Macrosegregation Formation in an Al–Si Casting Sample with Cross-sectional Change During Directional Solidification

A unidirectional solidification experiment of hypoeutectic Al-7.0 wt% Si alloy against gravity direction in a cylindrical mold with cross-sectional change was made, and the macrosegregation in different parts of the as-solidified sample was investigated (Ghods et al. in J Cryst Growth 441:107–116, 2016; J Cryst Growth 449:134–147, 2016). The current study is to use a two-phase columnar solidification model to analyze the segregation mechanisms as used in this experiment. Following flow phenomena and their contributions to the formation of macrosegregation are simulated and compared: (1) solidification shrinkage-induced feeding flow; (2) thermo-solutal convection; and (3) combined thermo-solutal convection and shrinkage-induced feeding flow. The shrinkage-induced feeding flow leads to an inverse (positive) segregation in the bottom part, and a severe negative segregation in the part below cross-sectional change. Thermo-solutal buoyancy leads to a so-called steepling convection in the main part of the sample (away from the bottom and cross-sectional change), and this kind of flow leads to a positive macrosegregation near the sample surface. The calculations have successfully explained the experimental result of macrosegregation.     

H ∞ Filtering of Two-Dimensional T-S Fuzzy Systems

The H _∞ filtering problem for two-dimensional Takagi–Sugeno fuzzy systems described by the Fornasini–Marchesini (FM) model is studied. Attention is focused on the design of an H _∞ fuzzy filter such that the filter error system is asymptotically stable and preserves a guaranteed H _∞ performance. By using basis-dependent Lyapunov functions and adding slack matrix variables, the coupling between the Lyapunov matrix and the system matrices is eliminated. Then, a linear matrix inequality (LMI)-based approach is developed for designing the H _∞ fuzzy filter. Finally, an illustrative example is provided to show the effectiveness of the proposed approach and less conservatism.     

Stabilization of uncertain saturated discrete-time switching systems

This paper presents sufficient conditions for the stabilization of uncertain switching discrete-time linear systems subject to actuator saturations. These conditions are obtained by using output feedback control laws and are formulated in terms of LMIs. Two different sets of LMIs are presented for the output feedback case when saturations are allowed, that differ in complexity and conservativeness. A numerical example is used to illustrate the proposed techniques.     

Process Simulation for the Metallurgical Industry: New Insights into Invisible Phenomena

In order to demonstrate how advanced process simulation can help to understand metallurgical process details and thus to improve industrial productivity, a number of examples are shown and discussed. The paper covers recent simulation results gained at the Chair of Simulation and Modeling of Metallurgical Processes, namely (i) the flow and shell formation in thin slap casting of steel, (ii) multiphase flow and magneto-hydrodynamic during Electro-Slag-Remelting, (iii) mold filling, surface wave dissipation and solidification during horizontal centrifugal casting of rolls, and (iv) forced and natural convection during electro-refining of copper in an industrial-size tankhouse cell.     

Application of Microprobe Analysis to the Reconstruction and Characterization of Dendritic Structures

The electron probe microanalyzer (EPMA or “microprobe”) is a powerful tool for nondestructive chemical analysis of solid materials. The work presented in this article proofs the concept of reconstructing three-dimensional (3-D) dendritic structures in steel based on 5 two-dimensional (2-D) EPMA concentration maps. The EPMA measurements are focused on the concentration distribution of Mn, which has a distinct microsegregation tendency in steel. Because the concentration maps must be taken from different depths of the investigated sample, serial sectioning of the sample is required for each microprobe measurement. These measured concentration maps are processed with a commercial software tool to smooth and to merge the maps, as well as to consider the temperature gradient that occurred during solidification on the microsegregation pattern. Afterward, the concentration maps are stored in a 3-D array, and the neighboring array entries with the same predefined threshold concentration value are connected with surfaces to build a 3-D dendritic structure. Because the concentration of certain alloying elements in the solid phase increases during the solidification process, it is possible to visualize the dendritic growth by increasing the solid fraction. Finally, a simple correlation was used to relate the specific surface area to the solid volume fraction of the dendrites. The obtained 3-D structures can be used for subsequent investigations in finite-element (FE) or computational fluid dynamics (CFD) simulation tools.     

ECG signal filtering based on CEEMDAN with hybrid interval thresholding and higher order statistics to select relevant modes

Multimedia Tools and Applications - In this paper, we propose a novel ECG signal enhancement method based on Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) and Higher...     

A new alternating direction method for solving variational inequalities

We introduce a modified alternating direction method for structured monotone variational inequalities by performing an additional projection step at each iteration and another optimal step length is employed to reach substantial progress in each iteration. This method only needs functional values for given variables in the solution process and avoids the task of estimating the co-coercive modulus. All the computing process are easily implemented and the global convergence is also presented under mild assumptions. Some preliminary computational results are given.     

A blind digital audio watermarking scheme based on EMD and UISA techniques

In this paper, a new perceptual spread spectrum audio watermarking scheme is discussed. The watermark embedding process is performed in the Empirical Mode Decomposition (EMD) domain, and the hybrid watermark extraction process is based on the combination of EMD and ISA (Independent Subspace Analysis) techniques, followed by the generic detection system, i.e. inverse perceptual filter, predictor filter and correlation based detector. Since the EMD decomposes the audio signal into several oscillating components–the intrinsic mode functions (IMF)–the watermark information can be inserted in more than one IMF, using spread spectrum modulation, allowing hence the increase of the insertion capacity. The imperceptibility of the inserted data is ensured by the use of a psychoacoustical model. The blind extraction of the watermark signal, from the received watermarked audio, consists in the separation of the watermark from the IMFs of the received audio signal. The separation is achieved by a new proposed under-determined ISA method, here referred to as UISA. The proposed hybrid watermarking system was applied to the SQAM (Sound Quality Assessment Material) audio database (Available at http://sound.media.mit.edu/mpeg4/audio/sqam/) and proved to have efficient detection performances in terms of Bit Error Rate (BER) compared to a generic perceptual spread spectrum watermarking system. The perceptual quality of the watermarked audio was objectively assessed using the PEMO-Q (Tool for objective perceptual assessment of audio quality) algorithm. Also, using our technique, we can extract the different watermarks without using any information of original signal or the inserted watermark. Experimental results exhibit that the transparency and high robustness of the watermarked audio can be achieved simultaneously with a substantial increase of the amount of information transmitted. A reliability of 1.8 10^???4 (against 1.5 10^???2 for the generic system), for a bit rate of 400 bits/s, can be achieved when the channel is not disturbed.     

Improving Arabic morphological analyzers benchmark

The various tools dedicated to Arabic natural language processing have undergone significant development during recent years. Among these tools, Arabic morphological analyzers are of great importance because they are often used within other projects that are more advanced such as syntactic parsers, search engines, machine translation systems, etc. Thus, researchers are forced to make a decision concerning which morphological analyzer to use in their research projects, and this task is very difficult since there are many criteria to take into account. In order to facilitate this choice, we considered the problem of benchmarking morphological analyzers in a previous work by proposing a solution that allows returning a set of metrics of each analyzer that are: accuracy, precision, recall, F-measure and the execution time. In this article, we present two new major improvements to our solution: the establishment of the first version of our corpus that is dedicated to the evaluation of morphological analyzers, as well as the introduction of a new metric, which combines all metrics related to results as well as the execution time of the analyzers.