Sol derived gold–palladium bimetallic nanoparticles on TiO2: structure and catalytic activity in CO oxidation

Bimetallic AuPd catalysts were prepared by deposition of bimetallic aqueous sols formed in different ways: (i) co-reduction of the precursor Au and Pd ions by Na-citrate/tannic acid mixture, (ii) reduction of Au(III) ions onto preformed Pd sol, and (iii) reduction of Pd(II) ions onto a preformed Au sol. The Au/TiO₂ and Pd/TiO₂ samples as references were prepared from their respective sols. The structure of the samples was characterized by XRF, XRD, XPS, TEM and CO chemisorption both in the as-prepared state and after calcination and reduction. The catalytic activities of the calcined/reduced catalysts in the CO oxidation were compared. The presence of bimetallic crystalline phases was evidenced in all three samples both in the as prepared and calcined/reduced states, however, various extents of Pd surface enrichment were determined. The catalytic activity of the bimetallic samples regardless of the preparation method, is about the same as that of the mixture of the monometallic samples. No significant synergism is suggested in the present bimetallic samples.     

INTEGRAL EQUATION APPEOACH FOZ SIHULATION-OF - HEAT AND MASS TRANSFER PROCESSES

An integral equation approach was recommended for modelling and simulation of heat and mass transfer processes. It was shown that several mixing models that have been dealt with up to now dlfferently, can be unified in a single integral equation. An effective numerical method was developed for the solution of non-linear integral equation. A construction method for the source and kernel functions were lntroduced in connection with the simulation and control of heat treatlng processes taking place in tunnel kiln and heat and mass transfer processes in tunnel dryer.

We have concluded that our method is advantageous If the slmulated process 1s slgnlficantly affected by the degree of mixing and/or the kernel function can be determined by direct measurement of the streaming phases including feedback, recirculation etc.     

Personal RF exposimetry in urban area

The purpose of the current study was to evaluate the usefulness of a radiofrequency (RF) personal exposimeter (dosimeter) for assessing individual RF exposure in an urban environment. Measurements taken by RF personal dosimeter were also compared to preliminary site measurements taken around mobile base stations. The results from personal exposure showed that one third of the participants spent 40–70% of 24 h recording time above the detection limits (0.05 V/m), and half of subjects spent less than 10%. The highest exposure was detected during the traveling period and the lowest in bed at home. Based on our results, we concluded that site measurements cannot be used to accurately determine personal exposure. We also concluded that duration of time exposed to RF levels above the detection limit of the personal dosimeter is a useful exposure metric to compare and contrast individual RF exposure of study subjects.     

Field-coupled computing in magnetic multilayers

This paper presents a computational study of ion-beam patterned cobalt-platinum multilayers, which could be used for field-coupled computing. We use micromagnetic simulations to reproduce measured hysteresis curves. This parameterized micromagnetic simulator then will be used for simulating interacting magnetic dots. We demonstrate how logic gates can be built from such coupled dots. We also show how electrical wires—placed beneath or above the magnetic dots—can provide a magnetic field, which propagates the magnetic signals.     

Some new aspects of the phase diagram of the NH 4 + /H+-W-O system

The phase composition of partially-reduced products of ammonium paratungstate (APT) was investigated. The samples were prepared by reducing the APT in a H₂ + N₂/129 volume ratio/atomosphere in the temperature range 610 to 860 K, and studied by means of chemical analysis, by X-ray diffraction analysis and by thermoanalytical methods. The reduction products can be described by the general formula of M _xWO_3–y+x/2 where M can be either H⁺ and/or NH ₄ ⁺ . Products considered as tungsten bronzes (TB) can be formed in a fairly narrow temperature range. Another product, the so-called decomposed APT (DAPT) is a mixture of bronzes and of some other compounds characterized by y/2 and considered as some intermediate phases between TB and tungstates.     

Addressing the Risk of Surface Water Intrusion in Old Romanian Salt Mines

In Romania, surface waters near underground salt mines represent a significant risk to the stability of the mine workings. Such problems occur in many salt exploiting facilities, i.e. Slanic Prahova, Targu Ocna, Praid. In this paper, the authors present a method of dealing with this issue at the Praid salt mine with research targeted at avoiding the hazard presented by intrusion of surface waters into old mine workings. Monitoring activities are proposed to prevent damage due to the seepage of Corund Creek water into the subsurface salt body, which could compromise and even produce collapses in the salt mine sanatorium and old and new mines.     

Andreev and normal reflections at normal metal—Superconductor boundaries: Limitations of the semiclassical approximation

We study the scattering of quasiparticles at a normal metal—superconductor interface using Bogoliubov-de Gennes equations, taking the motion parallel to the interface fully into account. We show that while the Andreev reflection is the dominant scattering process in case of nearly perpendicular impacts (as predicted by the semiclassical theory), the normal reflection becomes increasingly important for quasiparticles with large momenta parallel to the interface, and the semiclassical approximation becomes progressively inadequate. We work out consequence of this feature for spectra of bound states in superconductor—normal metal—superconductor junctions.     

Adaptive statistical algorithms in network reliability analysis

The paper is concerned with introducing novel algorithms, such as adaptive approximation and deterministic radial basis function (RBF) method, for calculating the average loss (AL). Different approximators are trained to approximate the loss function and, after a short learning period, AL can be evaluated analytically with fast calculations. An improvement of the Li–Silvester (LS) method is also presented which yields a sharper lower bound on AL. The efficiency of the new methods are proven by theoretical analysis as well as demonstrated by excessive simulations.     

Interactions and Chemical Transformations of Coronene Inside and Outside Carbon Nanotubes

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures are prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π–π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor‐phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes.     

Effects of pulsed laser radiation on epitaxial self-assembled Ge quantum dots grown on Si substrates

Laser irradiation of Ge quantum dots (QDs) grown on Si(100) substrates by solid-source molecular beam epitaxy has been performed using a Nd:YAG laser (532 nm wavelength, 5 ns pulse duration) in a vacuum. The evolution of the Ge QD morphology, strain and composition with the number of laser pulses incident on the same part of the surface, have been studied using atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The observed changes in the topographical and structural properties of the QDs are discussed in terms of Ge-Si diffusion processes. Numerical simulations have been developed for the investigation of the temperature evolution of the QDs during laser irradiation. The obtained results indicate that the thermal behaviour and structural variation of the nanostructures differ from conventional thermal annealing treatments and can be controlled by the laser parameters. Moreover, an unusual island motion has been observed under the action of subsequent laser pulses.