427 research outputs found
Performance Analysis of a Reciprocating Piston Expander and a Plate Type Exhaust Gas Recirculation Boiler in a Water-Based Rankine Cycle for Heat Recovery from a Heavy Duty Diesel Engine
The exhaust gas in an internal combustion engine provides favorable conditions for a waste-heat recovery (WHR) system. The highest potential is achieved by the Rankine cycle as a heat recovery technology. There are only few experimental studies that investigate full-scale systems using water-based working fluids and their effects on the performance and operation of a Rankine cycle heat recovery system. This paper discusses experimental results and practical challenges with a WHR system when utilizing heat from the exhaust gas recirculation system of a truck engine. The results showed that the boilerâs pinch point necessitated trade-offs between maintaining adequate boiling pressure while achieving acceptable cooling of the EGR and superheating of the water. The expander used in the system had a geometric compression ratio of 21 together with a steam outlet timing that caused high re-compression. Inlet pressures of up to 30 bar were therefore required for a stable expander power output. Such high pressures increased the pump power, and reduced the EGR cooling in the boiler because of pinch-point effects. Simulations indicated that reducing the expanderâs compression ratio from 21 to 13 would allow 30% lower steam supply pressures without adversely affecting the expanderâs power output
Patterns of responding differentiate intravenous nicotine self-administration from responding for a visual stimulus in C57BL/6J mice
Testing genetically engineered mice in a reliable nicotine self-administration procedure could provide important insights into the molecular mechanisms underlying nicotine reinforcement.
We assessed operant responding for intravenous nicotine infusions in C57BL/6J male mice under a fixed-ratio 3 schedule of reinforcement in which a visual cue was contingently associated with drug delivery.
Acquisition, dose-response function, extinction, and cue-induced reinstatement of operant behavior were characterized. Low nicotine doses (0.001-0.06Â mg/kg/infusion) elicited response rates similar to those supported by saline, whereas a higher dose (0.1Â mg/kg/infusion) decreased responding. Using an identical procedure to assess cocaine self-administration in an independent group of mice yielded an inverted U-shaped dose-response curve. Other mice trained to respond exclusively for the visual stimulus earned a similar number of reinforcers as mice self-administering saline or low nicotine doses, although with a lower selectivity for the active lever and their response rates were sensitive to the discontinuation and resumption of cue light presentation. Finally, patterns of responding for nicotine, cocaine, or the visual stimulus alone were analyzed using frequency distributions of inter-response intervals and extended return maps. These analyses revealed unique properties of nicotine, which dose-dependently delayed the first response post-timeout and increased the regularity of lever pressing activity.
Nicotine did not enhance the reinforcing properties of the visual cue paired with drug delivery. Interestingly, however, patterns of responding could differentiate nicotine self-administration from responding for a visual stimulus or saline and indicated that nicotine functioned as a salient stimulus driving highly regular operant behavior
Identification des dermatophytes par spectrométrie de masse MALDI-TOF
Introduction
Lâidentification des dermatophytes par les mĂ©thodes microbiologiques conventionnelles est souvent longue et fastidieuse. La technique de spectromĂ©trie de masse et sa variante MALDI-TOF (Matrix Assisted Laser Desorption Ionisation-Time of Flight) est un nouvel outil utilisĂ© pour lâidentification des bactĂ©ries et des levures dans les laboratoires dâanalyses mĂ©dicales. Nous avons rĂ©cemment dĂ©veloppĂ© une mĂ©thode standardisĂ©e pour lâidentification en routine des champignons filamenteux Ă partir de culture en milieu solide. Lâobjectif de cette Ă©tude est dâĂ©tendre cette mĂ©thode standardisĂ©e Ă lâidentification des dermatophytes dans lâactivitĂ© de routine du laboratoire.
Matériel et méthode
Une banque de rĂ©fĂ©rence contenant les spectres de masse de 44 souches parfaitement caractĂ©risĂ©es correspondants Ă 13 espĂšces de dermatophytes a Ă©tĂ© gĂ©nĂ©rĂ©e sur un UltraFlex (BruckerDaltonics, Allemagne) couplĂ© au logiciel MaldiBiotyper v2.1. Par la suite, 133 souches isolĂ©es de prĂ©lĂšvements cliniques ont Ă©tĂ© identifiĂ©es en comparant leur spectre Ă ceux inclus dans la banque de rĂ©fĂ©rence : lâidentification dâespĂšce a Ă©tĂ© retenue si le Log Score (LS) obtenu Ă©tait supĂ©rieur ou Ă©gal Ă 1,7. Enfin, lâidentification par MALDI-TOF a Ă©tĂ© considĂ©rĂ©e comme correcte en cas de concordance avec lâidentification morphologique ou molĂ©culaire des isolats cliniques.
RĂ©sultats
Lâidentification par spectromĂ©trie de masse(SM) a Ă©tĂ© correcte pour 130 (97,8 %) des isolats. Pour 2 isolats identifiĂ©s conventionnellement comme Microsporum canis, lâidentification par SM nâa pas pu gĂ©nĂ©rer de spectre avec un LS valide. Pour un isolat correspondant Ă Microsporum audouinii, la SM a gĂ©nĂ©rĂ© une mauvaise identification. Tous les isolats ont pu ĂȘtre identifiĂ©s aprĂšs seulement 3 à 6 jours de culture avant lâapparition des caractĂšres morphologiques conventionnels dâidentification.
Conclusion
Le protocole de SM utilisĂ© pour lâidentification des champignons filamenteux au laboratoire est applicable aux dermatophytes. Une identification dâespĂšce peut ĂȘtre obtenue en 3 à 6 jours alors quâune identification conventionnelle qui nĂ©cessite notamment des milieux de cultures complĂ©mentaires demande 2 à 3 semaines
Supersymmetric Self-Gravitating Solitons
We show that the `instantonic' soliton of five-dimensional Yang-Mills theory
and the closely related BPS monopole of four-dimensional Yang-Mills/Higgs
theory continue to be exact static, and stable, solutions of these field
theories even after the inclusion of gravitational, electromagnetic and, in the
four-dimensional case, dilatonic interactions, provided that certain
non-minimal interactions are included. With the inclusion of these
interactions, which would be required by supersymmetry, these exact
self-gravitating solitons saturate a gravitational version of the Bogomol'nyi
bound on the energy of an arbitrary field configuration.Comment: 39 pages, DAMTP R-93/27, phyzz
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