Physical world and mathematics

Internal energy

Internal energy, also called thermodynamic energy, is the total energy a thermodynamic system contains through its molecules' motion and interactions, excluding the system's overall motion or position.

Internal phosphorus loading

Internal phosphorus loading is the release of phosphorus from a lake's own sediments into the water, distinct from external loading, and often the main summer phosphorus load in eutrophic lakes.

Internal resistance

Internal resistance is the resistance to current flow within a voltage source such as a battery or cell, causing terminal voltage to fall below the emf when current is drawn.

Internal resonance

Internal resonance, also called autoparametric resonance, is a nonlinear vibration phenomenon in which modes with commensurate integer frequency ratios exchange energy, producing amplitude saturation and used in MEMS frequency stabilization.

Internal rotation barrier

The internal rotation barrier is the potential energy maximum hindering rotation of part of a molecule, often a methyl group, about a single bond, measured by microwave spectroscopy.

Internal standard

An internal standard is a compound added in a known, constant amount to samples, calibration standards, and quality controls so its measured response corrects variability affecting the analyte.

Internal structure of Jupiter

The internal structure of Jupiter is the layered arrangement of hydrogen, helium, and heavier elements inside the largest planet, inferred indirectly from gravity and magnetic-field measurements.

Internal structure of Mars

The internal structure of Mars is its layered crust, mantle, and core, revealed by NASA's InSight lander, which measured a thin mantle and a large, liquid iron–nickel core.

Internal structure of the Moon

The internal structure of the Moon is its division into a crust, a silicate mantle 1,100 to 1,300 km thick, and a core of 300 to 400 km radius.

Internal tide

An internal tide, also called a baroclinic tide, is an internal gravity wave with tidal periodicity, generated in the stratified ocean where tidal currents flow over ridges, seamounts, and shelf breaks. It drives deep-ocean mixing.

Internal transport barrier

An internal transport barrier (ITB) is a region inside a magnetically confined fusion plasma where turbulent heat and particle transport is suppressed, steepening core temperature and density gradients.

Internal validity

Internal validity is the degree to which a study shows that the treatment, not some other factor, caused the observed outcome, a term coined by Donald T. Campbell in 1957.

Internal wave

An internal wave is a wave that propagates within a density-stratified fluid such as the ocean or atmosphere, where gravity restores displaced water and amplitudes can reach hundreds of meters.

International Arctic Buoy Programme

The International Arctic Buoy Programme (IABP) is an international cooperative program maintaining drifting buoys across the Arctic Ocean, providing meteorological and oceanographic data continuously since 1979.

International Association for Mathematical Geosciences

The International Association for Mathematical Geosciences (IAMG) is a non-profit scientific association, founded in Prague in 1968, that promotes mathematics, statistics, and informatics in the geosciences and publishes four journals.

International Association for the Evaluation of Educational Achievement

The International Association for the Evaluation of Educational Achievement (IEA) is an independent cooperative of national research institutions that runs large-scale comparative studies of educational achievement, including TIMSS and PIRLS.

International Association of Hydrogeologists

The International Association of Hydrogeologists (IAH) is a UK-based charitable organization of groundwater professionals, founded in 1956, with over 5,000 members in more than 130 countries.

International Association of Hydrological Sciences

The International Association of Hydrological Sciences (IAHS) is a UK-registered non-profit organization promoting hydrology worldwide, founded in 1922, with more than 13,000 members in over 170 countries.

International Association of Physics Students

The International Association of Physics Students (IAPS) is a student-run nonprofit organization of physics students worldwide, founded in Debrecen, Hungary, in 1987 and known for its annual ICPS conference and PLANCKS competition.

International Asteroid Warning Network

The International Asteroid Warning Network (IAWN) is a UN-endorsed, NASA-coordinated collaboration of asteroid astronomers, created in 2013 after the Chelyabinsk airburst, that tracks hazardous near-Earth objects and issues impact warnings.

International Atomic Time

International Atomic Time (TAI, Temps Atomique International) is a continuous time scale computed by the BIPM from about 450 atomic clocks worldwide, with no leap seconds.

International Axion Observatory

The International Axion Observatory (IAXO) is a proposed fourth-generation axion helioscope that would search for solar axions and axion-like particles using a large superconducting magnet and X-ray detectors.

International Bureau of Weights and Measures

The International Bureau of Weights and Measures, or Bureau International des Poids et Mesures, is the intergovernmental organization that maintains the SI and Coordinated Universal Time (UTC).

International Celestial Reference Frame

The International Celestial Reference Frame (ICRF) is the official realization of the International Celestial Reference System, defined by quasar positions measured with very long baseline interferometry since 1998.

International Centre for Diffraction Data

The International Centre for Diffraction Data (ICDD), founded in 1941 and based in Newtown Square, Pennsylvania, is a non-profit organization publishing the Powder Diffraction File database of powder diffraction data.

International Colloquium on Group Theoretical Methods in Physics

The International Colloquium on Group Theoretical Methods in Physics (ICGTMP) is a conference series on group theory and symmetry in physics, founded in Marseille in 1972.

International Commission on Radiation Units and Measurements

The International Commission on Radiation Units and Measurements (ICRU) is an international standards body defining radiation quantities, units, and measurement procedures, founded in London in 1925.

International Commission on Radiological Protection

The International Commission on Radiological Protection (ICRP), founded in 1928 as the International X-ray and Radium Protection Committee, is a UK charity whose recommendations on ionizing radiation protection are translated into national law.

International Commission on Stratigraphy

The International Commission on Stratigraphy (ICS), the largest and oldest scientific body of the International Union of Geological Sciences, defines the periods, epochs, and ages of the geologic time scale.