Adaptive discretization of convex multistage stochastic programs

We propose a new scenario tree reduction algorithm for multistage stochastic programs, which integrates the reduction of a scenario tree into the solution process of the stochastic program. This allows to construct a scenario tree that is highly adapted on the optimization problem. The algorithm starts with a rough approximation of the original tree and locally refines this approximation as long as necessary. Promising numerical results for scenario tree reductions in the settings of portfolio management and power management with uncertain load are presented.     

Aggregation/Disaggregation Iterative Methods Applied to Leontev Systems and Markov Chains

The paper surveys some recent results on iterative aggregation/disaggregation methods (IAD) for computing stationary probability vectors of stochastic matrices and solutions of Leontev linear systems. A particular attention is paid to fast IAD methods.     

Basicity Limits of Neutral Organic Superbases

The potential limits of superbasicity achievable with different families of neutral bases by expanding the molecular framework are explored using DFT computations. A number of different core structures of non‐ionic organosuperbases are considered (such as phosphazenes, guanidinophosphazenes, guanidino phosphorus ylides). A simple model for describing the dependence of basicity on the extent of the molecular framework is proposed, validated, and used for quantitatively predicting the ultimate basicities of different compound families and the rates of substituent effect saturation. Some of the considered bases (guanidino phosphorus carbenes) are expected to reach gas‐phase basicity around 370 kcal mol^?1, thus being the most basic neutral bases ever reported. Also, the classical substituted alkylphosphazenes were predicted to reach pK_a values of around 50 in acetonitrile, which is significantly higher than previously expected.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Application of enriched stable 196Hg isotope for monitoring the stability of total mercury in water samples

A novel tool for the investigation of stability of total mercury in water samples is presented. The study focuses on the application of enriched ¹⁹⁶Hg stable isotopic reagent for the stability studies. Natural abundance of ¹⁹⁶Hg in water samples is only 0.15%. Thus, the use of the ¹⁹⁶Hg isotope spike represents a major advantage, when it can be assumed that all the measured isotope is the same as is accurately added by the analyst, and the change in its mass concentration can be followed simply and reliably. Tests were carried out with industrial waste water and two type of the natural water. Cold vapour (CV) inductively coupled plasma mass spectrometer (ICP-MS) technique was applied for the mercury measurements. Monitoring was continued for approximately 100 days. It is commonly advised that the measurement for total mercury in water samples should be carried out within 14 days. In this study the samples were observed to be stable for more than three months, if they were stored at a temperature of 4–6°C. The results of this stability study were in line with the guidance presented in EPA standard 1631. However, the samples were noticed to be stable for a much longer time than is presented in the standard method ISO 17852.     

Preparation of Bragg mirrors on silica optical fibers and inner walls of silica capillaries by employing the sol–gel method,and titanium and silicon alkoxides

Journal of Sol-Gel Science and Technology - The paper presents results on sol–gel preparation and characterization of multilayered coatings, Bragg mirrors, on silica slides, silica fibers,...     

Multi-objective Geometry Optimization of a Gas Cyclone Using Triple-Fidelity Co-Kriging Surrogate Models

Cyclone separators are widely used in a variety of industrial applications. A low-mass loading gas cyclone is characterized by two performance parameters, namely the Euler and Stokes numbers. These parameters are highly sensitive to the geometrical design parameters defining the cyclone. Optimizing the cyclone geometry therefore is a complex problem. Testing a large number of cyclone geometries is impractical due to time constraints. Experimental data and even computational fluid dynamics simulations are time-consuming to perform, with a single simulation or experiment taking several weeks. Simpler analytical models are therefore often used to expedite the design process. However, this comes at the cost of model accuracy. Existing techniques used for cyclone shape optimization in literature do not take multiple fidelities into account. This work combines cheap-to-evaluate well-known mathematical models of cyclones, available data from computational fluid dynamics simulations and experimental data to build a triple-fidelity recursive co-Kriging model. This model can be used as a surrogate with a multi-objective optimization algorithm to identify a Pareto set of a finite number of solutions. The proposed scheme is applied to optimize the cyclone geometry, parametrized by seven design variables.     

Multifrequency electron paramagnetic resonance characterization of PpoA, a CYP450 fusion protein that catalyzes fatty acid dioxygenation

PpoA is a fungal dioxygenase that produces hydroxylated fatty acids involved in the regulation of the life cycle and secondary metabolism of Aspergillus nidulans . It was recently proposed that this novel enzyme employs two different heme domains to catalyze two separate reactions: within a heme peroxidase domain, linoleic acid is oxidized to (8R)-hydroperoxyoctadecadienoic acid [(8R)-HPODE]; in the second reaction step (8R)-HPODE is isomerized within a P450 heme thiolate domain to 5,8-dihydroxyoctadecadienoic acid. In the present study, pulsed EPR methods were applied to find spectroscopic evidence for the reaction mechanism, thought to involve paramagnetic intermediates. We observe EPR resonances of two distinct heme centers with g-values typical for Fe(III) S = (5)/(2) high-spin (HS) and Fe(III) S = (1)/(2) low-spin (LS) hemes. (14)N ENDOR spectroscopy on the S = (5)/(2) signal reveals resonances consistent with an axial histidine ligation. Reaction of PpoA with the substrate leads to the formation of an amino acid radical on the early millisecond time scale concomitant to a substantial reduction of the S = (5)/(2) heme signal. High-frequency EPR (95- and 180-GHz) unambiguously identifies the new radical as a tyrosyl, based on g-values and hyperfine couplings from spectral simulations. The radical displays enhanced T(1)-spin-lattice relaxation due to the proximity of the heme centers. Further, EPR distance measurements revealed that the radical is distributed among the monomeric subunits of the tetrameric enzyme at a distance of approximately 5 nm. The identification of three active paramagnetic centers involved in the reaction of PpoA supports the previously proposed reaction mechanism based on radical chemistry.     

Analysis of selenomethylselenocysteine and selenomethionine by LC-ESI-MS/MS with diethyl ethoxymethylenemalonate derivatization

A simple method to identify and determine Selenomethionine (SeMet) and Selenomethylselenocysteine (Se-MeSeCys) with diethyl ethoxymethylenemalonate (DEEMM) derivatization and LC-ESI-MS/MS determination was developed. Separation of SeMet and Se-MeSeCys was achieved in 15.3 minutes. The calibration graph was linear in the range of 0.32 pmol to 49 pmol for SeMet and 0.34 pmol to 40 pmol for Se-MeSeCys. To prevent oxidation of SeMet, 2-mercaptoethanol was introduced to the calibration solutions. Detection limits were 0.1 pmol, which are comparable to LC-ICP-MS analysis. The developed method therefore offers an alternative to LC-ICP-MS offering similar sensitivity and additionally allows identification. The method was used to determine Se-MeSeCys and SeMet in onion samples.