Insight into the extractability of metals from soils using an implementation of the linear adsorption isotherm model

This paper deals with an often overlooked artifact in sequential and single extraction of metals from soils, viz. the volume to mass (V/m) ratio as a potential source for inadequate extraction yields. We offer a theoretical framework to get a grip on this intricate parameter and came up with a model based on a linear adsorption isotherm to derive the correct maximal metal extractability for a certain extractant. We verified the model experimentally using 0.1 mol l⁻¹ nitric acid for extraction of seven metals (Cr, Co, Cu, Cd, Pb, Ni and Zn) from an urban soil sample, and concluded that commonly used V/m ratios in the range of 10-40 ml g⁻¹ may give as much as 50% too low extraction yields. Thus, a strong caveat is in place as to be very critical what V/m ratios to use and preferably apply the model derived to obtain the correct maximal extractability using a variable V/m ratio method.     

A bump triangular dynamic factorization algorithm for the simplex method

A dynamic factorization algorithm is developed which algebraically partitions the basis inverse in such a manner so that the simplex method can be executed from a series of small inverses and the basis itself. This partition is maintained dynamically so that the additional memory required to represent the basis inverse reduces to this series of small inverses for in-core implementations.The algorithm is intended for use in solving general large-scale linear programming problems. This new method of basis representation should permit rather large problems to be solved completely in-core.Preliminary computational experience is presented and comparisons are made with Reid's sparsity-exploiting variant of the Bartels—Golub decomposition for linear programming bases. The computational experience indicated that a significant reduction in memory requirements can usually be obtained using the dynamic factorization approach with only a slight (up to about 20%) degradation of execution time.This research was supported in part by the Air Force Office of Scientific Research, Air Force System Command, USAF, under AFOSR Contract/Grant Number AFOSR-74-2715.     

Radioactive waste partitioning and transmutation within advanced fuel cycles: Achievements and challenges

If nuclear power becomes a sustainable source of energy, a safe, robust, and acceptable solution must be pursued for existing and projected inventories of high-activity, long-lived radioactive waste. Remarkable progress in the field of geological disposal has been made in the last two decades. Some countries have reached important milestones, and geological disposal (of spent fuel) is expected to start in 2020 in Finland and in 2022 in Sweden. In fact, the licensing of the geological repositories in both countries is now entering into its final phase. In France, disposal of intermediate-level waste (ILW) and vitrified high-level waste (HLW) is expected to start around 2025, according to the roadmap defined by an Act of Parliament in 2006. In this context, transmutation of part of the waste through use of advanced fuel cycles, probably feasible in the coming decades, can reduce the burden on the geological repository. This article presents the physical principle of transmutation and reviews several strategies of partitioning and transmutation (P&T). Many recent studies have demonstrated that the impact of P&T on geological disposal concepts is not overwhelmingly high. However, by reducing waste heat production, a more efficient utilization of repository space is likely. Moreover, even if radionuclide release from the waste to the environment and related calculated doses to the population are only partially reduced by P&T, it is important to point out that a clear reduction of the actinide inventory in the HLW definitely reduces risks arising from less probable evolutions of a repository (i.e., an increase of actinide mobility in certain geochemical situations and radiological impact by human intrusion).     

On star and caterpillar arboricity

We give new bounds on the star arboricity and the caterpillar arboricity of planar graphs with given girth. One of them answers an open problem of Gyárfás and West: there exist planar graphs with track number 4. We also provide new NP-complete problems.     

A look at surfactant partitioning in polymeric latexes using conductivity measurements

An attempt was made to analyse the partitioning of anionic surfactants in a mixed surfactant system using surface tension and conductivity measures. This last technique gives us access to the quantity of free ions in solution, and thus a measure of the amount of anionic surfactant available in the aqueous phase. The range of surfactant concentrations studied here is such that the global surface coverage (assuming that the totality of the emulsifier is at the particle surface) varies around 100%.     

The influence of 1-butyl-3-methyl-imidazolium bromide on the partitioning of l-tyrosine within the {polyethylene glycol 600 + potassium citrate} aqueous biphasic system at T = 298.15 K

Partitioning in aqueous biphasic systems (ABS) is widely recognized today as a rapid, gentle, and highly efficient technique for the separation of soluble as well as particulate biomaterials. This technique has gained increasing attention as the separation method of choice in biotechnology. In recent years, a new approach has been proposed based on the use of ionic liquids (ILs) as adjuvants for the separation and purification of bio-molecules using polymer-based ABS. In this regard, the influence of IL 1-butyl-3-methylimidazolium bromide ([C₄mim]Br) on the phase behavior and extraction capability of {PEG 600 + tri-potassium citrate (K₃C₆H₅O₇)} ABS for l-tyrosine (Tyr) is investigated here. For this purpose, phase diagrams and the liquid–liquid equilibrium (LLE) data for the {PEG 600 + K₃C₆H₅O₇} ABS with the addition of small quantities of IL were determined at T = 298.15 K. It was found that, for the studied polymer-based ABS, the addition of 5 wt% of [C₄mim]Br to ABS caused the expansion of two-phase area in the salt-rich region; while, for the PEG-rich region no change was observed. The partition coefficients of l-tyrosine (K_Tyr) within the studied system were determined at T = 298.15 K. The results obtained indicate that the addition of small quantities of [C₄mim]Br to the {PEG 600 + K₃C₆H₅O₇} ABS could enhance the extraction efficiency for l-tyrosine. In addition, the experimental data are correlated using the NRTL model. The comparisons between the correlation and the experimental data reveal a good agreement.     

The maximum saving partition problem

The input to the MAXIMUM SAVING PARTITION PROBLEM consists of a set V={1,…,n}, weights w_i, a function f, and a family S of feasible subsets of V. The output is a partition (S₁,…,S_l) such that S_i∈S, and is maximized. We present a general -approximation algorithm, and improved algorithms for special cases of the function f.     

Clustering of financial time series

This paper addresses the topic of classifying financial time series in a fuzzy framework proposing two fuzzy clustering models both based on GARCH models. In general clustering of financial time series, due to their peculiar features, needs the definition of suitable distance measures. At this aim, the first fuzzy clustering model exploits the autoregressive representation of GARCH models and employs, in the framework of a partitioning around medoids algorithm, the classical autoregressive metric. The second fuzzy clustering model, also based on partitioning around medoids algorithm, uses the Caiado distance, a Mahalanobis-like distance, based on estimated GARCH parameters and covariances that takes into account the information about the volatility structure of time series. In order to illustrate the merits of the proposed fuzzy approaches an application to the problem of classifying 29 time series of Euro exchange rates against international currencies is presented and discussed, also comparing the fuzzy models with their crisp version.