710 research outputs found
Genomic view on origin of foraminifera and their relationships with other amoeboid protists
Abstrac
Brisure d'axisymétrie à l'instabilité primaire du jet rond
La plupart des études du jet rond libre considèrent des nombres de Reynolds (défini sur la vitesse de sortie de l'injecteur Vzo et le diamètre D de la buse) assez importants (Re > 300, cf., par ex.), de sorte que les effets non visqueux prévalent sur les effets visqueux. Pour ce type d'écoulements, le scénario qui caractérise l'évolution du jet dans la zone proche de la buse est bien connu. Récemment, nous avons réalisé des simulations de la zone proche de sortie d'un jet rond évoluant dans le temps et dans l'espace au nombre de Reynolds de 500. Bon nombre de résulats connus ont été retrouvés, prouvant la pertinence de ce type de simulations pour l'étude des détails du comportement dynamique du jet rond. La transition à l'instationnarité et ses mécanismes ont, en revanche, été très peu étudiés pour ce type d'écoulement. Nous avons alors considéré des variations fines dans une plage de nombres de Reynolds plus bas. Une instabilité primaire du jet accompagnée par la brisure de l'axisymétrie a ainsi été mise en évidence. Ses mécanismes principaux sont décrits dans cette étude
Layer-resolved imaging of domain wall interactions in magnetic tunnel junction-like trilayers
We have performed a layer-resolved, microscopic study of interactions between
domain walls in two magnetic layers separated by a non-magnetic one, using
high-resolution x-ray photoemission electron microscopy. Domain walls in the
hard magnetic Co layer of a Co/Al2O3/FeNi trilayer with in-plane uniaxial
anisotropy strongly modify the local magnetization direction in the soft
magnetic FeNi layer. The stray fields associated to the domain walls lead to an
antiparallel coupling between the local Co and FeNi moments. For domain walls
parallel to the easy magnetization axis this interaction is limited to the
domain wall region itself. For strongly charged (head-on or tail-to-tail)
walls, the antiparallel coupling dominates the interaction over radial
distances up to several micrometers from the centre of the domain wall.Comment: Published version, J. Phys.: Condens. Matter 19, 476204 (2007
Combined heuristic task and motion planning for bi-manual robots
Planning efficiently at task and motion levels allows the setting of new challenges for robotic manipulation problems, like for instance constrained table-top problems for bi-manual robots. In this scope, the appropriate combination of task and motion planning levels plays an important role. Accordingly, a heuristic-based task and motion planning approach is proposed, in which the computation of the heuristic addresses a geometrically relaxed problem, i.e., it only reasons upon objects placements, grasp poses, and inverse kinematics solutions. Motion paths are evaluated lazily, i.e., only after an action has been selected by the heuristic. This reduces the number of calls to the motion planner, while backtracking is reduced because the heuristic captures most of the geometric constraints. The approach has been validated in simulation and on a real robot, with different classes of table-top manipulation problems. Empirical comparison with recent approaches solving similar problems is also reported, showing that the proposed approach results in significant improvement both in terms of planing time and success rate.Peer ReviewedPostprint (author's final draft
On the calculation of the bandgap of periodic solids with MGGA functionals using the total energy
During the last few years, it has become more and more clear that functionals of the meta generalized gradient approximation (MGGA) are more accurate than GGA functionals for the geometry and energetics of electronic systems. However, MGGA functionals are also potentially more interesting for the electronic structure, in particular, when the potential is nonmultiplicative (i.e., when MGGAs are implemented in the generalized Kohn-Sham framework), which may help to get more accurate bandgaps. Here, we show that the calculation of bandgap of solids with MGGA functionals can also be done very accurately in a non-self-consistent manner. This scheme uses only the total energy and can, therefore, be very useful when the self-consistent implementation of a particular MGGA functional is not available. Since self-consistent MGGA calculations may be difficult to converge, the non-self-consistent scheme may also help to speed up the calculations. Furthermore, it can be applied to any other types of functionals, for which the implementation of the corresponding potential is not trivial
Coulomb gas transitions in three-dimensional classical dimer models
Close-packed, classical dimer models on three-dimensional, bipartite lattices
harbor a Coulomb phase with power-law correlations at infinite temperature.
Here, we discuss the nature of the thermal phase transition out of this Coulomb
phase for a variety of dimer models which energetically favor crystalline dimer
states with columnar ordering. For a family of these models we find a direct
thermal transition from the Coulomb phase to the dimer crystal. While some
systems exhibit (strong) first-order transitions in correspondence with the
Landau-Ginzburg-Wilson paradigm, we also find clear numerical evidence for
continuous transitions. A second family of models undergoes two consecutive
thermal transitions with an intermediate paramagnetic phase separating the
Coulomb phase from the dimer crystal. We can describe all of these phase
transitions in one unifying framework of candidate field theories with two
complex Ginzburg-Landau fields coupled to a U(1) gauge field. We derive the
symmetry-mandated Ginzburg-Landau actions in these field variables for the
various dimer models and discuss implications for their respective phase
transitions.Comment: 15 pages, 19 figure
The Rhodococcus erythropolis DCL14 limonene-1,2-epoxide hydrolase gene encodes an enzyme belonging to a novel class of epoxide hydrolases
AbstractRecently, we reported the purification of the novel enzyme limonene-1,2-epoxide hydrolase involved in limonene degradation by Rhodococcus erythropolis DCL14. The N-terminal amino acid sequence of the purified enzyme was used to design two degenerate primers at the beginning and the end of the 50 amino acids long stretch. Subsequently, the complete limonene-1,2-epoxide hydrolase gene (limA) was isolated from a genomic library of R. erythropolis DCL14 using a combination of PCR and colony hybridization. The limA gene encoded a 149-residue polypeptide with a deduced molecular mass of 16.5 kDa. It was functionally expressed in Escherichia coli. The amino acid sequence of limA contains neither any of the conserved regions of the α,β-hydrolase fold enzymes, to which most of the previously reported epoxide hydrolases belong, nor any of the conserved motifs present in leukotriene A4 hydrolase. The structural data presented in this paper confirm previous physical and biochemical findings [van der Werf et al. (1998) J. Bacteriol. 180, 5052–5057] that limonene-1,2-epoxide hydrolase is the first member of a new class of epoxide hydrolases
Using PIC and PIC-MHD to investigate cosmic ray acceleration in mildly relativistic shocks
Astrophysical shocks create cosmic rays by accelerating charged particles to
relativistic speeds. However, the relative contribution of various types of
shocks to the cosmic ray spectrum is still the subject of ongoing debate.
Numerical studies have shown that in the non-relativistic regime, oblique
shocks are capable of accelerating cosmic rays, depending on the Alfv\'enic
Mach number of the shock. We now seek to extend this study into the mildly
relativistic regime. In this case, dependence of the ion reflection rate on the
shock obliquity is different compared to the nonrelativistic regime. Faster
relativistic shocks are perpendicular for the majority of shock obliquity
angles therefore their ability to initialize efficient DSA is limited. We
define the ion injection rate using fully kinetic PIC simulation where we
follow the formation of the shock and determine the fraction of ions that gets
involved into formation of the shock precursor in the mildly relativistic
regime covering a Lorentz factor range from 1 to 3. Then, with this result, we
use a combined PIC-MHD method to model the large-scale evolution of the shock
with the ion injection recipe dependent on the local shock obliquity. This
methodology accounts for the influence of the self-generated or pre-existing
upstream turbulence on the shock obliquity which allows study substantially
larger and longer simulations compared to classical hybrid techniques.Comment: 38th International Cosmic Ray Conference, Proceedings of Science
(ICRC2023) 54
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