Robust scatter correction method for cone-beam CT using an interlacing-slit plate

Cone-beam computed tomography(CBCT) has been widely used in medical imaging and industrial nondestructive testing,but the presence of scattered radiation will cause significant reduction of image quality.In this article,a robust scatter correction method for CBCT using an interlacing-slit plate(ISP) is carried out for convenient practice.Firstly,a Gaussian filtering method is proposed to compensate the missing data of the inner scatter image,and simultaneously avoid too-large values of calculated inner scatter and smooth the inner scatter field.Secondly,an interlacing-slit scan without detector gain correction is carried out to enhance the practicality and convenience of the scatter correction method.Finally,a denoising step for scatter-corrected projection images is added in the process flow to control the noise amplification The experimental results show that the improved method can not only make the scatter correction more robust and convenient,but also achieve a good quality of scatter-corrected slice images.     

On array models theoretical predictions versus measurements for the growth of cells and dendrites in the transient solidification of binary alloys

Most of the theoretical studies of the growth of cells/dendrites in the literature are based on the assumption that it is a steady-state phenomenon. The analysis of cells/dendritic structures in the unsteady-state regime is very important, since it encompasses the majority of industrial solidification processes. The aim of the present investigation was to validate the predictions furnished by the cellular and primary dendritic growth models in the literature for unsteady-state conditions against a large spectrum of experimental data, which includes those for a variety of Al alloys (Al–Cu, Al–Si, Al–Fe, Al–Bi, Al–Ni, Al–Sn) and low thermal diffusivity alloys, such as Sn–Pb and Pb–Sb. The predictions furnished by the Hunt–Lu model do not match the cellular experimental scatter for any examined alloy system. However, this model matches well with the primary dendritic growth of Al alloys, with the exception of Al–Sn alloys, for which the Hunt–Thomas approach has to be applied. The primary dendritic predictions of Bouchard–Kirkaldy's model, performed with the originally suggested a ₁ calibration factors are, in most cases, located above the experimental points. Experimental growth laws relating cellular and dendritic spacings with the tip growth rate and the cooling rate, respectively, are established.     

A comparison of models used as alternative magnetic resonance image reconstruction methods

In magnetic resonance (MR) imaging, excellent reconstructions are obtained on large data sets using the inverse discrete Fourier transform (IDFT). Modeling procedures have been proposed to overcome the image artifacts from the truncation of small data sets. In this paper, a relationship between image reconstruction using modeling and the standard IDFT is presented. A comparison of the assumptions behind the Smith and Haacke models is given and an experimental evaluation of the validity of the models provided. Various methods of evaluating model coefficients are discussed. Images are reconstructed from both models using the Transient Error reconstruction approach (TERA) algorithm. TERA is an algorithm that reintroduces data information components that cannot be modeled: useful when the assumed model characteristics do not completely match all portions of the image. Although very different in their basic assumptions, both the Smith and Haacke models were found to reduce truncation artifacts and improve resolution when used with the TERA algorithm.     

Leader channel models for long air positive electrical discharges

The models proposed for the positive long air gap electrical discharge can be considered to be either engineering or physical in their approach. In this work, we make a general review of the available models and use two of them for a comparison with experimental data. Common underlying assumptions were found in most of the models analyzed. The comparison with the experimental data revealed that the results obtained from the models were a good representation of the physical situation when the leader potential distribution and the leader-corona region evolution were described with certain physical assumptions.     

闪光照相中源尺寸和散射对成像的影响

 利用Monte Carlo(MC)模拟技术解释实验中心线灰度曲线的各部分波形。结果发现，系统中的散射照射量、光源的尺寸和H-D特征曲线的形状对实验灰度曲线的各部分波形均有影响：散射量越大，中心信号幅度越低;H-D曲线趾部的非线性越严重，中心信号幅度也越低;光源尺寸造成图像越模糊。指出了用实验波形可以半定量确定系统散射程度和光源尺寸。在测量照射量时，应该尽可能避免散射的干扰,用台阶法测量H-D曲线时，应使台阶远离剂量片而前移。     

Island models and the catalytic oxidation of carbon monoxide and carbon monoxide-olefin mixtures

Simple kinetic models which take account of the formation of islands of adsorbate on a catalyst surface are proposed, and are compared with an elementary step model for CO oxidation and oxidation of a CO-butene or CO-propylene mixture. The island models give fits to data from step change transient experiments which are comparable with the elementary step model, and give better fits to steady-state and continuously oscillating data (the latter with hydrocarbon present). Theoretical predictions of chaotic behaviour in CO oxidation can be obtained with the island models. Comparisons between island models suggest that islands of CO have the most significant effect on simulations at the experimental conditions.     

A two-frame approach for scene-based nonuniformity correction in array sensors

This paper introduces a new scene-based technique to correct the fixed-pattern noise (FPN) in array sensors. This method registers a pair of image frames exhibiting small relative scene translation and then the noise pattern can be reconstructed using the constrained least-squares estimation. The key advantage of this technique is that the accurate estimates of the bias nonuniformity can be obtained with only two images, without imposing any assumptions on the structure of the FPN. Besides, the method works on almost static scene, and therefore does not require larger scale global motion and statistical assumptions on the scene irradiance. We test our method on synthetically generated FPN as well as with real infrared data, and experimental results demonstrate the significant reduction in FPN, validating the effectiveness of our approach. Finally, we validate the feasibility and validity of using the proposed method as a first step fostering the success of more sophisticated registration-based time-evolving correction algorithms.     

基于高光谱成像技术的番茄茎秆灰霉病早期诊断研究

共采集了112个番茄茎秆高光谱数据（光谱范围400～1 030 nm）,结合图像处理和化学计量学方法建立了番茄茎秆灰霉病早期诊断模型。应用偏最小二乘法（PLS）模型的隐含变量载荷分布选取了七个特征波长（EW）,并建立了番茄茎秆灰霉病早期诊断的最小二乘支持向量机（LS-SVM）模型。结果表明,经过变量标准化（SNV）及多元散射校正（MSC）预处理所建立的EW-LS-SVM模型获得了满意的判别效果,且优于全波段的PLS模型。说明高光谱成像技术进行番茄茎秆灰霉病的早期诊断是可行的,为番茄病害早期诊断和预警提供了新的方法。     

Kinetic investigation on sono-degradation of Reactive Black 5 with core–shell nanocrystal

The experimental data of sonocatalytic degradation of Reactive Black 5 (RB5) as an azo dye by core–shell nanocrystals (CdS–TiO₂) were applied to the proper kinetic models. In this work, two kinetic models were proposed and fitted properly to the data. In the first one, the heterogeneous reaction was considered similar to the Langmuir–Hinshelwood (L–H) mechanism and the kinetic rate parameters were determined. In this model, short time of sonication with initial concentration changes has been applied and the contribution of the reaction intermediates has been neglected in degradation. Hence, this model may not be valid for longer reaction times where the reaction intermediates effects prevail. In the second one, two first-order reactions in series provided the most convincing rate form for the sonodegradation of dyes adsorbed on the synthesized nanocomposite. In these series reactions, the first step is the conversion of colored dye to colored intermediate, and the second step is the conversion to colorless product(s). The obtained results were in good agreement with the proposed kinetic models. The rate constants of degradation of catalyzed reaction were higher than that obtained without catalyst, solar and UV irradiation.     

Volume effects in the thermodynamics of ternary austenites

Elastic measurements have been made as a function of temperature and composition on a series of Fe-based substitutional solid solutions containing Mn, Ni and Cr. These data have been used to calculate the degree of error involved in applying statistical models to ternary carbon or nitrogen austenites when such models ignore the dilation of the substitutional lattice as a function of its composition.The results show that the error in the partial thermodynamic quantities and in the isothermal variation of the activity of the interstitial species with composition is of the order of scatter found in experimental thermodynamic data measured at constant pressure.     

KDP晶体台阶生长动力学的激光干涉实验研究

采用迈克尔逊干涉技术 ,通过测量KDP晶体生长的法向速率和台阶斜率来研究其台阶生长的动力学系数、台阶自由能、溶质在边界层内的扩散特征以及激发晶体生长台阶的位错活性 .实验表明 ,KDP中不同活性位错的台阶动力学系数差异较大 ,例如高活性和低活性台阶动力学系数分别为 10 .3× 10 -2 和 5 .2 1× 10 -2 cm/s,位错源在晶体表面的形状、面积的变化 ,以及Burgers矢量的变化是造成晶体生长动力学测量数据重复性差的主要原因     

A diffusion model for describing the bilayer growth (FeB/Fe2B) during the iron powder-pack boriding

In this paper, a diffusion model is proposed for studying the bilayer growth kinetics (FeB/Fe₂B) on pure iron substrate during the powder-pack boriding in the temperature range of 1023-1273 K.This model based on Fick's laws was solved, under certain assumptions, considering a parabolic growth of iron borides.For this purpose, a computer simulation program was created for predicting the boride layer thickness as a function of process parameters (temperature, time and surface boron content). A fairly good agreement was observed between the simulation calculations and experimental data derived from the literature.     

Coupled harmonic oscillator models of carbon monoxide adsorbed on stepped,platinum surfaces

Harmonic oscillator models are used to explain recent experimental data on infrared absorption by CO molecules adsorbed on two stepped platinum surfaces. These data reveal only a lower frequency band at low coverage and only a higher frequency band at high coverage. Both bands exist over a range of intermediate coverages. The data are explained by a coupled-dipole model which includes the effects of electronic polarizability, the tilted orientation of CO molecules at step sites, and the electric field enhancement at step sites. The lower-frequency band is associated with CO molecules adsorbed on step sites and the higher-frequency band is associated with two-dimensional islands consisting of both step and terrace CO. The model explains the observed variation of frequency and intensity with coverage for CO adsorption on Pt(533) and Pt(432) surfaces. The model calculations indicate that the wavenumber for a single, linearly bonded CO molecule is about 9 cm⁻¹ higher on a terrace site than on a step site.     

Experimental and modeling studies of grain size and moisture content effects on radon emanation

Some models have already been developed to explain the effect of moisture content on the radon emanation fraction of soil. For this purpose, “microscopic” soil models, which are easy to deal with mathematically but cannot take grain size into consideration, have been designed. These previous models consist basically of two opposite grain surfaces and pores between the grains. In the present study, in order to study the effect of not only moisture content but also grain size, we present a simple modeling approach based on two “macroscopic” soil models: (1) a single-grain model and (2) a multiple-grain model. The latter model represents a configuration of spherical grains packed in a simple cubic structure. Based on these soil models and general assumptions, the radon emanation fraction was calculated as a function of grain size or moisture content by Monte Carlo simulation. The results for the multiple-grain model show that the radon emanation fraction is markedly increased with grain sizes ranging from 10 to 100 μm and reaches a constant value of 50% when moisture content is 0% and the radium is uniformly distributed on the grain surface. Moreover, a drastic increase is seen at smaller grain sizes with increasing moisture content. From these results, we concluded that the calculation of radon emanation depends greatly on the pore size between a Ra-bearing grain and a neighboring grain. The validity of the model was also evaluated by comparison to experimental data.     

高光谱成像的油菜和杂草分类方法

利用高光谱成像技术结合化学计量学方法对油菜中的杂草进行分类识别。采用近红外高光谱技术,通过正态变量变换(SNV)、去趋势化(De-trending)、多元散射校正(MSC)、移动平均平滑法(MA)、多项式卷积平滑法(SG)、基线校正(baseline)及归一化(normalize)算法对光谱数据进行预处理,采用主成分载荷(PCA loadings)、载荷系数法(x-LW)、回归系数法(RC)、连续投影算法(SPA)分别进行特征波长提取,采用偏最小二乘判别分析(PLS-DA)、极限学习机(ELM)和支持向量机(SVM)建立分类模型。结果表明,基于De-trending 预处理,通过PCA loadings,x-loading weights及SPA特征波长提取方法,基于极限学习机ELM算法建立的模型取得了最优的分类效果,建模集和预测集的分类精度均达到100%,另引入平均分类精度的指标,发现不同试验时间下,模型分类精度变化不大,表明应用近红外高光谱成像技术对油菜和杂草进行分类是可行的。     

Method for developing HPGe detector model in Monte Carlo simulation codes

This paper describes a simulation model for a high-purity germanium (HPGe) detector by scanning the detector with a low-energy collimated source and calibrating the efficiency of the detector. The parameters of the initial simulation model, particularly the dead-layer thickness, were modified step by step according to the experimental results. The validity of codes, models, and methods was shown by implementing the model into the FLUKA and MCNPX codes and cross-checking against the experimental data.     

The various facets of the deuteron

Models of the nucleon-nucleon interaction are based on both experimental data and theoretical assumptions. It is shown that some of the present models which exhibit differences with this last respect are to some extent equivalent up to a unitary transformation. Consequences for predictions of observables in the deuteron are examined.     

Analysis of the thermophysical properties of some rare-earth hydroxides through crystal field effects

A crystal field analysis of the experimental results on the magnetic susceptibilities and their anisotropies in Ho(OH)₃ and Tb(OH)₃ was made with a view to resolve the previous anomalies observed in the results of specific heat studies. A pronounced thermal effect on lattice specific heat has been observed in Ho(OH)₃ but not in Tb(OH)₃. For Er(OH)₃, the total specific heat was calculated with reasonable assumptions over a wide temperature range, but no experimental data are yet available for comparison.     

Spin-averaged mass formulas and the mass spectrum of low lying Δ-resonances in harmonic-oscillator-like quark models

By spin-averaging the masses of one species of particle over a sufficient number of multiplets we argue that the resulting spin-averaged mass is insensitive to mass operators which are not spin-scalar. This approach may be applied to averaging over quantum numbers other than spin. We discuss the assumptions necessary to restricting the average to only relatively few multiplets and show how mass formulas between averaged masses may be constructed. This approach reduces the number of parameters and predicts patterns of splittings which should be common to many analyses. We apply our results to the low lying Δ-resonances in harmonic-oscillator-like models and examine the comparison of theory with experiment for four different assumptions about which states should be included in particular averages. Using data from experiment we find that the prediction for the spin-averaged mass of the Δ-resonances from (56,1 ₃ ^? ) is, on average, 150 MeV higher than the spin-averaged mass of the experimental Δ states plausibly assigned to the (56,1 ₃ ^? ). This result is insensitive to which of the assumptions is made. Some suggestions are made about rectifying this discrepancy.     

A comparison of two angular dependent ESCA algorithms useful for constructing depth profiles of surfaces

Two approaches for developing composition/depth profiles were examined and compared. Model A, a technique previously presented by R.W. Paynter (1981), uses an iterative method to match calculated relative ESCA intensities with experimental data. Model B, a new approach which incorporates ideas from inverse theory, applies a linear approximation of the delta function to represent the intensity attenuation function in order to create a set of linear functions. This set is solved by matrix inversion to yield a smoothed depth profile from angular dependent ESCA data. Each model was tested with real and simulated ESCA data from radio-frequency (RF) plasma-poly-merized perfluoropropane coatings on quartz and polyurethane coatings on glass. Both models are restricted by certain assumptions, yet each offers advantages. A method combining both models is presented as the best approach for efficiently generating nondestructive depth profiles. Overlayer thicknesses obtained by using these models were found to be in reasonable agreement with results from other thickness determination methods.