Self-induced System Research Articles

Self-induced systems

A minimal Cantor system is said to be self-induced whenever it is conjugate to one of its induced systems. Substitution subshifts and some odometers are classical examples, and we show that these are the only examples in the equicontinuous or expansive case. Nevertheless, we exhibit a zero entropy self-induced system that is neither equicontinuous nor expansive. We also provide non-uniquely ergodic self-induced systems with infinite entropy. Moreover, we give a characterization of self-induced minimal Cantor systems in terms of substitutions on finite or infinite alphabets.

Optimal coding rate of punctured convolutional codes in multiservice wireless cellular systems

The microcellular link performance of future multimedia wireless systems could he improved by using error-correcting punctured convolutional codes in conjunction with slow-frequency hopping. However, the bandwidth expansion due to coding leads to a decrease in the signal-to-interference ratio (SIR) of a frequency-division time-division multiple-access (FD-TDMA) cellular radio link if the system capacity is to be maintained for a given bandwidth allocation. This work determines the best compromise between the power of error correction due to coding and the strength of the self-induced system interference in terms of numerous criteria for speech and data transmission. The aforementioned tradeoff is evaluated in terms of the average bit error rate (BER), the frame error rate, and the burst error distribution for voice transmission. For data transmission with a type 1 hybrid selective-repeat automatic repeat-request (ARQ) protocol, the criteria are average throughput and throughput distribution, the round-trip acknowledgment transmission delay distribution, and the buffering requirements at the transmitter and receiver. The study highlights that punctured codes can significantly improve performance for wireless data links in comparison with the rate 1/2 convolutional coding case or the no-coding case.

Multiplicité des systèmes de transport de la β-alanine et du γ-aminobutyrate chez Pseudomonas aeruginosa

Summary The active transport of β-alanine (β-Ala) and of γ-amino butyric acid (GABA), contrarily to what is observed with α-amino acids, appears to be an inducible process in Pseudomonas aeruginosa A 237 , strain. The transport of β-Ala is induced not only by β-Ala, but also by GABA, β-amino isobutyric acid (β-AIB), 2-amino ethylphosphonic acid (2-AEPh) and 3-amino propylphosphonic acid (3-APrPh). The three above mentioned carboxylic compounds will induce a single β-Ala transport system, whereas their phosphonic analogues give rise to a biphasic uptake. Whatever inducing molecule experimented, β-Ala uptake is inhibited only by GABA and by β-AIB, either competitively (β-Ala or β-AIB induction) or non competitively (GABA, 2-AEPh or 3-APrPh induction). The transport of GABA is similar to that of β-Ala, the same inductors and inhibitors being observed in both cases ; GABA is however the only compound able to induce a single and strictly specific system. The two β-amino acids, β-Ala and β-AIB, inhibit both low and high affinity self-induced systems ; Dixon plots show a purely competitive inhibition at high GABA concentrations and an hyperbolic competitive inhibition at low GABA concentrations. These β-amino acids also appeared as competitive inhibitors for the high affinity systems which were induced by 2-AEPh and 3-APrPh. Despite the fact that β-Ala and β-AIB, as well as 2-AEPh and 3-APrPh, induce transport systems possessing similar kinetics and specificty, the behaviour of the permease activities towards osmotic shock treatment was different : a severe reduction of β-Ala and GABA entry into the cells was observed only after growth on β-Ala, 2-AEPh and GABA. Our results emphasize the complexity of ω-amino acid uptake in Ps. aeruginosa .