A spirobiscalix[4]azacrown: synthesis and complexing properties

The synthesis and complexation properties of a novel type of calix[4]azacrown, in which two cone calix[4]arenes are linked via a spiro C-atom incorporated into polyaminoalkylene chains are presented.     

Investigation of the intracavity frequency doubling of a gain-switched InGaAs/GaAs pulsed diode laser

A mathematical model describing the dynamic emission of the intracavity frequency doubling (IFD) of a gain-switched two-section InGaAs/GaAs diode laser has been presented. One section is electrically pumped to provide gain, while the second section is unpumped (reverse biased) to provide a saturable absorber. The three-dimensional physical problem is reduced to one-dimensional model using adiabatic approximation, which allows the separation of the wavefunction. The suggested model in this paper allows studying the impact of the variations of the input InGaAs/GaAs/KTP diode laser parameters on the output pulsation characteristics. The proposed mathematical model is solved numerically using fourth-order Runge-Kutta method. The numerical calculations reflect the influence of the variation of the applied gain current and saturable bias current on the output laser pulse characteristics. The numerical results show good consistency with the available experimental data in references.     

Chromatographic analysis of plant sterols in foods and vegetable oils.

This paper reviews recently published chromatographic methods for the analysis of plant sterols in various sample matrices with emphasis on vegetable oils. An overview of structural complexities and biological/nutritional aspects including hypocholesterolemic activities of phytosterols is provided in the Section 1. The principal themes of the review highlight the development and application of chromatographic techniques for the isolation, purification, separation and detection of the title compounds. Pertinent gas chromatographic and high-performance liquid chromatographic methods from the literature are tabulated to illustrate common trends and methodological variability. The review also covers specific analyses of natural/synthetic standard mixtures to shed light on potential applicability in plant sample assays. Examples of combined chromatographic techniques linked in tandem for the analysis of complex samples are included. Elution characteristics of sterol components are discussed in the context of analyte substituent effects, structural factors and stationary/mobile phase considerations.     

Numerical investigation of the stagnation point flow of radiative magnetomicropolar liquid past a heated porous stretching sheet

Journal of Thermal Analysis and Calorimetry - In this paper, we have investigated the two-dimensional magnetohydrodynamic steady boundary layer flow of a viscous magnetomicropolar liquid via an...     

Numerical calculations of intracavity dye Q-switched ruby laser

A mathematical model describing the dynamic emission of the Q-switched ruby laser has been adapted. The suggested model allows the investigation of the effects of a dye cell on the mode characteristics of the ruby laser and, moreover, the study of the effect of the laser input parameters on the output laser pulse. This model simulates the nonlinear effects of dye pulse modulation on the laser emission.In addition, a numerical solution of a nonlinear rate equation system of the adapted model is discussed. The solution estimates the density of the emitted radiation, population inversion and energy transfer processes of the ruby laser rod and dye cell for different emission regimes (one pulse regime, free running pulses, repetition periodic pulses). The estimated results of the laser output pulse characteristics are in a good agreement with the other calculated and experimental results.     

Separations of tocopherols and methylated tocols on cyclodextrin-bonded silica

-, β-, γ-, and δ-tocopherols (methyl-substituted tocols) and 5,7-dimethyltocol were separated by normal-phase HPLC on β- or γ-cyclodextrin-bonded silica (CDS) with fluorescence detection. The HPLC behavior of the tocol components was studied under various mobile phase conditions. Hexane or cyclohexane was used in combination with oxygen-containing solvents (alcohol, ether, and esters) in binary and ternary mobile phases. Capacity factors (k′) and separation factors () for adjacent tocol components were determined. Incorporation of non-polar ethers in the hydrocarbon (hexane or cyclohexane) mobile phases favored the separation of β- and γ-tocopherols with improved values, which enabled trace analysis of the β-isomer present in soybean oil. Analyte solutes tended to be more strongly adsorbed in mobile phases containing branched-chain alcohols and ethers than in those containing the corresponding straight-chain solvents. Generally, the k′ values obtained with hexane mobile phases or with the β-CDS phase were greater than those observed in HPLC with cyclohexane mobile phases or with the γ-CDS phase.     

Interaction between p-tetraphenyl tetrahomodioxacalix[4]arene amide derivatives and alkali and alkaline-earth metal cations

The binding properties of four amido derivatives of p-tetraphenyl tetrahomodioxacalix[4]arene towards alkali and alkaline-earth metal cations using UV-absorption spectrophotometry, ¹H NMR and ESI-mass spectrometry techniques are reported.     

On the global well-posedness for the axisymmetric Euler equations

This paper deals with the global well-posedness of the 3D axisymmetric Euler equations for initial data lying in critical Besov spaces B_p,1^1+3/p{B_{p,1}^{1+3/p}}. In this case the BKM criterion is not known to be valid and to circumvent this difficulty we use a new decomposition of the vorticity.     

Thorium series disequilibrium and geochemical processes in estuarine sediments of Mandovi river

The measurements of natural radioactivity due to thorium isotopes have been carried out in estuarine sediments of Mandovi river (Goa). The geochemical behaviour of these sediments has been studied by leaching the samples with 5 % ethylenediaminetetraacetic acid at pH 3.0 in order to investigate the processes occurring on the surface of the sediment particles and the distribution of natural thorium in estuarine sediments. The²²⁸Th/²³²Th activity ratios have been found to be in the range of 2.00 to 2.12. This anomaly between²³²Th and²²⁸Th has been attributed to the preferential leaching of²²⁸Ra by water flowing over these sediments. The activities of²²⁸Ra on the surface labile layers of the sediments have also been determined. The²³⁰Th/²³²Th activity ratios have been found to be in the range of 0.94 to 1.04. These ratios are mainly dependent on the precipitation action of²³⁰Th on adjacent sediments.     

Complexation Studies of a Calix[4](aza)crown and Crystal Structure of its Magnesium Complex

A systematic study of extraction properties and complexation behaviour of the calix[4](aza)crown 1 towards alkaline earth (Mg²⁺, Ca²⁺,Sr²⁺, Ba²⁺) and transition metal (Co²⁺, Ni²⁺, Cu²⁺,Zn²⁺) cations is presented. The binding behaviour of 1 was also investigated by ¹H-NMR and the crystal structure of the 1:1 complex with Mg²⁺ isdescribed.