Nonlinear processes are often governed by selection rules imposed by the symmetries of the molecular configurations. The most well-known examples include the role of centrosymmetry breaking for the generation of even harmonics, and the selection rule related to the rotational symmetry in harmonic generation for fundamental beams with circular polarizations. While the role of centrosymmetry breaking in second harmonic generation has been extensively studied in plasmonic systems, the investigation of selection rules pertaining to circular polarization states of harmonic generation is limited to crystals, i.e., symmetries at the atomic level. In this Letter we demonstrate the rotational symmetry dependent third harmonic generation from nonlinear plasmonic metacrystals. We show that the selection rule can be imposed by the rotational symmetry of metacrystals embedded into an isotropic organic nonlinear thin film. The results presented here may open new avenues for designing symmetry-dependent nonlinear optical responses with tailored plasmonic nanostructures.

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We tested the hypothesis that rotifer species in the micro‐ and mesozooplankton are a potential food source for zebra mussels. We labeled phytoplankton with 14C, fed them to two species of rotifers (140–210 µm length) that were previously found abundantly in the Hudson River and had declined following a zebra mussel invasion, and estimated the assimilation of carbon. Assimilation efficiencies were found to be ~37.47–54.0%. Combined with our feeding experiments, the data on rotifer densities before and after the invasion allowed us to calculate the energy budgets for zebra mussels. Before zebra mussels dominated the Hudson River in 1992, the absorption of energy from rotifers was about two to three times higher than that necessary to maintain its routine metabolic rate and contributed about 0.349–0.662 J h−1 to mussel growth and reproduction, conferring a positive scope for growth. Since the zebra mussels became abundant in the Hudson River, assimilation of rotifers is still sufficient to explain ~16.4–23.1% of the mussels' routine metabolic rate. Therefore, rotifers play a conceivably large role in the energy budget of zebra mussels, whether at high rotifer concentrations (before the invasion) or at low rotifer concentrations (after the invasion). This is the first quantitative evidence for a trophic link between benthic bivalve mollusks and larger micro‐ and mesozooplankton that might extend to marine systems where bivalves can derive nutrition from microzooplankton, including planktonic invertebrate larvae. Combined with other recent results, this study documents a benthos‐zooplankton trophic loop, demonstrating potentially strong top‐down control by dense bivalves on aquatic systems.

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Low-loss optical waveguides based on a negative tone epoxy Novolak resin polymer have been fabricated using electron-beam direct writing. This polymer has a high refractive index, high sensitivity, large hardness, and Tg>200 °C. For single-mode channel waveguides with upper claddings, the propagation losses measured were 0.22 and 0.48 dB/cm at 1330 and 1550 nm, respectively. For waveguides without upper claddings, the losses were 0.5 dB/cm at both wavelengths. The stability of these waveguides was also investigated, and no significant change was observed after 200 h at 90 °C and 95% relative humidity.

Robot-assisted training combined with neural guided strategy has been increasingly applied to stroke rehabilitation. However, the induced neuroplasticity is seldom characterized. It is still uncertain whether this kind of guidance could enhance the long-term training effect for stroke motor recovery. This study was conducted to explore the clinical improvement and the neurological changes after 20-session guided or non-guided robot hand training using two measures: changes in brain discriminant ability between motor-imagery and resting states revealed from electroencephalography (EEG) signals and changes in brain network variability revealed from resting-state functional magnetic resonance imaging (fMRI) data in 24 chronic stroke subjects. The subjects were randomly assigned to receive either combined action observation (AO) with EEG-guided robot-hand training (RobotEEG_AO, n = 13) or robot-hand training without AO and EEG guidance (Robotnon−EEG_Text, n = 11). The robot hand in RobotEEG_AO group was activated only when significant mu suppression (8–12 Hz) was detected from subjects' EEG signals in ipsilesional hemisphere, while the robot hand in Robotnon−EEG_Text group was randomly activated regardless of their EEG signals. Paretic upper-limb motor functions were evaluated at three time-points: before, immediately after and 6 months after the interventions. Only RobotEEG_AO group showed a long-term significant improvement in their upper-limb motor functions while no significant and long-lasting training effect on the paretic motor functions was shown in Robotnon−EEG_Text group. Significant neuroplasticity changes were only observed in RobotEEG_AO group as well. The brain discriminant ability based on the ipsilesional EEG signals significantly improved after intervention. For brain network variability, the whole brain was first divided into six functional subnetworks, and significant increase in the temporal variability was found in four out of the six subnetworks, including sensory-motor areas, attention network, auditory network, and default mode network after intervention. Our results revealed the differences in the long-term training effect and the neuroplasticity changes following the two interventional strategies: with and without neural guidance. The findings might imply that sustainable motor function improvement could be achieved through proper neural guidance, which might provide insights into strategies for effective stroke rehabilitation. Furthermore, neuroplasticity could be promoted more profoundly by the intervention with proper neurofeedback, and might be shaped in relation to better motor skill acquisition.