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The abstract of the paper Fluctuation-induced current from freestanding graphene [1]: > At room temperature, micron-sized sheets of freestanding graphene are i

The abstract of the paper Fluctuation-induced current from freestanding graphene [1]: > At room temperature, micron-sized sheets of freestanding graphene are in constant motion, even in the presence of an applied bias voltage. We quantify the out-of-plane movement by collecting the displacement current using a nearby small-area metal electrode and present an Ito-Langevin model for the motion coupled to a circuit containing diodes. 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. However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath. The exact power formula is similar to Nyquist's noise power formula, except that the rate of change of diode resistance significantly boosts the output power, and the movement of the graphene shifts the power spectrum to lower frequencies. We have calculated the equilibrium average of the power by asymptotic and numerical methods. Excellent agreement is found between experiment and theory. [1] https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.042101 https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.0...

mannykannot 6y ago
"However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath." 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. http://atmosadam.com/howitworks.html http://atmosadam.com/howitworks.html
- gus_massa 6y ago
  The clock in your link uses the temperature fluctuations, for example if it hot during the day and cool during the night. So you can have a flux of heat from the hot part to the cold part, and extract a small part as useful energy. 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.
  - digikata 6y ago
    It is difficult to tell at this level if they're claiming to have built Maxwell's Daemon out of graphene - or at least an approximation thereof.
    - trhway 6y ago
      imagine a very thin and very short wire - just for one electron to move a bit left and a bit right. The surrounding environment - in particular Brownian motion molecules, especially the ones with large dipole moment, and the background EM radiation - will cause the electron to move left-right. Thus we have electric current generation. Now diode-terminate the wire to allow aggregating of many of such wires without mutual cancellation of the current generated by those wires. Well, meet the Maxwell's Daemon remote cousin - Maxwell's Diode. 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.
  - mannykannot 6y ago
    I am not inclined to take the press release at face value, as its author is apparently unaware of just how radical its claims are, if taken at face value, which in turn suggests that the author is out of his depth. 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."

mannykannot 6y ago

"However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath." 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. http://atmosadam.com/howitworks.html http://atmosadam.com/howitworks.html

gus_massa 6y ago
The clock in your link uses the temperature fluctuations, for example if it hot during the day and cool during the night. So you can have a flux of heat from the hot part to the cold part, and extract a small part as useful energy. 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.
- digikata 6y ago
  It is difficult to tell at this level if they're claiming to have built Maxwell's Daemon out of graphene - or at least an approximation thereof.
  - trhway 6y ago
    imagine a very thin and very short wire - just for one electron to move a bit left and a bit right. The surrounding environment - in particular Brownian motion molecules, especially the ones with large dipole moment, and the background EM radiation - will cause the electron to move left-right. Thus we have electric current generation. Now diode-terminate the wire to allow aggregating of many of such wires without mutual cancellation of the current generated by those wires. Well, meet the Maxwell's Daemon remote cousin - Maxwell's Diode. 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.
- mannykannot 6y ago
  I am not inclined to take the press release at face value, as its author is apparently unaware of just how radical its claims are, if taken at face value, which in turn suggests that the author is out of his depth. 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."