Overview.

Etymology.

The first recorded use of the term "libertarian" was in 1789, when William Belsham wrote about libertarianism in the context of metaphysics. As early as 1796, libertarian came to mean an advocate or defender of liberty, especially in the political and social spheres, when the London Packet printed on 12 February the following: "Lately marched out of the Prison at Bristol, 450 of the French Libertarians". It was again used in a political sense in 1802 in a short piece critiquing a poem by "the author of Gebir" and has since been used with this meaning.  The use of the term "libertarian" to describe a new set of political positions has been traced to the French cognate "libertaire", coined in a letter French libertarian communist Joseph Déjacque wrote to mutualist Pierre-Joseph Proudhon in 1857. Déjacque also used the term for his anarchist publication "Le Libertaire, Journal du mouvement social" ("Libertarian: Journal of Social Movement") which was printed from 9 June 1858 to 4 February 1861 in New York City. Sébastien Faure, another French libertarian communist, began publishing a new "Le Libertaire" in the mid-1890s while France's Third Republic enacted

Definition.

Although libertarianism originated as a form of left-wing politics, the development in the mid-20th century of modern libertarianism in the United States led several authors and political scientists to use two or more categorizations to distinguish libertarian views on the nature of property and capital, usually along left–right or socialist–capitalist lines, Unlike right-libertarians, who reject the label due to its association with conservatism and right-wing politics, calling themselves simply "libertarians", proponents of free-market anti-capitalism in the United States consciously label themselves as "left-libertarians" and see themselves as being part of

Philosophy.

All libertarians begin with a conception of personal autonomy from which they argue in favor of civil liberties and a reduction or elimination of the state. People described as being left-libertarian or right-libertarian generally tend to call themselves simply libertarians and refer to their philosophy as libertarianism. As a result, some political scientists and writers classify the forms of libertarianism into two or more groups to distinguish libertarian views on the nature of property and capital. In the United States, proponents of free-market anti-capitalism consciously label themselves as left-libertarians and see themselves as being part of a broad libertarian left.  Left-libertarianism encompasses those libertarian beliefs that claim the Earth's natural resources belong to everyone in an egalitarian manner, either unowned or owned collectively. Contemporary left-libertarians such as Hillel Steiner, Peter Vallentyne, Philippe Van Parijs, Michael Otsuka and David Ellerman believe the appropriation of land must leave "enough and as good" for others or be taxed by society to compensate for the exclusionary effects of private property. Socialist libertarians such as social and individualist anarchists, libertarian Marxists, council communists, Luxemburgists and De Leonists promote usufruct and socialist economic theories, including

Typology.

In the United States, "libertarian" is a typology used to describe a political position that advocates small government and is culturally liberal and fiscally conservative in a two-dimensional political spectrum such as the libertarian-inspired Nolan Chart, where the other major typologies are "conservative", "liberal" and "populist". "Libertarians" support legalization of victimless crimes such as the use of marijuana while opposing high levels of taxation and government spending on health, welfare and education. "Libertarian" was adopted in the United States, where "liberal" had become associated with a version that supports extensive government

History.

Liberalism.

Although elements of libertarianism can be traced as far back as the ancient Chinese philosopher Lao-Tzu and the higher-law concepts of the Greeks and the Israelites, it was in 17th-century England that libertarian ideas began to take modern form in the writings of the Levellers and John Locke. In the middle of that century, opponents of royal power began to be called Whigs, or sometimes simply Opposition or Country, as opposed to Court writers.  During the 18th century and Age of Enlightenment, liberal ideas flourished in Europe and North America. Libertarians of various schools were influenced by liberal ideas.

Anarchism.

Modern anarchism sprang from the secular or religious thought of the Enlightenment, particularly Jean-Jacques Rousseau's arguments for the moral centrality of freedom.  As part of the political turmoil of the 1790s in the wake of the French Revolution, William Godwin developed the first expression of modern anarchist thought. According to Peter Kropotkin, Godwin was "the first to formulate the political and economical conceptions of anarchism, even though he did not give that name to the ideas developed in his work" while Godwin attached his anarchist ideas to an early Edmund Burke.  Godwin is generally regarded as the founder of the school of thought known as philosophical anarchism. He argued in "Political Justice" (1793) that government has an inherently malevolent influence on society and that it perpetuates dependency and ignorance. He thought that the spread of the use of reason to the masses would eventually cause government to wither away as an unnecessary force. Although

Libertarian socialism.

"Libertarian communism", "libertarian Marxism" and "libertarian socialism" are all terms which activists with a variety of perspectives have applied to their views. Anarchist communist philosopher Joseph Déjacque was the first person to describe himself as a "libertarian". Unlike mutualist anarchist philosopher Pierre-Joseph Proudhon, he argued that "it is not the product of his or her labor that the worker has a right to, but to the satisfaction of his or her needs, whatever may be their nature". According to anarchist historian Max Nettlau, the first use of the term "libertarian communism" was in November 1880, when a French anarchist congress employed it to more clearly identify its doctrines. The French anarchist journalist Sébastien Faure started the weekly paper "Le Libertaire" ("The Libertarian") in 1895.  Individualist anarchism represents several traditions of thought within the anarchist movement that emphasize the individual and their will over any kinds of external determinants such as groups, society, traditions, and ideological systems. An influential form of individualist anarchism called egoism or egoist anarchism was expounded by one of the earliest and best-known proponents of individualist anarchism, the German Max Stirner. Stirner's "The Ego and Its Own", published in 1844, is a founding text of the philosophy. According to Stirner, the only limitation on the rights of the individual is their power to obtain what they desire, without regard for God, state or morality. Stirner advocated self-assertion and foresaw unions of egoists, non-systematic associations continually renewed by all parties' support through an act of will, which Stirner proposed as a form of organisation in place of the state. Egoist anarchists argue that egoism will foster genuine and spontaneous union between individuals. Egoism has inspired many interpretations of Stirner's philosophy. Stirner's philosophy was re-discovered and promoted by German philosophical anarchist and LGBT activist John Henry Mackay.

Individualist anarchism in the United States.

The indigenous anarchist tradition in the United States was largely individualist. In 1825, Josiah Warren became aware of the social system of utopian socialist Robert Owen and began to talk with others in Cincinnati about founding a communist colony. When this group failed to come to an agreement about the form and goals of their proposed community, Warren "sold his factory after only two years of operation, packed up his young family, and took his place as one of 900 or so Owenites who had decided to become part of the founding population of New Harmony, Indiana". Warren termed the phrase "cost the limit of price" and "proposed a system to pay people with certificates indicating how many hours of work they did. They could exchange the notes at local time stores for goods that took the same amount of time to produce". He put his theories to the test by establishing an experimental labor-for-labor store called the Cincinnati Time Store where trade was facilitated by labor notes. The store proved successful and operated for three years, after which it was closed so that Warren could pursue establishing colonies based on mutualism, including Utopia and Modern Times. After New Harmony failed, Warren shifted his "ideological loyalties" from socialism to anarchism "which was no great leap, given that Owen's socialism had been predicated on Godwin's anarchism". Warren is widely regarded as the first American anarchist and the four-page weekly paper "The Peaceful Revolutionist" he edited during 1833 was the first anarchist periodical published,

Georgism and geolibertarianism.

Henry George was an American political economist and journalist who advocated that all economic value derived from land, including natural resources, should belong equally to all members of society. Strongly opposed to feudalism and the privatisation of land, George created the philosophy of Georgism, or geoism, influential among many left-libertarians, including geolibertarians and geoanarchists. Much like the English Digger movement, who held all material possessions in common, George claimed that land and its financial properties belong to everyone, and that to hold land as private property would lead to immense inequalities, including authority from the private owners of such ground.  Prior to states assigning property owners slices of either once populated or uninhabited land, the world's earth was held in common. When all resources that

Modern libertarianism in the United States.

By around the start of the 20th century, the heyday of individualist anarchism had passed. H. L. Mencken and Albert Jay Nock were the first prominent figures in the United States to describe themselves as libertarians as they believed Franklin D. Roosevelt had co-opted the word liberal for his New Deal policies which they opposed and used libertarian to signify their allegiance to individualism. In 1914, Nock joined the staff of "The Nation" magazine which at the time was supportive of liberal capitalism. A lifelong admirer of Henry George, Nock went on to become co-editor of "The Freeman" from 1920 to 1924, a publication initially conceived as a vehicle for the single tax movement, financed by the wealthy wife of the magazine's other editor Francis Neilson. Critic H. L. Mencken wrote that "[h]is editorials during the three brief years of the "Freeman" set a mark that no other man of his trade has ever quite managed to reach. They were well-informed and sometimes even learned, but there was never the slightest trace of pedantry in them".  Executive Vice President of the Cato Institute David Boaz wrote: "In 1943, at one of the lowest points for liberty and humanity in history, three remarkable women published books that could be said to have given birth to the modern libertarian movement". Isabel Paterson's "The God of the Machine", Rose Wilder Lane's "The Discovery of Freedom" and Ayn Rand's "The Fountainhead" each promoted individualism and capitalism. None of the three used the term libertarianism to

Contemporary libertarianism.

Contemporary libertarian socialism.

A surge of popular interest in libertarian socialism occurred in Western nations during the 1960s and 1970s. Anarchism was influential in the counterculture of the 1960s and anarchists actively participated in the protests of 1968 which included students and workers' revolts. In 1968, the International of Anarchist Federations was founded in Carrara, Italy during an international anarchist conference held there in 1968 by the three existing European federations of France, the Italian and the Iberian Anarchist Federation as well as the Bulgarian Anarchist Federation

Contemporary libertarianism in the United States.

In the United States, polls (circa 2006) find that the views and voting habits of between 10% and 20%, or more, of voting age Americans may be classified as "fiscally conservative and socially liberal, or libertarian". This is based on pollsters and researchers defining libertarian views as fiscally conservative and socially liberal (based on the common United States meanings of the terms) and against government intervention in economic affairs and for expansion of personal freedoms. In a 2015 Gallup poll this figure had risen to

Contemporary libertarian organizations.

Current international anarchist federations which identify themselves as libertarian include the International of Anarchist Federations, the International Workers' Association and International Libertarian Solidarity. The largest organized anarchist movement today is in Spain, in the form of the Confederación General del Trabajo (CGT) and the CNT. CGT membership was estimated to be around 100,000 for 2003. Other active syndicalist movements include the Central Organisation of the Workers of Sweden and the Swedish Anarcho-syndicalist Youth Federation in Sweden; the Unione Sindacale Italiana in Italy; Workers Solidarity Alliance in the United States; and Solidarity Federation in the United Kingdom. The revolutionary industrial unionist Industrial Workers of the World claiming 2,000 paying members

Criticism.

Criticism of libertarianism includes ethical, economic, environmental, pragmatic and philosophical concerns, especially in relation to right-libertarianism, including the view that it has no explicit theory of liberty. It has been argued that "laissez-faire" capitalism does not necessarily produce the best or most efficient outcome, nor does its philosophy of individualism and policies of deregulation prevent the abuse of natural resources. Critics such as Corey Robin describe this type of libertarianism as fundamentally a reactionary conservative ideology united with more traditionalist conservative thought and goals by a desire to enforce hierarchical power and social relations.  Similarly, Nancy MacLean has argued that it is a radical right ideology that has stood against democracy. According to MacLean, libertarian-leaning Charles and David Koch have used anonymous, dark money campaign contributions, a network of libertarian institutes and lobbying for the appointment of libertarian, pro-business judges to United States federal and state courts to oppose taxes, public education, employee protection laws, environmental protection laws and the New Deal Social Security program.  Moral and pragmatic criticism of libertarianism also includes allegations of utopianism, tacit authoritarianism and vandalism towards feats of civilisation.

Allegation of utopianism.

Libertarian philosophies such as anarchism are evaluated as unfeasible or utopian by their critics, often in general and formal debate. European history professor Carl Landauer argued that anarchy is unrealistic and that government is a "lesser evil" than a society without "repressive force". He also argued that "ill intentions will cease

Government decentralization.

John Donahue argues that if political power were radically shifted to local authorities, parochial local interests would predominate at the expense of the whole and that this would exacerbate current problems with

Lack of real-world examples.

Michael Lind has observed that of the 195 countries in the world today, none have fully actualized a society as advocated by American libertarians:  Furthermore, Lind has

Tacit authoritarianism.

The anarchist tendency known as platformism has been

Libertarianism (from, meaning "freedom"), or libertarism (from, meaning "libertarian"), is a political philosophy and movement that upholds liberty as a core principle. Libertarians seek to maximize political freedom and autonomy, emphasizing freedom of choice, voluntary association and individual judgment. Libertarians share a skepticism of authority and state power, but they diverge on the scope of their opposition to existing economic and political systems. Various schools of libertarian thought offer a range of views regarding the legitimate functions of state and private power, often calling for the restriction or dissolution of coercive social institutions. Different categorizations have been used to distinguish various forms of libertarianism. This is done to distinguish libertarian views on the nature of property and capital, usually along left–right or socialist–capitalist lines.

自由意志主义(Libertarianism),又常被译为新古典自由主义、自由人主义、放任自由主义、自由意志论、自由至上主义、自由至上论,是一套把自由奉为核心原则的政治理念及运动,其主张把人的政治自由及自主权最大化,并强调选择自由、自由结社、个人判断的重要性。尽管大多自由意志主义者会对政治权威及国家公权力持怀疑态度,但他们对于该反对哪些既有经济及政治制度存有内部分歧。各个自由意志主义学派对于公权力及私权力的合法职能存有不同看法,不过他们往往会要求限制或废除具有强制性的社会制度。现时已有区分各个自由意志主义学派的大致分类,一般以特定思想对于财产和资本的看法,来把其于左-右(或社会主义-资本主义)连续体当中分类。


Regeneration.

In order for an injury to be healed by regeneration, the cell type that was destroyed must be able to replicate. Cells also need a collagen framework along which to grow. Alongside most cells there is either a basement membrane or a collagenous network made by fibroblasts that will guide the cells' growth. Since ischaemia and most toxins do not destroy collagen, it will continue to exist even when the cells around it are dead.

Example.

Acute tubular necrosis (ATN) in the kidney is a case in which cells heal completely by regeneration. ATN occurs when the epithelial cells that line the kidney are destroyed by either a lack of oxygen (such as in hypovolemic shock, when blood supply to the kidneys is dramatically reduced), or by toxins (such as some antibiotics, heavy metals or carbon tetrachloride).  Although many of these epithelial cells are dead, there is typically patchy necrosis, meaning that there are patches of epithelial cells still alive. In addition, the collagen framework of the tubules remains completely intact.  The existing epithelial cells can replicate, and, using the basement membrane as a guide, eventually bring the kidney back to normal. After regeneration is complete, the damage is undetectable, even microscopically.  Healing must happen by repair in the case of injury to cells that are unable to regenerate (e.g. neurons). Also, damage to the collagen network (e.g. by enzymes or physical destruction), or its total collapse (as can happen in an infarct) cause healing to take place by repair.

Genetics.

Many genes play a role in healing. For instance, in wound healing, P21 has been found to allow mammals to heal spontaneously. It even allows some mammals (like mice) to heal wounds without scars. The LIN28 gene also plays a role in wound healing. It is dormant in most mammals. Also, the proteins MG53 and TGF beta 1 play important roles in wound healing.

Wound healing.

In response to an incision or wound, a wound healing cascade is unleashed. This cascade takes place in four phases: clot formation, inflammation, proliferation, and maturation.

Clotting phase.

Healing of a wound begins with clot formation to stop bleeding and to reduce infection by bacteria, viruses and fungi. Clotting is followed by neutrophil invasion three to 24 hours after the wound has been incurred, with mitoses beginning in epithelial cells after 24 to 48 hours.

Inflammation phase.

In the inflammatory phase, macrophages and other phagocytic cells kill bacteria, debride damaged tissue and release chemical factors such as growth hormones that encourage fibroblasts, epithelial cells and endothelial cells which make new capillaries to migrate to the area and divide.

Proliferative phase.

In the proliferative phase, immature granulation tissue containing plump, active fibroblasts forms. Fibroblasts quickly produce abundant type III collagen, which fills the defect left by an open wound. Granulation tissue moves, as a wave, from the border of the injury towards the center.  As granulation tissue matures, the fibroblasts produce less collagen and become more spindly in appearance. They begin to produce the much stronger type I collagen. Some of the fibroblasts mature into myofibroblasts which contain the same type of actin found in smooth muscle, which enables them to contract and reduce the size of the wound.

Maturation phase.

During the maturation phase of wound healing, unnecessary vessels formed in granulation tissue are removed by apoptosis, and type III collagen is largely replaced by type I. Collagen which was originally disorganized is cross-linked and aligned along tension lines. This phase can last a year or longer. Ultimately a scar made of collagen, containing a small number of fibroblasts is left.

Tissue damaged by inflammation.

After inflammation has damaged tissue (when combatting bacterial infection for example) and pro-inflammatory eicosanoids have completed their function, healing proceeds in 4 phases.

Recall phase.

In the recall phase the adrenal glands increase production of cortisol which shuts down eicosanoid production and inflammation.

Resolution phase.

In the Resolution phase, pathogens and damaged tissue are removed by macrophages (white blood cells). Red blood cells are also removed from the damaged tissue by macrophages. Failure to remove all of the damaged cells and pathogens may retrigger inflammation. The two subsets of macrophage M1 & M2 plays a crucial role in this phase, M1 macrophage being a pro inflammatory while as M2 is a regenerative and the plasticity between the two subsets determine the tissue inflammation or repair.

Regeneration phase.

In the Regeneration phase, blood vessels are repaired and new cells form in the damaged site similar to the cells that were damaged and removed. Some cells such as neurons and muscle cells (especially in the heart) are slow to recover.

Repair phase.

In the Repair phase, new tissue is generated which requires a balance of anti-inflammatory and pro-inflammatory eicosanoids. Anti-inflammatory eicosanoids include lipoxins, epi-lipoxins, and resolvins, which cause release of growth hormones.

Healing is the process of the restoration of health from an unbalanced, diseased, damaged or unvitalized organism. The result of healing can be to cure the cause of a health challenge, but one can grow without being cured or heal without "a cure".

疗愈,是让患病或受伤的生物恢复健康的过程。生物在遭受到物理损伤或罹患疾病时,会使生物的细胞、组织、器官、生物系统无法发挥其原本的功能,疗愈可以使生物从这样的状态中恢复健康。在精神病学及心理学中,疗愈是指将对象从悲伤等负面情绪中脱离、或是使减缓、消除精神病对对象的影响。


History.

Archaeological evidence indicates that invasions have been frequent occurrences since prehistory. In antiquity, before radio communications and fast transportation, the only way for a military to ensure adequate reinforcements was to move armies as one massive force. This, by its very nature, led to the strategy of invasion. With invasion came cultural exchanges in government, religion, philosophy, and technology that shaped the development of much of the ancient world.  Before the days of package tours and cut-price airlines, military invasions functioned as a standard major form of proto-tourism - bringing large numbers of foreign visitors into new environments, with the consequential social, cultural and economic impacts on indigenous populations and on the invaders.

Defenses.

States with potentially hostile neighbors typically adopt defensive measures to delay or forestall an invasion. In addition to utilizing geographical barriers such as rivers, marshes, or rugged terrain, these measures have historically included fortifications. Such a defense can be intended to actively prevent invading forces from entering the country by means of an extended and well-defended barrier; the Great Wall of China, Hadrian's Wall, and the Danewerk are famous examples. Such barriers have also included trench lines and, in more modern times, minefields, cameras, and motion-sensitive sensors. However, these barriers can require a large military force to provide the defense, as well as maintain the equipment and positions, which can impose a great economic burden on the country. Some of those same techniques can also be turned against defenders, used to keep them from escape or resupply. During Operation Starvation, Allied forces used airdropped mines to severely disrupt Japanese logistical operations within their own borders. Alternatively, the fortifications can be built up at a series of sites, such as castles or forts placed near a border. These structures are designed to delay an invasion long enough for the defending nation to mobilize an army of a size sufficient for defense or, in some cases, counter-invasion—such as, for example, the Maginot Line. Forts can be positioned so that the garrisons can interdict the supply lines of the invaders. The theory behind these spaced forts is that the invader cannot afford to bypass these defenses, and so must lay siege to the structures.  In modern times, the notion of constructing large-scale static defenses to combat land-based threats has largely become obsolete. The use of precision air campaigns and large-scale mechanization have made lighter, more mobile defenses desirable to military planners. The obsolescence of large fortifications was displayed by the failure of the Maginot Line in the beginning of World War Two. Nations defending against modern invasions normally use large population centers such as cities or towns as defensive points. The invader must capture these points to destroy the defender's ability to wage war. The defender uses mobile armored and infantry divisions to protect these points, but the defenders are still very mobile and can normally retreat. A prominent example of the use of cities as fortifications can be seen in the Iraqi Army's stands in the 2003 invasion of Iraq at Baghdad, Tikrit, and Basra in the major combat in the Iraq War. A defender can also use these mobile assets to precipitate a counteroffensive like the Soviet Red Army at the Battle of Kursk or the Northern Alliance in Afghanistan.  However, static emplacements remain useful in both defense against naval attacks and defense against air attacks. Naval mines is still an inexpensive but effective way to defend ports and choke off supply lines. Large static air defense systems that combine antiaircraft guns with missile launchers are still the best way to defend against air attacks. Such systems were used effectively by the North Vietnamese around Hanoi. Also, the United States has invested considerable time and money into the construction of a National Missile Defense system, a static defense grid intended to intercept nuclear intercontinental ballistic missiles.  Island nations, such as the United Kingdom or Japan, and continental states with extensive coasts, such as the United States, have utilized a significant naval presence to forestall an invasion of their country, rather than fortifying their border areas. A successful naval defense, however, usually requires a preponderance of naval power and the ability to sustain and service that defense force.  In particularly large nations, the defending force may also retreat to facilitate a counterattack by drawing the invaders deeper into hostile territory. One effect of this tactic is that the invading force becomes too spread out, making supply difficult and making the lines more susceptible to attack. This tactic, although costly, helped the Soviets stop the German advance at Stalingrad. It can also cause the invading force to extend too far, allowing a pincer movement to cut them off from reinforcements. This was the cause of the British defeat at the Battle of Cowpens during the American Revolutionary War. Finally, sending too many reinforcements can leave too few defenders in the attackers' territory, allowing a counter-invasion from other areas, as happened in the Second Punic War.

Methods.

There are many different methods by which an invasion can take place, each method having arguments both in their favour and against. These include invasion by land, sea, or air, or any combination of these methods.

Invasion by land.

Invasion over land is the straightforward entry of armed forces into an area using existing land connections, usually crossing borders or otherwise defined zones, such as a demilitarized zone, overwhelming defensive emplacements and structures. Although this tactic often results in a quick victory, troop movements are relatively slow and subject to disruption by terrain and weather. Furthermore, it is hard to conceal plans for this method of invasion, as most geopolitical entities take defensive positions in areas that are most vulnerable to the methods mentioned above.  In modern warfare, invasion by land often takes place after, or sometimes during, attacks on the target by other means. Air strikes and cruise missiles launched from ships at sea are a common method of "softening" the target. Other, more subtle, preparations may involve secretly garnering popular support, assassinating potentially threatening political or military figures, and closing off supply lines where they cross into neighboring countries. In some cases, those other means of attack eliminate the need for ground assault; the 1945 atomic-bombing of Hiroshima and Nagasaki ultimately made it unnecessary for the Allies to invade the Japanese home islands with infantry troops. In cases such as this, while some ground troops are still needed to occupy the conquered territory, they are allowed to enter under the terms of a treaty and as such are no longer invaders. As unmanned, long-range combat evolves, the instances of basic overland invasion become fewer; often the conventional fighting is effectively over before the infantry arrives in the role of peacekeepers (see "Applications regarding non-state combatants" in this article).

Invasion by sea.

Invasion by sea is the use of a body of water to facilitate the entry of armed forces into an area, often a landmass adjoining the body of water or an island. This is generally used either in conjunction with another method of invasion, and especially before the invention of flight, for cases in which there is no other method to enter the territory in question. Arguments in favor of this method usually consist of the ability to perform a surprise attack from sea, or that naval defenses of the area in question are inadequate to repel such an attack. However, the large amount of specialized equipment, such as amphibious vehicles and the difficulty of establishing defenses—usually with a resulting high casualty count—in exchange for a relatively small gain, are often used as arguments against such an invasion method. Underwater hazards and a lack of good cover are very common problems during invasions from the sea. At the Battle of Tarawa, Marine landing craft became hung up on a coral reef and were shelled from the beach. Other landers were sunk before they could reach the shore, and the tanks they were carrying were stranded in the water. Most of the few survivors of the first wave ended up pinned down on the beach. The island was conquered but at a heavy cost, and the loss of life sparked mass protests from civilians in the United States.

Invasion by air.

Invasion by air is an invention of the 20th century and modern warfare. The idea involves sending military units into a territory by aircraft. The aircraft either land, allowing the military units to debark and attempt their objective, or the troops exit the aircraft while still in the air, using parachutes or similar devices to land in the territory being invaded. Many times air assaults have been used to pave the way for a ground- or sea-based invasion, by taking key positions deep behind enemy lines such as bridges and crossroads, but an entirely air-based invasion has never succeeded. Two immediate problems are resupply and reinforcement. A large airborne force cannot be adequately supplied without meeting up with ground forces; an airborne force too small simply places themselves into an immediate envelopment situation. Arguments in favor of this method generally relate to the ability to target specific areas that may not necessarily be easily accessible by land or sea, a greater chance of surprising the enemy and overwhelming defensive structures, and, in many cases, the need for a reduced number of forces due to the element of surprise. Arguments against this method typically involve capacity to perform such an invasion—such as the sheer number of planes that would be needed to carry a sufficient number of troops—and the need for a high level of intelligence in order for the invasion to be successful.  The closest examples to a true air invasion are the Battle of Crete, Operation Thursday (the Chindits second operation during the Burma Campaign) and Operation Market Garden. The latter was an assault on the German-occupied Netherlands conducted in September 1944. Nearly 35,000 men were dropped by parachute and glider into enemy territory in an attempt to capture bridges from the Germans and make way for the Allies' advance. However, even with such a massive force taking the Germans completely by surprise, the assault was a tactical failure and after 9 days of fighting the Allies managed only to escape back to their own lines, having sustained over 18,000 casualties. In the 21st century, as vast improvements are made in anti-aircraft defenses, it seems that the air invasion is a strategy whose time may never come.

Pacification.

Once political boundaries and military lines have been breached, pacification of the region is the final, and arguably the most important, goal of the invading force. After the defeat of the regular military, or when one is lacking, continued opposition to an invasion often comes from civilian or paramilitary resistance movements. Complete pacification of an occupied country can be difficult, and usually impossible, but popular support is vital to the success of any invasion.  Media propaganda such as leaflets, books, and radio broadcasts can be used to encourage resistance fighters to surrender and to dissuade others from joining their cause. Pacification, often referred to as "the winning of hearts and minds", reduces the desire for civilians to take up resistance. This may be accomplished through reeducation, allowing conquered citizens to participate in their government, or, especially in impoverished or besieged areas, simply by providing food, water, and shelter. Sometimes displays of military might are used; invading forces may assemble and parade through the streets of conquered towns, attempting to demonstrate the futility of any further fighting. These displays may also include public executions of enemy soldiers, resistance fighters, and other conspirators. Particularly in antiquity, the death or imprisonment of a popular leader was sometimes enough to bring about a quick surrender. However, this has often had the unintended effect of creating martyrs around which popular resistance can rally. An example of which was Sir William Wallace, who, centuries after his execution by the English, is still a symbol of Scottish nationalism.

Support.

Logistics.

Without a steady flow of supplies, an invading force will soon find itself retreating. Before his invasion of Greece, Xerxes I spent three years amassing supplies from all over Asia; Herodotus wrote that the Persian army was so large it "drank the rivers dry".  In most invasions, even in modern times, many fresh supplies are gathered from the invaded territories themselves. Before the laws of war, invaders often relied heavily on the supplies they would win by conquering towns along the way. During the Second Punic War, for example, Hannibal diverted his army to conquer cities simply to gather supplies; his strategy in crossing the Alps necessitated traveling with as few provisions as possible, expecting the Roman stores to sustain them when they had breached the border. The scorched earth tactics used in Russia forced Napoleon to withdraw his forces due to lack of food and shelter. Today, the Law of land warfare forbids looting and the confiscation of private property, but local supplies, particularly perishables, are still purchased when possible for use by occupying forces, and airplanes often use parachutes to drop supplies to besieged forces. Even as rules become stricter, the necessities of war become more numerous; in addition to food, shelter, and ammunition, today's militaries require fuel, batteries, spare mechanical parts, electronic equipment, and many other things. In the United States, the Defense Logistics Agency employs over 22,000 civilians with the sole task of logistics support, and 30,000 soldiers graduate from the U.S. Army Logistics Management College each year.

Communication.

Another consideration is the importance of leadership being able to communicate with the invasion force. In ancient times, this often meant that a king needed to lead his armies in person to be certain his commands were timely and followed, as in the case of Alexander the Great (356–323 BCE). At that time, the skills needed to lead troops in battle were as important as the skills needed to run a country during peacetime. When it was necessary for the king to be elsewhere, messengers would relay updates back to the rear, often on horseback or, in cases such as the Battle of Marathon (490 BCE), with swift runners.  When possible, sloops and cutters were used to relay information by sea. brought Britain the first news that Nelson had defeated the French forces at the Battle of Trafalgar in 1805.  The development of Morse Code, and later of voice communications by radio and satellite, have allowed even small units of skirmishers to remain in contact with a larger invasion force, to verify orders or to call for artillery support and air strikes. These communications were critical to the German blitzkrieg strategy, as infantry commanders relayed defensive positions to tanks and bombers.

Public relations.

In diplomatic, public-relations and propaganda terms, it may help an invader (or a potential invader) to have an invitation as an excuse to intervene with a view to "restoring order" or "righting wrongs". Dissident groups, fifth columns or official circles may conspire to "call in" foreign assistance. Cases include:  National foundation-legends can echo the theme of inviting foreign warriors to come and rule a people: note the traditional account in the "Tale of Bygone Years" of how Varangian invaders came establish long-term rule in Novgorod (and subsequently throughout Russia).

Applications regarding non-state combatants.

In the 20th and 21st centuries, questions arose regarding the effectiveness of the invasion strategy in neutralizing non-state combatants, a type of warfare sometimes referred to as "fourth generation warfare". In this case, one or more combatant groups are controlled not by a centralized state government but by independent leadership, and these groups may be made up of civilians, foreign agents, mercenaries, politicians, religious leaders, and members of the regular military. These groups act in smaller numbers, are not confined by borders, and do not necessarily depend on the direct support of the state. Groups such as these are not easily defeated by straightforward invasion, or even constant occupation; the country's regular army may be defeated, the government may be replaced, but asymmetric warfare on the part of these groups can be continued indefinitely. Because regular armed forces units do not have the flexibility and independence of small covert cells, many believe that the concept of a powerful occupying force actually creates a disadvantage.  An opposing theory holds that, in response to extremist ideology and unjust governments, an invasion can change the government and reeducate the people, making prolonged resistance unlikely and averting future violence. This theory acknowledges that these changes may take time—generations, in some cases—but holds that immediate benefits may still be won by reducing membership in, and choking the supply lines of, these covert cells. Proponents of the invasion strategy in such conflicts maintain the belief that a strong occupying force can still succeed in its goals on a tactical level, building upon numerous small victories, similar to a war of attrition.  Contemporary debate on this issue is still fresh; neither side can claim to know for certain which strategies will ultimately be effective in defeating non-state combatants. Opponents of the invasion strategy point to a lack of examples in which occupying or peacekeeping forces have met with conclusive success. They also cite continuing conflicts such as Northern Ireland, Israel, Chechnya, and Iraq, as well as examples which they claim ultimately proved to be failures, such as Lebanon, and Afghanistan. Supporters of the invasion strategy hold that it is too soon to call those situations failures, and that patience is needed to see the plan through. Some say that the invasions themselves have, in fact, been successful, but that political opponents and the international media skew the facts for sensationalism or political gain.

Outcomes.

The outcomes of an invasion may vary according to the objectives of both invaders and defenders, the success of the invasion and the defense, and the presence or absence of an agreed settlement between the warring parties. The most common outcome is the loss of territory, generally accompanied by a change in government and often the loss of direct control of that government by the losing faction. This sometimes results in the transformation of that country into a client state, often accompanied by requirements to pay reparations or tribute to the victor. In other cases the results of a successful invasion may simply be a return to the status quo; this can be seen in wars of attrition, when the destruction of personnel and supplies is the main strategic objective, or where a nation previously subdued and currently occupied by an aggressive third party is restored to control of its own affairs (i.e. Western Europe following the Normandy landings in 1944, or Kuwait following the defeat of Iraq in 1991). In some cases, the invasion may be strategically limited to a geographical area, which is carved into a separate state as with the Bangladesh Liberation War in 1971.

An invasion is a military offensive in which large numbers of combatants of one geopolitical entity aggressively enter territory owned by another such entity, generally with the objective of either conquering; liberating or re-establishing control or authority over a territory; forcing the partition of a country; altering the established government or gaining concessions from said government; or a combination thereof. An invasion can be the cause of a war, be a part of a larger strategy to end a war, or it can constitute an entire war in itself. Due to the large scale of the operations associated with invasions, they are usually strategic in planning and execution.

入侵(侵入、侵略)传统意义上是指一种军事行动,地缘政治实体的一方武装进入另一方控制的领土,通常带有领土征服的目的,或者改变原有政府。侵入可能引发战争,通常作为结束战争的战略的一部分,侵入的过程本身可以构成战争整体。入侵有很多方法,而进行每一种方法前都得经过大多数人的赞同。这包括海、陆、空的入侵或这三种方法的任何结合。


History.

Objective-C was created primarily by Brad Cox and Tom Love in the early 1980s at their company Productivity Products International.  Leading up to the creation of their company, both had been introduced to Smalltalk while at ITT Corporation's Programming Technology Center in 1981. The earliest work on Objective-C traces back to around that time. Cox was intrigued by problems of true reusability in software design and programming. He realized that a language like Smalltalk would be invaluable in building development environments for system developers at ITT. However, he and Tom Love also recognized that backward compatibility with C was critically important in ITT's telecom engineering milieu.  Cox began writing a pre-processor for C to add some of the abilities of Smalltalk. He soon had a working implementation of an object-oriented extension to the C language, which he called "OOPC" for Object-Oriented Pre-Compiler. Love was hired by Schlumberger Research in 1982 and had the opportunity to acquire the first commercial copy of Smalltalk-80, which further influenced the development of their brainchild. In order to demonstrate that real progress could be made, Cox showed that making interchangeable software components really needed only a few practical changes to existing tools. Specifically, they needed to support objects in a flexible manner, come supplied with a usable set of libraries, and allow for the code (and any resources needed by the code) to be bundled into one cross-platform format.  Love and Cox eventually formed PPI to commercialize their product, which coupled an Objective-C compiler with class libraries. In 1986, Cox published the main description of Objective-C in its original form in the book "Object-Oriented Programming, An Evolutionary Approach". Although he was careful to point out that there is more to the problem of reusability than just what Objective-C provides, the language often found itself compared feature for feature with other languages.

Popularization through NeXT.

In 1988, NeXT licensed Objective-C from StepStone (the new name of PPI, the owner of the Objective-C trademark) and extended the GCC compiler to support Objective-C. NeXT developed the AppKit and Foundation Kit libraries on which the NeXTSTEP user interface and Interface Builder were based. While the NeXT workstations failed to make a great impact in the marketplace, the tools were widely lauded in the industry. This led NeXT to drop hardware production and focus on software tools, selling NeXTSTEP (and OpenStep) as a platform for custom programming.  In order to circumvent the terms of the GPL, NeXT had originally intended to ship the Objective-C frontend separately, allowing the user to link it with

Apple development and Swift.

After acquiring NeXT in 1996, Apple Computer used OpenStep in its then-new operating system, Mac OS X. This included Objective-C, NeXT's Objective-C-based developer tool, Project Builder, and its interface design tool, Interface Builder,

Syntax.

Objective-C is a thin layer atop C and is a "strict superset" of C, meaning that it is possible to compile any C program with an Objective-C compiler and to freely include C language code within an Objective-C class.  Objective-C derives its object syntax from Smalltalk. All of the syntax for non-object-oriented operations (including primitive variables, pre-processing, expressions, function declarations, and function calls) are identical to those of C, while the syntax for object-oriented features is an implementation of Smalltalk-style messaging.

Messages.

The Objective-C model of object-oriented programming is based on message passing to object instances. In Objective-C one does not "call a method"; one "sends a message". This is unlike the Simula-style programming model used by C++. The difference between these two concepts is in how the code referenced by the method or message name is executed. In a Simula-style language, the method name is in most cases bound to a section of code in the target class by the compiler. In Smalltalk and Objective-C, the target of a message is resolved at runtime, with the receiving object itself interpreting the message. A method is identified by a "selector" or — a unique identifier for each message name, often just a -terminated string representing its name — and resolved to a C method pointer implementing it: an. A consequence of this is that the message-passing system has no type checking. The object to which the message is directed —

Interfaces and implementations.

Objective-C requires that the interface and implementation of a class be in separately declared code blocks. By convention, developers place the interface in a header file and the implementation in a code file. The header files, normally suffixed.h, are similar to C header files while the implementation (method) files, normally suffixed.m, can be very similar to C code files.

Interface.

This is analogous to class declarations as used in other object-oriented languages, such as C++ or Python.  The interface of a class is usually defined in a header file. A common convention is to name the header file after the name of the class, e.g. would contain the interface for the class.  An interface declaration takes the form:  @interface classname : superclassname { + classMethod1; + (return_type)classMethod2; + (return_type)classMethod3:(param1_type)param1_varName;  - (return_type)instanceMethod1With1Parameter:(param1_type)param1_varName; - (return_type)instanceMethod2With2Parameters:(param1_type)param1_varName param2_callName:(param2_type)param2_varName; @end In the above, plus signs denote class methods, or methods that can be called on the class itself (not on an instance), and minus signs denote instance methods, which can only be called on a particular

Implementation.

The interface only declares the class interface and not the methods themselves: the actual code is written in the implementation file. Implementation (method) files normally have the file extension codice_1, which originally signified "messages". @implementation classname + (return_type)classMethod - (return_type)instanceMethod @end Methods are written using their interface declarations. Comparing Objective-C and C: - (int)method:(int)i  int function (int i)  The syntax allows pseudo-naming of arguments.  - (void)changeColorToRed:(float)red green:(float)green blue:(float)blue  //Called like so: [myColor changeColorToRed:5.0 green:2.0 blue:6.0]; Internal representations of

Instantiation.

Once an Objective-C class is written, it can be instantiated. This is done by first allocating an uninitialized instance of the class (an object) and then by initializing it. An object is not fully functional until both steps have been completed. These steps should be accomplished with one line of code so

Notes.

Compilation is performed, for example, by:  One can experiment by leaving out the and lines and omitting in compilation. The program will still run. This means that it is possible to "mix-and-match" added categories if needed; if a category does not need to have some ability, it can simply not be compile in.

Posing.

Objective-C permits a class to wholly replace another class within a program. The replacing class is said to "pose as" the target class.  Class posing was declared deprecated with Mac OS X v10.5, and is unavailable in the 64-bit runtime. Similar functionality can be achieved by using method swizzling in categories, that swaps one method's

#import.

In the C language, the codice_3 pre-compile directive always causes a file's contents to be inserted into the

Linux Gcc Compilation.

// FILE: hello.m int main (int argc,

Other features.

Objective-C's features often allow for

Language variants.

Objective-C++.

Objective-C++ is a language variant accepted by the front-end to the GNU Compiler Collection and Clang, which can compile source files that use

Objective-C 2.0.

At the 2006 Worldwide Developers Conference, Apple announced the release of "Objective-C 2.0," a revision of the Objective-C language to include "modern garbage collection, syntax enhancements, runtime performance improvements, and 64-bit support". Mac OS X v10.5, released in October 2007, included an Objective-C 2.0 compiler. GCC 4.6 supports many new Objective-C features, such as declared and synthesized properties, dot syntax, fast enumeration, optional protocol methods, method/protocol/class attributes, class extensions, and a new GNU Objective-C runtime API.  The naming Objective-C 2.0 represents a break in the versioning system of the language, as the last Objective-C version for NeXT was "objc4". This project name was kept in the last release of legacy Objective-C runtime source code in Mac OS X Leopard (10.5).

Garbage collection.

Objective-C 2.0 provided an optional conservative, generational garbage collector. When run in backwards-compatible mode, the runtime turned reference counting operations such as "retain" and "release" into no-ops. All objects were subject to garbage collection when garbage collection was enabled. Regular C pointers could be qualified with "__strong" to also trigger the underlying write-barrier compiler intercepts and thus participate in garbage collection. A zero-ing weak subsystem was also provided

Properties.

Objective-C 2.0 introduces a new syntax to declare instance variables as properties, with optional attributes to configure the generation of accessor methods. Properties are, in a sense, public instance variables; that is, declaring an instance variable as a property provides external classes with access (possibly limited, e.g. read only) to that property. A property may be declared as "readonly", and may be provided with storage semantics such as codice_5, codice_6 or codice_7. By default, properties are considered codice_8, which results in a lock preventing multiple threads from accessing them at the same time. A property can be declared as codice_9, which removes this lock. @interface Person : NSObject {  @property(copy) NSString *name; @property(readonly) int age;  -(id)initWithAge:(int)age; @end Properties are implemented by way of the codice_10 keyword, which generates

Non-fragile instance variables.

Objective-C 2.0 provides non-fragile instance variables where supported by the runtime (i.e. when building code for 64-bit macOS, and all iOS). Under

Fast enumeration.

Instead of using an NSEnumerator object or indices to iterate through a collection, Objective-C 2.0 offers the fast enumeration syntax. In Objective-C 2.0, the following loops are functionally equivalent, but have different performance traits. // Using NSEnumerator NSEnumerator *enumerator = [thePeople objectEnumerator];

Class extensions.

A class extension has the same syntax as a category declaration with no category name, and the methods and properties declared in it are added directly to the main

Implications for Cocoa development.

All Objective-C applications developed for macOS that make use of the above improvements for Objective-C 2.0 are incompatible with all operating systems prior to 10.5 (Leopard). Since fast enumeration does not generate exactly the same binaries as standard enumeration, its use will cause an application to crash on Mac OS X version 10.4 or earlier.

Blocks.

Blocks is a nonstandard extension for Objective-C (and [[C (programming language)|C]] and [[C++]]) that uses special syntax to create [[Closure (programming)|closures]]. Blocks are only supported in [[Mac OS

Modern Objective-C.

Apple has added some additional features to Objective 2.0 over time. The additions only apply to the "Apple [[LLVM]] compiler", i.e. clang frontend of the language. Confusingly, the versioning used by Apple differs from that of the LLVM upstream; refer to for a translation to open-source LLVM version numbers.

Automatic Reference Counting.

Automatic Reference Counting (ARC) is a compile-time feature that eliminates the need for programmers to manually manage retain counts using codice_7 and codice_16. Unlike [[garbage collection (computer science)|garbage collection]], which occurs at run time, ARC eliminates the overhead of a

Literals.

NeXT and Apple Obj-C runtimes have long included a short-form way to create new strings, using the literal syntax codice_17, or drop to CoreFoundation constants codice_18 and codice_19 for codice_20 with Boolean values. Using this format saves the programmer from having to use the longer codice_21 or similar methods when doing certain operations.  When using Apple [[LLVM]] compiler 4.0 (XCode 4.4) or later, arrays, dictionaries, and numbers (codice_22, codice_23, codice_20 classes) can also be created using literal syntax instead of methods. (Apple LLVM compiler 4.0 translates to open source LLVM

Subscripting.

When using Apple [[LLVM]] compiler 4.0 or later, arrays and dictionaries (codice_22 and codice_23 classes) can be manipulated using subscripting. Subscripting can be used to retrieve values from indexes (array) or keys (dictionary), and with mutable objects, can also be used to set objects to indexes or keys. In code, subscripting is represented using brackets codice_27.  Example without subscripting: id object1 = [someArray objectAtIndex:0]; id object2 = [someDictionary objectForKey:@"key"]; [someMutableArray replaceObjectAtIndex:0 withObject:object3]; [someMutableDictionary setObject:object4 forKey:@"key"]; Example with subscripting: id object1 = someArray[0]; id object2 = someDictionary[@"key"]; someMutableArray[0] = object3; someMutableDictionary[@"key"] = object4;

"Modern" Objective-C syntax (1997).

After the purchase of NeXT by Apple, attempts were made to make the language more acceptable to programmers more familiar with [[Java (programming language)|Java]] than Smalltalk. One of these attempts was introducing what was dubbed "Modern Syntax" for

mulle-objc.

The mulle-objc project is another re-implementation of Objective-C. It supports [[GNU Compiler Collection|GCC]] or [[Clang]]/[[LLVM]]

Portable Object Compiler.

Besides the [[GNU Compiler Collection|GCC]]/[[NeXT]]/[[Apple Inc.|Apple]] implementation, which added several extensions to the original [[Stepstone]] implementation, another [[Free and open source software|free, open-source]] Objective-C implementation called the Portable Object Compiler also exists. The set of extensions implemented by the Portable Object Compiler differs from the GCC/NeXT/Apple implementation; in particular, it

GEOS Objective-C.

The [[GEOS (16-bit operating system)|PC GEOS]] system used a programming language known as GEOS Objective-C or

Clang.

The [[Clang]] compiler suite, part of the [[LLVM]] project, implements Objective-C and other languages. After GCC 4.3 (2008) switched to GPLv3, Apple abandoned it in favor of clang,

GNU, GNUstep, and WinObjC.

The GNU project has, for a long time, been interested in a platform to port NeXT and Obj-C programs to. The ChangeLog for the directory in GCC suggests that it existed before 1998 (GCC 2.95), and its README further points at a rewrite in 1993 (GCC 2.4).  The NeXT frontend source code was released since it was made as part of GCC, released [[GNU Public License]] which forces ones making derivative works to do so. Apple continued this tradition in releasing its fork of GCC up to 4.2.1, after which they abandoned the compiler. GCC maintainers took in the changes, but did not invest much in supporting newer features such as the Objective-C 2.0 language.  The GNUstep developers, interested in the new

Library use.

Objective-C today is often used in tandem with a fixed library of standard objects (often known as a "kit" or "framework"), such as [[Cocoa (API)|Cocoa]], [[GNUstep]] or [[ObjFW]]. These libraries often come with the operating system: the GNUstep libraries often come with [[Linux]]-based distributions and Cocoa comes with macOS. The programmer is not forced to inherit functionality from the existing base class (NSObject / OFObject). Objective-C allows for the declaration of new root classes that do not inherit any existing functionality. Originally, Objective-C-based programming environments typically offered an Object class as the base class from which almost all other classes inherited. With the introduction of OpenStep, NeXT created a new base class

Analysis of the language.

Objective-C implementations use a thin [[Run time system|runtime system]] written in C, which adds little to the size of the application. In contrast, most object-oriented systems at the time that it was created used large [[virtual machine]] runtimes. Programs written in Objective-C tend to be not much larger than the size of their code and that of the libraries (which generally do not need to be included in the software distribution), in contrast to Smalltalk systems where a large amount of memory was used just to open a window. Objective-C applications tend to be larger than similar C or C++ applications because Objective-C dynamic typing does not allow methods to be stripped or inlined. Since the programmer has such freedom to delegate, forward calls, build selectors on the fly, and pass them to the runtime system, the Objective-C compiler cannot assume it is safe to remove unused methods or to inline calls.  Likewise, the language can be implemented atop extant C compilers (in [[GNU Compiler Collection|GCC]], first as a preprocessor, then as a module) rather than as a new compiler. This allows Objective-C to leverage the huge existing collection of C code, libraries, tools, etc. Existing C libraries can be wrapped in Objective-C [[Adapter pattern|wrappers]] to provide an OO-style interface. In this aspect, it is similar to [[GObject]] library and [[Vala (programming language)|Vala]] language, which are widely used in development of [[GTK]] applications.  All of these practical changes lowered the [[Barriers to entry|barrier to entry]], likely the biggest problem for the widespread acceptance of Smalltalk in the 1980s.  A common criticism is that Objective-C does not have language support for [[namespaces]]. Instead, programmers are forced to add prefixes to their class names, which are traditionally shorter than namespace names and thus more prone to collisions. As of 2007, all macOS classes and functions in the [[Cocoa (software)|Cocoa]] programming environment are prefixed with "NS" (e.g. NSObject, NSButton) to identify them as belonging to the macOS or iOS core; the "NS" derives from the names of the classes as defined during the development of [[NeXTSTEP]].  Since Objective-C is a strict superset of C, it does not treat C primitive types as [[first-class object]]s.  Unlike [[C++]], Objective-C does not support [[operator overloading]]. Also unlike C++, Objective-C allows an object to directly inherit only from one class (forbidding [[multiple inheritance]]). However, in most cases, categories and protocols may be used as alternative ways to achieve the same results.  Because Objective-C uses dynamic runtime typing and because all method calls are function calls (or, in some cases, syscalls), many common performance optimizations cannot be applied to Objective-C methods (for example: inlining, constant propagation, interprocedural optimizations, and scalar replacement of aggregates). This limits the performance of Objective-C abstractions relative to similar abstractions in languages such as C++ where such optimizations are possible.

External links.

[[Category:Objective-C| ]] [[Category:C programming language family]] [[Category:Class-based programming languages]] [[Category:Dynamically typed programming languages]] [[Category:GNUstep]] [[Category:NeXT]] [[Category:Object-oriented programming languages]] [[Category:Programming languages created in 1986]]

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It was the main programming language supported by Apple for macOS, iOS, and their respective application programming interfaces (APIs), Cocoa and Cocoa Touch, until the introduction of Swift in 2014.

Objective-C是一种通用、高级、面向对象的编程语言。它扩展了标准的ANSI C编程语言,将Smalltalk式的消息传递机制加入到ANSI C中。目前主要支持的编译器有GCC和Clang(采用LLVM作为后端)。


Name.

One of the etymologies for the name Vättern is from "vatten", the Swedish word for water. This origin is, however, unclear and in dispute. It has also been suggested that the archaic term "vätter", meaning forest or lake spirits, is the origin of the lake's name.

Geography.

The lake's total surface area is about, with a drainage basin a little over double that, about. The deepest known point, located to the south of the island of Visingsö, is. The average depth is. The lake has a perimeter of about. The volume is. These numbers tend to be fixed, as the level of the lake is regulated.  Situated in Götaland, the lake is drained by Motala ström, starting at Motala, and flowing ultimately through a controlled canal into the Baltic Sea. The lake includes the scenic island of Visingsö, located outside Gränna. Other towns on the lake include Vadstena, Jönköping, Hjo, Askersund, Åmmeberg and Karlsborg. It is bounded by the Provinces of Västergötland, Närke, Östergötland and Småland.  In the north there is a scenic but not mountainous inland fjord, Alsen. About 62% of the drainage basin is still covered with spruce, pine and deciduous forest. About 26.7% is dedicated to agriculture.

Geology.

While many of smaller lakes in southern Sweden are thought to have originated by glacial stripping of an irregular weathering mantle in the last 2.5 million years Vättern formed by tectonics as a graben 700 to 800 million years ago in the Neoproterozoic. Granitic basement rocks in the lake are deformed (foliated) by the Protogine Zone that crosses the area. The basin is partially filled by sedimentary rock of the Visingsö Group of Neoproterozoic age. This group include rocks such as conglomerate, sandstone, arkose and carbonates. The older of these sediments deposited before the Vättern came into existence as a graben. Acritarch microfossils such as "Chuaria circularis" are common in Visingsö Group.  During the most recent millions of years multiple glaciations have covered the lake and its surroundings, leaving glacial striations and drumlins as they receded.  The present-day lake began as an independent body of water left by the receding Scandinavian glacier after the last glacial period around 10,000 BP. It became a minor bay of the Baltic ice lake. Most of the lake's relict species (like the Arctic char) date from that time. Subsequently, it was a bay of Yoldia Sea and then became connected to Ancylus Lake, discharging from the north end of its extent. At about 8000 BP an accident of the uneven Scandinavian isostatic land rise brought Vättern above Ancylus and the two became distinct.  The annual post-glacial rebound today is in northeastern Motala and in southern Jönköping. This means that Vättern is tilting to the south by every year.

Biology.

The lake contains both phytoplankton and zooplankton, such as Copepoda and Cladocera. The benthos species include Crustacea, Oligochaeta, Diptera and Bivalvia. In addition are several species of fish, including "Salvelinus salvelinus", "Coregonus lavaretus" and "Salmo salar". The lake is known for its Vättern char, as it is called, "Salvelinus alpinus". The Vättern char is genetically close to the Sommen char in nearby Lake Sommen and chars of Lake Ladoga in Russia.  It is said that there is a lake monster inhabiting Vättern. It is however not nearly as famous as the one supposedly living in Storsjön.

Uses.

The lake.

Vättern has been famous for the excellent quality of its transparent water. Many of the municipalities in the area receive their drinking water directly from Vättern. The lake water requires very little treatment before being pumped into the municipal systems and the natural, untreated water can be safely drunk from almost any point in the lake. It has been suggested that Vättern is the largest body of potable water in the world. The surrounding municipalities process 100% of their sewage.  Vättern is known for the annual recreational cycling race Vätternrundan, attracting some 20,000 participants to finish the 300 km trip around the shores of the lake.  Vättern is also noted for its fishing, serving people in the nearby districts. Tourist sport fishermen and vacationers are free to fish in the lake as long as they don't use nets. The lake is also used for commercial fishing.

The drainage basin.

A number of industries provide employment in the drainage basin: mining, manufacturing, forestry and paper. Agriculturalists raise cattle, sheep, swine and poultry.

Cultural notes.

According to the Catholic Church, Saint Catherine of Vadstena performed a miracle involving three people in peril on lake ice.  Thomas Nashe mentions this lake (Lake Vether) in his "Terrors of the Night" (published 1594), although he mistakenly locates the lake in Iceland: Admirable, above the rest, are the incomprehensible wonders of the bottomless Lake Vether, over which no fowl flies but is frozen to death, nor any man passeth but he is senselessly benumbed like a statue of marble.  All the inhabitants round about it are deafened with the hideous roaring of his waters when the winter breaketh up, and the ice in his dissolving gives a terrible crack like to thunder, whenas out of the midst of it, as out of Mont-Gibell, a sulphureous stinking smoke issues, that wellnigh poisons the whole country. Lake Vether is also mentioned in Samuel Johnson's essay for "The Idler" No. 96, on Hacho of Lapland.  Ingmar Bergman shot a scene in his classic film "Wild Strawberries" on a restaurant terrace overlooking Vättern.

Vättern (, ) is the second largest lake by surface area in Sweden, after Vänern, and the sixth largest lake in Europe. It is a long, finger-shaped body of fresh water in south central Sweden, to the southeast of Vänern, pointing at the tip of Scandinavia.

韦特恩湖()是瑞典的一个湖泊。就面积而言,韦特恩湖是瑞典第二大湖泊(仅次于维纳恩湖)。


Construction.

Early tubular spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclinations the bubble travels away from the marked center position. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.  Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface. Alcohols also have a much wider liquid temperature range, and won't break the vial as water could due to ice expansion. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.  A variant of the linear spirit level is the bull's eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass face with a circle at the center. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube.

Calibration.

To check the accuracy of a carpenter's type level, a perfectly horizontal surface is not needed. The level is placed on a flat and "roughly" level surface and the reading on the bubble tube is noted. This reading indicates to what extent the surface is parallel to the horizontal plane, according to the level, which at this stage is of unknown accuracy. The spirit level is then rotated through 180 degrees in the horizontal plane, and another reading is noted. If the level is accurate, it will indicate the same orientation with respect to the horizontal plane. A difference implies that the level is inaccurate.  Adjustment of the spirit level is performed by successively rotating the level and moving the bubble tube within its housing to take up roughly half of the discrepancy, until the magnitude of the reading remains constant when the level is flipped.  A similar procedure is applied to more sophisticated instruments such as a surveyor's optical level or a theodolite and is a matter of course each time the instrument is set up. In this latter case, the plane of rotation of the instrument is levelled, along with the spirit level. This is done in two horizontal perpendicular directions.

Sensitivity.

The sensitivity is an important specification for a spirit level; its accuracy depends on its sensitivity. The sensitivity of a level is given as the change of angle or gradient required to move the bubble by unit distance. If the bubble housing has graduated divisions, then the sensitivity is the angle or gradient change that moves the bubble by one of these divisions. is the usual spacing for graduations; on a surveyor's level, the bubble will move 2 mm when the vial is tilted about 0.005 degree. For a precision machinist level with 2 mm divisions, when the vial is tilted one division, the level will change of one foot from the pivot point, referred to as 5 ten-thousandths per foot.

Types.

There are different types of spirit levels for different uses:  A spirit level is usually found on the head of combination squares.

Surveyor's leveling instrument.

"Tilting level", dumpy level or "automatic level" are terms used to refer to types of "leveling instruments" as used in surveying to measure height differences over larger distances. It has a spirit level mounted on a telescope (perhaps 30 power) with cross-hairs, itself mounted on a tripod. The observer reads height values off two graduated vertical rods, one 'behind' and one 'in front', to obtain the height difference between the ground points on which the rods are resting. Starting from a point with a known elevation and going cross country (successive points being perhaps apart) height differences can be measured cumulatively over long distances and elevations can be calculated. Precise levelling is supposed to give the difference in elevation between two points apart correct to within a few millimeters.

Carpenter's level.

A traditional carpenter's spirit level looks like a short plank of wood and often has a wide body to ensure stability, and that the surface is being measured correctly. In the middle of the spirit level is a small window where the bubble and the tube is mounted. Two notches (or rings) designate where the bubble should be if the surface is level. Often an indicator for a 45 degree inclination is included.

Line level.

A line level is a level designed to hang on a builder's string line. The body of the level incorporates small hooks to allow it to attach and hang from the string line. The body is lightweight, so as not to weigh down the string line, it is also small in size as the string line in effect "becomes" the body; when the level is hung in the center of the string, each "leg" of the string line extends the level's plane.

Engineer's precision levels.

An engineer's precision level permits leveling items to greater accuracy than a plain spirit level. They are used to level the foundations, or beds of machines to ensure the machine can output workpieces to the accuracy pre-built in the machine.

History.

Melchisédech Thévenot, a French scientist, invented the instrument some time before February 2, 1661. This date can be established from Thevenot's correspondence with scientist Christiaan Huygens. Within a year of this date the inventor circulated details of his invention to others, including Robert Hooke in London and Vincenzo Viviani in Florence. It is occasionally argued that these bubble levels did not come into widespread use until the beginning of the eighteenth century, the earliest surviving examples being from that time, but Adrien Auzout had recommended that the Académie Royale des Sciences take "levels of the Thevenot type" on its expedition to Madagascar in 1666. It is very likely that these levels were in use in France and elsewhere long before the turn of the century.  Thevenot is often confused with his nephew, the traveler Jean de Thevenot (born 1633; died 1667). There is evidence to suggest that both Huygens and Hooke later laid claim to the invention, although only within their own countries.  The Fell All-Way precision level, one of the first successful American made bull's eye levels for machine tool use, was invented by William B. Fell, Rockford, Illinois prior to WWII in 1939. The device was unique in that it could be placed on a machine bed and show tilt on the x-y axes simultaneously; eliminating the need to rotate the level 90 degrees. The level was so accurate it was restricted from export during World War II. The device set a new standard of.0005 inches per foot resolution (five ten thousands per foot or five arc seconds tilt). The level's production stopped around 1970. Production restarted in the 1980s by Thomas Butler Technology, Rockford, Illinois, but finally ended in the mid 1990s. However, there are still hundreds of the highly prized devices in existence.

Today.

Today level tools are available in most smartphones by using the device's accelerometer. These mobile apps come with various features and easy designs. Also new web standards allow websites to get orientation of devices.

Alternatives.

Alternatives include:  Digital levels are increasingly common in replacing conventional spirit levels, particularly in civil engineering applications such as traditional building construction and steel structure erection, for on-site angle alignment and leveling tasks. The industry practitioners often refer to those levelling tools as a “construction level”, “heavy duty level”, "inclinometer", or “protractor”. These modern electronic levels are (i) capable of displaying precise numeric angles within 360° with 0.1° to 0.05° accuracy, (ii) digital readings can be read from a distance with clarity, (iii) affordably priced due to mass adoption. They provide features that traditional levels are unable to match. Typically, these features enable steel beam frames under construction to be precisely aligned and levelled to the required orientation, which is vital to ensure the stability, strength and rigidity of steel structures on sites. Digital levels, embedded with angular MEMS technology effectively improve productivity and quality of many modern civil structures. Some recent models feature waterproof IP65 and impact resistance features for harsh working environments.

A spirit level, bubble level or simply a level is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.

水准管,又称管水准器、水-{平}-仪、水-{平}-尺或平水尺,是一种量度水平及铅直的测量工具,形状就像尺一样。


Overview.

Geoinformatics has been described as "the science and technology dealing with the structure and character of spatial information, its capture, its classification and qualification, its storage, processing, portrayal and dissemination, including the infrastructure necessary to secure optimal use of this information" or "the art, science or technology dealing with the acquisition, storage, processing production, presentation and dissemination of geoinformation".  Geomatics is a similarly used term which encompasses geoinformatics, but geomatics focuses more so on surveying. Geoinformatics has at its core the technologies supporting the processes of acquiring, analyzing and visualizing spatial data. Both geomatics and geoinformatics include and rely heavily upon the theory and practical implications of geodesy.  Geography and earth science increasingly rely on digital spatial data acquired from remotely sensed images analyzed by geographical information systems (GIS) and visualized on paper or the computer screen.  Geoinformatics combines geospatial analysis and modeling, development of geospatial databases, information systems design, human-computer interaction and both wired and wireless networking technologies. Geoinformatics uses geocomputation and geovisualization for analyzing geoinformation.  Branches of geoinformatics include:

Research.

Research in this field is used to support global and local environmental, energy and security programs. The Geographic Information Science and Technology group of Oak Ridge National Laboratory is supported by various government departments and agencies including the United States Department of Energy. It is currently the only group in the United States Department of Energy National Laboratory System to focus on advanced theory and application research in this field. A lot of interdisciplinary research exists that involves geoinformatics fields including computer science, information technology, software engineering, biogeography, geography, conservation, architecture, spatial analysis and reinforcement learning.

Applications.

Many fields benefit from geoinformatics, including urban planning and land use management, in-car navigation systems, virtual globes, public health, local and national gazetteer management, environmental modeling and analysis, military, transport network planning and management, agriculture, meteorology and climate change, oceanography and coupled ocean and atmosphere modelling, business location planning, architecture and archeological reconstruction, telecommunications, criminology and crime simulation, aviation, biodiversity conservation and maritime transport. The importance of the spatial dimension in assessing, monitoring and modelling various issues and problems related to sustainable management of natural resources is recognized all over the world. Geoinformatics becomes very important technology to decision-makers across a wide range of disciplines, industries, commercial sector, environmental agencies, local and national government, research, and academia, national survey and mapping organisations, International organisations, United Nations, emergency services, public health and epidemiology, crime mapping, transportation and infrastructure, information technology industries, GIS consulting firms, environmental management agencies), tourist industry, utility companies, market analysis and e-commerce, mineral exploration, etc. Many government and non government agencies started to use spatial data for managing their day-to-day activities.

Geoinformatics is the science and the technology which develops and uses information science infrastructure to address the problems of geography, cartography, geosciences and related branches of science and engineering.

地理信息科学(英语:Geographic Information Science,简称英语:GI Science)或空间资讯科学(英语:Geoinformatics)是由全球定位系统(GPS)、地理信息系统(GIS)、遥感(RS)、计算机技术和数字传输网络等一系列现代技术高度集成,及在信息科学与地球系统科学交叉基础上形成的,以信息流为手段,研究地球系统内部物质流、能量流和人流运动规律的一门应用科学,由美籍英裔地理学家迈克尔·弗兰克·古德柴尔德于1992年提出。