Ultrafast and widely tuneable vertical-external-cavity surface-emitting laser, mode-locked by a graphene-integrated distributed Bragg reflector.

We report a versatile way of controlling the unsaturated loss, modulation depth and saturation fluence of graphene-based saturable absorbers (GSAs), by changing the thickness of a spacer between a single layer graphene (SLG) and a high-reflection mirror. This allows us to modulate the electric field intensity enhancement at the GSA from 0 up to 400%, due to the interference of incident and reflected light at the mirror. The unsaturated loss of the SLG-mirror-assembly can be reduced to ∼0. We use this to mode-lock a vertical-external-cavity surface-emitting laser (VECSEL) from 935 to 981 nm. This approach can be applied to integrate SLG into various optical components, such as output coupler mirrors, dispersive mirrors or dielectric coatings on gain materials. Conversely, it can also be used to increase the absorption (up to 10%) in various graphene based photonics and optoelectronics devices, such as photodetectors.

Quantifying defects in graphene via Raman spectroscopy at different excitation energies.

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

Seasonality of gestational weight gain and foetal growth in rural Malawi.

OBJECTIVE: To study seasonal variation of maternal anthropometry and newborn weights. DESIGN: A retrospective descriptive study from 1995 to 1998. SETTING: Lungwena, a rural health centre in Malawi, southeast Africa. SUBJECTS: One thousand and thirty two women with singleton pregnancy, a minimum of eight weeks antenatal follow-up and a baby who was weighed in the first month of life. Maternal data were sought from a health centre antenatal register and linked with infant information collected from a newborn clinic. RESULTS: The mean (SD) gestational weight and fundal height gains among the pregnant women were 240 (200) grams and 0.9 (0.2) cm/week and the mean (SD) newborn weight 3360 (530) grams. Gestational weight gains followed a seasonal pattern and they were typically highest among women delivering in the third quarter of the year (mean gain 250-300 g/week) and lowest among those delivering in January-May (mean gain 100-200 g/week) (p < 0.001 for seasonality, ANOVA). For maternal fundal height gains and newborn weights, seasonality was less obvious (but statistically significant, p < 0.05, ANOVA) and its pattern was influenced by year of study. On average, newborn weights peaked in the last quarter (mean 3350-3400 grams) and nadired during the second quarter (mean 3200-3300 grams). There was only a modest correlation between maternal weight gain in pregnancy and the weight of her newborn (Pearson's correlation coefficient 0.13). CONCLUSION: In rural Malawi, maternal weight gains during pregnancy are more strongly associated with season than fundal height gains or newborn weights. In adverse environmental conditions, foetal growth ismaintained at least partially at the expense of mother's nutritional status.

Seasonality of growth and the relationship between weight and height gain in children under three years of age in rural Malawi.

AIM: To describe the seasonal pattern of growth and analyse the relationship between weight and height gain in children under 3 y of age. METHODS: A population-based cohort of 767 children was prospectively followed from birth until 36 mo of age in rural Malawi, southeast Africa. Weight and height measurements were collected at monthly intervals until 18 mo of age and quarterly thereafter. Gains in weight and height and prevalence of malnutrition in different seasons were calculated. The relationship between weight and height gain was analysed using a series of correlation analyses. RESULTS: Both weight gain and linear growth velocity showed an age-dependent seasonal pattern. After infancy, periods of maximal or minimal height increments systematically occurred 3 mo after those for weight gain. The prevalence of malnutrition also followed a seasonal pattern, peaking a few months after periods of reduced growth. Despite the overall pattern, weight gain and subsequent linear growth were not correlated on an individual level. At any point, however, a child's weight for height was directly, albeit weakly, correlated to height gain in the subsequent 3-mo interval. CONCLUSION: Growth of children under 3 y of age followed an age-dependent seasonal pattern. The poor correlation between children's weight and height increments suggests that seasonality affected weight gain and linear growth through different mechanisms.

Timing of growth faltering in rural Malawi.

AIM: To determine the timing of growth faltering among under 3 year old children. METHODS: Prospective population based cohort study in Lungwena, rural Malawi, southeast Africa. A total of 767 live born babies were regularly visited from birth until 3 years of age. Weight, height, and mid upper arm circumference were measured at monthly intervals until 18 months and at three month intervals thereafter. Growth charts were constructed using the LMS method and comparisons made to two international databases: the traditional United States National Center for Health Statistics/World Health Organisation (NCHS/WHO) reference and the recently developed 2000 Centers for Disease Control (CDC) growth reference. RESULTS: Compared to the 2000 CDC reference population, newborns in Lungwena were on average 2.5 cm shorter and 510 g lighter. On a population level, height faltering was present at birth and continued throughout the first three years. Weight faltering, on the other hand, occurred mainly between 3 and 12 months of age. At 36 months, the mean weight and height of the study children were 2.3 kg and 10.5 cm lower than those of the reference population, respectively. The results remained essentially similar when the comparisons were made to the NCHS/WHO reference. CONCLUSIONS: The fact that weight and height faltering do not follow identical time patterns suggests that they may have different origin and determinants. Further studies on the aetiology of height faltering and different approaches to preventive interventions are needed.

Male biased mortality among 1-2 year old children in rural Malawi.

We performed a community based cohort study in rural Malawi and documented a twofold mortality risk among 1-2 year old boys compared to girls of the same age. Because of its potential implications for child survival programmes, further studies should investigate whether sex differences in childhood mortality are more widespread in Sub-Saharan Africa.

Determinants of linear growth and predictors of severe stunting during infancy in rural Malawi.

UNLABELLED: Stunting is common among children under 5 y of age in sub-Saharan Africa. Several risk factors have been associated with poor growth but few studies have prospectively addressed the development of linear growth faltering and stunting during the first year of life. The present study was designed to analyse typical growth among rural Malawian infants, focusing particularly on the impact of birth size, adherence to feeding guidelines and morbidity in the development of severe stunting during infancy. A community-based cohort of 613 singleton newborns was prospectively followed by monthly home visits. Data were collected on the children's socioeconomic background, maternal size and weight gain during pregnancy, birth events, morbidity, breastfeeding and complementary feeding, growth and mortality. Univariate and multivariate analyses were used to determine associations between predictor variables and poor linear growth. The proportions of stunted infants (Height-for-age Z-score < -2) at 3, 6 and 9 mo of age were 27%, 51%, and 63%, respectively. At I y of age, over two-thirds (71%) of the infants were at least moderately (HAZ < -2) and 31% severely stunted (HAZ < -3). CONCLUSION: The strongest predictor of severe stunting at 12 mo of age was small birth size. Other variables independently associated with this outcome included inappropriate complementary feeding, high morbidity, maternal short stature, male gender, and home delivery. Faltering of linear growth started soon after birth and continued throughout infancy. Interventions increasing birth size could have a significant role in the prevention of early childhood stunting. The ideal strategy should also emphasize the importance of appropriate infant feeding and decreasing the number of illness episodes amongst the infants.

Breastfeeding and complementary feeding practices in rural Malawi.

UNLABELLED: To facilitate optimal growth of newborns, many countries have developed infant feeding recommendations, usually suggesting 4-6 mo of exclusive breastfeeding and then the gradual introduction of complementary foods. We prospectively studied the changes in infant diets and predictors of adherence to national infant feeding recommendations in a cohort of 720 newborn babies in rural Malawi, Sub-Saharan Africa. Monthly interviews of the main guardians indicated that breastfeeding was universal for 18 mo. As most babies were given water or other supplemental foods soon after birth, the exclusive breastfeeding rates were only 19%, 8%, 2% and 0% at ages 1, 2, 3 and 4 mo, respectively. Complementary foods and family foods were introduced at median ages of 2.5 and 6.3 mo, i.e. much earlier than recommended. Better adherence to recommendations was associated with smaller number of children in the family, increased maternal education and some other socio-economic or environmental variables. CONCLUSION: Exclusive breastfeeding is uncommon and complementary foods were introduced early to newborns among these rural families. Education and family planning may improve adherence to infant feeding recommendations and reduce the incidence of early childhood malnutrition in Malawi.

Gestational health and predictors of newborn weight amongst pregnant women in rural Malawi.

This study was conducted to provide community-based data on maternal health and predictors of newborn weight in rural Malawi. Data were obtained prospectively from a community-based cohort of 581 pregnant women who attended an antenatal clinic and delivered a term, live-born, singleton infant in Lungwena, rural Malawi. Morbidity from infectious diseases and anaemia was common. Maternal weight gain in rural Malawi was slower but fundal height gain was comparable to that of an affluent western population. The mean +/- SD weight of term newborns was 3.2 +/- 0.5 kilograms. A regression model including data from all routine investigations explained only 24% of the variance in newborn weights, suggesting that routine antenatal measurements had a limited power to predict the size of term live-born babies. Maternal parity, initial weight, the duration of pregnancy and gestational weight gain were associated with newborn weights and should, therefore, be systematically recorded in rural Malawian antenatal clinics.

Epidemiology and predictors of infant morbidity in rural Malawi.

In rural Malawi, 703 newborns were visited monthly for 1 year to describe the epidemiology and health-seeking behaviour during acute episodes of diarrhoea, respiratory infections (ARI) and malaria. On average, the infants suffered from 1.3 annual episodes (11.0 illness days) of diarrhoea, 1.1 episodes (9.4 days) of ARI and 0.7 episodes (4.8 days) of malaria. Multivariate analysis with polychotomous logistic regression indicated that the amount of morbidity was associated with the child's area of residence, weight in early life, number of siblings, father's marital status and the source of drinking water. Diarrhoea and malaria were most common at 6-12 months of age and during the rainy months whereas respiratory infections peaked at 1-3 months of age and in the cold season. Ten per cent of diarrhoea, 9% of ARI and 7% of malaria episodes lasted for more than 14 days. Fifty-eight infants died, giving case fatality rates of 1% for diarrhoea, 2% for ARI and 4% for malaria. One-third (37%) of the illness episodes were managed at home without external advice. A traditional healer was consulted in 16% of episodes and a medical professional in 55% of episodes. If consulted, traditional healers were seen earlier than medical professionals (median duration after the onset of symptoms 0.7 vs. 1.8 days, P < 0.001). Traditional healers were significantly more commonly used by those families whose infants died than by those whose infants did not die (odds ratio 1.8, 95% CI 1.1, 3.0). Our results emphasise the influence of seasonality, care and living conditions on the morbidity of infants in rural Malawi. Case fatality for diarrhoea, ARI and malaria was high and associated with health-seeking behaviour among the guardians. Future interventions must aim at early and appropriate management of common childhood illnesses during infancy.

The relationship between antenatal risk characteristics, place of delivery and adverse delivery outcome in rural Malawi.

OBJECTIVE: To describe and compare the frequency of antenatally identified maternal 'risk' characteristics, place of delivery and occurrence of delivery complications. METHODS: A prospective cohort study of 780 pregnant women completing antenatal follow-up at a rural health center in Malawi. RESULTS: Three-quarters of the subjects had at least one commonly accepted risk characteristic. Only 30% of these women, and 22% of those with no risk characteristics, delivered in a modern health facility. Four women died, 127 experienced other delivery complications and there were 52 perinatal deaths. The 'at-risk' classification had over 80% sensitivity but less than 30% specificity to predict delivery complications or perinatal deaths. The positive predictive values were as low as 20% for delivery complications and 7% for perinatal mortality. Most individual 'risk' characteristics were not associated with adverse delivery outcomes, even when adjusted for the place of delivery. CONCLUSIONS: Antenatal risk identification failed to promote safe deliveries because of a poor predictive value of the 'risk' variables and the failure of the identified 'at-risk' individuals to deliver in modern health facilities.

The importance of preterm births for peri- and neonatal mortality in rural Malawi.

Peri- and neonatal mortality remain high in developing countries, especially in sub-Saharan Africa. In the present study, we quantified and identified the most important predictors of early mortality in rural Malawi. Data were obtained from a community-based cohort of 795 pregnant women and their 813 fetuses, followed prospectively from mid-pregnancy. In this group, peri- and neonatal mortality rates were 65.3 deaths per 1000 births and 37.0 deaths per 1000 live births respectively. When controlled for month of birth, maternal age and selected socio-economic variables, preterm birth was the strongest independent predictor of both peri- and neonatal mortality (adjusted odds ratios 9.6 for perinatal and 11.0 for neonatal mortality; 95% confidence intervals: [4.4, 21.0] and [3.7, 32.7] respectively). Weaker risk factors for mortality included a maternal history of stillbirth and abnormal delivery. Preterm delivery was associated with primiparity and peripheral malaria parasitaemia of the mother, and it accounted for 65% of the population-attributable risk for perinatal and 68% of the neonatal mortality. Successful intervention programmes to reduce peri- and neonatal mortality in Malawi have to include strategies to predict and prevent prematurity.

Antenatal and perinatal predictors of infant mortality in rural Malawi.

BACKGROUND: The slow pace in the reduction of infant mortality in sub-Saharan Africa has partially been attributed to the epidemic of human immunodeficiency virus (HIV) infection. To facilitate early interventions, antenatal and perinatal predictors of 1st year mortality were identified in a rural community in southern Malawi. METHODS: A cohort of 733 live born infants was studied prospectively from approximately 24 gestation weeks onwards. Univariate analysis was used to determine relative risks for infant mortality after selected antenatal and perinatal exposures. Multivariate modelling was used to control for potential confounders. FINDINGS: The infant mortality rate was 136 deaths/1000 live births. Among singleton newborns, the strongest antenatal and perinatal predictors of mortality were birth between May and July, maternal primiparity, birth before 38th gestation week, and maternal HIV infection. Theoretically, exposure to these variables accounted for 22%, 22%, 17%, and 15% of the population attributable risk for infant mortality, respectively. INTERPRETATION: The HIV epidemic was an important but not the main determinant of infant mortality. Interventions targetting the offspring of primiparous women or infants born between May and July or prevention of prematurity would all have considerable impact on infant survival.

Health for all in the 21st century?

Approximately two decades ago world health authorities met in Alma-Ata to discuss the unequal distribution of health and other global questions. The meeting produced a declaration that emphasized the role of primary care in the provision of health services. Furthermore, adequate socioeconomic support, such as availability of food security, clean water, appropriate housing, and education, were all considered integral parts of health development. After the meeting, the World Health Organization developed a programme called 'Health for All by 2000', outlining strategies towards maximal health improvements all over the world. Thereafter, individual countries have developed national modifications from this agenda, and global development of health has on average been favourable. In the economically least developed countries, however, progress has been significantly slower than elsewhere. This editorial discusses the problem of inadequate socioeconomic development and increasing global health disparity through an example from Lungwena, a rural area in Sub-Saharan Africa. In the 21st century, poverty reduction is the key strategy towards health improvement in the least developed countries.

Socio-economic support for good health in rural Malawi.

OBJECTIVE: To study the socio-economic support for good health among subsistence farmers in rural Malawi. DESIGN: A cross-sectional survey. SETTING: Lungwena, a rural area with 17,000 inhabitants in southern Malawi. PARTICIPANTS: Seven hundred and ninety five pregnant women who attended the antenatal clinic at Lungwena Health Centre between June 1995 and September 1996. INTERVENTIONS: Interviews about socio-economic conditions. Measurements of cultivated land areas and distances between home and the local health centre. MAIN OUTCOME MEASURES: Proportion of households lacking literate adults, adequate water source and sanitation, easy access to modern health care or food security. RESULTS: Only 14% of the interviewed women could read and write and half of the households had no literate members. Every fifth household was lacking both an access to safe drinking water and a proper sanitary facility. The distance to the health centre was more than 5 km among half of the households and only 37% had enough land to grow food for all family members. When other potential means of obtaining food were taken into account, 27% of the households had no food security. Numerous households were lacking more than one socio-economic prerequisites of good health: three or more were missing from a quarter of the families. CONCLUSIONS: Socio-economic prerequisites of health were commonly missing in Lungwena. Subsequent health interventions should strengthen the investments into general poverty alleviation.

Childhood immunization in rural Malawi: time of administration and predictors of non-compliance.

A cohort of 760 newborns was followed prospectively for 2 years to ascertain the time of administration of childhood vaccinations in rural Malawi and to study predictors of non-compliance with national vaccination recommendations. At 1 year of age, 99% of the infants were fully vaccinated against tuberculosis, 91% against polio, 90% against diphtheria, pertussis and tetanus and 64% against measles. At 2 years, the corresponding vaccination coverages were 99%, 93%, 93% and 84%. On average, all vaccinations were given 1-3 months later than recommended. Many of the delayed measles vaccinations were given during a separate vertical campaign, during which 25% of previously unvaccinated 21-23-month-old children were identified and immunized. Non-compliance with vaccination recommendations was associated with living in villages with no access to mobile vaccination teams, birth between April and June and birth at home. In this rural Malawian area, most vaccination services were functioning well. To increase measles vaccination coverage, regular outreach activities should be encouraged.

Interaction between proxyphylline and salbutamol.

Salbutamol increased significantly the bronchodilating effect of proxyphylline both in experimental animals and in asthmatic patients. In guinea pigs (modified Konzett-Rössler method) the reduction in response to metacholine caused by increasing doses of proxyphylline and salbutamol significantly exceeded that of either drug alone. In a double-blind, randomized cross-over study conducted on 3 consecutive days, asthmatic patients received 500 mg proxyphylline orally three times daily. On the 2nd or 3rd day a significantly greater improvement in the peak expiratory flow was found after the combination of proxyphylline and salbutamol (3 mg p.o.) in comparison with proxyphylline and placebo. Salbutamol had no significant effect on the plasma concentrations of proxyphylline, which varied between 14 and 22 microgram/ml. The combination of oral proxyphylline and salbutamol is clinically useful in increasing drug response without increased adverse effects.