As the "thermal bath" is supplying power, this seems consistent with it being a Carnot-equivalent heat engine.
There is certainly nothing in physics that prevents the extraction of energy from an environment in which the temperature fluctuates - devices that do so to keep mechanical clocks running indefinitely have been around for some time.
If we take the press release at face value, in this device there is no difference of temperature. So if the Second Law of Thermodynamics is correct it is not possible to extract some useful energy to do something interesting, like turning on the lamp in the animation.
Basically, there are always local micro gradients even though the macro integration of those gradients gives 0. It may as well happen that graphene being few atoms thick and thus dipping into the local scale properties may bridge and aggregate without [total] mutual cancellation those properties into the macro scale (graphehe sheet vibrations may happen be [one of] such a filter, kind of piezoelectric effect). There is no violation of the 2nd law as extracted work/energy wouldn't be larger than the entropy increase resulting from the smoothing of the micro gradients (bringing the Universe's heat death closer).
Or even imagine a pond with no visible movement of water and place over it a myriad of very very small water mill wheels - they will be rotating chaotically back and forward due to small perturbances in the water (and the smaller a giving wheel the larger share of local gradient it will be extracting as the smaller share of it will be mutually cancelling with the neighboring gradients under the wheel). That chaotic rotation of that myriad of wheels can be aggregated into usable work/energy.
The above quote is from the abstract, and just before it, we see the much more reasonable "numerical simulations show that the system reaches thermal equilibrium and the average rates of heat and work provided by stochastic thermodynamics tend quickly to zero."
It make sense, but the problem is more subtle. It's better compare the clock with a brick.
In the example of the clock there is a temperature difference that can be used to extract "useful" energy. You can use it to move the clock, or make a sound or light or something.
(I'm saying "useful" as in the a quote of the main author of the paper "What we did was reroute the current in the circuit and transform it into something useful.” .)
If you put a brick in a oven and keep it at the same temperature for some time, until the temperature, humidity and other properties have stabilized, you reach thermal equilibrium. It doesn't mean that the heat energy in the brick is perfectly constant, it exchanges heat with the oven. The heat energy has small random variations.
But unlike in the clock scenario, you can't use this additional accumulated energy for something "useful". To check if it is in a high or a low, you need a variant od the Maxwell's Demon. You can measure the energy exchange and analyze the theoretical and experimental properties anyway.
(Also, if you put the clock in the oven at a constant temperature for a long enough time, it will stop working.)
Stealing the name from a sibling thread, to make the grapheme device produce "useful" energy, you probably need a Maxwell's Diode.
What is 'the problem' that you are apparently trying to address here? Everyone in the discussion is well aware that the 2nd. law of thermodynamics prevents the continuous extraction of work from ambient heat without there being a temperature difference. Are you saying that the paper is claiming that this has been done? If not that, are you claiming that the device, as described in the paper, is incapable of generating power from fluctuations in the ambient temperature? Have you identified some other problem in the paper? Alternatively - I don't think you are saying this, but I will put it in for completeness - could it be that you are saying that the paper shows that this team really has invented a Maxwell's diode, capable of continuously extracting work from the ambient heat of a closed system in thermal equilibrium?
If you are still only taking issue with the press release, you are just nerdsplaining to a bunch of people who already get it, thank you very much.
Probably not, but it is good to know that you are.
The paper is not about a device that harvest energy from the thermal variations of the environment. There is no mention of macroscopic thermal variations in the press release or in the abstract of the paper. Also, the graphene is inside a ultra high vacuum chamber, that is a weird place to put a device that that depends on the macroscopic thermal variations of the environment.
From the abstract:
> However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath.
My interpretation is that the resistor is dissipating some power (from the graphics ~1pW), but it is also absorbing the same amount of power due to the 2nd law. It is not a Carnot engine that produces work from heat.
Are you taking the quoted passage as implying it is performing 100% conversion? This would indeed be a problem, as there is no heat sink at 0K here. That quote, however, is ambiguous, as it says power supplied by the heat bath and not lost from it, and may merely be a statement that it obeys the conservation of energy (i.e. the point being made here may be that the power being supplied to the load comes from the heat bath, as opposed to coming from another possible source, such as the bias voltage supply.)
I really should buy and read the paper, but I am not that motivated yet.
A real engine transform heat into electric energy that can be used to dissipate heat inside a container at any temperature. In particular at a higher temperature that the graphene and the support and the circuit. In the PR they claim that it produce "something useful" that I interpret as "work" or "electrical energy", but in that case it breaks the Second Law even if in their setup the resistor is at the same temperature.
After reading the paragraph again, I'm not sure if your interpretation is right and they are claiming that the device is transferring energy from the graphene to the resistor, but that breaks the second law, in spite in the PR they claim it doesn't.
I think they never claim a 100% conversion anyway. They just don't have a temperature difference to operate the engine.
Another way of thinking about it is that random noise although uniform at large scale, is intrinsically noisy when you zoom in.
I don't remember something like the clock at the molecular level, but I think it is "theoretically possible" (or to be more accurate, "not theoretically impossible").
[Weird example warning]
In the mitochondria the ATP synthase https://en.wikipedia.org/wiki/ATP_synthase use the H+ difference of the inner and outer part to produce ATP. The main problem is how to create this difference without sugar or pyruvate, using only a change of temperature.
Perhaps it is possible to put a weak acid outside of a mitochondria, and select the weak acid that changes the dissociation constant a lot with the temperature.
So when temperature is high it is mostly dissociated and the acidity is high and the mitochondria produces ATP. But after some time there is no difference in the concentration of H+ inside and outside of the mitochondria and the process stop.
Then reduce the temperature so the acidity outside is low, and the H+ inside the mitochondria can escape by other pores. (Perhaps we need to make some additional pores for this? The pores must be small and not very polar.) After some time, the concentration of H+ inside the mitochondria is low again. And we can repeat the cycle.
[/Weird example warning]
This will be painfully slow and painfully inefficient. My biochemistry level is too low to be sure this is possible, but at lest I think it is not theoretically impossible.
It is a small system, so I think it is a relevant comparison in spite it is very different of a graphene membrane in a vacuum chamber.