A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the best-known of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never found in isolation; they can only be found within hadrons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves. There are six different types of quarks, known as flavors: up, down, charm, strange, top, and bottom. Up and down quarks are generally stable and the most common in the universe, whereas charm, strange, top, and bottom quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators). Quarks are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions.
Read the rest of this article: <http://en.wikipedia.org/wiki/Quark> _______________________________ Today's selected anniversaries: 1830: During the opening of the Liverpool and Manchester Railway , one of the world's first intercity passenger railways in which all the trains were timetabled and operated for most of the distance solely by steam locomotives, British Member of Parliament William Huskisson was struck and killed by the locomotive engine Rocket. <http://en.wikipedia.org/wiki/Liverpool_and_Manchester_Railway> 1831: The John Bull, currently the oldest operable steam locomotive in the world, ran for the first time in New Jersey on the Camden and Amboy Railroad. <http://en.wikipedia.org/wiki/John_Bull_%28locomotive%29> 1835: During the second voyage of HMS Beagle, Charles Darwin reached the Galápagos Islands, where he further developed his theories of evolution. <http://en.wikipedia.org/wiki/Gal%C3%A1pagos_Islands> 1935: Nazi Germany enacted the Nuremberg Laws, which deprived German Jews of citizenship, and adopted a new national flag emblazoned with a swastika. <http://en.wikipedia.org/wiki/Nuremberg_Laws> 2008: The financial crisis of 2007–2009: The global financial-services firm Lehman Brothers filed for bankruptcy while holding over US$600 billion in assets, the largest such filing in U.S. history. <http://en.wikipedia.org/wiki/Bankruptcy_of_Lehman_Brothers> _____________________________ Wiktionary's word of the day: wherewithal (n): The ability and the financial means required to accomplish some task <http://en.wiktionary.org/wiki/wherewithal> ___________________________ Wikiquote quote of the day: If we had no faults we should not take so much pleasure in noting those of others. --François de La Rochefoucauld <http://en.wikiquote.org/wiki/Fran%C3%A7ois_de_La_Rochefoucauld> _______________________________________________ Wikipedia Daily Article mailing list. To unsubscribe, visit: https://lists.wikimedia.org/mailman/listinfo/daily-article-l Questions or comments? Contact [email protected]
