X¯ chart with adaptive sample sizes

Standard Shewhart control charts employ fixed sample sizes at equal sampling intervals. By varying the sample size depending on the current location of the process mean, the mean time to detect an off-target condition can be reduced. The adaptive-sample-size control chart is compared with the fixed-sample-size control chart in terms of average run length under shifts in the process mean of variable magnitude. Significant improvements have been obtained with the adaptive-sample-size charts, particularly for small shifts. These improvements are achieved without increasing the in-control average sample size beyond that of the fixed-sample-size approach. A fast initial response is suggested and advantages of the procedure over fixed-sample-size control are illustrated with two examples from discrete manufacturing processes.     

Unconditional performance of the X¯ chart: Comparison among five standard deviation estimators

To design the control chart, the in-control process mean and standard deviation must be estimated from historical samples, negatively affecting the chart's performance. The grand mean of a sample is the well-established estimator for the process mean. However, regarding the standard deviation, the chart's user has at least five different estimators available in the literature to choose from. In this paper, using intensive simulations, we study and compare the performance of the chart (under normality assumption and three-sigma limits) among the most five used standard deviation estimators. The unconditional in-control run length (RL₀) is the most commonly used performance measure of a control chart, and many authors base their comparisons on the expectation of the RL₀ or on the mean square error of the estimators. In contrast, we based our comparison on the proportions of the RL₀ concentrated at some intervals that are usually considered undesired by the practitioner due to the high incidence of false alarms during the process monitoring (e.g., RL₀ between 1 and 200), occurring earlier than expected when compared with known parameter situations. From our results, all the studied standard deviation estimators generate similar performances. However, even with this similarity, we showed that one of the most recommended standard deviation estimators in the literature in control charts with estimated parameters may be the most inappropriate choice based on the undesired RL₀ proportions.     

Bayesian estimation of the rate at which a process,monitored by an X̄ chart,goes out of control

This paper examines a process that is monitored by an X? chart. It is assumed that the process may go out of control due to the occurrence of any of several independent assignable causes. The time until each specific assignable cause occurs is exponential, but the distributional parameters of the various causes are unknown and are not necessarily identical. A Bayesian approach is used to estimate these parameters. The approach encompasses prior knowledge about the parameters as well as observations of the process, including when the out-of-control situation was detected and the associated assignable cause. Numerical illustrations are provided that indicate how the posterior results depend upon the choice of the parameters of the prior distributions.     

A simplified procedure for the economic design of X¯ -charts

A simple procedure for selecting the optimal economic design of an X¯ control chart for a single assignable cause system is presented that can be applied at the workshop level. The procedure only consists of solving an explicit equation for h (sampling interval) in terms of n (sample size) and k (control limit factor). We conclude that our model is not only more accurate, more applicable, and more flexible, but also simpler to solve than those of Duncan's model (1956), Goel et al.'s model (1968) and Chiu and Wetherill's model (1974).     

Properties of hydrothermally modified silica gels — Effect of the parameters of porous structure on the course of the modification process

The effect of the parameters of globular structure (diameter of globules and number of their contact points) on the course of a texture modification process has been examined. Modification of silica gels was carried out in an autoclave at elevated pressure in the temperature range 110–300°C and in a water vapour atmosphere. Silica gels having specific surface area of 64–830 m²/g and predominant pore radii of 40–1000 Å were modified. The mechanism of hydrothermal treatment is relatively complex. It depends, among other things on different parameters of globular texture, the temperature of a process and on the presence of different admixtures in the adsorbent being modified. Above 200°C the course of hydrothermal modification depends only slightly on the nature of the silica gel (narrow or wide porous).     

What is the appropriate length of the publication period over which to assess research performance?

National research assessment exercises are conducted in different nations over varying periods. The choice of the publication period to be observed has to address often contrasting needs: it has to ensure the reliability of the results issuing from the evaluation, but also reach the achievement of frequent assessments. In this work we attempt to identify which is the most appropriate or optimal publication period to be observed. For this, we analyze the variation of individual researchers’ productivity rankings with the length of the publication period within the period 2003–2008, by the over 30,000 Italian university scientists in the hard sciences. First we analyze the variation in rankings referring to pairs of contiguous and overlapping publication periods, and show that the variations reduce markedly with periods above 3 years. Then we will show the strong randomness of performance rankings over publication periods under 3 years. We conclude that the choice of a 3 year publication period would seem reliable, particularly for physics, chemistry, biology and medicine.     

A protein powder agglomeration process using açaí pulp as the binder: An analysis of the process parameters

This work investigated the fluidized bed agglomeration of a plant protein powder blend using an açaí pulp binder in order to improve the physical and handling properties. The blend was prepared mixing isolated pea protein powder and concentrated rice protein powder. The influence of air temperature and binder flow rate on the moisture content, particle size and process yield was evaluated using a factorial design. The anthocyanins content, wettability and flowability of the powder was also evaluated. The agglomeration produced large granules with better physical properties, indicating that açaí pulp can be used as a binder. Statistical analysis showed that binder flow rate had the greatest influence on moisture content and process yield; air temperature had a greater effect on particle size. The optimum condition (T = 75 °C, Q = 2.0 mL/min) resulted in granules that were twice as large as the initial particles. Anthocyanins were incorporated (2.34 mg/100 g) with an acceptable moisture content (≤10%) and a high yield (>75%). Flowability was greater in the agglomerated powder than in the raw material with a wetting time reduction of about 77.0%. The resulting protein powder combines the properties of an instant powder with health and nutritional benefits.     

Improving the machining performance characteristics of the µEDM drilling process by the online cryogenic cooling approach

Productivity and surface quality would significantly affect the performance of the micro electrical discharge machining process (µEDM). Thus, the machining performance would be enhanced by improving the material removal rate (MRR) and surface quality. In this investigation, cryogenic LN₂ cooling was introduced to the conventional µEDM setup for developing an innovative process of cryogenically cooled µEDM process (CµEDM). The favorable outcomes of this process were estimated by selecting discharge current (I_p) and pulse on duration (T_on) for determining the effects of the machining performance including MRR and surface integrity. Surface quality was also analyzed by microstructural analysis and a scanning electron microscope (SEM) for evaluating the effects of the cryogenically cooled µEDM process. The experimental result shows 54–62% improvement in MRR and 22–36% improvement in average roughness values. Hence, it is suggested that cryogenically cooled µEDM facilitates improvement in productivity and surface quality.     

The influence of process parameters on the structure and morphology of pulsed plasma‐polymerized octafluorotoluene films

Abstract

This work describes amorphous fluorinated polymer films deposited by pulsed plasma polymerizations of octafluorotoluene (PPP‐OFT) monomers on ITO glass as the hole‐injection layer of organic electroluminescent (EL) devices, in order to study the influence of sample position and duty cycle on PPP‐OFT film characteristics, and also to find a good process to yield a higher retention degree of monomers and lower roughness of PPP‐OFT fluorocarbon films. Experimental results revealed that PPP‐OFT films deposited at positions far away from the RF coil and close to the monomer inlet showed less roughness than films deposited near the high RF‐flux regions. In addition, the retention of the monomers in the PPP‐OFT layer will be high if the deposition is conducted near the monomer inlet but some distance away from the RF electrode. Moreover, amorphous fluorinated polymer films can be deposited with higher fluorine to carbon (F/C) ratios and CF₂ contents at proper substrate positions by means of different sticking coefficients of free radicals dissociated by octafluorotoluene monomers.     

The lateral load-deformation response of RC walls with a consideration of the height–length ratio

Reinforced concrete (RC) walls play an important role in resisting earthquakes, so understanding the lateral load-deformation response of an RC wall subjected to an axial load, shear, and moment is essential to nonlinear structural analysis. In this study, the moment-bending deformation response of an RC wall under an axial load and moment is obtained from moment–curvature analysis using the wall’s proper plastic hinge length. Furthermore, modified compression-field theory, adjusted according to the height–length ratio of the wall, is used to calculate the shear–shear deformation response of the wall under an axial load and shear. By integrating the moment-bending deformation and the shear–shear deformation responses, the lateral load-deformation response of the RC wall under axial load–moment–shear interaction can be reasonably determined. To confirm the reliability of the proposed method, experimental results for 67 RC walls are compared with analysis results from the proposed method. The statistical results show that the proposed method accurately predicts the lateral ultimate load but somewhat underestimates the lateral ultimate deformation. Finally, this paper gives an example using an equivalent column to simulate an RC wall using SAP2000 pushover analysis.     

Experimental investigation of the stability of a clearance‐excited rotor system with optimal parameters

Abstract

The instability caused by aerodynamic forces from blade‐tip clearance is one of the most troublesome problems found in high performance tur‐bomachinery. An optimization technique has been proposed in previous work to improve the stability of a rotor‐bearing system. In this work, the validity and the practical procedure of the optimization technique are experimentally verified and demonstrated using a rotor‐bearing system. The experimental results verify the important theoretical conclusion that the threshold of stability of a rotor‐bearing system can be significantly increased by slight modification of the rotor diameters. Two examples are given to show the detailed procedure when the proposed optimization technique is used to increase the threshold of stability of an existing rotor‐bearing system.     

Integrating copper at the nanometer length scale with Sn–3·5Ag solder to develop high performance nanocomposites

Abstract

In the present study, copper at the nanometer length scale is integrated with Sn–3·5Ag using the technique of powder metallurgy incorporating energy efficient microwave sintering. Superior mechanical characteristics were realised for the formulations containing nanometer length scale copper in excess of 1 vol.-%. Sn–3·5Ag reinforced with 2·5 vol.% nanosize copper particulates exhibited the best overall mechanical characteristics. Particular emphasis is placed on studying the effect of the increasing presence of nanosize copper particulates on the microstructure and property evolution of the Sn–3·5Ag matrix.     

Influence of material and process parameters on microstructure evolution during the fabrication of carbon–carbon composites: a review

Journal of Materials Science - Carbon–carbon composites (CCCs) are a unique form of carbon fiber-reinforced materials that exhibit excellent thermomechanical properties under extreme...     

The control of the diameter and length of α-MnO2 nanorods by regulation of reaction parameters and their thermogravimetric properties

α-MnO₂-type single-crystal nanorods were synthesized under hydrothermal conditions based on the redox reaction of KMnO₄ in an acidic environment. Several reaction parameters, like the reaction temperature, the reaction time and the concentration of KMnO₄ in the reaction mixture, were varied in order to determine their impact on the structure, the dimensions of the synthesized nanorods, and as well on their thermogravimetric properties. It was found that the reaction time has no significant influence on the diameter, although it has a strong influence on the length of the obtained nanorods. On the other hand, the concentration of KMnO₄ in the reaction mixture has a strong impact on both the diameter and the length. With an increasing concentration of KMnO₄ in the reaction mixture the average lengths and diameters of the isolated MnO₂ nanorods are reduced. The change in dimensions of the synthesized nanorods is reflected in their thermogravimetric properties.     

Identification of thermomechanical parameters based on the virtual fields method combined with the sampling moiré method

Thermomechanical parameters are important indicators for evaluating the mechanical properties of superalloys and generally include the coefficients of stiffness and thermal expansion at high temperatures. At present, there are few methods for simultaneously characterising the thermomechanical parameters of superalloys, especially single-crystal superalloys. To satisfy the demand for simultaneously identifying the thermomechanical parameters of orthotropic superalloys, an optimised virtual fields method for decoupling the thermomechanical parameters was developed in this study by combining the self-developed heat-resistant grids and the sampling moiré method. First, several factors, including the oblique angle of the grids, image noise and thermomechanical coupling phenomena, were studied through numerical experiments to analyse their influences on the identification accuracy. Then, an optimised identification strategy was established. Finally, the thermomechanical parameters of Ni-based polycrystalline and single-crystal superalloys were successfully identified and comparatively studied. The identification results demonstrate that the proposed method is highly accurate and robust. This research will provide an effective way to accurately characterise the multiple parameters of superalloys at high temperatures.     

Investigation of the effect of solidification processing parameters on the rod spacings and variation of microhardness with the rod spacing in the Sn–Cu hypereutectic alloy

Sn–3 wt% Cu hypereutectic alloy was prepared in a graphite crucible under the vacuum atmosphere. The samples were directionally solidified upwards under argon atmosphere with different temperature gradients (G = 4.24–8.09 K/mm) at a constant growth rate (V = 7.64 μm/s) and with different growth rates (V = 2.24–133.33 μm/s) at a constant temperature gradient (G = 4.24 K/mm) by using a Bridgman type directional solidification apparatus. The microstructure of directional solidified Sn–3 wt% Cu alloy seems to be rod eutectic structure. The influence of the growth rate (V) and temperature gradient (G) on the rod spacing (λ) and undercooling (ΔT) were analysed. The values of λ²V, λ²G, ΔTλ, ΔTV^−0.5 and ΔTG^−0.5 were determined by using the Jackson–Hunt eutectic theory. The dependence of microhardness (HV) on the rod spacing (λ) was analyzed. According to present results, it has been found that the value of HV increases with the increasing the value of λ.     

Simulating the behaviour of fresh concrete with the Distinct Element Method – Deriving model parameters related to the yield stress

This article describes a numerical approach based on the Distinct Element Method (DEM) as a means of simulating fresh concrete during its different working processes. First, a rheological model for fresh concrete and its implementation into a DEM code are presented. Then the main focus is directed at establishing an algorithm to derive the model parameters related to yield stress according to the Bingham model. For this an analytical prediction of stress distribution at the beginning of the slump-flow test is used as reference for the corresponding numerical analysis. For the sake of validation, the analytical and numerical predictions of the final shape of the concrete cake in the slump-flow test are compared. The validation was performed for three different reference values of yield stress. Additionally, the numerical and analytical results of the so-called LCPC-box test were evaluated for the same sets of parameters. The results of the numerical analysis agreed well with the results predicted by analytical solutions for all parameter combinations. Therefore, the proposed algorithm was shown to be a sound procedure in linking yield stress of the simulated concrete to the bond strength, which is the main parameter of the model suggested.     

Mill,material, and process parameters – A mechanistic model for the set-up of wet-stirred media milling processes

Stirred media milling is frequently used to generate nanoparticles for industrial applications such as paints, inks, and food or for the life sciences. Each product suspension has different requirements and therefore different material and formulation parameters. The first attempts to set up a new process are experimental in nature, especially the determination of a suitable composition. To adapt a process to the production scale, more experimental work is often needed to determine suitable operation parameters with regard to energy consumption, throughput, and investment cost. The energy consumption is influenced by operation parameters such as the size of the grinding media or the stirrer tip speed, whereas the investment costs are influenced by the mill geometry and size and the type of grinding media used. Therefore, it is challenging to transfer or scale up processes because lab-scale mills are smaller and may have different geometries than production-scale mills. Moreover, it is well known that the lab-scale operation parameters cannot be easily adapted to the production scale. In this study, the stress model developed by Kwade was improved by introducing parameters corresponding to the mill and the material in addition to the process parameters. Using this model, the optimum operating conditions for stirred media milling processes can be determined with a reduced amount of experimental work, even for geometrically unequal mills.