All articles starting with Q

Quadrants and regions of abdomen

Quadrants and regions of abdomen: two topographic systems dividing the abdominal surface. Four quadrants (RUQ, LUQ, RLQ, LLQ) from planes through the umbilicus at L3-L4; nine regions from midclavicular, subcostal, and transtubercular planes.

Oct 21, 2026

Quadraro

Quadraro, Rome: area on the lower Via Latina with Roman villas (1st c. BC-4th c. AD, found 1987), funerary monuments, and the 14th-century Torre del Quadraro at Piazza dei Consoli.

Quadrat sampling

Quadrat sampling is an ecological field method in which square plots of fixed size are placed in a habitat to estimate the abundance, density, cover, or biomass of organisms.

Quadratic assignment problem

The quadratic assignment problem (QAP) is a strongly NP-hard combinatorial optimization problem, introduced by Koopmans and Beckmann in 1957, of assigning facilities to locations to minimize total cost.

Quadratic equation

A quadratic equation, also called a second degree equation, is a polynomial equation of degree two, written ax² + bx + c = 0 and solved by the quadratic formula.

Quadratic field

A quadratic field is a number field of degree 2 over the rationals, of the form Q(√d) for a unique squarefree integer d; real when d > 0, imaginary when d < 0.

Quadratic form

A quadratic form is a homogeneous polynomial of degree 2 in several variables, equivalent to a symmetric matrix, and first studied systematically by Gauss in his 1801 Disquisitiones Arithmeticae.

Quadratic formula

The quadratic formula, also called Sridharacharya's formula, is an algebraic formula giving the roots of any quadratic equation directly from its coefficients, derived by completing the square.

Quadratic function

A quadratic function, also called a quadratic trinomial or second-order polynomial, is a polynomial of degree two, written f(x) = ax² + bx + c, whose graph is a parabola.

Quadratic interpolation

Quadratic interpolation is a numerical analysis method that estimates intermediate function values by fitting the unique parabola through three known data points and evaluating it between them.

Quadratic programming

Quadratic programming (QP) optimizes a quadratic objective function subject to linear constraints. Convex QP is solvable reliably and arises in portfolio optimization, support vector machines, and model predictive control.

Quadratic reciprocity

Quadratic reciprocity is a number theory theorem relating the solvability of x² ≡ q (mod p) and x² ≡ p (mod q) for distinct odd primes.

Quadratic regression

Quadratic regression is a statistical method that fits a second-degree polynomial curve to data, estimating U-shaped or inverted-U relationships between one predictor and an outcome.

Quadratic residue

Quadratic residue, also called quadratic residuosity, describes an integer a for which x² ≡ a (mod m) is solvable; the concept underlies quadratic reciprocity and cryptosystems like Goldwasser–Micali.

Quadratic sieve

The quadratic sieve is a general-purpose integer factorization algorithm invented by Carl Pomerance in 1981, fastest known until 1996 and still used below roughly 100 digits.

Quadratic variation

Quadratic variation, also called the bracket or quadratic-variation process, measures a stochastic process's accumulated squared fluctuations; for Brownian motion it equals t, which produces the second-order term in Itô's formula.

Quadratic-programming whole-body control

Quadratic-programming whole-body control is a robot-control method for legged robots that solves a quadratic program each control tick, balancing competing tasks like footsteps, balance, and reaching under physical limits.

Quadrature amplitude modulation

Quadrature amplitude modulation (QAM) is a digital modulation method that encodes data by varying both the amplitude and phase of a carrier wave, used in cable modems, digital television, and Wi-Fi.

Quadrature Capital

Quadrature Capital is a secretive London-based systematic proprietary trading firm founded by Greg Skinner and Suneil Setiya, trading only its partners' capital and giving over $1.7bn to climate causes.

Quadrature phase-shift keying

Quadrature phase-shift keying (QPSK) is a digital modulation scheme that encodes two bits per symbol using four carrier phases, doubling the spectral efficiency of BPSK.

Quadrature rule

A quadrature rule is a numerical method that approximates a definite integral of a function by a weighted sum of its values at selected points, or nodes.

Quadrature spatial modulation

Quadrature spatial modulation (QSM) is a MIMO transmission technique that sends the real and imaginary parts of a data symbol from separately chosen antennas, proposed in 2013.

Quadratus lumborum block

The quadratus lumborum block is an ultrasound-guided fascial plane block injecting local anesthetic near the quadratus lumborum muscle to relieve pain after abdominal and hip surgery.

Quadratus lumborum muscle

Quadratus lumborum: posterior abdominal wall muscle between the iliac crest, 12th rib, and L1-L4 transverse processes; weak lumbar stabilizer, inspiration accessory, and target of the quadratus lumborum block.

Oct 21, 2026

Quadriburgium

Quadriburgium: Latin "square castle," a small square Late Roman fort type with four corner towers, and a Rhine fort at modern Qualburg, Germany, named by Ammianus among places Julian repaired in 359.

Quadric

A quadric, also known as a quadric surface or quadric hypersurface, is a geometric set defined by a degree-two polynomial equation; ellipsoids, hyperboloids, cones, cylinders, and paraboloids are familiar quadric surfaces.

Quadriceps

Quadriceps femoris, the four-headed anterior thigh muscle group (rectus femoris, vastus medialis, lateralis, intermedius), the primary knee extensor innervated by the femoral nerve L2-L4, central to patellofemoral pain rehabilitation.

Quadrics

Quadrics was a British company based in Bristol that made the QsNet high-performance interconnect used in TOP500 supercomputers such as ASCI Q before closing in 2009.

Oct 21, 2026

Quadricuspid aortic valve

Quadricuspid aortic valve (QAV), a rare congenital four-cusp aortic valve (0.013-0.043% prevalence), types A-G, usually causing aortic regurgitation; diagnosed by TEE, surgery in about half of patients.