1,635 research outputs found
Isolating effects of large and small scale turbulence on thermodiffusively unstable premixed hydrogen flames
Lean turbulent premixed hydrogen/air flames have substantially increased
flame speeds, commonly attributed to differential diffusion effects. In this
work, the effect of turbulence on lean hydrogen combustion is studied through
Direct Numerical Simulation using detailed chemistry and detailed transport.
Simulations are conducted at six Karlovitz numbers and three integral length
scales. A general expression for the burning efficiency is proposed which
depends on the conditional mean chemical source term and gradient of a progress
variable. At a fixed Karlovitz number, the normalized turbulent flame speed and
area both increase linearly with the integral length scale ratio. The effect on
the mean source term profile is minimal, indicating that the increase in flame
speed can solely be attributed to the increase in flame area. At a fixed
integral length scale, both the flame speed and area first increase with
Karlovitz number before decreasing. At higher Karlovitz numbers, the
diffusivity is enhanced due to penetration of turbulence into the reaction
zone, significantly dampening differential diffusion effects
Characterization of the aerosol produced by infrared femtosecond laser ablation of polyacrylamide gels for the sensitive inductively coupled plasma mass spectrometry detection of selenoproteins
A 2D high repetition rate femtosecondlaserablation strategy (2-mm wide lane) previously developed for the detection of selenoproteins in gel electrophoresis by inductively coupled plasma mass spectrometry was found to increase signal sensitivity by a factor of 40 compared to conventional nanosecond ablation (0.12-mm wide lane) [G. Ballihaut, F. Claverie, C. PĂ©cheyran, S. Mounicou, R. Grimaud and R. Lobinski, Sensitive Detection of Selenoproteins in Gel Electrophoresis by High Repetition Rate FemtosecondLaserAblation-Inductively Coupled Plasma Mass Spectrometry, Anal. Chem. 79 (2007) 6874â6880]. Such improvement couldn't be explained solely by the difference of amount of material ablated, and then, was attributed to the aerosol properties. In order to validate this hypothesis, the characterization of the aerosolproduced by nanosecond and high repetition rate femtosecondlaserablation of polyacrylamidegels was investigated. Our 2D high repetition rate femtosecondlaserablation strategy of 2-mm wide lane was found to produce aerosols of similar particle size distribution compared to nanosecond laserablation of 0.12-mm wide lane, with 38% mass of particles < 1 ”m. However, at high repetition rate, when the ablated surface was reduced, the particle size distribution was shifted toward thinner particle diameter (up to 77% for a 0.12-mm wide lane at 285 ”m depth). Meanwhile, scanning electron microscopy was employed to visualize the morphology of the aerosol. In the case of larger ablation, the fine particles ejected from the sample were found to form agglomerates due to higher ablation rate and then higher collision probability. Additionally, investigations of the plasma temperature changes during the ablation demonstrated that the introduction of such amount of polyacrylamidegel particles had very limited impact on the ICP source (ÎT~ 25 ± 5 K). This suggests that the cohesion forces between the thin particles composing these large aggregates were weak enough to have negligible impact on the ICPMS detection
Angular momentum evolution in laser-plasma accelerators
The transverse properties of an electron beam are characterized by two
quantities, the emittance which indicates the electron beam extend in the phase
space and the angular momentum which allows for non-planar electron
trajectories. Whereas the emittance of electron beams produced in laser- plasma
accelerator has been measured in several experiments, their angular momentum
has been scarcely studied. It was demonstrated that electrons in laser-plasma
accelerator carry some angular momentum, but its origin was not established.
Here we identify one source of angular momentum growth and we present
experimental results showing that the angular momentum content evolves during
the acceleration
Wearable Sensor Data Based Human Activity Recognition using Machine Learning: A new approach
International audienceRecent years have witnessed the rapid development of human activity recognition (HAR) based on werable sensor data. One can find many practical applications in this area, especially in the field of health care. Many machine learning algorithms such as Decision Trees, Support Vector Machine, Naive Bayes, K-Nearest Neighbor and Multilayer Perceptron are successfully used in HAR. Although these methods are fast and easy for implementation, they still have some limitations due to poor performance in a number of situations. In this paper, we propose a novel method based on the ensemble learning to boost the performance of these machine learning methods for HAR
Chapter 8. Lifecycle and sustainability
International audienceThe concept of sustainability was developed in order to improve the present human living standards while maintaining the availability of the natural resources for future generations. According to this definition, technological development is a way to improve the sustainability, because it enables to meet human needs by transforming natural resources into useful products. By 2050, the urban world population is expected to approximately double to an estimated 6.4 billion2 and we are aware that the Earthâs natural resources are already limited. In this context, less impacting and more efficient industrial processesâ design represents a real challenge for engineers. From now on, the impacts of new technologies have to be assessed in detail, all along their life cycle, even before their massive industrial deployment.We should be sure that the generated impacts are actually counterbalanced by the improvement of the living standards on Earth. In this chapter, we will consider new technologies related to the development and treatment of lithium batteries. In the first part, we will demonstrate how existing studiesare already taking into account environmental impacts assessment and we will particularly emphasize the main assumptions realized using life cycle assessment (LCA) approaches. In the second part, we will focus on the end-of-life (EOL) of lithium batteries to demonstrate that the entire value chain has to be considered while arbitrating on the acceptability or not of a design decision from an environmental perspective.Les batteries de type lithium connaissent et vont connaitre un essor considĂ©rable compte tenu d'une part de leurs bonnes performances et d'autre part d'une demande sans cesse croissante d'Ă©nergie notamment pour les applications transports. Cet accroissement entraĂźne une consommation accrue de matiĂšres premiĂšres et exige, dĂšs aujourd'hui, de penser « cycle de vie » et « dĂ©veloppement durable » afin de prĂ©server et de pĂ©renniser les ressources naturelles. Ce chapitre dĂ©crit dans un premier temps la mĂ©thodologie de l'« analyse du cycle de vie » appliquĂ©e aux batteries au lithium Ă partir de l'analyse de travaux publiĂ©s dans la littĂ©rature. En particulier les points clefs de ces Ă©tudes sont soulignĂ©s et des amĂ©liorations indispensables dans l'application de la mĂ©thode sont proposĂ©es. Dans un deuxiĂšme temps, le chapitre dĂ©crit un rapide Ă©tat de l'art du recyclage et pointe la nĂ©cessitĂ© d'intĂ©grer et de modĂ©liser tout le cycle de vie des batteries depuis l'extraction des ressource primaires jusqu'Ă la fin de vie
Understanding antral contraction in human stomach through comparison with soft elastic reactor
IntroductionHuman digestion, a major concern due to the rapid development of nutrition-related chronic diseases,rely apart from enzymatic reactions on homogenization of the gastric content by antral contractions.Although recent CFD studies made it possible to explore the influence of the rheologicalproperties of the gastric content on the efficiency of gastric mixing, this key step is yet far from beingfully understood.ObjectiveThis work aims at discussing the influences of contraction frequency and viscosity of the digestain human gastric mixing by comparison with the mixing efficiency of an innovative soft elastic reactor(SER), that induces mixing by vibration of its wall in a similar way as antral contraction waves(ACWs) promote stomach motility.MethodologyIn this view, the SER mixing curve, recently established by Delaplace et al. (2018) using a dimensionalanalysis approach, was considered in order to determine the flow regime under which thegastric mixing of foods (viscosity ranging from 10-3 to 1 Pa.s) was performedMain findingsIt was shown that depending on the viscosity of the SER/stomach content and the amplitude of penetration/ACWs, the number of strikes/contractions required to achieve homogenization was largelydifferent. Moreover, the operating points of SER and ACWs mixing were close, justifying the comparisonbetween both reactors.ConclusionBased on this, the level of mechanical solicitation provided by human peristalsis was shown to benot as high as expected, and the mixing performance of distal region, confined in laminar regime,was found limited and not only due to mechanical solicitations. Further efforts are needed to investigatethe role of other physiological processes such as gastric secretions and gastric emptying inmixing performance of intragastric fluid homogenized by the antral contraction
Reactivity differences between 2,4- and 2,5-disubstituted zirconacyclopentadienes: a highly selective and general approach to 2,4-disubstituted phospholes.
International audienceMixtures of 2,4- and 2,5-disubstituted zirconacyclopentadienes were obtained by the reductive dimerisation of terminal alkynes using the Cp2ZrCl2/lanthanum system. Reactions of dihalophosphines with these mixtures afforded selectively the corresponding 2,4-disubstituted phospholes and 1,4-disubstituted butadienes. A new series of phospholes was characterized by multi-nuclear NMR spectroscopy and X-ray analysis. A possible explanation for the observed selectivity was obtained from X-ray studies and DFT analysis of the intermediate zirconacyclopentadienes
Dynamics of Femtosecond Laser Interactions with Dielectrics
review article written in common (LBNL+CEA)Femtosecond laser pulses appear as an emerging and promising tool for processing wide band-gap dielectric materials for a variety of applications. This article aims to provide an overview of recent progress in understanding the fundamental physics of femtosecond laser interactions with dielectrics that may have the potential for innovative materials applications. The focus of the overview is the dynamics of femtosecond laser-excited carriers and the propagation of femtosecond laser pulses inside dielectric materials
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