Le problème des isopérimètres sur les surfaces ouvertes à courbure positive

Sans résumé     

Photoacoustic spectroscopy of photoactive matter — Applications to photographic emulsions

A new technique — the photoacoustic spectroscopy with microphone detection has been successfully applied to the studies of spectral sensitivity of silver halide emulsions. Regardless of the fact that the sensitivity of photographic emulsions is greater or comparable with the detectivity of real photoacoustic transducers (i.e. the photoacoustic cell with microphone or piezoelectric transducer), absorption-like spectra of strongly diffusive and nontransparent silver halide emulsions can be readily recorded. Applications of this new technique for the studies of silver halide emulsions bears full potential advantages of photoacoustic spectroscopy. Particularly we demonstrate priority of the new technique over the conventional photographic sensitometry or reflectance spectroscopy both in qualitative and quantitative manner. Photoacoustic measurements of photochemical decomposition rates are shown and suggestions for the measurements of excitation energy transfer efficiencies are given. The results clearly show a unique applicability of the technique in fundamental as well as industrial research and process control of the photographic emulsion production.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.The autors would like to acknowledge the ORWO co. (German Democratic Republik) for supplying the model silver halide emulsions, the ILFORD co. for the supply of the sample of commercial films materials and FUJI co. for sending the sensitogram of their film NEOPAN SS).     

Detection of Pesticides in the Environment Using Biosensors Based on Cholinesterases

Abstract

Amperometric biosensors based on acetylcholinesterase or butyrylcholinesterase were used for the kinetic determination of organophosphate and carbamate pesticides. The current of the biosensor I_ss was measured continuously with substrate; the addition of samples with pesticides resulted in the time decrease of the current dl/dt. The relative inhibition RI=(dl/dt)I_ss was used as the signal for evaluations. For several pesticides, different calibration curves (dependencies of RI on concentration c) were obtained depending on the affinity of the individual pesticide to the cholinesterase used. This affinity was described using the bimolecular inhibition constant k_i. The single calibration curve independent on the type of pesticide was obtained as the dependence of RI on the product k_ic, thus indicating the effects of both concentration and inhibiting properties on the response of the biosensor. The relative inhibition was used to characterise anticholinesterase toxicity of the sediments collected from the Morava River and its tributary streams. The influence of both point (large cities) and nonpoint (agriculture) sources of pollution was identified.     

Über einige gemischte Äther des Hydrochinons

Ohne Zusammenfassung     

A theory of a receiving antenna in a moving isotropic plasma

We analyze the response of a dipole antenna to the noise-like and/or regular (quasimonochromatic) plasma oscillations and waves. The antenna is immersed in an isotropic plasma moving with velocity greater than the electron thermal velocity. In the case of a noise field, we calculate the squared spectral power density of the noise voltage at the input of a receiving antenna for frequencies close to the electron plasma frequency. It is shown that the main contribution to the noise is made by the radiation due to the excitation of waves at anomalous Doppler frequencies. In the case of an incident monochromatic wave, the mean square voltage at the antenna input is calculated as a function of the wave frequency and angle of arrival. It is shown that the effective antenna length can differ strongly from the geometrical length of the dipole. This fact results from the dispersion of longitudinal waves ensuring that many plane waves (a continuum, in the limiting case) contribute to the re-radiated field for a given direction of propagation of the radiation energy.     

Comparative Electrochemical and Spectroscopic Studies of I‐Motif‐forming DNA Nonamers

The paper shows the structural diversity of cytosine (C)‐rich oligodeoxynucleotides (ODNs) arising from their detail nucleotide sequence and experimental conditions. In slightly acidic solutions, the ODN nonamers with different adenine (A) and cytosine (C) sequences can adopt non‐canonical structures involving protonated bases. A distinct secondary structure formed in (C)‐rich sequences, called i‐motif (iM), consists of hemiprotonated and intercalated cytosine base pairs (C.C⁺). Folding and unfolding of particular structures in solutions were monitored by ¹H NMR and CD spectroscopies and native polyacrylamide gel electrophoresis (PAGE), which are capable to determine their structural characteristics. Effects of sequences and their proclivity to formation of the iM on electrochemical behaviour of the ODN nonamers were studied by electrochemical methods. The LSV signals of A and C obtained from the reductive dissolution of ODN adsorption layers on a hanging mercury drop electrode were processed by elimination voltammetry with linear scan (EVLS), which revealed complex effects of the nonamer properties (namely their primary and secondary structure confirmed in solution) on their adsorption and reduction activity.     

Experimental investigations on steady wake effects in a high-lift turbine cascade

This paper reports on the investigation of steady wake effects in cascades. An annular cascade rig, where two stators having the same blade pitch can be circumferentially traversed relatively to each other, is used to analyse the profile losses and the boundary layer development of the downstream stator for different circumferential positions of the upstream stator (clocking positions). Different measurement techniques are used such as three-hole pressure probes, and hot wire- and surface-mounted hot-film probes. The results show a varying pressure loss coefficient of the downstream cascade (S2) for different clocking positions of the upstream cascade (S1_SP).