romikgosai/squad_modified_2 huggingface dataset:
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.

Q1: When is the next hypothetical mission to Neptune?
A1: late 2020s
Q2: What about Neptune did NASA propose in 2003 in their "Vision Missions Studies"?
A2: Neptune Orbiter with Probes
Q3: When will Argo be launched?
A3: 2019
Q4: What will Argo visit?
A4: Jupiter, Saturn, Neptune, and a Kuiper belt object
Q5: When can we expect Argo to visit Triton?
A5: 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.

Q1: What is of the factors the capital cost of electrification system depends on?
A1: maintenance
Q2: How do some locomotives function in order to be more flexible in operation?
A2: can switch to different supply voltages
Q3: What are two types of revenue obtained through railway transportation?
A3: freight and passenger traffic
Q4: What is the main disadvantage of railway electrification?
A4: 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.

Q1: What is used to haul passengers cars?
A1: electric locomotives
Q2: How is electricity being generated for electric locomotives?
A2: generating stations
Q3: What entity provides distribution lines, switches and transformers?
A3: 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.

Q1: What is the principal alternative to electric railways?
A1: diesel engine
Q2: What locomotives are usually more reliable?
A2: Electric locomotives
Q3: What do some electric traction systems provide?
A3: regenerative braking
Q4: What type of fuel do diesel locomotives use?
A4: petroleum
Q5: What is one of the sources electricity is being generated from?
A5: 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.

Q1: What is a safety hazard to track workers?
A1: voltages on contact wires
Q2: What issue can complicate electric railway service?
A2: different supply voltages and frequencies,
Q3: What is a safer alternative to third rails?
A3: Overhead wires
Q4: Why overhead wires are not being widely used?
A4: 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.

Q1: What is speed limit for railways?
A1: variable speeds
Q2: Why is DC motor being used more than AC type?
A2: conversion was not well developed
Q3: What are two types of railway transportation still use DC motor?
A3: 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.)

Q1: Why do motors have little space for insulation?
A1: low voltage ratings
Q2: Why 1kV voltage is almost always used by rail systems?
A2: safety reasons
Q3: What is most common volatage range used by railway system?
A3: below 1 kV
Q4: Which system uses higher voltages?
A4: overhead wires
Q5: Is "low" voltage used by trains safe for people?
A5: 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.

Q1: What type of electric power garantees lesser loss?
A1: DC
Q2: Which type of supply for electric motors creates electromagnetic radiation?
A2: AC
Q3: Which type of power does require three-phase transmission?
A3: AC
Q4: What can electromagnetic radiation interfere with?
A4: signalling and communications
Q5: Where was an experimental 6kV DC railway built?
A5: 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.

Q1: What is most common voltage for DC supply?
A1: 1,500 V
Q2: How many narrow-gauge lines in Slovakia?
A2: two
Q3: What railway line is DC being used in Portugal?
A3: the Cascais Line
Q4: Where in India line has been converted to AC?
A4: 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.

Q1: What voltage is being used in railway system of South Africa and Chile?
A1: 3 kV DC
Q2: Besides using 3kV DC what other power type is used in the former Soviet Union countries?
A2: 25 kV 50 Hz AC
Q3: What was New Jersey Transit called before?
A3: Western Railroad
Q4: What does the railway system of US use DC or AC?
A4: 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.

Q1: What type is mostly used third rail or overhead wires?
A1: overhead wires
Q2: Is trird rail system being used exclusively with AC or DC ?
A2: DC distribution
Q3: What depth does the alternating current penetrate in a steel rail?
A3: skin depth
Q4: What is more prefferable for subway lines?
A4: Third rail
Q5: What is physically more compact tird rail or overhead wires?
A5: 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.

Q1: Why DC system can effect the speed of trains?
A1: low voltages
Q2: Can DC systems use low-level platform?
A2: cannot
Q3: Besides speed and size what else the low voltage of DC system can effect?
A3: air-conditioning
Q4: What is the speed limit for third rail system trains?
A4: 160 km/h
Q5: What can become unreliable if the speed exceeds the limit of 100 mph for DC system trains?
A5: 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.

Q1: What is the other name for the street trams?
A1: streetcars
Q2: Where is third rail situated in the street trams system?
A2: below street level
Q3: What area in US discontinued using overhead wires for streetcars in 1962?
A3: Washington, D.C.
Q4: What external and weather factors can effect conduit slot?
A4: leaves and snow
Q5: What are the main reasons the conduit lines were converted to overhead  wire system?
A5: 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.

Q1: What year the "second generation" of tram system began to operate in France?
A1: 2003
Q2: When was the original system discontinued?
A2: 1958
Q3: How is the circuit of the third rail divided?
A3: energized segment
Q4: Does energized segment of third rail pose the threat to pedestrians if uncovered?
A4: 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.

Q1: What type of system does London Underground use?
A1: four-rail system
Q2: What is the purpose of the forth rail?
A2: carries the electrical return
Q3: What is the volatage surge of the third rail of London Underground system?
A3: +420v DC
Q4: What is the voltage of the return rail?
A4: −210v DC
Q5: Where was the system similar to London Underground used as well?
A5: Milan
The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.

Q1: What danger can return currents cause?
A1: electrolytic damage
Q2: How are stray earth currents kept to a manageable levels?
A2: by using resistors
Q3: What insures minimal current leak during power rails instalation?
A3: ceramic chairs
Q4: How did return current effect water and gas in iron pipes?
A4: water and gas mains
Q5: What is the crucial advantage of four-rail system?
A5: running rail carries any current
On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply. These routes were originally solely electrified on the four-rail system by the LNWR before National Rail trains were rewired to their standard three-rail system to simplify rolling stock use.

Q1: Why some sections of Bakerloo and District lines were rewired to three-rail system?
A1: to simplify rolling stock use
Q2: What is the voltage shared two types of trains UK railroad system?
A2: 660 V
Q3: How did it become possible to share the voltage for different types of train?
A3: the centre rail is connected to the running rails
A few lines of the Paris Métro in France operate on a four-rail power scheme because they run on rubber tyres which run on a pair of narrow roadways made of steel and, in some places, concrete. Since the tyres do not conduct the return current, the two guide rails provided outside the running 'roadways' double up as conductor rails, so at least electrically it is a four-rail scheme. One of the guide rails is bonded to the return conventional running rails situated inside the roadway so a single polarity supply is required. The trains are designed to operate from either polarity of supply, because some lines use reversing loops at one end, causing the train to be reversed during every complete journey. The loop was originally provided to save the original steam locomotives having to 'run around' the rest of the train saving much time. Today, the driver does not have to change ends at termini provided with such a loop, but the time saving is not so significant as it takes almost as long to drive round the loop as it does to change ends. Many of the original loops have been lost as lines were extended.

Q1: Why some lines of Paris Metro have to operate on a four-rail system?
A1: rubber tyres
Q2: What was the solution for the return current problem in Paris Metro?
A2: two guide rails
Q3: What is required in order for the guide rails to operate properly?
A3: a single polarity supply
Q4: How train is able to turn around after each completed journey?
A4: reversing loops
Q5: Why was the reversing loop created?
A5: having to 'run around' the rest of the train
An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.

Q1: How can different range of voltages be supplied for AC locomotives?
A1: multiple taps on the transformer
Q2: What was a disadvantage of DC system?
A2: power-wasting resistors
Q3: What taps can provide lighting supply?
A3: low-voltage transformer windings
Q4: What will AC/DC motor be replaced with?
A4: three-phase induction motor
Q5: What is the main advantage of an induction motor?
A5: can run equally well on DC or AC of any frequency
DC commutating electric motors, if fitted with laminated pole pieces, become universal motors because they can also operate on AC; reversing the current in both stator and rotor does not reverse the motor. But the now-standard AC distribution frequencies of 50 and 60 Hz caused difficulties with inductive reactance and eddy current losses. Many railways chose low AC frequencies to overcome these problems. They must be converted from utility power by motor-generators or static inverters at the feeding substations or generated at dedicated traction powerstations.

Q1: How can DC motor turn universal?
A1: if fitted with laminated pole pieces
Q2: What problems did AC distribution cause?
A2: inductive reactance and eddy current losses
Q3: How do railways try to solve the problem of inductive reactance of AC system?
A3: low AC frequencies
Q4: How can low frequencies be obtained?
A4: converted from utility power