Abstract: The invention relates to a process for bleaching preoxidized paper pulp enabling a pulp having a very high degree of whiteness to be obtained with a limited number of treatment steps and enabling pollution to be reduced without degrading the qualities of the pulp; such a process essentially comprises the combination of the three successive treatment steps, namely:(a) a first step of hot chlorination with gaseous chlorine at a temperature of between about 30.degree. and 80.degree. C., and preferably between 35.degree. and 50.degree. C., in the presence of urea used at a rate of 0.5 to 5% by weight of the chlorine used, and preferably from 1 to 3%, with a concentration of pulp of between 3 and 30%, and a duration of retention of the chlorine of 30 seconds to 45 minutes;(b) a second step of alkaline extraction in the presence of an oxidizing agent of the hypochlorite or peroxide type, at a temperature of between about 30.degree. and 70.degree. C., and at a pH of between about 8 and 12, and preferably between 10.

Abstract: A signal peak detector which can be used for echo suppressors, has a memory in which is written a value which is variable as a function of the incident signal and represents the peak sought, an attenuator of the memorized value; four comparators; three of which compare the instantaneous value of the incident signal with, respectively the memorized value, the attenuated memorized value and a fixed threshold, and the fourth of which compares the attenuated memorized value with the fixed threshold; and a control unit which modifies the memorized value as a function of the result of those comparisons.

Abstract: The invention comes within the field of four-wire telephony. To avoid the closing of a loop between the two unidirectional channels, a half-echo suppressor is provided for each terminal, which comprises mainly a speech detector for the emitting channel, said speech detector having two operational modes: the first sends out a speech indicator signal based on the characteristics of amplitude and sign change on the emitting channel whereas the second compares the amplitude on the emitting channel and the amplitude on the receiving channel and is effective when the receiving channel is active. The invention applies more particularly to a PCM network in combination with a concentrator which uses the inactivity periods of the circuits.