37,112 research outputs found
Arbitrary bi-dimensional finite strain crack propagation
In the past two decades numerous numerical procedures for crack propagation have been developed. Lately,
enrichment methods (either local, such as SDA or global, such as XFEM) have been applied with success to simple
problems, typically involving some intersections. For arbitrary finite strain propagation, numerous difficulties are
encountered: modeling of intersection and coalescence, step size dependence and the presence of distorted finite
elements. In order to overcome these difficulties, an approach fully capable of dealing with multiple advancing
cracks and self-contact is presented (see Fig.1). This approach makes use of a coupled Arbitrary Lagrangian-Eulerian
method (ALE) and local tip remeshing. This is substantially less costly than a full remeshing while retaining its full
versatility. Compared to full remeshing, angle measures and crack paths are superior. A consistent continuationbased
linear control is used to force the critical tip to be exactly critical, while moving around the candidate set.
The critical crack front is identified and propagated when one of the following criteria reaches a material limiting
value: (i) the stress intensity factor; or (ii) the element-ahead tip stress. These are the control equations.
The ability to solve crack intersection and coalescence problems is shown. Additionally, the independence from
crack tip and step size and the absence of blade and dagger-shaped finite elements is observed. Classic benchmarks
are computed leading to excellent crack path and load-deflection results, where convergence rate is quadratic
Effective restoration of chiral and axial symmetries at finite temperature and density
The effective restoration of chiral and axial symmetries is investigated
within the framework of the SU(3) Nambu-Jona-Lasinio model. The topological
susceptibility, modeled from lattice data at finite temperature, is used to
extract the temperature dependence of the coupling strength of the anomaly. The
study of the scalar and pseudoscalar mixing angles is performed in order to
discuss the evolution of the flavor combinations of pairs and its
consequences for the degeneracy of chiral partners. A similar study at zero
temperature and finite density is also realized.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape
Town, South Africa, 15-20 September, 200
Long-Time Behaviour and Self-Similarity in a Coagulation Equation with Input of Monomers
For a coagulation equation with Becker-Doring type interactions and
time-independent monomer input we study the detailed long-time behaviour of
nonnegative solutions and prove the convergence to a self-similar function.Comment: 30 pages, 5 Figures, now published in Markov Processes and Related
Fields 12, 367-398, (2006
Suite of simple metrics reveals common movement syndromes across vertebrate taxa
ecause empirical studies of animal movement are most-often site- and species-specific, we lack understanding of the level of consistency in movement patterns across diverse taxa, as well as a framework for quantitatively classifying movement patterns. We aim to address this gap by determining the extent to which statistical signatures of animal movement patterns recur across ecological systems. We assessed a suite of movement metrics derived from GPS trajectories of thirteen marine and terrestrial vertebrate species spanning three taxonomic classes, orders of magnitude in body size, and modes of movement (swimming, flying, walking). Using these metrics, we performed a principal components analysis and cluster analysis to determine if individuals organized into statistically distinct clusters. Finally, to identify and interpret commonalities within clusters, we compared them to computer-simulated idealized movement syndromes representing suites of correlated movement traits observed across taxa (migration, nomadism, territoriality, and central place foraging)
Statistical analysis of Ni nanowires breaking processes: a numerical simulation study
A statistical analysis of the breaking behavior of Ni nanowires is presented.
Using molecular dynamic simulations, we have determined the time evolution of
both the nanowire atomic structure and its minimum cross section (Sm(t)).
Accumulating thousands of independent breaking events, Sm histograms are built
and used to study the influence of the temperature, the crystalline stretching
direction and the initial nanowire size. The proportion of monomers, dimers and
more complex structures at the latest stages of the breaking process are
calculated, finding important differences among results obtained for different
nanowire orientations and sizes. Three main cases have been observed. (A) [111]
stretching direction and large nanowire sizes: the wire evolves from more
complex structures to monomers and dimers prior its rupture; well ordered
structures is presented during the breaking process. (B) Large nanowires
stretched along the [100] and [110] directions: the system mainly breaks from
complex structures (low probability of finding monomers and dimers), having
disordered regions during their breakage; at room temperature, a huge histogram
peak around Sm=5 appears, showing the presence of long staggered pentagonal Ni
wires with ...-5-1-5-... structure. (C) Initial wire size is small: strong size
effects independently on the temperature and stretching direction. Finally, the
local structure around monomers and dimmers do not depend on the stretching
direction. These configurations differ from those usually chosen in static
studies of conductance.Comment: 18 pages, 13 figure
Predicting language learners' grades in the L1, L2, L3 and L4: the effect of some psychological and sociocognitive variables
This study of 89 Flemish high-school students' grades for L1 (Dutch), L2 (French), L3 (English) and L4 (German) investigates the effects of three higher-level personality dimensions (psychoticism, extraversion, neuroticism), one lower-level personality dimension (foreign language anxiety) and sociobiographical variables (gender, social class) on the participants' language grades. Analyses of variance revealed no significant effects of the higher-level personality dimensions on grades. Participants with high levels of foreign language anxiety obtained significantly lower grades in the L2 and L3. Gender and social class had no effect. Strong positive correlations between grades in the different languages could point to an underlying sociocognitive dimension. The implications of these findings are discussed
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