We prove the existence of oscillatory solutions of the nonlinear wave equation, under irrationality conditions stronger than the usual Diophantine one, by perturbative techniques inspired by the Lindstedt series method originally introduced in classical mechanics to study the existence of invariant tori in quasi-integrable Hamiltonian systems.

An enzyme preparation catalyzing the 2’-hydroxylation of thymidine was prepared from mycelial extracts of Neurospora crassa strain STA 4 (FGSC 2628) by chromatography on hydroxylapatite and DEAE-Sephadex A-50. The enzyme had an isoelectric point of 4.6 and a molecular weight of 47,000 (determined by gel filtration). The reaction product was identical with thymine riboside on ion exchange and th...

Poincare plots are commonly used to study nonlinear behaviour of physiologic signals. Analysis of Poincare plots for various lags can provide interesting insights into the autonomic control of the heart. Furthermore, the width of Poincare plots can be considered as a criterion of short-term variability in heart rate signals. The hypothesis that Poincare plot indexes of heart rate variability (H...

The Lindstedt series were introduced in the XIX century in Astronomy to study perturbatively quasi-periodic motions in Celestial Mechanics. In Mathematical Physics, after getting the attention of Poincaré, who studied them widely by pursuing to all orders the analysis of Lindstedt and Newcomb, their use was somehow superseded by other methods usually referred to as KAM theory. Only recently, af...

Recenzja książki: Iwona Lindstedt, „Piszę tylko muzykę”. Kazimierz Serocki, Kraków 2020. Książka Iwony Lindstedt o Serockim to jedna z najbardziej wartościowych propozycji PWM-u, adresowana do szerokiego odbiorcy. Jest lekturą wymagającą i obszerną, gdyż wymyka się kategorii popularnych dziś wydań kieszonkowych, ocierających niebezpiecznie zarzut „wszystkiego niczego jednocześnie“. Nie uwodzi r...

Presently T-wave alternans (TWA) has become a clinical index of non-invasive diagnosis for heart sudden death prediction, and detecting T-wave alternate accurately is particularly important. This paper introduces an algorithm for detecting TWA using Poincare mapping method which is a technique for nonlinear dynamic systems to display periodic behavior. Sample series of beat to beat cycles were ...