The cyclic trimer of formaldehyde, $(\mathrm{C}{\mathrm{H}}_2\mathrm{O}{)}_3$. Acid-catalysed acetal cleavage can regenerate formaldehyde, which is strongly hydrated in water.

A shallow acceptor can bind an electron hole through the screened Coulomb potential of a negatively charged impurity. A scalar band effective mass approximation gives a hydrogen-like bound-state ladder. Actual valence-band degeneracy and anisotropy can split levels and limit that approximation.

Dengue virus exposure can be investigated through antibodies in serum, but antibody detection must be distinguished from identification of current infection. Cross-reactivity with antibodies to other related viruses can limit interpretation.^[ref]

A retrovirus replicates through reverse transcription of its RNA into DNA, followed by a DNA stage that can integrate into the host genome. Viral gene expression can then use cellular transcription machinery.

Rous sarcoma virus is a transforming avian retrovirus used to dissect the relationship between viral replication, Src-dependent transformation and cellular growth-control genes.

The retroviral life cycle includes entry, RNA-to-DNA copying by reverse transcriptase, a DNA intermediate and gene expression followed by particle production. Integration as a provirus can make the genetic change persistent across cell divisions.

A provirus is a viral DNA form integrated into a cellular genome. Its location and regulatory sequences can influence both viral expression and neighbouring cellular genes.

A poxviral disease important in some red squirrel declines. Differential susceptibility and field exposure both matter when attributing population change. ^[ref]

A protein shell enclosing a viral genome. Protection from nuclease is consistent with enclosure but does not alone demonstrate infectivity.

An infection caused by a virus. Entry, genome expression and production of infectious particles are distinct stages; detecting viral nucleic acid does not alone measure all of them.

Exam sources held for the University of Cambridge, checked on 18 October 2026. Each year range means at least one held paper in every listed year; it does not promise every paper or module for that year. Links lead to existing course or exam articles; bold course names have no dedicated article yet. Download links lead to public originals, sometimes inside larger releases.

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For Physics courses, the official past-paper search requires University sign-in; its exact-year solution holdings remain unverified except for the public sets identified below.

The two undated sheets above are retained separately from dated papers. The MPhil Nuclear Energy 2021 data book is accompanying reference material, not an additional examination paper. Historical module titles are retained even where today’s course names differ.

A shunt electrical resistance $R$ inserted between the conductors of a uniform lossless transmission line of characteristic impedance $Z$ has voltage reflection coefficient $r=-Z/(2R+Z)$ and transmission amplitude $t=1+r$. Equally spaced shunts produce coherent reflected waves. The round-trip phase between neighbours is $2kL$, so interference repeats in frequency with spacing $v_p/(2L)$ for nondispersive phase speed $v_p$.

A periodic lossless line can consist of equal-length sections with impedances $Z_1,Z_2$. Its semi-infinite input is a fixed point of the two-section impedance transformation. The physical solution selects a forward-energy or decaying Bloch wave. At special frequencies where the cell matrix is the identity, the fixed-point equation alone loses uniqueness; limiting absorption or a termination specifies the response.

A length $\ell$ with impedance ratio $\alpha$ between identical matched lossless lines has multiple internal reflections. Summing their amplitudes gives the displayed power transmission when the propagation speed is the same in all sections. It is unity at half-wave resonances even though either individual interface reflects. Matched remote terminations remove external echoes but not this frequency dependence.

Coupling models at different spatial or temporal resolutions while making their interfaces, units and conservation requirements explicit.