667 research outputs found
Entropy and Poincar\'e recurrence from a geometrical viewpoint
We study Poincar\'e recurrence from a purely geometrical viewpoint. We prove
that the metric entropy is given by the exponential growth rate of return times
to dynamical balls. This is the geometrical counterpart of Ornstein-Weiss
theorem. Moreover, we show that minimal return times to dynamical balls grow
linearly with respect to its length. Finally, some interesting relations
between recurrence, dimension, entropy and Lyapunov exponents of ergodic
measures are given.Comment: 11 pages, revised versio
Trajectory binning scheme and non-active treatment of zero-point energy leakage in quasi-classical dynamics
By expressing an unknown state in terms of a complete set, a simple scheme for approximate quantization of the continuous vibrational-rotational energy distributions that are obtained from quasi-classical trajectory calculations is suggested. The problem of zero-point energy leakage is also revisited, and the new method tested on the prototype OÂ +Â OH and HÂ +Â D2 reactions.http://www.sciencedirect.com/science/article/B6TFN-4NCJCX1-3/1/cba1ca88eec1685b1502de957a8cc17
Approximate Quantum Mechanical Cross Sections and Rate Constants for the H + O3 Atmospheric Reaction Using Novel Elastic Optimum Angle Adiabatic Approaches
Three-dimensional quantum dynamics computations of cross sections and rate constants for the atmospheric reaction H + O3 → O2 + OH are presented. Using a novel elastic optimum angle adiabatic approach published in a previous paper (Varandas, A. J. C.; Szichman, H. Chem. Phys. Lett. 1998, 295, 113), the calculated cross sections cover the range of translational energies 0.035 ≤ Etr/eV ≤ 0.300. Applications of the new approach using both single-path and multiple-path schemes are reported. The results are compared with available classical trajectory and infinite-order-sudden-approximation results. It may be concluded that the calculations obtained from the single-path model give an improved agreement with respect to the sudden ones when compared with the classical trajectory results. In turn, the quantum elastic optimum angle adiabatic multiple-path results show excellent agreement with the same classical results
Travelers' Diarrhea in Children Visiting Tropical Countries
We studied a group of 174 Portuguese children (aged 2 mo-16 y) who mostly traveled to tropical Portuguese-speaking countries and found an attack rate of 21.8% for travelers' diarrhea, much lower than previously described. We also showed that African rate analysis by region may hide significant differences between countries
Test studies on the potential energy surface and rate constant for the OH+O3 atmospheric reaction
We report a single-valued potential energy surface for HO4(2A) from the double many-body expansion method. All n-body (n=2-4) energy terms are taken from published studies on the relevant fragments, with a five-body energy term of Gaussian form added to mimic the experimental activation energy for the OH(v=0)+O3 reaction. A detailed dynamics study of this reaction is also reported using classical trajectories. Good agreement with existing experimental data is obtained.http://www.sciencedirect.com/science/article/B6TFN-41WBCGK-M/1/f846c63bce20f7a4c43e3cdd2338c85
Singularities in the Hamiltonian at electronic degeneracies
http://www.sciencedirect.com/science/article/B6TFM-414NVKS-4/1/a2e26328672bde0840300eafd471860
Equilibrium states for non-uniformly expanding maps: decay of correlations and strong stability
We study the rate of decay of correlations for equilibrium states associated
to a robust class of non-uniformly expanding maps where no Markov assumption is
required. We show that the Ruelle-Perron-Frobenius operator acting on the space
of Holder continuous observables has a spectral gap and deduce the exponential
decay of correlations and the central limit theorem. In particular, we obtain
an alternative proof for the existence and uniqueness of the equilibrium states
and we prove that the topological pressure varies continuously. Finally, we use
the spectral properties of the transfer operators in space of differentiable
observables to obtain strong stability results under deterministic and random
perturbations.Comment: 29 pages, Annales de l'Institut Henri Poincare - Analyse non lineaire
(to appear
Single-Valued DMBE Potential Energy Surface for HSO: A Distributed n-Body Polynomial Approach
An accurate single-valued double many-body expansion (DMBE) potential energy surface is reported for the ground electronic state of HSO based on novel MR CISD ab initio energies suitably corrected for the complete one-electron basis set/complete CI limit. To improve the accuracy of the fit, we have suggested a n-body distributed polynomial approach which implies using individual multinomial developments at the various stationary points. For simplicity, only the three most relevant such points have been considered: two minima (HSO, HOS) and the saddle point connecting them
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