Quality Improvement for Dynamic Ordered Categorical Response Using Grey Relational Analysis

Product design is increasingly complicated and some quality characteristics cannot be directly measured. These quality characteristics are generally classified into several categories by visually examining the externals of products and forming an ordered system response. Most studies of quality improvement focus primarily on the quantitative form. Studies of ordered categorical response in a state system have been proposed over recent years. However, cases of an ordered categorical response in a dynamic system have rarely been seen. This study utilises grey relational analysis, from grey system theory, to develop a procedure for improving the ordered categorical response in a dynamic system, based on Taguchi’s parameter design. The proposed procedure can determine effectively the optimal factor level combination for an ordered categorical response in a dynamic system. A case study for improving the uniformity of plating in the lead frame process involved in semiconductor packaging is provided to demonstrate the effectiveness of the proposed procedure. ID="A1"Correspondance and offprint requests to: Dr C.-H. Wang, Department of Industrial Engineering and Management, Chinmin College, Miao-Li, Taiwan, 351. E-mail: wch@ms.chinmin.edu.tw     

Kinetic and autocatalytic effects during the hydrogen production by methane decomposition over carbonaceous catalysts

The reaction kinetics of methane decomposition to yield hydrogen and carbon has been investigated comparing different types of carbonaceous catalysts: two ordered mesoporous carbons (CMK-3 and CMK-5) and two commercial carbon blacks (CB-bp and CB-v). The evolution of the reaction rate along the time has been analyzed concluding that it is governed by different and opposite events: reduction of active sites by carbon deposition, autocatalytic effects of the carbon deposits and pore blockage and diffusional constraints. A relatively simple kinetic model has been developed that fits quite well the experimental reaction rate curves in spite of the complexity of the involved phenomena.     

Testing and estimation of purely nonparametric effects in repeated measures designs

The several sample case of the so-called nonparametric Behrens-Fisher problem in repeated measures designs is considered. That is, even under the null hypothesis, the marginal distribution functions in the different groups may have different shapes, and are not assumed to be equal. Moreover, the continuity of the marginal distribution functions is not required so that data with ties and, particularly, ordered categorical data are covered by this model. A multiple relative treatment effect is defined which can be estimated by using the mid-ranks of the observations within pairwise samples. The asymptotic distribution of this estimator is derived, along with a consistent estimator of its asymptotic covariance matrix. In addition, a multiple contrast test and related simultaneous confidence intervals for the relative marginal effects are derived and compared to rank-based Wald-type and ANOVA-type statistics. Simulations show that the ANOVA-type statistic and the multiple contrast test appear to maintain the pre-assigned level of the test quite accurately (even for rather small sample sizes) while the Wald-type statistic leads, as expected, to somewhat liberal decisions. Regarding the power, none of the statistics is uniformly superior. A real data set illustrates the application.     

Discovery of ordered tetragonal and cubic phases in the morphotropic phase boundary region of (1-x)Bi(Mg3/4W1/4)O3-xPbTiO3 piezoceramics

Studies on (1-x)[Bi(Mg_3/4W_1/4)O₃]-xPbTiO₃ ceramics across morphotropic phase boundary have been done to investigate the crystal structure and structure-property correlations. Rietveld structure refinement reveals that the structure of the morphotropic phase boundary compositions consists of coexisting ordered tetragonal and cubic phases for 0.55 < x < 0.72, not reported earlier. The structure is B-site ordered cubic (space group Fm-3m) for the compositions with x ≤ 0.55, B-site ordered tetragonal (space group I4/m) for x ≥ 0.72. The structure gradually transforms into disordered tetragonal phase (space group P4mm) for higher concentrations (x) of PbTiO₃. Raman studies also confirm the B-site ordered structure for the compositions close to morphotropic phase boundary. For all the compositions investigated, two peaks are observed in the temperature dependence of the permittivity, originating due to dielectric relaxation and structural transition from tetragonal (I4/m) to cubic (Fm-3m) phase. A new phase diagram of the solid solution is established.     

Hydrogen storage in cobalt-embedded ordered mesoporous carbon

Ordered mesoporous carbons (OMCs) were synthesized by using ordered mesoporous silica as a template, and chitosan as carbon precursors. A novel process of pre-impregnation is proposed to prepare cobalt-embedded OMC. This process is based on using cobalt chelated chitosan as carbon precursor. The surface functional groups and metal contents were determined by X-ray photoelectron spectroscopy. The bulk cobalt contents in the cobalt-embedded OMCs were measured by an atomic absorption spectrometer. The morphology of the OMCs was observed by small angle X-ray scattering analysis and transmission electron microscope. The OMC texture characteristics were determined by using nitrogen adsorption analysis. Hydrogen capacities of the OMCs were obtained by a volumetric method. The cobalt-embedded OMCs possess obviously higher hydrogen adsorption capacity than that of pure OMC. At 298 K and under 5.5 MPa, the hydrogen capacities of the OMC and OMC–Co-5 are 0.2 and 0.45 wt%, respectively. The H₂/Co ratio of the hydrogen adsorbed on the OMC–Co-5 is 1.54 indicating a Kubas-type interaction between Co and H₂. In addition, the hydrogen spillover effect might occur in parallel.     

Ordering of silver flowerlike nanosheet structures on an aluminium substrate

We present a facile method for ordering flowerlike structures of silver nanosheets on an aluminium covered surface. It is shown that using a combination of electron-beam lithography and standard silver mirror reaction, structures of silver nanosheets can be grown at predefined positions as single or multiple “flowers”, depending on the underling bare aluminium pattern. Arbitrary shaped areas, defined by electron-beam lithography, can be covered with closely packed silver nanosheets.     

Ordered oxygen deficient ‘112’ perovskites,LnBaCo<Subscript>2</Subscript>O<Subscript>5·50+<Emphasis Type="Italic">δ</Emphasis></Subscript>: complex magnetism and transport properties

The ordered oxygen deficient ‘112’ perovskites, LnBaCo₂O_5·50+δ (Ln = lanthanide or Y), exhibit a very flexible structure which can either uptake (δ > 0) or release oxygen (δ < 0) depending on the experimental conditions of synthesis and on the size of the lanthanide. These compounds exhibit remarkably complex magnetic transitions, metal-insulator transition and exceptionally high magnetoresistance. We show herein that their physics is mainly dominated by three different ferromagnetic states, depending on the cobalt valency: FM1 for δ = 0 (Co³⁺), FM2 for δ < 0 (Co²⁺/Co³⁺) and FM3 for δ > 0 (Co³⁺/Co⁴⁺). The competition between ferromagnetism and antiferromagnetism in these phases and the various transitions are discussed taking into consideration the spin state of cobalt, the issue of phase separation and the effect of cobalt coordination and disproportionation. In honour of Prof. C N R Rao on his 75th birthday     

Gaseous infiltration method for preparation of three-dimensionally ordered macroporous polyethylene

Three-dimensionally ordered macroporous polyethylenes (3DOM PE) with pore size ranging from 135 nm to 410 nm were prepared using supported catalysts on the surface of silica microsphere as template, followed infiltration of gaseous ethylene and polymerization. The morphology of 3DOM PE was characterized by SEM and the reflectance spectrum was recorded by UV-vis. It is shown that the pores are uniform, flexible and arranged in a highly ordered fashion. Reflectance spectrum of 3DOM PE also provided verification of the uniform nature of the sample. Moreover, the effect of confined space on polymerization was investigated by GPC and DSC. The results indicate that the porous PE possesses higher M_w compared with bulk PE, and exhibits lower melting temperature and crystallinity than those of bulk PE.     

Injury severity in delivery-motorcycle to vehicle crashes in the Seoul metropolitan area

More than 56% of motorcycles in Korea are used for the purpose of delivering parcels and food. Since such delivery requires quick service, most motorcyclists commit traffic violations while delivering, such as crossing the centerline, speeding, running a red light, and driving in the opposite direction down one-way streets. In addition, the fatality rate for motorcycle crashes is about 12% of the fatality rate for road traffic crashes, which is considered to be high, although motorcycle crashes account for only 5% of road traffic crashes in South Korea. Therefore, the objective of this study is to analyze the injury severity of vehicle-to-motorcycle crashes that have occurred during delivery. To examine the risk of different injury levels sustained under all crash types of vehicle-to-motorcycle, this study applied an ordered probit model. Based on the results, this study proposes policy implications to reduce the injury severity of vehicle-to-motorcycle crashes during delivery.     

Synthesis and characterization of platinum supported on surface-modified ordered mesoporous carbons by self-assembly and their electrocatalytic performance towards oxygen reduction reaction

Ordered mesoporous carbons (OMCs) were fabricated by an organic–organic self-assembly process. Surface-modified OMCs were also prepared via the conventional acid-oxidation, H₂O₂ oxidation and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEPTMS) grafted routes. Pt nanoparticles (NPs) supported on OMC (Pt/OMC) and modified OMC (Pt/OMC-H₂SO₄, Pt/OMC-H₂O₂ and Pt/OMC-AEPTMS) were synthesized and characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) analysis. It was found that acid-oxidation (H₂SO₄/HNO₃) method led to formation of a much wider Pt distribution with mean particle size of 6.8 nm. Unlike Pt/OMC-H₂SO₄ samples, Pt NPs (ca. 2.0 nm) were supported uniformly on AEPTMS-modified OMC with low electrical conductivity. Among three surface-modified methods, the H₂O₂ treatment method was an easily controllable way for surface modification of OMC which possesses desirable electrical conductivity, well-dispersed and nanosized Pt (ca. 3 nm). Accordingly, the Pt/OMC-H₂O₂ samples were observed to have superior electrocatalytic activity for oxygen reduction reaction as compared to synthesized Pt/OMC, Pt/OMC-H₂SO₄, Pt/OMC-AEPTMS and the commercial electrocatalysts (Pt supported on XC-72).