Separation of Indium from Acid Sulfate-Containing Solutions by Ion Exchange with Impregnated Resins

Indium separation using ion exchange resins from acidic polymetallic and very diluted solutions are investigated. Since the selectivity of commercial ion exchange resins have proven to be too low for an effective separation from solutions with high content of other metals, Lewatit® TP 208 was impregnated with common extractants to enhance its properties. By resin impregnation with D2EHPA and Cyanex 272, not only the selective indium recovery was reached but also the resin capacity was increased approx. two times. The best loading and elution performance were shown by Cyanex 272-impregnated Lewatit® TP 208, increasing the indium purity in the eluate from 0.75 % to 85 %.     

Efficient Metal‐Free Aerobic Photooxidation of Sulfides to Sulfoxides Mediated by a Vitamin B2 Derivative and Visible Light

We have developed a metal‐free process for the aerobic photooxygenation of sulfides to sulfoxides mediated by riboflavin tetraacetate or riboflavin (vitamin B₂) photocatalysts and visible light (450 nm) in an acetonitrile‐water (85:15 v/v) mixture. The optimised solvent system leads to both singlet‐oxygen and electron‐transfer pathways in photooxygenation, thus allowing oxidation of electron‐poor and electron‐rich thioanisoles, dialkyl sulfides and sterically hindered sulfides. Besides having a broad substrate scope, the method has very short reaction times and requires low catalyst loading (down to 0.1 mol%). These properties are due to the high photocatalyst stability and the extremely high quantum yields (1.3 for thioanisole oxygenation). Moreover, the method is chemoselective, producing only sulfoxides without overoxidation to sulfones. Taking into account the broad substrate scope, high selectivity and high efficiency, this method distinguishes itself from those previously reported. Other advantages include easy work‐up of the reaction mixture, the availability and biodegradability of the photocatalysts and mild reaction conditions. We demonstrated, on a preparative scale, its practical application in the synthesis of the psychostimulant modafinil, in the selective oxidation of methionine derivatives, and in the detoxification of mustard gas.

     

Determination of compounding formulation of cured rubber by reverse engineering

The present work deals with reverse engineering on four rubber formulations. Information about the material composition of the compounding formulations was obtained by using techniques such as acetone extract, thermogravimetric analysis, energy dispersive X‐ray fluorescence studies, and Fourier transform infrared (FTIR) spectroscopy in attenuated total reflection mode. The reverse engineered formulations were compared on a qualitative and quantitative basis with the initial formulations. The aim was to ascertain the validity of the methodology, which may be used as reverse engineering of rubber compounds to quantitatively analyze unknown ground tire rubber in future. The state of the art was based on a fractional mass transfer from acetone extract to the rubbers detected in TGA. Through this new approach, the formulations calculated were very consistent with the formulations employed, thus establishing the validity of the methodology used. POLYM. ENG. SCI., 55:1450–1458, 2015. © 2015 Society of Plastics Engineers     

DPP-4 Cleaves α/β-Peptide Bonds: Substrate Specificity and Half-Lives

The incorporation of β-amino acids into a peptide sequence has gained particular attention as β- and α/β-peptides have shown remarkable proteolytic stability, even after a single homologation at the scissile bond. Several peptidases have been shown to cleave such bonds with high specificity but at a much slower rate compared to α-peptide bonds. In this study, a series of analogs of dipeptidyl peptidase-4 (DPP-4) substrate inhibitors were synthesized in order to investigate whether β-amino acid homologation at the scissile bond could be a valid approach to improving peptide stability towards DPP-4 degradation. DPP-4 cleaved the α/β-peptide bond after the N-terminal penultimate Pro with a broad specificity and retained full activity regardless of the β³-amino acid side chain and peptide length. Significantly improved half-lives were observed for β³Ile-containing peptides. Replacing the penultimate Pro with a conformationally constrained Pro mimetic led to proteolytic resistance. DPP-4 cleavage of α/β-peptide bonds with a broad promiscuity represents a new insight into the stability of peptide analogs containing β-amino acids as such analogs were thought to be stable towards enzymatic degradation.     

The details matter: methodological nuances in the evaluation of student models

The core of student modeling research is about capturing the complex learning processes into an abstract mathematical model. The student modeling research, however, also involves important methodological aspects. Some of these aspects may seem like technical details not worth significant attention. However, the details matter. We discuss three important methodological issues in student modeling: the impact of data collection, the splitting of data into a training set and a test set, and the details concerning averaging in the computation of predictive accuracy metrics. We explicitly identify decisions involved in these steps, illustrate how these decisions can influence results of experiments, and discuss consequences for future research in student modeling.     

Comparison of Isolated Indentation and Grid Indentation Methods for HVOF Sprayed Cermets

This paper compares the results of two approaches of instrumented indentation for characterization of mechanical properties of HVOF coatings. Three types of HVOF sprayed coatings (Cr₃C₂-NiCr, WC-Co, (Ti, Mo)(C,N)-NiCo) were investigated by the means of isolated nanoindentation and grid indentation methods. The results of the isolated indentation revealed hardness and elastic modulus of the individual phases in very good agreement with the corresponding bulk material. The grid indentation method, based on statistical evaluation of a large number of indentations, was influenced by the carbide-matrix interface, which gave rise to a third peak apart from the two peaks corresponding to the carbides and metallic matrix. As a consequence, the bimodal Gaussian fit was insufficient and a trimodal fit had to be used. The results extracted from low load grid nanoindentations were quite close to the results of isolated indentations whereas higher load grid nanoindentation revealed overall properties of the coating.     

The two-regime method for optimizing stochastic reaction–diffusion simulations

Spatial organization and noise play an important role in molecular systems biology. In recent years, a number of software packages have been developed for stochastic spatio-temporal simulation, ranging from detailed molecular-based approaches to less detailed compartment-based simulations. Compartment-based approaches yield quick and accurate mesoscopic results, but lack the level of detail that is characteristic of the computationally intensive molecular-based models. Often microscopic detail is only required in a small region (e.g. close to the cell membrane). Currently, the best way to achieve microscopic detail is to use a resource-intensive simulation over the whole domain. We develop the two-regime method (TRM) in which a molecular-based algorithm is used where desired and a compartment-based approach is used elsewhere. We present easy-to-implement coupling conditions which ensure that the TRM results have the same accuracy as a detailed molecular-based model in the whole simulation domain. Therefore, the TRM combines strengths of previously developed stochastic reaction–diffusion software to efficiently explore the behaviour of biological models. Illustrative examples and the mathematical justification of the TRM are also presented.     

Long-term lining performance - Civil engineering problem of potential retrieval of buried spent nuclear fuel

The current solution for the spent fuel, high-level and long-lived radioactive waste is to store them at surface facilities from which they will be subsequently moved to a deep repository. No such repositories are in operation currently but several such facilities are close to the construction phase. A deep repository can be situated in several types of geological conditions including clay formations, salt sediments, argillites and tuffitic and granitic rocks. The character of the host rock is the key factor determining the design and specific requirements of individual components of such a facility. The future potential retrieval of canisters containing nuclear waste from the repository is a further influential factor. The reason for retrieval of containers lies in the development of fast reactors and increased interest for spent fuel reprocessing. Naturally, the decision as to whether retrievability is technically feasible must be made before finalising the design and construction process of the repository. If the decision is made to retrieve, a design which will include all the relevant safety aspects for the potential retrieval of canisters must be determined. The lay-out of the repository, the materials to be used and the design of the various structures of the facility (e.g. access tunnels, disposal shafts, buffer and backfill) are not the only issues to be addressed. The long-term stability of the system as a whole, i.e. of all the components, is crucial. Depending on the disposal concept chosen, the thermal load generated by the waste in the disposal container, saturation by water from the surrounding environment and the loading of the host rock massif will constitute the main processes which will affect the behaviour, safety and future functioning of the repository from the civil engineering point of view. The long-term stability of the lining of disposal galleries is a basic precondition for the safe removal of spent nuclear waste from deep underground repositories. The stability problems of tunnel linings exposed to long-term thermal load have not yet been properly addressed and form the subject of the European TIMODAZ project (Thermal Impact on the Damaged Zone around a Radioactive Waste Disposal in Clay Host Rocks) and also supported by the “Complex System of Methods for Directed Design and Assessment of Functional Properties of Building Materials” project. This paper describes the design, construction and currently available results of a 1:1 scale “in situ” disposal tunnel model which has been built at the Josef Underground Educational Facility in the Czech Republic.