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. A theoretical treatment reveals the universal character of our findings for delay-coupled systems.

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. Lack of household help was more common for women than for men and women were more likely than men to carry on with domestic tasks into extreme old age. Weakness, arthritis and failing vision were the chief health problems leading to a need for more help. Since these are all correlated with age, it is hard to separate these two factors. Increasing levels of migration may deprive old people of their children's services and some move in order to get the care they need.

Going home: migration careers of southern Nigerians.

PIP: Using data on the career migration histories of 533 residents (over 60 years old) of 3 southern Nigerian cities and 471 residents (over 60 years old) of 21 villages within 30 km of these cities, this study compares nonmigrants, returnees, and immigrants on educational and occupational background and ages at 1st and last migration. Findings show that 1) a large majority intend to return home, but many never do; 2) the majority of returnees go home before retirement; 3) migrants over age 65, and especially over age 75, are unlikely to return home; 4) as education and opportunities expand, it is likely that the majority of present cohorts of migrants will spend most of their working lives away from home; 5) economic success may be used to build a house in the city to which one has migrated or to retire in one's home village; 6) most Nigerians look forward to self-employment which facilitates migration and a return home; 7) more widespread wage-employment, with compulsory retirement at age 60, may greatly change the age pattern of returns; and 8) automatic village care is declining as a large proportion of villagers spend their mature years away and those who remain behind may be unable to cope with the increasing number of old people, returnees, and nonmigrants; thus, movement to towns in old age is increasing, especially among women.^ieng

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. Other forms of therapy, which are more controversial, should be reserved for patients with refractory cor pulmonale and should be instituted cautiously and their effects monitored closely.

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). An oxygen-conserving nasal cannula and oxygen concentrator were used. Baseline PaO2, PvO2, and hemodynamics were identical in each group and hemodynamics after four hours and 48 hours of continuous oxygen therapy were unchanged. Ten patients were catheterized after four months of continuous oxygen therapy (group 1, n = 4; group 2, n = 6). Although PvO2 in group 2 had been raised to normal levels (39.2 +/- 1.2 mm Hg), there was no significant improvement in pulmonary hemodynamics. Our preliminary study suggests that oxygen titrated to raise PvO2 to the normal range has no greater hemodynamic effect than oxygen therapy as it is currently prescribed.