Linking fluctuation and dissipation in spatially extended out-of-equilibrium systems.

For systems in equilibrium at a temperature T, thermal noise and energy damping are related to T through the fluctuation-dissipation theorem (FDT). We study here an extension of the FDT to an out-of-equilibrium steady state: a microcantilever subject to a constant heat flux. The resulting thermal profile in this spatially extended system interplays with the local energy dissipation field to prescribe the amplitude of mechanical fluctuations. Using three samples with different damping profiles (localized or distributed), we probe this approach and experimentally demonstrate the link between fluctuations and dissipation. The thermal noise can therefore be predicted a priori from the measurement of the dissipation as a function of the maximum temperature of the micro-oscillator.

Thermal noise of a cryocooled silicon cantilever locally heated up to its melting point.

The Fluctuation-Dissipation Theorem (FDT) is a powerful tool to estimate the thermal noise of physical systems in equilibrium. In general, however, thermal equilibrium is an approximation or cannot be assumed at all. A more general formulation of the FDT is then needed to describe the behavior of the fluctuations. In our experiment we study a microcantilever brought out of equilibrium by a strong heat flux generated by the absorption of the light of a laser. While the base is kept at cryogenic temperatures, the tip is heated up to the melting point, thus creating the highest temperature difference the system can sustain. We independently estimate the temperature profile of the cantilever and its mechanical fluctuations as well as its dissipation. We then demonstrate how the thermal fluctuations of all the observed degrees of freedom, though increasing with the heat flux, are much lower than what is expected from the average temperature of the system. We interpret these results using a minimal extension of the FDT: this dearth of thermal noise arises from a dissipation shared between clamping losses and distributed damping.

Experimental and archaeological data for the identification of projectile impact marks on small-sized mammals.

The role of small game in prehistoric hunter-gatherer economy is a highly debated topic. Despite the general assumption that this practice was uneconomic, several studies have underlined the relevance of the circumstance of capture - in terms of hunting strategies and technology - in the evaluation of the actual role of small mammals in human foraging efficiency. Since very few studies have focused on the recognition of bone hunting lesions, in a previous work we explored the potential of 3D microscopy in distinguishing projectile impact marks from other taphonomic marks, developing a widely-applicable diagnostic framework based on experimental data and focused on Late Epigravettian projectiles. Even though we confirmed the validity of the method on zooarchaeological remains of large-sized mammals, the reliability of the experimental record in relation to smaller animals needed more testing and verification. In this report we thus present the data acquired through a new ballistic experiment on small mammals and compare the results to those previously obtained on medium-sized animals, in order to bolster the diagnostic criteria useful in bone lesion identification with specific reference to small game. We also present the application of this renewed methodology to an archaeological context dated to the Late Glacial and located in the eastern Italian Alps.