Comparative Study of the Physiological Effects of Three Passive Relaxation Techniques Administered to Mentally Retarded Children

Problem Passive relaxation techniques require no intellectual or physical effort from the receiver. This study examined effects of three passive relaxation techniques on galvanic skin resistance (GSR), pulse rate (PR), and peripheral skin temperature (PST) of 3 profoundly (PMR) and severely (SMR) mentally retarded children. Method Twenty-four PMR and SMR children under twelve years were randomly assigned among four groups. The first group received slow stroking of the midline back; the second slow rocking; the third lay quietly; and the fourth was a control group. At the beginning and end of twelve ten-minute sessions, the subjects\u27 GSR, PR, and PST were measured. Results Ancova and anova analyses showed significant differences among groups on several days. Stroking and rocking produced similar relaxation levels ; lying quietly was less effective; lack of treatment was ineffective. Conclusions Passive relaxation techniques with this population seem plausible. Techniques applied directly to the body appear most effective

Damage classification in reinforced concrete beam by acoustic emission signal analysis

Acoustic Emission (AE) is a non-destructive testing technique which can be used to identify both the damage level and the nature of that damage such as tensile cracks and shear movements at critical zones within a structure. In this work, the acoustic emission parameters of amplitude, rise time, average frequency and signal strength were used to classify the damage and to determine the damage level. Laboratory experiments were performed on a beam (150 x 250 x 1900 mm). The acoustic emission analysis was successfully used to determine crack movements and classify damage levels in accordance with the observations made during an increasing loading cycle

Optimized placement of parasitic vibration energy harvesters for autonomous structural health monitoring

Energy harvesting, based on sources including vibration and thermal gradients, has been exploited in recent years to power telemetry, small devices, or to charge batteries or capacitors. Generating the higher levels of power which have thus far been required to run sensor systems such as those needed for structural health monitoring has been more challenging. In addition, harvesters such as those required to capture vibration often require additional elements (e.g. cantilevers) to be added to the structure and harvest over a relatively narrow band of frequencies. In aerospace applications, where weight is at a premium and vibrations occur over a broader range of frequencies, this is non-ideal. With the advent of new, lower power monitoring systems, the potential for energy harvesting to be utilized is significantly increased. This article optimizes the placement of a set of parasitic piezoelectric patches to harvest over the broad band of frequencies found in an aircraft wing and validates the results experimentally. Results are compared with the requirements of a low-power structural health monitoring system, with a closing of the gap between the energy generated and that required being demonstrated

Improved acoustic emission source location during fatigue and impact events in metallic and composite structures

In order to overcome the difficulties in applying traditional Time-Of Arrival (TOA) techniques for locating Acoustic Emission (AE) events in complex structures and materials, a technique termed “delta-t mapping” was developed. This paper presents a significant improvement on this, in which the difficulties in identifying the precise arrival time of an AE signal are addressed by incorporating the Akaike Information Criteria (AIC). The performance of the TOA, the delta-t mapping and the AIC delta-t mapping techniques is assessed by locating artificial AE sources, fatigue damage and impact events in aluminium and composite materials respectively. For all investigations conducted the improved AIC delta-t technique shows a reduction in average Euclidean source location error irrespective of material or source type. For locating H-N sources on a complex aluminium specimen the average source location error (Euclidean) is 32.6, (TOA), 5.8 (delta-t) and 3mm (AIC delta-t). For locating fatigue damage on the same specimen the average error is 20.2, (TOA), 4.2 (delta-t) and 3.4mm (AIC delta-t). For locating H-N sources on a composite panel the average error is 19.3, (TOA), 18.9 (delta-t) and 4.2mm (AIC delta-t). Finally the AIC delta-t mapping technique had the lowest average error (3.3mm) when locating impact events when compared with the delta-t (18.9mm) and TOA (124.7mm) techniques. Overall the AIC delta-t mapping technique is the only technique which demonstrates consistently the lowest average source location error (greatest average error 4.2mm) when compared with the delta-t (greatest average error 18.9mm) and TOA (greatest average error 124.7mm) techniques. These results demonstrate that the AIC delta-t mapping technique is a viable option for AE source location, increasing the accuracy and likelihood of damage detection, irrespective of material, geometry and source type

Electrohydraulic effects on the modelling of a vehicle active suspension

A car suspension incorporating a Lotus actuator and a TVR suspension/wheel unit is studied both experimentally and analytically. An emphasis is placed on hydraulic modelling using a series of transfer functions linking the hydraulic and suspension components. This is significantly aided by the use of a Moog 2000 programmable servo controller (PSC) to equalize the extending and retracting flow gains of the servovalve in the Lotus actuator control loop, justifying the use of combined extending and retracting transient data for parameter identification. This then allows the system equations to be developed using linear state-space theory, and a suitable form is proposed for further design studies. It is shown that the hydraulic components significantly contribute to the system dynamics and hence cannot be neglected when control schemes are formulated. In particular, the significance of hydraulic bulk modulus on dynamic performance is evaluated, and the importance of accurately determining all components of velocity-type damping is highlighted

A comparison study of water diffusion in unidirectional and 2D woven carbon/epoxy composites

he use of CFRP composites is significantly increasing in the aerospace, automotive, and marine industries, particularly in safety critical primary structures. This work presents a newly developed experimental approach to investigate the directional diffusion of water in CFRP composites with the use of Fick's law. The approach is used to study the effect of fiber architecture on directional diffusion rates, with a particular focus on the role of fiber waviness in the diffusion process. A comparison of water diffusion is made in three different fiber architectures: Unidirectional (UD), plain weave, and twill weave. The specimens were fully immersed in 90°C purified water until their maximum moisture saturation was achieved, with some specimens being selectively exposed from the edges only to obtain the directional diffusion coefficients. The water penetration process into the CFRP structure initiate from the micro-cracks and defects. The experimental work of this study shows sharp mass increases within the first stage followed by an equilibrium stage where saturation is present. The interfacial region is found to be a critical parameter where detachment of the interfacial fiber/matrix bonding is observed further demonstrating the potential effect of different fiber architecture in this region. UD fiber architecture showed ~20% higher diffusion coefficient in the Dx,y direction compared with plain and twill woven architectures. The weave patterns in 2D woven fiber architectures are therefore believed to play a key role on the moisture ingress mechanism and subsequently contributed in slowing down the capillary process in the interfacial region. This has implications for materials development and selection for CFRP composites used in moist environments

The influence of water absorption on unidirectional and 2D woven CFRP composites and their mechanical performance

This paper discusses a key parameter ‘fibre architecture’ that is believed to play a major part in the performance of CFRP composites when subjected to water absorption. Unidirectional, plain, and twill weave CFRP specimens were immersed in water at 70 °C for 40 days. The condition of the matrix was examined using a Scanning Electron Microscope (SEM). The mechanical properties dominated by the condition of the matrix and interfacial regions such as compression, shear, and impact resistance were assessed for un-aged and aged specimens. A reduction in strength was observed for all aged specimens. However, the observed reduction in strength varies depending on both the fibre architecture used and the specific load case. The largest effect on properties was observed in unidirectional materials, which leads to the recommendation that less conservative safety factors should be used for woven fibre architectures