The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
A. Caravel - One of the best experts on this subject based on the ideXlab platform.
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Stabilisateurs passifs de tension ou de courant en pont
EDP Sciences, 1Co-Authors: A. CaravelAbstract:The use of a stabilizing Zener diode leaves a slight variation of the output voltage when the input voltage varies. To suppress this residual effect the diode is introduced into a Wheatstone bridge as one of the arms and the bridge dynamically balanced. A careful choice of the elements gives a small output résistance. The anode current of a pentode can be regulated by the same means.Une diode Zener utilisée comme stabilisateur laisse subsister une légère variation de la tension de sortie quand la tension d'alimentation change. On supprime cet effet résiduel en prenant la diode comme branche d'un pont de Wheatstone équilibré en régime dynamique. Par un choix judicieux des éléments, on peut obtenir une faible résistance de sortie. Le même principe peut s'appliquer aux Pentodes pour une régulation de courant
John Linsley Hood - One of the best experts on this subject based on the ideXlab platform.
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Valve Operated Audio Power Amplifiers
Valve and Transistor Audio Amplifiers, 1997Co-Authors: John Linsley HoodAbstract:In a valve amplifier, the output transformer is a source of waveform distortion, so, for an output total harmonic distortion (THD) of better than 0.1% over the bulk of the audible frequency spectrum, overall loop negative feedback (NFB), including the output transformer, must be employed. The amount of this, which is needful to employ, would depend mainly on the quality of the output transformer and on the type of output valve used. For a well made LS transformer and triode connected output valves, this degree of linearity could be met with some 20dB of negative feedback (NFB). For U-L connected beam-tetrodes, this performance would require some 26dB of NFB, while pentode or beam-tetrode output valves; an NFB ratio of nearer 30dB was needed. Beam tetrodes were, in general, slightly more linear than Pentodes.
Cecilia Leao - One of the best experts on this subject based on the ideXlab platform.
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transport and utilization of hexoses and pentoses in the halotolerant yeast debaryomyces hansenii
Applied and Environmental Microbiology, 1999Co-Authors: Alexandra Nobre, Cândida Lucas, Cecilia LeaoAbstract:Debaryomyces hansenii is a yeast species that is known for its halotolerance. This organism has seldom been mentioned as a pentose consumer. In the present work, a strain of this species was investigated with respect to the utilization of pentoses and hexoses in mixtures and as single carbon sources. Growth parameters were calculated for batch aerobic cultures containing pentoses, hexoses, and mixtures of both types of sugars. Growth on pentoses was slower than growth on hexoses, but the values obtained for biomass yields were very similar with the two types of sugars. Furthermore, when mixtures of two sugars were used, a preference for one carbon source did not inhibit consumption of the other. Glucose and xylose were transported by cells grown on glucose via a specific low-affinity facilitated diffusion system. Cells derepressed by growth on xylose had two distinct high-affinity transport systems for glucose and xylose. The sensitivity of labeled glucose and xylose transport to dissipation of the transmembrane proton gradient by the protonophore carbonyl cyanide m-chlorophenylhydrazone allowed us to consider these transport systems as proton symports, although the cells displayed sugar-associated proton uptake exclusively in the presence of NaCl or KCl. When the Vmax values of transport systems for glucose and xylose were compared with glucose- and xylose-specific consumption rates during growth on either sugar, it appeared that transport did not limit the growth rate.
B. Bowers - One of the best experts on this subject based on the ideXlab platform.
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A century of electronics [the evolution of vacuum tubes]
Iee Review, 2004Co-Authors: B. BowersAbstract:This article traces the evolution of vacuum tubes (thermionic valves) from their origins in incandescent filament lamps. It details the use of diodes and triodes in early radio transmission and detection, being the building blocks of rectifiers, amplifiers and oscillators. It also mentions the later developments of tetrodes and Pentodes and concludes that the end of the vacuum tube era began with the introduction of the point contact transistor.
Sébastien Givry - One of the best experts on this subject based on the ideXlab platform.
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Optimisation de procédés de fermentation lactique sur sirop de son de blé et Purification et caractérisation d'une arabinose isomérase de Lactobacillus bifermentans
2006Co-Authors: Sébastien GivryAbstract:La production d’acide lactique à partir de ressources renouvelables telles que le son de blé comme alternative aux produits dérivés du pétrole présente un intérêt grandissant, notamment pour la production de polymère biodégradable d’acide lactique. Le son de blé est un co-produit composé d’hexoses et de pentoses et son utilisation comme substrat de faible coût dans diverses industries est envisagée. Cependant, peu de microorganismes consomment rapidement et efficacement les pentoses pour donner un seul et même produit. Dans le but de fermenter ces pentoses, un criblage a été réalisé et a permis d’isoler, une bactérie lactique Lactobacillus bifermentans qui par la suite nous avons cherché à optimiser la production d’acide lactique de cette souche par des méthodes statistiques de surfaces de réponse, et cela, pour deux procédés de fermentation en réacteur batch : cellules libres et par inclusion des cellules sur calcium-alginate. Dans un second temps, nous avons optimisé la production des activités xylose isomérase et arabinose isomérase de Lactobacillus bifermentans. Ces enzymes présentent en effet un intérêt commercial important au niveau industriel pour la production de sirop de fructose et de tagatose. La xylose isomérase joue également un rôle dans la production d’éthanol à partir du xylose en fermentation simultanée avec des levures. Après amélioration des conditions de culture, ces enzymes ont été produites en fermenteur, purifiées et caractérisées. Finalement, Lactobacillus bifermentans ne possède qu’une seule enzyme, l’arabinose isomérase, qui réalise ces deux activités et qui présente des similitudes avec l’arabinose isomérase de Lactobacillus pentosus.