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Formulae are given for calculating ring asymmetry parameters and e.s.d.'s from the out-of-plane displacements of the atoms of a ring.The asymmetry parameters have been proposed by Duax, Weeks & Rohrer (1976) to give a quantitative evaluation of how a ring of any size deviates from ideal symmetry and to help in describing its conformation. These parameters are calculated as r.m.s.'s of the sums of mirror-related torsion angles (ACs) or r.m.s.'s of the differences of twofoldaxis-related torsion angles (AC2).Similar parameters, but directly connected with Cremer & Pople's (1975) total puckering amplitude, can be defined using the perpendicular displacements of the atoms from the mean plane through them. These parameters, which could be called displacement asymmetry parameters, are defined, together with their e.s.d.'s, by the following equations, where n is the number of the atoms of the ring, r i is the perpendicular displacement of atom i from the mean plane and R i is its distance from the center of the ring (the nomenclature is that proposed by Duax et al.). all the possible cases are as follows.

The coordinates of hydroxyl (alcohol, phenol, etc.) and water H atoms can be easily calculated, within acceptable approximation, by combined geometric and force-®eld calculations on the basis of hydrogen-bonding interactions. To perform this kind of calculation the computer program HYDROGEN has been developed.

This paper reports on how emotional states elicited by affective sounds can be effectively recognized by means of estimates of Autonomic Nervous System (ANS) dynamics. Specifically, emotional states are modeled as a combination of arousal and valence dimensions according to the well-known circumplex model of affect, whereas the ANS dynamics is estimated through standard and nonlinear analysis of Heart rate variability (HRV) exclusively, which is derived from the electrocardiogram (ECG). In addition, Lagged Poincaré Plots of the HRV series were also taken into account. The affective sounds were gathered from the International Affective Digitized Sound System and grouped into four different levels of arousal (intensity) and two levels of valence (unpleasant and pleasant). A group of 27 healthy volunteers were administered with these standardized stimuli while ECG signals were continuously recorded. Then, those HRV features showing significant changes (p<0.05 from statistical tests) between the arousal and valence dimensions were used as input of an automatic classification system for the recognition of the four classes of arousal and two classes of valence. Experimental results demonstrated that a quadratic discriminant classifier, tested through Leave-One-Subject-Out procedure, was able to achieve a recognition accuracy of 84.72% on the valence dimension, and 84.26% on the arousal dimension.