Samples Of Different Sizes Research Articles

EFFECT OF SAMPLE SIZE ON EVALUATION OF MIXING QUALITY OF FINELY DISPERSE POWDERS

over, it should be compared with the size of the functional microcell in which all particles of the components exist in a given proportion. The number of samples should represent rather completely the general population of the mixture being tested. Correct evaluation of the mixture can be guaranteed only with such testing of the mixture. It is natural that similar testing requires significant effort and time. During actual industrial production, however, it is possible to convert the testing of each powder mixture into a long-term research study; for practical purposes, therefore, an attempt has been made to compare experimentally and theoretically samples of different size from different batches with the same components and same proportions of their content in a mixture. The formula of the theoretical standard deviation σ for the completely disordered equilibrium state of a two-component mixture, which is proposed in [3], is adopted as the basis for solution of the problem in question: σ = P 0.5 (1 ‐ P) 0.5 n ‐0.5 , (1)

Critical state analysis in bulk MgB2 by means of a quantitative magneto-optical technique

Abstract This paper is aimed at investigating the superconducting properties of the MgB2 new compound (bulk) with particular emphasis on the correlation and/or competition between microstructural and magnetic granularity. Standard magnetic characterizations are reported in order to provide background information about the material under study at higher magnetic fields. At low fields, two samples of different sizes are analysed with the magneto-optical (MO) technique. The central investigation method is an extended quantitative MO analysis coupled with microstructural analysis. The main results consist in finding out that, however large the sample, and notwithstanding the structural granularity, at low fields the magnetic flux penetrates in an apparent single-crystal-like fashion, if macroscopic cracks are not present. The local current distribution inside the small sample is calculated as a function of field at different temperatures by means of an inverted two-dimensional Biot-Savart model. From the resu...

Kinetics of wood-anhydride reactions: a novel approach

The reaction kinetics of wood (Corsican pine) with acetic, propionic, succinic, and hexenyl succinic anhydride dissolved in pyridine were investigated. To determine reaction kinetics, anhydride depletion of the reactive liquid was monitored. This approach allows to collect a complete sequence of kinetic data from a single experiment. The results carry information on reaction kinetics without allowing for a precise determination of reaction turnover vs time. For all anhydrides investigated, the reaction kinetics of wood samples of different size (300 μm–4 mm) do not depend on sample size, hence the reaction is activation- not diffusion-controlled. All results are consistent with a remarkably simple model of purely activation-controlled reaction kinetics with a single activation energy. Activation energies were determined. The result for propionic anhydride agrees with an earlier investigation based on weight gain of reacted wood.

A simple glow discharge ion source for direct solid analysis by on-axis time-of-flight mass spectrometry

A simple and small-sized direct current glow discharge (dc-GD) ion source has been designed and constructed for direct analysis of solid samples. The glow discharge (about 100 mm3 of internal volume) was coupled to a commercial on-axis time-of-flight mass spectrometer (TOFMS) for fast simultaneous multielement-selective detection. The commercial TOFMS used was originally coupled to an inductively coupled plasma (ICP) ion source. Therefore, the GD source presented in this study was designed aiming at being easily exchanged with the ICP source of a commercial ICP-TOFMS instrument (LECO Corporation). The distance between the cathode (sample) and the sampler cone was kept at about 4 mm.The proposed source is able to analyse planar conducting samples of different sizes with good long-term stability (better than ±5% when isotope ratioing techniques were applied). The spectral mass resolving power was about 1520 (at mass 120 u).Finally, the expected benefits of the fast simultaneous multielemental capabilities of TOFMS detection to carry out direct depth profile analysis of solid samples are demonstrated and discussed.

Coulomb correlation gap: Finite-size analysis

A semiclassical model with randomly distributed N donor and K× N acceptor sites and with infinite-range Coulomb interaction is investigated by means of computer simulations on two-dimensional samples of different sizes. The shape of the Coulomb correlation gap in the density of one-electron excitations g( ε) is obtained for different values of K within a wide energy interval around the Fermi energy μ. Using simple scaling arguments we demonstrate that the true behavior of g( ε) in the immediate neighborhood of μ is hidden by the finite-size effects and find that g( ε) further away from μ is described by a power-law with an exponent, depending on K and the sign of ε− μ.

Factors determining the spatial structure of benthic communities of a shallow bay

The species composition and the spatial structure of benthos were studied along a transect running at a depth of 1–18 m on the soft bottom substrates of Zapadnaya Bight of Furugelm Island (Peter the Great Bay, Sea of Japan). This area has been proposed as a major site for long-term monitoring of the Far Eastern State Marine Reserve. Hydrobiological samples of different sizes (16 cm2, 0.025, and 1 m2) were taken by a diving method at 5-m intervals from the shore. Benthic communities were distinguished using principal component analysis (PCA), Sorensen's similarity indices, and similarity dendrograms. The grain size composition of bottom sediment was determined. Three benthic communities at depths of 1–3, 4–8, and 14–18 m and two transitional zones were distinguished in Zapadnaya Bight. The benthic communities are characterized by a relative constancy of species composition within their boundaries, and by stable ratios of quantitative characteristics of other species from different ecological groups. The transitional zones, which are comparable in extension with the communities themselves, are characterized by changes in species composition and the presence of characteristic species; here, the substrate type changes and sediment grain sorting is decreased.

Ground-state study of a donor–acceptor model with finite charge-transfer energy

A donor–acceptor model with randomly distributed N donor and N acceptor sites and with finite charge transfer energy Δ is investigated at zero temperature by means of computer simulations on two-dimensional samples of different sizes. We demonstrate that the density of one-electron excitations g( ε) for acceptors in the vicinity of the Fermi energy μ depends essentially on the size of the sample investigated and that g( ε) further away from μ exhibits a size-independent power-law with the non-universal exponent decreasing with increasing Δ. Rigorous relations for μ and for the mapping of g( ε) for donors into g( ε) for acceptors are also given.

Research on dependence of resistivity changing anisotropy on microcracks extending in rock with experiment

Multiple electrodes are arranged on the surfaces of cubic granite samples of different sizes according to pre-designed patterns. Samples are fully saturated with water in vacuum. Waterproof insulation glue is coated on the measuring surface and a small parts (including two arrises) of the adjacent surfaces of the saturated sample to ensure that the electric current flows only within the sample through the connection between the electrodes. The multiple electrodes are combined form arrays of different direction and spacing with symmetrical four-electrode method according to need of measuring of resistivity changing anisotropy, electric profiling and electric sounding. The samples are placed into container filled with water. The samples are uniaxially compressed along the direction parallel to the longest dimension of the cubic, and the variation of resistivity during the whole loading process is observed. In the experiments, some samples are loaded to rupture with macro-fractures, some are only loaded to the stage, which shows obvious precursors in variation of resistivity associated with the indication of forthcoming rupture. Finally a quantitative comparison between the dominant orientation of pre-existing cracks in photo-micrography of unruptured samples and those macro-fractures in ruptured sample is made, together with their respective resistivity changing anisotropy behaviors. The experimental results are the following: (1) For measuring points in areas that are passed by cracks or rupture bands, the directions of principal anisotropy axes deduced from four kinds of combined equation sets are essentially identical with each other, and accord with the orientation of cracks or main rupture bands approximately. For measuring points in area without crack or rupture band passing through, either the directions of calculated principal anisotropy axes by different combinatorial arrays are inconsistent with each other, or the principal anisotropy axis cannot be determined, especially in the cases where the crack plane is parallel to the measuring surface. (2) The dominant orientation of microfractures or rupture bands shown from micrographs is close to the direction of principal anisotropy axis along which the variation in resistivity is the greatest. (3) The results of electric profiling can be used for detecting the localization of cracks.

Using the bootstrap for estimation in group sequential designs: an application to a clinical trial for nasopharyngeal cancer.

We investigate a resampling method for bias correction in group sequential designs with censored survival data using logrank testing. The method draws nested bootstrap samples of different sizes from the observed data in order to mimic the large sample independent increment property of statistics resulting from sequential designs. The motivation for this problem came from the very positive results and early termination of a randomized clinical trial for nasopharyngeal cancer co-ordinated by the Southwest Oncology Group.

Using the bootstrap for estimation in group sequential designs: an application to a clinical trial for nasopharyngeal cancer

We investigate a resampling method for bias correction in group sequential designs with censored survival data using logrank testing. The method draws nested bootstrap samples of different sizes from the observed data in order to mimic the large sample independent increment property of statistics resulting from sequential designs. The motivation for this problem came from the very positive results and early termination of a randomized clinical trial for nasopharyngeal cancer co-ordinated by the Southwest Oncology Group. Copyright © 1999 John Wiley & Sons, Ltd.

Sensitivity in the measurement of microwave surface resistance of high- superconducting samples of different sizes by the cavity method

Cavity resonators are conventional devices for measuring the temperature and frequency dependence of microwave surface resistance, , of superconducting samples. The temperature dependence can provide information about the losses due to those conduction electrons that are not condensed into the superconducting state. Since surface resistance characterizes the response to the electromagnetic field near the surface, it qualifies the suitability of the superconducting material for microwave device applications. The measurement of by the cavity technique is performed by replacing the end plate of mode cavity with the superconducting sample. The sensitivity of measurement is restricted for the samples whose dimension is less than that of the end plate. In this paper, we report the measurement of surface resistance of bulk samples of varying dimensions, using a lamina with a circular opening in the end plate. Sensitivity and the error in the measurement of is discussed with respect to the uncertainties in the Q-value and the -value of the background copper cavity.

Experimental validation of multiple scattering calculations with high energy X-ray photons

Experimental data and results of numerical simulations of multiple scattering of polarized X-ray photons are presented and compared. The simulations were performed with a Monte Carlo code developed by the authors optimized to simulate Compton scattering experiments. The ultimate goal is to validate a procedure for correction of experimental Compton profiles. Measurements were done on Al samples with synchrotron radiation and the contribution of photons suffering several scattering events was enhanced by minimizing or canceling out the single scattering part. This was achieved by either taking advantage of the polarization properties of the beam or by making the difference of spectra with the same single scattering component. Samples of different sizes and thickness were measured in transmission and reflection geometry. Good agreement with simulations was observed in all cases and even detailed spectral structure of the multiple scattering component was properly reproduced by the calculations.

ROOTEDGE: Software for Measuring Root Length from Desktop Scanner Images

AbstractOne approach for measuring the length of roots washed from soil samples is to use a desktop scanner to acquire binary images and then use image analysis procedures to determine root length. Normally, this approach requires user‐adjusted exposure thresholding. The objectives of this study were to develop a procedure for obtaining binary images of root samples with a desktop scanner that does not require user‐adjusted exposure thresholding of each image and to test the performance of the newly developed ROOTEDGE program by using images containing single or multiple root segments of corn (Zea mays L.). ROOTEDGE was developed for measuring the length of digitized roots using the edge chord algorithm. It is insensitive to object orientation, has four image‐processing operations, and holds only seven lines of the image in memory. Visual comparisons of digitized images with actual root segments showed that root segments with diameters less than 0.15 mm were not being completely digitized by the image acquisition procedure and were fragmented in the images. The most complete root images were produced by using the highest available scanner resolution and the lowest scanner threshold level for exposure. Using the closing image‐processing operation in ROOTEDGE with a test coefficient of 1 also helped to join fragmented objects within images and improved the correlation of ROOTEDGE measurements to direct measurements. Ratios of ROOTEDGE length measurements to manual line‐intersection length measurements ranged from 0.98 to 0.88 for four corn root samples of different sizes. In general, the ROOTEDGE software and image acquisition system accurately measured corn root length without user‐adjusted exposure thresholding.

A.c. impedance analysis of electrochemical lithium intercalation into highly oriented pyrolytic graphite

Electrochemical lithium intercalation into graphite was studied by cyclic voltammetry and a.c. impedance spectroscopy. Highly oriented pyrolytic graphite was used as a model graphite material to distinguish the difference in electrochemical behavior between the basal and the edge planes at graphite. A comparison between cyclic voltammograms of the basal plane and the whole surface of highly oriented pyrolytic graphite revealed that electrochemical lithium intercalation proceeds predominantly at the edge plane/electrolyte interface. The charge-transfer resistance changed continuously with electrode potential, and no significant change was observed at stage transition potentials (210, 120, and 90 mV versus Li/Li +). From the variations of the Warburg impedance of samples of different sizes, it was concluded that lithium diffuses from the edge plane to the interior in the direction parralel to the basal plane and that its diffusivity changes with the stage structure of the bulk lithium—graphite intercalation compound.

Through a narrow window: Sample size and the perception of correlation.

A theoretical analysis (Y. Kareev, 1995b) of the sampling distribution of correlations led to the surprising conclusion that the use of small samples has a potential advantage for the early detection of a correlation. This is so because the distribution is highly skewed, and the smaller the sample size, the more the distribution is skewed. This article describes 2 experiments that were designed as empirical tests of this conclusion. In Experiment 1 (N = 112), the authors compared the predictions of participants differing in their working-memory capacity (hence in the size of the samples they were likely to consider). In Experiment 2 (N = 144), the authors compared the predictions of participants who viewed samples of different sizes, whose size was determined by the authors. The results fully supported Y. Kareev's conclusion : In both experiments, participants with lower capacity (or smaller samples) indeed perceived the correlation as more extreme and were more accurate in their predictions.

Statistical Methods for Assessing Compliance with the Respirable Dust Standard

Abstract Adequate statistical methods should be used to assess the compliance with the respirable dust standard accurately. The objectives of this article are to study the statistical methods that can be used in compliance hypothesis testing under the assumption that the time-weighted-average dust concentrations follow a lognormal distribution, and to analyze the testing power under different situations. Through simulation, the statistical methods are compared in terms of testing power, at different given type I errors for samples of different sizes and different geometric standard deviations. Based on the results, suggestions are given concerning the possible use of these methods. The power of a test depends on the chosen type I error, geometric standard deviation, sample size, and the ratio of the mean dust level upon which compliance is based to the respirable dust standard. The impact of each factor is studied. With samples of small size (e.g., 5), the testing powers can be high only under very specif...

Conditional statistics of vertical heat fluxes in local advection conditions

Turbulent fluctuations have been investigated in the internal boundary layer (IBL) which forms after a dry-to-wet surface transition. The IBL is defined as that part of the atmospheric surface layer where the influence of the downstream surface is noticeable. The results of the application of three different quadrant analysis techniques are presented. The three techniques, in increasing order of the amount of information supplied, provide: (1) the diurnal variation of quadrant contribution (Ci), number fraction (Ti) and conditional average (% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiiYdd9qrFfea0dXdf9vqai-hEir8Ve% ea0de9qq-hbrpepeea0db9q8as0-LqLs-Jirpepeea0-as0Fb9pgea% 0lrP0xe9Fve9Fve9qapdbaqaaeGacaGaaiaabeqaamaabaabcaGcba% GaeyykJeUabm4DayaafaGabm4CayaafaGaeyOkJe-aaSbaaSqaaiaa% dMgaaeqaaaaa!4215!\[\langle w's'\rangle _i \], with s = T or q) of vertical sensible and latent heat fluxes, (2) the quadrant contribution and number of samples of different sizes depending on the relative magnitude of each sample, and (3) the distribution of the nondimensional probability density function. The results show that in the IBL the vertical flux of sensible heat is maintained by (i) a small fraction of large samples with warm air carried upwards, and (ii) a larger fraction of small samples with cool air carried downwards. Both processes are almost equal in importance. In the morning and near the top of the IBL negative temperature fluctuations are limited by the near-uniform temperature conditions upstream and above the IBL. This limitation reduces, at that location, the conditional average of the sinking motions of cool air. Closer to the wet surface the negative temperature fluctuations are less susceptible to the above mentioned limitation. As a consequence contributions from all four quadrants are almost equal leading to a very small vertical heat flux. In the presence of a temperature inversion over both the upstream and the downstream terrain, shear-generated turbulence appears to be the cause of the relative abundance of sinking motions of warm air and rising motions of cool air, leading to a reversal of the sensible heat flux. The latent heat flux is positive (i.e. directed away from the surface) at all times and is maintained in almost equal amount by (i) a small number of large magnitude samples with moist air carried upwards, and (ii) small magnitude samples with sinking motions of dry air. These sinking motions of dry air are far more numerous, especially in the morning, but their conditional average is very small. The abundance of sinking motions of dry air is attributed to the fact that over the downstream terrain evaporation is greatly enhanced, leading to a skewed w′q′ signal. This skewness is clearly visible in the w′q′-probability density distribution of the morning runs. In the evening the asymmetry between these two different contributions disappears. This is because evaporation is greatly reduced and large positive humidity fluctuations no longer occur.

Modified maximum likelihood estimation for rayleigh distribution

For defining a Modified Maximum Likelihood Estimate of the scale parameter of Rayleigh distribution, a hyperbolic approximation is used instead of linear approximation for a function which appears in the Maximum Likelihood equation. This estimate is shown to perform better, in the sense of accuracy and simplicity of calculation, than the one based on linear approximation for the same function. Also the estimate of the scale parameter obtained is shown to be asymptotically unbiased. Numerical computation for random samples of different sizes from Rayleigh distribution, using type I1 censoring is done and is shown to be better than that obtained by Lee et al. (1980)

The application of fracture mechanics to crack propagation in dry soil

SummaryThe application of fracture mechanics to dry soil has been investigated. Discs moulded from sand and kaolinite pastes, into which artificial tension cracks were introduced, were fractured using the indirect tension technique. The basic linear elastic fracture mechanics (LEFM) approach was found inadequate to describe the observed relation between the imposed flaw size and the failure stress. Fracture mechanics have been extended to dry soil by adding a crack length increment, Δc, to the imposed flaw size, c, to account for energy dissipation by processes other than the creation of new surfaces. This increment seems to represent the effective size of a ‘process zone’ ahead of the crack tip in which energy is dissipated by micro‐cracking and internal friction. Further experiments done using specimens containing two collinear cracks separated by a variable distance and using samples of different size showed that the two cracks behaved effectively as one for separation distances less than about Δc. For specimen sizes much bigger than Δc fracture testing was found to be scale‐invariant for geometrically similar specimens.

The Accuracy of Cross‐Validation Results in Forecasting

ABSTRACTThe widespread use of regression analysis as a business forecasting tool and renewed interest in the use of cross‐validation to aid in regression model selection make it essential that decision makers fully understand methods of cross‐validation in forecasting, along with the advantages and limitations of such analysis. Only by fully understanding the process can managers accurately interpret the important implications of statistical cross‐validation results in their determination of the robustness of regression forecasting models. Through a multiple regression analysis of a large insurance company's customer database, the Herzberg equation for determining the criterion of validity [11] and analysis of samples of different size from the two regions covered by the database, we illustrate the use of statistical cross‐validation and test a set of factors hypothesized to be related to the statistical accuracy of validation. We find that increasing sample size will increase reliability. When the magnitude of population model differences is small, validation results are found to be unreliable, and increasing sample size has little or no effect on reliability. In addition, the relative fit of the model for the derivative sample and the validation sample has an impact on validation accuracy, and should be used as an indicator of when further analysis should be undertaken. Furthermore, we find that the probability distribution of the population independent variables has no effect on validation accuracy.