A linear encoder is a sensor, transducer or readhead paired with a scale that encodes position. The sensor reads the scale in order to convert the encoded position into an analog or digital signal, which can be decoded into position by a digital readout or motion controller; the encoder can be either absolute. Motion can be determined by change in position over time. Linear encoder technologies include optical, inductive and eddy current. Optical technologies include self imaging and interferometric. Linear encoders are used in metrology instruments, motion systems and high precision machining tools ranging from digital calipers and coordinate measuring machines to stages, CNC Mills, manufacturing gantry tables and semiconductor steppers. Linear encoders are transducers that exploit many different physical properties in order to encode position: Optical linear encoders dominate the high resolution market and may employ shuttering/Moiré, diffraction or holographic principles. Optical encoders are the most accurate of the standard styles of encoders, the most used in industrial automation applications.
When specifying an optical encoder, it’s important that the encoder have extra protection built in to prevent contamination from dust and other conditions common to industrial environments. Typical incremental scale periods vary from hundreds of micrometers down to sub-micrometer. Interpolation can provide resolutions as fine as a nanometre. Light sources used include visible LEDs, miniature light-bulbs and laser diodes. Magnetic linear encoders employ either active or passive scales and position may be sensed using sense-coils, Hall effect or magnetoresistive readheads. With coarser scale periods than optical encoders resolutions in the order of a micrometer are the norm. Capacitive linear encoders work by sensing the capacitance between a scale. Typical applications are digital calipers. One of the disadvantages is the sensitivity to uneven dirt, which can locally change the relative permittivity. Inductive technology is robust to contaminants, allowing calipers and other measurement tools that are coolant-proof.
A well known application of the inductive measuring principle is the Inductosyn. US Patent 3820110, "Eddy current type digital encoder and position reference", gives an example of this type of encoder, which uses a scale coded with high and low permeability, non-magnetic materials, detected and decoded by monitoring changes in inductance of an AC circuit that includes an inductive coil sensor. Maxon makes an example product; the sensors are based on an image correlation method. The Sensor takes subsequent pictures from the surface being measured and compares the images for displacement. Resolutions down to 1 nm are possible. There are two main areas of application for linear encoders: Measurement application include coordinate-measuring machines, laser scanners, gear measurement, tension testers, digital read outs. Servo controlled motion systems employ linear encoder so as to provide accurate, high-speed movement. Typical applications include machine tools, pick-and-place PCB assembly equipment.
Linear encoders can have digital outputs. The industry standard, analog output for linear encoders is cosine quadrature signals; these are transmitted differentially so as to improve noise immunity. An early industry standard was 12 µA peak-peak current signals but more this has been replaced with 1V peak to peak voltage signals. Compared to digital transmission, the analog signals' lower bandwidth helps to minimise emc emissions. Quadrature sine/cosine signals can be monitored by using an oscilloscope in XY mode to display a circular Lissajous Figure. Highest accuracy signals are obtained if the Lissajous Figure is circular and centred. Modern encoder systems employ circuitry to trim these error mechanisms automatically; the overall accuracy of the linear encoder is a combination of the scale accuracy and errors introduced by the readhead. Scale contributions to the error budget include slope. Readhead error mechanisms are described as cyclic error or sub-divisional error as they repeat every scale period.
The largest contributor to readhead inaccuracy is signal offset, followed by signal imbalance and phase error. Overall signal size does not affect encoder accuracy, signal-to-noise and jitter performance may degrade with smaller signals. Automatic signal compensation mechanisms can include automatic offset compensation, automatic balance compensation and automatic gain control. Phase is more difficult to compensate dynamically and is applied as one time compensation during installation or calibration. Other forms of inaccuracy include signal distortion. A linear incremental encoder has two digital output signals, A and B, which issue quadrature squarewaves. Depending on its internal mechanism, an encoder may derive A and B directly from sensors which are fundamentally digital in nature, or it may interpolate its internal, analogue sine/cosine signals. In the latter case, the interpolation process sub-divides the scale period and thereby achieves higher measurement resolution. In either case, the encoder will output quadrature squarewaves, with the distance between edges of the two channels being the reso
The screen-door effect is a visual artifact of displays, where the fine lines separating pixels become visible in the displayed image. This can be seen in digital projector images and regular displays under magnification or at close range, but the increases in display resolutions have made this much less significant. More the screen door effect has been an issue with virtual reality headsets and other head-mounted displays, because these are viewed at a much closer distance, stretch a single display across a much wider field of view; this appears because projector optics have higher pixel density than the image they project, allowing these fine lines, which are much smaller than the pixels themselves, to be seen. This results in an image that appears as if viewed through a fine screen or mesh such as those used on anti-insect screen doors, it most appears as a rectangular mesh or sometimes as a hexagonal structure. The screen door effect was noticed on the first digital projector: an LCD projector made in 1984 by Gene Dolgoff.
To eliminate this artifact, Dolgoff invented depixelization, which used various optical methods to eliminate the visibility of the spaces between the pixels. The dominant method made use of a microlens array, wherein each micro-lens caused a magnified image of the pixel behind it, filling in the previously-visible spaces between pixels. In addition, when making a projector with a single, full-color LCD panel, an additional appearance of pixelation was visible due to the noticeability of green pixels adjacent to red and blue pixels, forming a noticeable repeating light and dark pattern. Use of a micro-lens array at a greater distance created new pixel images, with each "new" pixel being a summation of six neighboring sub-pixels. Since there were as many micro-lenses as there were original pixels, no resolution was lost, confirmed with modulation transfer function measurements; the screen door effect on Digital Light Processing projectors can be mitigated by deliberately setting the projected image out of focus, which blurs the boundaries of each pixel to its neighbor.
This minimizes the effect by filling the black pixel perimeters with adjacent light. Some older LCD projectors have a more noticeable screen door effect than first generation DLP projectors. Newer DLP chip designs promise closer spacing of the mirror elements. Use of Dolgoff's depixelization method could produce a DLP projector without noticeable pixelation. Rainbow effect, an artifact associated with single-chip DLP projectors Silk screen effect Scan line Hi Fi Writer, "What is the'screen door effect'?"
A programmer, coder, or software engineer is a person who creates computer software. The term computer programmer can refer to a specialist in one area of computers, or to a generalist who writes code for many kinds of software. One who practices, or professes, a formal approach to programming may be known as a programmer analyst. On the other hand, "code monkey" is a derogatory term for a programmer who writes code without any involvement in the design or specifications. A programmer's primary computer language is prefixed to these titles, those who work in a web environment prefix their titles with web. A range of occupations—including: software developer, web developer, mobile applications developer, embedded firmware developer, software engineer, computer scientist, game programmer, game developer, or software analyst—that involve programming require a range of other skills; the use of the term programmer for these positions is sometimes considered an insulting or derogatory simplification.
British countess and mathematician Ada Lovelace is considered the first computer programmer, as she was the first to publish an algorithm intended for implementation on Charles Babbage's analytical engine, in October 1842, intended for the calculation of Bernoulli numbers. Because Babbage's machine was never completed to a functioning standard in her time, she never saw this algorithm run; the first person to run a program on a functioning modern electronically based computer was computer scientist Konrad Zuse, in 1941. The ENIAC programming team, consisting of Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman were the first working programmers. International Programmers' Day is celebrated annually on 7 January. In 2009, the government of Russia decreed a professional annual holiday known as Programmers' Day to be celebrated on 13 September, it had been an unofficial international holiday before that. The word "software" did not appear in print until the 1960s.
Before this time, computers were programmed either by customers, or the few commercial computer vendors of the time, such as UNIVAC and IBM. The first company founded to provide software products and services was Computer Usage Company in 1955; the software industry expanded in the early 1960s immediately after computers were first sold in mass-produced quantities. Universities and business customers created a demand for software. Many of these programs were written in-house by full-time staff programmers; some were distributed between users of a particular machine for no charge. Others were done on a commercial basis, other firms such as Computer Sciences Corporation started to grow; the computer/hardware makers started bundling operating systems, system software and programming environments with their machines. The industry expanded with the rise of the personal computer in the mid-1970s, which brought computing to the desktop of the office worker. In the following years, it created a growing market for games and utilities.
DOS, Microsoft's first operating system product, was the dominant operating system at the time. In the early years of the 21st century, another successful business model has arisen for hosted software, called software-as-a-service, or SaaS. From the point of view of producers of some proprietary software, SaaS reduces the concerns about unauthorized copying, since it can only be accessed through the Web, by definition, no client software is loaded onto the end user's PC. By 2014, the role of cloud developer had been defined. Computer programmers write, test and maintain the detailed instructions, called computer programs, that computers must follow to perform their functions. Programmers conceive and test logical structures for solving problems by computer. Many technical innovations in programming — advanced computing technologies and sophisticated new languages and programming tools — have redefined the role of a programmer and elevated much of the programming work done today. Job titles and descriptions may vary, depending on the organization.
Programmers work in many settings, including corporate information technology departments, big software companies, small service firms and government entities of all sizes. Many professional programmers work for consulting companies at client sites as contractors. Licensing is not required to work as a programmer, although professional certifications are held by programmers. Programming is considered a profession. Programmers' work varies depending on the type of business for which they are writing programs. For example, the instructions involved in updating financial records are different from those required to duplicate conditions on an aircraft for pilots training in a flight simulator. Simple programs can be written in a few hours, more complex ones may require more than a year of work, while others are never considered'complete' but rather are continuously improved as long as they stay in use. In most cases, several programmers work together as a team under a senior programmer’s supervision.
Programmers write programs according to the specifications determined b
Social Democratic Party (Estonia)
The Social Democratic Party is a social-democratic political party in Estonia led by Jevgeni Ossinovski. The party was known as the Moderate People's Party; the SDE has been a member of the Party of European Socialists since 16 May 2003 and a member of the Socialist International since November 1990. In spite of its nominal ideology, it has governed with the right-wing parties. For the history of Estonian Social Democracy before the 1980s, see Estonian Social Democratic Workers' Party During the perestroika era the Estonian Social Democratic Party was formed as Estonia's social-democratic movements merged in 1990; the movements were: the Estonian Democratic Labour Party, the Estonian Social Democratic Independence Party, the Russian Social Democratic Party of Estonia and the Estonian Socialist Party's Foreign Association. The ESDP's first leader was Marju Lauristin, they restored their contacts with the Socialist International in 1990. ESDP formed an electoral alliance with the agrarian Estonian Rural Centre Party for 1992 and 1995 elections.
In 1996, after electoral defeat these two parties merged and named themselves the Moderates. The Moderates were accepted as a full member of the Socialist International at its 20th congress in September 1999. In 1999 the Moderates and the centre-right People's Party, set up in May 1998 after a fusion of Peasants' Party and People's Party of Republicans and Conservatives, formed the Moderate People's Party; the unlikely decision to fuse took place on 29 May 1999, with some foreign commentators drawing parallels with'right-wing socialists'. In November the same year, the unification was formally approved by party's general assembly; the Moderates' contacts with People's Party predecessors had started in 1998. The two parties had a joint list in 1999 parliamentary election and formed a governing coalition with Pro Patria Union and Reform Party. In 2003, the Moderate People's Party joined the Party of European Socialists. After disappointing election results in 2003, the party renamed itself the Social Democratic Party on 7 February 2004.
It was the most successful party in the 2004 European Parliamentary Election, obtaining 36.8% of the national vote and returning 3 MEPs. The SDE is committed to the social market economy model, in addition to conventional social-democratic values including equality, social justice and the welfare state. On 10 May 2005 Sven Mikser joined them. On 28 November former social-liberal Mark Soosaar re-joined the SDE; the party was in opposition from 2002 on, but they participated talks for a common alternative presidential candidate to Arnold Rüütel, SDE's Toomas Hendrik Ilves was elected on 23 September 2006 as the next president of Estonia. After last elections to the local government councils on 16 October 2005, the party in most major cities is in opposition, but are a part of the governing coalition in Rakvere and Tapa; the party improved its position in most areas. In Tallinn, it formed a joint list with the agrarian People's Union, which got 6 seats out of 63 seats with 11.1% share of votes. Comparing to 2003.
Elections to the local government council in Tallinn SDE and People's Union gained seats. In the 2003 election, SDE got a 4.9% share of votes and People's Union 3.4% share of votes, which were both below a 5% election threshold. In Estonia, SDE local lists won 6.43% share of votes. In 2003 they got only 4.39% share of votes nationally. SDE is governing in 20 local councils. After the 2003 election the party was represented in 104 local councils out of 247. SDE's aim in the 2007 Estonian parliamentary election was to win at least 17 seats out of 101. Independent member of current Riigikogu Liina Tõnisson ran as a candidate in their list. All SDE's MEPs and their current MPs were candidates in the 2007 election; the party got 58,354 votes, a gain of +3.6%. In April 2007, the Social Democrats joined the coalition government led by the Estonian Reform Party. In the 2011 parliamentary election on 6 March 2011, the SDE received 17.1 % of 19 seats. The small Russian Party in Estonia merged into the SDE in 2012.
Following the resignation of Prime Minister Andrus Ansip, a new cabinet was sworn in on 26 March 2014, with Taavi Rõivas of the Reform Party serving as Prime Minister in coalition with the SDE. In the 2014 European elections held on 25 May 2014, the SDE won 13.6% of the national vote, electing a single Member of the European Parliament. In the 2015 parliamentary election on 1 March 2015, the SDE received 15.2% of the vote and 15 seats in the Riigikogu. After the coalition formation with Reform and IRL, MP Jevgeni Ossinovski announced that he would challenge Sven Mikser in the party congress on 30 May 2015. Mikser however stepped down before the election at the congress and Ossinovski was chosen as the new party leader. On 7 November 2016, the Social Democratic Party and IRL announced that they were asking Prime Minister Taavi Rõivas to resign and were planning on negotiating a new majority government. In the following vote of confidence on 9 November, the majority of Riigikogu voted in favor of removing the prime minister’s government.
On 23 November 2016, a new coalition government consisting of
Unschooling is an educational method and philosophy that advocates learner-chosen activities as a primary means for learning. Unschooling students learn through their natural life experiences including play, household responsibilities, personal interests and curiosity and work experience, books, elective classes, family and social interaction. Unschooling encourages exploration of activities initiated by the children themselves, believing that the more personal learning is the more meaningful, well-understood and therefore useful it is to the child. While courses may be taken, unschooling questions the usefulness of standard curricula, conventional grading methods, other features of traditional schooling in the education of each unique child; the term "unschooling" was coined in the 1970s and used by educator John Holt regarded as the father of unschooling. While considered a subset of homeschooling, unschoolers may be as philosophically separate from other homeschoolers as they are from advocates of conventional schooling.
While homeschooling has been subject to widespread public debate, little media attention has been given to unschooling in particular. Critics of unschooling see it as an extreme educational philosophy, with concerns that unschooled children will lack the social skills and motivation of their schooled peers, while proponents of unschooling say the opposite is true: self-directed education in a natural environment better equips a child to handle the "real world." A fundamental premise of unschooling is that children want to learn. From this an argument can be made that institutionalizing children in a so-called "one size fits all" or "factory model" school is an inefficient use of the children's time, because it requires each child to learn specific subject matter in a particular manner, at a particular pace, at a specific time regardless of that individual's present or future needs, goals, or any pre-existing knowledge he or she might have about the topic. Many unschoolers believe that opportunities for valuable hands-on, community-based and real-world experiences may be missed when educational opportunities are limited to, or dominated by, those inside a school building.
Unschoolers note that psychologists have documented many differences between children in the way they learn, assert that unschooling is better equipped to adapt to these differences. People vary in their "learning styles", that is, the preference in. However, research has demonstrated that this preference is not related to increased learning or improved performance. Students have different learning needs. In a traditional school setting, teachers evaluate an individual student differently from other students, while teachers use different methods, this is sometimes haphazard and not always with regard to an individual student. Developmental psychologists note that just as children reach growth milestones at different ages from each other, children are prepared to learn different things at different ages. Just as some children learn to walk during a normal range of eight to fifteen months, begin to talk across an larger range, unschoolers assert that they are ready and able to read, for example, at different ages, girls earlier, boys later.
In fact, experts have discovered that natural learning produces far greater changes in behavior than do traditional learning methods, though not an increase in the amount of information learned. Traditional education requires all children to begin reading at the same time and do multiplication at the same time. Unschoolers sometimes state that learning any specific subject is less important than learning how to learn, they assert, in the words of Holt: Since we can't know what knowledge will be most needed in the future, it is senseless to try to teach it in advance. Instead, we should try to turn out people who love learning so much and learn so well that they will be able to learn whatever must be learned, it is asserted that this ability to learn on their own makes it more that when these children are adults, they can continue to learn what they need to know to meet newly emerging needs and goals. Many unschoolers disagree that there is a particular body of knowledge that every person, regardless of the life they lead, needs to possess.
Unschoolers argue that, in the words of John Holt, "If children are given access to enough of the world, they will see enough what things are important to themselves and to others, they will make for themselves a better path into that world than anyone else could make for them." Parents of unschoolers provide resources, guidance and advice to facilitate experiences that aid their children in accessing and making sense of the world. Common parental activities include sharing interesting books and activities with their children, helping them find knowledgeable people to explore an interest with, helping them set goals and figure out what they need to do to meet their goals. Unschooling's interest-based nature does not mean. Parents tend to involve themselves with younger children (older children, unless new to unschooling, often
Defensive end is a defensive position in the sport of American and Canadian football. This position has designated the players at each end of the defensive line, but changes in formations over the years have changed how the position is played. Early formations, with six- and seven-man lines, used the end as a containment player, whose job was first to prevent an "end run" around his position secondarily to force plays inside; when most teams adopted a twelve-man line, two different styles of end play developed: "crashing" ends, who rushed into the backfield to disrupt plays, "stand-up" or "waiting" ends, who played the more traditional containment style. Some teams would use both styles of end play, depending on game situations. Traditionally, defensive ends are in a three-point stance, with their free hand cocked back ready to "punch" the offensive lineman, or in a "two-point stance" like a linebacker so they can keep containment; some defensive ends play the position due to their size. Other ends play the position due to their agility.
These ends can time the snap of the ball in order to get a jump on the rush, stop the play. Most of the time it is the job of the defensive end in run defense to keep outside or contain, which means that no one should get to their outside; the defensive ends are fast for players of their size the fastest and smallest players on the defensive line. They must be able to shed blockers to get to the ball. Defensive ends are often used to cover the outside area of the line of scrimmage, to tackle ball carriers running to the far right or left side, to defend against screen passes. Since the creation of zone blitz defenses in the late 1990s, defensive ends have sometimes been used in pass coverages, dropping back to cover routes run close to the line of scrimmage. In the 3–4 defense, defensive ends are used as run stoppers and are much larger, they are 285–315 pounds. The position is played by a more agile or undersized defensive tackle; because of the increased popularity of the 3–4 defense, the value of a defensive tackle prospect that can be used in this manner has increased.
They are used to distract the offensive lineman on pass rushing plays to let the outside linebackers get a sack. They are 6'3"–6'8", they block screen are put outside the offensive tackles to get a sack. Glossary of American football