Non-Fickian dispersion in a single fracture

Solute transport in fractured rocks is of major interest in many applications, from the petroleum industry to ground water management. This work focuses on the dispersion process in a transparent replica of a real single fracture. The fracture exhibits strong changes in heterogeneity, with the first half very heterogeneous and the second half fairly homogeneous. Three models have been used to interpret the tracer experiments: the classical advection-dispersion equation (ADE), the continuous time random walk (CTRW), and the stratified model. The main goals were to test these models and to study possible correlations between fitting parameters and heterogeneities. As expected, the solution derived from the ADE equation appears to be unable to model long-time tailing behavior. On the other hand, the results confirm the CTRW robustness and the coefficient beta seems well correlated to heterogeneities. Finally, the stratified model is also able to describe non-Fickian dispersion. The parameters defined by this model are correlated to the heterogeneities of the fracture.     

Biodegradation of chlorpyrifos by either single or combined cultures of some soilborne plant pathogenic fungi

Abstract

Biodegradation of chlorpyrifos was studied in liquid culture media amended with either single or combined eight different plant pathogenic fungi isolated from the continuous cropping wheat fields. The average recovery of chlorpyrifos from the liquid media was found to be 86.1%. The detection limit of chlorpyrifos by the analytical method used was 19 ppb. Data showed that the growth of mixed fungi at concentrations up to 200 ppm of chlorpyrifos was higher than in the control treatment. Chlorpyrifos concentrations declined in the medium of combined fungi more than it did in the medium of any single fungus with increase in the incubation period. The amount of chlorpyrifos recovered was 79.8 ppm (39.9%) in the combined fungal cultures after 21 days. However, those recovered from the media of Fusarium graminearum, F. oxysporum, Rhizoctonia solani, Cladosporhim cladosporiodes, Cephalosporium sp., Trichoderma viridi, Alternaria alternata, and Cladorrhinum brunnescens, ranged from 48.0 to 74.8%. The half‐life value (T_1/2) for chlorpynfos was 15.8 day in the medium amended with mixed fungi. However, for the single cultures it ranged from 19.3 to 33.0 day.     

Using Twitter to communicate conservation science from a professional conference

Scientists are increasingly using Twitter as a tool for communicating science. Twitter can promote scholarly discussion, disseminate research rapidly, and extend and diversify the scope of audiences reached. However, scientists also caution that if Twitter does not accurately convey science due to the inherent brevity of this media, misinformation could cascade quickly through social media. Data on whether Twitter effectively communicates conservation science and the types of user groups receiving these tweets are lacking. To address these knowledge gaps, we examined live tweeting as a means of communicating conservation science at the 2013 International Congress for Conservation Biology (ICCB). We quantified and compared the user groups sending and reading live tweets. We also surveyed presenters to determine their intended audiences, which we compared with the actual audiences reached through live tweeting. We also asked presenters how effectively tweets conveyed their research findings. Twitter reached 14 more professional audience categories relative to those attending and live tweeting at ICCB. However, the groups often reached through live tweeting were not the presenters’ intended audiences. Policy makers and government and non‐governmental organizations were rarely reached (0%, 4%, and 6% of audience, respectively), despite the intent of the presenters. Plenary talks were tweeted about 6.9 times more than all other oral or poster presentations combined. Over half the presenters believed the tweets about their talks were effective. Ineffective tweets were perceived as vague or missing the presenters’ main message. We recommend that presenters who want their science to be communicated accurately and broadly through Twitter should provide Twitter‐friendly summaries that incorporate relevant hashtags and usernames. Our results suggest that Twitter can be used to effectively communicate speakers’ findings to diverse audiences beyond conference walls.     

Residence and place image

Data are presented for a particular population on its perception of English and Welsh local authority areas in terms of desirability for residence. The method employed permits a distinction between positive and negative judgements as well as a measure of the differing degree to which areas figure in the mind at all. It is established that the areas are seen in terms of a sharply differentiated hierarchy of preference and that there is considerable variation in the extent to which areas are “visible”. In aggregate negative judgements predominate and the most frequently expressed attitude is strong dislike. Places in the south‐west are popular as are some places in the north. London Boroughs are unpopular although in varying degrees. The most favoured place is Cornwall and the least favoured is Wolverhampton. It is argued that perceptions studied in the “direct” way used here are important to complement those employing an “oblique” method in which criteria of choice are assumed or established by social survey and then used to create a profile of preference against which places can be measured and ranked.     

Small towns in the united states: a perspective

Small towns are an important part of the rural settlement fabric in the United States, but there is very little substantive research into their capacity to survive or their intrinsic importance. However, recently there has been increasing interest shown by social scientists in these problems. This paper looks at features of this research from the point of view of the population and economic structure of small towns. It concludes by arguing that the problems of small towns are not indigenous to the towns, and calls for a comprehensive national urban policy.     

Twenty-five years of HAZOPs

The HAZOP or hazard and operability study was developed by ICI over 25 years ago and is in wide use today throughout the world. The technique is intended to review, in a formalized manner, the design of a system such as a chemical process production plant to detect potential problems in the operation of the system. The system has been extended for use on all types of production, storage and distribution units. Experience in the use of hazard studies has lead to the development of a phased approach with three distinct design phases.     

Sensitivity of Ozone Production to the Nmhc Composition, Aerosol Back-Scattering and High Chimney Emission

In this paper, three sensitivity studies are designed to analyze the effect of the NMHC (Non-Methane HydroCarbon) composition, the aerosol back-scattering and the high chimney NO_x emission to the photochemical prodution of ozone by using a one-dimensional photochemistry-diffusion model under a favourable meteorological condition. Measurements of the NMHC composition in Taipei indicated that the percentage of iso-butene, cis-2-butene, trans-2-butene and benzene in a unit volume was much higher than of those observed in other major cities. the high ratio of benzene was directly linked to its high percentage in gasoline. As to the unusually high amount of iso-butene, cis-2-butene and trans-2-butene, more researches are needed to identify their source. Concerns are raised as to how productive is NMHC composition is to the photochemical production of the surface ozone. A rough estimate shows that the total reactivity of the Taipei NMHC composition is about 1.21 × 10^-9 cm³ s^-1 which is 1.6 times that of the Los Angeles (LA) NMHC composition, while the simulated noon peak will be different by 28 ppbv, i.e. 18% more than that simulated with a LA composition.

Meanwhile, high aerosol loading is a serious problem in Taipei. the attenuation of the UV radiation by aerosols cannot be ignored. A numerical simulation shows that the noon ozone level will decrease from 178 to 141ppbv, i. e. about 21% reduction, with deterioration of the visual range from 85 to 5 km.

In the southern Taiwan, industry parks are mixed with the populated Kaohsiung city, hence the large emission of NO_x from high chimneys cannot be ignored. in this study, NO_x is assumed to be emitted in the layer between 235-460 m high with an emission rate of 0.05 or 0.145 ppbv/sec. the results show that the NO_x emitted from the elevated stack lead to a considerable reduction of surface ozone. Such conclusion is obtained due to the fact that a one-dimensional model is used in this paper. Whereas, if a three-dimensional regional model was used, then a higher productivity of ozone downstream would be simulated.     

A composite medium approximation for unsaturated flow in layered sediments

Saturated-unsaturated flow in strictly layered sediments proceeds via conductors in parallel in the direction parallel to bedding, and via resistors in series in the direction perpendicular to bedding. On sufficiently small scales of space and time, flow in such media will be subject to approximate capillary equilibrium locally, which provides a basis for approximating the effective hydraulic conductivity of a composite multi-layer medium in terms of the conductivities of the individual layers. Equations for the hydraulic conductivity tensor in "composite medium approximation" (COMA) are given in a coordinate system aligned with bedding. Hydraulic conductivity parallel to bedding is generally larger than in the perpendicular direction. The anisotropy depends on the spread of the conductivity distribution, and tends to increase for dryer conditions. The COMA model was implemented in a multi-phase flow simulator and tested by comparison with high-resolution simulations in which all layering heterogeneity is resolved explicitly. Under favorable conditions, COMA is found to accurately represent sub-grid scale flow and transport processes, providing a practical method for simulating field-scale flow and transport in layered media. The approximation improves when layers are thinner, and when flow rates are smaller.     

Production of radioactive particles for use in environmental studies

This paper presents an aerosol generation technique developed to produce dry aerosol particles of various sizes from aqueous solutions of salt. The technique was tested with sodium chloride, lithium carbonate and uranyl acetate at various aqueous concentrations which produced particles in the size range of 0.13-1.37 microm Mass Median Diameter (MMD). The generated aerosols were acceptably monodisperse with a geometric standard deviation of 1.4-2. Both MMD and Mass Median Aerodynamic Diameter (MMAD) increased significantly (p<0.001) with increased concentration of the salt in solution. The technique can also be used to generate aerosols of different chemical species. The results obtained indicate that the system is convenient for use with various aerosol-forming materials, with a stable particle size distribution being maintained for a long period of steady operation. The technique was successfully applied in wind tunnel studies to simulate the release of submicron radioactive particles and their interception by crops, grass and tree canopies. The relevance and application of the technique in other areas of environmental assessment studies is discussed.     

基于流媒体技术的远程教育平台的设计与实现

流媒体技术采用流式传输的方式在Internet／Intranet播放的媒体格式，其数据流随时传送随时播放，缩短了启动延时，降低了对系统缓存容量的需求，极大地减少了用户的等待时间，因此广泛应用于网络教育、网络电台、视频点播、收费播放等方面。文中主要介绍了流媒体技术的特点、原理，进一步阐述了用于在局域网和Internet中传送流式多媒体内容的开发工具windows media，给出了一种利用Windows media流媒体技术构建远程教育系统的具体方案，很好的解决了音频，视频信息的传送问题和数据间的同步问题。