Translational-symmetry alternating phase shifting mask grating mark used in a linear measurement model of lithographic projection lens aberrations

2009 ◽  
Vol 48 (19) ◽  
pp. 3654 ◽  
Author(s):  
Zicheng Qiu ◽  
Xiangzhao Wang ◽  
Qunyu Bi ◽  
Qiongyan Yuan ◽  
Bo Peng ◽  
...  
Author(s):  
Vishal Ramnath

In scientific metrology practise the application of Monte Carlo simulations with the aid of the GUM Supplement 2 (GS2) technique for performing multivariate uncertainty analyses is now more prevalent, however a key remaining challenge for metrologists in many laboratories is the implicit assumption of Gaussian characteristics for summarizing and analysing measurement model results. Whilst non-Gaussian probability density functions (PDFs) may result from Monte Carlo simulations when the GS2 is applied for more complex non-linear measurement models, in practice results are typically only reported in terms of multivariate expected and covariance values. Due to this limitation the measurement model PDF summary is implicitly restricted to a multivariate Gaussian PDF in the absence of additional higher order statistics (HOS) information. In this paper an earlier classical theoretical result by Rosenblatt that allows for an arbitrary multivariate joint distribution function to be transformed into an equivalent system of Gaussian distributions with mapped variables is revisited. Numerical simulations are performed in order to analyse and compare the accuracy of the equivalent Gaussian system of mapped random variables for approximating a measurement model’s PDF with that of an exact non-Gaussian PDF that is obtained with a GS2 Monte Carlo statistical simulation. Results obtained from the investigation indicate that a Rosenblatt transformation offers a convenient mechanism to utilize just the joint PDF obtained from the GS2 data in order to both sample points from a non-Gaussian distribution, and also in addition which allows for a simple two-dimensional approach to estimate coupled uncertainties of random variables residing in higher dimensions using conditional densities without the need for determining parametric based copulas.


Author(s):  
Nina Fei ◽  
Youlong Yang ◽  
Xuying Bai

Structural equation modeling (SEM) is a system of two kinds of equations: a linear latent structural model (SM) and a linear measurement model (MM). The latent structure model is a causal model from the latent parent node to the latent child node. Meanwhile, MM’s link is from latent variable parent node to observed variable child node. However, researchers should determine the initial causal order between variables based on experience when applying SEM. The main reason is that SEM does not fully construct causal models between observed variables (OVs) from big data. When the artificial causal order is contrary to the fact, the causal inference from SEM is doubtful, and the implicit causal information between the OVs cannot be extracted and utilized. This study first objectively identifies the causal order of variables using the DirectLiNGAM method widely accepted in recent years. Then traditional SEM is converted to expanded SEM (ESEM) consisting of SM, MM and observation model (OM). Finally, through model testing and debugging, ESEM with good fit with data is obtained.


2017 ◽  
Vol 84 (7-8) ◽  
Author(s):  
Ding Luo ◽  
Thomas Längle ◽  
Jürgen Beyerer

AbstractEstimation accuracy of conventional shape from focus techniques is strongly coupled with the number of images in the focal stack, limiting the measurement speed. In this article, a novel compressive shape from focus scheme is proposed with an exemplary algorithm based on modified Laplacian operator and principal component analysis. Simulation with synthetic focal stacks have demonstrated comparable results to the conventional method. A test with 6 compressively captured images achieves the same level of performance to that of the conventional method with 100 images. Several other focus measure algorithms are also implemented and tested under the compressive scheme, which demonstrates the wide applicability of the proposed method.


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