In his book "Ideals of the Samurai" translator William Scott Wilson states: "The warriors in the Heike Monogatari served as models for the educated warriors of later generations, and the ideals depicted by them were not assumed to be beyond reach. Rather, these ideals were vigorously pursued in the upper echelons of warrior society and recommended as the proper form of the Japanese man of arms. With the Heike Monogatari, the image of the Japanese warrior in literature came to its full maturity." Wilson then translates the writings of several warriors who mention the Heike Monogatari as an example for their men to follow.


As aristocrats for centuries, samurai developed their own cultures that influenced Japanese culture as a whole. The culture associated with the samurai such as the tea ceremony, monochrome ink painting, rock gardens and poetry were adopted by warrior patrons throughout the centuries 1200–1600. These practices were adapted from the Chinese arts. Zen monks introduced them to Japan and they were allowed to flourish due to the interest of powerful warrior elites. Musō Soseki (1275–1351) was a Zen monk who was advisor to both Emperor Go-Daigo and General Ashikaga Takauji (1304–58). Musō, as well as other monks, acted as political and cultural diplomat between Japan and China. Musō was particularly well known for his garden design. Another Ashikaga patron of the arts was Yoshimasa. His cultural advisor, the Zen monk Zeami, introduced tea ceremony to him. Previously, tea had been used primarily for Buddhist monks to stay awake during meditation.


For example, the full name of Oda Nobunaga would be "Oda Kazusanosuke Saburo Nobunaga" (織田上総介三郎信長), in which "Oda" is a clan or family name, "Kazusanosuke" is a title of vice-governor of Kazusa province, "Saburo" is a formal nickname (yobina), and "Nobunaga" is an adult name (nanori) given at genpuku, the coming of age ceremony. A man was addressed by his family name and his title, or by his yobina if he did not have a title. However, the nanori was a private name that could be used by only a very few, including the Emperor.


A samurai could take concubines but their backgrounds were checked by higher-ranked samurai. In many cases, taking a concubine was akin to a marriage. Kidnapping a concubine, although common in fiction, would have been shameful, if not criminal. If the concubine was a commoner, a messenger was sent with betrothal money or a note for exemption of tax to ask for her parents' acceptance. Even though the woman would not be a legal wife, a situation normally considered a demotion, many wealthy merchants believed that being the concubine of a samurai was superior to being the legal wife of a commoner. When a merchant's daughter married a samurai, her family's money erased the samurai's debts, and the samurai's social status improved the standing of the merchant family. If a samurai's commoner concubine gave birth to a son, the son could inherit his father's social status.


A samurai could divorce his wife for a variety of reasons with approval from a superior, but divorce was, while not entirely nonexistent, a rare event. A wife's failure to produce a son was cause for divorce, but adoption of a male heir was considered an acceptable alternative to divorce. A samurai could divorce for personal reasons, even if he simply did not like his wife, but this was generally avoided as it would embarrass the person who had arranged the marriage. A woman could also arrange a divorce, although it would generally take the form of the samurai divorcing her. After a divorce samurai had to return the betrothal money, which often prevented divorces.


Maintaining the household was the main duty of samurai women. This was especially crucial during early feudal Japan, when warrior husbands were often traveling abroad or engaged in clan battles. The wife, or okugatasama (meaning: one who remains in the home), was left to manage all household affairs, care for the children, and perhaps even defend the home forcibly. For this reason, many women of the samurai class were trained in wielding a polearm called a naginata or a special knife called the kaiken in an art called tantojutsu (lit. the skill of the knife), which they could use to protect their household, family, and honor if the need arose.


Traits valued in women of the samurai class were humility, obedience, self-control, strength, and loyalty. Ideally, a samurai wife would be skilled at managing property, keeping records, dealing with financial matters, educating the children (and perhaps servants, too), and caring for elderly parents or in-laws that may be living under her roof. Confucian law, which helped define personal relationships and the code of ethics of the warrior class required that a woman show subservience to her husband, filial piety to her parents, and care to the children. Too much love and affection was also said to indulge and spoil the youngsters. Thus, a woman was also to exercise discipline.


This does not mean that samurai women were always powerless. Powerful women both wisely and unwisely wielded power at various occasions. After Ashikaga Yoshimasa, 8th shogun of the Muromachi shogunate, lost interest in politics, his wife Hino Tomiko largely ruled in his place. Nene, wife of Toyotomi Hideyoshi, was known to overrule her husband's decisions at times and Yodo-dono, his concubine, became the de facto master of Osaka castle and the Toyotomi clan after Hideyoshi's death. Tachibana Ginchiyo was chosen to lead the Tachibana clan after her father's death. Chiyo, wife of Yamauchi Kazutoyo, has long been considered the ideal samurai wife. According to legend, she made her kimono out of a quilted patchwork of bits of old cloth and saved pennies to buy her husband a magnificent horse, on which he rode to many victories. The fact that Chiyo (though she is better known as "Wife of Yamauchi Kazutoyo") is held in such high esteem for her economic sense is illuminating in the light of the fact that she never produced an heir and the Yamauchi clan was succeeded by Kazutoyo's younger brother. The source of power for women may have been that samurai left their finances to their wives.


As the Tokugawa period progressed more value became placed on education, and the education of females beginning at a young age became important to families and society as a whole. Marriage criteria began to weigh intelligence and education as desirable attributes in a wife, right along with physical attractiveness. Though many of the texts written for women during the Tokugawa period only pertained to how a woman could become a successful wife and household manager, there were those that undertook the challenge of learning to read, and also tackled philosophical and literary classics. Nearly all women of the samurai class were literate by the end of the Tokugawa period.


The English sailor and adventurer William Adams (1564–1620) was the first Westerner to receive the dignity of samurai. The Shogun Tokugawa Ieyasu presented him with two swords representing the authority of a samurai, and decreed that William Adams the sailor was dead and that Anjin Miura (三浦按針), a samurai, was born. Adams also received the title of hatamoto (bannerman), a high-prestige position as a direct retainer in the Shogun's court. He was provided with generous revenues: "For the services that I have done and do daily, being employed in the Emperor's service, the Emperor has given me a living" (Letters). He was granted a fief in Hemi (逸見) within the boundaries of present-day Yokosuka City, "with eighty or ninety husbandmen, that be my slaves or servants" (Letters). His estate was valued at 250 koku. He finally wrote "God hath provided for me after my great misery", (Letters) by which he meant the disaster-ridden voyage that initially brought him to Japan.


Jan Joosten van Lodensteijn (1556?–1623?), a Dutch colleague of Adams' on their ill-fated voyage to Japan in the ship De Liefde, was also given similar privileges by Tokugawa Ieyasu. It appears Joosten became a samurai[citation needed] and was given a residence within Ieyasu's castle at Edo. Today, this area at the east exit of Tokyo Station is known as Yaesu (八重洲). Yaesu is a corruption of the Dutchman's Japanese name, Yayousu (耶楊子). Also in common with Adam's, Joostens was given a Red Seal Ship (朱印船) allowing him to trade between Japan and Indo-China. On a return journey from Batavia Joosten drowned after his ship ran aground.


In the same war, the Prussian Edward Schnell served the Aizu domain as a military instructor and procurer of weapons. He was granted the Japanese name Hiramatsu Buhei (平松武兵衛), which inverted the characters of the daimyo's name Matsudaira. Hiramatsu (Schnell) was given the right to wear swords, as well as a residence in the castle town of Wakamatsu, a Japanese wife, and retainers. In many contemporary references, he is portrayed wearing a Japanese kimono, overcoat, and swords, with Western riding trousers and boots.


As far back as the seventh century Japanese warriors wore a form of lamellar armor, this armor eventually evolved into the armor worn by the samurai. The first types of Japanese armors identified as samurai armor were known as yoroi. These early samurai armors were made from small individual scales known as kozane. The kozane were made from either iron or leather and were bound together into small strips, the strips were coated with lacquer to protect the kozane from water. A series of strips of kozane were then laced together with silk or leather lace and formed into a complete chest armor (dou or dō).


In the 1500s a new type of armor started to become popular due to the advent of firearms, new fighting tactics and the need for additional protection. The kozane dou made from individual scales was replaced by plate armor. This new armor, which used iron plated dou (dō), was referred to as Tosei-gusoku, or modern armor. Various other components of armor protected the samurai's body. The helmet kabuto was an important part of the samurai's armor. Samurai armor changed and developed as the methods of samurai warfare changed over the centuries. The known last use of samurai armor occurring in 1877 during the satsuma rebellion. As the last samurai rebellion was crushed, Japan modernized its defenses and turned to a national conscription army that used uniforms.


The term samurai originally meant "those who serve in close attendance to nobility", and was written with a Chinese character (or kanji) that had the same meaning. In Japanese, it was originally recorded in the Nara Period as a verb *samorapu ("to watch, to keep watch, to observe, to be on the lookout for something; to serve, to attend"), which is believed to be derived from the frequentative form (*morapu 守らふ) of the verb moru (守る, "to watch, to guard, to be on the lookout; to keep, to protect, to take care of, to be in charge of, to have as one's ward"). By the Heian period, this word had developed into the verb saburahu (さぶらふ, "to serve, to attend"), from which a deverbal noun saburahi (さぶらひ, "servant, attendant") was later derived, and this noun then yielded samurahi (さむらひ) in the Edo period. In Japanese literature, there is an early reference to samurai in the Kokinshū (古今集, early 10th century):


Bushi was the name given to the ancient Japanese soldiers from traditional warrior families. The bushi class was developed mainly in the north of Japan. They formed powerful clans, which in the 12th century were against the noble families who were grouping themselves to support the imperial family who lived in Kyoto. Samurai was a word used by the Kuge aristocratic class with warriors themselves preferring the word bushi. The term Bushidō, the "way of the warrior", is derived from this term and the mansion of a warrior was called bukeyashiki.


Most samurai were bound by a code of honor and were expected to set an example for those below them. A notable part of their code is seppuku (切腹, seppuku?) or hara kiri, which allowed a disgraced samurai to regain his honor by passing into death, where samurai were still beholden to social rules. Whilst there are many romanticized characterizations of samurai behavior such as the writing of Bushido (武士道, Bushidō?) in 1905, studies of Kobudo and traditional Budō indicate that the samurai were as practical on the battlefield as were any other warrior.


Despite the rampant romanticism of the 20th century, samurai could be disloyal and treacherous (e.g., Akechi Mitsuhide), cowardly, brave, or overly loyal (e.g., Kusunoki Masashige). Samurai were usually loyal to their immediate superiors, who in turn allied themselves with higher lords. These loyalties to the higher lords often shifted; for example, the high lords allied under Toyotomi Hideyoshi (豊臣秀吉) were served by loyal samurai, but the feudal lords under them could shift their support to Tokugawa, taking their samurai with them. There were, however, also notable instances where samurai would be disloyal to their lord or daimyo, when loyalty to the Emperor was seen to have supremacy.


Jidaigeki (literally historical drama) has always been a staple program on Japanese movies and television. The programs typically feature a samurai. Samurai films and westerns share a number of similarities and the two have influenced each other over the years. One of Japan’s most renowned directors, Akira Kurosawa, greatly influenced the samurai aspect in western film-making.[citation needed] George Lucas’ Star Wars series incorporated many aspects from the Seven Samurai film. One example is that in the Japanese film, seven samurai warriors are hired by local farmers to protect their land from being overrun by bandits; In George Lucas’ Star Wars: A New Hope, a similar situation arises. Kurosawa was inspired by the works of director John Ford and in turn Kurosawa's works have been remade into westerns such as The Seven Samurai into The Magnificent Seven and Yojimbo into A Fistful of Dollars. There is also a 26 episode anime adaptation (Samurai 7) of The Seven Samurai. Along with film, literature containing samurai influences are seen as well.


Most common are historical works where the protagonist is either a samurai or former samurai (or another rank or position) who possesses considerable martial skill. Eiji Yoshikawa is one of the most famous Japanese historical novelists. His retellings of popular works, including Taiko, Musashi and Heike Tale, are popular among readers for their epic narratives and rich realism in depicting samurai and warrior culture.[citation needed] The samurai have also appeared frequently in Japanese comics (manga) and animation (anime). Samurai-like characters are not just restricted to historical settings and a number of works set in the modern age, and even the future, include characters who live, train and fight like samurai. Examples are Samurai Champloo, Requiem from the Darkness, Muramasa: The Demon Blade, and Afro Samurai. Some of these works have made their way to the west, where it has been increasing in popularity with America.


Just in the last two decades,[when?] samurai have become more popular in America. “Hyperbolizing the samurai in such a way that they appear as a whole to be a loyal body of master warriors provides international interest in certain characters due to admirable traits” (Moscardi, N.D.). Through various medium, producers and writers have been capitalizing on the notion that Americans admire the samurai lifestyle. The animated series, Afro Samurai, became well-liked in American popular culture due to its blend of hack-and-slash animation and gritty urban music.


Created by Takashi Okazaki, Afro Samurai was initially a doujinshi, or manga series, which was then made into an animated series by Studio Gonzo. In 2007 the animated series debuted on American cable television on the Spike TV channel (Denison, 2010). The series was produced for American viewers which “embodies the trend... comparing hip-hop artists to samurai warriors, an image some rappers claim for themselves (Solomon, 2009). The storyline keeps in tone with the perception of a samurais finding vengeance against someone who has wronged him. Starring the voice of well known American actor Samuel L. Jackson, “Afro is the second-strongest fighter in a futuristic, yet, still feudal Japan and seeks revenge upon the gunman who killed his father” (King 2008). Due to its popularity, Afro Samurai was adopted into a full feature animated film and also became titles on gaming consoles such as the PlayStation 3 and Xbox. Not only has the samurai culture been adopted into animation and video games, it can also be seen in comic books.


American comic books have adopted the character type for stories of their own like the mutant-villain Silver Samurai of Marvel Comics. The design of this character preserves the samurai appearance; the villain is “Clad in traditional gleaming samurai armor and wielding an energy charged katana” (Buxton, 2013). Not only does the Silver Samurai make over 350 comic book appearances, the character is playable in several video games, such as Marvel Vs. Capcom 1 and 2. In 2013, the samurai villain was depicted in James Mangold’s film The Wolverine. Ten years before the Wolverine debuted, another film helped pave the way to ensure the samurai were made known to American cinema: A film released in 2003 titled The Last Samurai, starring Tom Cruise, is inspired by the samurai way of life. In the film, Cruise’s character finds himself deeply immersed in samurai culture. The character in the film, “Nathan Algren, is a fictional contrivance to make nineteenth-century Japanese history less foreign to American viewers”.(Ravina, 2010) After being captured by a group of samurai rebels, he becomes empathetic towards the cause they fight for. Taking place during the Meiji Period, Tom Cruise plays the role of US Army Captain Nathan Algren, who travels to Japan to train a rookie army in fighting off samurai rebel groups. Becoming a product of his environment, Algren joins the samurai clan in an attempt to rescue a captured samurai leader. “By the end of the film, he has clearly taken on many of the samurai traits, such as zen-like mastery of the sword, and a budding understanding of spirituality”. (Manion, 2006)


As the number of possible tests for even simple software components is practically infinite, all software testing uses some strategy to select tests that are feasible for the available time and resources. As a result, software testing typically (but not exclusively) attempts to execute a program or application with the intent of finding software bugs (errors or other defects). The job of testing is an iterative process as when one bug is fixed, it can illuminate other, deeper bugs, or can even create new ones.


Although testing can determine the correctness of software under the assumption of some specific hypotheses (see hierarchy of testing difficulty below), testing cannot identify all the defects within software. Instead, it furnishes a criticism or comparison that compares the state and behavior of the product against oracles—principles or mechanisms by which someone might recognize a problem. These oracles may include (but are not limited to) specifications, contracts, comparable products, past versions of the same product, inferences about intended or expected purpose, user or customer expectations, relevant standards, applicable laws, or other criteria.


A primary purpose of testing is to detect software failures so that defects may be discovered and corrected. Testing cannot establish that a product functions properly under all conditions but can only establish that it does not function properly under specific conditions. The scope of software testing often includes examination of code as well as execution of that code in various environments and conditions as well as examining the aspects of code: does it do what it is supposed to do and do what it needs to do. In the current culture of software development, a testing organization may be separate from the development team. There are various roles for testing team members. Information derived from software testing may be used to correct the process by which software is developed.


Software faults occur through the following processes. A programmer makes an error (mistake), which results in a defect (fault, bug) in the software source code. If this defect is executed, in certain situations the system will produce wrong results, causing a failure. Not all defects will necessarily result in failures. For example, defects in dead code will never result in failures. A defect can turn into a failure when the environment is changed. Examples of these changes in environment include the software being run on a new computer hardware platform, alterations in source data, or interacting with different software. A single defect may result in a wide range of failure symptoms.


A fundamental problem with software testing is that testing under all combinations of inputs and preconditions (initial state) is not feasible, even with a simple product.:17-18 This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, non-functional dimensions of quality (how it is supposed to be versus what it is supposed to do)—usability, scalability, performance, compatibility, reliability—can be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.


Software developers can't test everything, but they can use combinatorial test design to identify the minimum number of tests needed to get the coverage they want. Combinatorial test design enables users to get greater test coverage with fewer tests. Whether they are looking for speed or test depth, they can use combinatorial test design methods to build structured variation into their test cases. Note that "coverage", as used here, is referring to combinatorial coverage, not requirements coverage.


It is commonly believed that the earlier a defect is found, the cheaper it is to fix it. The following table shows the cost of fixing the defect depending on the stage it was found. For example, if a problem in the requirements is found only post-release, then it would cost 10–100 times more to fix than if it had already been found by the requirements review. With the advent of modern continuous deployment practices and cloud-based services, the cost of re-deployment and maintenance may lessen over time.


There are many approaches available in software testing. Reviews, walkthroughs, or inspections are referred to as static testing, whereas actually executing programmed code with a given set of test cases is referred to as dynamic testing. Static testing is often implicit, as proofreading, plus when programming tools/text editors check source code structure or compilers (pre-compilers) check syntax and data flow as static program analysis. Dynamic testing takes place when the program itself is run. Dynamic testing may begin before the program is 100% complete in order to test particular sections of code and are applied to discrete functions or modules. Typical techniques for this are either using stubs/drivers or execution from a debugger environment.


White-box testing (also known as clear box testing, glass box testing, transparent box testing and structural testing, by seeing the source code) tests internal structures or workings of a program, as opposed to the functionality exposed to the end-user. In white-box testing an internal perspective of the system, as well as programming skills, are used to design test cases. The tester chooses inputs to exercise paths through the code and determine the appropriate outputs. This is analogous to testing nodes in a circuit, e.g. in-circuit testing (ICT).


Black-box testing treats the software as a "black box", examining functionality without any knowledge of internal implementation, without seeing the source code. The testers are only aware of what the software is supposed to do, not how it does it. Black-box testing methods include: equivalence partitioning, boundary value analysis, all-pairs testing, state transition tables, decision table testing, fuzz testing, model-based testing, use case testing, exploratory testing and specification-based testing.


Specification-based testing aims to test the functionality of software according to the applicable requirements. This level of testing usually requires thorough test cases to be provided to the tester, who then can simply verify that for a given input, the output value (or behavior), either "is" or "is not" the same as the expected value specified in the test case. Test cases are built around specifications and requirements, i.e., what the application is supposed to do. It uses external descriptions of the software, including specifications, requirements, and designs to derive test cases. These tests can be functional or non-functional, though usually functional.


One advantage of the black box technique is that no programming knowledge is required. Whatever biases the programmers may have had, the tester likely has a different set and may emphasize different areas of functionality. On the other hand, black-box testing has been said to be "like a walk in a dark labyrinth without a flashlight." Because they do not examine the source code, there are situations when a tester writes many test cases to check something that could have been tested by only one test case, or leaves some parts of the program untested.


Grey-box testing (American spelling: gray-box testing) involves having knowledge of internal data structures and algorithms for purposes of designing tests, while executing those tests at the user, or black-box level. The tester is not required to have full access to the software's source code.[not in citation given] Manipulating input data and formatting output do not qualify as grey-box, because the input and output are clearly outside of the "black box" that we are calling the system under test. This distinction is particularly important when conducting integration testing between two modules of code written by two different developers, where only the interfaces are exposed for test.


By knowing the underlying concepts of how the software works, the tester makes better-informed testing choices while testing the software from outside. Typically, a grey-box tester will be permitted to set up an isolated testing environment with activities such as seeding a database. The tester can observe the state of the product being tested after performing certain actions such as executing SQL statements against the database and then executing queries to ensure that the expected changes have been reflected. Grey-box testing implements intelligent test scenarios, based on limited information. This will particularly apply to data type handling, exception handling, and so on.


There are generally four recognized levels of tests: unit testing, integration testing, component interface testing, and system testing. Tests are frequently grouped by where they are added in the software development process, or by the level of specificity of the test. The main levels during the development process as defined by the SWEBOK guide are unit-, integration-, and system testing that are distinguished by the test target without implying a specific process model. Other test levels are classified by the testing objective.


Unit testing is a software development process that involves synchronized application of a broad spectrum of defect prevention and detection strategies in order to reduce software development risks, time, and costs. It is performed by the software developer or engineer during the construction phase of the software development lifecycle. Rather than replace traditional QA focuses, it augments it. Unit testing aims to eliminate construction errors before code is promoted to QA; this strategy is intended to increase the quality of the resulting software as well as the efficiency of the overall development and QA process.


The practice of component interface testing can be used to check the handling of data passed between various units, or subsystem components, beyond full integration testing between those units. The data being passed can be considered as "message packets" and the range or data types can be checked, for data generated from one unit, and tested for validity before being passed into another unit. One option for interface testing is to keep a separate log file of data items being passed, often with a timestamp logged to allow analysis of thousands of cases of data passed between units for days or weeks. Tests can include checking the handling of some extreme data values while other interface variables are passed as normal values. Unusual data values in an interface can help explain unexpected performance in the next unit. Component interface testing is a variation of black-box testing, with the focus on the data values beyond just the related actions of a subsystem component.


Operational Acceptance is used to conduct operational readiness (pre-release) of a product, service or system as part of a quality management system. OAT is a common type of non-functional software testing, used mainly in software development and software maintenance projects. This type of testing focuses on the operational readiness of the system to be supported, and/or to become part of the production environment. Hence, it is also known as operational readiness testing (ORT) or Operations readiness and assurance (OR&A) testing. Functional testing within OAT is limited to those tests which are required to verify the non-functional aspects of the system.


A common cause of software failure (real or perceived) is a lack of its compatibility with other application software, operating systems (or operating system versions, old or new), or target environments that differ greatly from the original (such as a terminal or GUI application intended to be run on the desktop now being required to become a web application, which must render in a web browser). For example, in the case of a lack of backward compatibility, this can occur because the programmers develop and test software only on the latest version of the target environment, which not all users may be running. This results in the unintended consequence that the latest work may not function on earlier versions of the target environment, or on older hardware that earlier versions of the target environment was capable of using. Sometimes such issues can be fixed by proactively abstracting operating system functionality into a separate program module or library.


Regression testing focuses on finding defects after a major code change has occurred. Specifically, it seeks to uncover software regressions, as degraded or lost features, including old bugs that have come back. Such regressions occur whenever software functionality that was previously working correctly, stops working as intended. Typically, regressions occur as an unintended consequence of program changes, when the newly developed part of the software collides with the previously existing code. Common methods of regression testing include re-running previous sets of test-cases and checking whether previously fixed faults have re-emerged. The depth of testing depends on the phase in the release process and the risk of the added features. They can either be complete, for changes added late in the release or deemed to be risky, or be very shallow, consisting of positive tests on each feature, if the changes are early in the release or deemed to be of low risk. Regression testing is typically the largest test effort in commercial software development, due to checking numerous details in prior software features, and even new software can be developed while using some old test-cases to test parts of the new design to ensure prior functionality is still supported.


Beta testing comes after alpha testing and can be considered a form of external user acceptance testing. Versions of the software, known as beta versions, are released to a limited audience outside of the programming team known as beta testers. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Beta versions can be made available to the open public to increase the feedback field to a maximal number of future users and to deliver value earlier, for an extended or even indefinite period of time (perpetual beta).[citation needed]


Destructive testing attempts to cause the software or a sub-system to fail. It verifies that the software functions properly even when it receives invalid or unexpected inputs, thereby establishing the robustness of input validation and error-management routines.[citation needed] Software fault injection, in the form of fuzzing, is an example of failure testing. Various commercial non-functional testing tools are linked from the software fault injection page; there are also numerous open-source and free software tools available that perform destructive testing.


Load testing is primarily concerned with testing that the system can continue to operate under a specific load, whether that be large quantities of data or a large number of users. This is generally referred to as software scalability. The related load testing activity of when performed as a non-functional activity is often referred to as endurance testing. Volume testing is a way to test software functions even when certain components (for example a file or database) increase radically in size. Stress testing is a way to test reliability under unexpected or rare workloads. Stability testing (often referred to as load or endurance testing) checks to see if the software can continuously function well in or above an acceptable period.


Development Testing is a software development process that involves synchronized application of a broad spectrum of defect prevention and detection strategies in order to reduce software development risks, time, and costs. It is performed by the software developer or engineer during the construction phase of the software development lifecycle. Rather than replace traditional QA focuses, it augments it. Development Testing aims to eliminate construction errors before code is promoted to QA; this strategy is intended to increase the quality of the resulting software as well as the efficiency of the overall development and QA process.


In contrast, some emerging software disciplines such as extreme programming and the agile software development movement, adhere to a "test-driven software development" model. In this process, unit tests are written first, by the software engineers (often with pair programming in the extreme programming methodology). Of course these tests fail initially; as they are expected to. Then as code is written it passes incrementally larger portions of the test suites. The test suites are continuously updated as new failure conditions and corner cases are discovered, and they are integrated with any regression tests that are developed. Unit tests are maintained along with the rest of the software source code and generally integrated into the build process (with inherently interactive tests being relegated to a partially manual build acceptance process). The ultimate goal of this test process is to achieve continuous integration where software updates can be published to the public frequently.


Bottom Up Testing is an approach to integrated testing where the lowest level components (modules, procedures, and functions) are tested first, then integrated and used to facilitate the testing of higher level components. After the integration testing of lower level integrated modules, the next level of modules will be formed and can be used for integration testing. The process is repeated until the components at the top of the hierarchy are tested. This approach is helpful only when all or most of the modules of the same development level are ready.[citation needed] This method also helps to determine the levels of software developed and makes it easier to report testing progress in the form of a percentage.[citation needed]


It has been proved that each class is strictly included into the next. For instance, testing when we assume that the behavior of the implementation under test can be denoted by a deterministic finite-state machine for some known finite sets of inputs and outputs and with some known number of states belongs to Class I (and all subsequent classes). However, if the number of states is not known, then it only belongs to all classes from Class II on. If the implementation under test must be a deterministic finite-state machine failing the specification for a single trace (and its continuations), and its number of states is unknown, then it only belongs to classes from Class III on. Testing temporal machines where transitions are triggered if inputs are produced within some real-bounded interval only belongs to classes from Class IV on, whereas testing many non-deterministic systems only belongs to Class V (but not all, and some even belong to Class I). The inclusion into Class I does not require the simplicity of the assumed computation model, as some testing cases involving implementations written in any programming language, and testing implementations defined as machines depending on continuous magnitudes, have been proved to be in Class I. Other elaborated cases, such as the testing framework by Matthew Hennessy under must semantics, and temporal machines with rational timeouts, belong to Class II.


Several certification programs exist to support the professional aspirations of software testers and quality assurance specialists. No certification now offered actually requires the applicant to show their ability to test software. No certification is based on a widely accepted body of knowledge. This has led some to declare that the testing field is not ready for certification. Certification itself cannot measure an individual's productivity, their skill, or practical knowledge, and cannot guarantee their competence, or professionalism as a tester.


Software testing is a part of the software quality assurance (SQA) process.:347 In SQA, software process specialists and auditors are concerned for the software development process rather than just the artifacts such as documentation, code and systems. They examine and change the software engineering process itself to reduce the number of faults that end up in the delivered software: the so-called "defect rate". What constitutes an "acceptable defect rate" depends on the nature of the software; A flight simulator video game would have much higher defect tolerance than software for an actual airplane. Although there are close links with SQA, testing departments often exist independently, and there may be no SQA function in some companies.[citation needed]


Germany is a federal republic consisting of sixteen federal states (German: Bundesland, or Land).[a] Since today's Germany was formed from an earlier collection of several states, it has a federal constitution, and the constituent states retain a measure of sovereignty. With an emphasis on geographical conditions, Berlin and Hamburg are frequently called Stadtstaaten (city-states), as is the Free Hanseatic City of Bremen, which in fact includes the cities of Bremen and Bremerhaven. The remaining 13 states are called Flächenländer (literally: area states).


The creation of the Federal Republic of Germany in 1949 was through the unification of the western states (which were previously under American, British, and French administration) created in the aftermath of World War II. Initially, in 1949, the states of the Federal Republic were Baden, Bavaria (in German: Bayern), Bremen, Hamburg, Hesse (Hessen), Lower Saxony (Niedersachsen), North Rhine Westphalia (Nordrhein-Westfalen), Rhineland-Palatinate (Rheinland-Pfalz), Schleswig-Holstein, Württemberg-Baden, and Württemberg-Hohenzollern. West Berlin, while officially not part of the Federal Republic, was largely integrated and considered as a de facto state.


In 1952, following a referendum, Baden, Württemberg-Baden, and Württemberg-Hohenzollern merged into Baden-Württemberg. In 1957, the Saar Protectorate rejoined the Federal Republic as the Saarland. German reunification in 1990, in which the German Democratic Republic (East Germany) ascended into the Federal Republic, resulted in the addition of the re-established eastern states of Brandenburg, Mecklenburg-West Pomerania (in German Mecklenburg-Vorpommern), Saxony (Sachsen), Saxony-Anhalt (Sachsen-Anhalt), and Thuringia (Thüringen), as well as the reunification of West and East Berlin into Berlin and its establishment as a full and equal state. A regional referendum in 1996 to merge Berlin with surrounding Brandenburg as "Berlin-Brandenburg" failed to reach the necessary majority vote in Brandenburg, while a majority of Berliners voted in favour of the merger.


Federalism is one of the entrenched constitutional principles of Germany. According to the German constitution (called Grundgesetz or in English Basic Law), some topics, such as foreign affairs and defense, are the exclusive responsibility of the federation (i.e., the federal level), while others fall under the shared authority of the states and the federation; the states retain residual legislative authority for all other areas, including "culture", which in Germany includes not only topics such as financial promotion of arts and sciences, but also most forms of education and job training. Though international relations including international treaties are primarily the responsibility of the federal level, the constituent states have certain limited powers in this area: in matters that affect them directly, the states defend their interests at the federal level through the Bundesrat (literally Federal Council, the upper house of the German Federal Parliament) and in areas where they have legislative authority they have limited powers to conclude international treaties "with the consent of the federal government".


The use of the term Länder (Lands) dates back to the Weimar Constitution of 1919. Before this time, the constituent states of the German Empire were called Staaten (States). Today, it is very common to use the term Bundesland (Federal Land). However, this term is not used officially, neither by the constitution of 1919 nor by the Basic Law (Constitution) of 1949. Three Länder call themselves Freistaaten (Free States, which is the old-fashioned German expression for Republic), Bavaria (since 1919), Saxony (originally since 1919 and again since 1990), and Thuringia (since 1994). There is little continuity between the current states and their predecessors of the Weimar Republic with the exception of the three free states, and the two city-states of Hamburg and Bremen.


A new delimitation of the federal territory keeps being debated in Germany, though "Some scholars note that there are significant differences among the American states and regional governments in other federations without serious calls for territorial changes ...", as political scientist Arthur B. Gunlicks remarks. He summarizes the main arguments for boundary reform in Germany: "... the German system of dual federalism requires strong Länder that have the administrative and fiscal capacity to implement legislation and pay for it from own source revenues. Too many Länder also make coordination among them and with the federation more complicated ...". But several proposals have failed so far; territorial reform remains a controversial topic in German politics and public perception.


Federalism has a long tradition in German history. The Holy Roman Empire comprised many petty states numbering more than 300 around 1796. The number of territories was greatly reduced during the Napoleonic Wars (1796–1814). After the Congress of Vienna (1815), 39 states formed the German Confederation. The Confederation was dissolved after the Austro-Prussian War and replaced by a North German Federation under Prussian hegemony; this war left Prussia dominant in Germany, and German nationalism would compel the remaining independent states to ally with Prussia in the Franco-Prussian War of 1870–71, and then to accede to the crowning of King Wilhelm of Prussia as German Emperor. The new German Empire included 25 states (three of them, Hanseatic cities) and the imperial territory of Alsace-Lorraine. The empire was dominated by Prussia, which controlled 65% of the territory and 62% of the population. After the territorial losses of the Treaty of Versailles, the remaining states continued as republics of a new German federation. These states were gradually de facto abolished and reduced to provinces under the Nazi regime via the Gleichschaltung process, as the states administratively were largely superseded by the Nazi Gau system.


During the Allied occupation of Germany after World War II, internal borders were redrawn by the Allied military governments. No single state comprised more than 30% of either population or territory; this was intended to prevent any one state from being as dominant within Germany as Prussia had been in the past. Initially, only seven of the pre-War states remained: Baden (in part), Bavaria (reduced in size), Bremen, Hamburg, Hesse (enlarged), Saxony, and Thuringia. The states with hyphenated names, such as Rhineland-Palatinate, North Rhine-Westphalia, and Saxony-Anhalt, owed their existence to the occupation powers and were created out of mergers of former Prussian provinces and smaller states. Former German territory that lie east of the Oder-Neisse Line fell under either Polish or Soviet administration but attempts were made at least symbolically not to abandon sovereignty well into the 1960s. However, no attempts were made to establish new states in these territories as they lay outside the jurisdiction of West Germany at that time.


Upon its founding in 1949, West Germany had eleven states. These were reduced to nine in 1952 when three south-western states (South Baden, Württemberg-Hohenzollern, and Württemberg-Baden) merged to form Baden-Württemberg. From 1957, when the French-occupied Saar Protectorate was returned and formed into the Saarland, the Federal Republic consisted of ten states, which are referred to as the "Old States" today. West Berlin was under the sovereignty of the Western Allies and neither a Western German state nor part of one. However, it was in many ways de facto integrated with West Germany under a special status.


Later, the constitution was amended to state that the citizens of the 16 states had successfully achieved the unity of Germany in free self-determination and that the Basic Law thus applied to the entire German people. Article 23, which had allowed "any other parts of Germany" to join, was rephrased. It had been used in 1957 to reintegrate the Saar Protectorate as the Saarland into the Federal Republic, and this was used as a model for German reunification in 1990. The amended article now defines the participation of the Federal Council and the 16 German states in matters concerning the European Union.


A new delimitation of the federal territory has been discussed since the Federal Republic was founded in 1949 and even before. Committees and expert commissions advocated a reduction of the number of states; academics (Rutz, Miegel, Ottnad etc.) and politicians (Döring, Apel, and others) made proposals –  some of them far-reaching –  for redrawing boundaries but hardly anything came of these public discussions. Territorial reform is sometimes propagated by the richer states as a means to avoid or reduce fiscal transfers.


The debate on a new delimitation of the German territory started in 1919 as part of discussions about the new constitution. Hugo Preuss, the father of the Weimar Constitution, drafted a plan to divide the German Reich into 14 roughly equal-sized states. His proposal was turned down due to opposition of the states and concerns of the government. Article 18 of the constitution enabled a new delimitation of the German territory but set high hurdles: Three fifth of the votes handed in, and at least the majority of the population are necessary to decide on the alteration of territory. In fact, until 1933 there were only four changes in the configuration of the German states: The 7 Thuringian states were merged in 1920, whereby Coburg opted for Bavaria, Pyrmont joined Prussia in 1922, and Waldeck did so in 1929. Any later plans to break up the dominating Prussia into smaller states failed because political circumstances were not favorable to state reforms.


After the Nazi Party seized power in January 1933, the Länder increasingly lost importance. They became administrative regions of a centralised country. Three changes are of particular note: on January 1, 1934, Mecklenburg-Schwerin was united with the neighbouring Mecklenburg-Strelitz; and, by the Greater Hamburg Act (Groß-Hamburg-Gesetz), from April 1, 1937, the area of the city-state was extended, while Lübeck lost its independence and became part of the Prussian province of Schleswig-Holstein.


As the premiers did not come to an agreement on this question, the Parliamentary Council was supposed to address this issue. Its provisions are reflected in Article 29. There was a binding provision for a new delimitation of the federal territory: the Federal Territory must be revised ... (paragraph 1). Moreover, in territories or parts of territories whose affiliation with a Land had changed after 8 May 1945 without a referendum, people were allowed to petition for a revision of the current status within a year after the promulgation of the Basic Law (paragraph 2). If at least one tenth of those entitled to vote in Bundestag elections were in favour of a revision, the federal government had to include the proposal into its legislation. Then a referendum was required in each territory or part of a territory whose affiliation was to be changed (paragraph 3). The proposal should not take effect if within any of the affected territories a majority rejected the change. In this case, the bill had to be introduced again and after passing had to be confirmed by referendum in the Federal Republic as a whole (paragraph 4). The reorganization should be completed within three years after the Basic Law had come into force (paragraph 6).


In the Paris Agreements of 23 October 1954, France offered to establish an independent "Saarland", under the auspices of the Western European Union (WEU), but on 23 October 1955 in the Saar Statute referendum the Saar electorate rejected this plan by 67.7% to 32.3% (out of a 96.5% turnout: 423,434 against, 201,975 for) despite the public support of Federal German Chancellor Konrad Adenauer for the plan. The rejection of the plan by the Saarlanders was interpreted as support for the Saar to join the Federal Republic of Germany.


Paragraph 6 of Article 29 stated that if a petition was successful a referendum should be held within three years. Since the deadline passed on 5 May 1958 without anything happening the Hesse state government filed a constitutional complaint with the Federal Constitutional Court in October 1958. The complaint was dismissed in July 1961 on the grounds that Article 29 had made the new delimitation of the federal territory an exclusively federal matter. At the same time, the Court reaffirmed the requirement for a territorial revision as a binding order to the relevant constitutional bodies.


In his investiture address, given on 28 October 1969 in Bonn, Chancellor Willy Brandt proposed that the government would consider Article 29 of the Basic Law as a binding order. An expert commission was established, named after its chairman, the former Secretary of State Professor Werner Ernst. After two years of work, the experts delivered their report in 1973. It provided an alternative proposal for both northern Germany and central and southwestern Germany. In the north, either a single new state consisting of Schleswig-Holstein, Hamburg, Bremen and Lower Saxony should be created (solution A) or two new states, one in the northeast consisting of Schleswig-Holstein, Hamburg and the northern part of Lower Saxony (from Cuxhaven to Lüchow-Dannenberg) and one in the northwest consisting of Bremen and the rest of Lower Saxony (solution B). In the Center and South West either Rhineland-Palatinate (with the exception of the Germersheim district but including the Rhine-Neckar region) should be merged with Hesse and the Saarland (solution C), the district of Germersheim would then become part of Baden-Württemberg.


The Basic Law of the Federal Republic of Germany, the federal constitution, stipulates that the structure of each Federal State's government must "conform to the principles of republican, democratic, and social government, based on the rule of law" (Article 28). Most of the states are governed by a cabinet led by a Ministerpräsident (Minister-President), together with a unicameral legislative body known as the Landtag (State Diet). The states are parliamentary republics and the relationship between their legislative and executive branches mirrors that of the federal system: the legislatures are popularly elected for four or five years (depending on the state), and the Minister-President is then chosen by a majority vote among the Landtag's members. The Minister-President appoints a cabinet to run the state's agencies and to carry out the executive duties of the state's government.


The governments in Berlin, Bremen and Hamburg are designated by the term Senate. In the three free states of Bavaria, Saxony, and Thuringia the government is referred to as the State Government (Staatsregierung), and in the other ten states the term Land Government (Landesregierung) is used. Before January 1, 2000, Bavaria had a bicameral parliament, with a popularly elected Landtag, and a Senate made up of representatives of the state's major social and economic groups. The Senate was abolished following a referendum in 1998. The states of Berlin, Bremen, and Hamburg are governed slightly differently from the other states. In each of those cities, the executive branch consists of a Senate of approximately eight, selected by the state's parliament; the senators carry out duties equivalent to those of the ministers in the larger states. The equivalent of the Minister-President is the Senatspräsident (President of the Senate) in Bremen, the Erster Bürgermeister (First Mayor) in Hamburg, and the Regierender Bürgermeister (Governing Mayor) in Berlin. The parliament for Berlin is called the Abgeordnetenhaus (House of Representatives), while Bremen and Hamburg both have a Bürgerschaft. The parliaments in the remaining 13 states are referred to as Landtag (State Parliament).


The Districts of Germany (Kreise) are administrative districts, and every state except the city-states of Berlin, Hamburg, and Bremen consists of "rural districts" (Landkreise), District-free Towns/Cities (Kreisfreie Städte, in Baden-Württemberg also called "urban districts", or Stadtkreise), cities that are districts in their own right, or local associations of a special kind (Kommunalverbände besonderer Art), see below. The state Free Hanseatic City of Bremen consists of two urban districts, while Berlin and Hamburg are states and urban districts at the same time.


Local associations of a special kind are an amalgamation of one or more Landkreise with one or more Kreisfreie Städte to form a replacement of the aforementioned administrative entities at the district level. They are intended to implement simplification of administration at that level. Typically, a district-free city or town and its urban hinterland are grouped into such an association, or Kommunalverband besonderer Art. Such an organization requires the issuing of special laws by the governing state, since they are not covered by the normal administrative structure of the respective states.


Municipalities (Gemeinden): Every rural district and every Amt is subdivided into municipalities, while every urban district is a municipality in its own right. There are (as of 6 March 2009[update]) 12,141 municipalities, which are the smallest administrative units in Germany. Cities and towns are municipalities as well, also having city rights or town rights (Stadtrechte). Nowadays, this is mostly just the right to be called a city or town. However, in former times there were many other privileges, including the right to impose local taxes or to allow industry only within city limits.


The municipalities have two major policy responsibilities. First, they administer programs authorized by the federal or state government. Such programs typically relate to youth, schools, public health, and social assistance. Second, Article 28(2) of the Basic Law guarantees the municipalities "the right to regulate on their own responsibility all the affairs of the local community within the limits set by law." Under this broad statement of competence, local governments can justify a wide range of activities. For instance, many municipalities develop and expand the economic infrastructure of their communities through the development of industrial trading estates.


Many applications of silicate glasses derive from their optical transparency, which gives rise to one of silicate glasses' primary uses as window panes. Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light. Glass can be colored by adding metallic salts, and can also be painted and printed with vitreous enamels. These qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or molded into any shape, and also because it is a sterile product, it has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also been used for paperweights, marbles, and beads. When extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, and when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects historically were so commonly made of silicate glass that they are simply called by the name of the material, such as drinking glasses and reading glasses.


Most common glass contains other ingredients to change its properties. Lead glass or flint glass is more 'brilliant' because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses.[citation needed] Iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.


Fused quartz is a glass made from chemically-pure SiO2 (silica). It has excellent thermal shock characteristics, being able to survive immersion in water while red hot. However, its high melting-temperature (1723 °C) and viscosity make it difficult to work with. Normally, other substances are added to simplify processing. One is sodium carbonate (Na2CO3, "soda"), which lowers the glass transition temperature. The soda makes the glass water-soluble, which is usually undesirable, so lime (calcium oxide [CaO], generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.


Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks. After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish. Container glass for common bottles and jars is formed by blowing and pressing methods. This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance. Further glass forming techniques are summarized in the table Glass forming techniques.


Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as "crystal" when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.


The most familiar, and historically the oldest, types of glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide, also called lime (CaO), and several minor additives. A very clear and durable quartz glass can be made from pure silica, but the high melting point and very narrow glass transition of quartz make glassblowing and hot working difficult. In glasses like soda lime, the compounds added to quartz are used to lower the melting temperature and improve workability, at a cost in the toughness, thermal stability, and optical transmittance.


Glass is in widespread use largely due to the production of glass compositions that are transparent to visible light. In contrast, polycrystalline materials do not generally transmit visible light. The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light resulting in diffuse reflection. Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material. The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface. These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing—i.e., colored.


Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or ancient Egypt. The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.


Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses). Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt% produce a green tint, which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black. A glass melt can also acquire an amber color from a reducing combustion atmosphere. Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide. When used in art glass or studio glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures and 'cook' times. Most colored glass used in the art market is manufactured in volume by vendors who serve this market although there are some glassmakers with the ability to make their own color from raw materials.


Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. Indigenous development of glass technology in South Asia may have begun in 1730 BCE. In ancient China, though, glassmaking seems to have a late start, compared to ceramics and metal work. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance. Glass objects have been recovered across the Roman empire in domestic, industrial and funerary contexts.[citation needed]


Glass was used extensively during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was also used in jewelry. From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203–1248) and the East end of Gloucester Cathedral. Stained glass had a major revival with Gothic Revival architecture in the 19th-century. With the Renaissance, and a change in architectural style, the use of large stained glass windows became less prevalent. The use of domestic stained glass increased until most substantial houses had glass windows. These were initially small panes leaded together, but with the changes in technology, glass could be manufactured relatively cheaply in increasingly larger sheets. This led to larger window panes, and, in the 20th-century, to much larger windows in ordinary domestic and commercial buildings.


In the 20th century, new types of glass such as laminated glass, reinforced glass and glass bricks have increased the use of glass as a building material and resulted in new applications of glass. Multi-storey buildings are frequently constructed with curtain walls made almost entirely of glass. Similarly, laminated glass has been widely applied to vehicles for windscreens. While glass containers have always been used for storage and are valued for their hygienic properties, glass has been utilized increasingly in industry. Optical glass for spectacles has been used since the late Middle Ages. The production of lenses has become increasingly proficient, aiding astronomers as well as having other application in medicine and science. Glass is also employed as the aperture cover in many solar energy systems.


From the 19th century, there was a revival in many ancient glass-making techniques including cameo glass, achieved for the first time since the Roman Empire and initially mostly used for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy producing colored vases and similar pieces, often in cameo glass, and also using luster techniques. Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. From about 1960 onwards there have been an increasing number of small studios hand-producing glass artworks, and glass artists began to class themselves as in effect sculptors working in glass, and their works as part fine arts.


Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.


There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.


The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance. Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.


New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition). Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.


In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed "splat cooling" by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become "locked into" a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.


In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed "q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.


Glass-ceramic materials share many properties with both non-crystalline glass and crystalline ceramics. They are formed as a glass, and then partially crystallized by heat treatment. For example, the microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.


The term mainly refers to a mix of lithium and aluminosilicates that yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.


Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centered in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.


The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another. This assumption is incorrect, as once solidified, glass stops flowing. The reason for the observation is that in the past, when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not absolutely flat; the edges of the disk became a different thickness as the glass spun. When installed in a window frame, the glass would be placed with the thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window. Occasionally such glass has been found installed with the thicker side at the top, left or right.


In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. The term glass is often used to describe any amorphous solid that exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the rigidity theory. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.


Some people consider glass to be a liquid due to its lack of a first-order phase transition where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. The glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Nonetheless, the equilibrium theory of phase transformations does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.


Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature. A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and in some cases will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.


First recognized in 1900 by Max Planck, it was originally the proportionality constant between the minimal increment of energy, E, of a hypothetical electrically charged oscillator in a cavity that contained black body radiation, and the frequency, f, of its associated electromagnetic wave. In 1905 the value E, the minimal energy increment of a hypothetical oscillator, was theoretically associated by Einstein with a "quantum" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle, as opposed to an electromagnetic wave. It was eventually called the photon.


Classical statistical mechanics requires the existence of h (but does not define its value). Eventually, following upon Planck's discovery, it was recognized that physical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, the "quantum of action", now called the Planck constant. Classical physics cannot explain this fact. In many cases, such as for monochromatic light or for atoms, this quantum of action also implies that only certain energy levels are allowed, and values in between are forbidden.


Equivalently, the smallness of the Planck constant reflects the fact that everyday objects and systems are made of a large number of particles. For example, green light with a wavelength of 555 nanometres (the approximate wavelength to which human eyes are most sensitive) has a frequency of 7014540000000000000♠540 THz (7014540000000000000♠540×1012 Hz). Each photon has an energy E = hf = 6981358000000000000♠3.58×10−19 J. That is a very small amount of energy in terms of everyday experience, but everyday experience is not concerned with individual photons any more than with individual atoms or molecules. An amount of light compatible with everyday experience is the energy of one mole of photons; its energy can be computed by multiplying the photon energy by the Avogadro constant, NA ≈ 7023602200000000000♠6.022×1023 mol−1. The result is that green light of wavelength 555 nm has an energy of 7005216000000000000♠216 kJ/mol, a typical energy of everyday life.


In the last years of the nineteenth century, Planck was investigating the problem of black-body radiation first posed by Kirchhoff some forty years earlier. It is well known that hot objects glow, and that hotter objects glow brighter than cooler ones. The electromagnetic field obeys laws of motion similarly to a mass on a spring, and can come to thermal equilibrium with hot atoms. The hot object in equilibrium with light absorbs just as much light as it emits. If the object is black, meaning it absorbs all the light that hits it, then its thermal light emission is maximized.


The assumption that black-body radiation is thermal leads to an accurate prediction: the total amount of emitted energy goes up with the temperature according to a definite rule, the Stefan–Boltzmann law (1879–84). But it was also known that the colour of the light given off by a hot object changes with the temperature, so that "white hot" is hotter than "red hot". Nevertheless, Wilhelm Wien discovered the mathematical relationship between the peaks of the curves at different temperatures, by using the principle of adiabatic invariance. At each different temperature, the curve is moved over by Wien's displacement law (1893). Wien also proposed an approximation for the spectrum of the object, which was correct at high frequencies (short wavelength) but not at low frequencies (long wavelength). It still was not clear why the spectrum of a hot object had the form that it has (see diagram).


Prior to Planck's work, it had been assumed that the energy of a body could take on any value whatsoever – that it was a continuous variable. The Rayleigh–Jeans law makes close predictions for a narrow range of values at one limit of temperatures, but the results diverge more and more strongly as temperatures increase. To make Planck's law, which correctly predicts blackbody emissions, it was necessary to multiply the classical expression by a complex factor that involves h in both the numerator and the denominator. The influence of h in this complex factor would not disappear if it were set to zero or to any other value. Making an equation out of Planck's law that would reproduce the Rayleigh–Jeans law could not be done by changing the values of h, of the Boltzmann constant, or of any other constant or variable in the equation. In this case the picture given by classical physics is not duplicated by a range of results in the quantum picture.


The black-body problem was revisited in 1905, when Rayleigh and Jeans (on the one hand) and Einstein (on the other hand) independently proved that classical electromagnetism could never account for the observed spectrum. These proofs are commonly known as the "ultraviolet catastrophe", a name coined by Paul Ehrenfest in 1911. They contributed greatly (along with Einstein's work on the photoelectric effect) to convincing physicists that Planck's postulate of quantized energy levels was more than a mere mathematical formalism. The very first Solvay Conference in 1911 was devoted to "the theory of radiation and quanta". Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta".


The photoelectric effect is the emission of electrons (called "photoelectrons") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real.


Prior to Einstein's paper, electromagnetic radiation such as visible light was considered to behave as a wave: hence the use of the terms "frequency" and "wavelength" to characterise different types of radiation. The energy transferred by a wave in a given time is called its intensity. The light from a theatre spotlight is more intense than the light from a domestic lightbulb; that is to say that the spotlight gives out more energy per unit time and per unit space(and hence consumes more electricity) than the ordinary bulb, even though the colour of the light might be very similar. Other waves, such as sound or the waves crashing against a seafront, also have their own intensity. However, the energy account of the photoelectric effect didn't seem to agree with the wave description of light.


The "photoelectrons" emitted as a result of the photoelectric effect have a certain kinetic energy, which can be measured. This kinetic energy (for each photoelectron) is independent of the intensity of the light, but depends linearly on the frequency; and if the frequency is too low (corresponding to a photon energy that is less than the work function of the material), no photoelectrons are emitted at all, unless a plurality of photons, whose energetic sum is greater than the energy of the photoelectrons, acts virtually simultaneously (multiphoton effect)  Assuming the frequency is high enough to cause the photoelectric effect, a rise in intensity of the light source causes more photoelectrons to be emitted with the same kinetic energy, rather than the same number of photoelectrons to be emitted with higher kinetic energy.


Niels Bohr introduced the first quantized model of the atom in 1913, in an attempt to overcome a major shortcoming of Rutherford's classical model. In classical electrodynamics, a charge moving in a circle should radiate electromagnetic radiation. If that charge were to be an electron orbiting a nucleus, the radiation would cause it to lose energy and spiral down into the nucleus. Bohr solved this paradox with explicit reference to Planck's work: an electron in a Bohr atom could only have certain defined energies En


Bohr also introduced the quantity , now known as the reduced Planck constant, as the quantum of angular momentum. At first, Bohr thought that this was the angular momentum of each electron in an atom: this proved incorrect and, despite developments by Sommerfeld and others, an accurate description of the electron angular momentum proved beyond the Bohr model. The correct quantization rules for electrons – in which the energy reduces to the Bohr model equation in the case of the hydrogen atom – were given by Heisenberg's matrix mechanics in 1925 and the Schrödinger wave equation in 1926: the reduced Planck constant remains the fundamental quantum of angular momentum. In modern terms, if J is the total angular momentum of a system with rotational invariance, and Jz the angular momentum measured along any given direction, these quantities can only take on the values


where the uncertainty is given as the standard deviation of the measured value from its expected value. There are a number of other such pairs of physically measurable values which obey a similar rule. One example is time vs. energy. The either-or nature of uncertainty forces measurement attempts to choose between trade offs, and given that they are quanta, the trade offs often take the form of either-or (as in Fourier analysis), rather than the compromises and gray areas of time series analysis.


The Bohr magneton and the nuclear magneton are units which are used to describe the magnetic properties of the electron and atomic nuclei respectively. The Bohr magneton is the magnetic moment which would be expected for an electron if it behaved as a spinning charge according to classical electrodynamics. It is defined in terms of the reduced Planck constant, the elementary charge and the electron mass, all of which depend on the Planck constant: the final dependence on h1/2 (r2 > 0.995) can be found by expanding the variables.


In principle, the Planck constant could be determined by examining the spectrum of a black-body radiator or the kinetic energy of photoelectrons, and this is how its value was first calculated in the early twentieth century. In practice, these are no longer the most accurate methods. The CODATA value quoted here is based on three watt-balance measurements of KJ2RK and one inter-laboratory determination of the molar volume of silicon, but is mostly determined by a 2007 watt-balance measurement made at the U.S. National Institute of Standards and Technology (NIST). Five other measurements by three different methods were initially considered, but not included in the final refinement as they were too imprecise to affect the result.


There are both practical and theoretical difficulties in determining h. The practical difficulties can be illustrated by the fact that the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another. The most likely reason is that the measurement uncertainty for one (or both) of the methods has been estimated too low – it is (or they are) not as precise as is currently believed – but for the time being there is no indication which method is at fault.


The theoretical difficulties arise from the fact that all of the methods except the X-ray crystal density method rely on the theoretical basis of the Josephson effect and the quantum Hall effect. If these theories are slightly inaccurate – though there is no evidence at present to suggest they are – the methods would not give accurate values for the Planck constant. More importantly, the values of the Planck constant obtained in this way cannot be used as tests of the theories without falling into a circular argument. Fortunately, there are other statistical ways of testing the theories, and the theories have yet to be refuted.


A watt balance is an instrument for comparing two powers, one of which is measured in SI watts and the other of which is measured in conventional electrical units. From the definition of the conventional watt W90, this gives a measure of the product KJ2RK in SI units, where RK is the von Klitzing constant which appears in the quantum Hall effect. If the theoretical treatments of the Josephson effect and the quantum Hall effect are valid, and in particular assuming that RK = h/e2, the measurement of KJ2RK is a direct determination of the Planck constant.


The gyromagnetic ratio γ is the constant of proportionality between the frequency ν of nuclear magnetic resonance (or electron paramagnetic resonance for electrons) and the applied magnetic field B: ν = γB. It is difficult to measure gyromagnetic ratios precisely because of the difficulties in precisely measuring B, but the value for protons in water at 7002298150000000000♠25 °C is known to better than one part per million. The protons are said to be "shielded" from the applied magnetic field by the electrons in the water molecule, the same effect that gives rise to chemical shift in NMR spectroscopy, and this is indicated by a prime on the symbol for the gyromagnetic ratio, γ′p. The gyromagnetic ratio is related to the shielded proton magnetic moment μ′p, the spin number I (I = 1⁄2 for protons) and the reduced Planck constant.


A further complication is that the measurement of γ′p involves the measurement of an electric current: this is invariably measured in conventional amperes rather than in SI amperes, so a conversion factor is required. The symbol Γ′p-90 is used for the measured gyromagnetic ratio using conventional electrical units. In addition, there are two methods of measuring the value, a "low-field" method and a "high-field" method, and the conversion factors are different in the two cases. Only the high-field value Γ′p-90(hi) is of interest in determining the Planck constant.


The Faraday constant F is the charge of one mole of electrons, equal to the Avogadro constant NA multiplied by the elementary charge e. It can be determined by careful electrolysis experiments, measuring the amount of silver dissolved from an electrode in a given time and for a given electric current. In practice, it is measured in conventional electrical units, and so given the symbol F90. Substituting the definitions of NA and e, and converting from conventional electrical units to SI units, gives the relation to the Planck constant.


The X-ray crystal density method is primarily a method for determining the Avogadro constant NA but as the Avogadro constant is related to the Planck constant it also determines a value for h. The principle behind the method is to determine NA as the ratio between the volume of the unit cell of a crystal, measured by X-ray crystallography, and the molar volume of the substance. Crystals of silicon are used, as they are available in high quality and purity by the technology developed for the semiconductor industry. The unit cell volume is calculated from the spacing between two crystal planes referred to as d220. The molar volume Vm(Si) requires a knowledge of the density of the crystal and the atomic weight of the silicon used. The Planck constant is given by


There are a number of proposals to redefine certain of the SI base units in terms of fundamental physical constants. This has already been done for the metre, which is defined in terms of a fixed value of the speed of light. The most urgent unit on the list for redefinition is the kilogram, whose value has been fixed for all science (since 1889) by the mass of a small cylinder of platinum–iridium alloy kept in a vault just outside Paris. While nobody knows if the mass of the International Prototype Kilogram has changed since 1889 – the value 1 kg of its mass expressed in kilograms is by definition unchanged and therein lies one of the problems – it is known that over such a timescale the many similar Pt–Ir alloy cylinders kept in national laboratories around the world, have changed their relative mass by several tens of parts per million, however carefully they are stored, and the more so the more they have been taken out and used as mass standards. A change of several tens of micrograms in one kilogram is equivalent to the current uncertainty in the value of the Planck constant in SI units.


The legal process to change the definition of the kilogram is already underway, but it had been decided that no final decision would be made before the next meeting of the General Conference on Weights and Measures in 2011. (For more detailed information, see kilogram definitions.) The Planck constant is a leading contender to form the basis of the new definition, although not the only one. Possible new definitions include "the mass of a body at rest whose equivalent energy equals the energy of photons whose frequencies sum to 7050135639273999999♠135639274×1042 Hz", or simply "the kilogram is defined so that the Planck constant equals 6966662606895999999♠6.62606896×10−34 J⋅s".


Public policy and political leadership helps to "level the playing field" and drive the wider acceptance of renewable energy technologies. Countries such as Germany, Denmark, and Spain have led the way in implementing innovative policies which has driven most of the growth over the past decade. As of 2014, Germany has a commitment to the "Energiewende" transition to a sustainable energy economy, and Denmark has a commitment to 100% renewable energy by 2050. There are now 144 countries with renewable energy policy targets.


Total investment in renewable energy (including small hydro-electric projects) was $244 billion in 2012, down 12% from 2011 mainly due to dramatically lower solar prices and weakened US and EU markets. As a share of total investment in power plants, wind and solar PV grew from 14% in 2000 to over 60% in 2012. The top countries for investment in recent years were China, Germany, Spain, the United States, Italy, and Brazil. Renewable energy companies include BrightSource Energy, First Solar, Gamesa, GE Energy, Goldwind, Sinovel, Trina Solar, Vestas and Yingli.


EU member countries have shown support for ambitious renewable energy goals. In 2010, Eurobarometer polled the twenty-seven EU member states about the target "to increase the share of renewable energy in the EU by 20 percent by 2020". Most people in all twenty-seven countries either approved of the target or called for it to go further. Across the EU, 57 percent thought the proposed goal was "about right" and 16 percent thought it was "too modest." In comparison, 19 percent said it was "too ambitious".