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Ozone
Ozone (O₃), also called trioxygen, is a gas of three oxygen atoms that shields Earth from ultraviolet radiation in the stratosphere but is a toxic pollutant at ground level.
Ozone depletion
Ozone depletion is the thinning of the ozone layer caused by CFCs and halons, discovered over Antarctica in 1985 and now slowly recovering under the Montreal Protocol.
Ozone generation
Ozone generation is the on-site production of ozone, an unstable strong oxidant that cannot be stored, typically by dielectric barrier discharge, used mainly for water treatment and pulp bleaching.
Ozone layer
The ozone layer, also called the ozone shield, is the stratospheric region, 15 to 35 kilometers up, that absorbs most of the Sun's harmful ultraviolet radiation.
Ozonolysis
Ozonolysis is an organic reaction in which ozone cleaves an alkene's carbon–carbon double bond, replacing it with carbonyl groups; the workup determines whether aldehydes or carboxylic acids form.
P (complexity)
P, also called PTIME, is the class of decision problems solvable by a deterministic Turing machine in time bounded by a polynomial in the input length.
P and R branches
The P and R branches are the two series of rotational fine-structure lines flanking a vibration-rotation band in an infrared spectrum, with ΔJ = −1 and ΔJ = +1.
P chloronitrobenzene
p-Chloronitrobenzene (1-chloro-4-nitrobenzene, PNCB) is the para isomer of chloronitrobenzene, a yellow crystalline solid used almost exclusively as a chemical intermediate in dyes, pharmaceuticals, and rubber antioxidants.
P Cygni
P Cygni is a luminous blue variable star in Cygnus, famous for a giant eruption in 1600 and for the spectral line shape named after it.
P versus NP problem
The P versus NP problem asks whether every problem whose solutions can be checked quickly can also be solved quickly, one of the Clay Mathematics Institute's $1 million Millennium Prize Problems.
P wave
The P wave, or primary wave, is the fastest seismic wave an earthquake produces, compressing rock parallel to its direction of travel and arriving first at seismic stations.
P-adic analysis
P-adic analysis, also known as ultrametric calculus, is the branch of analysis over the p-adic number fields, created by Kurt Hensel around 1899 and central to modern number theory.
P-adic exponential function
The p-adic exponential is the classical exponential power series interpreted over the p-adic numbers, where it converges only on a small disk around the origin, unlike the real exponential.
p-adic field
A p-adic field, also called a p-adic local field, is a field that is a finite extension of the p-adic numbers for a prime p, studied in algebraic number theory.
P-adic Hodge theory
P-adic Hodge theory is a branch of arithmetic geometry that compares the p-adic cohomology theories, étale, de Rham, and crystalline, of algebraic varieties over p-adic fields.
p-adic integer
A p-adic integer is an element of the ring Z_p, written in base p with digits extending infinitely to the left; it completes the ordinary integers under the p-adic norm.
P-adic L-function
A p-adic L-function is a p-adically valued analytic function that interpolates special values of classical L-functions such as the Riemann zeta function, introduced by Kubota and Leopoldt in 1964.
P-adic number
A p-adic number, or p-adic, is a number obtained by completing the rational numbers with a distance based on divisibility by a prime p, introduced by Kurt Hensel in 1897.
p-adic numbers
The p-adic numbers are a family of number systems, one for each prime p, built by completing the rational numbers; introduced by Kurt Hensel in 1897.
P-adic valuation
The p-adic valuation, also called the p-adic order, measures how deeply a rational number is divisible by a fixed prime p, taking the value infinity at 0.
p-Aminohippuric acid
p-Aminohippuric acid (PAH) is a synthetic organic anion that the kidneys clear almost completely in one pass, making its clearance the classic nonradioactive measure of effective renal plasma flow.
P-chart
The p-chart is an attribute control chart in statistical process control that monitors the proportion of defective units in samples of varying size, using binomial control limits.
P-Chiral phosphine
A P-chiral phosphine, also called a P-stereogenic phosphine, is an organophosphorus compound whose stereogenic center is the trivalent phosphorus atom itself, used mainly as a chiral ligand in asymmetric catalysis.
p-Coumaric acid
p-Coumaric acid, also known as 4-hydroxycinnamic acid, is a hydroxycinnamic acid found in edible plants and a key intermediate of the phenylpropanoid pathway, with antioxidant and antimicrobial uses in food preservation.
P-curve
P-curve is a meta-analytic technique introduced by Simonsohn, Nelson, and Simmons in 2013 that examines the distribution of significant p-values across studies to detect evidential value or selective reporting, though recent critiques recommend against its use.
p-Cymene
p-Cymene, also called p-cymol, is an aromatic hydrocarbon with the formula C₁₀H₁₄ that occurs in essential oils of thyme and oregano and is used industrially as a solvent.
P-group
A p-group, also called a primary group, is a group whose every element has order a power of a fixed prime p, central to finite group theory.
p-Hydroxybenzaldehyde
p-Hydroxybenzaldehyde, also called 4-hydroxybenzaldehyde or 4-formylphenol, is a white crystalline aromatic aldehyde (C₇H₆O₂) made from phenol, used mainly as an intermediate for vanillin, flavors, fragrances, and pharmaceuticals.
P-Phenylenediamine
P-Phenylenediamine (PPD), also known as P-diaminobenzene, is an aromatic diamine that is the primary intermediate in oxidative permanent hair dyes and a potent skin sensitizer.
p-polarization
P-polarization, also called TM polarization, is the state of light whose electric field oscillates entirely in the plane of incidence, and which is not reflected at all at Brewster's angle.