Progressive delamination growth analysis using discontinuous layered element

In this paper, a fracture mechanic approach is used to analyze delamination propagation between layers of composite laminates. A finite element method based on layer-wise theory is extended for the analysis of delamination growth. In this approach, delamination is modeled by jump discontinuity conditions at the interfaces. The layer-wise finite element is developed to calculate the strain energy release rates based on the virtual crack closure technique (VCCT). A procedure is proposed to handle the progressive delamination of laminates. Finally, analyses of the edge delamination propagation for several composite laminates are performed and the corresponding failure stresses are calculated. The predicted results are compared with the available experimental and numerical results. It is shown that the predicted failure stresses using this method are comparable with those obtained using interface elements.     

Data hiding in MPEG-2 bitstream by creating exceptions in code space

In this work, we have developed a file-size preserving algorithm to hide data directly in MPEG-2 bitstreams without violating the syntax. The approach is based on the realization that embedding of a bit directly in the bitstream can be achieved by creating an exception in the code space. An exception is created by inserting code words not occurring in the original content into the bitstream. Because the entropy-coded segment of MPEG-2 is fully used, every valid code word appears somewhere in the video. However, exceptions can still be created by recognizing that there are certain variable length codes (VLC) that never occur together in any video block. These are unused VLC pairs and although they vary from stream to stream, they always exist. It is then possible to embed one bit of data by forcing an unused pair in a block subject to a number of constraints, including transparency, file-size preservation and quality metric. The list of unused pairs constitutes a secure key that can be identified by pointer. This pointer can be efficiently encoded for sharing through a secure download. The content-dependence of the key allows a secure exchange of information because each key is valid only for the corresponding video. Because the cover video still uses standard VLCs, the marked bitstream is transparent to external observers. Application areas for the proposed approach are metadata binding and general data hiding when the size of the key is less important than the security and value of attaching data to content. Examples are surveillance video footage and medical applications.     

A generalized plane-strain crack density-based model for evaluating the finite fracture toughness of composite laminates

The present study focuses on a developed crack density-based model for evaluating the material properties of an orthotropic composite ply containing a specified matrix-cracking density. Furthermore, more complementary details of this model, including a closed form solution for evaluating the stress fields as well as stiffness degradation of a damaged ply, will be presented. The derived relations will be applied for evaluating the master plot curve, which is applicable for obtaining the finite fracture toughness (G_mc) of laminated composites. The obtained results will be compared with the available experimental results.     

Design of code division multiple access filters based on sampled fiber Bragg grating by using global optimization algorithms

In this article, we focus on the design of code division multiple access filters (used in data transmission) composed of a particular optical fiber called sampled fiber Bragg grating (SFBG). More precisely, we consider an inverse problem that consists in determining the effective refractive index profile of an SFBG that produces a given reflected spectrum. In order to solve this problem, we use an original multi-layers semi-deterministic global optimization method based on the search of suitable initial conditions for a given optimization algorithm. The results obtained with our optimization algorithms are compared, in term of complexity and final design, with those given by an hybrid genetic algorithm (the method generally considered in the literature for designing SFBGs).     

Integrating AHP with QFD for robot selection under requirement perspective

Selection of a robot is an important task, as improper selection may adversely affect a firm's production by reducing the quality of the product, thereby reducing productivity as well as profitability. To effectively select a robot for a specified job, several factors have to be considered. The objective of this paper is to explain how, using a combined AHP/QFD model, the authors are able to determine if the deployment of robots in industry helped in performance enhancement from requirement perspective. Incorporating a simple and novel cost factor measure in the proposed integrated AHP/QFD model aids justification of the implementation of a robotic system in a manufacturing firm from an economic point of view also. The proposed integrated approach also identifies technical requirements followed by customer requirements. In this paper, an integrated model combining AHP and QFD has been delineated for the industrial robot selection problem. Seven technical requirement factors have been considered for the case study.     

Fuzzy Controller for Seismically Excited Nonlinear Buildings

This paper focuses on the benchmark control problems for seismically excited nonlinear buildings. The benchmark study focuses on three typical steel structures, 3-, 9-, and 20-story buildings designed for the SAC project for the Los Angeles region. This paper reports the application of the active control scheme on the 3- and 20-story benchmark buildings, where the control action is achieved by a fuzzy logic controller. The main advantage of the fuzzy controller is its inherent robustness and ability to handle any nonlinear behavior of the structure. The performance of the controller is validated through the computer simulation on MATLAB. The control scheme satisfies the control constraints and is presented according to the evaluation criteria provided with the benchmark problems for comparison with other schemes. Four different earthquakes (El Centro 1940, Hachinohe 1968, Northridge 1994, and Kobe 1995) will be used in the simulation.     

Ambulatory system for human motion analysis using a kinematic sensor: monitoring of daily physical activity in the elderly

A new method of physical activity monitoring is presented, which is able to detect body postures (sitting, standing, and lying) and periods of walking in elderly persons using only one kinematic sensor attached to the chest. The wavelet transform, in conjunction with a simple kinematics model, was used to detect different postural transitions (PTs) and walking periods during daily physical activity. To evaluate the system, three studies were performed. The method was first tested on 11 community-dwelling elderly subjects in a gait laboratory where an optical motion system (Vicon) was used as a reference system. In the second study, the system was tested for classifying PTs (i.e., lying-to-sitting, sitting-to-lying, and turning the body in bed) in 24 hospitalized elderly persons. Finally, in a third study monitoring was performed on nine elderly persons for 45-60 min during their daily physical activity. Moreover, the possibility-to-perform long-term monitoring over 12 h has been shown. The first study revealed a close concordance between the ambulatory and reference systems. Overall, subjects performed 349 PTs during this study. Compared with the reference system, the ambulatory system had an overall sensitivity of 99% for detection of the different PTs. Sensitivities and specificities were 93% and 82% in sit-to-stand, and 82% and 94% in stand-to-sit, respectively. In both first and second studies, the ambulatory system also showed a very high accuracy (> 99%) in identifying the 62 transfers or rolling out of bed, as well as 144 different posture changes to the back, ventral, right and left sides. Relatively high sensitivity (> 90%) was obtained for the classification of usual physical activities in the third study in comparison with visual observation. Sensitivities and specificities were, respectively, 90.2% and 93.4% in sitting, 92.2% and 92.1% in "standing + walking," and, finally, 98.4% and 99.7% in lying. Overall detection errors (as percent of range) were 3.9% for "standing + walking," 4.1% for sitting, and 0.3% for lying. Finally, overall symmetric mean average errors were 12% for "standing + walking," 8.2% for sitting, and 1.3% for lying.     

A method for detection and classification of events in neural activity

We present a method for the real time prediction of punctuate events in neural activity, based on the time-frequency spectrum of the signal, applicable both to continuous processes like local field potentials (LFPs) as well as to spike trains. We test it on recordings of LFP and spiking activity acquired previously from the lateral intraparietal area (LIP) of macaque monkeys performing a memory-saccade task. In contrast to earlier work, where trials with known start times were classified, our method detects and classifies trials directly from the data. It provides a means to quantitatively compare and contrast the content of LFP signals and spike trains: we find that the detector performance based on the LFP matches the performance based on spike rates. The method should find application in the development of neural prosthetics based on the LFP signal. Our approach uses a new feature vector, which we call the 2d cepstrum.     

ISDN frame relay and its congestion control

Frame relay is a new ISDN (integrated services digital network) packet mode bearer service which is expected to provide an efficient means of information transport using high-speed transmission media. Several new applications requiring high bandwidth, such as file transfer, video and packetized voice, are suitable candidates to use this streamlined protocol. However, as there are no control frames present within the network for traffic flow management, congestion may arise during periods of peak offered loads. Efficient congestion control mechanisms are needed to make the frame relay effective. In this paper, after a brief discussion of the frame relay protocol, we consider the congestion problem in networks using this protocol and evaluate the performance. Specifically, we consider static and dynamic window flow control methods and develop models to determine the throughput under various load conditions. The throughput of the static window flow control model is determined by computing the frame loss probability and the virtual retransmission time, which is the time between arrivals of retransmitted frames at the destination. The frame loss probability is calculated by modelling the bottleneck resource as a finite state Markov chain. The results are validated by simulation. Furthermore, to analyse the dynamic interactions between the virtual circuits and their effect on the throughput and delay characteristics, we develop a simulation model which incorporates a dynamic window congestion control mechanism. It is shown that when the offered load is high, the performance of dynamic window flow control is superior to that of static window flow control.     

Solid modelling in a virtual reality environment

This paper presents a constraint-based methodology for intuitive and precise solid modelling in a virtual reality (VR) environment. A hierarchically structured and constraint-based data model is developed to support solid modelling in the VR environment. A constraint reasoning engine is also developed to automatically deduce allowable motions for precise constraint-based 3D manipulations. A prototype system of product modelling has been successfully developed, and experimental results demonstrate the advantage of precise solid modelling through constraint-based manipulation in virtual environments.