Edge ranking and searching in partial orders

We consider a problem of searching an element in a partially ordered set (poset). The goal is to find a search strategy which minimizes the number of comparisons. Ben-Asher, Farchi and Newman considered a special case where the partial order has the maximum element and the Hasse diagram is a tree (tree-like posets) and they gave an O(n⁴log³n)-time algorithm for finding an optimal search strategy for such a partial order. We show that this problem is equivalent to finding edge ranking of a simple tree corresponding to the Hasse diagram, which implies the existence of a linear-time algorithm for this problem.Then we study a more general problem, namely searching in any partial order with maximum element. We prove that such a generalization is hard, and we give an -approximate polynomial-time algorithm for this problem.     

Martingale and stationary solutions for stochastic Navier-Stokes equations

Summary We prove the existence of martingale solutions and of stationary solutions of stochastic Navier-Stokes equations under very general hypotheses on the diffusion term. The stationary martingale solutions yield the existence of invariant measures, when the transition semigroup is well defined. The results are obtained by a new method of compactness.     

Concentration Dependence of Anti- and Pro-Oxidant Activity of Polyphenols as Evaluated with a Light-Emitting Fe2+-Egta-H2O2 System

Hydroxyl radical (^•OH) scavenging and the regeneration of Fe²⁺ may inhibit or enhance peroxidative damage induced by a Fenton system, respectively. Plant polyphenols reveal the afore-mentioned activities, and their cumulative net effect may determine anti- or pro-oxidant actions. We investigated the influence of 17 phenolics on ultra-weak photon emission (UPE) from a modified Fenton system (92.6 µmol/L Fe²⁺, 185.2 µmol/L EGTA (ethylene glycol-bis(β-aminoethyl-ether)-N,N,N′,N,-tetraacetic acid) and 2.6 mmol/L H₂O₂ pH = 7.4). A total of 8 compounds inhibited (antioxidant effect), and 5 enhanced (pro-oxidant effect) UPE at all studied concentrations (5 to 50 µmol/L). A total of 4 compounds altered their activity from pro- to antioxidant (or vice versa) along with increasing concentrations. A total of 3 the most active of those (ferulic acid, chlorogenic acid and cyanidin 3-O-glucoside; mean UPE enhancement by 63%, 5% and 445% at 5 µmol/L; mean UPE inhibition by 28%, 94% and 24% at 50 µmol/L, respectively) contained catechol or methoxyphenol structures that are associated with effective ^•OH scavenging and Fe²⁺ regeneration. Most likely, these structures can determine the bidirectional, concentration-dependent activity of some phenolics under stable in vitro conditions. This is because the concentrations of the studied compounds are close to those occurring in human fluids, and this phenomenon should be considered in the case of dietary supplementation with isolated phenolics.     

Synthesis and characterization of variable-architecture thermosensitive polymers for complexation with DNA

Copolymers of N-isopropylacrylamide with a fluorescent probe monomer were grafted to branched poly(ethyleneimine) to generate polycations that exhibited lower critical solution temperature (LCST) behavior. The structures of these polymers were confirmed by spectroscopy, and their phase transitions before and after complexation with DNA were followed using ultraviolet and fluorescence spectroscopy and light scattering. Interactions with DNA were investigated by ethidium bromide displacement assays, while temperature-induced changes in structure of both polymers and polymer-DNA complexes were evaluated by fluorescence spectroscopy, dynamic light scattering, laser Doppler anemometry, and atomic force microscopy (AFM) in water and buffer solutions. The results showed that changes in polymer architecture were mirrored by variations in the architectures of the complexes and that the overall effect of the temperature-mediated changes was dependent on the graft polymer architecture and content, as well as the solvent medium, concentrations, and stoichiometries of the complexes. Furthermore, AFM indicated subtle changes in polymer-DNA complexes at the microstructural level that could not be detected by light scattering techniques. Uniquely, variable-temperature aqueous-phase AFM was able to show that changes in the structures of these complexes were not uniform across a population of polymer-DNA condensates, with isolated complexes compacting above LCST even though the sample as a whole showed a tendency for aggregation of complexes above LCST over time. These results indicate that sample heterogeneities can be accentuated in responsive polymer--DNA complexes through LCST-mediated changes--a factor that is likely to be important in cellular uptake and nucleic acid transport.     

SO(2) Symmetry of a Maxwell p-Form Theory

We find a universal SO(2) symmetry of a p-form Maxwell theory for both odd and even p. For odd p, it corresponds to the duality rotations but for even p, it defines a new set of transformations which is not related to duality rotations. In both cases, a symmetry group defines a subgroup of the O(2,1) group of R-linear canonical transformations which has also a natural representation on the level of quantization condition for p-brane dyons.     

Two Ecdysteroids Isolated from Micropropagated Lychnis flos-cuculi and the Biological Activity of Plant Material

Genetically uniform plant material, derived from Lychnis flos-cuculi propagated in vitro, was used for the isolation of 20-hydroxyecdysone and polypodine B and subjected to an evaluation of the antifungal and antiamoebic activity. The activity of 80% aqueous methanolic extracts, their fractions, and isolated ecdysteroids were studied against pathogenic Acanthamoeba castellani. Additionally, a Microtox^® acute toxicity assay was performed. It was found that an 80% methanolic fraction of root extract exerts the most potent amoebicidal activity at IC₅₀ of 0.06 mg/mL at the 3rd day of treatment. Both ecdysteroids show comparable activity at IC₅₀ of 0.07 mg/mL. The acute toxicity of 80% fractions at similar concentrations is significantly higher than that of 40% fractions. Crude extracts exhibited moderate antifungal activity, with a minimum inhibitory concentration (MIC) within the range of 1.25–2.5 mg/mL. To the best of our knowledge, the present report is the first to show the biological activity of L. flos-cuculi in terms of the antifungal and antiamoebic activities and acute toxicity. It is also the first isolation of the main ecdysteroids from L. flos-cuculi micropropagated, ecdysteroid-rich plant material.     

A Convenient Synthesis of ω-[(Arylphosphonomethyl)Amino] Alkylphosphonic and Carboxylic Acids via in Situ–Generated Arylideneaminoalkyl- Phosphonic or Carboxylic Acids

ω-[(Arylphosphonomethyl)amino]alkylphosphonic and carboxylic acids are prepared in an easy work-up procedure, by addition of diethyl phosphite to in situ–generated arylideneaminoalkylphosphonic or carboxylic acids followed by hydrolysis with hydrochloric acid     

Theoretical Treatment of a Cathodic Stripping Mechanism of an Insoluble Salt Coupled with a Chemical Reaction in Conditions of Square Wave Voltammetry. Application to 6‐Mercaptopurine‐9‐D‐Riboside in the Presence of Ni(II)

Cathodic stripping mechanism of an insoluble salt coupled with a homogenous chemical reaction is considered both theoretically and experimentally under conditions of square‐wave voltammetry. For the mercury electrode in aqueous solution, the electrode reaction is described as L(aq)+Hg(l)=HgL(s)+2e^?, where L(aq) is the reactive ligand that forms a sparingly soluble compound HgL(s). The electrode reaction is coupled with a homogenous, first‐order chemical reaction, A(aq)=L(aq). Theoretical predictions are confirmed by experiments with 6‐mercaptopurine‐9‐D‐riboside in the presence of nickel(II) ions.     

Multiresidue determination of 160 pesticides in wines employing mixed-mode dispersive-solid phase extraction and gas chromatography-tandem mass spectrometry

A new multiresidue method for the efficient screening, identification and quantification of over 160 pesticides belonging to different chemical classes in red, rose and white wines have been developed. The analysis was based on gas chromatographic-tandem quadrupole mass spectrometric determination (GC-QqQ-MS/MS). An optimization strategy involved the selection of buffering conditions and sorbents for dispersive-solid phase extraction (dispersive-SPE) in order to achieve acceptably high recoveries and reduce co-extractives in the final extracts. As a result, the optimized procedure allowed us to obtain consistent recoveries of the target pesticides including problematic ones such as captan, chlorothalonil, dichlofluanid, folpet and tolylfluanid. The attained recoveries were typically between 80 and 110% (89% on average) with RSD values typically lower than 10% (8% on average) at three spiking levels of 0.01, 0.05 and 0.2 mg kg⁻¹. Linearity was studied in the range between 0.005 and 0.2 mg kg⁻¹ using pesticide standards prepared both in pure solvent and in the presence of matrix, showing coefficients of determination (R²) higher than 0.99 for all the pesticides except for desmedipham, thiabendazole and thiamethoxam in pure solvent. The study of the ratio of the slopes obtained in solvent and in matrix provided information about the matrix effects, which was <10%, 10-20% and >20% for 33, 36 and 31% of the studied pesticides, respectively. To improve accuracy, matrix matched standards were always used for calculation of the quantification results. The expanded uncertainties were estimated by using a “top-down” approach as being 17% on average (coverage factor k = 2, confidence level 95%). Finally, the method was used with success to detect and quantify pesticide residues in commercial wines.