An extensometer measures the change in distance between two specimen points. Its gauge length defines the reference length used to calculate engineering strain.

Crosshead displacement is the measured travel of a testing machine's moving crosshead. Depending on the readout and apparatus, it includes deformation outside the specimen segment measured by an extensometer. It is affected by machine compliance.

Cited passages: equations (1)–(3), mass thickness, and photon-energy dependence.

Spatial variation of the valence band and conduction band edges associated with a varying electric potential. Near a semiconductor boundary it can deplete mobile charge carriers or create a semiconductor inversion layer.

Institutional appendix; no separate personal byline. Defines stopping powers, CSDA and projected ranges, and detour factor.

For a fast ion traversing a fixed material thickness with only a small fractional energy loss, the dipole excitation probability per atomic encounter scales as $Z^2/v^2$ at fixed impact parameter. Summing transferred excitation energies and integrating the encounter measure $2\pi bdb$ gives the leading electronic stopping power scaling, with slower logarithmic dependence from the allowed excitation energies and impact-parameter range.

At fixed ion kinetic energy $E=M{v}^2/2$, a heavier isotope is slower, so the leading loss scales as $Z^{2}M/E$. At fixed velocity, isotopes of the same element instead have approximately the same electronic loss; plotting against energy per nucleon removes the leading isotope mass dependence. The charge should be the effective projectile charge if its bound electrons screen the nucleus. At lower speeds, excitation thresholds, slow-passage suppression, charge exchange and nuclear energy transfer invalidate a simple extrapolation of the high-speed law.

A quantum fluid is a fluid whose collective behavior requires quantum mechanics, particularly when the thermal de Broglie wavelength becomes comparable with particle spacing. Exchange statistics and interactions then affect the state in ways that a dilute classical particle model cannot capture. Low temperature favors this regime, but temperature alone is insufficient without a density and particle-mass scale.

Superfluid helium-4, degenerate fermionic matter described by a Fermi liquid, and dilute ultracold atomic gases provide different realizations. A quantum fluid need not be a superfluid, and quantum degeneracy does not by itself remove dissipation. Measurements of heat capacity, collective waves and response to flow distinguish the relevant states. The useful organizing question is which low-energy excitations carry energy, momentum and conserved particle number, rather than whether individual particles merely have small kinetic energies.

A non-Fermi liquid is an interacting fermionic state whose low-energy behavior is not described by the long-lived quasiparticles of a Fermi liquid. In the conventional Fermi liquid picture, excitations close enough to the Fermi surface become sharp compared with their excitation energy. If that organizing principle fails, extending the same quasiparticle approximation toward zero energy can give the wrong response.

The term describes a failure of one framework, rather than one unique replacement theory. A one-dimensional Luttinger liquid provides a controlled example: its long-wavelength excitations are collective density modes, and its correlation functions need not have the free-fermion form. An anomalous finite-temperature transport curve alone does not establish a particular zero-temperature non-Fermi liquid. Spectral and thermodynamic measurements must be interpreted alongside the relevant dimensionality, interactions and accessible energy range.

An energy landscape assigns an energy to each possible state and describes its variation between neighbouring states. Its local minima and intervening energy barriers help distinguish favourable states from states that a specified dynamics can reach quickly. In a Hopfield network, the assigned energy is an objective function and need not be a conserved physical quantity.

Thermal activation is barrier crossing enabled by thermal fluctuations. A system can remain for a long time near a local minimum of an energy landscape, then receive a fluctuation large enough to cross an energy barrier. Its most probable state and its waiting time for escape are therefore different questions.

In a simple high-barrier regime, the escape rate is approximated by $r(T)=r_0\exp [-\Delta E/(k_{B}T)]$, an Arrhenius equation. The barrier $\Delta E$ controls the strong temperature dependence, while the prefactor $r_0$ depends on dynamics near the initial state and transition region. Plotting $\log r$ against $1/T$ tests the exponential model: a constant prefactor gives slope $-\Delta E/k_B$. Interpreting a slope still requires care if several escape paths compete or the prefactor varies with temperature. A large barrier can delay approach to thermal equilibrium even when the final equilibrium state is known.