The Doppler effect (or Doppler shift), named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

The Republican Party, also commonly called the GOP (for "Grand Old Party"), is one of the two major contemporary political parties in the United States, the other being the Democratic Party. Founded by anti-slavery activists in 1854, it dominated politics nationally for most of the period from 1860 to 1932. There have been 18 Republican presidents, the first being Abraham Lincoln, serving from 1861 to 1865, and the most recent being Donald Trump who began serving in 2017.

The expert predicted that America's gross domestic product will return to more than 3 percent yearly expansion. For example, Dow Chemical is investing $4 billion in Texas plastics production that will be operational by 2019. Such growth requires cheap oil and natural gas - and "by 2022 or so, the United States will surpass Saudi Arabia in oil output, and Russia in gas." He continued: "The big attraction is the low price of natural gas, the lowest-carbon fossil fuel, which can be produced profitably at about a third the price per unit of energy as other hydrocarbons. That is particularly attractive to chemical companies. It is the raw material for plastics, Styrofoam, tires, sealants, adhesives, films, liquid crystal screens, nylons, polyesters - nearly everything around us."

The title Grandmaster is awarded to chess players by the world chess organization FIDE. Apart from World Champion, Grandmaster is the highest title a chess player can attain. Once achieved, the title is held for life.

Since 1944, the County of Los Angeles Department of Parks and Recreation has been meeting the diverse needs of not only residents, but also visitors from around the world. With over 63,000 acres of parks, gardens, lakes, trails, natural areas, and the world's largest public golf course system, the Department of Parks and Recreation is committed to providing the public with social, cultural, and recreational activities to enjoy the whole year.