Texture changes during uniaxial compression of Mg-3AI-1Zn

The mechanical anisotropy of wrought Mg alloys is very high. For example the yield stress of extruded Mg-3Al-1Zn tested in tension can be as high as twice that obtained in compression [1]. To solve the problems this creates for product design it is necessary to understand the sensitivity of texture to processing parameters. Uniaxial compression tests at different temperatures were performed on cylindrical samples of an extruded Mg-3Al-1Zn bar. The texture
during this deformation changes from a situation where all crystal c-axes are nearly perpendicular to the sample axis to one where the c-axes are all nearly parallel to this axis. Compression was stopped at different strains to examine the rate of this texture change. Textures were examined using EBSD measurements. It was found that different mechanisms operate depending on the temperature of deformation and that a variety of textures can be created. Also it was seen that an annealing treatment performed after compression has an influence on the texture. Afterwards the samples were subjected to another uniaxial compression test to examine the influence of texture on room temperature properties.

Nonparametric rank tests for non-stationary panels

We develop a set of nonparametric rank tests for non-stationary panels based on multivariate variance ratios which use untruncated kernels. As such, the tests do not require the choice of tuning parameters associated with bandwidth or lag length and also do not require choices with respect to numbers of common factors. The tests allow for unrestricted cross-sectional dependence and dynamic heterogeneity among the units of the panel, provided simply that a joint functional central limit theorem holds for the panel of differenced series. We provide a discussion of the relationships between our setting and the settings for which first- and second generation panel unit root tests are designed. In Monte Carlo simulations we illustrate the small-sample performance of our tests when they are used as panel unit root tests under the more restrictive DGPs for which panel unit root tests are typically designed, and for more general DGPs we also compare the small-sample performance of our nonparametric tests to parametric rank tests. Finally, we provide an empirical illustration by testing for income convergence among countries.

Testing for panel cointegration with a level break

This paper proposes four simple tests for the null hypothesis of no cointegration in the presence of a level break. The tests are general enough to allow for endogenous regressors, serial correlation and heterogeneous breaks of unknown timing. The limiting distributions of the tests are derived and critical values are provided. We also conduct a small Monte Carlo study to investigate their finite sample properties. © 2005 Elsevier B.V. All rights reserved.

Testing for panel cointegration with multiple structural breaks

This paper proposes a Lagrange multiplier (LM) test for the null hypothesis of cointegration that allows for the possibility of multiple structural breaks in both the level and trend of a cointegrated panel regression. The test is general enough to allow for endogenous regressors, serial correlation and an unknown number of breaks that may be located at different dates for different individuals. We derive the limiting distribution of the test and conduct a small Monte Carlo study to investigate its finite sample properties. In our empirical application to the solvency of the current account, we find evidence of cointegration between saving and investment once a level break is accommodated. © Blackwell Publishing Ltd, 2006.

Mixed signals among tests for panel cointegration

In this paper, we study the effect that different serial correlation adjustment methods can have on panel cointegration testing. As an example, we consider the very popular tests developed by Pedroni [Pedroni, P. (1999). Critical values for cointegration tests in heterogeneous panels with multiple regressors. Oxford Bulletin of Economics and Statistics 61, 653670., Pedroni, P. (2004). Panel cointegration: asymptotic and finite sample properties of pooled time series tests with an application to the PPP hypothesis. Econometric Theory 20, 597-625.]. Results based on both simulated and real data suggest that different adjustment methods can lead to significant variations in test outcome, and thus also in the conclusions. © 2007 Elsevier B.V. All rights reserved.

Output and labor productivity in organized manufacturing: a panel cointegration analysis for India

One of the policy puzzles faced in India during the last two and half decades has been the weak association between output and labor markets, particularly in the manufacturing sector. In this research, we investigate the long-run relationship between output, labor productivity and real wages in the case of organized manufacturing. We adjust the measure of labor productivity incorporating bottlenecks, such as lack of infrastructure, access to external finance, and labor regulations, which all may influence labor market outcomes. Using panel data from seventeen manufacturing industries, we establish long-run dynamics for the output-labor productivity-real wages series over a period of nearly three decades. We employ recently developed panel unit root and cointegration tests for cross-sectional dependence to incorporate heterogeneity across industries. Long-run elasticities are generally found to be low for labor productivity compared to real wages due to the changes in manufacturing output. There are variations across industries within the manufacturing sector for the effects of the labor market on manufacturing output. In some industries, lower wages are associated with higher output, and the reason for the positive relationship in other industries could be due to workers' bargaining power.

Transient temperature distribution in functionally graded graphite/Polymer nanocomposites based on temperature dependent properties

Transient heat conduction in a functionally graded graphite/polymer nanocomposite (FGN) plate is analyzed using finite element method (FEM). Stepwise gradient structure consisted of four different nanocomposite layers with 0, 5, 10 and 20 wt% of graphite. Thermal conductivity and specific heat capacity of the individual layers were determined using C-Therm TCi Thermal Conductivity Analyzer (Canada) in temperature range of -20 to 100 °C. Temperature history and temperature distribution across the thickness of the plate with two different configurations for two positive and negative temperature gradients are presented.

Preparation, characterization and dielectric properties of temperature stable SrTiO3/PEEK composites for microwave substrate applications

Poly(ether ether ketone) (PEEK) is a potential candidate for electronic applications due to its low permittivity, low loss, high melting point, better chemical resistance, excellent insulating properties and easy processibility. Present paper discusses the preparation and characterization of SrTiO3 filled PEEK composite for microwave substrate applications. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the composites have been studied up to 1 MHz using an Impedance Analyzer. Different theoretical approaches have been employed to predict the effective permittivity of composite systems and the results are compared with that of the experimental data. The crystallinity of the bulk composite is studied by X-ray diffraction studies. Scanning electron microscopic technique has been employed to study the dispersion of the particulate filler in PEEK matrix. Vickers hardness of pure and filled PEEK composite has been measured using Microhardness Tester. The effect of particle size on the dielectric as well as mechanical properties of SrTiO3/PEEK composite system is also studied by incorporating micronsize and nanosize fillers. Present study shows that a temperature stable composite can be realized by judiciously selecting appropriate filler concentration in the PEEK matrix.

Synthesis and properties of ambient temperature molten salts based on the quaternary ammonium ion

The synthesis of 16 tetraalkyl ammonium bis(trifluoromethane sulfonyl) imide salts, (C_nH_2n+1)₄ +N -N (SO₂CF₃)₂ (n = 1, 2, 3, 4),  (C₂H₅)₂(i-C₃H₇)₂ +N -N(SO₂CF₃)₂, (C₂H₅)(CH₃)(i-C₃H₇)₂+N-N(SO₂CF₃)₂, (n-C₇H₁₅)(C₂H₅)i-C₃H₇)₂+N-N(SO₂CF₃)₂ and (C_nH_2n+1)(C_mH_2m+1)₃+N-N(SO₂CF₃)₂ (n = 6,7,8; m = 1, 2, 4) are reported in this paper. Trends in properties of these salts are discussed. The symmetrical tetraalkyl ammonium salts with the bis(trifluoromethyl sulfonyl) imide anion exhibited a lower melting point than that of corresponding ammonium halides. The salts with low symmetry ammonium cations were found to be of generally lower melting point, and many were stable liquids at room temperature. Several of these did not crystallize during cooling below room temperature and exhibited glass transition temperatures in the region of −60 °C∼−80 °C. A comparison of properties between the ammonium imide salts and corresponding trifluoromethane sulfonates is also presented.

Phase dissolution of γ-Mg17Al12 during homogenization of As-Cast AZ80 magnesium alloy and its effect on room temperature mechanical properties

As-cast AZ80 Mg alloy contains α-Mg, partially divorce eutectic of α and γ (Mg 17Al 12), fully divorce eutectic of α and γ, and lamellar eutectic of α and γ phases. During homogenization, second phase (γ-Mg 17Al 12) gets dissolved can change the mechanical properties. Therefore, the aim of the present work is to bring out the kinetics of dissolution of γ phase and evaluate its effect on mechanical properties. Microstructure evolution during homogenization was investigated as a function of time for 0.5 to 100 h and at the temperatures of 400° and 439°C. In as-cast state, this material was found to contain 70% α-Mg and 30% eutectic phase. With increasing homogenization time, dissolution of lamellar eutectic occurs first which is followed by dissolution of fully divorce eutectic and partially divorce eutectic. The dissolution kinetics of γ phase was analyzed based on the decrease in its volume fraction as a function of time. The time exponent for dissolution was found to be 0.38 and the activation energy for the dissolution of γ phase was found to be 84.1 kJ/mol. This dissolution of γ phase leads to decrease in hardness and tensile strength with increase in homogenization time.

Temperature-agile and structure-tunable optical properties of VO 2/Ag thin films

By integrating together VO2’s unique near-room-temperature (RT) semiconductor–metal (S–M) phase transition with a thin silver (Ag) layer’s plasmonic properties, VO2/Ag multilayers could present a much enhanced optical transmission change when increasing the temperature from RT to over VO2’s S–M phase-transition temperature. Changing VO2 and Ag layer thicknesses can also significantly tune their transmission and absorption properties, which could lead to a few useful designs in optoelectronic and energy-saving industries.

Asymmetric rolling of interstitial-free steel using differential roll diameters. Part I : mechanical properties and deformation textures

IF steel sheets were processed by conventional symmetric and asymmetric rolling (ASR) at ambient temperature. The asymmetry was introduced in a geometric way using differential roll diameters with a number of different ratios. The material strength was measured by tensile testing and the microstructure was analyzed by optical and transmission electron microscopy as well as electron backscatter diffraction (EBSD) analysis. Texture was also successfully measured by EBSD using large surface areas. Finite element (FE) simulations were carried out for multiple passes to obtain the strain distribution after rolling. From the FE results, the velocity gradient along selected flow lines was extracted and the evolution of the texture was simulated using polycrystal plasticity modeling. The best mechanical properties were obtained after ASR using a roll diameter ratio of 2. The textures appeared to be tilted up to 12 deg around the transverse direction, which were simulated with the FE-combined polycrystal plasticity modeling in good agreement with measurements. The simulation work revealed that the shear component introduced by ASR was about the same magnitude as the normal component of the rolling strain tensor.