A local site of converging sensory axons and interactions with postsynaptic cells. Molecular identity and other developmental mechanisms contribute to targeting.

For uniform samples at rate $f_s$, the frequency $f_s/2$ is the Nyquist frequency. A real baseband signal confined below this boundary can avoid spectral overlap when an appropriate anti-aliasing filter is used.

Start with an inflationary patch of physical radius $H_i^{-1}$ in units $c=1$. After $N$ e-folds and subsequent expansion, its present radius is $H_i^{-1}{e}^N{a}_0/a_{\mathrm{reh}}$. Requiring it to cover the present Hubble radius gives the displayed inequality. With instantaneous conversion to radiation, fixed relativistic degrees of freedom and a fixed ratio $H_i/H_{\mathrm{end}}$, energy conservation gives $H_i\propto T_{\mathrm{reh}}^2$, whereas adiabatic subsequent expansion gives $a_0/a_{\mathrm{reh}}\propto T_{\mathrm{reh}}$. Thus the required $N$ increases approximately as $\log T_{\mathrm{reh}}$. Holding $H_i$ fixed while varying the end energy independently is a different comparison and reverses that simple temperature-only trend. The inflationary energy history and post-inflationary entropy history must be specified.^[ref]

The Jukes-Cantor model is a symmetric four-state continuous-time Markov chain for DNA evolution. Each change to a specified different base has rate $q$, so the total rate of actual changes is $3q$. Its same-base probability is $1/4+(3/4)e^{-4qt}$ and its probability for one specified different base is $(1/4)(1-e^{-4qt})$. The probability of any mismatch is three times the latter, tending to $3/4$ at long times. Distinguish the exponent parameter $4q$ from the actual per-site mutation rate $3q$ when fitting this model.

Mapping DNA fragments protected during controlled micrococcal-nuclease digestion. Digestion titration and fragment validation help distinguish nucleosome occupancy from sequence bias and other protected complexes.

The core histone assembly containing two copies each of H2A, H2B, H3 and H4 around which nucleosomal DNA wraps.

DNA connecting adjacent nucleosome cores. Its length and accessibility affect nucleosome-array organization.

Transient local unwrapping and rewrapping of nucleosomal DNA. This changes the accessibility of DNA and histone surfaces without requiring complete and irreversible loss of the histone octamer.

Resistance of a histone–DNA particle to loss or rearrangement of its components under specified conditions. Competitor-induced histone transfer can reveal destabilization even while a DNA-binding protein remains attached.

Movement of histones from one DNA substrate or complex to another. In competition experiments, loss of histones from a labelled complex need not release free DNA if another DNA-binding protein remains attached.

Nucleosome reconstitution assembles histones with DNA outside the cell to produce defined nucleosome substrates. It permits controlled comparison of DNA sequence, histone composition and associated factors. For example, comparing the same DNA with and without a nucleosome tests how packaging changes access by a DNA-binding protein. A simplified preparation isolates mechanisms but omits cellular processes such as ongoing transcription, histone turnover and chromosome-scale constraints. ^[ref]

A Meisenheimer complex is a sigma-bonded anionic addition species associated with suitable nucleophilic aromatic substitution reactions. Delocalization into ortho or para nitro groups can stabilize its negative charge.

Vicarious nucleophilic substitution replaces aromatic hydrogen using a nucleophile that carries its own leaving group. In nitroarenes, reversible carbanion addition gives a sigma-H adduct; base-induced elimination of the hydrogen and the nucleophile-borne leaving group, followed by protonation, gives substitution without expelling hydride.

An intramolecular aryl transfer to a carbon nucleophile. A tethered carbon anion attacks an aromatic ipso carbon and displaces the original oxygen-, nitrogen- or sulfur-based attachment.

An intramolecular nucleophilic aromatic substitution that transfers an aryl group between sites in one molecule.

Exchange of an ester alkoxy group through reaction with an alcohol, commonly using acid or base catalysis. Excess exchanging alcohol can shift the chemical equilibrium.

Breaking an ester linkage can proceed by different bonds and mechanisms. Acyl–oxygen and alkyl–oxygen cleavage should be distinguished when explaining protecting-group selectivity.

Acid-catalysed ester formation from a carboxylic acid and an alcohol, proceeding through carbonyl addition and elimination with net water formation.

Formation of a lactone by intramolecular esterification or acyl substitution. Favourable ring sizes can help trap an intermediate, but do not make the product universally unreactive.

Base-promoted bimolecular acyl substitution: nucleophile addition gives a tetrahedral intermediate, then a leaving group departs from the acyl carbon.