Enhanced synchronous spectrofluorimetric determination of aflatoxin B1 in pistachio samples using multivariate analysis

The determination of aflatoxin B₁ (AFB1) in pistachio has been accomplished by normal and synchronous fluorimetry in combination with some multivariate calibration methods and derivative techniques. Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan was used to obtain the optimized Δλ for AFB1 in pistachio sample. The methods are based on the enhanced fluorescence of AFB1 by β-cyclodextrine in 10% (v/v) methanol-water solution. Twenty-six pistachio samples containing AFB1 in the range 0-15 ppb were used as calibration set. Eighteen combinational methods were tested to make best model for prediction of AFB1 and finally best results obtained using a method based on synchronous fluorimetry in combination with multiple linear regressions (MLR). For concentrations ranging from 0 to 15 ppb of AFB1 in 22 pistachio samples as prediction set, the values of root mean square difference (RMSD) and relative error of prediction (REP) using MLR were 0.328 and 4.453%, respectively were observed. Two naturally contaminated pistachio samples were analyzed by synchronous fluorimetry using MLR and compared with HPLC results.     

The phenomenon of simplified scattering from rough surfaces to reflection in fractional space

In this paper, the scattering of incident plane waves from rough surfaces has been modeled in a fractional space. It is shown how wave scattering from a rough surface could correspond to a simple reflection problem in a fractional space. In an integer dimensional space, fluctuations of the surface result in wave scattering, while in the fractional space, these fluctuations are compensated by the geometry of space. In the fractional space, reflection is equivalent to scattering from the integer dimensional space. Comparing scattered wave functions from different self-affine rough surfaces in the framework of the Kirchhoff theory with the results from the fractional space, we see good agreement between them.     

Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography

A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r² = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples.     

Suppression of harmonic perturbations and bifurcation control in tracking objectives of a boiler–turbine unit in power grid

In the presence of harmonic disturbances, boiler–turbine units may demonstrate quasi-periodic behaviour due to the occurrence of various types of bifurcation. In this article, a nonlinear model of boiler–turbine unit is considered in which drum pressure, electric output and drum water level are controlled via manipulation of valve positions for fuel, steam and feed-water flow rates. For bifurcation control in tracking problem, two controllers are designed based on gain scheduling and feedback linearization (FBL). To investigate the efficiency of control strategies, three cases are considered for desired tracking objectives (a sequence of steps, ramps/steps, and a combination of them). According to the results, FBL controller works successfully in suppression of harmonic perturbations and consequently bifurcation control. As it is implemented, quasi-periodic solutions (caused by Hopf bifurcation) are vanished; leading to the appearance of periodic solutions with low amplitudes. Consequently, appropriate tracking performance with less oscillatory behaviour is observed for the drum pressure, electric output, and drum water level (desirable for the power grid). In addition, when FBL controller is used, less control efforts are predicted for the bifurcation control.     

Chemical Cleaning of Microfiltration Membranes Fouled by Whey

Millipore hydrophobic polyvinylidene fluoride (PVDF) microfiltration membranes were used for whey processing. Fouled membranes were cleaned with acid (HCl), alkaline (NaOH) and surfactant (Triton‐X100). The latter resulted in maximum flux recovery and resistance removal. Hydrochloric acid had a moderate effect and sodium hydroxide was the weakest cleaning agent. This is due to the cleaning strength of emulsifiers compared to acid or alkali. However acids are more efficient than alkaline solutions for removal of mineral compounds which remain on the membrane surface. Cleaning efficiency depends on the concentration of cleaning agent being higher for higher surfactant concentration. For acids and alkali, the efficiency increases with increasing the concentration of the reagent reaches a maximum (optimum concentration) and then decreases. This can be explained by changes in permeability of the deposit layer with the concentration of the cleaning agent. Another explanation is the breakage of proteins by acid or alkali which produces more fouling materials and causes less cleaning efficiency. Operating conditions affect the cleaning process. At higher stirring speeds (turbulent flow) or longer cleaning time better removal of deposits and higher cleaning efficiency were observed. The sequential cleaning process may or may not improve the cleaning efficiency. When acidic cleaning was followed by washing with a surfactant an improvement was achieved. This can be attributed to the incomplete removal of deposits by acid. However further cleaning with acid can not improve the cleaning efficiency. During whey processing fouling occurs by deposition of foulants of mostly proteins and macromolecules on the membrane surface or in the membrane matrix. Large substances (compared to the membrane pores) settle on the membrane surface and the small species penetrate and are adsorbed in the membrane pores. Cleaning dissolves and removes the adsorbed foulants from the membrane.     

A lupane triterpenoid and other constituents of Salvia eremophila

Phytochemical investigation of the aerial parts of Salvia eremophila led to the isolation of a lupane triterpenoid, 3β, 20-dihydroxylupane-28-oic acid (1), together with eight other compounds, comprising three diterpene, two triterpene, two flavonoids and a steroidal glucoside. Their structures were elucidated by interpretation of their one-dimensional and two-dimensional NMR spectra and completed by the analysis of the HRESIMS data. Compounds 1, 2-4 and 8 were evaluated for their cytotoxicities against five human tumour cell lines. Compounds 1 and 3 hold a good potential for use in future studies due to their anti-cancer properties.     

Control of nonlinear systems on Poincaré section via quasi-sliding mode method

The order of some dynamical systems can be reduced by finding a good Poincaré section for them. In such a case the problem of controlling the main continuous system, can be reduced into controlling the discrete Poincaré map of the system which is usually nonlinear. In this paper, this idea is implemented for a simple nonlinear system. A quasi-sliding mode controller is used to stabilize the unstable fixed point of the discrete system and the control signal obtained, is applied to the main continuous system, where a corresponding limit cycle is observed. The process happens to be useful in understanding the necessary conditions for the existence of periodic responses in the system.     

Supersymmetric Solutions of PT-/non-PT-symmetric and Non-Hermitian Central Potentials via Hamiltonian Hierarchy Method

The supersymmetric solutions of PT-/non-PT-symmetric and non-Hermitian deformed Morse and Pöschl-Teller potentials are obtained by solving the Schrödinger equation. The Hamiltonian hierarchy method is used to get the real energy eigenvalues and corresponding eigenfunctions.