Reducing cycle times in manufacturing and supply chains by input and service rate smoothing

A key performance parameter of a manufacturing network or supply chain is its cycle time; the time that a typical item spends in the network. A previous simulation study on a semiconductor assembly and test facility showed that cycle times could be reduced by having smooth input and service rates. This suggested that there is a “cycle time principle” that, for a system with a specified throughput or input rate, the shortest cycle times are obtained when the input and service rates do not vary over time. We prove that this principle is true for the M/G/1 and M/M/s queueing systems and Jackson networks. The analysis involves establishing several results on the concavity of waiting time probabilities and the convexity of expected waiting times and queue lengths, as functions of input and service rates. These results also have natural uses in other optimization problems.     

Tracking-error model-based predictive control for mobile robots in real time

In this paper, a model-predictive trajectory-tracking control applied to a mobile robot is presented. Linearized tracking-error dynamics is used to predict future system behavior and a control law is derived from a quadratic cost function penalizing the system tracking error and the control effort. Experimental results on a real mobile robot are presented and a comparison of the control obtained with that of a time-varying state-feedback controller is given. The proposed controller includes velocity and acceleration constraints to prevent the mobile robot from slipping and a Smith predictor is used to compensate for the vision-system dead-time. Some ideas for future work are also discussed.     

Experimental investigations of machining characteristics and removal mechanisms of advanced ceramics in high speed deep grinding

Machining characteristics and surface integrity of advanced ceramics, including alumina, alumina–titania, and yttria partially stabilized tetragonal zirconia, were studied under high speed deep grinding conditions. Material removal mechanisms involved in the grinding processes were explored. The material removal in the grinding of alumina and alumina–titania was dominated by grain dislodgement or lateral cracking along grain boundaries. The removal for zirconia was via both local micro fracture and ductile cutting. It was found that under a feed rate of 500 mm/min and for all the wheel speeds used, an increase in the wheel depth of cut (DOC) from 0.1–2 mm slightly improved the ground surface finish, but greatly prolonged the wheel life. This increase did not deepen the subsurface damage layer for the alumina and alumina–titania, but resulted in a slightly deeper damage layer for the zirconia.     

Infrared emission properties and energy transfer in ZnO-SiO2:Yb composites

Intense near-infrared emission at 1 μm has been obtained in ZnO-SiO₂:Yb³⁺ composites via a facile sol-gel method upon broadband ultraviolet light excitation. Systematic optical measurements including static and time-resolved photoluminescence have been performed to elucidate the energy transfer from ZnO quantum dots to Yb³⁺ ions. The dependence of energy transfer efficiency on Yb³⁺ concentration has been investigated in detail. Codoping with Li⁺ ions leads to about twice enhancement of the near-infrared luminescence intensity around 1 μm at room temperature. The enhancement in the luminescence intensity could be mostly attributed to the modification of the local symmetry around Yb³⁺ ions by codoping with Li⁺ ions.     

Contextualizing the ideas of technology in Korea—Questions of technology and early modern experiences

In the early to mid-2000s, Korea was touted as a strong IT (information technology) nation. But its IT success story has faded into the background less than half a decade’s time. Critiques hold among others the problem of hardware-oriented, commercialistic, and consumerist nature of IT environment including the centralized, statist IT governance responsible for hindering an IT take-off in Korea. This problematic environment of IT is fundamentally a material consequence of particular ideas of technology Korean society maintains—ideas of hardwarism, commercialism, and consumerism. Then the important question is the origin of these ideas. A large body of research argues the national modernization drive of the 1960s as an embryonic momentum in which hardware-centric, commercially oriented, and consumerist ideas of technology were disseminated in earnest. Persuasive as this argument is, the question still remains concerning how such perceptions about technology were embraced by the general populace at that moment with outright enthusiasm. This study argues that they were already gestated during the nation’s initial contact with modernity mostly by way of Japan in the context of the imperialistic world order of the late 19th century. And embedded as a paradigmatic structure, these ideas have been critical in the shaping of the trajectory of technology development and broadly a basic framework of modernization in Korea.     

High speed flow visualization of a closed loop pulsating heat pipe

We provide the high speed flow visualization results for the closed loop pulsating heat pipes (PHPs). It is identified that there exists the bulk circulation flow which lasts longer and the local flow direction switch flow. The bubble displacements and velocities do display the sine oscillation waves but the local oscillation waves were superimposed with short periods and small oscillation amplitudes. Distinct with the methanol PHP, the water PHP has quasi-rectangular shape for the bubble displacements, behaving the periodic stationary-fast movement characteristics. Dispersed bubbles, vapor plugs and the transition flow patterns from the dispersed bubbles to the vapor plugs are the major flow patterns in PHP. Long vapor plugs are only observed for the methanol PHP, not observed in the water PHP, due to the vapor plug deformation and breakup mechanism, which was analyzed in the present paper. Bubble sizes have quasi-fixed distributions versus time over the entire PHP, but have unsymmetry distributions among various tubes. The complicated combined effects of bubble nucleation, coalescence and condensation are responsible for the oscillation flow in PHP.     

Stereoscopic view synthesis based on region-wise rendering and sparse representation

Depth image-based rendering (DIBR), which is used to render virtual views with a color image and the corresponding depth map, is one of the key techniques in the 2D to 3D conversion process. One of the main problems in DIBR is how to reduce holes that occur on the generated virtual view images. In this paper, we make two main contributions to deal with the problem. Firstly, a region-wise rendering framework, which divides the original image regions into three special classes and renders each with optimal adaptive process respectively, is introduced. Then, a novel sparse representation-based inpainting method, which can yield visually satisfactory results with less computational complexity for high quality 2D to 3D conversion, is proposed. Numerical experimental results demonstrate the good performance of the proposed methods.     

Multisoliton complexes in fiber lasers

The formation of stationary and non-stationary pulse groups is regularly observed in multiple pulse soliton fiber lasers. The environment developed in this study for the flexible investigation of this phenomenon is based on the cavity comprising a semiconductor saturable absorber mirror (SESAM) with complex dynamics of absorption recovery and all-fiber dispersion management. The detailed experimental and theoretical considerations show that multiple pulsing in fiber systems offers numerous embodiments ranging from stationary bound states to chaotic bunches. The pulse interaction through the dispersive waves was found to produce a principal impact on the bound state formation. The stability and transformation of stationary bound states and bunch propagation have been also addressed.