Existing Sampling Methods Research Articles

Traffic sensing and characterization in multi-channel wireless networks for cognitive networking

Traffic sensing and characterization is an important building block of cognitive networking systems, however, it is very challenging to perform traffic characterization in multi-channel multi-radio wireless networks. Due to the presence of network traffic in multiple channels, the existing count-based packet sampling methods demand continuous capture on each channel to be effective; this requires a dedicated wireless interface per channel, and hence the existing sampling methods require a very expensive infrastructure and have poor scalability. Time-based sampling methods, on the other hand, offer a cost-effective and scalable solution by reducing the amount and cost of the resources necessary to monitor and characterize the wireless spectrum.The contributions of this paper include the following: (i) a discussion of packet sampling techniques for traffic sensing in multi-channel wireless networks, (ii) a comparison of various time-based sampling strategies using the Kullback–Leibler divergence (KLD) measure, (iii) a study on the effect of the sampling parameters on the accuracy of the sampling strategies, (iv) development of sampling accuracy graphs for easing the process of best sampling scheme selection in multi-channel wireless networks, (v) the proposal of a new metric (traffic intensity) which estimates the busyness of channels by taking into consideration not only the successfully received packets but also corrupt or broken packets, (vi) implementation of time-based sampling in a prototype traffic sensor device for multi-channel traffic sensing in IEEE 802.11 b/g networks, and (vii) characterization of a campus IEEE 802.11 network environment in a spatio-temporal–spectral fashion using sampled traffic traces collected by traffic sensors.

Within-household sampling: searching for a better methodconditional on household size information

Abstract Survey research has been used widely in various social sciences. A random selection of a survey respondent at the household level (so called within-household sampling) is critical for any valid statistical inference with the survey data. In this paper, we will review existing sampling methods. Some methods ensure the randomness, but require a lengthy and intrusive process and hence reduce cooperation. Some methods provide a quick and simple sampling at the expense of the randomness. Although household size information is collected in most of these methods, this information is not fully used. The question that these methods try to answer is how to randomly sample a person. In this paper, we argue that the method should be developed not to answer this question but to answer the question about how to randomly sample a person conditional on (or given) the household size. Compared to the current “one size fit all” methods, it is always better to use a method that allows for different ways of sampling for different household sizes. We then develop a sampling method that is conditional on the household size and use it for a survey in Qatar, a country with large household size population, a characteristic which is typical to the Middle East and Developing countries. We will show difficulties when current methods are applied to these countries and how our method can overcome these difficulties.

Multi-class blue noise sampling

Sampling is a core process for a variety of graphics applications. Among existing sampling methods, blue noise sampling remains popular thanks to its spatial uniformity and absence of aliasing artifacts. However, research so far has been mainly focused on blue noise sampling with a single class of samples. This could be insufficient for common natural as well as man-made phenomena requiring multiple classes of samples, such as object placement, imaging sensors, and stippling patterns. We extend blue noise sampling to multiple classes where each individual class as well as their unions exhibit blue noise characteristics. We propose two flavors of algorithms to generate such multi-class blue noise samples, one extended from traditional Poisson hard disk sampling for explicit control of sample spacing, and another based on our soft disk sampling for explicit control of sample count. Our algorithms support uniform and adaptive sampling, and are applicable to both discrete and continuous sample space in arbitrary dimensions. We study characteristics of samples generated by our methods, and demonstrate applications in object placement, sensor layout, and color stippling.

Multi-class blue noise sampling

Sampling is a core process for a variety of graphics applications. Among existing sampling methods, blue noise sampling remains popular thanks to its spatial uniformity and absence of aliasing artifacts. However, research so far has been mainly focused on blue noise sampling with a single class of samples. This could be insufficient for common natural as well as man-made phenomena requiring multiple classes of samples, such as object placement, imaging sensors, and stippling patterns.

Isolation and preservation of schistosome eggs and larvae in RNAlater® facilitates genetic profiling of individuals

Although field-sampling procedures to capture gDNA from individual schistosome larval stages directly from their natural hosts exist, they do pose some technical and logistical challenges hampering certain epidemiological studies. The aim of this study was to develop, refine and evaluate an alternative methodology, which enables better preservation of large numbers of individual schistosome larval stages and eggs collected in low resource endemic areas, to provide PCR-quality DNA for multi-locus genetic analysis. The techniques reported here present simple and effective short-term field and long-term laboratory preservation and storage systems for individually sampled schistosome eggs and larval stages using a commercially available aqueous stabilisation reagent, RNAlater® eliminating the need for more cumbersome resources such as refrigerators, heaters and centrifuge equipment for immediate specimen processing. Adaptations to a general gDNA extraction method are described, that enables the acquisition of a gDNA extract (~50 μl), facilitating multiple molecular analyses of each sampled schistosome. The methodology provided PCR-quality mitochondrial and nuclear DNA from laboratory cercariae, miracidia and eggs that had been stored at up to 37°C for 2 weeks and at 4°C for 6 months and also from field collected samples. This present protocol provides significant epidemiological, ethical and practical advantages over existing sampling methods and has the potential to be transferred to studies on other organisms, especially where specimens are unable to be seen by the naked eye, are difficult to handle and need to be obtained from a field environment.

Reducing test costs in electronics mass-production

This paper studies the simultaneous optimisation of quality and costs in mass-production of complex electronics products. Testing has become a critical bottleneck for assuring quality, requiring a large amount of time and resources. The volume of especially functional testing must be minimised to reduce costs. Sampling is a potential way to obtain this. Unfortunately, existing sampling methods are not functional in the modern electronics environment with multiple tests. This paper presents new efficient methods, based on continuous sampling plan (CSP) procedures. The applicability of the developed methods is confirmed empirically by analysing and simulating real industrial data.

New Device and Method for Flux-Proportional Sampling of Mobile Solutes in Soil and Groundwater

The importance of monitoring the transport of organic contaminants in soil and groundwater, and the pros and cons of existing sampling methods, are outlined. A new, alternative sampling method is proposed, using a passive sampler that functions as a water-permeable, semi-infinite sink for passing solutes of interest. Tracers integrated in the device store information on the volume of water passing through the sampler during the installation period. The conceptual basis of the sampling method is described. This device enables flux-proportional monitoring of the concentrations of mobile contaminants in the soil and groundwater. 14C-labeled phenanthrene (PHEN) and glyphosate (GLY) are used as case study compounds in laboratory experiments. The sorption capacities and uptake kinetics of 13 adsorbents are screened and compared, as well as the dissolution kinetics of three tracer salts: calcium citrate, calcium fluoride (CaF2), and calcium hydrogen phosphate (CaHPO4). The application of the passive sampler is then demonstrated in long-term laboratory experiments, using large soil columns under steady-state hydraulic conditions. The accumulated flux of PHEN was sampled with an accuracy of 3.6%-17.8%, using graphitized carbon, hexagonal mesoporous silica, and cross-linked polymers as adsorbents. The accumulated flux of GLY was sampled with an accuracy of 12.4%, using gamma-alumina as an adsorbent. The advantages and limitations of this new environmental monitoring method are discussed.

Optimization of a mist chamber (Cofer scrubber) for sampling water-soluble organics in air.

While the atmospheric fate and transport of biogenic and anthropogenic hydrocarbons has been extensively studied, little is known about the behavior of first-, second-, and third generation photo-oxidation products that arise from OH radical oxidation of the parent species. The results of chamber experiments establish that *OH oxidation of biogenic and anthropogenic hydrocarbons yields carbonyls, dicarbonyls, hydroxycarbonyls, and keto-acids. However, little is known about the generation and fate of these products in the ambient atmospheric environment. This is changing because of the advent of methods that rely on 0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatization of carbonyls in concert with gas chromatography/ion trap mass spectrometry. Such methods provide the means to identify and quantify water-soluble organics, which historically have been difficult to measure. A limitation of existing sampling methods, however, is the use of devices that require low flow rates (0.5-1 L min(-1)). Accordingly, long sampling times (3-4 h) are needed to obtain pptv-ppbv detection limits. The mist chamber is an attractive device because of the high flow rates (25-70 L min(-1)) compatible with its use. Herein, we evaluate a mist chamber using a flow rate of 25-30 L min(-1) to provide short (10 min) sampling times and pptv limits of detection. The results establish a relationship between the Henry's law constant (KH) and the collection efficiency and demonstrate the suitability of the method to measure analytes with KH > or = 10(3) M atm(-1). Adjusting the pH, adding quaternary ammonium salts, or decreasing the temperature of the collecting solution in the mist chamber did not significantly affect the collection efficiency. We tested the method by sampling photooxidation products of isoprene (glyoxal, methylglyoxal, hydroxyacetone, and glycolaldehyde) in the Blodgett Forest, CA. This is the first report of a study the employs the mist chamberto sample hydroxycarbonyls. The accuracy and the reproducibility of the method were evaluated by the analysis of duplicate samples and field spikes. The mean recovery of field spikes was > or =80%, and the relative standard deviation was < or =22% between duplicate measurements. The detection limits were 48, 15, 7.7, and 2.7 pptv for glycolaldehyde, hydroxyacetone, methylglyoxal, and glyoxal, respectively. This work demonstrates the power of the mist chamber in concert with PFBHA derivatization and mass spectrometry to measure pptv concentrations of water-soluble organics with a sampling time of 10 min.

Population Ecology of European Tortoises: Review of Field Techniques

AbstractField techniques used in recent studies of the population ecology of European tortoises are discussed. An efficient marking system suitable for large sample sizes is described. The dual problems ofageing adults and sexing juveniles are highlighted. The relative merits of sampling techniques are dependent on habitat and population density. Mark-recapture techniques are most suitable when sampling is conducted within a grid system which enables results to be stratified, allowing for differential ease of location. However, grid sampling is only practical where tortoise densities are high. At low density sites, or for brief surveys, recording numbers observed per man hour along random paths is the most convenient method, but allowances must be made for differential observer skill. Existing sampling methods bias against finding inactive animals and where these form a large proportion of the population, sample size is strongly influenced by habitat type.

A multi-channel, electro-optical turbidity meter

A multi-channel, electro-optical turbidity meter has been developed with an operating range of 0-10000 parts per million by weight. The instrument is based on a pulsed-light system which eliminates ambient light effects. The turbidity meter is described in detail together with the specially developed calibration apparatus. The calibration characteristics of the system were found to agree well with previous theoretically derived expressions, thus easing the calibration requirements of the probe. Calibration results are presented for natural sands and polystyrene spheres both for finely graded samples and a sample having a broad spread of particle sizes. The instrument calibration was also found to be independent of mean particle velocity. The use of the instrument for measuring the concentration distribution in a transient sediment cloud is described and the results are shown to give a significant improvement in spatial and temporal resolution when compared with existing sampling methods.

Sampling of Liquid Steel for Dissolved Oxygen

An improved bomb-sampling technique for obtaining samples for oxygen analysis from liquid steel is described. Analyses of samples taken from open-hearth furnaces by the improved method show sufficient agreement with laboratory data to indicate the accuracy of the method is better than that of other existing sampling methods.