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.     

Be radioactive beam production at CIRCE and its utilization in basic and applied physics

A pure ⁷Be beam with an energy E = 1-8 MeV is available for nuclear and applied physics at the 3 MV Pelletron tandem accelerator CIRCE in Caserta. The beam is produced using an offline technique. Typical analyzed beam intensities are about 2 ppA, using cathodes with an activity of the order of 200 MBq. The ⁷Be implantation has been used for both fundamental nuclear physics and applied physics. In particular, different metals have been implanted with ⁷Be in order to study the influence of the chemical composition and of the number of quasi-free electrons of the host material on the ⁷Be half-life. In the field of applied physics, the ⁷Be implantation turns out to be very interesting for wear measurement. In fact, in this case ⁷Be is used as a depth-sensitive tracer. The continuous detection of the sample activity during the wear allows a high sensitivity measurement of wearing speed. The ⁷Be beam production at CIRCE, the implantation procedure and the results obtained from the ⁷Be half-life measurements and the wear characterization of implanted steel samples are described.     

Producing hollow granules from hydrophobic powders in high-shear mixer granulators

The formation of hollow granules from hydrophobic powders in a high-shear mixer granulator has been investigated by changing the binder/powder mass ratio and studying its effects on granule size and structure. In this study, a mixer granulator was filled with 100 g of hydrophobic fumed silica and then varying quantities of 5% Hydroxy Propyl Cellulose solution was slowly sprayed into granulator. A range of liquid to solid mass ratios between from 0.5:1 to 15:1 was used. Granules were then dried at 60 °C in a fan forced oven. This paper compares the particle size distributions, scanning electron microscopy (SEM) images and X-ray tomography (XRT) images of hollow granules as a function of the liquid to solid mass ratio. The granule mean size increased and the fraction of un-granulated (fine) particles decreased as the liquid to solid mass ratio increased. Simultaneously, the morphology and structure of the hollow granules changed from a spherical to a deformed structure which indicates the importance of choosing the optimal liquid to solid mass ratio. The optimal liquid to solid mass ratio for Aerosil R202 powder in this study was found to be between 3:1 and 6:1. The final granule shape and size distribution are dependent on the liquid to solid ratio if the liquid marble nucleation process starts with a preformed droplet template.     

Comparison of the Translational Potential of Human Mesenchymal Progenitor Cells from Different Bone Entities for Autologous 3D Bioprinted Bone Grafts

Reconstruction of segmental bone defects by autologous bone grafting is still the standard of care but presents challenges including anatomical availability and potential donor site morbidity. The process of 3D bioprinting, the application of 3D printing for direct fabrication of living tissue, opens new possibilities for highly personalized tissue implants, making it an appealing alternative to autologous bone grafts. One of the most crucial hurdles for the clinical application of 3D bioprinting is the choice of a suitable cell source, which should be minimally invasive, with high osteogenic potential, with fast, easy expansion. In this study, mesenchymal progenitor cells were isolated from clinically relevant human bone biopsy sites (explant cultures from alveolar bone, iliac crest and fibula; bone marrow aspirates; and periosteal bone shaving from the mastoid) and 3D bioprinted using projection-based stereolithography. Printed constructs were cultivated for 28 days and analyzed regarding their osteogenic potential by assessing viability, mineralization, and gene expression. While viability levels of all cell sources were comparable over the course of the cultivation, cells obtained by periosteal bone shaving showed higher mineralization of the print matrix, with gene expression data suggesting advanced osteogenic differentiation. These results indicate that periosteum-derived cells represent a highly promising cell source for translational bioprinting of bone tissue given their superior osteogenic potential as well as their minimally invasive obtainability.     

Implicit and Explicit Memory in Children With Congenital and Acquired Brain Disorder.

Implicit and explicit memory were examined in 8- to 15-year-old children with myelomeningocele and shunted hydrocephalus, severe traumatic brain injuries, or orthopedic injuries. Each group included between 22 and 29 children. Children completed a fragmented picture identification task to assess perceptual priming and a semantic decision-making task to assess conceptual priming. Each task also assessed procedural learning as well as explicit recall and recognition. All 3 groups showed significant perceptual and semantic priming of similar magnitude. In contrast, both brain-disordered groups displayed poorer explicit memory than did the comparison group. No group showed significant procedural learning on either task. Age and IQ were stronger predictors of explicit recall than of implicit memory. The findings indicate that implicit memory is relatively intact in many children with congenital and acquired brain disorders, despite deficits in explicit memory, and support the existence of separate memory systems in children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Silicon Mobilization in Soils: the Broader Impact of Land Use

Dissolved Si (DSi) provision from land systems triggers diatom growth and CO₂ sequestration. Soils and ecosystems act as a Si “filter”, transforming DSi originated from mineral weathering into biogenic Si (BSi) after DSi uptake by plants, or into other pedogenic forms of Si (non-BSi). Land use changes the quantity of BSi and non-BSi pools along the soil profile. However, methods used to isolate Si pools include chemical extractions at high temperatures and alkaline environments and therefore are unable to provide information concerning the dissolution potential of BSi and non-BSi pools under normal conditions of temperature and pH. Here, we conducted a batch experiment where forest, pasture and cropland soil samples were mixed with water at 25 °C and pH 7. The soil samples were collected from a temperate land use gradient located in the Belgian Loess Belt. We measured dissolved Si and aluminium (Al) during 80 days. BSi and non-BSi pool contents along the soil profile were known, as they had been established previously through chemical extraction. Results show that BSi and non-BSi enriched samples present distinct Si and Al dissolution curves. While non-BSi pools contribute significantly with immediate availability of Si, BSi pools present an initial slow dissolution. Therefore, croplands that were depleted of phytoliths and had poorly organic horizons display higher concentrations of initial dissolved Si, while pastures and forests, where pedogenic pools dominate only at depths below 40 cm, have more limited initial Si release.

     

Characterization of recombination centers in Si epilayers after He implantation by direct measurement of local lifetime distribution with the AC lifetime profiling technique

The distribution of recombination centers induced in Si epi-substrates by helium (He) implantation is obtained for the first time by direct measurement of local recombination lifetime profile along the layer, using the ac differential lifetime profiling technique. The different energy levels of the recombination centers induced by He implantation at different doses and energies have been extracted, as a function of the position in the layer, by temperature scanning of the lifetime profiles. The lifetime measurements clearly demonstrate the presence of a secondary defect distribution that extend from the region of maximum primary damage both at lower and higher depths respect to the stopping range depth, due to the relatively large concentration of primary defects created near the stopping range, and give a coherent picture of the effects of He implant on the "local" lifetime.     

X-ray Micro Computed Tomography investigation of accelerated thermal degradation of epoxy resin/glass microsphere syntactic foam

The heat resistance and the structural integrity of syntactic foam materials are vital for their high performance. Syntactic foam made of hollow glass microspheres and Diglycidyl Ether of Bisphenol A (DGEBA) based epoxy resin cured with Isophorone Diamine (IPD) hardener was subjected to oxidative thermal stress cycles. The degraded syntactic foam sample was examined using an X-ray Micro Computed Tomography (XμCT) to evaluate its internal damage between each state in a combined effect of cycling and increased temperature. Glass microsphere fracture, void enlargement and resin microcracks were observed as a result of the thermal stress using 3D XμCT images. The reconstructed slice representation showed the microcracks and microsphere damage distribution inside the sample. The damaged glass spheres percentage is shown to increase sharply with the progress of the thermal cycle. There was no change in the local density of the syntactic foam as a result of the thermal cycle. An XμCT system proves to be a successful non-destructive technique for examining syntactic foam for defects and structural damages in the micron scale.