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排序方式: 共有1256条查询结果,搜索用时 15 毫秒
81.
Guillaume Mouret Dominique Thomas Sandrine Chazelet Jean-Christophe Appert-Collin Denis Bemer 《Journal of aerosol science》2009,40(9):762-775
This paper presents experimental data for penetration of nanoparticles in the 4–30 nm size range through fibreglass filters perforated with defined pinholes at 5 and 15 cm/s. Results show that, when the filter is damaged, penetration increases with decreasing particle diameter. This lower performance is more significant for filters with high airflow resistance. A model explaining the experimental data has been designed based on balanced, laminar airflow inside the pinhole; these conditions were confirmed by detailed study. The experimental points agreed very closely with this model. 相似文献
82.
Bernard Charra Guillaume Jean Jean-Marc Hurot Jean-Claude Terrat Thierry Vanel Cyril VoVan Foued Maazoun Charles Chazot 《Hemodialysis international. International Symposium on Home Hemodialysis》2001,5(1):42-50
While nephrologists wait for the ideal, non invasive, inexpensive, precise, and reproducible tool to evaluate extracellular volume (ECV), they need to exert their clinical acumen in the quest of that holy grail, dry weight (DW). Estimation of DW using a clinical approach based on blood pressure (BP) and ECV is feasible and reliable as shown by successful experiences in various dialysis modes over more than three decades. But a need still exists to resolve difficulties associated with accurate assessment of BP (methods and circumstances of measurement, and the confounding effects of antihypertensive drugs) and ECV (evaluation of weight changes unrelated to ECV, lack of specificity and sensitivity of clinical symptoms, lag time, confusion in terminology). An essential point in clinical assessment of DW is that a normal BP is at the same time the target and the crucial index of DW achievement. For this reason, a trialand‐error “probe” process has to be used at intervals to make sure that the dry weight target point is correctly estimated. The various “non clinical” methods proposed for dry weight assessment increase the complexity and the cost of hemodialysis. They are, in the present state of things, more clinical research than practice tools. They do not replace clinical judgment. 相似文献
83.
Russell G. Smith William F. Reiter Guillaume Vitupier Steven C. Lovejoy 《Canadian Metallurgical Quarterly》2005,10(1):5-11
Stress analysis of the components of a sheave used to transfer loads between the lift span and counterweight in a movable span bridge is investigated. Stress analysis is a requirement for properly designing such sheaves. Modeling of the mechanism of load transfer from the wire ropes to the sheave is accomplished in three ways: (1) the traditional manner using a uniform pressure distribution; (2) using a varying pressure distribution developed from belt/pulley theory; and (3) using the finite-element method with nonlinear contact elements between the wire rope and the sheave. Internal stresses in the sheave are calculated using uniform distributed pressure and a varying pressure distribution. It is determined that the load distribution on the sheave from the wire ropes is precisely the same for the nonlinear contact analysis and the belt/pulley analysis. The internal stress analysis results show that the traditional, uniformly distributed load representation is less conservative than the more realistic belt/pulley load representation. A methodology is developed that can be utilized to more accurately model the load transfer representation without the complexity of nonlinear analyses. 相似文献
84.
In this study, the sooting tendencies of primary reference fuels (PRFs) are measured in term of yield sooting indices (YSIs) in methane diffusion flames doped with the vapors of PRFs. The present paper represents an incremental advance complementing the original methodology prescribed by McEnally and Pfefferle. The influence of both PRF formulation and CO2 dilution of the coflowing air on the YSIs is also assessed. The diffusion flames burning in a coflowing oxidizer stream are established over the Santoro’s burner and vapor of the liquid fuel to be investigated is injected into the fuel stream. Laser extinction measurements are performed to map the two-dimensional field of soot volume fraction in the flame. For the pure liquid hydrocarbons investigated, i.e., n-hexane, n-heptane, isooctane, and benzene, the YSI reported in the original paper by McEnally and Pfefferle quantitatively predict the sooting propensities, measured here at much higher dopant concentrations. The present study therefore extends the consistency of the YSI methodology on the Santoro’s burner. For blends of n-heptane and isooctane, the sooting tendency of doped flames exhibits regular and monotonic trends and decreases with increasing n-heptane mole fraction or CO2 dilution. Interestingly, the evolution of YSI with the isooctane mole fraction exhibits a strong similarity for varying CO2 mole fraction. A quadratic least-squares fit is then derived, providing a phenomenological model of YSI as a function of both isooctane mole fraction in the fuel stream and CO2 mole fraction in the oxidizer. A non-negligible cross effect of PRF formulation and CO2 dilution on YSI is revealed. The method elaborated within the framework of the present paper could be extended to surrogate fuels. This would help develop a comprehensive database and empirical correlations that could predict the sooting propensities of different surrogate fuels, therefore their potentially mitigationed soot production through control of fuel composition and/or exhaust gas recirculation. This database would also be useful for the validation of CFD simulations incorporating sophisticated model of soot production. 相似文献
85.
Hydrogen is a clean and energetic fuel, and its oxidation mechanism is a subset of the oxidation mechanisms of all hydrocarbons. Therefore, the validation of the available kinetic schemes is of great importance. In the current study, experimental measurements of laminar flame speeds and modeling studies were performed for H2–air premixed flames over a wide range of equivalence ratios (0.5–4.0) and pressures (0.2–3 bar). The large scale in mixture and thermodynamic conditions allows a better understanding of the peculiar behavior of hydrogen flame speeds with pressure. Two very recent detailed chemical kinetic mechanisms for hydrogen combustion were selected. Excellent agreement was observed between calculations and experimental results, confirming the validity of the kinetic schemes selected. The kinetic analyses performed allow proposing an explanation for the nonmonotonic variation of hydrogen/air flame speed with pressure observed in the experiments. 相似文献
86.
87.
In this paper, the chemical response of different species to turbulent effects is investigated in the context of one-dimensional laminar non-premixed flamelets. Turbulent effects are modeled as abrupt changes in the scalar dissipation rate. One-dimensional unsteady flamelet calculations assuming unity-Lewis number for all species are performed for an ethylene/air configuration. From the time-evolution of the species mass fractions, it is found that transient effects are not substantial for radicals such as OH and H, and species such as CO,CO2 and C2H2, consistent with their small characteristic chemical time scales. The steady state flamelet assumption for these species is well justified and their mass fractions can be pre-tabulated using the steady state flamelet solutions legibly. On the other hand, aromatic species are characterized by relatively slow chemistry, and substantial transient effects are observed for these species. The evolution of their mass fractions and chemical source terms are studied through a reaction flux analysis. Specifically for Polycyclic Aromatic Hydrocarbons (PAH), the chemical production terms are found to be linearly proportional to the mass fraction of smaller aromatic species, and the chemical consumption terms are found to be linearly proportional to their own mass fractions. Based on the unsteady flamelet results, the validity of various existing flamelet-based pre-tabulation methods is examined, and a new linear relaxation model is proposed for PAH. The proposed relaxation model is validated through the unsteady flamelet formulation, and results are compared against full chemistry calculations. 相似文献
88.
A Complete Separation of Hexane Isomers by a Functionalized Flexible Metal Organic Framework 下载免费PDF全文
Patricia A. P. Mendes Patricia Horcajada Sébastien Rives Hong Ren Alírio E. Rodrigues Thomas Devic Emmanuel Magnier Philippe Trens Hervé Jobic Jacques Ollivier Guillaume Maurin Christian Serre José A. C. Silva 《Advanced functional materials》2014,24(48):7666-7673
The separation ability of branched alkane isomers (nHEX, 3MP, 22DMB) of the flexible and functionalized microporous iron(III) dicarboxylate MIL‐53(Fe)‐(CF3)2 solid is evaluated through a combination of breakthrough experiments (binary or ternary mixtures), adsorption isotherms, X‐ray diffraction temperature analysis, quasi‐elastic neutron scattering measurements and molecular dynamics simulations. A kinetically controlled molecular sieve separation between the di‐branched isomer of hexane 22DMB from a mixture of paraffins is achieved. The reported total separation between mono‐ and di‐branched alkanes which was neither predicted nor observed so far in any class of porous solids is spectacular and paves the way towards a potential unprecedented upgrading of the RON of gasoline. 相似文献
89.
Morin G Juillot F Casiot C Bruneel O Personné JC Elbaz-Poulichet F Leblanc M Ildefonse P Calas G 《Environmental science & technology》2003,37(9):1705-1712
The oxidation of Fe(II) in acid mine drainage (AMD) leads to the precipitation of Fe(III) compounds which may incorporate toxic elements, such as arsenic (As), within their structure or adsorb them at their surface, thus limiting their mobility. The present work provides evidence for spatial and seasonal variations of microbial activity that influence arsenite oxidation and As immobilization in the heavily contaminated AMD from the Carnoulès mine, Gard, France ([As III] = 80 to 280 mg x L(-1) in the acidic spring draining the waste-pile). In the first tens of meters of the AMD, the rapid oxidation of Fe(II) leads to the coprecipitation of large amounts of As with Fe(III) in bacterial mats. XRD, XANES, and SEM analyses of sediments and stromatolite samples revealed the unusual formation of As(III)-rich compounds, especially nanocrystalline tooeleite, Fe6(AsO3)4(SO4)(OH)4 x 4H2O, a rare ferric arsenite sulfate oxy-hydroxide mineral, together with XRD-amorphous mixed As(III)/As(V)-Fe(III) oxy-hydroxide compounds. In the wet season, the suspended sediments of the upstream zone essentially consist of tooeleite associated with am-As(III)-Fe(III) oxy-hydroxides, while am-As(V)-Fe(III) oxy-hydroxides, having As:Fe molar ratios as high as 0.6-0.8, dominate in the dry season. Comparing natural and bioassay samples revealed that the formation of As(III)-rich compounds in the wet season may be related to the metabolic activity of bacterial strains able to oxidize Fe(II) but not As(III). One of these strains, having an Acidithiobacillus ferrooxidans genotype, has been isolated from the Carnoulès AMD. In contrast, the formation of As(V)-rich compounds in the dry season can be related to both biotic and abiotic oxidation of As(III) to As(V). Some Thiomonas strains isolated from the Carnoulès AMD were shown to be able to catalyze the oxidation of As(III) to As(V) in solution. Therefore, they can promote the formation of mixed As(V)-Fe(III) oxy-hydroxides, provided enough Fe(II) oxidizes. These results yield a better understanding of natural processes at this site and may help in designing efficient As-removal processes. 相似文献
90.
Guillaume Castanet Bruno Frackowiak Cameron Tropea Fabrice Lemoine 《International Journal of Heat and Mass Transfer》2011,54(15-16):3267-3276
The temperature field within evaporating ethanol droplets is investigated, relying on the two-color laser induced fluorescence (LIF) measurement technique and on a Direct Numerical Simulation (DNS). The configuration studied corresponds to a monodisperse droplet stream in a diffusion flame sustained by the droplet vapor. An experimental probe volume, small compared to the droplet size, is used to characterize the temperature field within the droplets, whereas DNS takes into account key aspects of the droplet heating and evaporation such as the non-uniform and transient stress, and the mass and heat transfer coefficients at the droplet surface. These investigations reveal that the frictional stresses are strongly reduced due to the small spacing between the droplets. They also show that the Marangoni effect has a significant influence on the internal motion and hence on the internal temperature field. 相似文献