Capteur de resine chelatante pour le prelevement la preconcentration et la determination de metaux traces toxiques (Zn, Cd, Hg, Pb) dans les eaux

The subject of this article is the elaboration of a catcher of toxic metals (Zn, Cd, Hg, Pb) which enables them to be determined at μg 1⁻¹ level.It is known that, at these low concentrations, it is advisable to prevent the sample from being altered in any way between the time of taking and the time of analysis; moreover, it is necessary to proceed, on the one hand, to the pre-concentration of the wanted elements and, on the other hand, to the elimination of the main elements present in water and likely to interfere at the time of analytical determination.We therefore made a catcher which makes it possible to achieve these two desired effects by chromatographic separation and to carry out the conditioning of the sample, in the field, in a well-defined, chemical form, stable in time as a small volume in a solid state, easy to carry and to store.The catcher is in the shape of a small, cylindrical capsule (diameter = 29 mm, thickness = 10 mm) in Makrolon (Lexan) whose bases are made of a nylon cloth and which contains a chelating resin load (Chelex-100, 100–200 mesh).At the time of use, the catcher is put into a dismountable filtering-apparatus which permits percolation of the solution containing the wanted metal traces.Then, to proceed to the analytical determination of the elements it is possible to use two methods: analysis in solution after elution;X-ray fluorescence spectrometry, or else activation analysis on the catcher dried and then pelletized when hot in an hydraulic press.The experimentation has included the following points:

1. 1. Determination of the conditions of chromatographic separation on Chelex-100 resin which permits optimal fixation of Zn, Cd, Hg and Pb and the elution of the main elements Ca, Mg and Fe. We chose soda-citrate medium 7.1 · 10⁻² M at pH = 7.00;

2. 2. Determination of the conditions of use of the catcher and its efficiency according to the main elements in the sample of water.

The process we chose involves a sample of 1 l. of water which is acidified at pH 1 by concentrated HNO₃ and then filtered through a membrane (0.45 μm).The solid residue is examined by X-ray fluorescence spectrometry.To the filtrate are added 100 ml of soda-citrate buffer 7.1 · 10⁻¹ M and the pH is set to seven by addition of NaOH. Then the filtrate is percolated through the Chelex-100 resin catcher (flux = 1.5 ml min⁻¹).Then, it is possible to proceed: either to the elution of toxic metals by HNO₂ 2M to determine them in solution (atomic absorption spectrophotometry, anodic stripping voltammetry); or to pelletizing of the catcher and to the analytical determination by X-ray fluorescence spectromy or activation analysis.The results of these methods are compared with different water: (1) spring warer: (2) over waters and (3) sea-water. The elution method as well as direct analysis of the pelletized catcher gave satisfactory agreement.     

Transmission suivant deux trajets à évanouissement de Rayleiqh : récepteurs optimaux

Propagation over two paths dispersive channel is investigated. The time delay between the two paths is supposed stable and known. The channel is a random one following two statistical laws for the independant two paths : a Rayleigh law for the modulus of the received signal, and a uniform law for the phasis. The structure of the optimal receiver is given either for the simple detection or the transmission of binary data. The probability of instantaneous error as well as other parameters related with the quality of transmission are also evaluated.     

In-pile creep study on mixed oxide (U,Pu)O2

The in-pile creep of a mixed oxide UO₂-PuO₂ under compression was studied up to fission rate of $\text{6 × 10}{}^{13}\text{f cm}{}^{\mathrm{?3}}\text{s}{}^{\mathrm{?1}}$, for stresses up to 26.5 MN m^?2, at temperatures ranging from 700 to 900°C. The results obtained agree with those of other authors. The creep rate is proportional to the applied stress and to the fission yield. However, it is athermal within the temperature range explored and is not affected by the burn-up, which has so far reached 30000 MWd t^?1 (3.6% FIMA). When the sample is under compression the fuel swells under the action of the fission products formed in the oxide during its irradiation. The swelling rate is about that commonly accepted for a clad fuel element. Finally it seems that the oxide swells more when free from stress than when subjected to a stress field, but this point has to be confirmed.     

Multichannel equalised and stabilised gain amplifier for WDMtransmissions

The authors present a new type of optical amplifier for WDM systems. A theoretical comparison between transmission lines using either a conventional stabilised flattened gain amplifier or the proposed multichannel equalised and stabilised gain amplifier shows that the latter can improve WDM transmissions     

Behavior of Bragg gratings, written in germanosilicate fibers,against γ-ray exposure at low dose rate

Bragg gratings have been written within four germanosilicate fibers either by a pulsed or by a continuous-wave exposure of each fiber to a coherent UV two-beam interference pattern. These gratings have been exposed under steady state conditions to γ-ray doses as high as 10 ⁴ Grays. The dose rates ranged between 10 Gy/h and 1.3×10² Gy/h. The transmission spectra of the fibers have been recorded during and after the ⁶⁰Co irradiation, near the grating Bragg wavelengths. Whereas the induced loss reached 600 dB/km near 1.3 μm, no significant change in the spectral characteristics of the gratings could be detected within the experimental accuracy, enabling their future use in a nuclear environment     

Au delà d’une vitesse de groupe: vitesse d’onde et vitesse de signal

A radiated fieldalways appears in a dual, spatial and temporal, aspect. Its spatial one is the wave the author should observe at a given time. Its temporal one is the signalhe receive at a given point. The aim of this paper is then to determine bulk velocities of both signal and wave — without any limiting assumption on their spectral widths — in case the field is being radiated thru a dispersive medium. A realistic criterion is first adopted that enables an accurate measurement of the instant position of the wave, by means of a definite space-marker (the wave center. The same criterion also leads to a similar timemarker (the signal center,) that will be used in measuring the receiving time of the signal. By studying the motion of these markers, an operator U spontaneously appears beside the phase velocity This operator has the same analytical expression as the usual group/signal velocity of a wave packet. Therefore U should be also called group velocity. Both group and phase velocities depend on the transmitting medium only. To the travelling wave then corresponds an uniform motion of its wave center, with some wave velocity. The latter consists of the mean of operator U in a state which is associated with the wave structure at the time origin. To the signal, when received by a fixed transductor, also corresponds some signal velocity. Its value is the inverse of the mean of operator U ^?1 in a state which is associated with the signal structure at the transmitter. Thus, wave velocity and signal velocity not only depend on the transmitting medium, but depend on the emitted signal form too. However both of them become identified with the group velocity U in the particular case of a very narrow spectrum. Thus agreeing with the usual wave packet. In such a case the group velocity turns out to be the velocity of the very marker that belongs to the amplitude of the transmitted analytic signal. Such an approach also enables us to describe signal distortion in a dispersive medium. By analogy, it leads to relating that distortion to Fresnel diffraction. Outside anomalous zones, the above properties are roughly maintened when attenuation is taken into account in relation to dispersion.     

Pretreatment and cleaning of hyperfiltration (reverse osmosis) membranes in municipal wastewater renovation

Membrane fouling is a common cause of poor performance in hyperfiltration systems especially when treating wastewaters usually because it reduces the product flux to uneconomical levels. In the present paper various membrane cleaning methods are reviewed and related factors affecting process performance such as pretreatment, system geometry and membrane choice are discussed. Several leads in developing new membrane cleaning and pretreatment methods are also presented.     

Cathodic behaviour of p-toluenesulfonamides in organic solvents

Cathodic reduction of several secondary and tertiary p-toluenesulfonamides and gem-N-disulfonamides were investigated by cyclic voltammetry and controlled potential electrolysis at mercury electrode in aprotic and protic dmf. In the cleavage of tertiary p-toluenesulfonamides two Faradays per mole were consummed, resulting in the formation of amine and the sulfinate ion. In the case of secondary p-toluenesulfonamides, electrochemically inactive sulfonamide anions were formed at the electrode surface by acid–base reaction between acidic substrate and electrogenerated bases. Sulfonamides anions were obtained also in the solution bulk with adding strong base and by cathodic cleavage of gem-N-disulfonamides in aprotic media. General reduction mechanisms are postulated and structure effects on the scope of the reduction are discussed for more complex sulfonamides.