Thickness Dependent Properties in Oxide Heterostructures Driven by Structurally Induced Metal–Oxygen Hybridization Variations

Thickness‐driven electronic phase transitions are broadly observed in different types of functional perovskite heterostructures. However, uncertainty remains whether these effects are solely due to spatial confinement, broken symmetry, or rather to a change of structure with varying film thickness. Here, this study presents direct evidence for the relaxation of oxygen‐2p and Mn‐3d orbital (p–d) hybridization coupled to the layer‐dependent octahedral tilts within a La_2/3Sr_1/3MnO₃ film driven by interfacial octahedral coupling. An enhanced Curie temperature is achieved by reducing the octahedral tilting via interface structure engineering. Atomically resolved lattice, electronic, and magnetic structures together with X‐ray absorption spectroscopy demonstrate the central role of thickness‐dependent p–d hybridization in the widely observed dimensionality effects present in correlated oxide heterostructures.     

3D Dislocation structure evolution in strontium titanate: Spherical indentation experiments and MD simulations

In the present work, the dislocation structure evolution around and underneath the spherical indentations in (001) oriented single crystalline strontium titanate (STO) was revealed by using an etch‐pit technique and molecular dynamics (MD) simulations. The 3D defect structure at various length scales and subsurface depths was resolved with the help of a sequential polishing, etching, and imaging technique. This analysis, combined with load‐displacement data, shows that the incipient plasticity (manifested as sudden indenter displacement bursts) is strongly influenced by preexisting dislocations. In the early stage of plastic deformation, the dislocation pile‐ups are all aligned in 〈100〉 directions, lying on {110}₄₅ planes, inclined at 45° to the (001) surface. At higher mean contact pressure and larger indentation depth, however, dislocation pile‐ups along 〈110〉 directions appear, lying on {110}₉₀ planes, perpendicular to the (100) surface. MD simulations confirm the glide plane nature and provide further insights into the dislocation formation mechanisms by tracing the evolution of the complete dislocation line network as function of indentation depth.     

Demand Response Potenziale in der chemischen Industrie

A supply system geared to renewable energy sources requires a high degree of flexibility to ensure system stability. Load management can make a big contribution. The chemical industry as one of the largest consumers of electrical energy can play an important role there. The analysis of the so far conducted studies shows great potential for the chlor‐alkali process and air liquefaction. The variable costs are comparable to other flexibility options. To determine the realizable potential further investigations are needed.     

Separation efficiency of particle-packed HPLC microchips

We report an experimental study of separation efficiency in microchip high-performance liquid chromatography (HPLC). For this study, prototype HPLC microchips were developed that are characterized by minimal dead volume, a separation channel with trapezoidal cross section, and on-chip UV detection. A custom-built stainless steel holder enabled microchip packing under pressures of up to 400 bar and ultrasonication. Bed densities were investigated with respect to the packing conditions and consistently related to pressure drop over the packed microchannels and separation efficiency under isocratic elution conditions. The derived plate height curves show a decrease of mobile phase mass transfer resistance with increasing bed density. High bed densities are critical to separation performance in noncylindrical packed beds, because only at low bed porosities does hydrodynamic dispersion in noncylindrical packings come close to that of cylindrical packings. At higher bed porosities, the presence of fluid channels of advanced flow velocity in the corners of noncylindrical packings affects hydrodynamic dispersion strongly. We demonstrate that the separation channels of HPLC microchips can be packed as densely as the cylindrical fused-silica capillaries used in nano-HPLC and that consequently microchip-HPLC separation efficiencies comparable to those of nano-HPLC can be achieved.     

Elevated nitrate levels in the groundwater of the Gaza Strip: distribution and sources

Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO(3)(-) in the groundwater of the Gaza Strip and to identify the sources of NO(3)(-) in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO(3)(-) concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO(3)(-) source materials in Gaza are animal manure N, synthetic NH(4) based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in delta(15)N of solid manure samples was +7.5 to +11.9 per thousand. The range in delta(15)N of sludge samples was +4.6 to +7.4 per thousand, while four brands of synthetic fertilizers commonly used in Gaza had delta(15)N ranging from +0.2 to +1.0 per thousand. Sludge amended soil had delta(15)N ranging from +2.0 to +7.3 per thousand. For both delta(18)O and delta(15)N, the ranges of groundwater NO(3)(-) were -0.1 to +9.3 per thousand and +3.2 to 12.8 per thousand, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided delta(15)N of sludge represents the maximum delta(15)N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.     

Benzene, alkylated benzenes, chlorinated hydrocarbons and monoterpenes in snow/ice at Jungfraujoch (46.6 degrees N, 8.0 degrees E) during CLACE 4 and 5

Benzene, alkylated benzenes, chlorinated hydrocarbons and monoterpenes were measured in snow/ice collected directly in-cloud at Jungfraujoch (3580 m asl) in February and March 2005 and 2006 during the CLoud and Aerosol Characterization Experiments CLACE 4 and CLACE 5. Melted snow/ice samples were analyzed by headspace-solid-phase-dynamic-extraction (HS-SPDE) followed by gas chromatography/mass spectrometry (GC/MS). Generally, there was a tendency in the results that higher concentrations were found after longer precipitation-free periods, suggesting that higher concentrations in snow/ice may be caused by the washout effect of precipitation. High concentration variations in snow/ice samples taken at the same time at the same place highlight the heterogeneous nature of snow/ice. Air concentrations calculated by scavenging ratios and measured snow/ice values markedly exceed the typically reported concentrations of benzene and alkylbenzenes in air (Li Y, Campana M, Reimann S, Schaub KS, Staehlin J, Peter T. Hydrocarbon concentrations at the alpine mountain sites Jungfraujoch and Arosa. Atmos Environ 2005;39:1113-27). This argues for an efficient snow/ice scavenging of those compounds from the atmosphere during precipitation formation.     

Macro‐ and Nanomechanical Properties and Strain Rate Sensitivity of Accumulative Roll Bonded and Equal Channel Angular Pressed Ultrafine‐Grained Materials

Several processes of severe plastic deformation are suitable for the production of materials with ultrafine‐grained microstructures which are known to exhibit high strength and often good ductility as well as strain rate sensitive behavior. The most promising ones are equal channel angular pressing (ECAP) for bulk material and accumulative roll bonding (ARB) for the production of sheet material. In order to evaluate the influence of the process on these mechanical properties and the strain rate sensitivity, tensile tests, and nanoindentation tests were performed on material produced up to similar effective plastic strains of ε_ARB = 6.4 and ε_ECAP = 6.3. It could be shown that the macroscopic strength is slightly higher for ARB than for ECAP material and vice versa in nanoindentation. Independent of the testing method, the strain rate sensitivities and activation volumes are similar for both materials. Thus, both processes performed up to similar effective plastic strains lead to comparable improvements in the mechanical properties. Additionally it could be shown, that this comparison allows the identification of the dominant deformation mechanism which is responsible for the observed strain rate sensitivity.