Glossary

This glossary defines the terms that recur across the reference in one place, grouped into four families: the foundations of open-system operation, the five parameters of the master formula, the transport-and-rectification concepts, and the modelling and contextual terms. Each entry is deliberately brief; where a term is developed at length elsewhere, the relevant chapter is linked. Symbols are written in mathematical notation, and the canonical formula they belong to is stated at the equation with a compact symbol table at the notation reference.

Open-system foundations

Open system

A system that continuously exchanges energy and momentum with its surroundings across a defined control surface. The framework is defined only for open systems; a closed system in equilibrium would give zero output. See open thermodynamic systems.

Non-equilibrium

A condition in which the system is not in thermal equilibrium with a single reservoir at one temperature, typically because it is held out of balance by a sustained external drive. Net continuous work extraction is permitted in this condition but forbidden in equilibrium.

External drive

The sustained ambient flux that maintains the converter away from equilibrium. It enters the formula through $\Phi(E,\theta,t)$ and is treated as an imposed boundary condition, not a device property.

Entropy export

The continuous transfer of entropy from the converter to its surroundings that accompanies conversion in an open, driven system. It is what reconciles continuous work output with the second law.

Control surface

The boundary across which the power balance is drawn. All quantities in the formula are defined relative to it; see system boundaries.

Second law (Kelvin–Planck statement)

The principle that no cyclic device operating with a single reservoir at one temperature can produce net work. It constrains closed equilibrium systems but not open driven ones, which is why the framework does not contradict it.

The five parameters

Flux density Φ(E,θ,t)

The ambient resource: incident field energy per unit area, per unit time, per unit solid angle, per unit energy, as a function of energy $E$, incidence angle $\theta$, and time $t$. It is the only factor carrying explicit time dependence in the basic form.

Scattering cross-section σ(E)

The energy-dependent effective area [m²] measuring how strongly the incident field couples to the converter material. Overlap between $\sigma(E)$ and $\Phi$ governs how much resource is intercepted. See sigma analysis.

Momentum transfer Δp

The net directed momentum [kg m/s] deposited per interaction after the isotropic, cancelling part is averaged away. It is the symmetry-breaking factor; $\Delta p \to 0$ in equilibrium, and then the output vanishes.

Phonon velocity v_ph

The velocity [m/s] at which the crystal lattice transports transferred momentum away from the interaction site before it randomises. It acts as the transport rate in the conversion chain.

Conversion efficiency η_conv

The dimensionless fraction, constrained to $0 \le \eta_{\text{conv}} \le 1$, of collected directed energy actually rectified into usable power. It absorbs all aggregate losses and bounds the output from above.

Power output P(t)

The instantaneous usable electrical power [W] delivered by the converter at time $t$ — the quantity the whole framework computes. It carries a time argument because it tracks a fluctuating environment.

Transport and rectification

Rectification

The conversion of a fluctuating or oscillating input into a net directed output. In the framework, rectification of directed momentum into usable power is what $\eta_{\text{conv}}$ quantifies; it succeeds only when symmetry is broken.

Symmetry breaking

The absence of the spatial or temporal symmetry that would otherwise make opposing momentum contributions cancel. It is the necessary condition for a non-zero $\Delta p$ and hence for any output.

Directed momentum

The component of transferred momentum that points, on average, in a definite direction and therefore survives averaging over fluctuations. Only this component contributes to $\Delta p$.

Brownian ratchet

A model system in which broken symmetry rectifies unbiased fluctuations into directed transport. It is the conceptual template for how the framework obtains net output from a fluctuating drive. See non-equilibrium energy conversion.

Phonon

A quantum of lattice vibration. Phonons carry the transferred momentum through the crystal at the velocity $v_{\text{ph}}$, linking a microscopic interaction to a macroscopic current.

Spectral matching

The alignment of the cross-section $\sigma(E)$ with the energy distribution of the flux $\Phi$, so that the material couples most strongly where the resource is most abundant. Good matching maximises the energy integral.

Quasi-static response

The assumption that the material factors respond effectively instantaneously to changes in flux, so that all time dependence in $P(t)$ flows from $\Phi(E,\theta,t)$. See mathematical architecture.

Model and context

Master formula

The Schubart Master Formula. Its single canonical form is the compact volume equation $P(t) = \eta \cdot \int_V \Phi_{\text{eff}}(\mathbf{r},t) \cdot \sigma_{\text{eff}}(E)\,dV$. Its expanded physical representation (a spectral–transport decomposition, which unpacks but does not replace the canonical form) is $P(t) = \iint \Phi\,\sigma\,\Delta p\,v_{\text{ph}}\,\eta_{\text{conv}}\,dE\,d\theta$. Every chapter elaborates one of its parts.

Representative slice

A single-band approximation, $P \approx \Phi\,\sigma\,\Delta p\,v_{\text{ph}}\,\eta_{\text{conv}}\,\Delta E\,\Delta\theta$, obtained by assuming one dominant window of energy and angle carries most of the integral. It is what the interactive explorer evaluates; see full derivation.

Technology-neutral

The property that the framework is agnostic about which physical channel or device realises the conversion. Specific technologies are special cases obtained by supplying concrete factor forms.

Illustrative order of magnitude

A placeholder numerical value chosen to exercise the structure or units of the formula, explicitly not a measured or claimed result. All internal numbers in this reference are so flagged; see dimensional analysis.

Effective parameter

An aggregate quantity that stands in for a great deal of microscopic detail — as $\eta_{\text{conv}}$ stands in for all conversion losses — treated as a single measurable number in the framework.

Neutrinovoltaics

One possible application of the general framework, never its definition, in which the ambient flux and coupling are given a particular physical identity. Any output predicted for it is a model projection pending independent validation; see future extensions.

Model projection

An output computed from assumed or estimated factor values, as distinct from a measured result. Composite predictions of the framework are projections until validated end to end; see scientific questions.