Linear stability analysis of oscillating Ekman boundary layers

The analysed Ekman layer is generated in a fluid layer rotating around an axis normal to its two bounding rigid plates. One of the plates is stationary, the other moving at certain Reynolds numbers. An additional oscillation is added to the moving plate at different amplitudes and frequencies. The linear stability of this system is determined via a Floquet analysis and a Galerkin-approximation of the corresponding Navier-Stokes-Equations. If the frequencies of the oscillations are small the critical Reynolds numbers of the Type I and Type II instabilities do not differ much from steady Ekman layers. Also for a purely oscillating system the critical values of the instabilities are almost consistent with those for a steady system. Interestingly, for higher frequencies the Type II instability does not appear any more. Instead the boundary layer becomes unstable only in terms of a Type I instability. In comparison with findings of other authors these results seem to be quite reasonable. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Linearization of holomorphic germs with quasi-Brjuno fixed points

Let f be a germ of holomorphic diffeomorphism of mathbb Cⁿ{mathbb {C}^{n}} fixing the origin O, with d f _O diagonalizable. We prove that, under certain arithmetic conditions on the eigenvalues of d f _O and some restrictions on the resonances, f is locally holomorphically linearizable if and only if there exists a particular f -invariant complex manifold. Most of the classical linearization results can be obtained as corollaries of our result.     

Characterization of Cyclic N-Acyliminium Ions by Infrared Ion Spectroscopy

N-Acyliminium ions are highly reactive intermediates that are important for creating CC-bonds adjacent to nitrogen atoms. Here we report the characterization of cyclic N-acyliminium ions in the gas phase, generated by collision induced dissociation tandem mass spectrometry followed by infrared ion spectroscopy using the FELIX infrared free electron laser. Comparison of DFT calculated spectra with the experimentally observed IR spectra provided valuable insights in the conformations of the N-acyliminium ions.     

Spectrofluorimetric determination of cephradine in commercial formulation using ethylacetoacetate-formaldehyde as fluorogenic agent

A simple, precise and sensitive spectrofluorimetric method was developed for the determination of cephradine in pharmaceutical formulations. The method is based on reaction of cephradine with ethyl acetoacetate (EAA) in the presence of formaldehyde in acidic media. The fluorescence intensity of the resultant fluorescent derivative was measured at 443 nm after excitation at 350 nm. The effects of various experimental parameters on the formation of the fluorescent product were studied and optimized. A linear relationship between concentration of cephradine and fluorescence intensity was found over the range of 0.1–5.0 μg/mL. The limit of detection and quantification were calculated an found 1.09 × 10^?2 ± 3.64 × 10^?3 μg/mL and 3.64 × 10^?2 ± 3.64 × 10^?3 μg/mL, respectively and with relative standard deviation (RSD) 4.14%. Accuracy of the method was checked by standard addition method and applied to four different commercial formulations. The percentage recovery was found in the range of 97.03 to 103.80% for Velora suspension, 98.16 to 102.90% for velocef injection, 99.00 to 108.10% for Velora capsule and 99.06 to 104.90% for Cefradin capsule. The good percentage recoveries from all samples indicated that there were no interferences from the common excipients of formulations. The proposed method was successfully applied to the analysis of commercial suspension, capsule and injections. The result obtained by the proposed method was statistically validated with reference HPLC method. No significant difference in the results of the two methods was found regarding accuracy and precision using Student’s t-test and the variance ratio F-test.     

Spectrophotometric determination of methylamine moiety containing pesticides using ninhydrine reagent

A spectrophotometric method has been proposed for the determination of pesticides containing methylamine moiety. These pesticides afforded methylamine upon alkaline hydrolysis, which was subsequently reacted with ninhydrin in the presence of pyridine. The absorbance of the resulting blue-purple product was measured spectrophotometrically at 570 nm. The Beer??s law showed a linear relationship between absorbance and concentration of the pesticide in the range 0.04?C5.0 ??g/mL. The limit of detection and limit of quantification were 0.012 and 0.02 ??g/mL, respectively. The repeatability was 0.22 expressed as RSD. The performance of this newly developed method was compared with the established spectrophotometric methods for the determination of these pesticides. The method has been successfully applied to the evaluation of these pesticides in commercial pesticide formulation and to the determination of monocrotophos in fruit samples.     

Effect of annealing on the supercapacitor performance of CuO-PAA/CNT films

We report the synthesis of CuO-poly(acrylic) acid/CNT hybrid thin films by a cost-effective spin-coating technique for supercapacitor application. Hybrid films were annealed at 300, 400, and 500 °C to study its effect on the supercapacitor behavior. X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy techniques were used for the phase identification and determination of the organic component in the hybrid films, respectively. Surface morphology of the films was examined by scanning electron microscopy and revealed the novel ring-like structures. The average diameter of the ring changes from 0.5 to 1.2 μm with increase in annealing temperature. Cyclic voltammetry is employed to estimate the specific capacitance (C _sp) of the films in 1 M H₂SO₄ electrolyte. It is observed that the C _sp increases from 188 to 258 Fg⁻¹ with increase in annealing temperature.