Influence Of Sampling Strategy Research Articles

Artificial Neural Networks-Based Material Parameter Identification for Numerical Simulations of Additively Manufactured Parts by Material Extrusion.

To be able to use finite element (FE) simulations in structural component development, experimental investigations for the characterization of the material properties are required to subsequently calibrate suitable material cards. In contrast to the commonly used computational and time-consuming method of parameter identification (PI) by using analytical and numerical optimizations with internal or commercial software, a more time-efficient method based on machine learning (ML) is presented. This method is applied to simulate the material behavior of additively manufactured specimens made of acrylonitrile butadiene styrene (ABS) under uniaxial stress in a structural simulation. By using feedforward artificial neural networks (FFANN) for the ML-based direct inverse PI process, various investigations were carried out on the influence of sampling strategies, data quantity and data preparation on the prediction accuracy of the NN. Furthermore, the results of hyperparameter (HP) search methods are presented and discussed and their influence on the prediction quality of the FFANN are critically evaluated. The investigations show that the NN-based method is applicable to the present use case and results in material parameters that lead to a lower error between experimental and calculated force-displacement curves than the commonly used optimization-based method.

Estimating the prevalence and intensity of Schistosoma mansoni infection among rural communities in Western Tanzania: The influence of sampling strategy and statistical approach.

BackgroundSchistosoma mansoni is a parasite of major public health importance in developing countries, where it causes a neglected tropical disease known as intestinal schistosomiasis. However, the distribution of the parasite within many endemic regions is currently unknown, which hinders effective control. The purpose of this study was to characterize the prevalence and intensity of infection of S. mansoni in a remote area of western Tanzania.Methodology/Principal findingsStool samples were collected from 192 children and 147 adults residing in Gombe National Park and four nearby villages. Children were actively sampled in local schools, and adults were sampled passively by voluntary presentation at the local health clinics. The two datasets were therefore analysed separately. Faecal worm egg count (FWEC) data were analysed using negative binomial and zero-inflated negative binomial (ZINB) models with explanatory variables of site, sex, and age. The ZINB models indicated that a substantial proportion of the observed zero FWEC reflected a failure to detect eggs in truly infected individuals, meaning that the estimated true prevalence was much higher than the apparent prevalence as calculated based on the simple proportion of non-zero FWEC. For the passively sampled data from adults, the data were consistent with close to 100% true prevalence of infection. Both the prevalence and intensity of infection differed significantly between sites, but there were no significant associations with sex or age.Conclusions/SignificanceOverall, our data suggest a more widespread distribution of S. mansoni in this part of Tanzania than was previously thought. The apparent prevalence estimates substantially under-estimated the true prevalence as determined by the ZINB models, and the two types of sampling strategies also resulted in differing conclusions regarding prevalence of infection. We therefore recommend that future surveillance programmes designed to assess risk factors should use active sampling whenever possible, in order to avoid the self-selection bias associated with passive sampling.

Assessment of Occupational Exposure to Chemicals by Air Sampling for Comparison With Limit Values: The Influence of Sampling Strategy

This study was aimed at quantifying the impact of sampling duration and the number of measurements taken on the quality of assessing occupational exposure to toluene. To this end, a measurement database was built, based on four campaigns carried out in an industrial printing facility. Five homogeneous exposure groups (HEGs) were set up and between 120 and 290 individual measurements lasting from 2 to 8 h were collected for each of them. These measurements were performed with the objective of comparing them to the 8-h Occupational Exposure Limit (8-h OEL). The resulting data were used to define a reference exposure profile per HEG: the 'gold standard'. This exposure profile corresponds to a log-normal distribution of measurements from which compliance/non-compliance with the 8-h OEL decision is derived. To simulate the possible sampling strategies used by industrial hygienists, six scenarios were defined, each containing a different number of measurements: 2, 3, 4, 6, 9, and 12 measurements performed per HEG, over different working days and different seasons of the year. The measurement values per scenario were simulated by sampling from the real measurement per HEG. For each scenario, 1000 simulated exposure profiles and corresponding simulated compliance decisions were computed. They were compared to the gold standard compliance decision using statistical indicators. Three methods were used for computing the simulated compliance decision: (i) the 95th percentile must be lower than the 8-h OEL, (ii) the exceedance fraction with respect to the 8-h OEL must be <0.1% (as defined by standard CEN 689, Appendix D), and (iii) the 70% upper confidence limit of the exceedance fraction with respect to the 8-h OEL must be <5% (as defined by French regulations). The results show that exposure assessment quality increases with both the number of measurements and sampling duration when using the 95th percentile and exposure assessment based on French regulations, whereas it decreases when using the standard. Moreover, guidelines for the efficient evaluation of chemical exposure in the workplace can be drawn up to help professional occupational hygienists. Indeed, boundaries can be recommended regarding the number of measurements and sampling duration necessary to obtain a reliable exposure assessment while minimizing effort devoted to sampling and analysis.

Sampling strategies for estimating brook trout effective population size

The influence of sampling strategy on estimates of effective population size (N e ) from single-sample genetic methods has not been rigorously examined, though these methods are increasingly used. For headwater salmonids, spatially close kin association among age-0 individuals suggests that sampling strategy (number of individuals and location from which they are collected) will influence estimates of N e through family representation effects. We collected age-0 brook trout by completely sampling three headwater habitat patches, and used microsatellite data and empirically parameterized simulations to test the effects of different combinations of sample size (S = 25, 50, 75, 100, 150, or 200) and number of equally-spaced sample starting locations (SL = 1, 2, 3, 4, or random) on estimates of mean family size and effective number of breeders (N b ). Both S and SL had a strong influence on estimates of mean family size and $$ \hat{N}_{b} , $$ however the strength of the effects varied among habitat patches that varied in family spatial distributions. The sampling strategy that resulted in an optimal balance between precise estimates of N b and sampling effort regardless of family structure occurred with S = 75 and SL = 3. This strategy limited bias by ensuring samples contained individuals from a high proportion of available families while providing a large enough sample size for precise estimates. Because this sampling effort performed well for populations that vary in family structure, it should provide a generally applicable approach for genetic monitoring of iteroparous headwater stream fishes that have overlapping generations.

The influence of sampling strategies and spatial variation on the detected soil bacterial communities under three different land-use types

To determine the influence of pooling strategies on detected soil bacterial communities, we sampled 45 soil cores each from a eucalypt woodland, a sown pasture and a revegetated site in an Australian landscape. We assessed the spatial variation within each land-use plot, including the influence of sampling distance, soil chemical characteristics and, where appropriate, proximity to trees on the soil bacterial community, by generating terminal restriction fragment length polymorphism profiles of the bacterial 16S rRNA genes. The soil bacterial community under the revegetated site was more similar to the original woodland than the pasture, and this result was found regardless of the soil- or the DNA-pooling strategy used. Analyzing as few as eight cores per plot was sufficient to detect significant differences between the bacterial communities under the different plots to be distinguished. Soil pH was found to be most strongly associated with soil bacterial community composition within the plots and there was no association found with proximity to trees. This study has investigated sampling strategies for further research into the transitions of soil microbial communities with land-use change across broader temporal and spatial scales.

Influence of sampling strategies on the monitoring of cyanobacteria in shallow lakes: Lessons from a case study in France

Sampling cyanobacteria in freshwater ecosystems is a crucial aspect of monitoring programs in both basic and applied research. Despite this, few papers have dealt with this aspect, and a high proportion of cyanobacteria monitoring programs are still based on monthly or twice-monthly water sampling, usually performed at a single location. In this study, we conducted high frequency spatial and temporal water sampling in a small eutrophic shallow lake that experiences cyanobacterial blooms every year. We demonstrate that the spatial and temporal aspects of the sampling strategy had a considerable impact on the findings of cyanobacteria monitoring in this lake. In particular, two peaks of Aphanizomenon flos-aquae cell abundances were usually not picked up by the various temporal sampling strategies tested. In contrast, sampling once a month was sufficient to provide a good overall estimation of the population dynamics of Microcystis aeruginosa. The spatial frequency of sampling was also important, and the choice in the location of the sampling points around the lake was very important if only two or three sampling points were used. When four or five sampling points were used, this reduced the impact of the choice of the location of the sampling points, and allowed to obtain fairly similar results than when six sampling points were used. These findings demonstrate the importance of the sampling strategy in cyanobacteria monitoring, and the fact that it is impossible to propose a single universal sampling strategy that is appropriate for all freshwater ecosystems and also for all cyanobacteria.

Influence of Sampling Strategy and Utility of Rectal Biopsy in the Diagnosis of Collagenous and Lymphocytic Colitis

Influence of Sampling Strategy and Utility of Rectal Biopsy in the Diagnosis of Collagenous and Lymphocytic Colitis

Influence of Sampling Strategy on Microbiologic Results Before and After Periodontal Treatment

The aim of this study was to test whether different sampling strategies would influence the microbiologic outcomes by assessing the bacterial load and composition of the subgingival microbiota by means of anaerobic culturing before and after periodontal treatment. The first study (1 versus 4 [1vs4]) included 33 patients with generalized chronic periodontitis. Two sampling strategies were compared, sampling one site from the deepest pocket in the mouth (M1) versus a pooled sample of four sites from the deepest pockets in each quadrant (M4). The second study (2 versus 4 [2vs4]) included 20 patients with generalized chronic periodontitis. The strategy M4 was compared to a pooled sample of two non-adjacent sites in the same quadrant (M2). All samples were processed identically by means of anaerobic culturing. In both studies, a pretreatment sampling was taken. However, in the second study (2vs4), subgingival samples were also taken at 1, 3, and 6 months after periodontal therapy. Quantitative data were compared between strategies by means of t test and signed-rank test; qualitative data were compared by means of 2 x 2 contingency tables. Pretreatment samples showed that total anaerobic counts were significantly higher for M4 compared to M1 (P <0.001) and M2 (P = 0.025). However, there were no significant differences in regard to percentage of microbiota and counts for each pathogen. Most of the qualitative differences between strategies were caused by false negatives in M1 and M2. Post-treatment samples showed a reduction in total counts and a limited impact in the frequency of detection of periodontal pathogens. M2 detected a significant decrease in the frequency of detection of Porphyromonas gingivalis, which was not confirmed by the M4 strategy. The criteria of selection and the number of sites selected when sampling the subgingival biofilm in patients with generalized chronic periodontitis may influence the detection and quantitation of periodontal pathogens when evaluated by culture especially after treatment.

Comparison of simple techniques for estimating chlorophyll a concentration in the intertidal zone using high spectral-resolution field-spectrometer data

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 274:31-40 (2004) - doi:10.3354/meps274031 Comparison of simple techniques for estimating chlorophyll a concentration in the intertidal zone using high spectral-resolution field-spectrometer data Véronique Carrère1,3,*, Nicolas Spilmont1, Dominique Davoult2 1Laboratoire Biogéochimie et Environnement du Littoral (LABEL), UMR CNRS 8013 ELICO, Université du Littoral Côte d¹Opale, Maison de la Recherche en Environnement Naturel, 32 avenue Foch, 62930 Wimereux, France 2Station Biologique de Roscoff, UMR CNRS 7127, Université Pierre et Marie Curie, Place Georges Teissier, BP 74, 29682 Roscoff Cedex, France 3Present address: Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, Faculté des Sciences et Techniques, 2 rue de la Houssinière, BP 92208, Nantes Cedex 3, France *Email: veronique.carrere@chimie.univ-nantes.fr ABSTRACT: We compared 3 simple techniques for estimating the concentration of microphytobenthos chlorophyll a at the sediment surface using high spectral-resolution field spectra. The techniques are based on relationships established between chlorophyll a (chl a) absorption at ~673 nm estimated from field reflectance spectra and chl a concentration in field samples. For ease of application, the best approach should provide an estimate that is independent of the physical properties of the sediment such as grain size, moisture content, etc. and of sediment type and illumination conditions. To achieve as comprehensive a picture as possible, tidal flats from the French shore of the eastern English Channel that differed in sediment type and dynamics were studied at low tide and at various times of the year in order to cover seasonal blooms and illumination variations. The preliminary results show that all 3 methods are fairly robust (R2 > 0.8), with very little difference between them, indicating little influence of the measurement conditions on reflectance in the wavelength range used (570 to 720 nm) and great stability of the instrument (a portable field spectrometer) used in the field. Validation of the 3 approaches was made with further, more recently acquired data set, and a very close correlation (R2 > 0.93, slope ~1) was found between measured and estimated chl a concentrations for all 3 techniques at the range of chlorophyll concentrations encountered that time at the Baie de Somme site (50 to 200 mg m-2). The influence of sampling strategy and sediment optical properties with respect to spectral signatures must, however, be investigated in more detail. More measurements are required to fully validate the relationships found and to ensure that they are generally applicable to most intertidal flat environments. KEY WORDS: Chlorophyll a · Reflectance spectra · Microphytobenthos · Intertidal · English Channel Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 274. Online publication date: June 24, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Alpha-synuclein pathology is highly dependent on the case selection.

Lewy bodies and dystrophic neurites have been considered a common substrate for dementia, but they are also frequently found in the normal elderly population. The primary component of this pathology involves alpha-synuclein. The main objective of the present study was to estimate the prevalence of alpha-synuclein pathology in aged population, and to assess its relative significance in relation to dementia. The study also investigated whether differences could be detected in alpha-synuclein pathology in relation to age, gender or concomitant Alzheimer's pathology. Furthermore, the influence of sampling strategies was analysed. Alpha-synuclein pathology was assessed using immunohistochemistry in well-characterized post-mortem material. The investigation included patients from a longitudinal study of dementia of Alzheimer's type (n = 103, 85% demented), subjects from a prospective longitudinal clinical study of ageing (n = 69, 29% demented), a cohort of consecutive clinical post-mortem cases collected for 1 year (n = 262, 12% demented), a sample of forensic post-mortem cases collected for 6 months (n = 121, 15% demented) and a sample of Brain Bank material (n = 234, 26% demented). Overall, alpha-synuclein pathology was found in 14% of all 774 subjects over 40 years of age, and this percentage varied from 8% to 27% according to sampling strategies. These results indicate that the prevalence of alpha-synuclein pathology clearly depends on the selection of material. Furthermore alpha-synuclein pathology was found in 23% of clinically demented patients and in 11% of non-demented subjects. The load of alpha-synuclein pathology was significantly greater in the demented patients versus non-demented subjects indicating that alpha-synuclein pathology is indeed of importance in the pathogenesis of dementia.

The influence of sampling strategy on a circular feature in coordinate measurements

This paper investigates the influence of the sampling strategy for circular section measurements when using coordinate measuring machines. The intention is to determine the relationship between the number of measured points and the computer results which give a true representation of the geometric circular feature. In order to identify the optimum number of points for measurement of a precision part, an analysis has been carried out using a calibrated ring gauge. The influence of the sampling strategy is predominantly considered. The influence of form errors (in the out-of-roundness of a measured component) and probe lobing errors are also examined briefly.

Influence of sampling strategy on detecting preferential flow paths in water-repellent sand

Rapid response tensiometers or TDR (time domain reflectometry) probes in soil profiles, or early arrival of solutes in groundwater or drainwater after a rain event, provide direct evidence of preferential flow in soils. However, little information about the amount and magnitude of preferential flow paths is obtained by such measurement methods. Here, two intensively sampled vertical trenches illustrate the effect of sample spacing and the effect of sample size on the detection of preferential flow paths. In a water-repellent sandy soil, a sample spacing of up to 22 cm over a distance of several metres is just sufficient to collect information about preferential flow paths. Using larger sample spacings, the water content distributions apparently became more horizontally stratified. Increasing the sample size by pooling pairs of adjacent 100 cm 3 soil samples over a distance of several metres, still allowed the detection of preferential flow paths. Preferential flow paths were no longer observed for larger sample sizes. Enlarging the sample size reduces the calculated standard deviation and coefficient of variation. As preferential flow paths may vary in space and time, so the optimal number of samples to detect these paths in vertical trenches may vary, indicating that sampling strategies need to be flexible in design.

The influence of sampling strategy on the apparent population dynamics of planktonic rotifers

The influence of sampling strategy on the apparent population dynamics of planktonic rotifers

Aspirin and gastrointestinal haemorrhage: A methodologic assessment

The literature on the association between Aspirin (ASA) use and gastrointestinal haemorrhage (GIH) has been reviewed. Thirteen control-studies were selected and examined for (i) the type of design (ii) the choice of outcome measures, and (iii) the adequacy of satisfying defined causation criteria and the influence of sampling strategies on one of these criteria—strength of association. Of the 13 studies seven were large scale randomized control trials (RCTs) and six were case-control studies. Among the outcome measures utilized in these studies and currently available for the assessment of GIH, we found none were uniquely satisfactory for use as a “gold standard”. Furthermore, in none of these studies was the particular chosen outcome measure sufficiently satisfactory to allow firm conclusions on the issue of causation. None of the studies adequately met all the defined causation criteria or adequately eliminated the potential biases in the chosen sampling strategies. Thus the evidence that aspirin causes GIH fails to stand up to critical evaluation. This, of course, does not mean that ASA does not cause GIH. However, it is common practice for physicians to advise their patients with a prior history of GIH and or gastrointestinal symptoms to refrain from ASA use. This is probably sound advice in the setting where ASA is being used as a casual or short term analgesic or anti-inflammatory agent. But in the context of severe inflammatory joint disease when the use of ASA is clinically indicated, it should not be withheld on the basis of the risk of GIH. There is a widespread belief in medicine that by implication aspirin and other nonsteroidal anti inflammatory drugs are a common cause of bleeding from the gastrointestinal tract, yet it has been pointed out frequently [1–3] that the evidence to support the belief is weak and circumstantial. Despite this the perceived association of aspirin with gastrointestinal bleeding influences both pharmaceutical and clinical practice and often hinders or prevents the prescription of anti-inflammatory medication to patients with severe inflammatory joint disease. It was felt that a proper critical appraisal of the evidence was essential. It is unfortunate that the evidence most frequently cited implicating ASA as a cause of GIH is almost entirely related to the casual use of the drug. Thus our conclusions must be viewed with some caution in the patient group where this knowledge would be of most importance, that is in patients with inflammatory joint disease.

Influence of sampling strategy on the relationships between fauna and vegetation structure, plant lifeform and floristics

AbstractThe effect of sampling strategy on animal‐habitat relationships was evaluated with data collected from a 50 ha area containing a sequence of tropical vegetation types.Sampling sites were located randomly within defined habitat types (i.e. stratified random sampling) and systematically irrespective of habitat type. At each site the fauna, comprising birds (63 species), reptiles (15 species), amphibia (13 species) and grasshoppers (32 species) were sampled for the abundance of species. Simultaneously, vegetation and related data, comprising vertical structure (52 attributes), ground surface condition (18 attributes), plant lifeform (18 attributes) and the abundance of plant species (200) were recorded.Random and systematic data matrices, comprising sites defined by animal or vegetation attributes, were reduced dimensionally by correspondence analysis. Animal first dimension vectors were then regressed on the first dimension vectors of vegetation structure, lifeform and floristics, respectively.With stratified random sampling, vegetation structure (comprising vertical and ground attributes) and lifeform explained most of the variation in the fauna; floristics were not a significant factor. On the other hand with the systematic data, fioristics explained almost all of the variation in animal abundance and distribution. By removing the ecotonal sites from the systematic data set and recalculating vectors, the animal—vegetation relationships became similar to those generated from the stratified random sampling data.Clearly, the sampling strategy employed in a faunal survey has a major influence on the inventory of species, and on the relative importance of vegetation structure, lifeform and floristics in explaining animal distribution. The presence of ecotones in the systematic data set was highlighted as the key to the difference between the sampling strategies.