All articles A–Z

Dual gauge

Dual gauge, also called mixed gauge or twin gauge, is railway track carrying trains of two different wheel gauges, usually by laying three rails, used in Australia, Spain, and Switzerland.

Sep 23, 2026

Dual Government of Bengal

The Dual Government of Bengal (দ্বৈত শাসন) was a 1765 to 1772 system in which the East India Company collected Bengal's revenue while the Nawab kept administration.

Dual gradient drilling

Dual gradient drilling (DGD) is an offshore technique, part of managed pressure drilling, that maintains two pressure gradients so wellbore pressure matches formation limits better.

Dual graph

The dual graph, or planar dual, of a planar graph has one vertex for each face and one edge for each pair of faces sharing an edge.

Dual in-line package

The dual in-line package (DIP) is an integrated circuit housing with two parallel rows of pins, introduced at Fairchild in 1965 and dominant for roughly two decades.

A dual international cricketer represents one country at full international level in cricket and another sport; Australia's Ellyse Perry, also a Matildas midfielder, played in both cricket and football World Cups.

Dual learning

Dual learning is a machine learning framework that jointly trains two related tasks, such as translating between two languages, so each improves the other from unlabeled data.

Dual licensing

Dual licensing is the practice of releasing the same work, usually software, under two licenses, typically a free license like the GPL plus a paid commercial one.

Dual map

The dual map, also called the transpose, is the linear map between dual spaces that a linear map induces, running in the opposite direction; its matrix is the transpose.

Dual matroid

The dual matroid of a matroid M is the matroid M on the same ground set whose bases are the complements of M's bases, introduced by Hassler Whitney in 1935.

Dual modular redundancy

Dual modular redundancy (DMR) is a fault-tolerance technique that duplicates a module and compares outputs to detect errors, but cannot correct them without external recovery.

Dual module

The dual module of a module M is Hom_R(M, R), the module of linear maps from M to the ring R, generalizing dual vector spaces.

Dual monarchy

The Dual Monarchy was the constitutional structure of Austria-Hungary between 1867 and 1918. It reorganized the Habsburg Monarchy into two states sharing a common ruler and joint ministries.

Dual monarchy of England and France

Dual monarchy of England and France, or Lancastrian dual monarchy: political order created by the Treaty of Troyes (21 May 1420) making Henry V and his heirs kings of both kingdoms, each keeping its own laws; it collapsed with the fall of Paris in 1436.

Dual number

A dual number is an expression of the form a + εb, where ε is nonzero with ε² = 0, introduced by Clifford in 1873 and used in automatic differentiation.

Dual pair of topological vector spaces

A dual pair of topological vector spaces is two vector spaces over the same field with a non-degenerate bilinear form and topologies built from that pairing.

Oct 22, 2026

Dual photoredox–cobaloxime catalysis

Dual photoredox–cobaloxime catalysis is a two-catalyst strategy in organic synthesis, merged in 2015, that pairs a visible-light photoredox catalyst with a cobaloxime, a vitamin B12 mimic.

Dual polarization interferometry

Dual polarization interferometry (DPI) is a label-free optical biosensing technique that measures the thickness, density, and mass of molecular layers adsorbing at a solid–liquid interface in real time.

Dual polyhedron

A dual polyhedron is a polyhedron paired with another so that the faces of one occupy the positions of the vertices of the other, exchanged by reciprocation.

Dual power

Dual power (dvoevlastie) is the 1917 Russian coexistence of the Provisional Government and the Petrograd Soviet, analyzed by Lenin in April 1917 as a transitional, unstable interlocking of two dictatorships resolved by October.

Dual process theory

Dual process theory (Type 1/Type 2, System 1/System 2) is a psychology framework distinguishing fast, automatic, unconscious cognition from slow, deliberative, working-memory-dependent reasoning; originated with Wason and Evans (1974) and widely applied and criticized.

Dual quasar

A dual quasar is a pair of quasars powered by two different supermassive black holes, shining simultaneously in a single merging galaxy system, typically separated by kiloparsecs.

Dual quaternion

A dual quaternion is an eight-component number, formed from two quaternions and the nilpotent dual unit ε, that represents a rigid-body pose, combining rotation and translation compactly.

Dual representation

The dual representation, or contragredient representation, is the representation a group or Lie algebra induces on the dual space of its representation space, preserving the natural pairing.

Dual RNA-seq

Dual RNA-seq is a transcriptomics method that simultaneously sequences host and pathogen RNA from one infected sample, separating the two transcriptomes computationally rather than physically.

Dual SIM

Dual SIM is the capability of a single mobile device to hold and use two SIM subscriptions at once, giving the user two phone numbers on one handset.

Dual space

The dual space of a vector space V is the vector space V of all linear functionals on V, that is, linear maps from V to its scalar field.

Dual staining

Dual staining is a histology and cytology method that detects two different targets, such as antigenic epitopes or RNA sequences, on one tissue section or cell preparation.

Dual Summer and Winter Olympic athletes

Dual Summer and Winter Olympic athletes compete at both Games, usually in different sports; 142 had done so through 2018, with Eddie Eagan the only double gold medalist.