title: Barred owl

text: In normal circumstances, barred owls tend to pair bond for life. Courting pairs are usually newly mature birds but also possibly widowed owls or those re-establishing existing pair bonds after the winter. During courtship, barred owl males especially may engage in nodding, bowing with half-spread wings and may wobble and twist their head from side to side. Copulation between pairs usually occurs in late winter, February to March, and occurs several times, probably to ensure implantation. The female enters a pre-breeding lethargy stage wherein she is fed by the male. In barred owls, egg laying occurs at two to three day intervals. Egg laying typically begins in March and runs throughout April. In more tropical locales like Florida, egg laying may occur as early as late December, though 22 were laid in between early January and early March. At similar latitudes in Texas, 22 first eggs were laid between as early as mid-February to as late as early June (although the latter may have been a replacement clutch). 23 clutches in Iowa and Illinois were initiated in between late February and late April, with roughly corresponding initial egg dates in New Jersey and probably western Maryland as well. 63 initial eggs in New England were laid between mid-March and mid-May. Further north, 38 clutches in Nova Scotia were initiated in between late March and late May, with initial clutches dates about a week later in Ontario. Normally the female lays 2 to 3 eggs, although as many as 5 is possible, directly on the base of the nest site. The mean clutch size in three broad samples from several parts of the range was between 2.22 and 2.46. In Minnesota, the mean clutch size was 2.68. The eggs are pure white, slightly rough and not glossy, and oval in shape. In 157 eggs, the length of the egg could measure from while the diameter could range from , with a mean of . 25 eggs in Nova Scotia averaged slightly smaller, at . The mean weight of the egg is around . The female alone incubates, doing so for about 28 days, while the male gathers food for her.


title: Barred owl

text: The female tends to closely brood the young for three weeks. Then after, she begins to hunt for the young. Both parents normally continue hunt for the young until they are about 6 weeks old and can fly well. During the first three weeks, the male does all prey deliveries, either bringing prey directly into the nest or leaves for the female at the nest entrance or on a nearby branch. The mean number of prey deliveries when the young are 6–10 days old is 2.4 per night, 1.4 when they are 11–15 days old, 3.6 when they are 16–20 days old and 2.2 when they are 21–25 days old. He will continue hunting until the young disperse. The female's prey deliveries are much more frequent when she resumes hunting, ranging from a mean of 4.8 to 8 deliveries nightly. Male prey deliveries are often sporadically at any point through the night while female deliveries tend to be clustered immediately after sunset or just before sunrise. Barred owls have a variable reaction to human disturbance. Some parent owls remain sitting, while some leave the nest upon a person's approach and some attack people climbing to the nest, as well as those approaching young on or near the ground. There are several accounts of barred owls engaging in fierce nest defense against humans, sometimes reportedly knocking people out of trees. However, their aggression is variable and, based on studies of similar owls like tawny and Ural owls from Europe, attacks tend to only occur when intrusions and disturbance by humans are frequent. A distraction display was recorded by a female barred owl when humans approached. In it, she spread and quivered her wings and engaged in chittering and squealing, somewhat similar to the sounds made by begging young.


title: Barred owl

text: The average hatchling weighs about . Like most birds, the young are initially altricial. The white down feathers that the barred owls are hatched with is replaced by white-tipped barred-buff second down at two to three weeks of age, correspondingly with growth of the wing primaries. The earlier chicks are bigger and stronger, while the latter ones may not survive if food is scarce. Size differences between barred owl nestlings may be less pronounced if the female does not begin incubation until the laying of the second egg. The larger young may fight with the younger siblings for food. The young barred owls first start moving about the nest at around this 3 week point and may start to perform threat displays if scared. Adult-like feathers begin to appear at six weeks of age, starting at the scapulars, then radiating down across the abdomen and flanks up through the upper breast, with the last wisps of down remaining for up to 4 months. The young often start exploring around the nest tree, often falling to ground, which makes them quite vulnerable to predation despite the parents' continued protection. However, the fledglings can usually clamber back up the tree using their feet and bills, constantly wing-flapping.


title: Barred owl

text: Fledging occurs at about 36–39 days. After that, both parents continue to hunt for the young but prey deliveries taper off as the young begin to make their first flights and practice hunting. Short flights are typical when the young barred owls are up to around 10 weeks old with longer flights commencing at about 14 weeks. By the time they are flying and hunting somewhat assuredly in early to mid-autumn, the young move away and gain independence. Dispersal of 5 young from Nova Scotia was away from their nests of origin. Furthermore, a recovered 6 month old was away from its nest of origin, while five encountered as adults were found at a distance of from the nests where they hatched. An exceptional dispersal distance from Nova Scotia was away to Stoney Creek, Ontario. The post-dispersal stage is one of great mortality among young owls. Usually juvenile owls are considered "floaters", often hovering around the perimeter of fiercely defended territories for some time. In some areas, floaters may make use of nest boxes more readily than mature birds. Yearlings have been known to breed only very rarely, otherwise barred owl usually first breed when they are around two (sometimes three) years old. Therefore, around two years old is considered the age of maturity. The percentages of successful nests (i.e. at least 1 fledgling produced per attempt), per study were found to be: 86% of 22 clutches in Minnesota (with a mean of 2.42 fledglings per successful attempt), 66% of 114 clutches in Michigan (with a mean of 1.97 fledglings per successful attempt), 25% of 6 clutches in Maryland (with a mean of 1 fledgling per all attempts and 1.48 per successful attempts), 69% of 48 clutches in Nova Scotia (with a mean of 0.25 fledgling per all attempts and 2 per successful attempts) and 50% of 12 nests in Washington state. Little is known about the specific factors that dictate breeding success, but are likely to include the quality of the nesting site, the food supply in the area, the levels of disturbance from outside actors (usually humans) and the maturity of the pair.


title: Barred owl

text: The barred owl is a naturally long-living bird. Some record lifespans recorded per banding studies in the wild are 18 years 2 months (initial banding Kentucky, died in Ohio) and 24 years and 1 month in Minnesota. There are several records of breeding barred owls nesting successfully for a decade or more. The record lifespan for a barred owl in captivity, where many animals can live longer without the stresses of surviving in wild conditions, was 34 years and 1 month, with six records of captive barred owls living over 30 years. Known causes of mortality are diverse, some due to predation (largely great horned owls, for nestlings to adults, and probably raccoons, for eggs, nestlings and fledglings). Some mortality is known to occur during hunting accidents. There are cases of barred owls being inadvertently killed in furbearer traps. Sometimes deaths occurs due to the defenses of prey. One barred owl was killed by the bite of an unknown rodent that was likely defending itself. Some cases of cannibalism between adult barred owls have been reported as well. This species, like other forest owls, is vulnerable to the respiratory disease aspergillosis. Spontaneous infections of West Nile fever are also known to kill wild barred owls. Barred owls were the most regularly infected with West Nile Virus of owl species in Georgia, as about 15% of studied barred tested positive (still at a lower rate than some hawks). Cases of Avipoxvirus are also known in barred owls but, as with West Nile virus, the rate of mortality to viral infection is not well-known. A case of follicular thyroid cancer was found in a wild barred owl that was unable to continue to fly. Fatty liver diseases have been recorded for barred owls in captivity. Eye lesions are fairly common in barred owls, but can be survived and possibly surgically corrected.


title: Barred owl

text: Parasitism is frequent in barred owls as expected for many different kinds of wild birds. The parasite load was determined to be higher in larger owls in Florida like the barred and great horned owl and lower in smaller owl species, like eastern screech owl. While parasitic infestations are not typically detected as direct mortality causes, in some severe cases complications or direct death can occur. These cases of mortality are most widely recorded in cases of "Toxoplasmosis", although generally owls have lower rates of this dangerous parasite than some other species of birds of prey. Of barred owls in one study, 26.7% had "Toxoplasma gondii", the cause of "Toxoplasmosis", upon necropsy study, with adults having it more often than immature birds. Lethal cases of "Trichomoniasis" are also known. The effect of other parasites are more poorly known beyond generally compromising their condition but in one case "Sarcocystis" may have caused paralysis in one barred owl. Other parasites recorded in barred owls include "Eimeria varia", "Novyella", "Neodiplostomum" as well as apparently rare species of "Centrorhynchus" and "Tetrameres" that were first found within barred owls. Trematode flatworms such as strigeids as well as "Tylodelphys" and "Brachylaima" are found in intermediate volume in barred owls relative to other owls. Invertebrates such as hippoboscid flies and "Mallophaga" are known to infect barred owls as ectoparasites but seldom at severe levels. Concern was expressed that barred owls may compromise spotted owl populations with novel parasites. However, studies of "Haemoproteus" in barred and spotted owls in northwestern California found that native parasites were finding a new host in barred owls and may have been transmitted from spotted to barred owls but that the barred owl acted as a poor parasite host and may have diluted the parasite levels in owl populations. Furthermore, there was no evidence found that barred owls were spreading parasites to spotted owls.


title: Barred owl

text: The barred owl is one of the most common owls in North America. Partners in Flight estimates that the barred owl may number up to 3 million individuals globally, making it the perhaps the second most numerous North American owl behind the great horned owl and perhaps slightly ahead of other commoner species like barn owls and northern saw-whet owls. It estimated that Canada in total holds about 10,000-50,000 pairs. Canadian Maritimes had highest densities known, with 3600 pairs, being found in 80% of blocks totaling 377; this was a conspicuously higher density than that recorded in Ontario, where they were in 28% of 1824 study blocks. Iowa, Tennessee and Maryland had the highest densities of pairs apparently in the United States, being present from 39 to 47% of blocks. Throughout the year, the mean number of sightings per route is 0.12 sightings while during Christmas Bird Counts (CBC), the mean in 0.25 per route.


title: Barred owl

text: Barred owls are thought to be partly responsible for the recent decline of the northern spotted owl, native to British Columbia, Washington, Oregon, and California. The 2011 Revised Recovery Plan for the Northern Spotted Owl (p. vi) states "Based on the best available scientific information, competition from the barred owl ("S. varia") poses a significant and complex threat to the spotted owl." Northern spotted owls were thought to be already declining considerably before barred owls moved into their range, mostly in sync with large-scale logging operations and land development carried out by humans, with their problems now further exacerbated by the barred species's presence. There are ecological discrepancies between the species in areas of sympatry. While both species prefer old-growth forest areas, the spotted owls tend to live in significantly higher elevation areas in Washington's Cascade mountains, with nest sites averaging metres above sea level against a mean of for barred owls, in areas with more steep slopes. The barred owls of the area additionally prefer wetter, more variable forest areas, down to riparian zones with limited forested land, while the spotted tended to cluster in more homogeneous upland and ancient coniferous forests. However, little is known on the feasibility or benefits of habitat maintenance that favors spotted over barred owls. Habitat management measures are hypothesized to be insufficient to mitigate the negative effect the barred owls are having. In areas where barred owls moved in within of a spotted owl nest area, 39% of spotted owls disappeared and were not seen again, while in areas still free of barred owls (so spared from this interspecific pressure), 11% of spotted owls disappeared and were not found again.


title: Barred owl

text: Since the 1960s, barred owls have been expanding their range westward from the eastern US and Canada. While some authors have described the expansion of barred owls into the west as "natural", others state that this is a mischaracterization, as there is little to suggest that the barred owls could have reached the spotted's range without the inadvertent aid of humans— increasing temperatures, wildlife suppression, and tree planting likely facilitated the range increase. When spotted owls and barred owls share the same area, the barred owls generally are more aggressive and out-compete the spotted owls, leading to decreased populations of the native owls. The more aggressive response of barred owls to interspecific stimuli has been verified with experiments incorporating vocalization and owl dummies. Additionally, the adult survival rates appear higher for barred owls (an estimated 91%) than for spotted owls (an estimated 82%). Therefore, the barred owl is considered "demographically superior". Another potential threat is that barred owls and spotted owls occasionally interbreed, creating hybrids ("sparred owl" or "botted owl"). Only 47 hybrids with barred owls (all between female barred owls and male spotted owls) were found in an analysis of more than 9,000 banded spotted owls; consequently, hybridization between these two species is considered to be "an interesting biological phenomenon that is probably inconsequential compared with the real threat—direct competition between the two species for food and space". Most hybrids favor their barred owl heritage with similar and more pale overall coloring than spotted owls, though the back tends to be intermediate in color between the two and the beak coloring is variable. However, there has been much variation described. Due to variances in appearance, previously hybrids between the species were overestimated from field identification, only being certainly identified by genetic loci. Moreover, no recent hybrids could be detected in a survey of the Cascade Mountains.


title: Barred owl

text: John James Audubon illustrated the barred owl in "Birds of America" (published in London, 1827–1838) as Plate 46, where it is shown threatening a grey squirrel. The image was engraved and colored by Robert Havell's London workshops. The original aquatint by Audubon is owned by the Brooklyn Museum.


title: Binary-coded decimal

text: In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used for a sign or other indications (e.g. error or overflow).


title: Binary-coded decimal

text: In byte-oriented systems (i.e. most modern computers), the term "unpacked" BCD usually implies a full byte for each digit (often including a sign), whereas "packed" BCD typically encodes two digits within a single byte by taking advantage of the fact that four bits are enough to represent the range 0 to 9. The precise 4-bit encoding, however, may vary for technical reasons (e.g. Excess-3).


title: Binary-coded decimal

text: The ten states representing a BCD digit are sometimes called "tetrades" (for the nibble typically needed to hold them is also known as a tetrade) while the unused, don't care-states are named , "pseudo-decimals" or "pseudo-decimal digits".


title: Binary-coded decimal

text: BCD's main virtue, in comparison to binary positional systems, is its more accurate representation and rounding of decimal quantities, as well as its ease of conversion into conventional human-readable representations. Its principal drawbacks are a slight increase in the complexity of the circuits needed to implement basic arithmetic as well as slightly less dense storage.


title: Binary-coded decimal

text: BCD was used in many early decimal computers, and is implemented in the instruction set of machines such as the IBM System/360 series and its descendants, Digital Equipment Corporation's VAX, the Burroughs B1700, and the Motorola 68000-series processors. BCD "per se" is not as widely used as in the past, and is unavailable or limited in newer instruction sets (e.g., ARM; x86 in long mode). However, decimal fixed-point and decimal floating-point formats are still important and continue to be used in financial, commercial, and industrial computing, where the subtle conversion and fractional rounding errors that are inherent in binary floating point formats cannot be tolerated.


title: Binary-coded decimal

text: BCD takes advantage of the fact that any one decimal numeral can be represented by a four-bit pattern. The most obvious way of encoding digits is "Natural BCD" (NBCD), where each decimal digit is represented by its corresponding four-bit binary value, as shown in the following table. This is also called "8421" encoding.


title: Binary-coded decimal

text: This scheme can also be referred to as "Simple Binary-Coded Decimal" ("SBCD") or "BCD 8421", and is the most common encoding. Others include the so-called "4221" and "7421" encoding – named after the weighting used for the bits – and "Excess-3". For example, the BCD digit 6, in 8421 notation, is in 4221 (two encodings are possible), in 7421, while in Excess-3 it is (formula_1).


title: Binary-coded decimal

text: The following table represents decimal digits from 0 to 9 in various BCD encoding systems. In the headers, the "codice_1" indicates the weight of each bit. In the fifth column ("BCD 84−2−1"), two of the weights are negative. Both ASCII and EBCDIC character codes for the digits, which are examples of zoned BCD, are also shown.


title: Binary-coded decimal

text: As most computers deal with data in 8-bit bytes, it is possible to use one of the following methods to encode a BCD number:


title: Binary-coded decimal

text: As an example, encoding the decimal number codice_2 using unpacked BCD results in the following binary pattern of two bytes:


title: Binary-coded decimal

text: Hence the numerical range for one unpacked BCD byte is zero through nine inclusive, whereas the range for one packed BCD byte is zero through ninety-nine inclusive.


title: Binary-coded decimal

text: To represent numbers larger than the range of a single byte any number of contiguous bytes may be used. For example, to represent the decimal number codice_3 in packed BCD, using big-endian format, a program would encode as follows:


title: Binary-coded decimal

text: Here, the most significant nibble of the most significant byte has been encoded as zero, so the number is stored as codice_4 (but formatting routines might replace or remove leading zeros). Packed BCD is more efficient in storage usage than unpacked BCD; encoding the same number (with the leading zero) in unpacked format would consume twice the storage.


title: Binary-coded decimal

text: Shifting and masking operations are used to pack or unpack a packed BCD digit. Other bitwise operations are used to convert a numeral to its equivalent bit pattern or reverse the process.


title: Binary-coded decimal

text: In packed BCD (or simply packed decimal), each of the two nibbles of each byte represent a decimal digit. Packed BCD has been in use since at least the 1960s and is implemented in all IBM mainframe hardware since then. Most implementations are big endian, i.e. with the more significant digit in the upper half of each byte, and with the leftmost byte (residing at the lowest memory address) containing the most significant digits of the packed decimal value. The lower nibble of the rightmost byte is usually used as the sign flag, although some unsigned representations lack a sign flag. As an example, a 4-byte value consists of 8 nibbles, wherein the upper 7 nibbles store the digits of a 7-digit decimal value, and the lowest nibble indicates the sign of the decimal integer value.


title: Binary-coded decimal

text: Standard sign values are 1100 (hex C) for positive (+) and 1101 (D) for negative (−). This convention comes from the zone field for EBCDIC characters and the signed overpunch representation. Other allowed signs are 1010 (A) and 1110 (E) for positive and 1011 (B) for negative. IBM System/360 processors will use the 1010 (A) and 1011 (B) signs if the A bit is set in the PSW, for the ASCII-8 standard that never passed. Most implementations also provide unsigned BCD values with a sign nibble of 1111 (F). ILE RPG uses 1111 (F) for positive and 1101 (D) for negative. These match the EBCDIC zone for digits without a sign overpunch. In packed BCD, the number 127 is represented by 0001 0010 0111 1100 (127C) and −127 is represented by 0001 0010 0111 1101 (127D). Burroughs systems used 1101 (D) for negative, and any other value is considered a positive sign value (the processors will normalize a positive sign to 1100 (C)).


title: Binary-coded decimal

text: No matter how many bytes wide a word is, there is always an even number of nibbles because each byte has two of them. Therefore, a word of "n" bytes can contain up to (2"n")−1 decimal digits, which is always an odd number of digits. A decimal number with "d" digits requires ("d"+1) bytes of storage space.


title: Binary-coded decimal

text: For example, a 4-byte (32-bit) word can hold seven decimal digits plus a sign and can represent values ranging from ±9,999,999. Thus the number −1,234,567 is 7 digits wide and is encoded as:


title: Binary-coded decimal

text: Like character strings, the first byte of the packed decimal that with the most significant two digits is usually stored in the lowest address in memory, independent of the endianness of the machine.


title: Binary-coded decimal

text: In contrast, a 4-byte binary two's complement integer can represent values from −2,147,483,648 to +2,147,483,647.


title: Binary-coded decimal

text: While packed BCD does not make optimal use of storage (using about 20% more memory than binary notation to store the same numbers), conversion to ASCII, EBCDIC, or the various encodings of Unicode is made trivial, as no arithmetic operations are required. The extra storage requirements are usually offset by the need for the accuracy and compatibility with calculator or hand calculation that fixed-point decimal arithmetic provides. Denser packings of BCD exist which avoid the storage penalty and also need no arithmetic operations for common conversions.


title: Binary-coded decimal

text: Packed BCD is supported in the COBOL programming language as the "COMPUTATIONAL-3" (an IBM extension adopted by many other compiler vendors) or "PACKED-DECIMAL" (part of the 1985 COBOL standard) data type. It is supported in PL/I as "FIXED DECIMAL". Beside the IBM System/360 and later compatible mainframes, packed BCD is implemented in the native instruction set of the original VAX processors from Digital Equipment Corporation and some models of the SDS Sigma series mainframes, and is the native format for the Burroughs Corporation Medium Systems line of mainframes (descended from the 1950s Electrodata 200 series).


title: Binary-coded decimal

text: Ten's complement representations for negative numbers offer an alternative approach to encoding the sign of packed (and other) BCD numbers. In this case, positive numbers always have a most significant digit between 0 and 4 (inclusive), while negative numbers are represented by the 10's complement of the corresponding positive number. As a result, this system allows for 32-bit packed BCD numbers to range from −50,000,000 to +49,999,999, and −1 is represented as 99999999. (As with two's complement binary numbers, the range is not symmetric about zero.)


title: Binary-coded decimal

text: Fixed-point decimal numbers are supported by some programming languages (such as COBOL and PL/I). These languages allow the programmer to specify an implicit decimal point in front of one of the digits. For example, a packed decimal value encoded with the bytes 12 34 56 7C represents the fixed-point value +1,234.567 when the implied decimal point is located between the fourth and fifth digits:


title: Binary-coded decimal

text: The decimal point is not actually stored in memory, as the packed BCD storage format does not provide for it. Its location is simply known to the compiler, and the generated code acts accordingly for the various arithmetic operations.


title: Binary-coded decimal

text: If a decimal digit requires four bits, then three decimal digits require 12 bits. However, since 2 (1,024) is greater than 10 (1,000), if three decimal digits are encoded together, only 10 bits are needed. Two such encodings are "Chen–Ho encoding" and "densely packed decimal" (DPD). The latter has the advantage that subsets of the encoding encode two digits in the optimal seven bits and one digit in four bits, as in regular BCD.


title: Binary-coded decimal

text: Some implementations, for example IBM mainframe systems, support zoned decimal numeric representations. Each decimal digit is stored in one byte, with the lower four bits encoding the digit in BCD form. The upper four bits, called the "zone" bits, are usually set to a fixed value so that the byte holds a character value corresponding to the digit. EBCDIC systems use a zone value of 1111 (hex F); this yields bytes in the range F0 to F9 (hex), which are the EBCDIC codes for the characters "0" through "9". Similarly, ASCII systems use a zone value of 0011 (hex 3), giving character codes 30 to 39 (hex).


title: Binary-coded decimal

text: For signed zoned decimal values, the rightmost (least significant) zone nibble holds the sign digit, which is the same set of values that are used for signed packed decimal numbers (see above). Thus a zoned decimal value encoded as the hex bytes F1 F2 D3 represents the signed decimal value −123:


title: Binary-coded decimal

text: Some languages (such as COBOL and PL/I) directly support fixed-point zoned decimal values, assigning an implicit decimal point at some location between the decimal digits of a number. For example, given a six-byte signed zoned decimal value with an implied decimal point to the right of the fourth digit, the hex bytes F1 F2 F7 F9 F5 C0 represent the value +1,279.50:


title: Binary-coded decimal

text: IBM used the terms "Binary-Coded Decimal Interchange Code" (BCDIC, sometimes just called BCD), for 6-bit "alphanumeric" codes that represented numbers, upper-case letters and special characters. Some variation of BCDIC "alphamerics" is used in most early IBM computers, including the IBM 1620 (introduced in 1959), IBM 1400 series, and non-Decimal Architecture members of the IBM 700/7000 series.


title: Binary-coded decimal

text: The IBM 1400 series are character-addressable machines, each location being six bits labeled "B, A, 8, 4, 2" and "1," plus an odd parity check bit ("C") and a word mark bit ("M"). For encoding digits "1" through "9", "B" and "A" are zero and the digit value represented by standard 4-bit BCD in bits "8" through "1". For most other characters bits "B" and "A" are derived simply from the "12", "11", and "0" "zone punches" in the punched card character code, and bits "8" through "1" from the "1" through "9" punches. A "12 zone" punch set both "B" and "A", an "11 zone" set "B", and a "0 zone" (a 0 punch combined with any others) set "A". Thus the letter A, which is "(12,1)" in the punched card format, is encoded "(B,A,1)". The currency symbol $, "(11,8,3)" in the punched card, was encoded in memory as "(B,8,2,1)". This allows the circuitry to convert between the punched card format and the internal storage format to be very simple with only a few special cases. One important special case is digit "0", represented by a lone "0" punch in the card, and "(8,2)" in core memory.


title: Binary-coded decimal

text: The memory of the IBM 1620 is organized into 6-bit addressable digits, the usual "8, 4, 2, 1" plus "F", used as a flag bit and "C", an odd parity check bit. BCD "alphamerics" are encoded using digit pairs, with the "zone" in the even-addressed digit and the "digit" in the odd-addressed digit, the "zone" being related to the "12", "11", and "0" "zone punches" as in the 1400 series. Input/Output translation hardware converted between the internal digit pairs and the external standard 6-bit BCD codes.


title: Binary-coded decimal

text: In the Decimal Architecture IBM 7070, IBM 7072, and IBM 7074 "alphamerics" are encoded using digit pairs (using two-out-of-five code in the digits, not BCD) of the 10-digit word, with the "zone" in the left digit and the "digit" in the right digit. Input/Output translation hardware converted between the internal digit pairs and the external standard 6-bit BCD codes.


title: Binary-coded decimal

text: With the introduction of System/360, IBM expanded 6-bit BCD "alphamerics" to 8-bit EBCDIC, allowing the addition of many more characters (e.g., lowercase letters). A variable length Packed BCD "numeric" data type is also implemented, providing machine instructions that perform arithmetic directly on packed decimal data.


title: Binary-coded decimal

text: On the IBM 1130 and 1800, packed BCD is supported in software by IBM's Commercial Subroutine Package.


title: Binary-coded decimal

text: Today, BCD data is still heavily used in IBM processors and databases, such as IBM Db2, mainframes, and Power6. In these products, the BCD is usually zoned BCD (as in EBCDIC or ASCII), Packed BCD (two decimal digits per byte), or "pure" BCD encoding (one decimal digit stored as BCD in the low four bits of each byte). All of these are used within hardware registers and processing units, and in software. To convert packed decimals in EBCDIC table unloads to readable numbers, you can use the OUTREC FIELDS mask of the JCL utility DFSORT.


title: Binary-coded decimal

text: The Digital Equipment Corporation VAX-11 series includes instructions that can perform arithmetic directly on packed BCD data and convert between packed BCD data and other integer representations. The VAX's packed BCD format is compatible with that on IBM System/360 and IBM's later compatible processors. The MicroVAX and later VAX implementations dropped this ability from the CPU but retained code compatibility with earlier machines by implementing the missing instructions in an operating system-supplied software library. This is invoked automatically via exception handling when the defunct instructions are encountered, so that programs using them can execute without modification on the newer machines.


title: Binary-coded decimal

text: The Intel x86 architecture supports a unique 18-digit (ten-byte) BCD format that can be loaded into and stored from the floating point registers, from where computations can be performed.


title: Binary-coded decimal

text: In more recent computers such capabilities are almost always implemented in software rather than the CPU's instruction set, but BCD numeric data are still extremely common in commercial and financial applications. There are tricks for implementing packed BCD and zoned decimal add–or–subtract operations using short but difficult to understand sequences of word-parallel logic and binary arithmetic operations. For example, the following code (written in C) computes an unsigned 8-digit packed BCD addition using 32-bit binary operations:


title: Binary-coded decimal

text: BCD is very common in electronic systems where a numeric value is to be displayed, especially in systems consisting solely of digital logic, and not containing a microprocessor. By employing BCD, the manipulation of numerical data for display can be greatly simplified by treating each digit as a separate single sub-circuit. This matches much more closely the physical reality of display hardware—a designer might choose to use a series of separate identical seven-segment displays to build a metering circuit, for example. If the numeric quantity were stored and manipulated as pure binary, interfacing with such a display would require complex circuitry. Therefore, in cases where the calculations are relatively simple, working throughout with BCD can lead to an overall simpler system than converting to and from binary. Most pocket calculators do all their calculations in BCD.


title: Binary-coded decimal

text: The same argument applies when hardware of this type uses an embedded microcontroller or other small processor. Often, representing numbers internally in BCD format results in smaller code, since a conversion from or to binary representation can be expensive on such limited processors. For these applications, some small processors feature dedicated arithmetic modes, which assist when writing routines that manipulate BCD quantities.


title: Binary-coded decimal

text: It is possible to perform addition by first adding in binary, and then converting to BCD afterwards. Conversion of the simple sum of two digits can be done by adding 6 (that is, 16 − 10) when the five-bit result of adding a pair of digits has a value greater than 9. The reason for adding 6 is that there are 16 possible 4-bit BCD values (since 2 = 16), but only 10 values are valid (0000 through 1001). For example:


title: Binary-coded decimal

text: 10001 is the binary, not decimal, representation of the desired result, but the most significant 1 (the "carry") cannot fit in a 4-bit binary number. In BCD as in decimal, there cannot exist a value greater than 9 (1001) per digit. To correct this, 6 (0110) is added to the total, and then the result is treated as two nibbles:


title: Binary-coded decimal

text: The two nibbles of the result, 0001 and 0111, correspond to the digits "1" and "7". This yields "17" in BCD, which is the correct result.


title: Binary-coded decimal

text: This technique can be extended to adding multiple digits by adding in groups from right to left, propagating the second digit as a carry, always comparing the 5-bit result of each digit-pair sum to 9. Some CPUs provide a half-carry flag to facilitate BCD arithmetic adjustments following binary addition and subtraction operations. The Intel 8080, the Zilog Z80 and the CPUs of the x86 family provide the opcode DAA (Decimal Adjust Accumulator).


title: Binary-coded decimal

text: Subtraction is done by adding the ten's complement of the subtrahend to the minuend. To represent the sign of a number in BCD, the number 0000 is used to represent a positive number, and 1001 is used to represent a negative number. The remaining 14 combinations are invalid signs. To illustrate signed BCD subtraction, consider the following problem: 357 − 432.


title: Binary-coded decimal

text: In signed BCD, 357 is 0000 0011 0101 0111. The ten's complement of 432 can be obtained by taking the nine's complement of 432, and then adding one. So, 999 − 432 = 567, and 567 + 1 = 568. By preceding 568 in BCD by the negative sign code, the number −432 can be represented. So, −432 in signed BCD is 1001 0101 0110 1000.


title: Binary-coded decimal

text: Since BCD is a form of decimal representation, several of the digit sums above are invalid. In the event that an invalid entry (any BCD digit greater than 1001) exists, 6 is added to generate a carry bit and cause the sum to become a valid entry. So, adding 6 to the invalid entries results in the following:


title: Binary-coded decimal

text: Thus the result of the subtraction is 1001 1001 0010 0101 (−925). To confirm the result, note that the first digit is 9, which means negative. This seems to be correct since 357 − 432 should result in a negative number. The remaining nibbles are BCD, so 1001 0010 0101 is 925. The ten's complement of 925 is 1000 − 925 = 75, so the calculated answer is −75.


title: Binary-coded decimal

text: If there are a different number of nibbles being added together (such as 1053 − 2), the number with the fewer digits must first be prefixed with zeros before taking the ten's complement or subtracting. So, with 1053 − 2, 2 would have to first be represented as 0002 in BCD, and the ten's complement of 0002 would have to be calculated.


title: Binary-coded decimal

text: Various BCD implementations exist that employ other representations for numbers. Programmable calculators manufactured by Texas Instruments, Hewlett-Packard, and others typically employ a floating-point BCD format, typically with two or three digits for the (decimal) exponent. The extra bits of the sign digit may be used to indicate special numeric values, such as infinity, underflow/overflow, and error (a blinking display).


title: Binary-coded decimal

text: Signed decimal values may be represented in several ways. The COBOL programming language, for example, supports five zoned decimal formats, with each one encoding the numeric sign in a different way:


title: Binary-coded decimal

text: 3GPP developed TBCD, an expansion to BCD where the remaining (unused) bit combinations are used to add specific telephony characters, with digits similar to those found in telephone keypads original design.


title: Binary-coded decimal

text: The mentioned 3GPP document defines TBCD-STRING with swapped nibbles in each byte. Bits, octets and digits indexed from 1, bits from the right, digits and octets from the left.


title: Binary-coded decimal

text: If errors in representation and computation are more important than the speed of conversion to and from display, a scaled binary representation may be used, which stores a decimal number as a binary-encoded integer and a binary-encoded signed decimal exponent. For example, 0.2 can be represented as 2.


title: Binary-coded decimal

text: This representation allows rapid multiplication and division, but may require shifting by a power of 10 during addition and subtraction to align the decimal points. It is appropriate for applications with a fixed number of decimal places that do not then require this adjustment—particularly financial applications where 2 or 4 digits after the decimal point are usually enough. Indeed, this is almost a form of fixed point arithmetic since the position of the radix point is implied.


title: Binary-coded decimal

text: The Hertz and Chen–Ho encodings provide Boolean transformations for converting groups of three BCD-encoded digits to and from 10-bit values that can be efficiently encoded in hardware with only 2 or 3 gate delays. Densely packed decimal (DPD) is a similar scheme that is used for most of the significand, except the lead digit, for one of the two alternative decimal encodings specified in the IEEE 754-2008 floating-point standard.


title: Binary-coded decimal

text: The BIOS in many personal computers stores the date and time in BCD because the MC6818 real-time clock chip used in the original IBM PC AT motherboard provided the time encoded in BCD. This form is easily converted into ASCII for display.


title: Binary-coded decimal

text: The Atari 8-bit family of computers used BCD to implement floating-point algorithms. The MOS 6502 processor has a BCD mode that affects the addition and subtraction instructions. The Psion Organiser 1 handheld computer's manufacturer-supplied software also entirely used BCD to implement floating point; later Psion models used binary exclusively.


title: Binary-coded decimal

text: Early models of the PlayStation 3 store the date and time in BCD. This led to a worldwide outage of the console on 1 March 2010. The last two digits of the year stored as BCD were misinterpreted as 16 causing an error in the unit's date, rendering most functions inoperable. This has been referred to as the Year 2010 problem.


title: Binary-coded decimal

text: In the 1972 case "Gottschalk v. Benson", the U.S. Supreme Court overturned a lower court's decision that had allowed a patent for converting BCD-encoded numbers to binary on a computer. The decision noted that a patent "would wholly pre-empt the mathematical formula and in practical effect would be a patent on the algorithm itself". This was a landmark judgement that determining the patentability of software and algorithms.


title: Tejas Express

text: The Tejas Express is a semi-high speed fully air-conditioned train introduced by Indian Railways. It features modern onboard facilities with doors which are operated automatically. Tejas means "sharp", "lustre", or "brilliance" in many Indian languages. It is one of 3 semi-high speed trains running in India, the others being the Vande Bharat Express and the Gatimaan Express.


title: Tejas Express

text: The inaugural run of Tejas Express was on 24 May 2017 from Chhatrapati Shivaji Maharaj Terminus, Maharashtra to Karmali, Goa. It covered 552 km in 8 hours and 30 minutes. On 1 March 2019, the second Tejas Express of the country was flagged off between Chennai Egmore and Madurai Junction by Prime Minister Narendra Modi. It covered 497 km in 6 hours and 30 minutes.


title: Tejas Express

text: Tejas Express on New Delhi – Chandigarh route is expected to commence its services soon after its first announcement in 2016 whereas the Lucknow – New Delhi route running currently as the train has been included in the current Trains at Glance, the official train time-table booklet, with "Date of Introduction to be declared" condition and at the same time news websites have quoted railway officials saying a hold of three years. Meanwhile, the train service which was expected to be launched on Mumbai – Surat and New Delhi- Jalandhar route has also been put on hold.


title: Tejas Express

text: Lucknow – New Delhi Tejas Express, which was inaugurated on 4 October 2019, is India's first train operated by private operators, IRCTC, a subsidiary of Indian Railways.


title: Tejas Express

text: Recently Agartala – Anand Vihar Rajdhani Express was upgraded to Tejas style sleeper rake and was named as Tejas Rajdhani special. This train leaves Agartala on Monday and arrives at Anand Vihar on Wednesday morning and leaves Anand Vihar on Wednesday evening and arrives in Agartala on Friday. Earliar Rajdhani used to run on this slot between Agartala and Anand Vihar Terminus (Delhi). This train became the country's first sleeper Tejas express. The Mumbai Rajdhani Express, and the Rajendra Nagar Patna Rajdhani Express are also both now run with Tejas LHB coach, replacing the former Rajdhani LHB coach.


title: Tejas Express

text: The coaches of first Tejas Express of India, which runs between Chhatrapati Shivaji Maharaj Terminus (CSMT), Mumbai and Karmali are manufactured at Rail Coach Factory, Kapurthala in Kapurthala district of Punjab. The coaches of second Tejas express, which runs between Chennai Egmore and Madurai, were manufactured at Integral Coach Factory, Chennai. The train is designed to run at a maximum speed of but the maximum operating speed allowed is due to track and safety constraints. Presently, the train runs at an average speed of .


title: Tejas Express

text: There are 14 non-executive chair cars and they can seat up to 72 passengers each in 3+2 configuration. The coaches have energy-efficient LED lights and digital destination display boards. It also has two executive chair cars in 2+2 configuration. The executive chair cars have a seating capacity of 56 passengers with adjustable head-rests, arm support and leg support. The leg support is not available in non-executive chair cars. The seats on tejas express are also very comfortable in terms of height on the contrary of regular AC chair car seats.


title: Tejas Express

text: Coaches have bio-vacuum toilets, water level indicators, tap sensors, hand dryers, integrated braille displays, LED TV for each passenger with phone sockets, local cuisine, celebrity chef menu, WiFi, tea & coffee vending machines, magazines, snack tables, CCTV cameras, fire & smoke detection and suppression system. The fares will be 20% to 30% more than Shatabdi fares. The Tejas Express has redesigned seats with eco-leather. Toilets are equipped with soap dispensers, touch-less water taps, odour-control systems and occupancy indicators. Doors are centrally controlled.


title: Tejas Express

text: Indian Railways started to upgrade Rajdhani coaches to Tejas coaches known as the Tejas-Rajdhani Express. This replaced its traditional LHB Rajdhani coaches.


title: Bill W.

text: William Griffith Wilson (November 26, 1895 – January 24, 1971), also known as Bill Wilson or Bill W., was the co-founder of Alcoholics Anonymous (AA).


title: Bill W.

text: AA is an international mutual aid fellowship with about two million members worldwide belonging to over 123,000 A.A. groups, associations, organizations, cooperatives, and fellowships of alcoholics helping other alcoholics achieve and maintain sobriety. Following AA's Twelfth Tradition of anonymity, Wilson is commonly known as "Bill W." or "Bill". In order to identify each other, members of AA will sometimes ask others if they are "friends of Bill". Although this question can be confusing, because "Bill" is a common name, it does provide a means of establishing the common experience of AA membership. After Wilson's death in 1971, and amidst much controversy within the fellowship, his full name was included in obituaries by journalists who were unaware of the significance of maintaining anonymity within the organization.


title: Bill W.

text: Wilson's sobriety from alcohol, which he maintained until his death, began December 11, 1934. In 1955 Wilson turned over control of AA to a board of trustees. Wilson died in 1971 of emphysema complicated by pneumonia from smoking tobacco. In 1999 "Time" listed him as "Bill W.: The Healer" in the .


title: Bill W.

text: Wilson was born on November 26, 1895, in East Dorset, Vermont, the son of Emily (née Griffith) and Gilman Barrows Wilson. He was born at his parents' home and business, the Mount Aeolus Inn and Tavern. His paternal grandfather, William C. Wilson, was also an alcoholic. Influenced by the preaching of an itinerant evangelist, some weeks before, William C. Wilson climbed to the top of Mt. Aeolus and had a spiritual experience and never drank alcohol again.


title: Bill W.

text: Both of Bill's parents abandoned him soon after he and his sister were bornhis father never returned from a purported business trip, and his mother left Vermont to study osteopathic medicine. Bill and his sister were raised by their maternal grandparents, Fayette and Ella Griffith. As a teen, Bill showed little interest in his academic studies and was rebellious. During a summer break in high school, he spent months designing and carving a boomerang to throw at birds, raccoons, and other local wildlife. After many difficult years during his early-mid teens, Bill became the captain of his high school's football team, and the principal violinist in its orchestra. Bill also dealt with a serious bout of depression at the age of seventeen, following the death of his first love, Bertha Bamford, who died of complications from surgery.


title: Bill W.

text: Wilson met his wife Lois Burnham during the summer of 1913, while sailing on Vermont's Emerald Lake; two years later the couple became engaged. He entered Norwich University, but depression and panic attacks forced him to leave during his second semester. The next year he returned, but was soon suspended with a group of students involved in a hazing incident. Because no one would take responsibility, and no one would identify the perpetrators, the entire class was punished.


title: Bill W.

text: The June 1916 incursion into the U.S. by Pancho Villa resulted in Wilson's class being mobilized as part of the Vermont National Guard and he was reinstated to serve. The following year he was commissioned as an artillery officer. During military training in Massachusetts, the young officers were often invited to dinner by the locals, and Wilson had his first drink, a glass of beer, to little effect. A few weeks later at another dinner party, Wilson drank some Bronx cocktails, and felt at ease with the guests and liberated from his awkward shyness; "I had found the elixir of life", he wrote. "Even that first evening I got thoroughly drunk, and within the next time or two I passed out completely. But as everyone drank hard, not too much was made of that."


title: Bill W.

text: Wilson married Lois on January 24, 1918, just before he left to serve in World War I as a 2nd lieutenant in the Coast Artillery. After his military service, Wilson returned to live with his wife in New York. He failed to graduate from law school because he was too drunk to pick up his diploma. Wilson became a stock speculator and had success traveling the country with his wife, evaluating companies for potential investors. During these trips Lois had a hidden agenda: she hoped the travel would keep Wilson from drinking. However, Wilson's constant drinking made business impossible and ruined his reputation.


title: Bill W.

text: In 1933 Wilson was committed to the Charles B. Towns Hospital for Drug and Alcohol Addictions in New York City four times under the care of William Duncan Silkworth. Silkworth's theory was that alcoholism was a matter of both physical and mental control: a craving, the manifestation of a physical allergy (the physical inability to stop drinking once started) and an obsession of the mind (to take the first drink). Wilson gained hope from Silkworth's assertion that alcoholism was a medical condition, but even that knowledge could not help him. He was eventually told that he would either die from his alcoholism or have to be locked up permanently due to "Wernicke encephalopathy" (commonly referred to as "wet brain").


title: Bill W.

text: In November 1934, Wilson was visited by old drinking companion Ebby Thacher. Wilson was astounded to find that Thacher had been sober for several weeks under the guidance of the evangelical Christian Oxford Group. Wilson took some interest in the group, but shortly after Thacher's visit, he was again admitted to Towns Hospital to recover from a bout of drinking. This was his fourth and last stay at Towns Hospital under Silkworth's care and he showed signs of delirium tremens. There, Bill W had a "White Light" spiritual experience and quit drinking. Earlier that evening, Thacher had visited and tried to persuade him to turn himself over to the care of Jesus Christ who would liberate him from alcohol. According to Wilson, while lying in bed depressed and despairing, he cried out, "I'll do anything! Anything at all! If there be a God, let Him show Himself!" He then had the sensation of a bright light, a feeling of ecstasy, and a new serenity. He never drank again for the remainder of his life. Wilson described his experience to Silkworth, who told him, "Something has happened to you I don't understand. But you had better hang on to it".


title: Bill W.

text: Wilson joined the Oxford Group and tried to help other alcoholics, but succeeded only in keeping sober himself. During a failed business trip to Akron, Ohio, Wilson was tempted to drink again and decided that to remain sober he needed to help another alcoholic. He called phone numbers in a church directory and eventually secured an introduction to Bob Smith, an alcoholic Oxford Group member. Wilson explained Silkworth's theory that alcoholics suffer from a physical allergy and a mental obsession. Wilson shared that the only way he was able to stay sober was through having had a spiritual experience. Smith was familiar with the tenets of the Oxford Group and upon hearing Wilson's experience, "began to pursue the spiritual remedy for his malady with a willingness that he had never before been able to muster. After a brief relapse, he sobered, never to drink again up to the moment of his death in 1950". Wilson and Smith began working with other alcoholics. After that summer in Akron, Wilson returned to New York where he began having success helping alcoholics in what they called "a nameless squad of drunks" in an Oxford Group there.


title: Bill W.

text: In 1938, after about 100 alcoholics in Akron and New York had become sober, the fellowship decided to promote its program of recovery through the publication of a book, for which Wilson was chosen as primary author. The book was given the title "Alcoholics Anonymous" and included the list of suggested activities for spiritual growth known as the Twelve Steps. The movement itself took on the name of the book. Bill incorporated the principles of nine of the Twelve Traditions, (a set of spiritual guidelines to ensure the survival of individual AA groups) in his foreword to the original edition; later, Traditions One, Two, and Ten were clearly specified when all twelve statements were published. The AA general service conference of 1955 was a landmark event for Wilson in which he turned over the leadership of the maturing organization to an elected board.


title: Bill W.

text: In 1939, Wilson and Marty Mann visited High Watch Farm in Kent, CT. They would go on to found what is now High Watch Recovery Center, the world's first alcohol and addiction recovery center founded on Twelve Step principles.


title: Bill W.

text: Wilson strongly advocated that AA groups have not the "slightest reform or political complexion". In 1946, he wrote "No AA group or members should ever, in such a way as to implicate AA, express any opinion on outside controversial issues – particularly those of politics, alcohol reform or sectarian religion. The Alcoholics Anonymous groups oppose no one. Concerning such matters they can express no views whatever." Reworded, this became "Tradition 10" for AA.


title: Bill W.

text: During the last years of his life, Wilson rarely attended AA meetings to avoid being asked to speak as the co-founder rather than as an alcoholic. A heavy smoker, Wilson eventually suffered from emphysema and later pneumonia. He continued to smoke while dependent on an oxygen tank in the late 1960s. While notes written by nurse James Dannenberg say that Bill Wilson asked for whiskey four times (December 25, 1970, January 2, 1971, January 8, 1971, and January 14, 1971) in his final month of living, he drank no alcohol for the final 36 years of his life.


title: Bill W.

text: Francis Hartigan, biographer of Bill Wilson and personal secretary to Lois Wilson in her later years, wrote that in the mid-1950s Bill began a fifteen-year affair with Helen Wynn, a woman 18 years his junior that he met through AA. Hartigan also asserts that this relationship was preceded by other marital infidelities. Wilson arranged in 1963 to leave 10 percent of his book royalties to Helen Wynn and the rest to his wife Lois.


title: Bill W.

text: Historian Ernest Kurtz was skeptical of the veracity of the reports of Wilson's womanizing. He judged that the reports were traceable to a single person, Tom Powers, a formerly close friend of Wilson's with whom he had a falling-out in the mid-1950s.


title: Bill W.

text: Personal letters between Wilson and Lois spanning a period of more than 60 years are kept in the archives at Stepping Stones, their former home in Katonah, New York, and in AA's General Service Office archives in New York.


title: Bill W.

text: In the 1950s, Wilson used LSD in medically supervised experiments with Betty Eisner, Gerald Heard, and Aldous Huxley, taking LSD for the first time on August 29, 1956. With Wilson's invitation, his wife Lois, his spiritual adviser Father Ed Dowling, and Nell Wing also participated in experimentation of this drug. Later Wilson wrote to Carl Jung, praising the results and recommending it as validation of Jung's spiritual experience. (The letter was not in fact sent as Jung had died.) According to Wilson, the session allowed him to re-experience a spontaneous spiritual experience he had had years before, which had enabled him to overcome his own alcoholism.


title: Bill W.

text: Bill was enthusiastic about his experience; he felt it helped him eliminate many barriers erected by the self, or ego, that stand in the way of one's direct experience of the cosmos and of God. He thought he might have found something that could make a big difference to the lives of many who still suffered. Bill is quoted as saying: "It is a generally acknowledged fact in spiritual development that ego reduction makes the influx of God's grace possible. If, therefore, under LSD we can have a temporary reduction, so that we can better see what we are and where we are goingwell, that might be of some help. The goal might become clearer. So I consider LSD to be of some value to some people, and practically no damage to anyone. It will never take the place of any of the existing means by which we can reduce the ego, and keep it reduced." Wilson felt that regular usage of LSD in a carefully controlled, structured setting would be beneficial for many recovering alcoholics. However, he felt this method only should be attempted by individuals with well-developed super-egos.


title: Bill W.

text: In 1957, Wilson wrote a letter to Heard saying: "I am certain that the LSD experiment has helped me very much. I find myself with a heightened colour perception and an appreciation of beauty almost destroyed by my years of depressions." Most AAs were strongly opposed to his experimenting with a mind-altering substance.


title: Bill W.

text: Wilson met Abram Hoffer and learned about the potential mood-stabilizing effects of niacin. Wilson was impressed with experiments indicating that alcoholics who were given niacin had a better sobriety rate, and he began to see niacin "as completing the third leg in the stool, the physical to complement the spiritual and emotional". Wilson also believed that niacin had given him relief from depression, and he promoted the vitamin within the AA community and with the National Institute of Mental Health as a treatment for schizophrenia. However, Wilson created a major furor in AA because he used the AA office and letterhead in his promotion.


title: Bill W.

text: For Wilson, spiritualism was a lifelong interest. One of his letters to adviser Father Dowling suggests that while Wilson was working on his book "Twelve Steps and Twelve Traditions", he felt that spirits were helping him, in particular a 15th-century monk named Boniface. Despite his conviction that he had evidence for the reality of the spirit world, Wilson chose not to share this with AA. However, his practices still created controversy within the AA membership. Wilson and his wife continued with their unusual practices in spite of the misgivings of many AA members. In their house they had a "spook room" where they would invite guests to participate in seances using a Ouija board.


title: Bill W.

text: Alcoholics Anonymous has over 120,000 registered local groups and over two million active members worldwide.


title: Bill W.

text: Wilson has often been described as having loved being the center of attention, but after the AA principle of anonymity had become established, he refused an honorary degree from Yale University and refused to allow his picture, even from the back, on the cover of "Time". Wilson's persistence, his ability to take and use good ideas, and his entrepreneurial flair are revealed in his pioneering escape from an alcoholic "death sentence", his central role in the development of a program of spiritual growth, and his leadership in creating and building AA, "an independent, entrepreneurial, maddeningly democratic, non-profit organization".


title: Bill W.

text: Wilson is perhaps best known as a synthesizer of ideas, the man who pulled together various threads of psychology, theology, and democracy into a workable and life-saving system. Aldous Huxley called him "the greatest social architect of our century", and "Time" magazine named Wilson to their ""Time" 100 List of The Most Important People of the 20th Century". Wilson's self-description was a man who, "because of his bitter experience, discovered, slowly and through a conversion experience, a system of behavior and a series of actions that work for alcoholics who want to stop drinking."


title: Bill W.

text: Biographer Susan Cheever wrote in "My Name Is Bill", "Bill Wilson never held himself up as a model: he only hoped to help other people by sharing his own experience, strength and hope. He insisted again and again that he was just an ordinary man".


title: Bill W.

text: Wilson bought a house that he and Lois called Stepping Stones on an estate in Katonah, New York, in 1941, and he lived there with Lois until he died in 1971. After Lois died in 1988, the house was opened for tours and is now on the National Register of Historic Places; it was designated a National Historic Landmark in 2012.


title: Bill W.

text: Over the years, Bill W., the formation of AA and also his wife Lois have been the subject of numerous projects, starting with "My Name Is Bill W.", a 1989 CBS Hallmark Hall of Fame TV movie starring James Woods as Bill W. and James Garner as Bob Smith. Woods won an Emmy for his portrayal of Wilson. He was also depicted in a 2010 TV movie based on Lois' life, "", adapted from a 2005 book of the same name written by William G. Borchert. The film starred Winona Ryder as Lois Wilson and Barry Pepper as Bill W.


title: Bill W.

text: The band El Ten Eleven's song "Thanks Bill" is dedicated to Bill W. since lead singer Kristian Dunn's wife got sober due to AA. He states "If she hadn't gotten sober we probably wouldn't be together, so that's my thank you to Bill Wilson who invented AA".


title: Bill W.

text: In Michael Graubart's "Sober Songs Vol. 1", the song "Hey, Hey, AA" references Bill's encounter with Ebby Thatcher which started him on the path to recovery and eventually the creation of Alcoholics Anonymous. The lyric reads, "Ebby T. comes strolling in. Bill says, 'Fine, you're a friend of mine. Don't mind if I drink my gin.


title: Katalin Novák

text: Katalin Éva Novák (born 6 September 1977) is a Hungarian politician serving as the current president of Hungary, having been elected in the 2022 presidential election. Novák is the first woman to hold the presidency, as well as the youngest president in the history of Hungary, elected at the age of 44. A member of Fidesz, Novák has additionally served as member of the National Assembly from 2018 to 2022, and as Minister for Family Affairs in the fourth Orbán Government from 2020 until 2021.


title: Katalin Novák

text: After completing her secondary education at the Ságvári Endre Secondary School at Szeged in 1996, Novák studied economics at the Corvinus University of Budapest and law at the University of Szeged. While a student, she additionally studied abroad at the Paris Nanterre University. In addition to Hungarian, Novák speaks French, English, and German.


title: Katalin Novák

text: Novák started work at the Foreign Ministry in 2001, specializing in European Union and European matters. In 2010 she became a ministerial advisor and in 2012 was appointed Head of Cabinet of the Ministry of Human Resources.


title: Katalin Novák

text: In 2014 she became State Secretary for Family and Youth Affairs at the Ministry of Human Capacities, eventually becoming Minister of Family Affairs in October 2020, a position held until December 2021.


title: Katalin Novák

text: On 21 December 2021, Prime Minister Viktor Orbán announced that Novák would be his nominee in the 2022 presidential election. On 10 March 2022, she won gaining 137 out of 188 votes in the National Assembly.


title: Katalin Novák

text: Katalin Novák is married and has three children. Her husband is economist István Veres, director of the Financial Market and Foreign Exchange Market Directorate at the Hungarian National Bank (MNB). She is a Reformed Christian.


title: Emirate of Granada

text: The Emirate of Granada (), also known as the Nasrid Kingdom of Granada (), was an Islamic realm in southern Iberia during the Late Middle Ages. It was the last independent Muslim state in Western Europe.


title: Emirate of Granada

text: Muslims had been present in the Iberian Peninsula, which they called "Al-Andalus", since the early eighth century. At its greatest geographical extent, Muslim-controlled territory occupied most of the peninsula and part of present-day southern France. From the ninth to the tenth century, under the Caliphate of Córdoba, the region was one of the most prosperous and advanced in Europe. Conflict with the northern Christian kingdoms was recurrent, while mounting civil strife led to a fragmenting of Muslim states in the early eleventh century. This marked a precipitous decline in Muslim power and facilitated the centuries-long Christian "Reconquista."


title: Emirate of Granada

text: By 1230, the Almohad Caliphate in Morocco ruled the remaining Muslim territories in southern Iberia. Exploiting the Almohad's dynastic strife, the ambitious Muhammad ibn al-Ahmar rose to power and established the Nasrid dynasty in control of a sizeable portion of this territory, roughly corresponding to the modern Spanish provinces of Granada, Almería, and Málaga. By 1250, the emirate was the last Muslim polity in the peninsula. Although effectively a vassal of the rising Crown of Castile, for over two centuries, Granada enjoyed considerable cultural and economic prosperity; much of the famed Alhambra palace complex was built during this period, and the Nasrids would be the longest-lived Muslim dynasty in Iberia.


title: Emirate of Granada

text: Nascent Christian power in Iberia meant that Granada's existence was always precarious. In 1491, after a decade of intermittent warfare known as the Granada War, the emirate was forced to capitulate to the Catholic Monarchs. The following year, Muhammad XII, the last Nasrid ruler of Granada, formally relinquished his sovereignty and surrendered his territories to Castile, eventually moving to North Africa in exile. This marked the end of independent Muslim rule in Iberia.


title: Emirate of Granada

text: With the Reconquista in full swing after the conquest of Córdoba in June 1236, Mohammed I ibn Nasr aligned Granada with Ferdinand III of Castile in 1246, thereby making it a tributary state, or "taifa", under the Crown of Castile. Granada remained a tributary state for the next 250 years, with Nasrid emirs paying tribute () to Castilian kings mostly in the form of gold from present-day Mali and Burkina Faso, brought to Iberia by the merchant routes in the Sahara. The Nasrids also provided military assistance to Castile for its other conquests.


title: Emirate of Granada

text: In 1306, Granada conquered Ceuta, but lost control of the city in 1309 to the Kingdom of Fez which was assisted by the Crown of Aragon. Granada re-captured Ceuta a year later, but again lost it in 1314. Granada again held the city from 1315 to 1327. In 1384, Granada again re-took Ceuta but lost it finally to the Kingdom of Fez in 1386. Ceuta would be taken by the Portuguese Empire in 1415 and came into the Spanish Empire in 1580.


title: Emirate of Granada

text: Granada's peace with Castile broke down on various occasions. Granada lost territory to Castile at the Battle of Teba in 1330. In 1340, Granada under Yusuf I, supported the failed Marinid invasion of the Iberian Peninsula, which ended at the Battle of Río Salado.


title: Emirate of Granada

text: Granada also served as a refuge for Muslims fleeing during the Reconquista. Regardless of its comparative prosperity, intra-political strife was constant. Skirmishes along the border of Granada occurred frequently and the territory was gradually lost to Castile.


title: Emirate of Granada

text: The war of Granada would offer an opportunity for Ferdinand and Isabella to harness the restless Castilian nobility against a common enemy and instill subjects with a sense of loyalty to the crown. The Emirate's attack on the Castilian frontier town of Zahara in December 1481 led to a prolonged war. The Granada War began in 1482, with Christian forces capturing Alhama de Granada in February 1482. This marked the beginning of a grinding 10-year war. The Christian force was made up of troops provided by Castilian nobles, towns, and the "Santa Hermandad", as well as Swiss mercenaries. The Catholic Church also encouraged other Christian countries to offer their troops and their finances to the war effort. Meanwhile, civil war erupted in Granada as a result of succession struggles in the Nasrid ruling house. Castile used this internal strife as an opportunity to push further into Granada. By 1491, the city of Granada itself lay under siege. On November 25, 1491, the Treaty of Granada was signed, setting out the conditions for surrender. On January 2, 1492, the last Muslim leader, Muhammad XII, known as "Boabdil" to the Spanish, gave up complete control of Granada to Ferdinand and Isabella, "Los Reyes Católicos" ("The Catholic Monarchs").


title: Emirate of Granada

text: The Christian ousting of Muslim rule on the Iberian Peninsula with the conquest of Granada did not extinguish the spirit of the "Reconquista". Isabella urged Christians to pursue a conquest of Africa. About 200,000 Muslims are thought to have emigrated to North Africa after the fall of Granada. Initially, under the conditions of surrender, the Muslims who remained were guaranteed their property, laws, customs, and religion. This however, was not the case, causing the Muslims to rebel against their Christian rulers, culminating with an uprising in 1500. The rebellion was seen as a chance to formally end the treaty of Granada, and the rights of Muslims and Jews were withdrawn. Muslims in the area were given the choice of expulsion or conversion. In 1568–1571, the descendants of the converted Muslims revolted again, leading to their expulsion from the former Emirate to North Africa and Anatolia.


title: Emirate of Granada

text: For Jews as well, a period of tolerance under Muslim rule in the Iberian Peninsula came to an end with their expulsion by the Christian monarchy in 1492.


title: Emirate of Granada

text: Granada's status as a tributary state and its favorable geographic location, with the Sierra Nevada as a natural barrier, helped to prolong Nasrid rule and allowed the Emirate to prosper as a regional entrepôt with the Maghreb and the rest of Africa. The city of Granada was one of the largest cities during this time: it accepted numerous Muslim refugees expelled from Christian controlled areas, doubling the size of the city and even becoming the largest city of Europe in 1450 in terms of population. During this time there were 137 mosques in the Medina of Granada.


title: Emirate of Granada

text: Granada was tightly integrated into Mediterranean trade networks and heavily financed by Genoese bankers aiming to gain control of the gold trade carried in through the Trans-Saharan trade routes. However, after Portugal opened direct trade routes to Sub-Saharan Africa by sea in the 15th century, Granada became less important as a regional commercial center. With the union of Castile and Aragon in 1469, these kingdoms set their sights on annexing Granada.


title: Emirate of Granada

text: Ibn al-Khatib was a polymath and poet of the Nasrid period. He authored many works in various fields, and his poetry is carved into the walls of the Alhambra palace.


title: Emirate of Granada

text: The architecture of Nasrid Granada embraced extensive surface decoration in wood, stucco, and "zillij" tiling, as well as making use of elaborate "muqarnas" sculpting in many buildings. The Nasrids' most famous architectural legacy is the Alhambra, a hilltop palace district protected by heavy fortifications and containing some of the most famous and best-preserved palaces of western Islamic architecture, including what is known today as the Comares Palace and the Courtyard of the Lions. The palace complex was developed throughout the period but some of the most important contributions were generally made during the rule of Yusuf I and Muhammad V during the 14th century. The summer palace and gardens known as the Generalife were also created nearby, in a tradition reminiscent of the Almohad-era Agdal Gardens of Marrakesh and the Marinid Royal Gardens of Fes. Other notable buildings and structures known from this era are the Madrasa al-Yusufiyya (now known as the Palacio del Madraza), the Funduq al-Jadida (now known as the Corral del Carbón), parts of Granada's city walls, the Alcázar Genil, and the Cuarto Real de Santo Domingo in Granada, in addition to many various other fortifications and smaller monuments across the former emirate's territory.


title: Emirate of Granada

text: Gharnati music () is a variety of Andalusi music that originated in Granada and moved to North Africa where it survived to this day.


title: Emirate of Granada

text: Constantly under threat by both the Christian kingdoms to the north and the Muslim Marinid Sultanate to the south, the population of the Emirate of Granada developed a "siege mentality". The country consequently maintained a strong military. Its border territories were dotted with castles maintained by frontier warriors ("thagri") led by armoured elite warriors who were influenced by and comparable to the Christian knights. However, the core of the emirate's army consisted of highly mobile light cavalry as well as light infantry.


title: Emirate of Granada

text: The Granadan army was ethnically and culturally mixed. A large part were recruited locally through the "jund" system in which families with military obligations were registered and conscripted for service. In addition, the Granadan rulers encouraged North African warriors to migrate to the country and serve as "ghazi". These immigrants were mostly Zenata (or Zanata) Berbers and eventually organized as Volunteers of the Faith, a factually autonomous and very powerful unit within the Granadan military. The Zenata served as light cavalry, which gave rise to the Spanish term "jinete" (derived from the name 'Zenata'), which denoted this type of light cavalry. They formed the backbone of the Granadan army, serving both in crucial battles as well as in regular raids inside Christian territory. They were highly mobile on the field, armed with lances, javelins, and small round shields known for their flexibility, and used their own characteristic set of tactics. They sometimes also served as auxiliaries in Castilian armies, sent by the Nasrid emirs of Granada to aid their allies. They were recruited and led by exiled members of the Marinid family and settled within the kingdom of Granada. Their Marinid commander was known as the "shaykh al-ghuzāt" ('chief of the "ghazis"'), but in 1374 Muhammad V suppressed this office due to their political interference, after which they were commanded by a Nasrid or Andalusi general.


title: Emirate of Granada

text: Muhammad V reduced the status of the Volunteers and reformed the military, strengthening instead the Andalusian components of the Granadan military. The smallest part of the regular Granadan military were Christians and ex-Christians who had been hired by the emirs or defected to them. These were often Spanish knights and termed Mamluks; these warriors were organized as elite bodyguards by some emirs. To augment their army, the Granadans also hired foreign mercenaries.


title: Emirate of Granada

text: In regard to its organization, the Granadan military was formally headed by the emir and divided into several units. The frontier areas were possibly commanded by "rais", while each important frontier garrison was led by a "shaykh khassa". The army was divided into major divisions, each led by a "wali", under whom military "emirs" served as leaders for 5,000 troops, followed by "qaid" leading 1,000, "naqib" leading 200, and finally "nazir" leading eight. The Volunteers of the Faith were initially commanded by the "shaykh al-ghuzat". In addition, there existed a Gendarmerie-like "shurta" in Granada city, commanded by the "sahib al-shurta". The Granadan army was usually accompanied by a corps of guides ("dalil"), religious figures who tended to morale, armourers, medics, and some poets as well as orators.


title: Compressor

text: A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.


title: Compressor

text: Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. The main distinction is that the focus of a compressor is to change the density or volume of the fluid, which is mostly only achievable on gases. Gases are compressible, while liquids are relatively incompressible, so compressors are rarely used for liquids. The main action of a pump is to pressurize and transport liquids.


title: Compressor

text: Many compressors can be staged, that is, the fluid is compressed several times in steps or stages, to increase discharge pressure. Often, the second stage is physically smaller than the primary stage, to accommodate the already compressed gas without reducing its pressure. Each stage further compresses the gas and increases its pressure and also temperature (if inter cooling between stages is not used).


title: Compressor

text: A positive displacement compressor is a system that compresses the air by the displacement of a mechanical linkage reducing the volume (since the reduction in volume due to a piston in thermodynamics is considered as positive displacement of the piston).


title: Compressor

text: Put another way, a positive displacement compressor is one that operates by drawing in a discrete volume of gas from its inlet then forcing that gas to exit via the compressor's outlet. The increase in the pressure of the gas is due, at least in part, to the compressor pumping it at a mass flow rate which cannot pass through the outlet at the lower pressure and density of the inlet.


title: Compressor

text: Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over are commonly found in large industrial and petroleum applications. Discharge pressures can range from low pressure to very high pressure (>18000 psi or 180 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, and more costly than comparable rotary units.


title: Compressor

text: Another type of reciprocating compressor, usually employed in automotive cabin air conditioning systems, is the swash plate or wobble plate compressor, which uses pistons moved by a swash plate mounted on a shaft (see "axial piston pump").


title: Compressor

text: Household, home workshop, and smaller job site compressors are typically reciprocating compressors 1½ hp or less with an attached receiver tank.


title: Compressor

text: This type of compressor can compress a wide range of gases, including refrigerant, hydrogen, and natural gas. Because of this, it finds use in a wide range of applications in many different industries and can be designed to a wide range of capacities, by varying size, number of cylinders, and cylinder unloading. However, it suffers from higher losses due to clearance volumes, resistance due to discharge and suction valves, weighs more, is difficult to maintain due to having a large number of moving parts, and it has inherent vibration.


title: Compressor

text: An ionic liquid piston compressor, "ionic compressor" or "ionic liquid piston pump" is a hydrogen compressor based on an ionic liquid piston instead of a metal piston as in a piston-metal diaphragm compressor.


title: Compressor

text: Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from to over and from low pressure to moderately high pressure (>).


title: Compressor

text: The classifications of rotary screw compressors vary based on stages, cooling methods, and drive types among others. Rotary screw compressors are commercially produced in Oil Flooded, Water Flooded and Dry type.


title: Compressor

text: The efficiency of rotary compressors depends on the air drier, and the selection of air drier is always 1.5 times volumetric delivery of the compressor.


title: Compressor

text: Screw compressors have less moving components, larger capacity, less vibration and surging, can operate at variable speeds, and typically have higher efficiency. Small sizes or low rotor speeds are not practical due to inherent leaks caused by clearance between the compression cavities or screws and compressor housing. They depend on fine machining tolerances to avoid high leakage losses and are prone to damage if operated incorrectly or poorly serviced.


title: Compressor

text: Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing that is either circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing. Thus, a series of increasing and decreasing volumes is created by the rotating blades. Rotary vane compressors are, with piston compressors one of the oldest of compressor technologies.


title: Compressor

text: With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., ) for bulk material movement while oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.


title: Compressor

text: The Rolling piston in a rolling piston style compressor plays the part of a partition between the vane and the rotor. Rolling piston forces gas against a stationary vane.


title: Compressor

text: 2 of these compressors can be mounted on the same shaft to increase capacity and reduce vibration and noise. A design without a spring is known as a swing compressor.


title: Compressor

text: In refrigeration and air conditioning, this type of compressor is also known as a rotary compressor, with rotary screw compressors being also known simply as screw compressors.


title: Compressor

text: It offers higher efficiency than reciprocating compressors due to less losses from the clearance volume between the piston and the compressor casing, its 40% to 50% smaller and lighter for a given capacity (which can impact material and shipping costs when used in a product), causes less vibration, has fewer components and is more reliable than a reciprocating compressor. But its structure does not allow capacities beyond 5 refrigeration tons, is less reliable than other compressor types, and is less efficient than other compressor types due to losses from the clearance volume.


title: Compressor

text: A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves. They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range.


title: Compressor

text: Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls.


title: Compressor

text: Due to minimum clearance volume between the fixed scroll and the orbiting scroll, these compressors have a very high volumetric efficiency.


title: Compressor

text: These compressors are extensively used in air conditioning and refrigeration because they are lighter, smaller and have fewer moving parts than reciprocating compressors and they are also more reliable. They are more expensive though, so peltier coolers or rotary and reciprocating compressors may be used in applications where cost is the most important or one of the most important factors to consider when designing a refrigeration or air conditioning system.


title: Compressor

text: This type of compressor was used as the supercharger on Volkswagen G60 and G40 engines in the early 1990s.


title: Compressor

text: When compared with reciprocating and rolling piston compressors, scroll compressors are more reliable since they have fewer components and have a simpler structure, are more efficient since they have no clearance volume nor valves, and possess the advantages both of surging less and not vibrating so much. But, when compared with screw and centrifugal compressors, scroll compressors have lower efficiencies and smaller capacities.


title: Compressor

text: A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in contact with the gas being compressed.


title: Compressor

text: The degree of flexing and the material constituting the diaphragm affects the maintenance life of the equipment. Generally stiff metal diaphragms may only displace a few cubic centimeters of volume because the metal can not endure large degrees of flexing without cracking, but the stiffness of a metal diaphragm allows it to pump at high pressures. Rubber or silicone diaphragms are capable of enduring deep pumping strokes of very high flexion, but their low strength limits their use to low-pressure applications, and they need to be replaced as plastic embrittlement occurs.


title: Compressor

text: Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.


title: Compressor

text: The photograph on the right depicts a three-stage diaphragm compressor used to compress hydrogen gas to for use in a prototype compressed hydrogen and compressed natural gas (CNG) fueling station built in downtown Phoenix, Arizona by the Arizona Public Service company (an electric utilities company). Reciprocating compressors were used to compress the natural gas. The reciprocating natural gas compressor was developed by Sertco.


title: Compressor

text: The prototype alternative fueling station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas.


title: Compressor

text: Also known as a trompe. A mixture of air and water generated through turbulence is allowed to fall into a subterranean chamber where the air separates from the water. The weight of falling water compresses the air in the top of the chamber. A submerged outlet from the chamber allows water to flow to the surface at a lower height than the intake. An outlet in the roof of the chamber supplies the compressed air to the surface. A facility on this principle was built on the Montreal River at Ragged Shutes near Cobalt, Ontario in 1910 and supplied 5,000 horsepower to nearby mines.


title: Compressor

text: Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. Their application can be from to thousands of horsepower. With multiple staging, they can achieve high output pressures greater than .


title: Compressor

text: This type of compressor, along with screw compressors, are extensively used in large refrigeration and air conditioning systems. Magnetic bearing (magnetically levitated) and air bearing centrifugal compressors exist.


title: Compressor

text: Many large snowmaking operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium-sized gas turbines.


title: Compressor

text: Centrifugal compressors are the largest available compressors, offer higher efficiencies under partial loads, may be oil-free when using air or magnetic bearings which increases the heat transfer coefficient in evaporators and condensers, weigh up to 90% less and occupy 50% less space than reciprocating compressors, are reliable and cost less to maintain since less components are exposed to wear, and only generate minimal vibration. But, their initial cost is higher, require highly precise CNC machining, the impeller needs to rotate at high speeds making small compressors impractical, and surging becomes more likely. Surging is gas flow reversal, meaning that the gas goes from the discharge to the suction side, which can cause serious damage, specially in the compressor bearings and its drive shaft. It is caused by a pressure on the discharge side that is higher than the output pressure of the compressor. This can cause gases to flow back and forth between the compressor and whatever is connected to its discharge line, causing oscillations.


title: Compressor

text: Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to an axial rather than radial direction. Comparative to the conventional centrifugal compressor (of the same stage pressure ratio), the value of the speed of the mixed flow compressor is 1.5 times larger.


title: Compressor

text: Axial compressors are dynamic rotating compressors that use arrays of fan-like airfoils to progressively compress a fluid. They are used where high flow rates or a compact design are required.


title: Compressor

text: The arrays of airfoils are set in rows, usually as pairs: one rotating and one stationary. The rotating airfoils, also known as blades or "rotors", accelerate the fluid. The stationary airfoils, also known as "stators" or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage. Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio a compressor will not function unless fitted with features such as stationary vanes with variable angles (known as variable inlet guide vanes and variable stators), the ability to allow some air to escape part-way along the compressor (known as interstage bleed) and being split into more than one rotating assembly (known as twin spools, for example).


title: Compressor

text: Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial compressors are used in medium to large gas turbine engines, natural gas pumping stations, and some chemical plants.


title: Compressor

text: Compressors used in refrigeration systems must exhibit near-zero leakage to avoid the loss of the refrigerant if they are to function for years without service. This necessitates the use of very effective seals, or even the elimination of all seals and openings to form a hermetic system. These compressors are often described as being either hermetic, open, or semi-hermetic, to describe how the compressor is enclosed and how the motor drive is situated in relation to the gas or vapor being compressed. Some compressors outside of refrigeration service may also be hermetically sealed to some extent, typically when handling toxic, polluting, or expensive gasses, with most non-refrigeration applications being in the petrochemical industry.


title: Compressor

text: In hermetic and most semi-hermetic compressors, the compressor and motor driving the compressor are integrated, and operate within the pressurized gas envelope of the system. The motor is designed to operate in, and be cooled by, the refrigerant gas being compressed. Open compressors have an external motor driving a shaft that passes through the body of the compressor and rely on rotary seals around the shaft to retain the internal pressure.


title: Compressor

text: The difference between the hermetic and semi-hermetic, is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair; if the hermetic fails it is simply replaced with an entire new unit. A semi-hermetic uses a large cast metal shell with gasketed covers with screws that can be opened to replace motor and compressor components. The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. The main advantages of open compressors is that they can be driven by any motive power source, allowing the most appropriate motor to be selected for the application, or even non-electric power sources such as an internal combustion engine or steam turbine, and secondly the motor of an open compressor can be serviced without opening any part of the refrigerant system.


title: Compressor

text: An open pressurized system such as an automobile air conditioner can be more susceptible to leak its operating gases. Open systems rely on lubricant in the system to splash on pump components and seals. If it is not operated frequently enough, the lubricant on the seals slowly evaporates, and then the seals begin to leak until the system is no longer functional and must be recharged. By comparison, a hermetic or semi-hermetic system can sit unused for years, and can usually be started up again at any time without requiring maintenance or experiencing any loss of system pressure. Even well lubricated seals will leak a small amount of gas over time, particularly if the refrigeration gasses are soluble in the lubricating oil, but if the seals are well manufactured and maintained this loss is very low.


title: Compressor

text: The disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor must be replaced if a motor fails. A further disadvantage is that burnt-out windings can contaminate the whole systems, thereby requiring the system to be entirely pumped down and the gas replaced (This can also happen in semi hermetic compressors where the motor operates in the refrigerant). Typically, hermetic compressors are used in low-cost factory-assembled consumer goods where the cost of repair and labor is high compared to the value of the device, and it would be more economical to just purchase a new device or compressor. Semi-hermetic compressors are used in mid-sized to large refrigeration and air conditioning systems, where it is cheaper to repair and/or refurbish the compressor compared to the price of a new one. A hermetic compressor is simpler and cheaper to build than a semi-hermetic or open compressor.


title: Compressor

text: A compressor can be idealized as internally reversible and adiabatic, thus an isentropic steady state device, meaning the change in entropy is 0. By defining the compression cycle as isentropic, an ideal efficiency for the process can be attained, and the ideal compressor performance can be compared to the actual performance of the machine. Isotropic Compression as used in ASME PTC 10 Code refers to a reversible, adiabatic compression process


title: Compressor

text: Let formula_5 be heat, formula_6 be work, formula_7 be kinetic energy and formula_8 be potential energy.


title: Compressor

text: Therefore, work-consuming devices such as pumps and compressors (work is negative) require less work when they operate reversibly.


title: Compressor

text: By making the following assumptions the required work for the compressor to compress a gas from formula_19 to formula_20 is the following for each process:


title: Compressor

text: By comparing the three internally reversible processes compressing an ideal gas from formula_19 to formula_20, the results show that isentropic compression (formula_23) requires the most work in and the isothermal compression(formula_28 or formula_29) requires the least amount of work in. For the polytropic process (formula_26) work in decreases as the exponent, n, decreases, by increasing the heat rejection during the compression process. One common way of cooling the gas during compression is to use cooling jackets around the casing of the compressor.


title: Compressor

text: NOTE: The isentropic assumptions are only applicable with ideal cycles. Real world cycles have inherent losses due to inefficient compressors and turbines. The real world system are not truly isentropic but are rather idealized as isentropic for calculation purposes.