Solving a bi-criteria permutation flow-shop problem using shuffled frog-leaping algorithm

Flow shop problems as a typical manufacturing challenge have gained wide attention in academic fields. In this paper, we consider a bi-criteria permutation flow shop scheduling problem, where the weighted mean completion time and the weighted mean tardiness are to be minimized simultaneously. Due to the complexity of the problem, it is very difficult to obtain optimum solution for this kind of problems by means of traditional approaches. Therefore, a new multi-objective shuffled frog-leaping algorithm (MOSFLA) is introduced for the first time to search locally Pareto-optimal frontier for the given problem. To prove the efficiency of the proposed algorithm, various test problems are solved and the reliability of the proposed algorithm, based on some comparison metrics, is compared with three distinguished multi-objective genetic algorithms, i.e. PS-NC GA, NSGA-II, and SPEA-II. The computational results show that the proposed MOSFLA performs better than the above genetic algorithms, especially for the large-sized problems.     

New wireless connection between user and VE using speech processing

This paper presents a novel speak-to-VR virtual-reality peripheral network (VRPN) server based on speech processing. The server uses a microphone array as a speech source and streams the results of the process through a Wi-Fi network. The proposed VRPN server provides a handy, portable and wireless human machine interface that can facilitate interaction in a variety interfaces and application domains including HMD- and CAVE-based virtual reality systems, flight and driving simulators and many others. The VRPN server is based on a speech processing software development kits and VRPN library in C++. Speak-to-VR VRPN works well even in the presence of background noise or the voices of other users in the vicinity. The speech processing algorithm is not sensitive to the user’s accent because it is trained while it is operating. Speech recognition parameters are trained by hidden Markov model in real time. The advantages and disadvantages of the speak-to-VR server are studied under different configurations. Then, the efficiency and the precision of the speak-to-VR server for a real application are validated via a formal user study with ten participants. Two experimental test setups are implemented on a CAVE system by using either Kinect Xbox or array microphone as input device. Each participant is asked to navigate in a virtual environment and manipulate an object. The experimental data analysis shows promising results and motivates additional research opportunities.     

Nonlinear free vibration of temperature-dependent sandwich beams with carbon nanotube-reinforced face sheets

In this research, large amplitude free vibrations of a sandwich beam with stiff core and carbonnanotube (CNT)-reinforced face sheets are analysed. The distribution of CNTs across the thickness of the facesheets may be uniform or functionally graded. The equivalent single- layer theory of Timoshenko is used toconstruct the Hamiltonian of the beam under the von Kármán type of geometrical nonlinearity assumptions.A uniform temperature field through the beam is also included in the formulation. The Ritz method withpolynomial basis functions is used to discrete the equations of motion and establish the matrix representation ofthe governing equations. A nonlinear eigenvalue problem is obtained and solved using a standard continuationprocedure. After validating the developed solution method and formulation, parametric studies are conductedto examine the influences of thermal environment, core thickness-to-face sheet thickness ratio, boundaryconditions, amplitude of vibrations, CNTs volume fraction and their distribution pattern. It is concludedthat an increase in the volume fraction of CNTs results in higher fundamental frequency and decreases thenonlinear-to-linear frequency ratio.     

Influence of the underneath cavity on buoyant‐forced cooling of the integrated photovoltaic panels in building roof: a thermography study

Airflow around building‐integrated photovoltaics (BIPV) has a significant impact on their hygrothermal behavior and degradation. The potential of reducing the temperature of BIPV using an underneath cavity is experimentally and numerically investigated in literature. Most of the models are oversimplified in terms of modeling the impact of 3D flow over/underneath of PV modules, which can result in a non‐uniform surface temperature and consequently a non‐homogenous thermal degradation. Moreover, the simultaneous presence of radiation and convection related to upstream wind, in addition to the combined impact of back‐ventilation and surface convection, is barely addressed in literature. However, these simplifications can result in the unrealistic loading climate conditions. This paper aims to present a unique experimental setup to provide more realistic climate conditions for investigating the ventilation potential of the underneath. The setup consists of a solar simulator and a building prototype with installed PV, placed inside an atmospheric wind tunnel to control upstream wind velocity. Thermography is performed using an infrared camera to monitor the surface temperature of the BIPV. The potential of an underneath cavity with various cavity heights and PV arrangement is further investigated in this paper. The outcome would be eventually useful in the development of practical guidelines for BIPV installation. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis and Optimization of Current-Driven Passive Mixers in Narrowband Direct-Conversion Receivers

Properties of the current-driven passive mixer are explored to maximize its performance in a zero-IF receiver. Since there is no reverse isolation between the RF and baseband sides of the mixer, the mixer reflects the baseband impedance to the RF and vice versa through simple frequency shifting. It is also shown that in an IQ down-conversion system the lack of reverse isolation causes a mutual interaction between the two quadrature mixers, which results in different high- and low-side conversion gains, and unexpected IIP2 and IIP3 values. With a thorough and accurate mathematical analysis it is shown how to design this mixer and its current buffer, and how to size components to get the best linearity, conversion gain and noise figure while alleviating the IQ cross-talk problem.     

A Jini service to reconstruct tomographic data

Distributed computing that uses dynamic networks will change the way we work and communicate thanks to the interaction of devices and services, that are automatically added and removed from the network as needed. The Jini technology, which is built atop the Java programming language, provides a homogenous view of the network and extends the ability of code to migrate in Java. This software design model simplifies the configuration and access to hardware devices and software services in a network. Thus, it becomes possible to execute new services without pre-installing software on client machines. This new programming paradigm is especially important in medical applications, where the reliable transmission of information is essential. This paper demonstrates how single photon emission computerized tomography data can be iteratively reconstructed using a Jini service.     

A hybrid multi-objective shuffled frog-leaping algorithm for a mixed-model assembly line sequencing problem

In this paper, a mixed-model assembly line (MMAL) sequencing problem is studied. This type of production system is used to manufacture multiple products along a single assembly line while maintaining the least possible inventories. With the growth in customers’ demand diversification, mixed-model assembly lines have gained increasing importance in the field of management. Among the available criteria used to judge a sequence in MMAL, the following three are taken into account: the minimization of total utility work, total production rate variation, and total setup cost. Due to the complexity of the problem, it is very difficult to obtain optimum solution for this kind of problems by means of traditional approaches. Therefore, a hybrid multi-objective algorithm based on shuffled frog-leaping algorithm (SFLA) and bacteria optimization (BO) are deployed. The performance of the proposed hybrid algorithm is then compared with three well-known genetic algorithms, i.e. PS-NC GA, NSGA-II, and SPEA-II. The computational results show that the proposed hybrid algorithm outperforms the existing genetic algorithms, significantly in large-sized problems.