Measurements of Photon Mass Attenuation Coefficients for Ge and BGO Crystals at 10 Me V

The photon mass attenuation coefficients of the important materials for γ-ray detection, Ge and BGO (Bi₄Ge₃O₁₂) crystals, have been measured for 10.0 MeV γ-rays. The measurement system using the laser-Compton backscattering γ-rays and the high-resolution high-energy photon spectrometer has been developed and utilized. The effectiveness of the system achieving the total systematic uncertainties of 0.5% for the measurements of the photon mass attenuation coefficients was demonstrated. It was shown that the measured photon mass attenuation coefficients, 318.1 ± 1.7 [cm²/g] for the Ge crystal and 425.2 ± 2.4 [cm²/g] for the BGO crystal, agree within the achieved experimental uncertainties with the evaluated values including atomic and nuclear processes at 10.0 MeV.     

山溪坝后式取水及明渠弯道除沙方式研究

随着我国水利水电工程建设的发展,水电站分布越来越集中于偏远山区,供水系统往往需自行建设。为了解决工程建设施工及生活用水问题,通常是将工程附近水源水质较好的山溪作为取水点,并经简单沉沙处理后投入使用。传统的坝前式山溪取水及大型沉沙池除沙普遍面临着汛期取水头部易被泥石流淤积、山溪内施工部位狭窄等问题,根据弯道环流原理,结合杨房沟水电站供水系统取水头部设计及运行使用经验,研究验证了坝后式取水代替传统的坝前式取水,以及明渠除沙代替大型沉沙池除沙方式的实际效果。实践表明,新的取水方式可以满足抗淤能力强、施工占地少,同时除沙能力理想的要求,可为今后类似情况下山溪取水及除沙方式的选择提供参考。     

Carrying and spine loading

The advantages and disadvantages of different methods of carrying objects on spine loading are still not fully understood. Previous studies have either examined the effects of carrying using physiological measures or examined isolated spine segments using biomechanical models. Additionally, most studies have been restricted to only a small number of carrying conditions. Very few studies have attempted to examine the various factors influencing spine loading together. To improve understanding of interacting factors on carrying, this study assessed the lumbar spine loads of 16 subjects as they assumed six styles of carrying at two weight levels and two activity levels (walking vs. standing). Concurrent with each trial, a subject-specific biomechanical model was used to assess spine forces over the full lumbar spine. Most carrying methods in the trials resulted in relatively low levels of spine loading. Anterior/posterior (A/P) shear loading was the only spine-loading dimension that reached biomechanically meaningful levels. Two carrying conditions, with bins carried in front of the body, significantly increased A/P shear compared with other carrying styles. This increase appeared to be due to the greater moment arms occurring in these conditions. Many of the other carrying styles produced A/P shears that were similar to those observed when carrying nothing at all. Of all the tasks, the backpack carry characteristically produced especially low spine loads. The findings of the study suggest that to achieve optimal carrying in terms of spine loading, loads should be positioned close to the body, even when carrying relatively light loads.     

MDS800-60双吸泵的研制与开发

根据辽源泵业公司现有泵型及技术力量在MD580-60泵的基础上对吸水段和首级叶轮进行设计改造,开发出一种新产品MD580-60双吸泵,以扩大市场竞争力。     

Research to reality: a critical review of the validity of various criteria for the prevention of occupationally induced low back pain disability

Criteria have been suggested to reduce the incidence, or severity of low back pain disability. Five underlying theories for such criteria have been identified in the literature, and a critical review of the validity of these criteria has been carried out. Despite attributions elsewhere, peer-reviewed validation of the various criteria range from modest to nil. The need for a validation criterion for use in workplace design in order to reduce low back pain disability, or severity, is identified and the need for an international protocol to allow cross-study validation of present and future criteria is suggested.     

Fault‐tolerant control using command‐filtered adaptive back‐stepping technique: Application to hypersonic longitudinal flight dynamics

In this paper, the adaptive back‐stepping controller is investigated for a class of strict‐feedback systems using the command filter technique. Adaptive laws are designed for updating the controller parameters when both the plant parameters and actuator‐failure parameters are unknown. Furthermore, the auxiliary dynamics is developed to deal with the input constraints. Closed‐loop stability and asymptotic‐state tracking are ensured. The method is applied to the longitudinal dynamics of a generic hypersonic aircraft in the presence of actuator faults and input constraints. Based on the parameter estimation, the command‐filtered adaptive back‐stepping control is presented. Simulation results on the control‐oriented model show that the proposed approach achieves good tracking performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Hamstring stretching significantly changes the sitting biomechanics

The tightened hamstring connecting the tibia to the pelvis provides more posterior pelvic tilting and consequent backward curvature of the sacral and lumbar vertebrae. Therefore, the study goal was to quantitatively investigate the effect of hamstring and low back stretching on the trunk biomechanics in a system-level perspective. Twelve healthy subjects performed two stretching interventions (hamstring only (HS); hamstring + low back (HLS)) for 40 s on two separate days. They sat on a stool before and after the intervention while capturing trunk kinematics and EMG. In addition, the lumbar flexion angle at which the L4 paraspinals deactivate (i.e., flexion-relaxation phenomenon; FRP) was monitored while trunk flexion-extension trials, performed before and after the protocol. The FRP onset angle was captured to verify the biomechanical changes in the lower extremity and trunk systems. In the results, the stretching intervention significantly increased the reaching distance by 6.3 cm in the sit-and-reach test performed immediately before and after the intervention. The flexible hamstring improved the lumbar flexion angle and head postures in both the HS and HLS. However, the HLS induced laxity in lumbar passive tissues, as confirmed by changes in the FRP, and significantly increased co-activation in the low back. The stress-relaxation of the hamstring and surrounding passive tissues could help to maintain better lumbar flexion angle (i.e., lumbar lordosis) while sitting. Periodic HS for 40 s without any significant lumbar flexion may be recommendable for office workers who sit for long periods.     

异型铆钉冲模前、后模的电火花加工

电火花加工在民用,国防生产部门和科学研究、模具生产中已经获得了广泛应用。分析了一种异型铆钉冲模前、后模的结构特点,采用电火花来加工此零件。在加工此零件时,通过采用合理的粗、精加工放电参数,保证了零件的加工质量并提高了加工效率。     

ERRORS IN THE PERCEPTION OP RAILWAY SIGNALS

This paper is based upon observations of train drivers at work, and defines certain kinds of errors which may be made by drivers in perceiving railway signals. It discusses hypotheses relating incidence of error to various factors. It is suggested that the investigation of hypotheses of this kind, derived from the observation of the normal performance of the operative, is a valid method of accident study.     

Participation in workplace design with reference to low back pain: a case for the improvement of the police patrol car

Thirty Canadian police officers, divided into six groups, participated in the redesign of the interior of the patrol car. Three of the groups consisted of individuals having a history of low back disease. The effect of participating in a design process on the characteristics of the final design and on the perception of the low back pain was studied in a semi-experimental setting. The participants developed a strong commitment to the participatory design process, which was reflected in their productions. The differences between participants with and without a history of a low back disease was not marked. The former tended to stress posture-related elements in their analysis and design.