Coral community changes in response to a high sedimentation event: A case study in southern Hainan Island

A high sedimentation event caused by dredging and dumping of sediment was recorded on Xiaodonghai Reef in Yulin Bay,southern Hainan Island,China.Significantly high sedimentation and constant light shading were observed during the sediment dumping event(SD Event).Using long-term video transects,we quantified coral community changes and responses to the SD Event between 2008 and 2010.The SD Event caused severe coral mortality on Xiaodonghai Reef at a depth of 6 m,while corals at 3 m were less affected.Total live coral cover at 6 m decreased from 54.3% to 14.8%,and Diploastrea heliopora replaced Galaxea fascicularis as the dominant coral species at 6 and 9 m.The density of juvenile corals also declined after the SD Event,especially for the genera Galaxea and Platygyra.However,the density of juvenile Porites and Pocillopora spp.slightly increased.Monitoring for 11 months after the SD Event indicated no recovery of coral communities on Xiaodonghai Reef.Long-term video transect data also revealed that mean live coral cover dramatically declined,from 30.5% in 2008 to 9% in 2010,while the dominant corals in Yulin Bay shifted to more tolerant coral species,such as massive Porites spp.and D.heliopora.The rapid coral community degradation in Yulin Bay between 2008 and 2010 was probably caused by high sediment deposition resulting from intensive dredging and land-clearing activities.These results highlight the necessity for an integrated watershed management to control sediment deposition on near-shore coral reefs.     

Design study for the cascaded HGHG experiment based on the SDUV-FEL

Cascading stages of high-gain harmonic generation(HGHG) free electron laser(FEL) is a promising way to produce fully coherent X-ray radiation.As a test facility for modern FEL R&D,the Shanghai deep ultraviolet FEL(SDUV-FEL) is now under upgrading for the cascading two stages of HGHG experiment.Since the energy of the electron beam is as low as about 185 MeV after upgrade,the total harmonic number of this two stages HGHG is only 2×2,and the wavelength of the final radiation is 196.5 nm which is the 4th harmonic of the 786 nm seed laser.With help of three-dimensional simulation codes,design studies on the FEL physics for the cascaded HGHG experiment are present based on the parameters of the upgraded SDUV-FEL facility.It is found from the simulation results that the part of the electron beam which has been used in the first stage can still generate powerful radiation in the radiator of the second stage,and this radiation will be difficult to be separated from the radiation generated by the fresh part of the electron beam.To overcome this problem,a novel method based on the energy spectrum of the electron beam is proposed in this paper to demonstrate the "fresh bunch" technique.     

Metals in water and surface sediments from Henan reaches of the Yellow River, China

The concentrations of Cd, Cr, Cu, Ni, Pb and Zn were determined in the water and surface sediments from the Henan reaches of the Yellow River. Twenty-three sampling sites along the Yellow River and its tributaries were selected. Generally, metal concentrations were found to decrease in sequences of Zn > Cu > Pb > Cr > Ni > Cd in water and Zn > Cr > Pb > Ni > Cu > Cd in sediments. High levels of metal concentration were determined at a few stations of the river and its tributaries, such as Yiluo River, Si River and Qin River. The pollution of the Yellow River by Cd, Cr, Cu, Ni, Pb and Zn can be regarded as much higher compared to the background values, US EPA criteria (1999) and China water quality criteria (2002). For sediments, metal levels except Pb did not significantly exceed the average shale levels and backgrounds in several countries including China. Data analysis manifests that positive correlations were found between Cu, Ni and Zn in water, and Pb, Ni, Zn and Cr in sediments. The Pearson correlation coefficient analysis and Cluster analysis were provided to assess the possible contamination sources. The results indicate a general appearance of serious pollution along the banks of the Yellow River. The wastewaters discharged by the mine plants, smelter plants, power plants, battery plants, tannery plants, etc., and sewage inputs from the cities along the river banks may be the sources of metals.     

Degradation of the antibiotic sulfamonomethoxine sodium in aqueous solution by photo-Fenton oxidation

In this study, photo-Fenton oxidation was applied to degradation of sulfamonomethoxine sodium (SMMS) in aqueous solution. The operation parameters of pH, temperature, and concentrations of H2O2, Fe2+ and SMMS were investigated. The optimum conditions for the photo-Fenton process were determined as follows: [SMMS]=4.53 mg/L, pH 4.0, [H2O2]=0.49 mmol/L, [Fe2+]= 19.51 μmol/L and T=25°C. Under these conditions 98.5% of the SMMS degraded. The kinetics were also studied, and degradation of SMMS by the photo-Fenton process could be described by first-order kinetics. The apparent activation energy was calculated as 23.95 kJ/mol. Mineralization of the process was investigated by measuring the chemical oxygen demand (COD), and the COD decreased by 99% after 120 min. This process could be used as a pretreatment method for wastewater containing sulfamonomethoxine sodium.     

Fluorescence and sensitization performance of phenylene-vinylene-substituted polythiophene

A new kind of polythiophene derivative, Poly(3-{2-[4-(2-ethylhexyloxy)-phenyl]-vinyl}-2,2′-bithiophene) (PTh), was applied in dye-sensitized solar cell to extend the light response of nanocrystalline TiO2 electrode. UV-vis absorption and fluorescence spectra were employed to investigate the interaction of PTh with nanocrystalline TiO2. The absorption coefficient of the PTh was high in visible part of spec- trum, and the fluorescence emission of the PTh can be efficiently quenched by TiO2 nanoparticles ow- i...     

从头计算分子动力学方法及其应用

从头计算分子动力学方法把密度泛函理论和分子动力学方法有机地结合起来，使电子的极化效应及化学键的本质均可用计算机分子模拟方法进行研究，是目前计算机模拟实验中最先进、最重要的方法之一。文章简述了从头计算分子动力学方法的基本原理，介绍了该方法在水、水溶液及其他氢键液体的结构与动力学研究中的应用。     

Metals in water and surface sediments from Henan reaches of the Yellow River,China

The concentrations of Cd,Cr,Cu,Ni,Pb and Zn were determined in the water and surface sediments from the Henan reaches of the Yellow River.Twenty-three sampling sites along the Yellow River and its tributaries were selected.Generally,metal concentrations were found to decrease in sequences of Zn>Cu>Pb>Cr>Ni>Cd in water and Zn>Cr>Pb>Ni>Cu>Cd in sediments.High levels of metal concentration were determined at a few stations of the river and its tributaries,such as Yiluo River,Si River and Qin River.The pollutio...     

Absolute Measurement of Important Branching Fractions of the Ds Meson

Absolute measurement of branching fractions of purely leptonic decay, semi-leptonic decay and φπ⁺ decay of the D_s meson at a c.m. energy of 4.03 GeV were completed from the BES experiment at the BEPC electron-positron collider. The method by using combined confidence level for pion and kaon separation, the D_s single and double tagging technology, and the maximum likelihood functions in the estimate of the D_s branching fractions are described in details. Discussion and comments on these physics results are made. Prospect for improved measurement of D_s physics in future is also given.     

Performance of a quantum heat engine cycle working with harmonic oscillator systems

A cycle model of an irreversible heat engine working with harmonic systems is established in this paper. Based on the equation of motion of an operator in the Heisenberg picture and semi-group approach, the first law of thermodynamics for a harmonic system and the time evolution of the system are obtained. The general expressions for several important parameters, such as the work, efficiency, power output, and rate of entropy production are derived. By means of numerical analysis, the optimally operating regions and the optimal values of performance parameters of the cycle are determined under the condition of maximum power output. At last, some special cases, such as high temperature limit and frictionless case, are dis-cussed in brief.     

电子商务软件负载能力评估的实例分析

负载能力是表征电子商务软件性能的一项重要标准。负载能力的评价方法包括在线系统的数据统计和估算、程序测算、基于测试的评估方法等。其中，基于测试的评估方法越来越受到人们的重视。本文以一个小型电子商务系统为例，采用基于测试的评估方法进行了系统的负载能力分析。结果表明，对于以优化为目标的系统评估，可以在优化后采用逐步细化的负载测试方式得到最佳负载预测数据。同时，在负载能力的评估过程中，需要根据系统的主要功能来选择合理的评估指标。