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Documentation for Release 2024.1
Chaste Units
This page provides information on the units used within Chaste.
Cardiac Units
Note: $F$=Farad, $S$=Siemen=Amp/Volt, $A$=Ampere
| Quantity | Units | Notes |
|---|---|---|
| Length | $cm$ | hence surface-area-to-volume ratio is $cm^{-1}$ etc. |
| Time | $ms$ | |
| Voltage or intra- or extracellular potential | $mV$ | |
| Capacitance per unit surface area | $\mu F \thickspace cm^{-2}$ | $C_m$ which we refer to as the capacitance, is actually a capacitance per unit area. The SI unit of capicitance is the Farad ( = Coulombs/Volts) ($C=Q/V$) |
| Conductivities | $mS \thickspace cm^{-1}$ | |
| (Stimulus) currents per unit volume | $\mu A \thickspace cm^{-3}$ | Applies to (intracellular) stimulus currents given to cells in mono/bidomain problems (ie a stimulus current as a RHS source term in the bidomain equations. Note we don’t allow RHS extracellular stimuli) |
| Currents per unit area | $\mu A \thickspace cm^{-2}$ | Applies to all ionic currents (single-cell/mono/bidomain equations), intracellular stimuli in single-cell problems or applied as Neumann boundary conditions, and extracellular stimuli through electrodes (which are also Neumann boundary conditions) |
Cell-based
| Quantity | Units | Notes |
|---|---|---|
| Length | dimensionless | Nondimensionalised by typical cell diameter (approx $10^{-5}$ m) |
| Time | hours |
Mechanics
Material laws parameters, pressures, and active stresses (in cardiac
electro-mechanics) are in kPa. For mechanics simulations the user is free to
choose the units for all other quantities, but should do so consistently. For
example, if gravity is applied, then [* gravitational acceleration](density)
should be equal kPa/[length] (here [] denotes “units of”), since the
governing equations state that divergence of stress summed with density times
gravitational acceleration is zero.