Prediction of the elastic behaviour of hybrid and non-hybrid woven composites

A micromechanical model called MESOTEX is presented for prediction of the elastic behaviour of composites reinforced with non-hybrid weave (plain weave, satin weave and twill weave) and hybrid weave (hybrid plain weave and hybrid twill weave) fabrics. By using the classical thin laminate theory applied to each woven structure, this analytical model takes into account the strand undulations in the two directions and also integrates the geometrical and mechanical parameters of each constituent (resin, fill and warp strands). A representative volume is chosen for each woven composite and the fibre architecture is described by several functions. To determine the effectiveness of this analysis, the elastic properties predicted for each woven composite are compared with experimental results and results extracted from the literature. This correlation shows excellent agreement between measured and predicted values, with a very low calculation cost (CPU time of less than 0·01 s).     

The Dübendorf Study: a population-based investigation on normal values of blood pressure self-measurement

In a retrospective study of 50 consecutive children with posterior fossa tumors treated at Texas Children's Hospital, Houston, Tex., in 1989-1992, we evaluated perioperative factors which might influence the development of postoperative cerebrospinal fluid leaks. Factors analyzed included the presence of preoperative hydrocephalus, the institution of cerebrospinal fluid diversion, and the method of dural closure. No statistically significant impact on subsequent cerebrospinal fluid leakage was demonstrated.     

Carbon fibre composites based on polyimide/silica ceramers: aspects of structure-properties relationship

Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. 7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. 14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content.     

Identification of Hammerstein systems with asymmetric dead-zone nonlinearities using canonical parameterized model

A non-iterative identification method with parameterization of the unknown dead-zone is proposed for Hammerstein systems in presence of asymmetric dead-zone nonlinearities.The canonical parameterized model which is a single expression without segmentation is utilized to describe the dead-zone,based on which a universal-type parametric model can be established to approximate the entire system.This model can be established without separating the nonlinear part from the linear part.The dead-zone parameters and the coefficients in the linear transfer function can be estimated simultaneously according to the proposed algorithm.Numerical experiments are presented to illustrate the effectiveness of the proposed scheme.     

Organisation and management of shared documents in super-peer networks based semantic hierarchical cluster trees

A super-peer semantic network defines the semantic groups that client peers and their super peers use to connect with each other according to the semantic similarity of shared documents in peers. This will result in a query that can be evaluated locally thus reducing query process time and the amount of communication required to obtain related data. In this study, new algorithms are proposed to arrange shared documents in peers into hierarchical cluster tree structures, and links will be set up to connect semantically related super peers. During query evaluation, only related peers will be searched thus the complexity of computing is significantly reduced. Consideration is also given to automatically deciding the threshold for clustering and the construction and other essential operations for hierarchical cluster trees. The experiment results illustrate the features of the approach developed in this study.     

Catalytic oxidation and flow detection of carbohydrates at ruthenium dioxide modified electrodes

Ruthenium dioxide (RuO2) containing carbon paste electrodes exhibiting electrocatalytic response toward carbohydrates are described. The electrocatalytic behavior is exploited for developing a highly stable and sensitive flow detection scheme for carbohydrates at a low and fixed potential (+0.4 V vs Ag/AgCl). The effects of pH, flow rate, operating potential, surface "loading", concentration, and other variables are explored. The electrode response was stable for more than 48 h, with a signal loss of less than 10% over this period. The detection limits at the picomole level and a relative standard deviation of 1.2% (n = 72) are reported. Electrocatalytic oxidation is described also for related polyhydroxyl compounds (aldonic and aldaric acids and alditols).     

Phase transformation and densification during pressureless sintering of Si3N4 with MgO and Y3Al5O12 additives

The - transformation of Si₃N₄ during liquid-phase sintering appears to be controlled by the growth of the -Si₃N₄ grains in the direction perpendicular to thec-axis in the case of MgO additive. The diffusion through the liquid is the rate-controlling step in the case of the Y₄Al₅O₁₂ additive. The density of the sintered body at the solid skeleton stage was influenced by the change in the - transformation rate and/or by a change of the transformation mechanism. The indirect proportionality between the -phase content in the starting powder and the density at the solid skeleton stage was found. The microstructure of the sintered body is influenced by both the -phase content in the starting powder and the chemical composition of the additive. Fine, uniform microstructure with a high aspect ratio of -grains is obtained, when the -phase content in the starting powder is as small as possible and when the - transformation is controlled by grain growth.     

Isothermal transformation and decomposition ofβ 1 phase in a CuZnAl alloy

In the present paper, the crystallography of isothermal transformation and decomposition ofβ, phase have been studied by means of transmission electron microscopy and diffraction in the CuZnAl shape memory alloy. It has been proved that the bainite formed inβ ₁, matrix when the samples were transformed isothermally at moderate temperature. The crystallography of the isothermal bainitic transformation is identical to that of martensite in the same system. When the specimens were aged at moderate temperatures for longer time, the bainite and matrix decomposed to equilibrium phases. The decomposition process can be summarized as follows: $$\begin{gathered} bainite (9R) \to 9R + \alpha \left( {fcc} \right) \to \alpha + \beta \left( {bcc} \right) \hfill \\ matrix (B2) \to 2H + B2 \to \beta \left( {bcc} \right) \hfill \\ \end{gathered} $$ There are definite orientation relationships among these phases during the decomposition process and they are shown below: $$\begin{gathered} \left( {111} \right)_\alpha \parallel \left( {001} \right)_B ,\left[ {0\bar 11} \right]_\alpha \parallel \left[ {\bar 110} \right]_B \hfill \\ \left( {111} \right)_\alpha 5^ \circ away from \left( {110} \right)_\beta ,\left[ {0\bar 11} \right]_\alpha \parallel \left[ {1\bar 1\bar 1} \right]_\beta \hfill \\ \left( {110} \right)_M \parallel \left( {001} \right)_{2H} ,\left[ {001} \right]_M \parallel \left[ {010} \right]_{2H} \hfill \\ \end{gathered} $$ Thus, the crystallography of isothermal transformation and decomposition ofβ ₁ phase and the sequence of transitions have been revealed.     

Numerical study of the variable-order fractional version of the nonlinear fourth-order 2D diffusion-wave equation via 2D Chebyshev wavelets

Engineering with Computers - In this article, the 2D Chebyshev wavelets (CWs) are used for designing a proper procedure to solve the variable-order (VO) fractional version of the nonlinear...