Pion
In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: π) is any of three subatomic particles: π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons (and, more generally, the lightest hadrons), because they are composed of the lightest quarks (the u and d quarks). They are unstable, with the charged pions π+ and π− decaying with a mean lifetime of 26 nanoseconds (6992260000000000000♠2.6×10−8 seconds), and the neutral pion π0 decaying with a much shorter lifetime of 6983840000000000000♠8.4×10−17 seconds. Charged pions most often decay into muons and muon neutrinos, and neutral pions into gamma rays.
The exchange of virtual pions, along with the vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but are produced commonly in high energy accelerators in collisions between hadrons. All types of pions are also produced in natural processes when high energy cosmic ray protons and other hadronic cosmic ray components interact with matter in the Earth's atmosphere. Recently, detection of characteristic gamma rays originating from decay of neutral pions in two supernova remnant stars has shown that pions are produced copiously in supernovas, most probably in conjunction with production of high energy protons that are detected on Earth as cosmic rays.
Pion (disambiguation)
A pion is a type of subatomic particle.
Pion may also refer to:
Protein pigeon homolog
Protein pigeon homolog also known as gamma-secretase activating protein (GSAP) is a protein that in humans is encoded by the PION gene.
Gene
The human PION gene is located on the long (q) arm of chromosome 7 at band 11.23, from base pair 76,778,007 to base pair 76,883,653. Highly conserved PION orthologs have been identified in most vertebrates for which complete genome data are available. More distantly related orthologs are also expressed in insects including the pigeon gene in Drosophila melanogaster that when mutated produces the "pigeon" phenotype. The name of the human PION gene derives the corresponding Drosophila gene.
Protein
The transcribed human pigeon homolog protein is 854 amino acid residues in length. A 16 kDa fragment (GSAP-16K) derived from 121 residues from the C-terminus region of the full length protein is known as the γ-secretase activating protein (GSAP).
Function
γ-secretase activating protein (GSAP) increases β-amyloid production through a mechanism involving its interactions with both γ-secretase and its substrate, the amyloid precursor protein (APP). By binding to both the γ-secretase enzyme and its APP substrate, GSAP increases the affinity and the selectivity of the enzyme for this particular substrate.
Retrospective
Retrospective (from Latin retrospectare, "look back") generally means to take a look back at events that already have taken place. As a noun, retrospective has specific meanings in medicine, software development, popular culture and the arts. It is applied as an adjective, synonymous with the term retroactive, to laws, standards, and awards.
Medicine
A medical retrospective is an examination of a patient's medical history and lifestyle.
Arts and popular culture
An retrospective exhibition presents works from an extended period of an artist's activity. Similarly, a retrospective compilation album is assembled from a recording artist's past material, usually their greatest hits. A television or newsstand special about an actor, politician, or other celebrity will present a retrospective of the subject's career highlights. A leading (usually elderly) academic may be honored with a Festschrift, an honorary book of articles or a lecture series relating topically to a retrospective of the honoree's career. Celebrity roasts good-naturedly mock the career of the guest of honor, often in a retrospective format.
Retrospective (X Marks the Pedwalk album)
Retrospective 88-99 is the name of the third "best-of" album by German industrial music band X Marks the Pedwalk. It was released by Metropolis Records in North America in CD format.
Track listing
Retrospective (Rosanne Cash album)
Retrospective was a 1995 compilation, encapsulating Rosanne Cash's sixteen years with Columbia, released as she was leaving the label. Rather than relying on radio hits, Retrospective focused on lesser known album tracks, unreleased material and live recordings. In the years since, as Columbia has let the majority of Cash's albums go out of print, it has become, along with her Greatest Hits collection, the primary source for listeners to obtain most of her material.
Track listing
References
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