Dependence of grip strength on shoulder position and its implications for ergonomics practice

Grip strength (GS) variability due to positional changes in the upper extremity joints is of importance while designing workstations and work methods. This study was conducted to analyze the GS variations due to positional changes at shoulder joint when some important variables were under control. The GSs of dominant and nondominant hands were measured in eight shoulder (0°, 45°, 90°, and 135° of flexion and abduction) and standard test positions (STP). One hundred and thirteen subjects 20–30 years old completed the study. At the dominant side, no significant difference was observed in the pairwise comparisons between STP and the others. Maximum and minimum GSs were obtained in 0° abduction and 45° flexion and abduction, respectively. At the nondominant side, GSs were significantly lower (p < 0.001) in the corresponding test positions and demonstrated more variability. The findings of this study can contribute to the available knowledge to guide occupational ergonomists in their practices.     

磁场环境下铝电解熔融铝液成分激光诱导击穿光谱原位测量分析

铝电解车间具有高温、强磁、多粉尘等环境特点,当前生产过程中熔融原铝的成分检测主要是人工取样然后离线分析,化验过程及结果具有较大的滞后性,故将激光诱导击穿光谱(LIBS)技术应用于铝电解车间铝液成分原位、实时测量具有重要意义。实验采用Nd:YAG脉冲激光器,多通道光纤光谱仪和电感耦合器件(CCD)探测器组成的激光诱导击穿光谱测量系统对电流为400kA电解槽中熔融铝液的主要成分铁、硅进行了探测,对原铝中部分元素的特征谱线进行了归属分析。考察了激光能量在磁场环境下的衰减变化及谱线梯度变迁规律,结果表明,距离电解槽边缘约2m处激光能量衰减达最大。分析了磁场对测试系统的影响,并建立了定标曲线,铁和硅两种元素按照内标法建立的定标曲线拟合度分别为93.50%和97.10%,采用该模型进行了测试实验,并用国标GB/T 7999—2015中光电直读发射光谱(OES)测试的相关指标验证测试结果的重复性与允许差。实验证明,LIBS技术在电解铝行业在线检测方面具有较好的应用前景,但是测试的稳定性与重复性也是面临的一个重要问题。     

基于克里金理论的辐射剂量场插值重构与可视化研究

使用基于克里金理论的插值计算方法对均匀网格与随机排列等不同分布类型的辐射剂量场进行了数据重构与可视化研究,并将重构结果与常用的反距离加权插值法进行了对比,分析了不同插值方法对辐射剂量场重构精度与可视化显示效果的影响。结果表明:对于多数情况,克里金插值法在辐射剂量场重构的精度与可视化显示的效果上均明显优于反距离加权插值法,算例中克里金插值法的结果与原始数据之间的偏差在10%以内,而反距离加权插值法的结果与原始数据之间的偏差基本在15%以上;但在辐射剂量场梯度变化较大且已知数据极少的区域,克里金插值法的计算结果偏差会增大,此时可使用反距离加权插值作为其补充,综合使用。本文的研究工作,验证了克里金插值法在辐射剂量场重构与可视化方面的应用潜力,可为推动辐射剂量场可视化仿真技术的发展提供技术支持。     

Evaluation of physiological workload assessment methods using heart rate and accelerometry for a smart wearable system

Work metabolism (WM) can be accurately estimated by oxygen consumption (VO₂), which is commonly assessed by heart rate (HR) in field studies. However, the VO₂–HR relationship is influenced by individual capacity and activity characteristics. The purpose of this study was to evaluate three models for estimating WM compared with indirect calorimetry, during simulated work activities. The techniques were: the HR-Flex model; HR branched model, combining HR with hip-worn accelerometers (ACC); and HR?+?arm-leg ACC model, combining HR with wrist- and thigh-worn ACC. Twelve participants performed five simulated work activities and three submaximal tests. The HR?+?arm-leg ACC model had the overall best performance with limits of agreement (LoA) of ?3.94 and 2.00?mL/min/kg, while the HR-Flex model had ?5.01 and 5.36?mL/min/kg and the branched model, ?6.71 and 1.52?mL/min/kg. In conclusion, the HR?+?arm-leg ACC model should, when feasible, be preferred in wearable systems for WM estimation.

Practitioner Summary: Work with high energy demand can impair employees’ health and life quality. Three models were evaluated for estimating work metabolism during simulated tasks. The model combining heart rate, wrist- and thigh-worn accelerometers showed the best accuracy. This is, when feasible, suggested for wearable systems to assess work metabolism.     

The enhanced photocatalytic activity of Na0.9Mg0.45Ti3.55O8 co‐loaded with silver and platinum

Noble metals Ag and Pt were loaded on Na_0.9Mg_0.45Ti_3.55O₈ (NMTO) by chemical bath deposition method, which was synthesized firstly in our recent work. The scanning electron microscopy and transmission electron microscopy results show that Ag and Pt nanoparticles were distributed on the different surfaces of NMTO. NMTO loaded with Ag and Pt can efficiently enhance the separation of photogenerated electron‐hole pairs, exhibiting much higher photodegradative ability for methylene blue and rhodamine B than the pure NMTO. The best weight concentrations of Ag and Pt are 9.00% and 3.70%, respectively. The electrostatic field is built in the Schottky barrier between NMTO and noble metals, leading to the energy band bending. Then, photogenerated electrons and holes are efficiently separated to enhance the photocatalytic activity.     

Crude Oil Production

Current data on crude oil, field/lease condensate, and natural gas liquids produced from NGL plants. Updated on a monthly basis.     

积分中值屈服准则解析厚板轧制椭圆速度场

为解决非线性Mises比塑性功率积分困难以及由此导致的轧制功率解析式难以获得的问题,本文通过建立并利用线性比塑性功率表达式对提出的椭圆速度场进行能量分析,得到了轧制力能参数的解析解.文中通过对变角度屈服函数求积分中值,构建了一个新的屈服准则,它是主应力分量的线性组合,在π平面上的轨迹是逼近Mises圆的等边非等角的十二边形,其基于Lode参数表达式的理论结果也与实验数据吻合较好.同时,根据厚板轧制时金属流动速度从入口到出口逐渐增大的特点,提出了水平速度分量满足椭圆方程的速度场,该速度场满足运动许可条件.通过相应的轧制能量分析,获得了基于线性屈服准则的内部变形功率以及基于应变矢量内积法上的摩擦功率与剪切功率.在此之上,通过泛函的极值变分导出了轧制力矩、轧制力以及应力状态系数的解析解,并与现场实测数据进行了对比,结果表明利用本文提出的屈服准则与速度场所建立的轧制力矩与轧制力模型与实测值吻合较好,其中轧制力误差小于5.3%,轧制力矩误差在6%左右.     

Thermal and hydraulic characteristics of a large-scaled parabolic trough solar field (PTSF) under cloud passages

To better understand the characteristics of a large-scaled parabolic trough solar field (PTSF) under cloud passages, a novel method which combines a closed-loop thermal hydraulic model (CLTHM) and cloud vector (CV) is developed. Besides, the CLTHM is established and validated based on a pilot plant. Moreover, some key parameters which are used to characterize a typical PTSF and CV are presented for further simulation. Furthermore, two sets of results simulated by the CLTHM are compared and discussed. One set deals with cloud passages by the CV, while the other by the traditionally distributed weather stations (DWSs). Because of considering the solar irradiance distribution in a more detailed and realistically way, compared with the distributed weather station (DWS) simulation, all essential parameters, such as the total flowrate, flow distribution, outlet temperature, thermal and exergetic efficiency, and exergetic destruction tend to be more precise and smoother in the CV simulation. For example, for the runner outlet temperature, which is the most crucial parameter for a running PTSF, the maximum relative error reaches −15% in the comparison. In addition, the mechanism of thermal and hydraulic unbalance caused by cloud passages are explained based on the simulation.     

机械密封腔流场内粒子对密封腔壁面及波纹管冲蚀分析

为研究机械密封腔内混有固体颗粒的流体,在复杂工况下对密封腔壁面及波纹管表面冲蚀的影响,以CFD理论及方法,采用k-ε湍流模型和离散项DPM模型,对固液混合流场进行模拟分析,获得密封腔内流体中介质作用下密封腔壁面及波纹管外表面的压力场分布,分析不同工作状态下固体颗粒作用下密封腔内壁和波纹管外表面的冲蚀区域分布、固体颗粒在流场中的运动轨迹,以及机械密封工作过程中流场内固体颗粒的逃逸量、运动状态的变化。结果表明:粒子主要受颗粒阻力、浮重力、压力梯度力及波纹管和密封腔表面反作用力的影响;在旋转流场中,粒子作与旋转方向一致的螺旋方式前进;无转速时,冲蚀多发生在靠近入口处的波纹管外表面,旋转流场中,冲蚀多发生在密封腔靠后位置的壁面;随着转速增加,粒子逃逸率下降。研究结论为机械密封腔的设计布局及机械密封装置的优化提供理论依据。     

相场法模拟GaAs衬底上InGaAs异质结表面形貌

本工作采用相场法模拟GaAs衬底上生长的In_(0.3)Ga_(0.7)As多层异质结构薄膜表面。通过引入多序参量,使用半隐性傅里叶谱方法求解Cahn-Hilliard方程可以求得带缓冲层结构的薄膜表面形貌。计算结果模拟了薄膜生长过程,研究显示,使用In0.15-Ga0.85As缓冲层,厚度从1nm增加到4nm,薄膜表面临界波长从34nm提升到80nm。随着缓冲层的厚度从1nm增加到10nm,使用正弦波表面的模拟结果显示,薄膜表面粗糙度从2.87nm下降到0.43nm,随机叠加波表面的模拟结果也类似,表面粗糙度从1.21nm下降到0.18nm。热力学分析和应变分布分析可以解释缓冲层对薄膜表面形貌演化的作用。该模拟计算方式对设计缓冲层结构有很大的帮助,模拟计算的结果可以与实验相比对。