Revisiting Newton's rings with a plasmonic optical flat for high-accuracy surface inspection.

Two parallel optical surfaces often exhibit colorful fringes along the lines of equal thickness because of the interference of light. This simple phenomenon allows one to observe subwavelength corrugations on a reflective surface by simply placing on it a flat reference dielectric surface, a so-called optical flat, and inspecting the resultant interference pattern. In this work, we extend this principle from dielectric surfaces to two-dimensional plasmonic nanostructures. Optical couplings between an Au nanodisk array and an Au thin film were measured quantitatively using two different techniques, namely, the classical Newton's rings method and a closed-loop nano-positioning system. Extremely high spectral sensitivity to the inter-surface distance was observed in the near-field coupling regime, where a 1-nm change in distance could alter the resonance wavelength by almost 10 nm, >40 times greater than the variation in the case without near-field coupling. With the help of a numerical fitting technique, the resonance wavelength could be determined with a precision of 0.03 nm, corresponding to a distance precision as high as 0.003 nm. Utilizing this effect, we demonstrated that a plasmonic nanodisk array can be utilized as a plasmonic optical flat, with which nanometer-deep grooves can be directly visualized using a low-cost microscope.

[Study the restoration technology of concentrated application-natural diffusion about amendments of acidified soil of hilly woodland].

Through concentrated application of lime, sewage sludge and lime + sewage sludge on the sloping top of the hilly woodlands, the restoration effects of the three soil amendments on the acidified soil of hilly woodland were studied. The results showed that: (1) Joint application of sewage sludge + lime can significantly (P < 0.05) decrease soil acidity, promote the rapid increase in soil organic matter and nitrogen content, increase soil cation exchange capacity, and effectively improve acidified soil. (2) Through natural diffusion mechanisms of surface and subsurface runoff, a large area of acidified soil of hilly woodlands can be restored by concentrated application of soil amendments on the sloping top of the hilly woodlands. (3) It is conducive to solve the pollution problems of the urban sewage sludge by using municipal sewage sludge to restore acidified soil, but only for the restoration of acidified soil of timber forest.

[Effects of elevated CO2 concentration and nitrogen deposition on the biomass accumulation and allocation in south subtropical main native tree species and their mixed communities].

A 5-year experiment was conducted to study the effects of simulated elevated CO2 concentration, nitrogen deposition, and their combination on the biomass accumulation and allocation in five south subtropical native tree species Schima superba, Ormosia pinnata, Acmena acuminatissima, Syzygium hancei, and Castanopsis hystrix and their mixed communities. The test tree species had different responses in their biomass accumulation and allocation to the elevated CO2 concentration and nitrogen deposition. Elevated CO2 concentration and nitrogen deposition increased the biomass of legume species by 49.3% and 71.0%, respectively, and promoted the biomass accumulation in sun species. Nitrogen deposition increased the biomass of shade-preference species significantly, but elevated CO2 concentration was in adverse. Elevated CO2 concentration inhibited the biomass allocation in the belowground part of sun species but promoted the biomass allocation in the belowground part of shade-preference species. Elevated CO2 concentration, nitrogen deposition, and their interaction all promoted the biomass accumulation in mixed communities. Elevated CO2 concentration increased the biomass accumulation in the belowground part of the communities, while nitrogen deposition increased the biomass accumulation in the aboveground part. Under the background of global climate change, Ormosia pinnata and Castanopsis hystrix tended to be the appropriate species for carbon fixation in south subtropical area.

[Effects of precipitation intensity on soil organic carbon fractions and their distribution under subtropical forests of South China].

From December 2006 to June 2008, a field experiment was conducted to study the effects of natural precipitation, doubled precipitation, and no precipitation on the soil organic carbon fractions and their distribution under a successional series of monsoon evergreen broad-leaf forest, pine and broad-leaf mixed forest, and pine forest in Dinghushan Mountain of Southern China. Different precipitation treatments had no significant effects on the total organic carbon (TOC) concentration in the same soil layer under the same forest type (P > 0.05). In treatment no precipitation, particulate organic carbon (POC) and light fraction organic carbon (LFOC) were mainly accumulated in surface soil layer (0-10 cm); but in treatments natural precipitation and doubled precipitation, the two fractions were infiltrated to deeper soil layers. Under pine forest, soil readily oxidizable organic carbon (ROC) was significantly higher in treatment no precipitation than in treatments natural precipitation and doubled precipitation (P < 0.05). The percentage of soil POC, ROC, and LFOC to soil TOC was much greater under the forests at early successional stage than at climax stage, suggesting that the forest at early successional stage might not be an ideal place for soil organic carbon storage. Precipitation intensity less affected TOC, but had greater effects on the labile components POC, ROC, and LFOC.