RESUMEN
Optical physical unclonable function (PUF) is one of the most promising hardware security solutions, which has been proven to be resistant to machine learning attacks. However, the disordered structures of the traditional optical PUFs are usually deterministic once they are manufactured and therefore exhibit fixed challenge-response behaviors. Herein, a reconfigurable PUF (R-PUF) is proposed and demonstrated by using the reversible phase transition behavior of VO2 nanocrystals combined with TiO2 disordered nanoparticles. Both the simulation and experiment results show that the near-infrared laser speckle pattern of the R-PUF can be almost completely altered after the phase transition of VO2 nanocrystals, resulting in a reconfigurable and reproducible optical response. The similarity of the response speckles shows an obvious hysteresis loop during the rise and drop of temperature, providing a simple way to regulate and control the response behaviors of the R-PUF. More importantly, the hysteretic characteristic provides a new dimension to describe the challenge-response behavior of the R-PUF besides the laser speckle, providing an effective way to improve the security and encoding capacity of the optical PUFs. The proposed R-PUF can be employed as a promising security primitive for high robustness and high-security authentication and encryption.
RESUMEN
Dissolved sulfide, iron (Fe), and phosphorus (P) in a mudflat (Jiaozhou Bay, China) impacted by shellfish aquaculture were measured in situ by the diffusive gradients in thin films (DGT) technique. A combination of porewater and solid-phase chemistry was used to characterize the interplays of Fe and S, and their control on P mobilization. Below the subsurface layer, two times higher fluxes (FDGT) of dissolved Fe2+ from porewater to the DGT device than those of dissolved sulfide indicate that dissimilatory iron reduction (DIR) dominates over sulfate reduction (SR). Spatial coupling of dissolved Fe2+ and P points to P release driven mainly by reductive dissolution of Fe. Much higher FDGT values of dissolved Fe2+ relative to dissolved P imply that oxidative regeneration of Fe oxides at the sediment-water interfaces (SWIs) of the transitional mudflat serves as an effective "iron curtain" of upward diffusing P. In the mudflat sediments of DIR prevalence, the accumulation of total reduced inorganic sulfur (TRIS) is dampened, which can largely ascribed to enhanced oxidative loss of sulfide and/or limited availability of degradable organic carbon in the dynamic regimes. Low dissolved sulfide concentrations in the sediments leave the majority of reactive Fe unsulfidized and thus abundantly available to buffer newly produced sulfide.
