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The Hubble constant is most frequently quoted in km/s/Mpc, which gives the speed of a galaxy 1 megaparsec (3.09 × 10 19 km) away as 70 km/s. Simplifying the units of the generalized form reveals that H 0 specifies a frequency (SI unit: s −1), leading the reciprocal of H 0 to be known as the Hubble time (14.4 billion years). The Hubble ...
In statistics, the 68–95–99.7 rule, also known as the empirical rule, and sometimes abbreviated 3sr or 3 σ, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: approximately 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean ...
The apparent plural form in English goes back to the Latin neuter plural mathematica , based on the Greek plural ta mathēmatiká (τὰ μαθηματικά) and means roughly "all things mathematical", although it is plausible that English borrowed only the adjective mathematic(al) and formed the noun mathematics anew, after the pattern of ...
The number π (/ p aɪ / ⓘ; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.
PZT is a ceramic made from a combination of powders of PbO2, ZrO2, and TiO2 (hence PZT) in a certain ratio of about 0.52:0.48 of Zr:Ti to obtain the optimum piezoelectric effect. The powders have to be mixed & heated to a certain temperature to get them to form the new structure (the perovskite structure) of PZT--calcination & sintering.
[2] [29] [30] [31] According to these biographers, Pythagoras's father was not born on the island, although he got naturalized there, [30] but according to Iamblichus he was a native of the island. [32]
As the number of protons increases, so does the ratio of neutrons to protons necessary to ensure a stable nucleus (see graph at right). For example, although the neutron:proton ratio of 3 2 He is 1:2, the neutron:proton ratio of 238 92 U is greater than 3:2. A number of lighter elements have stable nuclides with the ratio 1:1 (Z = N). The ...
Changchun [a] is the capital and largest city of Jilin Province in China. [8] Lying in the center of the Songliao Plain, Changchun is administered as a sub-provincial city, comprising 7 districts, 1 county and 3 county-level cities. [9]