1,042 research outputs found
Recommended from our members
Bézier polynomials over triangles and the construction of piecewise Cr polynomials
Fermions in the pseudoparticle approach
The pseudoparticle approach is a numerical technique to compute path
integrals without discretizing spacetime. The basic idea is to integrate over
those field configurations, which can be represented by a sum of a fixed number
of localized building blocks (pseudoparticles). In a couple of previous papers
we have successfully applied the pseudoparticle approach to pure SU(2)
Yang-Mills theory. In this work we discuss how to incorporate fermionic fields
in the pseudoparticle approach. To test our method, we compute the phase
diagram of the 1+1-dimensional Gross-Neveu model in the large-N limit.Comment: 11 pages, 10 figure
Design, Synthesis and Biological Evaluation of New 5,5-Diarylhydantoin Derivatives as Selective Cyclooxygenase-2 Inhibitors
A new group of 5,5-diarylhydantoin derivatives bearing a methylsulfonyl COX-2 pharmacophore at the para position of the C-5 phenyl ring were designed and synthesized as selective COX-2 inhibitors. In vitro COX-1/COX-2 inhibition structure-activity relationships identified 5-[4-(methylsulfonyl)phenyl]-5-phenyl-hydantoin (4) as a highly potent and selective COX-2 inhibitor (COX-2 IC50 = 0.077 μM; selectivity index > 1298). It was more selective than the reference drug celecoxib (COX-2 IC50 = 0.060 μM; selectivity index = 405). A molecular modeling study where 4 was docked in the binding site of COX-2 indicated that the p-MeSO2 COX-2 pharmacophore group on the C-5 phenyl ring is oriented in the vicinity of the COX-2 secondary pocket. The results of this study showed that the type of substituent on the N-3 hydantoin ring substituent is important for COX-2 inhibitory activity
Adsorption and diffusion of Ru adatoms on Ru(0001)-supported graphene: Large-scale first-principles calculations
Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moirécell, there are three distinct regions: fcc, hcp, and mound, in which the C6-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a localdiffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001).The following article appeared in Journal of Chemical Physics 143, 16 (2015): 164706 and may be found at doi: 10.1063/1.4934349.</p
L-systems in Geometric Modeling
We show that parametric context-sensitive L-systems with affine geometry
interpretation provide a succinct description of some of the most fundamental
algorithms of geometric modeling of curves. Examples include the
Lane-Riesenfeld algorithm for generating B-splines, the de Casteljau algorithm
for generating Bezier curves, and their extensions to rational curves. Our
results generalize the previously reported geometric-modeling applications of
L-systems, which were limited to subdivision curves.Comment: In Proceedings DCFS 2010, arXiv:1008.127
A survey of partial differential equations in geometric design
YesComputer aided geometric design is an area
where the improvement of surface generation techniques
is an everlasting demand since faster and more accurate
geometric models are required. Traditional methods
for generating surfaces were initially mainly based
upon interpolation algorithms. Recently, partial differential
equations (PDE) were introduced as a valuable
tool for geometric modelling since they offer a number
of features from which these areas can benefit. This work
summarises the uses given to PDE surfaces as a surface
generation technique togethe
Continuum viscoplastic simulation of a granular column collapse on large slopes: μ(I) rheology and lateral wall effects
We simulate here dry granular flows resulting from the collapse of granular columns on an inclined channel (up to 22°) and compare precisely the results with laboratory experiments. Incompressibility is assumed despite the dilatancy observed in the experiments (up to 10%). The 2-D model is based on the so-called μ(I) rheology that induces a Drucker-Prager yield stress and a variable viscosity. A nonlinear Coulomb friction term, representing the friction on the lateral walls of the channel, is added to the model. We demonstrate that this term is crucial to accurately reproduce granular collapses on slopes ≳10°, whereas it remains of little effect on the horizontal slope. Quantitative comparison between the experimental and numerical changes with time of the thickness profiles and front velocity makes it possible to strongly constrain the rheology. In particular, we show that the use of a variable or a constant viscosity does not change significantly the results provided that these viscosities are of the same order. However, only a fine tuning of the constant viscosity (η=1 Pa s) makes it possible to predict the slow propagation phase observed experimentally at large slopes. Finally, we observed that small-scale instabilities develop when refining the mesh (also called ill-posed behavior, characterized in the work of Barker et al. [“Well-posed and ill-posed behaviour of the μ(I)-rheology for granular flow,” J. Fluid Mech. 779, 794–818 (2015)] and in the present work) associated with the mechanical model. The velocity field becomes stratified and the bands of high velocity gradient appear. These model instabilities are not avoided by using variable viscosity models such as the μ(I) rheology. However we show that the velocity range, the static-flowing transition, and the thickness profiles are almost not affected by them
Comparing faceted and smoothed tool surface descriptions in sheet metal forming simulation
This study deals with different tool surface description
methods used in the finite element analysis of sheet metal
forming processes. The description of arbitrarily-shaped tool
surfaces using the traditional linear finite elements is compared
with two distinct smooth surface description approaches:
(i) Bézier patches obtained from the ComputerAided
Design model and (ii) smoothing the finite element
mesh using Nagata patches. The contact search algorithm is
presented for each approach, exploiting its special features in
order to ensure an accurate and efficient contact detection. The
influence of the tool modelling accuracy on the numerical
results is analysed using two sheet forming examples, the
unconstrained cylindrical bending and the reverse deep drawing
of a cylindrical cup. Smoothing the contact surfaces with
Nagata patches allows creating more accurate tool models,
both in terms of shape and normal vectors, when compared
with the conventional linear finite element mesh. The computational
efficiency is evaluated in this study through the total
number of increments and the required CPU time. The mesh
refinement in the faceted description approach is not effective
in terms of computational efficiency due to large discontinuities
in the normal vector field across facets, even when
adopting fine meshes.The authors gratefully acknowledge the financial
support of the Portuguese Foundation for Science and Technology (FCT)
via the projects PTDC/EME-TME/118420/2010 and PEst-C/EME/
UI0285/2013 and by FEDER funds through the program COMPETE –
Programa Operacional Factores de Competitividade, under the project
CENTRO-07-0224-FEDER-002001 (MT4MOBI). The first author is
also grateful to the FCT for the PhD grant SFRH/BD/69140/2010.info:eu-repo/semantics/publishedVersio
- …