Problem: 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.
Which type of power does require three-phase transmission?
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Answer: AC

Problem: Although the Palaeologi emperors recaptured Constantinople from the Western Europeans in 1261, they were never able to regain control of much of the former imperial lands. They usually controlled only a small section of the Balkan Peninsula near Constantinople, the city itself, and some coastal lands on the Black Sea and around the Aegean Sea. The former Byzantine lands in the Balkans were divided between the new Kingdom of Serbia, the Second Bulgarian Empire and the city-state of Venice. The power of the Byzantine emperors was threatened by a new Turkish tribe, the Ottomans, who established themselves in Anatolia in the 13th century and steadily expanded throughout the 14th century. The Ottomans expanded into Europe, reducing Bulgaria to a vassal state by 1366 and taking over Serbia after its defeat at the Battle of Kosovo in 1389. Western Europeans rallied to the plight of the Christians in the Balkans and declared a new crusade in 1396; a great army was sent to the Balkans, where it was defeated at the Battle of Nicopolis. Constantinople was finally captured by the Ottomans in 1453.
In what year did Bulgaria become a vassal of the Ottomans?
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Answer: 1366

Problem: As of the first decade of the 21st century, contemporary neoclassical architecture is usually classed under the umbrella term of New Classical Architecture. Sometimes it is also referred to as Neo-Historicism/Revivalism, Traditionalism or simply neoclassical architecture like the historical style. For sincere traditional-style architecture that sticks to regional architecture, materials and craftsmanship, the term Traditional Architecture (or vernacular) is mostly used. The Driehaus Architecture Prize is awarded to major contributors in the field of 21st century traditional or classical architecture, and comes with a prize money twice as high as that of the modernist Pritzker Prize.
What is awarded to architects who contribute to 21st-century classical architecture?
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Answer:
unanswerable