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A parasite is an organism benefiting from parasitism. Microparasite and macroparasite distinguish useful transmission-model descriptions of within-host multiplication and distributed parasite burden.

A biological host provides the environment or resources used by a parasite or other associated organism.

A parasitoid develops on or in a host and eventually kills it. Host-parasitoid transmission therefore has different offspring accounting from ordinary predation or a nonlethal parasite-burden model.

Pancreatic islets are endocrine cell clusters within the pancreas. Their different cell types include alpha cells, beta cells and delta cells, producing signals with different roles in metabolic regulation. Interactions within the cluster complement the circulating effects of their hormones.

Online text: farside.ph.utexas.edu/teaching/315/Waveshtml/node12.html

Cited passages: Richard Fitzpatrick, Damped Harmonic Oscillation, equations 2.19–2.22; his mν equals the coefficient b used here.

Online text: farside.ph.utexas.edu/teaching/315/Waves/node98.html

Cited passages: Richard Fitzpatrick, Two-Dimensional Fourier Optics, equations 10.78–10.87 and Table 10.1.

Cited passages: Fitzpatrick, §10.9, equations 10.70–10.74: path expansion and aperture superposition; Richard Fitzpatrick, University of Texas at Austin, Two-Dimensional Fourier Optics, circular-aperture first minimum; Richard Fitzpatrick, Wave Optics, §10.9: Two-dimensional Fourier optics.

Anharmonicity is departure from the motion of a harmonic oscillator, often caused by nonquadratic terms in a potential energy. It can make the oscillation frequency depend on amplitude and generate higher harmonics. A quartic oscillator has one such anharmonic potential energy.

By Yoshihiro Ohno.

Online text: www.nist.gov/publications/radiometry-and-photometry-review-vision-optics

Cited passages: Abstract: distinction between radiometry and photometry; Abstract: luminous flux in lumens and spectral weighting; Abstract: radiometric quantities and units; photometry weights radiation by the eye's spectral response.

Online text: openstax.org/books/organic-chemistry/pages/10-2-preparing-alkyl-halides-from-alkanes-radical-halogenation

Cited passages: Organic Chemistry by John McMurry, §10.2, Figure 10.2 and following paragraphs: radical combination terminates the chain; further substitution gives product mixtures.

Online text: openstax.org/books/organic-chemistry/pages/6-6-radical-reactions

Cited passages: Organic Chemistry by John McMurry, §6.6: chlorine photolysis and the two-step methane chlorination cycle.

Online text: openstax.org/books/organic-chemistry/pages/26-4-peptides-and-proteins

Online text: openstax.org/books/organic-chemistry/pages/26-2-amino-acids-and-the-henderson-hasselbalch-equation-isoelectric-points