Studies on parametric sensitivity and safe operation criteria of batch processes

Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.     

A Convergence-Free Predistortion Technique for Adaptive Linearisation of RF Power Amplifiers

Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB.     

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.     

Miscibility of some chlorinated poly(hydrocarbons) with ethylene-acrylic rubber

The compatibility of an ethylene-acrylic rubber (R) with poly (chloroprene) (CR) and two chlorinated poly-ethylenes, containing 48 (CPE 48) and 25 (CPE 25) wt.-% chlorine, was investigated. Blends with the latter polymer were studied in the complete composition range. The techniques used were phase-contrast microscopy, differential scanning calorimetry, dynamic mechanical and stress-strain testing. The single T_g relaxation of blends and its almost linear variation with composition, together with results obtained using the techniques mentioned, support the view that the systems are miscible at the segmental level. At low rubber contents an antiplasticisation effect was observed for the R/CPE 25 system. At high rubber compositions a small reduction of crystallinity and a melting point depression of the PE phase in CPE were observed. Various equations proposed to predict the T_g of blends and their modulus using pure component data were also tested at varying compositions and temperatures.     

Preparation of a selective receptor for ephedrine for the development of an optical spot test for the detection of ephedrine in human urine using stabilized in air lipid films with incorporated receptor

The present technique describes the preparation of a selective receptor for ephedrine and a simple sensitive spot optical test for the rapid one-shot detection of ephedrine in human urine using lipid films with an incorporated receptor that are synthesized by a chemical reaction with a methacrylate polymer on a glass fiber filter. The selective receptor was synthesized using a resorcin[4]arene receptor and by transforming all the -OH groups into methoxy groups. The lipid films without this receptor provided fluorescence under a UV lamp. The use of the receptor in these films quenched this fluorescence, and the color became similar to that of the filters without the lipid films. A drop of aqueous solution of ephedrine provided a "switching on" of the fluorescence, which allows the rapid detection of this stimulant in human urine at the levels of 10(-8) M concentrations. The effect of potent interferences (i.e., proteins, lipids, ascorbic aid, glucose, leucine, glycine, tartrate, citrate, bicarbonate, and caffeine) was examined. The results showed no interferences from these compounds in concentration levels usually found in human urine samples. Dopamine was also investigated as a potent interfering agent, and the results have shown that the transformation of the hydroxy to methoxy groups has altered the selectivity of the receptor. This species does not cause interference at concentration levels lower than 10(-6) M. A drop of urine containing ephedrine provided also a "switching on" of the fluorescence, which allows the rapid detection of this stimulant in human urine at the levels of 10(-8) M concentrations. The reproducibility of the method was checked in approximately 100 samples, and all of them were found to provide similar results. Note that the colors of the filters remain stable for periods of more than 2 months.     

The net effect of ultraviolet radiation on atmospheric dimethylsulphide over the Southern Indian Ocean

Dimethylsulphide (DMS) in the atmosphere may play an important role in the climate system. This study shows an inverse relationship between ultraviolet extremes and atmospheric DMS, independent of changes in wind speed, sea-surface temperature and photosynthetically active radiation, as measured at Amsterdam Island in the Southern Indian Ocean.     

Mechanical relaxations of poly(vinylidene fluoride) and some of its copolymers

The dynamic mechanical properties of poly(vinylidene fluoride) have been studied under isochronal conditions and the effect of thermal treatment examined. The results are compared with a product of different molecular weight distribution. The study also included the mechanical relaxation spectra of copolymers of vinylidene fluoride and chlorotrifluoroethylene at four compositions and four frequencies as a function of temperature. The thermodynamic parameters associated with the main relaxations were determined and the results discussed on the basis of available information on the drgree of crystallinity, copolymer heterogeneity, and main chain flexibility.