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Poul Heegaard
Poul Heegaard (1871–1948) was a Danish mathematician whose 1898 Copenhagen thesis introduced the Heegaard splitting of 3-manifolds and whose counterexample to Poincaré duality reshaped algebraic topology.
Poul Olesen
Poul Olesen, born 1939, is a Danish theoretical physicist, emeritus at the Niels Bohr Institute in Copenhagen, known for the Nielsen-Olesen vortex and the KNO scaling law.
Pound (force)
The pound-force (lbf) is a unit of force in U.S. customary and foot–pound–second systems, defined as the weight of one pound of mass at standard gravity, exactly 4.4482216152605 newtons.
Pound (mass)
The pound (symbol lb) is a unit of mass equal to exactly 0.45359237 kilogram, fixed by international agreement in 1959 and still common in the United States.
Pound-foot (torque)
The pound-foot (lb·ft), sometimes written lbf·ft, is a unit of torque in the foot-pound-second system, equal to one pound-force acting on a one-foot lever, or 1.355818 newton meters.
Pound–Drever–Hall technique
The Pound–Drever–Hall technique is a laser frequency stabilization method that reflects phase-modulated light from a stable reference cavity to generate an error signal, published in 1983 and central to LIGO.
Pound–Rebka experiment
The Pound–Rebka experiment was a 1960 Harvard test in which Robert Pound and Glen Rebka measured the gravitational redshift of gamma rays over 74 feet, confirming Einstein's prediction.
Pounds per square inch
The pound per square inch (psi) is a unit of pressure equal to one pound-force per square inch, widely used in the United States for tire pressures.
Pourbaix diagram
A Pourbaix diagram, also called a potential–pH or E–pH diagram, maps the thermodynamically stable phases of an element in water as electrode potential and pH vary.
POVM
A POVM, or positive operator-valued measure, is a mathematical description of a quantum measurement as a collection of non-negative operators, called effects, whose outcome probabilities follow the Born rule; projective measurements are a special case.
Powder
A powder is a dry bulk solid of many fine particles whose collective behavior is governed by interparticle forces, handled at scale in pharmaceutical, food, chemical, and mining industries.
Powder diffraction
Powder diffraction is an analytical technique in which X-rays or neutrons directed at a crystalline powder identify phases, determine unit cells, and refine crystal structures.
Powder River Basin
The Powder River Basin is a structural basin in northeastern Wyoming and southeastern Montana, holding the largest low-sulfur subbituminous coal resources in the United States.
Power (physics)
Power in physics is the rate at which work is done or energy is transferred, measured in watts, with one watt equal to one joule per second.
Power analysis
Power analysis is the statistical calculation of how sample size, significance level, power, and effect size determine one another, letting researchers design studies to detect a given effect.
Power band
A power band is the range of engine speeds within which an engine produces most of its usable power, a term used mainly for motorcycles and performance cars.
Power dissipation index
The power dissipation index (PDI) is a measure of tropical cyclone destructive potential, summing maximum sustained wind speed cubed, introduced by MIT's Kerry Emanuel in 2005.
Power factor
Power factor is the ratio of real power to apparent power in an alternating-current circuit, equal to the cosine of the phase angle between voltage and current.
Power iteration
Power iteration, also called the power method or Von Mises iteration, is a numerical linear algebra algorithm that finds a square matrix's dominant eigenvalue and a corresponding eigenvector.
Power law
A power law is a mathematical relationship in which one quantity is proportional to a fixed power of another, describing city sizes, earthquake magnitudes, wealth, and word frequencies.
Power of 10
A power of 10 is a number like 100 or 1000, written 10 to the nth power, that underlies decimal notation and the SI metric prefixes.
Power of a test
The power of a test, also called statistical power, is the probability that a test rejects a false null hypothesis for a given effect size.
Power of two
A power of two is a number written as 2 to a whole-number exponent, beginning 1, 2, 4, 8, 16, 32, and important in computing.
Power series
A power series is an infinite series of the form Σcₙ(x−a)ⁿ, an infinite polynomial that represents functions, converging within a radius of convergence R around its center.
Power set
The power set of a set A, written P(A) or 2^A, is the set of all subsets of A, always including the empty set and A itself.
Power transform
A power transform is a family of parametric data transformations built from powers of a variable that reshapes a distribution toward normality, constant variance, or linearity, including the Box–Cox transformation.
Power-associative algebra
A power-associative algebra is a not-necessarily-associative algebra in which powers of any single element are well defined, a concept introduced by A. A. Albert in his 1948 paper Power-Associative Rings.
Power-law fluid
A power-law fluid, also called the Ostwald–de Waele model, is an idealized non-Newtonian fluid whose shear stress is proportional to a fixed power of the shear rate.
Power-to-weight ratio
Power-to-weight ratio, also called specific power, is a performance measure defined as power output divided by mass, typically in watts per kilogram, used to compare engines, vehicles, batteries, and athletes.
Poynting vector
The Poynting vector, or Poynting flux, is the vector describing the directional energy flux of an electromagnetic field, the rate of energy transfer per unit area, in watts per square meter.