Depositing supernova energy into dense unresolved gas can radiate it away before a numerically resolved expansion develops. Equal injected energy therefore need not imply equal outflow momentum or heating at different resolution. A feedback model should represent the coupling and cooling phase it intends to approximate, and comparisons should include gas recycling and the resulting stellar and circumgalactic properties.

For two approximately spherical stars approaching with speed $v_{\infty }$, contact at separation $R_1+R_2$ has gravitationally focused cross section $\pi (R_1+R_2{)}^2[1+2G(m_1+m_2)/((R_1+R_2)v_{\infty }^2)]$. This measures direct stellar encounters, not the probability of a collective encounter between their host galaxies.

Estimating astronomical ages from radioactive abundance ratios. A ratio evolves as $Q=Q_0{e}^{-({\lambda }_1-{\lambda }_2)t}$ for decay constants ${\lambda }_1,{\lambda }_2$. The initial production ratio and subsequent enrichment or mixing must be constrained; an observed ratio alone does not specify a unique age.

A cosmological age must exceed the ages of its oldest stellar populations plus their formation interval. globular cluster ages use the main-sequence turnoff with modeled distances, composition, nuclear rates and stellar transport. Their errors are correlated with these inputs, so a lower age bound must propagate the stellar and distance uncertainties rather than treating an isochrone as an exact clock.^[ref]

The body-centred cubic iron-rich solid phase of ordinary low-temperature steel, with low equilibrium carbon solubility.

The face-centred cubic iron-rich solid phase of steel. Its transformation products depend on composition and cooling history.

Cementite is iron carbide, $\mathrm{F}{\mathrm{e}}_3\mathrm{C}$, a hard phase important in many steel microstructures. It can occur with ferrite in organized mixtures such as pearlite.

The amount, size, and distribution of cementite affect mechanical behavior because a carbide particle interacts differently with deformation than the surrounding iron-rich phase. Chemical composition and spatial arrangement must therefore be considered together.

A lamellar two-phase microconstituent of ferrite and cementite, rather than a single thermodynamic phase. Shorter diffusion distances at greater undercooling generally produce finer lamellae before diffusional transformation is bypassed.

A product of a displacive transformation. In carbon steel, rapid cooling can trap carbon in a distorted iron lattice, producing high hardness and low as-quenched toughness.

A chart of the time needed to reach specified transformation fractions after cooling to, and holding at, a fixed temperature. Its curves are not themselves continuous-cooling histories; estimating a critical cooling rate from their nose is an approximation.

Heating quenched steel below the austenitizing range to adjust its microstructure and relieve stresses. Carbon redistribution and carbide formation can improve toughness at a cost in hardness.

A nitric-acid/alcohol metallographic etchant. In pearlitic steel it can preferentially remove ferrite, leaving cementite standing higher. In an atomic force microscopy height image, darker then means lower surface height, not an optical reflectivity or atomic-number contrast.

A learned method for predicting certain cellular perturbation responses from single-cell RNA sequencing data. Generalization to evaluated held-out cell types or conditions does not establish predictive validity for all interventions.^[ref]

Representation of one categorical outcome by a vector with one component equal to one and all other components zero.

Classification with more than two mutually exclusive outcome classes. A softmax output can represent a normalized distribution over the classes.

Prediction of several labels that can occur together. Independent sigmoid outputs do not impose the sum-to-one constraint used for mutually exclusive classes.

A predictive dependence in which the effect of one input feature changes with another. A product term is a simple example that cannot be represented by a purely additive linear predictor.

Progression away from the basal compartment toward specialized surface layers. Differentiation, delamination and subsequent cell loss need not occur simultaneously.

Every finite acyclic impartial game under the normal-play convention has a Grundy number. The Grundy number of a sum of independent games is the bitwise exclusive or of their individual Grundy numbers, so the sum is losing exactly when that value is zero.

A microsporangium is a sporangium in which microspores are produced. In a heterosporous plant, those microspores develop into male gametophytes; production of sperm is a later step.

In a flowering plant, the anther contains microsporangia. Distinguishing the enclosing structure, the microspore and the mature pollen grain prevents several different developmental stages from being treated as synonyms.