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Saturday, April 30, 2022

Immigration to Europe

From Wikipedia, the free encyclopedia

Immigration to Europe has a long history, but increased substantially in the later 20th century. Western Europe countries, especially, saw high growth in immigration after World War II and many European nations today (particularly those of the EU-15) have sizeable immigrant populations, both of European and non-European origin. In contemporary globalization, migrations to Europe have accelerated in speed and scale. Over the last decades, there has been an increase in negative attitudes towards immigration, and many studies have emphasized marked differences in the strength of anti-immigrant attitudes among European countries.

Beginning in 2004, the European Union has granted EU citizens a freedom of movement and residence within the EU, and the term "immigrant" has since been used to refer to non-EU citizens, meaning that EU citizens are not to be defined as immigrants within the EU territory. The European Commission defines "immigration" as the action by which a person from a non-EU country establishes his or her usual residence in the territory of an EU country for a period that is or is expected to be at least twelve months. Between 2010 and 2013, around 1.4 million non-EU nationals, excluding asylum seekers and refugees, immigrated into the EU each year using regular means, with a slight decrease since 2010.

History

Historical migration into or within Europe has mostly taken the form of military invasion, but there have been exceptions; this concerns notably population movements within the Roman Empire under the Pax Romana; the Jewish diaspora in Europe was the result of the First Jewish–Roman War of AD 66–73.

With the collapse of the Roman Empire, migration was again mostly coupled with warlike invasion, not least during the so-called Migration period (Germanic), the Slavic migrations, the Hungarian conquest of the Carpathian Basin, the Islamic conquests and the Turkic expansion into Eastern Europe (Kipchaks, Tatars, Cumans). The Ottomans once again established a multi-ethnic imperial structure across Western Asia and Southeastern Europe, but Turkification in Southeastern Europe was due more to cultural assimilation than to mass immigration. In the late medieval period, the Romani people moved into Europe both via Anatolia and the Maghreb.

There were substantial population movements within Europe throughout the Early Modern period, mostly in the context of the Reformation and the European wars of religion, and again as a result of World War II.

From the late 15th century until the late 1960s and early 1970s, Greece, Ireland, Italy, Germany, Norway, Sweden, Denmark, Belgium, Portugal, Spain and the United Kingdom were primarily sources of emigration, sending large numbers of emigrants to the Americas, Australia, Siberia and Southern Africa. A number also went to other European countries (notably France, Switzerland, Germany and Belgium). As living standards in these countries have risen, the trend has reversed and they were a magnet for immigration (most notably from Morocco, Somalia, Egypt to Italy and Greece; from Morocco, Algeria and Latin America to Spain and Portugal; and from Ireland, India, Pakistan, Germany, the United States, Bangladesh, and Jamaica to the United Kingdom).

Migration within Europe after the 1985 Schengen Agreement

As a result of the Schengen Agreement, signed on June 14, 1985, there is free travel within part of Europe — known as the Schengen area — for all citizens and residents of all 27 member states; however, non-citizens may only do so for tourism purpose, and for up to three months. Moreover, EU citizens and their families have the right to live and work anywhere within the EU; citizens of non-EU or non-EEA states may obtain a Blue Card or long-term residency.

A large proportion of immigrants in western European states have come from former eastern bloc states in the 1990s, especially in Spain, Greece, Germany, Italy, Portugal and the United Kingdom. There are frequently specific migration patterns, with geography, language and culture playing a role. For example, there are large numbers of Poles who have moved to the United Kingdom and Ireland and Iceland, while Romanians and also Bulgarians have chosen Spain and Italy. With the earlier of the two recent enlargements of the EU, although most countries restricted free movement by nationals of the acceding countries, the United Kingdom did not restrict for the 2004 enlargement of the European Union and received Polish, Latvian and other citizens of the new EU states. Spain was not restricted for the 2007 enlargement of the European Union and received many Romanians and Bulgarians as well other citizens of the new EU states.

Many of these Polish immigrants to the UK have since returned to Poland, after the serious economic crisis in the UK. Nevertheless, free movement of EU nationals is now an important aspect of migration within the EU, since there are now 27 member states, and has resulted in serious political tensions between Italy and Romania, since Italy has expressed the intention of restricting free movement of EU nationals (contrary to Treaty obligations and the clear jurisprudence of the European Court of Justice).

Another migration trend has been that of Northern Europeans moving toward Southern Europe. Citizens from the European Union make up a growing proportion of immigrants in Spain, coming chiefly from the United Kingdom and Germany, but also from Italy, France, Portugal, The Netherlands, Belgium, etc. British authorities estimate that the population of British citizens living in Spain is much larger than Spanish official figures suggest, establishing them at about 1,000,000, with 800,000 being permanent residents. According to the Financial Times, Spain is the most favoured destination for Western Europeans considering to move from their own country and seek jobs elsewhere in the EU.

Immigration from outside Europe since the 1980s

While most immigrant populations in European countries are dominated by other Europeans, many immigrants and their descendants have ancestral origins outside the continent. For the former colonial powers France, Britain, the Netherlands, Belgium, Spain, and Portugal, most immigrants, and their descendants have ties to former colonies in Africa, the Americas, and Asia. In addition, Germany, Austria, Switzerland, the Netherlands, and Belgium recruited Turkish and Moroccan guest workers beginning in the 1960s, and many current immigrants in those countries today have ties to such recruitment programs.

Moroccan immigrants also began migrating substantially to Spain and Italy for work opportunities in the 1980s. In the Scandinavian countries of Sweden, Denmark, Norway, and Finland, the bulk of non-Western immigrants are refugees and asylum seekers from the Middle East, East Africa, and other regions of the world arriving since the 1980s and 1990s. Increasing globalization has brought a population of students, professionals, and workers from all over the world into major European cities, most notably London, Paris, and Frankfurt. The introduction of the EU Blue Card in May 2009 has further increased the number of skilled professional immigrants from outside of the continent.

Illegal immigration and asylum-seeking in Europe from outside the continent have been occurring since at least the 1990s. While the number of migrants was relatively small for years, it began to rise in 2013. In 2015, the number of asylum seekers arriving from outside Europe increased substantially during the European migrant crisis (see timeline). However, the EU-Turkey deal enacted in March 2016 dramatically reduced this number, and anti-immigrant measures starting in 2017 by the Italian government further cut illegal immigration from the Mediterranean route.

Some scholars claim that the increase in immigration flows from the 1980s is due to global inequalities between poor and rich countries. In 2017, approximately 825,000 persons acquired citizenship of a member state of the European Union, down from 995,000 in 2016. The largest groups were nationals of Morocco, Albania, India, Turkey and Pakistan. 2.4 million non-EU migrants entered the EU in 2017. In addition, cheaper transportation and more advanced technology have further aided migration.

Immigrants in the Nordic countries in 2000–2020

The Nordic countries have differed in their approach to immigration. While Norway and Sweden used to have generous immigration policies, Denmark and Finland had more restricted immigration. Although both Denmark and Finland have experienced a significant increase in their immigrant populations between 2000 and 2020 (6.8% points in Denmark and 5.0% in Finland), Norway (11.9%) and Sweden (11.0%) have seen far greater relative increases.

The table below shows the percentage of the total population in the Nordic countries that are either (1) immigrants or (2) children of two immigrant parents:

First and second generation immigrants
Nr Country 2000 2010 2015 2016 2017 2020
1  Sweden  14.5% 19.1% 21.5% 22.2% 23.2% 25.5%
2  Norway  6.3% 11.4% 15.6% 16.3% 16.8% 18.2%
3  Iceland  3.2% 8.9% 10.0% 10.8% 12.0% 15.6%
4  Denmark  7.1% 9.8% 11.6% 12.3% 12.9% 13.9%
5  Finland  2.9% 4.4% 6.2% 6.6% 7.0% 7.9%

Denmark

For decades, Danish immigration and integration policy were built upon the assumption that with the right kind of help, immigrants and their descendants will eventually tend to the same levels of education and employment as Danes. This assumption was proved by a 2019 study by the Danish Immigration Service and the Ministry of Education, while the second generation non-Western immigrants do better than the first generation, the third generation of immigrants with non-Western background do even better education and employment wise than the second generation. One of the reasons was that second-generation immigrants from non-Western countries marry someone from their country of origin and so Danish is not spoken at home which disadvantages children in school. Thereby the process of integration has to start from the beginning for each generation.

Norway

In January 2015 the "immigrant population" in Norway consisted of approximately 805,000 people, including 669,000 foreign-born and 136,000 born in Norway to two immigrant parents. This corresponds to 15.6% of the total population. The cities with the highest share of immigrants are Oslo (32%) and Drammen (27%). The six largest immigrant groups in Norway are Poles, Swedes, Somalis, Lithuanians, Pakistanis and Iraqis.

In the years since 1970, the largest increase in the immigrant population has come from countries in Asia (including Turkey), Africa and South America, increasing from about 3500 in 1970 to about 300,000 in 2011. In the same period, the immigrant population from other Nordic countries and Western Europe has increased modestly from around 42,000 to around 130,000.

Sweden

Immigrants (red) and emigrants (blue), Sweden 1850-2007

In 2014 the "immigrant population" in Sweden consisted of approximately 2.09 million people, including 1.60 million foreign-born and 489,000 born in Sweden to two immigrant parents. This corresponds to 21.5% of the total population.

Of the major cities Malmö has the largest immigrant population, estimated to be 41.7% in 2014. However, the smaller municipalities Botkyrka (56.2%), Haparanda (55.5%) and Södertälje (49.4%) all have a higher share of immigrants. In the Swedish capital Stockholm 31.1% (in 2014) of the population are either foreign-born or born in Sweden by two foreign-born parents.

In 2014 127,000 people immigrated to Sweden, while 51,000 left the country. Net immigration was 76,000.

Sweden has been transformed from a nation of emigration ending after World War I to a nation of immigration from World War II onwards. In 2009, Sweden had the fourth largest number of asylum applications in the EU and the largest number per capita after Cyprus and Malta. Immigrants in Sweden are mostly concentrated in the urban areas of Svealand and Götaland and the five largest foreign born populations in Sweden come from Finland, Yugoslavia, Iraq, Poland and Iran.

Finland

Immigration has been a major source of population growth and cultural change throughout much of the history of Finland. The economic, social, and political aspects of immigration have caused controversy regarding ethnicity, economic benefits, jobs for non-immigrants, settlement patterns, impact on upward social mobility, crime, and voting behavior.

At the end of 2017, there were 372,802 foreign born people residing in Finland, which corresponds to 6.8% of the population, while there are 384,123 people with a foreign background, corresponding to 7.0% of the population. Proportionally speaking, Finland has had one of the fastest increases in its foreign-born population between 2000 and 2010 in all of Europe. The majority of immigrants in Finland settle in the Helsinki area, although Tampere, Turku and Kuopio have had their share of immigrants in recent years.

France

As of 2008, the French national institute of statistics (INSEE) estimated that 5.3 million foreign-born immigrants and 6.5 million direct descendants of immigrants (born in France with at least one immigrant parent) lived in France. This represents a total of 11.8 million, or 19% of the population. In terms of origin, about 5.5 million are European, four million Maghrebi, one million Sub-Saharan African, and 400,000 Turkish. Among the 5.3 million foreign-born immigrants, 38% are from Europe, 30% from Maghreb, 12.5% from Sub-Saharan Africa, 14.2% from Asia and 5.3% from America and Oceania. The most significant countries of origin as of 2008 were Algeria (713,000), Morocco (653,000), Portugal (580,000), Italy (317,000), Spain (257,000), Turkey (238,000) and Tunisia (234,000). However, immigration from Asia (especially China, as well as the former French colonies of Vietnam, Cambodia and Laos), and from Sub-Saharan Africa (Senegal, Mali, Nigeria and others), is gaining in importance.

The region with the largest proportion of immigrants is the Île-de-France (Greater Paris), where 40% of immigrants live. Other important regions are Rhône-Alpes (Lyon) and Provence-Alpes-Côte d’Azur (Marseille).

Among the 802,000 newborns in metropolitan France in 2010, 27.3% had at least one foreign-born parent and about one quarter (23.9%) had at least one parent born outside Europe. Including grandparents; almost 40% of newborns in France between 2006 and 2008 had at least one foreign-born grandparent. (11% were born in another European country, 16% in Maghreb, and 12% in another region of the world.)

United Kingdom

London has become multiethnic as a result of immigration.

In 2014 the number of people who became naturalised British citizens rose to a record 140,795 - a 12% increase from the previous year, and a dramatic increase since 2009. Most new citizens came from Asia (40%) or Africa (32%); the largest three countries of origin were India, Pakistan and Bangladesh with Indians making the largest group. In 2005, an estimated 565,000 migrants arrived to live in the United Kingdom for at least a year, primarily from Asia and Africa, while 380,000 people emigrated from the country for a year or more, chiefly to Australia, Spain and the United States.

In 2014 the net increase was 318,000: immigration was 641,000, up from 526,000 in 2013, while the number of people emigrating (for more than 12 months) was 323,000.

Italy

The total immigrant population of the country is now of 5 million and 73 thousand, about 8.3 percent of the population (2014). However, over 6 million people residing in Italy have an immigration background. Since the expansion of the European Union, the most recent wave of migration has been from surrounding European nations, particularly Eastern Europe, and increasingly Asia, replacing North Africa as the major immigration area. Some 1,200,000 Romanians are officially registered as living in Italy, replacing Albanians (500,000) and Moroccans (520,000) as the largest ethnic minority group. Others immigrants from Central-Eastern Europe are Ukrainians (230,000), Polish (110,000), Moldovans (150,000), Macedonians (100,000), Serbs (110,000), Bulgarians (54,000) Germany (41,000), Bosnians (40,000), Russians (39,600), Croatians (25,000), Slovaks (9,000), Hungarians (8,600). Other major countries of origin are China (300,000), Philippines (180,000), India (150,000), Bangladesh (120,000), Egypt (110,000), Peru (105,000), Tunisia (105,000), Sri Lanka (100.000), Pakistan (100,000), Ecuador (90,000) and Nigeria (80,000). In addition, around 1 million people live in Italy illegally. (As of 2014, the distribution of foreign born population is largely uneven in Italy: 84.9% of immigrants live in the northern and central parts of the country (the most economically developed areas), while only 15.1% live in the southern half of the peninsula.)

Spain

Caravan protesting European closed borders policies in Pamplona

Since 2000, Spain has absorbed around six million immigrants, adding 12% to its population. The total immigrant population of the country now exceeds 5,730,677 (12.2% of the total population). According to residence permit data for 2011, more than 710,000 were Moroccan, another 410,000 were Ecuadorian, 300,000 were Colombian, 230,000 were Bolivian and 150,000 were Chinese; from the EU around 800,000 were Romanian, 370,000 (though estimates place the true figure significantly higher, ranging from 700,000 to more than 1,000,000) were British, 190,000 were German, 170,000 were Italian and 160,000 were Bulgarian. A 2005 regularisation programme increased the legal immigrant population by 700,000 people that year. By world regions, in 2006 there were around 2,300,000 from the EU-27, 1,600,000 from South America, 1,000,000 from Africa, 300,000 from Asia, 200,000 from Central America & Caribbean, 200,000 from the rest of Europe, while 50,000 from North America and 3,000 from the rest of the world.

Portugal

Portugal, long a country of emigration, has now become a country of net immigration, from both its former colonies and other sources. By the end of 2003, legal immigrants represented about 4% of the population, and the largest communities were from Cape Verde, Brazil, Angola, Guinea-Bissau, the United Kingdom, Spain, France, China and Ukraine.

Slovenia

On 1 January 2011 there were almost 229,000 people (11.1%) living in Slovenia with foreign country of birth. At the end of March 2002 when data on the country of birth for total population were for the first and last time collected by a conventional (field) census, the number was almost 170,000 (8.6%). Immigration from abroad, mostly from republics of former Yugoslavia, was the deciding factor for demographic and socioeconomic development of Slovenia in the last fifty years. Also after independence of Slovenia the direction of migration flows between Slovenia and abroad did not change significantly. Migration topics remain closely connected with the territory of former Yugoslavia. Slovenia was and still is the destination country for numerous people from the territory of former Yugoslavia. The share of residents of Slovenia with countries of birth from the territory of former Yugoslavia among all foreign-born residents was 88.9% at the 2002 Census and on 1 January 2011 despite new migration flows from EU Member States and from non-European countries still 86.7%. 

Middle East migrants pass through Slovenia on their way to Germany, 22 October 2015

Other countries

Opposition

According to a Yougov poll in 2018, majorities in all seven polled countries were opposed to accepting more migrants: Germany (72%), Denmark (65%), Finland (64%), Sweden (60%), United Kingdom (58%), France (58%) and Norway (52%).

A February 2017 poll of 10 000 people in 10 European countries by Chatham House found on average a majority (55%) were opposed to further Muslim immigration, with opposition especially pronounced in a number of countries: Austria (65%), Poland (71%), Hungary (64%), France (61%) and Belgium (64%). Except for Poland, all of those had recently suffered jihadist terror attacks or been at the centre of a refugee crisis. Of those opposed to further Muslim immigration, 3/4 classify themselves as on the right of the political spectrum. Of those self-classifying as on the left of the political spectrum, 1/3 supported a halt.

Denmark

In Denmark, the parliamentary party most strongly associated with anti-immigration policies is the Danish People's Party.

According to a Gallup poll in 2017, two out of three (64%) wished for limiting immigration from Muslim countries which was an increase from 2015 (54%).

According to a 2018 Yougov poll, 65% of Danes opposed accepting more migrants into the country.

On August 14, 2020, the Ministry of Immigration and Integration in Denmark revealed that it denied 83 people Danish citizenship in the past two years because they have committed serious crimes.

Finland

According to a 2018 Yougov poll, 64% of Finns opposed accepting more migrants into the country.

France

In France, the National Front seeks to limit immigration. Major media, political parties, and a large share of the public believe that anti-immigration sentiment has increased since the country's riots of 2005.

According to a 2018 Yougov poll, 58% of the French opposed accepting more migrants into the country.

Germany

In Germany, the National Democratic Party and the Alternative for Germany oppose immigration.

In 2018, a poll by Pew Research found that a majority (58%) wanted fewer immigrants to be allowed into the country, 30% wanted to keep the current level and 10% wanted to increase immigration.

According to a 2018 Yougov poll, 72% of Germans opposed accepting more migrants into the country.

Greece

In February 2020, more than 10 000 individuals attempted to cross the border between Greece and Turkey after Turkish president Recep Tayyip Erdoğan opened its border to Europe, but they were blocked by Greek army and police forces. Hundreds of Greek soldiers and armed police resisted the trespassers and fired tear gas at them. Among those who attempted to cross were individuals from Africa, Iran and Afghanistan. Greece responded by refusing to accept asylum applications for a month.

In March 2020, migrants set fires and threw Molotov cocktail firebombs over to the Greek side in order to break down the border fence. Greek and European forces responded with tear gas and by trying to keep the fence intact. By 11 March, 348 people had been arrested and 44,353 cases of unlawful entry had been prevented.

Italy

Public anti-immigrant discourse started in Italy in 1985 by the Bettino Craxi government, which in a public speech drew a direct link between the high number of clandestine immigrants and some terrorist incidents. Public discourse by the media hold that the phenomenon of immigration is uncontrollable and of undefined proportions.

According to poll published by Corriere della Sera, one of two respondents (51%) approved closing Italy's ports to further boat migrants arriving via the Mediterranean, while 19% welcomed further boat migrants.

In 2018, a poll by Pew Research found that a majority (71%) wanted fewer immigrants to be allowed into the country, 18% wanted to keep the current level and 5% wanted to increase immigration.

Norway

In Norway, the only parliamentary party that seeks to limit immigration is the Progress Party. Minor Norwegian parties seeking to limit immigration are the Democrats in Norway, the Christian Unity Party, the Pensioners' Party and the Coastal Party.

According to a 2018 Yougov poll, 52% of Norwegians opposed accepting more migrants into the country.

Poland

A 2015 opinion poll conducted by the Centre for Public Opinion Research (CBOS) found that 14% thought that Poland should let asylum-seekers enter and settle in Poland, 58% thought Poland should let asylum-seekers stay in Poland until they can return to their home country, and 21% thought Poland should not accept asylum-seekers at all. Furthermore, 53% thought Poland should not accept asylum-seekers from the Middle East and North Africa, with only 33% thinking Poland should accept them.

Another opinion poll conducted by the same organisation found that 86% of Poles think that Poland does not need more immigrants, with only 7% thinking Poland needs more immigrants.

Despite above in year 2017, 683 000 immigrants from outside of EU arrived to Poland. 87.4% out of them immigrated for work. "Among the EU Member States, Poland issued the highest number (683 thousand) of first residence permits in 2017, followed by Germany (535 thousand) and the United Kingdom (517 thousand)." 

Sweden

In response to the high immigration of 2015, the anti-immigration party Sweden Democrats rose to 19.9% in the Statistics Sweden poll.

In late 2015, Sweden introduced temporary border checks on the Øresund Bridge between Denmark and Sweden and public transport operators were instructed to only let people with residence in Sweden board trains or buses. The measures reduced the number of asylum seekers from 163 000 in 2015 to 29 000 in 2016.

In 2018, a poll by Pew Research found that a small majority (52%) wanted fewer immigrants to be allowed into the country, 33% wanted to keep the current level and 14% wanted to increase immigration.

According to a 2018 Yougov poll, 60% of Swedes opposed accepting more migrants into the country.

In February 2020 finance minister Magdalena Andersson encouraged migrants to head for other countries than Sweden. Andersson stated in an interview that integration of immigrants in Sweden wasn't working since neither before nor after 2015 and that Sweden cannot accept more immigration than it is able to integrate.

Switzerland

During the 1990s under Christoph Blocher, the Swiss People's Party started to develop an increasingly eurosceptic and anti-immigration agenda. In 2014, they launched a popular initiative titled "Against mass immigration" that was narrowly accepted. They are currently the largest party in the National Council with 53 seats.

United Kingdom

Anti-immigration sentiment in the United Kingdom has historically focused on non-indigenous African, Afro-Caribbean and especially South Asian migrants, all of whom began to arrive from the Commonwealth of Nations in greater numbers following World War II. Since the fall of the Soviet Union and the enlargement of the European Union, the increased movement of people out of countries such as Poland, Romania and Lithuania has shifted much of this attention towards migrants from Eastern Europe. While working-class migrants tend to be the focus of anti-immigration sentiment, there is also some discontent about Russian, Chinese, Singaporean and Gulf Arab multimillionaires resident in the UK, particularly in London and South East England. These residents often invest in property and business, and are perceived as living extravagant "jet-set" lifestyles marked by conspicuous consumption while simultaneously taking advantage of tax loopholes connected to non-dom status.

Policies of reduced immigration, particularly from the European Union, are central to the manifestos of parties such as the UK Independence Party. Such policies have also been discussed by some members of the largest parties in Parliament, most significantly the Conservatives.

Statistics

By host country

Statistics for European Union 27 (post-Brexit)

Immigration and emigration between EU-27 countries and non-EU-27 countries. Source: Eurostat 2020
 
EU-27 data source Eurostat.
Country Refused entry illegally present Order to leave Returned outside the EU
EU 27 (2018) 454600
456700 145900
EU 27 (2019) 717600 627900 491200 142300
2018-2019 change (%) +58% +10% +8% -2.5%

2013 UN data

This is a list of European countries by immigrant population, based on the United Nations report Trends in International Migrant Stock: The 2013 Revision.

Country Number of immigrants Percentage of
total number of
immigrants
in the world
Immigrants as
percentage of
national population
 Russia 11,048,064 4.8 7.7
 Germany 9,845,244 4.3 11.9
 United Kingdom 7,824,131 3.4 12.4
 France 7,439,086 3.2 11.6
 Spain 5,891,208 2.8 9.6 (2016)
 Italy 5,721,457 2.5 9.4
 Ukraine 5,151,378 2.2 11.4
  Switzerland 2,335,059 1.0 28.9
 Netherlands 1,964,922 0.9 11.7
 Turkey 1,864,889 0.8 2.5
 Sweden 1,130,025 0.7 15.9
 Austria 1,333,807 0.6 15.7
 Belgium 1,159,801 0.5 10.4
 Belarus 1,085,396 0.5 11.6
 Greece 988,245 0.4 8.9
 Portugal 893,847 0.4 8.4
 Croatia 756,980 0.3 17.6
 Ireland 735,535 0.3 15.9
 Norway 694,508 0.3 13.8
 Poland 663,755 0.3 0.9
 Denmark 556,825 0.3 9.9
 Serbia 532,457 0.3 5.6
 Hungary 449,632 0.3 4.7
 Finland 446,434 0.3 8.1
 Czech Republic 439,116 0.2 4.0
 Moldova 391,508 0.2 11.2
 Azerbaijan 323,843 0.2 3.4
 Armenia 317,001 0.2 10.6
 Latvia 282,887 0.2 13.8
 Slovenia 233,293 0.2 11.3
 Luxembourg 229,409 0.1 43.3
 Estonia 209,984 0.1 16.4
 Cyprus 207,313 0.1 18.2
 Romania 198,839 0.1 0.9
 Georgia 189,893 0.1 4.4
 Lithuania 147,781 0.1 4.9
 North Macedonia 139,751 0.1 6.6
 Albania 96,798 0.1 3.1
 Bulgaria 84,101 0.1 1.2
 Andorra 45,086 0.1 56.9
 Isle of Man 44,688 0.1 52.0
 Iceland 34,377 0.1 10.7
 Monaco 24,299 0.1 64.2
 Bosnia and Herzegovina 23,197 0.1 0.6
 Liechtenstein 12,208 0.1 33.1
 Gibraltar 9,662 0.1 33.0
 San Marino 4,399 0.1 15.4
  Vatican City 799 0.1 100.0

2010 data for European Union 28

In 2010, 47.3 million people lived in the EU, who were born outside their resident country. This corresponds to 9.4% of the total EU population. Of these, 31.4 million (6.3%) were born outside the EU and 16.0 million (3.2%) were born in another EU member state. The largest absolute numbers of people born outside the EU were in Germany (6.4 million), France (5.1 million), the United Kingdom (4.7 million), Spain (4.1 million), Italy (3.2 million), and The Netherlands (1.4 million).

State Total population (millions) Total Foreign-born (millions) % Born in other EU state (millions) % Born in a non-EU state (millions) %
 Germany 81.802 9.812 12.0 3.396 4.2 6.415 7.8
 France 64.716 7.196 11.1 2.118 3.3 5.078 7.8
 United Kingdom 62.008 7.012 11.3 2.245 3.6 4.767 7.7
 Spain 46.000 6.422 14.0 2.328 5.1 4.094 8.9
 Italy 61.000 4.798 8.5 1.592 2.6 3.205 5.3
 Netherlands 16.575 1.832 11.1 0.428 2.6 1.404 8.5
 Greece 11.305 0.960 9.6 0.320 2.3 0.640 6.3
 Ireland 3.758 0.766 20.0 0.555 14.8 0.211 5.6
 Sweden 9.340 1.337 14.3 0.477 5.1 0.859 9.2
 Austria 8.367 1.276 15.2 0.512 6.1 0.764 9.1
 Belgium 10.666 1.380 12.9 0.695 6.5 0.685 6.4
 Portugal 10.637 0.793 7.5 0.191 1.8 0.602 5.7
 Denmark 5.534 0.500 9.0 0.152 2.8 0.348 6.3
 Slovenia 2.050 0.228 11.1 0.021 1.8 0.207 9.3
EU 28 501.098 47.348 9.4 15.980 3.2 31.368 6.3

2005 UN data

According to the United Nations report World Population Policies 2005, European countries that have the highest net foreign populations are:

Country Population Percentage
 Russia 12,080,000 8.5
 Germany 10,144,000 12.3
 Ukraine 6,833,000 14.7
 France 6,471,000 10.2
 United Kingdom 5,408,000 9
 Italy 5,000,000 8.2
 Spain 4,790,000 10.8
  Switzerland 1,660,000 23
 Netherlands 1,638,000 10
 Austria 1,234,000 15

The European countries with the highest proportion or percentage of non-native residents are small nations or microstates. Andorra is the country in Europe with the highest percentage of immigrants, 77% of the country's 82,000 inhabitants. Monaco is the second with the highest percentage of immigrants, they make up 70% of the total population of 32,000; and Luxembourg is the third, immigrants are 37% of the total of 480,000; in Liechtenstein they are 35% of the 34,000 people; and in San Marino they comprise 32% of the country's population of 29,000.

Countries in which immigrants form between 25% and 10% of the population are: Switzerland (23%), Latvia (19%), Estonia (15%), Austria (15%), Croatia (15%), Ukraine (14.7%), Cyprus (14.3%), Ireland (14%), Moldova (13%), Germany (12.3%), Sweden (12.3%), Belarus (12%), Slovenia (11.1%), Spain (10.8%, 12.2% in 2010), France (10.2%), and the Netherlands (10%).[116] The United Kingdom (9%), Greece (8.6%), Russia (8.5%), Finland (8.1%), Iceland (7.6%), Norway (7.4%), Portugal (7.2%), Denmark (7.1%), Belgium (6.9%) and the Czech Republic (6.7%), each have a proportion of immigrants between 10% and 5% of the total population.

2006 data

Eurostat data reported in 2006 that some EU member states as receiving "large-scale" immigration. The EU in 2005 had an overall net gain from international migration of 1.8 million people, which accounted for almost 85% of Europe's total population growth that year. In 2004, a total of 140,033 people immigrated to France. Of them, 90,250 were from Africa and 13,710 from elsewhere in Europe. In 2005, the total number of immigrants fell slightly, to 135,890.

By origin

In 2019

In the European union, in 2019, 706 400 persons acquired citizenship, the main nation of origin for citizenship grant were by decreasing number: Morocco, Albania, the United Kingdom, Syria and Turkey.

the largest groups were Moroccans (66 800, or 9.5 %), followed by Albanians (41 700, or 5.9 %), Britons (29 800, or 4.2 %), Syrian (29 100, or 4.1 %) and Turks (28 600, or 4.0 %). The majority of Moroccans acquired citizenship of Spain (37 %), Italy (24 %) or France (24 %), while the majority of Albanians received Italian citizenship (62 %). Almost half of the Britons received German citizenship (46 %) and more than half of the Syrians received Swedish citizenship (69 %). The majority of Turks acquired German citizenship (57 %)

— eurostat

Previous years

This is a breakdown by major area of origin of the 72.4 million migrants residing in Europe (out of a population of 742 million) at mid-2013, based on the United Nations report Trends in International Migrant Stock: The 2013 Revision.

Area of origin Number of immigrants
to Europe (millions)
Percentage of total
number of immigrants
to Europe
Africa 8.9 12
Asia 18.6 27
Europe 37.8 52
Latin America and the Caribbean 4.5 6
Northern America 0.9 1
Oceania 0.3 0.4
Various 1.3 2
TOTAL 72.4 100

Approximate populations of non-European origin in Europe (about 20 - 30+ millions, or 3 - 4% (depending on the definition of non-European origin), out of a total population of approx. 831 million):

  • Black Africans (including Afro-Caribbeans and others by descent): approx. 9 to 10 million in the European Union and around 12.5 in Europe as a whole. Between 4 and 5 million Sub-Saharan and Afro-Caribbeans live in France but also 2.5 million in the United Kingdom, Italy, Germany, Spain, Belgium, the Netherlands and Portugal. (in Spain and Portugal Afro-Caribbean and Afro-Latin American are included in Latin Americans)
  • Turks (including Turks from Turkey and Northern Cyprus): approx. 9 million (this estimate does not include the 10 million Turks within the European portion of Turkey); of whom 3 to over 7 million in Germany but also the rest in France and the Netherlands with over 2 million Turks in France and Turks in the Netherlands, Austria, the United Kingdom, Belgium, Sweden, Switzerland, Denmark, Italy, Bulgaria, Macedonia, Greece, Romania, Finland, Serbia and Norway. (see Turks in Europe)
  • Arabs (including North African and Middle Eastern Arabs): approx. 6 to 7 million Arabs live in France but also Spain with 1.6 to 1.8 million Arabs, 1.2 million Arabs in Germany, the United Kingdom, Italy, Greece, Sweden, the Netherlands, Denmark, Belgium, Norway, Switzerland, Finland and Russia. (see Arabs in Europe) Many Arabs in Europe are Lebanese and Syrian.
  • Indians: approx. 2.5 million; 1.9 million mostly in the United Kingdom but also 473,520 in France including the overseas territories, 240,000 in the Netherlands, 203,052 in Italy, 185,085 in Germany, Ireland and Portugal.
  • Pakistanis: approx. 1.1 million in the United Kingdom, but also 120,000 in France, 118,181 in Italy, Spain, and Norway.
  • Bengali: approx. 600,000 mostly in United Kingdom, but also 85,000 in Italy, 35,000 in France, Spain, Sweden, Finland and Greece.
  • Latin Americans (includes Afro-Latin Americans, Afro-Caribbeans, Native Americans, White Latin Americans, miscegenation, etc.): approx. 5.0 million; mostly in Spain (c. 2.9 million) but also 1.3 million in France, 354,180 in Italy, +100,000 in Portugal, 245,000 in the United Kingdom and some in Germany.
  • Armenians: approx. 2 million; mostly in Russia but also 800,000 in France, Ukraine, Greece, Bulgaria, Spain, Germany, Poland, the United Kingdom and Belgium.
  • Berbers: approx. 2 million live in France but also Italy, the Netherlands, Belgium and Spain.
  • Kurds: approx. 2 million; mostly in Germany, France, Sweden, Russia, the Netherlands, Belgium and the United Kingdom.
  • Chinese: approx. 1 million; 600,000-700,000 of them live in France, 433,000 live in the United Kingdom, Russia, Italy, Spain, Germany and the Netherlands.
  • Vietnamese: approx. 800,000; mostly in France, Germany, the United Kingdom, Poland, Norway, the Netherlands, Finland, Sweden, Denmark and Russia.
  • Filipinos: approx. 600,000; mostly in the United Kingdom, France, Italy, Spain, Germany, the Netherlands, Sweden, Austria and Ireland.
  • Iranians: approx. 250,000; mostly in Germany, Sweden, the United Kingdom, Russia, the Netherlands, France, Austria, Norway, Spain and Denmark.
  • Somalis: approx. 200,000; mostly in the United Kingdom, Sweden, the Netherlands, Norway, Germany, Finland, Denmark and Italy.
  • Assyrians/Chaldeans/Syriacs: approx. 200,000; mostly in Sweden, Germany, Russia, France and The Netherlands.

Irregular border crossings

The EU Border and Coast Guard Agency (Frontex) uses the terms "illegal" and "irregular" border crossings for crossings of an EU external border but not at an official border-crossing point. These include people rescued at sea. Because many migrants cross more than one external EU border (for instance when traveling through the Balkans from Greece to Hungary), the total number of irregular EU external border crossings is often higher than the number of irregular migrants arriving in the EU in a year. News media sometimes misrepresent these figures as given by Frontex.

Frontex tracks and publishes data on numbers of crossings along the main six routes twice a year. The following table summarises the number of "irregular crossings" of the European Union's various external borders. Note that the figures do not add up to the total number of people coming into the EU illegally in a given year, since many migrants are counted twice (for instance, once when entering Greece and a second time upon entering Hungary).

Studies

Gallup has published a study estimating potential migrants in 2010. The study estimated that 700 million adults worldwide would prefer to migrate to another country. Potential migrants were asked for their country of preference if they were given free choice.

The total number of potential migrants to the European Union is estimated at 200 million, comparable to the number for North America (USA and Canada). In addition, an estimated 40 million potential migrants within the EU desire to move to another country within the EU, giving the EU the highest intra-regional potential migration rate.

The study estimates that from 2015 to 2017, there were about 750 million potential migrants. One in five potential migrants (21%), or about 158 million adults worldwide name the U.S. as their desired future residence. Canada, Germany, France, Australia and the United Kingdom each appeal to more than 30 million adults. Apart from the United States, the top desired target countries were:Canada (47 million), Germany (42 million), France (36 million), Australia (36 million) and the United Kingdom (34 million).

The study also compared the number of potential migrants to their desired destination's population, resulting in a Net Migration Index expressing potential population growth. This list is headed by Singapore, which would experience population growth by +219%. Among European countries, Switzerland would experience the highest growth, by +150%, followed by Sweden (+78%), Spain (+74%), Ireland (+66%), the United Kingdom (+62%) and France (+60%). The European countries with highest potential population loss are Kosovo and North Macedonia, with -28% each.

Computational science

From Wikipedia, the free encyclopedia

Computational science, also known as scientific computing or scientific computation (SC), is a field in mathematics that uses advanced computing capabilities to understand and solve complex problems. It is an area of science that spans many disciplines, but at its core, it involves the development of models and simulations to understand natural systems.

In practical use, it is typically the application of computer simulation and other forms of computation from numerical analysis and theoretical computer science to solve problems in various scientific disciplines. The field is different from theory and laboratory experiments, which are the traditional forms of science and engineering. The scientific computing approach is to gain understanding through the analysis of mathematical models implemented on computers. Scientists and engineers develop computer programs and application software that model systems being studied and run these programs with various sets of input parameters. The essence of computational science is the application of numerical algorithms and computational mathematics. In some cases, these models require massive amounts of calculations (usually floating-point) and are often executed on supercomputers or distributed computing platforms.

The computational scientist

Ways to study a system

The term computational scientist is used to describe someone skilled in scientific computing. Such a person is usually a scientist, an engineer, or an applied mathematician who applies high-performance computing in different ways to advance the state-of-the-art in their respective applied disciplines in physics, chemistry, or engineering.

Computational science is now commonly considered a third mode of science, complementing and adding to experimentation/observation and theory (see image on the right). Here, one defines a system as a potential source of data, an experiment as a process of extracting data from a system by exerting it through its inputs and a model (M) for a system (S) and an experiment (E) as anything to which E can be applied in order to answer questions about S. A computational scientist should be capable of:

  • recognizing complex problems
  • adequately conceptualizing the system containing these problems
  • designing a framework of algorithms suitable for studying this system: the simulation
  • choosing a suitable computing infrastructure (parallel computing/grid computing/supercomputers)
  • hereby, maximizing the computational power of the simulation
  • assessing to what level the output of the simulation resembles the systems: the model is validated
  • adjusting the conceptualization of the system accordingly
  • repeat the cycle until a suitable level of validation is obtained: the computational scientist trusts that the simulation generates adequately realistic results for the system under the studied conditions

Substantial effort in computational sciences has been devoted to developing algorithms, efficient implementation in programming languages, and validating computational results. A collection of problems and solutions in computational science can be found in Steeb, Hardy, Hardy, and Stoop (2004).

Philosophers of science addressed the question to what degree computational science qualifies as science, among them Humphreys and Gelfert. They address the general question of epistemology: how does gain insight from such computational science approaches? Tolk uses these insights to show the epistemological constraints of computer-based simulation research. As computational science uses mathematical models representing the underlying theory in executable form, in essence, they apply modeling (theory building) and simulation (implementation and execution). While simulation and computational science are our most sophisticated way to express our knowledge and understanding, they also come with all constraints and limits already known for computational solutions.

Applications of computational science

Problem domains for computational science/scientific computing include:

Predictive computational science

Predictive computational science is a scientific discipline concerned with the formulation, calibration, numerical solution, and validation of mathematical models designed to predict specific aspects of physical events, given initial and boundary conditions, and a set of characterizing parameters and associated uncertainties. In typical cases, the predictive statement is formulated in terms of probabilities. For example, given a mechanical component and a periodic loading condition, “the probability is (say) 90% that the number of cycles at failure (Nf) will be in the interval N1<Nf<N2”.

Urban complex systems

In 2018, over half the world's population lives in cities. By 2050, the United Nations estimates, 68% of the world's population will be urban. This urban growth is focused in the urban populations of developing countries where city dwellers will more than double, increasing from 2.5 billion in 2009 to almost 5.2 billion in 2050. Cities are massively complex systems created by humans, made up of humans, and governed by humans. Trying to predict, understand and somehow shape the development of cities in the future requires complex thinking and computational models and simulations to help mitigate challenges and possible disasters. The focus of research in urban complex systems is, through modeling and simulation, to build a greater understanding of city dynamics and help prepare for the coming urbanization.

Computational finance

In financial markets, huge volumes of interdependent assets are traded by a large number of interacting market participants in different locations and time zones. Their behavior is of unprecedented complexity and the characterization and measurement of the risk inherent to this highly diverse set of instruments is typically based on complicated mathematical and computational models. Solving these models exactly in closed form, even at a single instrument level, is typically not possible, and therefore we have to look for efficient numerical algorithms. This has become even more urgent and complex recently, as the credit crisis has clearly demonstrated the role of cascading effects going from single instruments through portfolios of single institutions to even the interconnected trading network. Understanding this requires a multi-scale and holistic approach where interdependent risk factors such as market, credit, and liquidity risk are modeled simultaneously and at different interconnected scales.

Computational biology

Exciting new developments in biotechnology are now revolutionizing biology and biomedical research. Examples of these techniques are high-throughput sequencing, high-throughput quantitative PCR, intra-cellular imaging, in-situ hybridization of gene expression, three-dimensional imaging techniques like Light Sheet Fluorescence Microscopy, and Optical Projection (micro)-Computer Tomography. Given the massive amounts of complicated data that is generated by these techniques, their meaningful interpretation, and even their storage, form major challenges calling for new approaches. Going beyond current bioinformatics approaches, computational biology needs to develop new methods to discover meaningful patterns in these large data sets. Model-based reconstruction of gene networks can be used to organize the gene expression data in a systematic way and to guide future data collection. A major challenge here is to understand how gene regulation is controlling fundamental biological processes like biomineralization and embryogenesis. The sub-processes like gene regulation, organic molecules interacting with the mineral deposition process, cellular processes, physiology, and other processes at the tissue and environmental levels are linked. Rather than being directed by a central control mechanism, biomineralization and embryogenesis can be viewed as an emergent behavior resulting from a complex system in which several sub-processes on very different temporal and spatial scales (ranging from nanometer and nanoseconds to meters and years) are connected into a multi-scale system. One of the few available options to understand such systems is by developing a multi-scale model of the system.

Complex systems theory

Using information theory, non-equilibrium dynamics, and explicit simulations, computational systems theory tries to uncover the true nature of complex adaptive systems.

Computational science in engineering

Computational science and engineering (CSE) is a relatively new discipline that deals with the development and application of computational models and simulations, often coupled with high-performance computing, to solve complex physical problems arising in engineering analysis and design (computational engineering) as well as natural phenomena (computational science). CSE has been described as the "third mode of discovery" (next to theory and experimentation). In many fields, computer simulation is integral and therefore essential to business and research. Computer simulation provides the capability to enter fields that are either inaccessible to traditional experimentation or where carrying out traditional empirical inquiries is prohibitively expensive. CSE should neither be confused with pure computer science, nor with computer engineering, although a wide domain in the former is used in CSE (e.g., certain algorithms, data structures, parallel programming, high-performance computing), and some problems in the latter can be modeled and solved with CSE methods (as an application area).

Methods and algorithms

Algorithms and mathematical methods used in computational science are varied. Commonly applied methods include:

Historically and today, Fortran remains popular for most applications of scientific computing.Other programming languages and computer algebra systems commonly used for the more mathematical aspects of scientific computing applications include GNU Octave, Haskell, Julia, Maple, Mathematica, MATLAB, Python (with third-party SciPy library), Perl (with third-party PDL library), R, Scilab, and TK Solver. The more computationally intensive aspects of scientific computing will often use some variation of C or Fortran and optimized algebra libraries such as BLAS or LAPACK. In addition, parallel computing is heavily used in scientific computing to find solutions of large problems in a reasonable amount of time. In this framework, the problem is either divided over many cores on a single CPU node (such as with OpenMP), divided over many CPU nodes networked together (such as with MPI), or is run on one or more GPUs (typically using either CUDA or OpenCL).

Computational science application programs often model real-world changing conditions, such as weather, airflow around a plane, automobile body distortions in a crash, the motion of stars in a galaxy, an explosive device, etc. Such programs might create a 'logical mesh' in computer memory where each item corresponds to an area in space and contains information about that space relevant to the model. For example, in weather models, each item might be a square kilometer; with land elevation, current wind direction, humidity, temperature, pressure, etc. The program would calculate the likely next state based on the current state, in simulated time steps, solving differential equations that describe how the system operates, and then repeat the process to calculate the next state.

Conferences and journals

In 2001, the International Conference on Computational Science (ICCS) was first organized. Since then, it has been organized yearly. ICCS is an A-rank conference in CORE classification.

The Journal of Computational Science published its first issue in May 2010. The Journal of Open Research Software was launched in 2012. The ReScience C initiative, which is dedicated to replicating computational results, was started on GitHub in 2015.

Education

At some institutions, a specialization in scientific computation can be earned as a "minor" within another program (which may be at varying levels). However, there are increasingly many bachelor's, master's, and doctoral programs in computational science. The joint degree program master program computational science at the University of Amsterdam and the Vrije Universiteit in computational science was first offered in 2004. In this program, students:

  • learn to build computational models from real-life observations;
  • develop skills in turning these models into computational structures and in performing large-scale simulations;
  • learn theories that will give a firm basis for the analysis of complex systems;
  • learn to analyze the results of simulations in a virtual laboratory using advanced numerical algorithms.

George Mason University was one of the early pioneers first offering a multidisciplinary doctorate Ph.D. program in Computational Sciences and Informatics in 1992 that focused on a number of specialty areas, including bioinformatics, computational chemistry, earth systems, and global changes, computational mathematics, computational physics, space sciences, and computational statistics.[citation needed]

The School of Computational and Integrative Sciences, Jawaharlal Nehru University (erstwhile School of Information Technology) also offers a vibrant master's science program for computational science with two specialties: Computational Biology and Complex Systems.

Related fields

Electronic oscillator

From Wikipedia, the free encyclopedia
 

An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.

Oscillators are often characterized by the frequency of their output signal:

  • A low-frequency oscillator (LFO) is an electronic oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
  • An audio oscillator produces frequencies in the audio range, about 16 Hz to 20 kHz.
  • An RF oscillator produces signals in the radio frequency (RF) range of about 100 kHz to 100 GHz.

In AC power supplies, an oscillator that produces AC power from a DC supply is usually called an inverter. Before the advent of diode-based rectifiers, an electromechanical device that similarly converted AC power to DC was called a converter, though the term is now used more commonly to refer to DC-DC buck converters.

There are two main types of electronic oscillator – the linear or harmonic oscillator and the nonlinear or relaxation oscillator.

Crystal oscillators are ubiquitous in modern electronics and produce frequencies from 32 kHz to over 150 MHz, with 32 kHz crystals commonplace in time keeping and the higher frequencies commonplace in clock generation and RF applications.

1 MHz electronic oscillator circuit which uses the resonant properties of an internal quartz crystal to control the frequency. Provides the clock signal for digital devices such as computers.

Harmonic oscillators

Block diagram of a feedback linear oscillator; an amplifier A with its output vo fed back into its input vf through a filter, β(jω).

The harmonic, or linear, oscillator produces a sinusoidal output. There are two types:

Feedback oscillator

The most common form of linear oscillator is an electronic amplifier such as a transistor or operational amplifier connected in a feedback loop with its output fed back into its input through a frequency selective electronic filter to provide positive feedback. When the power supply to the amplifier is switched on initially, electronic noise in the circuit provides a non-zero signal to get oscillations started. The noise travels around the loop and is amplified and filtered until very quickly it converges on a sine wave at a single frequency.

Feedback oscillator circuits can be classified according to the type of frequency selective filter they use in the feedback loop:

  • In an RC oscillator circuit, the filter is a network of resistors and capacitors. RC oscillators are mostly used to generate lower frequencies, for example in the audio range. Common types of RC oscillator circuits are the phase shift oscillator and the Wien bridge oscillator. LR oscillators, using inductor and resistor filters also exist, however they are much less common due to the required size of an inductor to achieve a value appropriate for use at lower frequencies.

Two common LC oscillator circuits, the Hartley and Colpitts oscillators
  • In a crystal oscillator circuit the filter is a piezoelectric crystal (commonly a quartz crystal). The crystal mechanically vibrates as a resonator, and its frequency of vibration determines the oscillation frequency. Crystals have a very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers and quartz clocks. Crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the tuned circuit; the Pierce oscillator circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30 MHz or below. Other types of resonators, dielectric resonators and surface acoustic wave (SAW) devices, are used to control higher frequency oscillators, up into the microwave range. For example, SAW oscillators are used to generate the radio signal in cell phones.

Negative-resistance oscillator

(left) Typical block diagram of a negative resistance oscillator. In some types the negative resistance device is connected in parallel with the resonant circuit. (right) A negative-resistance microwave oscillator consisting of a Gunn diode in a cavity resonator. The negative resistance of the diode excites microwave oscillations in the cavity, which radiate out the aperture into a waveguide.

In addition to the feedback oscillators described above, which use two-port amplifying active elements such as transistors and operational amplifiers, linear oscillators can also be built using one-port (two terminal) devices with negative resistance, such as magnetron tubes, tunnel diodes, IMPATT diodes and Gunn diodes. Negative-resistance oscillators are usually used at high frequencies in the microwave range and above, since at these frequencies feedback oscillators perform poorly due to excessive phase shift in the feedback path.

In negative-resistance oscillators, a resonant circuit, such as an LC circuit, crystal, or cavity resonator, is connected across a device with negative differential resistance, and a DC bias voltage is applied to supply energy. A resonant circuit by itself is "almost" an oscillator; it can store energy in the form of electronic oscillations if excited, but because it has electrical resistance and other losses the oscillations are damped and decay to zero. The negative resistance of the active device cancels the (positive) internal loss resistance in the resonator, in effect creating a resonator with no damping, which generates spontaneous continuous oscillations at its resonant frequency.

The negative-resistance oscillator model is not limited to one-port devices like diodes; feedback oscillator circuits with two-port amplifying devices such as transistors and tubes also have negative resistance. At high frequencies, three terminal devices such as transistors and FETs are also used in negative resistance oscillators. At high frequencies these devices do not need a feedback loop, but with certain loads applied to one port can become unstable at the other port and show negative resistance due to internal feedback. The negative resistance port is connected to a tuned circuit or resonant cavity, causing them to oscillate. High-frequency oscillators in general are designed using negative-resistance techniques.

Some of the many harmonic oscillator circuits are listed below:

Active devices used in oscillators and approximate maximum frequencies
Device Frequency
Triode vacuum tube ~1 GHz
Bipolar transistor (BJT) ~20 GHz
Heterojunction bipolar transistor (HBT) ~50 GHz
Metal–semiconductor field-effect transistor (MESFET) ~100 GHz
Gunn diode, fundamental mode ~100 GHz
Magnetron tube ~100 GHz
High electron mobility transistor (HEMT) ~200 GHz
Klystron tube ~200 GHz
Gunn diode, harmonic mode ~200 GHz
IMPATT diode ~300 GHz
Gyrotron tube ~600 GHz

Relaxation oscillator

A nonlinear or relaxation oscillator produces a non-sinusoidal output, such as a square, sawtooth or triangle wave. It consists of an energy-storing element (a capacitor or, more rarely, an inductor) and a nonlinear switching device (a latch, Schmitt trigger, or negative-resistance element) connected in a feedback loop. The switching device periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform.

Square-wave relaxation oscillators are used to provide the clock signal for sequential logic circuits such as timers and counters, although crystal oscillators are often preferred for their greater stability. Triangle-wave or sawtooth oscillators are used in the timebase circuits that generate the horizontal deflection signals for cathode ray tubes in analogue oscilloscopes and television sets. They are also used in voltage-controlled oscillators (VCOs), inverters and switching power supplies, dual-slope analog to digital converters (ADCs), and in function generators to generate square and triangle waves for testing equipment. In general, relaxation oscillators are used at lower frequencies and have poorer frequency stability than linear oscillators.

Ring oscillators are built of a ring of active delay stages. Generally the ring has an odd number of inverting stages, so that there is no single stable state for the internal ring voltages. Instead, a single transition propagates endlessly around the ring.

Some of the more common relaxation oscillator circuits are listed below:

Voltage-controlled oscillator (VCO)

An oscillator can be designed so that the oscillation frequency can be varied over some range by an input voltage or current. These voltage controlled oscillators are widely used in phase-locked loops, in which the oscillator's frequency can be locked to the frequency of another oscillator. These are ubiquitous in modern communications circuits, used in filters, modulators, demodulators, and forming the basis of frequency synthesizer circuits which are used to tune radios and televisions.

Radio frequency VCOs are usually made by adding a varactor diode to the tuned circuit or resonator in an oscillator circuit. Changing the DC voltage across the varactor changes its capacitance, which changes the resonant frequency of the tuned circuit. Voltage controlled relaxation oscillators can be constructed by charging and discharging the energy storage capacitor with a voltage controlled current source. Increasing the input voltage increases the rate of charging the capacitor, decreasing the time between switching events.

History

The first practical oscillators were based on electric arcs, which were used for lighting in the 19th century. The current through an arc light is unstable due to its negative resistance, and often breaks into spontaneous oscillations, causing the arc to make hissing, humming or howling sounds which had been noticed by Humphry Davy in 1821, Benjamin Silliman in 1822, Auguste Arthur de la Rive in 1846, and David Edward Hughes in 1878. Ernst Lecher in 1888 showed that the current through an electric arc could be oscillatory. An oscillator was built by Elihu Thomson in 1892 by placing an LC tuned circuit in parallel with an electric arc and included a magnetic blowout. Independently, in the same year, George Francis FitzGerald realized that if the damping resistance in a resonant circuit could be made zero or negative, the circuit would produce oscillations, and, unsuccessfully, tried to build a negative resistance oscillator with a dynamo, what would now be called a parametric oscillator. The arc oscillator was rediscovered and popularized by William Duddell in 1900. Duddell, a student at London Technical College, was investigating the hissing arc effect. He attached an LC circuit (tuned circuit) to the electrodes of an arc lamp, and the negative resistance of the arc excited oscillation in the tuned circuit. Some of the energy was radiated as sound waves by the arc, producing a musical tone. Duddell demonstrated his oscillator before the London Institute of Electrical Engineers by sequentially connecting different tuned circuits across the arc to play the national anthem "God Save the Queen". Duddell's "singing arc" did not generate frequencies above the audio range. In 1902 Danish physicists Valdemar Poulsen and P. O. Pederson were able to increase the frequency produced into the radio range by operating the arc in a hydrogen atmosphere with a magnetic field, inventing the Poulsen arc radio transmitter, the first continuous wave radio transmitter, which was used through the 1920s.

A 120 MHz oscillator from 1938 using a parallel rod transmission line resonator (Lecher line). Transmission lines are widely used for UHF oscillators.

The vacuum-tube feedback oscillator was invented around 1912, when it was discovered that feedback ("regeneration") in the recently invented audion vacuum tube could produce oscillations. At least six researchers independently made this discovery, although not all of them can be said to have a role in the invention of the oscillator. In the summer of 1912, Edwin Armstrong observed oscillations in audion radio receiver circuits and went on to use positive feedback in his invention of the regenerative receiver. Austrian Alexander Meissner independently discovered positive feedback and invented oscillators in March 1913. Irving Langmuir at General Electric observed feedback in 1913. Fritz Lowenstein may have preceded the others with a crude oscillator in late 1911. In Britain, H. J. Round patented amplifying and oscillating circuits in 1913. In August 1912, Lee De Forest, the inventor of the audion, had also observed oscillations in his amplifiers, but he didn't understand the significance and tried to eliminate it until he read Armstrong's patents in 1914, which he promptly challenged. Armstrong and De Forest fought a protracted legal battle over the rights to the "regenerative" oscillator circuit which has been called "the most complicated patent litigation in the history of radio". De Forest ultimately won before the Supreme Court in 1934 on technical grounds, but most sources regard Armstrong's claim as the stronger one.

The first and most widely used relaxation oscillator circuit, the astable multivibrator, was invented in 1917 by French engineers Henri Abraham and Eugene Bloch. They called their cross-coupled, dual-vacuum-tube circuit a multivibrateur, because the square-wave signal it produced was rich in harmonics, compared to the sinusoidal signal of other vacuum-tube oscillators.

Vacuum-tube feedback oscillators became the basis of radio transmission by 1920. However, the triode vacuum tube oscillator performed poorly above 300 MHz because of interelectrode capacitance. To reach higher frequencies, new "transit time" (velocity modulation) vacuum tubes were developed, in which electrons traveled in "bunches" through the tube. The first of these was the Barkhausen–Kurz oscillator (1920), the first tube to produce power in the UHF range. The most important and widely used were the klystron (R. and S. Varian, 1937) and the cavity magnetron (J. Randall and H. Boot, 1940).

Mathematical conditions for feedback oscillations, now called the Barkhausen criterion, were derived by Heinrich Georg Barkhausen in 1921. The first analysis of a nonlinear electronic oscillator model, the Van der Pol oscillator, was done by Balthasar van der Pol in 1927. He showed that the stability of the oscillations (limit cycles) in actual oscillators was due to the nonlinearity of the amplifying device. He originated the term "relaxation oscillation" and was first to distinguish between linear and relaxation oscillators. Further advances in mathematical analysis of oscillation were made by Hendrik Wade Bode and Harry Nyquist in the 1930s. In 1969 K. Kurokawa derived necessary and sufficient conditions for oscillation in negative-resistance circuits, which form the basis of modern microwave oscillator design.

Representation of a Lie group

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Representation_of_a_Lie_group...