Description: Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating AB B[Symbol: see text]AC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Butz, Benjamin -- Dolle, Christian -- Niekiel, Florian -- Weber, Konstantin -- Waldmann, Daniel -- Weber, Heiko B -- Meyer, Bernd -- Spiecker, Erdmann -- England -- Nature. 2014 Jan 23;505(7484):533-7. doi: 10.1038/nature12780. Epub 2013 Dec 18.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Nanoanalysis and Electron Microscopy, Friedrich-Alexander-Universitat Erlangen-Nurnberg, Cauerstrasse 6, 91058 Erlangen, Germany. ; Interdisziplinares Zentrum fur Molekulare Materialien und Computer-Chemie-Centrum, Friedrich-Alexander-Universitat Erlangen-Nurnberg, Nagelsbachstrasse 25, 91052 Erlangen, Germany. ; Lehrstuhl fur Angewandte Physik, Friedrich-Alexander-Universitat Erlangen-Nurnberg, Staudtstrasse 7, 91058 Erlangen, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24352231" target="_blank"〉PubMed〈/a〉

Description: A particle-into-liquid sampler coupled to a total organic carbon analyzer (PILS-TOC) quantified particulate water-soluble organic carbon (WSOC) mass concentrations during the May 2010 deployment of the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter in the CalNex field study. WSOC data collected during 16 flights provide the first spatiotemporal maps of WSOC in the San Joaquin Valley, Los Angeles Basin, and outflow regions of the Basin. WSOC was consistently higher in concentration within the Los Angeles Basin, where sea breeze transport and Basin topography strongly influence the spatial distribution of WSOC. The highest WSOC levels were associated with fire plumes, highlighting the importance of both primary and secondary sources for WSOC in the region. Residual pollution layers enriched with WSOC are observed aloft up to an altitude of 3.2 km and the highest WSOC levels for each flight were typically observed above 500 m. Simultaneous ground WSOC measurements during aircraft overpasses in Pasadena and Riverside typically exhibit lower levels, especially when relative humidity (RH) was higher aloft suggestive of the influence of aerosol-phase water. This points to the underestimation of the radiative effects of WSOC when using only surface measurements. Reduced aerosol-phase water in the eastern desert outflow region likely promotes the re-partitioning of WSOC to the gas phase and suppression of processes to produce these species (partitioning, multiphase chemistry, photolytic production); as a result, WSOC is reduced relative to sulfate (but not as much as nitrate) as aerosol is advected from the Basin to the outflows.

Description: Four new six-coordinate and one pentacoordinate iron(II) complexes with imidazole as axial ligand were synthesised and characterised. For two of the complexes crystals suitable for X-ray structure analysis were obtained and an extended network of hydrogen bonds was observed in both cases. Magnetic susceptibility studies revealed, that two of the octahedral complexes are high-spin complexes in the entire temperature range, whereas for the other two gradual spin transitions are observed.

Description: ABSTRACT Understanding fracture orientations is important for optimal field development of fractured reservoirs because fractures can act as conduits for fluid flow. This is especially true for unconventional reservoirs (e.g., tight gas sands and shale gas). Using walkaround Vertical Seismic Profiling (VSP) technology presents a unique opportunity to identify seismic azimuthal anisotropy for use in mapping potential fracture zones and their orientation around a borehole. Saudi Aramco recently completed the acquisition, processing and analysis of a walkaround VSP survey through an unconventional tight gas sand reservoir to help characterize fractures. In this paper, we present the results of the seismic azimuthal anisotropy analysis using seismic traveltime, shear-wave splitting and amplitude attenuation. The azimuthal anisotropy results are compared to the fracture orientations derived from dipole sonic and image logs. The image log interpretation suggests that an orthorhombic fracture system is present. VSP data show that the P-wave traveltime anisotropy direction is NE to SW. This is consistent with the cemented fractures from the image log interpretation. The seismic amplitude attenuation anisotropy direction is NW to SE. This is consistent with one of the two orientations obtained using transverse to radial amplitude ratio analysis, with the dipole sonic and with open fracture directions interpreted from image log data.

Description: An increasing number of studies have reported on forest declines and vegetation shifts triggered by drought. In the Swiss Rhone valley (Valais), one of the driest inner-Alpine regions, the species composition in low-elevation forests is changing: The sub-boreal Scots pine ( Pinus sylvestris L.) dominating the dry forests is showing high mortality rates. Concurrently the sub-Mediterranean pubescent oak ( Quercus pubescens Willd.) has locally increased in abundance. However, it remains unclear whether this local change in species composition is part of a larger-scale vegetation shift. To study variability in mortality and regeneration in these dry forests we analyzed data from the Swiss National Forest Inventory (NFI) on a regular grid between 1983 and 2003, and combined it with annual mortality data from a monitoring site. Pine mortality was found to be highest at low elevation (below 1000 m a.s.l.). Annual variation in pine mortality was correlated with a drought index computed for the summer months prior to observed tree death. A generalized linear mixed-effects model indicated for the NFI data increased pine mortality on dryer sites with high stand competition, particularly for small-diameter trees. Pine regeneration was low in comparison to its occurrence in the overstorey, while oak regeneration was comparably abundant. While both species regenerated well at dry sites, pine regeneration was favoured at cooler sites at higher altitude and oak regeneration was more frequent at warmer sites, indicating a higher adaptation potential of oaks under future warming. Our results thus suggest that an extended shift in species composition is actually occuring in the pine forests in the Valais. The main driving factors are found to be climatic variability, particularly drought, and variability in stand structure and topography. Thus, pine forests at low elevations are developing into oak forests with unknown consequences for these ecosystems and their goods and services. © 2012 Blackwell Publishing Ltd

Description: An overview and evaluation of different technologies is presented, which can be applied to remove problematic silane and siloxane compounds from exhaust air. In a lab screening, 96 % H 2 SO 4 was identified to be the most efficient and practical absorbent to remove hexamethyldisiloxane (HMDSO) from exhaust air. Lab scale results were transferred to pilot scale, where the superiority of 96 % H 2 SO 4 in comparison with a previously used scrubber solution (NaOH/MeOH) was demonstrated. In several large scale experiments, the elimination factors of HMDSO from different exhaust airs by 96 % H 2 SO 4 and the capacity of the absorbent were determined. The practicability and robustness of the developed scrubber system using 96 % H 2 SO 4 will allow its easy applicability in API production processes. Experimental work and the corresponding scale-up are presented to overcome the challenge of removing volatile siloxane compounds in a complex exhaust air from a synthesis process of an active pharmaceutical ingredient. The capability of 96 % H 2 SO 4 for the removal of hexamethyldisiloxane from an exhaust air on a technical scale is presented.

Description: The Pacific sardine (Sardinops sagax) showed significant differences in spawning habitat area, spawning habitat quality and availability of survivor habitat as the Pacific Ocean went through the La Niña state in April 2002 to a weak El Niño in April 2003. During another El Niño/Southern Oscillation transition period in 2006–2007 when the El Niño state retreated and the La Niña returned, a similar pattern in spawning habitat quality was seen. The coupling between the atmospheric forcing, the physical ocean states and the properties of the sardine egg spawning are investigated using dynamically consistent data-assimilation fits of the available physical oceanographic observations during these months. Fits were executed using the Regional Ocean Modeling System four-dimensional variational assimilation platform along with adjoint model runs using a passive tracer to deduce source waters for the areas of interest. Analysis using the data-assimilation model runs reveals that unusually strong equatorward wind-forcing drives offshore transport during the La Niña conditions, which extends the spawning habitat for sardine further offshore. A statistical model of sardine spawning habitat shows better habitat quality during the El Niño conditions, which is associated with higher egg densities and corresponded to higher daily egg production. Concentration of eggs is also increased by convergence of water. The results of the source waters analysis using the adjoint data assimilation model support the idea that offshore transport extends the spawning habitat, and show that higher levels of nutrient are brought into the spawning habitat with high concentration of sardine eggs.

Description: Disentangling the functional consequences of the connectivity between optic-flow processing neurons Nature Neuroscience 15, 441 (2012). doi:10.1038/nn.3044 Authors: Franz Weber, Christian K. Machens & Alexander Borst

Description: CO 2 fugacity difference is the driving force for CO 2 -selective membranes used in post-combustion capture. The ambient pressure of the flue gas makes it very difficult to use only a single membrane stage to achieve the CO 2 purity required by pipeline transport and storage, e.g., 95 mol.-%. On the basis of a general multi-stage membrane concept, an energy-efficient membrane cascade is developed. The correlation of energy consumption and membrane area of a cascaded membrane process is investigated, considering 50 %, 70 %, and 90 % degree of CO 2 separation. In addition to an idealized flue gas consisting of N 2 and CO 2 only, also a quasi-real flue gas is studied. Pressure loss in membrane modules and their influence on process energy consumption are discussed. An energy-efficient membrane cascade is developed on the basis of a general multi-stage membrane concept to achieve the CO 2 purity required by pipeline transport and storage. The correlation of energy consumption and membrane area of a cascaded membrane process is investigated for different degrees of CO 2 separation.

Description: In this study, physical and chemical properties of ultrafine aerosol particles are investigated at an urban site in Bakersfield, California, during the CalNex 2010 (California Research at the Nexus of Air Quality and Climate Change) campaign in May and June. Ultrafine particle measurements include particle number size distributions by a scanning Differential Mobility Analyzer (DMA) and size resolved aerosol chemical composition determined with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). Growth events of ultrafine particles were observed on most days and had a very regular pattern. A nucleation mode centered at ∼20 nm appeared in the morning and grew to 40–100 nm throughout the day. Microphysical modeling and size-resolved HR-ToF-AMS concentrations showed that organic components provided most of the particle growth in the ultrafine mode, and sulfate provided on most days only a minor contribution to the mass of this mode. The ultrafine particle mass was largely dominated by organics (77%), and was at maximum during the afternoon. Elemental carbon (EC) and the AMS tracer C4H9+ for hydrocarbon-like organic aerosol (HOA) peaked in the early morning during rush hour, indicative of primary emissions. The fact that the particle number concentration peaked in the afternoon, when EC was at minimum, indicates that the midday increase in number concentration was likely due to new particle formation. The potential importance of solar radiation, the condensation sink of vapor on existing particles, concentrations of OH, O3, SO2, NH3, and VOCs for both condensational growth and new particle formation is evaluated based on the covariation of these parameters with ultrafine mass. The results suggest that the ultrafine particles are from secondary sources that are co-emitted or co-produced with glyoxal and formaldehyde.