All articles starting with R

Rotation matrix

A rotation matrix is a real orthogonal square matrix, determinant 1, that rotates vectors while preserving their lengths and handedness; the n×n ones form the group SO(n).

In quantum mechanics, the rotation operator U(R) is the unitary operator that applies a spatial rotation R to a system's states, generated by the angular momentum operators; a 2π rotation multiplies half-integer spin states by −1.

Rotational angiography

Rotational angiography is an X-ray technique in which a rotating C-arm reconstructs contrast-filled vessels into a 3D image, used mainly for cerebral aneurysms and cardiac imaging.

Rotational atherectomy

Rotational atherectomy is a percutaneous coronary intervention technique that uses a high-speed diamond-coated burr to grind away severely calcified plaque so stents can be placed.

Rotational constant

A rotational constant is a spectroscopic parameter inversely proportional to a molecule's moment of inertia; it sets rotational energy level spacing and reveals molecular structure.

Oct 22, 2026

Rotational Doppler effect

The rotational Doppler effect is the frequency shift when a wave carrying angular momentum scatters off a rotating object, equal to the angular momentum change times the rotation rate.

Rotational energy

Rotational energy, also known as rotational kinetic energy, is the kinetic energy a body has because of rotation about an axis, equal to ½Iω² for a rigid body.

Rotational frequency

Rotational frequency, also called rotational speed or rotation rate, is the number of complete revolutions a rotating body makes per unit time, defined by ISO 80000-3 with symbol n.

Rotational grazing

Rotational grazing is a grazing management method that moves livestock sequentially among paddocks so each is grazed briefly and rested for forage regrowth, used in dairy, beef, and sheep systems.

Rotational latency

Rotational latency, also called rotational delay, is the wait for the desired data sector to rotate under a hard drive's read/write head, averaging half of one full rotation.

Rotational molding

Rotational molding, or rotomolding, is a low-pressure plastics process that makes hollow parts like tanks and kayaks by rotating a heated mold on two axes.

Rotational partition function

The rotational partition function is the factor of a molecule's partition function that counts its quantized rotational states, summing the Boltzmann weight of every allowed rotational energy level at a given temperature.

Rotational spectroscopy

Rotational spectroscopy studies transitions between the quantized rotational energy levels of gas-phase molecules, observed mainly in the microwave region, and is the primary method for identifying molecules in interstellar space.

Rotational symmetry

Rotational symmetry is the property of a figure that looks the same after being rotated about a fixed point or axis by some angle less than a full turn.

Rotational temperature

Rotational temperature in molecular physics is the rotational constant of a molecule expressed as an equivalent temperature, or a gas temperature inferred from rotational line intensities.

Rotational thromboelastometry

Rotational thromboelastometry (ROTEM) is a point-of-care viscoelastic test that measures clot formation, firmness, and lysis in whole blood, guiding hemostatic therapy in trauma, cardiac surgery, and obstetrics.

Rotational transform

The rotational transform, denoted ι, measures how far a magnetic field line twists poloidally per toroidal circuit in a torus, introduced by Lyman Spitzer in early stellarator work.

Rotational vibration

Rotational vibration (RV) is a hard disk drive failure mode where torque from neighboring spinning drives rocks the drive, pushing heads off track and cutting performance.

Rotational–vibrational spectroscopy

Rotational–vibrational spectroscopy, also called rovibrational spectroscopy, is the branch of molecular spectroscopy covering infrared and Raman spectra in which transitions change both vibrational and rotational states of molecules.

Rotator cuff

Rotator cuff: the four-muscle group (supraspinatus, infraspinatus, subscapularis, teres minor) stabilizing the shoulder joint. Covers anatomy, tears, impingement, diagnosis, and surgery-versus-therapy evidence.

Rotator cuff repair

Rotator cuff repair is a surgical procedure that reattaches a torn rotator cuff tendon to its footprint on the humerus, aiming to relieve pain and restore shoulder strength and motion.

Rotator cuff tear

Rotator cuff tear: partial or complete detachment of one of the four shoulder rotator cuff tendons from the humerus. Most tears are degenerative; 80-85% improve without surgery, and repair re-attaches the tendon.

Oct 21, 2026

ROTAVAC 5D

ROTAVAC 5D is Bharat Biotech's liquid, ready-to-use oral rotavirus vaccine (116E strain, G9P[11]), WHO prequalified 18 June 2021, stored at 2-8°C for 24 months, given as 5 drops in a 3-dose infant schedule, non-inferior to frozen ROTAVAC.

Rotavirus

Rotavirus is a segmented double-stranded RNA virus causing severe childhood gastroenteritis, discovered in 1973; oral vaccines RotaTeq and Rotarix (also Rotavac, Rotasiil) prevent most severe disease, though US recommendations changed in 2026.

Oct 21, 2026

Rotavirus alphagastroenteritidis

Rotavirus alphagastroenteritidis (rotavirus A, RVA) is a Sedoreoviridae dsRNA virus with 11 genome segments causing infant gastroenteritis; distinguished by triple-layered ~100 nm virions, NSP4 enterotoxin, and WHO-prequalified oral vaccines.

Rotavirus vaccine

Rotavirus vaccine: oral live attenuated infant vaccine (Rotarix, RotaTeq, Rotavac, RotaSiil) against rotavirus gastroenteritis; WHO-prequalified, used in 123 countries, 55% coverage, low intussusception risk.

Rotax

Rotax, formally BRP-Rotax GmbH & Co KG, is an Austrian engine manufacturer in Gunskirchen owned by BRP since 2003, whose 912 four-stroke family dominates light-sport and ultralight aircraft.

Rotax 582

The Rotax 582 is a liquid-cooled, two-cylinder, two-stroke aircraft engine produced by BRP-Rotax in Gunskirchen, Austria, since 1989 as a development of the Rotax 532, and became one of its best-selling models.

Rotax 912

The Rotax 912 is a four-cylinder, four-stroke aircraft engine produced by BRP-Rotax in Gunskirchen, Austria, since 1989, the standard powerplant for light sport and ultralight aircraft.