5,046 research outputs found
Long-term recovery of macroinvertebrate biota in grossly polluted streams: Re-colonisation as a constraint to ecological quality
No full textTo meet targets imposed by the European Water Framework Directive (2000/60/EC) it is vital that measures to improve the status of rivers are both effective and economically viable. Achievement of such aims needs robust understanding of biological responses to changes in water quality vis-à-vis mechanisms of and constraints to the colonization of previously polluted sites. This study therefore examined the long-term chemical and biological changes in historically polluted rivers to elucidate the responses of macroinvertebrate biota to improvements in chemical water quality. For three historically polluted sites in the English Midlands, data from surveys over a period of ca. 50 years were analysed. Ammonia (NH3) and 5-day biochemical oxygen demand (BOD5) were used as chemical water quality indicators. Variations in the ecological recovery of the study sites were assessed using an average pollution sensitivity score (Average Score Per Taxon) and the number of taxa present (usually to family level) present in hand-net samples. Ecological recovery varied widely and was influenced by the intensity and spatial extent of the pollution and the proximity of available sources of potential colonisers. At the site most isolated from potential sources of colonizing taxa, no clean-water macroinvertebrate taxa were recorded 30 years after the major sources of pollution ceased. Where clean-water colonisers were more readily available, significant improvements in ecological quality followed within 2–5 years of the improvements in chemical quality. Macroinvertebrate communities and hence monitoring data may thus be indicative of long past conditions or of biological isolation rather than contemporaneous chemical conditions. Combined chemical and biological data were used to explore a generic model for predicting recovery rates and success. Neither BOD5 nor NH3 were found to provide a consistent and meaningful prediction of either average pollution tolerance of macroinvertebrate taxa or of the number of taxa present. Long-term relationships between macroinvertebrate variables and chemical water quality variables, however, were non-linear, suggesting that water quality thresholds may have to be exceeded before biological recovery can occur. Even when chemical water quality has been improved substantially, the apparent ecological status of macroinvertebrate communities may not reflect reduced pollution levels attained until adequate time to allow for re-colonisation (possibly decades) has elapsed
Measurements of fibre laser losses via relaxation oscillation
No full textWe describe a simple method for measuring fibre laser losses. The method is based on inducing relaxation oscillations by modulating the laser gain. From the oscillation frequency and known fibre parameters a loss figure can be extracted. Loss measurements performed on a Nd-doped fibre laser are presented
Past veterinarians in South Africa
No full textAn alphabetical list containing short biographies of all deceased South African veterinarians up to 1990.[compiled by] P.J. (Bill) PosthumusVolume 1: AL -- Volume 2: M-ZAlso available in print http://137.215.9.20/record=b1893606ab2013ab201
Piano selections from 'Carmen' and 'Coppelia'. No. 44 [music] /
No full textCover title.; "Arranged by P.J. Mansfield."--Caption.; Date approximated from Guide to dating music published in Sydney and Melbourne, 1899-1899, vol.2, part 3 / Prue Neidorf. Sydney : University of Wollongong, 1999. p.265.; Copyright 1926 by Bayley & Ferguson. Toreador's song / Bizet -- Valse de la poupée / Delibes -- Castanet song / Bizet -- Valse in E flat / Delibes -- Seguidilie / Bizet -- Valse des heues / Delibes -- Chorus of boys / Bizet -- Selecton / Delibes -- Habanera / Bizet -- Marche de la cloche/ Delibes -- Intermezzo / Bizet -- Mazurka / Delibes.Piano music. Selections; arranged
Open brief aan den WelEdel. Gestr. Heer P.J. Joubert
No full textleyds-70-7201.pdf created from original pamphlet in the WJ Leyds Collection held in the Africana Section of the Stellenbosch University Library and Information Service.Dutch open letter to P.J. Joubert concerning a railroad concession granted to the author and two of his friends in 1885
Design, Modeling and Simulation of a 52MHz MEMS Gyroscope Device in 1.5um SOI
No full textIn this thesis , a simulation model of a MEMS gyroscope is presented. The model enables mode matching and analysis of the dynamic behavior of a gyroscope. Furthermore, the model allows the optimization the design parameters of the gyroscope. The simulated gyroscope operates at a frequency of 52MHz with amplitudes of 10nm and quality factor of 50,000. Finally, the drive mode measurements are presented at different bias voltages.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Het gemeentelijk Investeringsraadsel: Het verband tussen gemeentelijke investeringen en lokale welvaartsontwikkeling
No full textDit proefschrift gaat over de vraag in hoeverre in Nederland de lokale welvaartsontwikkeling wordt bepaald door de gemeentelijke investeringsinspanning. Op project niveau is meestal wel het een en ander bekend over de maatschappelijke effecten, maar over de impact van de totale investeringsinspanning ontbreekt zowel fundamentele als toepasbare kennis. Het is een raadsel dat nog opgelost dient te worden. De doelstelling van dit proefschrift is daaraan een bijdrage te leveren.Housing System
Coupled thermo–hydro–mechanical processes for the Dutch radioactive waste repository
No full textDisposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the Boom Clay is considered as a potential host rock when designing a generic waste repository in the Netherlands. For design and evaluation of a repository for geologic disposal of nuclear wastes one of its principal concern is the thermal loading. High-level radioactive waste and spent fuel generate considerable amounts of heat. When those waste types are disposed in a geological repository the elevated thermal effect on the behaviour of soils surrounding nuclear waste disposal give rise to change in hydraulic and mechanical properties is a significant factor for repository design. Understanding these time-dependent phenomena processes in relation to both the effects of pore water dissipation and of the thermal expansion is essential for reliably assessing repository performance and evaluating the safety case. This paper presents some of the investigation on the thermal processes with emphasis on the coupled Thermo-Hydro- Mechanical (THM) processes for the disposal concept of a radioactive waste disposal facility, in Boom Clay at a depth of about 500m.Geo-engineerin
Probabilistic performance assessment of a deep tunnel for a radioactive waste repository in French COx claystone
No full textA preliminary probabilistic study of the stability of a circular drift excavated for a radioactive waste repository in the French Callovo-Oxfordian claystone is presented and discussed. An analytical mechanical model assuming isotropic elastic behaviour and linear plastic softening was used. Particular emphasis here is placed on the uncertainty of mechanical property values. The test results from several laboratories showed considerably variable property values and they have been interpreted statistically in this investigation. The obtained statistical results were used in a Monte Carlo framework. The performance of the drift was evaluated in terms of the probability of threshold exceedance in the extent of the plastic zone.Geo-engineerin
- …
