Numerical study of simultaneous natural convection heat transfer from both surfaces of a uniformly heated thin plate with arbitrary inclination

 Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating rate were used to vary the modified Rayleigh number over the range of 4.8×10⁶ to 1.87×10⁸. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10^∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation while for inclination angle larger than 10^∘, the average Nusselt number can be correlated into an elegant correlation. Received on 18 April 2001 / Published online: 29 November 2001     

Determination of 3-Chloro-4-(Dichloromethyl)-5-Hydroxy-2(5H)-Furanone (Toxicant MX) in Drinking Water by Chromatography–Tandem Mass Spectrometry

It is shown that toxicant MX can be reliably identified and determined quantitatively by ion-trap tandem mass spectrometry with an accuracy as high as that for high-resolution mass spectrometry.     

Application of time-variable feedback to the input amplifier of pulse magnetic resonance spectrometers: Experimental studies

Experimental research on the improvement of the sensitivity and time resolution of pulsed magnetic resonance spectrometers is discussed. It is shown that application of a time-variable feedback of a signal to the input of the receiver amplifier can decouple, the “fixed” relationship between the quality factorQ and the ringdown time of the resonance system. Experiments were performed with low-frequency, radio-frequency and microwave pulse-type magnetic resonance receivers. Modifications of an S/C-band electron spin echo modulation spectrometer carried out to check the “time-variable feedback” performance are described. It is demonstrated that the application of a time-variable feedback can significantly reduce the ringdown time and improve the recovery properties of the magnetic resonance receiver system. It is also demonstrated that the time-variable feedback can improve the overall receiver sensitivity due to the fact that the working bandwidth of the resonance system can be optimized separately for the transmitting and the receiving mode. Signal values could be increased at least three times and the signal-to-noise ratio about 1.5–2 times. The largest improvement is achieved with the initially overcoupled resonator. Experimental spectra of test samples for different settings of the time-variable feedback are shown.     

A rapid and sensitive extractive spectrophotometric determination of copper(II) in pharmaceutical and environmental samples using benzildithiosemicarbazone.

Benzildithiosemicarbazone (BDTSC) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of copper(II). BDTSC reacts with copper(II) in the pH range 1.0-7.0 to form a yellowish complex. Beer's law is obeyed in the concentration range 0.5-0.4 microg cm(-3). The yellowish Cu(II)-BDTSC complex in chloroform shows a maximum absorbance at 380 nm, with molar absorptivity and Sandell's sensitivity values of 1.63 x 10(4) dm3 mol(-1) cm(-1) and 0.00389 microg cm(-2), respectively. A repetition of the method is checked by finding the relative standard deviation (RSD) (n = 10), which is 0.6%. The composition of the Cu(II)-BDTSC complex is established as 1:1 by slope analysis, molar ratio and Asmus' methods. An excellent linearity with a correlation coefficient value of 0.98 is obtained for the Cu(II)-BDTSC complex. The instability constant of the complex calculated from Edmond and Birnbaum's method is 7.70 x 10(-4) and that of Asmus' method is 7.66 x 10(-4), at room temperature. The method is successfully employed for the determination copper(II) in pharmaceutical and environmental samples. The reliability of the method is assured by analyzing the standard alloys (BCS 5g, 10g, 19e, 78, 32a, 207 and 179) and by inter-comparison of experimental values, using an atomic absorption spectrometer.     

Synthesis of Palladium and Nickel Complexes with Octaphenyltetraazaporphyrins

Palladium(II) and nickel(II) complexes with octaphenyltetraazaporphyrin, octakis(4-bromophenyl)tetraazaporphyrin, and octakis(4-nitrophenyl)tetraazaporphyrin were obtained by reactions of octaphenyltetraazaporphyrin, Mg octaphenyltetraazaporphyrin, octakis(4-bromophenyl)tetraazaporphyrin, and octakis(4-nitrophenyl)tetraazaporphyrin with palladium(II) and nickel(II) chlorides in DMF.     

Reaction of Chloroacetone with Cytisine and d-Pseudoephedrine Alkaloids

Alkylation of cytisine and d-pseudoephedrine alkaloids with chloroacetone was performed. The target product of the reaction with cytisine is aminoacetone and of the reaction with d-pseudoephedrine, a morpholine derivative.     

Nonnegative curvature and cobordism type

We show that in each dimension n = 4k, k≥ 2, there exist infinite sequences of closed simply connected Riemannian n-manifolds with nonnegative sectional curvature and mutually distinct oriented cobordism type. W. Tuschmann’s research was supported in part by a DFG Heisenberg Fellowship.