Diffusive movement of simazine and lindane in river-bed sediments

River-bed sediments are active zones for pesticide deposition and subsequent movement by diffusion, mass transport and sorption to solids. The aim of this work was to investigate the importance of diffusion as a means of pesticide movement. In laboratory experiments, simazine and lindane were introduced to well-mixed aqueous solutions overlying two different river sediments. Sediment cores were sectioned horizontally and analyzed for pesticide content by supercritical fluid extraction. Experiments were used to determine sorption isotherms of the compounds to suspended sediments at 10°C. Vertical profiles of the pesticides in the sediments showed that the compounds reached a maximum depth of 89 mm over a period of 37 days. A mathematical model was developed to describe pesticide transport by diffusion within the sediment porewaters and sediment sorbed phases, taking into account sorption of the compounds to sediment particles. Effective diffusion coefficients ((0.5–1.6)×10^-10 m² s^-1) were obtained for simazine and lindane in the characterized sediments. These were used to calculate values for diffusion in the dissolved phase (0.38×10^-10 and 6·16×10^-10 m² s^-1 for simazine and lindane respectively) and diffusion in the sorbed phase (0.39×10^-10 m² s^-1 for simazine and negligible for lindane). Sorption onto the sediment significantly influenced the rate of penetration of the compounds into the sediment; thus although lindane had a larger effective diffusion coefficient than simazine, its larger sorption affinity and negligible diffusion in the sorbed phase led to less penetration into the sediment. © 1998 Society of Chemical Industry     

Formation of molecular chlorine from the photolysis of ozone and aqueous sea-salt particles

Halogen atoms from the reactions of sea-salt particles may play a significant role in the marine boundary layer. Reactions of sodium chloride, the major component of sea-salt particles, with nitrogen oxides generate chlorine atom precursors. However, recent studies suggest there is an additional source of chlorine in the marine troposphere. This study shows that molecular chlorine is generated from the photolysis of ozone in the presence of sea-salt particles above their deliquescence point; this process may also occur in the ocean surface layer. Given the global distribution of ozone, this process may provide a global source of chlorine.     

Comparison of white spot syndrome virus quantification of fleshy shrimp Fenneropenaeus chinensis in outdoor ponds between different growing seasons by TaqMan real‐time polymerase chain reaction

In the present study, we used TaqMan real‐time polymerase chain reaction to quantify and compare infection of white spot syndrome virus (WSSV) with shrimp production of Fenneropenaeus chinensis cultured in outdoor ponds along the west coast of the South Korea. In 2007, a total of 60 specimens in summer and 116 specimens in autumn were collected from 12 growing‐out ponds and 12 harvest ponds respectively. Pond harvest data were obtained from farmers. Of the summer samples, all specimens were WSSV positive, with a wide range of 12.4–7.0 × 10⁷ (mean 7.5 × 10⁶) copies ng^?1 DNA; shrimp production was 1.7 metric tonnes per hectare (mt ha^?1). Of the 116 autumn‐sample specimens, 81 (69.8%) were WSSV positive; WSSV infection had been decreased dramatically, to 0–7.2 (mean 3.5) copies ng^?1 DNA. Shrimp production of autumn ponds was 2.1 mt ha^?1. Statistical analysis indicated that the difference in WSSV infections detected in summer and autumn was highly significant (P<0.01). In summer, seven ponds (58.3%) with low‐WSSV infection loads (0–1000 WSSV copies ng^?1 DNA) had shrimp production of 2.7 mt ha^?1; the others had shrimp production of only 0.2 mt ha^?1. The mean shrimp production between the two infection levels showed a highly statistically significant difference (P<0.01).     

简论当代大学生价值观功利化倾向及其克服

从社会转型的负面影响、西方社会思潮的渗透和冲击、各种传媒的错误导向、大学生思想政治教育机制不健全、大学生自身存在的弱点等几方面分析了当代大学生价值观功利化倾向形成的原因,进而提出了用社会主义核心价值体系教育学生、发挥正确舆论导向功能、加强大学生价值观的正面引导、提升德育教师素质等对策。     

Vegetation development over four years on two green roofs in the UK

Carefully designed green roofs have the potential to be used as mitigation for habitats lost at ground level. The development of plant assemblages on two green roofs designed to emulate diverse brownfield habitats (brown roofs), by using recycled demolition aggregate as part of a low-fertility growth substrate, were studied over the first four years of their development. The cover-abundance of flowering plants and habitat structural components (e.g. bare ground, moss) were measured on the Domin-Krajina scale within all identified microhabitats. Drought disturbance was one of the main controlling factors on assemblage development. Annual plants were abundant and successful in the first growth season, and thereafter only re-appeared in any numbers following drought disturbances in subsequent years. Moss and Sedum acre L. increased through the study period until these plants dominated coverage. The cover-abundance of perennial wildflower species was strongly influenced by drought disturbance. The influence of drought disturbance varied between different brown roof microhabitats, with plant assemblages in coarser and less fertile microhabitats more resistant to these disturbances. Observed responses to drought were consistent with the following two hypotheses: (i) Areas of coarse substrate can act as disturbance refugia for plants during drought by helping preserve pockets of water under large clasts and within absorbent materials such as brick. (ii) The plant assemblages living in areas of more fertile substrates, which grow more luxuriantly when water availability is high, are more vulnerable to drought disturbance. Green roofs should be designed to include a range of substrate types to create several microhabitats that will collectively support more species than any single microhabitat.     

Perspectives in Helioseismology

Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates.     

Differential Rotation and Dynamics of the Solar Interior

Splitting of the sun's global oscillation frequencies by large-scale flows can be used to investigate how rotation varies with radius and latitude within the solar interior. The nearly uninterrupted observations by the Global Oscillation Network Group (GONG) yield oscillation power spectra with high duty cycles and high signal-to-noise ratios. Frequency splittings derived from GONG observations confirm that the variation of rotation rate with latitude seen at the surface carries through much of the convection zone, at the base of which is an adjustment layer leading to latitudinally independent rotation at greater depths. A distinctive shear layer just below the surface is discernible at low to mid-latitudes.     

Positive Effects of Melatonin Treatment on the Reproductive Performance of Young Border Leicester Rams Mated to Merino Ewes in Spring: Preliminary Observations

Poor reproductive performance of Merino ewe flocks when mated to Border Leicester rams during spring may be due to seasonality of the Border Leicester breed. Two approaches were taken to test this assumption. Six young (12 months old) or six mixed‐age (12, 24 and ≥36 months old) Border Leicester rams were either treated or not treated with melatonin implants (2 × 2 design) 6 weeks before the four groups of rams were each put with approximately 300 Merino ewes for an 8‐week mating period. Implants were inserted in early September (experiment 1). The second approach was to yard or not yard ewes and mixed‐age rams on several occasions during the first 3 weeks of the mating period (experiment 2). Pregnancy rate and twinning percentage were assessed by ultrasonography. In experiment 1, melatonin treatment in young rams increased (p < 0.001) pregnancy rate from 5.0% to 92.6%, but mixed‐age rams did not respond (90.7% vs 89.5% for melatonin and non‐melatonin treatments, respectively). Twinning rate was similar (p > 0.05) for ewes mated to either melatonin or non‐melatonin‐treated young rams (36.8% vs 40.0%, respectively), whereas melatonin significantly improved (p < 0.05) twinning rate in those ewes mated to mixed‐age rams (49.1% vs 36.1%). After 6 weeks of melatonin treatment, scrotal circumference was greater (p < 0.05) in both young and mixed‐aged rams than in untreated counterparts. In experiment 2, yarding of ewes and rams overnight on several occasions early in the mating period reduced (p < 0.001) pregnancy rate compared with non‐yarded counterparts (89.5% vs 65.5%). Twinning rate was not affected (37.7% vs 36.1%, respectively). In summary, melatonin treatment of Border Leicester rams significantly improved flock reproductive performance in spring due to improved pregnancy rates with young rams and improved litter size with mixed‐age rams.