Microstructure–property relationship in textured ZnO-based varistors

The relationship between microstructure texturing and electrical characteristics of a ZnO-based varistor system was investigated in comparison with a varistor system having the same chemical composition but conventional microstructure. Highly textured ZnO-based varistors were produced via the templated grain growth (TGG) technique. Stereological analysis, electron back-scattered diffractometry (EBSD) and X-ray diffractometry (XRD) were conducted to analyze texture development and orientation distribution. The degree of orientation, r, calculated from the (0 0 0 1) EBSD pole figure, was 0.34; the texture fraction, f (Lotgering factor), calculated from the XRD data, was 0.98 for the samples produced via TGG. The threshold voltages were found to be anisotropic, consistent with the observed morphological texture. The non-linear coefficients, α, did not exhibit a significant difference as a function of direction, even in the highly textured samples. However, different types of grain boundary characteristics depending on the direction were identified with 0.42, 0.69 and 1.14 eV Schottky barrier heights.     

Antibacterial activities of essential oils and extracts of Turkish Achillea,Satureja and Thymus species against plant pathogenic bacteria

BACKGROUND: The aims of this study were to examine the chemical composition of the essential oils and hexane extracts of the aerial parts of Satureja spicigera (C. Koch) Boiss., Thymus fallax Fisch. & CA Mey, Achillea biebersteinii Afan, and Achillea millefolium L. by GC and GC–MS, and to test antibacterial efficacy of essential oils and n‐hexane, chloroform, acetone and methanol extracts as an antibacterial and seed disinfectant against 25 agricultural plant pathogens. RESULTS: Thymol, carvacrol, p‐cymene, thymol methyl ether and γ‐terpinene were the main constituents of S. spicigera and T. fallax oils and hexane extracts. The main components of the oil of Achillea millefolium were 1,8‐cineole, δ‐cadinol and caryophyllene oxide, whereas the hexane extract of this species contained mainly n‐hexacosane, n‐tricosane and n‐heneicosane. The oils and hexane extracts of S. spicigera and T. fallax exhibited potent antibacterial activity over a broad spectrum against 25 phytopathogenic bacterial strains. Carvacrol and thymol, the major constituents of S. spicigera and T. fallax oils, also showed potent antibacterial effect against the bacteria tested. The oils of Achillea species showed weak antibacterial activity. Our results also revealed that the essential oil of S. spicigera, thymol and carvacrol could be used as potential disinfection agents against seed‐borne bacteria. CONCLUSION: Our results demonstrate that S. spicigera, T. fallax oils, carvacrol and thymol could become potentials for controlling certain important agricultural plant pathogenic bacteria and seed disinfectant. Copyright © 2009 Society of Chemical Industry     

Hydrodynamics of a turbulent slot jet flow impinging on a concave surface

This study investigates hydrodynamic characteristics of a slot jet flow impinging on a concave surface experimentally and numerically. Six different concave plates with varying surface curvature and a flat plate are used. Air is used as the impinging coolant. In the experimental work, the slot nozzle used was specially designed with a sixth degree polynomial in order to provide a uniform velocity profile at its exit. The experiments were carried out for the jet Reynolds numbers in the range of 3000 < Re < 12500, the dimensionless nozzle-to-surface distance range of 1 ≤ H/W ≤ 14 for dimensionless value of the curvature of impinging surfaces in the range of R/L = 0.5, 0.5125, 0.566, 0.725, and 1.3. The pressure coefficient, C_p, for each test case was obtained across dimensionless arc length, s/W. Numerical computations were performed by using the k-ε turbulence model with enhanced wall functions for the concave plate with R/L = 0.725 and for the flat plate. The numerical results showed a reasonable agreement with the experimental data.     

Construction of kernels G l, 0 l of the nonlinear collision integral in the Boltzmann equation for arbitrary l

It was shown in [1] that kernels L _l (v, v ₁) of linear collision integral and kernels G _{l, 0} ^l (v, v ₁, v ₂) of nonlinear collision integral are related by the Laplace transform. Here, analytical expressions are derived for nonlinear kernels G _{l, 0} ^+l (v, v ₁, v ₂) with arbitrary l for models of hard spheres and pseudo-Maxwellian molecules using the Laplace transform method.     

Nonlinear System Identification Using Deterministic Multilevel Sequences

A new exact method of measuring the Volterra kernels of finite-order discrete nonlinear systems is presented. The kernels are rearranged in terms of multivariate crossproducts in vector form. The one-, two-, . . . , and ℓ-dimensional kernel vectors are determined using a deterministic multilevel sequence with ℓ distinct levels at the input of the system. It is shown that the defined multilevel sequence with ℓ distinct levels is persistently exciting for a truncated Volterra filter with nonlinearities of polynomial degree ℓ. Examples demonstrating the rearrangement of the Volterra kernels and a novel method for estimation of the kernels are presented. Simulation results are given to illustrate the effectiveness of the proposed method.     

Mathematical modelling and fuzzy logic based position control of an electrohydraulic servosystem with internal leakage

This paper describes an application of a fuzzy logic position control to an electrohydraulic servosystem. Mathematical model of the electrohydraulic servosystem is obtained considering the internal leakage within the servosystem. Electrohydraulic servosystems are one of the most commonly used actuators. However, electrohydraulic servosystems are difficult to control due to nonlinearity and complexity of their mathematical models. In this paper, as a first step, the mathematical models of the main components of the servosystem are obtained. The effect of compressibility, friction, internal leakage in servovalve, leakage in actuator and inertia are included in the model. Since the system has a complex structure and the system characteristics are time dependent. Fuzzy Logic Control (FLC) is applied to the electrohydraulic servosystem. The error and change in error are employed in the FLC. The effect of internal leakage on the mathematical model and performance of the position control system is investigated. Numerical simulation results for position control under a square wave reference input are obtained. Results are presented in graphical form. Physical trends of numerical simulation results are discussed. Although leakage is often ignored in dynamic analysis of servosystems, results shown in the paper indicate that the leakage has a significant effect on the mathematical model and performance of the position control system at small spool displacements.     

Influence of keeping system on the fatty acid composition in the <Emphasis Type="Italic">longissimus</Emphasis> muscle of bulls and odorants formed after pressure-cooking

German Simmental bulls were kept either in a stable (group 1) or on a pasture (group 2). For both groups the intramuscular fat content of the longissimus muscle and the fatty acid composition in phospholipids and triacylglycerols were investigated. Significant influences of feeding were shown in most fatty acids measured in both lipid classes. In concentrate-fed bulls a higher content of linoleic acid (C18:2n-6) was detected, corresponding to the large amount of linoleic acid found in concentrate used as feed. In contrast, bulls fed grass proved to have a higher linolenic acid (C18:3n-3) content, also correlating well with the larger amount of linolenic acid found in grass. Pressure-cooking of the beef followed by an analysis of eight important meat odorants revealed that, in line with the higher concentrations of the precursor fatty acids C18:3n-3 and C18:1 in muscle of group 2, (E,Z)-2,6-nonadienal (from C18:3n-3) as well as nonanal and octanal (from C18:1) were much higher in the processed meat of animals fed grass. On the other hand, the much higher amounts of C18:2n-6 in bulls fed concentrate were well-reflected by higher concentrations of five aroma compounds known to be formed by a thermal degradation of this acid, e.g. (E,E)-2,4-decadienal.