A Study on the Strength Surplus Coefficient of Cement

This study considers P.O42.5 cement from different sources and evaluates the related surplus coefficient(defined as the proportionality factor linking the measured compressive strength value of the cement after 28 days to the“standard”value of cement strength).The needed tests have been conducted using a mixer,a pressure testing machine,a flexural testing machine,a vibrating table a ramming rod,a feeder and a metal ruler.The average value of the measured cement strength surplus coefficient of cement produced by five distinct cement manufacturers has been found to be 1.16.These results can be used as the basis to reduce the production cost and improve the performance of commercial concrete.

Optimization of Coarse Aggregate Content based on Efficacy Coefficient Method

The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate content,with coarse aggregate content of 0%,40%,50%,60%,75%,and 80%,respectively.Slump,compressive and flexural tensile strengths,elastic modulus,and water penetration were tested to research the effect of coarse aggregate content on concrete.The experimental results reveal that slump reduces with increasing of coarse aggregate content,while compressive strength,elastic modulus and flexural tensile strength increase with the coarse aggregate content increasing,and water penetration reduces with coarse aggregate content increasing before 75% then increased.Workability,strength,durability and economical indexes system were established to optimize the coarse aggregate content in concrete based on efficacy coefficient method.The optimization results show that when coarse aggregate content is 60%,the system efficacy coefficient reaches to 0.89,and it expresses the better comprehensive performance.

Effect of colouring green stage zirconia on the adhesion of veneering ceramics with different thermal expansion coefficients

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients （TECs）, when zirconia ceramics were coloured at green stage. Zirconia blocks （N=240; 6 mm x 7 mm x 7 mm） were manufactured from two materials namely, ICE Zirconia （Group 1） and Prettau Zirconia （Group 2）. In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid （shade A2）, Three different veneering ceramics with different TEC （ICE Ceramic, GC Initial Zr and IPS e.max Ceram） were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys （Esteticor Plus） veneered with ceramic （VM 13） （n= 16） acted as the control group. Core-veneer interface of the specimens were subjected to shear force in the Universal Testing Machine （0.5 mm-min-1）. Neither the zirconia core material （P=0.318） nor colouring （P=0.188） significantly affected the results （three-way analysis of variance, Tukey＇s test）. But the results were significantly affected by the veneering ceramic （P=0.000）. Control group exhibited significantly higher mean bond strength values （45.7__.8） MPa than all other tested groups （（27.1__.4.1）-（39.7__.4.7） and （27.4__.5.6）-（35.9___4.7） MPa with and without colouring, respectively） （P^0.001）. While in zirconia-veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering ~ 1/3 of the substrate surface, in the metal-ceramic group, veneering ceramic was left adhered 1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core-veneer adhesion. Metal-ceramic adhesion was more reliable than all zirconia-veneer ceramics tested.

Advances in joint roughness coefficient (JRC) and its engineering applications

The joint roughness coefficient (JRC), introduced in Barton (1973) represented a new method in rock mechanics and rock engineering to deal with problems related to joint roughness and shear strength estimation. It has the advantages of its simple form, easy estimation, and explicit consideration of scale effects, which make it the most widely accepted parameter for roughness quantification since it was proposed. As a result, JRC has attracted the attention of many scholars who have developed JRC-related methods in many areas, such as geological engineering, multidisciplinary geosciences, mining mineral processing, civil engineering, environmental engineering, and water resources. Because of such a developing trend, an overview of JRC is presented here to provide a clear perspective on the concepts, methods, applications, and trends related to its extensions. This review mainly introduces the origin and connotation of JRC, JRC-related roughness measurement, JRC estimation methods, JRC-based roughness characteristics investigation, JRC-based rock joint property description, JRC's influence on rock mass properties, and JRC-based rock engineering applications. Moreover, the representativeness of the joint samples and the determination of the sampling interval for rock joint roughness measurements are discussed. In the future, the existing JRC-related methods will likely be further improved and extended in rock engineering.

Rock joint coefficients and their computerized classification

A computerized method for determining rock joint coefficients is presented.Two relative similarity indicators are introduced to classify surface morphology of rock joints.The classification enables to compare investigated and database rock joints.Such a comparison aims at finding the couple of surfaces that are distinguished by the highest dynamical conformity.The first absolute indicator results from the Fourier matrix and evaluates wavy shapes of surfaces.The second absolute indicator quantifies the heights of surface reliefs and is defined as the root mean square height of the surface outline.Numerical reliability of these indicators is tested within the surface analysis of a series of limestone specimens.Besides the computerized assessment,25 people have performed visual assessment of these limestone specimens.The results of visual assessments have been statistically processed and compared to the results received from the computerized procedure.The newly introduced absolute indicators have proved to be prospective numerical tools for evaluating joint rock coefficients.

土石坝高喷桩防渗墙抗压强度与渗透系数相关性及分布模型研究

防渗墙的抗压强度与渗透系数之间的相关性及其分布模型是影响土石坝防渗墙强度及大坝渗透可靠性的关键因素。收集了9座土石坝高喷桩防渗墙检测数据,采用AIC准则识别抗压强度与渗透系数的最优边缘分布类型与构造相关联合分布模型的最优Copula函数,Bootstrap方法模拟识别结果的统计不确定性。结果表明:抗压强度和渗透系数之间存在显著负相关性、主要服从威布尔分布,构造两参数相关非正态联合分布的最优Copula函数为Frank Copula,识别结果差异主要来源于防渗墙施工质量导致的频率分布差异。研究结果可为土石坝高喷桩防渗墙强度可靠度与坝体/坝基渗透稳定可靠度分析提供简单、有效的分布模型。

运动疗法激活臀肌改善青年男性膝前痛患者的下肢肌力

背景:目前发现膝前痛与下肢生物力学有关,但仍缺少臀肌训练对膝关节及下肢日常活动影响的研究。目的:探究臀肌激活运动疗法对青年男性膝前痛患者髋、膝关节肌群肌肉力量和疼痛的影响。方法:纳入25例男性青年膝前痛患者,随机分为2组,臀肌激活组12例和空白对照组13例。臀肌激活组进行40 min/次、3次/周、为期6周的臀肌激活运动;空白对照组不进行任何干预。入组和干预6周后评估患侧髋关节、膝关节在60(°)/s和180(°)/s下等速屈伸运动测试的相对峰力矩、总功、屈伸肌群比值、肌肉耐力值,爬楼运动测试中停止爬楼的楼层,以及目测类比评分。结果与结论:①等速屈伸运动测试:髋关节,干预后臀肌激活组在60(°)/s和180(°)/s的相对峰力矩较干预前显著提高29.74%和25.95%(P=0.022,P=0.024);空白对照组在180(°)/s时的肌耐力较干预前降低12.12%(P=0.000)。膝关节,干预后臀肌激活组在60(°)/s和180(°)/s的相对峰力矩较干预前显著提高18.69%和7.27%(P=0.006,P=0.033);空白对照组各指标干预前后无著性变化(P>0.05)。②爬楼运动测试:臀肌激活组爬楼运动停止时的楼层数较空白对照组高(6.41±6.1)层(P=0.024),干预后较干预前增高(P=0.016);空白对照组干预前后无显著改变(P>0.05)。③疼痛评估:干预后臀肌激活组目测类比评分显著低于空白对照组(P=0.036),干预后较干预前降低(P=0.000);空白对照组干预前后无显著性变化(P>0.05)。结果表明:6周臀肌激活运动疗法可改善下肢肌群的爆发力和耐力,减轻膝前痛程度,对于膝前痛患者有必要进行臀肌训练,以促进康复。

2023版ASME规范Ⅰ卷管道集箱强度计算变化介绍

本文主要介绍了2023版ASME Ⅰ卷规范管道集箱强度计算公式中温度系数y的变化对强度计算的影响,供有关技术人员参考。

隧道弃渣制备免烧透水砖及性能研究

以隧道弃渣作为骨料,水泥为胶结剂,粉煤灰为辅助原料,通过压制成型法制备免烧透水砖,考察了不同因素对样品性能的影响。结果表明,当配合比设计参数为:孔隙率20%,隧道弃渣、水泥和粉煤灰质量比8∶1∶1,水灰比0.3,减水剂用量1%,得到透水砖的最佳工艺条件,即成型压力为2.5 MPa,保压时间为50 s,采用标准养护28 d。此条件下制得的免烧透水砖抗压强度为12.3 MPa,透水系数为3.25×10^(-2) cm/s,本研究为隧道弃渣综合利用提供了新途径。

血流限制训练法联合抗阻训练对运动者肌肉相关指标影响的Meta分析

目的:通过收集血流限制训练法联合抗阻训练的相关文献,依照系统评价和Meta分析的范式,分析血流限制训练法联合抗阻训练与抗阻训练对运动者肌肉相关指标和专项能力的不同影响,旨在为运动者在训练实践中运用血流限制训练提供数据支持。方法:检索中外数据库(中国知网、万方、PubMed、Web of Science和SPORTDiscus),应用血流限制训练法联合抗阻训练对对象为运动者中大学生运动者肢体围度、肌肉质量、肌肉力量和专项运动能力影响的随机对照试验,检索起止时间为2000-01-01/2023-10-12。至少2名研究者采用Cochrane协作网偏倚风险评估工具和标准对纳入文献进行质量评价。使用RevMan 5.4软件进行异质性检验、数据合并、亚组分析、绘制森林图和敏感性分析,绘制漏斗图并进行发表偏倚评价和敏感性分析。评价指标为肢体围度、肌肉厚度、肌肉力量和专项能力等,对不同专项运动能力进行亚组分析。结果:①共纳入18项随机对照试验,共403例受试者,根据Cochrane协作网偏倚风险评估工具,纳入文献中文献质量为A级的有16篇,B级有2篇。②将血流限制训练法联合抗阻训练与抗阻训练之间的效果进行对比,在肢体围度方面,两组间无显著性差异(SMD=0.03,95%CI:-0.16-0.21,P=0.78);在肌肉厚度方面(SMD=0.14,95%CI:0.01-0.27,P=0.03)及肌肉力量方面(SMD=0.37,95%CI:0.14-0.60,P=0.001)两组间有显著性差异。③对专项能力指标进行亚组分析结果显示,距离指标的分析结果存在高异质性(I2=73%),时间指标的分析结果存在高异质性(I2=55%),分析可能原因是各研究的测试方法及评估指标意义的不同导致;功率指标的分析结果显示无异质性(I2=0%);血流限制训练法联合抗阻训练对距离指标具有显著影响(P<0.01)。④合并效应结果显示,血流限制训练法联合抗阻训练比较抗阻训练对于专项能力的影响(P=0.41),提示不同训练方法对于专项能力不存在显著性影响。结论:①两种训练方法均能够促进大学生运动者的肌肉厚度、肌肉力量和专项能力,血流限制训练法联合抗阻训练相较于抗阻训练在促进运动员肌肉厚度、肌肉力量和部分专项能力方面具有显著性效果。因此,可以在专项训练之中科学合理地融合血流限制训练法,以差异性的生理刺激综合作用于肌肉,以取得更好的训练效果。②然而,由于纳入的研究数量较少,以及其他可能存在的局限性,今后需要纳入更多的高质量、多项目类型和性别的随机对照试验来证实。

高厚径比印刷线路板环氧树脂塞孔油墨的制备及应用

为了实现高厚径比印刷线路板(PCB)树脂塞孔的同时并保证油墨的性能,本文以环氧树脂为基体,改性后的微米/纳米SiO_(2)为填料,搭配固化剂甲基六氢苯酐和其他助剂在特定工艺条件下制成塞孔油墨。利用差示扫描量热法(DSC)确定油墨的固化工艺参数;红外光谱(FT-IR)对改性前后的SiO_(2)进行表征分析;通过热膨胀测试(CTE)、拉伸强度测试、树脂塞孔测试,研究不同粒径填料添加比例对油墨性能的影响,确定油墨的最佳配方。结果表明:本实验制备的W/N70-30油墨的热膨胀系数和拉伸强度比油墨产品PHP-3F-DS和PHP-900好;塞孔后发现5 mm的PCB板上0.13 mm和0.15 mm孔径的通孔背面都呈现出油现象,其塞孔效果最好,因此本实验制备的W/N70-30油墨能够应用于高厚径比(40:1)印刷线路板。

孤岛工作面沿空掘巷窄煤柱承载特征研究

孤岛工作面复杂的支承压力分布状态致使沿空巷道的围岩稳定性受到了极大影响。为探究孤岛工作面沿空掘巷窄煤柱承载特征,采用理论分析方法探究了煤柱塑性区宽度与多种因素相关性,运用数值模拟方法分析了支护参数对巷道围岩稳定性的影响。研究表明:随着侧压系数的增加,塑性区宽度近似线性增加;而随着支护强度的增加,塑性区宽度则近似线性减小。凝聚力和摩擦角的增加均会导致塑性区宽度的减小,但减小的幅度逐渐变小。增加锚杆长度和预紧力可以扩大压动范围,有效控制巷道围岩变形;而间排距的调整需要在保证支护强度的前提下,选择适当的宽度以提高施工效率和经济性。通过工业实验,采用合理的煤柱宽度和支护结构后,巷道围岩变形趋于稳定,确保了巷道的安全与正常使用,验证了支护方案的有效性。

不对称性等速肌力训练联合电子生物反馈对老年脑卒中康复患者生活质量的影响

目的 探讨不对称性等速肌力训练联合电子生物反馈对老年脑卒中康复患者生活质量的影响。方法 选取2020年5月至2023年5月我院收治的102例老年脑卒中期神经系统功能恢复患者,按随机数字表法分为观察组和对照组各51例,对照组采用不对称性等速肌力锻炼治疗,观察组在此基础上辅以电子生物反馈训练,采用Fugl-Meyer上肢运动功能评价量表(FMA)和下肢运动功能评价量表(FMA-LE)评价肢体运动功能;采用脑卒中特异性生活质量量表(SS-QOL)评价生活质量,比较两组训练前后患侧肘屈/伸动作肌力水平[峰力矩(PT)、到达峰力矩时间(TPT)],肢体运动功能及生活质量的差异。结果 训练后,两组肌力水平中PT伸展、PT屈曲以及FMA、FMA-LE和SS-QOL量表中各维度均较训练前升高,且观察组高于对照组(P<0.05);TPT伸展和TPT屈曲均较训练前降低,且观察组低于对照组(P<0.05)。结论 不对称性等速肌力训练与电子生物反馈的联合应用,可显著促进老年脑卒中康复期患者的患侧肌力水平提升,使上、下肢功能得到全面改善,并有效提升患者生活质量。

Stability analysis of shallow tunnels subjected to seepage with strength reduction theory

Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water seepage were presented and compared with those without considering seepage. The comparisons indicate that the maximum difference does not exceed 3.7%,which proves the present method credible. The results show that stability numbers of shallow tunnels considering seepage are much less than those without considering seepage,and that the difference of stability numbers between considering seepage and without considering seepage increase with increasing the depth ratio. The stability numbers decrease with increasing permeability coefficient and groundwater depth. Seepage has significant effects on the stability numbers of shallow tunnels.

Research on testing method of resin sand high temperature compressive strength

High temperature compressive strength is one of the most important performances of resin sand; its value directly concerns the quality of castings. In order to seek the best testing method of resin sand high temperature compressive strength, a self-developed instrument was used to carry out experiments, and the sample shape and size were designed and studied. The results show that a hollow cylinder sample can reflect the strength difference of different resin sands better than a solid cylinder sample, and its data is stable. The experiments selected φ20/5×30 mm as the size of the hollow cylinder samples. The high temperature compressive strengths of phenol-formaldehyde resin coated sand, furan resin self-setting sand, and TEA resin sand were each tested. For the resin sand used for cast steel and cast iron, 1,000 ℃ was selected as the test temperature; for the resin sand used for cast non-ferrous alloy, 800 ℃ was selected as the test temperature; and for all the resin sand samples, 1 min was selected as the holding time. This testing method can truthfully reflect the high temperature performance of three kinds of resin sand; it is reproducible, and the variation coefficients of test values are under 10%.

Swirling-strength based large eddy simulation of turbulent flow around single square cylinder at low Reynolds numbers

In view of the fact that large scale vortices play the substantial role of momentum transport in turbulent flows, large eddy simulation （LES） is considered as a better simulation model. However, the sub-grid scale （SGS） models reported so far have not ascertained under what flow conditions the LES can lapse into the direct nu-merical simulation. To overcome this discrepancy, this paper develops a swirling strength based the SGS model to properly model the turbulence intermittency, with the primary characteristics that when the local swirling strength is zero, the local sub-grid viscosity will be vanished. In this paper, the model is used to investigate the flow characteris-tics of zero-incident incompressible turbulent flows around a single square cylinder （SC） at a low Reynolds number range Re ∈ [103, 104]. The flow characteristics investigated include the Reynolds number dependence of lift and drag coefficients, the distributions of time-spanwise averaged variables such as the sub-grid viscosity and the logarithm of Kolmogorov micro-scale to the base of 10 at Re=2 500 and 104, the contours of spanwise and streamwise vorticity components at t = 170. It is revealed that the peak value of sub-grid viscosity ratio and its root mean square （RMS） values grow with the Reynolds number. The dissipation rate of turbulent kinetic energy is larger near the SC solid walls. The instantaneous factor of swirling strength intermittency （FSI） exhibits some laminated structure involved with vortex shedding.

Detection of Thermophysical Properties for High Strength Concrete after Exposure to High Temperature

Using the detection principle of infrared thermal imaging technique and the detection principle of DRH thermal conductivity tester laboratory,we investigated the infrared thermal image inspection,coefficient of thermal conductivity,apparent density,and compressive strength test on C80 high-strength concrete（HSC） in the presence and absence of polypropylene fibers under completely heated conditions.Only slight damages were detected below 400 ℃,whereas more and more severe deterioration events were expected when the temperature was above 500 ℃.The results show that the elevated temperature through infrared images generally exhibits an upward trend with increasing temperature,while the coefficient of thermal conductivity and apparent density decrease gradually.Additionally,the addition of polypropylene fibers with appropriate length,diameter,and quantity contributes to the improvement of the high-temperature resistance of HSC.

An experimental analysis on the turnover time of railway freight transportation based on the impact strength of factors

Based on the factors impact strength model(FISM), we studied on calculation formulas of influence strength and key elements of FISM, and analyzed the turnover time of railway freight transportation of China. The results show that wagon transfer time is the most critical factor among the three subjective factors of wagons turnover time. The FISM based analysis of wagon transfer time show that the wagon turnover time is significantly correlated with transit time with resorting. Among the seven factors of detention time of transit time with resorting, the time of waiting to departing, converging, and waiting to break-up are key factors, while the time of make-up, break-up, arrival and departure are general factors. We carried out one empirical research based on the data of Baoji East Railway Station in 2015. The results of empirical research and FISM are consistent completely.

Prediction of Antifrccze Critical Strength of Infant Age Concrete

The rule of infant age concrete strength development under low temperature and complex affecting factors is researched. An efficient and reliable mathematical forecast model is set up to predict the infant age concrete antifreeze critical strength under low temperature at construction site. On the basis of the revision of concrete equivalent coefficient under complex influencing factors, least-squares curve-fitting method is applied to approximate the concrete strength under standard curing and the forecast formula of concrete compressive strength could be obtained under natural temperature condition by various effects. When the amounts of double-doped are 10% fly ashes and 4% silica fumes as coment replacement, the antifreeze critical strength changes form 3.5-4.1MPa under different low temperature curing. The equivalent coefficient correction formula of concrete under low temperature affected by various factors could be obtained. The obtained equivalent coefficient is suitable for calculating the strength which is between 10% to 40% of standard strength and the curing temperature from 5-20 ℃. The forecast value of concrete antifreeze critical strength under low temperature could be achieved by combining the concrete antifreeze critical strength value with the compressive strength forecast of infant age concrete under low temperature. Then the theory for construction quality control under low temperature is provided.

Determining the Onset and Strength of Unforced Wave Breaking in A Numerical Wave Tank

A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra： constant amplitude spectrum, constant steepness spectrum and Pierson-Moscowitz spectrum. Numerical tests are performed to validate the model results. Then, the onset of wave breaking is discussed with geometric, kinematic, and dynamic breaking criteria. The strength of wave breaking, which is always characterized by the fractional energy loss and breaking strength coefficient, is studied for different spectra. The results show how the energy growth rate is better than the initial wave steepness on estimating the fractional energy losses as well as breaking strength coefficient.