Dynamical crossover from motor-dominated to drag-dominated transport in a minimal active transport network

Motor-driven intracellular transport is often described in terms of motor activity, but macroscopic transport also depends on how effectively motor-generated force is converted into coherent motion. Motivated by cytoplasmic streaming, a minimal active transport network is examined in which motor-driven transport competes with an effective slip-related dissipative resistance. The model is not intended as a quantitative reconstruction of Nitella cytoplasmic streaming, but as a minimal system for isolating the relation between motor activity, resistance, and transport output. A controlled scan over ${\gamma }_{\mathrm{S}\mathrm{l}\mathrm{i}\mathrm{p}}$ and ${\alpha }_m$, with three independent seeds per condition, shows that increasing ${\gamma }_{\mathrm{S}\mathrm{l}\mathrm{i}\mathrm{p}}$ strongly suppresses mean transport speed while leaving the motor-bound fraction nearly unchanged. The mean load and motor force remain finite in the high-${\gamma }_{\mathrm{S}\mathrm{l}\mathrm{i}\mathrm{p}}$ regime, indicating that motors remain mechanically active even when transport is suppressed. The dependence of transport speed on ${\alpha }_m$ progressively disappears with increasing ${\gamma }_{\mathrm{S}\mathrm{l}\mathrm{i}\mathrm{p}}$: the motor dominance ratio decreases from $R\approx 1.69$ to $R\approx 1.01$, and the corresponding velocity difference decreases from $\sim 1.9\mu \mathrm{m}\mathrm{/}\mathrm{s}$ to $\sim 0.003\mu \mathrm{m}\mathrm{/}\mathrm{s}$. These results indicate a dynamical crossover from motor-dominated to drag-dominated transport. The minimal model provides a compact physical scenario in which active force generation persists while its contribution to net transport is suppressed by increased effective dissipative resistance.