Driving performance and road sign identification by multifocal contact lens wearers in a driving simulator

PurposeThe purpose of this study was to compare sign identification distances and driving performance metrics in presbyopic participants while wearing multifocal contact lenses (MFCL) and while wearing progressive addition lens (PAL) spectacles.Methods19 presbyopic participants completed PAL spectacle assessments and contact lens fitting and follow up visits before driving assessments began. These assessments occurred in a simulator equipped with a full-sized sedan on a motion platform and a 260 degree screen. Participants completed the driving task with PAL and with MFCL. Participants followed a lead car and identified signs at various distances from the road. For the two wearing conditions, comparisons of the distance along the road at which signs were identified were made using repeated measures ANOVA. Paired t-tests were used to compare driving performance for the two conditions.ResultsThere was no statistical difference in sign identification distance between PAL and MFLC for signs 32.0 m from the road side of the road (182 ± 46 m for MFCL; 205 ± 45 m for PAL; P = 0.07) or 51.4 m from the side of the road (204 ± 43 m for MFCL; 216 ± 36 m for PAL; P = 0.3). Only signs 70.2 m from the roadside showed a significant difference (207 ± 42 m with MFCL; 232 ± 39 m with PAL; P = 0.01), All distances were greater than those required to safely stop a vehicle. There were no significant differences in the driving performance metrics between the refractive corrections.ConclusionDriving performance metrics were similar for MFCL and PAL spectacles. Sign identification distances with both eyewear types were well within the distances required for safe vehicle stopping.     

微通道板表面羟基化工艺研究北大核心

研究了3种微通道板基底羟基化的方法,测量了羟基化处理后微通道板基底表面水接触角及通道端面的形貌变化,分析了各种方法中微通道板基底的亲水性和腐蚀情况。实验结果表明:氨水双氧水溶液对基体表面的亲水性能提升不大,NaOH溶液对基体有腐蚀作用,经食人鱼溶液处理的基体表面亲水性明显提高且无腐蚀作用。研究了微通道板在食人鱼溶液中的浸泡时间和浸泡温度对表面亲水性的影响。结果表明:随着浸泡温度的增加,微通道板表面水接触角先减小后增大,当温度为80℃时达到极小值,浸泡时间对微通道板表面的亲水性影响不大。最终确定了微通道板表面羟基化工艺:浸泡温度为80℃,静置时间为20~60 min。     

Theoretical investigation of intrinsic point defects and the oxygen migration behavior in rare earth hafnates

In this work, the composition-dependent point defect types and formation energies of RE₂Hf₂O₇ (RE = La, Ce, Pr, Nd, Pm, Sm, Eu and Gd) as well as the oxygen diffusion behavior are systematically investigated by first-principles calculations. The possible defect reactions and dominant defect complexes under stoichiometric and non-stoichiometric conditions are revealed. It is found that O Frenkel pairs are the predominant defect in stoichiometric pyrochlore hafnates. Hf-RE cation anti-site defects, accompanied by RE vacancies and/or oxygen interstitials, are stable in the non-stoichiometric case of HfO₂ excess. On the other hand, RE-Hf anti-site defects together with oxygen vacancies and/or RE interstitials are preferable in the case of RE₂O₃ excess. The energy barriers for the migration along the V_O48f - V_O48f pathway of pyrochlore hafnates were calculated to be between 0.81 eV and 0.89 eV. Based on these results, a defect engineering strategy is proposed and the pyrochlore hafnates investigated here are predicted to exhibit potential oxygen ionic conductivity.     

Analytical modeling of complex contact behavior between rock mass and lining structure

Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact modes are classified into dense contact, local non-contact, and loose contact. Subsequently, the corresponding mechanical model for each contact mode is developed according to its mechanical characteristics using the complex variable method. In the proposed mechanical model, a special algorithm is introduced to detect whether the local non-contact zone is re-contacted. Besides, a novel conformal mapping method is also proposed to accurately calculate the mechanical response of the concrete lining. Finally, the accuracy of the proposed method is verified by comparing it with the finite element method (FEM). Several parameter investigations are conducted to analyze the effects of different contact modes on the rock–lining interaction. The results show that: (i) the height of the local non-contact area does not have a significant effect on the contact stress distribution if no re-contact occurs; (ii) backfill grouting can reduce the local stress concentration caused by poor contact modes; and (iii) reducing the friction coefficient of the interface can lead to a more uniform distribution of internal forces in the concrete lining.     

接触器触头系统振动机理分析及算法优化

为了解决合闸过程中动、静触头接触引起的振动弹跳问题.本文建立了接触系统的二自由度运动微分方程,并利用遗传算法对交流接触器吸合过程进行优化,同时通过高速摄影实验对接触弹跳的全过程进行了观察和分析.结果表明:理论与实验结果高度一致,铁心在触头分离前发生碰撞,进一步加剧触头弹跳;铁芯弹跳再次碰撞时,触头的弹跳不受影响;在接触器运行过程中,动铁芯的运动会引起系统轻微振动;采用遗传算法优化的接触器触头弹跳时间和最大振幅均减小.研究结果为进一步控制和减小接触弹跳提供了理论依据.     

径向弹簧蓄能密封结构最大接触应力的有限元分析

为研究径向弹簧蓄能密封结构的密封特性，针对典型径向弹簧蓄能密封结构，分析其密封机制以及O形弯曲金属螺旋弹簧的弹性特性；采用ANSYS有限元分析软件，建立典型弹簧蓄能密封结构的非线性有限元分析模型，对弹簧蓄能密封圈在不同压缩率、不同介质压力下的接触应力进行分析，研究在多种工况下最大接触应力的变化情况。结果表明：压缩率保持不变时，最大接触应力随着介质压力的增大而增大；介质压力保持不变时，随着压缩率的增大，最大接触应力先增大再减小。对压缩率、介质压力与最大接触应力的关系进行曲线拟合，可用于指导弹簧蓄能密封结构的精确设计。     

基于有限元仿真的发泡硅橡胶老化规律研究

通过力学性能测试得到发泡硅橡胶应力应变曲线,结合Ogden(Foam) 3阶超弹本构模型,建立发泡硅橡胶静密封系统的有限元仿真模型,得到大压缩量下发泡硅橡胶的von Mises应力及接触压力分布情况。仿真结果表明:大压缩量下发泡硅橡胶对称中心线位置的von Mises应力、接触压力值较大,在橡胶边缘和靠近限位环处接触应力数值有突增。开展140℃热空气老化试验,测定老化后发泡硅橡胶应力应变曲线,结合有限元仿真模型分析发泡硅橡胶老化后von Mises应力、接触压力的变化规律。结果表明:经过热空气老化后,在一定载荷下发泡硅橡胶等效应力和接触压力均呈增大的趋势。     

CFD modeling of thermal contact resistance between solid contacting surfaces

Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft, and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance (TCR) is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of TCR in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, inverse problem method solution is utilized as a proper method for estimation of TCR value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of TCR. A comparison between the measured values and obtained values from the simulation show the errors for flat-flat, flat-cylinder, and cylinder-cylinder configuration after 10 min from starting the experiment are 4.6074%, 0.1662%, and 0.5622%, respectively. And in steady-state condition, the corresponding errors are 6.06e-3%, 1.506%, and 0.846%, respectively. In conclusion, the final results establish the fact that the inverse problem method solution can predict TCR values between contacting surfaces.     

Droplet behaviors on inclined surfaces with dynamic contact angle

Dynamic contact angle (DCA) is of crucial importance in the numerical investigation of water management problems in proton exchange membrane fuel cells (PEMFCs). In order to well predict the gas-liquid two-phase flow in the complex flow field in PEMFCs, first, it is very critical to build a robust DCA model that is capable of simulating droplet behaviors on a single surface under various conditions. In our previous research work, an advancing-receding DCA (AR-DCA) model is developed and has been successfully validated against a series of experiments from the available literature for droplet impact on surfaces. In this study, the AR-DCA model is further applied to simulate droplet behaviors on inclined surfaces with different droplet impact velocities, impact angles and viscosities. It is found that the droplet spreading and deformation from the simulations have excellent agreement with those captured in the corresponding experiments. The results also indicate that higher impact velocity and impact angle can facilitate the spreading trend at the droplet trailing edge and have no notable effects on the leading edge. In addition, the increase of droplet viscosity leads to a transition from droplet deposition phenomenon to partial rebound on the surface.     

Analysis of P. aeruginosa disinfectant sensitivity and microbial adhesions to worn cosmetic contact lenses

PurposeTo compare the sensitivity of two genotypes of P. aeruginosa to various disinfectant solutions and analyze the attached bacteria on worn cosmetic contact lenses (cosCLs).MethodsIn this prospective study, healthy volunteers wore etafilcon (brown), nelfilcon (gray), or hilafilcon (black) cosCLs and microbial adhesion analysis was performed. A rub-off test determined pigment dislodgement. Disinfectant sensitivity to Optifree Replenish (Alcon), Optifree Pure Moist (Alcon), Renu Fresh (Bausch & Lomb), and AoSept Plus (Ciba Vision) was tested at various disinfection times and compared between various genotypes and Type III secretion (T3S) system mutants.ResultsOf the 1152 cosCLs collected, 364 were culture positive (32%). The highest rate of culture-positive lens was hilafilcon (chi square, P = 0.0001). Hilafilcon also had a significantly greater number of isolates than etafilcon (P < 0.0001). Hilafilcon was the only lens to fail the rub-off test. Cytotoxic strains were significant more resistant to Renu Fresh than were invasive strains, even at 100% of recommended disinfection time (P = 0.0005). Of the tested disinfectants, Renu Fresh was significantly less effective in killing both genotypes of P. aeruginosa compared to AoSept Plus at all time points (25%, 50%, 75%, and 100% recommended disinfection time, P = 0.0001, 0.0001, 0.0005, and 0.0005, respectively). When the T3S system was dysfunctional, mutant strains were all susceptible to disinfectants (P = 0.0001 for both invasive and cytotoxic strains).ConclusionPseudomonas species is commonly found on cosCLs of asymptomatic individuals. Wearers of cosCLs that dislodge pigments may be predisposed to microbial contamination. Cytotoxic strains are more resistant to disinfectant solutions, especially to Renu Fresh. P. aeruginosa disinfectant resistance requires a functional T3S system.