Interconversion of a carbonyl compound with its enol or enolate-derived forms. Reprotonation of a planar intermediate can epimerize an alpha stereocentre.

temperature can smear measured spectral or transport features through the spread of occupied energies and through temperature-dependent scattering. Fermi-edge occupation broadening and phonon-induced lifetime broadening are different mechanisms and should not be equated.

A disconnectivity graph summarizes how local minima of an energy landscape become connected as the allowed maximum energy increases. Each terminal branch represents a basin around a local minimum. Two branches merge at the lowest threshold for which a permitted path joins their basins without exceeding that threshold. Vertical height therefore carries barrier information; horizontal spacing is usually chosen for readability.

For example, two low-energy states may sit at similar energies but merge only high in the graph, indicating a difficult transition between them. A cluster of branches merging low down instead suggests easy rearrangement within that group. The graph is useful for separating energetic preference from kinetic accessibility in thermal activation. It does not determine transition rates by itself: the allowed dynamics, path widths and kinetic prefactors remain necessary. Changing the permitted moves changes which paths exist and can therefore change the graph.

At fixed environmental constraints, integrate out unobserved coordinates to obtain an equilibrium probability density for a chosen reaction coordinate $x$. Relative to a specified coordinate measure, the displayed free energy reproduces that density. A change of coordinate can add a Jacobian term, so the profile is not independent of its coordinate convention. Minima identify probable basins, while barriers relative to an initial basin contribute to activated kinetics; a kinetic prefactor still requires dynamics. A conjugate force tilts the profile by $-Fx$.

Energy per unit mass, with units such as $\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}$ or $\mathrm{Wh}\mathrm{k}{\mathrm{g}}^{-1}$. Active-material, cell and packaged-system mass bases can give very different values.

Mechanical energy harvesting converts supplied motion or deformation into recoverable energy in an electrical load. A vibrating support can drive a moving magnet, a variable capacitor or a device using piezoelectricity. These are different transducers coupling a mechanical input to an electrical load.

A small generator attached to a vibrating beam provides a useful experiment: measure both the electrical output and the change in the beam's motion as the load is varied. Extracting energy introduces a resisting force or effective damping, so the transducer can change the vibration that drives it. Available average power, response frequency and losses all matter. A large open-circuit voltage alone does not establish useful output power; the device must deliver energy to a specified load while an external source sustains the mechanical motion.

Collection of ambient light, heat flow, thermal cycling, motion or other available energy into a usable electrical supply. Available average power, conversion loss and peak-load buffering must be distinguished.

An early endosome is an early sorting compartment for internalized material. Delivery to it, recycling from it and onward trafficking are experimentally distinct from uptake across the plasma membrane.

A maturing degradative compartment distinguished from early sorting endosomes by changes in proteins, lipids, lumenal conditions and fusion competence.

Progressive changes in endosomal membrane identity and lumenal processing, accompanied by sorting and retrieval rather than uniform conversion of all endocytosed cargo into a degradative route.

An endoplasmic reticulum exit site is a region organizing export machinery and cargo departure from the ER. Local coat assembly, cargo concentration and membrane supply can be coordinated there.

The endoplasmic reticulum lumen is the aqueous space enclosed by the ER membrane. A soluble lumenal cargo cannot directly contact a cytoplasmic coat across an intact membrane.

endoplasmic reticulum stress arises when ER demands exceed its processing or homeostatic capacity. It can alter folding, degradation and transport, confounding interpretation of a supposedly selective secretion defect.

The path length along a polymer backbone. For $N$ links of length $a$ it is $Na$, whereas the end-to-end distance of a polymer chain cannot exceed it. A statistical segment count need not equal the chemical degree of polymerization.

An organized structural unit of mammalian crown enamel. Its architecture is a derived tissue organization, distinct from the deeper origin of the enamel tissue itself.

An emulsion stabilized by particles adsorbed at the liquid–liquid interface. A partially wetting sphere has a detachment-energy scale $\pi r^2\gamma (1-|\cos \theta |{)}^2$, which can greatly exceed $k_{B}T$ for nanoparticles; complete wetting and insufficient coverage prevent a universal stability guarantee.

A surfactant-stabilized dispersion can remain macroscopically uniform while its two liquids remain distinct phases. Lower interfacial tension reduces the work of making droplets, and repulsive interfacial films can slow droplet coalescence. Kinetic emulsion stability does not by itself establish equilibrium molecular miscibility or a thermodynamically stable microemulsion.

Merging of droplets after their separating film fails. This differs from clustering of still-distinct droplets. Interfacial protection can delay merging without making the two bulk liquid phases molecularly miscible.

Two coherent waves with common propagation direction and frequency can combine into a polarization ellipse. Take circular components $E_x=A\cos \psi$, $E_y=A\sin \psi$ and add $B\cos \psi$ along $x$. The resulting semiaxes are $|A+B|$ and $|A|$. Choosing positive $A,B$ gives a nondegenerate ellipse with unequal axes. Uncorrelated relative phases do not describe the same fixed pure polarization.