476 research outputs found
Feedback Enhances Simultaneous Wireless Information and Energy Transmission in Multiple Access Channels
In this report, the fundamental limits of simultaneous information and energy
transmission in the two-user Gaussian multiple access channel (G-MAC) with and
without feedback are fully characterized. More specifically, all the achievable
information and energy transmission rates (in bits per channel use and
energy-units per channel use, respectively) are identified. Furthermore, the
fundamental limits on the individual and sum- rates given a minimum energy rate
ensured at an energy harvester are also characterized. In the case without
feedback, an achievability scheme based on power-splitting and successive
interference cancellation is shown to be optimal. Alternatively, in the case
with feedback (G-MAC-F), a simple yet optimal achievability scheme based on
power-splitting and Ozarow's capacity achieving scheme is presented. Finally,
the energy transmission enhancement induced by the use of feedback is
quantified. Feedback can at most double the energy transmission rate at high
SNRs when the information transmission sum-rate is kept fixed at the
sum-capacity of the G-MAC, but it has no effect at very low SNRs.Comment: INRIA REPORT N{\deg}8804, accepted for publication in IEEE
transactions on Information Theory, March, 201
Biochemical characterization of a cefotaximehydrolysing β-lactamase encoded by a conjugative plasmid
During the nosocomials infections occurring in the intensive care unit of the military hospital of Tunis in 2005, the Enterobacter cloacae BW 1150 strain was isolated from a stool culture. This strain was found to have a high level resistance to broad-spectrum -lactams. Resistance profile against thevarious families of antibiotics was determined using the disc diffusion test. The minimal inhibitory concentrations values showed that this strain was resistant to the -lactams such as ampicillin and the extended spectrum cephalosporins (cefotaxime, ceftriaxon and cefpirome). Analysis of this strain by the disk diffusion test revealed synergies between amoxicillin-clavulanate (AMX-CA) and ceftriaxon, ceftazidime and cefotaxime. Cell sonicate of this isolate is very active against cefotaxime and showed aspecific activity (AS) of 7.54 U/mg for the same antibiotic. This activity was inhibited by the sulbactam and the clavulanic acid. Isoelectrofocusing methods revealed that the crude extract of the E. cloacae BW 1150 strain showed 1 - lactamase activity with an isoelectric piont (pI) of about 8. This activity was transferred by conjugation and was highly expressed in the transconjugant
Electrochemical polymerisation of phenol in aqueous solution on a Ta/PbO2 anode
This paper deals with the treatment of aqueous phenol solutions using an electrochemical technique. Phenol can be partly eliminated from aqueous solution by electrochemically initiated polymerisation. Galvanostatic electrolyses of phenol solutions at concentration up to 0.1 mol dmâ3 were carried out on a Ta/PbO2 anode. The polymers formed are insoluble in acidic medium but soluble in alkaline. These polymers were filtered and then dissolved in aqueous solution of sodium hydroxide (1 mol dmâ3). The polymers formed were quantified by total organic carbon (TOC) measurement. It was found that the conversion of phenol into polymers increases as a function of initial concentration, anodic current density, temperature, and solution pH. The percentage of phenol polymerised can reach 15%
Influence of temperature and applied potential on the permeability of polyphenol films prepared on vitreous carbon in acid and alkaline media
The electrochemical polymerization of phenol is known to rapidly produce a thin insulating film at the anode surface. This film generally blocks further polymerization. The objective of this study is to show that, depending on the operating conditions, polymeric films resulting from phenol oxidation present different properties and that certain films can be so porous that they allow the oxidation of phenol to continue. The deposition of polyphenol films with improved permeability could be attractive in the removal of phenol from polluted solutions. Polyphenol films were prepared in aqueous solution on a vitreous carbon anode either by cyclic voltammetry or by electro-oxidation at constant potential. The apparent permeability P (%) of the films prepared by these techniques was evaluated by monitoring changes in the electrode response towards phenol and potassium ferricyanide at 25 and 85°C and as a function of the potential applied during electropolymerization performed either in acidic (1 mol L-ÂčHâSOâ) or in alkaline (1 mol L-Âč NaOH) aqueous solution. It was shown that: (1) the polyphenol film electrosynthesized in alkaline medium was more permeable than that prepared in acidic medium, (2) the apparent permeability was higher when the polyphenol film was electrosynthesized with simultaneous oxygen evolution and (3) the use of a high temperature in the polyphenol film preparation, especially in the presence of a concomitant oxygen evolution, significantly enhanced its apparent permeability (P â„ 100 %). These results are interpreted in terms of a mixed-transport mechanism involving both pore and membrane diffusion. The effect of the permeability of the polymeric film on the removal of phenol from aqueous solution by electropolymerization is discussed
Comparaison de la composition physicochimique du lait camelin et bovin du Sud tunisien; variation du pH et de lâaciditĂ© Ă diffĂ©rentes tempĂ©ratures
La composition physicochimique du lait de chamelle est variable selon lâalimentation des animaux, les conditions environnementales ainsi que la pĂ©riode de lactation. Dans le but de dĂ©terminer la composition du lait de chamelle du sud tunisien, le lait camelin de la rĂ©gion a Ă©tĂ© comparĂ© Ă celui bovin sur le plan de lâaciditĂ© et du pH du lait des deux espĂšces en fonction de la tempĂ©rature du milieu. Le lait de chamelle est plus acide (17,25 ± 1,035°D) et moins dense (d= 1,027± 0,003) que le lait de vache. Le lait de vache est plus riche en matiĂšre protĂ©ique (34,15 ± 3,11 g/L), matiĂšre sĂšche (119,43 ± 15,34g/L) et azote non protĂ©ique NPN (1,04 ± 0,08g/L). Le suivi de la variation du pH et de lâaciditĂ© du lait camelin et bovin Ă trois tempĂ©ratures diffĂ©rentes (tempĂ©rature ambiante (25°C), Ă 4°C et Ă -4°C) a rĂ©vĂ©lĂ© une acidification plus lente du lait de chamelle dans les trois cas avec une conservation durant 30 heures Ă tempĂ©rature ambiante, 7 jours dans le rĂ©frigĂ©rateur (4°C) alors quelle est de 5 jours pour le lait de vache Ă la mĂȘme tempĂ©rature. La congĂ©lation du lait Ă -4°C peut ainsi constituer une mĂ©thode simple pour la conservation du lait camelin qui nâest accessible que dans les rĂ©gions de sa production.Mots-clĂ©s : Lait, chamelle, vache, composition physicochimique, aciditĂ©,tempĂ©ratur
Influence of temperature and applied potential on the permeability of polyphenol films prepared on vitreous carbon in acid and alkaline media
The electrochemical polymerization of phenol is known to rapidly produce a thin insulating film at the anode surface. This film generally blocks further polymerization. The objective of this study is to show that, depending on the operating conditions, polymeric films resulting from phenol oxidation present different properties and that certain films can be so porous that they allow the oxidation of phenol to continue. The deposition of polyphenol films with improved permeability could be attractive in the removal of phenol from polluted solutions. Polyphenol films were prepared in aqueous solution on a vitreous carbon anode either by cyclic voltammetry or by electro-oxidation at constant potential. The apparent permeability P (%) of the films prepared by these techniques was evaluated by monitoring changes in the electrode response towards phenol and potassium ferricyanide at 25 and 85°C and as a function of the potential applied during electropolymerization performed either in acidic (1 mol L-ÂčHâSOâ) or in alkaline (1 mol L-Âč NaOH) aqueous solution. It was shown that: (1) the polyphenol film electrosynthesized in alkaline medium was more permeable than that prepared in acidic medium, (2) the apparent permeability was higher when the polyphenol film was electrosynthesized with simultaneous oxygen evolution and (3) the use of a high temperature in the polyphenol film preparation, especially in the presence of a concomitant oxygen evolution, significantly enhanced its apparent permeability (P â„ 100 %). These results are interpreted in terms of a mixed-transport mechanism involving both pore and membrane diffusion. The effect of the permeability of the polymeric film on the removal of phenol from aqueous solution by electropolymerization is discussed
CO2 laser beam welding of AM60 magnesium-based alloy
The authors are grateful to FONDERIE MESSIER HONSEL group that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Moraru of the LSIS Laboratory-Arts et MĂ©tiers ParisTech-Aix En Provence-France.Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal
Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots
We report strong heavy hole-light mixing in GaAs quantum dots grown by
droplet epitaxy. Using the neutral and charged exciton emission as a monitor we
observe the direct consequence of quantum dot symmetry reduction in this strain
free system. By fitting the polar diagram of the emission with simple
analytical expressions obtained from kp theory we are able to extract
the mixing that arises from the heavy-light hole coupling due to the
geometrical asymmetry of the quantum dot.Comment: 4 pages, 2 figure
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