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The two-domain system recognizes bacteria and archaea as the two primary lineages, placing the nuclear ancestry of eukaryotes within archaea. In this model, archaea as a complete clade includes that eukaryotic lineage; restricting the name to prokaryotic members describes a different grouping. Williams and colleagues' study, published online in 2019 and in a 2020 journal issue, found support for this model and a close relationship to Asgard archaea. See Williams et al., 2020: Phylogenomics provides robust support for a two-domains tree of life.

This updates the interpretation of the 1977 and 1990 classifications rather than undoing their discovery of deep differences between bacteria and archaea. Deep phylogenetic trees depend on the sampled genes, organisms and inference model; the precise closest archaeal relatives and early sequence of events require further evidence. Bacterial ancestry of mitochondria through endosymbiosis is a separate part of eukaryotic history.

The three-domain system recognizes bacteria, archaea and eukaryotes as three domains. In 1990, Woese, Kandler and Wheelis proposed the domain rank and the names Bacteria, Archaea and Eucarya, using molecular comparisons to argue that the older prokaryote/eukaryote division hid important differences. See Woese, Kandler and Wheelis, 1990: Towards a natural system of organisms.

The associated three-domain ancestry model places the nuclear lineage of eukaryotes alongside archaea, rather than within them. This historically influential interpretation should be distinguished from the two-domain system; listing three familiar groups does not establish three independent primary branches.

Online text: diveintosystems.org/book/C11-MemHierarchy/caching.html

Cited passages: Dive into Systems, section 11.4.2: Cache Misses and Associative Designs, compulsory, capacity and conflict misses; Dive into Systems, section 11.4: CPU Caches, opening discussion of hits, misses and filling the cache.

A prion disease is associated with self-propagating abnormal folding of a protein. Its epidemiological interpretation requires distinguishing exposure, infection, clinical onset and diagnostic detection.

A group of metabolic disorders characterized by persistently elevated blood glucose due to inadequate insulin secretion, action or both. Its forms differ in mechanism despite the shared glycemic result.^[ref]

Online text: ocw.mit.edu/courses/6-262-discrete-stochastic-processes-spring-2011/3a19ce0e02d0008877351bfa24f3716a_MIT6_262S11_chap02.pdf

Cited passages: Chapter 2, section 2.2.4, printed pp. 78-79: counting-process definition and its equivalence to exponential interarrival times.

Coordinating CPU and device access to a DMA buffer, including any required memory cache maintenance and ordering. A completed device write must be made visible before the CPU consumes it. The Linux kernel distinguishes coherent mappings from streaming mappings needing synchronization at ownership changes; even coherent mappings can require ordering of writes. ^[ref][ref]

An address supplied to a device for DMA, in the device's address system. The Linux kernel's mapping interface returns this separately from the CPU's virtual address; an IOMMU can translate it to a physical address. ^[ref]

A region of computer memory prepared for DMA. In the four-byte receive example it is the payload destination, and must remain available until the transfer and required DMA buffer synchronization are complete.

Rescaling dimensional quantities by chosen characteristic scales produces dimensionless variables. The remaining dimensionless ratios identify independent parameters and possible asymptotic regimes.

In the simple pendulum equation, choose the time scale $t_{\ast }=\sqrt{\ell /g}$ and put $\tau =t/t_{\ast }$. The chain rule gives $\ddot{\theta }=(g/\ell )d^2\theta /d{\tau }^2$, so the equation becomes $d^2\theta /d{\tau }^2+\sin \theta =0$. This removes $\ell$ and $g$ from the equation, while the initial conditions still include angular amplitude and dimensionless initial angular speed. A solution can therefore be calculated once and rescaled to many physical lengths and gravity values with the same dimensionless initial data.

Online text: www.nist.gov/pml/diatomic-spectral-database/diatomic-spectral-database-1s-ground-state-molecules

Rate-zonal centrifugation resolves an initially narrow sample zone by differences in sedimentation coefficient during a finite interval. Its bands remain transient: extending the interval can carry material into a centrifugation pellet. Thus a density gradient need not imply an equilibrium buoyant density measurement.^[ref]

A typical preparation layers a narrow sample above a preformed density gradient, often containing sucrose. The initial zone must be narrow enough that differences in starting position do not overwhelm the later separation. The run ends while useful bands remain inside the liquid. In the simple case where all particles are denser than every part of the column, none has an interior isopycnic centrifugation position.^[ref][ref]

The sedimentation coefficient $s=(m-{\rho }_{f}V)/f$ explains why separation is not an ordering by mass alone. At fixed local centrifugal acceleration, increasing displaced volume can increase buoyancy, while a less compact shape can increase the linear friction coefficient and reduce velocity. Even for a sphere, Stokes's law gives $s=2b^2({\rho }_p-{\rho }_f)/(9\eta )$, so both the density difference and the dynamic viscosity matter. The resulting sedimentation coefficient can change along a density gradient.