液体射流泵空化噪声与振动试验

针对液体射流泵的空化噪声与振动进行了试验研究;运用B＆K加速度仪和水听器对射流泵各部位在不同工况下的空化噪声与振动进行了测量。结果表明：（1）射流泵空化噪声以单极子声源为主,随着流速和紊流度的增大,偶极子作用逐渐增大;（2）射流泵空化噪声与振动随空化程度加剧而更强烈,最强烈处也从喉管向扩散管转移;（3）射流泵面积比越小,达到临界空化前噪声频谱波动越强,临界空化之后噪声谱级趋于平稳,随频率增加而递减;（4）初生空化出现前后噪声在整个频域范围内都有一个较大的跃升,约5-10 dB,此跃升可作为判断初生空化的参考方法;（5）泵体3个正交方向振动并不相同,径向振动较轴向更为明显。     

The effect of training on stride parameters in a cohort of National Hunt racing Thoroughbreds: A preliminary study

Reasons for performing study: The influence of training on stride parameters is controversial and to date there is no information on how training influences stride parameters during high‐speed locomotion in the field. Objective: To determine the influence of training on stride variables during high‐speed locomotion in Thoroughbred racehorses. Methods: Speed, stride frequency, stance and protraction times were quantified in 8 Thoroughbreds with foot mounted accelerometers and GPS sensors during their first week of canter after the summer break and 6 months into training. Results: At a speed of 11 m/s, stride frequency was (mean ± s.d.) 2.160 ± 0.120 strides/s pre‐ and 2.167 ± 0.083 strides/s post training; mean stance time was 125.3 ± 9 ms pre‐ and 125.9 ± 7 ms post training; protraction time was 340.7 ± 20.4 ms pre‐ and 337.2 ± 14.3 ms post training. The increase in stride frequency and the decrease in protraction time after training were significant. There was no statistically significant difference in the maximum speed reached by each horse pre‐ and post training. Conclusions: Stance time stayed constant throughout the training season in the tested horses. A significant decrease in protraction time and a corresponding significant increase in stride frequency were observed after training. Potential relevance: Training of racehorses could be adapted to maximise the effect on modifiable parameters and reduce the risk of training‐induced pathologies. Further research will be conducted to investigate the effect of different training protocols on a large number of horses.     

Determining cessation of brain activity during depopulation or euthanasia of broilers using accelerometers

The threat of avian influenza virus is a major concern for poultry growers worldwide. In response to avian influenza virus outbreaks in the United States and the existence of zoonotic strains causing human infection and death in Eastern Asia, a mass emergency depopulation method using water-based foam was developed for floor-reared broilers and turkeys. During foam depopulation, birds cannot be observed directly. As a result, several methods for monitoring bird activity during field depopulation research were explored. Accelerometers were found to be a simple, effective means of detecting motion and subsequently the cessation of motion after terminal convulsions ceased. In a previous study, it was shown that motion cessation may coincide with a lack of measureable brain activity. In this study, broilers were monitored with electroencephalograph, electrocardiograph, and motion sensors and treated with 1 of 3 methods of depopulation or euthanasia (Ar-CO₂ gas, CO₂ gas, or water-based foam). The differences between the accelerometer motion cessation and electrocardiogram signal stabilization were significant, as were the differences between motion cessation and electroencephalogram silence. Although the differences are statistically significant, these do not invalidate the use of an accelerometer to detect cessation of measurable brain activity during depopulation or euthanasia research.     

Design and fabrication of a novel resonator for resonant accelerometer

A novel resonator for accelerometer with sensing and actuating combs was designed and fabricated based on micro electromechanical system (MEMS) process. Driving force and demand voltage of the resonator were analyzed by analytical method and Finite Element Method (FEM). Sensing capacitance on resonance state and Q factor under atmosphere was calculated by these two methods. The micro fabrication process was planned and realized using MEMS (Micro electromechanical System) method. The testing results show the performance of the resonator is high; the natural frequency of the resonator is 54 523.5 Hz, which has the error of 13.6％ with the theorical value.     

不同距离急停跳投起跳阶段腰腹部肌肉活动特征分析

目的:了解学生日常体力活动现状,探讨影响学生日常体力活动的因素。方法:应用ActiGraPh GT3X-Plus三轴加速度计对18名男性健康高中生进行为期一周的日常体力活动监测。结果:学生有四成以上时间以静态活动状态为主,平时日和周末日坐的时间>躺的时间>站的时间（P<0.001）,而休息日则躺的时间>坐的时间>站的时间（P<0.001）。学生从事中等强度及其以上活动时间仅占全天总时间的10%左右,平时日和周末日静态活动强度时间>中等强度时间>轻体力活动时间>大强度时间>剧烈活动时间,休息日为静态活动强度时间>轻体力活动时间>中等强度时间>大强度时间>剧烈活动时间,经检验不同强度时间之间均有非常显著性差异,P<0.001。休息日能量消耗（339.3±145.7kcal）明显低于平时日（515.3±166.0kcal）和周末日能量消耗（510.9±164.6kcal）,P<0.01具有非常显著性差异。双因素方差分析显示,活动日对学生躺时间（P<0.001）、静态活动时间（P<0.01）、中等强度活动时间（P<0.01）和全天能量消耗（P<0.01）有显著性影响;年级仅对静态活动时间（P<0.05）、轻体力活动时间（P<0.05）和剧 烈活动时间（P<0.05）有影响;年级*活动日期双重因素对静态活动时间P<0.05）有显著影响。结论:高中男生主要以静态生活方式为主,且体力活动不足。上学日和非上学日对学生的日常体力活动影响显著。在今后对于学生日常体力活动的研究中不必过多地考虑年级因素的影响,但有必要按活动日的不同进行具体分析。     

Dairy cattle behavior classifications based on decision tree learning using 3‐axis neck‐mounted accelerometers

Demand has been increasing recently for an automated monitoring system of animal behavior as a tool for the management of livestock animals. This study investigated the association between the behavior of dairy cattle and the acceleration data collected using three‐axis neck‐mounted accelerometers, as well as the feasibility of improving the precision of behavior classifications through machine learning. In total 38 Holstein dairy cows were used, and kept in four different farms. A logger was mounted to each collar to obtain acceleration data for calculating the activity level and variations. At the same time the behavior of the cattle was observed visually. Characteristic acceleration waves were recorded for eating, rumination, and lying, respectively; and the activity level and variations were significantly different among these behaviors (p < 0.01). Decision tree learning was performed on the data set from Farm A and validated its precision; which proved to be 99.2% in cross‐validation, and 100% in test data sets from Farms B to D. This study showed that highly precise classifications for eating, rumination, and lying is possible by using decision tree learning to calculate the activity level and variations of cattle based on the data obtained by three‐axis accelerometers mounted to a collar.     

The use of accelerometer to measure sleeping posture of beef cows

Sleep is one of the essential behaviors for mammals. The aims of this study were to validate the use of accelerometer for measuring sleeping posture of cattle. Duration of sleeping posture of seven Japanese Black cows from 19.00 to 07.00 hours was measured by both accelerometer and video, and a total of 67 accelerometer and video measurement sets were collected. We calculated Cohen's κ coefficient between accelerometer and video measurements and 91.5% of the κ‐values were >0.80. Intra‐ and inter‐observer coefficient of variance showed that specific acceleration waveform patterns of sleeping posture could be easily and accurately detected by independent observers. There were no significant differences in the frequency of sleeping posture occurrences between accelerometer and video measurements. We compared averaged sleeping posture bout, and the total sleeping posture time between accelerometer and video measurements using regression. In each trait, the slope was close to 1 and the intercept was not different from 0, which showed a strong agreement between accelerometer and video measurements. This shows that an accelerometer could accurately detect sleeping postures of cattle. We conclude that adequate measurements of sleeping postures can be made using an accelerometer.     

Effects of a synthetic all‐weather waxed track versus a crushed sand track on 3D acceleration of the front hoof in three horses trotting at high speed

Reasons for performing study: Inadequate track surfaces are believed to be a risk factor in the occurrence of musculoskeletal injuries, but quantification of the shocks and vibrations provoked by hoof impact on different ground surfaces (including new synthetic tracks) has been insufficiently documented in trotters under high‐speed training conditions. Objectives: To test the reliability and sensitivity of an accelerometric device to discriminate between the biomechanical effects of 2 different tracks at high speed. Methods: Three French Trotters were used and their right front hooves were equipped with one triaxial accelerometer. Two different track surfaces (crushed sand track: S and all‐weather waxed track: W) were tested when horses were trotting in a straight line. For each session of measurements, trials were repeated 3 times in a Latin square design. The speed of the runs was set at 10 m/s, controlled by the driver and recorded synchronously. Sample rate was set at 6 kHz. Acceleration of the hoof (resultant vector and 3D components), power spectral density at impact and variability (between strides, trials, sessions and horses) were analysed. Statistical differences were tested using a GLM procedure (SAS). Least square mean differences were used for comparisons between tracks (P<0.05). Results: Results showed that the deceleration of the hoof (magnitude of the resultant vector) was statistically different between the 2 tracks with an attenuation of the shock of about 50% on the all‐weather waxed track. Magnitude of the power spectral density was reduced at higher frequencies on W. Conclusions and clinical relevance: These preliminary results demonstrate the sensitivity of the tool to discriminate between the different behaviours of the hoof on the different track surfaces at high speed. Deceleration and vibration of the hoof at impact were reduced on W compared to S, suggesting a better shock‐absorbing quality of this track.