Orthokeratology with increased compression factor in adolescent myopia control:a 2-year prospective randomized clinical trial

AIM:To explore the long-term efficacy,safety,and optical mechanism of orthokeratology with increased compression factor in adolescent myopia control.METHODS:A prospective,double-masked,and randomized clinical trial was performed from May 2016 to June 2020.Subjects aged between 8 and 16y,with myopia(-5.00 to-1.00 D),low astigmatism(≥-1.50 D)and anisometropia(≤1.00 D),were stratified into low(-2.75 to-1.00 D)and moderate(-5.00 to-3.00 D)myopia groups.Then they were randomly assigned to wear either increased compression factor(ICF;1.75 D)orthokeratology or conventional compression factor(CCF;0.75 D)orthokeratology.The data were recorded including axial length(AL),spherical equivalent(SE),best corrected visual acuity(BCVA),near visual acuity(NVA),corneal staining(using Efron grading scales),corneal hysteresis(CH),corneal resistance factor(CRF),higher-order aberrations(HOAs,expressed as root mean square,RMS_(h)),and subfoveal choroidal thickness(SFCh T)in the 2-year followup period.Pearson's correlation coefficient was conducted to analyze the association between the changes in AL and RMS_(h),SFCh T.RESULTS:At the 2-year visit,there were no statistical differences in all the parameters between the ICF group and the CCF group in low myopia subjects(P>0.05).For the moderate myopia subjects,the ICF group had shorter AL elongation(0.23±0.08 vs 0.30±0.11 mm,P=0.015),higher RMS_(h)(1.94±0.50 vs 1.65±0.51μm,P=0.041),and higher SFCh T(279.04±35.72 vs 254.08±29.60μm,P=0.008)than those in CCF group.The change in AL was negatively correlated with RMS_(h)(r=-0.687,P<0.001)and SFCh T(r=-0.464,P=0.013).CONCLUSION:ICF orthokeratology can control the progression of moderate myopia more effectively,which might be related to greater RMS_(h) and SFCh T.

Electron G-Factor Anomaly and the Charge Thickness

The electron g-factor relates the magnetic moment to the spin angular momentum. It was originally theoretically calculated to have a value of exactly 2. Experiments yielded a value of 2 plus a very small fraction, referred to as the g-factor anomaly. This anomaly has been calculated theoretically as a power series of the fine structure constant. This document shows that the anomaly is the result of the electron charge thickness. If the thickness were to be zero, g = 2 exactly, and there would be no anomaly. As the thickness increases, the anomaly increases. An equation relating the g-factor and the surface charge thickness is presented. The thickness is calculated to be 0.23% of the electron radius. The cause of the anomaly is very clear, but why is the charge thickness greater than zero? Using the model of the interior structure of the electron previously proposed by the author, it is shown that the non-zero thickness, and thus the g-factor anomaly, are due to the proposed positive charge at the electron center and compressibility of the electron material. The author’s previous publication proposes a theory for splitting the electron into three equal charges when subjected to a strong external magnetic field. That theory is revised in this document, and the result is an error reduced to 0.4% in the polar angle where the splits occur and a reduced magnetic field required to cause the splits.

A novel correlation approach for prediction of natural gas compressibility factor

Gas compressibility factor （z-Factor） is one of the most important parameters in upstream and downstream calculations of petroleum industries.The importance of z-Factor cannot be overemphasized in oil and gas engineering calculations.The experimental measurements,Equations of State （EoS） and empirical correlations are the most common sources of z-Factor calculations.There are more than twenty correlations available with two variables for calculating the z-Factor from fitting in an EoS or just through fitting techniques.However,these correlations are too complex,which require initial value and more complicated and longer computations or have magnitude error.The purpose of this study is to develop a new accurate correlation to rapidly estimate z-Factor.Result of this correlation is compared with large scale of database and experimental data also.Proposed correlation has 1.660 of Absolute Percent Relative Error （EABS） versus Standing and Katz chart and has also 3.221 of EABS versus experimental data.The output of this correlation can be directly assumed or be used as an initial value of other implicit correlations.This correlation is valid for gas coefficient of isothermal compressibility （cg） calculations also.

Rapidly Estimating Natural Gas Compressibility Factor

Natural gases containing sour components exhibit different gas compressibility factor （Z） behavior than do sweet gases. Therefore, a new accurate method should be developed to account for these differences. Several methods are available today for calculating the Z-factor from an equation of state. However, these equations are more complex than the foregoing correlations, involving a large number of parameters, which require more complicated and longer computations. The aim of this study is to develop a simplified calculation method for a rapid estimating Z-factor for sour natural gases containing as much as 90% total acid gas. In this article, two new correlations are first presented for calculating the pseudo- critical pressure and temperature of the gas mixture as a function of the gas specific gravity. Then, a simple correlation on the basis of the standard gas compressibility factor chart is introduced for a quick estimation of sweet gases＇ compressibility factor as a function of reduced pressure and temperature. Finally, a new corrective term related to the mole fractions of carbon dioxide and hydrogen sulfide is developed.

An efficient correlation for calculating compressibility factor of natural gases

Compressibility factor （z-factor） values of natural gases are necessary in most petroleum engineering calculations.Necessity arises when there are few available experimental data for the required composition,pressure and temperature conditions.One of the most common methods of calculating z-factor values is empirical correlation.Firstly,a new correlation based on the famous Standing-Katz （S-K） Chart is presented to predict z-factor values.The advantage of this correlation is that it is explicit in z and thus does not require an iterative solution as is required by other methods.Secondly,the comparison between new one and other correlations is carried out and the results indicate the superiority of the new correlation over the other correlations used to calculate z-factor.

Experimental determination and prediction of the compressibility factor of high CO_2 content natural gas with and without water vapor

In order to study the effect of different CO2 contents on gas compressibility factor（Z-factor）,the JEFRI-PVT apparatus has been used to measure the Z-factor of dry natural gas with CO2 content range from 10.74 to 70.42 mol%at the temperature range from 301.2 to 407.3 K and pressure range from 7 to 44 MPa.The results show that Z-factor decreases with increasing CO2 content in natural gas at constant temperature and increases with increasing temperature for natural gas with the same CO2 content.In addition,the Z-factor of water-saturated natural gas with high CO2 content has been measured.A comparison of the Z-factor between natural gas with and without saturated water vapor indicates that the former shows a higher Z-factor than the latter.Furthermore,Peng-Robinson,Hall-Yarborough,and Soave-Benedict-Webb- Rubin equations of state（EoS）are used for the calculation of Z-factor of high CO2 content natural gas with and without water vapor.The optimal binary interaction parameters（BIP）for PR EoS are presented.The measured Z-factor is compared with the calculated Z-factor based on three models,which shows that PR EoS combined with van der Waals mixing rule for gas without water and Huron-Vidal mixing rule for water-saturated gas,are in good agreement with the experimental data.

An accurate empirical correlation for predicting natural gas compressibility factors

The compressibility factor of natural gas is an important parameter in many gas and petroleum engineering calculations. This study presents a new empirical model for quick calculation of natural gas compressibility factors. The model was derived from 5844 experimental data of compressibility factors for a range of pseudo reduced pressures from 0.01 to 15 and pseudo reduced temperatures from 1 to 3. The accuracy of the new empirical correlation has been compared with commonly used existing methods. The comparison indicates the superiority of the new empirical model over the other methods used to calculate compressibility factor of natural gas with average absolute relative deviation percent （AARD%） of 0.6535.

Closing law and stress intensity factor of elliptical crack under compressive loading

The solution of surface displacement of an elliptical crack under compressive-shear loading was obtained by using the complex function method. The closing mode was established by analyzing the geometrical condition of closing crack, and the corresponding critical stress was solved. The result corrects the traditional viewpoint, in which there exist only open or close states for an elliptical crack, and points out that the local closing is also one of crack states. Based on them, the effect of the closed crack on stress intensity factor was discussed in detail, and its rational formulae are put forward.

Application of caustic method to determining stress intensity factor of compressive shear crack

The caustic method is applied to compressive shear experiment and used to detect the stress intensity factors of cracks prefabricated on plexiglass sample. Loading, friction of crack planes and influence among cracks are not needed to know as they are combined and transformed into the caustic shadow used in detecting the stress intensity factor. Even boundary condition is not necessary. Therefore it is effective to determine the stress intensity factor of compressive shear crack.

基于改进PSO算法的光伏阵列MPPT研究

为解决传统粒子群优化(PSO)算法在寻优过程中出现粒子早熟、收敛速度慢、易陷入局部优化等问题,提出一种基于反向学习的Logistic-Tent双重混沌映射和时变双重压缩因子(TVCF)策略的改进粒子群优化(LT-TVCFPSO)算法,在传统PSO算法基础上,引入了Logistic-Tent混沌映射和TVCF,既可增强种群多样性,避免粒子早熟,跳出局部优化,又能加快粒子收敛,提升全局寻优能力。最后在MATLAB/Simu-link上进行仿真。仿真结果表明:相比于传统MPPT算法,LT-TVCFPSO算法能够快速准确地追踪到全局最大功率点(GMPP)。

计及氢气注入与压缩因子的综合能源系统能流计算

为实现“双碳”目标,综合能源系统(integrated energy systems, IES)成为了近几年的重要研究方向之一,然而传统的IES能流计算已经无法精确地反映电制气(power-to-gas, P2G)技术带来的氢气注入天然气网络后的混合燃气的参数变化对IES的影响。为此,在传统天然气系统稳态分析方法的基础上加入了SRK(Soawk-Redlich-Kwong)气体状态方程,将压缩因子作为状态变量,提出可以反映氢气注入天然气系统,对气体流量和混合燃气热值产生影响的稳态分析方法。以此为基础,提出了计及氢气注入与压缩因子的电-热-气IES能流分解求解计算方法。最后通过算例验证了所提方法可有效反映混合燃气的参数变化对IES的影响。

基于因子分析法的大深度黄土压缩模量影响因素分析

以中平(中卫─平凉)铁路扩能改造项目62个最大深度21.9~93.7m勘探点的625组土工试验数据为依托,根据物性指标分布特征将大深度范围内的黄土划分为三层,基于因子分析法研究了黄土物性指标与压缩模量的相关性,分析了压缩模量的主要影响因素,提出大深度范围内黄土压缩模量的经验预测方法。结果表明:筛选出大于25 m的黄土层、小于等于25 m的黄土层三个影响最大的公共因子分别为孔隙比、饱和度、液限和孔隙比、含水率、液限;所建立模型的预测结果与实测数据误差较小,对三层黄土压缩模量预测的平均误差分别为5.8%、4.3%、5.6%,比视作单一土层拟合模型的12.4%的平均误差减小一半还多;对大深度黄土分层进行土力学分析,可以提高分析的准确度,但压缩模量的主要影响因素相近,浅层范围内含水率和压缩模量的相关性更高,而深层黄土饱和度与压缩模量的相关性更好。

天然气压缩因子计量核查的研究与应用

天然气压缩因子的准确性对现场标况体积流量和标准热量的计算至关重要,GB/T 17747-2011《天然气压缩因子的计算》标准中对压缩因子定义、AGA8-92DC算法、SGERG88算法做了详细的介绍。本文介绍了天然气现场计量所涉及的规范及国家标准,用于天然气测量孔板、涡轮和气体超声波流量计的测量原理。针对天然气压缩因子计算复杂、不易核查的难题,依据GB/T 17747-2011《天然气压缩因子的计算》所研发的“天然气流量计算机压缩因子核查软件”,结合现场天然气介质组份、实时工况温度、实时工况压力值等数据,进行天然气的计量核查,实现了软件自动化快速计算,有效提升了计量的工作效率和可靠性。

煤吸附CO_(2)压缩因子快速计算模型研究

为研究Virial、V-d-W、R-K、S-R-K、P-R、童景山等6种工程常用气体状态方程中适合煤吸附CO_(2)压缩因子最优方程及快速计算模型,以3种不同变质程度煤样为研究对象,采用容量法实测了试验温度为30℃时应用以上6种方程所得煤的CO_(2)吸附量、CO_(2)吸附常数及吸附等温线。研究表明:与美国国家标准技术研究所(NIST)提供的CO_(2)压缩因子相比,采用Virial状态方程得到的CO_(2)压缩因子最大、绝对误差最小,为0.38%;吸附等温线拟合优度最高,CO_(2)吸附常数a值绝对值误差最小,确定出煤吸附CO_(2)压缩因子最优方程为Virial方程;同时,提出试验温度为30℃时,CO_(2)压缩因子一种简便快捷计算模型,经检验,该模型相对美国标准计算所得CO_(2)吸附常数a值绝对值误差最大不超过1%,且操作简便,快速精确。

新型智能孔板天然气计量装置原理与应用

为了解决天然气流量计及其计算机系统现场测量精度不足、校正流程繁琐、数据实时性差等问题,通过对现有流量测量系统进行智能式优化改造,实现对流量检测的精准执行与数据的精密搜集,可以实时监控气体流量,并完成了压缩因数与流量数值的实时运算。研究结果显示,通过融合PXI机箱与PXI板卡的相关技术以编写数据搜集与处理程序,实现了天然气动态监测与独立核算。实验数据表明,现场流量与设备测量值的相对误差远低于系统预设的0.3%标准,满足了现场测量要求,确保了天然气计量任务的顺利完成。

应用OCS可编程控制器实现天然气计量核查

天然气计量现场需要对流量计算机进行计量核查,一次表流量计种类不同、组态参数配置复杂、受液晶显示窗口限制无法同步采集计量核查数据等问题制约了现场操作的可行性。本文研发了一种基于OCS可编程控制器的天然气计量网关,可针对不同厂家流量计算机的数据参数表,动态配置数据类型、从机地址、字节顺序、读写权限并映射到OCS的%R设备寄存器,解决了天然气计量核查数据预采集的难题;结合现场天然气介质组份、实时工况温度、实时工况压力值等数据,使用依据GB/T17747-2011《天然气压缩因子的计算》所研发的“天然气流量计算机压缩因子核查软件”,按流量计算机参数设置进行的计量核查;使用依据GB/T11062-2020《天然气发热量、密度、相对密度和沃泊指数的计算方法》所研发的“天然气流量能量计量核查软件”,进行天然气能量计量核查;针对天然气的现场计量核查,实现了硬件自动化采集预处理,软件自动化快速计算,有效提升了计量的工作效率和可靠性。

老年女性骨质疏松性骨折相邻椎体再骨折的影响因素及列线图预测模型构建

背景:有关老年女性骨质疏松性椎体压缩性骨折患者相邻椎体再骨折的研究较多,但其相关危险因素仍在争论中,如何将其风险直观地呈现以便于临床应用的研究较少。目的:分析影响老年女性骨质疏松性椎体压缩性骨折患者相邻椎体再骨折的危险因素并构建列线图(Nomogram)预测模型。方法:选择2018年1月至2022年11月赣州市人民医院收治的268例老年女性骨质疏松性椎体压缩性骨折患者,经皮穿刺椎体成形术后3个月根据是否发生相邻椎体再骨折分为研究组(发生相邻椎体再骨折,n=31)和对照组(未发生相邻椎体再骨折,n=237)。比较两组患者一般临床资料,采用多因素Logistic回归分析影响老年女性骨质疏松性椎体压缩性骨折患者相邻椎体再骨折的独立风险因素,利用R软件“rms”包构建Nomogram预测模型。结果与结论:①两组患者的年龄、绝经年龄、体质量指数、骨折病史、术前骨折椎体数、骨水泥渗漏、骨密度、术后后凸畸形角度、术前Oswestry功能障碍指数比较差异均有显著性意义(P<0.05);②多因素Logistic回归分析结果显示,年龄(>69岁)、绝经年龄(≤51岁)、体质量指数(>24.7 kg/m^(2))、骨折病史(有)、术前骨折椎体数(≥2)、术后后凸畸形角度(>13°)是影响老年女性骨质疏松性椎体压缩性骨折患者相邻椎体再骨折的独立危险因素(P<0.05);③Nomogram预测模型决策曲线结果显示,当风险阈值>0.09时,此预测模型可以提供显著额外的临床净收益;④结果表明,年龄较大、绝经年龄较低、体质量指数较高、有骨折病史、术前骨折椎体数较多、术后后凸畸形角度较大是老年女性骨质疏松性椎体压缩性骨折患者相邻椎体再骨折的独立影响因素,基于此构建的Nomogram预测模型可为此类患者相邻椎体再骨折的防治提供重要的策略指导。

骨质疏松性椎体压缩骨折术后临近椎体再发骨折的危险因素分析

目的:分析骨质疏松性椎体压缩骨折(osteoporotic vertebral compression fracture OVCF)经皮椎体成形术(percutaneous vertebroplasty,PVP)或经皮椎体后凸成形术(percutaneous kyphoplasty,PKP)治疗后临近椎体再发骨折(adjacentvertebral compression fracture,AVCF)的相关危险因素。方法:回顾性分析2018年4月至2020年2月郑州市第一人民医院脊柱外科行PVP或PKP手术治疗的148例OVCF患者的临床资料,根据术后有无临近椎体再骨折分成AVCF组(27例)和非AVCF组(121例)。记录患者的年龄、性别、初始骨折椎体数量、初始骨折部位(T10-L2、非T10-L2)、体重指数(BMI)、手术方式(PVP、PKP)、术前腰1椎体CT值、术后伤椎高度恢复率。采用Logistic回归分析确定潜在危险因素。结果:所有患者随访6~18mon,平均10 mon。148例中共发现AVCF 27例(18.2%)。两组患者在性别、年龄、初次骨折椎体数、初次骨折部位、手术方式及BMI方面差异均无统计学意义(P>0.05)。AVCF组腰1椎体CT值明显低于非AVCF组(P<0.05),而AVCF组伤椎高度恢复率明显高于非AVCF组(P<0.05)。单因素分析结果显示:腰1椎体CT值与伤椎高度恢复率与OVCF术后AVCF明显相关(P<0.05);多因素分析结果显示:腰1椎体CT值≤80 HU及伤椎高度恢复率是导致OVCF术后AVCF的独立危险因素。结论:腰1椎体CT值伤椎高度恢复率是OVCF患者PVP或PKP术后AVCF的危险因素。

老年胸腰椎骨质疏松性椎体压缩性骨折经皮椎体成形术治疗效果不佳的影响因素分析

目的探讨分析老年胸腰椎骨质疏松性椎体压缩性骨折(OVCF)经皮椎体成形术(PVP)治疗效果不佳的影响因素。方法选取2021年1月至2022年1月安阳市第三人民医院收治的82例行PVP治疗的老年胸腰椎OVCF患者作为研究对象,收集患者性别、年龄、体重指数(BMI)、术前骨密度(BMD)、骨折椎体数、有无高血压、有无糖尿病、手术入路方式、单个椎体骨水泥注入量、有无骨水泥渗漏、术后是否规范行抗骨质疏松治疗等资料,并根据PVP术后1个月的治疗效果将其分为效果满意组和效果不佳组,多因素Logistic回归分析老年胸腰椎OVCF患者PVP治疗效果不佳的相关影响因素。结果82例老年胸腰椎OVCF患者PVP术后1个月治疗效果满意67例(81.71%),设为效果满意组;治疗效果不佳15例(18.29%),设为效果不佳组。单因素分析结果显示,效果不佳组患者年龄明显大于效果满意组(t=3.745,P<0.001),术前BMD明显小于效果满意组(t=2.914,P=0.005),骨折椎体数≥2个、有骨水泥渗漏以及术后未规范行抗骨质疏松治疗者比例均明显高于效果满意组(χ^(2)=9.019、13.988、13.566,P=0.003、P<0.001、P<0.001),单个椎体骨水泥注入量明显少于效果满意组(t=6.158,P<0.001)。多因素Logistic回归分析结果显示,高龄、术前BMD低、骨折椎体数≥2个及有骨水泥渗漏是老年胸腰椎OVCF患者PVP治疗效果不佳的独立危险因素(95%CI为1.517~12.797、2.298~16.314、1.774~19.234、1.328~17.859,P=0.006、0.000、0.004、0.017)。结论PVP治疗老年胸腰椎OVCF的效果可受患者年龄、术前BMD、骨折椎体数及有无骨水泥渗漏影响。

广义圆端形钢管混凝土短柱轴压承载力公式

为研究圆形、圆端形、变圆心角圆端形和矩形钢管混凝土短柱轴压承载力的统一计算公式,采用两种不同本构关系建立广义圆端形钢管混凝土轴压短柱的ABAQUS有限元模型,利用90个钢管混凝土短柱轴压试验数据与有限元计算结果进行对比,验证了有限元模型的可靠性。通过改变构件的截面形状和材料强度,设置了9组共90个广义圆端形钢管混凝土轴压短柱有限元模型。对有限元计算结果展开参数分析,研究截面平直段高宽比和截面圆心角对钢管混凝土约束效应的影响。基于统一理论和约束分区方法,以截面形状影响系数对套箍系数进行了修正,并在GB 50936—2014推荐的圆形钢管混凝土短柱轴压承载力公式的基础上,建立了广义圆端形钢管混凝土短柱的轴压承载力简化计算公式,最后采用452个广义圆端形钢管混凝土短柱轴压试验数据对公式的准确性进行了验证。结果表明:当材料强度和含钢率一定时,广义圆端形钢管混凝土柱的套箍约束效应随着截面平直段高宽比的增大而减小,随着截面圆心角的增大而增大;简化公式的计算结果与试验结果吻合良好,适用于圆形、圆端形、变圆心角圆端形及矩形钢管混凝土短柱的轴压承载力计算。