EVALUATION OF WHOLE-BODY VIBRATION IN VEHICLES

The vibration in 100 different vehicles has been measured, evaluated and assessed according to British Standard BS 6841 (1987) and International Standard ISO 2631 (1997). Vibration was measured in 14 categories of vehicle including cars, lift trucks, tractors, lorries, vans and buses. In each vehicle, the vibration was measured in five axes: vertical vibration beneath the seat, fore-and-aft, lateral and vertical vibration on the seat pan and fore-and-aft vibration at the backrest. The alternative methods of evaluating the vibration (use of different frequency weightings, different averaging methods, the inclusion of different axes, vibration dose values and equivalent r.m.s. acceleration) as defined in the standards have been compared. BS 6841 (1987) suggests that an equivalent acceleration magnitude is calculated using vibration measured at four locations around the seat (x -, y -, z -seat and x -backrest); ISO 2631 (1997) suggests that vibration is measured in the three translational axes only on the seat pan but only the axis with the most severe vibration is used to assess vibration severity. Assessments made using the procedure defined in ISO 2631 tend to underestimate any risks from exposure to whole-body vibration compared to an evaluation made using the guidelines specified in BS 6841; the measurements indicated that the 17 m/s^1.75 “health guidance caution zone” in ISO 2631 was less likely to be exceeded than the 15 m/s^1.75 “action level” in BS 6841. Consequently, ISO 2631 “allows” appreciably longer daily exposures to whole-body vibration than BS 6841.     

EFFECT OF MUSCLE TENSION ON NON-LINEARITIES IN THE APPARENT MASSES OF SEATED SUBJECTS EXPOSED TO VERTICAL WHOLE-BODY VIBRATION

In subjects exposed to whole-body vibration, the cause of non-linear dynamic characteristics with changes in vibration magnitude is not understood. The effect of muscle tension on the non-linearity in apparent mass has been investigated in this study. Eight seated male subjects were exposed to random and sinusoidal vertical vibration at five magnitudes (0·35-1·4 m/s² r.m.s.). The random vibration was presented for 60 s over the frequency range 2·0-20 Hz; the sinusoidal vibration was presented for 10 s at five frequencies (3·15, 4·0, 5·0, 6·3 and 8·0 Hz). Three sitting conditions were adopted such that, in two conditions, muscle tension in the buttocks and the abdomen was controlled. It was assumed that, in these two conditions, involuntary changes in muscle tension would be minimized. The force and acceleration at the seat surface were used to obtain apparent masses of subjects. With both sinusoidal and random vibration, there was statistical support for the hypothesis that non-linear characteristics were less clear when muscle tension in the buttocks and the abdomen was controlled. With increases in the magnitude of random vibration from 0·35 to 1·4 m/s² r.m.s., the apparent mass resonance frequency decreased from 5·25 to 4·25 Hz with normal muscle tension, from 5·0 to 4·38 Hz with the buttocks muscles tensed, and from 5·13 to 4·5 Hz with the abdominal muscles tensed. Involuntary changes in muscle tension during whole-body vibration may be partly responsible for non-linear biodynamic responses.     

EFFECT OF PHASE ON HUMAN RESPONSES TO VERTICAL WHOLE-BODY VIBRATION AND SHOCK—ANALYTICAL INVESTIGATION

The effect of the “phase” on human responses to vertical whole-body vibration and shock has been investigated analytically using alternative methods of predicting subjective responses (using r.m.s., VDV and various frequency weightings). Two types of phase have been investigated: the effect of the relative phase between two frequency components in the input stimulus, and the phase response of the human body. Continuous vibrations and shocks, based on half-sine and one-and-a-half-sine accelerations, each of which had two frequency components, were used as input stimuli. For the continuous vibrations, an effect of relative phase was found for the vibration dose value (VDV) when the ratio between two frequency components was three: about 12% variation in the VDV of the unweighted acceleration was possible by changing the relative phase. The effect of the phase response of the body represented by frequency weightings was most significant when the frequencies of two sinusoidal components were about 3 and 9 Hz. With shocks, the effect of relative phase was observed for all stimuli used. The variation in the r.m.s. acceleration and in the VDV caused by variations in the relative phase varied between 3 and 100%, depending on the nature of stimulus and the frequency weighting. The phase of the frequency weightings had a different effect on the r.m.s. and the VDV.     

EFFECTS OF POSTURE AND VIBRATION MAGNITUDE ON APPARENT MASS AND PELVIS ROTATION DURING EXPOSURE TO WHOLE-BODY VERTICAL VIBRATION

The effect of variations in posture and vibration magnitude on apparent mass and seat-to-pelvis pitch transmissibility have been studied with vertical random vibration over the frequency range 1·0-20 Hz. Each of 12 subjects was exposed to 27 combinations of three vibration magnitudes (0·2, 1·0 and 2·0m/s² r.m.s.) and nine sitting postures (“upright”, “anterior lean”, “posterior lean”, “kyphotic”, “back-on”, “pelvis support”, “inverted SIT-BAR” (increased pressure beneath ischial tuberosities), “bead cushion” (decreased pressure beneath ischial tuberosities) and “belt” (wearing an elasticated belt)).Peaks in the apparent masses were observed at about 5 and 10 Hz, and in the seat-to-pelvis pitch transmissibilities at about 12 Hz. In all postures, the resonance frequencies in the apparent mass and transmissibility decreased with increased vibration magnitude, indicating a non-linear softening system. There were only small changes in apparent mass or transmissibility with posture, although peaks were lower for the apparent mass in the “kyphotic” posture and were lower for the transmissibility in the “belt” posture. The changes in apparent mass and transmissibility caused by changes in vibration magnitude were greater than the changes caused by variation in posture.     

EFFECTS RELATED TO RANDOM WHOLE-BODY VIBRATION AND POSTURE ON A SUSPENDED SEATWITH AND WITHOUT BACKREST

WBV-exposures are often linked with forced postures as prolonged sitting, bent forward sitting, or sitting without a backrest. No quantitative data are available to describe the exposure-effect relationships for different conditions of seating, posture, and the biological variability of workers. Experiments and subsequent predictions of forces acting within the spine during WBV can help to improve the assessment of the health risk. An experimental study was performed with 39 male subjects sitting on a suspension seat with or with no backrest contact. They were exposed to random whole-body vibration with a weighted r.m.s. value of 0·6 m/s² at a relaxed or a forward bending posture. A two-dimensional finite element model was used for the calculation of the internal spinal load. The model simulates the human response on a suspension driver seat. Individual exposure conditions were considered by including the transfer functions between the seat cushion and the seat base as well as between the backrest and the seat base for the calculation of the vibration input to the buttocks and to the back respectively. The average peak seat transmissibility was higher for the seat with the backrest, but the peak seat-to-head transmissibility was higher for the seat without the backrest for both postures. The peak transmissibilities between the accelerations at the seat base and the compressive forces at L5/S1 were highest for the seat without the backrest during the bending posture. Various biological effects can result from identical exposures combined with different backrest contact and postures. The backrest contact and posture conditions should not be neglected in the assessment of health risk caused by whole-body vibration.     

SURVEY OF TECHNICAL PREVENTATIVE MEASURES TO REDUCE WHOLE-BODY VIBRATION EFFECTS WHEN DESIGNING MOBILE MACHINERY

Engineering solutions to minimize the effects on operators of vibrating mobile machinery can be conveniently grouped into three areas:

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Reduction of vibration at source by improvement of the quality of terrain, careful selection of vehicle or machine, correct loading, proper maintenance, etc.

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Reduction of vibration transmission by incorporating suspension systems (tyres, vehicle suspensions, suspension cab and seat) between the operator and the source of vibration.

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Improvement of cab ergonomics and seat profiles to optimize operator posture. These paper reviews the different techniques and problems linked to categories (2) and (3). According to epidemiological studies, the main health risk with whole-body vibration exposure would appear to be lower back pain. When designing new mobile machinery, all factors which may contribute to back injury should be considered in order to reduce risk. For example, optimized seat suspension is useless if the suspension seat cannot be correctly and easily adjusted to the driver's weight or if the driver is forced to drive in a bent position to avoid his head striking the ceiling due to the spatial requirement of the suspension seat.

     

THE EFFECT OF LATTICE VIBRATION ON THE MAGNETISM IN METALLIC HYDROGEN

In this note, a new approach is adopted to the magnetism in metallic hydrogen, i.e., based on the Kim theory and Stoner model the electron-phonon interaction is introduced into the itinerant electron mag-netism theory. A calculation of spontaneous magnetization of metallic hydrogen at T=0 K shows that in spite of no change in the para- to ferro-magnetism value, r_sc of W-S radius r_s, the spontaneous magnetic moment of electron in ferromagnetic state, where r_s>>r_sc, is considerably reduced by lattice vibrations.     

MYOELECTRIC RESPONSE OF BACK MUSCLES TO VERTICAL RANDOM WHOLE-BODY VIBRATION WITH DIFFERENT MAGNITUDES AT DIFFERENT POSTURES

Back muscle forces contribute essentially to the whole-body vibration-induced spinal load. The electromyogram (EMG) can help to estimate these forces during whole-body vibration (WBV). Thirty-eight subjects were exposed to identical random low-frequency WBV (0·7, 1·0 and 1·4 m/s^-2 r.m.s. weighted acceleration) at a relaxed, erect and bent forward postures. The acceleration of the seat and the force between the seat and the buttocks were measured. Six EMGs were derived from the right side of the m. trapezius pars descendens, m. ileocostalis lumborum pars thoracis, m. ileocostalis lumborum pars lumborum; m. longissimus thoracis pars thoracis, m. longissimus thoracis pars lumborum, and lumbar multifidus muscle. All data were filtered for anti-aliasing and sampled with 1000 Hz. Artefacts caused by the ECG in the EMG were identified and eliminated in the time domain using wavelets. The individually rectified and normalized EMGs were averaged across subjects. The EMGs without WBV exhibited characteristic patterns for the three postures examined. The coherence and transfer functions indicated characteristic myoelectric responses to random WBV with several effects of posture and WBV magnitude. A comprehensive set of transfer functions from the seat acceleration or the mean normalized input force to the mean processed EMG was presented.The results can be used for the development of more sophisticated models with a separate control of various back muscle groups. However, the EMG-force relationship under dynamic conditions needs to be examined in more detail before the results can be implemented. Since different reflex mechanisms depending on the frequency of WBV are linked with different types of active muscle fibres, various time delays between the EMG and muscle force may be necessary.     

弹簧质量对振动的影响

给出了弹簧质量不可忽略的弹簧振子系统的振动解，导出了弹簧的有效质量的渐近级数表达式、指出振动呈拟周期性。     

EVALUATION OF FREQUENCY WEIGHTING (ISO 2631-1) FOR ACUTE EFFECTS OF WHOLE-BODY VIBRATION ON GASTRIC MOTILITY

The aim of this study was to investigate the effects of exposure to whole-body vibration (WBV) and the ISO 2631/1-1997 frequency weighting on gastric motility. The gastric motility was measured by electrogastrography (EGG) in nine healthy volunteers. Sinusoidal vertical vibration at a frequency of 4, 6·3, 8, 12, 16, 31·5, or 63 Hz was given to the subjects for 10 min. The magnitude of exposure at 4 Hz was 1·0m/s² (r.m.s.). The magnitudes of the other frequencies gave the same frequency-weighted acceleration according to ISO 2631/1-1997. The pattern of the dominant frequency histogram (DFH) was changed to a broad distribution pattern by vibration exposure. Vibration exposure had the effect of significantly reducing the percentage of time for which the dominant component had a normal rhythm and increasing the percentage of time for which there was tachygastria (p<0·05). Vibration exposure generally reduced the mean percentage of time with the dominant frequency in normal rhythm component. There was a significant difference between the condition of no vibration and exposure to 4 and 6·3 Hz of vibration frequency (p<0·05). The frequency weighting curve given in ISO 2631/1-1997 was not adequate for use in evaluating the physiological effects of WBV exposure on gastric motility.     

银片上茜素的表面增强共振喇曼散射效应及模式标识

本文对吸附在经连续的氧化 还原循环(ORC)过程处理的银片衬底上的茜素的表面增强共振喇曼散射(SERRS)特性进行了研究,并对茜素SERRS谱中的振动模式做了标识.结果表明,吸附在经氧化.还原循环(ORC)处理的银片衬底上的茜素分子,其表面增强喇曼散射的强度,主要是由于最靠近银片的一层分子的增强,而第一层以外的分子贡献很小.也就是说,表面增强喇曼散射具有单层饱和效应.茜素在经ORC处理的银片上和在银镜上所显示的SERRS特征基本一致,其中有些振动模式存在小的频移,这与银片、银镜各自的表面特性有关.     

晶格振动对激子运动的影响

在本文中用Haga研究极化子时提出的微扰法讨论晶格振动对激子运动的影响。把作者过去的工作推广到电子和空穴质量不相等的普遍情形。在忽略反冲效应中不同波矢的声子之间的相互作用时,导出了激子的基态能量、有效质量、约化质量和内部势能。指出:激子的有效质量和电子、空穴与声子的相互作用有关;激子的约化质量不仅和电子、空穴与声子的相互作用有关,而且还和电子空穴质量比有关;激子形成自陷态的条件并非由电子、空穴与声子相互作用的大小,而是由电子、空穴质量比决定。形成激子自陷的条件是电子、空穴质量比0.261<μ_e/μ_h<3.83。在μ_e/μ_h<0.261或μ_e/μ_h>3.83的情形,激子极化晶体中并不形成自陷态。 关键词：     

共振实验在生命中应用研究Ⅰ──共振与生物频率

本文提出可以利用共振原理来纠正癌分子振动方向，阻止癌细胞繁殖，最后达到和正常分子的振动频率一致的观点。     

X射线全息记录过程中影响分辨率的主要因素分析

分析了Ｘ射线全息记录过程中影响分辨率的一些主要因素。在完全相干的条件下，Ｘ射线无透镜傅里叶变换全息图的最小分辨距离不可能小于记录时用的Ｘ射线聚束器的焦斑或滤波小孔的半径，而Ｘ射线同轴全息图不可能获得比记录介质的截止频率更高的分辨率。在部分相干的条件下，Ｘ射线无透镜傅里叶变换全息所要求的相干长度和分辨率与样品半径成二次线型关系。Ｙ射线同轴全息所要求的相干长度和分辨率的平方以及样品到全息图的距离成正比，而与样品尺寸无关。随着Ｘ射线全息图分辨率的提高，其所要求的相干长度将大幅度增长。 关键词：     

EFFECT OF ELASTIC FOUNDATION ON ASYMMETRIC VIBRATION OF POLAR ORTHOTROPIC LINEARLY TAPERED CIRCULAR PLATES

Asymmetric vibrations of polar orthotropic circular plates of linearly varying thickness resting on an elastic foundation of Winkler type are discussed on the basis of the classical plate theory. Ritz method has been employed to obtain the natural frequencies of vibration using the functions based upon the static deflection of polar orthotropic plates, which has faster rate of convergence as compared to the polynomial co-ordinate functions. Frequency parameter of the plate with elastically restrained edge conditions are presented for various values of taper parameter, rigidity ratio and foundation parameter. A comparison of the results with those available in the literature obtained by finite element method, receptance method and polynomial co-ordinate functions shows an excellent agreement.     

单摆振动周期随摆角变化实验之讨论

本文就如何选择恰当的计时仪器来测量单摆振动周期随摆角变化的问题进行了讨论。主要说明要根据具体的实验装置和具体的实验内容合理地选择仪器的灵敏度。     

APPLICATION OF MODIFIED VLASOV MODEL TO FREE VIBRATION ANALYSIS OF BEAMS RESTING ON ELASTIC FOUNDATIONS

The purpose of this paper is to apply the modified Vlasov model to the free vibration analysis of beams resting on elastic foundations and to analyze the effects of the subsoil depth, the beam length, their ratio and the value of the vertical deformation parameter within the subsoil on the frequency parameters of beams on elastic foundations. This analysis has been carried out by the aid of a computer program based on the finite element method. The first ten frequency parameters are presented in tabular and graphical forms to evaluate the effects of the parameters considered in this study. Then mode shapes corresponding to the first six of the frequency parameters are given in figures. It is concluded that the effect of the subsoil depth on the frequency parameters of beams on an elastic foundation is generally larger than those of the other parameters considered in this study.     

外场下机械振动对高温超导带材交流损耗的影响

高温超导带材在磁场中传输交变电流时,将受到电磁力的作用而产生机械振动,振动对带材的交流损耗将产生影响.本文讨论了振动情况下交流损耗的测量方法,在平行于带面的直流磁场下,测量了Bi-2223/Ag高温超导带材在不同振动情况下的交流损耗.结果显示:当传输电流频率偏离样品的共振频率时,振动对带材的交流损耗影响不大;只有当电流频率在共振频率附近时,样品产生剧烈振动,交流损耗才有明显的增加;另外,带材振动时的交流损耗随频率变化曲线的斜率比不振动时略有增加.     

铁磁体中缺陷对自旋波的影响

本文提出了一个处理磁性杂质或其他缺陷在磁性晶体中对自旋波频谱的影响的一般理论方法,并特别着重讨论了局域模自旋波。以一维线性格子为例进行计算的结果显示出:一个代位磁性杂质,可能产生不只一个高于连续带顶的局域模。其产生的条件和其能级位置均通过J′S′/JS和J′/J表达出来,这里S′和S各为杂质原子和基质原子的自旋量子数,J′和J各为杂质与近邻之间和一般近邻之间的交换作用系数。高度集中的应变和间隙原子如致使邻近处的交换作用增大,也导致局域模的出现。我们也考虑了磁偶极矩相互作用的影响,证明其并不破坏这些局域模的