Bioconvection in oxytactic microorganism-saturated porous square enclosure with thermal radiation impact

This investigation addresses bioconvection of oxytactic microorganisms in a porous square enclosure by thermal radiation impact. The bioconvection flow and heat transfer in porous media are formulated based on Darcy model of Boussinesq approximation. Appropriate transformations lead to the non-dimensionalized governing partial differential equations. Galerkin finite element method for the resulting equations is computed. The role of relevant parameters on the streamlines, isotherms, isoconcentrations of oxygen and microorganisms and average Nusselt number is analysed in the outputs. It is revealed that the flow intensity of bioconvection is pronounced with larger Rayleigh number and reduced with radiation parameter. Furthermore, the temperature distribution is affected significantly with Rayleigh number. Radiation parameter serves to fasten the heat transfer in the enclosure. Oxygen density is enhanced with Rayleigh number and radiation parameter. The profile of motile isoconcentrations is boosted with Rayleigh number. The stability of microorganisms is improved with the radiation parameter.

     

The determination of GC-MS relative molar responses of benzene and biphenyl derivatives

The dependence of relative response factors on the carbon and chlorine atom number related to naphthalene has been investigated by using gas chromatography-mass spectrometry (GC-MS). The main goal of these investigations is to find some relationship between the GC-MS signal (peak area) and the test molecule chemical structure. By means of the knowledge of correlations of relative molar response, the quantitative analysis passes into easier and fewer reference materials are needed to investigate a sample having lot of component, because the sensitivities can be determined from the correlations studied in this paper. This is very important in daily analytical tasks, particularly for impurity profiling studies. Relative responses of some polychlorinated benzenes, polychlorinated biphenyls and n-alkylbenzenes are compared in the experiments. Linear correlation is found between the molecular structures of n-alkylbenzenes, i.e. the carbon atom number, and relative molar response. Relative molar responses of polychlorinated biphenyls also provided linear correlation taken as a function of chlorine atom number. Under given conditions, the increments of CH₂ unit and chlorine atom number to the relative molar responses are 0.221 and 0.198, respectively. However, relative responses of polychlorinated benzenes showed diversity plotted against chlorine atom number, and their isomer compounds also gave various results according to the first ionization energy. The measurement conditions can influence the relative responses. The low injector temperature, the interface and the ion source temperature affected relative responses of high volatile compounds. However, when the parameters are kept under control, the results can become accurate and reproducible.     

Sensitivity to local dipole fields in the CRAZED experiment: an approach to bright spot MRI

Local dipole fields such as those created by small iron-oxide particles are used to produce regions of low intensity (dark contrast) in many molecular magnetic resonance imaging applications. We have investigated, with computer simulations and experiments at 17.6 T, how the COSY revamped with asymmetric z-gradient echo detection (CRAZED) experiment that selects intermolecular double-quantum coherences can also be used to visualize such local dipole fields. Application of the coherence-selection gradient pulses parallel to the main magnetic field produced similar, dark contrast as conventional gradient echo imaging. Application of the gradient along the magic angle leads to total loss of signal intensity in homogeneous samples. In the presence of local dipole fields, the contrast was inverted and bright signals from the dipoles were observed over a very low background. Both simulations and experiments showed that the signal strongly decreased when a phase-cycle suppressing single-quantum coherences was employed. Therefore, we conclude that most of the signal comes from directly refocused magnetization or intermolecular single-quantum coherences. Finally, we demonstrate that bright contrast from local dipole fields can also be obtained, when the pair of coherence-selection gradient pulses is deliberately mismatched. Both methods allowed visualization of local dipole fields in phantoms in experimental times of about 3 min.     

Comparison of quantitative analytical methods in headspace gas chroamtography of residual solvents

Summary The aim of this work was to compare quantitative methods used for headspace gas chromatographic analysis of residual solvents in standard aqueous solutions and to apply the methods to the analysis of medicines. We found that all three quantitative methods (external standard, ESTD; internal standard, ISTD; and standard addition, ASTD) enable determination of the total amount of solute in the equilibrated system by analysis of defined volumes of headspace gas. The results showed that the ISTD method is more precise than ESTD and ASTD when there is no strong interaction between the residual solvents and the pharmaceutical base material. When, however, there is a strong polarpolar interaction between them, the ESTD and ISTD methods give worse results than the ASTD method, because the ASTD method can eliminate the matrix effect. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Structure-Stability Study of Cyclodextrin Complexes with Selected Volatile Hydrocarbon Contaminants of Soils

The association constants for the inclusion compounds of various hydrocarbons (linear alkanes, cycloalkanes, aromatics) with different cyclodextrins (CDs) in aqueous solution have been determined using static headspace gas chromatography (SHSGC). The structure-stability relationship was examined.