10,644 research outputs found
Approximate polynomial preconditioning applied to biharmonic equations on vector supercomputers
Applying a finite difference approximation to a biharmonic equation results in a very ill-conditioned system of equations. This paper examines the conjugate gradient method used in conjunction with the generalized and approximate polynomial preconditionings for solving such linear systems. An approximate polynomial preconditioning is introduced, and is shown to be more efficient than the generalized polynomial preconditionings. This new technique provides a simple but effective preconditioning polynomial, which is based on another coefficient matrix rather than the original matrix operator as commonly used
Spontaneous Lorentz and Diffeomorphism Violation, Massive Modes, and Gravity
Theories with spontaneous local Lorentz and diffeomorphism violation contain
massless Nambu-Goldstone modes, which arise as field excitations in the minimum
of the symmetry-breaking potential. If the shape of the potential also allows
excitations above the minimum, then an alternative gravitational Higgs
mechanism can occur in which massive modes involving the metric appear. The
origin and basic properties of the massive modes are addressed in the general
context involving an arbitrary tensor vacuum value. Special attention is given
to the case of bumblebee models, which are gravitationally coupled vector
theories with spontaneous local Lorentz and diffeomorphism violation. Mode
expansions are presented in both local and spacetime frames, revealing the
Nambu-Goldstone and massive modes via decomposition of the metric and bumblebee
fields, and the associated symmetry properties and gauge fixing are discussed.
The class of bumblebee models with kinetic terms of the Maxwell form is used as
a focus for more detailed study. The nature of the associated conservation laws
and the interpretation as a candidate alternative to Einstein-Maxwell theory
are investigated. Explicit examples involving smooth and Lagrange-multiplier
potentials are studied to illustrate features of the massive modes, including
their origin, nature, dispersion laws, and effects on gravitational
interactions. In the weak static limit, the massive mode and
Lagrange-multiplier fields are found to modify the Newton and Coulomb
potentials. The nature and implications of these modifications are examined.Comment: 27 pages two-column REVTeX, accepted in Physical Review
Dynamical System of Scalar Field from 2-Dimension to 3-D and its Cosmological Implication
We give the three-dimensional dynamical autonomous systems for most of the
popular scalar field dark energy models including (phantom) quintessence,
(phantom) tachyon, k-essence and general non-canonical scalar field models,
change the dynamical variables from variables to observable
related variables , and show the intimate
relationships between those scalar fields that the three-dimensional system of
k-essence can reduce to (phantom) tachyon, general non-canonical scalar field
can reduce to (phantom) quintessence and k-essence can also reduce to (phantom)
quintessence for some special cases. For the applications of the
three-dimensional dynamical systems, we investigate several special cases and
give the exactly dynamical solutions in detail. In the end of this paper, we
argue that, it is more convenient and also has more physical meaning to express
the differential equations of dynamical systems in instead of variables and to investigate the
dynamical system in 3-Dimension instead of 2-Dimension. We also raise a
question about the possibility of the chaotic behavior in the spatially flat
single scalar field FRW cosmological models in the presence of ordinary matter.Comment: 20 pages, 8 figures,some references added. Minor changes according to
the suggestions from referee
Design and Synthesis of CB1 Receptor Ligands and Synthesis of Amphibian Alkaloids
Our project was aimed at the development of novel CB1 cannabinoid receptor antagonists that may have clinical applications for the treatment of cannabinoid and psychostimulant addiction. In this study, we designed, synthesized, and established the CB1 affinity for the 1,5-diaryl-1,2,3- triazole esters, a series of 4,5-diaryl-1-substituted-1,2,3-triazole analogues and a series of 4,5- diaryl-2-substituted-1,2,3-triazoles. Our research group has been interested in the synthesis of amphibian alkaloids due to their interesting biological activities. We have recently developed a general synthetic strategy which can rapidly prepare a few amphibian alkaloids simply from the abundant natural product (-)- cocaine This strategy was first successfully applied to the synthesis of (-)-monomorine. More recently, this strategy has also been utilized in the syntheses of both of the enantiomers of cispyrrolidine 225H and (+)-gephyrotoxin 287C
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