ηi-Mode Related Properties of Collisionless Anisotropic Plasmas

An extended eigenvalue problem for collisionless electrostatic driftwaves in cylindrical and slab geometry is discussed and solved in local approximation. The fact of a minimum threshold for the ITG instability (η_i-mode) is used to get a unique concept for profile determination.     

Determination of manganese and zinc in powdered chocolate samples by slurry sampling using sequential multi-element flame atomic absorption spectrometry

In the present work, a slurry sampling flame atomic absorption spectrometric method to determine directly manganese and zinc in powdered chocolate samples is proposed. The optimization step was performed using univariate methodology involving the following factors: nature and concentration of the acid solution, sonication time, and particle size. The established conditions led to the use of a sample mass of 150 mg, 2.0 mol L^− 1 nitric acid solution, sonication time of 15 min, and a slurry volume of 50 mL. This method allows the determination of manganese and zinc with detection limit of 52 and 61 ng g^− 1, respectively, and a precision expressed as relative standard deviation (RSD) of 2.6% and 3.2% (both, n = 10) for contents of manganese and zinc of 52.4 and 100.0 μg g^− 1, respectively. The proposed method was applied for determination of manganese and zinc in five powdered chocolate samples. In these, the manganese content varied from 42.8 to 52.7 and from 88.6 to 102.4 μg g^− 1 of zinc. The analytical results were compared with the results obtained by analysis of these samples after digestion using open vessel and acid bomb digestion procedures and determination using FS-FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Determination of lead in seawater by inductively coupled plasma optical emission spectrometry after separation and pre-concentration with cocrystallized naphthalene alizarin

An analytical method for separation and pre-concentration of lead in seawater for determination by inductively coupled plasma optical emission spectrometry has been investigated. Lead was retained in the solid phase (0.5 g) composed of co-precipitated naphthalene and alizarin red. The solid phase quantitatively sorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 ml of 2 mol l⁻¹ nitric acid. The effect of NaCl, KCl, BaCl₂, CaCl₂, Na₂SO₄, MgCl₂ and Na₃PO₄ on the sorption of Pb(II) in the solid phase was studied. A set of solutions containing varying amounts of electrolytes (0.5; 1.0; 3.0 and 5.0% m/v) with Pb (50 μg) was prepared and the recommended procedure applied. The Na₃PO₄ was found to interfere; the other electrolytes did not interfere up to 5% m/v. A pre-concentration factor of 40 was obtained in this analytical procedure. The limit of detection and limit of quantification for Pb(II) were 53 and 176 μg l⁻¹, respectively. Lead was determined in seawater samples collected in Salvador city, Bahia, Brazil. The precision, expressed as R.S.D., was 1.8–4.6%, and the recovery of lead added to seawater samples was 95–97%.     

Use of cetyltrimethylammonium bromide as surfactant for the determination of copper and chromium in gasoline emulsions by electrothermal atomic absorption spectrometry

In this work, the use of cetyltrimethylammonium bromide as surfactant for the preparation of oil-in-water emulsions for the determination of Cu and Cr in gasoline by electrothermal atomic absorption spectrometry (ET AAS) was evaluated. The surfactant amount was tested in the range of 25 to 300 mg, added to 2 ml of gasoline, and completed to 10 mL with 0.1% (v/v) nitric acid solution. 150 mg of surfactant was found optimum, and a sonication time of 10 min sufficient to form an oil-in-water emulsion that was stable for several hours. The ET AAS temperature program was established based on pyrolysis and atomization curves. The pyrolysis temperatures were set at 700 and 1300 °C for Cu and Cr, respectively and the selected atomization temperatures were 2400 and 2500 °C. The time and temperature of the drying stage and the atomization time were experimentally tested to provide optimum conditions. The limits of detection were found to be 5 μg L^− 1 and 1.5 μg L^− 1 for Cu and Cr, respectively in the original gasoline samples. The relative standard deviation (RSD) ranged from 4 to 9% in oil-in-water emulsions spiked with 5 μg L^− 1 and 15 μg L^− 1 of each metal, respectively. Recoveries varied from 90 to 98%. The accuracy of the proposed method was tested by an alternate procedure using complete evaporation of the gasoline sample. The method was adequate for the determination of Cu and Cr in gasoline samples collected from different gas stations in Salvador, BA, Brazil.     

Experimental evidence for supercontinuum generation by fission of higher-order solitons in photonic fibers

We report on an experimental study of supercontinuum generation in photonic crystal fibers with low-intensity femtosecond pulses, which provides evidence for a novel spectral broadening mechanism. The observed results agree with our theoretical calculations carried out without making the slowly varying envelope approximation. Peculiarities of the measured spectra and their theoretical explanation demonstrate that the reason for the white-light generation in photonic crystal fibers is fission of higher-order solitons into redshifted fundamental solitons and blueshifted nonsolitonic radiation.     

Reactions involving fluoride ion. Part 40. Amines as initiators of fluoride ion catalysed reactions

Tetrakis(dimethylamino)ethene (TDAE) and trimethylamine react with anhydrous unsaturated fluorocarbons to produce, ‘in situ’, powerful fluoride- ion sources. These are used to initiate carbon- carbon bond forming reactions eg. oligomerisation and polyfluoroalkylation, and many of these reactions occur efficiently in the absence of a solvent.     

Regenerative amplification of femtosecond laser pulses in Ti:sapphire at multikilohertz repetition rates

We have generated and applied noncoherent x-ray radiation in an all-solid-state laser system operating at repetition rates up to 20 kHz. Based on a model that takes into account the strong thermal loading of the Ti:sapphire rod, a laser cavity with low sensitivity to thermal lensing was chosen. With a maximum pump power of 80 W, an output power as high as 27 W was obtained in gain-switched operation, and, with a seeding from a femtosecond oscillator, 60-fs, 0.8-mJ (8-W) pulses at 10 kHz and 0.32-mJ (6.5-W) pulses at 20 kHz were generated. High power femtosecond output was used to generate x-ray continuum radiation up to 5 keV from a liquid-gallium jet target.     

Rescattering of ultralow-energy electrons for single ionization of Ne in the tunneling regime

Electron emission for single ionization of Ne by 25 fs, 1.0 PW/cm(2) laser pulses at 800 nm has been investigated in a kinematically complete experiment using a "reaction microscope." Mapping the complete final state momentum space with high resolution, a distinct local minimum is observed at P(e parallel )=0, where P(e parallel ) is the electron momentum parallel to the laser polarization. Whereas tunneling theory predicts a maximum at zero momentum, our findings are in good agreement with recent semiclassical predictions which were interpreted to be due to "recollision."