Article: Non-English terms for air defence include the German Flak (Fliegerabwehrkanone, "aircraft defence cannon", also cited as Flugabwehrkanone), whence English flak, and the Russian term Protivovozdushnaya oborona (Cyrillic: ), a literal translation of "anti-air defence", abbreviated as PVO. In Russian the AA systems are called zenitnye (i.e. "pointing to zenith") systems (guns, missiles etc.). In French, air defence is called DCA (Defense contre les aeronefs, "aeronef" being the generic term for all kind of airborne device (airplane, airship, balloon, missile, rocket, etc.)).

Question: How is the Russian term for air defence abbreviated?
Ans: PVO

Article: In tumbling, athletes perform an explosive series of flips and twists down a sprung tumbling track. Scoring is similar to trampolining. Tumbling was originally contested as one of the events in Men's Artistic Gymnastics at the 1932 Summer Olympics, and in 1955 and 1959 at the Pan American Games. From 1974 to 1998 it was included as an event for both genders at the Acrobatic Gymnastics World Championships. The event has also been contested since 1976 at the Trampoline World Championships. Since the recognition of Trampoline and Acrobatic Gymnastics as FIG disciplines in 1999, official Tumbling competitions are only allowed as an event in Trampoline gymnastics meets.

Question: What do athletes perform for tumbling?
Ans: an explosive series of flips and twists down a sprung tumbling track

Article: Ion gauges are used in ultrahigh vacuum. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 103 torr to 1010 torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold cathode gauges are accurate from 102 torr to 109 torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.

Question: Why does a mass spectrometer need to be used with gauge to be accurate at high vacuum gas measurement?
Ans: composition of gases at high vacuums will usually be unpredictable

Article: Shih-Shan Henry Tsai writes that the Yongle Emperor sent his eunuch Yang Sanbao into Tibet in 1413 to gain the allegiance of various Tibetan princes, while the Yongle Emperor paid a small fortune in return gifts for tributes in order to maintain the loyalty of neighboring vassal states such as Nepal and Tibet. However, Van Praag states that Tibetan rulers upheld their own separate relations with the kingdoms of Nepal and Kashmir, and at times "engaged in armed confrontation with them."

Question: Why did the emperor pay a small fortune in gifts?
Ans:
to maintain the loyalty of neighboring vassal states