Physical world and mathematics

Open set

An open set is a subset of a topological space declared open by the topology, generalizing a region where every point has room around it.

Open Source Physics is a project offering free, open-source computer-based resources for teaching physics and computation, including Java and JavaScript simulations, the Tracker video analysis tool, and textbooks.

Open system (systems theory)

An open system is a system that exchanges energy, matter, and information with its environment; Ludwig von Bertalanffy introduced the concept in biology in a 1950 Science paper.

Open textbook

An open textbook, also called an open source textbook, is a textbook in the public domain or under an open license, free to reuse, revise, and redistribute.

Open-circuit test

The open-circuit test, or no-load test, is an electrical test on a transformer in which one winding is energized at rated voltage to measure core loss and shunt parameters.

Open-pit mining

Open-pit mining, also called opencast or open-cut mining, is a surface method that extracts near-surface ore from benches in a deepening pit; Utah's Bingham Canyon is a notable example.

OpenBLAS

OpenBLAS is an open-source, optimized implementation of the Basic Linear Algebra Subprograms (BLAS), based on Goto's GotoBLAS2 and including LAPACK, with hand-tuned assembly kernels for many CPU architectures.

OpenBUGS

OpenBUGS is an open source package for Bayesian analysis of complex statistical models using MCMC, the first open source version of the BUGS software family.

OpenFermion

OpenFermion is an open-source Python library, announced by Google in 2017, for compiling and analyzing quantum algorithms that simulate fermionic systems, translating molecular specifications into quantum circuits.

OpenFOAM

OpenFOAM (Open Field Operation and Manipulation) is a free, open-source C++ toolbox for computational fluid dynamics, released in 2004 and maintained by the OpenFOAM Foundation and OpenCFD.

OpenIFS

OpenIFS is a portable version of the Integrated Forecasting System (IFS), the European Centre for Medium-Range Weather Forecasts' global weather prediction model, launched in 2011.

OpenKIM

OpenKIM, the Open Knowledgebase of Interatomic Models, is an open online resource, begun in 2009, that archives, tests, and retrieves interatomic potentials for atomistic materials simulations.

OpenMM

OpenMM is an open-source toolkit for molecular dynamics simulation, usable stand-alone or called from user code, with custom forces, a hardware-independent API, and high performance especially on GPUs.

OpenQASM

OpenQASM (Open Quantum Assembly Language) is an open, imperative programming language for describing quantum circuits, proposed by IBM in 2017; version 3 added classical control flow in 2022.

OpenStax

OpenStax, also known as OpenStax College, is a nonprofit education initiative of Rice University that publishes free, peer-reviewed, openly licensed textbooks for college and high school courses.

Operand

An operand is the number, variable, or data that an operator acts on in mathematics or computing, as in 7 + 5, where 7 and 5 are operands.

Operando 18O isotope labeling of the oxygen evolution reaction

Operando 18O isotope labeling of the oxygen evolution reaction is an experimental method that traces whether evolved O2 comes from water or the catalyst lattice.

Sep 29, 2026

Operando spectroscopy

Operando spectroscopy characterizes a material while it is working under real reaction conditions, measuring its structure and performance on the same sample at the same time.

Operando X-ray absorption spectroscopy

Operando X-ray absorption spectroscopy (operando XAS) is an analytical method that records a material's X-ray absorption spectrum while it is actively working, measuring catalytic activity at the same time.

Operando X-ray microscopy

Operando X-ray microscopy is the imaging of working batteries and catalysts with X-rays while their activity is measured at the same time, capturing short-lived states that extracted samples miss.

Operating characteristic curve

An operating characteristic curve is a graph used in acceptance sampling that plots the probability of accepting a lot against its true quality, as the fraction defective.

Operation (mathematics)

In mathematics, an operation is a function that takes a fixed number of elements of a set as inputs and returns one element of the same set.

Operation Plowshare

Operation Plowshare was a US Atomic Energy Commission program, established in 1957, that tested nuclear explosions for civil projects such as harbors, canals, and gas well stimulation.

Operational definition

An operational definition specifies a concept by the exact procedure, instrument, or criterion used to measure it, a practice traced to physicist Percy Bridgman's 1927 operationalism.

Operational interpretations of quantum entropies

Operational interpretations of quantum entropies identify which quantum entropy answers which physical task: conditional entropy prices state merging, min- and max-entropies govern guessing and decoupling.

Operationalism

Operationalism, also called operationism, is the doctrine that a scientific concept's meaning is given by the operations used to measure it, formulated by Percy Bridgman in 1927.

Operator (mathematics)

In mathematics, an operator, or mathematical operator, is a mapping that takes one function or vector to another, most commonly a linear map on a vector space.

Operator (physics)

In physics, an operator is a mathematical object acting on a system's state; in quantum mechanics, every measurable quantity, or observable, is represented by a linear operator.

Operator K-theory

Operator K-theory is the branch of K-theory assigning K₀ and K₁ groups to C-algebras through projections and unitaries, central to classification and topological phases of matter.