Grain shape effects in bed load sediment transport.

Bed load sediment transport, in which wind or water flowing over a bed of sediment causes grains to roll or hop along the bed, is a critically important mechanism in contexts ranging from river restoration1 to planetary exploration2. Despite its widespread occurrence, predictions of bed load sediment flux are notoriously imprecise3,4. Many studies have focused on grain size variability5 as a source of uncertainty, but few have investigated the role of grain shape, even though shape has long been suspected to influence transport rates6. Here we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport datasets4,7,8. We develop a theory that accounts for grain shape effects on fluid drag and granular friction and predicts that the onset and efficiency of transport depend on the coefficients of drag and bulk friction of the transported grains. Laboratory experiments confirm these predictions and reveal that the effect of grain shape on sediment transport can be difficult to intuit from the appearance of grains. We propose a shape-corrected sediment transport law that collapses our experimental measurements. Our results enable greater accuracy in predictions of sediment transport and help reconcile theories developed for spherical particles with the behaviour of natural sediment grains.

Palladium-catalyzed cross-coupling of H-phosphinate esters with chloroarenes.

The palladium-catalyzed cross-coupling reaction between H-phosphinate esters and chloroarenes or chloroheteroarenes is described. This reaction is the first general metal-catalyzed phosphorus-carbon bond-forming reaction between a phosphorus nucleophile and chloroarenes.

Strategies for the asymmetric synthesis of H-phosphinate esters.

Access to P-chiral H-phosphinates via desymmetrization of hypophosphite esters was investigated. The use of chiral auxiliaries, chiral catalysts, and of a bulky prochiral group that could lead to kinetic resolution was explored. A chiral NMR assay for enantiomeric excess determination of H-phosphinates was developed. An asymmetric route to C-chiral H-phosphinates is also examined and an assay was developed.

Congenital heart defects and fetal alcohol spectrum disorders.

OBJECTIVE: Review of the prevalence of congenital heart defects (CHD) and fetal alcohol spectrum disorder (FASD). DESIGN: We conducted a search of the Medline and Pubmed databases to identify papers reporting the association. We then searched the reference lists of the papers and reference books for additional sources. RESULTS: We found 29 studies that met our inclusion criteria. In the 12 case series studies of subjects with FASD, the proportion of cases with a CHD (atrial [ASD] and ventricular [VSD] septal defects, other defects, or unspecified CHD) ranged from 33% to 100%. From the 14 retrospective studies, the rate of septal defects was 21%, other structural defects 6% and unspecified defects was 12%. For the 2 case-control studies, the odds of CHD ranged from 1.0 (subjects with fetal alcohol effect) to 18.0 (subjects with fetal alcohol syndrome). In the 1 prospective study of CHD the OR for a child to have CHD and FASD was 1.0. KEY CONCLUSION: Pediatric cardiologists may have frequent contact with children with FASD and increased levels of attention to prenatal alcohol exposure as a potential etiology of CHD is indicated.

A staged screening strategy for prenatal alcohol exposure and maternal risk stratification.

AIMS: To present an incremental process for a staged screening strategy to identify women at increased risk of having a child with fetal alcohol spectrum disorder (FASD) and to enhance the management of women using alcohol during pregnancy. We include an illustrative example of the development of a screening component using an existing data set. METHODS: We describe a seven-step protocol to screen for alcohol use during pregnancy. The screening process begins with a one-question initial screen, followed by exposure assessment, maternal risk stratification to estimate risk for FASD, and concludes with recommendations for intervention and monitoring of exposure for women drinking during pregnancy. CONCLUSIONS: This screening process has very modest time commitments in the early stages. Time commitments increase for women drinking during pregnancy and the process focuses on the population at highest risk of having a child with FASD. The process has the benefit of risk specificity, since the process refines risk estimates for an adverse outcome specific for FASD. The process concludes with a programme to facilitate intervention and to monitor changes in prenatal alcohol exposure during pregnancy. Prevention of FASD is an important public health priority. In addition to the ongoing study of clinical strategies to improve detection rates of alcohol exposure at all stages of pregnancy, additional research on the tools and the process used in screening efforts is urgently needed. The efforts should also include research on both the screening tools and the outcome of the screening process in routine prenatal care settings.