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River ecosystems have been disturbed and aggravated by increasing human activities including those activities wherein forest area is changed to agricultural area in riparian zones and intensive fertilizer usage in agriculture. These anthropogenic activities lead to an increase in the light received by the surface of the river and nutrient (nitrogen and phosphorus) enrichment in the river. Denitrification driven by microorganisms in sediments is the most important path for the removal of nitrogen from aquatic ecosystems. The alteration of light intensity influences the denitrification process owing to the change in the amount of available organic carbon produced via the metabolism of algae and photosynthetic bacteria. We added slow-releasing fertilizer into the river to simulate nutrient enrichment similar to the effect of fertilization from the agricultural industry. We also covered a part of the stream surface to achieve conditions similar to those of rivers in headwaters with thick forest coverage. We selected six streams to conduct manipulated experiments at the core area in the natural reserve in the upper Jinshui River, Hanjiang, to assess the responses of denitrification to the different treatments-nutrient addition and coverage. We also analyzed subsequent changes in community structure and diversity of bacteria using the encoding nirS gene by MiSeq high-throughput sequencing technology. The results showed that artificial shading above streams can reduce the denitrification activity of sediments, relative abundances of dominant bacteria (Dechloromonas) and the diversity of bacteria as indicated by the encoding nirS gene. Furthermore, nutrient addition into the stream increased the denitrification activity of sediments, whereas there was a decrease in relative abundance of dominant bacteria and the diversity of bacteria. The preliminary results confirmed the increase in denitrification activity of stream sediments as a result of increasing light intensity and nutrient content. This study has allowed us to understand the denitrifying capacity of rivers and provides scientific primary data for river management.

To meet the ultra-high precision manufacture demands of spherical surfaces and aspherical surfaces in an optical system of Deep Ultra Violet (DUV) and Extreme Ultra Violet (EUV), a series of motion-precision control methods in bonnet-polishing were proposed. Firstly, the temperatures of main operation units were finely controlled to allow the motion-precision of polishing to be to 50 m. Then, the coordinates transmitting method was used to guarantee the two-dimension unity between measured data and operating data to be 0.30-0.70 mm. Furthermore, the convergence efficiency of surface-error in fine polishing was improved by bonnet removal estimation method and feedback correction method. Finally, the vertical position accuracy between bonnet and work piece was improved to 10 m by probing-correction method. The experiment results on a actual polishing by using motion-precision control methods indicate that the surface machining accuracy is 0.8 nm (RMS) in polishing a flat with a diameter of 280 mm, and that is 1.1 nm (RMS) in polishing a concave with a diameter of 160 mm. The proposed methods realize ultra-high precision polishing for spherical surfaces and aspherical surfaces, and they are also suitable for other contact small tool computer controlled polishing. , 2015, Chinese Academy of Sciences. All right reserved.

Issues around the loss of diversity caused by fast-growing tree plantations such as Eucalyptus have aroused controversy for many years.It is generally believed that Eucaluptus plantations bring about a decrease of plant′s biodiversity by influencing resource competitions,allelopathy,or the level of soil fertility.Above and below-ground of forest ecosystems interact implicitly.Complex interactions between above-belowground biodiversity may provide important feedbacks regulating ecosystem.However,seldom information was available on the soil organism′s diversity in Eucalyptus plantations.Furthermore,most of the previous studies were being conducted in the short-term rotation Eucalyptus plantations with a certain plantation age,which might limit our understanding of the actual plantation ecosystem process.Therefore,the abundance and diversity of plants and soil biodiversity were simultaneously measured across a range of eucalypt plantation ages(1—10 years) in southwest China to determine how Eucalyptus grandis afforestation of agricultural lands affected the native biodiversity.The present results showed that afforestation of E.grandis caused changes in plant and soil biodiversity with soil depth and was dependent on the stand age.The species richness,abundance and the diversity of understory plants and soil organisms showed a parallel development during the process of the succession,viz.both of them increased significantly with time but with a 'dip' around 4 years old.CCA analysis showed that the plant′s life forms transited from liana,hemicryptophytes and therophytes into perennial herbaceous-phanerophytes and phanerophytes.Bacteria quantitatively dominated the soil microbe in E.grandis regardless of plantation age.The individual proportion of saprozoic group quantitatively dominated in the soils of the all the study sites,followed by omnivorous group.The proportion of saprozoic groups decreased in 1—7 year old stands and then increased significantly with time.The proportion of omnivorous group increased as S shape with the plantation age.The proportion of predators and phytophage groups decreased significantly with time.The individual percentage of nematode decreased with the plantation age,but that of acarina and the number ratio of the acarina and collembola present the S shape increasing trend over time.The multiple comparisons test showed that plant diversity of the understory vegetation in 1,2 and 4—7 years-old plantations were significantly lower than that in the control forests(Pinus massoniana).Plant diversity in 1—10 year-old E.grandis plantations were significantly higher than that of the control arable land.Soil biodiversity in the plantations before the rotation period has no significant differences compared with agricultural lands,but were significantly higher in the plantations on or after the rotation period than the crop land.There were significant correlations between the plant′ s and soil organism′s diversity index and the correlation coefficient decreased with soil depth.

On account of the characteristics of laser double-pass processing,a Nd∶ YAG pulsed laser is chosen as the light source,and a laser time-sharing control system for double-pass outputs is developed.A concrete implemented project for time-sharing spectral technology is put forward,the beam split device is designed to achieve time-sharing beam split,and the time-sharing control circuit is designed to control the device in real time.Then,system program procedure is determined.Finally,laser outputs from different ports in different time are obtained under keeping the output powers.In order to avoid fiber damaging because of the jittering from beam split device,black photographic paper is used to sample of facula.The result shows that the best delay time is 300 ms from changing the holophote position to laser output.This system can not only realize time-share multiplexing and dynamic spectral splitting,but also can satisfy the need of double-pass outputs.Furthermore,the system has a stronger expanding ability,and can provide the convenience for laser improvement and upgrade according to the laser processing condition in reality.