Transport of Dissolved Si from Soil to River: A Conceptual Mechanistic Model

This paper reviews the processes which determine the concentrations of dissolved silicon (DSi) in soil water and proposes a conceptual mechanistic model for understanding the transport of Si through soils to rivers. The net DSi present in natural waters originates from the dissolution of mineral and amorphous Si sources in the soil, as well as precipitation processes. Important controlling factors are soil composition (mineralogy and saturated porosity) and soil water chemistry (pH, concentrations of organic acids, CO₂ and electrolytes). Together with production, polymerization and adsorption equations they constitute a mechanistic framework determining DSi concentrations. We discuss how key controls differ across soil horizons and how this can influence the DSi transport. A typical podzol soil profile in a temperate climate is used as an example, but the proposed model is transferrable to other soil types. Additionally, the impact of external forcing factors such as seasonal climatic variations and land use is evaluated. This blueprint for an integrated model is a first step to mechanistic modelling of Si transport processes in soils. Future implementation with numerical methods should validate the model with field measurements.     

The Global Biogeochemical Silicon Cycle

Silicon is one of the most important elements in the current age of the anthropocene. It has numerous industrial applications, and supports a high-tech multi-billion Euro industry. Silicon has a fascinating biological and geological cycle, interacting with other globally important biogeochemical cycles. In this review, we bring together both biological and geological aspects of the silicon cycle to provide a general, comprehensive review of the cycling of silicon in the environment. We hope this review will provide inspiration for researchers to study this fascinating element, as well as providing a background environmental context to those interested in silicon.     

Dietary exposure of the Belgian population to emulsifiers E481 (sodium stearoyl-2-lactylate) and E482 (calcium stearoyl-2-lactylate)

A dietary exposure assessment of food emulsifiers E481 (sodium stearoyl-2-lactylate) and E482 (calcium stearoyl-2-lactylate) in the Belgian population was performed. Nationally representative food consumption data from the Belgian National Food Consumption Surveys 2004 (BNFCS2004) and 2014 (BNFCS2014) were used for calculations. A conservative approach (combining individual food consumption data with the maximum permitted level (MPL) of foods (tier 2), was compared with more refined estimates (combining individual food consumption data with actual concentrations measured in food products available on the Belgian market (tier 3)). Estimated daily intakes were compared to the acceptable daily intake (ADI) of the stearoyl-2-lactylates. The results of tier 2 demonstrated that 92% of the children (3–9 years), 53% of the adolescents (10–17 years), 15% of the adults (18–64 years) and 26% of the elderly (64–98 years) had a potential intake higher than the ADI. When replacing the MPL with maximum analysed concentration levels in foods, daily intake estimates decreased dramatically. The estimated daily intake of the food emulsifiers was below the ADI for all age groups, except for a small percentage of children (1.9%) for which the intake exceeded the ADI. The main contributors to the exposure of E481 and E482 were bread, rolls and fine bakery wares.     

High aspect ratio via etch development for Cu nails in 3-D-stacked ICs

In this study the etch development of high aspect ratio vias in Si for the fabrication of Cu nails is described. To enable subsequent metallisation, these vias need to meet strict requirements with respect to uniformity, slope, sidewall roughness and undercut. For aspect ratios up to 5 a SiO₂ hard mask based SF6/O₂ etch approach is used. For aspect ratios up to 10, a resist based passivation polymer type etch approach with C4F8/SF6 was used to successfully pattern vias in Si. Typical problems of this process and optimization to overcome the issues are described.     

The two-factorial symptom structure of post-traumatic stress disorder: depression-avoidance and arousal-anxiety

BACKGROUND: Yeast pyruvate kinase (PK) catalyzes the final step in glycolysis. The enzyme therefore represents an important control point and is allosterically activated by fructose-1,6-bisphosphate (FBP). In mammals the enzyme is found as four different isozymes with different regulatory properties: two of these isozymes are produced by alternate splicing. The allosteric regulation of PK is directly related to proliferation of certain cell types, as demonstrated by the expression of an allosterically regulated isozyme in tumor cells. A model for the allosteric transition from the inactive (T) state to the active (R) state has been proposed previously, but until now the FBP-binding site had not been identified. RESULTS: We report here the structures of PK from yeast complexed with a substrate analog and catalytic metal ions in the presence and absence of bound FBP. The allosteric site is located 40 A from the active site and is entirely located in the enzyme regulatory (C) domain. A phosphate-binding site for the allosteric activator is created by residues encoded by a region of the gene corresponding to the alternately spliced exon of mammalian isozymes. FBP activation appears to induce several conformational changes among active-site sidechains through a mechanism that is most likely to involve significant domain motions, as previously hypothesized. CONCLUSIONS: The structure and location of the allosteric activator site agrees with the pattern of alternate genetic splicing of the PK gene in multicellular eukaryotes that distinguishes between a non-regulated isozyme and the regulated fetal isozymes. The conformational differences observed between the active sites of inactive and fully active PK enzymes is in agreement with the recently determined thermodynamic mechanism of allosteric activation through a 'metal relay' that increases the affinity of the enzyme for its natural phosphoenolpyruvate substrate.     

Influence of low-k dry etch chemistries on the properties of copper and a Ta-based diffusion barrier

In this study, the film properties of Cu and a Ta-based diffusion barrier deposited on organic polymer and SSQ-based low-k materials with subtractive porosity were investigated. Emphasis was put on the effects of exposure of the low-k materials to the dry etch plasmas prior to metal deposition. The metal film properties were influenced by the type of the dry etch plasma chemistry used and by the porosity of the low-k material. Thermal desorption spectra (TDS) obtained during annealing of these metal films revealed an increased amount of species with m/e 44, attributed to CO₂, and H₂O desorbing from the Cu film at high temperatures. The TDS data for the Ta film did not contain such high temperature desorption peaks for these species mentioned. Surface morphology of the Cu and Ta films observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) also showed a poor wetting of the metal films on the porous low-k materials that have been dry etch plasma treated.     

Dissolved Silicon and Its Origin in Belgian Beers—A Multivariate Analysis

Beer is a quintessential part of Belgian heritage. We performed a detailed analysis of factors controlling Si content in Belgian beers as a case study to coincide with the 2011 IBiS meeting in Antwerp (Belgium). Beer is one of the richest dietary sources of Si. Three decades of research have yielded evidence of a role for Si in human physiology: it plays an essential role in bone mineral density and reduces the biological availability of aluminium. We analysed 119 Belgian beers: highest dissolved Si concentrations were found in high fermentation, traditionally brewed ales. Concentrations ranged between 214 and 2,071 μmol L^???1. This is probably due to the complexity and length of the brewing procedure: longer, more complicated processing and presence of brewing sediment in the bottle allows more Si to dissolve out of the base products like hop, barley or even rice. As a side effect of fermentation, alcohol content was related to Si content.     

The Vegetation Silica Pool in a Developing Tidal Freshwater Marsh

Tidal marshes play an important role in the estuarine Si cycle. Dissolved silicon (DSi) is taken up by marsh diatom communities and by tidal marsh vegetation. Delivery of DSi back to the estuary after biogenic silica dissolution potentially increases the resilience of the estuary against harmful effects of DSi depletion events. Tidal freshwater marsh vegetation, often dominated by reed (Phragmites australis) has previously been hypothesized to contribute to the Si buffering function of tidal marshes, by dissolution of reed biogenic Si (BSi) into the soil pore water and consequent seepage of DSi to the estuary. In this study the Si pool in the vegetation of a restored tidal freshwater marsh was quantified using species-based cover-biomass relationships and Si analyses. The Si pool in the aboveground biomass increased from 1.2 to 6.5 t km^?2 during the first 6 years of colonization by tidal freshwater marsh species. Our results indicate that young tidal freshwater marshes have a high potential to build up a large vegetation Si pool quickly, mostly due to colonization by species that have both high Si concentrations and high biomass production (e. g. P. australis). This Si pool in vegetation could act both as a long-term sink for Si along estuaries (should Si remain buried in the sediments) or as a short-term source for DSi (should Si be dissolved to DSi).