nx_stability.nx

nx_stability.nx -- ICH Q1A(R2)/Q1E STABILITY rung: the temperature physics that turns "how long is it good for" into a computed number instead of a printed guess. Serves the peptide / supplement / frozen-dessert lanes alike, because degradation kinetics does not care what the product is. ===== WHY THIS EXISTS ============================================ nx_shelf_life already models Q10 scaling, but ONLY at decade-aligned temperature steps -- and the actual regulatory question is 25 C vs 40 C, a FIFTEEN degree gap. The organ returned -1 for the one comparison the whole category rests on. This rung supplies the Arrhenius layer beneath it and the ICH machinery above it. ===== THE KEYSTONE: Ea IS RECOVERED, NOT ASSERTED ================ Every stability model needs an activation energy, and asserting one is how a plausible-looking shelf life becomes a lie. We do not assert it. ICH Q1A(R2) declares that 6 months at the accelerated condition (40 C) supports a 24-month re-test period at the long-term condition (25 C). Two conditions the regulation itself calls EQUIVALENT uniquely determine the kinetics between them: acceleration factor = 24/6 = 4 over dT = 15 C Q10 = 4^(10/15) = 2.512 (published pharma/food band: 2 - 3) Ea = R*ln(4)*T1*T2/dT = 71.6 kJ/mol (published band: 60 - 100) BOTH recovered figures land inside independently published bands that were never used as inputs. That is the liar-kill: the regulation's own arithmetic agrees with the thermal-degradation literature. This is the same discipline nx_thermal_process used to recover the pasteurisation z-value from the PMO's two equivalent schedules. ===== ⚠THE RECOVERED Ea IS LUMPED, AND SAYING SO IS THE POINT ===== ICH's two conditions are 25 C / 60% RH and 40 C / 75% RH. They differ in TEMPERATURE **AND IN HUMIDITY**. Two conditions differing in two variables cannot separate two parameters -- the system is underdetermined -- so the figure recovered above is an EFFECTIVE activation energy that carries the moisture contribution inside it, not a pure thermal Ea.