2,016 research outputs found
Irreducible Hamiltonian BRST-anti-BRST symmetry for reducible systems
An irreducible Hamiltonian BRST-anti-BRST treatment of reducible first-class
systems based on homological arguments is proposed. The general formalism is
exemplified on the Freedman-Townsend model.Comment: LaTeX 2.09, 35 page
Coordination of Foliar and Wood Anatomical Traits Contributes to Tropical Tree Distributions and Productivity along the Malay-Thai Peninsula
Drought is a critical factor in plant species distributions. Much research points to its relevance even in moist tropical regions. Recent studies have begun to elucidate mechanisms underlying the distributions of tropical tree species with respect to drought; however, how such desiccation tolerance mechanisms correspond with the coordination of hydraulic and photosynthetic traits in determining species distributions with respect to rainfall seasonality deserves attention. In the present study, we used a common garden approach to quantify inherent differences in wood anatomical and foliar physiological traits in 21 tropical tree species with either widespread (occupying both seasonal and aseasonal climates) or southern (restricted to aseasonal forests) distributions with respect to rainfall seasonality. Use of congeneric species pairs and phylogenetically independent contrast analyses allowed examination of this question in a phylogenetic framework. Widespread species opted for wood traits that provide biomechanical support and prevent xylem cavitation and showed associated reductions in canopy productivity and consequently growth rates compared with southern species. These data support the hypothesis that species having broader distributions with respect to climatic variability will be characterized by traits conducive to abiotic stress tolerance. This study highlights the importance of the well-established performance vs. stress tolerance trade-off as a contributor to species distributions at larger scales
Unconventional continuous phase transition in a three dimensional dimer model
Phase transitions occupy a central role in physics, due both to their
experimental ubiquity and their fundamental conceptual importance. The
explanation of universality at phase transitions was the great success of the
theory formulated by Ginzburg and Landau, and extended through the
renormalization group by Wilson. However, recent theoretical suggestions have
challenged this point of view in certain situations. In this Letter we report
the first large-scale simulations of a three-dimensional model proposed to be a
candidate for requiring a description beyond the Landau-Ginzburg-Wilson
framework: we study the phase transition from the dimer crystal to the Coulomb
phase in the cubic dimer model. Our numerical results strongly indicate that
the transition is continuous and are compatible with a tricritical universality
class, at variance with previous proposals.Comment: 4 pages, 3 figures; v2: minor changes, published versio
Placement optimal de caméras contraintes pour la synthèse de nouvelles vues
International audienceNous étudions le problème du placement optimal sous contraintes, de plusieurs caméras, pour la synthèse de nouvelles vues. Une telle configuration optimale est définie comme celle qui minimise l'incertitude de projection des pixels des caméras de prise de vue sur la vue à synthétiser. Le rendu de cette vue est souvent précédé d'une phase de reconstruction 3D approximative. Nous dérivons la matrice de covariance associée à l'incertitude sur la géométrie, puis nous propageons l'erreur sur le plan de la nouvelle vue. Nous observons l'influence de l'interoculaire et de la distance focale des caméras sur l'erreur projetée, pour des distributions de points aléatoires à diverses profondeurs
Towards Interpretable Deep Learning Models for Knowledge Tracing
As an important technique for modeling the knowledge states of learners, the
traditional knowledge tracing (KT) models have been widely used to support
intelligent tutoring systems and MOOC platforms. Driven by the fast
advancements of deep learning techniques, deep neural network has been recently
adopted to design new KT models for achieving better prediction performance.
However, the lack of interpretability of these models has painfully impeded
their practical applications, as their outputs and working mechanisms suffer
from the intransparent decision process and complex inner structures. We thus
propose to adopt the post-hoc method to tackle the interpretability issue for
deep learning based knowledge tracing (DLKT) models. Specifically, we focus on
applying the layer-wise relevance propagation (LRP) method to interpret
RNN-based DLKT model by backpropagating the relevance from the model's output
layer to its input layer. The experiment results show the feasibility using the
LRP method for interpreting the DLKT model's predictions, and partially
validate the computed relevance scores from both question level and concept
level. We believe it can be a solid step towards fully interpreting the DLKT
models and promote their practical applications in the education domain
Triplectic Quantization of W2 gravity
The role of one loop order corrections in the triplectic quantization is
discussed in the case of W2 theory. This model illustrates the presence of
anomalies and Wess Zumino terms in this quantization scheme where extended BRST
invariance is represented in a completely anticanonical form.Comment: 10 pages, no figure
A Frequency-Controlled Magnetic Vortex Memory
Using the ultra low damping NiMnSb half-Heusler alloy patterned into
vortex-state magnetic nano-dots, we demonstrate a new concept of non-volatile
memory controlled by the frequency. A perpendicular bias magnetic field is used
to split the frequency of the vortex core gyrotropic rotation into two distinct
frequencies, depending on the sign of the vortex core polarity inside
the dot. A magnetic resonance force microscope and microwave pulses applied at
one of these two resonant frequencies allow for local and deterministic
addressing of binary information (core polarity)
Hamiltonian BRST-anti-BRST Theory
The hamiltonian BRST-anti-BRST theory is developed in the general case of
arbitrary reducible first class systems. This is done by extending the methods
of homological perturbation theory, originally based on the use of a single
resolution, to the case of a biresolution. The BRST and the anti-BRST
generators are shown to exist. The respective links with the ordinary BRST
formulation and with the -covariant formalism are also established.Comment: 34 pages, Latex fil
- …