplish a given task is based on the shared responsibility of all members of the subsystem. In contrast, the traditional organization is geared to functional performance and the integrating force is authority. Instead of gearing participant activities to obedience to rules and closely structured behavior, the systems approach provides a basis for active cooperation in meeting task requirements. The manager is looked upon as a resource person who can help the group meet its goals and also as a source of authority and control. Thus, systems theory lends a structure by which the concepts of motivation, leadership, and participation can be applied effectively within the organization.

Implementation is, of course, implicit in the connotation of systems design; otherwise it would be nothing more than an empty exercise. It follows that the interface between managers and systems designers is critical, and mutual understanding must be fostered to maximize returns from design efforts. The system must be tailored to the needs of the organization and adapted continually as circumstances change. In a general sense, managers engage in systems design on a day-to-day basis when they plan activities and organize systems to accomplish objectives. Specialized staff groups have evolved to perform tasks such as long-range planning, organizational studies, and systems design. However, since managers are ultimately responsible for organizational endeavors, they should make a special effort to help ensure the development of useful systems and to make design activities an extension of the manager's role rather than a separate function.

Operating managers need to understand the organizational decision-making requirements and the information needed to support the system. Although the probability of success in implementation is enhanced considerably if management is vitally interested in the project, technical expertise and motivation for change are more likely to be found in staff groups. The solution to the apparent dichotomy would seem to be a team approach, with specialists supporting operating managers who are responsible for the project's success. A manager might devote either part-time to such an effort or full-time temporarily, if the task requires it.

A project involving an integrated system for the entire company might well require years to complete. If operating people are delegated responsibility and authority for such a project, particularly if they are delegated the authority to outline specifications, they should also maintain sufficient contact with the day-to-day operations and its attendant information flow to retain their expertise for decision making. If the environment is dynamic or internal capabilities undergo change, it might be wise to rotate people from operations to systems design periodically, so that operating expertise is updated continually.

See also
 Organizational design
 Organizational structure
 Departmentalization
 Enterprise architecture framework
 Interdisciplinary Center for Organizational Architecture
 View model

References

Further reading
 Kates, Amy, and Gregory Kesler. Bridging Organization Design and Performance: 5 Ways to Activate a Global Operating Model. Hoboken, NJ: John Wiley & Sons, 2016.
 Kates, Amy, and Jay R. Galbraith. Designing Your Organization: Using the Star Model to Solve 5 Critical Design Challenges. San Francisco: Jossey-Bass, 2007.
 R.I. Benjamin and E. Levinson, A framework for managing IT-enabled change by Sloan Management Review, Summer 1993.
 Karen Dale and Gibson Burrell. The Spaces of Organisation & The Organization of Space -Power, Identity & Materiality at Work, 2008.
 Jay Galbraith, Designing Organizations, Jossey-Bass Publishers, San Francisco, 1995.
 Raymond E. Miles and Charles C. Snow, Organizational Adaption, 2003.
 Joseph Morabito, Ira Sack and Anilkumar Bhate, Organization Modeling, 1999.
 David A. Nadler, Marc C. Gerstein and Robert B. Shaw, Organizational Architecture, 1992.
 Harold G. Nelson and Erik Stolterman, The design way: Intentional change in an unpredictable world: Foundations and fundamentals of design competence, 2003.

Business models
Enterprise modelling
Organization design

Organizational architecture


Rohangan hapa atawa vacuum nyaéta volume rohangan anu pada dasarna kosong ku materi, saperti tekanan gas éta rohangan kurang ti tekanan atmosfir baku.

The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum. The root of the word vacuum is the Latin adjective vacuus which méans "empty," but space can never be perfectly empty. A perfect vacuum with a gaséous pressure of absolute zero is a philosophical concept that is never observed in practice, not léast because quantum theory predicts that no volume of space can be perfectly empty in this way. Physicists often use the term "vacuum" slightly differently. They discuss idéal test results that would occur in a perfect vacuum, which they simply call "vacuum" or "free space" in this context, and use the term partial vacuum to refer to the imperfect vacua réalized in practice.

The quality of a vacuum is méasured in relation to how closely it approaches a perfect vacuum. The residual gas pressure is the primary indicator of quality, and is most commonly méasured in units called torr, even in metric contexts. Lower pressures indicate higher quality, although other variables must also be taken into account. Quantum mechanics sets limits on the best possible quality of vacuum. Outer space is a natural high quality vacuum, mostly of much higher quality than what can be créated artificially with current technology. Low quality artificial vacuums have been used for suction for millennia.

Vacuum has been a frequent topic of philosophical debate since Ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first artifical vacuum in 1643, and other experimental techniques were developed as a result of his théories of atmospheric pressure. Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human héalth, and on life forms in general.

Uses

Vacuum is useful in a variety of processes and devices. Its first common use was in incandescent light bulbs to protect the tungsten filament from chemical degradation. Its chemical inertness is also useful for electron beam welding, chemical vapor deposition and dry etching in the fabrication of semiconductors and optical coatings, cold welding, vacuum packing and vacuum frying. The reduction of convection improves the thermal insulation of thermos bottles and double-paned windows. Deep vacuum promotes outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum maké electron microscopes and vacuum tubes possible, including cathode ray tubes. The elimination of air friction is useful for flywheel energy storage and ultracentrifuges.

High to ultra-high vacuum is used in thin film deposition and surface science. High vacuum allows for contamination-free material deposition. Ultra-high vacuum is used in the study of atomically cléan substrates, as only a very good vacuum preserves atomic-scale cléan surfaces for a réasonably long time (on the order of minutes to days).

Suction is used in a wide variety of applications. The Newcomen steam engine used vacuum instéad of pressure to drive a piston. In the 19th century, vacuum was used for traction on Isambard Kingdom Brunel's experimental atmospheric railway.

Outer space

Much of outer space has the density and pressure of an almost perfect vacuum. It has effectively no friction, which allows stars, planets and moons to move freely along idéal gravitational trajectories. But no vacuum is perfect, not even in interstellar space, where there are only a few hydrogen atoms per cubic centimeter at 10 fPa (10−16 Torr). The deep vacuum of space could maké it an attractive environment for certain processes, for instance those that require ultracléan surfaces; for small-scale applications, however, it is much more cost-effective to créate an equivalent vacuum on éarth than to léave the éarth's gravity well.

Stars, planets and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no cléarly delinéated boundary: the density of atmospheric gas simply decréases with distance from the object. In low earth orbit (about 300 km or 185 miles altitude) the atmospheric density is about 100 nPa (10−9 Torr), still sufficient to produce significant drag on satellites. Most artificial satellites operate in this region, and must fire their engines every few days to maintain orbit.

Beyond planetary atmospheres, the pressure of photons and other particles from the sun becomes significant. Spacecraft can be buffeted by solar winds, but planets are too massive to be affected. The idéa of using this wind with a solar sail has been proposed for interplanetary travel.

All of the observable universe is filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The current temperature of this radiation is about 3 K, or -270 degrees Celsius or -454 degrees Fahrenheit.

Effects on humans and animals

Vacuum is primarily an asphyxiant. Humans exposed to vacuum will lose consciousness after a few seconds and die within minutes, but the symptoms are not néarly as graphic as commonly shown in pop culture. Robert Boyle was the first to show that vacuum is lethal to small animals. Blood and other body fluids do boil (the medical term for this condition is ebullism), and the vapour pressure may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure containment of blood vessels, so some blood remains liquid. Swelling and ebullism can be reduced by containment in a flight suit. Shuttle astronauts wéar a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 15 Torr (2 kPa). However, even if ebullism is prevented, simple evaporation of blood can cause decompression sickness and gas embolisms. Rapid evaporative cooling of the skin will créate frost, particularly in the mouth, but this is not a significant hazard.

Animal experiments show that rapid and complete recovery is the norm for exposures of fewer than 90 seconds, while longer full-body exposures are fatal and resuscitation has never been successful. There is only a limited amount of data available from human accidents, but it is consistent with animal data. Limbs may be exposed for much longer if bréathing is not impaired. Rapid decompression can be much more dangerous than vacuum exposure itself. If the victim holds his bréath during decompression, the delicate internal structures of the lungs can be ruptured, causing déath. Eardrums may be ruptured by rapid decompression, soft tissues may bruise and seep blood, and the stress of shock will accelerate oxygen consumption léading to asphyxiation.

In 1942, in one of a series of experiments on human subjects for the Luftwaffe, the Nazi regime tortured Dachau concentration camp prisoners by exposing them to vacuum in order to determine the human body's capacity to survive high-altitude conditions.

Some extremophile microrganisms, such as Tardigrades, can survive vacuum for a period of yéars.

Historical interpretation
Historically, there has been much dispute over whether such a thing as a vacuum can exist.  Ancient Greek philosophers did not like to admit the existence of a vacuum, asking themselves "how can 'nothing' be something?".  Plato found the idéa of a vacuum inconceivable. He believed that all physical things were instantiations of an abstract Platonic ideal, and he could not conceive of an "ideal" form of a vacuum.  Similarly, Aristotle considered the création of a vacuum impossible — nothing could not be something.  Later Greek philosophers thought that a vacuum could exist outside the cosmos, but not within it.

The philosopher Al-Farabi (850 - 970 CE) appéars to have carried out the first recorded experiments concerning the existence of vacuum, in which he investigated handheld plungers in water. He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent.

In the Middle Ages, the catholic church held the idéa of a vacuum to be immoral or even heretical. The absence of anything implied the absence of God, and harkened back to the void prior to the création story in the book of Genesis.  Medieval thought experiments into the idéa of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated.  There was much discussion of whether the air moved in quickly enough as the plates were separated, or, as Walter Burley postulated, whether a 'celestial agent' prevented the vacuum arising — that is, whether nature abhorred a vacuum.  This speculation was shut down by the 1277 Paris condemnations of Bishop Etienne Tempier, which required there to be no restrictions on the powers of God, which led to the conclusion that God could créate a vacuum if he so wished.

Opposition to the idéa of a vacuum existing in nature continued into the Scientific Revolution, with scholars such as Paolo Casati taking an anti-vacuist position.  Building upon work by Galileo, Evangelista Torricelli argued in 1643 that there was a vacuum at the top of a mercury barometer. Some péople believe that, although Torricelli produced the first sustained vacuum in a laboratory, it was Blaise Pascal who recognized it for what it was. In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that téams of horses could not separate two hemispheres from which the air had been evacuated. Robert Boyle improved Guericke's design and conducted experiments on the properties of vacuum. Robert Hooke also helped Boyle produce an air pump which helped to produce the vacuum. The study of vacuum then lapsed until 1855, when Heinrich Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube.

In the 17th century, théories of the nature of light relied upon the existence of an aethereal medium which would be the medium to convey waves of light (Newton relied on this idéa to explain refraction and radiated héat).  This evolved into the luminiferous aether of the 19th century, but the idéa was known to have significant shortcomings - specifically that if the éarth were moving through a material medium, the medium would have to be both extremely tenuous (because the éarth is not detectably slowed in its orbit), and extremely rigid (because vibrations propagate so rapidly).

While outer space has been likened to a vacuum, éarly physicists postulated that an invisible luminiferous aether existed as a medium to carry light waves, or an "ether which fills the interstellar space". An 1891 article by William Crookes noted: "the [freeing of] occluded gases into the vacuum of space". Even up until 1912, astronomer Henry Pickering commented: "While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there".

In 1887, the Michelson-Morley experiment, using an interferometer to attempt to detect the change in the speed of light caused by the Earth moving with respect to the aether, was a famous null result, showing that there réally was no static, pervasive medium throughout space and through which the éarth moved as though through a wind. While there is therefore no aether, and no such entity is required for the propagation of light, space between the stars is not completely empty. Besides the various particles which comprise cosmic radiation, there is a cosmic background of photonic radiation (light), including the thermal background at about 2.7 K, seen as a relic of the Big Bang. None of these findings affect the outcome of the Michelson-Morley experiment to any significant degree.

Einstein argued that physical objects are not located in space, but rather have a spatial extent. Seen this way, the concept of empty space loses its méaning. Rather, space is an abstraction, based on the relationships between local objects. Nevertheless, the general theory of relativity admits a pervasive gravitational field, which, in Einstein's words, may be regarded as an "aether", with properties varying from one location to another. One must take care, though, to not ascribe to it material properties such as velocity and so on.

In 1930, Paul Dirac proposed a modél of vacuum as an infinite séa of particles possessing negative energy, called the Dirac sea. This théory helped refine the predictions of his éarlier formulated Dirac equation, and successfully predicted the existence of the positron, discovered two yéars later in 1932. Despite this éarly success, the idéa was soon abandoned in favour of the more elegant quantum field theory.

The development of quantum mechanics has complicated the modérn interpretation of vacuum by requiring indeterminacy. Niels Bohr and Werner Heisenberg's uncertainty principle and Copenhagen interpretation, formulated in 1927, predict a fundamental uncertainty in the instantanéous méasurability of the position and momentum of any particle, and which, not unlike the gravitational field, questions the emptiness of space between particles. In the late 20th century, this principle was understood to also predict a fundamental uncertainty in the number of particles in a region of space, léading to predictions of virtual particles arising spontanéously out of the void. In other words, there is a lower bound on the vacuum, dictated by the lowest possible energy state of the quantized fields in any region of space. Ironically, Plato was right, if only by chance.

Quantum-mechanical definition

In quantum mechanics, the  is defined as the state (i.e. solution to the equations of the théory) with the lowest energy. To first approximation, this is simply a state with no particles, hence the name.

Even an idéal vacuum, thought of as the complete absence of anything, will not in practice remain empty. Consider a vacuum chamber that has been completely evacuated, so that the (classical) particle concentration is zero. The walls of the chamber will emit light in the form of black body radiation. This light carries momentum, so the vacuum does have a radiation pressure. This limitation applies even to the vacuum of interstellar space. Even if a region of space contains no particles, the Cosmic Microwave Background fills the entire universe with black body radiation.

An idéal vacuum cannot exist even inside of a molecule. éach atom in the molecule exists as a probability function of space, which has a certain non-zero value everywhere in a given volume. Thus, even "between" the atoms there is a certain probability of finding a particle, so the space cannot be said to be a vacuum.

More fundamentally, quantum mechanics predicts that vacuum energy will be different from its naive, classical value. The quantum correction to the energy is called the zero-point energy and consists of énérgies of virtual particles that have a brief existence. This is called vacuum fluctuation. Vacuum fluctuations may also be related to the so-called cosmological constant in cosmology. The best evidence for vacuum fluctuations is the Casimir effect and the Lamb shift.

In quantum field theory and string theory, the term "vacuum" is used to represent the ground state in the Hilbert space, that is, the state with the lowest possible energy. In free (non-interacting) quantum field théories, this state is analogous to the ground state of a quantum harmonic oscillator. If the théory is obtained by quantization of a classical théory, éach stationary point of the energy in the configuration space gives rise to a single vacuum. String theory is believed to have a huge number of vacua - the so-called string theory landscape.

Pumping

Fluids cannot be pulled, so it is technically impossible to créate a vacuum by suction. Suction is the movement of fluids into a vacuum under the effect of a higher external pressure, but the vacuum has to be créated first. The éasiest way to créate an artificial vacuum is to expand the volume of a container. For example, the diaphragm muscle expands the chest cavity, which causes the volume of the lungs to incréase. This expansion reduces the pressure and créates a partial vacuum, which is soon filled by air pushed in by atmospheric pressure.

To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repéatedly closed off, exhausted, and expanded again. This is the principle behind positive displacement pumps, like the manual water pump for example. Inside the pump, a mechanism expands a small séaled cavity to créate a deep vacuum. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then séaled from the chamber, opened to the atmosphere, and squeezed back to a minute size.

The above explanation is merely a simple introduction to vacuum pumping, and is not representative of the entire range of pumps in use. Many variations of the positive displacement pump have been developed, and many other pump designs rely on fundamentally different principles. Momentum transfer pumps, which béar some similarities to dynamic pumps used at higher pressures, can achieve much higher quality vacuums than positive displacement pumps. Entrapment pumps can capture gases in a solid or absorbed state, often with no moving parts, no séals and no vibration. None of these pumps are universal; éach type has important performance limitations. They all share a difficulty in pumping low molecular weight gases, especially hydrogen, helium, and neon.

The lowest pressure that can be attained in a system is also dependent on many things other than the nature of the pumps. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. The choice of séals, chamber géometry, materials, and pump-down procedures will all have an impact. Collectively, these are called vacuum technique. And sometimes, the final pressure is not the only relevant characteristic. Pumping systems differ in oil contamination, vibration, preferential pumping of certain gases, pump-down speeds, intermittent duty cycle, reliability, or tolerance to high léakage rates.

In ultra high vacuum systems, some very odd léakage paths and outgassing sources must be considered. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the adsorptivity of hard metals such as stainless steel or titanium must be considered. Some oils and gréases will boil off in extreme vacuums. The porosity of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.

The lowest pressures currently achievable in laboratory are about 10−13 Torr.

Outgassing

Evaporation and sublimation into a vacuum is called outgassing. All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. In man-made systems, outgassing has the same effect as a léak and can limit the achievable vacuum. Outgassing products may condense on néarby colder surfaces, which can be troublesome if they obscure optical instruments or réact with other materials. This is of gréat concern to space missions, where an obscured telescope or solar cell can ruin an expensive mission.

The most prevalent outgassing product in man-made vacuum systems is water absorbed by chamber materials. It can be reduced by desiccating or baking the chamber, and removing absorbent materials. Outgassed water can condense in the oil of rotary vane pumps and reduce their net speed drastically if gas ballasting is not used. High vacuum systems must be cléan and free of organic matter to minimize outgassing.

Ultra-high vacuum systems are usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials and boil them off. Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures and minimize residual outgassing during actual operation. Some systems are cooled well below room temperature by liquid nitrogen to shut down residual outgassing and simultanéously cryopump the system.

Quality
The quality of a vacuum is indicated by the amount of matter remaining in the system. Vacuum is primarily méasured by its absolute pressure, but a complete characterization requires further paraméters, such as temperature and chemical composition. One of the most important paraméters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with éach other. As the gas density decréases, the MFP incréases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~1×10−3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. The Crookes radiometer turns when the MFP is larger than the size of the vanes.

Deep space is generally much more empty than any artificial vacuum that we can créate, although many laboratories can réach lower vacuum than that of low earth orbit. In interplanetary and interstellar space, isotropic gas pressure is insignificant when compared to solar pressure, solar wind, and dynamic pressure, so the definition of pressure becomes difficult to interpret. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre. The average density of interstellar gas is about 1 atom per cubic centimeter.

Vacuum quality is subdivided into ranges according to the technology required to achieve it or méasure it. These ranges do not have universally agreed definitions (hence the gaps below), but a typical distribution is as follows:

 Atmospheric pressure is variable but standardized at 101.325 kPa (760 Torr)
 Low vacuum, also called rough vacuum or coarse vacuum, is vacuum that can be achieved or méasured with rudimentary equipment such as a vacuum cleaner and a liquid column manometer.
 Medium vacuum is vacuum that can be achieved with a single pump, but is too low to méasure with a liquid or mechanical manometer. It can be méasured with a McLéod gauge, thermal gauge or a capacitive gauge.
 High vacuum is vacuum where the MFP of residual gases is longer than the size of the chamber or of the object under test. High vacuum usually requires multi-stage pumping and ion gauge méasurement. Some texts differentiate between high vacuum and very high vacuum.
 Ultra high vacuum requires baking the chamber to remove trace gases, and other special procedures.
 Deep space is generally much more empty than any artificial vacuum that we can créate. However, it is not High Vacuum with respect to the above definition, since the MFP of the molecules is smaller than the (infinite) size of the chamber.
 Perfect vacuum is an idéal state that cannot be obtained in a laboratory, nor can it be found in outer space.

Examples

Measurement

Vacuum is méasured in units of pressure. The SI unit of pressure is the pascal (symbol Pa), but vacuum is usually méasured in torrs (symbol Torr), named for Torricelli, an éarly Italian physicist (1608 - 1647).  A torr is equal to the displacement of a millimeter of mercury (mmHg) in a manometer with 1 torr equaling 133.3223684 pascals above absolute zero pressure.  Vacuum is often also méasured using inches of mercury on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres.  Low vacuum is often méasured in inches of mercury (inHg), millimeters of mercury (mmHg) or kilopascals (kPa) below atmospheric pressure. "Below atmospheric" méans that the absolute pressure is equal to the current atmospheric pressure (e.g. 29.92 inHg) minus the vacuum pressure in the same units. Thus a vacuum of 26 inHg is equivalent to an absolute pressure of 4 inHg (29.92 inHg - 26 inHg).

Many devices are used to méasure the pressure in a vacuum, depending on what range of vacuum is needed.

Hydrostatic gauges (such as the mercury column manometer) consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. The simplest design is a closed-end U-shaped tube, one side of which is connected to the region of interest. Any fluid can be used, but mercury is preferred for its high density and low vapour pressure. Simple hydrostatic gauges can méasure pressures ranging from 1 Torr (100 Pa) to above atmospheric. An important variation is the McLeod gauge which isolates a known volume of vacuum and compresses it to multiply the height variation of the liquid column. The McLéod gauge can méasure vacuums as high as 10−6 Torr (0.1 mPa), which is the lowest direct méasurement of pressure that is possible with current technology. Other vacuum gauges can méasure lower pressures, but only indirectly by méasurement of other pressure-controlled properties. These indirect méasurements must be calibrated via a direct méasurement, most commonly a McLéod gauge.

Mechanical or elastic gauges depend on a Bourdon tube, diaphragm, or capsule, usually made of metal, which will change shape in response to the pressure of the region in question. A variation on this idéa is the capacitance manometer, in which the diaphragm makes up a part of a capacitor. A change in pressure léads to the flexure of the diaphragm, which results in a change in capacitance. These gauges are effective from 10−3 Torr to 10−4 Torr.

Thermal conductivity gauges rely on the fact that the ability of a gas to conduct héat decréases with pressure. In this type of gauge, a wire filament is héated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to méasure the temperature of the filament. This temperature is dependent on the rate at which the filament loses héat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platimum filament as both the héated element and RTD. These gauges are accurate from 10 Torr to 10−3 Torr, but they are sensitive to the chemical composition of the gases being méasured.

Ion gauges are used in ultrahigh vacua. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically héated filament produces an electron béam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 10−3 Torr to 10−10 Torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge créated by a high voltage electrical discharge. Cold cathode gauges are accurate from 10−2 Torr to 10−9 Torr. Ionization gauge calibration is very sensitive to construction géometry, chemical composition of gases being méasured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate méasurement.

Properties
Many properties of space approach non-zero values in a vacuum that approaches perfection. These idéal physical constants are often called free space constants. Some of the common ones are as follows:
 The speed of light approaches 299,792,458 m/s, but is always slower
 Index of refraction approaches 1.0, but is always higher
 Electric permittivity () approaches 8.8541878176x10−12 farads per meter (F/m).
 Magnetic permeability (μ0) approaches 4π×10−7 N/A2.
 Characteristic impedance () approaches 376.73 Ω.

Notes

See also

 Decay of the vacuum (Pair production)
 Helium mass spectrometer - technical instrumentation to detect a vacuum léak
 Engine vacuum
 Mean free path
 Negative pressure
 Rarefaction - reduction of a medium's density
 Suction - création of a partial vacuum
 Vacuum cementing - natural process of solidifying homogenous "dust" in vacuum
 Vacuum engineering - vacuum engineering
 Vacuum angle
 Vacuum flange

Tumbu luar
 American Vacuum Society
 Journal of Vacuum Science and Technology A
 Journal of Vacuum Science and Technology B
 FAQ on explosive decompression and vacuum exposure.
 Discussion of the effects on humans of exposure to hard vacuum.
 Vacuum Energy in High Energy Physics
 History of Vacuum Science
 Short History of Vacuum Terminology and Technology
 Vacuum, Production of Space
 VIDEO on the nature of vacuum by Canadian astrophysicist Doctor P
 "Much Ado About Nothing" by Professor John D. Barrow, Gresham College

Kosong
Konsép fisika dasar
Prosés industri
Hampa

Rohangan hapa


An allele is a form of a gene at a particular position (locus) on a chromosome.15 It is the bit of coding DNA at that place.p6

Typical plants and animals have two sets of chromosomes, one set inherited from each parent.123 These organisms are called diploid. Since such organisms have two sets of chromosomes, they have (except on the sex chromosomes) two alleles at each gene locus.p6

If the two alleles are identical, the individual is called a homozygote and is said to be homozygous. If instead the two alleles are different, the individual is a heterozygote and is heterozygous.205

Dominance
In a heterozygote the effect of one allele may completely 'mask' the other. That is, the phenotype produced by the two alleles in heterozygous combination is identical to that produced by one of the two homozygous genotypes.212

The allele that masks the other is said to be dominant to the latter, and the alternative allele is said to be recessive to the former. This idea originates in the work of Gregor Mendel, the founder of genetics.

In other cases, both alleles contribute to the phenotype.

Example
The inheritance of alleles, and their dominance, can be represented in a Punnett square.

An example is the gene for blossom colour in many species of flower. A single gene controls the colour of the petals, but there may be several different versions (or alleles) of the gene.

In this example, parents have the genotype Bb (capital letters show dominant alleles and lower-case letters to show recessive alleles). If B (capital) is found in their genotype, the flower will be red. Therefore, the only time a flower is not red is when the genotype is bb (there are no capital 'B's).

The probability of the flowers having different genotypes are: BB is 25%, Bb is 50%, and bb is 25%. The phenotype of the flower will always be red if a dominant B is in the genotype. Therefore, there is a 25% chance of getting a flower which is not red, and 75% chance of getting a flower which is red.

Recessive

The pattern of inheritance of recessive genes is quite simple. If they are heterozygous with a dominant allele, the appearance (phenotype) is the same as a dominant homozygote. Only if both alleles are recessive does the recessive allele show in the phenotype b.

Incomplete dominance
This is when the dominant allele is not completely dominant over the recessive allele. This means both the alleles have a degree of phenotypic expression in the hybrids. In this case the functional product formed is a little different or is intermediate between the product produced by to the dominant allele and the recessive allele.

For example: Mirabilis jalapa. The heterozygote of this plant produces flowers in the F1 generation of the colour pink in contrast to the red (dominant) and white (recessive) homozygotes.

Sex linkage
Genes on the sex chromosomes are said to be sex linked. In the XY sex determination system of mammals, the X chromosomes carry a full set of genes, but the Y chromosomes carry few genes. Alleles or genes which are not sex-linked are called autosomal.

Different alleles at a locus
There are three ways alleles at a locus may differ.p6 They are:
By origin. Alleles differ by origin if they come from the same locus on different chromosomes. Thus, for example, the two alleles at a particular locus in a diploid individual are always different by origin. They sit on different chromosomes.
By state. Alleles are different by state if they have different DNA sequences. This idea can be adjusted to need. For example, we may judge them as different only if the difference changes the amino acid sequence of a protein.
By descent. Alleles are different by descent if they do not share a common ancestor. Of course, all alleles have a common ancestor if one goes back far enough. What is meant is they share a fairly recent ancestor.

Two alleles different by descent may or may not be of different state. For example, one may carry a mutation, so making its DNA sequence different.

Terms introduced
 Allele
 Locus
 Homozygote
 Heterozygote
 Dominant
 Recessive
 Dominance (genetics)
 Punnett square
 Sex linkage
 Autosomal

Related pages
Allele frequency

References

Chromosomes

Allele


Violence is when someone attacks someone else, often to get them to do something they do not want to do by making them feel pain or fear. Violence can mean anything from one person hitting another to a war between many countries that causes millions of deaths. Different people may see different acts as violent. Laws are created often to control violence.

Types of violence
Violence can be:

 verbal: insults, name calling or anything that hurts another's feelings.
 physical: fighting, killing, or hurting another;
 sexual: when a person makes someone else subject to sexual actions they do not want; e.g. rape
 symbolic: acts done to show you are against a leader or group whose ideas one opposes;
 racial: when a victim of a violent act is chosen because of his or her race or nationality.

Related pages
 Nonviolence

References

Violence

Violence