Differences between oculomotor and perceptual artifacts for temporally limited head mounted displays

We used perceptual and oculomotor measures to understand the negative impacts of low (phantom array) and high (motion blur) duty cycles with a high‐speed, AR‐likehead‐mounted display prototype. We observed large intersubject variability for the detection of phantom array artifacts but a highly consistent and systematic effect on saccadic eye movement targeting during low duty cycle presentations. This adverse effect on saccade endpoints was also related to an increased error rate in a perceptual discrimination task, showing a direct effect of display duty cycle on the perceptual quality. For high duty cycles, the probability of detecting motion blur increased during head movements, and this effect was elevated at lower refresh rates. We did not find an impact of the temporal display characteristics on compensatory eye movements during head motion (e.g., VOR). Together, our results allow us to quantify the tradeoff of different negative spatiotemporal impacts of user movements and make subsequent recommendations for optimized temporal HMD parameters.     

纵轴式掘进机截割头载荷影响因素的仿真分析

针对现有掘进机截割头载荷特性研究方法采用单一影响因素不能全面反映截割头载荷及其波动变化规律的问题,通过分析截割头瞬时载荷,确定了纵轴式掘进机在水平截割工况下截割头载荷的主要影响因素有截割岩石特性、截割头掏槽深度、截割头吃刀深度、截割头转速和截割臂摆速。针对某纵轴式掘进机水平截割工况,采用Matlab对影响截割头载荷的多种因素进行仿真分析,得到了各向载荷及其波动随各因素的变化规律:截割头载荷随着岩壁普氏系数的增大而增加,其中横向阻力增加尤为明显,横向阻力波动程度高于其他方向载荷,且随着岩壁普氏系数的增大呈减小趋势;随着截割头掏槽深度的增加,截割头各向载荷近似呈线性增加,其中升力增加幅度最大,各向载荷波动则随着截割头掏槽深度的增大而减小;随着吃刀深度的增加,截割头载荷总体呈增大趋势,载荷波动程度则随之减小;在截割头转速一定的情况下,截割头载荷均随着截割臂摆速的增加而增大,在同一摆速下,截割头载荷随着截割头转速的减小而增大,横向阻力波动明显高于升力和推进阻力波动,横向阻力和推进阻力波动按截割头载荷规律变化,升力波动则与之相反。截割头载荷波动变化规律与截割头载荷变化规律不尽一致,有时甚至相互冲突。因此,掘进机作业过程中应合理选择截割头掏槽深度、吃刀深度等操作参数和截割头转速、截割臂摆速等运动参数,使各参数相互匹配,以减小掘进机振动,延长使用寿命。     

Role of Cyclooxygenase-2 in Head and Neck Tumorigenesis

The cyclooxygenase-2 (COX-2) is a potent enzyme that converts arachidonic acid to prostaglandins (PG), including PGE2, a key mediator of inflammation and angiogenesis. Importantly, COX-2 is activated in response to inflammatory stimuli, where it is also believed to promote the development and progression of head and neck cancers (HNC). COX-2 can mediate its protumorigenic effect through various mechanisms, such as inducing cell proliferation, inhibition of apoptosis, and suppressing the host’s immune response. Furthermore, COX-2 can induce the production of vascular endothelial growth factors, hence, promoting angiogenesis. Indeed, the ability of COX-2 inhibitors to selectively restrict the proliferation of tumor cells and mediating apoptosis provides promising therapeutic targets for cancer patients. Thus, in this comprehensive review, we summarized the reported differential expression patterns of COX-2 in different stages of head and neck carcinogenesis—from potentially premalignant lesions to invasive carcinomas. Furthermore, we examined the available meta-analysis evidence for COX-2 role in the carcinogenesis of HNC. Finally, further understanding of the biological processes of COX-2 and its role in orchestrating cell proliferation, apoptosis, and angiogenesis may give therapeutically beneficial insight to develop the management plan of HNC patients and improve their clinical outcomes.     

浅谈液压夹具在转向油缸铸造缸盖加工上的应用

随着液压夹具在机械加工中运用推广,该公司引用液压夹具多年来取得一定成效,文章针对转向油缸的铸造缸盖铣、钻序前后加工工装进行对比分析,重点突出应用全自动液压夹具后可提升装夹效率、加工质量以及降低劳动强度等,可以在不添置设备的情况下,满足产能提升的需求。     

压水堆核电厂压力容器开盖时刻主冷却剂放射性浓度控制要求研究

压水堆核电厂停堆开盖时刻主冷却剂放射性浓度限值是核电厂的重要设计参数。本文基于停堆开盖后厂内辐射风险来源分析,建立了适用于压水堆核电厂停堆压力容器开盖时刻主冷却剂中的放射性浓度控制值评估方法,并采用欧洲第三代压水堆技术方案(EPR)堆型核电厂的设计参数对建立的方法进行了验证。验证结果表明:基于此方法得出的停堆开盖限值与EPR堆型核电厂原设计较接近。     

Study of new flow field geometries to enhance water redistribution and pressure head losses reduction within PEM fuel cell

Efficiency of fuel cell is dependent on reactant distribution, products evacuation, pressure losses and many of these factors is dependent on the design of flow field plate. With an effective design, reactant distribution, pressure drop, and water and heat management can be further improved. In this work, two new designs, as multi-serpentine set-up with additional slots and hybrid geometry, on stainless steel bipolar plates, are presented. Electrical performance, and pressure head losses are analyzed by electrochemical methods such as polarization curve and use of electrochemical noise as a diagnostic tool to further understand the impact of water management on performance. On the one hand, multi-serpentine design shows the best electrical performance with an increase of 0.2 V (66%) at 0.9 A/cm² in comparison of traditional serpentine design. On the other hand, hybrid design reveals the lowest pressure head losses, with a decrease of 2 mbar (about 50%) in comparison of traditional serpentine design, and a higher stability with time that can be useful to downsize compressor and provide lower impact on fuel cell stack durability.     

低压燃气喷射低速双燃料发动机缸盖优化

以二冲程双燃料发动机缸盖为研究对象,建立计算模型,采用温度场试验数据来标定计算模型边界条件;并使用热机耦合分析模型,研究不同的缸盖设计方案,如冷却孔和喷油孔位置布置,缸盖法兰厚度对缸盖应力分布的影响。研究结果表明,缸盖双层冷却孔设计可改善冷却孔的应力分布,但改善效果不明显;增加缸盖法兰厚度可明显改善缸盖上层的应力分布状况,而对缸盖下层应力分布不利,但是不利影响较小。这为后续缸盖的设计优化提供了方向。     

基于ANSYS及加速寿命试验台对油缸单耳环活塞杆杆头断裂进行设计改进

该文对某工程机械油缸单耳环活塞杆杆头断裂进行失效分析,提出了在毛坯锻造工艺满足设计要求的条件下,单耳环活塞杆杆头变截面处应力集中导致残余应力过大,是单耳环活塞杆杆头断裂的主要原因。从这方面出发,优化了单耳环活塞杆杆头变截面处的残余应力,通过ANSYS软件对优化后的结构进行应力分析,并用油缸加速寿命可靠性试验台做2F台架实验和整机多批次小批量试装来验证改进措施的有效性,最终提高了油缸单耳环活塞杆杆头在极限工况下抗疲劳的强度。     

基于ABAQUS的发动机缸盖工装强度分析

分析计算某型号发动机缸盖及工装的应力与局部位移,基于HyperMesh软件建立缸盖及工装的仿真模型,使用ABAQUS软件进行静力学计算,对处于夹紧状态下的发动机缸盖进行4个典型工位的加工工况分析计算,得出工件加工位置最大位移与工装所受最大应力。通过强度和位移校核,最终结果满足缸盖的加工需求,为工艺制定提供了有效的数据支持。     

Design and analysis of a class of redundant collaborative manipulators with 2D large rotational angles

The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers. This paper focuses on designing a class of 2R1T (R: Rotation; T: Translation) parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension (2D) large rotational angles. In order to construct 2D rotational degrees of freedom (DOFs), a platform with 2D revolute joints is proposed first. Based on the constraint screw theory, the feasible limbs that can be connected in the platform are synthesized. In order to provide constant rotational axis for the platform, a class of redundant limbs are designed. A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion. The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform. The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed. The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.