Physical world and mathematics

One-pot synthesis

One-pot synthesis is a chemical strategy in which successive reactions run in a single reactor without isolating intermediates, reducing waste, time, and cost across pharmaceutical and polymer chemistry.

One-way analysis of variance

The one-way analysis of variance (one-way ANOVA) is a statistical test of whether the means of three or more independent groups differ, defined by a single factor.

One-way mirror

A one-way mirror, also called a two-way mirror or transparent mirror, is partially reflective glass that acts as a mirror on its lit side, allowing observation from a darker side.

One-way quantum computer

The one-way quantum computer, the founding scheme of measurement-based quantum computing, performs computation entirely by single-qubit measurements on an entangled cluster state; proposed by Raussendorf and Briegel in 2001.

One-way speed of light

The one-way speed of light is the speed of light measured over a single path, which cannot be measured without a convention for synchronizing distant clocks.

Ones' complement

Ones' complement is a method of representing signed integers in binary in which a negative number is formed by inverting every bit, used by early computers like the CDC 6600 and PDP-1.

ONIOM

ONIOM is a multiscale quantum chemistry method that treats a molecule's active region accurately and its surroundings cheaply, introduced by Mats Svensson and colleagues in 1996.

Online focus groups

An online focus group is a qualitative research method in which a moderated group discussion is conducted over the internet, either in real time or asynchronously on discussion boards.

Online interview

An online interview, also called an e-interview, is a research interview conducted over the internet by text, voice, or video, either in real time or asynchronously.

Onsager reciprocal relations

The Onsager reciprocal relations, derived by Lars Onsager in 1931, are symmetry relations stating that the cross-coefficients in linear transport laws near equilibrium are equal in both directions.

Onyx

Onyx is a banded variety of chalcedony, a microcrystalline form of quartz, whose straight parallel bands distinguish it from agate; black-and-white material is the classic form.

Oolite

Oolite is a sedimentary rock, usually limestone, composed of ooids, concentrically layered calcium carbonate grains under 2 mm that form in shallow, agitated seawater like the Bahamas.

Opacity (optics)

Opacity is a measure of how well a material hides a surface behind it or blocks the transmission of light, defined quantitatively in printing, coatings, metallizing, and astrophysics.

Opal

Opal, historically called ceraunium, is a hydrated amorphous form of silica prized as a gemstone for its play-of-color, with Australia supplying about 95% of the world's precious opal.

OPC water model

The OPC (Optimal Point Charge) water model is a rigid, non-polarizable water model for molecular simulations, introduced in 2014 at Virginia Tech, with its three-site counterpart OPC3 following in 2016.

Open access and open education movement in physics

The open access and open education movement in physics promotes freely readable research and openly licensed teaching materials, rooted in the 1991 founding of arXiv and OpenStax textbooks.

Open ball

An open ball in a metric space is the set of all points within a given distance of a center, and it is always an open set.

Open Catalyst Project

The Open Catalyst Project is a research collaboration between Meta's FAIR and Carnegie Mellon University, launched in 2020 to use AI to find new catalysts for renewable energy storage.

Open cluster

An open cluster, also called a galactic cluster, is a loosely gravitationally bound group of up to a few thousand stars that formed together and gradually disperses.

Open clusters as tracers of Galactic structure

Open clusters trace Galactic structure because stars born together share a distance, age, and composition, letting astronomers map the Milky Way's spiral arms and disc.

Open coding

Open coding is a qualitative data analysis technique in which researchers break data into segments and attach provisional conceptual labels, called codes, without a predefined framework.

Open cover

An open cover of a set in a topological space is a collection of open sets whose union contains it, and compactness means every open cover has a finite subcover.

Open DAC 2023

Open DAC 2023 (ODAC23) is an open dataset of density functional theory calculations of CO2 and H2O adsorption on metal-organic frameworks, built by Meta researchers for direct air capture.

Open educational resources in physics

Open educational resources in physics are freely reusable teaching materials like simulations, problem sets, and open textbooks, a term adopted at the 2002 UNESCO forum on open courseware.

Open Force Field Initiative

The Open Force Field Initiative is a network of academic and industry researchers building open molecular mechanics force fields for drug discovery, launched in 2018 with releases including Parsley and Sage.

Open Journal Systems

Open Journal Systems (OJS) is free, open source software for managing and publishing scholarly journals online, first released in 2001 by the Public Knowledge Project at the University of British Columbia.

Open map

An open map is a function between topological spaces that sends every open set to an open set; every homeomorphism is open, and non-constant holomorphic functions are open maps.

Open mapping theorem (functional analysis)

The open mapping theorem, or Banach–Schauder theorem, is a functional analysis result stating that every surjective bounded linear operator between Banach spaces sends open sets to open sets.

Open science

Open science is a set of principles and practices making scientific research accessible to everyone, spanning open access, open data, open source software, and open peer review.