Arsenic speciation in xylem sap of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm⁻³ arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.     

Kinetics of silver nanoparticle growth in aqueous polymer solutions

Silver nanoparticles were prepared in aqueous AgNO₃ solution by using hydroquinone and sodium citrate as reducing agents with neutral polymers poly(vinylpyrrolidone) and poly(vinyl alcohol) as stabilizers. The rate of particle formation was determined with a diode array UV-Vis spectrophotometer. The effects of the polymer concentration on the reaction rate, the size, and the size distribution of the particles formed were studied by transmission electron microscopy. Both the reaction rate and the size of silver nanoparticles decreased with increasing polymer concentration in the range 0.07–0.50 w/v%.     

Reagentless enzyme electrode based on phenothiazine mediation of horseradish peroxidase for subnanomolar hydrogen peroxide determination

The development and characterization of a highly sensitive enzyme immobilized carbon based electrode for the determination of subnanomolar concentrations of hydrogen peroxide in aqueous samples is described. The biosensor consists of horseradish peroxidase (HRP) immobilized in solid carbon paste along with a suitable redox mediator. The latter allows the acceleration of the electroreduction of HRP in the presence of hydrogen peroxide. Several phenothiazines as mediators are investigated in a comparative manner and with respect to dimethylferrocene using cyclic voltammetry and amperometry. Insolubilization of the HRP in the solid carbon paste is achieved by cross-linking the enzyme with glutaraldehyde and bovine serum albumin. Several experimental parameters such as pH, mediator and enzyme content are considered. The hydrogen peroxide determination is better carried out in 0.1 M acetate buffer, pH 4.5, by amperometry at an applied potential of 0.0 V versus Ag/AgCl, 3 M NaCl concentration and by using the phenothiazine base as redox mediator. The biosensor response is linear over the concentration range 2 nM-10 microM with a detection limit of 1 nM. The linear range of the hydrogen peroxide response without a mediator in the biosensor is found between 2 and 40 microM. The biosensor can be used for more than 180 measurements. Additional modification of the electrode by incorporation of Nafion SAC-13 microparticles in the solid carbon paste allows detection of concentrations of hydrogen peroxide as low as 0.1 nM.     

Anchored expansion and random walk

This paper studies anchored expansion, a non-uniform version of the strong isoperimetric inequality. We show that every graph with i-anchored expansion contains a subgraph with isoperimetric (Cheeger) constant at least i. We prove a conjecture by Benjamini, Lyons and Schramm (1999) that in such graphs the random walk escapes with a positive lim inf speed. We also show that anchored expansion implies a heat-kernel decay bound of order exp(—cn ^1/3). Submitted: September 1999, Revision: January 2000.     

Classifying Regions of High Model Error Within a Data-Driven RANS Closure: Application to Wind Turbine Wakes

Flow, Turbulence and Combustion - Data-driven Reynolds-averaged Navier–Stokes (RANS) turbulence closures are increasing seen as a viable alternative to general-purpose RANS closures, when LES...     

Photodegradation of Direct Blue-199 in carpet industry wastewater using iron-doped TiO2 nanoparticles and regenerated photocatalyst

Fe-doped TiO_2, Ti_1–xFe_xO₂ (x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10), photocatalysts have been successfully synthesized via citric acid–assisted autocombustion method. The synthesized photocatalysts were characterized using different characterization techniques, such as X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX), and x-ray photoelectron spectroscopy (XPS). The XRD diffraction patterns revealed that synthesized photocatalysts have the anatase phase of TiO₂. The DRS analysis indicates a slight increment in absorbance in the visible light region by the Fe doping in TiO₂. The FT-IR spectra reveal the various stretching and bending vibrational bands of the Ti–O lattice. The XPS spectra confirm the presence of elements titanium, oxygen, and iron in the synthesized samples and determine binding energy of elements. TEM analysis shows the shape of the synthesized photocatalyst, and it was used to calculate the average particle sizes of undoped and Fe-doped TiO₂ (Ti_0.96Fe_0.04O₂) photocatalysts using a histogram. The photocatalytic activities of synthesized photocatalysts were determined by photodegradation of dye (Direct Blue 199), contaminating carpet industry wastewater in the photochemical reactor and open pan reactor. The maximum photodegradation activity was shown by the Ti_0.96Fe_0.04O₂ photocatalyst among all the synthesized undoped and Fe-doped photocatalysts. The synthesized photocatalyst (Ti_0.96Fe_0.04O₂) had better photocatalytic activity when compared to both, undoped TiO₂ and Aeroxide (Degussa) P-25. The used Fe-doped TiO₂ photocatalyst (Ti_0.96Fe_0.04O₂) was regenerated five times and investigated for its photocatalytic activity.     

Effects of Heavy Ion Irradiation on Short-Range Order of Fe–Cr–P–C Amorphous Alloys Investigated by Mössbauer and DSC Measurements

Rapidly quenched Fe–Cr–P–C amorphous alloys irradiated with 209 MeV energy ⁸⁴Kr ions were investigated by Mössbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry measurements. Significant changes were found between Mössbauer spectra of the irradiated and non-irradiated amorphous alloys. The changes were analysed by the hyperfine field distribution method, too. The crystallisation temperature as well as the phase composition at a certain stage of crystallisation were found to be different in the non-irradiated and irradiated samples. These results reflect the changes in the short-range ordering due to the irradiation with energetic heavy ions.     

Enhancement of photocatalytic activity and regeneration of Fe-doped TiO2 (Ti1−xFexO2) nanocrystalline particles synthesized using inexpensive TiO2 precursor

Research on Chemical Intermediates - Fe-doped TiO2, Ti1?xFexO2 (x?=?0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) photocatalysts with enhanced activity were synthesized via a...     

Impact-parameter dependence of ionization probabilities of the L sub-shells

Ionization probabilities of the L_I and L_III subshells have been calculated for ⁸²Pb by the impact of protons with in the frame work of binary encounter approximation (BEA) theory. The results obtained have been compared with the probabilities based on semi-classical approximation (SCA) theory.