Characterization of the chaos-hyperchaos transition based on return times.

We discuss the problem of the detection of hyperchaotic oscillations in coupled nonlinear systems when the available information about this complex dynamical regime is very limited. We demonstrate the ability of diagnosing the chaos-hyperchaos transition from return times into a Poincaré section and show that an appropriate selection of the secant plane allows a correct estimation of two positive Lyapunov exponents (LEs) from even a single sequence of return times. We propose a generalized approach for extracting dynamics from point processes that allows avoiding spurious identification of the dynamical regime caused by artifacts. The estimated LEs are nearly close to their expected values if the second positive LE is essentially different from the largest one. If both exponents become nearly close, an underestimation of the second LE may be obtained. Nevertheless, distinctions between chaotic and hyperchaotic regimes are clearly possible.

Quantifying chaotic dynamics from integrate-and-fire processes.

Characterizing chaotic dynamics from integrate-and-fire (IF) interspike intervals (ISIs) is relatively easy performed at high firing rates. When the firing rate is low, a correct estimation of Lyapunov exponents (LEs) describing dynamical features of complex oscillations reflected in the IF ISI sequences becomes more complicated. In this work we discuss peculiarities and limitations of quantifying chaotic dynamics from IF point processes. We consider main factors leading to underestimated LEs and demonstrate a way of improving numerical determining of LEs from IF ISI sequences. We show that estimations of the two largest LEs can be performed using around 400 mean periods of chaotic oscillations in the regime of phase-coherent chaos. Application to real data is discussed.

Response to cotrimoxazole in the management of childhood pneumonia in first-level health care facilities.

BACKGROUND: Reports of high levels of antimicrobial resistance to cotrimoxazole in children with non-severe pneumonia (NSP) have prompted calls for a change to amoxicillin in the therapeutic guidelines at the first-level health care facility (FLHF). FLHFs lack data about the use of World Health Organization (WHO) acute respiratory infection (ARI) standard case management (SCM). OBJECTIVE: To apply ARI SCM guidelines at the FLHF, assess clinical outcome of NSP with oral cotrimoxazole and determine the risk factors influencing treatment outcome. DESIGN: Health care workers (HCWs) at 14 health centres managed children aged 2-59 months with NSP according to ARI SCM guidelines. The primary outcome was treatment failure, including change of antibiotic therapy and loss to follow-up. RESULTS: Of 949 children enrolled, 110 (11.6%) failed therapy with oral cotrimoxazole. Clinical failure was significantly higher among children presenting with a fast respiratory rate of > or = 15 breaths/min above normal for age and wheezing on examination. CONCLUSIONS: To treat children with NSP at the FLHF, oral cotrimoxazole is an acceptable treatment choice in view of the efficacy, cost and ease of use. In children with wheezing and signs of pneumonia, the decision to use antibiotic therapy should be made after a trial of bronchodilator therapy.