Fast response and recovery of hydrogen sensing in Pd-Pt nanoparticle-graphene composite layers

This study reports the fast response and recovery of hydrogen sensing in nanoparticle-graphene composite layers fabricated using chemical methods and comprising of isolated Pd alloy nanoparticles dispersed onto graphene layers. For 2% hydrogen at 40?°C and 1 atm pressure, a response time of <2 s and a recovery time of 18 s are observed. The fast response and recovery observed during sensing are due to hydrogen-induced changes in the work function of the Pd alloy and modification in the distribution of defect states in the graphene band gap due to gas adsorption. The results of hydrogen sensing in the new class of Pd-Pt nanoparticle-graphene composite material are important for understanding the effect of gas adsorption on electronic conduction in graphene layers and for developing a new type of gas sensor based on changes in the electronic properties of the interface.     

Statistical analysis of fracture toughness data

The underlying causes for the variations in fracture toughness, which are observed experimentally, are discussed. A theory covering the statistics of fracture is briefly described, and the distribution function based on this theory is shown to be applicable to metals, ceramics and powder-filled epoxy resins. The distribution function can be expected to work for all materials since the theory behind it involves no assumption concerning materials. Since large, consistent sets of data are rarely to hand in practice, it is not possible to apply the theoretical distribution function in an exact way. Instead approximate, conservative methods based on this new distribution function must be used and such methods are demonstrated in the present paper for a number of possible cases which may arise in practice.     

调制度测量轮廓术高度信息获取新算法

理论分析表明,在正弦光栅成像面前后调制度分布是一种高斯分布,据此提出一种基于高斯曲线拟合的调制度测量轮廓术高度信息获取新算法：高斯曲线拟合法。该算法对调制度分布序列中极值位置附近的部分数据点利用高斯函数进行拟合,从获得的拟合曲线求出调制度极大值的真实位置,该位置对应的扫描距离即为对应点的高度信息。对同一测量数据利用三种高度算法分别计算高度,测量精度为：极值算法0．78mm、重心算法0．37mm和高斯曲线拟合算法0．22mm,表明高斯曲线拟合法可以获得更高的测量精度。     

Phase-space interpretation of deterministic phase retrieval

Deterministic phase retrieval is reinterpreted in terms of phase-space optics. A novel derivation of the transport-of-intensity equation is presented based on the Wigner distribution function and the ambiguity function. The phase retrieval problem is formulated as estimating the local first-order moment of the Wigner function from intensity information. A comparison with phase-space tomography suggests a generalization of deterministic phase retrieval that provides larger flexibility for signal recovery. In addition, one particular numerical implementation of generalized deterministic phase retrieval is presented. Simulated intensity data are used to validate the method.     

Specularity and shadow detection for the multisource photometric reconstruction of a textured surface

Textured surface analysis is essential for many applications. In this paper, we present a three-dimensional (3D) recovery approach for real textured surfaces based on photometric stereo. The aim is to be able to reconstruct the textured surfaces in 3D with a high degree of accuracy. For this, the proposed method uses a sequence of six images and a Lambertian bidirectional reflectance distribution function (BRDF) to recover the surface height map. A hierarchical selection of these images is employed to eliminate the effects of shadows and highlights for all surface facets. To evaluate the performances of our method, we compare it to other traditional photometric stereo methods on real textured surfaces using six or more images.     

Distributed dynamic load identification based on shape function method and polynomial selection technique

A new approach based on shape function method of moving least square fitting (SFM_MLSF) and polynomial selection technique is proposed in this paper for distributed dynamic load identification. The distributed dynamic load is represented as a product of spatial distribution function and time history, and the two parts are assumed to be independent. The modal transformation of structural dynamic equation throws light on the fact that all modal loads share the same form with the distributed dynamic load in time domain. As the structural modal parameters are known, the time history of dynamic load can be precisely identified through SFM_MLSF method which approximates the local dynamic load with shape functions in the moving supporting time domain. Then, the spatial distribution function of the load is substituted as a series of basic functions, and the identification of distribution function is transformed into a linear fitting problem. Through polynomial selection technique based on error reduction ratio, the significant components are picked out from the basis function responses, which greatly improves stability and precision of the load distribution function. During the inverse analyses of both the time history and distribution function, appropriate regularization methods are still applied to overcome the unavoidable ill-conditioned problem. Numerical examples demonstrate the validity and accuracy of the proposed method.     

Measurement of the Concentration of Substances by Gas Analyzers under Nonparametric Indeterminacy Conditions

Algorithms have been obtained for measurement of the concentration of substances by gas analyzers under nonparametric a priori indeterminacy conditions. They include an estimate of the probability distribution density for the analyzed random process. Various methods are proposed for obtaining these estimates, based on smoothing the empirical probability distribution function.     

用弹道理论模型和Weibull模型预测台阶爆破的爆堆形态

介绍了预测爆堆形态的弹道理论模型和Ｗｅｉｂｕｌ模型，提出了弹道理论的分条方法及抛掷轨道的计算公式。同时将Ｗｅｉｂｕｌ概率分布函数成功地引入爆堆形态的分布计算中，根据实测值提出了爆堆初始高度的修正方法。并以南芬露天铁矿为例进行了验证。     

Efficient structural reliability methods considering incomplete knowledge of random variable distributions

The determination of an exact distribution function of a random phenomena is not possible using a limited number of observations. Therefore, in the present paper the stochastic properties of a random variable are assumed as uncertain quantities and instead of predefined distribution types the maximum entropy distribution is used. Efficient methods for a reliability analysis considering these uncertain stochastic parameters are presented. Based on approximation strategies this extended analysis requires no additional limit state function evaluations. Later, variance based sensitivity measures are used to evaluate the contribution of the uncertainty of each stochastic parameter to the total variation of the failure probability.     

X-ray noninterferometric phase imaging: a unified picture

A unified theory of noninterferometric phase recovery based on the so-called ambiguity function is introduced. The theory is used to analyze previously published techniques and unify them with the methods of phase-space tomography applicable to partially coherent data. The theory is then used to propose some new approaches to noninterferometric phase recovery.     

Tests for Exponentiality When Origin and Scale Parameters Are Unknown

Several methods are examined for testing for the exponential distribution, using complete samples, when both the scale and location parameters are unknown. Percentage points are given for empirical distribution function (EDF) tests in which both parameters are estimated from the data, and power studies are reported to compare these tests with other goodness-offit techniques for the exponential distribution, particularly those based on regression methods. It is found that the EDF statistics W ² and A ² have overall good power properties, with A ² slightly superior.     

Multi-state systems with multi-fault coverage

The paper introduces a new model of fault level coverage for multi-state systems in which the effectiveness of recovery mechanisms depends on the coexistence of multiple faults in related elements. Examples of this effect can be found in computing systems, electrical power distribution networks, pipelines carrying dangerous materials, etc. For evaluating reliability and performance indices of multi-state systems with imperfect multi-fault coverage, a modification of the generalized reliability block diagram (RBD) method is suggested. This method, based on a universal generating function technique, allows performance distribution of complex multi-state series–parallel system with multi-fault coverage to be obtained using a straightforward recursive procedure. Illustrative examples are presented.     

Analysis of clusters and uniformity of distribution of states of polarization on the Poincaré sphere

An analysis of the clusters and the uniformity of distribution of states of polarization on the surface of a Poincaré sphere generated by rotating wave plates is given. The analysis of clusters of the states of polarization is based on a spherical radial distribution function. For uniform analysis of the distribution, two methods are proposed. The first method is based on calculation of the correlation coefficient; the second method is based on calculation of the angles between pairs of the states of polarization on the Poincaré sphere. For polarization scramblers consisting of eight or more rotating wave plates, nonclustered and near-uniform distribution of states of polarization is obtained.     

考虑余-废料资源回收的车间物料配送路径规划研究

针对离散制造生产过程中物料配送及余-废料资源回收效率低、成本高等问题,在分析车间物料流循环过程基础上结合物料配送时间窗限制,提出了物料配送和余-废料资源回收协同优化的物料再循环策略,并建立了以车间物料流总成本为目标的物料再循环路径规划模型。利用遗传算法在Matlab软件中对实例进行求解,验证了物料再循环策略应用于离散制造车间物料配送和余-废料资源回收的可行性和有效性。     

Blind phase shift estimation in phase-shifting interferometry

A blind phase shift estimation algorithm that allows simultaneous calculation of phases and phase shifts from three or more interferograms is presented. In phase-shifting interferometry, the phase shift errors introduce specific correlations between the calculated background intensity distribution and the fringe component. These correlations can be measured with a cross-power spectrum. By minimization of an objective function based on this cross-power spectrum, the actual phase shifts are estimated and used for phase recovery. The validity of this algorithm is verified by both the numerical simulation and the experiment results.     

Simulation of a non-Gaussian stochastic process based on a combined distribution of the UHPM and the GBD

To simulate non-Gaussian stochastic processes based on the first four moments, various simulation methods are presented, in which the determination of the transformation model and the calculation of the correlation coefficients between non-Gaussian stochastic processes and Gaussian stochastic processes are the critical procedures in these simulation methods. However, some existing simulation methods are limited to specific ranges. Furthermore, their practical applications are affected negatively due to the expensive cost of determining the transformation model and the correlation coefficients between non-Gaussian and Gaussian stochastic processes. Therefore, an accurate and efficient simulation method of a non-Gaussian stochastic process with a broader range is proposed in this article. Since the simulation of non-Gaussian processes and the Nataf transformation of non-Gaussian variables have some similar characteristics, a new combined distribution is proposed based on the unified Hermite polynomial model (UHPM) and the generalized beta distribution (GBD). Then, the combined distribution is employed in the simulation of non-Gaussian stochastic processes, in which the transformation model is deduced by the combined distribution. The correlation coefficient transformation function (CCTF) between the Gaussian and non-Gaussian stochastic processes can be evaluated through the interpolation method. Furthermore, numerical examples are presented to show the accuracy and effectiveness of the proposed simulation method for non-Gaussian stochastic processes.     

Integrated production–distribution planning in two-echelon systems: a resilience view

Global supply chains are increasingly exposed to operational and disruption risks that threaten their business continuity. This paper presents a novel two-stage scenario-based mixed stochastic-possibilistic programming model for integrated production and distribution planning problem in a two-echelon supply chain over a midterm horizon under risk. Operational risks are handled by introducing imprecise (i.e. possibilistic) parameters while disruption risks are accounted for through stochastic disruption scenarios. The proposed model accounts for the risk mitigation options and recovery of lost capacities in an integrated manner. In the first stage, the structure of the chain and proactive risk mitigation decisions are determined, while the second stage specifies the recovery plan of lost capacities in addition to production and distribution plans. Considering extra capacities in the production facilities, backup routes for transportation links and pre-positioning of emergency inventory in distribution centres are considered as feasible options to improve the resilience level of the supply chain. We propose a new indicator for optimising the resilience level of the chain based on restoration of lost capacities. For the sake of robustness, the expected worst case of the second stage’s objective function is considered by utilising the conditional value at risk (CVaR) measure. The validation and applicability of the proposed model are examined through several numerical experiments.     

Bootstrap tests for nonparametric comparison of regression curves with dependent errors

In this paper, the problem of testing the equality of regression curves with dependent data is studied. Several methods based on nonparametric estimators of the regression function are described. In this setting, the distribution of the test statistic is frequently unknown or difficult to compute, so an approximate test based on the asymptotic distribution of the statistic can be considered. Nevertheless, the asymptotic properties of the methods proposed in this work have been obtained under independence of the observations, and just one of these methods was studied in a context of dependence as reported by Vilar-Fernández and González-Manteiga (Statistics 58(2):81–99, 2003). In addition, the distribution of these test statistics converges to the limit distribution with convergence rates usually rather slow, so that the approximations obtained for reasonable sample sizes are not satisfactory. For these reasons, many authors have suggested the use of bootstrap algorithms as an alternative approach. Our main concern is to compare the behavior of three bootstrap procedures that take into account the dependence assumption of the observations when they are used to approximate the distribution of the test statistics considered. A broad simulation study is carried out to observe the finite sample performance of the analyzed bootstrap tests.      

Determination of single fibre strength distribution from fibre bundle testings

The strength of fibres used as reinforcement materials for advanced composites is often assumed to follow the two-parameter Weibull distribution function. However, the experimental process widely used for obtaining the two parameters is tedious and prone to error. In this paper, two simple methods for determining the parameters of the Weibull distribution function are developed based upon the analysis of the tensile curves of fibre bundles. The first method focuses on the relation between the shape of a fibre bundle tensile curve and the survivability of fibres; the second method makes use of the relation between the maximum load point of a fibre bundle tensile curve and the shape parameter of the Weibull distribution of fibre strength. These two methods, in particular the second one, have greatly simplified the fibre testing process. Experimental results on Thornel-300 carbon fibres further demonstrate the validity of these techniques.On leave from Northwestern Polytechnical University, Xian, Shaanxi, China.On leave from Yantze Valley Planning Office, Wuhan, China.     

自适应的彩色图像光照补偿新方法

环境光照变化、光照分布不均匀会影响彩色图像中人脸的正确检测。在融合了不同的基于空域的解决方案的基础上,提出了一种自适应的彩色图像光照补偿新方法。分别对光照过亮、过暗以及中间灰度区域进行自适应的处理。对亮度值最小、最大的5%的像素,如果这些像素的数目足够多(本文大于100),在变换后分别压缩为0和255;用对数函数做非线性变换函数来修正中间灰度区域。在人脸PIE数据库上对光照不均的彩色图像进行了实验,验证了该方法能对人脸检测中的光照进行有效的补偿。