An Investigation of the Relationship Between the Gaussian Process Model Parameters and Surface Area in Three Dimensions

In this paper, we study the relationship between the fitted parameters in a Gaussian process (kriging) model and the complexity of the resulting response surface. This study is done for models with one response and two input variables. An analytical calculation of surface roughness is used as a measure of the complexity of the response surface fit by the Gaussian process model. Our findings indicate that the size of the fitted model parameters as measured across different fits and data sets do not give indication as to the complexity of the surface. We do, however, show that the magnitude of each of the parameters in a single fitted model gives indication about the amount of variability in the direction of that fitted parameter. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of fracture toughness, driving force, and fracture energy for fractal cracks using the method of imaginary smooth crack

Theoretical expressions of the fracture toughness, driving force and fracture energy are derived for a perfect infinite plate with a solitary self-similar fractal crack of mode I considering the fractal effects of cracks in this work. The specific surface energy per unit fractal measure for concrete is fit based on test data. Thus, behaviors of the above four fracture parameters for concrete are studied as varying the initial length of the fractal crack.     

Stochastic sampling using moving least squares response surface approximations

This work discusses the simulation of samples from a target probability distribution which is related to the response of a system model that is computationally expensive to evaluate. Implementation of surrogate modeling, in particular moving least squares (MLS) response surface methodologies, is suggested for efficient approximation of the model response for reduction of the computational burden associated with the stochastic sampling. For efficient selection of the MLS weights and improvement of the response surface approximation accuracy, a novel methodology is introduced, based on information about the sensitivity of the sampling process with respect to each of the model parameters. An approach based on the relative information entropy is suggested for this purpose, and direct evaluation from the samples available from the stochastic sampling is discussed. A novel measure is also introduced for evaluating the accuracy of the response surface approximation in terms relevant to the stochastic sampling task.     

Determination of the full response function of personal neutron dosemeters

The response of neutron dosemeters may be determined directly from measurements, provided a sufficiently large number of measurements in monoenergetic neutron fields covering the entire energy range of interest is available. In practice this is not feasible due to the lack of monoenergetic neutron fields in the thermal and intermediate energy region (i.e. energies <24 keV). To deal with this difficulty, we have developed a method which can take into account additional information about the response of the dosemeter. Our analysis makes use of two types of data, measurements made using monoenergetic neutron beams and measurements made in neutron fields with broad energy distributions. The dosemeter responses are described using a parametrised model, based on a minimum of assumptions: that they should fit the data within experimental uncertainties, and that they should remain close to a simple interpolation of the monoenergetic and thermal neutron field data.     

Measurement of radio channels using an elastic convolver and spreadspectrum modulation. II. Results

A spread spectrum measurement system using a surface acoustic wave convolver has been used to measure radio wave propagation in steel works at 1.75 GHz with an echo delay resolution of ≈20 ns. Due to the high metal content of the factory halls, path loss is found to be small and its exponent to range between 1.1 and 2.3 only. We observed a delay spread between 82 and 548 ns depending on the size of the steel mill, its construction and machinery. Characterizing the radio channel by a stochastic delay line model the echo amplitude probability distribution is found to fit a Rician or log-normal distribution rather than a Rayleigh distribution. The fit of the amplitude distributions is determined by a χ² hypothesis test. From the channel impulse response the coherence bandwidth is deduced to range between 2.4 and 27.4 MHz     

Experimental investigation of the coefficient of restitution of particles colliding with surfaces in air and water

The coefficient of restitution is a parameter used to describe the result of a collision between either two particles or a particle and a surface. The coefficient of restitution is a measure of the amount of kinetic energy dissipation during a collision. This work aimed to study the behavior of the coefficient of restitution based on the velocity of the impacting particle and the properties of the surface and/or particle involved in the collision. This goal was achieved by establishing an experimental system to measure the coefficient of restitution, conducting experiments, and determining dependence between parameters using analytical tools.To measure the coefficient of restitution correctly, based on a large data basis and wide ranges of properties and operating conditions, experiments were conducted on different surfaces and particulate materials with different collision angles and velocities. These experiments were conducted in different surroundings (air and liquid), which posed an important issue. For accurate prediction, after analyzing the results, a correlation was proposed to estimate the value of the coefficient of restitution depending on the mechanical properties of the particle and surface, angle and speed of the collision, and characteristics of the collision medium. Most of the tests for the wide range of properties and conditions were fit to the final correlation by ±30%.     

Multifidelity Response Surface Approximations for the Optimum Design of Diffuser Flows

Response surface methods use least-squares regression analysis to fit low-order polynomials to a set of experimental data. It is becoming increasingly more popular to apply response surface approximations for the purpose of engineering design optimization based on computer simulations. However, the substantial expense involved in obtaining enough data to build quadratic response approximations seriously limits the practical size of problems. Multifidelity techniques, which combine cheap low-fidelity analyses with more accurate but expensive high-fidelity solutions, offer means by which the prohibitive computational cost can be reduced. Two optimum design problems are considered, both pertaining to the fluid flow in diffusers. In both cases, the high-fidelity analyses consist of solutions to the full Navier-Stokes equations, whereas the low-fidelity analyses are either simple empirical formulas or flow solutions to the Navier-Stokes equations achieved using coarse computational meshes. The multifidelity strategy includes the construction of two separate response surfaces: a quadratic approximation based on the low-fidelity data, and a linear correction response surface that approximates the ratio of high-and low-fidelity function evaluations. The paper demonstrates that this approach may yield major computational savings.     

Surface excitation parameter for electrons crossing the AlN surface

Fast electrons crossing a solid surface induce surface excitations. The total probability of such excitations for electrons moving outside the solid, i.e. in vacuum, is characterized by the surface excitation parameter (SEP). In the present work, the SEP was calculated for either incident or escaping electrons with normal or glancing crossing angles over the surface of aluminum nitride (AlN), a wide-band-gap semiconductor. These calculations were performed based on the dielectric response theory using the sum-rule-constrained extended Drude dielectric function with parameters obtained from a fit of this function to experimental optical data and electron energy-loss data. Dependences of the SEP on electron energy and crossing angle were analyzed. A simple formula was proposed for the fitting of SEP as a function of electron energy and crossing angle.     

Variable-complexity response surface approximations for wing structural weight in HSCT design

A procedure for generating and using a polynomial approximation to wing bending material weight of a High Speed Civil Transport (HSCT) is presented. Response surface methodology is used to fit a quadratic polynomial to data gathered from a series of structural optimizations. Several techniques are employed in order to minimize the number of required structural optimizations and to maintain accuracy. First, another weight function based on statistical data is used to identify a suitable model function for the response surface. In a similar manner, geometric and loading parameters that are likely to appear in the response surface model are also identified. Next, simple analysis techniques are used to find regions of the design space where reasonable HSCT designs could occur. The use of intervening variables along with analysis of variance reduce the number of polynomial terms in the response surface model function. Structural optimization is then performed by the program GENESIS on a 28-node Intel Paragon. Finally, optimizations of the HSCT are completed both with and without the response surface.This work was supported by NASA Grants NAG-1-1562 and NAG-1-1160.Dedicated to the 10th anniversary of Computational Mechanics     

基于激光点云数据的叶片型面三维重构

在四坐标叶片型面检测基础上,提出基于激光点云数据的叶片型面三维重构方法。激光位移传感器对叶片型面进行多视角扫描采样,快速采集叶片型面海量点云数据。运用由点到线到面的数学建模原理,先基于端点一阶导矢连续法拟合出光顺NURBS曲线,再依据分片能量法构建辅助曲面拟合出光顺NURBS曲面,最后对分片NURBS曲面进行统一描述,构造出精确光滑的叶片型面,实现叶片型面的三维重构。实验结果表明：采用该方法实现对各类叶片复杂型面的三维重构,重构误差均<0.015 mm,能够满足精密零件的测量需求。     

Fast Characterization of the Width of Vertical Cracks Using Pulsed Laser Spot Infrared Thermography

In-service non-destructive detection of cracks is a challenging task for industries to prevent failures. In the last decades several methods based on infrared thermography have been proposed to detect vertical cracks. In a recent paper, the authors used a lock-in thermography setup with focused laser excitation to characterize the width of infinite vertical cracks accurately. As this method is very time consuming, we propose in this work to measure the width of an infinite vertical crack using pulsed laser spot infrared thermography. A semi-analytical solution for the surface temperature of a sample containing such a crack when the surface is illuminated by a pulsed Gaussian laser spot close to the crack is obtained. Measurements of the surface temperature on samples containing calibrated cracks have been performed using an infrared camera. A least square fit of the surface temperature is used to retrieve the thickness of the crack. Very good agreement between the nominal and retrieved thickness of fissure is found, even for widths down to 1 \(\upmu \)m, confirming the validity of the model.     

偏最小二乘回归在响应面法可靠度分析中的应用

针对目前多维变量可靠度问题中广泛应用的均匀设计响应面法,分析了采用最小二乘法拟合样本数据回归模型时存在的局限性,并在已有方法的基础上提出了一种改进的方法。该方法将均匀设计与偏最小二乘回归技术相结合来回归响应面模型,从而计算结构的失效概率,有效的解决了变量间多重相关性及小样本条件下建立回归模型的问题。通过算例验证了该方法的适用性,尤其对于高维变量的可靠度问题,与最小二乘拟合响应面相比,计算结果更加精确。     

A critique of Rasch residual fit statistics

In test analysis involving the Rasch model, a large degree of importance is placed on the "objective" measurement of individual abilities and item difficulties. The degree to which the objectivity properties are attained, of course, depends on the degree to which the data fit the Rasch model. It is therefore important to utilize fit statistics that accurately and reliably detect the person-item response inconsistencies that threaten the measurement objectivity of persons and items. Given this argument, it is somewhat surprising that there is far more emphasis placed in the objective measurement of person and items than there is in the measurement quality of Rasch fit statistics. This paper provides a critical analysis of the residual fit statistics of the Rasch model, arguably the most often used fit statistics, in an effort to illustrate that the task of Rasch fit analysis is not as simple and straightforward as it appears to be. The faulty statistical properties of the residual fit statistics do not allow either a convenient or a straightforward approach to Rasch fit analysis. For instance, given a residual fit statistic, the use of a single minimum critical value for misfit diagnosis across different testing situations, where the situations vary in sample and test properties, leads to both the overdetection and underdetection of misfit. To improve this situation, it is argued that psychometricians need to implement residual-free Rasch fit statistics that are based on the number of Guttman response errors, or use indices that are statistically optimal in detecting measurement disturbances.     

一种简便有效的曲面拟合方法及其成像技术

本文旨在论述一种新的、简便有效的曲面拟合方法,该方法是建立在拉格朗日三次曲线拟合方法之上,通过在x和y两个方向同时作曲线拟合,构成一个空间曲面。文中还讨论了该空间曲面的成像技术。经编程验证,此法具有计算量小,拟合精度高,拟合出的曲面光滑等优点,有很好的实用价值。     

Relating electrospray ionization response to nonpolar character of small peptides

Nonpolar regions in biological molecules are investigated as a determining factor governing their electrospray ionization (ESI) mass spectrometric response. Response is compared for a series of peptides whose C-terminal residue is varied among amino acids with increasingly nonpolar side chains. Increased ESI response is observed for peptides with more extensive nonpolar regions. The basis for this increase is examined by comparing values of nonpolar surface area and Gibbs free energy of transfer for the different amino acid residues. Comparisons of response with octadecylamine are also made, and this highly surface-active ion is observed to outcompete all other analytes in ESI response. These observations are rationalized on the basis of the equilibrium partitioning model, which is used successfully to fit experimental data throughout the concentration range for several two-analyte systems. This model suggests that because excess charge exists on ESI droplet surfaces, an analyte's relative affinity for the droplet surface determines its relative ESI response. Increased nonpolar character, which leads to enhanced affinity for the surface phase, results in more successful competition for excess charge and higher ESI response.     

Multilayer resonant subwavelength gratings: effects of waveguide modes and real groove profiles

The boundary integral equation code PCGrate-S(X) is used to analyze diffraction on Hubble Space Telescope Cosmic Origins Spectrograph gratings at different boundary shapes and layer thicknesses. An effect of resonance anomalies excited in nonconformal dielectric layers overcoated on the surface of metallic grating on the efficiency is studied for the first time to our knowledge. Refractive indices (RIs) for bulk MgF2 taken from well-known references are found to be not suitable for thin optical layers at wavelengths between 115 and 170 nm. A method based on scale fitting of calculated and measured grating efficiencies is outlined for derivation of thin-film optical constants at hard to measure wavelengths. The calculated efficiency based on real boundary profiles and derived RIs of the G185M subwavelength grating is shown to fit within 9.6% or better to the measured data.     

Measurement of Quench Depth in Railroad Wheels by Diffuse Ultrasonic Backscatter

In this article, the measurement of quench depth in railroad wheels is demonstrated using a diffuse ultrasonic backscatter technique. A singly-scattered response (SSR) model that accounts for the gradation of lamellar spacing (duplex microstructure) within grains in the direction of ultrasonic propagation is developed based on the previous single-phase model. The effects of a graded microstructure on ultrasonic scattering are observed by comparing the spatial variance curve measured from the tread surface to that measured from the cross section. The experimental results show that the graded SSR model fits the spatial variance curve from the tread surface much better than the uniform SSR model. The spatial variance peaks increase in amplitude and shift to later times when the material path is increased (deeper focus). The experimental variance curve from the tread surface is then fit with the model in a least-squares sense such that the quench depth can be estimated. The diffuse ultrasonic backscatter technique can be used not only to distinguish microstructure changes, but also to quantify the quench depth, an outcome that may be applicable for quality control during manufacturing.     

Gloss optical elementary representative surface

Roughness measurements are of main importance in characterizing the optical properties of papers and prints. However, there is a lack of knowledge concerning the surface size and the spacing of the measures to be optically representative of the surface structure. Paper is a multiscale medium, and the roughness parameters extracted from the three-dimensional (3D) surface mapping depend on both the size and the step of discretization. Ray tracing, based on optical geometry, could be a tool to model the light reflection on a paper surface. Ray-tracer software was therefore developed. A new optical device was used to measure paper surface topographies at various scales. Ray tracing simulations were then performed on the 3D mapping and compared to the scattering indicatrix obtained with a classical goniometer. Hence it was possible to identify a magnification for various types of paper grades that is optically representative of the specular gloss.     

Developing an emotional distress item bank for cancer patients

Emotional distress is common among cancer patients during and after treatment. Many instruments have been used to measure emotional distress; however, none of them has emerged as a standard. Although the diversity of instruments has some merit, the lack of a common measure limits our ability to compare studies. This paper describes how we constructed a 46-item emotional distress bank. Using expert judgment, we selected a pool of items with emotional content from this six-instrument set. Rasch rating scale analysis helped us identify a set of general distress items with good model fit and a measurement gap causing floor effects. Additional items were written to augment the measure where found deficient. The resulting set of items reflects a spectrum of positive and negative affect. The measure demonstrated excellent reliability (person separation reliability = .96) and a wide range of emotional distress and was able to distinguish among levels of disease severity.     

非线性隐式极限状态方程失效概率计算的组合响应面法

提出组合响应面的新方法,用以计算设计点附近非线性程度较大的隐式极限状态方程的失效概率。该方法用主响应面和多个次响应面近似对失效概率贡献较大的区域,其响应面函数形式为不含交叉的二次多项式。主响应面依据传统响应面法通过选择适当的插值点和迭代运算获得,其设计点为主设计点。延坐标轴正负方向偏移主设计点得到拟均值点。以拟均值点为基础得到一组次响应面和次设计点。通过主次响应面在各自设计点处的切平面建立组合响应面近似原隐式极限状态方程,并计算其失效概率。算例结果说明所提方法具有较高精度。