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Internal Revenue Code section 1031

Internal Revenue Code section 1031 (26 U.S.C. §1031), the like-kind exchange provision: defers gain or loss on exchanging investment or business real property for like-kind real property, via 45-day identification and 180-day completion deadlines, qualified intermediaries, carryover basis, and the 2017 restriction to real property.

Internal Revenue Service

Internal Revenue Service (IRS), US Treasury agency administering the Internal Revenue Code since 1862 (named IRS in 1953); collected $4.7 trillion in FY 2023, estimated a $496 billion annual tax gap for 2014-2016, and lost about a quarter of its workforce in 2025.

Internal ribosome entry site

An internal ribosome entry site (IRES) is a structured RNA sequence, usually in a messenger RNA's 5′ untranslated region, that initiates translation without the 5′ cap.

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 Security Forces (قوى الأمن الداخلي) (Syria)

Internal Security Forces (قوى الأمن الداخلي), renamed from the General Security Service on 25 May 2025, are Syria's Ministry of Interior gendarmerie, grown from HTS policing structures and about 8,000 to tens of thousands of personnel, now absorbing the SDF's Asayish.

Internal Settlement

The Internal Settlement was the March 3, 1978 agreement signed in Salisbury, Rhodesia, by Ian Smith and three black nationalist leaders, providing for majority rule.

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 thoracic artery

The internal thoracic artery, also called the internal mammary artery, is a paired artery from the subclavian artery that supplies the anterior chest and upper abdominal walls.

Internal thoracic vein

Internal thoracic vein (vena thoracica interna, internal mammary vein): paired chest wall vein draining breast, pericardium, diaphragm, and anterior thorax into the brachiocephalic veins; often double, with xiphoid venous arch, used in flap reconstruction.

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 transcribed spacer

The internal transcribed spacer (ITS), or ITS sequence, is a non-coding ribosomal DNA region between rRNA genes that serves as the universal DNA barcode for identifying fungi.

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 troops of the Soviet Union

Internal troops of the Soviet Union (внутренние войска) were MVD-subordinated military formations for internal security: rear guard, suppression of uprisings, guarding installations, prisoner escort. Founded from Cheka troops in 1918; became Russia's National Guard in 2016.

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.

Oct 20, 2026

Internal virion protein Gp14

Gp14 (gene product 14) is the smallest internal core protein of bacteriophage T7, 196 residues and ~20.8 kDa, ejected first during infection to form a pore in the E. coli outer membrane for DNA delivery.

Oct 21, 2026

Internal virion protein Gp15

Internal virion protein gp15 (gene product 15) of Escherichia phage T7, UniProt P03725, 747 aa, 84 kDa. Internal core protein ejected with gp14 and gp16 to build the DNA-ejectosome channel; binds DNA with gp16.

Oct 20, 2026

Internal virion protein Gp16

Internal virion protein gp16 of bacteriophage T7 (gene product 16): a 144 kDa, 1,318-residue internal core protein ejected before the genome, carrying lytic transglycosylase activity and controlling DNA ejection, distinct from P22 gp16.

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.

Oct 21, 2026

Internalin A

Internalin A (InlA), encoded by inlA of Listeria monocytogenes, is an 800-amino-acid LPXTG-anchored leucine-rich-repeat surface protein that binds human E-cadherin to drive epithelial invasion, with species specificity set by E-cadherin residue 16.

Internalism and externalism

Internalism and externalism are opposed philosophical positions on whether justification, knowledge, or mental content depends only on factors internal to the individual or partly on the external environment, central to epistemology and philosophy of mind since the 1970s.

Internalized racism

Internalized racism, also called internalized racial oppression, is the internalized level of racism in which members of a racialized group absorb dominant-society racist ideologies about their own group; studied via scales like the IRRS and IRAAS and linked to worse mental and physical health.

Internally displaced person

An internally displaced person, or IDP, is a person forced to flee their home but who remains within their national borders. In 2025, 82.2 million people were in displacement.

International 14

The International 14 is a 14-foot two-person development-class dinghy granted International status in 1928, and a primary testbed for engineering advances like the trapeze and spinnaker.

Oct 10, 2026

International Accounting Standards Board

The International Accounting Standards Board (IASB) is the independent standard-setting body of the IFRS Foundation, responsible for IFRS Accounting Standards used in more than 140 jurisdictions.

International adoption of South Korean children

International adoption of South Korean children: roughly 200,000 children sent abroad since 1953, the world's largest intercountry adoptee diaspora. Also known as Korean overseas adoption or 해외입양. Marked by the 1961 orphan law, falsified records, a 2025 truth commission finding of state responsibility, and Hague Convention ratification effective October 1, 2025.

International Aerial Robotics Competition

The International Aerial Robotics Competition (IARC), founded by Robert C. Michelson in 1991 at Georgia Tech, is the world's longest-running collegiate aerial robotics competition, setting deliberately unsolved autonomous drone missions.