Determination of some trace elements by flame atomic absorption spectrometry after preconcentration and separation by Escherichia coli immobilized on multiwalled carbon nanotubes

We have immobilized living and non-living Escherichia coli (E. coli) bacteria on multiwalled carbon nanotubes (MWCNT) and used such materials as a biosorbent for the separation and preconcentration of copper, cobalt, cadmium and nickel prior to their determination by flame atomic absorption spectrometry (FAAS). E. coli bacteria cells were mixed with MWCNTs in a 1:1 ratio, dried and placed at the tip of a 50-mL syringe. The ions were retained on the sorbent and then eluted by drawing and ejecting back the sample (or standard solution) and an eluent, respectively. The effects of various experimental parameters on the sorption and elution were investigated. The analytes were quantitatively retained (at pH values of 7) and eluted (with 0.5 M nitric acid) with high precision, the RSD being <5%. The performances of the new sorbents were compared using certified reference materials. The sorbent modified with living E. coli has a higher adsorption capacity and displays somewhat better recoveries compared to sorbent based on non-living E. coli. Both sorbents were successfully used for the separation and preconcentration of copper, cobalt, cadmium and nickel prior to their determination by flame atomic absorption spectrometry.

Red phosphors in MgAl2Si2O8 doping with Mn4+, Gd3+ and Lu3+ and host-sensitized luminescence properties

Mn⁴⁺ doped and Gd³⁺, Lu³⁺ co-doped MgAl₂Si₂O₈-based phosphors were first of all synthesized by solid state reaction at about 1300.0 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors which showed broad red emission bands in the range of 610–715 nm and had a different maximum intensity when activated by UV illumination was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

On the Use of the Perturbation Technique for the Kinetic Analysis of Nonlinear Problems of Plasma Electrodynamics

We discuss the validity of the perturbation technique (i.e., power-series expansion in terms of the high-frequency field amplitude) applied for solving the kinetic equation. The case where the validity conditions of this method are formally violated for a “strongly localized” distribution function is considered. It is shown that in this case, the asymptotic expressions for the distribution-function moments remain correct not only in the linear, but also in quadratic approximation with respect to the field. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 5, pp. 406–413, May 2005.     

Mn4+-, Tb3+,4+-, and Er3+-activated red phosphors in the MgAl2Si2O8 system

Mn⁴⁺ doped and Tb^3+,4+, Er³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid-state synthesis at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had different maximum intensities when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

Managing transshipments in a multi-retailer system with approximate policies

Using the right transshipment policy is important when transshipments are exercised under demand uncertainty. Optimal transshipment policy can be quite complex in a multi-firm system as optimal actions depend on all system variables. Moreover, both how to select requested retailer and how to respond to requests are in question. We introduce simple, close-to-optimal heuristic transshipment policies for multiple retailers. We first show that heuristic policies may perform even better than self-optimal policy, which is explained by Braess’s paradox. Then we test the performances of various heuristics with respect to centrally optimal policy. When retailers can observe others’ inventory levels, more effective transshipments can be made. Otherwise, a random selection performs quite well. We also observe that although always-accept respond policy is quite close to centrally optimal in small systems, the performance of pairwise-optimal holdback levels to respond requests is more clear and consistent for larger systems.     

On the energy flux of stationary electromagnetic waves in anisotropic dissipative media with spatial dispersion

The special features of the propagation of electromagnetic wave in gyrotropic medium with dispersion and resonant dissipation (specifically, in a magnetoactive plasma) are studied. Even though the anti-Hermitian components of the permittivity tensor are substantial in magnitude, weakly damped waves can exist in such media. However, the well-known phenomenological expression for the energy flux of waves in a medium with spatial dispersion is inapplicable for them. A theory extending this expression to the case studied is developed. The modified expression for the energy flux is used to construct the Hamiltonian for the ray optics of such media.     

Rapid and sensitive ultra-high-pressure liquid chromatography-quadrupole time-of-flight mass spectrometry for the quantification of amitraz and identification of its degradation products in fruits

Liquid chromatography under high pressure in combination with quadrupole time-of-flight mass spectrometry (QqTOF-MS and MS/MS) has been used to detect amitraz degradation products in pears, to characterize their structures, and to evaluate their occurrences in samples of different origins. Using the proposed approach, the parent pesticide and four degradation products were identified. To this end, pear samples were extracted with ethyl acetate and anhydrous sodium sulphate. Amitraz was found to be rapidly decomposed into four related compounds, of which N-(2,4-dimethylphenyl)formamidine (DMPF) was the most abundant and persistent. N,N'-bisdimethylphenylformamidine (BDMPF), 2,4-dimethylformamidine (DMF) and 2,4-dimethyl aniline (DMA) were also main metabolites of amitraz. To our knowledge this is the first report that confirms the presence of BDMPF in pears. The method was validated using MS and MS/MS for those standard available (analytical or not). In MS, recoveries ranged from 83 to 101% with relative standard deviation (RSD) from 9 to 19% at the limit of quantification (LOQ) (between 5 and 20 microg kg(-1)). Using MS/MS, recoveries, linearity and precision were similar but LOQs were higher because the intense fragmentation of the protonated molecules in the product mass spectrum. BDMPF, as an approximation, was quantified based on the DMF metabolite. The results demonstrated that high-pressure LC-QqTOF-MS and MS/MS techniques enhance further the capabilities of LC-MS in the identification of polar species in complex food samples.     

Synthesis, characterization and liquid–liquid extraction properties of new methoxyaminobiphenylglyoxime derivatives and their complexes with some transition metals

In this study, three new aminobiphenylglyoximes, [L¹H₂] N-(2-methoxy)aminobiphenylglyoxime, [L²H₂] N-(3-methoxy)aminobiphenylglyoxime and L[³H₂] N-(4-methoxy)aminobiphenylglyoxime have been synthesized by the reaction of (E,E)-4′-biphenylchloroglyoxime with 2-Methoxyaniline, 3-Methoxyaniline and 4-Methoxyaniline in absolute ethanol. The preparation Ni^II, Co^II and Cu^II complexes of these ligands are described. The ligands and their complexes were characterized by elemental analyses, IR, mass, H¹ and ¹³C NMR spectra, thermogravimetric analyses (t.g.a) and magnetic susceptibility measurements. Ligands complexing properties were studied by the liquid–liquid extraction of selected alkali (Li⁺, Na⁺, K⁺, Cs⁺) and transition metals (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺). It has been observed that all ligands show a high affinity to Cu²⁺ ions, whereas almost no affinity to alkali metals. The extraction equilibrium constants (K _ex) for complexes of ligands with Cu²⁺ metal picrates between dichloromethane and water have been determined at 25°C.     

Cyclotron mechanism of free-electron lasing without inversion

We consider one of the “paradoxical” effects of the theory of radiation and matter interaction: stimulated emission in the absence of inversion. The theory of simultaneous inversionless emission of two high-frequency waves due to their parametric interaction with ensemble of free electrons in magnetic field is developed. The analytical investigation and numerical simulation of the most interesting scheme of this two-photon interaction are presented. New effects are revealed; namely they are self-induced parametric instability of sufficiently strong waves and enhanced parametric instability in sufficiently dense electron medium.     

Impact of domain structure restructuring on the photomagnetization of a garnet film illuminated with circularly polarized light

A photomagnetization effect is observed for a (Tm,Bi)₃(Fe,Ga)₅O₁₂ garnet film at T = 300 K due to the restructurization of its multidomain structure. Photomagnetization (ΔM) emerges under the action of circularly polarized laser radiation in the spectral range of 450–600 nm at lasing power P < 600 kW/cm² and pulse duration τ _i ～ 7ns. The dependences of ΔM are measured on the polarization of light and magnetic field, the latter being perpendicular to the surface of the film. The maximum value of ΔM is observed for the circular polarization of light without a magnetic field. Moreover, ΔM changes sign with as the circular polarization changes sign and is zero for linear polarization.