Publications

The mass loss from the West Antarctic Ice Sheet is dominated by numerous rapidly flowing ice streams, which are separated from stagnant ice in the adjacent ridges by zones of concentrated deformation known as shear margins. Because the discharge from a single ice stream depends sensitively on the ice stream width, determining the physical processes that control shear margin location is crucial to a full understanding of ice stream dynamics. Previous work has shown that the transition from a deforming to an undeforming bed within a shear margin concentrates large stresses on the undeforming bed beneath the ridge. In this paper we investigate how the presence of a drainage channel collocated with the transition from a deforming to an undeforming bed perturbs the stress field within the shear margin. We show that the channel limits the maximum shear stress on the undeforming bed and alters the yield strength of the till by changing the normal stress on the ice‐till interface. By comparing the maximum stress with the till strength, we show that the transition from a deforming to an undeforming bed can occur across a channel whenever the water flux in the channel exceeds a critical value. This critical flux is sensitive to the rheology and loading of the shear margin, but we conclude that there are some scenarios where the transition from a deforming to an undeforming bed can be collocated with a drainage channel, though this configuration is probably not typical.

Cadmium (Cd) accumulation in rice grains poses a serious threat to human health, however the underlying mechanisms remain incompletely understood. Here, we conducted a genome-wide association study and identified 29 loci associated with grain Cd content (LAGCCs). One of the top associated loci, LAGCC4, harbors the transporter gene OsPT1, whose haplotypes are tightly associated with Cd content in rice grains. A transposon, H-MITE, inserts into the 5' untranslated region of OsPT1, altering its expression pattern and leading to higher Cd accumulation. We further identified a transcription factor OsbHLH35 that specifically binds to the OsPT1^H-MITE promoter to regulate its transcription in response to Cd stress. Knocking out either the OsPT1^H-MITE or OsbHLH35 gene through CRISPR/Cas9 gene editing significantly reduced grain Cd content, with a reduction ranging from 61.7% to 80.6%. Our study uncovered a previously unknown mechanism responsible for high Cd accumulation in rice and identified targets for breeding rice varieties with lower Cd content.

We describe a multi-color microfluidic dye laser operating in whispering gallery mode based on a train of alternating droplets containing solutions of different dyes; this laser is capable of switching the wavelength of its emission between 580 nm and 680 nm at frequencies up to 3.6 kHz-the fastest among all dye lasers reported; it has potential applications in on-chip spectroscopy and flow cytometry.

This communication describes a new approach for controlling static charging (contact electrification), and resulting electrical discharging, that occurs when two contacting materials separate. The prevention of contact electrification is an important problem; unwanted adhesion between oppositely charged materials, spark-initiated explosions, and damage to microelectronic circuitry are some of the deleterious effects of static charging. Current strategies for controlling contact electrification rely upon dissipating an accumulated charge by making contacting surfaces conductive and, therefore, can be difficult to implement with electrically insulating materials. Specifically, using our understanding of the ion-transfer mechanism of contact electrification, we patterned glass slides with negatively charging areas (clean glass) and positively charging areas (glass silanized with a cationic siloxane terminated with a quaternary ammonium group). The rate of charge separation due to a steel sphere rolling on the patterned glass surface correlated linearly with the percentage of the glass surface that was silanized; the rate of charge transfer was minimal when 50% of the glass surface area was silanized. Patterned surfaces also prevented electrical discharges between electrically conducting (bare steel) or insulating (acrylate-coated steel) spheres rolling on the glass, because the rate of charging was sufficiently slow to prevent electric fields greater than the dielectric strength of air to develop. This strategy for preventing static charging therefore does not require one of the two contacting surfaces to be electrically conductive. More generally, these results show that our enhanced understanding of the ion-transfer mechanism of contact electrification enables the rational design of chemically tailored surfaces for functional electrets.

Current studies of phenotype diversity by genome-wide association studies (GWAS) are mainly focused on identifying genetic variants that influence level changes of individual traits without considering additional alterations at the system-level. However, in addition to level alterations of single phenotypes, differences in association between phenotype levels are observed across different physiological states. Such differences in molecular correlations between states can potentially reveal information about the system state beyond that reported by changes in mean levels alone. In this study, we describe a novel methodological approach, which we refer to as genome metabolome integrated network analysis (GEMINi) consisting of a combination of correlation network analysis and genome-wide correlation study. The proposed methodology exploits differences in molecular associations to uncover genetic variants involved in phenotype variation. We test the performance of the GEMINi approach in a simulation study and illustrate its use in the context of obesity and detailed quantitative metabolomics data on systemic metabolism. Application of GEMINi revealed a set of metabolic associations which differ between normal and obese individuals. While no significant associations were found between genetic variants and body mass index using a standard GWAS approach, further investigation of the identified differences in metabolic association revealed a number of loci, several of which have been previously implicated with obesity-related processes. This study highlights the advantage of using molecular associations as an alternative phenotype when studying the genetic basis of complex traits and diseases.

Paramagnetic ionic liquids (PILs) provide new capabilities to measurements of density using magnetic levitation (MagLev). In a typical measurement, a diamagnetic object of unknown density is placed in a container containing a PIL. The container is placed between two magnets (typically NdFeB, oriented with like poles facing). The density of the diamagnetic object can be determined by measuring its position in the magnetic field along the vertical axis (levitation height, h), either as an absolute value or relative to internal standards of known density. For density measurements by MagLev, PILs have three advantages over solutions of paramagnetic salts in aqueous or organic solutions: (i) negligible vapor pressures; (ii) low melting points; (iii) high thermal stabilities. In addition, the densities, magnetic susceptibilities, glass transition temperatures, thermal decomposition temperatures, viscosities, and hydrophobicities of PILs can be tuned over broad ranges by choosing the cation–anion pair. The low melting points and high thermal stabilities of PILs provide large liquidus windows for density measurements. This paper demonstrates applications and advantages of PILs in density-based analyses using MagLev.

Background— Previous studies on gene-lifestyle interaction and obesity have focused mostly on the FTO gene and physical activity, whereas little attention has been paid to sedentary behavior as indicated by television (TV) watching. Methods and Results— We analyzed interactions between TV watching, leisure time physical activity, and genetic predisposition in relation to body mass index (BMI) in 7740 women and 4564 men from 2 prospective cohorts: The Nurses' Health Study and the Health Professionals Follow-up Study. Data on physical activity and TV watching were collected 2 years before assessment of BMI. A weighted genetic risk score was calculated on the basis of 32 established BMI-associated variants. In both women and men, the genetic associations with BMI strengthened with increased hours of TV watching. An increment of 10 points in the weighted genetic risk score was associated with 0.8 (SE, 0.4), 0.8 (SE, 0.2), 1.4 (SE, 0.2), 1.5 (SE, 0.2), and 3.4 (SE, 1.0) kg/m 2 higher BMI across the 5 categories of TV watching (0–1, 2–5, 6–20, 21–40, and >40 h/wk; P for interaction=0.001). In contrast, the genetic association with BMI weakened with increased levels of physical activity. An increment of 10 points in the weighted genetic risk score was associated with 1.5 (SE, 0.2), 1.3 (SE, 0.2), 1.2 (SE, 0.2), 1.2 (SE, 0.2), and 0.8 (SE, 0.2) kg/m 2 higher BMI across the quintiles of physical activity. The interactions of TV watching and physical activity with genetic predisposition in relation to BMI were independent of each other. Conclusions— A sedentary lifestyle, indicated by prolonged TV watching, may accentuate the predisposition to elevated adiposity, whereas greater leisure time physical activity may attenuate the genetic association.