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We obtained WC–Cr3C2–Cu composite alloys by the copper melt infiltration into uncompacted WC and Cr3C2 powders (the reference alloys) and their mixtures with the weight ratio WC : Cr3C2 = 1 : 1. Impregnation of the uncompacted carbide powders with the copper melt was performed at low-frequency (~80 Hz) vertical vibration (LFV) of the crucible with the alloy components for 10 min in a resistance furnace under a flow-through argon atmosphere. We studied the influence of the heat treatment of the obtained model composites on interaction of the WС and Cr3С2 carbides under isothermal and dynamic temperature impact, as well as during high-speed cyclic heating of the alloy surface by an electric arc (120 A, 45 V, 2 Hz, 10 000 arc interruption cycles). We investigated the evolution of alloy structures by means of electron microscopy, X-ray spectral microanalysis, X-ray phase, and differential thermal analysis. We show that the impact on the sample surface by the temperature field created by the electric arc leads to intense interaction of the carbides. Here, the matrix copper transforms periodically into a melt and plays the role of a transfer medium (the diffusion medium). As a result of such heat treatment, in the upper layers of the alloys, finely dispersed compositions of complex carbide phases occurred with the sizes ≤1–2 μm, i.e., 1–2 orders of magnitude less than that of the initial carbides. [ABSTRACT FROM AUTHOR]

We report the results of magnetic force microscopy (MFM) investigations of low-coercivity Co nanodiscs, with 50 nm lateral size and 20 nm height, fabricated by e-beam lithography and ion etching. We observed two types of MFM contrast in the form of Gaussian and ring distributions caused by strong probe-particle interaction. We compared experimentally the transformation of the MFM contrast from these low-coercivity nanodiscs caused by an external magnetic field applied in situ, and compared the experimental results with theoretical simulations. Index Terms--Low-coercivity magnetic nanodiscs, magnetic force microscopy, tip-sample interaction.

We report the results of simulations of magnetic force microscope (MFM) contrast for low-coercive ferromagnetic and superparamagnetic nanoparticles. We show that two types of MFM contrast in the form of gaussian and ring distributions can be observed because of probe-particle interaction. We discuss stabilization of the magnetic moment of nanoparticles by an external magnetic field. We have calculated the values of stabilizing magnetic fields and their dependence on probe parameters and scanning heights. Index Terms--Low-coercive magnetic nanoparticles, magnetic force microscopy, superparamagnetic particles.

We report on the results of a magnetic force microscopy investigation of remagnetization processes in arrays of CoPt nanodisks with diameters of 35 and 200 nm and a thickness of 9.8 nm fabricated by e-beam lithography and ion etching. The controllable magnetization reversal of individual CoPt nanodisks by the magnetic force microscope (MFM) tip-induced magnetic field was demonstrated. We observed experimentally two essentially different processes of tip-induced remagnetization. Magnetization reversal of 200 nm disks was observed when the probe moved across the particle while in case of 35 nm nanodisks one-touch remagnetization was realized. Micromagnetic modeling based on the Landau–Lifshitz–Gilbert (LLG) equation demonstrated that the tip-induced magnetization reversal occurs through the essentially inhomogeneous states. Computer simulations confirmed that in case of 200 nm disks the mechanism of embryo nucleation with reversed magnetization and further dynamic propagation following the probe moving across the particle was realized. On the other hand one-touch remagnetization of 35 nm disks occurs through the inhomogeneous vortexlike state. Micromagnetic LLG simulations showed that magnetization reversal in an inhomogeneous MFM probe field has a lower energy barrier in comparison with the mechanism of coherent rotation, which takes place in a homogeneous external magnetic field. [ABSTRACT FROM AUTHOR]

Vanadium-based alloys with a BCC structure are considered to be an alternative to palladium alloys for hydrogen purification. Since the performance of membranes is influenced by not only their bulk characteristics but also their surface condition, we have investigated the effect of different surface preparation techniques (abrasive grinding and polishing, electrolytic polishing, and ion etching) on the surface microstructure of V85Ni15 membrane alloy using X-ray photoelectron spectroscopy. After electrolytic polishing and ion etching, we observed an increase in the percentages of vanadium and nickel metals in the surface layer of the alloy in comparison with its state after abrasive polishing. Such changes are expected to be favorable for an increase in the rate of hydrogen dissociation and recombination on the surface of the membrane material, eventually improving hydrogen transport efficiency. [ABSTRACT FROM AUTHOR]

A technique for production of high-density composite material (Cu-1 wt % Al2O3) by single-fold cold compacting and sintering was developed. It is known that presence of gases in ductile metals, e.g., copper, inhibits consolidation of powder metal products. The technique is able to succeed in degassing of the composite material during heating in a hydrogen atmosphere. The technique is based on addition of cobalt and copper oxalates in a mixture of Cu and Al2O3. The efficiency of the technique was estimated by the relative density and hardness values of produced Cu-Al2O3 composite materials. The mechanism of impact of activated sintering on compaction of composite materials was investigated. It was found that decomposition of cobalt and copper oxalates at heating in hydrogen atmosphere synchronizes activated reduction of copper oxides and degassing of products, supporting permeability of composite materials. Composition of active admixture 0.5 wt % CoC2O4 + (2-2.5) wt % CuC2O4 is optimized. It was found experimentally that addition of oxalates produces a positive impact on consolidation processes and properties of composite materials on the basis of copper and Al2O3 micro- and nanoparticles irrespective of preparation techniques: electrolysis, evaporation-condensation, salt decomposition, precipitation and coprecipitation of hydroxides with further reducing heat treatment and milling. Application of activated sintering of powders obtained by coprecipitation of hydroxides and compacted at 700 MPa enables the formation of Cu-1% Al2O3 composite material with improved properties. As a result, composite material with homogeneous structure (grain size of 2-10 μm), increased values of density (8.4 g/cm3), and Brinell hardness up to 780 MPa was produced. [ABSTRACT FROM AUTHOR]

Aim: To assess cerebral hemodynamics during sleep in patients with syndrome of obstructive sleep apnea., Methods: Long term monitoring of rheoencephalogram. Data processing consisted in construction of trends (curves of changes of rheographical parameters during any selected time interval)., Results and Conclusion: Cyclical periods of apnea are associated with negative changes of cerebral hemodynamics. At the end of period of apnea despite compensatory vasodilatation cerebral blood flow decreases. This occurs during pronounced hypoxemia and can predispose to ischemic disturbances. In ventilation phase rapid rise of heart rate and blood pressure at the background of continuing cerebral vasodilatation can increase risk of hemorrhagic complications.