Selective External Oxidation of the Intermetallic Compound, BaAg_5

The selective oxidation of BaAg_5 has been examined at 650–680°C in flowing 3%H2/Ar (po2 ≤ 1.1×x×10^–19atm). Under these conditions, a continuous external barium oxide scale formed. Depletion of Ba from the underlying BaAg_5 led to the formation of a continuous Ag layer between the oxide scale and the BaAg_5. Ba was only detected along grain boundaries in the continuous Ag layer, which was consistent with the negligible solubility reported for Ba in bulk Ag. The local thickness of the continuous Ag layer was inversely correlated to the local Ag grain size. Subsequent experiments with Ag-clad BaAg_5 revealed that surface oxide formation commenced at exposed Ag grain boundaries. BaAg_5 specimens clad with fine grained Ag foil exhibited more extensive oxide formation in a given time than specimens clad with coarse grained Ag foil. These observations confirmed that outward Ba migration through the continuous Ag layer occurred preferentially along Ag grain boundaries. This work demonstrates that an intermetallic compound may undergo external oxidation even when a continuous metallic (or intermetallic) layer, that possesses a low solubility for the oxidizable element, forms under the oxide scale

Soil properties of bare patches in rangelands of South African's grasslands

A loss of grassy cover accompanied by the development of bare soil patches, are the most notable forms of rangeland degradation in grasslands of South Africa. Concerns are growing over the threat of loss of nutritious perennial grass species and the lack of regrowth of the bare patches. Grazing and different rangeland tenure systems -communal and freehold, which is equal to continuous and rotational grazing system - are considered to be of major importance for rangeland degradation. The continuous grazing system is seen to be more affected, but the development of bare patches is not restricted to communal land. We hypothesized that (1) soil properties of bare patches in South Africa´s grasslands are not different in different tenure systems, and (2) soil properties differ with size of bare patches, where big patches are more degraded. To test this, we sampled soils at communal and commercial land in the Thaba Nchu area of South Africa with the following design: we selected three farms per tenure system, 6 randomly chosen plots (100x100m) per farm, and within these plots we sampled 5 bare patches of different sizes (0-10 cm) per plot, where the soil sample (3 replicates) were taken out of the middle of the bare patch. Additionally, soils of adjacent grass were sampled. The results showed that in total, there were more bare patches in continuous grazing systems, evaluated by aerial pictures, but we couldn´t find any differences in bulk density and carbon stocks, between the tenure systems. Additionally, and surprisingly, we found no significant differences in soil organic carbon stocks between bare soil samples and grass samples. There was no clear relationship between bare patch size and nutrient contents. Other nutrients like phosphor were significantly enlarged at the bare patch compared to the grass samples. According to our results, we conclude, that the bare patches seem to develop in different pathways: i) along tracks of grazing animals, (ii) around termite hills, where the termite construction seems to be an initial starting point of bare patches and (iii) on staying and lying places of the grazing animals, which aslo explain the higher nutrient contents at the bare patches

Mass uptake during oxidation of metallic alloys: literature data collection, analysis, and FAIR sharing

The area-normalized change of mass ($\Delta$m/A) with time during the oxidation of metallic alloys is commonly used to assess oxidation resistance. Analyses of such data can also aid in evaluating underlying oxidation mechanisms. We performed an exhaustive literature search and digitized normalized mass change vs. time data for 407 alloys. To maximize the impact of these and future mass uptake data, we developed and published an open, online, computational workflow that fits the data to various models of oxidation kinetics, uses Bayesian statistics for model selection, and makes the raw data and model parameters available via a queryable database. The tool, Refractory Oxidation Database (https://nanohub.org/tools/refoxdb/), uses nanoHUB's Sim2Ls to make the workflow and data (including metadata) findable, accessible, interoperable, and reusable (FAIR). We find that the models selected by the original authors do not match the most likely one according to the Bayesian information criterion (BIC) in 71% of the cases. Further, in 56% of the cases, the published model was not even in the top 3 models according to the BIC. These numbers were obtained assuming an experimental noise of 2.5% of the mass gain range, a smaller noise leads to more discrepancies. The RefOxDB tool is open access and researchers can add their own raw data (those to be included in future publications, as well as negative results) for analysis and to share their work with the community. Such consistent and systematic analysis of open, community generated data can significantly accelerate the development of machine-learning models for oxidation behavior and assist in the understanding and improvement of oxidation resistance

The effects of combined micron-/submicron-scale surface roughness and nanoscale features on cell proliferation and differentiation

Titanium (Ti) osseointegration is critical for the success of dental and orthopedic implants. Previous studies have shown that surface roughness at the micro- and submicro-scales promotes osseointegration by enhancing osteoblast differentiation and local factor production. Only relatively recently have the effects of nanoscale roughness on cell response been considered. The aim of the present study was to develop a simple and scalable surface modification treatment that introduces nanoscale features to the surfaces of Ti substrates without greatly affecting other surface features, and to determine the effects of such superimposed nano-features on the differentiation and local factor production of osteoblasts. A simple oxidation treatment was developed for generating controlled nanoscale topographies on Ti surfaces, while retaining the starting micro-/submicro-scale roughness. Such nano-modified surfaces also possessed similar elemental compositions, and exhibited similar contact angles, as the original surfaces, but possessed a different surface crystal structure. MG63 cells were seeded on machined (PT), nano-modified PT (NMPT), sandblasted/acid-etched (SLA), and nano-modified SLA (NMSLA) Ti disks. The results suggested that the introduction of such nanoscale structures in combination with micro-/submicro-scale roughness improves osteoblast differentiation and local factor production, which, in turn, indicates the potential for improved implant osseointegration in vivoTitanium (Ti) osseointegration is critical for the success of dental and orthopedic implants. Previous studies have shown that surface roughness at the micro- and submicro-scales promotes osseointegration by enhancing osteoblast differentiation and local factor production. Only relatively recently have the effects of nanoscale roughness on cell response been considered. The aim of the present study was to develop a simple and scalable surface modification treatment that introduces nanoscale features to the surfaces of Ti substrates without greatly affecting other surface features, and to determine the effects of such superimposed nano-features on the differentiation and local factor production of osteoblasts. A simple oxidation treatment was developed for generating controlled nanoscale topographies on Ti surfaces, while retaining the starting micro-/submicro-scale roughness. Such nano-modified surfaces also possessed similar elemental compositions, and exhibited similar contact angles, as the original surfaces, but possessed a different surface crystal structure. MG63 cells were seeded on machined (PT), nano-modified PT (NMPT), sandblasted/acid-etched (SLA), and nano-modified SLA (NMSLA) Ti disks. The results suggested that the introduction of such nanoscale structures in combination with micro-/submicro-scale roughness improves osteoblast differentiation and local factor production, which, in turn, indicates the potential for improved implant osseointegration in viv

Differential responses of osteoblast lineage cells to nanotopographically-modified, microroughened titaniumealuminumevanadium alloy surfaces

Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications.Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications

Role of a2b1 integrins in mediating cell shape on microtextured titanium surfaces

Surface microroughness plays an important role in determining osteoblast behavior on titanium. Previous studies have shown that osteoblast differentiation on microtextured titanium substrates is dependent on alpha-2 beta-1 (a2b1) integrin signaling. This study used focused ion beam milling and scanning electron microscopy, combined with three-dimensional image reconstruction, to investigate early interactions of individual cells with their substrate and the role of integrin a2b1 in determining cell shape. MG63 osteoblast-like cells on sand blasted/acid etched (SLA) Ti surfaces after 3 days of culturing indicated decreased cell number, increased cell differentiation, and increased expression of mRNA levels for a1, a2, aV, and b1 integrin subunits compared to cells on smooth Ti (PT) surfaces. a2 or b1 silenced cells exhibited increased cell number and decreased differentiation on SLA compared to wild-type cells. Wild-type cells on SLA possessed an elongated morphology with reduced cell area, increased cell thickness, and more apparent contact points. Cells on PT exhibited greater spreading and were relatively flat. Silenced cells possessed a morphology and phenotype similar to wild-type cells grown on PT. These observations indicate that surface microroughness affects cell response via a2b1 integrin signaling, resulting in a cell shape that promotes osteoblastic differentiation. VC 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 564–573, 2015.Surface microroughness plays an important role in determining osteoblast behavior on titanium. Previous studies have shown that osteoblast differentiation on microtextured titanium substrates is dependent on alpha-2 beta-1 (a2b1) integrin signaling. This study used focused ion beam milling and scanning electron microscopy, combined with three-dimensional image reconstruction, to investigate early interactions of individual cells with their substrate and the role of integrin a2b1 in determining cell shape. MG63 osteoblast-like cells on sand blasted/acid etched (SLA) Ti surfaces after 3 days of culturing indicated decreased cell number, increased cell differentiation, and increased expression of mRNA levels for a1, a2, aV, and b1 integrin subunits compared to cells on smooth Ti (PT) surfaces. a2 or b1 silenced cells exhibited increased cell number and decreased differentiation on SLA compared to wild-type cells. Wild-type cells on SLA possessed an elongated morphology with reduced cell area, increased cell thickness, and more apparent contact points. Cells on PT exhibited greater spreading and were relatively flat. Silenced cells possessed a morphology and phenotype similar to wild-type cells grown on PT. These observations indicate that surface microroughness affects cell response via a2b1 integrin signaling, resulting in a cell shape that promotes osteoblastic differentiation. VC 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 564–573, 2015

An Integrated Framework to Study Ecological Tipping Points in Social-Ecological Systems

Sudden regime shifts or tipping points pose a major threat to various ecosystems and people\u27s livelihoods worldwide. However, tipping points are still hard to predict and often occur without warning. To avoid dramatic social-ecological consequences, it is crucial to understand tipping point behaviour and to identify early warning indicators. Previous studies have hardly implemented an integrated social-ecological approach, which has led to a fragmented understanding and oversimplification of tipping point phenomena. Against this background, we present a systemic research framework that harmonizes ecological and social perspectives to gain a mechanistic understanding of tipping point behaviour. We utilize a social-ecological systems (SES) approach to identify drivers, consequences, and feasible preventive strategies. Our proposed framework consists of a retrospective, a comparative and a prospective perspective; each of them utilizes interdisciplinary studies in both sub systems at multiple scales. The research framework was developed by the members of NamTip, an inter- and transdisciplinary research project aiming to understand and manage desertification tipping points in Namibia’s semi-arid rangelands. The NamTip project represents a practical implementation of the research framework, that uses an integrated, social-ecological study design combining the threefold approach with dynamic modelling. This includes analyses of time-series and archival data, experimental and observational studies, as well as scenario development and exploration of decision-making with local farmers. After the initial practical implementation and with our ongoing evaluation, we are convinced that such an ambitious and complex framework will guide the way to a profound understanding of tipping point phenomena and feasible management options

Biogeochemie von Phosphat im Unterboden am Beispiel deutscher Dauerdüngungsversuche

Unterböden von Ackerstandorten verfügen über große Vorräte an Phosphat (P), allerdings ist nach wie vor unklar, ob, in welchem Umfang und unter welchen Bedingungen diese Nährstoffreserven im Unterboden zur Ernährung unserer Ackerkulturen beitragen. Wir vermuten, dass einerseits langjährige P-Limitierung dazu führen kann, dass mehr P aus dem Unterboden aufgenommen wird, dass aber andererseits die Zugänglichkeit zu P-Reserven im Unterboden auch abhängig ist von der Versorgung mit anderen Nährstoffen, wie z.B. Stickstoff (N) und Kalium (K). Um diese Hypothesen zu testen, beprobten wir unter anderem zwei Statische Nährstoffmangelversuche in Thyrow (Brandenburg) und Gießen (Hessen). Wir entnahmen Bodenproben bis in 100 cm Tiefe, aus Varianten, die seit über 60 Jahren entweder NPK, NK oder PK Düngung erhalten haben. Für diese Proben bestimmten wir die P Pools nach Hedley et al. (1), sowie die Sauerstoffisotopie des Phosphats nach Extraktion mit 1M HCl (δ18OHCl P), welches eine Differenzierung in primäre und sekundäre (d.h. nach vorherigem biologischem Cycling neu ausgefällte) P-Minerale ermöglicht. An beiden Standorten beobachteten wir, dass in den NK-gedüngten Varianten die Vorräte der labilen P Pools aus dem Hedley’schen Extraktionsschema im Unterboden (30 – 100 cm) 10 – 60% geringer waren als in den NPK-gedüngten Varianten. Die Vorräte an HCl P in den NK-Varianten waren jedoch v.a. in Thyrow bis zu 70% höher, während gleichzeitg die δ18OHCl P Werte deutlich niedriger waren als in den NPK-Varianten. Diese niedrigeren Isotopensignaturen deuten auf hauptsächlich primäre P-Minerale hin, sodass wir unsere Annahme von höherem P-Cycling im Unterboden bei Mangel im Oberboden widerrufen müssen. In den PK-gedüngten Varianten beobachteten wir, dass die Vorräte an labilem P im Unterboden 117% (Thyrow) und 22% (Gießen) größer waren als in der NPK-Variante. Dies stützt unsere zweite Annahme von einer Limitierung der P-Aufnahme aus dem Unterboden aufgrund des Mangels an anderen Nährstoffen, allerdings ergaben sich hier keine klaren Auswirkungen auf die δ18OHCl P Signatur des Phosphats. Im Folgenden sollen diese Beobachtungen nun an weiteren Standorten und unter weiteren Einflussparametern getestet werden. Zusammenfassend zeigen jedoch schon unsere bisherigen Ergebnisse, dass die effiziente Ausnutzung von P-Reserven im Unterboden nur unter optimaler Nährstoffversorgung im Oberboden erfolgt