Mn-containing catalytic materials for the total combustion of toluene: The role of Mn localisation in the structure of LDH precursor

Mg/Mn/Al mixed oxide systems of similar atomic ratios close to 2/0.5/1 were obtained by calcination of Mg,Al layered double hydroxide (LDH) type precursors containing Mn either in the cationic form within the brucite layer or as permanganate anions in the interlayer. The materials were characterised with PXRD, thermal analysis, XPS, ESR, TPR and BET. In mixed oxides derived from interlayer-doped precursor PXRD identified MgO–MnO solid solution and poorly crystalline Al-rich spinel phase, while those obtained from layer-doped LDH contained a better crystalline Mn-rich spinel. Surface of both materials was covered with poorly crystalline and/or amorphous Mn⁴⁺-containing phases. Higher reducibility of this surface coat in calcined layer-doped catalyst, as compared to interlayer-doped one, was attributed to the differences in the nature of underlying crystalline phases, and was considered the chief reason for the higher catalytic activity of this catalyst in the total oxidation of toluene.     

Photovoltaic effect and carrier transport mechanisms in Hg1-Mnxtdiodes

Hg_1-xMn_xTe semiconducting semimagnetic alloy has been examined in the context of its possible applications in infrared detectors. For analysis of detector properties the intrinsic carrier concentration has been calculated as a function of temperature and crystal composition. The starting material was In-doped Hg_1-xMn_xTe grown by the modified Bridgman method. The as-grown crystals with manganese content of 12-19% were p-type with carrier concentration and mobility of 100 cm²/ Vs at 77 K. An-type layer was formed on the surface by the annealing process in saturated Hg-vapour at 270-320° for 2 hrs. Capacitance-voltage curves have C^-3 dependence on applied voltage indicating that the junction is linearly graded. From standard electrical measurements and spectral characteristics the main detector parameters were determined and compared to those of Hg_1-xCd_xTe devices. The influence of material properties on detector parameters was analyzed. In order to estimate the carrier transport mechanisms, differential resistivities and current-voltage curves were measured over a wide range of temperaturesi.e. 25 to 300 K. From the temperature dependence of the R₀A product, it was established that at high temperatures (150-300 K) the carrier transport is dominated by a recombination-generation mechanism. In low temperature region the excess current at forward bias is probably attributed to carrier tunneling via energy states distributed randomly within the forbidden gap. At reverse bias the leakage surface or volume currents dominate in the carrier transport.     

AAOP-based dynamically reconfigurable monitoring system

A key aspect of resource management is efficient and effective deployment of available resources whenever needed. The issue typically covers two areas: monitoring of resources used by software systems and managing the consumption of resources. A key aspect of each monitoring system is its reconfigurability – the ability of a system to limit the number of resources monitored at a given time to those that are really necessary at any particular moment. The authors of this article propose a fully dynamic and reconfigurable monitoring system based on the concept of Adaptable Aspect-Oriented Programming (AAOP) in which a set of AOP aspects is used to run an application in a manner specified by the adaptability strategy. The model can be used to implement systems that are able to monitor an application and its execution environment and perform actions such as changing the current set of resource management constraints applied to an application if the application/environment conditions change. Any aspect that implements a predefined interface may be used by the AAOP-based monitoring system as a source of information. The system utilizes the concept of dynamic AOP, meaning that the aspects (which are sources of information) may be dynamically enabled/disabled.     

The Semantic Web: Collective Intelligence on the Web

The World Wide Web has turned hypertext into a success story by enabling world-wide sharing of unstructured information and informal knowledge. The Semantic Web targets the sharing of structured information and formal knowledge pursuing objectives of achieving collective intelligence on the Web. Germane to the structure of the Semantic Web is a layering and standardization of concerns. These concerns are reflected by an architecture of the Semantic Web that we present through a common use case. Semantic Web data for the use case is now found on the Web and is part of a quickly growing set of Semantic Web resources available for formal processing.     

An alternative approach to carbon nanotube sample preparation for TEM investigation

A two-stage replication technique (positive replica) is shown to be suitable for transmission electron microscopy (TEM) examination of carbon nanotubes (CNTs) and other one-dimensional nanostructures in their longitudinal direction. This method enables handling the fragile nanostructures, is fast and simple and allows to study the growth mechanism of nanofeatures, including the early stages of their growth. CNTs may also be examined when the growth layers are very thin, and even when only a few nanotubes are on a substrate. Replicas can be taken from various substrate shapes covered with nanostructures and from minute or specifically selected areas of the substrates. CNTs extracted by the replica are not disturbed, and their nanostructures are preserved. It is demonstrated that using positive replicas, HRTEM images from the nanosized carbon forms can also be obtained.     

Soldering of Mg Joints Using Zn-Al Solders

Magnesium has applications in the automotive and aerospace industries that can significantly contribute to greater fuel economy and environmental conservation. The Mg alloys used in the automotive industry could reduce mass by up to 70 pct, providing energy savings. However, alongside the advantages there are limitations and technological barriers to use Mg alloys. One of the advantages concerns phenomena occurring at the interface when joining materials investigated in this study, in regard to the effect of temperature and soldering time for pure Mg joints. Eutectic Zn-Al and Zn-Al alloys with 0.05 (wt pct) Li and 0.2 (wt pct) Na were used in the soldering process. The process was performed for 3, 5, and 8 minutes of contact, at temperatures of 425 °C, 450 °C, 475 °C, and 500 °C. Selected, solidified solder-substrate couples were cross-sectioned, and their interfacial microstructures were investigated by scanning electron microscopy. The experiment was designed to demonstrate the effect of time, temperature, and the addition of Li and Na on the kinetics of the dissolving Mg substrate. The addition of Li and Na to eutectic Zn-Al caused to improve mechanical properties. Higher temperatures led to reduced joint strength, which is caused by increased interfacial reaction.     

Hanle Effect of Charged and Neutral Excitons in Quantum Wells

We measured magnetic field depolarization of charged and neutral exciton cw photoluminescence of a system consisting of two coupled quantum wells with a residual concentration of holes. Using the Hanle expression, we obtained exciton lifetime and electron spin relaxation time, which are in agreement with results of time-resolved experiments. We suppose that the tunneling takes place via an emission of an LO phonon and we find this process spin conserving.     

MnTe and ZnTe grown on sapphire by molecular beam epitaxy

We report on growth of MnTe layers by molecular beam epitaxy on Al₂O₃ substrates and of ZnTe layers on hybrid MnTe/Al₂O₃ substrates. The aim of our work was to prepare hexagonal phases of epitaxial thin films of these two materials. In the case of MnTe, the hexagonal NiAs-type phase was prepared by depositing the film directly on Al₂O₃ substrates. On the other hand, the crystal structure of ZnTe layers grown on hybrid MnTe/Al₂O₃ substrates was found to depend on the layer thickness: layers thinner than 0.05 μm grew in a metastable hexagonal wurtzite structure, but with further increases of the thickness, the cubic zinc blende phase of ZnTe tended to appear. The structural properties of MnTe and ZnTe layers were characterized by high energy electron and X-ray diffraction methods. Electrical properties of MnTe films were assessed by the Hall effect measurements. The topography and microstructure were analyzed by atomic force microscope. The Néel temperature and magnetic domains structure of antiferromagnetic hexagonal MnTe layers were obtained from neutron experiments.     

Transamination Reactivity of Ti(NMe2)4 and Zr(NMe2)4 with 1,3,4,5,6-Pentamethyl-2-aminoborazine and Aryl Amines. Model Chemistry for the Formation of Metalloborazine Preceramic Polymers and MN/BN (M?=?Ti, Zr) Ceramic Composites

The transamination reactions between Ti(NMe₂)₄ and 1,3,4,5,6-pentamethyl-2-aminoborazine, (Me)₃N₃(Me)₂B₃(NH₂), and diphenylamine (Ph₂NH) and between [Zr(NMe₂)₄]₂ and 1,3,4,5,6-pentamethyl-2-aminoborazine, aniline (PhNH₂) and diphenylamine have been studied and the molecular product species have been isolated, spectroscopically characterized and single crystal X-ray structure analyses completed. The results of these studies have been used to interpret the outcome of reactions of Ti(NMe₂)₄ and Zr(NMe₂)₄ with borazinylamine preceramic polymers that, upon pyrolysis, produce TiN/BN, ZrN/BN and ZrH_0.6N/BN composite powders. The transamination reactivity of a two-point poly(borazinylamine) oligomer having terminal –NH₂ amino groups with Ti(NMe₂)₄ and Zr(NMe₂)₄ has been used to obtain metallated preceramic oligomers that, upon pyrolysis, give TiN/BN and ZrN/ZrH_0.6N/BN nanocomposites. Model reactions of 1,3,4,5,6-pentamethyl-2-amino borazine, aniline and Ph₂NH₂ with Ti(NMe₂)₄ and Zr(NMe₂)₄ are also described as models for the formation of the metallated oligomers. Molecular structure determinations for the metal amides are presented. We dedicate this paper to Professor Christopher W. Allen in recognition of his distinguished career and his accomplishments in inorganic ring and polymer chemistry.