Space-and frequency-division multiplexing in photonic second-order topological insulators

Higher-order topological insulators,originally proposed in quantum condensed matters,have provided a new avenue for localizing and transmitting light in photonic devices.Nontrivial band topology in crystals with certain symmetries can host robust topological edge states and lower dimensional topological corner states(TCS),making them a promising platform for photonics applications.Here,we have designed several types of TCS with only two specific C6v-symmetric photonic crystals with various seamless splicing boundaries,where all the supposed TCS with diverse electromagnetic characteristics are visualized via numerical simulations and experimental measurements.More interestingly,we have observed that those TCS overlapping in spectral and spatial space tend to interweaved,inducing spectrum division.Meanwhile,the equivalent corners appear to have TCS with a phase difference,which is critical for directional activation of pseudospin dependence.Our findings demonstrate that coupled TCS with phase difference at different nanocavities can be selectively excited by a chiral source,which indicates that the TCS at this time have pseudospin-dependent properties.We further design a specific splicing structure to prevent coupling between adjacent TCS.This work provides a flexible approach for space-and frequency-division multiplexing in photonic devices.

Spatial and temporal distribution of Mo in the overlying water of a reservoir downstream from mining area

This study aimed to evaluate the spatial and temporal variations of molybdenum(Mo)in the downstream water body of a Mo mine during three hydrologic periods(wet,dry and medium seasons).The physical properties in Luhun Reservoir reflected seasonal variations in different hydrological periods.The redox potential(ORP)and dissolved oxygen(DO)increased in the dry season.The concomitant decrease in temperature(T),conductivity(COND)and total dissolved solids(TDS)were lowest in the wet season.The p H value did not change significantly during the three hydrologic periods.The distribution of Mo in the dry season was high in upstream and low in downstream areas,which was significantly different from that of the wet and medium seasons.The total Mo concentration in wet(150.1μg/L)and medium season(148.2μg/L)was higher than that in the dry season,but the TDS(288.3 mg/L)and the percentage dissolved Mo(81.3%)in overlying water was lowest in the wet season.There was no significant relationship between the dissolved Mo and the total Mo with TDS.In the dry season,the mean total Mo concentration was 116.3μg/L,which was higher than the standard limit value(70μg/L)for drinking water(US EPA-United States Environmental Protection Agency recommended value 40μg/L).Non-point source pollution is the main characteristic of mining area pollution,which was closely related to rainfall.Thus,the Luhun Reservoir contains substantial Mo pollution,which was a significant concern given that it is used as a source of drinking and irrigation water.

Determining cadmium bioavailability in sediment profiles using diffusive gradients in thin films

Cadmium(Cd)uptake by plants or benthic organisms largely depends on its bioavailability in sediments,so it is necessary to understand Cd bio availability for determining its ecological risks in riverine sediments.Pore water is easily disturbed during sample collection,indicating that there was a shortage of traditional methods for investigating Cd bio availability.Here,sediment cores were collected from rivers,after which sequential extraction and diffusive gradients in thin films(DGT)method were employed to determine Cd potential bio availability in the sediments and pore water.We found that Cd concentrations measured by DGT were lower than that in pore water profiles,and Cd distribution in various fractions changed remarkably.Pearson correlation analysis showed significant positive correlations between Cd concentrations measured by DGT and total Cd concentrations(r^2=0.76),exchangeable and weak acid soluble fraction(r^2=0.68),ferromanganese fraction(r^2=0.72)and bound organic matter or oxidizable fraction(r^2=0.54).However,the correlation was relatively low between Cd concentrations measured by DGT and that in pore water profiles(r^2=0.26).These results demonstrated that DGT method could provide more accurate information of Cd bio availability in sediment profiles than traditional methods.