Oxidation of formic acid at a high surface area supported platinum modified by foreign metal adatoms

The anodic oxidation of formic acid was studied on platinum distributed in the form of small particles in a porous substrate modified by metal adatoms deposited at underpotentials. The rate of the reaction was greatly enhanced on the commercial catalyst Powercat 3000 (PC 3000). The hydrogen adsorption and the underpotential deposition of several metals at PC 3000 were shown to be dissimilar to that at smooth polycrystalline Pt. Steady-state and long-term experiments were performed to determine the stability of this electrode.     

Mechanical and fracture behavior of powder metalurgy processed Ti3Al-based alloys

This work considers structural and compression mechanical properties of three Ti₃Al-based alloys processed by powder metallurgy. Mechanically alloyed powders were compacted by hot-pressing to non-porous homogenous compacts. Prior to compression tests, all compacts were homogenized by a solution treatment at 1050°C (α + β region) for 1h, followed by water quenching. The compression tests were performed from room temperature to 500°C in vacuum at a strain rate of 2.4 × 10⁻³ s⁻¹. Detailed microstructural characterization has been evaluated by scanning electron microscopy (SEM), followed by electron dispersive spectroscopy (EDS) and X-ray diffraction analysis. Fracture topography was examined by SEM. The Ti₃Al-Nb alloy exhibits the highest ductility in the whole temperature range, whereas addition of Mo to Ti₃Al-Nb alloy yields the highest ultimate compression strength. A correlation between ductility and the fracture mode exists for all materials.     

Statistical Properties of Transition Amplitudes in Generic Systems

I review some recent results on the statistical properties of matrix elements of typical observables (transition amplitudes) in an eigenbasis of generic quantum Hamiltonian systems. The classical limit of an underlying system can be either integrable, or fully chaotic, or mixed with regular and irregular regions coexisting in phase space. In any case, the variance of transition amplitudes (the local average transition probability) as a function of energy and transition frequency can be calculated in terms of classical power spectra. The probability distribution of transition amplitudes in high energy (semiclassical) regime is derived by means of random matrix theory, whereas in low and intermediate energy (nonsemiclassical) regime the probability distribution of transition amplitudes exhibits universal exponential tails which still call for theoretical explanation.     

Simulation of Fuzzy-Logic-Based Intelligent Wheelchair Control System

Fuzzy logic control system for an intelligent wheelchair aimed for assistance by the severely handicapped persons is presented in the paper. It is based on a computer simulation of wheelchair navigation, in which fuzzy logic enables control priority to smoothly alternate between manual and automatic control of the wheelchair in the vicinity of obstacles. The main purpose of designing and simulating this control approach is to improve the safety of a wheelchair in the presence of obstacles. To analyze the success of the wheelchair control, a dynamic model of the wheelchair, together with the models of distance sensors, has been developed using Lagrange analysis.     

Stereometric analysis of nanostructured boehmite coatings synthesized by aluminum nitride powder hydrolysis

We studied the morphological properties of precipitated, nanostructured, boehmite coatings on a polished alumina surface by exploiting the aluminum nitride (AlN) powder hydrolysis at elevated temperatures. The hydrolysis tests of the 3 wt% AlN powder suspensions in the temperature range 50–90 °C were performed in order to estimate the time needed for the synthesis of the coatings. They consisted of interlocked boehmite lamellas, positioned perpendicularly to the ceramic surface, and they exhibited a strong temperature-dependent size and surface density. The aim of this research was a quantitative assessment of the as-formed boehmite coatings. Based on electron microscopy micrographs, a stereometric analysis of the as-prepared coatings was performed in order to estimate the relevant geometric parameters of the lamellas. In spite of the temperature-dependent lamellas’ size and surface density, the specific volume of the coatings was similar for all the synthesis temperatures.     

Power supplies for plasma column control in the COMPASS tokamak

The main magnetic fields in COMPASS – i.e. The Toroidal, Magnetising, Equilibrium, and Shaping Fields – are created by a set of four corresponding thyristor power supplies controlled in a 0.5 ms loop.The plasma position has to be controlled both radially and vertically by two additional magnetic fields provided by two fast amplifiers (FAs) based on MOSFET technology, each supplying ±100 V and up to ±5 kA.Currently, an ongoing project aims at ELM triggering by fast changes of the vertical position of the plasma column, also referred to as vertical kicks. For this purpose, a new Vertical Kicks Power Supply (VKPS) capable of quick change of vertical plasma position is being constructed. This power supply should operate at up to 1.2 kV with switching frequency up to 5 kHz. It is designed as a H-bridge but based on IGBT transistors which can be operated at higher voltages than MOSFETs.In this paper, we focus on the FAs and VKPS engineering design and required output parameters. Both the power supplies are based on modern components with highest available ratings in their categories. Unique design of the power supplies takes advantage of the short duration of the COMPASS discharge by overloading the transistors above their maximal steady-state rating.The FA is regularly operating, so that in addition to describing its design, we also describe the achieved performance parameters. Finally, the common controller unit, communication, and error handling is described.     

Investigating the tension load of rubber composites by impact dynamic testing

This work deals with establishing the tension load by impact dynamic testing of rubber composite conveyor belts. The value of tension load affects the shape of the used impactor and use of a support system as well as the weight of the ram and the impact height. An increase in the allowable stress when the belt is tensioned was examined during the test, to determine the effect of impact on the tension load. The obtained values of tension load are assessed using basic mathematical and statistical methods. Using the Design of Experiments method, factors that significantly affect the value of the tension load are identified.     

Corrosion of NiTi Wires with Cracked Oxide Layer

Corrosion behavior of superelastic NiTi shape memory alloy wires with cracked TiO₂ surface oxide layers was investigated by electrochemical corrosion tests (Electrochemical Impedance Spectroscopy, Open Circuit Potential, and Potentiodynamic Polarization) on wires bent into U-shapes of various bending radii. Cracks within the oxide on the surface of the bent wires were observed by FIB–SEM and TEM methods. The density and width of the surface oxide cracks dramatically increase with decreasing bending radius. The results of electrochemical experiments consistently show that corrosion properties of NiTi wires with cracked oxide layers (static load keeps the cracks opened) are inferior compared to the corrosion properties of the straight NiTi wires covered by virgin uncracked oxides. Out of the three methods employed, the Electrochemical Impedance Spectroscopy seems to be the most appropriate test for the electrochemical characterization of the cracked oxide layers, since the impedance curves (Nyquist plot) of differently bent NiTi wires can be associated with increasing state of the surface cracking and since the NiTi wires are exposed to similar conditions as the surfaces of NiTi implants in human body. On the other hand, the potentiodynamic polarization test accelerates the corrosion processes and provides clear evidence that the corrosion resistance of bent superelastic NiTi wires degrades with oxide cracking.