A New Approach to Correlate the Frictional Performance of Fin-and-Tube Heat Exchangers in Wet Conditions

This study presents a new approach to correlate the frictional performance of fin-and-tube heat exchangers in "completely wet" and "partially wet" conditions by using "completely dry" data. A total of 22 samples of uncoated plain fin-and-tube heat exchangers are used to develop the associated frictional correlation. The developed correlation is capable of predicting the frictional performance of "completely wet" and "partially wet" conditions with a mean deviation of 7.2%.     

Effect of LiClO4 on the thermal and morphological properties of organic/inorganic polymer hybrids

This paper describes the thermal properties, morphologies, and interactions within the binary and ternary blends of poly(methyl methacrylate) (PMMA), octa(phenol)octasilsesquioxane (OP-POSS), and LiClO₄. In the binary PMMA/OP-POSS blends, the OP-POSS molecules tend to aggregate and result in a decrease (19 °C) in the glass transition temperature. In the ternary PMMA/LiClO₄/OP-POSS blends, however, the OP-POSS molecules form small sphere-like domains (20 nm) leading to the composite's glass transition temperature increasing by up to 30 °C. Based on these FT-IR spectra, the addition of LiClO₄ influenced the probability of hydrogen bonds formed between PMMA and OP-POSS and these SEM micrographs, DSC, and XRD data indicated that the addition of LiClO₄ is a convenient and simple approach toward dispersing the OP-POSS nanoparticles within PMMA, where the presence of LiClO₄ changes the physical effect of OP-POSS from that of a diluent role to a cross-linker role.     

Thermal stability of indium tin oxide thin films co-sputtered with zinc oxide

The thermal stability of indium tin oxide (ITO) films and ITO co-sputtered with zinc oxide (ZnO) films at different zinc atomic ratios in various atmospheres are investigated. The resistivity of the annealed ITO films decreased with increased annealing temperatures. The improved electrical properties were attributed mainly to the increase in carrier concentration originating from the significant formation of oxygen vacancies in the ITO films. In contrast, due to the lower oxidation potential of zinc ions, the resistivity of the annealed co-sputtered films showed no significant reduction and an increase with annealing temperatures. The film decomposition due to the high degree outdiffusion of oxygen atoms and aggregation of In atoms observed from the metal-like In phase in the diffraction patterns was responsible for the drastic thermal degradation in the electrical and optical properties of the samples annealed at elevated temperatures in reducing gas atmosphere. In contrast, the superior thermal stability of the co-sputtered films, at an atomic ratio of 60% annealed in reducing gas atmospheres, was ascribed to the stable Zn₃In₂O₆ crystalline structure that appeared in the diffraction pattern. The absorption edge observed from the optical transmittance of these annealed films also showed evidence of carrier concentration evolution in various annealing atmospheres. The lower oxidation potential of the zinc atoms introduced into the ITO films was concluded to be efficient in compensating for the formation of oxygen vacancies resulting in the alleviated decomposition behavior during thermal annealing.     

An adaptive channel preemption model for small‐cell embedded large‐cellular networks

In this paper, we present an analytical model of adaptive channel preemption (ACP) for small‐cell embedded large‐cellular (SCELC) networks. An SCELC network consists of a fixed base station (FBS) with large coverage and many embedded base stations (EBS) with relatively small coverage. Channel capacity in an FBS cell may become insufficient when traffic is unexpectedly increased particularly in some special occasion. This paper considers two aspects of dynamically allocating channels for an SCELC network. First, by increasing one or more EBS cells within an FBS cell, the proposed ACP can reduce blocking probability of new calls. Second, to reduce dropping probability of handoff calls, the proposed ACP allows a handoff call to preempt an on‐going call, when the latter is located in an EBS cell or in the overlapping area of two adjacent FBS cells. For the purpose of performance evaluation, we build an analytical model with 4‐tuple Markov chains. Numerical results reveal that embedding one or more EBS cells inside an FBS cell needs to be done carefully since it results in a tradeoff between the reduction of new‐call blocking probability and the increase of handoff‐call dropping probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Method for determining the junction temperature of alternating current light-emitting diodes

A numerical simulation was used to simulate the temperature distribution during AC and DC operations of an alternating current light-emitting diode (AC LED). The relationship between the junction temperature and the temperature at the centre of the bottom surface of the submount of an AC LED was measured under DC operation. This relationship was confirmed by numerical simulation. The numerical results were consistent with the experimental observations in that the temperature at the centre of the bottom surface of the submount was insensitive to the current variations that occur in an AC LED, probably because of the large mass of the submount. However, it was difficult to measure the temperature oscillation at the junctions in an AC LED, although this oscillation can be clearly seen in the numerical results. Thus, the authors propose a formula for predicting the range of the oscillating junction temperature for an AC LED.     

Dynamics of a microchain of superparamagnetic beads in an oscillating field

The dynamics of microchains containing superparamagnetic particles in an oscillating field are studied experimentally. The chains are first formed by a static directional field, and then manipulated by an additional dynamical perpendicular field. The present methodology represents a simple reversible chaining process, whose particles can be re-dispersed after removal of the field. The motion of superparamagnetic chains is dominated by magnetic torque and induced hydrodynamic drag. The effects of key parameters, such as field strengths and the lengths of particle chains, are thoroughly analyzed. Distinct behaviors, from rigid body oscillations and bending distortions to rupture failures, are observed by increasing the amplitudes of oscillating fields or chains’ lengths. Because of lower induced drag, a shorter chain follows the field trajectory closely and oscillates more synchronically with the external field. On the other hand, the influences of field strengths are not consistent. Even the overall oscillating phase trajectory in a stronger external field deviates less significantly from the corresponding field trajectory, a stronger dynamical component of the external field results in larger phase angle lags at certain points. The experimental results confirm the criterion of ruptures can be effectively determined by the value of (N*Mn ^1/2), where Mn is the Mason number defined as the ratio of induced drag to dipolar attraction, and N represents the number of particles contained in a chain.     

Generally weighted moving average control chart for monitoring process variability

Most applications of the EWMA control chart for monitoring processes depend on detecting shifts in the process mean. The problem of detecting an increase in process variability, which can also strongly affect the quality of products, is perhaps more important. When a process moves from the pilot phase to the production phase, the mean may not shift but the variation will probably increase because new sources of variation are introduced, including new people and materials. A simulation is performed to evaluate the ARL to false alarm and to monitor the change in the process variability of the EWMA control chart and the GWMA control chart. An extensive comparison reveals that the GWMA control chart is more sensitive than the EWMA control chart in monitoring the variance of a process. The results of this study can be applied to monitor the process variability in automated industries.     

Integrating multivariate engineering process control and multivariate statistical process control

Multivariate engineering process control (MEPC) and multivariate statistical process control (MSPC) are two strategies for quality improvement that have developed independently. MEPC aims to minimize variability by adjusting process variables to keep the process output on target. On the other hand, MSPC aims to reduce variability by monitoring and eliminating assignable causes of variation. In this paper, the use of MEPC alone is compared to using the MEPC coupled with MSPC. We use simulations to evaluate the average run lengths (ARL) and the averages of the performance measure. The simulation results show that the use of both MEPC and MSPC can always outperform the use of either alone. To detect small sustained shifts of the mean vector, combing MEPC with a multivariate generally weighted moving average (MGWMA) chart (MEPC/MGWMA) is more sensitive than the MEPC/multivariate exponentially weighted moving average (MEWMA) chart and MEPC/Hotelling’s χ² chart. An example of the application, based on the proposed method, is also given.     

Testing multi-characteristic product capability indices

Recently, studies associated with testing the quality and performance of each process for a product with multi-characteristics are proposed more often. However, most studies are limited to discussing one single type of quality characteristic. Practically, a multi-characteristic product is potentially composed of three types: smaller-the-better, larger-the-better, and nominal-the-best. In this paper, we propose an integrated product capability index which considers these three different types of quality characteristics. According to the theory of testing hypothesis, we develop a testing procedure for the product capability index to judge whether the process capabilities of total quality characteristics meet the customers’ demands. In addition, the relationship between the product capability index and the yield of the entire product will be introduced. Finally, an example is provided as a practical application.     

Strengths and weaknesses of finite element modeling deep hole drilling as compared with beam and column equations

Deep hole drilling has been studied mainly experimentally in the past. Recently, some theories using beam or column equations have been proposed, which involved complicated mathematical efforts. This work analyzed deep hole drilling by a finite element model (FEM). Results of modal analysis on the established FEM were compared with results from Euler beam equations. Further analysis showed that the FEM could also predict straightness deviation as did the column equation. In addition, FEM could analyze the effects of variable support distance which neither beam nor column equation could. Other analysis results are also presented. The results in this study showed the strength and weakness of the FEM.