Real Distributions Research Articles

A virtual experimental approach to microscale composites testing

This paper presents a method for virtual testing composite microstructures with real fibre distributions, and compares the debonding and crack response with experimental results of identical microstructures under similar loading conditions. Prior to physical testing of HTA/6376 composite laminates, the fibre distribution of the undamaged physical specimen is automatically detected through image analysis and reconstructed as a 2D model in Abaqus software and tested following a sub-modelling approach. Once in-situ SEM micro-mechanical testing of the physical specimen is completed, the virtual and experimental crack paths can be directly compared to determine the viability of the virtual testing method. The influence of thermal residual stress on premature fibre-matrix debond initiation and crack propagation is also investigated. The results of the virtual testing presented in this paper give a strong correlation to the experimentally observed crack growth, where significant improvement on similar previously published virtual experimental results for composite materials in terms of both microstructure scale and accuracy of the crack representation, is observed. For the thermo-mechanically loaded models, thermal residual stresses were found to influence the crack path around certain fibres where localised thermal residual stresses were present, leading to a more accurate representation of damage than that given by the purely mechanically loaded models.

3D Microstructures for Materials and Damage Models

Abstract This article describes research at Los Alamos National Laboratory that is aimed at building a coupled experimental and computational methodology that supports the development of predictive damage capabilities by: (1) capturing real distributions of microstructural features from real material and implementing them as digitally generated microstructures in damage model development, and (2) distilling structure-property information to link microstructural details to damage evolution under a multitude of loading states.

Strong lensing signatures of luminous structure and substructure in early-type galaxies

The arrival times, positions, and fluxes of multiple images in strong lens systems can be used to infer the presence of dark subhalos in the deflector, and thus test predictions of cold dark matter models. However, gravitational lensing does not distinguish between perturbations to a smooth gravitational potential arising from baryonic and non-baryonic mass. In this work, we quantify the extent to which the stellar mass distribution of a deflector can reproduce flux ratio and astrometric anomalies typically associated with the presence of a dark matter subhalo. Using Hubble Space Telescope images of nearby galaxies, we simulate strong lens systems with real distributions of stellar mass as they would be observed at redshift $z_d=0.5$. We add a dark matter halo and external shear to account for the smooth dark matter field, omitting dark substructure, and use a Monte Carlo procedure to characterize the distributions of image positions, time delays, and flux ratios for a compact background source of diameter 5 pc. By convolving high-resolution images of real galaxies with a Gaussian PSF, we simulate the most detailed smooth potential one could construct given high quality data, and find scatter in flux ratios of $\approx 10\%$, which we interpret as a typical deviation from a smooth potential caused by large and small scale structure in the lensing galaxy. We demonstrate that the flux ratio anomalies arising from galaxy-scale baryonic structure can be minimized by selecting the most massive and round deflectors, and by simultaneously modeling flux ratio and astrometric data.

A collisional-radiative model for lithium impurity in plasma boundary region of Experimental Advanced Superconducting Tokamak

A green emission layer caused by lithium impurity is universally observed in plasma boundary region of Experimental Advanced Superconducting Tokamak (EAST) via a visible-light camera, where lithium coating is normally adopted as a routine technique of wall conditioning. In this article, in order to estimate the spatial distribution of green light intensity of this emission layer according to the given real parameter distributions of edge plasmas, a practicable method is proposed based on a collisional-radiative model. In this model, a finite number of energy levels of lithium are taken into account, and proper simplifications of convection-diffusion equations are made according to the order-of-magnitude analysis. We process the atomic data collected from the OPEN-ADAS database, and develop a corresponding program in Mathematica 10.4.1 to solve the simplified one-dimensional problem numerically. Estimation results are obtained respectively for the two sets of edge plasma profiles of EAST in L-mode and H-mode regimes, and both clearly show a good unimodal structure of the spatial distribution of green light intensity of this emission layer. These analyses actually provide the spatial distributions of lithium impurities at different energy levels, not only indicating the spatial distribution of the intensity of this emission layer induced by lithium impurity but also revealing the physical processes that lithium experiences in edge plasma. There are some different and common characteristics in the spatial distribution of the intensity of this emission layer in these two important cases. This emission layer is kept outside the last closed magnetic surface in both cases while it becomes thinner with a higher intensity peak in H-mode case. Besides, the sensitivity of this algorithm to the measurement error of edge plasma profile is also explored in this work. It is found that the relative errors of the numerical results obtained by our proposed method are comparable to those of edge plasma profiles. This work provides important theoretical references for developing a new practical technique of fast reconstructing edge plasma configurations in EAST based on the emission of lithium impurity, and may further contribute a lot to the studies of edge plasma behaviors when three-dimensional perturbation fields are adopted.

Online Variable Kernel Estimator

In this work, the authors propose a novel method called online variable kernel estimation of the probability density function (pdf). This new online estimator combines the characteristics and properties of two estimators namely nearest neighbors estimator and the Parzen-Rosenblatt estimator. Their approach allows a compact online adaptation of the estimated probability density function from the new arrival data. The performance of the online variable kernel estimator (OVKE) depends on the choice of the bandwidth. The authors present in this article a new technique for determining the optimal smoothing parameter of OVKE based on the maximum entropy principle (MEP). The robustness and performance of the proposed approach are demonstrated by examples of online estimation of real and simulated data distributions.

Modeling diameter distributions of Gmelina arborea plantation in Omo Forest Reserve, Nigeria with Johnson’s SB

ABSTRACTDiameter distribution modeling is an essential tool for obtaining reliable information on the structure, growth, and yield of forests. However, this tool has not been duly utilized in many forest plantations, especially in Nigeria. Thus, this article presents the effectiveness of using the Johnson SB function for modeling diameter distributions of a Gmelina arborea plantation in Omo Forest Reserve, Nigeria. Fifty plots of 0.04 ha were randomly selected across three age series. All trees with DBH ≥ 5.0 cm in the selected plots were measured. Three fitting methods for the SB distribution were compared: conditional maximum likelihood (CML), moments (MOM), and Knoebel and Burkhart (KB) methods. The parameter recovery model (PRM) was used to recover the parameters of the distribution. The assessment was based on Kolmogorov-Smirnov (K-S), mean square error (MSE), mean absolute error (MAE), and bias. The results showed that the underlying diameter distribution of the Gmelina arborea followed the Johnson’s SB distribution fitted with MOM. The number of rejections by the K-S test was zero for MOM and CML. The mean K-S value for MOM was statistically different from CML and KB methods. The results obtained after recovering the parameters of the SB distribution were comparable with the real distributions of the Gmelina arborea stand.

Iterative reconstruction of radially-sampled 31P bSSFP data using prior information from 1H MRI

The purpose of this study is to improve direct phosphorus (31P) MR imaging. Therefore, 3D density-adapted radially-sampled balanced steady-state free precession (bSSFP) sequences were developed and an iterative approach exploiting additional anatomical information from hydrogen (1H) data was evaluated. Three healthy volunteers were examined at B0=7T in order to obtain the spatial distribution of the phosphocreatine (PCr) intensities in the human calf muscle with a nominal isotropic resolution of 10mm in an acquisition time of 10min. Three different bSSFP gradient schemes were investigated. The highest signal-to-noise ratio (SNR) was obtained for a scheme with two point-reflected density-adapted gradients. Furthermore, the conventional reconstruction based on a gridding algorithm was compared to an iterative method using an 1H MRI constraint in terms of a segmented binary mask, which comprises prior knowledge. The parameters of the iterative approach were optimized and evaluated by simulations featuring 31P MRI parameters. Thereby, partial volume effects as well as Gibbs ringing artifacts could be reduced. In conclusion, the iterative reconstruction of 31P bSSFP data using an 1H MRI constraint is appropriate for investigating regions where sharp tissue boundaries occur and leads to images that represent the real PCr distributions better than conventionally reconstructed images.

Vertical winds and momentum fluxes due to equatorial planetary scale waves using all-sky meteor radar over Brazilian region

In the equatorial region planetary scale waves play an important role transporting significant amount of energy and momentum through atmosphere. Quantifying the momentum transported by these waves and its effects on the mean flow is rather important. Direct estimates of the momentum flux transported by waves require horizontal and vertical wind measurements. Ground-based meteor radars have provided continuous and reliable measurements of the horizontal wind components in the Mesosphere and Lower Thermosphere (MLT) region and have contributed to improve our knowledge of the dynamics of this region. However, instrumental limitations hinder its use for measuring vertical winds and momentum fluxes. On the other hand, according to Babu et al (2012), all- sky meteor radars are able to infer tridimensional winds when using a large number of meteor echoes centered at the meteor ablation peak. Following this approach, we have used measurements performed by a Meteor Radar installed at São João do Cariri, Brazil (7.4°S; 36.5°W) in order to measure vertical winds and calculate the momentum flux transported by equatorial planetary scale waves. In order to evaluate the accuracy of vertical wind values we have performed several tests based on a simple model considering real meteor distributions and theoretical equations for the MLT winds motion. From our tests, we inferred that Brazilian meteor radar data can be used for this purpose with an accuracy of ~ 1.8m/s. The results show that the vertical wind presents magnitudes of a few meters per second and occasionally reaches magnitudes around 10m/s. Below 92km the vertical wind is predominantly upward during the whole year and above exhibits a semi-annual oscillation with downward phase during the equinoxes. Variations associated to planetary scale waves in the vertical wind are also observed and some of them appear simultaneously in the zonal and meridional wind as well. Largest wave induced amplitudes in the vertical wind are found in the 3–4d band, reaching up to 4m/s. From the vertical and zonal wind measurements, we calculated the vertical transport of zonal momentum in the 3–4d band and found it to be maximum near autumn equinox, when its value reaches almost 20m2/s2, while minimum momentum flux is observed after the winter solstice.

Innovation vs. imitation and the evolution of productivity distributions

We develop a tractable dynamic model of productivity growth and technology spillovers that is consistent with the emergence of real world empirical productivity distributions. Firms can improve productivity by engaging in in-house R&D, or alternatively, by trying to imitate other firms’ technologies subject to limits to their absorptive capacities. The outcome of both strategies is stochastic. The choice between in-house R&D and imitation is endogenous, and based on firms’ profit maximization motive. Firms closer to the technological frontier have less imitation opportunities, and tend to choose more often in-house R&D, consistent with the empirical evidence. The equilibrium choice leads to balanced growth featuring persistent productivity differences even when starting from ex-ante identical firms. The long run productivity distribution can be described as a traveling wave with tails following Zipf’s law as it can be observed in the empirical data. Idiosyncratic shocks to firms’ productivities of R&D reduce inequality, but also lead to lower aggregate productivity and industry performance.

Investigate the relationship between multiwavelength lidar ratios and aerosol size distributions using aerodynamic particle sizer spectrometer

The real aerosol size distributions were obtained by aerodynamic particle sizer spectrometer (APS) in China YinChuan. The lidar ratios at wavelengths of 355nm, 532nm and 1064nm were calculated using Mie theory. The effective radius of aerosol particles reff and volume C/F ratio (coarse/fine) Vc/f were retrieved from the real aerosol size distributions. The relationship between multiwavelength lidar ratios and particle reff and Vc/f were investigated. The results indicate that the lidar ratio is positive correlated to the particle reff and Vc/f. The lidar ratio is more sensitive to the coarse particles. The short wavelength lidar ratio is more sensitive to the particle Vc/f and the long wavelength lidar ratio is more sensitive to the particle reff. The wavelength dependency indicated that the lidar ratios decrease with increasing the wavelength. The lidar ratios are almost irrelevant to the shape and total particles of aerosol size distributions.

What Do True Gender Ratios and Stereotype Norms Really Tell Us?

We present a Focused Review on work that was conducted to compare perceived distributions of men and women in occupations and other social roles with actual real world distributions. In previous work, we showed that means for the two sources were similar and the correlation between them was high. However, in the present paper, although we argue that comparing subjective gender stereotype norms and real world data about gender ratios is an interesting endeavor, we also discuss the limits to and difficulties in trying to determine the causal relationship between them. Most crucially, we argue that our data does not allow us to deduce with certainty that subjective gender norms are based directly on gender ratios.

Evaluation of electrical capacitance tomography sensor based on the coupling of fluid field and electrostatic field

Electrical capacitance tomography (ECT) is based on capacitance measurements from electrode pairs mounted outside of a pipe or vessel. The structure of ECT sensors is vital to image quality. In this paper, issues with the number of electrodes and the electrode covering ratio for complex liquid–solids flows in a rotating device are investigated based on a new coupling simulation model. The number of electrodes is increased from 4 to 32 while the electrode covering ratio is changed from 0.1 to 0.9. Using the coupling simulation method, real permittivity distributions and the corresponding capacitance data at 0, 0.5, 1, 2, 3, 5, and 8 s with a rotation speed of 96 rotations per minute (rpm) are collected. Linear back projection (LBP) and Landweber iteration algorithms are used for image reconstruction. The quality of reconstructed images is evaluated by correlation coefficient compared with the real permittivity distributions obtained from the coupling simulation. The sensitivity for each sensor is analyzed and compared with the correlation coefficient. The capacitance data with a range of signal-to-noise ratios (SNRs) of 45, 50, 55 and 60 dB are generated to evaluate the effect of data noise on the performance of ECT sensors. Furthermore, the SNRs of experimental data are analyzed for a stationary pipe with permittivity distribution. Based on the coupling simulation, 16-electrode ECT sensors are recommended to achieve good image quality.

Shift of localized surface plasmon resonance in monolayer of small gold nanoparticles: Simulation predictions of interparticle coupling

Localized surface plasmon resonance of gold nanoparticle layer is investigated by the experiment as well as theoretical calculations. The limits of analytical models are illustrated for compact nanoparticle film revealing signify cant discrepancy between experimental and simulated results while the numerical calculations based on finite-difference time-domain using thin film optical parameters are shown as suitable. There it is shown that 3D finite-difference time-domain simulation can be replaced by 2D simulation without losing accuracy of the calculation of localized surface plasmon resonance. The dependence of the localized surface plasmon resonance wavelength on the nanoparticle size, separation as well as local dielectric constant of surrounding environment is presented and applied for the real nanoparticle size and separation distributions observed in the experiment. Tuning of plasmon resonance in a wide range is demonstrated as a promising way for further applications.

Determination of maximum particle size in magnetic fluids

Higher-order moments of particle size distribution functions are determined for magnetic fluids from analysis of initial segments of magnetization curves. It is shown that the higher-order moments calculated using approximation of real particle size distributions by the Γ distribution are strongly overestimated. Agreement between the measured and calculated moments can be radically improved by truncating maximum particle size X max. A relation between X max and the parameters of the Γ distribution is proposed taking into account the degree of polydispersity of a magnetic fluid. Namely, the ratio between the maximum and most probable particle diameters is equal to the ratio between the mean-square magnetic moment of a particle and its squared average magnetic moment.

Nonlinear Electrical Impedance Tomography Reconstruction Using Artificial Neural Networks and Particle Swarm Optimization

Electrical impedance tomography (EIT) is an imaging technology that offers the advantages of being noninvasive, and it does not generate ionizing radiation. The main difficulty in applying EIT is to solve an ill-posed nonlinear inverse problem. Given a set of electrical voltages measured at the surface of a volume conductor, the goal is to identify the materials that are present in the domain by determining their electrical conductivities. However, since EIT is a nonlinear problem, various algorithms proposed in the literature can only approximate real conductivity distributions. Nonlinear algorithms, especially artificial neural networks (ANNs), have been proposed to solve this inverse problem, but these algorithms are usually limited by slow convergence issues during the training phase. In this paper, the particle swarm optimization (PSO) method is used to train an ANN to solve the EIT problem. It has been found that, compared with the back-propagation algorithm, PSO is capable of generating both faster and higher convergence. This paper also shows that the proposed method is capable of dealing with noisy data and the imperfections in the finite-element discretization, an important source of errors in EIT imaging.

Sensitivity analysis in PERT networks: Does activity duration distribution matter?

Abstract The Program Evaluation and Review Technique (PERT) is a stochastic network technique developed in the late 1950s. The original model assumes PERT β distribution for the activity durations. Later on, this was criticized by many researchers, and several new distribution types have been introduced, which were believed to be better in modelling the real activity duration distributions or were easier to handle from a mathematical point of view. Introduction of new activity duration distributions was criticized even by Clark—one of the pioneers of PERT—while other researchers were arguing that these new activity distributions could better describe the stochastic distributions of the activity durations and their application helps define the distribution of project duration better. In the course of our research, we have investigated the effect of various activity duration distribution types (PERT-beta, uniform, triangular, lognormal) on the project duration, as well as the impact of the inaccuracy of the activity durations' estimation when performing the PERT three-point estimation. Our basic assumption—that the differences in the distribution of the project duration caused by using different activity duration distributions are not considerable compared to the differences caused by the inaccuracy of the three-point estimations—has been tested on several hypothetical projects and case studies. Four different distributions have been applied, one at a time. The aim has been to clearly show the differences between the results of the application of the selected distributions, therefore the distributions have not been mixed. Monte Carlo analysis has been used to create the probabilistic distributions of the projects. All example projects have proved the basic assumption to be true. The results suggest that from a practical point of view, the accuracy of the three-point estimation is more important than the type of the activity duration distribution. Consequently, the selected activity duration distribution is essentially insignificant. The most important practical consequence of this research is that instead of the time-consuming and costly process of selecting the proper activity duration distributions, planners should devote more effort to adequately determine the activity durations.

Multifunctional thin film sensor system as monitoring system in production

The two most important measurement categories in production are temperature and load. Therefore commercial sensors are applied in machinery as near as possible to the working parts. For a cost efficient production the integration of sensor elements directly on top of the surface in the heavily loaded regions is essential to get the real temperature and load distributions during the production process. Therefore a new multifunctional thin film sensor system is in development. This multilayer system combines thermoresistive sensor structures with piezoresistive ones and exists out of wear resistant carbon based layers (Bewilogua and Hofmann, Surf Coat Technol 242:214---225, 2014; Biehl et al. Thin Solid Films 515:1171---1175, 2006; Biehl et al. Microsystem Technologies, Springer, 2010; Biehl et al. Microsystem Technologies, Springer, 2014; Robertson, Daim Relat Mater 12:79---84, 2003). The sensor data will lead to a deeper process understanding, to optimization of simulation tools, to reduction of rejects and to an improvement of flexibility in production.

The use of multibeam backscatter and bathymetry as a means of identifying faunal assemblages in a deep-sea cold seep

Deep-sea ecosystems have attracted considerable commercial interest in recent years because of their potential to sustain a diverse range of mankind's industrial needs. If these systems are to be preserved or exploited in a sustainable manner, mapping habitats and species distributions is critical. As biodiversity at cold-seeps or other deep-sea ecosystems is driven by habitat heterogeneity, imagery is the obvious choice for characterizing these systems and has indeed proven extremely valuable towards mapping biogenic habitats formed by dense aggregations of large sized species, such as coral reefs, tubeworm bushes or bivalve beds. However, the acquisition of detailed images with resolution sufficient for reliable identification is extremely time consuming, labor intensive and highly susceptible to logistical issues. We developed a novel method for quickly mapping cold seep fauna and habitats over large areas, at the scale of squares of kilometers. Our method uses multibeam echosounder bathymetry and acoustic backscatter data, both segmented and reclassified based on topographical features and then combined to obtain a raster containing unique values incorporating both backscatter and bathymetry data. Two datasets, obtained from 30m and 8m above the seafloor were used and the results from the two datasets were compared. The method was applied to a cold seep community located in a pockmark in the deep Congo channel and we were able to ground truth the accuracy of our method against images of the area. The two datasets, obtained from different altitudes gave varying results: the 8m altitude dataset reliably predicted tubeworms and carbonate rock, while the 30m altitude dataset predicted tubeworms and vesicomyid clams. The 30m dataset was more accurate than the 8m altitude dataset in predicting distributions of tubeworms. Overall, all the predictions were quite accurate, with at least 90% of predictions being within 5m of real distributions.

Noise Induced Phenomena in the Dynamics of Two Competing Species

Noise through its interaction with the nonlinearity of the living systems can give rise to counter-intuitive phenomena. In this paper we shortly review noise induced effects in different ecosystems, in which two populations compete for the same resources. We also present new results on spatial patterns of two populations, while modeling real distributions of anchovies and sardines. The transient dynamics of these ecosystems are analyzed through generalized Lotka-Volterra equations in the presence of multiplicative noise, which models the interaction between the species and the environment. We find noise induced phenomena such as quasi-deterministic oscillations, stochastic resonance, noise delayed extinction, and noise induced pattern formation. In addition, our theoretical results are validated with experimental findings. Specifically the results, obtained by a coupled map lattice model, well reproduce the spatial distributions of anchovies and sardines, observed in a marine ecosystem. Moreover, the experimental dynamical behavior of two competing bacterial populations in a meat product and the probability distribution at long times of one of them are well reproduced by a stochastic microbial predictive model.

Numerical and Experimental Investigation of Computed Tomography of Chemiluminescence for Hydrogen-Air Premixed Laminar Flames

Computed tomography of chemiluminescence (CTC) is a promising technique for combustion diagnostics, providing instantaneous 3D information of flame structures, especially in harsh circumstance. This work focuses on assessing the feasibility of CTC and investigating structures of hydrogen-air premixed laminar flames using CTC. A numerical phantom study was performed to assess the accuracy of the reconstruction algorithm. A well-designed burner was used to generate stable hydrogen-air premixed laminar flames. TheOH⁎chemiluminescence intensity field reconstructed from 37 views using CTC was compared to theOH⁎chemiluminescence distributions recorded directly by a single ICCD camera from the side view. The flame structures in different flow velocities and equivalence ratios were analyzed using the reconstructions. The results show that the CTC technique can effectively indicate real distributions of the flame chemiluminescence. The height of the flame becomes larger with increasing flow velocities, whereas it decreases with increasing equivalence ratios (no larger than 1). The increasing flow velocities gradually lift the flame reaction zones. A critical cone angle of 4.76 degrees is obtained to avoid blow-off. These results set up a foundation for next studies and the methods can be further developed to reconstruct 3D structures of flames.