1,576 research outputs found
Isotropic and anisotropic heat transfer in active wall porous media foam type
Positive buildings in energy are, nowadays, a recurrent objective of many
researches in the construction and energetic efficiency domain. Furthermore, to
achieve this objective, some studies about active and reactive walls have been
carried out employing porous medium as a main structure. Nevertheless, transfer
characterization in a foam type sample is not fully understood. The goal of
this study is to improve the characterization of heat transfer in isotropic and
anisotropic configurations of a porous medium. Thus, a finite volume method was
implemented to study a heat transfer through these media, in the interest of
achieving their ratio equivalent to fluid thermal conductivity (i.e. Nusselt
number). Finally, the results indicate a notable influence of the ratio of the
contact and the total inlet area on the isotropic configuration as well as
strong influence given by the different axis on the anisotropic model.
Moreover, the analysis shows that in an active wall constituted by two solid
phases, these effects will be preponderant for their characterization.Comment: 18\`eme Journ\'ees Internationales de Thermique (JITH 2017), Oct
2017, Monastir, Tunisi
An unconditionally stable nonstandard finite difference method applied to a mathematical model of HIV infection
We formulate and analyze an unconditionally stable nonstandard finite difference method for a mathematical model of HIV
transmission dynamics. The dynamics of this model are studied using the qualitative theory of dynamical systems. These
qualitative features of the continuous model are preserved by the numerical method that we propose in this paper. This
method also preserves the positivity of the solution, which is one of the essential requirements when modeling epidemic
diseases. Robust numerical results confirming theoretical investigations are provided. Comparisons are also made with the
other conventional approaches that are routinely used for such problems.IS
10401 Abstracts Collection -- Learning, Planning and Sharing Robot Knowledge for Human-Robot Interaction
From 03.10.10 to 08.10.10,the Dagstuhl Seminar 10401 ``Learning, Planning and Sharing Robot Knowledge for Human-Robot Interaction \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
On F-theory Quiver Models and Kac-Moody Algebras
We discuss quiver gauge models with bi-fundamental and fundamental matter
obtained from F-theory compactified on ALE spaces over a four dimensional base
space. We focus on the base geometry which consists of intersecting F0=CP1xCP1
Hirzebruch complex surfaces arranged as Dynkin graphs classified by three kinds
of Kac-Moody (KM) algebras: ordinary, i.e finite dimensional, affine and
indefinite, in particular hyperbolic. We interpret the equations defining these
three classes of generalized Lie algebras as the anomaly cancelation condition
of the corresponding N =1 F-theory quivers in four dimensions. We analyze in
some detail hyperbolic geometries obtained from the affine A base geometry by
adding a node, and we find that it can be used to incorporate fundamental
fields to a product of SU-type gauge groups and fields.Comment: 13 pages; new equations added in section 3, one reference added and
typos correcte
Characterization of a human coagulation factor Xa-binding site on Viperidae snake venom phospholipases A2 by affinity binding studies and molecular bioinformatics
<p>Abstract</p> <p>Background</p> <p>The snake venom group IIA secreted phospholipases A<sub>2 </sub>(SVPLA<sub>2</sub>), present in the <it>Viperidae </it>snake family exhibit a wide range of toxic and pharmacological effects. They exert their different functions by catalyzing the hydrolysis of phospholipids (PL) at the membrane/water interface and by highly specific direct binding to: (i) presynaptic membrane-bound or intracellular receptors; (ii) natural PLA<sub>2</sub>-inhibitors from snake serum; and (iii) coagulation factors present in human blood.</p> <p>Results</p> <p>Using surface plasmon resonance (SPR) protein-protein interaction measurements and an <it>in vitro </it>biological test of inhibition of prothrombinase activity, we identify a number of <it>Viperidae </it>venom SVPLA<sub>2</sub>s that inhibit blood coagulation through direct binding to human blood coagulation factor Xa (FXa) via a non-catalytic, PL-independent mechanism. We classify the SVPLA<sub>2</sub>s in four groups, depending on the strength of their binding.</p> <p>Molecular electrostatic potentials calculated at the surface of 3D homology-modeling models show a correlation with inhibition of prothrombinase activity. In addition, molecular docking simulations between SVPLA<sub>2 </sub>and FXa guided by the experimental data identify the potential FXa binding site on the SVPLA<sub>2</sub>s. This site is composed of the following regions: helices A and B, the Ca<sup>2+ </sup>loop, the helix C-β-wing loop, and the C-terminal fragment. Some of the SVPLA<sub>2 </sub>binding site residues belong also to the interfacial binding site (IBS). The interface in FXa involves both, the light and heavy chains.</p> <p>Conclusion</p> <p>We have experimentally identified several strong FXa-binding SVPLA<sub>2</sub>s that disrupt the function of the coagulation cascade by interacting with FXa by the non-catalytic PL-independent mechanism. By theoretical methods we mapped the interaction sites on both, the SVPLA<sub>2</sub>s and FXa. Our findings may lead to the design of novel, non-competitive FXa inhibitors.</p
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Enhancing scientific and community capacity to conserve Central African Lepidoptera
Research on the ecology and conservation of Lepidoptera (and other species) has historically neglected tropical diversity – but the Lepidoptera of tropical Africa have been particularly understudied. Central Africa represents a major centre of biodiversity for butterflies, moths and other taxa but major threats including habitat loss, habitat degradation/ disturbance and climate change are threatening their persistence. Additionally, a range of obstacles to research and conservation are apparent in Central Africa, including major socioeconomic disparity, persistent armed conflicts, corruption, and a lack of local resources (e.g., funding and museums). Here we outline the history of research on the butterflies of Central Africa and highlight the importance of further conservation efforts in maintaining the biodiversity of Lepidoptera and other understudied insects in the region. Proactive measures acknowledging the prevailing regional challenges must be taken immediately. Among the major recommendations, we suggest: 1) enhancing museum collections, 2) facilitating strong scientific collaboration that enhances local capacity, 3) ensuring that funded projects are not disrupted by corruption, and 4) working to advance the socioeconomic status of local communities. Potential for scientific and community advancement in the region is substantial if investment and research efforts are targeted effectively
Coalescence of Anderson-localized modes at an exceptional point in 2D random media
In non-hermitian systems, the particular position at which two eigenstates coalesce under a variation of a parameter in the complex plane is called an exceptional point. A non-perturbative theory is proposed which describes the evolution of modes in 2D open dielectric systems when permittivity distribution is modified. We successfully test this theory in a 2D disordered system to predict the position in the parameter space of the exceptional point between two Anderson-localized states. We observe that the accuracy of the prediction depends on the number of localized states accounted for. Such an exceptional point is experimentally accessible in practically relevant disordered photonic systems. Losses are inherent to most physical systems, either because of dissipation or as a result of openness. These systems are described mathematically by a non-hermitian Hamiltonian, where eigenvalues are complex and eigen-states form a nonorthogonal set. In such systems, interaction between pairs of eigenstates when a set of external parameters is varied is essentially driven by the existence of exceptional points (EP). At an EP, eigenstates coa-lesce: Complex eigenvalues degenerate and spatial distributions become collinear. In its vicinity, eigenvalues display a singular topology [1] and encircling the EP in the parameter space leads to a residual geometrical phase [2, 3]. Since their introduction by Kato in 1966 [4], EPs have turned to be involved in a rich variety of physical effects: Level repulsion [5], mode hybridization [6], quantum phase transition [7], lasing mode switching [8], PT symmetry breaking [9, 10] or even strong coupling [11]. They have been observed experimentally in different systems such as microwave billiards [12], chaotic optical mi-crocavities [13] or two level atoms in high-Q cavities [11]. Open random media are a particular class of non-hermitian systems. Here, modal confinement may be solely driven by the degree of scattering. For sufficiently strong scattering, the spatial extension of the modes becomes smaller than the system size, resulting in transport inhibition and Anderson localization [14]. Disordered-induced localized states have raised increasing interest. They provide with natural optical cavities in random lasers [15, 16]. They recently appeared to be good candidate for cavity QED [17, 18], with the main advantage of being inherently disorder-robust. These modes can be manipulated by a local change of the disorder and can be coupled to form necklace states [19-21], which open channels in a nominally localized system [22, 23]. These necklace states are foreseen as a key mechanism in the transition from localization to diffusive regime [24]. PT symmetry has been studied in the context of disordered media and Anderson localization [25-27] but so far EPs between localized modes have not been investigated. In this letter, coalescence at an EP between two Anderson-localized optical modes is demonstrated in a two dimensional (2D) dielectric random system. To bring the system in the vicinity of an EP, the dielectric permit-tivity is varied at two different locations in the random system. We first propose a general theory to follow the spectral and spatial evolution of modes in 2D dielectric open media. This theory is applied to the specific case of Anderson-localized modes to identify the position of an EP in the parameter space. This prediction is confirmed by Finite Element Method (FEM) simulations. We show that this is a highly complex problem of multiple mode interaction where a large number of modes are involved. We believe that our theory opens the way to a controlled local manipulation of the permittivity and the possibility to engineer the modes. Furthermore, we think this approach can be easily extended to others kinds of networks e.g. coupled arrays of cavities [28, 29]. We first consider the general case of a finite-size dielec-tric medium in 2D space, with inhomogeneous dielectric constant distribution, ǫ(r). In the frequency domain, the electromagnetic field follows the Helmholtz equation: ∆E(r, ω) + ǫ(r)ω 2 E(r, ω) = 0 (1) where E(r, ω) stands for the electrical field and the speed of light, c = 1. Eigensolutions of eq. (1), define the modes or eigenstates of the problem: (Ω i , |Ψ i) i∈N | ∆|Ψ i + ǫ(r)Ω 2 i |Ψ i = 0 (2) Because of its openness, the system has inherent losses, thus is described by a non-hermitian Hamiltonian. For non-hermitian systems, modes are a priori non-orthogonal, complex and their completeness is not ensured. Here, we consider open systems with finite range permittivity ǫ(r) and where a discontinuity in the permit-tivity provides a natural demarcation of the problem. Fo
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Seasonal Polyphenism in Bicyclus dorothea (Lepidoptera: Nymphalidae) Across Different Habitats in Cameroon
Many organisms exhibit changes in phenotypic traits as a response to seasonal environmental variation. We investigated the role of habitat in generating seasonal polyphenism in different populations of the light bush brown butterfly Bicyclus dorothea (Cramer, 1779) (Lepidoptera: Nymphalidae) in Cameroon. Butterflies were caught during the wet and dry seasons across four localities representing two distinct habitats, namely forest and ecotone (forest-savanna transition zone) over a 2-yr period (2015-2016). We found distinct variation in the wing pattern characteristics of butterflies in response to seasonality and habitat. Specifically we observed that: 1) all wing characters are not seasonally plastic in B. dorothea; 2) populations from ecotone tend to be more variable, with individuals exhibiting wings with large spots during the wet season and very reduced spots in the dry season while in forest populations, individuals exhibit wings with large spots during the wet season, but in the dry season, spots are not as greatly reduced as their ecotone counterparts; 3) this polyphenism in B. dorothea alternated consistently during the wet and dry seasons over the 2 yr of sampling. Bicyclus species have become a textbook example of seasonal polyphenism while this study extends this model system to the unique forest-ecotone gradient of Central Africa and demonstrates the complexity of seasonal forms in different habitats
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