Antimatter

In particle physics, antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but opposite charges, as well as other particle properties such as lepton and baryon numbers and quantum spin. Collisions between particles and antiparticles lead to the annihilation of both, giving rise to variable proportions of intense photons (gamma rays), neutrinos, and less massive particle–antiparticle pairs. The total consequence of annihilation is a release of energy available for work, proportional to the total matter and antimatter mass, in accord with the mass–energy equivalence equation, E = mc².

Antiparticles bind with each other to form antimatter, just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements. Studies of cosmic rays have identified both positrons and antiprotons, presumably produced by collisions between particles of ordinary matter. Satellite-based searches of cosmic rays for antideuteron and antihelium particles have yielded nothing.

Anno Domini

The term anno Domini is Medieval Latin, which means in the year of the Lord but is often translated as in the year of our Lord. It is occasionally set out more fully as anno Domini nostri Iesu (or Jesu) Christi ("in the year of Our Lord Jesus Christ"). The terms anno Domini (AD or A.D.) and before Christ (BC or B.C.) are used to label or number years in the Julian and Gregorian calendars.

This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525, but was not widely used until after 800.

The Gregorian calendar is the most widely used calendar in the world today. For decades, it has been the unofficial global standard, adopted in the pragmatic interests of international communication, transportation, and commercial integration, and recognized by international institutions such as the United Nations.

DH

DH, Dh or dh may refer to:

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H.D.

Hilda "H.D." Doolittle (September 10, 1886 – September 27, 1961) was an American poet, novelist, and memoirist known for her association with the early 20th century avant-garde Imagist group of poets such as Ezra Pound and Richard Aldington. She published under the pen name of H.D..

H.D. was born in Bethlehem, Pennsylvania, in 1886 and moved to London in 1911, where her publications earned her a central role within the then emerging Imagist movement. A charismatic figure, she was championed by the modernist poet Ezra Pound, who was instrumental in building and furthering her career. From 1916–17, she acted as the literary editor of the Egoist journal, while her poetry appeared in the English Review and the Transatlantic Review. During the First World War, H.D. suffered the death of her brother and the breakup of her marriage to the poet Richard Aldington, and these events weighed heavily on her later poetry. Glenn Hughes, an authority on Imagism, wrote that 'her loneliness cries out from her poems'. She had a deep interest in Ancient Greek literature, and her poetry often borrowed from Greek mythology and classical poets. Her work is noted for its incorporation of natural scenes and objects, which are often used to emote a particular feeling or mood.

Joel Hoffman

Joel Hoffman may refer to: