Electro-optic delay oscillator with nonlocal nonlinearity: Optical phase dynamics, chaos, and synchronization.

We demonstrate experimentally how nonlinear optical phase dynamics can be generated with an electro-optic delay oscillator. The presented architecture consists of a linear phase modulator, followed by a delay line, and a differential phase-shift keying demodulator (DPSK-d). The latter represents the nonlinear element of the oscillator effecting a nonlinear transformation.

Routes to chaos and multiple time scale dynamics in broadband bandpass nonlinear delay electro-optic oscillators.

The response of a nonlinear optical oscillator subject to a delayed broadband bandpass filtering feedback is studied experimentally, numerically, and analytically. The oscillator loop is characterized by a high cutoff frequency with a response time tau approximately 10 ps and by a low cutoff frequency with a response time theta approximately 1 micros. Moreover, the optoelectronic feedback also consists of a significant delay tauD of the order of 100 ns.

Versatile and robust chaos synchronization phenomena imposed by delayed shared feedback coupling.

In a joint experimental and modeling approach we demonstrate chaos synchronization imposed by a delayed shared feedback coupling between two nonlinear electro-optic oscillators. Robust identical synchronization is obtained for both symmetric and strongly asymmetric timing of the mutual coupling, offering great potential for applications such as chaos-based communications. We further demonstrate antisynchronization as well as generalized synchronization with vanishing linear correlation, by detuning the nonlinearity in one of the oscillators.

Zero-lag long-range synchronization via dynamical relaying.

We show that isochronous synchronization between two delay-coupled oscillators can be achieved by relaying the dynamics via a third mediating element, which surprisingly lags behind the synchronized outer elements. The zero-lag synchronization thus obtained is robust over a considerable parameter range. We substantiate our claims with experimental and numerical evidence of such synchronization solutions in a chain of three coupled semiconductor lasers with long interelement coupling delays.

Synchronization of delay-coupled oscillators: a study of semiconductor lasers.

Two delay-coupled semiconductor lasers are studied in the regime where the coupling delay is comparable to the time scales of the internal laser oscillations. Detuning the optical frequency between the two lasers, novel delay-induced scenarios leading from optical frequency locking to successive states of periodic intensity pulsations are observed. We demonstrate and analyze these dynamical phenomena experimentally using two distinct laser configurations.

Synchronization of chaotic semiconductor laser systems: a vectorial coupling-dependent scenario.

We demonstrate the influence of vectorial coupling on the synchronization behavior of complex systems. We study two semiconductor lasers subject to delayed optical feedback which are unidirectionally coherently coupled via their optical fields. Our experimental and numerical results demonstrate a characteristic synchronization scenario in dependence on the relative feedback phase leading cyclically from chaos synchronization to almost uncorrelated states, and back to chaos synchronization.

Health and physical support for the elderly in Nigeria.

This paper examines the help which elderly Nigerians get in the form of services from family, relatives and non-relatives and the effect of their age, sex, location (urban/rural) and state of health on the provision of these services. Children are by far the most important source of services, followed by grandchildren. Few old people have neither children nor grandchildren available to help them.

Health problems of elderly Nigerians.

A study of men and women over 60 in three cities and their rural hinterlands shows that women have more health problems than men and villagers more than urban residents. The number, nature and effects of health problems and sources of care are discussed, and policy implications of the findings are briefly considered.

Therapy of secondary pulmonary hypertension.

Secondary pulmonary hypertension is seen in disorders that either interfere with gas exchange within the lung or in which large portions of the pulmonary vasculature are obliterated. Because the causes are diverse, there is no uniform approach to therapy. The approach to treatment should be methodic, but aggressive and primarily directed at improving the underlying disease process.

Oxygen therapy titrated to raise mixed venous oxygen content in COPD.

Supplemental oxygen therapy delivered at concentrations which increase PaO2 greater than 60 mm Hg often has minimal effects on either pulmonary hemodynamics or the oxygen tension of mixed venous blood (PvO2). Since mixed venous hypoxemia has been shown to contribute to pulmonary vasoconstriction in experimental conditions and is a determinant of survival in chronic obstructive pulmonary disease (COPD), we evaluated the hemodynamic effects of oxygen therapy titrated to raise PvO2 in 12 COPD patients who underwent right heart catheterization. After room air measurements of mean pulmonary artery pressure, cardia output, and pulmonary vascular resistance, they were randomized to either supplemental oxygen therapy given to raise PaO2 greater than or equal to 60 mm Hg (group 1, n = 6) or to raise PvO2 greater than or equal to 36 mm Hg (group 2, n = 6).