Popular branchings and their dual certificates

Mathematical Programming - Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed...     

Nonlinear frequency response analysis: a recent review and perspectives

The nonlinear frequency response analysis (NFRA) can be seen as an extension of electrochemical impedance spectroscopy. NFRA gives a full and detailed representation of the system response and can establish a connection between model parameters and the experimentally observed phenomena. In this article, different theoretical NFRA approaches and the most recent application examples are discussed. A simple electrochemical example is used to showcase the benefits and disadvantages of analyzing the system response by using different approaches. In addition, it was shown how to extract experimental harmonic values and analyze them.     

Structural,Magnetic and Catalytic Properties of a New Vacancy Ordered Perovskite Type Barium Cobaltate BaCoO2.67

A new vacancy ordered, anion deficient perovskite modification with composition of BaCoO_2.67 (Ba₃Co₃O₈□₁) has been prepared via a two-step heating process. Combined Rietveld analysis of neutron and X-ray powder diffraction data shows a novel ordering of oxygen vacancies not known before for barium cobaltates. A combination of neutron powder diffraction, magnetic measurements, and density functional theory (DFT) studies confirms G-type antiferromagnetic ordering. From impedance measurements, the electronic conductivity of the order of 10⁻⁴ S cm⁻¹ is determined. Remarkably, the bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is found to be comparable to that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–y, confirming that charge-ordered anion deficient non-cubic perovskites can be highly efficient catalysts.     

Insight into Signal Response of Protein Ions in Native ESI-MS from the Analysis of Model Mixtures of Covalently Linked Protein Oligomers

Native ESI-MS is increasingly used for quantitative analysis of biomolecular interactions. In such analyses, peak intensity ratios measured in mass spectra are treated as abundance ratios of the respective molecules in solution. While signal intensities of similar-size analytes, such as a protein and its complex with a small molecule, can be directly compared, significant distortions of the peak ratio due to unequal signal response of analytes impede the application of this approach for large oligomeric biomolecular complexes. We use a model system based on concatenated maltose binding protein units (MBPn, n = 1, 2, 3) to systematically study the behavior of protein mixtures in ESI-MS. The MBP concatamers differ from each other only by their mass while the chemical composition and other properties remain identical. We used native ESI-MS to analyze model mixtures of MBP oligomers, including equimolar mixtures of two proteins, as well as binary mixtures containing different fractions of the individual components. Pronounced deviation from a linear dependence of the signal intensity with concentration was observed for all binary mixtures investigated. While equimolar mixtures showed linear signal dependence at low concentrations, distinct ion suppression was observed above 20 μM. We systematically studied factors that are most often used in the literature to explain the origin of suppression effects. Implications of this effect for quantifying protein–protein binding affinity by native ESI-MS are discussed in general and demonstrated for an example of an anti-MBP antibody with its ligand, MBP.

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Development of a Simple,Rapid, and Robust Isocratic Liquid Chromatographic Method for the Determination of Pyrimethamine and its Synthetic Impurities in Bulk Drugs and Pharmaceutical Formulations

Pyrimethamine is an important antiparasitic drug in the treatment of malaria and toxoplasmosis and is often used in combination with either sulfadoxine, sulfalene, or sulfadiazine. Determining the content of pyrimethamine and investigating the related substances is currently possible applying either a compendial monograph utilizing thin layer chromatography as well as liquid chromatographic methods used by the respective manufacturers. To provide a simple method which is capable of determining the content of pyrimethamine and of resolving four of its potential synthetic impurities a very simple, cheap, precise, and accurate isocratic RP-HPLC method was developed. All analytes can be separated within a total runtime of 30 min and the method was linear within the concentration ranges of 0.12–0.740, 0.104–0.621, 0.120–0.710, 2.0–11.8, and 1.01–5.80 µg mL^?1 for pyrimethamine, impurity A, impurity B, impurity C, and impurity D, respectively. These substances were separated by employing a Eurospher-II C₁₈H column (250 × 4.6 mm, 5 µm particle size), a mobile phase being a mixture of a 0.05 M KH₂PO₄ buffer solution (pH 2.6) and methanol in the ratio 40:60 (v/v). The analysis was carried out at 30 °C, applying a flow rate of 1.2 mL min^?1, and a detection wavelength of λ = 215 nm. The coefficients of determinations (R ²) for the five analytes were greater than 0.994 for pyrimethamine and all impurities. Results of recovery studies were within the range of 89.1–105.1% for all substances. In all tested genuine batches of pyrimethamine raw material impurities within the specified limits were present which is concurrent with results obtained from using the present manufacturer’s method.     

Fibril Structure Demonstrates the Role of Iodine Labelling on a Pentapeptide Self-Assembly

Iodination has long been employed as a successful labelling strategy to gain structural insights into proteins and other biomolecules via several techniques, including Small Angle X-ray Scattering, Inductively Coupled Plasma Mass Spectrometer (ICP-MS), and single-crystal crystallography. However, when dealing with smaller biomolecular systems, interactions driven by iodine may significantly alter their self-assembly behaviour. The engineering of amyloidogenic peptides for the development of ordered nanomaterials has greatly benefitted from this possibility. Still, to date, iodination has exclusively been applied to aromatic residues. In this work, an aliphatic bis-iodinated amino acid was synthesized and included into a custom pentapeptide, which showed enhanced fibrillogenic behaviour. Peptide single crystal X-ray structure and powder X-ray diffraction on its dried water solution demonstrated the key role of iodine atoms in promoting intermolecular interactions that drive the peptide self-assembly into amyloid fibrils. These findings enlarge the library of halogenated moieties available for directing and engineering the self-assembly of amyloidogenic peptides.     

Characteristics of in-out intermittency in delay-coupled FitzHugh–Nagumo oscillators

We analyze a pair of delay-coupled FitzHugh–Nagumo oscillators exhibiting in-out intermittency as a part of the generating mechanism of extreme events. We study in detail the characteristics of in-out intermittency and identify the invariant subsets involved – a saddle fixed point and a saddle periodic orbit – neither of which are chaotic as in the previously reported cases of in-out intermittency. Based on the analysis of a periodic attractor possessing in-out dynamics, we can characterize the approach to the invariant synchronization manifold and the spiralling out to the saddle periodic orbit with subsequent ejection from the manifold. Due to the striking similarities, this analysis of in-out dynamics also explains in-out intermittency