11,990 research outputs found
Nonabelian gauge field and dual description of fuzzy sphere
In matrix models, higher dimensional D-branes are obtained by imposing a
noncommutative relation to coordinates of lower dimensional D-branes. On the
other hand, a dual description of this noncommutative space is provided by
higher dimensional D-branes with gauge fields. Fuzzy spheres can appear as a
configuration of lower dimensional D-branes in a constant R-R field strength
background. In this paper, we consider a dual description of higher dimensional
fuzzy spheres by introducing nonabelian gauge fields on higher dimensional
spherical D-branes. By using the Born-Infeld action, we show that a fuzzy
-sphere and spherical D-branes with a nonabelian gauge field whose
Chern character is nontrivial are the same objects when is large. We
discuss a relationship between the noncommutative geometry and nonabelian gauge
fields. Nonabelian gauge fields are represented by noncommutative matrices
including the coordinate dependence. A similarity to the quantum Hall system is
also studied.Comment: 28 page
Predicting Skin Permeability by means of Computational Approaches : Reliability and Caveats in Pharmaceutical Studies
© 2019 American Chemical Society.The skin is the main barrier between the internal body environment and the external one. The characteristics of this barrier and its properties are able to modify and affect drug delivery and chemical toxicity parameters. Therefore, it is not surprising that permeability of many different compounds has been measured through several in vitro and in vivo techniques. Moreover, many different in silico approaches have been used to identify the correlation between the structure of the permeants and their permeability, to reproduce the skin behavior, and to predict the ability of specific chemicals to permeate this barrier. A significant number of issues, like interlaboratory variability, experimental conditions, data set building rationales, and skin site of origin and hydration, still prevent us from obtaining a definitive predictive skin permeability model. This review wants to show the main advances and the principal approaches in computational methods used to predict this property, to enlighten the main issues that have arisen, and to address the challenges to develop in future research.Peer reviewedFinal Accepted Versio
Trefftz Difference Schemes on Irregular Stencils
The recently developed Flexible Local Approximation MEthod (FLAME) produces
accurate difference schemes by replacing the usual Taylor expansion with
Trefftz functions -- local solutions of the underlying differential equation.
This paper advances and casts in a general form a significant modification of
FLAME proposed recently by Pinheiro & Webb: a least-squares fit instead of the
exact match of the approximate solution at the stencil nodes. As a consequence
of that, FLAME schemes can now be generated on irregular stencils with the
number of nodes substantially greater than the number of approximating
functions. The accuracy of the method is preserved but its robustness is
improved. For demonstration, the paper presents a number of numerical examples
in 2D and 3D: electrostatic (magnetostatic) particle interactions, scattering
of electromagnetic (acoustic) waves, and wave propagation in a photonic
crystal. The examples explore the role of the grid and stencil size, of the
number of approximating functions, and of the irregularity of the stencils.Comment: 28 pages, 12 figures; to be published in J Comp Phy
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