A DYNAMICS APPROACH TO THE COMPUTATION OF EIGENVECTORS OF MATRICES

We construct a family of dynamical systems whose evolution converges to the eigenvec-tors of a general square matrix, not necessarily symmetric. We analyze the convergenceof those systems and perform numerical tests. Some examples and comparisons with thepower methods are presented.     

Chemical Composition,Antioxidant and Anticancer Activities of Leptocarpha rivularis DC Flower Extracts

An evaluation of antioxidant and anticancer activity was screened in Leptocarpha rivularis DC flower extracts using four solvents (n-hexane (Hex), dichloromethane (DCM), ethyl acetate (AcOEt), and ethanol (EtOH)). Extracts were compared for total extract flavonoids and phenol contents, antioxidant activity (2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH), ferric reducing antioxidant potential (FRAP), total reactive antioxidant properties (TRAP) and oxygen radical absorbance capacity (ORAC)) across a determined value of reduced/oxidized glutathione (GSH/GSSG), and cell viability (the sulforhodamine B (SRB) assay). The most active extracts were analyzed by chromatographic analysis (GC/MS) and tested for apoptotic pathways. Extracts from Hex, DCM and AcOEt reduced cell viability, caused changes in cell morphology, affected mitochondrial membrane permeability, and induced caspase activation in tumor cell lines HT-29, PC-3, and MCF-7. These effects were generally less pronounced in the HEK-293 cell line (nontumor cells), indicating clear selectivity towards tumor cell lines. We attribute likely extract activity to the presence of sesquiterpene lactones, in combination with other components like steroids and flavonoids.     

Dark Energy： Relating the Evolutions of the Universe from the Past to the Future

Using the evolution history of the universe, one can make constraint on the parameter space of dynamic dark energy models. We discuss two different parameterized dark energy models. Our results further restrict the combined constraints obtained from supernova and the first-year Wilkinson-microwave-anisotropy-probe observations. From the allowed parameter space, it is found that our universe will experience an eternal acceleration. We also estimate the bound on the physically relevant regions both in the re-inflationary and inflationary phases.     

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.     

Indirect (hydrogen-driven) electrodeposition of porous silver onto a palladium membrane

Hydrogen permeation through a pure palladium film (25 μm thickness, optically dense) is employed to trigger electron transfer (hydrogen-driven) reactions at the external palladium | aqueous electrolyte interface of a two-compartment electrochemical cell. Two systems are investigated to demonstrate feasibility for (i) indirect hydrogen-mediated silver electrodeposition with externally applied potential and (ii) indirect hydrogen-mediated silver electrodeposition driven by external formic acid decomposition. In both cases, porous metal deposits form as observed by optical and electron microscopies. Processes are self-limited as metal deposition blocks the palladium surface and thereby slows down further hydrogen permeation. The proposed methods could be employed for a wider range of metals, and they could provide an alternative (non-electrochemical or indirect) procedure for metal removal or metal recovery processes or for indirect metal sensing.

Graphical abstract

     

Identification of selenium species in selenium-enriched Lens esculenta plants by using two-dimensional liquid chromatography-inductively coupled plasma mass spectrometry and [77Se]selenomethionine selenium oxide spikes

Selenium speciation in Se-enriched Lens esculenta grown in hydroponic culture containing inorganic selenium as Na(2)SeO(3) and Na(2)SeO(4) was performed. After 16 days of growth, the plants were collected and divided in two parts, roots and stems and then analysed to identify and quantify selenium species. Speciation studies of the enzymatic extracts were carried out by using anion-exchange (PRP-X100) and size-exclusion/ion-exchange (Shodex Asahipak) columns coupled to inductively coupled plasma mass spectrometry (ICP-MS). The need of using two independent chromatographic mechanisms for unambiguous species identification is demonstrated. Moreover, the use of a [(77)Se]selenomethionine selenium oxide spike turned out to be critical to discriminate between selenium selenomethioine selenium oxide and selenocysteine.     

Selenium methylselenocysteine protects human hepatoma HepG2 cells against oxidative stress induced by tert-butyl hydroperoxide

Selenium methylselenocysteine (Se-MeSeCys) is a common selenocompound in the diet with a tested chemopreventive effect. This study investigated the potential protective effect of Se-MeSeCys against a chemical oxidative stress induced by tert-butyl hydroperoxide (t-BOOH) on human hepatoma HepG2 cells. Speciation of selenium derivatives by liquid chromatography–inductively coupled plasma mass spectrometry depicts Se-MeSeCys as the only selenocompound in the cell culture. Cell viability (lactate dehydrogenase) and markers of oxidative status—concentration of reduced glutathione (GSH) and malondialdehyde (MDA), generation of reactive oxygen species (ROS) and activity of the antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR)—were evaluated. Pretreatment of cells with Se-MeSeCys for 20 h completely prevented the enhanced cell damage, MDA concentration and GR and GPx activity and the decreased GSH induced by t-BOOH but did not prevent increased ROS generation. The results show that treatment of HepG2 cells with concentrations of Se-MeSeCys in the nanomolar to micromolar range confers a significant protection against an oxidative insult.     

Formal and precise derivation of the Green functions for a simple potential

In formal scattering theory, the Green functions are obtained as solutions of a distributional equation. In this paper, we use the Sturm–Liouville theory to compute the Green functions within a rigorous mathematical theory. We shall show that both the Sturm–Liouville theory and the formal treatment yield the same Green functions. We shall also show how the analyticity of the Green functions as functions of the energy keeps track of the so-called “incoming” and “outgoing” boundary conditions.