romikgosai/squad_modified huggingface dataset:
An alternative concept is that they formed closer to the Sun, where the matter density was higher, and then subsequently migrated to their current orbits after the removal of the gaseous protoplanetary disc. This hypothesis of migration after formation is favoured, due to its ability to better explain the occupancy of the populations of small objects observed in the trans-Neptunian region. The current most widely accepted explanation of the details of this hypothesis is known as the Nice model, which explores the effect of a migrating Neptune and the other giant planets on the structure of the Kuiper belt.

Questions and answers:
['
Q: If Neptune formed closer to the sun, what is the matter density?
A: higher', "
Q: If Neptune formed closer to the sun, what caused it to migrate to it's current orbit?
A: removal of the gaseous protoplanetary disc", "
Q: What is the most widely accepted explanation of Neptune's formation called?
A: the Nice model", '
Q: What does The Nice model consider effected the migration of Neptune?
A: Kuiper belt.']
Neptune has 14 known moons. Triton is the largest Neptunian moon, comprising more than 99.5% of the mass in orbit around Neptune,[e] and it is the only one massive enough to be spheroidal. Triton was discovered by William Lassell just 17 days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, indicating that it was captured rather than forming in place; it was probably once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiralling inward because of tidal acceleration. It will eventually be torn apart, in about 3.6 billion years, when it reaches the Roche limit. In 1989, Triton was the coldest object that had yet been measured in the Solar System, with estimated temperatures of 38 K (−235 °C).

Questions and answers:
['
Q: How many moons does Neptune have?
A: 14', "
Q: What is Neptune's largest moon?
A: Triton", '
Q: Who discovered Triton? 
A: William Lassell', '
Q: What orbit does Triton have around Neptune? 
A: retrograde orbit', "
Q: What does Triton's orbit suggest about it's relation to Neptune?
A: that it was captured"]
From July to September 1989, Voyager 2 discovered six moons of Neptune. Of these, the irregularly shaped Proteus is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity. Although the second-most-massive Neptunian moon, it is only 0.25% the mass of Triton. Neptune's innermost four moons—Naiad, Thalassa, Despina and Galatea—orbit close enough to be within Neptune's rings. The next-farthest out, Larissa, was originally discovered in 1981 when it had occulted a star. This occultation had been attributed to ring arcs, but when Voyager 2 observed Neptune in 1989, Larissa was found to have caused it. Five new irregular moons discovered between 2002 and 2003 were announced in 2004. A new moon and the smallest yet, S/2004 N 1, was found in 2013. Because Neptune was the Roman god of the sea, Neptune's moons have been named after lesser sea gods.

Questions and answers:
['
Q: What discovered six moons of Neptune in 1989?
A: Voyager 2', '
Q: What is the second most massive Neptunian moon? 
A: Proteus', '
Q: What is notable about the moon Proteus?
A: irregularly shaped', "
Q: Which are Neptune's four innermost moons?
A: Naiad, Thalassa, Despina and Galatea", "
Q: When was Neptune's moon Larissa discovered? 
A: 1981"]
Because of the distance of Neptune from Earth, its angular diameter only ranges from 2.2 to 2.4 arcseconds, the smallest of the Solar System planets. Its small apparent size makes it challenging to study it visually. Most telescopic data was fairly limited until the advent of Hubble Space Telescope (HST) and large ground-based telescopes with adaptive optics (AO). The first scientifically useful observation of Neptune from ground-based telescopes using adaptive optics, was commenced in 1997 from Hawaii. Neptune is currently entering its spring and summer season and has been shown to be heating up, with increased atmospheric activity and brightness as a consequence. Combined with technological advancements, ground-based telescopes with adaptive optics are recording increasingly more detailed images of this Outer Planet. Both the HST and AO telescopes on Earth has made many new discoveries within the Solar System since the mid-1990s, with a large increase in the number of known satellites and moons around the Outer Planets for example. In 2004 and 2005, five new small satellites of Neptune with diameters between 38 and 61 kilometres were discovered.

Questions and answers:
["
Q: What is Neptune's angular diameter range?
A: 2.2 to 2.4 arcseconds", '
Q: The advent of what telescope made it easier to study Neptune?
A: Hubble Space Telescope', '
Q: When was the first useful observation of Neptune from the ground?
A: 1997', '
Q: What seasons are Neptune currently entering?
A: spring and summer', '
Q: What was discovered around Neptune in 2004 and 2005?
A: five new small satellites']
Voyager 2 is the only spacecraft that has visited Neptune. The spacecraft's closest approach to the planet occurred on 25 August 1989. Because this was the last major planet the spacecraft could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, similarly to what was done for Voyager 1's encounter with Saturn and its moon Titan. The images relayed back to Earth from Voyager 2 became the basis of a 1989 PBS all-night program, Neptune All Night.

Questions and answers:
['
Q: What is the only spacecraft to visit Neptune?
A: Voyager 2', '
Q: When did a spacecraft get closest to Neptune?
A: 25 August 1989', '
Q: What near Neptune did a spacecraft visit dangerously close?
A: Triton', '
Q: What program aired on PBS about Neptune?
A: Neptune All Night']
After the Voyager 2 flyby mission, the next step in scientific exploration of the Neptunian system, is considered to be a Flagship orbital mission. Such a hypothetical mission is envisioned to be possible at in the late 2020s or early 2030s. However, there have been a couple of discussions to launch Neptune missions sooner. In 2003, there was a proposal in NASA's "Vision Missions Studies" for a "Neptune Orbiter with Probes" mission that does Cassini-level science. Another, more recent proposal was for Argo, a flyby spacecraft to be launched in 2019, that would visit Jupiter, Saturn, Neptune, and a Kuiper belt object. The focus would be on Neptune and its largest moon Triton to be investigated around 2029. The proposed New Horizons 2 mission (which was later scrapped) might also have done a close flyby of the Neptunian system.

Questions and answers:
['
Q: When is the next hypothetical mission to Neptune?
A: late 2020s', '
Q: What about Neptune did NASA propose in 2003 in their "Vision Missions Studies"?
A: Neptune Orbiter with Probes', '
Q: When will Argo be launched?
A: 2019', '
Q: What will Argo visit?
A: Jupiter, Saturn, Neptune, and a Kuiper belt object', '
Q: When can we expect Argo to visit Triton?
A: 2029']
A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electrification has many advantages but requires significant capital expenditure. Selection of an electrification system is based on economics of energy supply, maintenance, and capital cost compared to the revenue obtained for freight and passenger traffic. Different systems are used for urban and intercity areas; some electric locomotives can switch to different supply voltages to allow flexibility in operation.

Questions and answers:
['
Q: What is of the factors the capital cost of electrification system depends on?
A: maintenance', '
Q: How do some locomotives function in order to be more flexible in operation?
A: can switch to different supply voltages', '
Q: What are two types of revenue obtained through railway transportation?
A: freight and passenger traffic', '
Q: What is the main disadvantage of railway electrification?
A: significant capital expenditure']
Electric railways use electric locomotives to haul passengers or freight in separate cars or electric multiple units, passenger cars with their own motors. Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches and transformers.

Questions and answers:
['
Q: What is used to haul passengers cars?
A: electric locomotives', '
Q: How is electricity being generated for electric locomotives?
A: generating stations', '
Q: What entity provides distribution lines, switches and transformers?
A: railway']
In comparison to the principal alternative, the diesel engine, electric railways offer substantially better energy efficiency, lower emissions and lower operating costs. Electric locomotives are usually quieter, more powerful, and more responsive and reliable than diesels. They have no local emissions, an important advantage in tunnels and urban areas. Some electric traction systems provide regenerative braking that turns the train's kinetic energy back into electricity and returns it to the supply system to be used by other trains or the general utility grid. While diesel locomotives burn petroleum, electricity is generated from diverse sources including many that do not produce carbon dioxide such as nuclear power and renewable forms including hydroelectric, geothermal, wind and solar.

Questions and answers:
['
Q: What is the principal alternative to electric railways?
A: diesel engine', '
Q: What locomotives are usually more reliable?
A: Electric locomotives', '
Q: What do some electric traction systems provide?
A: regenerative braking', '
Q: What type of fuel do diesel locomotives use?
A: petroleum', '
Q: What is one of the sources electricity is being generated from?
A: geothermal']
Disadvantages of electric traction include high capital costs that may be uneconomic on lightly trafficked routes; a relative lack of flexibility since electric trains need electrified tracks or onboard supercapacitors and charging infrastructure at stations; and a vulnerability to power interruptions. Different regions may use different supply voltages and frequencies, complicating through service. The limited clearances available under catenaries may preclude efficient double-stack container service. The lethal voltages on contact wires and third rails are a safety hazard to track workers, passengers and trespassers. Overhead wires are safer than third rails, but they are often considered unsightly.

Questions and answers:
['
Q: What is a safety hazard to track workers?
A: voltages on contact wires', '
Q: What issue can complicate electric railway service?
A: different supply voltages and frequencies,', '
Q: What is a safer alternative to third rails?
A: Overhead wires', '
Q: Why overhead wires are not being widely used?
A: considered unsightly.']
Railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, although such DC can be supplied from an AC catenary via on-board electric power conversion. Since such conversion was not well developed in the late 19th century and early 20th century, most early electrified railways used DC and many still do, particularly rapid transit (subways) and trams. Speed was controlled by connecting the traction motors in various series-parallel combinations, by varying the traction motors' fields, and by inserting and removing starting resistances to limit motor current.

Questions and answers:
['
Q: What is speed limit for railways?
A: variable speeds', '
Q: Why is DC motor being used more than AC type?
A: conversion was not well developed', '
Q: What are two types of railway transportation still use DC motor?
A: rapid transit (subways) and trams']
Motors have very little room for electrical insulation so they generally have low voltage ratings. Because transformers (prior to the development of power electronics) cannot step down DC voltages, trains were supplied with a relatively low DC voltage that the motors can use directly. The most common DC voltages are listed in the previous section. Third (and fourth) rail systems almost always use voltages below 1 kV for safety reasons while overhead wires usually use higher voltages for efficiency. ("Low" voltage is relative; even 600 V can be instantly lethal when touched.)

Questions and answers:
['
Q: Why do motors have little space for insulation?
A: low voltage ratings', '
Q: Why 1kV voltage is almost always used by rail systems?
A: safety reasons', '
Q: What is most common volatage range used by railway system?
A: below 1 kV', '
Q: Which system uses higher voltages?
A: overhead wires', '
Q: Is "low" voltage used by trains safe for people?
A: lethal']
There has, however, been interest among railroad operators in returning to DC use at higher voltages than previously used. At the same voltage, DC often has less loss than AC, and for this reason high-voltage direct current is already used on some bulk power transmission lines. DC avoids the electromagnetic radiation inherent with AC, and on a railway this also reduces interference with signalling and communications and mitigates hypothetical EMF risks. DC also avoids the power factor problems of AC. Of particular interest to railroading is that DC can supply constant power with a single ungrounded wire. Constant power with AC requires three-phase transmission with at least two ungrounded wires. Another important consideration is that mains-frequency 3-phase AC must be carefully planned to avoid unbalanced phase loads. Parts of the system are supplied from different phases on the assumption that the total loads of the 3 phases will even out. At the phase break points between regions supplied from different phases, long insulated supply breaks are required to avoid them being shorted by rolling stock using more than one pantograph at a time. A few railroads have tried 3-phase but its substantial complexity has made single-phase standard practice despite the interruption in power flow that occurs twice every cycle. An experimental 6 kV DC railway was built in the Soviet Union.

Questions and answers:
['
Q: What type of electric power garantees lesser loss?
A: DC', '
Q: Which type of supply for electric motors creates electromagnetic radiation?
A: AC', '
Q: Which type of power does require three-phase transmission?
A: AC', '
Q: What can electromagnetic radiation interfere with?
A: signalling and communications', '
Q: Where was an experimental 6kV DC railway built?
A: the Soviet Union']
1,500 V DC is used in the Netherlands, Japan, Republic Of Indonesia, Hong Kong (parts), Republic of Ireland, Australia (parts), India (around the Mumbai area alone, has been converted to 25 kV AC like the rest of India), France (also using 25 kV 50 Hz AC), New Zealand (Wellington) and the United States (Chicago area on the Metra Electric district and the South Shore Line interurban line). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In Portugal, it is used in the Cascais Line and in Denmark on the suburban S-train system.

Questions and answers:
['
Q: What is most common voltage for DC supply?
A: 1,500 V', '
Q: How many narrow-gauge lines in Slovakia?
A: two', '
Q: What railway line is DC being used in Portugal?
A: the Cascais Line', '
Q: Where in India line has been converted to AC?
A: Mumbai area']
3 kV DC is used in Belgium, Italy, Spain, Poland, the northern Czech Republic, Slovakia, Slovenia, South Africa, Chile, and former Soviet Union countries (also using 25 kV 50 Hz AC). It was formerly used by the Milwaukee Road from Harlowton, Montana to Seattle-Tacoma, across the Continental Divide and including extensive branch and loop lines in Montana, and by the Delaware, Lackawanna & Western Railroad (now New Jersey Transit, converted to 25 kV AC) in the United States, and the Kolkata suburban railway (Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz AC.

Questions and answers:
['
Q: What voltage is being used in railway system of South Africa and Chile?
A: 3 kV DC', '
Q: Besides using 3kV DC what other power type is used in the former Soviet Union countries?
A: 25 kV 50 Hz AC', '
Q: What was New Jersey Transit called before?
A: Western Railroad', '
Q: What does the railway system of US use DC or AC?
A: AC']
Most electrification systems use overhead wires, but third rail is an option up to about 1,200 V. Third rail systems exclusively use DC distribution. The use of AC is not feasible because the dimensions of a third rail are physically very large compared with the skin depth that the alternating current penetrates to (0.3 millimetres or 0.012 inches) in a steel rail). This effect makes the resistance per unit length unacceptably high compared with the use of DC. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.

Questions and answers:
['
Q: What type is mostly used third rail or overhead wires?
A: overhead wires', '
Q: Is trird rail system being used exclusively with AC or DC ?
A: DC distribution', '
Q: What depth does the alternating current penetrate in a steel rail?
A: skin depth', '
Q: What is more prefferable for subway lines?
A: Third rail', '
Q: What is physically more compact tird rail or overhead wires?
A: Third rail']
DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.

Questions and answers:
['
Q: Why DC system can effect the speed of trains?
A: low voltages', '
Q: Can DC systems use low-level platform?
A: cannot', '
Q: Besides speed and size what else the low voltage of DC system can effect?
A: air-conditioning', '
Q: What is the speed limit for third rail system trains?
A: 160 km/h', '
Q: What can become unreliable if the speed exceeds the limit of 100 mph for DC system trains?
A: contact between the shoe and the rail']
Some street trams (streetcars) used conduit third-rail current collection. The third rail was below street level. The tram picked up the current through a plough (U.S. "plow") accessed through a narrow slot in the road. In the United States, much (though not all) of the former streetcar system in Washington, D.C. (discontinued in 1962) was operated in this manner to avoid the unsightly wires and poles associated with electric traction. The same was true with Manhattan's former streetcar system. The evidence of this mode of running can still be seen on the track down the slope on the northern access to the abandoned Kingsway Tramway Subway in central London, United Kingdom, where the slot between the running rails is clearly visible, and on P and Q Streets west of Wisconsin Avenue in the Georgetown neighborhood of Washington DC, where the abandoned tracks have not been paved over. The slot can easily be confused with the similar looking slot for cable trams/cars (in some cases, the conduit slot was originally a cable slot). The disadvantage of conduit collection included much higher initial installation costs, higher maintenance costs, and problems with leaves and snow getting in the slot. For this reason, in Washington, D.C. cars on some lines converted to overhead wire on leaving the city center, a worker in a "plough pit" disconnecting the plough while another raised the trolley pole (hitherto hooked down to the roof) to the overhead wire. In New York City for the same reasons of cost and operating efficiency outside of Manhattan overhead wire was used. A similar system of changeover from conduit to overhead wire was also used on the London tramways, notably on the southern side; a typical changeover point was at Norwood, where the conduit snaked sideways from between the running rails, to provide a park for detached shoes or ploughs.

Questions and answers:
['
Q: What is the other name for the street trams?
A: streetcars', '
Q: Where is third rail situated in the street trams system?
A: below street level', '
Q: What area in US discontinued using overhead wires for streetcars in 1962?
A: Washington, D.C.', '
Q: What external and weather factors can effect conduit slot?
A: leaves and snow', '
Q: What are the main reasons the conduit lines were converted to overhead  wire system?
A: cost and operating efficiency']
A new approach to avoiding overhead wires is taken by the "second generation" tram/streetcar system in Bordeaux, France (entry into service of the first line in December 2003; original system discontinued in 1958) with its APS (alimentation par sol – ground current feed). This involves a third rail which is flush with the surface like the tops of the running rails. The circuit is divided into segments with each segment energized in turn by sensors from the car as it passes over it, the remainder of the third rail remaining "dead". Since each energized segment is completely covered by the lengthy articulated cars, and goes dead before being "uncovered" by the passage of the vehicle, there is no danger to pedestrians. This system has also been adopted in some sections of the new tram systems in Reims, France (opened 2011) and Angers, France (also opened 2011). Proposals are in place for a number of other new services including Dubai, UAE; Barcelona, Spain; Florence, Italy; Marseille, France; Gold Coast, Australia; Washington, D.C., U.S.A.; Brasília, Brazil and Tours, France.

Questions and answers:
['
Q: What year the "second generation" of tram system began to operate in France?
A: 2003', '
Q: When was the original system discontinued?
A: 1958', '
Q: How is the circuit of the third rail divided?
A: energized segment', '
Q: Does energized segment of third rail pose the threat to pedestrians if uncovered?
A: no danger']
The London Underground in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails. On the London Underground, a top-contact third rail is beside the track, energized at +420v DC, and a top-contact fourth rail is located centrally between the running rails at −210v DC, which combine to provide a traction voltage of 630v DC. London Underground is now upgrading its fourth rail system to 750v DC with a positive conductor rail energised to +500v DC and a negative conductor rail energised to -250v DC. However, many older sections in tunnels are still energised to 630v DC. The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary or a third rail.

Questions and answers:
['
Q: What type of system does London Underground use?
A: four-rail system', '
Q: What is the purpose of the forth rail?
A: carries the electrical return', '
Q: What is the volatage surge of the third rail of London Underground system?
A: +420v DC', '
Q: What is the voltage of the return rail?
A: −210v DC', '
Q: Where was the system similar to London Underground used as well?
A: Milan']