Home About us Contact
|
Home About us Contact | ||
|
|
||
Sampling Requirements (sampling + requirement)
Selected AbstractsDefining and measuring braiding intensityEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2008Roey Egozi Abstract Geomorphological studies of braided rivers still lack a consistent measurement of the complexity of the braided pattern. Several simple indices have been proposed and two (channel count and total sinuosity) are the most commonly applied. For none of these indices has there been an assessment of the sampling requirements and there has been no systematic study of the equivalence of the indices to each other and their sensitivity to river stage. Resolution of these issues is essential for progress in studies of braided morphology and dynamics at the scale of the channel network. A series of experiments was run using small-scale physical models of braided rivers in a 3 m , 20 m flume. Sampling criteria for braid indices and their comparability were assessed using constant-discharge experiments. Sample hydrographs were run to assess the effect of flow variability. Reach lengths of at least 10 times the average wetted width are needed to measure braid indices with precision of the order of 20% of the mean. Inherent variability in channel pattern makes it difficult to achieve greater precision. Channel count indices need a minimum of 10 cross-sections spaced no further apart than the average wetted width of the river. Several of the braid indices, including total sinuosity, give very similar numerical values but they differ substantially from channel-count index values. Consequently, functional relationships between channel pattern and, for example, discharge, are sensitive to the choice of braid index. Braid indices are sensitive to river stage and the highest values typically occur below peak flows of a diurnal (melt-water) hydrograph in pro-glacial rivers. There is no general relationship with stage that would allow data from rivers at different relative stage to be compared. At present, channel count indices give the best combination of rapid measurement, precision, and range of sources from which measurements can be reliably made. They can also be related directly to bar theory for braided pattern development. Copyright © 2008 John Wiley & Sons, Ltd. [source] A Case Study of Soil-Gas Sampling in Silt and Clay-Rich (Low-Permeability) SoilsGROUND WATER MONITORING & REMEDIATION, Issue 1 2009Todd A. McAlary Soil-gas sampling and analysis is a common tool used in vapor intrusion assessments; however, sample collection becomes more difficult in fine-grained, low-permeability soils because of limitations on the flow rate that can be sustained during purging and sampling. This affects the time required to extract sufficient volume to satisfy purging and sampling requirements. The soil-gas probe tubing or pipe and sandpack around the probe screen should generally be purged prior to sampling. After purging, additional soil gas must be extracted for chemical analysis, which may include field screening, laboratory analysis, occasional duplicate samples, or analysis for more than one analytical method (e.g., volatile organic compounds and semivolatile organic compounds). At present, most regulatory guidance documents do not distinguish between soil-gas sampling methods that are appropriate for high- or low-permeability soils. This paper discusses permeability influences on soil-gas sample collection and reports data from a case study involving soil-gas sampling from silt and clay-rich soils with moderate to extremely low gas permeability to identify a sampling approach that yields reproducible samples with data quality appropriate for vapor intrusion investigations for a wide range of gas-permeability conditions. [source] Spatial sampling requirements for monitoring upper-air climate change with radiosondesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2008Mark P. McCarthy Abstract The global climate observing system upper air network (GUAN) was established to provide a network of high quality radiosonde stations with sufficient historical data records, and a commitment to future observing, in support of the needs of the climate research community. An assessment of the spatial sampling requirements for such a network in order to monitor large-scale climate changes has been conducted. The GUAN provides adequate coverage for monitoring global, tropical and hemispheric mean climate. Priority stations within the GUAN have been identified based upon their unique contribution to the network. Further sampling improvements to the GUAN may be possible by utilizing radiosonde stations located in India, Africa and northern polar regions. To keep sampling-related trend error below 0.05 K/decade in the troposphere, and 0.1 K/decade in the stratosphere, requires a radiosonde station to be located approximately every 30° longitude and 15° latitude north of 30°N. The inhomogeneous distribution of radiosonde stations in the tropics and southern hemisphere place a stronger requirement of 20° longitude and 10° latitude south of 30°N. The radiosonde network is inadequate for monitoring humidity except in the northern mid-latitudes. © Crown Copyright 2007. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd [source] Portal-systemic shunting in patients with fibrosis or cirrhosis due to chronic hepatitis C: the minimal model for measuring cholate clearances and shuntALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 3 2007G. T. EVERSON Summary Background, Measurement of portal inflow and portal-systemic shunt using cholate clearances could be useful in monitoring patients with liver disease. Aim, To examine relationships of cholate clearances and shunt to cirrhosis and varices and to define minimal sampling requirements. Methods, Five hundred forty-eight studies were performed in 282 patients enrolled in the Hepatitis C Antiviral Long-term Treatment to prevent Cirrhosis (HALT-C) trial. Stable, non-radioactive isotopes of cholate were administered intravenously and orally, clearances (Cliv and Cloral) were calculated from [dose/area under curve (AUC)] and cholate shunt from [(AUCoral:AUCiv) x (Doseiv:Doseoral) x 100%]. Results, Cholate Cloral and cholate shunt correlated with prevalences of both cirrhosis and varices (P < 0.0001 for all). Peripheral venous sampling at 5, 20, 45, 60 and 90 min defined the minimal model. Linear regression of cholate shunt determined from five points within 90 min vs. the standard method of 14 points over 3 h yielded slope of 1.0 and intercept 0.5% (r2 = 0.98, P < 0.0001). Results were identical in the 189 validation studies (slope 1.0, intercept 0.5%, r2 = 0.99, P < 0.0001). Conclusions, Cholate Cloral and cholate shunt may be useful in monitoring patients with liver disease. The 5-point model enhances application of cholate Cloral and cholate shunt in the non-invasive assessment of the portal circulation. [source] Improving the assessment of species compositional dissimilarity in a priori ecological classifications: evaluating map scale, sampling intensity and improvement in a hierarchical classificationAPPLIED VEGETATION SCIENCE, Issue 4 2010B.E. Lawson Abstract Question: Can species compositional dissimilarity analyses be used to assess and improve the representation of biodiversity patterns in a priori ecological classifications? Location: The case study examined the northern-half of the South-east Queensland Bioregion, eastern Australia. Methods: Site-based floristic presence,absence data were used to construct species dissimilarity matrices (Kulczynski metric) for three levels of Queensland's bioregional hierarchy , subregions (1:500 000 scale), land zones (1:250 000 scale) and regional ecosystems (1:100 000 scale). Within- and between-class dissimilarities were compiled for each level to elucidate species compositional patterns. Randomized subsampling was used to determine the minimum site sampling intensity for each hierarchy level, and the effects of lumping and splitting illustrated for several classes. Results: Consistent dissimilarity estimates were obtained with five or more sites per regional ecosystem, 10 or more sites per land zone, and more than 15 sites per subregion. On average, subregions represented 4% dissimilarity in floristic composition, land zones approximately 10%, and regional ecosystems over 19%. Splitting classes with a low dissimilarity increased dissimilarity levels closer to average, while merging ecologically similar classes with high dissimilarities reduced dissimilarity levels closer to average levels. Conclusions: This approach demonstrates a robust and repeatable means of analysing species compositional dissimilarity, determining site sampling requirements for classifications and guiding decisions about ,lumping' or ,splitting' of classes. This will allow more informed decisions on selecting and improving classifications and map scales in an ecologically and statistically robust manner. [source] | ||||||||||