A regeneration-associated accumulation of progenitor cells. A blastema need not be a homogeneous pluripotent population; contributors can retain tissue and positional restrictions.

A plane through which reflection leaves an object unchanged. In a molecular skeleton, sites exchanged by a symmetry preserving all substituent identities can be chemically equivalent in an achiral NMR spectroscopy experiment.

The laboratory frame is the reference frame in which an experiment's measuring apparatus is at rest. It need not be the centre-of-momentum frame: a target at rest in the laboratory can be struck by a projectile carrying nonzero total momentum.

A claim about what entities and processes are made of, distinguished from a claim that every useful explanation must be expressed at the microscopic level.

The stronger claim that higher-level explanations can or should be replaced by explanations in terms of more basic components and their interactions.

Reduction driven by products formed as radiation from a radioactive solute deposits energy in the solvent. A chemical oxidation-state change in surviving atoms is distinct from transmutation of the emitting nuclei.

Transfer of one electron between species, often converting an enol or enolate into a radical. It must be distinguished from transfer of a two-electron hydride.

A chemical equilibrium involving coupled oxidation and reduction. Its position depends on activities and can be shifted by complexation, hydrolysis or precipitation, because these change the relative free energies of oxidation states.

The McCarthy 91 function is the nested recursive integer functionIts result is $91$ for every $n\le 101$ and $n-10$ for $n>101$. For instance, $M(100)=M(M(111))=M(101)=91$. The striking feature is that the recursive case first increases its argument and then makes a second recursive call, so a naive decreasing-argument termination argument fails. It is a standard example for reasoning about nested recursion and proving equivalence between a recursive definition and a simple piecewise function.

A methyl-accepting chemotaxis protein is a bacterial chemoreceptor whose signalling and adaptation are coupled to receptor modification. Receptor arrays interact with CheW and CheA to regulate downstream phosphorylation.

A family of soluble abscisic acid receptors. ABA-bound receptor complexes inhibit selected clade-A protein phosphatase 2C enzymes, allowing ABA-responsive kinases to remain active.

An acid-promoted skeletal migration of a cyclohexadienone followed by rearomatization to a phenol. Carbonyl protonation activates the conjugated system; migration from a suitably placed quaternary carbon and subsequent proton loss can change ring connectivity while restoring aromaticity.

Thermal power per active-core volume under a stated volume convention. Coolant channels can be included in that core volume even when excluded from fuel volume, so core and fuel power densities need not change together.

Thermal power generated per unit axial fuel-rod length, measured in $\mathrm{W}{\mathrm{m}}^{-1}$. At fixed rod radius and material state, it controls the conductive fuel-to-surface temperature rise; coolant conditions determine the surface temperature from which that rise begins.

An accident involving loss of reactor coolant through a breach of its pressure boundary. Depressurization, loss of inventory and changes in heat removal require a transient assessment; stopping the fission chain reaction does not remove decay heat.

The radical anion ${\mathrm{O}}_2^{\bullet -}$. Its production, reactivity and localization differ from those of hydrogen peroxide; the two should not be treated as an interchangeable oxidant measurement.

Directional plasma etching used for deep, high-aspect-ratio features. Alternating fluorine-based silicon etching and sidewall passivation is one implementation; transport, mask erosion, charging, scallops and aspect-ratio-dependent etch rate constrain the achievable structure.

A KRAS protein bearing cysteine in place of glycine at residue 12. The introduced cysteine permits selective covalent chemistry at a suitable pocket; this strategy does not automatically apply to other Ras mutations.