4,725 research outputs found

    Nonlinear multigrid based on local spectral coarsening for heterogeneous diffusion problems

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    This work develops a nonlinear multigrid method for diffusion problems discretized by cell-centered finite volume methods on general unstructured grids. The multigrid hierarchy is constructed algebraically using aggregation of degrees of freedom and spectral decomposition of reference linear operators associated with the aggregates. For rapid convergence, it is important that the resulting coarse spaces have good approximation properties. In our approach, the approximation quality can be directly improved by including more spectral degrees of freedom in the coarsening process. Further, by exploiting local coarsening and a piecewise-constant approximation when evaluating the nonlinear component, the coarse level problems are assembled and solved without ever re-visiting the fine level, an essential element for multigrid algorithms to achieve optimal scalability. Numerical examples comparing relative performance of the proposed nonlinear multigrid solvers with standard single-level approaches -- Picard's and Newton's methods -- are presented. Results show that the proposed solver consistently outperforms the single-level methods, both in efficiency and robustness

    What Do You Have to Offer Me?”: A Relationship Building Activity for Demonstrating Social Exchange Theory

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    This article describes “What Do You Have to Offer Me?,” an interactive classroom activity designed to help students encounter social exchange theory in action. During the exercise, each student selected seven cards, each containing a characteristic related to personality, physical appearance, family history, finances, ideology, and occupation. Next, students were asked to mill around the classroom and find someone with whom they would be interested in developing a relationship based on their assigned characteristics. Once all students found partners and took their seats, students reflected on the process of the activity and its application to social exchange theory. Along with providing details on the activity, we conclude with student reflections and evaluative data on the exercise

    Dynamic of a lacustrine sedimentary system during late rifting at the Cretaceous‐Palaeocene transition: Example of the Yacoraite Formation, Salta Basin, Argentina

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    The architecture of lacustrine systems is the result of the complex interaction between tectonics, climate and environmental parameters, and constitute the main forcing parameters on the lake dynamics. Field analogue studies have been performed to better assess such interactions, and their impact on the facies distribution and the stratigraphic architecture of lacustrine systems. The Yacoraite Formation (Late Cretaceous/Early Palaeocene), deposited during the sag phase of the Salta rift basin in Argentina, is exposed in world-class outcrops that allowed the dynamics of this lacustrine system to be studied through facies analysis and stratigraphic evolution. On the scale of the Alemania-Met\ue1n-El Rey Basin, the Yacoraite Formation is organized with a siliciclastic-dominated margin to the west, and a carbonate-dominated margin to the east. The Yacoraite can be subdivided into four main \u2018mid-term\u2019 sequences and further subdivided into \u2018short-term\u2019 sequences recording high frequency climate fluctuations. Furthermore, the depositional profiles and identified system tracts have been grouped into two end-members at basin scale: (a) a balanced \u2018perennial\u2019 depositional system for the lower part of the Yacoraite Formation and (b) a highly alternating \u2018ephemeral\u2019 depositional system for the upper part of the Yacoraite Formation. The transition from a perennial system to an ephemeral system indicates a change in the sedimentary dynamics of the basin, which was probably linked with the Cretaceous/Tertiary boundary that induced a temporary shutdown of carbonate production and an increase in siliciclastic supply

    Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis

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    International audienceEucalyptus grandis has a mixed-mating repro- ductive system. Malagasy Eucalyptus seed orchards were established 15 years ago with two aims both based on panmixia: open-pollinated seed production and genetic improvement. The panmixia hypothesis has never been confirmed in the seed orchard. From a seedling seed- orchard stand comprising 349 trees and using data obtained with six selected microsatellite markers, pater- nity analysis was performed for 724 offspring collected on 30 adult trees. Paternity assignment, based on exclu- sion procedures and likelihood-ratio method, was achieved with high accuracy; the exclusion probability value was 0.997. The outcrossing rate was very high (96.7%). More than 50% of potential male trees (199 out of 349) in the seed orchard contributed to pollination for 440 offspring of 30 progenies (8.6% of the basic population). The pollination rate from outside the seed orchard was high (39.2%), but might be due to the small size of this seed orchard. This study showed that "panmixia-like pollination" can be assume

    First report of early blight caused by Alternaria protenta on potato in Algeria

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    Potato (Solanum tuberosum L.) is one of the most important vegetable crop grown in Algeria. Although less studied than late blight, early blight caused by large-spored Alternaria species including A. solani, and A. grandis is an important foliar disease on these crops under Algerian climatic conditions. Over the past few years, this disease became a major constraint on potato production in Algeria and high incidences of early blight (up to 80 %) were recorded in the north-western parts of Algeria (Bessadat et al., 2016). During years 2012-2014, surveys were carried out and sampling was performed in 12 potato growing regions from East to West and from North to South of Algeria. Two hundred and forty-seven samples with typical early blight symptoms (dark, elongated or circular lesions with concentric rings surrounded by a yellow halo) were collected. Two to three lesions perleaf were excised, surface disinfested for 2 min in 0.1% (v/v) sodium hypochlorite solution and plated on potato dextrose agar medium at 22°C. Twenty-two pure cultures were induced to sporulate by plating on V8 medium and incubating for two weeks under alternating 12 h darkness and 12 h near UV light. Cultural and morphological characteristics of the isolates [color and pigmentation of the culture, shape and size of the conidia (conidial length and width, beak length)] compared with those in the literature (Simmons, 2007) did not clearly differentiate between the large-spored Alternaria species currently reported on potato crops. For identification at the species level, partial regions of the calmodulin (cal) and RNA polymerase second largest subunit (rpb2) genes were amplified using published primer sets (Gannibal et al., 2014; Woudenberg et al., 2014) and sequenced. Maximum likelihood cluster analyses of the resulting nucleotide sequences revealed two isolates (AD82 and AD86 isolated from potato samples collected in the El Oued region) with sequences at the two loci [GenBank accession Nos. KX870505 and KX870506 (cal locus), KX870507 and KX870508 (rpb2 locus)] that shared 100% sequence homology to A. protenta isolate CBS 116696 (KJ718394, JQ646236) and were thus assigned to this species. A. protenta was previously known in Africa only on Helianthus annuus (Simmons, 1986) but isolates from S. tuberosum and S. lycopersicum collected in New Zealand and USA and formerly recognized as A. solani, were recently moved to A. protenta based on phylogeny (Woudenberg et al., 2014). To confirm pathogenicity of the two A. protenta isolates, leaves of susceptible 3-week-old potato plants were inoculated with two 10 µL drops of a 104 conidia/ml suspension. All leaves inoculated with A. protenta showed extending lesions that may reach up 50% of the leaf area at 21 dpi. To our knowledge, we report the first occurrence of A. protenta as pathogen on potato in Algeria.

    Inhibition of protein kinase C decreases sensitivity of GABA receptor subtype to fipronil insecticide in insect neurosecretory cells.

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    Phosphorylation by serine/threonine kinases has been described as a new mechanism for regulating the effects of insecticides on insect neuronal receptors and channels. Although insect GABA receptors are commercially important targets for insecticides (e.g. fipronil), their modulation by kinases is poorly understood and the influence of phosphorylation on insecticide sensitivity is unknown. Using the whole-cell patch-clamp technique, we investigated the modulatory effect of PKC and CaMKinase II on GABA receptor subtypes (GABAR1 and GABAR2) in DUM neurons isolated from the terminal abdominal ganglion (TAG) of Periplaneta americana. Chloride currents through GABAR2 were selectively abolished by PMA and PDBu (the PKC activators) and potentiated by Gö6983, an inhibitor of PKC. Furthermore, using KN-62, a specific CaMKinase II inhibitor, we demonstrated that CaMKinase II activation was also involved in the regulation of GABAR2 function. In addition, using CdCl(2) (the calcium channel blocker) and LOE-908, a blocker of TRPγ, we revealed that calcium influx through TRPγ played an important role in kinase activations. Comparative studies performed with CACA, a selective agonist of GABAR1 in DUM neurons confirmed the involvement of these kinases in the specific regulation of GABAR2. Furthermore, our study reported that GABAR1 was less sensitive than GABAR2 to fipronil. This was demonstrated by the biphasic concentration-response curve and the current-voltage relationship established with both GABA and CACA. Finally, we demonstrated that GABAR2 was 10-fold less sensitive to fipronil following inhibition of PKC, whereas inhibition of CaMKinase II did not alter the effect of fipronil

    Terminal-repeat retrotransposons with GAG domain in plant genomes : a new testimony on the complex world of transposable elements

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    A novel structure of nonautonomous long terminal repeat (LTR) retrotransposons called terminal repeat with GAG domain (TR-GAG) has been described in plants, both in monocotyledonous, dicotyledonous and basal angiosperm genomes. TR-GAGs are relatively short elements in length (<4 kb) showing the typical features of LTR-retrotransposons. However, they carry only one open reading frame coding for the GAG precursor protein involved for instance in transposition, the assembly, and the packaging of the element into the virus-like particle. GAG precursors show similarities with both Copia and Gypsy GAG proteins, suggesting evolutionary relationships of TR-GAG elements with both families. Despite the lack of the enzymatic machinery required for their mobility, strong evidences suggest that TR-GAGs are still active. TR-GAGs represent ubiquitous nonautonomous structures that could be involved in the molecular diversities of plant genomes
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