Publications

Development of new synthetic methods for the modification of nanostructures has accelerated materials design advances to furnish complex architectures. Structures based on one-dimensional (1D) silicon (Si) structures synthesized using top-down and bottom-up methods are especially prominent for diverse applications in chemistry, physics, and medicine. Yet further elaboration of these structures with distinct metal-based and polymeric materials, which could open up new opportunities, has been difficult. We present a general electrochemical method for the deposition of conformal layers of various materials onto high aspect ratio Si micro- and nanowire arrays. The electrochemical deposition of a library of coaxial layers comprising metals, metal oxides, and organic/inorganic semiconductors demonstrate the materials generality of the synthesis technique. Depositions may be performed on wire arrays with varying diameter (70 nm to 4 μm), pitch (5 μ to 15 μ), aspect ratio (4:1 to 75:1), shape (cylindrical, conical, hourglass), resistivity (0.001-0.01 to 1-10 ohm/cm2), and substrate orientation. Anisotropic physical etching of wires with one or more coaxial shells yields 1D structures with exposed tips that can be further site-specifically modified by an electrochemical deposition approach. The electrochemical deposition methodology described herein features a wafer-scale synthesis platform for the preparation of multifunctional nanoscale devices based on a 1D Si substrate.

Abstract Maternal educational attainment (MEA) shapes offspring health through multiple potential pathways. Differential DNA methylation may provide a mechanistic understanding of these long-term associations. We aimed to quantify the associations of MEA with offspring DNA methylation levels at birth, in childhood and in adolescence. Using 37 studies from high-income countries, we performed meta-analysis of epigenome-wide association studies (EWAS) to quantify the associations of completed years of MEA at the time of pregnancy with offspring DNA methylation levels at birth ( n = 9 881), in childhood ( n = 2 017), and adolescence ( n = 2 740), adjusting for relevant covariates. MEA was found to be associated with DNA methylation at 473 cytosine-phosphate-guanine sites at birth, one in childhood, and four in adolescence. We observed enrichment for findings from previous EWAS on maternal folate, vitamin-B 12 concentrations, maternal smoking, and pre-pregnancy BMI. The associations were directionally consistent with MEA being inversely associated with behaviours including smoking and BMI. Our findings form a bridge between socio-economic factors and biology and highlight potential pathways underlying effects of maternal education. The results broaden our understanding of bio-social associations linked to differential DNA methylation in multiple early stages of life. The data generated also offers an important resource to help a more precise understanding of the social determinants of health.

Background and Purpose— Dysregulation of vessel wall formation, growth, and maintenance may confer susceptibility of stroke. Methods— We tested the hypothesis that variants in 2 genes encoding vascular endothelial growth factor and vascular endothelial growth factor receptor-2 are associated with susceptibility to stroke and its recurrence in a Chinese case–control study comprising 1849 patients with stroke and 1798 control subjects and replicated the investigation in an independent study comprising 327 cases and 327 control subjects. The correlation of variants with carotid artery intima media thickness was examined in 1123 healthy individuals. Results— Compared with their corresponding wild-type genotypes, one coding variant, rs2305948 (Val297Ile), in the vascular endothelial growth factor receptor-2 gene was associated with increased susceptibility to intracerebral hemorrhage (additive model: OR, 2.06; 95% CI, 1.64 to 2.59; P =7.6×10 −10 ; dominant model: OR, 2.20; 95% CI, 1.70 to 2.84; P =1.5×10 −9 ), a promoter variant rs2071559 (−604T>C) in the gene was associated with reduced susceptibility to atherothrombotic stroke (additive model: OR, 0.82; 95% CI, 0.71 to 0.93; P =0.003; dominant model: OR, 0.78; 95% CI, 0.65 to 0.92; P =0.004) and was reversely correlated with carotid artery intima media thickness ( P =2.8×10 −5 ). Replication in the second study yielded similar results. During a median 4.5 years of follow-up for the first stroke population, 355 recurrent strokes were documented. Subjects carrying 297Ile had a higher risk for stroke recurrence (relative risk, 1.40; 95% CI, 1.12 to 1.75; P =0.003), and those with −604C had a lower risk for recurrence (relative risk, 0.71; 95% CI, 0.58 to 0.89; P =0.002) than their wild-type carriers. Conclusions— The vascular endothelial growth factor receptor-2 gene variants may serve as novel genetic markers for the risk of stroke and its recurrence.

Scanning tunneling microscopy has been used to characterize directly the surface electronic structure of a series of single-crystal ${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Bi}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ superconductors. High-resolution spectroscopic measurements show that within \ifmmode\pm\else\textpm\fi{}0.5 eV of the Fermi level the Bi(Pb)-O electronic structure is independent of the Pb concentration (x\ensuremath{\le}0.7). Extended spectroscopic measurements demonstrate that the density of unfilled states at +1 eV systematically decrease as the concentration of Pb increases, although the filled states between 0 and -2 eV are essentially independent of the concentration of Pb. In addition, analysis of the differential conductivity indicates that the surface conductivity varies from weakly metallic to semiconducting as the tip-surface separation increases.

A series of eight symmetrically substituted diketopiperazines (DKPs) derived from 1-amino-1-carboxycycloalkanes (n = 3−7; 3,3,5,5-tetramethylcyclohexane; 4,4-dimethylcyclohexane; 2-indan) were synthesized and their crystal structures determined. In the solid state, all eight compounds form two pairs of hydrogen bonds with two adjacent molecules to form a one-dimensional structure that we refer to as "tapes". These molecules represent a range of volumes and shapes that contain a common molecular fragment (DKP ring). We examined this series of compounds with three objectives in mind: (i) to establish the ability of the hydrogen-bonded "tape" motif to persist through these differences in volume and shape; (ii) to provide a series of structurally related compounds to use to test computational methods of predicting crystal structure from molecular structure; (iii) to search for qualitative correlations between molecular structure and crystal packing. All compounds form tapes and with one exception, all tapes pack with their long axes parallel. When viewed down their long axis, two types of tapes emerge: planar and nonplanar. The type of tape that forms reflects the conformation adapted by the DKP ringplanar or boat. Planar tapes form when the angle (α) between the two planes defined by the cis-amides in the DKP ring is 180°; nonplanar tapes form when α < 180°. Five of the eight compounds studied form planar tapes, the remaining three compounds form nonplanar tapes. Despite the variability in volume and shape represented by this series of molecules, the persistence of the tape motif in their crystalline solids suggests that the hydrogen-bonding interactions between DKPs dominate the packing arrangement of these molecules. Void space in the crystalline solid is minimized by parallel alignment of tapes that pack in a manner that permits the interdigitation of substituents on adjacent tapes.

The structure of Bénard–Marangoni convection cells can be controlled by periodic topographic patterns on the heated surface that generates the convection. When the periodicity of the topographic pattern matches the intrinsic periodicity of the convection cells, a convective pattern is formed that is 1:1 commensurate with the topographic pattern. Arrays of hexagonal, square, and triangular convection cells were generated over the appropriately designed topographic patterns, and visualized by infrared imaging. For imposed patterns with periodicity in two dimensions, as the ratio of the intrinsic and perturbing length scales changes, the pattern of the convection cells shows sharp transitions between different patterns commensurate with the imposed pattern. For imposed patterns with periodicity in one dimension (i.e., lines) the convection cells use the unconstrained dimension to adapt continuously to the external perturbation. Topographically controlled convection cells can be used to assemble microscopic particles into externally switchable regular lattices.