Fixed–size confidence regions for the mean vector of a multinormal distribution

In this paper we propose two stage, modified two stage purely sequential, and three stage procedures to construct "fixed size" elliptic confidence regions for estimating the mean vector of a p–dimensional normal distribution when the dispersion matrix is of the form σ²H where σ ?(0,∞) and H is a p x p known positive definite matrix.We feel that the modified two-stage procedure can be almost as good as the three-stage procedure. In some applications, our modified two-stage procedure may be more appealing than the implementation of a three-stage scheme. So, our findings may possibly limit the usefulness of the three-stage sampling in some of the practical applications. Results and tools from Mukhopadhyay (1974, 1980, 1981), Ghosh and Mukhopadhyay (1975, 1976, 1979, 1981),Srivastava (1967),Woodroofe (1977),and Hall (1981) have been found to be extremely important and useful in this present study. We report extensive simulation studies in order to be able to put the competitive procedures in their proper perspectives.     

Development of mullite and spinel coatings on graphite for improved water-wettability and oxidation resistance

Mullite and spinel forming sols were prepared from hybrid precursors having both organic and inorganic origins. Refractory grade graphite flakes were coated by these sols and their performances were compared in terms of oxidation resistance and water-wettability. Particle size distribution, structural evolution and related characteristics of both mullite and spinel gels have been investigated by dynamic light scattering (DLS), differential thermal analysis (DTA), X-ray diffraction (XRD) and infrared spectra (IR) studies. Coated graphites have also been studied by IR and XRD tests along with scanning electron microscopy (SEM) with energy dispersive spectral (EDS) analysis. The better performance of spinel coated graphite was confirmed. The mechanism of spinel formation on graphite was suggested to take place via intermediate gamma alumina phase formation from boehmite sol. It was clarified by DLS, XRD and microstructural analysis of dried and calcined gels.     

Effect of the dissolution time on the structure and properties of lyocell‐fabric‐based all‐cellulose composite laminates

In this study, all‐cellulose composite laminates were prepared from lyocell fabric with ionic liquid (1‐butyl‐3‐methyl imidazolium chloride), a conventional hand layup method, and compression molding. Eight layers of lyocell fabric, which were impregnated with ionic liquid, were stacked symmetrically and hot‐pressed under compression molding for various times; this resulted in the partial dissolution of the surface of the lyocell fibers. The dissolved cellulose held the laminas together and resulted in a consolidated laminate. Finally, the prepared laminate was impregnated in water to remove the ionic liquid and to regenerate a matrix phase in situ; this was followed by hot‐press drying. Optical microscopy and scanning electron microscopy studies were used to analyze composite structures. With increasing dissolution time, the void content in the composites decreased, and the interlaminar adhesion improved. For LC‐2h and LC‐3h, the highest tensile strength and modulus values obtained were 48.2 MPa and 1.78 GPa, respectively. For LC‐4h, the highest flexural strength and modulus values obtained were 53.96 MPa and 1.2 GPa, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43398.     

Impact Energy Absorption Analysis of Spark Plasma Sintered Al2O3 Reinforced Bulk Multiwalled Carbon Nanotube Compacts Using Nanoindentation

For utilizing the outstanding energy absorbing capacity of highly elastic carbon nanotube (CNT), bulk multiwalled CNT (MWCNT) structure containing 15 wt% alumina (Al₂O₃) was fabricated using spark plasma sintering at 1600°C for 10 min under 50 MPa. The compacted mass was ~85% dense having morphologically stable MWCNTs. Microindentation studies up to 9.81 N indicated outstanding elastic recovery of the bulk structure leaving only a diffused indentation mark at indenter‐specimen interaction zone. Quantitative estimation of elastic response behavior of the fabricated structure using instrumented nanoindentation in 10–300 mN load range indicated promising applicability of Al₂O₃/MWCNT compact structure as energy absorbing material.     

Synthesis and characterization of in situ sodium‐activated and organomodified bentonite clay/styrene–butadiene rubber nanocomposites by a latex blending technique

In this article, we describe a method used to prepare an in situ sodium‐activated, organomodified bentonite clay/styrene–butadiene rubber nanocomposite master batch via a latex blending technique. The clay master batch was used for compound formulation. Octadecyl amine was used as an organic intercalate. The clay was purchased from local suppliers and was very cheap. Sodium chloride was used for in situ activation of the clay. The wide‐angle X‐ray diffraction data indicated that the in situ sodium activation helped to increase the intergallery distance from 1.28 to 1.88 nm. A transmission electron micrograph indicated intercalation and partial exfoliation. The thermal properties were relatively better in the case of the sodium‐activated, organomodified bentonite‐clay‐containing compound. A substantial improvement in physical properties such as the modulus, tensile strength, tear strength, and elongation at break was observed in the case of the in situ sodium‐activated compound. A cation‐exchange capacity equivalent (of the clay) of 1.5 times the octadecyl amine was the optimum dose for the modification. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of pyrophyllite on the mullitization in triaxial porcelain system

China clay (kaolin) was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 5% pyrophyllite as a replacement of china clay improved the fired strength by about 24% compared to that of the conventional body fired at 1300 °C. Percentage of mullite was found to increase in the fired specimens when kaolinite was progressively replaced by pyrophyllite. However, beyond 7.5% pyrophyllite addition, amorphous SiO₂ released from pyrophyllite dehydroxylate inhibited further recrystallization of mullite. There was very insignificant change in the phase compositions with mixes having pyrophyllite content higher than 7.5%. Entire phenomenon has been explained on the basis of structural reorganization of pyrophyllite during dehydroxylation. Presence of large amount of undissolved quartz of smaller size as well as isolated pores in the microstructures of specimens containing pyrophyllite more than 7.5% are assumed to hinder the propagation of crack and thereby improving the mechanical properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition.     

Pyrophyllite as raw material for ceramic applications in the perspective of its pyro-chemical properties

General pyro-chemical properties of pyrophyllite were studied using one Indian variety as sample. In addition to normal routine analysis, thermal expansion, infrared spectroscopy, DTA, XRD and SEM studies were also employed to understand the pyro-chemical properties of the specimen at different temperatures. The results indicate that the specimen contains pyrophyllite as major phase with sericite, quartz and diaspore as minor phases. Unlike kaolinite, pyrophyllite contains low alumina and high silica which on heating mainly produces mullite and amorphous silica. Mullite crystallization from pyrophyllite is rather easy than that from kaolinite. The silica in turn yields large amount of viscous liquid at high temperature. It is suggested that pyrophyllite may be utilized in such compositions favourably where mullite is a desirable phase by partial replacement of china clay which is a viable alternative particularly in the background of depleting reserves of kaolinite and its continuous cost escalation. Additionally amorphous silica produced in the reaction system may acts as an in situ produced filler material that reduces the use of quartz in such system.     

Control of exaggerated tungsten carbide grain growth at the diamond-substrate interface of polycrystalline diamond cutters (PDC)

Exaggerated tungsten carbide grain growth is common at the interface between the diamond table and the cobalt-cemented tungsten carbide (WC-Co) substrate in polycrystalline diamond cutters (PDC). The exaggerated WC grains at the interface can grow as large as 50 μm with an aspect ratio of 50:1. These large grains can also grow as clusters. The presence of large WC grains/clusters creates weakness at the diamond-substrate interface and impairs the strength of the PDC tool. In the present investigation, we tried to understand the root cause of exaggerated WC grain growth at the interface. Our findings show that WC grain growth at the interface decreases with a decrease in the carbon/tungsten (C/W) ratio. By adding 5 wt.% pure tungsten powder to the diamond, the C/W ratio decreased and we found no WC grain growth. By adding fully stoichiometric WC, which has 6.13 wt.% carbon, grain growth was reduced but still observed. Sintering on a substrate having η-phase (carbon deficient phase) also decreased the C/W ratio, and we did not observe WC grain growth.     

Evolution of a Nanocrystalline (Co,Ni)Al2O4 Spinel Phase from Quasicrystalline Precursor

This work reports on the synthesis of a spinel phase from a thermodynamically stable decagonal quasicrystalline Al₇₀Co₁₅Ni₁₅ alloy. The Al₇₀Co₁₅Ni₁₅ alloy, synthesized through slow cooling of the molten alloy, was subjected to milling in an attritor ball mill at 400 rpm for 5, 10, 20, 30, and 40 h with a ball to powder ratio of 20:1 in the hexane medium. The differential thermal analysis, X-ray diffraction, scanning, and transmission electron microscopy techniques have been used for characterization of milled as well as annealed powders. The Voigt function analysis has been used for calculation of the effective crystallite size and relative strain of ball-milled samples. The crystallite size has been found to be ∼14 nm after 40 h of milling along with a lattice strain of 8.1%. The annealing experiments have been carried out under two different conditions: (i) in vacuum and (ii) in air. The results of the present investigation clearly revealed that the nano-decagonal phase was stable in vacuum while annealing at 600°C for 40 h. However, during annealing under a similar condition in air, the formation of a nanospinel of (Ni,Co)Al₂O₄ of size ∼60 nm was identified. The possible structural evolution of the spinel from the quasicrystalline phase has been discussed.     

Effect of thermal radiation on unsteady mixed convection flow and heat transfer over a porous stretching surface in porous medium

An analysis is performed to investigate the effects of thermal radiation on unsteady boundary layer mixed convection heat transfer problem from a vertical porous stretching surface embedded in porous medium. The fluid is assumed to be viscous and incompressible. Numerical computations are carried out for different values of the parameters involved in this study and the analysis of the results obtained shows that the flow field is influenced appreciably by the unsteadiness parameter, mixed convection parameter, parameter of the porous medium and thermal radiation and suction at wall surface. With increasing values of the unsteadiness parameter, fluid velocity and temperature are found to decrease in both cases of porous and non-porous media. Fluid velocity decreases due to increasing values of the parameter of the porous medium resulting an increase in the temperature field in steady as well as unsteady case.