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Kabul International Airport

Kabul International Airport is located in the northern part of Kabul, Afghanistan. It is one of the country's main international airports, capable of housing over a hundred military and civilian aircraft. It is currently operated by UAE-based GAAC Holding and Afghanistan's Ministry of Transport and Civil Aviation.

The airport was originally named as Khwaja Rawash Airport because it was built in the area named Khwaja Rawash. It was given the name Kabul Airport in 1960 after the Soviet Union built a terminal and a concrete runway. From 2014 to 2021, it was named Hamid Karzai International Airport in honor of former President Hamid Karzai. After the Taliban returned to power in 2021, the name was changed back to Kabul International Airport.

Sitting at an altitude of approximately 1791 m above sea level, the airport is surrounded by parts of the Hindu Kush mountains. It serves as a hub for Ariana Airlines and Kam Air. International companies such as Air Arabia, Flydubai and Turkish Airlines also provide passenger services.

The airport has two separate terminals, one for international passengers and the other for domestic flights. It also has a number of empty military bases, which were previously used by the United States Armed Forces and NATO's International Security Assistance Force (ISAF) and later the Resolute Support Mission (RS). The Afghan Air Force also had a base at the airport, with the Afghan National Security Forces providing security inside the passenger terminals.

Prior to the withdrawal of US-led forces in 2021, the airport provided scheduled flights to and from China, India, Iran, Pakistan, Russia, Tajikistan, Turkey, Uzbekistan, and the Persian Gulf region. The most frequently serviced destination from the airport has been Dubai in the UAE, with no fewer than four passenger airlines flying the route, and some with multiple daily flights.

Other nearby major airports to Kabul are Bagram Air Base in neighboring Parwan Province to the north, Jalalabad Airport in Nangarhar Province to the east, Khost International Airport in Khost Province to the southeast, and Bamyan Airport in Bamyan Province to the northwest.

History

Kabul Airport was originally built during the Kingdom of Amanullah Khan in the 1920s, which housed aircraft of the Afghan Air Force and Afghan Post. It was modernized in 1960 by Soviet engineers. The airport was locally named Khwaja Rawash Airport because it was built in the area called Khwaja Rawash. Foreign tourists began visiting Afghanistan via Kabul Airport. This era ended after the 1978 Saur Revolution, especially after the 1979 Soviet invasion.

The airport was used by the Soviet Army during the Soviet–Afghan War from 1979 to 1989, and by the military forces of the former President of Afghanistan, Mohammad Najibullah. Control of the airport switched between different sides during the civil war after 1992. By November 1996, the Islamic Emirate of Afghanistan governed by Mullah Muhammad Omar was in possession of the airport, until late 2001 when they fled the city after the U.S. invasion of Afghanistan. Due to international sanctions during the Taliban government, the airport was closed in the late 1990s, with very limited international flights.

Following the U.S. invasion of Afghanistan after the September 11 attacks, Kabul Airport was bombed by United States and coalition forces. After the ISAF took over control, the airport began to be developed slowly over the years. A new radar system was installed in 2005, which was upgraded by the U.S. Federal Aviation Administration in 2010. A new $35 million terminal for international flights was inaugurated in November 2008, built with aid from the Japan International Cooperation Agency. This terminal has two jetbridges.The then-Afghan President Hamid Karzai attended the inauguration ceremony. The new terminal was officially opened to international flights in June 2009. The existing terminal has been refurbished and used for domestic flights.

Passenger movements reached 100,000 per year by 2010 or 300 per day. In early 2012, the radar system was upgraded to cover Afghanistan's entire air space.

In October 2014, the National Assembly of Afghanistan proposed naming the airport after former Afghan President Hamid Karzai, a month after his tenure ended, in recognition of his services and contributions to the country's rebuilding. This decision was approved by the Cabinet of the new President Ashraf Ghani, which renamed the structure as Hamid Karzai International Airport.

The North Side Cantonment – Kabul Airport facility was completed and turned over to the United States Armed Forces in October 2008. It houses the command facilities for the Afghan Air Force (AAF), and includes housing, administrative, operations, maintenance and recreation facilities. The project included two new hangar complexes, a new taxiway and ramps. It is the headquarters and main base (1st or 201st Wing) of the Afghan Air Force. The first hangar facility was turned over to the AAF in January 2008. The second hangar was completed later that year.

2021 NATO withdrawal from Afghanistan
In July 2021, the Taliban took over many areas in Afghanistan, including those near Kabul Airport. Turkey announced that it would provide security at the airport. U.S. and NATO forces were still deployed at the airport as well. A few weeks later, Kabul fell into the hands of the Taliban, prompting hundreds of people to flee to the airport in an attempt to leave the country. Seven people were alleged to have died at the airport after the crowds consisting of hundreds of people tried to forcibly enter planes leaving the airport. US forces fired in the air to prevent the crowds running onto the tarmac and runways. On 16 August 2021, the US Deputy Security Advisor announced the deployment of more forces to secure the airport. The Pentagon confirmed the head of U.S. Central Command, General Kenneth F. McKenzie Jr., met Taliban leaders in Qatar. The Taliban officials agreed to terms set by McKenzie for refugees to flee using the Kabul International Airport.

Following the fall of Kabul, the Afghan National Army and the Afghan National Police abandoned their posts. U.S. and allied forces subsequently took over the posts. On 16 August 2021, all commercial flights from Kabul Airport were cancelled indefinitely.

On 26 August 2021, more than 100 people were killed in an explosion outside Kabul Airport. The Islamic State of Iraq and the Levant - Khorasan (ISIS-K) claimed responsibility. The last American forces departed from the airport around midnight on 30 August, ending U.S. involvement in the 20-year war. The Taliban subsequently took control of the airport. Rough estimates by the Taliban calculated the damage to the airport at around $350 million. Abdul Hadi Hamadan, the Taliban head of the airport, later stated that the damage to the airport's terminal alone due to the evacuation was $1 million.

Following the Taliban takeover, the airport was closed. Much of its infrastructure had been degraded or destroyed during the evacuation. According to Qatari Minister of Foreign Affairs Mohammed bin Abdulrahman bin Jassim Al Thani, Qatar was to send technical assistance to Afghanistan to help reopen the airport as soon as possible. Mevlüt Çavuşoğlu, the Minister of Foreign Affairs of Turkey, stated that the Taliban and other countries had requested Turkey for help in resuming operations at the airport. The Minister of Foreign Affairs of the Netherlands, Sigrid Kaag, stated that her government was willing to support Turkey and Qatar in reopening the airport. Meanwhile, the security of the airport was handed over to the Al-Fatah Brigade of the special forces of the group on 3 September.

Several novels have been published following the dramatic US evacuation from the country. Those titles include: "Life and Death at Abbey Gate", "Saving Aziz", "Always Faithful", and "Kabul".

The airport reopened for Ariana Afghan Airlines' domestic flights between Kabul and the cities of Herat, Mazar-i-Sharif and Kandahar, as well as for receiving aid from other countries, on 4 September, following work carried out by a technical team from Qatar, which repaired the airport's runway. Taliban spokesman Zabiullah Mujahid stated on 6 September that Turkey and Qatar were trying to restart all flights from the airport. On 8 September 2021, a NOTAM was issued by the airport's NOTAM office, indicating that the airport is operating between 03:30 and 13:30 Coordinated Universal Time. Additional NOTAMs issued that day indicate that the airports instrument landing system is operative and that the airport's tower is operating again.

A Qatar Airways flight evacuating 113 nationals of other countries from Afghanistan was allowed to land at and depart from the airport on 9 September due to cooperation between the United States and the Taliban, marking the first such flight since the Taliban had completely taken over the facility. Meanwhile, the Taliban renamed the airport to Kabul International Airport, eliminating the reference to former Afghan President Hamid Karzai.

A Pakistan International Airlines flight landed at the airport on 13 September, marking the first international commercial flight to land since the Taliban takeover. Mahan Air resumed flights to the airport on 15 September, marking resumption of commercial flights between Iran and Afghanistan. The Ministry of Foreign Affairs on 26 September announced that the problems at the airport had been resolved and asked international airlines to resume their flights, promising full cooperation.

Facilities
The airport has two terminals: the original that opened in 1960 and a newer building that opened in 2008. The terminal that opened in 2008 is used for international flights; the original 1960 Soviet-constructed terminal is used for domestic flights. Several hangars along the runway are for military aircraft. There are no hangars for civilian (or transient) aircraft. The airport has seven helicopter pads which are used mostly for military traffic. Fire fighting equipment is present. The firefighting equipment has a present capacity of up to 12,000 L of water and has the ability to reach 90 m in height to manage fire outbreaks.

Transportation
Buses, taxi and private cars provide transportation to and from the airport. A four-lane highway connects the airport to Kabul.

Civilian

 * On 2 January 1962, Iran Air Flight 123, a Douglas DC-3 on a cargo flight, crashed while attempting to take-off from Kabul. During the take-off roll the captain noticed a malfunction in the number 1 engine followed by the aircraft veering to the left of the runway. To avoid a crash, the captain pulled the aircraft up into the air, but while attempting to turn the aircraft away from the airport, a wing struck the ground followed by a crash. Both crew members survived.
 * On 15 January 1969, Douglas DC-3 YA-AAB of Ariana Afghan Airlines was damaged beyond economic repair in a ground collision with Douglas DC-6 YA-DAN, also of Ariana.
 * On 21 September 1984, a McDonnell Douglas DC-10-30 of Ariana Afghan Airlines was hit by explosive bullets while on approach to Kabul Airport. All passengers and crew survived the incident.
 * On 12 June 1990, an Ilyushin Il-76 of Aeroflot was struck by a missile while flying at 22500 ft causing two engines to shut down. The aircraft made a forced landing in Kabul with no flaps on an unpaved runway. All 10 crew survived.
 * On 29 May 1992, an Ariana Afghan Airlines Tupolev Tu-154 was struck by a missile while landing at Kabul. The nose of the aircraft was damaged but it landed safely. All passengers and crew survived.
 * On 19 March 1998, a Boeing 727-200 of Ariana Afghan Airlines crashed into the 3000 ft Sharki Baratayi mountain while descending into Kabul. All 10 crew and 35 passengers on board died.
 * On 3 February 2005, Kam Air Flight 904, a Boeing 737-200 operated by Phoenix Aviation, vanished from radar screens on approach to Kabul in poor weather, sparking a massive Afghan National Army search operation for the 96 passengers and 8 crew. The wreckage of the aircraft was found two days later in the mountains east of Kabul, all 104 people on board had been killed.
 * On 17 May 2010, all contact with Pamir Airways Flight 112, an Antonov An-24 operated by Pamir Airways, was lost ten minutes after departure from Kunduz Airport. After search efforts lasting four days, wreckage from the flight was located 12 mi from Kabul. All 39 passengers and five crew on board the flight died.
 * On 8 May 2014, Ariana Afghan Airlines Flight 312, a Boeing 737-400, ran off the runway after landing at the airport. Flight 312 originated in Delhi, India and operated on a scheduled passenger service to Kabul. On landing the aircraft overshot runway 29, coming to rest on uneven terrain. The aircraft was heavily damaged and six passengers were slightly injured.

Military

 * On 11 March 1985, an Antonov An-30 of the Soviet Air Force was on an aerial photography flight in the Kabul area south of the Panjshir Valley. Upon returning to the airport, the aircraft was struck by a Strela missile. The captain tried to make an emergency landing at Bagram Airbase but was too high. A fire ignited by the missile strike then reached the aileron controls causing the pilots to lose control; three of the five crew members evacuated the aircraft safely, but the other two crew members died.
 * On 29 November 1986, a Soviet Air Force Antonov An-26 was hit by a Stinger missile while climbing out of Kabul. The aircraft was carrying several tons of S-24 rockets and 400 kg of explosives to Jalalabad in Afghanistan. All seven crew members perished.
 * On 21 October 1987, a Soviet Air Force Antonov An-12BK collided with a Mil Mi-24 helicopter while taking off in poor visibility. The aircraft was heading for the capital city of then Uzbek Soviet Socialist Republic, Tashkent; 18 of the 19 passengers and crew died.
 * On 21 December 1987, a Soviet Air Force Antonov An-26 was hit by a Stinger missile while circling to a safe altitude shortly after take-off. The number one engine was hit, puncturing the fuel tank. Smoke entered the cabin. All six crew members parachuted out; the captain jumped too close to the ground to open his parachute and died upon impact.
 * On 24 June 1988, a Soviet Air Force Antonov An-26 was hit by bullets fired from Mujahideen rebels. The aircraft crashed in Kabul, killing one of the six crew members on board.
 * On 28 August 1992, a Soviet Air Force Ilyushin Il-76MD was hit by a renegade Mujahideen rocket while boarding Russian embassy staff.
 * On 5 August 2008, a Lockheed C-130H Hercules of the United Arab Emirates Air Force overran the runway upon landing in Kabul, causing a fire in the forward section of the aircraft. The aircraft was carrying aid to Afghanistan. All crew members survived.
 * On 16 August 2021, as a Boeing C-17 Globemaster III of the United States Air Force was taking off, crowds of people trying to escape the 2021 Taliban offensive were seen running alongside and clinging onto the aircraft. The aircraft lifted up into the air with people still holding on, with at least two dying after falling from the aircraft and an unknown number possibly crushed and killed by the landing gear retracting; human remains were found in the wheel well. The incident was widely reported in U.S. and international media.

Non-aircraft related

 * On 31 August 1984, Afghan guerillas exploded a bomb at the airport where several Aeroflot planes were picking up passengers, killing 28 people and wounding 350 others.
 * On 8 September 2009, at around 8:22 AM local time, a suicide bombing took place near the entrance of the airport's military base.
 * On 3 July 2014, Taliban fighters fired two rockets into the airport, destroying four helicopters. One of the four helicopters belonged to Afghan President Hamid Karzai.
 * On 29 January 2015, three American defense contractors and one Afghan national were killed by a gunman outside the airport in late evening local time.
 * On 17 May 2015, a suicide bombing by the Taliban near the entrance of the airport occurred, killing three and injuring eighteen.
 * On 26 August 2021, more than 185 people were killed, including at least 13 U.S. service members and 90 Afghans, at the Kabul airport when two ISIS-K suicide bombers ripped through crowds trying to enter the American-controlled facility, disrupting the final push of the U.S.-led evacuation effort. The bombs were set off near a crowd of families at the airport gates who were desperately hoping to make one of the last evacuation flights out. Gunfire was reported in the aftermath of the explosions.
 * On 29 August 2021, smoke was seen rising from two explosions which occurred near the airport, one of which killed a child. Explosions occurred hours after U.S. President Joe Biden warned of another terrorist attack in Kabul.
 * On 30 August 2021, thermite bombs were used to disable several counter rocket, artillery and mortar systems used to protect the airfield from incoming ISIS-K fired rockets.

title: Kabul International Airport


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Innovia Metro

Innovia Metro is an automated rapid transit system manufactured by Alstom. Innovia Metro systems run on conventional metal rails and pull power from a third rail but are powered by a linear induction motor that provides traction by using magnetic force to pull on a "fourth rail" (a flat aluminum slab) placed between the running rails. However, newer versions of the technology are available with standard electric rotary propulsion.

The design was originally developed in the 1970s by the Urban Transportation Development Corporation (UTDC), a Government of Ontario–owned crown corporation. It was designed as a system that would provide economic rapid transit service in the suburbs, which would have ridership levels between what a bus could serve at the low-end, or a subway at the high-end. During development, the system was known as the ICTS (Intermediate Capacity Transit System). The ICTS was chosen for lines in Vancouver, Toronto, and Detroit. Further sales were not forthcoming and the Ontario government lost interest in the company, selling it to Lavalin of Quebec in 1986. Lavalin ran into serious financial difficulties and the UTDC returned to Ontario control, only to be immediately sold to Bombardier Transportation.

Bombardier used the name Advanced Rapid Transit (ART) after its acquisition of the technology. The company was much more active in developing and promoting this system, introducing a major new revision and winning several additional sales in New York City, Beijing, Kuala Lumpur and Yongin, near Seoul.

Bombardier would later be purchased by Alstom, which continues to market the technology. The latest version is marketed as the Innovia Metro, while previous models are retroactively branded as Innovia ART. The largest system is part of the Vancouver SkyTrain metro network, which has seen several major expansions over its lifetime. It operates just under 50 km of track compatible with Innovia Metro trains. Vancouver was the first to order Innovia Metro 300 vehicles. Since then, vehicle orders for the latest Innovia Metro technology have been made by transit authorities in Kuala Lumpur and Riyadh.

Development stage
During the 1950s, Toronto experienced the same sort of urban sprawl that was sweeping through the United States. This caused enormous traffic problems within the city, and a network of new highways to address the problem became part of the Official Plan in 1959. By the mid-1960s, there was a growing awareness that the growth of the suburbs led to a flight of capital from the city cores, resulting in the urban decay being seen throughout the US leading to freeway revolts across North America. Activists inspired by urbanist Jane Jacobs rallied to oppose development of the Spadina Expressway project. The government reconsidered and cancelled the construction of the Spadina Expressway and other planned expressways.

Instead of expressways, Bill Davis and his new Minister of Transport, Charles MacNaughton, outlined the "GO-Urban" plan. GO-Urban called for a system of three advanced mass transit lines that would be run by the newly formed GO Transit. The idea was to select a system with low capital costs, one that would be cost effective in low-density areas where a traditional subway would be too expensive to build and operate. Designed to have a design capacity half-way between buses and subways, the new system was referred to as the Intermediate Capacity Transit System or ICTS. The space age automated guideway transit (AGT) systems being designed in the late 1960s seemed like the right solution.

Toronto was not the only city looking for such a solution, and there appeared to be a large market for automated transit systems in the 1970s and 80s. As GO-Urban was larger than most networks being considered, practically every company working on an AGT, or hoping to, submitted a proposal. The first cut reduced the field to a still-large fourteen proposals. After a year-long selection process, GO selected the Krauss-Maffei Transurban maglev as the preferred solution. As a maglev, the system would be silent, addressing concerns about noise on elevated portions of the track. Additionally, the system's linear induction motor did not require physical contact for traction, which meant it would run with equal capacity in snow or icy conditions. Krauss-Maffei agreed to do all vehicle construction in Ontario, and allow the local office to handle all sales efforts in North America – a stipulation most US companies were not willing to agree to. Local testing, construction and sales were centralized in the newly created "Ontario Transportation Development Corporation" (OTDC).

Construction of a test track on the grounds of the Canadian National Exhibition started in late 1975, but shortly after this Krauss-Maffei announced that development funding provided by the German government was ending. Ontario was not willing to continue funding development of the system on their own, and cancelled the maglev plans.

Rebirth
Instead of returning to their earlier submissions, the OTDC decided to press ahead with many portions of the existing ICTS design. On April 14, 1975, the Ministry of Transportation arranged financing for Phase I and II studies to develop the new version. In June 1975, OTDC announced that it had arranged a consortium to continue the development of the ICTS, changing their name to "Urban Transportation Development Corporation" (UTDC) to avoid any "provinciality" during their efforts to market the design to other cities.

The result was essentially a larger, rubber-wheeled version of the original maglev vehicle. The consortium included of SPAR Aerospace for the linear induction motor, Standard Elektrik Lorenz (SEL) for the automatic control system, Dofasco for the bogies, Alcan and Canadair for the design of the car bodies and a set of prototypes, and Canadair as the overall prime contractor. The arrangements, funding and final system definitions were in place by 1976.

Between 1976 and 1980, three prototype cars were built. The first immediately demonstrated a problem with the rubber-wheeled bogies. The linear induction motor required very accurate positioning about 15 mm above its "reaction rail" in order to work efficiently and the slight give in the wheels was enough to make this a problem. The obvious solution to this would be to use steel wheels instead, but that would re-introduce the noise problem as the trains rounded curves in the tracks. A new solution was selected, using steel wheels with an articulated bogie that would steer each wheel set into the direction of the track and thereby avoid the rubbing between the flange and track that caused the screeching noise. UTDC bought two modern articulated bogie patents from a private developer in the United States, which were further developed by Dofasco.

A dedicated test facility was desired; modelled after the similar Transit Testing Center set up in the US as part of their own mass transit developments, the site would be open to use for any company that wanted to test new technologies without the need to build out their own testing sites. A 480 acre site in Millhaven, outside of Kingston, Ontario, was selected for the new test centre. Kingston had been home to the Canadian Locomotive Company that closed its doors in 1969, and the city lobbied hard for the new company to locate to their city.

The site was officially opened on September 29, 1978, by James Snow, the Minister of Transportation and Communications. The site included a 1.9 km oval test track that included at-grade, elevated and ramped sections, switches, and the automatic control centre. Phase III of the ICTS program ended on January 31, 1980, when testing on the prototype was completed at the Millhaven site, by this point the government had invested about $57.2 million, of a total $63 million spent on the product by the government and its industrial partners.

Initial sales
By the late 1970s, it appeared there were no more technology issues to overcome and efforts turned to debugging the system and developing methods for mass production. As this process started, UTDC started its own efforts to market the design. Toronto, the inspiration for the system, was an obvious target, but the company also found interest in the system in Ottawa, Hamilton, Vancouver, Detroit and Los Angeles.

A test system in Toronto was the primary concern. With the GO-Urban concept having since been cancelled, and GO Transit having turned to conventional heavy rail systems, the only suitable local market was the Toronto Transit Commission (TTC). The TTC had recently extended the east–west Bloor-Danforth subway line with the addition of another station on each end of the line, and had planned to further extend the line with streetcars running from those stations into the suburbs. Construction had already started on the streetcar system at the eastern end of the line at Kennedy station.

The provincial government asked the TTC to switch the streetcar line to the ICTS. The TTC was uninterested until the government threatened to pull their financing, which accounted for 75% of its capital budget. In exchange, the government agreed to pay for any cost overruns above the original streetcar budget. Construction of the internal streetcar platform and a turn-around loop had already been completed at the station. The platform had to be raised to the higher floor height of the ICTS, but UTDC claimed the vehicle would be able to make its way around the existing 18 m radius loop at 10 km/h without additional modification.

Vancouver proved very interested in the system on its own merits. As early as 1978, the city had been planning a transportation-themed event for its centennial in 1986, and in 1980 they won the rights to host the Expo '86 World's Fair, giving it the theme "Transportation and Communications". The city is newer than Toronto and more spread out, making a traditional subway unattractive – precisely the problem that the ICTS had been designed to solve. The ICTS vehicle design, with shorter vehicle heights, was also ideal, as the old heavy-rail Dunsmuir Tunnel in downtown Vancouver could be easily modified and split into two stacked tunnels. With UTDC interested in showcasing the system at the Expo, and the Expo backers interested in a transit solution that could be open in time for the show, a deal was quickly arranged that was attractive to both parties. At the time, it was a somewhat controversial project and had its detractors.

Detroit had been one of six cities selected for rapid development under the United States Urban Mass Transportation Administration (UMTA) Downtown People Mover (DPM) program. After ten years, little actual development had taken place and UMTA was mandated to install systems with all possible speed. None of the high-tech developments funded by UMTA had been installed, nor developed to the point where they were ready for service. Instead, the Detroit system was favouring the Cabinentaxi system from Germany, but that company decided to pull out of the contest in order to focus on a larger development in Hamburg. The UTDC responded to a "buy American" clause in UMTA by opening a branch office in Detroit, and that immediately swung the decision in their favour. However, with the Ronald Reagan administration taking office in 1981, DPM was rapidly de-funded. Four of the five cities ended their development plans, but Detroit and Miami (using a different design) decided to press ahead with their deployments.

Construction of the Toronto and Vancouver systems proceeded apace, with the Scarborough RT opening for service on March 22, 1985, followed by the SkyTrain on December 11, 1985, with passenger service starting in January.

Hiatus
Sales of additional ICTS systems went nowhere, and the government began to worry about UTDC's continued successes. The government pushed any potential deployment to buy from UTDC, but with only one product, and that product having many problems in Toronto, there was little interest from other cities. At the same time, the buy-UTDC clause locked Hawker Siddeley Canada out of many local projects, and they had formerly been a major supplier in the local market. The solution was to form a 50–50 combined company, Can-Car Rail, who marketed the combined product line. Hawker had a number of successful products, notably their Bombardier BiLevel Coach, and as these other products were selling well through this period, interest in actively selling ICTS waned.

In spite of Can-Car's success in other markets, as early as 1981 the government had considered selling UTDC to the private sector. Their concern was that without a manufacturing business, UTDC would find it difficult to make enough income to justify its Kingston operations. If the company did start a manufacturing side, it would be inappropriate for the company to remain government owned. The Can-Car deal put this on hold for a time.

In 1986 the new Ontario government announced their intention to sell UTDC to Lavalin, a large engineering company in Montreal. Lavalin purchased the company for only CAD$50 million, less than the $70 million spent on the UTDC by the government up to 1981. The sale was highly controversial at the time, due to several non-performance payments due to the early problems on the ICTS that had to be paid out by the government, to the tune of $39 million. Soon after, Hawker Siddeley announced that they were selling their remaining interest in Can-Car to Lavalin as well.

Innovia ART

A series of financial difficulties caused by Lavalin's rapid expansion led to its bankruptcy. A clause in the original sales contract returned UTDC to Ontario crown control, and they quickly sold it to Bombardier in 1991. Bombardier started a redesign effort for the ICTS, resulting in the larger, advanced rapid transit (ART) Mark II vehicle. Compared to the original ICTS (retroactively named Mark I), the newer ART cars are longer with more seating, and have a more open layout inside.

ART technology was selected for the AirTrain JFK project, which is widely considered a great success in spite of predictions to the contrary. After winning the SkyTrain Millennium Line contract in Vancouver, Bombardier further improved the design by introducing an articulating section between adjacent cars, replacing the coupling and doors of the older Mark I design. The articulation allows passengers to move freely between the cars, as well as adding more internal space for passenger seating. These versions of the Mark II design won several more contracts, and are currently operating on the Kelana Jaya Line in Kuala Lumpur, the Airport Express, Beijing Subway in China (in four-car trains), and the YongIn EverLine near Seoul in South Korea. When Bombardier started marketing ART as part of its Bombardier Innovia family of automated transit systems, the technology was rebranded as the Innovia ART 100 for the Mark I and Innovia ART 200 for the Mark II.

Vancouver continues to be the largest operator of an Innovia ART system, with 49.5 km of operational lines in its SkyTrain network (Expo Line and Millennium Line). This network increased in 2016 with the opening of a 10.9 km extension of the Millennium Line, named the Evergreen Extension. The SkyTrain system uses a mixed fleet of Innovia ART 100, 200 and 300 cars.

Innovia Metro
The latest version of the technology uses the name "Innovia Metro" and is marketed as a mid-size metro system. Innovia Metro is compatible with Bombardier's own CITYFLO 650 integrated transit automation system and is offered in variants compatible with both linear motor and electric rotary propulsion. Bombardier now markets the Innovia Metro alongside the larger Movia Metro and has touted its system versatility.

The first rotary-powered Innovia Metro 300 vehicles were ordered by Riyadh Metro in Saudi Arabia for Line 3 of its new rapid transit network. Those 47 vehicles will be equipped with Bombardier's MITRAC propulsion drives.

Control and signalling
The ICTS was the original platform for the SelTrac automated control system by Standard Elektrik Lorenz. This system has changed hands several times since then and is currently owned by Thales. SelTrac is a completely automated system, with centralized control. The system originally used a current loop in the track bed to signal to and from the vehicles, but this has been replaced in more modern versions with a variety of radio systems.

In the original system, the current loop also provided positioning by crossing the lines every metre, with an onboard sensor counting the number of times the polarity changed. Additional fine-tuning was available via a wheel rotation counter, which was used for positioning in stations.

The Toronto Transit Commission union, ATU Local 113, rejected automated control as they felt this was the start of a switch to automating the entire fleet, thereby cutting some of the highest paid jobs in the TTC. This led to the Scarborough Rapid Transit vehicles being modified at a high cost to include operator cabins and conventional controls. No other Innovia Metro system uses manual control.

The Innovia Metro 300 systems are marketed to use Bombardier's own CITYFLO 650 automation system, but can also use other automation systems, such as SelTrac.

Linear motor
The original versions of Innovia Metro were based on a linear induction motor (LIM) using vehicle-mounted windings and a track-mounted stator consisting of a thin aluminum plate mounted flat between the rails. The small size and flat shape of the motor, and its lack of a transmission connected to the bogies, allows the ART to be much closer to the ground than a traditional subway car. The motor is used for all control with the exception of final stopping and positioning using disc brakes and emergency braking using a track brake.

The new Innovia Metro still offers linear motor propulsion as the advantageous option but an electric rotary propulsion version is also an option. The first rotary-powered Innovia Metro 300 system is being implemented in Riyadh, Saudi Arabia.

Vehicle
The Innovia Metro vehicle was built using a lightweight aluminum frame riding on two sets of articulated trucks using small steel wheels. The original Innovia ART 100 cars are 12.7 m long. The second generation Innovia ART 200 cars are 16.7 m long each and come in articulated pairs.

By 2011, the Innovia ART 200 design has been updated and Bombardier is currently marketing the third generation as Innovia Metro 300 (retiring the ART branding). While three vehicle orders have been placed, new vehicles are still in the production stage. Vehicle dimensions are similar to the Innovia ART 200 vehicle, but passenger capacity has been increased through redesigned car layout. The vehicles appear sleeker, with larger windows on the sides of the train, and redesigned windows and headlights on the ends of the cars.

Similar designs
The linear motors and steerable axles used in Innovia Metro trains are relatively rare, although similar Japanese designed linear motor propulsion technologies are also used on a number of subway lines in East Asia, such as the Nagahori Tsurumi-ryokuchi Line, Toei Ōedo Line and Guangzhou Metro Line 5. However, the Innovia Metro system has a number of competitors in the field of automated light metros, including the VAL technology developed by Matra for the Lille Metro in France (and now owned by Siemens) and the Météor technology used by Paris Métro Line 14 (which is built to high-capacity, full metro standards). Furthermore, the CITYFLO and SelTrac signaling technologies are not specific to the Innovia Metro, but can also equip most conventional railway lines regardless of propulsion technology or carrying capacity.

Innovia Metro lines are designed to run on elevated structures, and indeed the systems that use these trains include such sections, with most being predominantly elevated. Using a grade-separated guideway, though, allows them to perform equally well on ground level and in tunnels, as they in fact do for a portion of both Vancouver's Expo and Millennium Lines (using a converted freight tunnel for the Expo line, and a bored tunnel under Clarke Road for the Evergreen Extension), Kuala Lumpur's Kelana Jaya Line, and Beijing's Airport Express. The Scarborough RT in Toronto also includes a short tunnelled section, though there are no stations within it. The Kuala Lumpur and Beijing systems, along with New York's Airtrain JFK, also incorporate platform screen doors commonly found in automated people movers around the world.

Prior to a change in approach to marketing and the introduction of the "Metro" branding, Innovia ART 100 and 200 technologies were sometimes referred to as "light rail", especially in Asia. Because of their use of automated operation and third-rail power, however, they are unsuitable for the unprotected, street-level trams that the term usually indicates in Europe and North America.

Toronto
In 1981, the Toronto Transit Commission (TTC) was planning to build a streetcar line serving the city's eastern district of Scarborough, but the Ontario provincial government convinced it, by threatening to withhold funding, to switch to the Innovia ART 100 technology. This would act as a demonstration system for other transit operators considering buying the trains. In exchange, the government agreed to pay for any cost overruns over the original LRT costs. The 7 km six-station Scarborough RT (now called Line 3 Scarborough) line opened in March 1985.

Although its Innovia ART 100 trains are capable of driving themselves, the TTC chose to run them semi-automatically with operators on board in order to keep peace with their main union. This conversion proved much more difficult than imagined; the small confines of the Innovia ART 100 car meant that the traditional Toronto solution of taking up the front-right corner of the cab left too little room for the operator to work in, and the entire front of the car had to be used up, reducing seating. Additionally, the Innovia ART 100 control system was based on "dumb" cars and "smart" control centres, so there was no system on the train itself for control or presenting information. These systems had to be retrofitted and were the cause of considerable expense and confusion.

Entering operation, the problems continued. The braking system had been designed to be fully automated but was now being operated by manual control, and the brakes were being over-applied. This led to problems with the wheels being rubbed flat in spots when the brakes were applied too strongly, producing buzzing noises when running at speed. Since the vehicles were brand-new, the TTC did not have a machine capable of grinding the small-diameter wheels, and one had to be purchased for $1.5 million. Another $250,000 was needed for a rail grinder to remove "totally unexpected rail corrugations". Additionally, the cars were found to be incapable of turning the short radius, 18 m turning loop at one end of the line, in spite of UTDC's claims it could, which was going to have to be re-built at a cost of about $6 million. Instead, this portion of the track was simply abandoned.

Over $1 million was originally budgeted to heat the third rail to prevent ice buildup but this feature was later removed as a cost-cutting move. It was believed that the rapid operation (short headways) would keep the rail free of snow as the passing cars heated the rail. This proved not to be the case and in operations at just the wrong conditions close to freezing, the opposite occurred: when the train passed and heated the rail, microscopically thin layers of snow would be melted, and if the rail was below zero as a whole, the water would freeze to the rail and cause ice buildup. Another retrofit was required to solve this problem, by adding wooden covers over the rail, a system used throughout Toronto's subway system. Even with these covers in place, the line can be shut down by any heavy snowfall that covers the fourth rail to a depth that fills the distance between the rail and the linear motor.

Only two of Line 3's stations have ridership comparable to those of the TTC's conventional subway lines, and most passengers see it merely as an extra transfer they must make in order to get onto a subway line running downtown. Although there had been proposals to extend Line 3, none of these gained traction.

With the Innovia ART 100 fleet overdue for replacement and expensive upgrades to the line needed to handle the longer Innovia ART 200 trains, replacement of the line was decided upon. One proposal would have converted the line to use conventional light rail vehicles and seen it extended west by 19 km, but the city council voted to ask for provincial and federal funding to extend Line 2 Bloor–Danforth, a subway line, from Kennedy station along a new route to Scarborough Centre. Line 3 Scarborough was scheduled to be decommissioned in November 2023, with bus service covering the route until the subway extension opens in 2030. However, an accident involving a car detachment and derailment on July 24, 2023, resulted in the TTC closing the line prematurely.

Vancouver
The SkyTrain metro network has the largest Innovia Metro system in operation, and currently has two such lines: the Expo Line and the Millennium Line. Vancouver's SkyTrain network continues to maintain on-time reliability over 95%. The Expo Line opened in late 1985, in time for Expo '86. With the opening of the Millennium Line in 2002, Vancouver added to its original Innovia ART 100 fleet the longer, articulated Innovia ART 200 trains first used in Kuala Lumpur, which allow for significantly greater rider capacities.

In 2012, Vancouver began construction of the Evergreen Extension, a 10.9 km extension from Burnaby to Coquitlam in the northeast, which the Millennium Line now re-routes to. Although at one point the extension was proposed to be a street-level LRT system that would not have used Innovia ART technology, in 2008 plans were changed back to the SkyTrain option by the provincial government to facilitate higher ridership from increased capacity, shortened travel times and to integrate seamlessly with the existing SkyTrain network. The extension opened on December 2, 2016.

The network of Innovia ART 100, Innovia ART 200, and Innovia Metro 300 are supported by Quester Tangent products, including braking as well as monitoring and diagnostic equipment.

An extension of the Millennium Line west from VCC–Clark station under the Broadway corridor to a station at Arbutus Street began construction in 2020; completion is expected in 2027. The Expo Line's extension from King George station to Langley has an anticipated opening date of 2028. A continuation of the Millennium Line from Arbutus station farther west to the University of British Columbia is pending the outcome of local public consultations.

Detroit
The 13-station Detroit People Mover is a fully automated system, using the same Innovia ART 100 trains as Toronto and Vancouver. The system had originally been part of UMTA's buildout, which included lines radiating outward from a central circle into the suburbs. However, UMTA was dramatically "downfunded" in the early 1980s, and the Detroit system lost the majority of the funding. Although most other cities on the UMTA list simply gave up on their plans, Detroit decided to press ahead with the portion they could build with the funds they already had, and completed the downtown loop.

The resulting system offers service to a limited area of the downtown core along a 4.7 km loop. The point-to-point distances are easily walkable, so the system sees low ridership levels on the order of 7,500 passengers a day. Originally designed to act as the hub of a system with 15 million riders a year, the 2 million riders it currently serves results in a very high cost-per-passenger. According to The Detroit News, this was about $3 per ride, against a fare of only 50 cents.

Kuala Lumpur
The Kelana Jaya Line in Kuala Lumpur, Malaysia, is a fully automated rail line that opened in 1998. It uses the Innovia ART 200 technology, featuring articulated trains. The line spans 37 stations and covers a distance of 46.4 km, making it the longest linear induction motor technology-based line.

Operation on the line began on September 1, 1998, between the Lembah Subang Depot and Kelana Jaya to Pasar Seni, with the second section from Pasar Seni to Gombak opening in June 1999. By 2002, the line had served 150 million passengers, with an average daily ridership of 160,000. An extension of the line, spanning 17 km, was completed in 2016.

In 2006, Bombardier was awarded a contract for 22 new four-car trains, with an option for an additional 13 trains if required. The order was expanded in 2007 with an additional purchase of 52 train sets. The first batch of new trains began service in December 2009, and by 2014, all 35 train sets had been delivered.

Following the line extension in 2016, a new order for 14 four-car Innovia Metro 300 trains was placed. The trains feature braking systems, monitoring, and diagnostic equipment developed by Quester Tangent. The trains began entering service at the end of 2016.

In October 2022, Rapid Rail, the operator of the Kelana Jaya Line, announced an order for 19 additional Innovia Metro 300 trainsets (76 cars) at a cost of MYR1.72billion (US$385 million). The new trainsets were intended to replace the original Innovia Metro 200 trainsets that had been operating on the line since 1999.

New York
AirTrain JFK, opened in December 2003, is an automated ART service with Innovia ART 200 rolling stock. Its two branches connect the New York City Subway and Long Island Rail Road to John F. Kennedy International Airport in New York City. This service uses non-articulated Innovia ART 200 cars in trains of one or two cars.

Beijing
The Airport Express of the Beijing Subway, opened in July 2008, uses Innovia ART 200 technology, with a fleet of 40 locally manufactured vehicles. The route is 28 km long and has four stations.

Yongin
The EverLine is an ART line, located in Yongin, a major city in the Seoul Capital Area. The line connects the city to Everland, South Korea's most popular theme park offering a transfer to the Suin–Bundang Line of the Seoul Metropolitan Subway at Giheung Station.

Demo cars
Two demonstrator/prototype Innovia ART 100 cars were built and used for testing at the UTDC urban transit facility Millhaven, Ontario. Unlike the production cars, the demo cars lacked doors at either end of the vehicle. Test Vehicle 1 had windows in the centre and on the driver cab, while Test Vehicle 2 is a trailer car only had a centre window and no driver's cab. The paint scheme on the lead car was orange and white, while the trailer was grey and orange. The interior of the vehicle was unfinished (no seats, incomplete floor/ceiling and plywood panelling covering wiring). Only Test Vehicle 2 remained at the facility and in 2011 it was donated to the Canada Science and Technology Museum in Ottawa.

A mock-up of an Innovia ART 100 car was stored at the Toronto Transit Commission St. Clair Carhouse by Disney Displays. This car was unpainted and non-operational. The fate of this vehicle is unknown.

BC Rail had an Innovia ART 200 test car delivered to test clearance in stations and tunnels for the Millennium Line. It was donated by BC Rapid Transit Company to the West Coast Railway Heritage Park in Squamish, BC in 2012.

ALRT car
The ALRT car was a proposed rapid-transit vehicle for Greater Toronto's GO ALRT in the early 1980s. The car was to: As the required capacity of the ALRT system rose, it eventually approached the size of conventional heavy rail, and ALRT was cancelled in favour of additional diesel units pulling Bombardier BiLevel Coaches, which have since gone on to be one of Bombardier's best-selling products.
 * be longer
 * use a pantograph
 * be an articulated version of the Scarborough RT car
 * be capable of high speeds needed for interurban operation

The original ALRT design was never produced, as the ALRT program was cancelled in 1985.

Former systems
A train derailment in July 2023 resulted in the Toronto Transit Commission permanently closing Toronto’s Line 3 Scarborough, which was the original system that made use of Innovia Metro technology, four months ahead of its scheduled closure in November 2023.

Appearances in TV and film
A scene in the 2003 movie Paycheck, filmed in Vancouver, shows Ben Affleck running in front of a mockup of a Vancouver SkyTrain Innovia ART 200 train. SkyTrain cars can also be seen in the opening credits of 21 Jump Street and variously in Smallville, The X-Files and in numerous other filmed productions shot in Vancouver.

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

title: Innovia Metro


text:
Hong Kong Supermarket

Hong Kong Supermarket is an Asian American supermarket chain started in the San Gabriel Valley region of Southern California. It operates mainly in the newer suburban overseas Chinese communities, particularly in the Los Angeles, Philadelphia, and New York City areas. Hong Kong Supermarket specializes mainly in imported Asian groceries. Many items are from Mainland China, Hong Kong, Macau, Japan, South Korea, Thailand, Taiwan, Vietnam, Indonesia, and the Philippines.

The supermarket caters to a specific customer base. The first store in Monterey Park, California, was a popular destination for Mainland Chinese emigres, and the Hong Kong Supermarkets in New York City focus on mainland Chinese immigrant customers (large community of mainlanders in Brooklyn).

Hong Kong Supermarket was established in 1981 by Jeffrey Wu with its former flagship store located in Monterey Park, California, where it is still among the popular Asian supermarkets, and is headquartered in New York City. It is currently owned by Jeffrey Wu (胡兆明) and his wife, former Hong Kong actress Veronica Yip. In Southern California, its main competitors were 99 Ranch Market and Shun Fat Supermarket. In the New York City area, it competes with Kam Man Food, Good Fortune Supermarket, New York Mart, and Great Wall Supermarket. In Boston, it competes with Kam Man, H Mart, and C-Mart.

In 2009, Hong Kong purchased Super 88, an Asian supermarket chain which had already closed three of its six stores in 2008, citing poor sales. Super 88 had also faced increasing competition and a $200,000 settlement after violating state wage and hour laws.

The chain sold much of its stores to the Good Fortune Supermarket chain.

Locations

 * Georgia
 * Norcross - 5495 Jimmy Carter Blvd
 * Massachusetts
 * Boston - 1095 Commonwealth Avenue
 * Malden - 188 Commercial St
 * New York
 * Chinatown, Manhattan - 157 Hester Street

Defunct locations

 * California
 * Monterey Park - 127 N Garfield Ave (became a Good Fortune Supermarket)
 * Rowland Heights (now HK2 Food District)
 * San Gabriel (now a Good Fortune Supermarket)
 * West Covina (now HK2 Food District)
 * West Covina (now Shun Fat Supermarket)
 * Monrovia (now a Good Fortune Supermarket)
 * Massachusetts
 * Allston, Massachusetts
 * Dorchester, Massachusetts
 * New Jersey
 * South Plainfield (closed in 2002)
 * East Brunswick
 * New York
 * Chinatown, Manhattan (East Broadway Location)(destroyed by fire on May 14, 2009) (now a Chinatown Supermarket Of Manhattan and a Fairfield Inn Hotel above)
 * Sunset Park (now an iFresh Market)
 * Elmhurst (now a US Supermarket)
 * Flushing (now a SuperHK Supermarket, part of Good Fortune Supermarket)
 * Pennsylvania
 * Philadelphia (now a Hong Kong Hypermarket)
 * Louisiana
 * Gretna (now a Hong Kong Food Market)

title: Hong Kong Supermarket


text:
1702 in Canada

Events from the year 1702 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch: William III (until March 8), Anne (starting March 8)

Governors

 * Governor General of New France: Louis-Hector de Callière
 * Governor of Acadia: Claude-Sébastien de Villieu then Jacques-François de Monbeton de Brouillan
 * Colonial Governor of Louisiana: Sauvolle then Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Joseph de Monic

Events

 * Having begun in Europe in 1701, the War of the Spanish Succession spreads to North America (Queen Anne's War) in Acadia and New England.
 * 1702-13: The short-lived Peace of Ryswick collapses with the outbreak of the War of the Spanish Succession, which erupts in the colonies as Queen Anne's War. It ends with France losing North American territory to Britain.
 * 1702-13: Queen Anne's War—Maine Abenakis and Iroquois from Quebec (Caughnawaga) attack the English colonists on behalf of the French, but lose. The European nations negotiate their settlement at the Treaty of Utrecht (1713); Louis XIV cedes Hudson Bay, Acadia (Nova Scotia) and Newfoundland (but not Cape Breton Island or St. John's Island) to Great Britain.

Deaths

 * September 20 - Charles Aubert de La Chesnaye, businessman (born 1632)

Historical documents
In several weeks of talks, Indigenous leaders and New York governor discuss alliance, trade, peace, war and French influence

"All the glory of it" - Cadillac describes rich region and progress of his promising new settlement, Detroit (Note: racial stereotypes)

New York official suggests missionary society send ministers to Five Nations because Jesuits have drawn so many to Montreal area

As England, France, and Spain go to war, this medical guide to amputation is timely

This guide to letter-writing offers timely example of letter from wounded man to his love, and her reply

title: 1702 in Canada


text:
1703 in Canada

Events from the year 1703 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch: Anne

Governors

 * Governor General of New France: Louis-Hector de Callière
 * Governor of Acadia: Jacques-François de Monbeton de Brouillan
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Daniel d'Auger de Subercase

Events

 * May 26 - Louis-Hector de Callière, Governor General of New France, dies in office.
 * May 27 - Philippe de Rigaud Vaudreuil becomes Governor General of New France.

Births

 * June 6 - Louis de la Corne, Chevalier de la Corne, explorer (died 1761).

Deaths

 * May 26 - Louis-Hector de Callière, Governor General of New France (born 1648)

title: 1703 in Canada


text:
1704 in Canada

Events from the year 1704 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Governor of Acadia: Jacques-François de Monbeton de Brouillan
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Daniel d'Auger de Subercase

Events

 * French forces destroy the English settlement at Bonavista, Newfoundland.

Historical documents
Massachusetts governor gives details of French and Indigenous attacks planned for Connecticut River and Maine and his attack on Acadia.

Account of a Massachusetts boy abducted by French and Indigenous raiders.

Massachusetts correspondent on huge benefit France has from commercial ascendancy and number of seamen in its Newfoundland fishery.

During war with France, defending St. John's complicated by soldier disorder and desertions and limited support from outports.

title: 1704 in Canada


text:
Army of Tennessee

The Army of Tennessee was the principal Confederate army operating between the Appalachian Mountains and the Mississippi River during the American Civil War. Named for the State of Tennessee, It was formed in the same state in late 1862 and fought until the end of the war in 1865, participating in most of the significant battles in the Western Theater.

1862
The army was formed on November 20, 1862, when General Braxton Bragg renamed the former Army of Mississippi and was divided into two corps (1st Corps and 2nd Corps) commanded by Leonidas Polk and William J. Hardee. A third corps was formed from troops from the Department of East Tennessee and commanded by Edmund Kirby Smith; it was disbanded in early December after one of its two divisions was sent to Mississippi. The remaining division was assigned to Hardee's corps while Kirby Smith returned to East Tennessee. The army's cavalry was consolidated into a single command under Joseph Wheeler. The army's first major engagement under its new name took place against the Army of the Cumberland on December 31 along the Stones River. The attacks started at 6 a.m. against the Union right wing and forced the Union flank back towards the Union supply route to Nashville, but the Confederates were unable to capture the road. Bragg expected Union commander William S. Rosecrans to retreat during the night but Rosecrans decided to remain. No fighting took place on January 1; the next day Bragg assigned one division to seize a ridge on the east side of Stones River but the division's attack was repulsed by heavy artillery fire. Bragg retreated during the night and halted near the Duck River.

1863

Following Stones' River, feuding broke out between Bragg and his corps and division commanders over who was responsible for the Confederate defeat; several officers stated that Bragg had lost the confidence of the army. When he learned of the dispute, Confederate President Jefferson Davis sent Joseph Johnston to inspect the army and take command if he thought it necessary to relieve Bragg. Johnston however refused to take command of the army. In the summer of 1863, Rosecrans began an offensive, generally known as the Tullahoma Campaign, a name taken from the location of the Confederate headquarters at the time. Due to the low level of the river, Bragg felt compelled to retreat back to his supply center of Chattanooga, Tennessee, where he established his headquarters. When the Union forces halted following the campaign, Bragg took the opportunity to make several command changes in the army. Hardee was transferred to Mississippi in July and replaced by D.H. Hill. Bragg's department was reorganized into the Department of Tennessee, which covered Alabama north of the Tennessee River and Georgia north of Atlanta; the Department of East Tennessee, now commanded by Simon Buckner, was merged with Bragg's department and Buckner's troops were designated the Third Corps. The cavalry was reorganized into two corps commanded by Wheeler and Forrest; a two-division Reserve Corps was also organized under the command of W.H.T. Walker. The Confederate government agreed to transfer James Longstreet's First Corps, Army of Northern Virginia to the army during this time, but due to the loss of Knoxville, Longstreet had to travel by rail through the Carolinas and Atlanta to northern Georgia; the movement started on September 9.

Rosecrans launched the Chickamauga Campaign in late August, staging demonstrations near Chattanooga and upstream of the city along the Tennessee River. This convinced Bragg that Rosecrans was crossing the river to the north; however, Union forces were actually crossing to the south of the city. This forced Bragg to fall back into northern Georgia, abandoning the important railroad hub of Chattanooga on September 8. Over the course of the next several days, Bragg attempted to launch several attacks on isolated parts of the Union army but each attempt failed. On the evening of September 18, Bragg concentrated the army near Chickamauga Creek; he thought that only part of the Union army was nearby but Rosecrans had concentrated his army faster than Bragg had expected. During September 19 at Chickamauga, both sides fed in reinforcements as the day progressed. Longstreet arrived on the battlefield during the night of the 19 and 20; Bragg divided the army into two wings, with Polk commanding one division of his corps along with Hill's and Walker's corps on the right, and Longstreet commanding the other division of Polk's corps with Buckner's corps and his own corps (commanded by John B. Hood), on the left. Polk was ordered to attack at daylight on September 20, with Longstreet attacking immediately afterwards, but Polk didn't launch his attack until midmorning. The left wing failed to dislodge the Union army but Longstreet's wing attacked a gap in the Union army which routed the Union right flank. A portion of the Union army rallied on Horseshoe Ridge and held off multiple Confederate attacks until evening, when it followed the rest of Rosecrans' army into Chattanooga.

After Chickamauga, the Army of Tennessee besieged the Union army in Chattanooga, taking up defensive positions on the surrounding hills, especially on Missionary Ridge, which formed the Confederate center, and Lookout Mountain on the Confederate left. Bragg considered a direct attack on the city too costly, and a lack of supplies and pontoons caused him to reject a plan to cross the river and break the Union supply line to Nashville. Instead he spread the Confederate army along the Tennessee River, cutting the Union railroad supply line into the city and reducing the amount of supplies the Union army could get into the city. During the next several weeks, Bragg became embroiled with a dispute with the army's corps commanders. Bragg became involved in a personal dispute with Forrest, which led to Forrest being reassigned to Mississippi and West Tennessee, with his cavalry corps merged with Wheeler's corps. Meanwhile, Hill, Buckner, and Longstreet, along with several division commanders, signed a petition to Davis, asking that Bragg be relieved of command. After Davis rejected the petition, Bragg made several changes to the command structure of the army. Polk was relieved of command and was charged with disobedience during the Chickamauga campaign and failure to attack when ordered; instead of being court martialed, Polk was transferred to Mississippi and Hardee took command of the First Corps. Hill was also relieved of command and replaced by John C. Breckinridge; both the Third Corps and Reserve Corps were merged into the other two corps, with Buckner and Walker demoted to division command.

During the month of September and into early October, the Army of the Cumberland was reinforced by the troops of Army of the Tennessee, commanded by Maj. Gen. William Tecumseh Sherman, along with two corps from the Army of the Potomac under Maj. Gen. Joseph Hooker. Ulysses S. Grant, now in overall command of Union forces in the west under the newly created Military Division of the Mississippi, replaced Rosecrans in command with George H. Thomas; Grant had command of the combined Union forces. During the early morning hours of October 27, Union forces captured Brown's Ferry, which opened a supply route to Alabama; A Confederate counterattack at Wauhatchie during the night of October 28–29 tried to recapture the ferry but failed. Bragg then on November 5 sent Longstreet's corps to Knoxville and nearly all of his cavalry away, reducing his army's strength; Bragg hoped that Grant would be forced to detach part of his own force to relieve the Union garrison at the city. The final Union attack on the Confederate army started November 24, when Hooker captured Lookout Mountain and threatened the Confederate left flank. The next day, Sherman attacked the Confederate right flank on Missionary Ridge but was stalemated. To help Sherman and to draw Confederate units from the right, Grant ordered a demonstration against the Confederate center. This demonstration by Thomas turned into a full-fledged attack which broke through the Confederate line. Bragg retreated back into north Georgia, regrouping around Dalton. His request to be relieved was accepted on December 1. Hardee temporarily took command of the army, but refused an offer or permanent command. Instead Davis appointed Joseph Johnston to command the army in December 1863.

1864
During the winter of 1864, the army went through other command changes: John B. Hood took command of the Second Corps, while Polk was transferred to the army in May with the Army of Mississippi, which was re-designated the Third Corps. In the 1864 Atlanta Campaign, Johnston faced the combined Northern armies of Maj. Gen. William T. Sherman, whose orders were to destroy the Army of Tennessee, with the capture of Atlanta as the secondary objective. Johnston, who felt the continued existence of his army was more important than protecting territory, tended to avoid battle with Sherman. During May and early June, Johnston took up several defensive positions but withdrew from each after Sherman outflanked each position. Polk was killed at Pine Mountain on June 14; he was temporarily replaced by W. W. Loring until July, when A. P. Stewart took command of the corps. Johnston's retreats caused impatience among the Confederate leadership in Richmond, particularly Confederate President Jefferson Davis, who had never gotten on well with Johnston, and feared that Johnston was planning to abandon Atlanta without a fight. Following Sherman's outflanking of Johnston's Line along the Chattahoochee River, forcing Johnston back on Atlanta itself, Johnston was replaced by Hood on July 9. Stephen D. Lee was reassigned from Mississippi to take command of the Second Corps. Hood launched several attacks on Sherman's forces around Atlanta, including at Peachtree Creek, Atlanta, and Ezra Church, but each attack failed. Sherman was able to cut Hood's last railroad supply line following the Battle of Jonesboro on September 1, which forced Hood to abandon the city the following day.

Hood then retreated southwest of Atlanta, first to Lovejoy's Station before stopping at Palmetto; there he met with Davis and P.G.T. Beauregard, who had just been appointed commander of the Military Division of the West. Hardee was transferred to take command of the Department of South Carolina, Georgia, and Florida, while Frank Cheatham took command of Hardee's Corps. Davis approved Hood's plan to attack Sherman's supply lines north of Atlanta; if Sherman followed him, Hood could then compel Sherman to attack him on ground of his own choosing. Hood started north at the end of September, capturing several Union railroad garrisons and destroying several miles of tracks. When Sherman followed the Confederates, Hood started moving west into Alabama instead of fighting in northern Georgia. By the end of October, Sherman decided to give up his pursuit of Hood and instead launched his March to the Sea. Instead of following Sherman's forces, Hood decided to head back north into Tennessee. Wheeler's cavalry corps was detached to Georgia and the Carolinas to fight Sherman's advance; Forrest's corps was then attached to Hood's army. The army reached Tuscumbia on the Tennessee River but a lack of supplies and the need to repair the railroad to the city in order to accumulate supplies prevented the army from crossing the river until November 20. Hood was faced in Middle Tennessee by Thomas and the Army of the Cumberland. Hood tried to trap part of the Union army under John M. Schofield near Columbia but failed; he then tried to march past Schofield and reach Nashville first before any Union reinforcements reached the city. However, Schofield, detecting Hood's march, ordered a retreat back to Nashville and managed to avoid being cut off at Spring Hill; despite Hood's orders that Confederate forces seize the Nashville Turnpike. Hood caught up with Schofield at Franklin and ordered an immediate frontal assault, despite only having two of his three infantry corps present; he also ignored the advice of his subordinates to outflank the Union fortifications and avoid a head-on attack. During the resulting battle, Hood lost 7,000 men, almost a quarter of his strength, including six generals killed or mortally wounded, another six wounded, and one captured. but continued to advance north into Middle Tennessee, where he attempted to besiege Nashville. He deployed the Confederate army along a range of hills and ridges south of the city in a line for a total of four miles and started digging entrenchments and redoubts. Cheatham's corps was on the right, Lee's corps in the center, and Stewart's corps on the left. Since there was a total of 21,000 men present in the army, Hood was unable to completely surround the city; the Confederate left was four miles from the Cumberland River, while the right was one mile from the river. On December 15, Thomas's troops launched their attack, feinting towards the Confederate right while the main assault fell on the Confederate left. Lee's corps was driven from its defensive works, forcing Hood to retreat to another line of hills to the south. Cheatham's corps was on the left, Stewart's corps in the center, and Lee's corps on the right. Thomas attacked again the next afternoon, using another feint against the Confederate right while launching another flanking attack against the Confederate left. Cheatham's and Stewart's corps were routed, while Lee's corps served as the rear guard as the Confederates retreated from the field. Hood decided to abandon the state due to the poor state of the army. Forrest's cavalry, along with eight brigades of infantry, formed the rear guard. The army initially retreated to Corinth but since the railroad was too damaged to supply the army, Hood ordered a further retreat to Tupelo. According to Robert Bevier of the 5th Missouri Infantry, "the Army of Tennessee ceased to exist" after completing the retreat from Nashville. While the army did not actually "cease to exist," Bevier's comment provides insight into the army's morale at that time.

1865
Hood resigned his command in January, and was briefly replaced by Richard Taylor. During late January and February, the army was transferred to the Carolinas, where it joined other Confederate forces fighting against Sherman's troops marching through the Carolinas. Stewart commanded the army during this time, with William W. Loring in command of Stewart's Corps, D. H. Hill commanding Lee's corps, and William B. Bate commanding Cheatham's corps (both Lee and Cheatham were still traveling from Mississippi). Wheeler's cavalry corps operated as part of Wade Hampton's cavalry command. General Joseph E. Johnston was given command of the Confederate forces in the region, which he dubbed the Army of the South.

At this time, the Army of Tennessee was reduced to only 4,500 men and lacked many supplies, including weapons, artillery, and wagons, and suffered from desertion along the way east from Mississippi. In very few weeks Johnston was able to rebuild this army into a force that could provide serious resistance to Sherman's advancing army.

Parts of the Army of Tennessee fought in several small engagements during the Carolinas Campaign, including Wise's Forks. The entire army fought at the Battle of Bentonville from March 19 to 21, when Johnston attacked one wing of Sherman's army, hoping to crush it before Sherman's other wing could arrive. In accordance with Johnston's plan, Stewart positioned his forces on the Confederate right wing facing south, with Loring on the left, Hill in the center, and Bate on the right. Johnston launched his attack shortly after 3 p.m. Stewart drove back the left wing of the Union XIV Corps, capturing three cannons and several hundred prisoners, but the army became disorganized as a result and the attack had to be temporarily halted for the army to reform. Part of the army was sent to assist the Confederate left wing and the rest attacked the Union XX Corps with troops from William J. Hardee's command; the Union troops were able to repulse each attack. During the night, Sherman brought his other wing to the battlefield, forcing Johnston to retreat back to the Confederate starting positions and refusing his flank in order to protect his line of retreat; Stewart's men occupied the Confederate center.

Johnston retreated during the night of March 21 and moved through Morrisville before arriving near Smithfield, North Carolina. During the three-week encampment around Smithfield, Johnston reorganized his force into a single army, adopting the name of the Army of Tennessee for the combined forces. Most of the regiments were consolidated into single units, while the infantry was divided into three corps commanded by Hardee, Stewart, and Lee; Hampton was given command of the cavalry corps, while Wheeler remained in command of the divisions formerly in his corps. The artillery was reorganized from sixteen batteries into seven batteries of four cannons each. Johnston's total strength was about 30,400 men.

When Sherman started after Johnston on April 10, Johnston retreated through Raleigh, North Carolina, abandoning the city on April 12 before continuing westward along the North Carolina Railroad to Hillsborough; he planned to surrender but thought that the Confederacy could get better terms if he negotiated from a position of strength. Johnston and Sherman met and negotiated terms of surrender on April 17 and 18 at the Bennett Place near Durham Station, North Carolina; Sherman not only accepted the surrender of the Army of Tennessee but promised to recognize the Confederate state governments. These terms were immediately rejected by the Union government, forcing Sherman and Johnston to negotiate a new agreement. The new terms of surrender, signed on April 26, were modeled on the terms given at Appomattox Court House and included not only the Army of Tennessee but also all other Confederate forces in Florida, Georgia, South Carolina, and North Carolina; the number of Confederate troops included in the surrender totaled almost 90,000 men.

Corps organization

 * First Corps
 * Second Corps
 * Third Corps
 * Forrest's Cavalry Corps — Nathan Bedford Forrest

Major battles and campaigns

 * Confederate Heartland Offensive
 * Battle of Stones River
 * Chickamauga Campaign
 * Battles of Chattanooga
 * Atlanta Campaign
 * Franklin-Nashville Campaign
 * Carolinas Campaign

title: Army of Tennessee


text:
1705 in Canada

Events from the year 1705 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Governor of Acadia: Jacques-François de Monbeton de Brouillan
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Daniel d'Auger de Subercase

Events

 * Jacques Raudot becomes co-Intendant of New France with his son Antoine-Denis Raudot.
 * Anthony Beale was appointed governor of the Hudson's Bay Company for Canada, replacing John Fullartine.

Deaths

 * Louis Hennepin, Récollet missionary, explorer (born 1626)

title: 1705 in Canada


text:
1706 in Canada

Events from the year 1706 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Governor of Acadia: Jacques-François de Monbeton de Brouillan then Daniel d'Auger de Subercase
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Daniel d'Auger de Subercase then Philippe Pastour de Costebelle

Events

 * In 1706, the census of New France was 16,417.

Births

 * February 2, 1706: Claude-Godefroy Coquart, missionary (died 1765)
 * August 21, 1706: Pierre Nicolas d'Incarville, French Jesuit and amateur botanist (died 1757)
 * James Abercrombie, British Army general and commander-in-chief of forces in North America during the French and Indian War (died 1781)

Deaths

 * July 9, 1706: Pierre Le Moyne d'Iberville: Canadian-born French explorer who established settlements in what is now southern Louisiana (born 1661).
 * October 11, 1706: Marguerite Bourdon (religious order name, Mother Saint-Jean-Baptiste): one of the foundresses of the Hôpital Général in Quebec; known for her work with the poor (born October 12, 1642).
 * November 25, Jacques Le Ber merchant and seigneur in Montreal, New France.

title: 1706 in Canada


text:
1707 in Canada

Events from the year 1707 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * English, Scottish and Irish Monarch (until May 1, 1707), British and Irish Monarch (beginning May 1, 1707): Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Governor of Acadia: Daniel d'Auger de Subercase
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Philippe Pastour de Costebelle

Events

 * Port Royal is attacked twice by the English from Massachusetts.

Deaths

 * Jean-Vincent d'Abbadie de Saint-Castin (born 1652)

title: 1707 in Canada


text:
1709 in Canada

Events from the year 1709 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * British and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Governor of Acadia: Daniel d'Auger de Subercase
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Philippe Pastour de Costebelle

Events

 * In New France, slavery becomes legal.

Births

 * September 7 (O.S. September 18 - Dr. Samuel Johnson born in Lichfield, Staffordshire. (died 1784)
 * September 26 - Jean-Louis Le Loutre, priest, Spiritan, and missionary (died 1772)

Deaths

 * August - Robert Giguère, pioneer in New France and founder of Sainte-Anne-de-Beaupré (born 1616)
 * September 9 - Jean-Baptiste Legardeur de Repentigny (born 1632)

Historical documents
Intendant's ordinance proclaims Panis and Blacks who have been purchased are property to be known as slaves (Note: "savages" used)

"Inhabitants remaining[...]are in a very bad condition" - Report to Queen Anne of aftermath of French attack on St. John's, Newfoundland

"Rotten and decay'd" - Indigenous spies sent by New York government report Canadian fortifications (except at Quebec City) are poor

"So great a plague to all Plantations in America" - New Englanders eager to attack Port Royal and its "nest of spoilers and robbers"

Inhabitants of Buoys Island (off Ferryland, Newfoundland) get evacuation offer but stay to meet possible third French attack

title: 1709 in Canada


text:
1710 in Canada

Events from the year 1710 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * British and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Colonial Governor of Louisiana: Daniel d'Auger de Subercase
 * Governor of Nova Scotia: Samuel Vetch
 * Governor of Plaisance: Philippe Pastour de Costebelle

Events

 * The English recapture Acadia, this time permanently, and rename it Nova Scotia.
 * Francis Nicholson captures Port Royal for England.
 * The English take Port Royal and name it Annapolis Royal.
 * Three Mohawk chiefs and one Mahican are received in Queen Anne's court in England as the Four Kings of the New World.

Births

 * October 7 - François-Josué de la Corne Dubreuil, a soldier and trader. (died 1753)
 * July 23 - Jonathan Belcher, lawyer, chief justice, and lieutenant governor of Nova Scotia (died 1776)

Historical documents
Squadron of Royal Navy ships and transports with 2,000 troops takes Port Royal from French garrison

Speaking to Queen Anne in London, Mohican and Kanien’kéhà:ka chiefs request conquest of Canada for their better hunting and trade

Haudenosaunee "inconstant in their Tempers, crafty, timorous, but quick of Apprehension, and very ingenious in their Way" (Note: stereotypes)

Governor Dudley says taking Canada and Nova Scotia will capture naval stores trade entirely and safeguard inland settlement

Argument for autumn offensive against Canada includes benefits of fairer winds and higher (but still ice-free) water

Detailed list of armaments and personnel in Canada from Riviere du Loup to Cataraqui on Lake Ontario

"A malignant fever[...]was very general both in Quebec and in the surrounding country [and] carried off a vast number of persons"

France has encroached on Newfoundland trade to point that "their riches and naval power[...]make all Europe stand in fear of them"

Newfoundlanders' work in fishery and demand for goods is strong, but conditions "very deplorable" from lack of protection from French

Geography of Ferryland, Newfoundland makes it excellent prospect for fortification to protect "every ship, stage, house and storehouse"

Mayors of English towns report how many ships will go to Newfoundland this year, and how much Royal Navy protection will be needed

title: 1710 in Canada


text:
1711 in Canada

Events from the year 1711 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * British and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Nova Scotia: Jean-Baptiste Le Moyne de Bienville
 * Governor of Plaisance: Philippe Pastour de Costebelle

Events

 * 1711-13 - Tuscarora War on North Carolina frontier fought between British settlers and Tuscarora Indians. Under the English Col. John Barnwell, then Col. James Moore, the Tuscarora Nation was repeatedly attacked, its chiefs tortured, its people sold (10 pounds sterling each) into slavery. The survivors fled northward and settled among the Haudenosee (Iroquois) 5 Nations.

Births

 * June 8 – Charles Morris, Canadian judge (d. 1781)
 * June 16 – François-Louis de Pourroy de Lauberivière, bishop of Quebec (died 1740), born in Grenoble, France.
 * August 19 – Daniel Liénard de Beaujeu, Canadian officer during the Seven Years' War (d. 1755)

title: 1711 in Canada


text:
1712 in Canada

Events from the year 1712 in Canada.

Incumbents

 * French Monarch: Louis XIV
 * British and Irish Monarch: Anne

Governors

 * Governor General of New France: Philippe de Rigaud Vaudreuil
 * Colonial Governor of Louisiana: Jean-Baptiste Le Moyne de Bienville
 * Governor of Nova Scotia: Samuel Vetch then Francis Nicholson
 * Governor of Plaisance: Philippe Pastour de Costebelle

Events

 * 1712-34 - Fox resistance against the French in the Great Lakes area. Fox Wars begin.

title: 1712 in Canada


text:
Domain (ring theory)

In algebra, a domain is a nonzero ring in which ab = 0 implies a = 0 or b = 0. (Sometimes such a ring is said to "have the zero-product property".) Equivalently, a domain is a ring in which 0 is the only left zero divisor (or equivalently, the only right zero divisor). A commutative domain is called an integral domain. Mathematical literature contains multiple variants of the definition of "domain".

Examples and non-examples

 * The ring $$\mathbb{Z}/6\mathbb{Z}$$ is not a domain, because the images of 2 and 3 in this ring are nonzero elements with product 0. More generally, for a positive integer $$n$$, the ring $\mathbb{Z}/n\mathbb{Z}$ is a domain if and only if $$n$$ is prime.
 * A finite domain is automatically a finite field, by Wedderburn's little theorem.
 * The quaternions form a noncommutative domain. More generally, any division ring is a domain, since every nonzero element is invertible.
 * The set of all Lipschitz quaternions, that is, quaternions of the form $$a+bi+cj+dk$$ where a, b, c, d are integers, is a noncommutative subring of the quaternions, hence a noncommutative domain.
 * Similarly, the set of all Hurwitz quaternions, that is, quaternions of the form $$a+bi+cj+dk$$ where a, b, c, d are either all integers or all half-integers, is a noncommutative domain.
 * A matrix ring Mn(R) for n ≥ 2 is never a domain: if R is nonzero, such a matrix ring has nonzero zero divisors and even nilpotent elements other than 0. For example, the square of the matrix unit E12 is 0.
 * The tensor algebra of a vector space, or equivalently, the algebra of polynomials in noncommuting variables over a field, $$ \mathbb{K}\langle x_1,\ldots,x_n\rangle, $$ is a domain. This may be proved using an ordering on the noncommutative monomials.
 * If R is a domain and S is an Ore extension of R then S is a domain.
 * The Weyl algebra is a noncommutative domain.
 * The universal enveloping algebra of any Lie algebra over a field is a domain. The proof uses the standard filtration on the universal enveloping algebra and the Poincaré–Birkhoff–Witt theorem.

Group rings and the zero divisor problem
Suppose that G is a group and K is a field. Is the group ring R = K[G] a domain? The identity

 * $$ (1-g)(1+g+\cdots+g^{n-1})=1-g^n,$$

shows that an element g of finite order n > 1 induces a zero divisor 1 − g in R. The zero divisor problem asks whether this is the only obstruction; in other words,

 * Given a field K and a torsion-free group G, is it true that K[G] contains no zero divisors?

No counterexamples are known, but the problem remains open in general (as of 2017).

For many special classes of groups, the answer is affirmative. Farkas and Snider proved in 1976 that if G is a torsion-free polycyclic-by-finite group and char K = 0 then the group ring K[G] is a domain. Later (1980) Cliff removed the restriction on the characteristic of the field. In 1988, Kropholler, Linnell and Moody generalized these results to the case of torsion-free solvable and solvable-by-finite groups. Earlier (1965) work of Michel Lazard, whose importance was not appreciated by the specialists in the field for about 20 years, had dealt with the case where K is the ring of p-adic integers and G is the pth congruence subgroup of GL(n, Z).

Spectrum of an integral domain
Zero divisors have a topological interpretation, at least in the case of commutative rings: a ring R is an integral domain if and only if it is reduced and its spectrum Spec R is an irreducible topological space. The first property is often considered to encode some infinitesimal information, whereas the second one is more geometric.

An example: the ring k[x, y]/(xy), where k is a field, is not a domain, since the images of x and y in this ring are zero divisors. Geometrically, this corresponds to the fact that the spectrum of this ring, which is the union of the lines x = 0 and y = 0, is not irreducible. Indeed, these two lines are its irreducible components.

title: Domain (ring theory)