Giant enhancement of second-harmonic generation in multiple diffraction orders from sub-wavelength resonant waveguide grating.

We demonstrate a purely dielectric resonant waveguide structure that enhances the efficiency of second-harmonic generation by a factor of at least 5500 compared to a flat reference surface in the same geometry. We also show that the structure emits second-harmonic radiation in four different directions when the sample is illuminated with fundamental radiation incident at the resonant angle of the sample.

Litter decomposition and nitrogen and phosphorus dynamics in peatlands and uplands over 12 years in central Canada.

The large accumulation of organic matter in peatlands has been partially attributed to litter decomposition rates, which are slowed by a high water table. To test this, we examined whether there were significant differences in the decomposition and N and P dynamics of ten foliar litters and wood blocks at three pairs of upland forest and peatland sites in the transitional grassland, high boreal and low subarctic regions of central Canada, using litterbags collected over a 12-year period. At two of the three pairs, the decomposition rate, as determined by proportion of the original mass remaining after 12 years and by the exponential decay coefficient (k), was faster overall at the upland than at the peatland. In the third pair, there was no significant difference, despite the water table being close to the peat surface; warmer soil temperatures in the peatland than the upland may be the cause. In general, there were small losses or gains of N in the litters after 12 years, compared to the original litter, though there were some differences among litter types and sites, net gains in N likely reflecting the higher exogenous N availability. P was lost from most litters at the two northern pairs of sites, but at the transitional grassland pair, there were large net gains in P and greater variation among litters. The N:P ratio in the original litters ranged from 5 to 26 and after 12 years the ratio narrowed, with the site average of the ten litters ranging from 13 to 22, varying with the soil ratio. Decomposition rates and N and P dynamics after 12 years are different between upland and peatland sites: although the water table is a primary control on these differences, other factors such as temperature and soil nutrient status are also important.

Mothers of very low birth weight infants have less atopy than mothers of full-term infants.

BACKGROUND: Studies on the pregnancy outcome of asthmatic mothers have suggested an increased rate of preterm deliveries. In contrast, our earlier study suggests that mothers of very low birth weight (VLBW) (<1500 g) infants less frequently had atopy than did mothers of full-term infants. METHODS: We inquired about symptoms of atopy and doctor-diagnosed atopy in parents of 370 infants of VLBW (<1500 g) and 544 parents of full-term infants. Odds ratios for atopic symptoms and diagnosed atopy were calculated, and groups were compared with a trend test. RESULTS: Mothers of preterm infants of birth weight (BW) <1000 g significantly less often had physician-diagnosed allergic rhinitis (AR) (P=0.02). Among all the mothers, a trend test showed that maternal AR was significantly (P=0.03) higher in parallel with a higher infant BW. Fathers of infants with different BWs showed no differences in prevalence of atopic symptoms. CONCLUSION: We thus infer that maternal balance between T-helper type 1 (Th1) and Th2 cells, shifted towards Th2 in those with AR, may have a favourable effect on maintenance of pregnancy before gestational week 30.

A dual long-term effect of breastfeeding on atopy in relation to heredity in children at 4 years of age.

BACKGROUND: The long-term effect of early feeding on atopic sensitization is still unsolved. The aim of this study was to evaluate the long-term effect of breastfeeding on atopy in groups of 4-year-old children stratified by atopic heredity. METHODS: We collected four groups of 4-year-old children from a birth cohort: two groups with differing backgrounds of atopic heredity, all exclusively breast-fed for at least 3 months; and two groups with differing atopic heredity, but all fed with cow's milk-based formula during their first weeks. The data were collected with a questionnaire, skin prick testing, and measurement of serum total and allergen-specific IgE levels. RESULTS: Breastfeeding significantly decreased the risk of allergic rhino-conjunctivitis [odds ratio (OR) 0.41, 95% confidence interval (CI) 0.18-0.95] and sensitization to furred pets, as measured by skin prick results, in children with atopic heredity, whereas in children without atopic heredity, breastfeeding was related to an increased risk of symptomatic atopy (OR 2.57, 95% CI 1.16-5.70), and high serum IgE values. A significant interaction was found between heredity and breastfeeding. CONCLUSIONS: The long-term effect of breastfeeding was dual: in children with atopic heredity, breastfeeding protected against atopy, whereas in children without atopic heredity, it increased the risk of atopy.

Prematurity at birth reduces the long-term risk of atopy.

BACKGROUND: Antigen exposure in early life has long-lasting effects on atopic sensitization. Thus the predisposition to atopy of children born preterm can be assumed to differ from that of children born at term. OBJECTIVE: The aim of this study was to evaluate the association between premature birth and atopy. METHODS: At an outpatient clinic, we examined 2 groups of 10-year-old children, 72 who were born preterm (birth weight < 1500 g) and 65 who were born at term (birth weight > 2500 g). The atopy data were collected with a questionnaire, by performing skin prick testing, and by measuring the serum total IgE level, 3 allergen-specific IgE levels, the eosinophil cationic protein level, and the blood eosinophil level. The data on perinatal and neonatal events affecting the preterm children were collected from the hospital records. RESULTS: By the age of 10 years, the children born preterm had significantly less atopy than the children born at term: 15% versus 31% of children in the 2 groups were defined as having had obvious atopy (P = .03, odds ratio 0.41, 95% CI 0.18-0.93). The mean value of total IgE level was significantly higher in the term group, 74 kU/L versus 41 kU/L (P = .02). By skin prick testing, the children born at term had positive reactions 2 to 3 times more often; 37% versus 17% of children in the groups had at least 1 positive reaction (P = .007). CONCLUSION: Our data show that prematurity at birth is linked with a decreased long-term risk of atopic sensitization.