Understanding Human Decision Making in an Interactive Landslide Simulator Tool via Reinforcement Learning.

Prior research has used an Interactive Landslide Simulator (ILS) tool to investigate human decision making against landslide risks. It has been found that repeated feedback in the ILS tool about damages due to landslides causes an improvement in human decisions against landslide risks. However, little is known on how theories of learning from feedback (e.g., reinforcement learning) would account for human decisions in the ILS tool. The primary goal of this paper is to account for human decisions in the ILS tool via computational models based upon reinforcement learning and to explore the model mechanisms involved when people make decisions in the ILS tool. Four different reinforcement-learning models were developed and evaluated in their ability to capture human decisions in an experiment involving two conditions in the ILS tool. The parameters of an Expectancy-Valence (EV) model, two Prospect-Valence-Learning models (PVL and PVL-2), a combination EV-PU model, and a random model were calibrated to human decisions in the ILS tool across the two conditions. Later, different models with their calibrated parameters were generalized to data collected in an experiment involving a new condition in ILS. When generalized to this new condition, the PVL-2 model's parameters of both damage-feedback conditions outperformed all other RL models (including the random model). We highlight the implications of our results for decision making against landslide risks.

Ultrafast modulation of optical metamaterials.

We show by pump-probe spectroscopy that the optical response of a fishnet metamaterial can be modulated on the femtosecond time scale. The modulation dynamics is dominated by pump-induced changes in the constituting dielectric medium, but the strength of modulation is dramatically enhanced through the plasmon resonance. The pump-induced spectral responses of the metamaterial provide understanding on how the resonance is modified by pump excitation. Our study suggests that metamaterials can be used as high-speed amplitude/phase modulators with terahertz-bandwidth.

Imaging of plasmonic modes of silver nanoparticles using high-resolution cathodoluminescence spectroscopy.

Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.

Ultrasmooth silver thin films deposited with a germanium nucleation layer.

We demonstrate an effective method for depositing smooth silver (Ag) films on SiO(2)/Si(100) substrates using a thin seed layer of evaporated germanium (Ge). The deposited Ag films exhibit smaller root-mean-square surface roughness, narrower peak-to-valley surface topological height distribution, smaller grain-size distribution, and smaller sheet resistance in comparison to those of Ag films directly deposited on SiO(2)/Si(100) substrates. Optically thin ( approximately 10-20 nm) Ag films deposited with approximately 1-2 nm Ge nucleation layers show more than an order of magnitude improvement in the surface roughness. The presence of the thin layer of Ge changes the growth kinetics (nucleation and evolution) of the electron-beam-evaporated Ag, leading to Ag films with smooth surface morphology and high electrical conductivity. The demonstrated Ag thin films are very promising for large-scale applications as molecular anchors, optical metamaterials, plasmonic devices, and several areas of nanophotonics.