The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination.
A hypothetical form of energy that fills all the space and tends to increase the rate of expansion of the Universe. Assuming the existence of dark energy is a way to explain recent observations that t
he Universe appears to be expanding at an increasing rate. Dark energy seems to be a kind of anti-gravity force and is supposed to be related to vacuum energy. Where gravity pulls things together at the more local level, dark energy tears them apart on the grander scale. The acceleration equation, one of Einstein's equations for the homogeneous Universe, indicates that if the Universe is accelerating, the pressure of the driving component should be strongly negative. The first indication of dark energy was provided by the observation of Type Ia supernovae. Other probes of dark energy are: baryon acoustic oscillations, weak gravitational lensing, and clusters of galaxies. In the standard model of cosmology, dark energy currently accounts for almost 74% of the total mass-energy of the Universe. Two proposed forms for dark energy are the cosmological constant and exotic component such as quintessence.
Matter that has no radiation and therefore cannot be detected directly, but whose presence can be inferred from dynamical phenomena produced by its gravitational influence. The existence of dark matte
r is deduced mainly from the rotational speeds of galaxies, velocities of galaxies in clusters, gravitational lensing by galaxy clusters, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter plays also a central role in cosmic structure formation. There exists a large number of non-baryonic dark matter candidates. They include, the hypothetical stable particles WIMPs, neutralinos, axions, gravitinos, etc. Among unstable candidates are gravitinos with mild R-parity violation and sterile neutrinos.
Matter that has no radiation and therefore cannot be detected directly, but whose presence can be inferred from dynamical phenomena produced by its gravitational influence. The existence of dark matte
r is deduced mainly from the rotational speeds of galaxies, velocities of galaxies in clusters, gravitational lensing by galaxy clusters, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter plays also a central role in cosmic structure formation. There exists a large number of non-baryonic dark matter candidates. They include, the hypothetical stable particles WIMPs, neutralinos, axions, gravitinos, etc. Among unstable candidates are gravitinos with mild R-parity violation and sterile neutrinos.
Dark gaseous ejections on the Sun visible in Ha. They usually originate from small subflare-like brightenings. Material is usually seen to be ejected, then decelerate at a gravitational rate, and to f
low back to the point of origin. DSDs can occur intermittently for days from an active region.
The Darwin Core is body of standards. It includes a glossary of terms (in other contexts these might be called properties, elements, fields, columns, attributes, or concepts) intended to facilitate th
e sharing of information about biological diversity by providing reference definitions, examples, and commentaries. The Darwin Core is primarily based on taxa, their occurrence in nature as documented by observations, specimens, samples, and related information. Included are documents describing how these terms are managed, how the set of terms can be extended for new purposes, and how the terms can be used. The normative document for the terms [RDF-NORMATIVE] is written in the Resource Description Framework (RDF) and is the definitive resource to understand the term definitions and their relationships to each other. The Simple Darwin Core [SIMPLEDWC] is a specification for one particular way to use the terms - to share data about taxa and their occurrences in a simply structured way - and is probably what is meant if someone suggests to "format your data according to the Darwin Core". (see: http://rs.tdwg.org/dwc/)