In situ analysis of metal-oxide systems used for selective oxidation catalysis: how essential is chemical complexity?

The mode of operation of selective oxidation reactions is described by a series of chemical rules defining the catalyst and some reaction intermediates. In contrast to catalytic processes over metallic elements, little is known, however, about the atomistic details of selective oxidation. In particular, the participation of the subsurface region of the catalyst in the kinetically relevant elementary steps (Mars–van Krevelen mechanism) is not positively verified. Using in situ X-ray absorption techniques to study binary and ternary molybdenum oxides the present contribution shows that it is possible to tackle some of the problems in selective oxidation by direct experimental observation. The modification of the Mo–O local bonding interaction upon thermal reduction of MoO₃to MoO_3-x is illustrated. This was also found for mixed Mo–V oxides in which the chemical state of the vanadium seemed unaffected by the reaction but the surface Mo:V ratio varied substantially with the gas phase composition. It is further shown that the solid-state phase transformation between reduced and oxidised forms of molybdenum oxides occur so rapidly, that possibly relevant suboxide cannot be identified by ex situ phase analysis. Observation of the time-law of redox transformations showed that lattice oxygen is only available for selective oxidation if the associated solid-state transformation occurs in the kinetic regime of reaction control and not in that of diffusion control.     

Hybrid nanocomposites based on superparamagnetic and ferromagnetic particles: A comparison of their magnetic and dielectric properties

Nanocomposites of magnetic nanoparticles and polymer matrices combine the properties of their components, and as such are good examples of functional nanomaterials with excellent application potential. Against this background, experimental and theoretical studies of such composites are of great interest. In this study we aim to provide insight into the static and dynamic magnetic response, as well as the dielectric response, of magnetic nanocomposites subjected to external magnetic and electric fields. We directly compare the behavior of polyurethane films doped with superparamagnetic Fe₃O₄, and blocked ferromagnetic CoFe₂O₄ nanoparticles. While a reversible, Langevin magnetization curve is observed for Fe₃O₄@PU films, hysteretic magnetic behavior is found in case of CoFe₂O₄@PU films. The hysteresis observed for CoFe₂O₄ nanoparticles can be explained by interactions at the interface between particles and polymer matrix in conjunction with its ferromagnetic nature. The results of dielectric spectroscopy experiments revealed different effects of Fe₃O₄ and CoFe₂O₄ nanoparticles on polymer dynamics.     

Graybody radiation from conical flames

The spatial dependence of graybody radiation from a cone, the shape representative of small flames, has been computed. A comparison of the radiative heat flux from this model and experimental measurements of the total heat flux from a flame indicate that up to 74 percent of the total emitted intensity is radiative.     

When disasters strike environmental science: a case–control study of changes in scientific collaboration networks

Scientometrics - Studies of scientific collaboration networks reveal the social structure of scientific disciplines. Most of these studies assume scientists work under conditions of institutional...     

Neue Verbund‐Schrägseilbrücken (BW 29 und 4) im Zuge der BAB 30 – Nordumgehung Bad Oeynhausen

Zur Zeit befindet sich der Lückenschluss der BAB 30 als sogenannte Nordumgehung Bad Oeynhausen im Bau. In diesem Rahmen werden am östlichen und westlichen Ende der Nordumgehung die Bauwerke 29 und 4 erstellt. Hierbei handelt es sich um Schrägseilbrücken in Verbaundbauweise, welche architektonische Landmarken an den Enden der Nordumgehung Bad Oeynhausen setzen. Beide Bauwerke überführen die BAB 30 über den Fluss Werre. Die Stromöffnungen betragen ca. 68 m bzw. ca. 83 m und sind damit für Schrägseilbrücken vergleichsweise gering. Aufgrund der Lage im Krümmungsbereich, der örtlichen Randbedingungen (u. a. große Schiefe wegen des Kreuzungswinkels) sowie des FFH‐Status der Werre ergab sich im Rahmen der Entwurfsplanung eine anspruchsvolle Aufgabenstellung. Trotz eines ähnlichen Erscheinungsbildes unterscheiden sich beide Bauwerke jedoch maßgeblich in ihrer Konstruktion durch die Anzahl der Seilebenen und die Ausbildung der Seilquerträger. Der Aufsatz beschreibt die wesentlichen statisch‐konstruktiven Besonderheiten der Bauwerke aus Sicht der Entwurfsverfasser. New cable‐stayed bridges (Structure 29 and 4) in the course of the Autobahn A 30 – Northern bypass at Bad Oeynhausen. Closing a gap in the course of the Autobahn A 30, the Northern bypass at Bad Oeynhausen is currently under construction. Within this project two cable‐stayed bridges, Structure 29 and 4, are being constructed at the Western and Eastern ends of the bypass. The bridges are of composite construction and they have been architecturally designed to form landmarks at the respective ends of the Bad Oeynhausen bypass. Both structures carry the Autobahn A 30 across the river Werre. The main spans measure 68 m and 83 m respectively and are thus fairly short for cable‐stayed bridges. Due to the location in curved sections of the Autobahn, local constraints (such as a large skew because of the crossing angle) and the Werre being a nature reserve with FFH status, the structural design has been a demanding task. In spite of having a similar appearance both structures differ significantly in number of cable planes and the construction of the transversal girder for cable anchorages. This article describes the distinctive features of both bridges from a static and structural point‐of‐view.