1,721,041 research outputs found
Mathematical models linked to design and reconfigure cellular manufacturing systems. X° AITeM "Enhancing the Science of Manufacturing
No full textThe allocation of improvement programs in a flow shop for single and multi-products: A simulation assessment
No full textThe continuous improvement is crucial to increase the company's competitiveness in today's market. This paper proposes a multi-dimension simulation environment to test improvement programs in a flow shop context. The simulator developed tests the programs proposed in the literature: centralised, distributed and hybrid. The main original contributions of this research are: a simulation environment with higher details; the analysis of several performance measures as the throughput, lead time, work in process, average utilisation and the defected products for each workstation of the production line; the case of flow shop with multi-products. The experimental plan concerns the change of the following issues: set-up times, bottleneck position and process times. The flow shop without improvement programs is the benchmark of the performance measures. The simulation results show how the centralised policy is the better in a single product case, while the hybrid policy leads to the better results in case of multi-products
Review of Responsiveness and Sustainable Concepts in Cellular Manufacturing Systems
No full textCellular manufacturing systems are widely used due to their advantageous capability of combining the flexibility of the job-shop and the productivity of the flow-shop. In recent years, the reduction of the product life cycle, variation in demand products, and introduction of new technologies, have driven the manufacturing companies to improve responsiveness, thus reducing the cellular manufacturing life cycle with a focus on re-designing the cells. Another issue concerns the sustainability of the manufacturing systems due to the introduction of energy costs in the design model of cellular manufacturing systems. This study is an overview of the more recent works on design approaches to improve the responsiveness and the models to support the sustainability of cellular manufacturing systems. The analysis of the literature review highlights the main findings and suggests future development paths considering the open problems in this field
Structural Properties and Photoluminescence Study of CdSe/Si Epilayers Deposited by Laser Ablation
Full text linkStructural and optical characterization of CdSe thin films deposited by laser ablation technique on silicon (100)- and (111)-oriented substrates are reported. The effect of the substrate orientation on the growth and luminescence features of the two types of epilayers are investigated. Photoluminescence spectra of CdSe films measured from 10 up to 300 K and as a function of the laser excitation intensity give detailed information on the extrinsic levels localized in the forbidden gap. Temperature dependence of the energy of the n = 1 exciton line has been fitted by the Varshni's equation and by an expression containing the Bose-Einstein occupation factor for phonons. Parameters related to the electron-phonon interaction have been obtained. Temperature dependence of the broadening of exciton linewidth has been studied in terms of an expression containing both exciton-optical phonon and exciton-acoustic phonons coupling constants. Evaluated fitting parameters have shown the dominant contribution of optical phonons in mechanism of the exciton line broadening
Evaluation of cellular manufacturing configurations in dynamic conditions using simulation
No full textThis paper investigates the performance of classical cellular manufacturing systems compared to other two systems proposed in literature: fractal cells and remainder cells. This paper proposes three strategies to control a cellular manufacturing system with remainder cell and how to configure and control a fractal manufacturing system. The performance measures of the manufacturing systems are analyzed when several unforeseen events occur as: machine breakdowns, production mix changes, demand fluctuations, and processing time variability. A simulation environment developed by Arena® package was used to investigate the three manufacturing system configurations. The performance measures investigated are: throughput, throughput times of the parts, work in process, manufacturing utilization, and due date performance (tardiness). The simulation results show how the fractal and remainder cells can be a valid alternative to cellular manufacturing systems in a very dynamic environment
Temperature dependence of the optical properties of ZnSe films deposited on quartz substrate
No full textZnSe thin films were deposited by pulsed laser ablation
on quartz substrate. The filmswere investigated by different
characterization techniques, such as X-ray diffraction, Raman
microspectroscopy, absorption, reflectivity, and photoluminescence
spectroscopy. The XRD analysis showed the formation
of cubic phase polycrystalline films. The Raman spectra confirmed
the formation of ZnSe by the presence of TO and LO
peaks at 202 cm−1 and 252 cm−1, respectively. The analysis
of absorption and reflectivity measurements permits evaluation
of the band gap and excitonic energy at low temperature and
the temperature dependence of the energy gap. The photoluminescence
measurements indicated the possibility of obtaining
intrinsic band-band radiative emission up to room temperature
Temperature Dependence of the Red-shift and Broadening of the Exciton Line in CdSe/GaAs Laser Ablated Heterostructures
No full textA detailed photoluminescence investigation of the thermal red-shift and broadening of the excitonic line of CdSe films grown on bulk GaAs substrate by laser ablation technique is presented. Material parameters related to the electron-phonon interaction have been obtained by fitting the experimental data to phenomenological models. The relative contribution of both acoustic and optical phonons to the band gap shrinkage and the dominant role of impurity scattering, at low temperatures, in the excitonic line broadening are discussed
Effect of dielectric Barrier Discharge Plasma on Alumina electrodes evidenced by Thermoluminescence and Optically Stimulated Luminescence analysis
No full textContacting organic molecules by metal evaporation
No full textReproducible electrical contacts to organic molecules are created non-destructively by indirect electron beam evaporation of Pd onto molecular films on cooled substrates. In contrast, directly evaporated contacts damage the molecules seriously. Our conclusions are based on correlating trends in properties of a series of molecules with systematically varying, exposed functional groups, with trends in the electrical behaviour of Pd/molecule/GaAs junctions, where these same molecules are part of the junctions
Temperature Study of Absorption and Photoluminescence Spectra of CdSxSe1-x Films Grown on Quartz Substrate by Pulse Laser Ablation
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