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Exploding-bridgewire detonator
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Description
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Civilian use EBWs have found uses outside nuclear weapons, such as the Titan IV, safety conscious applications where stray electrical currents might detonate normal blasting caps, and applications requiring very precise timing for multiple point commercial blasting in mines or quarries. EBW detonators are much safer than regular electric detonators because unlike regular detonators EBWs do not have primary explosives. Primary explosives such as lead azide are very sensitive to static electricity, radio frequency, shock, etc.
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Exploding-bridgewire detonator
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Mechanism of operation
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The bridgewire is usually made of gold, but platinum or gold/platinum alloys can also be used. The most common commercial wire size is 0.038 mm (1.5 mils) in diameter and 1 mm (40 mils) in length, but lengths ranging from 0.25 mm to 2.5 mm (10 mils to 100 mils) can be encountered. From the available explosives, only PETN at low densities can be initiated by sufficiently low shock to make its use practical in commercial systems as a part of the EBW initiator. It can be chained with another explosive booster, often a pellet of tetryl, RDX or some PBX (e.g., PBX 9407). Detonators without such booster are called initial pressing detonators (IP detonators).
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Exploding-bridgewire detonator
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Mechanism of operation
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During initiation, the wire heats with the passing current until melting point is reached. The heating rate is high enough that the liquid metal has no time to flow away, and heats further until it vaporizes. During this phase the electrical resistance of the bridgewire assembly rises. Then an electric arc forms in the metal vapor, leading to drop of electrical resistance and sharp growth of the current, quick further heating of the ionized metal vapor, and formation of a shock wave. To achieve the melting and subsequent vaporizing of the wire in time sufficiently short to create a shock wave, a current rise rate of at least 100 amperes per microsecond is required.
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Exploding-bridgewire detonator
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Mechanism of operation
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If the current rise rate is lower, the bridge may burn, perhaps causing deflagration of the PETN pellet, but it will not cause detonation. PETN-containing EBWs are also relatively insensitive to a static electricity discharge. Their use is limited by the thermal stability range of PETN. Slapper detonators, which can use high density hexanitrostilbene, may used in temperatures up to almost 300 °C (572 °F) in environments ranging from vacuum to high pressures.
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Exploding-bridgewire detonator
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Firing system
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The EBW and the slapper detonator are the safest known types of detonators, as only a very high-current fast-rise pulse can successfully trigger them. However, they require a bulky power source for the current surges required. The extremely short rise times are usually achieved by discharging a low-inductance, high-capacitance, high-voltage capacitor (e.g., oil-filled, Mylar-foil, or ceramic) through a suitable switch (spark gap, thyratron, krytron, etc.) into the bridge wire. A very rough approximation for the capacitor is a rating of 5 kilovolts and 1 microfarad, and the peak current ranges between 500 and 1000 amperes. The high voltage may be generated using a Marx generator. Low-impedance capacitors and low-impedance coaxial cables are required to achieve the necessary current rise rate.
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Exploding-bridgewire detonator
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Firing system
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The flux compression generator is one alternative to capacitors. When fired, it creates a strong electromagnetic pulse, which is inductively coupled into one or more secondary coils connected to the bridge wires or slapper foils. A low energy density capacitor equivalent to a compression generator would be roughly the size of a soda can. The energy in such a capacitor would be 1⁄2·C·V2, which for the above-mentioned capacitor is 12.5 J. (By comparison, a defibrillator delivers ~200 J from 2 kV and perhaps 20 µF. The flash-strobe in a disposable camera is typically 3 J from a 300 V capacitor of 100 µF.) In a fission bomb, the same or similar circuit is used for powering the neutron trigger, the initial source of fission neutrons.
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MARKINT
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MARKINT
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Market intelligence, MARKINT is an intelligence gathering discipline used by the United States Intelligence Community (IC) that focuses on intelligence gathered from the global capital markets. It is analogous to other “INTs” in the IC’s domain, such as SIGINT (signals intelligence), ELINT (electronic intelligence) of (signals Intelligence), MASINT (measurement and signature intelligence), IMINT (imagery intelligence) and HUMINT (human intelligence). It is complementary to but different from FININT (financial intelligence), in which information about the financial affairs of entities of interest is gathered.
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MARKINT
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MARKINT
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Within the IC, MARKINT is defined as, “the systematic collection and analysis of confidential and open-source information from the global capital and commodities markets in order to derive actionable intelligence from the activities of market participants”. MARKINT is different from the traditional definition of Market Intelligence or Marketing Intelligence, in which information is gathered for purposes of enhancing commercial marketing efforts rather than for purposes of analysis relating to national security.
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Yamaha P-115
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Yamaha P-115
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The Yamaha P-115 is a portable digital piano introduced in 2015. It replaces its best-selling predecessor, the P-105.The P-115 has 14 different voices which range from Grand Piano to Rock Organ, and comes pre-loaded with 64 preset songs. There is a built in metronome as well as a built in recorder which can store roughly 100 KB (11,000 notes) for play back or upload to an external device. Keys are Yamaha's Graded hammer standard (GHS) which range in weight from the low keys to high keys to more accurately mimic the feel of an acoustic piano. The overall weight of the keyboard is 26 pounds. The keyboard can come in colors black or white (p115B or p115WH).
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Yamaha P-115
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Features
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64 preset songs (14 demo, 50 piano) USB to host line AUX out ([L/L+R][R]) 2 6.3mm front-facing headphone jacks Pedal output to accompany either a standard pedal or Yamaha's LP-5 three pedal unit.
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Jerry M. Chow
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Jerry M. Chow
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Jerry M. Chow is a physicist who conducts research in quantum information processing. He has worked as the manager of the Experimental Quantum Computing group at the IBM Thomas J. Watson Research Center in Yorktown Heights, New York since 2014 and is the primary investigator of the IBM team for the IARPA Multi-Qubit Coherent Operations and Logical Qubits programs. After graduating magna cum laude with a B.A. in physics and M.S. in applied mathematics from Harvard University, he went on to earn his Ph.D. in 2010 under Robert J. Schoelkopf at Yale University. While at Yale, he participated in experiments in which superconducting qubits were coupled via a cavity bus for the first time and two-qubit algorithms were executed on a superconducting quantum processor.His work at IBM has led to the publication of findings related to the characterization of a universal set of all-microwave gates that can be executed on two transmon qubits, as well as the implementation of a subsection of a surface code fault-tolerant superconducting quantum computing architecture. His leadership at IBM has led to progress being made in quantum error correction and quantum machine learning, as well as the release of the cloud-based IBM Quantum Experience. He was named a Fellow of the American Physical Society in 2021.
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Jerry M. Chow
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Personal life
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Jerry grew up in Sheepshead Bay neighborhood of Brooklyn.
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Fierz identity
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Fierz identity
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In theoretical physics, a Fierz identity is an identity that allows one to rewrite bilinears of the product of two spinors as a linear combination of products of the bilinears of the individual spinors. It is named after Swiss physicist Markus Fierz. The Fierz identities are also sometimes called the Fierz–Pauli–Kofink identities, as Pauli and Kofink described a general mechanism for producing such identities.
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Fierz identity
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Fierz identity
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There is a version of the Fierz identities for Dirac spinors and there is another version for Weyl spinors. And there are versions for other dimensions besides 3+1 dimensions. Spinor bilinears in arbitrary dimensions are elements of a Clifford algebra; the Fierz identities can be obtained by expressing the Clifford algebra as a quotient of the exterior algebra. When working in 4 spacetime dimensions the bivector ψχ¯ may be decomposed in terms of the Dirac matrices that span the space: ψχ¯=14(cS1+cVμγμ+cTμνTμν+cAμγμγ5+cPγ5) .The coefficients are cS=(χ¯ψ),cVμ=(χ¯γμψ),cTμν=−(χ¯Tμνψ),cAμ=−(χ¯γμγ5ψ),cP=(χ¯γ5ψ) and are usually determined by using the orthogonality of the basis under the trace operation. By sandwiching the above decomposition between the desired gamma structures, the identities for the contraction of two Dirac bilinears of the same type can be written with coefficients according to the following table.
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Fierz identity
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Fierz identity
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where S=χ¯ψ,V=χ¯γμψ,T=χ¯[γμ,γν]ψ/22,A=χ¯γ5γμψ,P=χ¯γ5ψ.
The table is symmetric with respect to reflection across the central element. The signs in the table correspond to the case of commuting spinors, otherwise, as is the case of fermions in physics, all coefficients change signs. For example, under the assumption of commuting spinors, the V × V product can be expanded as, (χ¯γμψ)(ψ¯γμχ)=(χ¯χ)(ψ¯ψ)−12(χ¯γμχ)(ψ¯γμψ)−12(χ¯γμγ5χ)(ψ¯γμγ5ψ)−(χ¯γ5χ)(ψ¯γ5ψ).
Combinations of bilinears corresponding to the eigenvectors of the transpose matrix transform to the same combinations with eigenvalues ±1. For example, again for commuting spinors, V×V + A×A, (χ¯γμψ)(ψ¯γμχ)+(χ¯γ5γμψ)(ψ¯γ5γμχ)=−((χ¯γμχ)(ψ¯γμψ)+(χ¯γ5γμχ)(ψ¯γ5γμψ)).
Simplifications arise when the spinors considered are Majorana spinors, or chiral fermions, as then some terms in the expansion can vanish from symmetry reasons.
For example, for anticommuting spinors this time, it readily follows from the above that χ¯1γμ(1+γ5)ψ2ψ¯3γμ(1−γ5)χ4=−2χ¯1(1−γ5)χ4ψ¯3(1+γ5)ψ2.
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Supplemental Punctuation
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Supplemental Punctuation
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Supplemental Punctuation is a Unicode block containing historic and specialized punctuation characters, including biblical editorial symbols, ancient Greek punctuation, and German dictionary marks.
Additional punctuation characters are in the General Punctuation block and sprinkled in dozens of other Unicode blocks.
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Supplemental Punctuation
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History
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The following Unicode-related documents record the purpose and process of defining specific characters in the Supplemental Punctuation block:
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5-meter band
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5-meter band
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The 5-meter band (60 MHz) is the middle portion of the very high frequency (VHF) radio spectrum allocated to amateur radio use.
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5-meter band
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History
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On October 10, 1924, the 5-meter band (56–64 MHz) was first made available to amateurs in the United States by the Third National Radio Conference. On October 4, 1927, the band was allocated on a worldwide basis by the International Radiotelegraph Conference in Washington, D.C. 56–60 MHz was allocated for amateur and experimental use.At the 1938 International Radiocommunication Conference in Cairo, television broadcasting was given priority in a portion of the 5- and 6-meter band in Europe. Television and low power stations, meaning those with less than 1 kW power, were allocated 56–58.5 MHz and amateurs, experimenters and low power stations were allocated 58.5–60 MHz in the European region. The conference maintained the 56–60 MHz allocation for other regions and allowed administrations in Europe latitude to allow amateurs to continue using 56–58.5 MHz.In 1940, television channel 2 was reallocated to 60 MHz and TV channel 1 was moved to 50–56 MHz maintaining a gap for the 5-meter amateur band. When the US entered World War II, transmissions by amateur radio stations were suspended for the duration of the war. After the war, the 5-meter band was briefly reopened to amateurs from 56 to 60 MHz until March 1, 1946. For British and some European amateurs were allocated the 5-meter band (58.5 MHz to 60 MHz) till 1949–1951, as by then the 5-metre band was given for television broadcasting.
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5-meter band
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History
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But 1955-1962 due to TV channel allocations Australian and New Zealand (shorter time) authorities allocated 56-60 MHz instead 50 MHz, but for International Geophysical Year additionally again returned 50-54 MHz range.
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5-meter band
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History
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Also around this time permission to YA1AA for 5-meter band in Afghanistan has been issued. In September 1957 (IGY) 56.5-58 MHz band allocated for local experiments in Romania, some UK stations in this range were heard.Following a request to be able to track the progression of propagation openings DSI report (CEPT Phase II) of 1995 noted the possibility that a beacon's allocation at 60 MHz should be reassessed when TV broadcasting is no longer operating below 68 MHz of VHF Band I.
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5-meter band
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History
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From 2007 the IARU R1 is encouraging member societies to try and obtain small allocation for beacons cluster at 60 MHz. In Viena Interim conference 2019 accepted to add the 40 MHz and the 60 MHz Bandplan (used in some countries) in the VHF-Handbook as separate dedicated section. They can serve as an example for future use in other countries of Region 1.
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5-meter band
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Allocations
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In January 1949 the 5-meter Band is removed from the amateur service (in some countries a transitional period up to 1951 was applied).
1955.11.01 - 1962.06.01 56-60 MHz band allocated for radio amateurs in Australia (VK).
1956.06.01 - 1959.01.31 56-60 MHz band allocated for radio amateurs in New Zealand (ZL) and overseas territories (ZK, ZM).
In April 2018, Ireland (EI) allocated much of the low VHF spectrum to Irish radio amateurs including 60 MHz.
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5-meter band
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Beacons
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In August 2007, the UK (G) approved the use of beacon at 60.050 MHz. Inactive from 2017.
2019.12.16 The Irish beacon EI1KNH started at 60.013 MHz 25 W, vertical dipole.
2022.09.25 The British beacon GB3MCB started at 60.3 MHz FT8/CW 5W, omnidirectional.
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5-meter band
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Propagation
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The 5-metre band shares many characteristics with the neighbouring 6-metre band and is a unique transition spot. However, as it is somewhat higher in frequency it does not display the same propagation mechanisms via the F2 ionospheric layer normally seen at HF which occasionally appear in 6 metres, leastwise not at temperate latitudes. However, Sporadic E is common on the band in summer, tropospheric propagation is marginally more successful than on the 6-metre band, and propagation via the Aurora Borealis and meteor scatter is highly effective.
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5-meter band
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Activity
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Around 1949, at least 18 countries worked in Europe on this band including Iceland and some overseas territories. A bit later from 1956 5-meter cross band (first VK-JA) and interstate Es activities take place in Australia, New Zealand and its overseas territories. 2019-08-29: Es EI4GNB - LY2YR FT8 2,036.3 km (1265 miles) 2022-05-18: Tropo EI9KP - EI4GNB FT8 ~205 km
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Amenable number
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Amenable number
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An amenable number is a positive integer for which there exists a multiset of as many integers as the original number that both add up to the original number and when multiplied together give the original number. To put it algebraically, for a positive integer n, there is a multiset of n integers {a1, ..., an}, for which the equalities n=∑i=1nai=∏i=1nai hold. Negative numbers are allowed in the multiset. For example, 5 is amenable since 5 = 1 + (-1) + 1 + (-1) + 5. All and only those numbers congruent to 0 or 1 (mod 4), except 4, are amenable. (Tamvakis & Lossers 1998) The first few amenable numbers are: 1, 5, 8, 9, 12, 13 ... OEIS: A100832 A solution for integers of the form n = 4k + 1 could be given by a set of 2k (+1)s and 2k (-1)s and n itself. (This generalizes the example of 5 given above.) Although not obvious from the definition, the set of amenable numbers is closed under multiplication (the product of two amenable numbers is an amenable number). All composite numbers would be amenable if the multiset was allowed to be of any length, because, even if other solutions are available, one can always obtain a solution by taking the prime factorization (expressed with repeated factors rather than exponents) and add as many 1s as necessary to add up to n. The product of this set of integers will yield n no matter how many 1s there are in the set. Furthermore, still under this assumption, any integer n would be amenable. Consider the inelegant solution for n of {1, -1, 1, -1, n}. In the sum, the positive ones are cancelled out by the negative ones, leaving n, while in the product, the two negative ones cancel out the effect of their signs.
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Amenable number
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Amenable number
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Amenable numbers should not be confused with amicable numbers, which are pairs of integers whose divisors add up to each other.
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Solar eclipse of December 25, 2000
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Solar eclipse of December 25, 2000
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A partial solar eclipse occurred on December 25, 2000, also known as the "Christmas 2000 Solar Eclipse". A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A partial solar eclipse occurs in the polar regions of the Earth when the center of the Moon's shadow misses the Earth. It is also the last solar eclipse of the 20th century.
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Solar eclipse of December 25, 2000
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Christmas
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This is the first Solar Eclipse on Christmas day since the annular solar eclipse of 1954.
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Solar eclipse of December 25, 2000
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Related eclipses
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Eclipses of 2000 A total lunar eclipse on January 21.
A partial solar eclipse on February 5.
A partial solar eclipse on July 1.
A total lunar eclipse on July 16.
A partial solar eclipse on July 31.
A partial solar eclipse on December 25.
Solar eclipses 2000–2003 This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit.Partial solar eclipses on February 5, 2000 and July 31, 2000 occur in the previous lunar year set.
Metonic series The metonic series repeats eclipses every 19 years (6939.69 days), lasting about 5 cycles. Eclipses occur in nearly the same calendar date. In addition, the octon subseries repeats 1/5 of that or every 3.8 years (1387.94 days). All eclipses in this table occur at the Moon's descending node.
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Tone policing
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Tone policing
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A tone argument (also called tone policing) is a type of ad hominem aimed at the tone of an argument instead of its factual or logical content in order to dismiss a person's argument. Ignoring the truth or falsity of a statement, a tone argument instead focuses on the emotion with which it is expressed. This is a logical fallacy because a person can be angry while still being rational. Nonetheless, a tone argument may be useful when responding to a statement that itself does not have rational content, such as an appeal to emotion.The notion of tone policing became widespread in U.S. social activist circles by the mid-2010s. It was widely disseminated in a 2015 comic issued by the Everyday Feminism website. Activists have argued that tone policing has been regularly employed against feminist and anti-racism advocates, criticizing the way that they presented their arguments rather than engaging with the arguments themselves.
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Gaplus
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Gaplus
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Gaplus is a 1984 fixed shooter arcade game developed and released by Namco. It is the third game in the Galaxian series, serving as a direct sequel to Galaga (1981). In North America, a modification kit was later released to change the name to Galaga 3, possibly to reflect its position in the series. It was the only game other than Phozon to run on the Namco Phozon hardware. A contemporary home port for the Commodore 64 was released in 1988. A "demastered" version of the game (in the style of the Nintendo Entertainment System) was included in Namco Museum Archives Vol. 2 as a bonus title.
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Gaplus
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Gameplay
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The objective of Gaplus is to score as many points as possible by defeating successive waves of enemies in levels called "Parsecs". Its core gameplay is very similar to Galaga: Enemies fly onto the screen in rows and join a formation near the top, then begin attacking the player's ship with kamikaze-like dives. The ship can move left and right, as well as vertically. Bonus lives are earned at certain score intervals, and can also be gained by collecting ship parts dropped by some enemies, as well as collecting Rally-X bonus flags from shooting stars. The player loses a life when struck by an enemy or one of their shots; the game ends when all lives are lost.
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Gaplus
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Gameplay
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Certain enemies drop upgrades that include a tractor beam which the player can use to capture enemies, a large drill that can destroy many enemies at once, powerups that temporarily slow down enemies or nullify their shots, and parts to create a new ship that awards an extra life when completed. Some stages begin with the star field reversing direction, with harder and faster waves of enemies appearing before resuming a normal formation.
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Gaplus
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Gameplay
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The game features bonus "Challenging Stages" just as Galaga did. However, instead of defeating a certain number of enemies, the objective of the challenging stage in Gaplus is to juggle enemies by hitting them as many times as possible. Each hit grants a dot (represented by a bee) in a word or phrase, with extra hits adding to horizontal lines above and below the word. Spelling the entire word or phrase will earn a bonus related to that phrase, and each hit scores bonus points at the end of the round.
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Gaplus
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Reception
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In Japan, Game Machine listed Gaplus on their May 15, 1984 issue as being the most-successful table arcade unit of the month.
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Gaplus
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Legacy
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The arcade version of Gaplus was released on mobile phones, and is also part of Namco Museum Remix (2007) and Namco Museum Megamix (2010) for the Wii with its original title being used. The original version was later re-released under its original name for the Wii Virtual Console on March 25, 2009. In 2011, Gaplus was released for iOS devices as part of Galaga 30th Collection, featuring updated visuals, sound, and achievements.In 2020, Namco released a "demastered" version of the game as a bonus game in the Namco Museum Archives Vol. 2 compilation. Developed by M2, this game emulates the visual style of the Nintendo Entertainment System, similar to the NES-style remake of Pac-Man Championship Edition in Vol. 1.
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Database trigger
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Database trigger
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A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for maintaining the integrity of the information on the database. For example, when a new record (representing a new worker) is added to the employees table, new records should also be created in the tables of the taxes, vacations and salaries. Triggers can also be used to log historical data, for example to keep track of employees' previous salaries.
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Database trigger
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Triggers in DBMS
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Below follows a series of descriptions of how some popular DBMS support triggers.
Oracle In addition to triggers that fire (and execute PL/SQL code) when data is modified, Oracle 10g supports triggers that fire when schema-level objects (that is, tables) are modified and when user logon or logoff events occur.
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Database trigger
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Triggers in DBMS
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Schema-level triggers After Creation Before Alter After Alter Before Drop After Drop Before InsertThe four main types of triggers are: Row-level trigger: This gets executed before or after any column value of a row changes Column-level trigger: This gets executed before or after the specified column changes For each row type: This trigger gets executed once for each row of the result set affected by an insert/update/delete For each statement type: This trigger gets executed only once for the entire result set, but also fires each time the statement is executed.
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Database trigger
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Triggers in DBMS
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System-level triggers From Oracle 8i, database events - logons, logoffs, startups - can fire Oracle triggers.
Microsoft SQL Server A list of all available firing events in Microsoft SQL Server for DDL triggers is available on Microsoft Docs.Performing conditional actions in triggers (or testing data following modification) is done through accessing the temporary Inserted and Deleted tables.
PostgreSQL Introduced support for triggers in 1997. The following functionality in SQL:2003 was previously not implemented in PostgreSQL: SQL allows triggers to fire on updates to specific columns; As of version 9.0 of PostgreSQL this feature is also implemented in PostgreSQL.
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Database trigger
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Triggers in DBMS
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The standard allows the execution of a number of SQL statements other than SELECT, INSERT, UPDATE, such as CREATE TABLE as the triggered action. This can be done through creating a stored procedure or function to call CREATE TABLE.Synopsis: Firebird Firebird supports multiple row-level, BEFORE or AFTER, INSERT, UPDATE, DELETE (or any combination of thereof) triggers per table, where they are always "in addition to" the default table changes, and the order of the triggers relative to each other can be specified where it would otherwise be ambiguous (POSITION clause.) Triggers may also exist on views, where they are always "instead of" triggers, replacing the default updatable view logic. (Before version 2.1, triggers on views deemed updatable would run in addition to the default logic.) Firebird does not raise mutating table exceptions (like Oracle), and triggers will by default both nest and recurse as required (SQL Server allows nesting but not recursion, by default.) Firebird's triggers use NEW and OLD context variables (not Inserted and Deleted tables,) and provide UPDATING, INSERTING, and DELETING flags to indicate the current usage of the trigger.
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Database trigger
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Triggers in DBMS
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As of version 2.1, Firebird additionally supports the following database-level triggers: CONNECT (exceptions raised here prevent the connection from completing) DISCONNECT TRANSACTION START TRANSACTION COMMIT (exceptions raised here prevent the transaction from committing, or preparing if a two-phase commit is involved) TRANSACTION ROLLBACKDatabase-level triggers can help enforce multi-table constraints, or emulate materialized views. If an exception is raised in a TRANSACTION COMMIT trigger, the changes made by the trigger so far are rolled back and the client application is notified, but the transaction remains active as if COMMIT had never been requested; the client application can continue to make changes and re-request COMMIT.
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Database trigger
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Triggers in DBMS
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Syntax for database triggers: MySQL/MariaDB Limited support for triggers in the MySQL/MariaDB DBMS was added in the 5.0 version of MySQL, launched in 2005.As of version 8.0, they allow for DDL (Data Definition Language) triggers and for DML (Data Manipulation Language) triggers. They also allow either type of DDL trigger (AFTER or BEFORE) to be used to define triggers. They are created by using the clause CREATE TRIGGER and deleted by using the clause DROP TRIGGER. The statement called upon an event happens is defined after the clause FOR EACH ROW, followed by a keyword (SET or BEGIN), which indicates whether what follows is an expression or a statement respectively.
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Database trigger
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Triggers in DBMS
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IBM DB2 LUW IBM DB2 for distributed systems known as DB2 for LUW (LUW means Linux, Unix, Windows) supports three trigger types: Before trigger, After trigger and Instead of trigger. Both statement level and row level triggers are supported. If there are more triggers for same operation on table then firing order is determined by trigger creation data. Since version 9.7 IBM DB2 supports autonomous transactions.Before trigger is for checking data and deciding if operation should be permitted. If exception is thrown from before trigger then operation is aborted and no data are changed. In DB2 before triggers are read only — you can't modify data in before triggers. After triggers are designed for post processing after requested change was performed. After triggers can write data into tables and unlike some other databases you can write into any table including table on which trigger operates. Instead of triggers are for making views writeable.
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Database trigger
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Triggers in DBMS
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Triggers are usually programmed in SQL PL language.
SQLite SQLite only supports row-level triggers, not statement-level triggers.
Updateable views, which are not supported in SQLite, can be emulated with INSTEAD OF triggers.
XML databases An example of implementation of triggers in non-relational database can be Sedna, that provides support for triggers based on XQuery. Triggers in Sedna were designed to be analogous to SQL:2003 triggers, but natively base on XML query and update languages (XPath, XQuery and XML update language).
A trigger in Sedna is set on any nodes of an XML document stored in database. When these nodes are updated, the trigger automatically executes XQuery queries and updates specified in its body. For example, the following trigger cancels person node deletion if there are any open auctions referenced by this person:
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Database trigger
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Row and statement level triggers
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To understand how trigger behavior works, you need to be aware of the two main types of triggers; these are Row and Statement level triggers. The distinction between the two is how many times the code within the trigger is executed, and at what time.
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Database trigger
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Row and statement level triggers
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Suppose you have a trigger that is made to be called on an UPDATE to a certain table. Row level triggers would execute once for each row that is affected by the UPDATE. It is important to keep in mind if no rows are affected by the UPDATE command, the trigger will not execute any code within the trigger. Statement level triggers will be called once regardless of how many rows are affected by the UPDATE. Here it is important to note that even if the UPDATE command didn't affect any rows, the code within the trigger will still be executed once.
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Database trigger
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Row and statement level triggers
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Using the BEFORE and AFTER options determine when the trigger is called. Suppose you have a trigger that is called on an INSERT to a certain table. If your trigger is using the BEFORE option, the code within the trigger will be executed before the INSERT into the table occurs. A common use of the BEFORE trigger is to verify the input values of the INSERT, or modify the values accordingly. Now let's say we have a trigger that uses AFTER instead. The code within the trigger is executed after the INSERT happens to the table. An example use of this trigger is creating an audit history of who has made inserts into the database, keeping track of the changes made. When using these options you need to keep a few things in mind. The BEFORE option does not allow you to modify tables, that is why input validation is a practical use. Using AFTER triggers allows you to modify tables such as inserting into an audit history table.
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Database trigger
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Row and statement level triggers
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When creating a trigger to determine if it is statement or row level simply include the FOR EACH ROW clause for a row level, or omit the clause for a statement level. Be cautious of using additional INSERT/UPDATE/DELETE commands within your trigger, because trigger recursion is possible, causing unwanted behavior. In the examples below each trigger is modifying a different table, by looking at what is being modified you can see some common applications of when different trigger types are used.
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Database trigger
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Row and statement level triggers
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The following is an Oracle syntax example of a row level trigger that is called AFTER an update FOR EACH ROW affected. This trigger is called on an update to a phone book database. When the trigger is called it adds an entry into a separate table named phone_book_audit. Also take note of triggers being able to take advantage of schema objects like sequences, in this example audit_id_sequence.nexVal is used to generate unique primary keys in the phone_book_audit table.
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Database trigger
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Row and statement level triggers
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Now calling an UPDATE on the phone_book table for people with the last name 'Jones'.
Notice that the phone_number_audit table is now populated with two entries. This is due to the database having two entries with the last name of 'Jones'. Since the update modified two separate row values, the created trigger was called twice; once after each modification.
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Database trigger
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Row and statement level triggers
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After - statement-level trigger An Oracle syntax statement trigger that is called after an UPDATE to the phone_book table. When the trigger gets called it makes an insert into phone_book_edit_history table Now doing exactly the same update as the above example, however this time with a statement level trigger. The result shows that the trigger was only called once, even though the update did change two rows.
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Database trigger
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Row and statement level triggers
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Before each - row-level trigger This example demonstrates a BEFORE EACH ROW trigger that modifies the INSERT using a WHEN conditional. If the last name is larger than 10 letters, using the SUBSTR function we change the last_name column value to an abbreviation.
Now performing an INSERT of someone with a large name.
The trigger worked as per the result above, modifying the value of the INSERT before it was executed.
Before - statement-level trigger Using a BEFORE statement trigger is particularly useful when enforcing database restrictions. This example demonstrate how to enforce a restriction upon someone named "SOMEUSER" on the table phone_book.
Now, when "SOMEUSER" is logged in after attempting any INSERT this error message will show: SQL Error: ORA-20050: Error message goes here.
Custom errors such as this one has a restriction on what the num variable can be defined as. Because of the numerous other pre-defined errors this variable must be in the range of -20000 to -20999.
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Web development
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Web development
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Web development is the work involved in developing a website for the Internet (World Wide Web) or an intranet (a private network). Web development can range from developing a simple single static page of plain text to complex web applications, electronic businesses, and social network services. A more comprehensive list of tasks to which Web development commonly refers, may include Web engineering, Web design, Web content development, client liaison, client-side/server-side scripting, Web server and network security configuration, and e-commerce development.
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Web development
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Web development
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Among Web professionals, "Web development" usually refers to the main non-design aspects of building Web sites: writing markup and coding. Web development may use content management systems (CMS) to make content changes easier and available with basic technical skills.
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Web development
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Web development
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For larger organizations and businesses, Web development teams can consist of hundreds of people (Web developers) and follow standard methods like Agile methodologies while developing Web sites. Smaller organizations may only require a single permanent or contracting developer, or secondary assignment to related job positions such as a graphic designer or information systems technician. Web development may be a collaborative effort between departments rather than the domain of a designated department. There are three kinds of Web developer specialization: front-end developer, back-end developer, and full-stack developer. Front-end developers are responsible for behavior and visuals that run in the user browser, while back-end developers deal with the servers. Since the commercialization of the Web with Tim Berners-Lee developing the World Wide Web at CERN, the industry has boomed and has become one of the most used technologies ever.
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Subversion and containment
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Subversion and containment
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Subversion and containment is a concept in literary studies introduced by Stephen Greenblatt in his 1988 essay "Invisible Bullets". It has subsequently become a much-used concept in new historicist and cultural materialist approaches to textual analysis. Literary critic Louis A. Montrose writes that the terms are often used to refer to the "capacity of the dominant order to generate subversion so as to use it to its own ends".
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Subversion and containment
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The English in the New World
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In his essay "Invisible Bullets", Stephen Greenblatt introduced the concept of subversion and containment as an instrument by describing Thomas Hariot's report on his experience in the colony of Virginia in 1586. Sir Walter Raleigh's duty had been in part to bring civilisation to the Native Americans (then referred to as Indians). As civilisation was purportedly impossible without Christianity, this was to be imposed upon the Native Americans. Harriot documented two relevant observations in his Brief and True Report of the New Found Land of Virginia. Firstly, that the natives had a degree of religion to their culture of which Harriot drew parallels to Christianity. Secondly, he noticed that everyday non-divine objects caused the natives to believe in the divinity of the invaders, noting "Most things they saw with us, as mathematical instruments, sea compasses, the virtue of the lodestone in drawing iron, a perspective glass whereby was shown many strange sights, burning glasses, wildfire works, gun, book, writing and reading, spring clocks that seemed to go off by themselves, and many other things that we had, were so strange unto them and so far exceeded their capabilities to comprehend the reason and means how they should be made and done that they thought they were rather the works of gods than of men, or at the leastwise they had been given and taught us of the gods"It would seem that Harriot used this to impose Christianity upon the natives. At one point, as the native crop was scarce one year, Harriot suggested that the Christian God would provide better for their land. Thus the subversion was both produced and contained. This theory immediately implies maliciousness and Machiavellian callousness; this is not always the case. Greenblatt takes pains to stress that Harriot may not have been acting maliciously. The name of the essay Invisible Bullets is so as the Subversion must be invisible to the Subverted; Harriot could not simply state that the Natives were being converted to (or assimilated into) another religion and culture. If the subversion and containment were invisible to Harriot, he would be merely an agent of hegemony. It is not unlikely that Harriot wholeheartedly believed that England and its people were blessed by the only true Christian God, that the very fact that he was born into the bourgeoisie provided his intellectual (and divine) superiority - in which case he would have been acting out of compassion.
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Subversion and containment
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Calculated production of subversion
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During Columbus's fourth voyage, the natives began aggression towards the invaders. Columbus, after consulting his calendars warned that God would demonstrate his favour towards the Europeans. Only he knew that a solar eclipse was to shortly occur. This subverted the natives' belief system.
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Subversion and containment
|
Application as Theatrical Theory
|
Greenblatt originally wrote of this theory in its application to theatre. He applied it extensively to Shakespeare's Henry IV, Part 1, Henry IV, Part 2 and Henry V, but has largely been disputed in his initial findings.Stephen Weeks, in his essay The Question of Liz: Staging the Prisoner in 'Our Country's Good' applied the Theory to Timberlake Wertenbaker's Our Country's Good. Here, Weeks chronicles the Machiavellian connotations shadowing the teaching of 'high' language to a group of convicts. The convicts have their own codes and culture. They are offered the chance to take part in a theatrical performance, which gives them 'high language' that can be used to get them out of trouble. The language, however, is packaged with parts of culture which eventually causes them to betray their own culture and dreams. On the surface, Our Country's Good is a play about people discovering art but Weeks exposes this as an empirical act of production and containment and subversion. Again it is ambiguous whether the English officer is callously converting the convicts or whether he is merely an agent of English imperial hegemony attempting benevolence.
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Lens board
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Lens board
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A lens board or lensboard is a photographic part used for securing a lens to the front standard of a large format view camera. The lens board itself is usually flat, square, and made of metal (most commonly aluminum), wood, or plastic. The lens board will have a hole of various diameters drilled dead center on the board. A lens board typically varies between 1 and 4 millimeters in thickness. The overall size and shape of the lens board depends on the brand of camera and film format used. Some cameras will use 2 to 4 screws to secure the lens board to the front standard of the view camera, most commonly however, the lens board will be secured by one or more locking levers or tabs to allow tool-less removal of the lens board. The rear surface of a lens board is usually painted matte black to keep light entering the camera through the lens during exposure from reflecting off the surface and interfering with the projected image.
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Lens board
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Lens board
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While most lens boards are flat, some are recessed to accommodate wider focal length lenses which must be positioned closer to the film plane. A recessed lens board effectively reduces the flange focal distance of a camera.
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Lens board
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Sizes
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Depending on the size and focal length of a particular lens, a certain diameter of hole is drilled in the center of the lens board to accommodate the shutter assembly. Lens boards are typically available pre-drilled by the camera manufacturer, however, if no replacement lens board is available from a camera manufacturer, then one can be custom fabricated by a machinist. Nearly all large format leaf shutters made since the 1990s are manufactured by the Nidec Copal Corporation, therefore the diameter of hole drilled is commonly referred to as the ‘Copal Number’.
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Lens board
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Sizes
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The Copal sizes are as follows: Copal #0 - 34.6 mm Copal #1 - 41.6 mm Copal #3 – 65 mm Copal #3s - 64.5 mmThe origin Compur/Compound sizes are as follows: Compur #00 - 26.3 mm Compur #0 - 34.6 mm Compur #1 - 41.6 mm Compur #2 - 52.5 mm (there were different versions like Compur II and Compur II 5/2) Compur #3 - 65.0 mm Compound Dagor - 38.0 mm Compound #3 Hülse 7 - 63.2 mm Compound #4 Hülse 9 - 69.1 mm Compound #4 Hülse 10 - 80.0 mm Compound #5 Hülse 12 - 93.4 mm
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Lens board
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Lens mounting
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Lenses are fitted to a lens board by placing the shutter assembly through the front of the board and securing the shutter assembly by threading a locknut to rear of the shutter. A front lens element will thread onto the mounted shutter and if necessary, a second lens element will thread onto the rear of the mounted shutter. This procedure can be accomplished by a camera technician, or by an end-user with the appropriate tools.
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Lens board
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Other uses
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Lens boards are used in photographic enlargers to secure an enlarging lens to the focus stage of the device.
Similar to large format photographic view cameras, a lens board is utilized by some reprographic cameras in the printing industry.
Lens boards may also be used by some medical and scientific imaging devices.
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Mir-671 microRNA precursor family
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Mir-671 microRNA precursor family
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In molecular biology mir-671 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
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Mir-671 microRNA precursor family
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Alcoholic and Non-Alcoholic Fatty Liver Disease
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miR-671 expression levels have been found to be vary significantly between the alcoholic and non-alcoholic forms of fatty liver disease.
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Mir-671 microRNA precursor family
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CDR1 regulation
|
miR-671 has been seen to negatively regulate the CDR1 (Cerebellar Degeneration-Related protein 1) gene, through the targeting and cleavage of a circular antisense transcript of the CDR1 locus. There is a partnered decrease in CDR1 mRNA levels with this downregulation.
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Mir-671 microRNA precursor family
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FN1 repression
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miR-671 is able to bind to and repress fibronection type 1 (FN1) mRNA at its 3'untranslated region binding site.
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Saturated set
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Saturated set
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In mathematics, particularly in the subfields of set theory and topology, a set C is said to be saturated with respect to a function f:X→Y if C is a subset of f 's domain X and if whenever f sends two points c∈C and x∈X to the same value then x belongs to C (that is, if f(x)=f(c) then x∈C ). Said more succinctly, the set C is called saturated if C=f−1(f(C)).
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Saturated set
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Saturated set
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In topology, a subset of a topological space (X,τ) is saturated if it is equal to an intersection of open subsets of X.
In a T1 space every set is saturated.
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Saturated set
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Definition
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Preliminaries Let f:X→Y be a map. Given any subset S⊆X, define its image under f to be the set: and define its preimage or inverse image under f to be the set: Given y∈Y, the fiber of f over y is defined to be the preimage: Any preimage of a single point in f 's codomain Y is referred to as a fiber of f.
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Saturated set
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Definition
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Saturated sets A set C is called f -saturated and is said to be saturated with respect to f if C is a subset of f 's domain X and if any of the following equivalent conditions are satisfied: C=f−1(f(C)).
There exists a set S such that C=f−1(S).
Any such set S necessarily contains f(C) as a subset and moreover, it will also necessarily satisfy the equality Im f, where Im := f(X) denotes the image of f.
If c∈C and x∈X satisfy f(x)=f(c), then x∈C.
If y∈Y is such that the fiber f−1(y) intersects C (that is, if f−1(y)∩C≠∅ ), then this entire fiber is necessarily a subset of C (that is, f−1(y)⊆C ).
For every y∈Y, the intersection C∩f−1(y) is equal to the empty set ∅ or to f−1(y).
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Saturated set
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Examples
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Let f:X→Y be any function. If S is any set then its preimage := f−1(S) under f is necessarily an f -saturated set. In particular, every fiber of a map f is an f -saturated set. The empty set ∅=f−1(∅) and the domain X=f−1(Y) are always saturated. Arbitrary unions of saturated sets are saturated, as are arbitrary intersections of saturated sets.
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Saturated set
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Properties
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Let S and T be any sets and let f:X→Y be any function. If S or T is f -saturated then If T is f -saturated then where note, in particular, that no requirements or conditions were placed on the set S.
If τ is a topology on X and f:X→Y is any map then set τf of all U∈τ that are saturated subsets of X forms a topology on X.
If Y is also a topological space then f:(X,τ)→Y is continuous (respectively, a quotient map) if and only if the same is true of f:(X,τf)→Y.
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Avaya ERS 5600 Series
|
Avaya ERS 5600 Series
|
Ethernet Routing Switch 5600 Series or (ERS 5600) in computer networking terms are stackable routers and switches designed and manufactured by Avaya. The ERS 5600 Switches can be stacked up to 8 units high to create a 1.152 Tbit/s backplane through the Flexible Advanced Stacking Technology (FAST) stacking technology configuration. The 5600 Series consists of five stackable models that can be mixed and matched together with other ERS 5600 models or other ERS 5500 models to meet configuration requirements. Additionally the ports on the switches incorporates the Avaya Energy Saver (AES) which can manage and dim down (reduce the wattage requirements of each port and/or the PoE wattage) the power requirements to save energy across all switches in the enterprise.
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Avaya ERS 5600 Series
|
Avaya ERS 5600 Series
|
The switches have an integrated time-domain reflectometer (TDR) built into every copper port, providing the ability to accomplish diagnostic monitoring and troubleshooting capabilities of the connected cables. This allows the equipment manager the ability to test and troubleshoot the cables for defects (crimped, cut, shorted or damaged cables) without going out to the switch room to test the cables from the switch to the end equipment. The tests can be accomplished on a single port or on multiple ports at the same time. The test can be accomplished through the command line or through one of several Graphical user interfaces called Device Manager (DM), Java Device Manager (JDM) or Enterprise Device Manager (EDM).
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Avaya ERS 5600 Series
|
History
|
In 2008 this Switch became available with the software release 6.0, which could be loaded on the newer 5600 models or the original 5500 models. The developmental history of this system extends back to the BayStack 5000 family shortly after the technology was bought from Bay Networks. Software version 6.0 added PIM-SM and Dual Agents. In June 2009 Software version 6.1 was released removing the licensing requirements for the IP Flow Information Export {IPFIX} feature, added force stack mode, and several security features. In July 2010 software version 6.2 became available adding Avaya Energy Saver, Bi-directional monitor port, and environmental commands.
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Avaya ERS 5600 Series
|
History
|
In March 2011 the Australian Department of Defense began deploying these Switches as routing and switching platforms within the Wiring Closet, Data Center aggregation and network core. In December 2011 this system completed evaluation and certification by the U.S. Joint Interoperability Test Command (JITC) testing center for use in the United States Department of Defense as an Assured Services Local Area Network (ASLAN).In July 2017 Extreme Networks acquired all of Avaya's core networking business, including the ERS 5600 series of switches.
|
Avaya ERS 5600 Series
|
System Scaling
|
Systems scaling is accomplished by stacking up to eight of the ERS 5632FD units to provide up to 64 ports of 10-gigabit ethernet through XFP transceivers and 192 ports of 1000BASE-X Small form-factor pluggable transceivers; or stacking four ERS 5698TFD units to provide up to 8 ports of 10-gigabit Ethernet through XFP transceivers modules and 24 ports of 1000BASE-X Small form-factor pluggable transceivers and 144 ports of copper 10/100/1000BASE-T; or stacking eight ERS 5650TD units to provide 16 ports of 10-gigabit ethernet through XFP transceivers and 384 ports of copper 10/100/1000BASE-T connections. The ERS 5600 also has the ability to mix any combination of Switches of up to 8 units or up to 384 ports, whichever is reached first.
|
Avaya ERS 5600 Series
|
Models
|
The specific models are the ERS 5632, 5650 and 5698 and the below table identifies the ports on each Switch.
|
Load–store architecture
|
Load–store architecture
|
In computer engineering, a load–store architecture (or a register–register architecture) is an instruction set architecture that divides instructions into two categories: memory access (load and store between memory and registers) and ALU operations (which only occur between registers).: 9–12 Some RISC architectures such as PowerPC, SPARC, RISC-V, ARM, and MIPS are load–store architectures.: 9–12 For instance, in a load–store approach both operands and destination for an ADD operation must be in registers. This differs from a register–memory architecture (for example, a CISC instruction set architecture such as x86) in which one of the operands for the ADD operation may be in memory, while the other is in a register.: 9–12 The earliest example of a load–store architecture was the CDC 6600.: 54–56 Almost all vector processors (including many GPUs) use the load–store approach.
|
Automorphic Forms on GL(2)
|
Automorphic Forms on GL(2)
|
Automorphic Forms on GL(2) is a mathematics book by H. Jacquet and Robert Langlands (1970) where they rewrite Erich Hecke's theory of modular forms in terms of the representation theory of GL(2) over local fields and adele rings of global fields and prove the Jacquet–Langlands correspondence. A second volume by Jacquet (1972) gives an interpretation of some results by Rankin and Selberg in terms of the representation theory of GL(2) × GL(2).
|
Crushed red pepper
|
Crushed red pepper
|
Crushed red pepper or red pepper flakes is a condiment or spice consisting of dried and crushed (as opposed to ground) red chili peppers. This condiment is most often produced from cayenne-type peppers, although commercial producers may use a variety of different cultivars, usually within the 30,000–50,000 Scoville unit range. Often there is a high ratio of seeds, which are erroneously believed to contain the most heat. Crushed red pepper is used by food manufacturers in pickling blends, chowders, spaghetti sauce, pizza sauce, soups and sausage.
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Crushed red pepper
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Crushed red pepper
|
Crushed red pepper in Turkey, served as a common condiment with very few seeds, is known as pul biber. One specially prepared variety of it is the urfa pul biber (isot).
|
Crushed red pepper
|
Background
|
Crushed red pepper, known for its spicy heat, comes with a range of capsicum peppers. Red pepper chilis originally start off green before ripening into an orange-red to deep dark red color and are best grown in the summer months—between 70–84 °F (21–29 °C) and sunny weather. One or multiple red chile peppers—up to four cultivars—can be used to create crushed red pepper. Jalapeños, serranos and Anaheim chilis are some of the most commonly used chilies to make crushed red pepper. Crushed red pepper are frequently found in a variety of dishes including Italian, Indian, Mexican and Caribbean.Over time, crushed red pepper loses its spiciness level and typically lasts up to 12 to 18 months. Today, China and Turkey are among the top countries to produce crushed red pepper.
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Crushed red pepper
|
History
|
Red chili peppers, which are a part of the Solanaceae (nightshade) family, were first found in Central and South America and have been harvested for use since about 7,500 BC. Spanish explorers were introduced to the pepper while on a search for black pepper. Once brought back to Europe, the red peppers were traded in Asian countries and were enjoyed primarily by Indian cooks. The village of Bukovo, North Macedonia, is often credited with the creation of crushed red pepper. The name of the village—or a derivative of it—is now used as a name for crushed red pepper in general in many Southeast European languages: "буковска пипер/буковец" (bukovska piper/bukovec, Macedonian), "bukovka" (Serbo-Croatian and Slovene) and "μπούκοβο" (boukovo, búkovo, Greek).
|
Crushed red pepper
|
History
|
Southern Italians popularized crushed red pepper beginning in the 19th century and heavily used them in the U.S. when they migrated over. Crushed red pepper was served with dishes at some of the oldest Italian restaurants in the U.S. Crushed red pepper shakers have become a standard on tables at Mediterranean restaurants—and especially pizzerias—around the world.
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Crushed red pepper
|
Health benefits
|
The source of bright red color that the peppers hold comes from carotenoids. Crushed red pepper also has antioxidants that are thought to help fight off heart disease and cancer. In addition, crushed red pepper contains fiber, capsaicin—the source of the heat in pepper chilis—and vitamins A, C, and B6. Capsaicin is believed to help kill off prostate cancer cells, to serve as an appetite suppressant which can contribute to weight loss, to improve digestion, and to help prevent diabetes and constipation.
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Vapor-compression refrigeration
|
Vapor-compression refrigeration
|
Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.
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Vapor-compression refrigeration
|
Vapor-compression refrigeration
|
Refrigeration may be defined as lowering the temperature of an enclosed space by removing heat from that space and transferring it elsewhere. A device that performs this function may also be called an air conditioner, refrigerator, air source heat pump, geothermal heat pump, or chiller (heat pump).
|
Vapor-compression refrigeration
|
Description
|
Vapor-compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Figure 1 depicts a typical, single-stage vapor-compression system. All such systems have four components: a compressor, a condenser, a metering device or thermal expansion valve (also called a throttle valve), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with either cooling water or cooling air flowing across the coil or tubes.
|
Vapor-compression refrigeration
|
Description
|
The superheated vapor then passes through the condenser. This is where heat is transferred from the circulating refrigerant to an external medium, allowing the gaseous refrigerant to cool and condense into a liquid. The rejected heat is carried away by either the water or the air, depending on the type of condenser.
|
Vapor-compression refrigeration
|
Description
|
The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.
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Vapor-compression refrigeration
|
Description
|
The cold refrigerant liquid and vapor mixture is then routed through the coil or tubes in the evaporator. Air in the enclosed space circulates across the coil or tubes due to either thermal convection or a fan. Since the air is warmer than the cold liquid refrigerant, heat is transferred which cools the air and causes evaporation of the liquid, returning it to a gaseous state whilst absorbing heat. While liquid remains in the refrigerant flow, its temperature will not rise above the boiling point of the refrigerant, which depends on the pressure in the evaporator. Most systems are designed to evaporate all of the refrigerant to ensure that no liquid is returned to the compressor.
|
Vapor-compression refrigeration
|
Description
|
To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor. Over time, the evaporator may collect ice or water from ambient humidity. The ice is melted through defrosting. The water from the melted ice or the evaporator then drips into a drip pan, and the water is carried away by gravity or a condensate pump.
|
Vapor-compression refrigeration
|
Description
|
Refrigerants The selection of working fluid has a significant impact on the performance of the refrigeration cycles and as such it plays a key role when it comes to designing or simply choosing an ideal machine for a certain task. One of the most widespread refrigerants is "Freon". Freon is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties: they were not flammable at room temperature and atmospheric pressure, nor obviously toxic as were the fluids they replaced, such as sulfur dioxide. Haloalkanes are also an order(s) of magnitude more expensive than petroleum-derived flammable alkanes of similar or better cooling performance.
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