This study focuses on the analysis of group scheduling heuristics in a dual-constrained, automated manufacturing cell, where labour utilization is limited to setups, tear-downs and loads/unloads. This scenario is realistic in today's automated manufacturing cells. The results indicate that policies for allocating labour to tasks have very little impact in such an environment. Furthermore, the performance of efficiency oriented, exhaustive, group scheduling heuristics deteriorated while the performance of the more complex, non-exhaustive heuristics improved. Thus, it is recommended that production managers use the simplest labour scheduling policy, and instead focus their efforts to activities such as job scheduling and production planning in such environments. 相似文献
An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young’s modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts.
In this study postbuckling behaviors of multiscale composite sandwich doubly curved piezoelectric shell with a flexible core and MR layers by employing Homotopy Perturbation Method in hygrothermal environment has been investigated. By using Reddy third shear deformable theory the face sheets and third-order polynomial theory of the flexible core the strains and stresses are obtained. A mathematical model for the multiscale composite layered shell with a flexible core and magnetorheological layer (MR) that incorporates the nonlinearity of the in-plane and the vertical displacements of the core is assumed. Three-phase composite shells with polymer/Carbon nanotube/fiber and polymer/Graphene platelet/fiber either uniformly or non-uniformly based on different patterns according to Halpin–Tsai model have been considered. The governing equations of multiscale shell have been derived by implementing Hamilton’s principle. Meanwhile, simply supported boundary conditions are employed to the shell. For investigating correctness and accuracy, this paper is validated by other previous researches. Finally, different parameters such as temperature rise, various distribution patterns, magnetic fields and curvature ratio are considered in this article. It is found these parameters have significant effect on the frequency–amplitude curves.
This article explores that the study on bending of magneto-electric-elastic nanobeams relies on nonlocal elasticity theory. The Vlasov’s model foundation utilizes the silica aerogel foundation. The guiding expressions of nonlocal nanobeams in the considered framework are used extensively and where parabolic third-order beam theory is achieved after using Hamilton’s principle. Parametric work is introduced to scrutinize the influence of the magneto-electro-mechanical loadings, nonlocal parameter, and aspect ratio on the deflection characteristics of nanobeams. It is noticed that the boundary conditions, nonlocal parameter, and beam geometrical parameters have significant effects on dimensionless deflection of nanoscale beams.
In this paper, we introduce a new adaptive controller design scheme for nonlinear telerobotic systems with varying time delays where the delays and their variation rates are unknown. The designed controller has the ability to synchronize the state behaviors of the local and the remote robots. In this paper, asymptotic stability in the presence of varying time delays is of interest. Using the proposed controller, asymptotic stability of the bilateral telerobotic system subject to any bounded yet unknown varying delay with a bounded yet unknown rate of change can be guaranteed. Besides the varying time delay, the proposed adaptive controller has the ability to adapt to the parameter variations in the local and the remote robots’ dynamics. It is shown that position and velocity errors between the local and the remote manipulators converge to the zero asymptotically, thus ensuring teleoperation transparency. Experimental and simulation results with a pair of PHANToM haptic devices and a pair of planar manipulators under varying time delays in the communication channel demonstrate the effectiveness of the proposed scheme. 相似文献
Microsystem Technologies - The original version of this article unfortunately contained a mistake. Farzad Ebrahimi was not listed among the authors. 相似文献
In many production environments where demand and lead times are variable, significant levels of safety stock inventory are required to assure timely production and delivery of the final product. Traditional models to determine the appropriate safety stock level may result in more safety stocks at sub-assembly and finished goods levels than necessary and thus lead to higher inventory carrying costs than desired. Such models generally incorrectly assume that the demand during the lead time follows a normal distribution. This paper revisits and analyses a re-ordering point inventory model developed by Estes (1973Estes, R. 1973. The joint probability approach and reorder point determination. Journal of Production and Inventory Management, 14(2): 50–56. [Google Scholar]) that accounts for demand and lead time variability without making any particular distributional assumptions. Instead, it focuses on historical data to determine the possible outcomes of the replenishment cycle. We compare the proposed model with the traditional model by conducting simulation analysis using three data sets obtained from an electronics manufacturer. The results indicate that the proposed model yields much closer to target service levels and lower inventory carrying costs than the traditional model, regardless of the data set used. 相似文献
Polystyrene (PS) finds diverse applications across various fields, often necessitating a hydrophilic PS surface. In this study, the PS films were prepared using PS–toluene solutions of 15, 20, and 25 mass percentage concentrations (% w/v). Here, the main focus is on the influence of concentration on the hydrophilization of the prepared PS thin films under atmospheric pressure air dielectric barrier discharge plasma treatment. The contact angle, surface energy measurements, atomic force microscopy, and Fourier-transform infrared spectroscopy analysis were conducted to evaluate the PS surface properties. Our results demonstrate, for the first time, the significant role of concentration in altering surface properties; the lower concentration of PS films leads to the most hydrophilic surface. Fourier-transform infrared spectroscopy analysis confirms an increase in the OH functional group on the PS surface. atomic force microscopy analysis reveals needle-shaped surface morphology, increased roughness and an expanded effective surface area. Surface energy analysis confirms an increase in the polar sector of surface energy. Overall, the findings from this research underscore the increase in film hydrophilicity with a decrease in PS–toluene concentration. 相似文献
Cellular processes are linked to the alignment (anisotropy) and orientation (directionality) of collagen fibers (i.e., landscape) in the native extracellular matrix (ECM). Given the vital role that cell-matrix interactions play in regulating biological functions, several microfluidic methods have successfully established anisotropic 3D collagen gels to develop quantitative relationships between structural cues and cellular responses. However, independently tailoring the fiber anisotropy and fiber directionality within a landscape remains a challenge. Here, a user-friendly microfluidic platform with a non-uniform channel geometry is used to control the degree of fiber anisotropy and directionality as a function of extensional strain rate and a defined flow path, respectively. New experimental capabilities, including independent control over the degree of fiber anisotropy and directionality, spatial gradients in anisotropy, and multi-material interfaces, are demonstrated. A channel peel-off technique provides direct access to the microengineered collagen landscapes, and the alignment of single MD-MB-231 cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC) is shown. Finally, the platform's modular capability is highlighted by integrating an ultrathin porous Parylene (UPP) membrane onto the microengineered collagen landscape as a method to control the degree of cell-matrix interaction. 相似文献
A series of heterogeneous catalysts including different molar ratios of CaO/talc was synthesized to study the transesterification reaction of canola oil and methanol under different reaction conditions. Characterization and kinetic results revealed that the activity of this catalyst was enhanced due to the increase of CaO/talc molar ratio value leading to an improvement in the biodiesel production. Moreover, the effect of various parameters on the activity of the undertaken catalysts was studied in order to determine the optimum process conditions. Leaching measurements and the durability of the CaO/talc catalyst under several reaction cycles were evaluated and proved it to be a stable catalyst. 相似文献
