Physical world and mathematics

Octupole deformation

Octupole deformation is a pear-shaped distortion of an atomic nucleus that breaks reflection symmetry, appearing as a static shape in nuclei like radium-224 and as octupole vibrations in many others.

Octyl methoxycinnamate

Octyl methoxycinnamate, also known as octinoxate or ethylhexyl methoxycinnamate, is an organic cinnamate ester developed in the 1950s that absorbs UV-B radiation in sunscreens and skin care products.

Octylamine (octan-1-amine), formula C8H19N, is a straight-chain primary fatty amine, a yellow, ammonia-smelling, water-insoluble liquid used mainly as a building block for surfactants, other chemicals, and nanocrystal ligands.

Oct 21, 2026

Octyldecyldimethyl ammonium chloride

Octyldecyldimethyl ammonium chloride (ODDAC, CAS 32426-11-2), a C8:C10 dialkyl quaternary ammonium disinfectant used on surfaces and in water treatment; EU pesticide status not approved (2004/129/EC), corrosive and very toxic to aquatic life.

Octylphenol

Octylphenol is a phenol with an eight-carbon alkyl chain, used almost entirely in resins for tire rubber; its main isomer, 4-tert-octylphenol, became the first EU substance of very high concern for endocrine effects in 2012.

Odd elasticity

Odd elasticity is a generalization of elasticity in which stress need not derive from a strain energy, so cyclic deformation can yield net work in active solids.

Odd Hassel

Odd Hassel was a Norwegian physical chemist at the University of Oslo who shared the 1969 Nobel Prize in Chemistry for showing that molecules take several interconverting three-dimensional shapes.

Odd radio circle

An odd radio circle (ORC) is a large, faint ring-shaped radio source surrounding a distant galaxy, named in 2021 after discoveries with the ASKAP telescope.

Odd viscosity

Odd viscosity, also called Hall viscosity or gyroviscosity, is the antisymmetric, non-dissipative part of a fluid's viscosity tensor, seen in quantum Hall fluids, superfluids, magnetized plasmas, and chiral active matter.

Odd viscosity in active matter

Odd viscosity in chiral active fluids, also known as Hall viscosity, is a dissipationless viscosity coefficient arising in fluids of self-spinning particles, producing flow perpendicular to an applied pressure gradient.

Odds

Odds are a way of expressing how likely an event is as a ratio of the chance that it happens to the chance that it does not happen.

Odds ratio

The odds ratio (OR), also called the log odds ratio, is a biostatistical measure of association computed as the ratio of odds of an outcome between exposed and unexposed groups.

Oct 10, 2026

Oded Schramm

Oded Schramm (1961–2008) was an Israeli mathematician at Microsoft Research who invented stochastic Loewner evolution, the one-parameter family of random curves describing two-dimensional random shapes, and won the Ostrowski Prize in 2007.

Odile Eisenstein

Odile Eisenstein, born 1949, is a French theoretical and computational chemist, a CNRS research director emeritus in Montpellier known for computational studies of transition-metal and lanthanide complexes.

Odometer

An odometer, also called a mileometer or milometer, is an instrument that measures and records the cumulative distance a vehicle travels, shown in the instrument cluster.

Odor

An odor is the sensation produced when volatile chemical molecules stimulate the olfactory organs, with about 400 functional human receptor genes detecting odorants in mixtures.

OECD Better Life Index

The OECD Better Life Index is an online tool launched by the OECD in 2011 that lets users compare well-being across countries using their own weights.

Oct 10, 2026

Oene Bottema

Oene Bottema (1901–1992) was a Dutch mathematician known as "the great geometer", professor of mathematics at Delft from 1941 to 1971 and co-author, with Bernard Roth, of Theoretical Kinematics (1979).

Oersted

The oersted (symbol Oe) is the CGS unit of magnetic field strength, named for Hans Christian Ørsted; one oersted equals about 79.577 amperes per meter in SI units.

Oersted Medal

The Oersted Medal, established in 1936 and named for physicist Hans Christian Oersted, is the American Association of Physics Teachers' award for lasting impact on physics teaching.

Of star

An Of star is a hot O-type star whose spectrum shows emission from ionized nitrogen and helium, a pattern marked by the "f" suffix that Nolan Walborn introduced in 1971.

Oct 10, 2026

Ofer Biham

Ofer Biham is an Israeli physicist at the Hebrew University of Jerusalem known for the Biham-Middleton-Levine traffic model and stochastic methods for chemistry on interstellar dust grains.

Ofer Zeitouni

Ofer Zaitûnî (עפר זיתוני) is an Israeli probability theorist, the Herman P. Taubman Professor at the Weizmann Institute, known for large deviations and random matrix theory.

Off-axis holography

Off-axis holography is a holographic recording geometry in which the reference wave strikes the medium at an angle, separating the twin image from the reconstruction.

Office for National Statistics

The Office for National Statistics (ONS, Swyddfa Ystadegau Gwladol) is the United Kingdom's recognized national statistical institute, producing official statistics on the economy, population, and society.

Offset tracking

Offset tracking, also called pixel-offset tracking, is a synthetic aperture radar technique that measures surface displacement, used for glacier flow and large earthquake deformation where InSAR fails.

Offshore groundwater

Offshore groundwater is low-salinity water stored in sediments and rocks below the seafloor, first documented off Florida in the 1960s and estimated at about 1 million cubic kilometers globally.

Ogallala Aquifer

The Ogallala Aquifer, formally the High Plains aquifer, is a groundwater system underlying about 174,000 square miles of the Great Plains in eight states, supplying about 30 percent of US irrigation groundwater.

Oganesson

Oganesson, also known as ununoctium or eka-radon, is a synthetic element with atomic number 118, first made in 2002 in Russia and named for Yuri Oganessian.