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排序方式: 共有718条查询结果,搜索用时 31 毫秒
41.
Metal uptake by young trees from dredged brackish sediment: limitations and possibilities for phytoextraction and phytostabilisation 总被引:8,自引:0,他引:8
Mertens J Vervaeke P De Schrijver A Luyssaert S 《The Science of the total environment》2004,326(1-3):209-215
Five tree species (Acer pseudoplatanus L., Alnus glutinosa L. Gaertn., Fraxinus excelsior L., Populus alba L. and Robinia pseudoacacia L.) were planted on a mound constructed of dredged sediment. The sediment originated from a brackish river mouth and was slightly polluted with heavy metals. This preliminary study evaluated the use of trees for site reclamation by means of phytoextraction of metals or phytostabilisation. Although the brackish nature of the sediment caused slight salt damage, overall survival of the planted trees was satisfactory. Robinia and white poplar had the highest growth rates. Ash, maple and alder had the highest survival rates (>90%) but showed stunted growth. Ash, alder, maple and Robinia contained normal concentrations of Cd, Cu, Pb and Zn in their foliage. As a consequence these species reduce the risk of metal dispersal and are therefore suitable species for phytostabilisation under the given conditions. White poplar accumulated high concentrations of Cd (8.0 mg kg(-1)) and Zn (465 mg kg(-1)) in its leaves and might therefore cause a risk of Cd and Zn input into the ecosystem because of autumn litter fall. This species is thus unsuitable for phytostabilisation. Despite elevated metal concentrations in the leaves, phytoextraction of heavy metals from the soil by harvesting stem and/or leaf biomass of white poplar would not be a realistic option because it will require an excessive amount of time to be effective. 相似文献
42.
BACKGROUND: Evaluation of the sustainability of iodine-deficiency disorders control programs guarantees successful and sustained virtual elimination of iodine deficiency. The Lesotho universal salt iodization legislation was enacted in 2000 as an iodine-deficiency disorders control program and has never been evaluated. OBJECTIVES: To assess the sustainability of the salt iodization program in Lesotho, 2 years after promulgation of the universal salt iodization legislation. METHODS: The proportion to population size method of sampling was used in 2002 to select 31 clusters in all ecological zones and districts of Lesotho. In each cluster, 30 women were selected to give urine and salt samples and 30 schoolchildren to give urine samples. The salt samples were analyzed by the iodometric titration method, and the ammonium persulfate method was used to analyze the urine samples. The chairperson of the iodine-deficiency disorders control program was interviewed on programmatic indicators of sustainability. SAS software was used for statistical analysis of the data. RESULTS: The urinary iodine concentrations of very few children (10.1% and 21.5%) and women (9.8% and 17.9%) were lower than 50 microg/L and 100 microg/L, respectively. At the household level, 86.9% of the households used adequately iodized salt. Only four indicators of sustainability have been attained by the salt iodization program in Lesotho. CONCLUSIONS; Iodine-deficiency disorders have been eliminated as a public health problem in Lesotho, but this elimination is not sustainable. Effective regular monitoring of salt iodine content at all levels, with special attention to iodization of coarse salt, is recommended, together with periodic evaluation of the iodization program. 相似文献
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44.
Pieter W Uys Paul D van Helden John W Hargrove 《Journal of the Royal Society Interface》2009,6(30):11-15
In a significant number of instances, an episode of tuberculosis can be attributed to a reinfection event. Because reinfection is more likely in high incidence regions than in regions of low incidence, more tuberculosis (TB) cases due to reinfection could be expected in high-incidence regions than in low-incidence regions. Empirical data from regions with various incidence rates appear to confirm the conjecture that, in fact, the incidence rate due to reinfection only, as a proportion of all cases, correlates with the logarithm of the incidence rate, rather than with the incidence rate itself. A theoretical model that supports this conjecture is presented. A Markov model was used to obtain a relationship between incidence and reinfection rates. It was assumed in this model that the rate of reinfection is a multiple, ρ (the reinfection factor), of the rate of first-time infection, λ. The results obtained show a relationship between the proportion of cases due to reinfection and the rate of incidence that is approximately logarithmic for a range of values of the incidence rate typical of those observed in communities across the globe. A value of ρ is determined such that the relationship between the proportion of cases due to reinfection and the logarithm of the incidence rate closely correlates with empirical data. From a purely theoretical investigation, it is shown that a simple relationship can be expected between the logarithm of the incidence rates and the proportions of cases due to reinfection after a prior episode of TB. This relationship is sustained by a rate of reinfection that is higher than the rate of first-time infection and this latter consideration underscores the great importance of monitoring recovered TB cases for repeat disease episodes, especially in regions where TB incidence is high. Awareness of this may assist in attempts to control the epidemic. 相似文献
45.
Pieter Coenen Idsart Kingma Cécile R.L. Boot Paulien M. Bongers Jaap H. van Dieën 《Applied ergonomics》2013
Valid and reliable low-back load assessment tools that can be used in field situations are needed for epidemiologic studies and for ergonomic practice. The aim of this study was to assess the inter-rater reliability of a low-back load video-analysis method in a field setting. 相似文献
46.
Pål J. From Jan T. GravdahlTommy Lillehagen Pieter Abbeel 《Control Engineering Practice》2011,19(8):809-819
Robots on ships have to endure large inertial forces due to the non-inertial motion of the ship. The ship motion affects both the motion planning and control of the manipulator, and accurate predictions can improve performance substantially. It is thus important to investigate to what extent it is possible to predict the future motion of a ship. Based on these predictions, this paper presents a new approach to motion planning and control of such manipulators. It is shown that the effects of the non-inertial forces can be eliminated—in fact, the robot can even leverage the inertial forces to improve performance compared to robots on a fixed base. In particular it is shown that by including the inertial forces in the motion planning the wear and tear on the robot due to these forces can be reduced substantially. To perform realistic experiments a 9-DoF robot is used. The first five joints are used to generate the real ship motion, and the last four joints are used for motion planning. The dynamic coupling between the first five and the last four joints is thus exactly the same as the dynamic coupling between a ship and a manipulator, which allows for very realistic experiments. 相似文献
47.
Development of a cost effective probe for the long term monitoring of straw bale buildings 总被引:1,自引:0,他引:1
Jim Carfrae Pieter De Wilde John Littlewood Steve Goodhew Peter Walker 《Building and Environment》2011
This paper reviews current methodologies for measuring the moisture content of straw bale walls in buildings. It discusses the development of an affordable and accurate moisture probe that has been designed to be easily assembled by the builder or owner of a straw bale building from items readily available in the United Kingdom (UK). The probe uses a timber block inserted into the wall, relying upon the measurable moisture variances of the timber and relating this to the surrounding straw. The probes are designed to be used in pairs of varying length, taking measurements at different depths to give an estimate of the moisture gradient through the wall. In order to properly calibrate this device, a full set of sorption and desorption isotherms were established for both Oat and Wheat straw and three different timber species. The results from an environmental chamber have been compared to readings from specimens of the new probe installed in a straw bale house in the south west of the UK. The results were found to be consistent, to within 2%, with the laboratory findings. 相似文献
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49.
Yegermal Tesfaw Atalay Steven Vermeir Nicolas Vergauwe Daan Witters Pieter Verboven Bart M. Nicolai Jeroen Lammertyn 《Microfluidics and nanofluidics》2012,12(5):779-786
This paper presents the implementation of a multiple analyte enzyme assay, based on the sequential injection of the different
enzyme solutions, in an electrokinetic driven microfluidic chip. The assay methodology for the simultaneous quantification
of d-glucose and d-fructose was reported in previous publications but here the real integration of both enzyme assays was achieved. When assays
were executed separately, good reproducibility was observed with average CV values of 5.2% and 4.5% for the d-glucose and d-fructose assay, respectively. Next, the assays for the quantification of d-glucose and d-fructose were integrated simultaneously on chip, where each assay was executed consecutively in the same microreactor by
applying a specific sequence of potentials at the reservoirs. This article proves the integration of a sequential based quantification
approach in continuous microfluidic chips with electrokinetic actuation. 相似文献
50.
Tony Wauters Joris Kinable Pieter Smet Wim Vancroonenburg Greet Vanden Berghe Jannes Verstichel 《Journal of Scheduling》2016,19(3):271-283
Scheduling projects is a difficult and time consuming process, and has far-reaching implications for any organization’s operations. By generalizing various aspects of project scheduling, decision makers are enabled to capture reality and act accordingly. In the context of the MISTA 2013 conference, the first MISTA challenge, organized by the authors, introduced such a general problem model: the Multi-Mode Resource-Constrained Multi-Project Scheduling Problem (MRCMPSP). The present paper reports on the competition and provides a discussion on its results. Furthermore, it provides an analysis of the submitted algorithms, and a study of their common elements. By making all benchmark datasets and results publicly available, further research on the MRCMPSP is stimulated. 相似文献