Hydrothermal synthesis of 3D NixCo1−xS2 particles/graphene composite hydrogels for high performance supercapacitors

In this work, three dimensional (3D) Ni_xCo_1−xS₂/graphene composite hydrogels with different Ni contents (denoted as Ni_xCo_1−xS₂/GH (x = 0, 0.31, 0.56, 0.66, 1)) have been synthesized by a simple one-step hydrothermal method and utilized as the active materials of supercapacitors. The as-prepared samples present a 3D interconnected porous network with the pore sizes in the range of several to tens micrometers. Interestingly, the Ni_xCo_1−xS₂ particles are uniformly located on the graphene network and the particle size is evolved from ∼50 nm to ∼1.5 μm with the increase of Ni content. The electrochemical measurements revealed that the specific capacitance, rate capability and cyclability of different Ni_xCo_1−xS₂/GH electrodes are strongly affected by their different Ni content. Among these, the 3D Ni_0.31Co_0.69S₂/GH composite has the highest specific capacitance of 1166 F/g at a current density of 1 A/g. Furthermore, a specific capacitance of 559 F/g can be still maintained at high current density of 20 A/g. After 1000 charge–discharge cycles at 5 A/g, the specific capacitance remains a high value of 755 F/g.     

Calorimetric study and thermodynamic description of Ga-Ge-Li liquid alloys

This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga_0.75Li_0.25)_1-xGe_x, (Ge_0.50Li_0.50)_1-xGa_x, (Ga_0.50Li_0.50)_1-xGe_x, (Ga_0.25Li_0.75)_1-xGe_x. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature.     

A bat-neural network multi-agent system (BNNMAS) for stock price prediction: Case study of DAX stock price

Creating an intelligent system that can accurately predict stock price in a robust way has always been a subject of great interest for many investors and financial analysts. Predicting future trends of financial markets is more remarkable these days especially after the recent global financial crisis. So traders who access to a powerful engine for extracting helpful information throw raw data can meet the success. In this paper we propose a new intelligent model in a multi-agent framework called bat-neural network multi-agent system (BNNMAS) to predict stock price. The model performs in a four layer multi-agent framework to predict eight years of DAX stock price in quarterly periods. The capability of BNNMAS is evaluated by applying both on fundamental and technical DAX stock price data and comparing the outcomes with the results of other methods such as genetic algorithm neural network (GANN) and some standard models like generalized regression neural network (GRNN), etc. The model tested for predicting DAX stock price a period of time that global financial crisis was faced to economics. The results show that BNNMAS significantly performs accurate and reliable, so it can be considered as a suitable tool for predicting stock price specially in a long term periods.     

Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation

Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co²⁺ was oxidized to Co³⁺ after oxidation reaction.     

Static and free vibration analysis of functionally graded plates based on a new quasi-3D and 2D shear deformation theories

In this study, two dimensional (2D) and quasi three-dimensional (quasi-3D) shear deformation theories are presented for static and free vibration analysis of single-layer functionally graded (FG) plates using a new hyperbolic shape function. The material of the plate is inhomogeneous and the material properties assumed to vary continuously in the thickness direction by three different distributions; power-law, exponential and Mori–Tanaka model, in terms of the volume fractions of the constituents. The fundamental governing equations which take into account the effects of both transverse shear and normal stresses are derived through the Hamilton's principle. The closed form solutions are obtained by using Navier technique and then fundamental frequencies are found by solving the results of eigenvalue problems. In-plane stress components have been obtained by the constitutive equations of composite plates. The transverse stress components have been obtained by integrating the three-dimensional stress equilibrium equations in the thickness direction of the plate. The accuracy of the present method is demonstrated by comparisons with the different 2D, 3D and quasi-3D solutions available in the literature.     

Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process.     

Electromagnetic shielding properties of iron oxide impregnated kenaf bast fiberboard

The electromagnetic shielding effectiveness of kenaf fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted for removing the lignin and extractives from the fibers and magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by the compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a variable frequency from 9 GHz to 11 GHz. Using the Scanning Electron Microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with the magnetizing treatments increased from 44.8 mJ/m² to 46.1 mJ/m², 48.8 mJ/m² and 53.0 mJ/m², respectively, while the modulus of elasticity reduced from 2875 MPa to 2729 MPa, 2487 MPa and 2007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30–50% to 60–70%, 65–75% and 70–80%, respectively.     

A simple approach for fabrication of interconnected graphitized macroporous carbon foam with uniform mesopore walls by using hydrothermal method

Three-dimensional (3D) highly interconnected graphitized macroporous carbon foam with uniform mesopore walls has been successfully fabricated by a simple and efficient hydrothermal approach using resorcinol and formaldehyde as carbon precursors. The commercially available cheap polyurethane (PU) foam and Pluronic F127 were used as a sacrificial polymer and mesoporous structure-directing templates, respectively. The graphitic structure of carbon foam was obtained by catalytic graphitization method using iron as catalyst. Three different carbon foams such as graphitized macro-mesoporous carbon (GMMC) foam, amorphous macro-mesoporous carbon (AMMC) foam and graphitized macroporous carbon (GMC) foam were fabricated and their physicochemical and mechanical properties were systematically measured and compared. It was found that GMMC possess well interconnected macroporous structure with uniform mesopores located in the macroporous skeletal walls of continuous framework. Besides, GMMC foam possesses a well-defined graphitic framework with high surface area (445 m²/g), high pore volume (0.35 cm³/g), uniform mesopores (3.87 nm), high open porosity (90%), low density (0.30 g/cm³) with good mechanical strength (1.25 MPa) and high electrical conductivity (11 S/cm) which makes it a promising material for many potential applications.     

Microstructure and mechanical properties of laser beam welded Al–Li alloy 2060 with Al–Mg filler wire

Alloy 2060-T8 is a newly developed high-strength Al–Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of α-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasicrystalline T₂ phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al–Li–Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T₂ phase forms in the laser-welded Al–Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone.