Using Pearson’s System of Curves to Approximate the Distributions of the Difference between Two Correlated Estimates of Signal-to-Noise Ratios: The Cases of Bivariate Normal and Bivariate Lognormal Distributions

Background: The signal-to-noise ratio (SNR) is recognized as an index of measurements reproducibility. We derive the maximum likelihood estimators of SNR and discuss confidence interval construction on the difference between two correlated SNRs when the readings are from bivariate normal and bivariate lognormal distribution. We use the Pearsons system of curves to approximate the difference between the two estimates and use the bootstrap methods to validate the approximate distributions of the statistic of interest. Methods: The paper uses the delta method to find the first four central moments, and hence the skewness and kurtosis which are important in the determination of the parameters of the Pearsons distribution. Results: The approach is illustrated in two examples;one from veterinary microbiology and food safety data and the other on data from clinical medicine. We derived the four central moments of the target statistics, together with the bootstrap method to evaluate the parameters of Pearsons distribution. The fitted Pearsons curves of Types I and II were recommended based on the available data. The R-codes are also provided to be readily used by the readers.

Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power systemtomaintain reliable operation.With equal conductor spacing grounding grid design,the distribution of the current in the grid is not uniform.Hence,unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing.This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors:the least-square curve fitting technique and the compression ratio techniquewith equal grid configuration for both square and rectangular grids.Particle Swarm Optimization(PSO)is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids.Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration.Simulation results are obtained by theMATLAB software developed.Percentage of improvement in ground potential rise,step voltage,touch voltage,and grid resistancewith variation in compression ratios are plotted.

Calculation method of sliding ratios for conjugate-curve gear pair and its application

The calculation method of sliding ratios for conjugate-curve gear pair, generated based on the theory of conjugate curves,is proposed. The theoretical model of conjugate-curve gear drive is briefly introduced. The general calculation formulas of sliding ratios are developed according to the conjugate curves. The applications to the circular arc gears based on conjugate curves and the novel involute-helix gears are studied. A comparison on the sliding coefficient with the conventional corresponding gear drive is also carried out. The influences of gear parameters such as spiral parameter, gear ratio and modulus on the sliding ratios of gear drive are discussed. Brief description of manufacturing method for conjugate-curve gear pair is given. The research results show that the sliding ratios of gear pair become smaller with the increase of spiral parameter and gear ratio, respectively. And it will be greater with the increase of modulus for the tooth profiles. The meshing characteristics of conjugate-curve gears are further reflected and the optimization design of tooth profiles with high performance may be obtained.

Analytical Algorithms for the Blend Ratios by Fibre-bundle Tensile Curves Part Ⅱ: Calculations of the Modulus Method and the Percentage Method

The principles for the modulus method and the percentage method are established and discussed in the part following Part Ⅰ of the series papers, in which we proposed the various algorithms of the strength method and the work method. The samples of Wool/PET blended fibre bundles, the method of fibre-bundle tensile tests and the typical specific stress-extension curves from the fibre bundles with different blend ratios are the same as in Part Ⅰ. It can be found that the theoretical results estimated by the modulus and percentage methods accord with the experimental values highly though the calculations of the two methods are slightly more complex than those of the strength and work methods. Especially, using the modulus method can not only avoid the influence of the error caused by the determination of the tensile curve of no fibre breaking in stretching, Y(e), but also need not to know the tensile curves of mono-component fibre bundles in certain calculation. The latter advantage of the modulus method exists in the percentage method too, but it should adopt the improved calculation of ones.

Effects of aspect ratio on unsteady solutions through curved duct flow

The effects of the aspect ratio on unsteady solutions through the curved duct flow are studied numerically by a spectral based computational procedure with a temperature gradient between the vertical sidewalls for the Grashof number 100 ≤ Gr ≤ 2 000. The outer wall of the duct is heated while the inner wall is cooled and the top and bottom walls are adiabatic. In this paper, unsteady solutions are calculated by the time history analysis of the Nusselt number for the Dean numbers Dn = 100 and Dn = 500 and the aspect ratios 1≤γ≤ 3. Water is taken as a working fluid （Pr =7.0）. It is found that at Dn = 100, there appears a steady-state solution for small or large Gr. For moderate Gr, however, the steady-state solution turns into the periodic solution if γ is increased. For Dn = 500, on the other hand, it is analyzed that the steady-state solution turns into the chaotic solution for small and large Gr for any γ lying in the range. For moderate Gr at Dn = 500, however, the steady-state flow turns into the chaotic flow through the periodic oscillating flow if the aspect ratio is increased.

ESTIMATION OF BLENDING RATIO OF TWO-COMPONENT FIBER BUNDLE FROM BUNDLE LOAD-ELONGATION CURVE

In this paper, two methods were developed to assess the blending ratio of two-componentfiber bundles. They were the peak-height method and the slope method. The relationship be-tween blending ratio and testing data was analysed, and the regression curves were obtained bystepwise regression method. It was pointed out that the testing errors of both methods were lessthan two percent. The validities of both methods were verified by experiments, All calculationsof both methods were completed by computer. The blending ratio was ascertained from the test-ing data of bundle fiber strength tester which was made by the authors themselves.

Analytical Algorithms for the Blend Ratios by Fibre-bundle Tensile Curves Part Ⅲ: The Definition Method and the Relationships between the Blend Ratio and Tensile Parameters Calculated from Different Ways

The algorithms of the strength, work, modulus and percentage methods have been introduced and discussed in Part Ⅰ and Part Ⅱ of the series papers. As the following, the percentage-function calculation and the frequency-function calculation of the definition method are defined and developed in detail. Meanwhile, the procedures to find the tensile parameters are analysed experimentally and involve “ED” being the average values of the corresponding tensile parameters of each bundle tensile curve measured; “EC” being the tensile parameters obtained from the averaged experimental tensile curve; and “TC” being the parameters of the theoretical tensile curve according to the corresponding nominal blend ratio. The theoretical and experimental results indicate that the blend ratio estimated by the definition method from wool/polyester blended fibre bundles has a high correlation with the actual blend ratio though the variables to be known in this method are the most of all the methods and there exist the difficulty to solve fibre bundle tensile behaviour without fibre broken in accuracy and that there are high correlations between the EC and TC data and the tensile parameters should be calculated using the EC method rather than the ED method with the exception of the bundle initial modulus. The relationships between blend ratios and the tensile properties of blended fibre bundles can be used to select the optimum blend ratio of blended tops or yarns.

THE RELATIONSHIP BETWEEN PROJECTIVE GEOMETRIC AND RATIONAL QUADRATIC B-SPLINE CURVES

Abstract For two rational quadratic B spline curves with same control vertexes, the cross ratio of four collinear points are represented: which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the two curves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Bézier curves, the value is generally related with the location of the ray, and the necessary and sufficient condition of the ratio being independent of the ray's location is showed. Also another cross ratio of the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initial vertex intersects respectively with the curve segment, the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only with the ray's location, but not with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments.

An Improved Unique Fatigue Crack Growth Rate Curve Model and Determination of the Model Shape Exponents

It is essential to precisely predict the crack growth,especially the near-threshold regime crack growth under different stress ratios,for most engineering structures consume their fatigue lives in this regime under random loading.In this paper,an improved unique curve model is proposed based on the unique curve model,and the determination of the shape exponents of this model is provided.The crack growth rate curves of some materials taken from the literature are evaluated using the improved model,and the results indicate that the improved model can accurately predict the crack growth rate in the nearthreshold and Paris regimes.The improved unique curve model can solve the problems about the shape exponents determination and weak ability around the near-threshold regime meet in the unique curve model.In addition,the shape exponents in the improved model at negative stress ratios are discussed,which can directly adopt that in the unique curve model.

Design of Linear Functional Noncircular Gear with High Contact Ratio Used in Continuously Variable Transmission

Continuously variable transmission(CVT)of noncircular gear has the technical advantages of large bearing capacity and high transmission efficiency.The key technology of CVT with noncircular gear has been broken through some countries,and is in the stage of deep application research.Although the characteristics and design methods of noncircular gear pairs have been continuously studied in China,the noncircular gear CVT is still in the preliminary exploration and research stage.The linear functional noncircular gear pair,whose transmission ratio is a linear function in the working section,to realize continuously variable transmission was the research object in this paper.According to the required transmission ratio in the working section,the transmission ratio function in the non-working section was constructed by using a polynomial.And then the influence of pitch curve parameters in the working section on which in the non-working section was also analyzed to obtain the pitch curve suitable for transmission of this gear pair.In addition,for improving the stability and bearing capacity of gear transmission,the noncircular gear pair transmission with high contact ratio was designed.Furthermore,the accurate value of the contact tooth length was calculated based on the gear principle and the characteristics of the involute tooth profile,from this the contact tooth length error was calculated by comparing the accurate value with its actual value obtained by the rolling experiment.Finally,an indirect method to verify the contact ratio by detecting the contact length error of the tooth profile was proposed.

Stereo Matching of Planar Curves Composed of Time Stamped Points

Matching features such as curve segments in stereo images play a very important role in scene recomtruction. In this paper, a stereo matching algorithm for the trajectories composed of time stamped points is proposed. Based on time stamped points, planar curve match measurements are given first, such as time constraint, cross-ratio invariant constraint and eplpolar geometry constraint; then, a trajectory matching method is proposed based on epipolar geometry constraint and cross-ratio invariant constraint. In order to match the planar curve segments projected by perspective projection system, the curve start time and end time are selected first to prepare match candidates. Then, the epipolar equation is used to discard the unmatched curve segment candidates. At last, a cross ratio invariant constxaint is used to find the most matched curve segments. If their match measurement is higher than the specialized threshold, a candidate with the least cross ratio difference is then selected as the match result; otherwise, no match is found. Unlike the conventional planar curve segments matching algorithm, this paper presents a weakly calibrated binocular stereo vision system which is based on wide baseline. The stamped points are obtained by targets detecting method of flying objects from image sequences. Due to wide baseline, there must exist the projection not in epipolar monotonic order or the curve segments located in very short distance and keeping the epipolar monotonic order. By using the method mentioned above, experiments are made to match planar curve segments not only in epipolar monotonic order but also not in epipolar monotonic order. The results show that the performance of our curve matching algorithm is effective for matching the arc-like planar trajectories composed of time stamped points.

重塑黄土的往返加卸载真三轴试验研究

针对不同应力路径往返加卸载条件下黄土累积塑性应变发展特性,以重塑黄土为研究对象,利用真三轴仪开展不同应力路径的往返加卸载试验研究,探究不同应力路径、应力幅值下黄土的循环应力时程曲线、滞回曲线、骨干曲线及累积塑性应变曲线的影响规律。揭示了应力路径对重塑黄土力学特性的影响,描述了各主应力与中主应力比b和应力幅值的相关性,提出了重塑黄土的滞回曲线近似呈椭圆形,长轴斜率随中主应力比b值的增大而增大,随应力幅值的增大而减小;随着中主应力比b值的增大,循环应力-应变骨干曲线随之硬化,累积塑性应变曲线依次降低,且累积塑性应变发展更早的进入平缓阶段,为解决相关黄土工程问题提供了参考。

垭口微地形下档内线路不均匀覆冰研究

明确垭口地形因子对垭口输电线路覆冰的影响规律,对山区输电线路的差异化防冰非常关键。该文基于水文分析中反地形理论提出山腰垭口,建立垭口风场数值模型,并通过风洞实验验证该模型。依据垭口风场分布,选定3类垭口线路的架设路径,得出垭口线路的风速区间。将初始状态下导线单次覆冰冰层厚度不得超过线径的7%作为覆冰步长取值依据,循环计算流场、粒子传输模型、热力学方程得出线路风速区间内导线的覆冰情况,进而得出垭口线路的冰荷载曲线,山腰、山脉、双山垭口线路冰荷载曲线在弧垂区分别出现了弯折、下行、下凹的走势。通过野外垭口线路自然覆冰实验,验证了覆冰计算的有效性,证实横跨垭口线路的不均匀覆冰性,不均匀覆冰规律与计算冰荷载曲线类似。计算不同地形因子组合下3类垭口的冰荷载曲线,并提出最大应力比概念,作为评判覆冰所引起线路事故可能性的标准,量化了不同垭口地形因子与线路最大应力比之间的关系。

卡托普利抑制试验在原发性醛固酮增多症诊断和分型以及临床转归中的应用

背景 原发性醛固酮增多症(PA)作为继发性高血压中发病率最高、心脑血管危害大但手术后治愈率高的疾病,已被各大高血压指南推荐扩大筛查、早期诊断和治疗。但该类患者的确诊、分型和治疗后临床转归判定方式繁多且存在较多争议。卡托普利抑制试验(CCT)因其便捷、安全可直接用于社区、门诊,期望CCT能对PA患者进行全程管理以改善预后。目的 探究CCT对PA的诊断、分型以及临床转归的判断能力。方法 选取2020-10-01—2022-12-30在四川大学华西医院内分泌代谢科接受内分泌性高血压病因筛查并登记的824例患者为研究对象。经筛选后最终370例患者纳入研究,其中123例原发性高血压(EH)患者纳入EH组,247例PA患者分别纳入单侧醛固酮瘤(APA)组81例、特发性醛固酮增多症(IHA)组55例和未分型PA(u-PA)组111例。比较4组间差异并绘制CCT后各指标及联合诊断PA的受试者工作特征(ROC)曲线,确定最佳截断值。其次绘制CCT后各指标诊断APA和IHA亚型的ROC曲线,计算ROC曲线下面积(AUC)评估CCT对APA和IHA的分型判断能力。最后根据术后临床结局将单侧肾上腺切除患者分为3组:未缓解组11例、临床改善组27例和临床缓解组54例,比较3组间差异并判断CCT对APA患者术后临床转归的判断能力。结果 CCT后血浆醛固酮浓度(PAC)对PA的诊断效能最高(AUC=0.921,95%CI=0.893~0.950),最佳截断值为11.7 ng/dL,灵敏度、特异度分别为84.6%和86.0%;CCT后醛固酮/肾素比值(ARR)对PA也有较好的诊断效能(AUC=0.868,95%CI=0.823~0.923),最佳截断值为2.8(ng/dL)/(mU/L),灵敏度、特异度分别为82.2%和81.0%。CCT后PAC>17.0 ng/dL可协助诊断APA亚型,CCT后PAC<11.7 ng/dL同时ARR<2.8(ng/dL)/(mU/L)的患者可排除APA亚型。在接受手术治疗的患者中,有87.2%患者经CCT后PAC<11.7 ng/dL,89.7%患者CCT后ARR<2.8(ng/dL)/(mU/L)均接近术后临床缓解水平(88.0%)。结论 CCT可全程用于PA患者的诊断、分型和临床转归评价,CCT后PAC及CCT后ARR诊断PA的最佳截断值分别为11.7 ng/dL和2.8(ng/dL)/(mU/L),也可用于APA的分型判断以及术后生化缓解的判断。CCT前采血检验临床意义小,可适当简化流程。

半刚接钢框架内填实体RC墙结构的地震易损性能评估

为评估半刚接钢框架内填实体RC墙结构(PSRCW)的地震易损性能及倒塌储备能力,考虑层数和抗震设防烈度影响合理设计了4个PSRCW结构基准算例,采用Latin超立方抽样方法考虑型钢、混凝土、钢筋等材料力学性能及内填RC墙体厚度几何尺寸的随机性,拓展为4组共计160个PSRCW算例.通过合理选取40条汶川地区实测地震记录,与每组40个PSRCW结构样本随机组合,构成了4组40个地震-结构样本对,通过弹塑性时程分析方法确定了PSRCW结构在“弹性极限”“完全运行”“运行”“生命安全”“接近倒塌”“倒塌”性态下的地震易损性曲线,并进行了抗震性能评估,量化了PSRCW结构的倒塌储备能力.分析结果表明:PSRCW结构的倒塌安全储备系数在3.0~4.3之间,具有良好的抗地震倒塌能力.

轴力对预应力高强混凝土管桩抗震性能的影响

目的研究轴力和往复荷载作用下预应力高强混凝土管桩的抗震性能,为预应力高强混凝土管桩的设计和实际工程应用提供参考依据。方法应用ABAQUS有限元软件对预应力高强混凝土管桩进行有限元模拟,并与已有试验结果对比,两者吻合良好,验证了模型的准确性。在此基础上,研究轴压比和有无普通钢筋及普通钢筋直径对预应力高强混凝土管桩滞回曲线、骨架曲线、刚度退化、延性及耗能能力的影响。结果配置普通钢筋可以提高预应力高强混凝土管桩的承载能力和延性,对刚度影响不大;随着轴压比的增加,预应力高强混凝土管桩的承载能力逐渐提高,但延性变差,轴压比为0.45时,预应力高强混凝土管桩发生脆性破坏。结论配置普通钢筋可以有效改善预应力高强混凝土管桩的抗震性能,预应力高强混凝土管桩的轴压比不宜超过0.3。

一种新型高阶齿扇齿条副的啮合性能分析

目前汽车转向器非圆齿轮副普遍采用C^(0)阶连续的变传动比曲线,其齿扇齿廓有尖点,不光滑,速度和加速度有突变,传动不够平顺。为此,以四次多项式为基函数设计C^(2)阶连续的变传动比曲线,采用齿廓法线法求解不同连续阶的齿扇齿廓,基于有限差分法推导齿廓曲率的计算公式,对比分析C^(0)、C^(1)、C^(2)阶传动比曲线的齿廓结构特点、传动中的速度与加速度的变化特点以及其齿廓光滑性。仿真结果表明汽车转向器非圆齿轮副传动比曲线的连续阶越高,其齿廓越光滑。

相对密实度和固结应力比对北部湾海砂动力特性影响的试验研究

北部湾地区拥有丰富的海洋资源,海洋工程在这一地区的发展日益重要,了解海砂在不同固结应力比和密实度条件下的动力特性,对于海岸线保护、港口建设、堤防工程等都至关重要。为探究北部湾海砂的动力特性,针对北部湾海砂开展了一系列的固结不排水循环动三轴试验,分析了相对密实度和固结应力比对北部湾海砂的轴向累积应变、动弹性模量、动孔压以及滞回曲线的影响。研究表明:在相同振次水平下,随着固结应力比和相对密实度的增大,海砂的轴向累积应变随之减小;动孔压随着固结应力比的增大线性减小,在低相对密实度(Dr≤50%)下,动孔压随振次的增大而增大,在高相对密实度(Dr=70%)下,动孔压随振次先增后减;动弹性模量随着振次的增加出现刚度软化现象,增大相对密实度与固结应力比,较明显地减缓了动弹性模量的衰减速率;随着固结应力比和相对密实度的增大,滞回曲线包围的面积减小,滞回曲线由不封闭曲线转为封闭曲线。这些研究成果可以为北部湾围填海工程提供一定的参考。

脉搏血氧仪校准方法的研究

本方法适用于光电式的脉搏血氧仪(计)、脉搏血氧饱和度监护仪以及多参数监护仪中脉搏血氧监护部分的校准。在脉搏血氧仪质量控制方面,国家并没有专门的计量标准,各地依据当地的实际情况出台了地方标准,但是均没有关于光吸收比率拟合曲线误差的测量。本文主要介绍了脉搏血氧仪的组成和用途,针对目前临床在用设备,研究了脉搏血氧仪的校准方法,增加了光吸收比率拟合曲线示值误差项目,并对该校准方法进行了验证实验。此研究的目的是为开展相应的质量控制工作提供技术依据,希望通过质量控制确保脉搏血氧仪设备良好运行,有效保障医疗安全。

粗骨料取代率对机制砂再生混凝土高温性能的影响

为探究不同粗骨料取代率对机制砂再生混凝土(RCM)高温性能的影响,以不同粗骨料取代率(0%、20%、40%、60%、80%、100%,质量分数)制备RCM并研究其单面受高温后的表面形貌、质量损失率、抗压强度、荷载变形曲线及微观形貌。结果表明,粗骨料取代率在40%~60%时,在低于600℃的高温试验下RCM表现良好。当温度在200℃时,各组试块表面形貌变化不大,质量损失率较小,抗压强度略微上升;当温度在400℃时,各组试块表面开始出现裂缝,质量损失率为4.35%~6.47%,抗压强度开始下降,此时粗骨料取代率影响不大;当温度达到600℃时,表面形貌变化明显,质量损失率上升到6.42%~8.70%,抗压强度最终降低到基准强度的80%左右,此时粗骨料取代率在40%~60%的试块表现良好;当温度达到800℃时,各组试块表面形貌变化进一步加剧,粗骨料取代率大于60%的试块受影响非常明显,同时各类性能参数表明混凝土已完全丧失工作性能。