Work stealing with private integer–vector–matrix data structure for multi‐core branch‐and‐bound algorithms

In this paper, the focus is put on multi‐core branch‐and‐bound algorithms for solving large‐scale permutation‐based optimization problems. We investigate five work stealing (WS) strategies with a new data structure called integer–vector–matrix (IVM). In these strategies, each thread has a private IVM allowing the local management of a set of subproblems enumerated using a factorial system. The WS strategies differ in the way the victim thread is selected and the granularity of stolen work units (intervals of factoradics). To assess the efficiency of the private IVM‐based WS approach, the five WS strategies have been extensively experimented on the flowshop scheduling permutation problem and compared with their conventional linked‐list‐based counterparts. The obtained results demonstrate that the IVM‐based WS outperforms the linked‐list‐based one in terms of CPU time, memory usage and number of performed WS operations. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermomechanical material parameters characterization of the superalloy PN 3601669-7 under low-velocity impacts

This work concerns the characterization of the thermodynamic behavior of the superalloy Airsist 215 (PN 3601669-7) containing cobalt. Such superalloys are used in aeronautical construction, in the hot parts of the turbine. They are frequently used for the production of the paddles. The parts in service are subjected to dynamic solicitations and thermal fluctuations over the course of time. They are responsible for modification and degradation of material properties. This can lead to the appearance of cracks and, in the long term, to the rupture of these parts. In this paper, a preliminary physical study is made on the appearance of the cracks, followed by experiments using shocks at ambient temperature and under a heating situation which simulates combustion. It is found that these dynamic loads have a significant impact on the development of the cracks that appear on the segments of the turbine nozzle. The study is devoted to the elastic shock of Hertz-Boussinesq extended to viscoelastic bodies by direct convolution of Riemann-Stielges. The interest resides in the local convolution and the distribution of stresses in the contact zone. The shock excitation method includes a deduced force in the load and disload phases. This force is an impulse which approaches a Dirac function. The sample can be modeled approximately by a system of one degree of freedom for natural frequency, damping and transfer function. The spectral response of the specified shock allows calculation of the damping. Every point of this spectrum gives the response for the linear system of the transfer function. Then, viscoelastic shock parameters are deduced.     

Finished surface morphology,microstructure and magnetic properties of selective laser melted Fe-50wt% Ni permalloy

This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characterized by a 3D profilometer, optical microscope, scanning electron microscope, X-ray diffraction, etc. The effects of the volume energy density of laser (LVED) on structure, and magnetic properties with coercivity (H_c), remanence (B_r), and power losses (P_50-1), were evaluated and discussed systematically. The results show that the relative porosity rate and the surface roughness of the SLMed specimens decreased with the increase in LVED. Only the γ-(FeNi) phase was detected in the X-ray diffraction patterns of the SLMed permalloys fabricated from the different LVEDs. Statistical analysis of optical microscopy images indicated that the grain coarsened at higher LVED. Furthermore, the microstructure of the SLMed parts was a typical columnar structure with an oriented growth of building direction. The highest microhardness reached 198 HV_0.1. Besides, the magnetic properties including B_r, H_c, and P_50-1 of SLMed samples decreased when the LVED ranged from 33.3 to 60.0 J/mm³ firstly and then increased while LVED further up to 93.3 J/mm³, which is related to the decrease in porosity and the increase in grain size, while the higher residual stress and microcracks presented in the samples manufactured using very high LVED. The observed evolution of magnetic properties and LVED provides a good compromise in terms of reduced porosity and crack formation for the fabrication of SLMed Fe-50wt% Ni permalloy. The theoretical mechanism in this study can offer guidance to further investigate SLMed soft magnetic alloys.     

Analysis and prediction of tool wear, surface roughness and cutting forces in hard turning with CBN tool

The main of the present study is to investigate the effects of process parameters (cutting speed, feed rate and depth of cut) on performance characteristics (tool life, surface roughness and cutting forces) in finish hard turning of AISI 52100 bearing steel with CBN tool. The cutting forces and surface roughness are measured at the end of useful tool life. The combined effects of the process parameters on performance characteristics are investigated using ANOVA. The composite desirability optimization technique associated with the RSM quadratic models is used as multi-objective optimization approach. The results show that feed rate and cutting speed strongly influence surface roughness and tool life. However, the depth of cut exhibits maximum influence on cutting forces. The proposed experimental and statistical approaches bring reliable methodologies to model, to optimize and to improve the hard turning process. They can be extended efficiently to study other machining processes.     

Rescheduling of power systems constrained with transient stability limits in restructured power systems

This paper investigates various approaches to relieve the transient stability constraint in restructured power systems. The approaches adopted fall into two broad categories: those based on eliminating the constraint in the least-cost way and those based on eliminating with the least possible rescheduling. The latter group can, on the other hand, emerge in the form of a pool-protected policy in which the bilateral contracts are rescheduled to maintain the stability or in the form of a contract-protected policy in which the realizable bilateral contracts are maximized while minimizing the rescheduling in pool market. Transient energy function (TEF) method is used as a tool to calculate the sensitivity of energy margin to the variations in the magnitude of generation and load. The effectiveness of the method is illustrated by case studies on Western System Coordinating Council (WSCC) 3-machine 9-bus power system and on the 10-machine 39-bus New England test system and the results are compared. The results are also verified by time domain simulations.     

Numerical simulation of the inhomogeneous barrier height of an Au/n-InP Schottky diodeKamel Zeghdar1, Lakhdar Dehimi1, 2, Achour Saadoune1, Nouredine Sengouga1,*

We report the current-voltage(I-V) characteristics of the Schottky diode(Au/n-InP) as a function of temperature. The SILVACO-TCAD numerical simulator is used to calculate the I-V characteristic in the temperature range of 280-400 K. This is to study the effect of temperature on the I-V curves and assess the main parameters that characterize the Schottky diode such as the ideality factor, the height of the barrier and the series resistance. The I-V characteristics are analyzed on the basis of standard thermionic emission(TE) theory and the inhomogeneous barrier heights(BHs) assuming a Gaussian distribution. It is shown that the ideality factor decreases while the barrier height increases with increasing temperature, on the basis of TE theory. Furthermore, the homogeneous BH value of approximately 0.524 eV for the device has been obtained from the linear relationship between the temperature-dependent experimentally effective BHs and ideality factors. The modified Richardson plot, according to the inhomogeneity of the BHs, has a good linearity over the temperature range. The evaluated Richardson constant A^* was 10.32 A·cm^-2·K^-2, which is close to the theoretical value of 9.4 A·cm^-2·K^-2 for n-InP. The temperature dependence of the I-V characteristics of the Au/n-InP Schottky diode have been successfully explained on the basis of the thermionic emission(TE) mechanism with a Gaussian distribution of the Schottky barrier heights(SBHs). Simulated I-V characteristics are in good agreement with the measurements[Korucu D, Mammadov T S. J Optoelectronics Advanced Materials, 2012, 14:41]. The barrier height obtained using Gaussian Schottky barrier distribution is 0.52 eV, which is about half the band gap of InP.