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Sampling Designs with Linear and Quadratic Probability Functions
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作者 Lennart Bondesson Anton Grafstrom Imbi Traat 《Open Journal of Statistics》 2014年第3期178-187,共10页
Fixed size without replacement sampling designs with probability functions that are linear or quadratic functions of the sampling indicators are defined and studied. Generality, simplicity, remarkable properties, and ... Fixed size without replacement sampling designs with probability functions that are linear or quadratic functions of the sampling indicators are defined and studied. Generality, simplicity, remarkable properties, and also somewhat restricted flexibility characterize these designs. It is shown that the families of linear and quadratic designs are closed with respect to sample complements and with respect to conditioning on sampling outcomes for specific units. Relations between inclusion probabilities and parameters of the probability functions are derived and sampling procedures are given. 展开更多
关键词 Complementary Midzuno Design conditional Sample Inclusion Probability Midzuno Design Mixture of Designs Parameters of Design Sample Complement Sinha Design
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Diffusion Process of High Concentration Spikes in a Quasi-Homogeneous Turbulent Flow
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作者 Masaya Endo Qianqian Shao +1 位作者 Takahiro Tsukahara Yasuo Kawaguchi 《Open Journal of Fluid Dynamics》 2016年第4期371-390,共21页
When a mass spreads in a turbulent flow, areas with obviously high concentration of the mass compared with surrounding areas are formed by organized structures of turbulence. In this study, we extract the high concent... When a mass spreads in a turbulent flow, areas with obviously high concentration of the mass compared with surrounding areas are formed by organized structures of turbulence. In this study, we extract the high concentration areas and investigate their diffusion process. For this purpose, a combination of Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques was employed to obtain simultaneously the two fields of the concentration of injected dye and of the velocity in a water turbulent channel flow. With focusing on a quasi-homogeneous turbulence in the channel central region, a series of PLIF and PIV images were acquired at several different downstream positions. We applied a conditional sampling technique to the PLIF images to extract the high concentration areas, or spikes, and calculated the conditional-averaged statistics of the extracted areas such as length scale, mean concentration, and turbulent diffusion coefficient. We found that the averaged length scale was constant with downstream distance from the diffusion source and was smaller than integral scale of the turbulent eddies. The spanwise distribution of the mean concentration was basically Gaussian, and the spanwise width of the spikes increased linearly with downstream distance from the diffusion source. Moreover, the turbulent diffusion coefficient was found to increase in proportion to the spanwise distance from the source. These results reveal aspects different from those of regular mass diffusion and let us conclude that the diffusion process of the spikes differs from that of regular mass diffusion. 展开更多
关键词 Turbulent Transport High Concentration Spikes Quasi-Homogeneous Turbulent Flow conditional sampling Technique PIV and PLIF Measurements Passive Scalar Diffusion
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Some Aspects of Ecology of Chrysichthys nigrodigitatus (Lacepede) in River Niger, Nigeria
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作者 Nwachi 0 F 《Journal of Northeast Agricultural University(English Edition)》 CAS 2016年第3期47-53,共7页
A study on the food and feeding habit of Chrysichthys nigrodigitatus (Lacepede) was conducted in River Niger within the region of Oshimili local government area of Delta State Nigeria. A total of 90 specimens were c... A study on the food and feeding habit of Chrysichthys nigrodigitatus (Lacepede) was conducted in River Niger within the region of Oshimili local government area of Delta State Nigeria. A total of 90 specimens were collected with the help of fishermen using gill net, cast net and traps. The fish samples were immediately taken to the laboratory for analysis. Morphometric characteristics such as weight, length, condition factor, egg weight, Gonado Somatic Index (GSI) and sex ratio were determined. The stomach content was analyzed using numerical method to determine the food content. The total length of the fish sampled ranged from 14.40-44.60 cm, while the standard length varied from 11.00 cm to 47.00 cm and the fish body weight ranged between 19.00 g to 503.20 g. Sex ratio 1 female to 1 male was observed. The mean condition factor for both male and female obtained was 1.67. Of all the 90 fishes sampled, none had empty gut representing 100%. The major food items were phytoplankton, plant part and Detritus. Out of 41 females sampled, only 17 had eggs and the eggs were matured at stage IV. 展开更多
关键词 MORPHOMETRIC numerical method PHYTOPLANKTON sampling and condition factor
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Comparison of sampling designs for calibrating digital soil maps at multiple depths 被引量:1
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作者 Yakun ZHANG Daniel D.SAURETTE +3 位作者 Tahmid Huq EASHER Wenjun JI Viacheslav I.ADAMCHUK Asim BISWAS 《Pedosphere》 SCIE CAS CSCD 2022年第4期588-601,共14页
Digital soil mapping (DSM) aims to produce detailed maps of soil properties or soil classes to improve agricultural management and soil quality assessment. Optimized sampling design can reduce the substantial costs an... Digital soil mapping (DSM) aims to produce detailed maps of soil properties or soil classes to improve agricultural management and soil quality assessment. Optimized sampling design can reduce the substantial costs and efforts associated with sampling, profile description, and laboratory analysis. The purpose of this study was to compare common sampling designs for DSM, including grid sampling (GS), grid random sampling (GRS), stratified random sampling (StRS), and conditioned Latin hypercube sampling (cLHS). In an agricultural field (11 ha) in Quebec, Canada, a total of unique 118 locations were selected using each of the four sampling designs (45 locations each), and additional 30 sample locations were selected as an independent testing dataset (evaluation dataset). Soil visible near-infrared (Vis-NIR) spectra were collected in situ at the 148 locations (1 m depth), and soil cores were collected from a subset of 32 locations and subdivided at 10-cm depth intervals, totaling 251 samples. The Cubist model was used to elucidate the relationship between Vis-NIR spectra and soil properties (soil organic matter (SOM) and clay), which was then used to predict the soil properties at all 148 sample locations. Digital maps of soil properties at multiple depths for the entire field (148 sample locations) were prepared using a quantile random forest model to obtain complete model maps (CM-maps). Soil properties were also mapped using the samples from each of the 45 locations for each sampling design to obtain sampling design maps (SD-maps). The SD-maps were evaluated using the independent testing dataset (30 sample locations), and the spatial distribution and model uncertainty of each SD-map were compared with those of the corresponding CM-map. The spatial and feature space coverage were compared across the four sampling designs. The results showed that GS resulted in the most even spatial coverage, cLHS resulted in the best coverage of the feature space, and GS and cLHS resulted in similar prediction accuracies and spatial distributions of soil properties. The SOM content was underestimated using GRS, with large errors at 0–50 cm depth, due to some values not being captured by this sampling design, whereas larger errors for the deeper soil layers were produced using StRS. Predictions of SOM and clay contents had higher accuracy for topsoil (0–30 cm) than for deep subsoil (60–100 cm). It was concluded that the soil sampling designs with either good spatial coverage or feature space coverage can provide good accuracy in 3D DSM, but their performances may be different for different soil properties. 展开更多
关键词 3D digital soil mapping conditioned Latin hypercube sampling grid sampling quantile random forest model stratified random sampling
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Effective condition numbers and small sample statistical condition estimation for the generalized Sylvester equation 被引量:1
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作者 DIAO HuaiAn SHI XingHua WEI YiMin 《Science China Mathematics》 SCIE 2013年第5期967-982,共16页
Abstract In this paper, we investigate the effective condition numbers for the generalized Sylvester equation (AX - YB, DX - YE) = (C,F), where A,D ∈ Rm×m B,E ∈ Rn×n and C,F ∈ Rm×n. We apply the ... Abstract In this paper, we investigate the effective condition numbers for the generalized Sylvester equation (AX - YB, DX - YE) = (C,F), where A,D ∈ Rm×m B,E ∈ Rn×n and C,F ∈ Rm×n. We apply the small sample statistical method for the fast condition estimation of the generalized Sylvester equation, which requires (9(m2n + mn2) flops, comparing with (-O(m3 + n3) flops for the generalized Schur and generalized Hessenberg- Schur methods for solving the generalized Sylvester equation. Numerical examples illustrate the sharpness of our perturbation bounds. 展开更多
关键词 generalized Sylvester equation Sylvester equation effective condition number perturbation bound small sample statistical condition estimation (SCE)
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