Mexican-hat dispersions and high carrier mobility of γ-SnX (X = O, S, Se, Te) single-layers: a first-principles investigation.

The shape of energy dispersions near the band-edges plays a decisive role in the transport properties, especially the carrier mobility, of semiconductors. In this work, we design and investigate the γ phase of tin monoxide and monochalcogenides γ-SnX (X = O, S, Se, and Te) through first-principles simulations. γ-SnX is found to be dynamically stable with phonon dispersions containing only positive phonon frequencies. Due to the hexagonal atomic lattice, the mechanical properties of γ-SnX single-layers are directionally isotropic and their elastic constants meet Born's criterion for mechanical stability. Our calculation results indicate that all four single-layers of γ-SnX are semiconductors with the Mexican-hat dispersions. The biaxial strain not only greatly changes the electronic structures of the γ-SnX single-layers, but also can cause a phase transition from semiconductor to metal. Meanwhile, the effects of an electric field on the electron states of γ-SnX single-layers are insignificant. γ-SnX structures have high electron mobility and their electron mobility is highly directional isotropic along the two transport directions x and y. The findings not only initially introduce the γ phase of group IV-VI compounds, but also serve as a premise for further studies on this material family with potential applications in the future, both theoretically and experimentally.

Prevalence and characteristics of gastroesophageal reflux disease in pregnant women.

INTRODUCTION AND AIMS: The prevalence of gastroesophageal reflux disease (GERD) has been reported to be increasing in recent years. However, there have been few reports on the prevalence of GERD during pregnancy in the Asian population. The aim of our study was to evaluate the prevalence and characteristics of GERD in Vietnamese pregnant women. MATERIALS AND METHODS: This cross-sectional study was conducted at the antenatal clinic of the Nhan Dan Gia Dinh Hospital, Ho Chi Minh, Vietnam. Four hundred females, at various stages of pregnancy, were enrolled. GERD was diagnosed if there was troublesome heartburn and/or acid regurgitation, at least once a week, during the current pregnancy. RESULTS: The overall prevalence of GERD in pregnancy was 38.5% (154/400). The prevalence of GERD in the third trimester was significantly higher than that in the second trimester (46.8% vs. 30.7%, P=0.008) and tended to be higher than its prevalence in the first trimester (46.8% vs. 35.4%, P=0.051). In the pregnant women with GERD, the frequency of regurgitation was significantly higher than that of heartburn (92.9% vs. 30.5%, P<0.001). Those typical symptoms were more prevalent in the daytime, compared with nighttime. CONCLUSION: Our study showed that GERD was prevalent during pregnancy in Vietnam. In the pregnant women with GERD, regurgitation was much more common than heartburn, and those typical reflux symptoms occurred more frequently in the daytime, compared with nighttime.

Relation of acanthosis nigricans to hyperinsulinemia and insulin sensitivity in overweight African American and white children.

OBJECTIVES: Acanthosis nigricans (AN) has been proposed as a reliable marker of hyperinsulinemia, but its utility for predicting hyperinsulinism has not been systematically evaluated in overweight children. We examined the relationship of AN to hyperinsulinemia and body adiposity. STUDY DESIGN: One hundred thirty-nine children underwent physical examination for AN, body composition studies, an oral glucose tolerance test, and a hyperglycemic clamp. RESULTS: Thirty-five children (25%) had AN. AN was more prevalent in African Americans (50.1%) than in white subjects (8.2%, P < .001). Independent of race, children with AN had greater body weight and body fat mass (P < .001); greater basal and glucose-stimulated insulin levels during oral glucose tolerance test (P < .001); greater first-phase, second-phase, and steady-state insulin levels (P < .001); and lower insulin sensitivity (P < .001) during the hyperglycemic clamp. After adjusting for body fat mass and age, none of these differences remained significant. When categorized by fasting insulin, 35% with fasting insulin levels > 20 microU/mL and 50% with fasting insulin levels > 15 microU/mL did not have AN. Eighty-eight percent of children with fasting insulin levels > or = 15 microU/mL had a body mass index SD score > or = 3.0. CONCLUSIONS: AN is not a reliable marker for hyperinsulinemia in overweight children. Children with a race-, sex-, and age-specific body mass index SD scores > or = 3.0 should be screened for hyperinsulinemia, whether or not they have AN.

Consistency of care with national guidelines for children with asthma in managed care.

OBJECTIVE: To evaluate the consistency of pediatric asthma care with the National Asthma Education and Prevention Program Guidelines. DESIGN: Cross-sectional survey at 2 managed care organizations in the United States (winter 1997-1998). The participants were parents of children (n = 318) age 5 to 17 years with asthma. There were no interventions. The outcome measures were indicators of care in 4 domains: (1) periodic physiologic assessment, (2) proper use of medications, (3) patient education, and (4) control of factors contributing to asthma severity. RESULTS: Of 533 eligible patients with asthma, 318 (60%) parents responded; 59% of children were male, 76% were white, and 60% were aged 5 to 10 years. Deficiencies in care were identified in all care domains including, for patients with moderate and severe persistent symptoms, only 55% used long-term control medication daily, 49% had written instructions for handling asthma attacks, 44% had instructions for adjustment of medication before exposures, 56% had undergone allergy testing, and 54% had undergone pulmonary function testing. CONCLUSIONS: There are significant opportunities to improve the quality of care for children with asthma enrolled in managed care. A comprehensive approach to improving care may be necessary to address multiple aspects of care where opportunities exist.

Insulin-like growth factors and bone mineral density in African American and White girls.

OBJECTIVES: African American children have greater bone mineral density (BMD) and bone mineral content (BMC) than white children. We examined the hypothesis that differences in insulin-like growth factors (IGFs) are important determinants of BMD during childhood. METHODS: We measured IGFs and IGF binding proteins in 59 African American and 59 white girls matched for age, body mass index, socioeconomic status, and pubertal stage. BMD and BMC were determined by dual emission x-ray absorptiometry. RESULTS: African American girls had greater total BMD (P <.001), BMC (P <.01), total IGF-1 (P <.001), and free IGF-1 (P <.01) than white girls. IGFBP-1, IGFBP-2, and IGFBP-3 were similar in both groups or lower in African Americans. IGF-1 was positively correlated with IGF-2 in white girls (P =.012) but was negatively correlated with IGF-2 in African Americans (P =.015). IGF-1 and free IGF-1 were positively correlated with BMD/BMC. Multiple regression analyses showed 80% of the variance in BMC could be accounted for by the use of body weight, height, and IGF-1 in the model. When IGF-1 was included as a factor, race did not add to the model's predictive power. CONCLUSION: IGF-1 and free IGF-1 are greater in African American than in white girls and may contribute to the greater BMD of African Americans.

Hierarchical analysis of linkage disequilibrium in Rhizobium populations: evidence for sex?

Many bacterial species exhibit strong linkage disequilibrium of their chromosomal genes, which apparently indicates restricted recombination between alleles at different loci. The extent to which restricted recombination reflects limited migration between geographically isolated populations versus infrequent mixis of genotypes within populations is more difficult to determine. We examined the genetic structure of Rhizobium leguminosarum biovar phaseoli populations associated with wild and cultivated beans (Phaseolus spp.) over several spatial scales, ranging from individual host plants to throughout the Western Hemisphere. We observed significant linkage disequilibrium at scales at least as small as a cultivated plot. However, the amount of disequilibrium was much greater among isolates collected throughout the Western Hemisphere than among isolates from one area of Mexico, even when disequilibrium was quantified using an index that scales for allelic diversity. This finding suggests that limited migration between populations contributes substantially to linkage disequilibrium in Rhizobium. We also compared the genetic structure for R. leguminosarum bv. phaseoli taken from a cultivated plot with that for Escherichia coli obtained from one human host in an earlier study. Even at this fine scale, linkage disequilibrium in E. coli was very near the theoretical maximum level, whereas it was much less extreme in the local population of Rhizobium. Thus, the genetic structure for R. leguminosarum bv. phaseoli does not exclude the possibility of frequent mixis within local populations.