Gemstone | EPFL Graph Search

A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, and obsidian) and occasionally organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity and notoriety are other characteristics that lend value to gemstones. Found all over the world, the industry of coloured gemstones (this meaning anything other than diamonds) is currently estimated to be around 10–12 billion US dollars. Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem expert is a gemologist, a gem

A microchip emitter for solid phase extraction – gradient elution – mass spectrometry

Natalia Gasilova, Hubert Girault, Dmitry Momotenko, Mohammad Reza Pourhaghighi, Liang Qiao

A microchip electrospray emitter with a magnetic bead trap has been designed for solid phase extraction-gradient elution-mass spectrometry (SPE-GEMS). The goal of this method is the detection of analytes at low concentrations and it is here demonstrated using reverse phase coated magnetic beads (Mbs) for the preconcentration and detection of the peptides. The sample is passed through the chip, and the peptides are retained and enriched in the trap. After washing, the peptides are released sequentially by stepwise gradient elution and electrosprayed for mass spectrometry analysis. This approach allows effective sample desalting, enrichment, sequential elution and MS detection without the introduction of an additional separation step after SPE. Efficient preconcentration of model peptides by SPE and sequential release and analysis of peptides by GEMS were demonstrated for diluted sample solutions within the range of 1 µM to 10 nM. Fortified human blood serum, protein digest and fractions collected after protein digest OFFGEL separation were analysed by SPE-GEMS allowing the detection of low abundance peptides usually not observed by direct mass spectrometry analysis. A mathematical model for gradient elution is proposed.

American Chemical Society2013

Effect of stone coverage on soil erosion

David Andrew Barry, Alessandro Brovelli, Seifeddine Jomaa

Soil surface coverage has a significant impact on water infiltration, runoff and soil erosion yields. In particular, surface stones protect the soils from raindrop detachment, they retard the overland flow therefore decreasing its sediment transport capacity, and they prevent surface sealing. Several physical and environmental factors control to what extent stones on the soil surface modify the erosion rates and the related hydrological response. Among the most important factors are the moisture content of the topsoil, stone size, emplacement, coverage density and soil texture. Owing to the different inter-related processes, there is ambiguity concerning the quantitative effect of stones, and process-based understanding is limited. Experiments were performed (i) to quantify how stone features affect sediment yields, (ii) to understand the local effect of isolated surface stones, that is, the changes of the soil particle size distribution in the vicinity of a stone and (iii) to determine how stones attenuate the development of surface sealing and in turn how this affects the local infiltration rate. A series of experiments using the EPFL 6-m × 2-m erosion flume were conducted at different rainfall intensities (28 and 74 mm h-1) and stone coverage (20 and 40%). The total sediment concentration, the concentration of the individual size classes and the flow discharge were measured. In order to analyze the measurements, the Hairsine and Rose (HR) erosion model was adapted to account for the shielding effect of the stone cover. This was done by suitably adjusting the parameters based on the area not covered by stones. It was found that the modified HR model predictions agreed well with the measured sediment concentrations especially for the long time behavior. Changes in the bulk density of the topsoil due to raindrop-induced compaction with and without stone protection revealed that the stones protect the upper soil surface against the structural seals resulting in negligible changes in the bulk density during the erosion event. Since the main process contributing to surface sealing development is the compaction due to the raindrop kinetic energy and associated physico-chemical changes, the protection provided by the stone cover is consistent with the area-averaging approach used in applying the HR model.

2010

Fusing Individual-based Models with Genome-scale Metabolic Networks - a Novel Approach for Quantifying Emergent Microbial Community Spatiotemporal Dynamics

Meriç Ataman, Vassily Hatzimanikatis, Dani Or

Metabolic capabilities of organisms govern their growth characteristics and their capability to adapt to changing environmental conditions. In natural systems, substrates can change dynamically and spatially with multiple species competing for resources. Genome-scale metabolic network models (GEMs) offer quantitative frameworks for consideration of the metabolism of organisms in the concourse. Community modeling has been used in studies to analyze multi-species consortia, however the high dimensionality of GEMs limits their use in complex systems especially for applications in spatially-explicit individual-based models (IBM). The use of IBM permits exploration of species interaction with their environment and neighbors within a prescribed physical domain. This study proposes to capitalize on recently developed algorithms, redGEM and lumpGEM for the unbiased and systematic reduction of GEMs into reduced metabolic models (rGEMs) that retain compatibility with their parent GEMs. The reduced computational burden of rGEMs makes them scalable and makes their incorporation in IBM frameworks feasible. We formulated a hybrid model fusing an individual-based model (IBM) with advanced thermodynamics-based flux analysis (TFA) and reanalyzed a 3-member consortium comprised of E. coli, S. enterica and M. extorquens. While the IBM provides detailed description of the physical environment, dispersion and motility characteristics of organisms, the rGEMs and TFA provide a reduced description of the stoichiometric properties and bioenergetics constraints imposed on organisms, including intracellular and extracellular concentrations of all defined metabolites at the local scale experienced by an individual. We report the first application of such a hybrid approach that systematically merges stoichiometric models and individual-based models for study of interacting multispecies communities in simple physical spaces (surfaces). The expansion to consideration of microbial communities in complex environments will be discussed.