Perpetual motion is motion of bodies that continues indefinitely. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source; this kind of machine is impossible, as it would violate the second law of thermodynamics. These laws of thermodynamics apply regardless of the size of the system. For example, the motions and rotations of celestial bodies such as planets may appear perpetual, but are subject to many processes that dissipate their kinetic energy, such as solar wind, interstellar medium resistance, gravitational radiation and thermal radiation, so they will not keep moving forever. Thus, machines that extract energy from finite sources will not operate indefinitely, because they are driven by the energy stored in the source, which will be exhausted. A common example is devices powered by ocean currents, whose energy is derived from the Sun, which itself will burn out. Machines powered by more obscure sources have been proposed, but are subject to the same inescapable laws, will wind down.
In 2017, new states of matter, time crystals, were discovered in which on a microscopic scale the component atoms are in continual repetitive motion, thus satisfying the literal definition of "perpetual motion". However, these do not constitute perpetual motion machines in the traditional sense or violate thermodynamic laws because they are in their quantum ground state, so no energy can be extracted from them; the history of perpetual motion machines dates back to the Middle Ages. For millennia, it was not clear whether perpetual motion devices were possible or not, but the development of modern theories of thermodynamics has shown that they are impossible. Despite this, many attempts have been made continuing into modern times. Modern designers and proponents use other terms, such as "over unity", to describe their inventions. Oh ye seekers after perpetual motion, how many vain chimeras have you pursued? Go and take your place with the alchemists. There is a scientific consensus that perpetual motion in an isolated system violates either the first law of thermodynamics, the second law of thermodynamics, or both.
The first law of thermodynamics is a version of the law of conservation of energy. The second law can be phrased in several different ways, the most intuitive of, that heat flows spontaneously from hotter to colder places. In other words: In any isolated system, one cannot create new energy; as a result, the thermal efficiency—the produced work power divided by the input heating power—cannot be greater than one. The output work power of heat engines is always smaller than the input heating power; the rest of the heat energy supplied is wasted as heat to the ambient surroundings. The thermal efficiency therefore has a maximum, given by the Carnot efficiency, always less than one; the efficiency of real heat engines is lower than the Carnot efficiency due to irreversibility arising from the speed of processes, including friction. Statements 2 and 3 apply to heat engines. Other types of engines which convert e.g. mechanical into electromagnetic energy, cannot operate with 100% efficiency, because it is impossible to design any system, free of energy dissipation.
Machines which comply with both laws of thermodynamics by accessing energy from unconventional sources are sometimes referred to as perpetual motion machines, although they do not meet the standard criteria for the name. By way of example and other low-power machines, such as Cox's timepiece, have been designed to run on the differences in barometric pressure or temperature between night and day; these machines have a source of energy, albeit one, not apparent, so that they only seem to violate the laws of thermodynamics. Machines which extract energy from long-lived sources - such as ocean currents - will run down when their energy sources do, they are not perpetual motion machines because they are consuming energy from an external source and are not isolated systems. One classification of perpetual motion machines refers to the particular law of thermodynamics the machines purport to violate: A perpetual motion machine of the first kind produces work without the input of energy, it thus violates the first law of thermodynamics: the law of conservation of energy.
A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. When the thermal energy is equivalent to the work done, this does not violate the law of conservation of energy. However, it does violate the more subtle second law of thermodynamics; the signature of a perpetual motion machine of the second kind is that there is only one heat reservoir involved, being spontaneously cooled without involving a transfer of heat to a cooler reservoir. This conversion of heat into useful work, without any side effect, is impossible, according to the second law of thermodynamics. A perpetual motion machine of the third kind is defined as one that eliminates friction and other dissipative forces, to maintain motion forever, it is impossible to make such a machine, as dissipation can n
Imperial College London
Imperial College London is a public research university located in London, England. In 1851, Prince Albert built his vision for a cultural area composed of the Victoria and Albert Museum, Natural History Museum, Royal Albert Hall, Royal Colleges, the Imperial Institute. In 1907, Imperial College was established by Royal Charter, bringing together the Royal College of Science, Royal School of Mines, City and Guilds College. In 1988, the Imperial College School of Medicine was formed through a merger with St Mary's Hospital Medical School. In 2004, Queen Elizabeth II opened the Imperial College Business School; the main campus is located with a new innovation campus in White City. The college has a research centre at Silwood Park, teaching hospitals throughout London. Imperial is organised through faculties of natural science, engineering and business, its emphasis is on the practical application of technology. With more than 140 countries represented on campus and 59% of students from outside the UK, the university has a international community.
In 2018–19, Imperial is ranked 8th globally in the QS World University Rankings, 9th in the THE World University Rankings, 24th in the Academic Ranking of World Universities, 8th in Reuters Top 100: World's Most Innovative Universities. Student and researcher affiliations include 14 Nobel laureates, 3 Fields Medalists, 1 Turing Award winner, 74 Fellows of the Royal Society, 87 Fellows of the Royal Academy of Engineering, 85 Fellows of the Academy of Medical Sciences; the college's origins can be traced back as far as the founding of the Royal College of Chemistry on Hanover Square in 1845, with the support of Prince Albert and parliament. Following some financial trouble, this was absorbed in 1853 into the newly formed Government School of Mines and Science Applied to the Arts, located on Jermyn Street; the school was renamed the Royal School of Mines a decade later. The medical school has roots in many different school across London, the oldest of which dates back to 1823, with the foundation of the teaching facilities at the West London Infirmary at Villiers Street.
Known as Charing Cross Hospital Medical School, it was designed to provide medical education for the needs of a university. This was followed in 1834 when Westminster Hospital surgeons started taking students under their care. Established on Dean Street, the school was forced to close in 1847, but was reopened in 1849 with a new specimen museum; the first teaching at St Mary's Hospital hospital in Paddington began in 1851, with St Mary's Hospital Medical School established in 1854. Proceeds from the Great Exhibition of 1851 were designated by Prince Albert to be used to develop a cultural area in South Kensington for the use and education of the public. Within the next 6 years the Victoria and Albert and Science museums had opened, joined by the Natural History Museum in 1881, in 1888 the Imperial Institute; as well as museums, new facilities for the royal colleges were constructed, with the Royal College of Chemistry and the Royal School of Mines moving to South Kensington between 1871 and 1872.
In 1881 the Normal School of Science was established in South Kensington under the leadership of Thomas Huxley, taking over responsibility for the teaching of the natural sciences and agriculture from the Royal School of Mines. The school was granted the name Royal College of Science by royal consent in 1890; as these institutions were not part of universities, they were unable to grant degrees to students, instead bestowed associateships such as the Associateship of the Royal College of Science. The Central Institution of the City and Guilds of London Institute, formed by the City of London's livery companies, was opened on Exhibition Road by the Prince of Wales, founded to focus on providing technical education, with courses starting in early 1885; the institution was renamed the Central Technical College in 1893, becoming a school of the University of London in 1900. At the start of the 20th century there was a concern that Britain was falling behind its key rivals – Germany – in scientific and technical education.
A departmental committee was set up at the Board of Education in 1904, to look into the future of the Royal College of Science. A report released in 1906 called for the establishment of an institution unifying the Royal College of Science and the Royal School of Mines, as well as – if agreement could be reached with the City and Guilds of London Institute – their Central Technical CollegeOn 8 July 1907, King Edward VII granted a Royal Charter establishing the Imperial College of Science and Technology; this incorporated the Royal College of Science. It made provisions for the Central Technical College to join once conditions regarding its governance were met, as well as for Imperial to become a college of the University of London; the college joined the University of London on 22 July 1908, with the Central Technical College joining Imperial in 1910 as the City and Guilds College. The main campus of Imperial College was constructed beside the buildings of the Imperial Institute, the new building for the Royal College of Science having opened across from it in 1906, the foundation stone for the Royal School of Mines building being laid by King Edward VII in July 1909.
As students at Imperial had to study separately for London degrees, in January 1919, students and alumni voted for a petition to make Imperial a university with its own degree awarding powers, independent of the University of London. In response, the University of London changed its regulations in 1925 so that the courses taught only at Imperial would be examined by the university, enabling students to ga
University of Strathclyde
The University of Strathclyde is a public research university located in Glasgow, Scotland. Founded in 1796 as the Andersonian Institute, it is Glasgow's second-oldest university, with the university receiving its royal charter in 1964 as the UK's first technological university, it takes its name from the historic Kingdom of Strathclyde. The University of Strathclyde is Scotland's third-largest university by number of students, with students and staff from over 100 countries; the institution was awarded University of the Year 2012 and Entrepreneurial University of the year 2013 by Times Higher Education. The annual income of the institution for 2017–18 was £304.4 million of which £68.9 million was from research grants and contracts, with an expenditure of £304.0 million. Entry into many of the courses in the university is competitive and successful entrants in 2015 had an average of 480 UCAS points, it is one of the 39 old universities in the UK comprising the distinctive second cluster of elite universities after Oxbridge.
The university was founded in 1796 through the will of John Anderson, professor of Natural Philosophy at the University of Glasgow who left instructions and the majority of his estate to create a second university in Glasgow which would focus on "Useful Learning" – specialising in practical subjects – "for the good of mankind and the improvement of science, a place of useful learning". The University named its city centre campus after him. In 1828, the institution was renamed Anderson's University fulfilling Anderson's vision of two universities in the city of Glasgow; the name was changed in 1887, to reflect the fact that there was no legal authority for the use of the title of'university'. As a result, the Glasgow and West of Scotland Technical College was formed, becoming the Royal Technical College in 1912, the Royal College of Science and Technology in 1956 concentrating on science and engineering teaching and research. Undergraduate students could qualify for degrees of the University of Glasgow or the equivalent Associate of the Royal College of Science and Technology.
Under Principal Samuel Curran, internationally respected nuclear physicist, the Royal College gained University Status, receiving its Royal Charter to become The University of Strathclyde in 1964, merging with the Scottish College of Commerce at the same time. Contrary to popular belief, The University of Strathclyde was not created as a result of the Robbins Report – the decision to grant the Royal College university status had been made earlier in the 1960s but delayed as a result of Robbins Report; the University of Strathclyde was the UK's first technological university reflecting its history and research in technological education. In 1993, the University incorporated Jordanhill College of Education; the university has grown from 4,000 full-time students in 1964 to over 20,000 students in 2003, when it celebrated the 100th anniversary of the laying of the foundation stone of the original Royal College building. In July 2015, Her Majesty The Queen opened the University of Strathclyde Technology and Innovation Centre.
Since taking over the Jordanhill college in 1993, the University operated two campuses - The John Anderson Campus and the Jordanhill campus until 2012 when the Jordanhill campus was closed and everything was moved to the John Anderson Campus. The centrepiece building has long been the massive Royal College Building. Started in 1903 and completed in 1912, it was opened in 1910 and at the time was the largest educational building in Europe for technical education. Built as the Glasgow and West of Scotland Technical College Building, it now houses Bioscience and Electronic and Electrical Engineering; the building is undergoing major internal renovation following the relocation of the Pharmacology and Bioscience departments to new accommodation in the John Arbuthnott building, the installation of a new heating system. The Livingstone Tower is a high rise building completed in 1965, it is home to departments including and Information Sciences and Mathematics and Statistics. Meanwhile, a new biomedical sciences building was opened in early 2010.
It was designed by Shepparrd Robson, aims to bring the multi-faceted disciplines of the Institute together under one roof. Sited on Cathedral Street in Glasgow, the 8,000 m2 building is the gateway to the University campus and city centre from the motorway; the James Weir Building has been reconstructed and reopened in 2014 after a serious fire resulted in many rooms being unusable. The Architecture Building, completed in 1967, was designed by Frank Fielden and Associates, Frank Fielden being the Professor of Architecture in the Architecture School at the time. In 2012, Historic Scotland granted Listed Building Status to it, along with the Wolfson Building designed by Morris and Steedman Architects. 2012 saw the 20th Century Society select the Architecture Building as their'Building of the Month' for September due to its cultural significance and enduring appeal. The University of Strathclyde Centre for Sports and Wellbeing is a leisure facility undergoing construction situated adjacent to 100 Cathedral Street.
Construction began in November 2016 and is due to be completed in Summer 2018. The Andersonian Library is the principal library of the University of Strathclyde. Established in 1796, it is one of the largest of its type in Scotland, it is situated in the Curran building. Situated over 5 floors at present, the Andersonian Library has more than 2,000 reader places, 450 computer places and extensive wi-fi zones for laptop use, it has around one million print volumes as well as access to over 540,000 electronic books, 239 databases and ov
Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure that resembles a football, made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge, it was first generated in 1984 by Eric Rohlfing, Donald Cox and Andrew Kaldor using a laser to vaporize carbon in a supersonic helium beam. In 1985 their work was repeated by Harold Kroto, James R. Heath, Sean O'Brien, Robert Curl, Richard Smalley at Rice University, who recognized the structure of C60 as buckminsterfullerine. Kroto and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of buckminsterfullerene and the related class of molecules, the fullerenes. Buckminsterfullerene is the most common occurring fullerene, it can be found in small quantities in soot. The molecule has been detected in deep space; the discoverers of the allotrope named the newfound molecule after Buckminster Fuller, who designed many geodesic dome structures that look similar to C60.
This is misleading, however, as Fuller's geodesic domes are constructed only by further dividing hexagons or pentagons into triangles, which are deformed by moving vertices radially outward to fit the surface of a sphere. A common, shortened name for buckminsterfullerene is "buckyballs". Theoretical predictions of buckyball molecules appeared in the late 1960s and early 1970s, but these reports went unnoticed. In the early 1970s, the chemistry of unsaturated carbon configurations was studied by a group at the University of Sussex, led by Harry Kroto and David Walton. In the 1980s, Smalley and Curl at Rice University developed experimental technique to generate these substances, they used laser vaporization of a suitable target to produce clusters of atoms. Kroto realized. Concurrent but unconnected to the Kroto-Smalley work, astrophysicists were working with spectroscopists to study infrared emissions from giant red carbon stars. Smalley and team were able to use a laser vaporization technique to create carbon clusters which could emit infrared at the same wavelength as had been emitted by the red carbon star.
Hence, the inspiration came to Smalley and team to use the laser technique on graphite to generate fullerenes. C60 was discovered in 1985 by Robert Curl, Harold Kroto, Richard Smalley. Using laser evaporation of graphite they found Cn clusters of which the most common were C60 and C70. A solid rotating graphite disk was used as the surface from which carbon was vaporized using a laser beam creating hot plasma, passed through a stream of high-density helium gas; the carbon species were subsequently ionized resulting in the formation of clusters. Clusters ranged in molecular masses, but Kroto and Smalley found predominance in a C60 cluster that could be enhanced further by allowing the plasma to react longer, they discovered that the C60 molecule formed a cage-like structure, a regular truncated icosahedron. For this discovery Curl and Smalley were awarded the 1996 Nobel Prize in Chemistry; the experimental evidence, a strong peak at 720 atomic mass units, indicated that a carbon molecule with 60 carbon atoms was forming, but provided no structural information.
The research group concluded after reactivity experiments, that the most structure was a spheroidal molecule. The idea was rationalized as the basis of an icosahedral symmetry closed cage structure. Kroto mentioned geodesic dome structures of the noted futurist and inventor Buckminster Fuller as influences in the naming of this particular substance as buckminsterfullerene. In 1989 physicists Wolfgang Krätschmer, Konstantinos Fostiropoulos, Donald R. Huffman observed unusual optical absorptions in thin films of carbon dust; the soot had been generated by an arc-process between two graphite electrodes in a helium atmosphere where the electrode material evaporates and condenses forming soot in the quenching atmosphere. Among other features, the IR spectra of the soot showed four discrete bands in close agreement to those proposed for C60. Another paper on the characterization and verification of the molecular structure followed on in the same year from their thin film experiments, detailed the extraction of an evaporable as well as benzene soluble material from the arc-generated soot.
This extract had TEM and X-ray crystal analysis consistent with arrays of spherical C60 molecules 1.0 nm in van der Waals diameter as well as the expected molecular mass of 720 u for C60 in their mass spectra. The method was simple and efficient to prepare the material in gram amounts per day which has boosted the fullerene research and is today applied for the commercial production of fullerenes; the discovery of practical routes to C60 led to the exploration of a new field of chemistry involving the study of fullerenes. Soot is produced by pyrolysis of aromatic hydrocarbons. Fullerenes are extracted from the soot with organic solvents using a Soxhlet extractor; this step yields a solution containing up to 75% of C60, as well as other fullerenes. These fractions are separated using chromatography; the fullerenes are dissolved in a hydrocarbon or halogenated hydrocarbon and separated using alumina columns. Buckminsterfullerene is a truncated icosahedron with 60 vertices and 32 faces with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C60 molecule is about 1.01 nanometers. The nucleus to nucleus diameter of a
New Scientist, first published on 22 November 1956, is a weekly, English-language magazine that covers all aspects of science and technology. New Scientist, based in London, publishes editions in the UK, the United States, Australia. Since 1996 it has been available online. Sold in retail outlets and on subscription, the magazine covers news, features and commentary on science and their implications. New Scientist publishes speculative articles, ranging from the technical to the philosophical; the magazine was founded in 1956 by Tom Margerison, Max Raison and Nicholas Harrison as The New Scientist, with Issue 1 on 22 November, priced one shilling. The British monthly science magazine Science Journal, published 1965–71, was merged with New Scientist to form New Scientist and Science Journal; the cover of New Scientist listed articles in plain text. Page numbering followed academic practice with sequential numbering for each quarterly volume. So, for example, the first page of an issue in March could be 649 instead of 1.
Issues numbered issues separately. From the beginning of 1961 "The" was dropped from the title. From 1965, the front cover was illustrated; until the 1970s, colour was not used except for on the cover. Since its first issue, New Scientist has written about the applications of science, through its coverage of technology. For example, the first issue included an article "Where next from Calder Hall?" on the future of nuclear power in the UK, a topic that it has covered throughout its history. In 1964 there was a regular "Science in British Industry" section with several items. An article in the magazine's 10th anniversary issues provides anecdotes on the founding of the magazine. In 1970, the Reed Group, which went on to become Reed Elsevier, acquired New Scientist when it merged with IPC Magazines. Reed retained the magazine when it sold most of its consumer titles in a management buyout to what is now TI Media. Throughout most of its history, New Scientist has published cartoons as light relief and comment on the news, with contributions from regulars such as Mike Peyton and David Austin.
The Grimbledon Down comic strip, by cartoonist Bill Tidy, appeared from 1970 to 1994. The Ariadne pages in New Scientist commented on the lighter side of science and technology and included contributions from Daedalus; the fictitious inventor devised plausible but impractical and humorous inventions developed by the DREADCO corporation. Daedalus moved to Nature. Issues of New Scientist from Issue 1 to the end of 1989 have been made free to read online. Subsequent issues require a subscription. In the first half of 2013, the international circulation of New Scientist averaged 125,172. While this was a 4.3% reduction on the previous year's figure, it was a much smaller reduction in circulation than many mainstream magazines of similar or greater circulation. For the 2014 UK circulation fell by 3.2% but stronger international sales, increased the circulation to 129,585. See #Website below. In April 2017, New Scientist changed hands when RELX Group known as Reed Elsevier, sold the magazine to Kingston Acquisitions, a group set up by Sir Bernard Gray, Louise Rogers and Matthew O’Sullivan to acquire New Scientist.
Kingston Acquisitions renamed itself New Scientist Ltd. New Scientist contains the following sections: Leader, Technology, Features, CultureLab, The Last Word and Jobs & Careers. A Tom Gauld cartoon appears on the Letters page. A readers' letters section discusses recent articles and discussions take place on the website. Readers contribute observations on examples of pseudoscience to Feedback, offer questions and answers on scientific and technical topics to Last Word. New Scientist has produced a series of books compiled from contributions to Last Word. There are 51 issues a year, with a New Year double issue; the double issue in 2014 was the 3,000th edition of the magazine. The Editor-in-chief is Emily Wilson, Executive Editor is Graham Lawton, Managing Editor is Rowan Hooper and Editor-at-Large is Jeremy Webb. Consultants include Fred Pearce, Marcus Chown, Linda Geddes. Simon Ings and former editor Alun Anderson are contributors.) Percy Cudlipp Nigel Calder Donald Gould Bernard Dixon Michael Kenward David Dickson Alun Anderson Jeremy Webb Roger Highfield Sumit Paul-Choudhury Emily Wilson The New Scientist website carries blogs and news articles.
Users with free-of-charge registration have limited access to new content and can receive emailed New Scientist newsletters. Subscribers to the print edition have full access to all articles and the archive of past content that has so far been digitised. Online readership takes various forms. Overall global views of an online database of over 100,000 articles are 8.0m by 3.6m unique users according to Adobe Reports & Analytics, as of September 2014. On social media there are 1.47m+ Twitter followers, 2.3m+ Facebook likes and 365,000+ Google+ followers as of January 2015. New Scientist has published books derived from its content, many of which are selected questions and answers from the Last Word section of the magazine and website: 1998; the Last Word. ISBN 978-0-19-286199-3 2000; the Last Word 2. ISBN 978-0-19-286204-4 2005. Does Anything Eat Wasps?. ISBN 978-1-86197-973-5 2006. Why Don't Penguins' Feet Freeze?. ISBN 978-1861978769 2007. How to
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
3D printing is any of various processes in which material is joined or solidified under computer control to create a three-dimensional object, with material being added together layer by layer. In the 1990s, 3D printing techniques were considered suitable only for the production of functional or aesthetical prototypes and a more appropriate term was rapid prototyping. Today, the precision and material range have increased to the point that 3D printing is considered as an industrial production technology, with the name of additive manufacturing. 3D printed objects can have a complex shape or geometry and are always produced starting from a digital 3D model or a CAD file. There are many different 3D printing processes, that can be grouped into seven categories: Vat photopolymerization Material jetting Binder jetting Powder bed fusion Material extrusion Directed energy deposition Sheet laminationThe most used 3D Printing process is a material extrusion technique called fused deposition modeling.
Metal Powder bed fusion has been gaining prominence during the immense applications of metal parts in the 3D printing industry. In 3D Printing, a three-dimensional object is built from computer-aided design model by successively adding material layer by layer, unlike the conventional machining process, where material is removed from a stock item, or the casting and forging processes which date to antiquity; the term "3D printing" referred to a process that deposits a binder material onto a powder bed with inkjet printer heads layer by layer. More the term is being used in popular vernacular to encompass a wider variety of additive manufacturing techniques. United States and global technical standards use the official term additive manufacturing for this broader sense; the umbrella term additive manufacturing gained popularity in the 2000s, inspired by the theme of material being added together. In contrast, the term subtractive manufacturing appeared as a retronym for the large family of machining processes with material removal as their common theme.
The term 3D printing still referred only to the polymer technologies in most minds, the term AM was more to be used in metalworking and end use part production contexts than among polymer, ink-jet, or stereo lithography enthusiasts. By early 2010s, the terms 3D printing and additive manufacturing evolved senses in which they were alternate umbrella terms for additive technologies, one being used in popular language by consumer-maker communities and the media, the other used more formally by industrial end-use part producers, machine manufacturers, global technical standards organizations; until the term 3D printing has been associated with machines low in price or in capability. 3D printing and additive manufacturing reflect that the technologies share the theme of material addition or joining throughout a 3D work envelope under automated control. Peter Zelinski, the editor-in-chief of Additive Manufacturing magazine, pointed out in 2017 that the terms are still synonymous in casual usage but some manufacturing industry experts are trying to make a distinction whereby Additive Manufacturing comprises 3D printing plus other technologies or other aspects of a manufacturing process.
Other terms that have been used as synonyms or hypernyms have included desktop manufacturing, rapid manufacturing, on-demand manufacturing. Such application of the adjectives rapid and on-demand to the noun manufacturing was novel in the 2000s reveals the prevailing mental model of the long industrial era in which all production manufacturing involved long lead times for laborious tooling development. Today, the term subtractive has not replaced the term machining, instead complementing it when a term that covers any removal method is needed. Agile tooling is the use of modular means to design tooling, produced by additive manufacturing or 3D printing methods to enable quick prototyping and responses to tooling and fixture needs. Agile tooling uses a cost effective and high quality method to respond to customer and market needs, it can be used in hydro-forming, injection molding and other manufacturing processes. 1981: Early additive manufacturing equipment and materials were developed in the 1980s.
In 1981, Hideo Kodama of Nagoya Municipal Industrial Research Institute invented two additive methods for fabricating three-dimensional plastic models with photo-hardening thermoset polymer, where the UV exposure area is controlled by a mask pattern or a scanning fiber transmitter.1984: On 16 July 1984, Alain Le Méhauté, Olivier de Witte, Jean Claude André filed their patent for the stereolithography process. The application of the French inventors was abandoned by the French General Electric Company and CILAS; the claimed reason was "for lack of business perspective". Three weeks in 1984, Chuck Hull of 3D Systems Corporation filed his own patent for a stereolithography fabrication system, in which layers are added by curing photopolymers with ultraviolet light lasers. Hull defined the process as a "system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed,". Hull's contribution was the STL file format and the digital slicing and infill strategies common to many processes today.
1988: The technology used by most 3D printers to date—especially hobbyist and consumer-oriented models—is fused deposition modeling, a special application of plastic extrusion, developed in 1988 by S