Experimental investigation,material modeling and parameter identification of a zinc die-casting alloy

The zinc die-casting alloy Zamak is widely used in the production of components of cars and machines. Because of its complex highly non-linear thermo-mechanical behavior, it is problematic to approximate its response with classical viscoplasticity models, such as von Mises-viscoplasticity. Based on an extensive experimental investigation on thin-walled cylindrical specimens, a proposal for the modeling of the rate- and temperature-dependent behavior of the alloy Zamak 5 is presented and its applicability through a numerical example is shown. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Reduced Order Cyclic Method for Computation of Limit Cycles

A reduced order cyclic method was developed to compute limit-cycle oscillations for large, nonlinear, multidisciplinary systems of equations. Method efficacy was demonstrated for two simplified models: a typical-section airfoil with nonlinear structural coupling and a nonlinear panel in high-speed flow. The cyclic method was verified to maintain second-order temporal accuracy, yield converged limit cycles in about 10 Newton iterates, and provide precise estimates of cycle frequency. This method was projected onto a low-order space using a set of variables governing the amplitudes of empirically derived modes, which were computed with the proper orthogonal decomposition. In this reduced order form, the cyclic Jacobian was greatly compressed, allowing accurate limit cycle solutions to be very efficiently computed.The U.S. Governments right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Conditional sampling of velocity and scalars in turbulent flames using simultaneous LDV-Raman scattering

The laser Doppler velocimeter (LDV) measures the velocity distribution of particles which is often an acceptable representation of the distribution of gas velocities. However, in turbulent two stream mixing flows, the particle velocity distribution will differ from the gas velocity distribution when the particle densities in the two streams are unequal. This bias is explored in a reacting and nonreacting turbulent jet which is surrounded by coflowing air. By adding seed particles to only the coflow air and then to only the jet fluid, the limits of this bias are established. Additional measurements with an LDV triggered laser Raman scattering system demonstrate that the bias in the LDV sampling is propagated to the Raman measurements. An analytical equation is presented which will generate unbiased velocity and scalar distributions from measurements obtained from seeding only one stream at a time.     

Ultra-compact TDLAS humidity measurement cell with advanced signal processing

In this paper, tunable diode laser absorption spectroscopy humidity measurements with an ultra-compact measurement cell are presented. The optical path length is 2 cm. The system uses a vertical cavity surface emitting laser at 1.854 μm. The main limiting factor of the humidity resolution is not the noise but interference fringes produced by reflecting surfaces. Next to the system setup, a novel rejection method to eliminate these fringes, based on Fourier domain analysis of the absorption line, is described. In contrast to other fringe rejection methods, the presented method is able to handle fringes, whose free spectral range is in the range of the half width of the absorption line. The achievable humidity resolution for the presented cell is below 0.25 % relative humidity at room temperature.     

On the Lebesgue decomposition for non-additive functions

A Lebesgue decomposition theorem for non-additive functions, acting on a \(\sigma \) -complete orthomodular lattice and taking values in Hausdorff uniform spaces, is established. No algebraic structure is required on target spaces. The Boolean case is also investigated.     

Reproducing subgroups of Sp(2,\mathbb R ). Part II: admissible vectors

In part I we introduced the class $\mathcal{E }_2$ of Lie subgroups of $Sp(2,\mathbb R )$ and obtained a classification up to conjugation ( see Theorem 6 below). Here, we determine for which of these groups the restriction of the metaplectic representation gives rise to a reproducing formula. In all the positive cases we characterize the admissible vectors with a generalized Calderón equation. They include products of 1D-wavelets, directional wavelets, shearlets, and many new examples.     

Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band

Classical molecular dynamics simulations have been carried out for gaseous CO(2) starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully compared with those of previous similar calculations before studies of the influences of the intermolecular potential and induced-dipole components are made. The calculated spectra show a significant sensitivity to anisotropic forces consistently with previous analyses limited to the spectral moments. The present results also demonstrate the importance of vibrational and back-induction contributions to the induced dipole. Comparisons between measured far infrared (0-250 cm(-1)) spectra at different temperatures and results calculated without the use of any adjustable parameter are made. When the best and more complete input data are used, the quality of our predictions is similar to that obtained by Gruszka et al. [Mol. Phys. 93, 1007 (1998)] after the introduction of ad hoc short-range overlap contributions. Our results thus largely obviate the need for such contributions the magnitudes of which remain questioned. Nevertheless, problems remain since, whereas good agreements with measurements are obtained above 50 cm(-1), the calculations significantly underestimate the absorption below, a problem which is discussed in terms of various possible error sources.     

Molecular dynamics simulations for CO2 spectra. III. Permanent and collision-induced tensors contributions to light absorption and scattering

Classical molecular dynamics simulations have been performed for gaseous CO(2) starting from an accurate anisotropic intermolecular potential. Through calculations of the evolutions of the positions and orientations of a large number of molecules, the time evolutions of the permanent and collision-induced electric dipole vector and polarizability tensor are obtained. These are computed from knowledge of static molecular parameters taking only the leading induction terms into account. The Laplace transforms of the auto-correlation functions of these tensors then directly yield the light absorption and scattering spectra. These predictions are, to our knowledge, the first in which the contributions of permanent and collision-induced tensors are simultaneously taken into account for gaseous CO(2), without any adjusted parameter. Comparisons between computations and measurements are made for absorption in the region of the ν(3) infrared band and for depolarized Rayleigh scattering in the roto-translational band. They demonstrate the quality of the model over spectral ranges from the band center to the far wings where the spectrum varies by several orders of magnitude. The contributions of the permanent and interaction-induced (dipole and polarizability) tensors are analyzed for the first time, through the purely permanent (allowed), purely induced, and cross permanent∕induced components of the spectra. It is shown that, while the purely induced contribution is negligible when compared to the collision-broadened allowed component, the cross term due to interferences between permanent and induced tensors significantly participates to the wings of the bands. This successfully clarifies the long lasting, confusing situation for the mechanisms governing the wings of the CO(2) spectra considered in this work.     

The degradation of poly(vinyl acetate) as a material for design objects: A multi-analytical study of the Cocoon lamps. Part 2

After the systematic study of poly(vinyl acetate) degradation presented in part 1, this work reports results from the analysis of polymeric materials from five Italian design lamps from the 1960s made of the material known as cocoon. Micro- and non-destructive molecular spectroscopic techniques have been applied directly on the object surfaces using an optical fibre probe and through examination of micro-samples: the combined use of Fourier-transform infrared spectroscopy (FTIR), pyrolysis gas-chromatography/mass-spectrometry (py-GC/MS) and Fluorescence spectroscopy allowed the assessment of the material composition and the chemical modifications of the polymers related to on-going deterioration processes. Fluorescence spectroscopy proved particularly sensitive for the detection of variations in composition among lamps and between areas on the same object, and was used to classify objects in different groups using principal component analysis of excitation emission spectra. Specific degradation products have been mapped using FTIR on micro-samples. Moreover, the interpretation of the emission spectra of the studied polymeric lamps suggests that fluorescence spectroscopy can be used for non-destructive monitoring of the degradation of historical polymeric objects.     

Investigation of 3,5-dichlorosalicylate-copper(II)-(3-pyridylmethanol or N,N′-diethylnicotinamide) complex systems by EPR spectroscopy

Copper(II) complex systems, containing 3,5-dichlorosalicylic acid (3,5-Cl₂salH) and different copper salts (Cu(ac)₂ or CuSO₄), with varying concentrations of 3-pyridylmethanol (ronicol, ron) or N,N′-diethylnicotinamide (denia) as ligands, were prepared. The effects of Cu(II) salts containing anions of different basicity and two different N-donor ligands with varying ligand-to-metal ratio (x) on the formation of the resultant complexes in the water/methanol solutions were studied by EPR spectroscopy at low temperature of 98 K. When ligand concentration was increased, the resolution and signal intensity of the ¹⁴N perpendicular super-hyperfine splitting patterns increased (for ron more progressively), becoming saturated at higher ligand concentrations. In comparing the ronicoland denia-containing systems, both g-factors (g _⊥, g _‖) are systematically higher and the parallel hyperfine splitting (A _‖) systematically lower in denia-containing systems for both Cu(II) salts.