Naturalistic data collection of head posture during smartphone use

Association between smartphone use and head-down tilt posture has not yet been quantitatively evaluated in natural settings. This study aimed to objectively assess the angle and duration of head-down tilt posture of smartphone users during a typical working day via naturalistic data collection. Thirty-one college students conducted their typical school activities while their head posture and smartphone-app usage records were collected simultaneously for 8?hours. Participants spent 125.9?minutes (median usage duration) on their smartphones with significantly larger head-down tilt (p?<?.05) than when they were not using the phone. Head tilt angle greater than 30° was found to be more common when using the phone, while head tilt less than 20° was more common when they were not using the phone. Study findings provide empirical evidence that supports an association between the duration of smartphone use and the intensity of head-down tilt posture.

Practitioner Summary: Head postures of young smartphone users were quantified for 8?hours continuously during a typical workday using a wearable sensor. Participants spent more time in larger head-down tilt postures (greater than 30°) when they were using their smartphones as compared to when they were not using them.     

一种外LET柔顺半铰的动力学建模与分析

对一种外LET柔顺半铰进行建模与动力学特性分析。采用斜率不连续的绝对节点坐标法（ANCF）建立了该柔顺半铰系统动力学方程；对外力作用下半铰中心线和外轮廓的运动变形进行仿真，与实验结果对比，证明了绝对节点坐标法对柔顺半铰动力学建模的有效性；进一步分析了半铰外形尺寸变化对其变形规律的影响。     

α-Stirling hydrogen engines for concentrated solar power

α-Stirling engines are receiving more and more attention for applications of concentrated solar power in small power installations (15–30 kW). The design of these engines has not experienced in recent years the breakthrough needed to deliver close to the Carnot Cycle energy conversion efficiencies. The delivered efficiencies are limited to mid-to-high 20% in the typical installations “Dish Stirling”. Here we review the latest studies made on α-Stirling engines, unfortunately mostly based on theoretical models of limited reliability, but also including very few examples of Computer-Aided Engineering (CAE) modeling followed by prototyping and testing. Finally, we present in detail one CAE model of an α-Stirling engine delivering energy conversion efficiencies of 42% with hydrogen as working fluid and adopting one hot cylinder, one cold cylinder, and one regenerator, with the hot fluid temperature of 800 °C. This efficiency is much higher than current air microturbines, which may deliver efficiencies of only about 20% working at much lower temperatures.     

A series of Er~(3+)-activated SrLaGa_3O_7 single crystal fibers for mid-infrared laser application

A multidisciplinary approach for the production and characterization of a series of high concentration Er~(3+)activated SrLaGa_3 O_7(abbreviated as Er:SLGO) crystal fibers is shown to have a great promise for implementation in mid-infrared laser applications.The current approach includes the design and formation of unique layered tetrahedral network structures with several kinds of rare earth(RE) ions including Er ions distributing statistically between layers,such as Er:SLGO,Er,Nd:SLGO,Er,Yb,Ho:SLGO,Er,Eu:SLGO and Er,Ho:SLGO.Five kinds of Er:SLGO crystal fibers were designed to grow via a micropulling down method.Spectroscopic analyses show that Er,Yb,Ho:SLGO and Nd,Er:SLGO crystal fibers were superiorly endowed with inhomogeneous broadening absorption and strong emission.The unique structural components design enables the generation of improved absorption and emission recombination,and the inhibition of self-termination as well.Generally,the use of structural components design may warrant high-efficiency emissions in RE-doped crystal fibers.     

模拟水环境下的压紧弹簧刚度试验及计算模型的研究

在模拟水环境下，对堆内构件压紧弹簧的缩比试样进行了刚度试验，并与有限元模拟、基于小扰度理论模型和大扰度随动模型的分析结果进行比较分析。结果表明，当摩擦系数按文献实验测值0.189取值时，有限元模拟、基于小扰度的理论模型和大扰度随动模型计算所得的刚度值均与试验所得的相近；卸载稳定段的刚度均明显小于加载稳定段的，是加载时的0.6倍左右。有限元模拟分析进一步阐明，在压紧弹簧变形过程中，压紧弹簧的截面存在转动，它与垫板之间的接触点并不是固定的，在加载和卸载过程中存在来回的径向位移。并且压紧弹簧接触面上的摩擦力方向是相反的，使得压紧弹簧在加载和卸载过程的刚度存在较大的差别。较小扰度理论模型、考虑压紧弹簧截面转动和接触点径向位移的大扰度随动模型所得的结果与有限元模拟更为接近。      

How platinum oxide affects the degradation analysis of PEM fuel cell cathodes

In this work, proton exchange membrane fuel cell cathodes are degraded with accelerated-stress-tests.These PtCo containing cathodes are analyzed at begin-of-life and end-of-test with a dedicated diagnostic procedure. For every individual load point, the oxygen transport resistance and voltage losses due to the formation of platinum oxides were obtained in addition to commonly measured electrochemical surface area, high frequency resistance, as well as cathode ionomer resistance. These data were used to break down the voltage losses into six different contributors. With this break down, performance gains and performance losses were determined at end-of-test. At low current densities, it was found that voltage losses due to degradation are dominated by the loss of specific activity and catalyst surface area - in line with the state-of-the-art knowledge. But by quantifying the losses from platinum oxide formation explicitly, we show that end-of-test an unassigned voltage loss is not only present at highest current densities, but already at low current density. More precisely, the unassigned voltage loss shows a linear increase with decreasing half cell voltage and is independent from the chosen accelerated stress test. As this unassigned loss depends on half cell voltage, it might arise from ionomer adsorption.     

双翻斗式雨量传感器自动调节检定系统设计

为解决超差双翻斗式雨量传感器在检定校准时精细定量调测问题,尤其针对：在大小雨强(4mm/min和1mm/min)测试时超差值为一正一负,目前只能通过目测观察法并依靠经验对容量调节螺母和定位螺母进行调节,这存在着一定的盲目性并且成功率低。提出了一套检定流程并利用红外光电传感器和步进电机模块,实现了上翻斗和计量翻斗的左右斗的翻动数据的定量测量以及定位螺母和容量调节螺母的自动调节,并且可自动记录和上传检定数据到上位机。结果表明：本系统能有效地判定和解决翻斗翻动平衡和协调性问题,并可为业务人员积累检定数据以便后续分析处理。     

Effect of expander shape on cooling characteristics by using a model pulse tube refrigerator

Pulse tube refrigerators do not have moving parts in the cold section, and they have low vibration, high reliability, and long life. The expander in refrigerators typically has an inverted U or coaxial shape because this attains a wider absorber area, lower height, and compactness. However, the performance of a Stirling-type pulse tube refrigerator is inferior to that of a Stirling refrigerator. Cooling characteristics of the pulse tube refrigerator greatly depend on the shape of the expander. In this study, an inertance-type refrigerator, which uses ambient air for the working gas, was developed to examine the effect of expander shape. This refrigerator model with changeable expander operated with a Stirling cycle, and it was composed of a reciprocating compressor, after-cooler, regenerator, absorber, pulse tube, hot-end, and inertance tube with reservoir. The following expander shapes were tested: in-line, L shape, L-L shape, and coaxial shape. The effect of expander shape on cooling capacity was examined experimentally and numerically using the model pulse tube refrigerator. The results of experiments showed that the L shape expander had the highest performance and the coaxial expander had the lowest performance. In addition, the characteristics of the gas flow in each expander were confirmed by fluid dynamics analysis.     

平面设计中视觉与触觉的审美构建

目的探索视觉与触觉在平面设计中的多元化呈现及应用路径。方法立足于平面设计中的审美与功能的双向视角,从视觉与触觉对平面设计的艺术潜力与价值进行挖掘,总结两者在平面设计中必须遵循的秩序性、冲击感和功能性三大原则,并在此基础上深度探寻应用领域,总结两者共同作用下的平面设计在合理构图、色彩搭配、材质升级、强化交互等方面的创新与突破,展示其中的典型案例,总结更高层面的审美价值的表达与创作。结论良好的触觉感知及视觉冲击在平面设计的发展壮大过程中发挥着重要作用,在有效提升平面设计水平的基础上,深度挖掘出平面设计本身的情趣,最大限度地满足了人们的审美需求,也找到了彼此融合与发展的共促路径。     

Heat transfer analysis for particle–fluid suspension thermomagnetohydrodynamic peristaltic flow with Darcy–Forchheimer medium

This theoretical analysis explores the effect of heat and mass transfer on particle–fluid suspension for the Rabinowitsch fluid model with the stiffness and dynamic damping effects through Darcy–Brinkman–Forchheimer porous medium. In this study, we also incorporate slip and transverse magnetic field effects. Using low Reynolds number, to neglect inertial forces and to keep the pressure constant during the flow, channel height is used largely as compared with the ratio of length of the wave. A numerical technique is used to solve flow governing system of differential equations. Particular attention is paid to viscous damping force parameter, stiffness parameter, and rigidity parameter; also, the numerical data for thermal profile, momentum, and concentration distribution are presented graphically. Outcomes are deliberated in detail for different fluid models (thinning, thickening, and viscous models). It is found that velocity profile increases for greater values of viscous damping effect and stiffness and rigidity parameter for shear thinning, but conflicting comportment is showed for thickening nature model. Viscous dissipation effects increases the thermal profile for all cases of fluid models. The scope of the present article is valuable in explaining the blood transport dynamics in small vessels while considering the important wall features with chemical reaction characteristics. The current analysis has extensive applications in biomedical engineering field, that is, peristaltic pumps.