Polycrystalline cubic boron nitride sintered with Ti(C,N)-W-Al mechanically alloyed binders

The structural changes in Ti(C,N)-W-Al mechanically alloyed (MA) binders and the sintering mechanism of PcBN were investigated by XRD, SEM and TEM techniques. The elastic properties of PcBN compacted were determined by ultrasound technique. Tungsten was efficiently dissolved in Ti(C,N) by mechanical alloying, forming homogeneous binders during sintering. Opposite strain effects were induced in the binders than in PcBN particles. Dissolution of W in Ti(C,N) enhanced the fracturing of the cBN particles and the formation of the nanostructured binder pools by increasing the hardness of binder particles. Poisson's ratios and Young's moduli of the new PcBN products were higher than the reference product. Micro-Vickers hardness of sintered products increased with milling time of the binder powder. Slightly higher hardness values were achieved when Al powder was mechanically alloyed with Ti(C,N) and W powders than when it was attrition milled with MA Ti(C,N)-W.     

Effect of the heating rate on crystallization behavior of mechanically alloyed amorphous alloy

The mechanical alloying is the most convenient method to produce Mg–Ni alloys. In this study, the effect of ball-to-powder weight ratios and the mechanical alloying time on amorphization of Mg₅₀Ni₅₀ alloy and its thermal stabilities were investigated. Mg₅₀Ni₅₀ alloy has been produced by using Spex 8000 D mixer/mill with different ball-to-powder weight ratios (5:1, 10:1, 20:1). Amorphization times by XRD analysis are found to be 60 h for 5:1 ball-to-powder weight ratio, 10 h for 10:1 ball-to-powder weight ratio and 5 h for 20:1 ball-to-powder weight ratio. The thermal stabilities of amorphous Mg₅₀Ni₅₀ alloys, obtained by different ball-to-powder weight ratios, have been determined and the effect of heating rates on the crystallization temperatures have also been investigated by DSC. The heating rates employed were 5, 10, 15, 20 °C/min. During the first crystallization reaction, the amorphous and Mg₂Ni intermetallic phases occurred. DSC studies show that increase in heating rates increased the crystallization temperatures for all samples. The apparent activation energies were determined by means of the Kissinger method.     

Electrochemical hydrogen storage characteristics of Mg1.5Al0.5−xZrxNi (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) alloys synthesized by mechanical alloying

Mg_1.5Al_0.5−xZr_xNi (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that Zr facilitated the amorphization of Mg₂Ni phase, while Al retarded the amorphization of this phase. The increase in the Zr content was observed to bring about significant improvement in the discharge capacities at all the ball milling durations. The stepwise replacement of Al with Zr, however, caused considerable reduction in the initial discharge capacities of the alloys. Despite the adverse effect of Al on the initial discharge capacity, it prevented the rapid degradation of Mg₂Ni phase with the charge/discharge cycles. When the beneficial effects of Zr and Al were combined by designing Mg_1.5Al_0.5−xZr_xNi type alloys, Mg_1.5Al_0.2Zr_0.3Ni alloy was found to have the highest discharge capacity at almost all the charge/discharge cycle steps. Among the obtained capacity retaining rates, Mg_1.5Al_0.4Zr_0.1Ni alloy had the best performance. This alloy has kept at least 50% of its initial discharge capacity at 20th cycle. The analysis by the electrochemical impedance spectroscopy revealed that the charge transfer resistances of Al-rich alloys were low at high depth of discharges. This observation was attributed to the formation of the porous unstable Mg(OH)₂ layer due to the intercalation of Al₂O₃ layers, which have the high rate of solubility in strongly basic solutions, and thus the exposition of the underlying electrocatalytically active Ni sites.     

Effect of V,Nb, Ti and graphite additions on the hydrogen desorption temperature of magnesium hydride

In this study the effects of mechanical milling with 5 wt.% of additives (V, Nb, Ti and Graphite) on the hydrogen desorption temperature of the magnesium hydride (MgH₂) were studied. The powder mixtures were mechanically milled for 2 h. X-ray diffraction (XRD), scanning electron microscope (SEM), and optical microscope (OM) techniques were used for the structural and morphological characterization of powders. Differential scanning calorimeter (DSC) was used to investigate the effects of the mechanical milling with additives on the hydrogen desorption temperature of the magnesium hydride powder. DSC results show that the hydrogen desorption temperatures of mechanically milled MgH₂ with additives are depressed about ∼40–50 °C compared with that of as-received MgH₂. The particle size analysis results indicate that decrease of the particle size of powders leads to a decrease of the hydrogen desorption temperature. Moreover, increasing specific surface area can also contribute to a decrease on the hydrogen desorption temperature.     

On the trade-off between energy efficiency and estimation error in compressive sensing

Compressive sensing (CS) refers to the process of reconstructing a signal that is supposed to be sparse or compressible. CS has wide applications, such as in cognitive radio networks. In this paper, we investigate effective CS schemes for the trade-off between energy efficiency and estimation error. We propose an enhancement to a Bayesian estimation approach and an enhancement to the isotonic regression approach that is based on nearly isotonic regression. We also show how to compute the routing matrix for selecting active sensor nodes. The proposed enhancements are evaluated with trace-driven simulations. Considerable gaps are observed between the original approaches and the proposed enhancements in the simulation results. The near isotonic regression method achieves the best performance among all the CS schemes examined in this paper.     

Sintering behaviour of nano-crystalline γ-Al2O3 powder without additives at 2-7 GPa

Al₂O₃ ceramics were fabricated without additives under high pressure (2-7 GPa) at different temperatures (600-1200 °C) using nanocrystalline alumina powder with metastable γ-Al₂O₃ phase as the starting material.It was shown that high pressure increases the nucleation rate while reducing the growth rate of the transformed α phase so that its grain size decreases and nano-scale grains in the sintered structure can be achieved.On the other hand the sintered samples at 7 GPa and high temperature (1000 °C) have shown micron-scale large grain sizes compared to those sintered at lower pressures, for the same temperature and sintering time. This could be attributed to the higher input energy in the system at high pressure and high temperature conditions, thereby reaching the final stage in sintering more quickly.In this work, the best combination of grain size (∼200 nm) and density (98.0% TD) was obtained under the sintering condition of 1000 °C at 7 GPa with a holding time of 1 min.Thus for high pressure/high temperature conditions, the sintering time should be reduced to prevent grain growth.     

Antifungal Activity of Olive Oil and Ozonated Olive Oil Against Candida Spp. and Saprochaete Spp.

Ozonated olive oil was investigated for their capacity to inhibit growth of 38 yeast strains of Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis, and Saprochaete capitata. Two different ozonated olive oil (OZO1, OZO2) and two different olive oil (OL1, OL2) samples having different biochemical parameters were assessed in terms of their antifungal ability and comparison was made. Fluconazole was chosen as control antifungal agent. Each sample’s antifungal activity decreased in the following order: OZO1 > OZO2 > OL1 ≥ OL2. This study demonstrated that ozonated olive oil may help to control some fluconazole-resistant and dose-dependent sensitive fungal strains.     

Recognition of Western style musical genres using machine learning techniques

This study uses machine learning techniques (ML) to classify and cluster different Western music genres. Three artificial neural network models (multi-layer perceptron neural network [MLP], probabilistic neural network [PNN]) and self-organizing maps neural network (SOM) along with support vector machines (SVM) are compared to two standard statistical methods (linear discriminant analysis [LDA] and cluster analysis [CA]). The variable sets considered are average frequencies, variance frequencies, maximum frequencies, amplitude or loudness of the sound and the median of the location of the 15 highest peaks in the periodogram. The results show that machine learning models outperform traditional statistical techniques in classifying and clustering different music genres due to their robustness and flexibility of modeling algorithms. The study also shows how it is possible to identify various dimensions of music genres by uncovering complex patterns in the multidimensional data.     

Effects of tungsten and aluminium on the oxidation and phase formation in mechanically alloyed Ti(C,N)–W–Al systems

The effects of milling parameters and composition of the powder mixtures on the transformations of Ti(C,N)–W–Al powders processed by high energy ball milling were investigated by XRD, SEM and TEM. The strain energy and the fine particle size contributed to the high chemical reactivity with oxygen of the powders milled for 12–24 h. Powders milled for 48 h were chemically stable. The affinity with oxygen decreased after W dissolution in Ti(C,N), and the subsequent decrease in lattice strains. Aluminium lowered the lattice strains, and subsequently the strain energy stored in the deformed crystals of Ti(C_0.5N_0.05) and W milled above 25 °C. Fracturing of hard particles dominated in the early stage of milling in the absence of Al, whereas with Al, plastic deformation of particles and cold welding of Ti(C,N) and W particles by the softer Al prevailed at the same time.