Dissipation sharing

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This article defines a novel term (that is hopefully sensibly chosen). The term is introduced to make a concept more concrete and understand its interrelationship with other topics related to atomically precise manufacturing. For details go to the page: Neologism.

Dissipation sharing is a technique enabled through smart usage of machine phase that allow to far surpass the efficiencies seen in already pretty efficient biological solution based systems.
To the authors knowledge "dissipation sharing" is a novel idea here presented for the first time.

For brevity in the following we will refer to

In machine phase (A) friction from superlubrication is not a disadvantage since it's far over-compensated by gains elsewhere

While in case (A) one has some very small losses due to the friction of the superlubricating bearings compared to completely free since thermally driven transport in case (B) the final deposition of the molecule(fragment) at the target location can be done so much more efficient in case (A) that it easily more than compensates the former disadvantage.

No possibility to receive energetic "exchange money" in diffusion based systems (B)

The problem in case (B) is that the bonding energy of the molecule to the target site is a fixed quantity. (Example: ATP in cells carries around a fixed amount of energy.) If the reactants are not held by manipulator tips the bonding energy cannot be collected/recuperated as "exchange money" by letting the reaction-pull-force do work to some energy storage elsewhere. Instead the "exchange money" is fully thermalized/devaluated.

The minimum price to pay to never go backwards

A little bit of thermalization/devaluation of energy is required though to make sure that the bonding reaction runs reliably forward. For the bonding reaction to run forward reliably the energy pumped into the thermal motions must significantly exceed the quantity kBT.

For a system to run predominantly in one direction (for it to have an arrow of time) the thermodynamic potential for the system must decrease. For solution phase chemistry the appropriate thermodynamic potential is the Gibbs free energy. One needs to devaluate/thermalize free energy.

For a single reaction the energy pumped into the thermal motions must significantly exceed kBT. Beside the obvious thing to lower the temperature (which has practical limits) there's another opportunity to drive down the price. Sharing.

Sticking together comes cheaper -- dissipation sharing

In advanced systems (A) there's a trick (the titular "dissipation sharing") that may allow one to avoid paying the minimum "tax" for every single reaction. One can thereby go to the limits and squeeze out the last little bits of efficiency towards 100%.

In solution based systems (B) reactions are mostly fully isolated from each other. Every reactant molecule has its own degrees of freedom. Stiff machine-phase-systems (A) allows one to link many reactions together. More concretely: Many of the molecular mills are linked together in the background stiffly by one common rotating shaft. This effectively reduces the many individual degrees of freedom for the atom depositions to just a single one. The rotation angle of the main shaft. Only for this one remaining common degree of freedom one needs to still expend/theralize/dissipate an amount of energy >> kBT to ensure forward motion.

The limits of sharing

How many reactions one can can couple together is a highly nontrivial but very important question. (TODO: investigate that) More accurately the question is how far can one stretch the spacial and temporal reach of the degree of freedom of one "virtual reaction". Elasticity modes in the background mechanics (e.g. lowest torsion twist eigenmodes in axles) introduce new unwanted degrees of freedom that need to be fed. Degrees of freedom can decouple the sites of mechanosynthesis into groups of in the worst case just one.

One can think of it like that: If there is enough flex in the axles in the background then even if the far away end is held firmly the reaction site van still fall/snap dissipatively in sharp energy minimum.

(TODO: add infographic)

Stretching the limits of sharing

Introducing mechanical advantage (gear train transmission) as soon as possible to gain high virtual stiffness in the background may be a feasible strategy.

What if you don't pay fully?

Occasionally running backwards a slight bit may be bad for a nanofactory. If the reactions are not fully reversible one might end up in an unknown failure state (atom at wrong location). When progressing with open loop control (manipulators working blindfolded to a good part will be normal in advanced nanosystems) the resulting errors effects may range from irrelevant over performance degrading to fatal for the local subsystem. Depending whether on the location of the error and the degree of consequential errors.

Conclusion

Advanced gemstone based atomically precise manufacturing system (A) operating in machine phase
will be able to do guided placement of molecule fragments much more efficiently than more primitive systems based on solution based self assembly (B) is able to its molecular assembly that is unguided and thermally driven .

Misc

Possible effect of location of deliberate dissipation elements?

  • too low down wastes energy?
  • to high up causes oscillation problems?

Related

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