Experimental study and discrete element method simulation of Geldart Group A particles in a small-scale fluidized bed

Geldart Group A particles are of great importance in various chemical processes because of advantages such as ease of fluidization, large surface area, and many other unique properties. It is very challenging to model the fluidization behavior of such particles as widely reported in the literature. In this study, a pseudo-2D experimental column with a width of 5 cm, a height of 45 cm, and a depth of 0.32 cm was developed for detailed measurements of fluidized bed hydrodynamics of fine particles to facilitate the validation of computational fluid dynamic (CFD) modeling. The hydrodynamics of sieved FCC particles (Sauter mean diameter of 148 µm and density of 1300 kg/m³) and NETL-32D sorbents (Sauter mean diameter of 100 µm and density of 480 kg/m³) were investigated mainly through the visualization by a high-speed camera. Numerical simulations were then conducted by using NETL’s open source code MFIX-DEM. Both qualitative and quantitative information including bed expansion, bubble characteristics, and solid movement were compared between the numerical simulations and the experimental measurement. The cohesive van der Waals force was incorporated in the MFIX-DEM simulations and its influences on the flow hydrodynamics were studied.     

The dynamic multi-period vehicle routing problem

This paper considers the dynamic multi-period vehicle routing problem which deals with the distribution of orders from a depot to a set of customers over a multi-period time horizon. Customer orders and their feasible service periods are dynamically revealed over time. The objectives are to minimize total travel costs and customer waiting, and to balance the daily workload over the planning horizon. This problem originates from a large distributor operating in Sweden. It is modeled as a mixed integer linear program, and solved by means of a three-phase heuristic that works over a rolling planning horizon. The multi-objective aspect of the problem is handled through a scalar technique approach. Computational results show that the proposed approach can yield high quality solutions within reasonable running times.     

Bio-optical relationships for the northern Adriatic Sea

The first three years of a time-series of marine bio-optical measurements performed from an oceanographic tower in the northern Adriatic Sea are used to derive empirical relationships for ocean colour applications in coastal waters. The site presents bio-optical characteristics pertaining to Case 1 and to Case 2 waters. Log linear relationships allow the diffuse attenuation coefficient for downwelling irradiance, K_{E d}, at different wavelengths to be derived from its value at 490?nm. A local empirical algorithm making use of the remote sensing reflectance ratio R _rs(490)/R _rs(555) is shown to provide lower surface chlorophyll-a values (by a factor of 2 to 4) in the range 0.1–1.0?mg?m^?3 than the SeaWiFS OC2v4 algorithm.     

Instrumented tracer for Lagrangian measurements in Rayleigh-Bénard convection

We have developed novel instrumentation for making Lagrangian measurements of temperature in diverse fluid flows. A small neutrally buoyant capsule is equipped with on-board electronics which measures temperature and transmits the data via a wireless radio frequency link to a desktop computer. The device has 80 dB dynamic range, resolving millikelvin changes in temperature with up to 100 ms sampling time. The capabilities of these "smart particles" are demonstrated in turbulent thermal convection in water. We measure temperature variations as the particle is advected by the convective motion and analyze its statistics. Additional use of cameras allow us to track the particle position and to report here the first direct measurement of Lagrangian heat flux transfer in Rayleigh-Bénard convection. The device shows promise for opening new research in a broad variety of fluid systems.     

Qualitative and quantitative conditions for the transitivity of perceived causation:

If A caused B and B caused C, did A cause C? Although laypersons commonly perceive causality as being transitive, some philosophers have questioned this assumption, and models of causality in artificial intelligence are often agnostic with respect to transitivity. We consider two formal models of causation that differ in the way they represent uncertainty. The quantitative model uses a crude probabilistic definition, arguably the common core of more sophisticated quantitative definitions; the qualitative model uses a definition based on nonmonotonic consequence relations. Different sufficient conditions for the transitivity of causation are laid bare by the two models: The Markov condition on events for the quantitative model, and a so-called saliency condition (A is perceived as a typical cause of B) for the qualitative model. We explore the formal and empirical relations between these sufficient conditions, and between the underlying definitions of perceived causation. These connections shed light on the range of applicability of each model, contrasting commonsense causal reasoning (supposedly qualitative) and scientific causation (more naturally quantitative). These speculations are supported by a series of three behavioral experiments.     

A Compared Study of Two Correctness Proofs for the Standardized Algorithm of ABR Conformance

The ABR conformance protocol is a real-time program that controls dataflow rates on ATM networks. A crucial part of this protocol is the dynamical computation of the expected rate of data cells. We present here a modelling of the corresponding program with its environment, using the notion of (parametric) timed automata. A fundamental property of the service provided by the protocol to the user is expressed in this framework and proved by two different methods. The first proof relies on inductive invariants, and was originally verified using theorem-proving assistant COQ. The second proof is based on reachability analysis, and was obtained using model-checker HYTECH. We explain and compare these two proofs in the unified framework of timed automata.     

Theoretical and Kinetic Analysis of the Esterification of Undecylenic Acid with Glycerol

The synthesis of undecylenic acid partial esters can be performed at mild temperature with a classical esterification reaction catalyzed by dodecylbenzene sulfonic acid (DBSA). A semi-empirical molecular modeling on the different reaction intermediates indicates that DBSA can strongly decrease their heats of formation through hydrogen bonding. Diester formation seems to be thermodynamically favored with a selectivity for alpha, alpha, or alpha, beta forms that depend on the geometry of the catalyst-intermediate configuration. Triesters are not favored but a high selectivity for monoesters requires a kinetic control. Experimental approach, considering different DBSA concentrations and temperature partially confirms the theoretical predictions but surfactant properties of DBSA and monoesters may induce nonpredicted geometries. Global apparent activation energies are calculated, corresponding to the formation and hydrolysis of mono and diesters. If water trapping allows the decrease of hydrolysis reaction constants, the presence of water and subsequent phase separation may explain differences between theoretical and experimental results and could help increasing monoester selectivity.     

Prevalence and characterization of antibiotic resistant Enterococcus faecalis in French cheeses

Prevalence of enterococci and antibiotic resistance profiles of Enterococcus faecalis was analyzed in 126 French cheeses from retail stores. Forty-four percent of pasteurized or thermised-milk cheeses, and up to 92% of raw-milk cheeses contained detectable enterococci. A total of 337 antibiotic resistant enterococci were isolated in 29% and 60% of pasteurized-milk and raw-milk cheeses, respectively. E. faecalis was the predominant antibiotic resistant species recovered (81%), followed by Enterococcus faecium (13%), and Enterococcus durans (6%). The most prevalent antibiotic resistances were tetracycline (Tet) and minocycline (Min), followed by erythromycin (Ery), kanamycin (Kan) and chloramphenicol (Cm). The most common multiple antibiotic resistance phenotype was Cm Ery Kan Min Tet. The occurrence of antibiotic genes, as searched by PCR, was 100 % for aph3′IIIa, 96 % for ermB, 90 % for tetM and 80 % for catA in isolates resistant to Kan, Ery, Tet or Cm, respectively. MLST analysis of 30 multidrug resistant E. faecalis revealed that ST19, CC21, CC25 and CC55 isolates were the most common in cheeses. In conclusion, as in many other European countries, French cheeses do contain enterococci with multiple antibiotics resistances. However, low occurrence of high-level gentamicin resistant or sulfamethoxazole/trimethoprim-resistant enterococci and absence of vancomycin- or ampicillin- resistant enterococci indicate that cheeses cannot be considered as a major reservoir for nosocomial multi-drug resistant enterococci.     

Epidemiological analysis of Salmonella enterica from beef sampled in the slaughterhouse and retailers in Dakar (Senegal) using pulsed-field gel electrophoresis and antibiotic susceptibility testing

Seventy-eight isolates of Salmonella spp. isolated from beef sampled from the official city slaughterhouse and from retailers in Dakar, Senegal were analyzed using serotyping, antimicrobial testing and macrorestriction profiling by Pulsed-Field Gel Electrophoresis (PFGE). These analyses were done to identify clonal relationships and potential transmission routes in beef channel. XbaI macrorestriction allowed defining 17 genotypes among the six main analyzed serotypes: Salmonella bredeney (3 genotypes), S. muenster (6), S. waycross (1), S. corvallis (3), S. kentucky (1) and S. brandenburg (3). The cross analysis of PFGE profiles and origin of the beef samples reveals a wide range of contamination sources in the beef channel in Dakar. Comparison of PFGE and antimicrobial resistance types shows that the Salmonella contamination sources are equally shared by the slaughterhouse (56% of the isolates) and by the distribution channel (44% of the isolates) by handlings and houseflies.     

Simultaneous determination of the main molecular species of soybean phosphatidylcholine or phosphatidylethanolamine and their corresponding hydroperoxides obtained by lipoxygenase treatment

A method for the simultaneous determination of the main molecular species of soybean phosphatidylcholine or phosphatidylethanolamine and their corresponding hydroperoxides is described. Hydroperoxides were formed by incubation of phospholipids with lipoxygenase at pH 9.2. Silicic acid column chromatography (silica Sep-Pak column) was used to separate the phospholipids into phosphatidylcholine and phosphatidylethanolamine. A single C−18 reverse-phase column was employed to separate the main molecular species of soybean phosphatidylcholine or phosphatidylethanolamine and their hydroperoxides by high-performance liquid chromatography. The mobile phase consisted of 5% 10 mM ammonium acetate at pH 5 and 95% methanol. The molecular species of phosphatidylcholine and phosphatidylethanolamine were detected at 205 nm; the eluate was mixed with a chemiluminescence reagent (isoluminol and microperoxidase) and monitored by fluorometry. Under the experimental conditions used, three individual molecular species of both soybean phosphatidylethanolamine and phosphatidylcholine (18∶3/18∶2, 18∶2/18∶2 and 16∶0/18∶2), together with their corresponding hydroperoxides, were identified and quantitated.