text:
Sharpless epoxidation

The Sharpless epoxidation reaction is an enantioselective chemical reaction to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols. The oxidizing agent is tert-butyl hydroperoxide. The method relies on a catalyst formed from titanium tetra(isopropoxide) and diethyl tartrate.

2,3-Epoxyalcohols can be converted into diols, aminoalcohols, and ethers. The reactants for the Sharpless epoxidation are commercially available and relatively inexpensive. K. Barry Sharpless published a paper on the reaction in 1980 and was awarded the 2001 Nobel Prize in Chemistry for this and related work on asymmetric oxidations. The prize was shared with William S. Knowles and Ryōji Noyori.

Catalyst
5–10 mol% of the catalyst is typical. The presence of 3Å molecular sieves (3Å MS) is necessary. The structure of the catalyst is uncertain although it is thought to be a dimer of [Ti(tartrate)(OR)$2$].

Selectivity
The epoxidation of allylic alcohols is a well-utilized conversion in fine chemical synthesis. The chirality of the product of a Sharpless epoxidation is sometimes predicted with the following mnemonic. A rectangle is drawn around the double bond in the same plane as the carbons of the double bond (the xy-plane), with the allylic alcohol in the bottom right corner and the other substituents in their appropriate corners. In this orientation, the (−) diester tartrate preferentially interacts with the top half of the molecule, and the (+) diester tartrate preferentially interacts with the bottom half of the molecule. This model seems to be valid despite substitution on the olefin. Selectivity decreases with larger R1, but increases with larger R2 and R3 (see introduction).

However, this method incorrectly predicts the product of allylic 1,2-diols.

Kinetic resolution
The Sharpless epoxidation can also give kinetic resolution of a racemic mixture of secondary 2,3-epoxyalcohols. While the yield of a kinetic resolution process cannot be higher than 50%, the enantiomeric excess approaches 100% in some reactions.

Synthetic utility
The Sharpless epoxidation is viable with a large range of primary and secondary alkenic alcohols. Furthermore, with the exception noted above, a given dialkyl tartrate will preferentially add to the same face independent of the substitution on the alkene.To demonstrate the synthetic utility of the Sharpless epoxidation, the Sharpless group created synthetic intermediates of various natural products: methymycin, erythromycin, leukotriene C-1, and (+)-disparlure.

As one of the few highly enantioselective reactions during its time, many manipulations of the 2,3-epoxyalcohols have been developed.

The Sharpless epoxidation has been used for the total synthesis of various saccharides, terpenes, leukotrienes, pheromones, and antibiotics.

The main drawback of this protocol is the necessity of the presence of an allylic alcohol. The Jacobsen epoxidation, an alternative method to enantioselectively oxidise alkenes, overcomes this issue and tolerates a wider array of functional groups.

title: Sharpless epoxidation


text:
GNU Units

GNU Units is a cross-platform computer program for conversion of units of quantities. It has a database of measurement units, including esoteric and historical units. This for instance allows conversion of velocities specified in furlongs per fortnight, and pressures specified in tons per acre. Output units are checked for consistency with the input, allowing verification of conversion of complex expressions.

History
GNU Units was written by Adrian Mariano as an implementation of the units utility included with the Unix operating system. It was originally available under a permissive license. The GNU variant is distributed under the GPL although the FreeBSD project maintains a free fork of units from before the license change.

units (Unix utility)
The original units program has been a standard part of Unix since the early Bell Laboratories versions. Source code for a version very similar to the original is available from the Heirloom Project.

The GNU implementation
GNU units includes several extensions to the original version, including
 * Exponents can be written with  or.
 * Exponents can be larger than 9 if written with  or.
 * Rational and decimal exponents are supported.
 * Sums of units (e.g., ) can be converted.
 * Conversions can be made to sums of units, termed unit lists (e.g., from degrees to degrees, minutes, and seconds).
 * Units that measure reciprocal dimensions can be converted (e.g.,  to  ).
 * Parentheses for grouping are supported. This sometimes allows more natural expressions, such as in the example given in Complex units expressions.
 * Roots of units (e.g.,  can be computed.
 * Nonlinear units conversions (e.g., °F to °C) are supported.
 * Functions such as sin, cos, ln, log, and log2 are included.
 * A script for updating the currency conversions is included; the script requires Python.

Units definitions, including nonlinear conversions and unit lists, are user extensible.

The plain text database definitions.units is a good reference in itself, as it is extensively commented and cites numerous sources.

Other implementations
UDUNITS is a similar utility program, except that it has an additional programming library interface and date conversion abilities. UDUNITS is considered the de facto program and library for variable unit conversion for netCDF files.

Version history
GNU Units version 2.19 was released on 31 May 2019, to reflect the new 2019 revision of the SI; Version 2.14 released on 8 March 2017 fixed several minor bugs and improved support for building on Windows. Version 2.10, released on 26 March 2014, added support for rational exponents greater than one, and added the ability to save an interactive session in a file to provide a record of the conversions performed. Beginning with version 2.10, a 32-bit Windows binary distribution has been available on the project Web page (a 32-bit Windows port of version 1.87 has been available since 2008 as part of the GnuWin32 project).

Version 2.02, released on 11 July 2013, added hexadecimal floating-point output and two other options to simplify changing the output format.

Version 2.0, released on 2 July 2012, added the ability to convert to sums of units, such as hours and minutes or feet and inches. In addition, this release added support for UTF-8 encoding. Provision for locale-specific unit definitions was added. The syntax for defining non-linear units was changed, and added optional domain and range specifications. The names of the standard and personal units data files were changed, and the currency definitions were placed in a separate data file; a Python script for updating the currency definitions was added.

The version history is covered in detail in the NEWS file included with the source distribution.

Usage
Units will output the result of the conversion in two lines. Usually, the first line (multiplication) is the desired result; the second line is the same conversion expressed as a division.

Units can also function as a general-purpose scientific calculator; it includes several built-in mathematical functions such as sin, cos, atan, ln, exp, etc.

Attempting to convert types of measurements that are incompatible will cause units to print a conformability error message and display a reduced form of each measurement.

Examples
The examples that follow show results from GNU units version 2.10.

Interactive mode
Currency exchange rates from www.timegenie.com on 2014-03-28 2729 units, 92 prefixes, 77 nonlinear units

You have: 10 furlongs You want: miles * 1.25       / 0.8 You have: 1 gallon + 3 pints You want: quarts * 5.5       / 0.18181818 You have: sqrt(meter) ^ Unit not a root You have: sqrt(acre) You want: ft       * 208.71033 / 0.0047913298 You have: 21 btu + 6500 ft lbf You want: btu * 29.352939       / 0.034068139 You have: _ You want: J       * 30968.99 / 3.2290366e-005 You have: 3.277 hr You want: time 3 hr + 16 min + 37.2 sec You have: 1|2 inch You want: cm       * 1.27 / 0.78740157

The underscore ('_') is used to indicate the result of the last successful unit conversion.

Complex units expressions
One form of the Darcy–Weisbach equation for fluid flow is

 * $$\Delta P = \frac {8} {\pi^2} \rho fL \frac {Q^2} {d^5} \,,$$

where ΔP is the pressure drop, ρ is the mass density, f is the (dimensionless) friction factor, L is the length of the pipe, Q is the volumetric flow rate, and d is the pipe diameter. It might be desirable to have the equation in the form

 * $$\Delta P = A_1 \,\rho fL \frac {Q^2} {d^5}$$

that would accept typical US units; the constant A1 could be determined manually using the unit-factor method, but it could be determined more quickly and easily using units:

Crane Technical Paper No. 410, Eq. 3-5, gives the multiplicative value as 43.5.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: GNU Units


text:
Fortnight

A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term fēowertīene niht, meaning "fourteen nights" (or "fourteen days", since the Anglo-Saxons counted by nights).

Astronomy and tides
In astronomy, a lunar fortnight is half a lunar synodic month, which is equivalent to the mean period between a full moon and a new moon (and vice versa). This is equal to 14.07 days. It gives rise to a lunar fortnightly tidal constituent (see: Long-period tides).

Analogs and translations
In many languages, there is no single word for a two-week period, and the equivalent terms "two weeks", "14 days", or "15 days" (counting inclusively) have to be used.

 * Celtic languages: in Welsh, the term pythefnos, meaning "15 nights", is used. This is in keeping with the Welsh term for a week, which is wythnos ("eight nights"). In Irish, the term is coicís.
 * Similarly, in Greek, the term δεκαπενθήμερο (dekapenthímero), meaning "15 days", is used.
 * The Hindu calendar uses the Sanskrit word पक्ष "pakṣa", meaning one half of a lunar month, which is between 14 and 15 solar days.
 * In Romance languages there are the terms quincena (or quince días) in Galician and Spanish, quinzena or quinze dies in Catalan and quinze dias or quinzena in Portuguese, quindicina in Italian, quinze jours or quinzaine in French, and chenzină in Romanian, all meaning "a grouping of 15"; there are also the terms bisettimanale in Italian, bisemanal in Spanish, bissemanal in Portuguese, bisetmanal in Catalan, bihebdomadaire in French, and bisǎptǎmânal in Romanian, that literally mean "biweekly".
 * Semitic languages have a "doubling suffix". When added at the end of the word for "week" it changes the meaning to "two weeks". In Hebrew, the single-word שבועיים (shvu′ayim) means exactly "two weeks". Also in Arabic, by adding the common dual suffix to the word for "week", أسبوع, the form أسبوعين (usbu′ayn), meaning "two weeks", is formed.
 * Slavic languages: in Czech the terms čtrnáctidenní and dvoutýdenní have the same meaning as "fortnight". In Ukrainian, the term два тижні is used in relation to "biweekly, two weeks".

title: Fortnight


text:
Platoon (automobile)

In transportation, platooning or flocking is a method for driving a group of vehicles together. It is meant to increase the capacity of roads via an automated highway system.

Platoons decrease the distances between cars or trucks using electronic, and possibly mechanical, coupling. This capability would allow many cars or trucks to accelerate or brake simultaneously. This system also allows for a closer headway between vehicles by eliminating reacting distance needed for human reaction.

Platoon capability might require buying new vehicles, or it may be something that can be retrofitted. Drivers would probably need a special license endorsement on account of the new skills required and the added responsibility when driving in the lead.

Smart cars with artificial intelligence could automatically join and leave platoons. The automated highway system is a proposal for one such system, where cars organise themselves into platoons of 8 to 25.

Potential benefits

 * Greater fuel economy due to reduced air resistance and by reducing the need for acceleration, deceleration, and stopping to maintain traffic flow.
 * Reduced congestion.
 * Substantially shorter commutes during peak periods.
 * On longer highway trips, vehicles could be mostly unattended whilst in following mode.
 * Fewer traffic collisions.
 * Vehicle to vehicle charging

Potential disadvantages

 * Some systems have failed in traffic, as they have been hacked by remote computers, creating a hazardous situation.
 * Drivers would feel less in control of their own driving, being at the hands of computer software or the lead driver.
 * Drivers may be less attentive than usual, and they may not be able to react as quickly to adverse situations if the software or hardware were to fail.
 * In the event of a traffic collision with the lead vehicle, the entire platoon may be caught in a multiple-vehicle collision due to the reduced vehicle spacing.

Automated highway system
An automated highway system (AHS), or smart road, is a proposed intelligent transportation system technology designed to provide for driverless cars on specific right-of ways. It is most often recommended as a means of traffic congestion relief, on the grounds that it would drastically reduce following distances and headway, thus allowing a given stretch of road to carry more cars.

Principle
In one scheme, the roadway has magnetized stainless-steel spikes driven one meter apart in its center. The car senses the spikes to measure its speed and locate the center of the lane. Furthermore, the spikes can have either magnetic north or magnetic south facing up. The roadway thus provides small amounts of digital data describing interchanges and recommended speeds.

The cars have power steering and automatic speed controls, which are controlled by a computer.

The cars organize themselves into platoons of 8 to 25 cars. The cars within a platoon drive themselves a meter apart, so that air resistance is minimized. The distance between platoons is the conventional braking distance. If anything goes wrong, the maximum number of harmed cars should be one platoon.

An overview of platooning systems is given in Bergenhem et al.

Platooning of trucks has been proposed as a concept to reduce the energy consumption of semi-trucks and improve the feasibility of electric semi-trucks.

Early development
The origin of research on AHS was done by a team from Ohio State University led by Robert E. Fenton, based on funding from the U.S. Federal Highway Administration. Their first automated vehicle was built in 1962, and is believed to be the first land vehicle to contain a computer. Steering, braking and speed were controlled through the onboard electronics, which filled the trunk, back seat and most of the front of the passenger side of the car. Research continued at OSU until federal funding was cut in the early 1980s.

United States
The USDOT-sponsored National Automated Highway System Consortium (NAHSC) project, a prototype automated highway system, was tested in San Diego County, California in 1997 along Interstate 15. However, despite the technical success of the program, investment has moved more toward autonomous intelligent vehicles rather than building specialized infrastructure. The AHS system places sensory technology in cars that can read passive road markings, and use radar and inter-car communications to make the cars organize themselves without the intervention of drivers. Such an autonomous cruise control system is being developed by Mercedes-Benz, BMW, Volkswagen and Toyota.

The Federal Highway Administration in 2013 funded two research projects in heavy truck platooning (without steering automation). One is led by Auburn University with Peterbilt, American Trucking Associations, Meritor Wabco, and Peloton Technology and the other is led by California Department of Transportation, with UC Berkeley and Volvo Trucks.

SARTRE
The SARTRE Project (Safe Road Trains for the Environment), is a European Commission funded project investigating implementation of platooning on unmodified European motorways. The project begun in September 2009, and vehicle platooning, as envisaged by the SARTRE project, is a convoy of vehicles in which a professional driver in a lead vehicle heads a line of closely following vehicles. Each following vehicle autonomously measures the distance, speed and direction and adjusts to the vehicle in front. Once in the platoon, drivers can do other things while the platoon proceeds towards its long-haul destination. All vehicles are detached and can leave the procession at any time.

In January 2011, SARTRE made the first successful demonstration of its platooning technology at the Volvo Proving Ground near Gothenburg, Sweden, in which a lead truck was followed by a car. In January 2012, SARTRE made a second demonstration in Barcelona, Spain, in which a lead truck was followed by three cars driven entirely autonomously at speeds of up to 90 kph with a gap between of at most 6 m. The companies that participated in SARTRE were Volvo Trucks and Volvo Car Corporation. During its Presidency of the European Union in 2016, the Netherlands organised a European Truck Platooning Challenge. Six brands of automated trucks – DAF Trucks, Daimler Trucks, Iveco, MAN Truck & Bus, Scania AB and Volvo Trucks – ran on public roads from several European cities to the Netherlands.
 * EU Truck Platooning Challenge

Japan
In January 2018, trucks from different manufacturers were successfully driven by platooning for the first time on the Shin-Tomei Expressway in Japan.

In February, 2021, Ministry of Economy, Trade and Industry (METI) and Ministry of Land, Infrastructure, Transport and Tourism (MLIT) successfully achieved traveling of trucks on part of the Shin-Tomei Expressway in a platoon in which no drivers were present in either the second or the following trucks, with staff in only the passenger seat for security purposes.

South Korea
In November 2019, Hyundai Motor Group successfully conducted its first platooning of trucks on a highway for the first time in Korea. Demonstrations of platooning, cut-in/cut-out of other vehicles, simultaneous emergency braking, and V2V communication technology were conducted.

title: Platoon (automobile)


text:
Mechanization

Mechanization (or mechanisation) is the process of changing from working largely or exclusively by hand or with animals to doing that work with machinery. In an early engineering text, a machine is defined as follows:

"Every machine is constructed for the purpose of performing certain mechanical operations, each of which supposes the existence of two other things besides the machine in question, namely, a moving power, and an object subject to the operation, which may be termed the work to be done. Machines, in fact, are interposed between the power and the work, for the purpose of adapting the one to the other."

In every fields, mechanization includes the use of hand tools. In modern usage, such as in engineering or economics, mechanization implies machinery more complex than hand tools and would not include simple devices such as an ungeared horse or donkey mill. Devices that cause speed changes or changes to or from reciprocating to rotary motion, using means such as gears, pulleys or sheaves and belts, shafts, cams and cranks, usually are considered machines. After electrification, when most small machinery was no longer hand powered, mechanization was synonymous with motorized machines. Extension of mechanization of the production process is termed as automation and it is controlled by a closed loop system in which feedback is provided by the sensors. In an automated machine the work of different mechanisms is performed automatically.

Ancient times
Water wheels date to the Roman period and were used to grind grain and lift irrigation water. Water-powered bellows were in use on blast furnaces in China in 31 AD. By the 13th century, water wheels powered sawmills and trip hammers, to pull cloth and pound flax and later cotton rags into pulp for making paper. Trip hammers are shown crushing ore in De re Metallica (1555).

Clocks were some of the most complex early mechanical devices. Clock makers were important developers of machine tools including gear and screw cutting machines, and were also involved in the mathematical development of gear designs. Clocks were some of the earliest mass-produced items, beginning around 1830.

Water-powered bellows for blast furnaces, used in China in ancient times, were in use in Europe by the 15th century. De re Metallica contains drawings related to bellows for blast furnaces including a fabrication drawing.

Improved gear designs decreased wear and increased efficiency. Mathematical gear designs were developed in the mid 17th century. French mathematician and engineer Desargues designed and constructed the first mill with epicycloidal teeth ca. 1650. In the 18th century involute gears, another mathematical derived design, came into use. Involute gears are better for meshing gears of different sizes than epicycloidal. Gear cutting machines came into use in the 18th century.

Industrial revolution
The Newcomen steam engine was first used, to pump water from a mine, in 1712. John Smeaton introduced metal gears and axles to water wheels in the mid to last half of the 18th century. The Industrial Revolution started mainly with textile machinery, such as the spinning jenny (1764) and water frame (1768).

Demand for metal parts used in textile machinery led to the invention of many machine tools in the late 1700s until the mid-1800s. After the early decades of the 19th century, iron increasingly replaced wood in gearing and shafts in textile machinery. In the 1840s self acting machine tools were developed. Machinery was developed to make nails ca. 1810. The Fourdrinier paper machine for continuous production of paper was patented in 1801, displacing the centuries-old hand method of making individual sheets of paper.

One of the first mechanical devices used in agriculture was the seed drill invented by Jethro Tull around 1700. The seed drill allowed more uniform spacing of seed and planting depth than hand methods, increasing yields and saving valuable seed. In 1817, the first bicycle was invented and used in Germany. Mechanized agriculture greatly increased in the late eighteenth and early nineteenth centuries with horse drawn reapers and horse powered threshing machines. By the late nineteenth century steam power was applied to threshing and steam tractors appeared. Internal combustion began being used for tractors in the early twentieth century. Threshing and harvesting was originally done with attachments for tractors, but in the 1930s independently powered combine harvesters were in use.

In the mid to late 19th century, hydraulic and pneumatic devices were able to power various mechanical actions, such as positioning tools or work pieces. Pile drivers and steam hammers are examples for heavy work. In food processing, pneumatic or hydraulic devices could start and stop filling of cans or bottles on a conveyor. Power steering for automobiles uses hydraulic mechanisms, as does practically all earth moving equipment and other construction equipment and many attachments to tractors. Pneumatic (usually compressed air) power is widely used to operate industrial valves.

Twentieth century
By the early 20th century machines developed the ability to perform more complex operations that had previously been done by skilled craftsmen. An example is the glass bottle making machine developed 1905. It replaced highly paid glass blowers and child labor helpers and led to the mass production of glass bottles.

After 1900 factories were electrified, and electric motors and controls were used to perform more complicated mechanical operations. This resulted in mechanized processes to manufacture almost all goods.

Categories

In manufacturing, mechanization replaced hand methods of making goods. Prime movers are devices that convert thermal, potential or kinetic energy into mechanical work. Prime movers include internal combustion engines, combustion turbines (jet engines), water wheels and turbines, windmills and wind turbines and steam engines and turbines. Powered transportation equipment such as locomotives, automobiles and trucks and airplanes, is a classification of machinery which includes sub classes by engine type, such as internal combustion, combustion turbine and steam. Inside factories, warehouses, lumber yards and other manufacturing and distribution operations, material handling equipment replaced manual carrying or hand trucks and carts.

In mining and excavation, power shovels replaced picks and shovels. Rock and ore crushing had been done for centuries by water-powered trip hammers, but trip hammers have been replaced by modern ore crushers and ball mills.

Bulk material handling systems and equipment are used for a variety of materials including coal, ores, grains, sand, gravel and wood products.

Construction equipment includes cranes, concrete mixers, concrete pumps, cherry pickers and an assortment of power tools.

Powered machinery
Powered machinery today usually means either by electric motor or internal combustion engine. Before the first decade of the 20th century powered usually meant by steam engine, water or wind.

Many of the early machines and machine tools were hand powered, but most changed over to water or steam power by the early 19th century.

Before electrification, mill and factory power was usually transmitted using a line shaft. Electrification allowed individual machines to each be powered by a separate motor in what is called unit drive. Unit drive allowed factories to be better arranged and allowed different machines to run at different speeds. Unit drive also allowed much higher speeds, which was especially important for machine tools.

A step beyond mechanization is automation. Early production machinery, such as the glass bottle blowing machine (ca. 1890s), required a lot of operator involvement. By the 1920s fully automatic machines, which required much less operator attention, were being used.

Military usage
The term is also used in the military to refer to the use of tracked armoured vehicles, particularly armoured personnel carriers, to move troops that would otherwise have marched or ridden trucks into combat. In military terminology, mechanized refers to ground units that can fight from vehicles, while motorized refers to units that go to battle in vehicles but then dismount and fight without them. Thus, a towed artillery unit is considered motorized while a self-propelled one is mechanized.

Mechanical vs human labour
When we compare the efficiency of a labourer, we see that he has an efficiency of about 1%–5.5% (depending on whether he uses arms, or a combination of arms and legs). Internal combustion engines mostly have an efficiency of about 20%, although large diesel engines, such as those used to power ships, may have efficiencies of nearly 50%. Industrial electric motors have efficiencies up to the low 90% range, before correcting for the conversion efficiency of fuel to electricity of about 35%.

When we compare the costs of using an internal combustion engine to a worker to perform work, we notice that an engine can perform more work at a comparative cost. 1 liter of fossil fuel burnt with an IC engine equals about 50 hands of workers operating for 24 hours or 275 arms and legs for 24 hours.

In addition, the combined work capability of a human is also much lower than that of a machine. An average human worker can provide work good for around 0,9 hp (2.3 MJ per hour) while a machine (depending on the type and size) can provide for far greater amounts of work. For example, it takes more than one and a half hour of hard labour to deliver only one kWh – which a small engine could deliver in less than one hour while burning less than one litre of petroleum fuel. This implies that a gang of 20 to 40 men will require a financial compensation for their work at least equal to the required expended food calories (which is at least 4 to 20 times higher). In most situations, the worker will also want compensation for the lost time, which is easily 96 times greater per day. Even if we assume the real wage cost for the human labour to be at US $1.00/day, an energy cost is generated of about $4.00/kWh. Despite this being a low wage for hard labour, even in some of the countries with the lowest wages, it represents an energy cost that is significantly more expensive than even exotic power sources such as solar photovoltaic panels (and thus even more expensive when compared to wind energy harvesters or luminescent solar concentrators).

Levels of mechanization
For simplification, one can study mechanization as a series of steps. Many students refer to this series as indicating basic-to-advanced forms of mechanical society.

 * 1) hand/muscle power
 * 2) hand-tools
 * 3) powered hand-tools, e.g. electric-controlled
 * 4) powered tools, single functioned, fixed cycle
 * 5) powered tools, multi-functioned, program controlled
 * 6) powered tools, remote-controlled
 * 7) powered tools, activated by work-piece (e.g.: coin phone)
 * 8) measurement
 * 9) selected signaling control, e.g. hydro power control
 * 10) performance recording
 * 11) automated machine action altered through measurement
 * 12) segregation/rejection according to measurement
 * 13) selection of appropriate action cycle
 * 14) correcting performance after operation
 * 15) correcting performance during operation

title: Mechanization


text:
APC

APC most often refers to:
 * Armoured personnel carrier, an armoured fighting vehicle

APC or Apc may also refer to:

Computing and technology

 * Auto Power Control, a system of powering e.g. laser diodes
 * Adaptive predictive coding, an analog-to-digital conversion system
 * Advanced process control, a concept in control theory
 * Alternative PHP Cache, a PHP accelerator program
 * Angled physical contact, a technique used in optical fiber connections
 * APC (magazine), Australian Personal Computer magazine
 * APC III or Advanced Personal Computer, a 1983 NEC microcomputer
 * American Power Conversion Corporation or simply APC, a manufacturer of uninterruptible power supplies, electronics peripherals and data center products, nowadays called APC by Schneider Electric
 * APC-7 connector, a coaxial connector used for high frequency applications
 * Application Program Command, a C1 control code
 * Asynchronous procedure call, a function that executes asynchronously in the context of a specific thread on Microsoft Windows
 * Atari Punk Console, a simple DIY noisemaker circuit
 * VIA APC, a low-cost Android PC computer

General

 * Article processing charge, a fee charged to authors for publication in an open access journal

Biology and medicine

 * Activated protein C, an anti-coagulant and anti-inflammatory protein
 * Adenomatous polyposis coli, a tumor suppressor protein encoded by the APC gene, mutations in which can cause colon cancer
 * Anaphase-promoting complex, a ubiquitin ligase cell cycle protein
 * Antigen-presenting cell, a type of cell that displays foreign antigens
 * Amino Acid-Polyamine-Organocation (APC) Family of transport proteins
 * APC Superfamily, a superfamily of transport proteins
 * APC tablet, analgesic compound of aspirin, phenacetin, and caffeine
 * Argon plasma coagulation, an endoscopic technique for controlling hemorrhage
 * Atrial premature complexes, a type of premature heart beat or irregular heart beat or arrhythmia which start in the upper two chambers of the heart

Chemistry

 * Allophycocyanin, a protein from the light-harvesting phycobiliprotein family
 * Allylpalladium chloride dimer, a chemical compound
 * Ammonium perchlorate, a powerful oxidizer used in solid rocket motors

Military

 * Armoured personnel carrier, type of armoured military vehicle
 * Armour-piercing capped, an anti-armor shell type
 * Army Proficiency Certificate, the training syllabus of the Army Cadet Force
 * B&T APC9 (Advanced Police Carbine), a submachine gun produced by B&T AG
 * B&T APC45, a variant of the B&T APC9
 * Two US Navy hull classification symbols: Coastal transport (APC) and Small coastal transport (APc)

Organizations

 * Astroparticle and Cosmology Laboratory, a research laboratory located in Paris
 * A.P.C., A French design group and clothing retailer
 * African, Caribbean and Pacific Group of States, a group of countries
 * African Paralympic Committee, a sports organization based in Cairo, Egypt
 * African People's Convention, a South African political party
 * Alianza Popular Conservadora, a political party in Nicaragua
 * Alien Property Custodian, a former office within the Government of the United States
 * All People's Congress, a political party in Sierra Leone
 * All Progressives Congress, a political party in Nigeria
 * Alternativa Popular Canaria, a separatist political party of the Canary Islands
 * American Pie Council, an organization committed to preserving America's pie heritage
 * American Plastics Council, a major trade association for the U.S. plastics industry
 * Americas Paralympic Committee, an umbrella organization of National Paralympic Committees
 * Anadarko Petroleum Corporation, a defunct American petroleum exploration company
 * Animal Procedures Committee, a UK public body and task force
 * Anti-Poverty Committee, a direct action organization in Vancouver, Canada
 * Apocalypse Production Crew, an MP3 warez organization
 * Arab Potash Company, a potash production company headquartered in Jordan
 * Armed Proletarians for Communism, an Italian far-left terrorist group of the 1970s
 * Arrangers' Publishing Company, a sheet music publishing company in the United States
 * Asia Pacific College, a joint venture between IBM Philippines and the SM Foundation
 * Asian Paralympic Committee, an umbrella organisation of National Paralympic Committees
 * Associated Presbyterian Churches, a Scottish Christian denomination
 * Association for Progressive Communications, a worldwide network of organisations helping others use the internet to promote social justice and sustainable development
 * Association of Professional Chaplains, internationally certified hospice chaplains
 * Atlantic-Pacific Capital, a US-based independent investment bank
 * Australian Paralympic Committee
 * Australian Polling Council, a polling industry body
 * Patriotic Alliance for Change, a Paraguayan political alliance (Alianza Patriótica por el Cambio)

Places

 * Apc, Hungary, a village in the Heves County of Hungary
 * Napa County Airport (IATA airport code APC), near Napa, California

Other uses

 * A Perfect Circle, an American rock supergroup
 * Alkali Pozzolan Cement, an alternative cement developed at Curtin University, Australia
 * Ambulatory Payment Classification
 * Attoparsec, an unusual minuscule unit of astronomic distance
 * Australian Provincial Championship, a rugby union competition in Australia
 * Automatic Performance Control, a system that was used on some Saab H engines
 * Average propensity to consume, the proportion of income spent
 * Levantine Arabic, by ISO 639-3 code
 * North Levantine Arabic, by a previously separate ISO 639-3 code, which has now been broadened to include Levantine Arabic
 * Vincent's APC, a discontinued analgesic compound of aspirin, phenacetin and caffeine, once popular in Australia

title: APC


text:
Whistler (radio)

A whistler is a very low frequency (VLF) electromagnetic (radio) wave generated by lightning. Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, with maximum frequencies usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies, and can be converted to audio using a suitable receiver. They are produced by lightning strikes (mostly intracloud and return-path) where the impulse travels along the Earth's magnetic field lines from one hemisphere to the other. They undergo dispersion of several kHz due to the slower velocity of the lower frequencies through the plasma environments of the ionosphere and magnetosphere. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.

Voyager 1 and 2 spacecraft detected whistler-like activity in the vicinity of Jupiter known as "Jovian Whistlers", supporting the visual observations of lightning made by Voyager 1.

Whistlers have been detected in the Earth's magnetosheath, where they are often called “lion roars” due to their frequencies of tens to hundreds of Hz.

History
Whistlers were probably heard as early as 1886 on long telephone lines, but the clearest early description was by Heinrich Barkhausen in 1919. British scientist Llewelyn Robert Owen Storey had shown lightning generated whistlers in his 1953 PhD dissertation. Around the same time, Storey had posited the existence of whistlers meant plasma was present in Earth's atmosphere, and that it moved radio waves in the same direction as Earth's magnetic field lines. From this he deduced but was unable to conclusively prove the existence of the plasmasphere, a thin layer between the ionosphere and magnetosphere. In 1963 American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz—independently of each other, and the latter using data from the Luna 2 spacecraft—experimentally proved the plasmasphere and plasmapause's existence, building on Storey's thinking.

American electrical engineer Robert Helliwell is also known for his research into whistlers. Helliwell and one of his students, Jack Mallinckrodt, were investigating lightning noise at very low radio frequencies at Stanford University in 1950. Mallinckrodt heard some whistling sounds and brought them to Helliwell's attention. As Helliwell recalled in an article in the October 1982 issue of the Stanford Engineer, he initially thought it was an artifact, but stood radio watch with Mallinckrodt until he heard the whistlers himself. Helliwell described these sounds as "weird, strange and unbelievable as flying saucers" in a 1954 article in the Palo Alto Times. Helliwell tried to understand the mechanism involved in the production of whistlers. He conducted experiments at the VLF outpost Siple Station in West Antarctica, which was active from 1971 to 1988. Since the wavelength of VLF radio signals is very large (a frequency of 10 kHz corresponds to a wavelength of 30 km), Siple Station had an antenna that was 13 mi long. The antenna was used to transmit VLF radio signals into Earth's magnetosphere, to be detected in Canada. It was possible to inject these signals into the magnetosphere, since the ionosphere is transparent to these low frequencies.

Etymology
Whistlers were named by British World War I radio operators. On the wide-band spectrogram, the observed characteristic of a whistler is that the tone rapidly descends over a few seconds—almost like a person whistling or an incoming grenade—hence the name "whistlers."

Nomenclature
A type of electromagnetic signal propagating in the Earth–ionosphere waveguide, known as a radio atmospheric signal or sferic, may escape the ionosphere and propagate outward into the magnetosphere. The signal is prone to bounce-mode propagation, reflecting back and forth on opposite sides of the planet until totally attenuated. To clarify which part of this hop pattern the signal is in, it is specified by a number, indicating the portion of the bounce path it is currently on. On its first upward path, it is known as a. After passing the geomagnetic equator, it is referred to as a. The + or - sign indicates either upward or downward propagation, respectively. The numeral represents the half-bounce currently in progress. The reflected signal is redesignated, until passing the geomagnetic equator again; then it is called  , and so on.

Relevant spacecraft

 * Advanced Composition Explorer (ACE), launched 1997, still operational.
 * FR-1, launched 1965, one of the earliest spacecraft to measure ionospheric and magnetospheric VLF waves, non-operational but still orbiting Earth.
 * Helios (spacecraft)
 * MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging), launched 2004, decommissioned 2015.
 * Radiation Belt Storm Probes
 * Solar Dynamics Observatory (SDO), launched 2010, still operational.
 * Solar and Heliospheric Observatory (SOHO), launched 1995, still operational.
 * Solar Maximum Mission (SMM), launched 1980, decommissioned 1989.
 * Solar Orbiter (SOLO), Launched in February 2020, Operational in November 2021.
 * Parker Solar Probe, launched in 2018, still operational.
 * STEREO (Solar TErrestrial RElations Observatory), launched 2006, still operational.
 * Transition Region and Coronal Explorer (TRACE), launched 1998, decommissioned 2010.
 * Ulysses (spacecraft), launched 1990, decommissioned 2009.
 * WIND (spacecraft), launched 1994, still operational.

title: Whistler (radio)


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Filter design

Filter design is the process of designing a signal processing filter that satisfies a set of requirements, some of which may be conflicting. The purpose is to find a realization of the filter that meets each of the requirements to an acceptable degree.

The filter design process can be described as an optimization problem. Certain parts of the design process can be automated, but an experienced designer may be needed to get a good result.

The design of digital filters is a complex topic. Although filters are easily understood and calculated, the practical challenges of their design and implementation are significant and are the subject of advanced research.

Typical design requirements
Typical requirements which may be considered in the design process are:
 * Frequency response
 * Phase shift or group delay
 * impulse response
 * Causal filter required?
 * Stable filter required?
 * Finite (in duration) impulse response required?
 * Computational complexity
 * Technology

The frequency function
The required frequency response is an important parameter. The steepness and complexity of the response curve determines the filter order and feasibility.

A first-order recursive filter will only have a single frequency-dependent component. This means that the slope of the frequency response is limited to 6 dB per octave. For many purposes, this is not sufficient. To achieve steeper slopes, higher-order filters are required.

In relation to the desired frequency function, there may also be an accompanying weighting function, which describes, for each frequency, how important it is that the resulting frequency function approximates the desired one.

Typical examples of frequency function are:
 * A low-pass filter is used to cut unwanted high-frequency signals.
 * A high-pass filter passes high frequencies fairly well; it is helpful as a filter to cut any unwanted low-frequency components.
 * A band-pass filter passes a limited range of frequencies.
 * A band-stop filter passes frequencies above and below a certain range. A very narrow band-stop filter is known as a notch filter.
 * An all-pass filter passes all frequencies equally in gain. Only the phase shift is changed, which also affects the group delay.
 * A differentiator has an amplitude response proportional to the frequency.
 * A low-shelf filter passes all frequencies, but increases or reduces frequencies below the shelf frequency by specified amount.
 * A high-shelf filter passes all frequencies, but increases or reduces frequencies above the shelf frequency by specified amount.
 * A peak EQ filter makes a peak or a dip in the frequency response, commonly used in parametric equalizers.

Phase and group delay

 * An all-pass filter passes through all frequencies unchanged, but changes the phase of the signal. Filters of this type can be used to equalize the group delay of recursive filters. This filter is also used in phaser effects.
 * A Hilbert transformer is a specific all-pass filter that passes sinusoids with unchanged amplitude but shifts each sinusoid phase by ±90°.
 * A fractional delay filter is an all-pass that has a specified and constant group or phase delay for all frequencies.

The impulse response
There is a direct correspondence between the filter's frequency function and its impulse response: the former is the Fourier transform of the latter. That means that any requirement on the frequency function is a requirement on the impulse response, and vice versa.

However, in certain applications it may be the filter's impulse response that is explicit and the design process then aims at producing as close an approximation as possible to the requested impulse response given all other requirements.

In some cases it may even be relevant to consider a frequency function and impulse response of the filter which are chosen independently from each other. For example, we may want both a specific frequency function of the filter and that the resulting filter have a small effective width in the signal domain as possible. The latter condition can be realized by considering a very narrow function as the wanted impulse response of the filter even though this function has no relation to the desired frequency function. The goal of the design process is then to realize a filter which tries to meet both these contradicting design goals as much as possible. An example is for high-resolution audio in which the frequency response (magnitude and phase) for steady state signals (sum of sinusoids) is the primary filter requirement, while an unconstrained impulse response may cause unexpected degradation due to time spreading of transient signals.

Causality
Any filter operating in real time (the filter response only depends on the current and past inputs) must be causal. If the design process yields a noncausal filter, the resulting filter can be made causal by introducing an appropriate time-shift (or delay).

Filters that do not operate in real time (e.g. for image processing) can be non-causal. Noncausal filters may be designed to have zero delay.

Stability
A stable filter assures that every limited input signal produces a limited filter response. A filter which does not meet this requirement may in some situations prove useless or even harmful. Certain design approaches can guarantee stability, for example by using only feed-forward circuits such as an FIR filter. On the other hand, filters based on feedback circuits have other advantages and may therefore be preferred, even if this class of filters includes unstable filters. In this case, the filters must be carefully designed in order to avoid instability.

Locality
In certain applications we have to deal with signals which contain components which can be described as local phenomena, for example pulses or steps, which have certain time duration. A consequence of applying a filter to a signal is, in intuitive terms, that the duration of the local phenomena is extended by the width of the filter. This implies that it is sometimes important to keep the width of the filter's impulse response function as short as possible.

According to the uncertainty relation of the Fourier transform, the product of the width of the filter's impulse response function and the width of its frequency function must exceed a certain constant. This means that any requirement on the filter's locality also implies a bound on its frequency function's width. Consequently, it may not be possible to simultaneously meet requirements on the locality of the filter's impulse response function as well as on its frequency function. This is a typical example of contradicting requirements.

Computational complexity
A general desire in any design is that the number of operations (additions and multiplications) needed to compute the filter response is as low as possible. In certain applications, this desire is a strict requirement, for example due to limited computational resources, limited power resources, or limited time. The last limitation is typical in real-time applications.

There are several ways in which a filter can have different computational complexity. For example, the order of a filter is more or less proportional to the number of operations. This means that by choosing a low order filter, the computation time can be reduced.

For discrete filters the computational complexity is more or less proportional to the number of filter coefficients. If the filter has many coefficients, for example in the case of multidimensional signals such as tomography data, it may be relevant to reduce the number of coefficients by removing those which are sufficiently close to zero. In multirate filters, the number of coefficients by taking advantage of its bandwidth limits, where the input signal is downsampled (e.g. to its critical frequency), and upsampled after filtering.

Another issue related to computational complexity is separability, that is, if and how a filter can be written as a convolution of two or more simpler filters. In particular, this issue is of importance for multidimensional filters, e.g., 2D filter which are used in image processing. In this case, a significant reduction in computational complexity can be obtained if the filter can be separated as the convolution of one 1D filter in the horizontal direction and one 1D filter in the vertical direction. A result of the filter design process may, e.g., be to approximate some desired filter as a separable filter or as a sum of separable filters.

Other considerations
It must also be decided how the filter is going to be implemented:
 * Analog filter
 * Analog sampled filter
 * Digital filter
 * Mechanical filter

Analog filters
The design of linear analog filters is for the most part covered in the linear filter section.

Digital filters
Digital filters are classified into one of two basic forms, according to how they respond to a unit impulse:

 * Finite impulse response, or FIR, filters express each output sample as a weighted sum of the last N input samples, where N is the order of the filter. FIR filters are normally non-recursive, meaning they do not use feedback and as such are inherently stable.  A moving average filter or CIC filter are examples of FIR filters that are normally recursive (that use feedback).  If the FIR coefficients are symmetrical (often the case), then such a filter is linear phase, so it delays signals of all frequencies equally which is important in many applications.  It is also straightforward to avoid overflow in an FIR filter.  The main disadvantage is that they may require significantly more processing and memory resources than cleverly designed IIR variants. FIR filters are generally easier to design than IIR filters - the Parks-McClellan filter design algorithm (based on the Remez algorithm) is one suitable method for designing quite good filters semi-automatically.  (See Methodology.)
 * Infinite impulse response, or IIR, filters are the digital counterpart to analog filters. Such a filter contains internal state, and the output and the next internal state are determined by a linear combination of the previous inputs and outputs (in other words, they use feedback, which FIR filters normally do not).  In theory, the impulse response of such a filter never dies out completely, hence the name IIR, though in practice, this is not true given the finite resolution of computer arithmetic.  IIR filters normally require less computing resources than an FIR filter of similar performance.  However, due to the feedback, high order IIR filters may have problems with instability, arithmetic overflow, and limit cycles, and require careful design to avoid such pitfalls.  Additionally, since the phase shift is inherently a non-linear  function of frequency, the time delay through such a filter is frequency-dependent, which can be a problem in many situations.  2nd order IIR filters are often called 'biquads' and a common implementation of higher order filters is to cascade biquads. A useful reference for computing biquad coefficients is the RBJ Audio EQ Cookbook.

Sample rate
Unless the sample rate is fixed by some outside constraint, selecting a suitable sample rate is an important design decision. A high rate will require more in terms of computational resources, but less in terms of anti-aliasing filters. Interference and beating with other signals in the system may also be an issue.

Anti-aliasing
For any digital filter design, it is crucial to analyze and avoid aliasing effects. Often, this is done by adding analog anti-aliasing filters at the input and output, thus avoiding any frequency component above the Nyquist frequency. The complexity (i.e., steepness) of such filters depends on the required signal-to-noise ratio and the ratio between the sampling rate and the highest frequency of the signal.

Theoretical basis
Parts of the design problem relate to the fact that certain requirements are described in the frequency domain while others are expressed in the time domain and that these may conflict. For example, it is not possible to obtain a filter which has both an arbitrary impulse response and arbitrary frequency function. Other effects which refer to relations between the time and frequency domain are

 * The uncertainty principle between the time and frequency domains
 * The variance extension theorem
 * The asymptotic behaviour of one domain versus discontinuities in the other

The uncertainty principle
As stated by the Gabor limit, an uncertainty principle, the product of the width of the frequency function and the width of the impulse response cannot be smaller than a specific constant. This implies that if a specific frequency function is requested, corresponding to a specific frequency width, the minimum width of the filter in the signal domain is set. Vice versa, if the maximum width of the response is given, this determines the smallest possible width in the frequency. This is a typical example of contradictory requirements where the filter design process may try to find a useful compromise.

The variance extension theorem
Let $$\sigma^{2}_{s}$$ be the variance of the input signal and let $$\sigma^{2}_{f}$$ be the variance of the filter. The variance of the filter response, $$\sigma^{2}_{r}$$, is then given by

 * $$\sigma^{2}_{r}$$ = $$\sigma^{2}_{s}$$ + $$\sigma^{2}_{f}$$

This means that $$\sigma_{r} > \sigma_{f}$$ and implies that the localization of various features such as pulses or steps in the filter response is limited by the filter width in the signal domain. If a precise localization is requested, we need a filter of small width in the signal domain and, via the uncertainty principle, its width in the frequency domain cannot be arbitrary small.

Discontinuities versus asymptotic behaviour
Let f(t) be a function and let $$F(\omega)$$ be its Fourier transform. There is a theorem which states that if the first derivative of F which is discontinuous has order $$n \geq 0$$, then f has an asymptotic decay like $$t^{-n-1}$$.

A consequence of this theorem is that the frequency function of a filter should be as smooth as possible to allow its impulse response to have a fast decay, and thereby a short width.

Methodology
One common method for designing FIR filters is the Parks-McClellan filter design algorithm, based on the Remez exchange algorithm. Here the user specifies a desired frequency response, a weighting function for errors from this response, and a filter order N. The algorithm then finds the set of N coefficients that minimize the maximum deviation from the ideal. Intuitively, this finds the filter that is as close as you can get to the desired response given that you can use only N coefficients. This method is particularly easy in practice and at least one text includes a program that takes the desired filter and N and returns the optimum coefficients. One possible drawback to filters designed this way is that they contain many small ripples in the passband(s), since such a filter minimizes the peak error.

Another method to finding a discrete FIR filter is filter optimization described in Knutsson et al., which minimizes the integral of the square of the error, instead of its maximum value. In its basic form this approach requires that an ideal frequency function of the filter $$F_{I}(\omega)$$ is specified together with a frequency weighting function $$W(\omega)$$ and set of coordinates $$x_{k}$$ in the signal domain where the filter coefficients are located.

An error function $$\varepsilon$$ is defined as

 * $$\varepsilon = \| W \cdot (F_{I} - \mathcal{F} \{ f \}) \|^{2}$$

where $$f(x)$$ is the discrete filter and $$\mathcal{F}$$ is the discrete-time Fourier transform defined on the specified set of coordinates. The norm used here is, formally, the usual norm on $$L^{2}$$ spaces. This means that $$\varepsilon$$ measures the deviation between the requested frequency function of the filter, $$F_{I}$$, and the actual frequency function of the realized filter, $$\mathcal{F} \{ f \}$$. However, the deviation is also subject to the weighting function $$W$$ before the error function is computed.

Once the error function is established, the optimal filter is given by the coefficients $$f(x)$$ which minimize $$\varepsilon$$. This can be done by solving the corresponding least squares problem. In practice, the $$L^{2}$$ norm has to be approximated by means of a suitable sum over discrete points in the frequency domain. In general, however, these points should be significantly more than the number of coefficients in the signal domain to obtain a useful approximation.

Simultaneous optimization in both domains
The previous method can be extended to include an additional error term related to a desired filter impulse response in the signal domain, with a corresponding weighting function. The ideal impulse response can be chosen independently of the ideal frequency function and is in practice used to limit the effective width and to remove ringing effects of the resulting filter in the signal domain. This is done by choosing a narrow ideal filter impulse response function, e.g., an impulse, and a weighting function which grows fast with the distance from the origin, e.g., the distance squared. The optimal filter can still be calculated by solving a simple least squares problem and the resulting filter is then a "compromise" which has a total optimal fit to the ideal functions in both domains. An important parameter is the relative strength of the two weighting functions which determines in which domain it is more important to have a good fit relative to the ideal function.

title: Filter design


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IIR

IIR may refer to:

 * Institute of International Relations (disambiguation)
 * Institute for International Research, a human capital development company acquired by Informa
 * International Institute of Refrigeration
 * Imaging infrared, in munitions guidance systems
 * Indo-Iranian languages
 * Infinite impulse response
 * Isobutylene isoprene rubber (butyl rubber)

title: IIR


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Geats

The Geats ( gēatas ; gautar ; götar ), sometimes called Goths, were a large North Germanic tribe who inhabited Götaland ("land of the Geats") in modern southern Sweden from antiquity until the Late Middle Ages. They are one of the progenitor groups of modern Swedes, along with Swedes (the tribe) and Gutes. The name of the Geats also lives on in the Swedish provinces of Västergötland and Östergötland, the western and eastern lands of the Geats, and in many other toponyms.

The Swedish dialects spoken in the areas that used to be inhabited by Geats form a distinct group, Götamål.

Etymology
The etymology of the name Geat (Old English Geatas, from a Proto-Germanic *Gautaz, plural *Gautōz) is similar to that of Goths and Gutes (*Gutô, plural *Gutaniz). The names derive from ablaut grades of the Proto-Germanic word *geutaną, meaning "to pour". They have the literal meaning "they who pour their seed". (For more information see Goths § Etymology.) The names could also allude to watercourses in the land where they were living, but this is not generally accepted to be the case, partly because that would mean that the names' similarity would be coincidental.

A more specific theory about the word Gautigoths is that it means the Goths who live near the river Gaut, today's Göta älv (Gautelfr). It might also have been a conflation of the word Gauti with a gloss of Goths. In the 17th century the name Göta älv, 'River of the Geats', replaced the earlier names Götälven and Gautelfr. The etymology of the word Gaut (as mentioned above) derives from the Proto-Germanic word *geutan, and the extended meaning of "to pour" is "flow, stream, waterfall", which could refer to Trollhättan Falls or to the river itself.

The short form of Gautigoths was the Old Norse Gautar, which originally referred to just the inhabitants of Västergötland, or the western parts of today's Götaland, a meaning which is retained in some Icelandic sagas.

Early history
The earliest known surviving mention of the Geats appears in Ptolemy (2nd century AD), who refers to them as Goutai. In the 6th century, Jordanes writes of the Gautigoths and Ostrogoths (the Ostrogoths of Scandza); and Procopius refers to Gautoi. The Norse Sagas know them as Gautar; Beowulf and Widsith as Gēatas. Beowulf and the Norse sagas name several Geatish kings, but only Hygelac finds confirmation in Liber Monstrorum where he is referred to as "Rex Getarum" and in a copy of Historiae Francorum where he is called "Rege Gotorum". These sources concern a raid into Frisia, ca 516, which is also described in Beowulf. C. 551, some decades after Hygelac's raid, Jordanes described the Geats as a nation which was "bold, and quick to engage in war".

The Anglo-Saxon settlement of Britain included many North Germanic people who were losers in the brutal tribal warfare of Scandinavia. The place-name -gate marks the site of Geatish settlement, often alongside strategically important Roman roads and nearby Visigothic and/or Jutish settlements. Defeated Jutes like Hengest and his brother Horsa fled to Kent, while Geats defeated by encroaching Swedes moved to Yorkshire where they founded Gillingshire by the Tees, originally the settlement of the Geatlings. It has also been suggested that East Anglia was settled by Geats at this time, or by Wulfings who also came from Götaland, bringing the traditions of Beowulf with them.

Any peace that eventually settled in southern Scandinavia was most likely due to exhaustion, and a Danish archaeologist has summarized that in the mid-6th century, and after, Scandinavia "went down to hell". Scandinavian wares appear to have stopped arriving in England, c. 550, suggesting that contact was broken.

Political centralization in Scandinavia
According to Procopius there were 13 "very numerous nations" on the Scandinavian peninsula in the 6th century, which is supported by recent archaeological analyses. Several scholars consider this to be a reasonable number of independent kingdoms at the time, with each consisting of one or more tribes, as reported by Jordanes. However, by 1350, these 13 kingdoms had been reduced in number to only two, Norway and Sweden. The Geats were one of the largest tribes.

Procopius and Jordanes both mention the Geats, but after them, foreign sources about Scandinavia are scarce until the 9th century, when Anglo-Saxon and Frankish sources do shed some light on the area. In these, the Geats are absent, which has led some scholars to conclude that they were no longer an independent nation and had been subsumed by the Swedes. Norwegian and Icelandic scaldic sources from the 10th century however indicate that they were still politically independent, sometimes opposing Norwegian kings. It has been suggested that their absence from older sources is instead due to their being an inland people.

The nature and the processes of how Geats and Swedes came to form one kingdom have been much debated among Swedish scholars. The scarcity and sometimes debated veracity of sources has left much room open for interpretation. The oldest medieval Swedish sources present the Swedish kingdom as retaining differences between provinces, in laws as well as in weights and measures. Some scholars have argued that the Geats were subjugated by the Swedes, and have suggested various dates for such an event, from the 6th to the 9th centuries. Others have wanted to see a more gradual merging, and that the Geats were slowly subsumed into the more powerful kingdom of Sweden, and in many respects they maintained their own cultural identity during the Middle Ages. Still others have put emphasis on how it was individual rulers, not ethnic groups, who were driving the process towards a unified kingdom, and that the process was very complicated.

Papal letters from the 1080s style the recipients as "king of the Swedes" or "king of the West Geats". In another papal letter from the 1160s, the title rex Sweorum et Gothorum is first attested. The Swedish kings began the custom of styling themselves as also the kings of the Geats in the 1270s.

Dynastic struggles
In the 11th century, the Swedish House of Munsö became extinct with the death of Emund the Old. Stenkil, a Geat, was elected king of the Swedes, and the Geats would be influential in the shaping of Sweden as a Christian kingdom. However, this election also ushered in a long period of civil unrest between Christians and pagans and between Geats and Swedes. The Geats tended to be more Christian, and the Swedes more pagan, which was why the Christian Swedish king Inge the Elder fled to Västergötland when deposed in favour of Blot-Sweyn, a king more favourable towards Norse paganism, in the 1080s. Inge would retake the throne and rule until his death c. 1100.

In his Gesta Danorum (book 13), the Danish 12th-century chronicler Saxo Grammaticus noted that the Geats had no say in the election of the king, only the Swedes. When the West Geatish law or Westrogothic law was put to paper, it reminded the Geats that they had to accept the election of the Swedes: Sveær egho konong at taka ok sva vrækæ meaning "It is the Swedes who have the right of choosing ["taking"] and also deposing the king" and then he rode Eriksgatan "mæþ gislum ofvan" – "with hostages from above [the realm]" through Södermanland, the Geatish provinces and then through Närke and Västmanland to be judged to be the lawful king by the lawspeakers of their respective things. One of these Swedish kings was Ragnvald Knaphövde, who in 1125 was riding with his retinue in order to be accepted as king by the different provinces. According to material appended to the oldest manuscript of the Westrogothic law, he decided not to demand hostages as he despised the Geats, and was slain near Falköping.

In a new general law of Sweden that was issued by Magnus Eriksson in the 1350s, it was stated that twelve men from each province, chosen by their things, should be present at the Stone of Mora when a new king was elected.

The distinction between Swedes and Geats lasted during the Middle Ages, but the Geats became increasingly important for Swedish national claims of greatness due to the Geats' old connection with the Goths. They argued that since the Goths and the Geats were the same nation, and the Geats were part of the kingdom of Sweden, this meant that the Swedes had defeated the Roman empire. The earliest attestation of this claim comes from the Council of Basel, 1434, during which the Swedish delegation argued with the Spanish about who among them were the true Goths. The Spaniards argued that it was better to be descended from the heroic Visigoths than from stay-at-homers. This cultural movement, which was not restricted to Sweden went by the name Gothicismus or in Swedish Göticism, i.e. Geaticism.

After the 15th century and the Kalmar Union, the Swedes and the Geats appear to have begun to perceive themselves as one nation, which is reflected in the evolution of svensk into a common ethnonym. It was originally an adjective referring to those belonging to the Swedish tribe, who are called svear in Swedish. As early as the 9th century, svear had been vague, both referring to the Swedish tribe and being a collective term including the Geats, and this is the case in Adam of Bremen's work where the Geats (Goths) appear both as a proper nation and as part of the Sueones. The merging/assimilation of the two nations took a long time, however. In the early-20th century, Nordisk familjebok noted that svensk had almost replaced svear as a name for the Swedish people.

At the same time, the Swedish ancestors were often referred to as Geats, especially when their heroism or connection to the Goths was to be stressed. This practice disappeared during the 19th century, when the vikings gradually took over the role as the heroic ancestors.

Society
The Geats were traditionally divided into several petty kingdoms, or districts, which had their own things (popular assemblies) and laws. The largest one of these districts was Västergötland (West Geatland), and it was in Västergötland that the Thing of all Geats was held every year, in the vicinity of Skara. Despite the name, the thing was only for the inhabitants of Västergötland and Dalsland. The equivalent in Östergötland was Lionga thing.

Unlike the Swedes, who used the division hundare, the Geats used hærrad (modern Swedish härad), like the Norwegians and the Danes. Surprisingly, it would be the Geatish name that became the common term in the Swedish kingdom. This is possibly related to the fact that several of the medieval Swedish kings were of Geatish extraction and often resided primarily in Götaland. In Västergötland and Dalsland, there were also a higher-level division where one or more hærrad made up a bo linked to a kongsgård.

Modern legacy
Today, the merger of the two nations is complete, as there is no longer any tangible identification in Götaland with a Geatish identity, apart from the common tendency of residents of the provinces of Västergötland and Östergötland to refer to themselves as västgötar (West Geats) and östgötar (East Geats), similarly to how residents of other provinces refer to themselves. The dialects spoken in those provinces and some surrounding areas are also collectively called götamål. Although the city Göteborg (Gothenburg) has formerly been considered to have been named after the river Göta älv, it may instead have been named after the Geats ('fortress of the Geats') when it was founded in 1621.

Until 1973 the official title of the Swedish king was "King of Sweden" (earlier: of the Swedes), the Geats/Goths and the Wends (with the formula Sveriges, Götes och Vendes konung, in Latin N.N. Dei Gratia, Suecorum, Gothorum et Vandalorum Rex). The title "King of the Wends" was copied from the Danish title, while the Danish kings called themselves "Kings of the Gotlanders" (which, like "Geats", was translated into "Goths" in Latin). "Wends" is a term normally used to describe the Slavic peoples who inhabited large areas of modern east Germany and Pomerania. See further in the Wikipedia articles King of the Goths and King of the Wends.

The titles, however, changed in 1973 when the new king Carl XVI Gustaf decided that his royal title should simply be "King of Sweden". The disappearance of the old title was his decision alone.

Goths
Geatas was originally Proto-Germanic *Gautoz and Goths and Gutar (Gotlanders) were *Gutaniz. *Gautoz and *Gutaniz are two ablaut grades of a Proto-Germanic word *geutan with the meaning "to pour" (modern Swedish gjuta, modern German giessen). The word comes from an Indo-European root meaning to pour, offer sacrifice. There were consequently two derivations from the same Proto-Germanic ethnonym.

It is a long-standing controversy whether the Goths were Geats. Both Old Icelandic and Old English literary sources clearly separate the Geats (Isl. Gautar, OEng Geatas) from the Goths/Gutar (Isl. Gotar, OEng. Gotenas); but the Gothic historian Jordanes wrote that the Goths came originally to Dacia from the island of Scandza. Moreover, he described that on this island there were three tribes called the Gautigoths (cf. Geat/Gaut), the Ostrogoths (cf. the Swedish province of Östergötland) and Vagoths (Gutar?) ‒ this implies that the Geats were Goths rather than vice versa. The word Goth is also a term used by the Romans to describe related, culturally linked tribes like the Tervingi and the Greuthungs, so it may be correct to label Geats as Goths.

Scandinavian burial customs, such as the stone circles (domarringar), which are most common in Götaland and Gotland, and stelae (bautastenar) appeared in what is now northern Poland in the 1st century AD, suggesting an influx of Scandinavians during the formation of the Gothic Wielbark culture. Moreover, in Östergötland, in Sweden, there is a sudden disappearance of villages during this period. Contemporary accounts beginning in the fourth century further associated these groups with the earlier Getae of Dacia, but this is now disputed.

Götaland theory
The Götaland theory (Swedish "Västgötaskolan") is a disparate group of theories, which have attempted to prove that some events and even places that are traditionally placed around Mälaren, especially ones that are associated with the formation of medieval Sweden, instead should be located to Västergötland. The methods ranged from relatively scholarly efforts to dowsing. This "school" was brought to prominence in the 1980s following a TV series by Dag Stålsjö. While some serious scholars have attempted to place more emphasis on the Geats in the early history of Sweden than was traditional, Västgötaskolan has never reached any acceptance.

Identity of the Gēatas
The generally accepted identification of Old English Gēatas as the same ethnonym as Swedish götar and Old Norse gautar is based on the observation that the ö monophthong of modern Swedish and the au diphthong of Old Norse correspond to the ēa diphthong of Old English.

Thus, Gēatas is the Old English form of Old Norse Gautar and modern Swedish Götar. This correspondence seems to tip the balance for most scholars. It is also based on the fact that in Beowulf, the Gēatas live east of the Dani (across the sea) and in close contact with the Sweon, which fits the historical position of the Geats between the Danes and the Swedes. Moreover, the story of Beowulf, who leaves Geatland and arrives at the Danish court after a naval voyage, where he kills a beast, finds a parallel in Hrólf Kraki's saga. In this saga, Bödvar Bjarki leaves Gautland and arrives at the Danish court after a naval voyage and kills a beast that has been terrorizing the Danes for two years (see also Origins for Beowulf and Hrólf Kraki).

Jutish hypothesis
There is a hypothesis that the Jutes also were Geats, and which was proposed by Pontus Fahlbeck in 1884. According to this hypothesis the Geats would have not only resided in southern Sweden but also in Jutland, where Beowulf would have lived.

The Geats and the Jutes are mentioned in Beowulf as different tribes, and whereas the Geats are called gēatas, the Jutes are called ēotena (genitive) or ēotenum (dative). Moreover, the Old English poem Widsith also mentions both Geats and Jutes, and it calls the latter ȳtum. However, Fahlbeck proposed in 1884 that the Gēatas of Beowulf referred to Jutes and he proposed that the Jutes originally also were Geats like those of southern Sweden. This theory was based on an Old English translation of Venerable Bede's Ecclesiastical History of the English People attributed to Alfred the Great where the Jutes (iutarum, iutis) once are rendered as gēata (genitive) and twice as gēatum (dative) (see e.g. the OED which identifies the Geats through Eotas, Iótas, Iútan and Geátas). Fahlbeck did not, however, propose an etymology for how the two ethnonyms could be related.

Fahlbeck's theory was refuted by Schück who in 1907 noted that another Old English source, the Anglo-Saxon Chronicle, called the Jutes īutna, īotum or īutum. Moreover, Schück pointed out that when Alfred the Great's translation mentions the Jutes for the second time (book IV, ch. 14(16)) it calls them ēota and in one manuscript ȳtena. Björkman proposed in 1908 that Alfred the Great's translation of Jutes as Geats was based on a confusion between the West Saxon form Geotas ("Jutes") and Gēatas ("Geats").

As for the origins of the ethnonym Jute, it may be a secondary formation of the toponym Jutland, where jut is derived from a Proto-Indo-European root *eud meaning "water".

Gutnish hypothesis
Since the 19th century, there has also been a suggestion that Beowulf's people were Gutes (from the island of Gotland in Sweden). According to the poem, the weather-geats or sea-geats, as they are called are supposed to have lived east of the Danes/Dacians and be separated from the Swedes by wide waters. Some researchers have found it a little far-fetched that wide waters relates to Vänern in Västergötland or Mälaren. The weather in weather-geats, and sea-geats marks a people living at a windy, stormy coast by the sea. The Geats of Västergötland were historically an inland people, making an epithet such as weather- or sea- a little strange. Moreover, when Beowulf dies he is buried in a mound at a place called Hrones-naesse, meaning "the cape of whales". Whales have for obvious reasons never lived in Vänern, where, according to Birger Nerman, Beowulf is buried. However, an expanse of water separates the island of Gotland from the Swedes. The island lies east of Denmark/Dacia and whales were once common in the Baltic Sea where Gotland is situated. The name of the Gutes in Swedish, Gutar, is an ablaut-grade of the same name as that of the Geats in Beowulf. These facts made the archaeologist Gad Rausing come to the conclusion that the weather-Geats may have been Gutes. This was supported by another Swedish archaeologist Bo Gräslund. According to Rausing, Beowulf may be buried in a place called Rone on Gotland, a name corresponding to the Hrones in Hrones-naesse. Not far from there lies a place called Arnkull corresponding to the Earnar-naesse in Beowulf, which according to the poem was situated closely to Hrones-naesse.

This theory does not exclude the ancient population of Västergötland and Östergötland from being Geats, but rather holds that the Anglo-Saxon name Geat could refer to West-geats (Västergötland), East-geats (Östergötland) as well as weather-geats (Gotland), in accordance with Jordanes account of the Scandinanian tribes Gautigoth, Ostrogoth and Vagoth.

title: Geats


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Anselm of Laon

Anselm of Laon (Anselmus; d. 1117), properly Ansel (Ansellus), was a French theologian and founder of a school of scholars who helped to pioneer biblical hermeneutics.

Biography
Born of very humble parents at Laon before the middle of the 11th century, he is said to have studied under Saint Anselm at Bec, though this is almost certainly incorrect. Other potential teachers of Anselm have been identified, including Bruno of Cologne and Manegold of Lautenbach. By around 1080, he had moved back to his place of birth and was teaching at the cathedral school of Laon, with his brother Ralph. Around 1109, he became dean and chancellor of the cathedral, and in 1115 he was one of Laon's two archdeacons. His school for theology and exegesis rapidly became the most well known in Europe. Famously, in 1113, he expelled Peter Abelard from his school.

The Liber Pancrisi (c. 1120) names him, with his brother Ralph, Ivo of Chartres, and William of Champeaux, as one of the four modern masters.

Works

Anselm's greatest work, an interlinear and marginal gloss on the 'Scriptures', the Glossa ordinaria, now attributed to him and his followers, was one of the great intellectual achievements of the Middle Ages. It has been frequently reprinted. The significance of the gloss, which was most likely assembled after Anselm's death by his students, such as Gilbert de la Porrée, and based on Anselm's teaching, is that it marked a new way of learning — it represented the birth of efforts to present discrete patristic and earlier medieval interpretations of individual verses of Scripture in a readily accessible, easily referenced way. This theme was subsequently adopted and extended by the likes of Hugh of St. Victor, Peter Lombard and later Thomas Aquinas, who gave us 'handbooks' for what we would now call theology.

Other commentaries apparently by Anselm have been ascribed to various writers, principally to Anselm of Canterbury.

The works are collected in Migne. Some of his Sententiae were edited at Milan by G. Lefevre in 1894. The commentary on the Psalms attributed to Haymo of Halberstadt by Migne has also been identified as possibly being the work of Anselm.

title: Anselm of Laon


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Hazarajat

Hazarajat, also known as Hazaristan  is a mostly mountainous region in the central highlands of Afghanistan, among the Kuh-e Baba mountains in the western extremities of the Hindu Kush. It is the homeland of the Hazara people who make up the majority of its population. Hazarajat denotes an ethnic and religious zone. Hazarajat is primarily made up of the provinces of Bamyan, Daykundi and large parts of Ghor, Ghazni, Uruzgan, Parwan, Maidan Wardak, and more. The most populous towns in Hazarajat are Bamyan, Yakawlang (Bamyan), Nili (Daykundi), Lal wa Sarjangal (Ghor), Sang-e-Masha (Ghazni), Gizab (Daykundi) and Behsud (Maidan Wardak). The Kabul, Arghandab, Helmand, Farah, Hari, Murghab, Balkh, and Kunduz rivers originate from Hazarajat.

Etymology and usage
The name "Hazara" first appears in the 16th-century book Baburnama, written by Mughal Emperor Babur. When the famous geographer Ibn Battuta arrived in Khurasan in 1333, he traveled across the country but did not record any place by the name of "Hazaristan".

The Hazara people and surrounding peoples use the names "Hazarajat" or "Hazaristan" to identify the historic Hazara lands. "Hazarajat" is a compound of "Hazara" and the Dari suffix "jat", which is used to make words associated with land in the south, central and west Asia.

Topography
The Hazarajat lies in the central Afghan highlands, among the Koh-e Baba mountains and the western extremities of the Hindu Kush. Its boundaries have historically been inexact and shifting. Its physical limitations, however, are roughly marked by the Bā-miān Basin to the north, the headwaters of the Helmand River to the south, Firuzkuh to the west, and the Unai Pass to the east. The regional terrain is mountainous and extends to the Safid Kuh and the Siāh Kuh mountains, where the highest peaks reach between 15,000 feet and 17,000 feet. Both sides of the Kuh-e Bābā range contain a succession of valleys. The north face of the range descends steeply, merging into low foothills and small semi-arid plains, while the south face stretches towards the Helmand Valley and the mountainous district of Behsud.

Northwestern Hazarajat encompasses the district of Ghor, long known for its mountain fortresses. The 10th-century geographer Estakhri wrote that mountainous Ghor was "the only region surrounded by Islamic territories and yet inhabited by infidels". The long resistance of the inhabitants of Ghor to the adoption of Islam indicates the region's inaccessibility; according to some travelers, the entire region is comparable to a fortress raised in the upper Central Asian highlands: from every approach, tall and steep mountains have to be traversed to reach the area. The language of the inhabitants of Ghor differed so much from that of the people of the plains that communication between the two required interpreters.

The northeastern part of the Hazarajat is the site of ancient Bamyan, a center of Buddhism and a key caravanserai on the Silk Road. The town stands at a height of 7,500 feet, surrounded by the Hindu Kush to the north and Koh-i Baba to the south. The Hazarajat was considered part of the larger geographic region of Khurasan (Kushan), the porous boundaries of which encompassed the vast region between the Caspian Sea and the Oxus River, thus including much of present-day Northern Iran and Afghanistan.

Climate
Hazarajat is mountainous, and a series of mountain passes extend along its eastern edge. One of them, the Salang Pass, is blocked by snow six months out of the year. Another, the Shibar Pass, at a lower elevation, is blocked by snow only two months out of the year. Bamyan is the colder part of the region, with severe winters.

Hazarajat is the source of the rivers that run through Kabul, Arghandab, Helmand, Hari, Murghab, Balkh, and Kunduz; during the spring and summer months it has some of the greenest pastures in Afghanistan. Natural lakes, green valleys and caves are found in Bamyan.

History

The area was ruled successively by the Achaemenids, Seleucids, Mauryas, Kushans, and Hephthalites before the Saffarids Islamized it and made it part of their empire. It was taken over by the Samanids, followed by the Ghaznavids and Ghurids before falling to the Delhi Sultanate. In the 13th century, it was invaded by Genghis Khan and his Mongol army. In the following decades, the Qarlughids emerged to create a local dynasty that offered a few decades of self-rule. Later, the area became part of the Timurid dynasty, the Mughal Empire and the Durrani Empire. The subjugation of the Hazarajat, particularly the mountain fortresses of Bamyan, proved difficult for the invaders at their conquest of the region. "adopted the language of the vanquished".

19th century
In the 18th and 19th centuries, a sense of "Afghan-ness" developed among the Hazaras and the Pashtuns began to coalesce. It has been suggested that in the 19th century there was an emerging awareness of ethnic and religious differences among the population of Kabul. This brought about divisions along "confessional lines" that became reflected in new "spatial boundaries". During the reign of Dost Mohammad Khan, Mir Yazdanbakhsh, a diligent chief of the Behsud Hazaras, consolidated many of the districts they controlled. Mir Yazdanbakhsh collected revenues and safeguarded caravans traveling on the Hajigak route through Bamyan to Kabul through Sheikh Ali and Behsud areas. The consolidation of the Hazarajat thus increasingly made the region and its inhabitants a threat to the Durrani state.

Until the late 19th century, the Hazarajat remained somewhat independent and only the authority of local chieftains was obeyed. Joseph Pierre Ferrier, a French author who supposedly traveled through the region in the mid-19th century, described the inhabitants settled in the mountains near the rivers Balkh and Kholm "The Hazara population is very less but ungovernable, and has no occupation but pillage; they will pillage and pillage only, and plunder from camp to camp". Subsequent British travelers doubted whether Ferrier had ever actually left Herat to venture into Afghanistan's central mountains and have suggested that his accounts of the region were based on hearsay, especially since very few people dared then to enter the Hazarajat; even Pashtun nomads would not take their flocks to graze there, and few caravans would pass through.

Afghanistan's Kuchi people, who are unsettled nomads who migrate between the Amu Darya and the Indus River, temporarily stayed in Hazarajat during some seasons, where they overran Hazara farmlands and pastures. Increasingly during summers, these nomads would camp in large numbers in the Hazarajat highlands.

The travels of Captains P. J. Maitland and M. G. Talbot from Herat, through Obeh and Bamyan, to Balkh, during the autumn and winter of 1885, explored the Hazarajat proper. Maitland and Talbot found the entire length of the road between Herat and Bamyan difficult to traverse. As a result of the expedition, parts of the Hazarajat were surveyed on one-eighth inch scale and thus made to fit into the mapped order of modern nation-states. More thought and attention was put into demarcating the definite borders of modern nations than ever before, which entailed great difficulties in frontier regions such as the Hazarajat.

During the Second Anglo-Afghan War, Colonel T. H. Holdich of the Indian Survey Department referred to the Hazarajat as "great unknown highlands". And for the next few years, neither the Survey nor the Indian Intelligence Department succeeded in obtaining any trustworthy information on the routes between Herat and Kabul through the Hazarajat. Various members of the Afghan Boundary Commission were able to gather the information that brought the geography of remote regions such as the Hazarajat further under state surveillance. In November 1884, the Commission crossed over the Koh-e Baba mountains by the Chashma Sabz Pass. General Peter Lumsden and Major C. E. Yate, who surveyed the tracts between Herat and the Oxus, visited the Qala-e Naw Hazaras in the Paropamisus mountain range, to the east of the Jamshidis of Kushk. Noting surviving evidence of terraced cultivation in times past, both described the northern Hazaras as semi-nomadic with large flocks of sheep and black cattle. They possessed an "inexhaustible supply of grass, the hills around being covered knee-deep with a luxuriant crop of pure rye". Yate noted clusters of kebetkas, or the summer dwellings of the Qala-e Naw Hazaras on the hillsides and described "flocks and herds grazing in all directions".

The geographical reach of the authority of the Afghan state was extended into the Hazarajat during the reign of Abdur Rahman Khan. Caught between the strategic interests of foreign powers and disappointed by the demarcation of the Durand Line in southern Afghanistan, which cut into Pashtun territory, he set out to bring the northern peripheries of the country more firmly under his control. This policy had disastrous consequences for the Hazarajat, whose inhabitants were singled out by Abdur Rahman Khan's regime as particularly troublesome: "The Hazara people had been for centuries past the terror of the rulers of Kabul".

20th and 21st century
In the 1920s the ancient Shibar Pass road which leads through Bamyan and east to the Panjshir Valley was paved for lorries, and it remained the busiest road across the Hindu Kush until the building of the Salang tunnel in 1964 and the opening of a winter route. The Hazarajat became increasingly depopulated as Hazaras migrated to cities and to surrounding countries, where they became laborers and undertook the hardest and lowest-paid work.

In 1979, there were reportedly one and a half million Hazaras in the Hazarajat and Kabul, although a reliable census has never been taken in Afghanistan. As the Afghan state weakened, uprisings broke out in the Hazarajat, freeing the region from state rule by the summer of 1979 for the first time since the death of Abdur Rahman Khan some Hazara resistance groups were formed in Iran, including Nasr and Sipah-i Pasdaran, with some being "committed to the idea of a separate Hazara national identity". During the war with the Democratic Republic of Afghanistan, most of the Hazarajat was unoccupied and free of Soviet or state presence. The region became ruled once again by local leaders, or mirs, and a new stratum of young radical Shiʿi commanders. Economic conditions are reported to have improved in the Hazarajat during the war, when Pashtun Kuchis stopped grazing their flocks in Hazara pastures and fields. The group ruling Hazarajat was the Revolutionary Council of Islamic Unity of Afghanistan or Shura-e Ettefaq, led by Sayyid Ali Beheshti. The region's geographic nature and un-strategic location meant that the government and Soviets ignored it as they fought rebels elsewhere. This effectively allowed the Shura-i Ettefaq administration to rule over the region and give autonomy to the Hazaras. Their politically opposing groups were mostly educated, secular and left-wing. Between 1982 and 1984, an internal civil war caused the Shura to be overthrown by the Sazman-i Nasr and Sepah-i Pasdaran groups. However inter-factional rivalry continued thereafter. Most of the Hazara groups united in 1987 and 1989 and formed the Hizb-e-Wahdat.

During the rule of the Taliban, once again, ethnic and sectarian violence struck Hazarajat. In 1997, a revolt broke out among Hazara people in Mazar-e Sharif when they refused to be disarmed by the Taliban; 600 Taliban were killed in subsequent fighting. In retaliation, the genocidal policies of Amir Abdur Rahman Khan's era were adopted by the Taliban. In 1998, six thousand Hazaras were killed in the north; the intention was ethnic cleansing of Hazara. At that stage, Hazarajat does not exist as an official region; the area comprises the administrative provinces of Bamyan, Ghor, Maidan Wardak, Ghazni, Oruzgan, Juzjan, and Samangan. In March 2001, two giant Buddhist statues, Buddhas of Bamiyan, were also destroyed even though there was a lot of condemnation.

Ethnic groups
The Hazaras constitute the majority of the Hazarajat population.

Language
Dari (Persian) is the official language of Hazarajat. People in different parts of the region with their special dialects where Ghazni, Daykundi, Behsud, Bamyan, Darah Sof and Sheikh Ali are from most popular.

Health
Leprosy has been reported in the Hazarajat region of Afghanistan. The vast majority (80%) of the leprosy victims are Hazara.

A 1989 report noted that common diseases in the Hazarajat included gastrointestinal infections, typhoid, whooping cough, measles, leprosy, tuberculosis, rheumatoid arthritis and malaria.

title: Hazarajat