Proportionate Adaptive Graph Signal Recovery

This paper generalizes the proportionate-type adaptive algorithm to the graph signal processing and proposes two proportionate-type adaptive graph signal recovery algorithms. The gain matrix of the proportionate algorithm leads to faster convergence than least mean squares (LMS) algorithm. In this paper, the gain matrix is obtained in a closed-form by minimizing the gradient of the mean-square deviation (GMSD). The first algorithm is the Proportionate-type Graph LMS (Pt-GLMS) algorithm which simply uses a gain matrix in the recursion process of the LMS algorithm and accelerates the convergence of the Pt-GLMS algorithm compared to the LMS algorithm. The second algorithm is the Proportionate-type Graph Extended LMS (Pt-GELMS) algorithm, which uses the previous signal vectors alongside the signal of the current iteration. The Pt-GELMS algorithm utilizes two gain matrices to control the effect of the signal of the previous iterations. The stability analyses of the algorithms are also provided. Simulation results demonstrate the efficacy of the two proposed proportionate-type LMS algorithms

Robust Adaptive Generalized Correntropy-based Smoothed Graph Signal Recovery with a Kernel Width Learning

This paper proposes a robust adaptive algorithm for smooth graph signal recovery which is based on generalized correntropy. A proper cost function is defined for this purpose. The proposed algorithm is derived and a kernel width learning-based version of the algorithm is suggested which the simulation results show the superiority of it to the fixed correntropy kernel version of the algorithm. Moreover, some theoretical analysis of the proposed algorithm are provided. In this regard, firstly, the convexity analysis of the cost function is discussed. Secondly, the uniform stability of the algorithm is investigated. Thirdly, the mean convergence analysis is also added. Finally, the complexity analysis of the algorithm is incorporated. In addition, some synthetic and real-world experiments show the advantage of the proposed algorithm in comparison to some other adaptive algorithms in the literature of adaptive graph signal recovery

Microstructural characterization, mechanical and tribological properties of ZC71 hybrid composite reinforced with SiC and MWCNT

In the present study, the influences of different SiC addition, MWCNTs and various SiC particle sizes on the structural, mechanical and tribological properties of ZC71 alloys were studied. The results revealed that the proper amount/size of SiC particles with the addition of MWCNTs had a considerable effect on the microstructural alteration, and mechanical and tribological properties of the ZC71 alloy. The Vickers hardness values of the ZC71 alloy improved with the addition of MWCNT and SiC. The UTS (216 MPa) and El.% (6.95 %) were achieved in the ZC71-5%SiC(15µm)-0.5%MWCNT. The cast ZC71 alloy showed brittle fracture with some quasi-cleavage characterizations. However, by adding 5% SiC (15 µm) and 0.5% MWCNT, the fracture mode changed to ductile fracture. The wear results showed that the ZC71-5%SiC-0.5%MWCNT hybrid composite had the highest wear resistance with the lowest friction coefficient and wear rate. Examination on the worn surface of the ZC71-5%SiC-0.5%MWCNT hybrid composite showed mild abrasion as the governing wear mechanism

The Influence of La and Ce Addition on Inclusion Modification in Cast Niobium Microalloyed Steels

The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In this study, different amounts of RE were added to a niobium microalloyed steel in as-cast condition to investigate its influence on: (i) type of inclusions and (ii) precipitation of niobium carbides. The characterization of the microstructure by optical, scanning and transmission electron microscopy shows that: (1) the addition of RE elements change the inclusion formation route during solidification; RE > 200 ppm promote formation of complex inclusions with a (La,Ce)(S,O) matrix instead of Al2O3-MnS inclusions; (2) the roundness of inclusions increases with RE, whereas more than 200 ppm addition would increase the area fraction and size of the inclusions; (3) it was found that the presence of MnS in the base and low RE-added steel provide nucleation sites for the precipitation of coarse niobium carbides and/or carbonitrides at the matrix–MnS interface. Thermodynamic calculations show that temperatures of the order of 1200 °C would be necessary to dissolve these coarse Nb-rich carbides so as to reprecipitate them as nanoparticles in the matrix.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).The authors from the University of Tehran gratefully acknowledge the financial support provided by the Office of International Affairs and the Office for Research Affairs, College of Engineering, for the project number 8107009.6.34. The authors from Centro Nacional de Investigaciones Metalúrgicas (CENIM) that belong to the Consejo Superior de Investigaciones Científicas (CSIC) would like to acknowledge the financial support from Comunidad de Madrid through the project Diseño Multiescala de Materiales Avanzados (DIMMAT-CM_S2013/MIT-2775). Javier Vivas acknowledges financial support in the form of a FPI (Formación de Personal Investigador) Grant BES-2014-069863. Authors are grateful to the Phase Transformations and Microscopy labs from CENIM-CSIC and to the Centro Nacional de Microscopia Electronica (CNME), located at Complutense Metals 2017, 7, 377 16 of 17 University of Madrid (UCM), for the provision of laboratory facilities. Mr. Javier Vara Miñambres from the Phase Transformations lab (CENIM-CSIC) is gratefully acknowledged for their continuous experimental suppor

Contributions of Rare Earth Element (La,Ce) Addition to the Impact Toughness of Low Carbon Cast Niobium Microalloyed Steels

In this research Rare Earth elements (RE), La and Ce (200 ppm), were added to a low carbon cast microalloyed steel to disclose their influence on the microstructure and impact toughness. It is suggested that RE are able to change the interaction between the inclusions and matrix during the solidification process (comprising peritectic transformation), which could affect the microstructural features and consequently the impact property; compared to the base steel a clear evolution was observed in nature and morphology of the inclusions present in the RE-added steel i.e. (1) they changed from MnS-based to (RE,Al)(S,O) and RE(S)-based; (2) they obtained an aspect ratio closer to 1 with a lower area fraction as well as a smaller average size. Besides, the microstructural examination of the matrix phases showed that a bimodal type of ferrite grain size distribution exists in both base and RE-added steels, while the mean ferrite grain size was reduced from 12 to 7 μm and the bimodality was redressed in the RE-added steel. It was found that pearlite nodule size decreases from 9 to 6 μm in the RE-added steel; however, microalloying with RE caused only a slight decrease in pearlite volume fraction. After detailed fractography analyses, it was found that, compared to the based steel, the significant enhancement of the impact toughness in RE-added steel (from 63 to 100 J) can be mainly attributed to the differences observed in the nature of the inclusions, the ferrite grain size distribution, and the pearlite nodule size. The presence of carbides (cementite) at ferrite grain boundaries and probable change in distribution of Nb-nanoprecipitation (promoted by RE addition) can be considered as other reasons affecting the impact toughness of steels under investigation.The authors from University of Tehran gratefully acknowledge the financial support provided by the office of international affairs and the office for research affairs, college of engineering, for the Project Number 8107009.6.34. The authors from CENIM-CSIC would like to acknowledge the financial support from Comunidad de Madrid through DIMMAT-CM_S2013/MIT-2775 Project. Authors are grateful to the Phase Transformations and Microscopy labs from CENIM-CSIC. Mr. Javier Vara Miñambres from the Phase Transformations lab (CENIM-CSIC) is gratefully acknowledged for his continuous experimental support.Peer Reviewe

Low-carbon cast microalloyed steel intercritically heat-treated at different temperatures: microstructure and mechanical properties

In this study, dual-phase (DP, ferrite + martensite) microstructures were obtained by performing intercritical heat treatments (IHT) at 750 and 800 °C followed by quenching. Decreasing the IHT temperature from 800 to 750 °C leads to: (i) a decrease in the volume fraction of austenite (martensite after quenching) from 0.68 to 0.36; (ii) ~ 100 °C decrease in martensite start temperature (Ms), mainly due to the higher carbon content of austenite and its smaller grains at 750 °C; (iii) a reduction in the block size of martensite from 1.9 to 1.2 μm as measured by EBSD. Having a higher carbon content and a finer block size, the localized microhardness of martensite islands increases from 380 HV (800 °C) to 504 HV (750 °C). Moreover, despite the different volume fractions of martensite obtained in DP microstructures, the hardness of the steels remained unchanged by changing the IHT temperature (~ 234 to 238 HV). Applying lower IHT temperature (lower fraction of martensite), the impact energy even decreased from 12 to 9 J due to the brittleness of the martensite phase. The results of the tensile tests indicate that by increasing the IHT temperature, the yield and ultimate tensile strengths of the DP steel increase from 493 to 770 MPa, and from 908 to 1080 MPa, respectively, while the total elongation decreases from 9.8 to 4.5%. In contrast to the normalized sample, formation of martensite in the DP steels could eliminate the yield point phenomenon in the tensile curves, as it generates free dislocations in adjacent ferrite.The authors are grateful to the Phase Transformations and Microscopy labs from CENIM-CSIC. Mr. Javier Vara Miñambres from the Phase Transformations lab (CENIM-CSIC) is gratefully acknowledged for his continuous experimental support. J. Vivas acknowledges financial support in the form of a FPI Grant BES-2014-069863 from the Ministerio de Economia y Competitividad (MINECO). Open access funding provided by Lulea University of Technology

Effect of Rotation Speed and Steel Microstructure on Joint Formation in Friction Stir Spot Welding of Al Alloy to DP Steel

In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). The effect of these parameters on the joint formation was evaluated by studying the plunging force response during the process and the main characteristics of the joint at (i) macrolevel, i.e., hook morphology and bond width, and (ii) microlevel, i.e., steel hook and sheet microstructure and intermetallic compounds. The plunging force was reduced by increased tool rotation speed while there was no significant effect from the initial steel microstructure ratio of martensite and ferrite on the plunging force. The macrostructural characterization of the joints showed that the hook morphology and bond width were affected by the steel sheet initial microstructures as well as by the tool rotation speed and by the material flow driver; tool pin or shoulder. At microstructural level, a progressive variation in the ratio of martensite and ferrite was observed for the steel hook and sheet microstructure. The zones closer to the tool presented a fully martensitic microstructure while the zones away from the tool showed a gradual increase in the ferrite amount until reaching the ratio of ferrite and martensite of the steel sheet initial microstructure. Different types of FexAly intermetallic compounds were found in three zones of the joint; the hook tips, in the hooks close to the exit hole and in the corner of the exit hole. These compounds were characterized by a brittle behavior with hardness values varying from 456 to 937 HV01