Descripción: This work describes simple decompositions of the energy of molecular systems according to schemes that partition the three-dimensional space. The components of those decompositions depend on one and two atomic domains thus providing a meaningful chemical information about the nature of different bondings among the atoms which compose the system. Our algorithms can be applied at any level of theory (correlated or uncorrelated wave functions). The results reported here, obtained at the Hartree-Fock level in selected molecules, show a good agreement with the chemical picture of molecules and require a low computational cost in comparison with other previously reported decompositions.

Descripción: The effective action for quantum fields on a d-dimensional spacetime can be computed using a non-local expansion in powers of the curvature. We show explicitly that, for conformal fields and up to quadratic order in the curvature, the non-local effective action is equivalent to the d + 1 action for classical gravity in AdSd+1 restricted to a (d - 1)-brane. This generalizes previous results about quantum corrections to the Newtonian potential and provides an alternative method for making local a non-local effective action. The equivalence can be easily understood by comparing the Kallen-Lehmann decomposition of the classical propagator with the spectral representation of the non-local form factors in the quantum effective action. © 2001 Published by Elsevier Science B.V.

Descripción: A procedure for the construction of balanced orthogonal nonseparable quincunx multiwavelets, having filters with good lowpass properties, is introduced. The matrix filter bank is viewed as the polyphase matrix of other filters, upon which the lowpass condition is imposed. The multiscaling functions obtained are plotted by means of the cascade algorithm. The process of transforming an image with these wavelets is outlined: formulae for analysis and synthesis are given, the first steps are illustrated with images, and the decomposition of the original image into two input images is addressed. Compression is achieved in a nonlinear process. Experimental results show that (i) the constructed multiwavelets having lowpass properties perform better than other nonseparable multiwavelets, (ii) the energy compaction in the fine detail subbands is greater for the multiwavelets than for the one-dimensional wavelets tried.

Descripción: A simple model based on the Hasegawa-Mima equation is used to study dipole vortex interactions and turbulence of electrostatic drift waves in a plasma. It is shown that if nonlinear effects are important during vortex collisions, dipoles are broken into monopoles. Nonadiabatic effects also affect dipole behavior, which can be destroyed by the instability of emitted waves (dipole vortex radiation). Simulations of turbulence in both decaying and driven cases show the appearance of long-lived monopole structures. These coherent structures contribute to stop the cascade of energy to large scales, and then to reach a self-organized stationary state. Some numerical evidence is done that Hasegawa-Mima turbulence has a long-time behavior that is much richer than the thermodynamic equilibrium state observed in two-dimensional hydrodynamics. In driven turbulence, an important departure from Gaussian statistics of vorticity fluctuations is found, giving some indication of intermittency. Using various analyzing techniques, in particular the proper orthogonal decomposition, we show that the turbulence can be characterized by a field of coherent structures, which dominates the dynamics of the system, and random waves interacting weakly with the coherent structures. (c) 1995 The American Physical Society © 1995 The American Physical Society.