Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F18: Mpemba Effect: anomalous cooling kinetics and its generalizationsInvited Session Live
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Sponsoring Units: GSNP Chair: Zhiyue Lu, University of North Carolina |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F18.00001: The Markovian Mpemba effect in large many-body systems, and its applications in optimal protocols. Invited Speaker: Oren Raz Finding the optimal heating/cooling protocol is a common task in many applications: from improving the power of a heat engine, through finding the ground state of a complex system, to making fast food . Intuitively, one expects the optimal heating/cooling protocol to include only the extrme temperatures. However, the Mpemba effect suggests that protocols with non-monotonic temperature might be supirior to the naive protocol, and that in some cases optimal protocols might be highly counter-intuitive, e.g. cooling a system can reduce its heating time. |
Tuesday, March 16, 2021 12:06PM - 12:42PM Live |
F18.00002: Exponentially faster cooling and heating in a colloidal system Invited Speaker: John Bechhoefer Since the temperature of an object that cools decreases as it relaxes to thermal equilibrium, naively a hot object should take longer to cool than a warm one. Yet, some 2300 years ago, Aristotle observed that “to cool hot water quickly, begin by putting it in the sun.” In the 1960s, this counterintuitive phenomenon was rediscovered as the statement that “hot water can freeze faster than cold water” and has become known as the “Mpemba effect.” While many specific mechanisms have been proposed, no general consensus exists as to the underlying cause. Here we demonstrate the Mpemba effect in a controlled setting, the thermal quench of a colloidal system immersed in water, which serves as a heat bath. Our results are reproducible and agree quantitatively with calculations based on a recently proposed theoretical framework. By carefully choosing parameters, we observe cooling that is exponentially faster than that observed using typical parameters, in accord with the recently predicted strong Mpemba effect. We then show that similar phenomena can be observed when heating—these are the first observations of an inverse Mpemba effect. In this case, a cold system placed in a hot bath will reach equilibrium more quickly than a warm one placed in identical conditions. Our experiments give a physical picture of the generic conditions needed to accelerate relaxation to thermal equilibrium and support the idea that the Mpemba effect is not simply a scientific curiosity concerning how water freezes into ice—one of the many anomalous features of water—but rather the prototype for a wide range of anomalous relaxation phenomena that may have significant technological application. |
Tuesday, March 16, 2021 12:42PM - 1:18PM Live |
F18.00003: The anomalous thermal relaxation of Langevin particles Invited Speaker: Marija Vucelja Comparing two identical systems in their relaxation to the environment, we expect that the system with a smaller mismatch between its and the environment's temperature will thermalize faster -- yet it is not always the case. The Mpemba effect is an example of an anomalous relaxation process, where "hot cools down faster than cold" or "cold heads up faster than warm." The effect was experimentally observed in water, magnetic systems, clathrate hydrates, polymers, and colloidal particle systems. It was simulated in granular fluids, spin-glasses, driven gasses, quantum systems, magnetic alloys, and gases without equipartition. The numerous occurrences of the effect imply that it is general. To understand the general nature of the Mpemba effect, we theoretically study a model system -- the overdamped dynamics of a particle moving on a potential surface. We connect the occurrence of the Mpemba effect with the properties of the potential, characteristics of its meta-stable states, and provide further insight into anomalous relaxation processes. |
Tuesday, March 16, 2021 1:18PM - 1:54PM Live |
F18.00004: The Mpemba effect as a far from equilibrium phenomenon Invited Speaker: Antonio Lasanta Becerra The Mpemba effect is the process in which two identical beakers of water, initially at two different temperatures, put in contact with a thermal reservoir at subzero (on the Celsius scale) temperature, evolve in a counter-intuitive manner. While one may expect that the initially cooler sample would freeze first, it has been observed that this is not always the case. In this talk, I will present recent results that show that a Mpemba-like effect appears not only in water but also in some prototypical examples of nonequilibrium systems, namely, granular fluids, Ising model water and spin glasses. Firstly, we will show the Mpemba effect is present in models of granular fluids, both in uniformly heated and in freely cooling systems. Secondly, using the custom built supercomputer Janus II, we were able to find the Mpemba effect in spin glasses and show that it is a non-equilibrium process, governed by the coherence length ξ of the system. The effect occurs when the bath temperature lies in the glassy phase. Finally, we have found a possible origin of the effect in solid and liquid water using well known computational models. The appearance of the Mpemba-like effect in those systems shares some similarities that will be outlined during this presentation. |
Tuesday, March 16, 2021 1:54PM - 2:30PM Live |
F18.00005: The Mpemba effect in spin glasses: a persistent memory effect. Invited Speaker: Enzo Marinari When a hot system cools faster than an initially colder one, and both are refrigerated in the same thermal reservoir, we have the so called Mpemba effect. Its features have bee discussed in many contexts, and, even if in many cases even its existence is far from easy to shows, it is clear that in different contexts it can have very different roots. |
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