A light coating of oil is known to increase the dust holding capacity of fibrous filter media. The underlying causes for this effect were investigated by performing filtration experiments with arrays ...of nylon and stainless steel fibers (diameters of 20, 30, and 44μm) coated with precisely defined amounts of oil. The single fiber efficiency in the inertial regime (Stokes numbers >0.5) was measured as a function of dust load, using 3.5μm polystyrene and 2.1μm silica particles in combination with various types of oils (0W-30, WD-40). Additionally, the influence of an oil film on the growth of particle deposit structures was investigated by optical microscopy.
It was found that dust deposition on oily fibers occurs in two distinct stages: at first particles are immersed in the oil film without any appreciable increase in fiber efficiency. Once the film is saturated with particles, further deposition leads to quasi-normal dendritic growth typical of dust deposition on dry fibers, and a sharp increase in single fiber efficiency. The maximum packing density inside the film which is reached at the transition from particle immersion to regular growth, was approximately 46% by volume, regardless of film thickness. There were no indications of flow-induced particle rearrangement inside the film during the first stage.
Comparative measurements were also made with standard paper media containing varying quantities of oil. The oil caused an increase in dust holding capacity by factors between about 1.5 and 3 compared to dry media, due to a delayed upswing of the filter pressure drop with dust loading. The penetration of dust through the media more than doubled.
We conclude that particle immersion in the oil film is responsible for both the delayed increase in fiber efficiency and fiber drag, and that this delay is roughly proportional to the amount of oil loading.
Pre-treating filter fibers with oil delays the formation of widespread particle dendrites, as collected particles get packed tightly inside the oil films. Until the film is saturated with particles, collection efficiency and drag increase only marginally, which ultimately leads to a higher dust holding capacity of oil-treated media. Display omitted
•An oil film on filter fibers absorbs particles up to 87% of its volume.•Single fiber efficiency and drag hardly increase until the film is loaded to capacity with particles.•The high packing density of immersed particles is responsible for the increased dust holding capacity of the filter.
Seven new archeointensity data are obtained through the analysis of groups of pottery and kiln fragments from ceramic workshops unearthed in France, precisely dated from the High Middle Ages. The ...measurements are carried out using the Triaxe magnetometer, following a dedicated experimental protocol that takes into account the effects of anisotropy and cooling rate (CR) on thermoremanent magnetization acquisition. The new data are consistent with the evolution of intensity variations described by our previous data obtained in France and Northern Italy, which display between the 5th and 10th c. a pronounced camel-back shape. In particular, they provide supporting evidence of an intensity minimum that occurred around the transition between the 7th and 8th century. These data, combined with a selection of previously published results within a 700 km radius of Beaune and re-examined based on CR correction, formed the basis of new regional mean intensity variation curves based on two independent modeling approaches. The first algorithm developed by Thébault and Gallet (2010) based on bootstrapping and now irregularly spaced knots according to the data distribution gives rather smooth intensity variations, while the second approach proposed by Livermore et al. (2018) based on a transdimensional Bayesian technique shows more abrupt variations with sometimes stronger amplitudes. We explore the dating potential of these two variations curves, which have an unprecedented resolution, by studying two medieval pottery workshops. Six fragment groups (three per workshop) are analyzed using the Triaxe protocol, providing mean archeointensity values for each of the two sites. Two different procedures are used for their dating, either by comparing the intensity value to be dated with the reference intensity variation curves obtained from the two modeling techniques or by analyzing the marginal posterior probability distribution of the age values derived from the method of Livermore et al. (2018). For France, the two techniques yield very similar results. The archeointensity dating results combined with archeological arguments and radiocarbon data, make it possible to better constrain the age of the end of activity of the two workshops. Archeointensity investigation of displaced materials thus appears as an effective means to obtain original chronological constraints on the age of their production, paving the way for a wide range of complementary research on Medieval pottery.
•7 new Triaxe archeointensity data are obtained from French medieval pottery workshops.•They allow a refinement of the evolution of intensities during the High Middle Ages.•A set of available intensity data is re-examined based on cooling rate correction.•We illustrate the sensitivity of regional intensity models to modeling strategies.•We discuss two different procedures for archeointensity dating.
Nutrient cycling is fundamental to ecosystem functioning. Despite recent major advances in the understanding of complex food web dynamics, food web models have so far generally ignored nutrient ...cycling. However, nutrient cycling is expected to strongly impact food web stability and functioning. To make up for this gap, we built an allometric and size structured food web model including nutrient cycling. By releasing mineral nutrients, recycling increases the availability of limiting resources for primary producers and links each trophic level to the bottom of food webs. We found that nutrient cycling can provide a significant part of the total nutrient supply of the food web, leading to a strong enrichment effect that promotes species persistence in nutrient poor ecosystems but leads to a paradox of enrichment at high nutrient inputs. The presence of recycling loops linking each trophic level to the basal resources weakly affects species biomass temporal variability in the food web. Recycling loops tend to slightly dampen the destabilising effect of nutrient enrichment on consumer temporal variability while they have opposite effects for primary producers. By considering nutrient cycling, this new model improves our understanding of the response of food webs to nutrient availability and opens perspectives to better link studies on food web dynamics and ecosystem functioning.
Recent compilations of archeomagnetic intensity data have shown the existence of outliers. Acknowledging this problem, we propose a new way of generating and studying the uniqueness of regional ...archeomagnetic master curves bypassing the need to assume a normal data error distribution. Our approach lessens the weight of outliers by applying an iteratively re‐weighted least‐squares method combined with a bootstrap algorithm. Given a particular set of archeomagnetic data associated with experimental and dating uncertainties, we produce an ensemble of curves that are designed to sample the conditional probability distribution of the ‘true’ master curve. Using this technique, we propose an archeointensity master curve with its probability density for the Middle East region that covers the past four millennia BC.
Soil biodiversity plays a key role in regulating the processes that underpin the delivery of ecosystem goods and services in terrestrial ecosystems. Agricultural intensification is known to change ...the diversity of individual groups of soil biota, but less is known about how intensification affects biodiversity of the soil food web as a whole, and whether or not these effects may be generalized across regions. We examined biodiversity in soil food webs from grasslands, extensive, and intensive rotations in four agricultural regions across Europe: in Sweden, the UK, the Czech Republic and Greece. Effects of land‐use intensity were quantified based on structure and diversity among functional groups in the soil food web, as well as on community‐weighted mean body mass of soil fauna. We also elucidate land‐use intensity effects on diversity of taxonomic units within taxonomic groups of soil fauna. We found that between regions soil food web diversity measures were variable, but that increasing land‐use intensity caused highly consistent responses. In particular, land‐use intensification reduced the complexity in the soil food webs, as well as the community‐weighted mean body mass of soil fauna. In all regions across Europe, species richness of earthworms, Collembolans, and oribatid mites was negatively affected by increased land‐use intensity. The taxonomic distinctness, which is a measure of taxonomic relatedness of species in a community that is independent of species richness, was also reduced by land‐use intensification. We conclude that intensive agriculture reduces soil biodiversity, making soil food webs less diverse and composed of smaller bodied organisms. Land‐use intensification results in fewer functional groups of soil biota with fewer and taxonomically more closely related species. We discuss how these changes in soil biodiversity due to land‐use intensification may threaten the functioning of soil in agricultural production systems.
As a by-product of the construction of a new World Digital Magnetic Anomaly Map over oceanic areas, we use an original approach based on the global forward modeling of seafloor spreading magnetic ...anomalies and their comparison to the available marine magnetic data to derive the first map of the equivalent magnetization over the World's ocean. This map reveals consistent patterns related to the age of the oceanic lithosphere, the spreading rate at which it was formed, and the presence of mantle thermal anomalies which affects seafloor spreading and the resulting lithosphere. As for the age, the equivalent magnetization decreases significantly during the first 10–15 Myr after its formation, probably due to the alteration of crustal magnetic minerals under pervasive hydrothermal alteration, then increases regularly between 20 and 70 Ma, reflecting variations in the field strength or source effects such as the acquisition of a secondary magnetization. As for the spreading rate, the equivalent magnetization is twice as strong in areas formed at fast rate than in those formed at slow rate, with a threshold at ∼40 km/Myr, in agreement with an independent global analysis of the amplitude of Anomaly 25. This result, combined with those from the study of the anomalous skewness of marine magnetic anomalies, allows building a unified model for the magnetic structure of normal oceanic lithosphere as a function of spreading rate. Finally, specific areas affected by thermal mantle anomalies at the time of their formation exhibit peculiar equivalent magnetization signatures, such as the cold Australian–Antarctic Discordance, marked by a lower magnetization, and several hotspots, marked by a high magnetization.
•Global distribution of the equivalent magnetization (EM) for oceanic domains derived.•Equivalent magnetization decreases within the first 15 Myr as an effect of alteration.•Equivalent magnetization varies like sample magnetization within the last 70 Myr.•Equivalent magnetization is twice stronger at fast spreading rate than at slow ones.•Mantle thermal anomalies and melting depth reflects on equivalent magnetization.
The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It ...updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined.
Ecology Letters (2011) 14: 1170–1181
Interactions among species drive the ecological and evolutionary processes in ecological communities. These interactions are effectively key components of ...biodiversity. Studies that use a network approach to study the structure and dynamics of communities of interacting species have revealed many patterns and associated processes. Historically these studies were restricted to trophic interactions, although network approaches are now used to study a wide range of interactions, including for example the reproductive mutualisms. However, each interaction type remains studied largely in isolation from others. Merging the various interaction types within a single integrative framework is necessary if we want to further our understanding of the ecological and evolutionary dynamics of communities. Dividing the networks up is a methodological convenience as in the field the networks occur together in space and time and will be linked by shared species. Herein, we outline a conceptual framework for studying networks composed of more than one type of interaction, highlighting key questions and research areas that would benefit from their study.
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