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Orbital speed
Orbital speed, or orbit velocity, is the speed at which a body travels along its orbit, increasing the closer it is to the central body.
Orbital torque
Orbital torque is a torque on a ferromagnet's magnetization produced when orbital angular momentum generated in an adjacent light metal is converted to spin by spin-orbit coupling.
Orbital torque and orbital Hall effect
The orbital Hall effect generates a transverse current of electron orbital angular momentum from an electric field; orbital torque arises when that current enters a ferromagnet.
Orbital-selective Mott phase
The orbital-selective Mott phase (OSMP) is an intermediate state of a multi-orbital correlated electron system in which some orbitals are Mott localized and others remain metallic.
Orbital-selective Mott transition
The orbital-selective Mott transition (OSMT) is a metal-insulator transition in multiorbital systems where some orbitals become Mott localized while others remain itinerant, with candidates including Ca2−xSrxRuO4 and iron chalcogenide superconductors.
Orbiter (simulator)
Orbiter, also known as Orbiter Space Flight Simulator, is a free space flight simulator for Windows PCs created by Martin Schweiger and first released in November 2000.
Orbitrap Fusion
The Orbitrap Fusion is a hybrid high-resolution mass spectrometer introduced by Thermo Fisher Scientific in 2013, the first commercial Tribrid LC-MS system, built for proteomics and other high-resolution applications.
Orbitrap mass spectrometry
Orbitrap mass spectrometry is an analytical technique that traps ions in an electrostatic field around a spindle-shaped electrode, giving high mass accuracy and resolving power.
OrbNet
OrbNet is a machine learning method for quantum chemistry, introduced at Caltech in 2020, that predicts DFT-quality molecular energies at roughly 1,000-fold lower cost using features from cheap semi-empirical calculations and a graph neural network.
Orchestrated objective reduction
Orchestrated objective reduction (Orch OR) is Penrose and Hameroff's quantum consciousness theory, proposing gravity-induced wavefunction collapse (Diósi–Penrose scheme) in neuronal microtubules; contested by Tegmark's decoherence calculations and not widely accepted.
Order (ring theory)
In ring theory, an order is a subring of the ring of integers of a number field that has finite index there, a concept introduced by Richard Dedekind.
Order finding and quantum period finding
Order finding is the problem of finding the smallest r such that a^r ≡ 1 mod N, solved by quantum period finding, the core subroutine of Shor's factoring algorithm.
Order of magnitude
An order of magnitude is a factor of ten, the power of ten representing a quantity's scale; about 61 orders separate the Planck length from the observable universe.
Order of operations
The order of operations, also called operator precedence, is the rule that mathematical expressions are evaluated parentheses first, then exponents, then multiplication and division, then addition and subtraction.
Order of reaction
The order of a chemical reaction is the exponent on a reactant's concentration in the experimentally determined rate law, with the overall order the sum of these exponents.
Order parameter
An order parameter is a thermodynamic quantity distinguishing phases, zero in the disordered phase and nonzero in the ordered one, introduced by Lev Landau in 1937.
Order statistic
An order statistic is one of a statistical sample's values arranged in increasing order; the first is the sample minimum and the last is the sample maximum.
Order statistics
Order statistics are the values of a random sample arranged in increasing order, with the jth smallest called the jth order statistic; the theory underlies the sample median, quantiles, trimmed means, and extremes.
Order theory
Order theory is the branch of mathematics that studies partially ordered sets, or posets, together with structures built on them such as lattices and ordered algebraic systems.
Order–disorder transition
An order–disorder transition is a transition in which the degree of order of a system changes; in alloys, atoms occupy preferred sublattices below a critical temperature.
Ordered abelian groups
An ordered abelian group is an abelian group with a total order compatible with addition, such as the integers, rationals, and reals; it is central to model theory.
Ordered logit
Ordered logit, also known as the proportional odds model, is a statistical regression method for ordinal outcomes with ordered categories, formulated by Peter McCullagh in 1980.
Ordered pair
An ordered pair (a, b) is a mathematical object with a first and second coordinate, so (a, b) equals (c, d) only when a = c and b = d.
Ordered probit model
The ordered probit model is a regression method for ordinal dependent variables, proposed by Aitchison and Silvey in 1957 and estimated by maximum likelihood, assuming normally distributed errors.
Orders of magnitude (length)
Orders of magnitude (length) are the powers of ten spanning the measurable range of distances, from the Planck length at 10⁻³⁵ m to the observable universe.
Orders of magnitude (mass)
Orders of magnitude survey the masses of physical objects across known physics, from the neutrino mass limit near 8 × 10⁻³⁷ kg to a critical-density Universe's 6 × 10⁵² kg.
Orders of magnitude (numbers)
Orders of magnitude express a number's approximate size as the nearest power of ten, and two quantities differ by one order when one is about 10 times the other.
Orders of magnitude (time)
Orders of magnitude (time) are the successive powers of ten used to describe durations, from the Planck time of about 5.4 × 10⁻⁴⁴ seconds up to cosmic timescales.
Ordinal analysis
Ordinal analysis, also known as proof theoretic ordinal, is a proof theory research program assigning each formal theory a characteristic ordinal, begun with Gentzen's 1936 consistency proof of Peano arithmetic.
Ordinal collapsing function
An ordinal collapsing function is a proof theory function that assigns large uncountable ordinals smaller countable ones, introduced by Heinz Bachmann and central to analyzing impredicative theories via the Bachmann–Howard ordinal.