Article: In Eastern Europe, Byzantium revived its fortunes under Emperor Basil I (r. 867886) and his successors Leo VI (r. 886912) and Constantine VII (r. 913959), members of the Macedonian dynasty. Commerce revived and the emperors oversaw the extension of a uniform administration to all the provinces. The military was reorganised, which allowed the emperors John I (r. 969976) and Basil II (r. 9761025) to expand the frontiers of the empire on all fronts. The imperial court was the centre of a revival of classical learning, a process known as the Macedonian Renaissance. Writers such as John Geometres (fl. early 10th century) composed new hymns, poems, and other works. Missionary efforts by both eastern and western clergy resulted in the conversion of the Moravians, Bulgars, Bohemians, Poles, Magyars, and Slavic inhabitants of the Kievan Rus'. These conversions contributed to the founding of political states in the lands of those peoplesthe states of Moravia, Bulgaria, Bohemia, Poland, Hungary, and the Kievan Rus'. Bulgaria, which was founded around 680, at its height reached from Budapest to the Black Sea and from the Dnieper River in modern Ukraine to the Adriatic Sea. By 1018, the last Bulgarian nobles had surrendered to the Byzantine Empire.

Question: During what period did Constantine VII reign?
Ans: 913959

Article: At a certain temperature, (usually between 1,500 F (820 C) and 1,600 F (870 C), depending on carbon content), the base metal of steel undergoes a change in the arrangement of the atoms in its crystal matrix, called allotropy. This allows the small carbon atoms to enter the interstices of the iron crystal, diffusing into the iron matrix. When this happens, the carbon atoms are said to be in solution, or mixed with the iron, forming a single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly, the iron will gradually change into its low temperature allotrope. When this happens the carbon atoms will no longer be soluble with the iron, and will be forced to precipitate out of solution, nucleating into the spaces between the crystals. The steel then becomes heterogeneous, being formed of two phases; the carbon (carbide) phase cementite, and ferrite. This type of heat treatment produces steel that is rather soft and bendable. However, if the steel is cooled quickly the carbon atoms will not have time to precipitate. When rapidly cooled, a diffusionless (martensite) transformation occurs, in which the carbon atoms become trapped in solution. This causes the iron crystals to deform intrinsically when the crystal structure tries to change to its low temperature state, making it very hard and brittle.

Question: What are the characteristics of steel if it is cooled to quickly?
Ans: very hard and brittle

Article: A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses.

Question: What is a solar chimney?
Ans: a passive solar ventilation system

Article: In his early years Popper was impressed by Marxism, whether of Communists or socialists. An event that happened in 1919 had a profound effect on him: During a riot, caused by the Communists, the police shot several unarmed people, including some of Popper's friends, when they tried to free party comrades from prison. The riot had, in fact, been part of a plan by which leaders of the Communist party with connections to Bela Kun tried to take power by a coup; Popper did not know about this at that time. However, he knew that the riot instigators were swayed by the Marxist doctrine that class struggle would produce vastly more dead men than the inevitable revolution brought about as quickly as possible, and so had no scruples to put the life of the rioters at risk to achieve their selfish goal of becoming the future leaders of the working class. This was the start of his later criticism of historicism. Popper began to reject Marxist historicism, which he associated with questionable means, and later socialism, which he associated with placing equality before freedom (to the possible disadvantage of equality).

Question: The 1919 riot involving Popper's comrades was part of what larger political move?
Ans:
a coup