Influences of initial plankton biomass and mixed layer depths on the outcome of iron-fertilization experiments

International audienceSeveral in situ iron-enrichment experiments have been conducted, where the response of the phytoplankton community differed. We use a marine ecosystem model to investigate the effect of iron on phytoplankton in response to different initial plankton conditions and mixed layer depths. Sensitivity analysis of the model results to the mixed layer depths reveals that the modeled response to the same iron enhancement treatment differed dramatically according to the different mixed layer depth. The magnitude of the iron-induced biogeochemical responses in the surface water, such as maximum chlorophyll, is inversely correlated with the mixed layer depth, as observed. The significant decrease in maximum surface chlorophyll with mixed layer depth results from the difference in diatom concentration in the mixed layer, which is determined by vertical mixing. Sensitivity of the model to initial mesozooplankton (as grazers on diatoms) biomass shows that column-integrated net community production and export production are strongly controlled by the initial mesozooplankton biomass. Higher initial mesozooplankton biomass yields high grazing pressure on diatoms, which results in less accumulation of diatom biomass. The initial diatom biomass is also important to the outcome of iron enrichment but is not as crucial as the mixed layer depth and the initial mesozooplankton biomass. This modeling study suggests not only mixed layer depth but also the initial biomass of diatoms and its principle grazers are crucial factors in the response of the phytoplankton community to the iron enrichments, and should be considered in designing future iron-enrichment experiments

Modeling the effects of size on patch dynamics of an inert tracer

Mesoscale iron enrichment experiments have revealed that additional iron affects the phytoplankton productivity and carbon cycle. However, the role of initial size of fertilized patch in determining the patch evolution is poorly quantified due to the limited observational capability and complex of physical processes. Using a three-dimensional ocean circulation model, we simulated different sizes of inert tracer patches that were only regulated by physical circulation and diffusion. Model results showed that during the first few days since release of inert tracer, the calculated dilution rate was found to be a linear function with time, which was sensitive to the initial patch size with steeper slope for smaller size patch. After the initial phase of rapid decay, the relationship between dilution rate and time became an exponential function, which was also size dependent. Therefore, larger initial size patches can usually last longer and ultimately affect biogeochemical processes much stronger than smaller patches

Abnormally high content of free glucosamine residues identified in a preparation of commercially available porcine intestinal heparan sulfate

Heparan sulfate (HS) polysaccharides are ubiquitous in animal tissues as components of proteoglycans, and they participate in many important biological processes. HS carbohydrate chains are complex and can contain rare structural components such as N-unsubstituted glucosamine (GlcN). Commercially available HS preparations have been invaluable in many types of research activities. In the course of preparing microarrays to include probes derived from HS oligosaccharides, we found an unusually high content of GlcN residue in a recently purchased batch of porcine intestinal mucosal HS. Composition and sequence analysis by mass spectrometry of the oligosaccharides obtained after heparin lyase III digestion of the polysaccharide indicated two and three GlcN in the tetrasaccharide and hexasaccharide fractions, respectively. (1)H NMR of the intact polysaccharide showed that this unusual batch differed strikingly from other HS preparations obtained from bovine kidney and porcine intestine. The very high content of GlcN (30%) and low content of GlcNAc (4.2%) determined by disaccharide composition analysis indicated that N-deacetylation and/or N-desulfation may have taken place. HS is widely used by the scientific community to investigate HS structures and activities. Great care has to be taken in drawing conclusions from investigations of structural features of HS and specificities of HS interaction with proteins when commercial HS is used without further analysis. Pending the availability of a validated commercial HS reference preparation, our data may be useful to members of the scientific community who have used the present preparation in their studies

JPL Energy Consumption Program (ECP) documentation: A computer model simulating heating, cooling and energy loads in buildings

The engineering manual provides a complete companion documentation about the structure of the main program and subroutines, the preparation of input data, the interpretation of output results, access and use of the program, and the detailed description of all the analytic, logical expressions and flow charts used in computations and program structure. A numerical example is provided and solved completely to show the sequence of computations followed. The program is carefully structured to reduce both user's time and costs without sacrificing accuracy. The user would expect a cost of CPU time of approximately $5.00 per building zone excluding printing costs. The accuracy, on the other hand, measured by deviation of simulated consumption from watt-hour meter readings, was found by many simulation tests not to exceed + or - 10 percent margin

Traffic by multiple species of molecular motors

We study the traffic of two types of molecular motors using the two-species symmetric simple exclusion process (ASEP) with periodic boundary conditions and with attachment and detachment of particles. We determine characteristic properties such as motor densities and currents by simulations and analytical calculations. For motors with different unbinding probabilities, mean field theory gives the correct bound density and total current of the motors, as shown by numerical simulations. For motors differing in their stepping probabilities, the particle-hole symmetry of the current-density relationship is broken and mean field theory fails drastically. The total motor current exhibits exponential finite-size scaling, which we use to extrapolate the total current to the thermodynamic limit. Finally, we also study the motion of a single motor in the background of many non-moving motors.Comment: 23 pages, 6 figures, late

Le coût du crédit aux entreprises selon leur catégorie.

Les PME ont une structure de financement bancaire spécifique par rapport aux grandes entreprises et ne bénéficient pas de ce fait des mêmes conditions de financement. L’article examine les principaux facteurs explicatifs des taux des crédits accordés aux PME et met en évidence l’impact de la crise financière de 2008 sur la tarification des crédits.PME, financement, crise financière.

An optical study of interdiffusion in ZnSe/ZnCdSe

Copyright 1996 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Applied Physics Letters 69, 1579 (1996) and may be found at

Predicting frictional losses generated by piston connecting-rod big end journal bearing for an internal combustion engine

The aim of the study is to investigate the tribological behaviour of the connecting-rod big end journal bearing under dynamic loading for a full engine cycle.In this study, a numerical analysis is used for solving the 2-D Reynolds equation based on Reynolds boundary condition. The 2-D Reynolds solution was derived by using a combination of approaches, namely finite difference method, Newton-Raphson method, and Taylor expansion series. Then, the formulated 2-D mathematical model is used to ascertain the tribological behaviour for both rigid and deformable bearing assumptions.For low loading conditions, the simulation results from both rigid and deformation models have only shown minor differences, demonstrating correlation with existing analytical and experimental results. However, once the loading capacity is increased, the simulation results from the deformation model assumption is shown to be much closer to the experimental results obtained from real engine analysis.In short, an elastic journal bearing assumption in simulating such tribological conjunction is believed to be more practical and reliable for real engine practices as compared to a rigid journal bearing assumption