Positive and Nontrivial Solutions for the Urysohn Integral Equation

We establish new criteria for the existence of either positive or nonzero solutions of the Urysohn integral equation. We also discuss the existence of an interval of positive eigenvalues and sufficient conditions for the existence of at least a positive eigenvalue with a nonzero or positive eigenfunction for the Urysohn integral operator. Among others, we employ techniques based on fixed point index theory for compact maps, which are new for this type of equation.     

Solvating,manipulating, damaging,and repairing DNA in a computer

This work highlights four different topics in modeling of DNA: (i) the importance of water and ions together with the structure and function of DNA; the hydration structure around the ions appears to be the determining factor in the ion coordination to DNA, as demonstrated in the results of our MD simulations; (ii) how MD simulations can be used to simulate single molecule manipulation experiments as a complement to reveal the structural dynamics of the studied biomolecules; (iii) how damaged DNA can be studied in computer simulations; and (iv) how repair of damaged DNA can be studied theoretically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Heavy Dirac and Majorana neutrino production ine + e − collisions

The production of heavy Dirac and Majorana neutrinos ine ⁺ e ^? collisions is investigated. The heavy Dirac and/or Majorana neutrinos can be produced in charged and neutral current processes $(e^ + e^ - \to N_1 \bar N_2 )$ . The production of a single heavy neutrino is possible if it mixes with the light neutrino species. The production of heavy neutrinos in Higgs channels is also studied, since in some specific models the Yukawa couplings could be large enough to make the production of heavy neutrinos through Higgs boson exchanges sufficiently large for detection. The most general left-right symmetric model with possibly complexV orA couplings is used in the analytic calculations of the production cross sections, but the numerical examples are given using simplified left-right symmetric model. The interference terms between different production channels have been studied in great detail and in some cases the interference terms are found to be non-negligible in wide range of production spectrum. The pair production cross section is larger in the Dirac case than it is in the Majorana case, but the single heavy Majorana neutrino production cross section is roughly twice as large as that of a Dirac neutrino.     

The use of chiral interaction reagents in the separation of D(−)-and L(+)-ascorbic acid by ion interaction reversed-phase HPLC

Summary An HPLC reversed-phase ion interaction reagent method is presented, which makes use of chiral compounds as the interaction reagents. By employing the optical isomeric forms of malic, tartaric and mandelic acids as the interaction reagents, a good separation of D(−) and L(+) ascorbic acid has been achieved. The method has also been applied to the identification of vitamin C in some medical formulations. The separation of te enantiomeric forms of DL malic acid has been attempted and a shor discussion is presented about the elution sequence in chromatographic separation of D- and L-enantiomers.     

Determination of Na(2)O from sodium aluminate NaAlO(2)

The aim of the work was to find a suitable method and conditions for determining Na(2)O wt.% from NaAlO(2). Problems were encountered while titrating NaAlO(2) with hydrochloric acid. The problematic area was the pH range 4-10 where aluminum precipitates as hydroxides. The different species of the aluminate solution were determined using potentiometric and complexometric titrations. The equivalent point of the potentiometric titration was detected using Gran's plotting method. Precipitation of aluminum hydroxides did not interfere with titrations, because in potentiometric titrations the pH value was over 10 and in complexometric titrations the pH was 4. The results were accurate and determinations were easy to carry out. Sodium was also determined by DCP-AES.     

Optimization by experimental design and artificial neural networks of the ion-interaction reversed-phase liquid chromatographic separation of twenty cosmetic preservatives

Particular attention are recently receiving antimicrobial agents added as preservatives in hygiene and cosmetics commercial products, since some of them are suspected to be harmful to the human health. The preservatives used belong to different classes of chemical species and are generally used in their mixtures. Multi-component methods able to simultaneously determinate species with different chemical structure are therefore highly required in quality control analysis. This paper presents an ion interaction RP-HPLC method for the simultaneous separation of the 20 typical antimicrobial agents most used in cosmetics and hygiene products, that are: benzoic acid, salicylic acid, 4-hydroxybenzoic acid, methyl-, ethyl-, propyl-, butyl-, benzyl-benzoate, methyl-, ethyl-, propyl-, butyl-, benzyl-paraben, o-phenyl-phenol, 4-chloro-m-cresol, triclocarban, dehydroacetic acid, bronopol, sodium pyrithione and chlorhexidine. For the development of the method and the optimization of the chromatographic conditions, an experimental design was planned and models were built by the use of artificial neural network to correlate the retention time of each analyte to the variables and their interactions. The neuronal models developed showed good predictive ability and were used, by a grid search algorithm, to optimize the chromatographic conditions for the separation of the mixture.     

Investigation of anthropic effects connected with metal ions concentration, organic matter and grain size in Bormida river sediments

An investigation on the sediment composition and grain size was carried out along the Bormida river (Piedmont, Northern Italy). The samples were taken both in the riverbed and on its banks. Multivariate statistical exploratory methods permitted to identify possible sources of primary pollution. In particular, principal component analysis (PCA) showed that there are probably at least three anthropogenic main causes of pollution, one connected with Cr, Ni and Sn, the second with cadmium and the last one with mercury. Some correlations were found between heavy metal ion concentrations and organic matter and/or the sediment grain size. Differences between the samples collected in the riverbed and on the banks were identified and the relationships between the principal components and the distance of the samples from the riverbed and from the hot spot represented by the ACNA industrial site were also analyzed.     

Determination of nitrite and nitrate in Venice lagoon water by ion interaction reversed-phase liquid chromatography

Ion interaction reversed-phase liquid chromatography with octylammonium orthophosphate as the interacting reagent and a reversed-phase C₁₈ column was applied to the identification and determination of nitrite and nitrate in Venice lagoon water. Interference by the high chloride concentration was systematically studied and the results obtained with different column packings were compared. With spectrophotometric detection at 230 nm, nitrite at 0.005 mg 1^?1 can be detected and determined even in the presence of 0.70 M chloride. The dependence of the retention time of nitrite on the chloride concentration was studied for two reversed-phase columns with different packings. Concentrations of 0.30 ± 0.05 mg 1^?1 of nitrite and 0.20 ± 0.05 mg 1^?1 of nitrate were found in Venice lagoon water.