中压电场预处理对苹果组织损伤程度及微观结构的影响

为了探究中压电场预处理(<100 V/cm)对苹果组织结构损伤程度的影响,从宏观层面上分析了电场强度(15~90 V/cm)、温度(30~70℃)、频率(50~1000 Hz)等处理参数对苹果组织结构损伤率的影响规律,解析了温度对苹果组织损伤过程的影响;从微观层面上对不同温度和电场强度下苹果组织微观结构进行了电镜扫描观察。结果表明,同样温度下,中压电场预处理时的苹果组织结构损伤率远高于水浴加热处理(P<0.05);场强较高(>45 V/cm)时苹果组织结构损伤率随温度的升高而线性增大;场强较低(<30 V/cm)处理时与水浴处理均呈现先缓慢上升再急剧增大的变化趋势,但中压电场预处理增速更快。温度低于70℃时,苹果组织结构损伤率随电场强度升高而增加,随频率的增大而减小。苹果组织结构损伤率随时间的变化符合一级反应动力学模型;中压电场强度30 V/cm时,通过组织损伤速率常数、特征损伤时间计算所得活化能分别为122.88和157.01 k J/mol;水浴处理时组织损伤速率常数所得活化能为143.82 k J/mol。苹果组织细胞微观结构观察显示,中压电场电、热协同作用更易损伤苹果组织。研究结果可为改进苹果深加工预处理工艺提供参考。

Damage warning of suspension bridges based on neural networks under changing temperature conditions

This paper aims at successive structural damage detection of long-span bridges under changing temperature conditions.First,the frequency-temperature correlation models of bridges are formulated by means of artificial neural network techniques to eliminate the temperature effects on the measured modal frequencies.Then,the measured modal frequencies under various temperatures are normalized to a reference temperature,based on which the auto-associative network is trained to monitor signal damage occurrences by means of neural-network-based novelty detection techniques.The effectiveness of the proposed approach is examined in the Runyang Suspension Bridge using 236-day health monitoring data.The results reveal that the seasonal change of environmental temperature accounts for variations in the measured modal frequencies with averaged variances of 2.0%.And the approach exhibits good capability for detecting the damage-induced 0.1% variance of modal frequencies and it is suitable for online condition monitoring of suspension bridges.

DAMAGE DETECTION FOR COMPOSITE STRUCTURE UNDER TEMPERATURE CHANGES USING LAMB WAVES

A two-step method is proposed for detection and identification of invisible impact damage in composite structure under temperature changes using Lamb waves.First,a statistical outlier analysis is employed to distinguish whether the changes of Lamb wave signals are induced by damage within a monitoring area or are only affected by temperature changes.Damage indices are defined after the Lamb wave signals are processed by Fourier transform,and a Monte Carlo procedure is used to obtain the damage threshold value for the damage indices at the undamaged state.If the damage indices in the operation state exceed the threshold value,the presence of damage is determined.Then,a probabilistic damage imaging algorithm displaying probabilities of the presence of damage within the monitoring area is adopted to fuse information collected from multiple actuator-sensor paths to identify the location of damage.Damage indices under damaged state are used to generate the diagnostic image.Experimental study on a stiffened composite panel with random temperature changes is performed to demonstrate the effectiveness of the proposed method.

Seismic Hazard Matrix of Buildings in Yunnan

Seismologists have begun to investigate the earthquake damage and assess the economic losses on the spot in the Yunnan area since the earthquakes with M_S6.7 and M_S6.9 that occurred on the boundary between China and Myanmar west of Menglian county,Yunnan Province,on April 23,1992.From 1992 to 2003,50 destructive earthquakes occurred in Yunnan,and large amounts of data on seismic hazard have been accumulated.With focus on the major building structures,the paper makes statistical analysis on the earthquake damage ratio,loss ratio and seismic hazard index in the areas with different seismic intensity of the 50 events,and presents the seismic hazard matrix of buildings for the Yunnan area.