Carbon Nanotube Microarchitectures for Mechanical Metamaterials

Metamaterials use ordered internal structure to exhibit properties uncommon or nonexistent in natural materials. To design a metamaterial with target performance, hierarchical specification of geometry and properties of the constituent elements is essential. Vertically aligned growth of carbon nanotubes (CNTs) is an attractive means to achieve such control because it is a scalable fabrication technique that can produce bulk thick films and patterned microstructures over a large area. CNTs also possess attractive properties such as high stiffness, strength, and electrical and thermal conductivities at low mass density. Therefore, the motivation of this dissertation is to develop methods to manipulate CNT growth and modification at the nano- and microscales, toward the realization of scalable CNT mechanical metamaterials. First, it is shown that CNT microstructures having complex three-dimensional shapes can be manufactured by controlling the CNT growth rate locally within each microstructure using a growth retardant layer patterned underneath the CNT growth catalyst film. Microstructures with complex trajectories are achieved by understanding the mechanical coupling among CNTs and designing the catalyst and offset patterns accordingly. The geometry of the strain-engineered microstructures is predicted using both an analytical model and the finite element method. Next, it is shown that the mechanics of CNT microstructures can be tuned by conformal coating at the nanoscale, via atomic layer deposition (ALD) of alumina. Using vertical cylindrical CNT micropillars, a stiffness tuning from 7 MPa to 50 GPa is demonstrated. The coating thickness also changes the dominant deformation behavior of the CNT microstructures, from buckling to brittle fracture. In the buckling regime, the coated CNT forests can withstand and fully recover compressive strain of up to 75%. Last, fabrication methods are developed toward application of the 3-D CNT microarchitectures. ALD, polymer infiltration, and lamination are used to fabricate a CNT microtruss nanocomposite having high stiffness and damping. Then, microstructure arrays with geometry mimicking the scales of a butterfly wing are fabricated and determined to exhibit superhydrophobic and directional wetting behaviors. Further work on 3-D CNT microarchitectures with engineered geometry, mechanics, and surface functionality may realize multifunctional materials with targeted combinations of mechanical, electrical, thermal, and/or optical properties.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109009/1/mvpsj_1.pd

Shape Memory Alloy Actuated Hand Held Stabilization Device

ME450 Capstone Design and Manufacturing Experience: Winter 2008Tremors affect millions of people in the United States, causing tasks like eating and application of makeup to be difficult, and sometimes impossible. Most current solutions such as drug treatments, surgical treatments and tremor suppression devices have uncomfortable or health threatening side effects. An active cancellation device could be a promising solution; however current devices are expensive and only available for precision surgeries, not for everyday home use. Shape memory alloy (SMA) actuators may solve the difficulty of producing this canceling motion within a very constrained package. This project aims to develop a handheld stabilizing device using SMA actuation to cancel the motion of hand tremors in utensils commonly used in daily tasks, allowing those with hand tremors to become self sufficient.Anupam Pathak Graduate Student Research Assistant, Mechanical Engineeringhttp://deepblue.lib.umich.edu/bitstream/2027.42/58699/1/me450w08project01_report.pd

Scaling the Stiffness, Strength, and Toughness of Ceramic‐Coated Nanotube Foams into the Structural Regime

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108652/1/adfm201400851-sup-0001-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/108652/2/adfm201400851.pd

Interplay of the forces governing steroid hormone micropollutant adsorption in vertically-aligned carbon nanotube membrane nanopores

Vertically-aligned carbon nanotube (VaCNT) membranes allow water to conduct rapidly at low pressures and open up the possibility for water purification and desalination, although the ultralow viscous stress in hydrophobic and low-tortuosity nanopores prevents surface interactions with contaminants. In this experimental investigation, steroid hormone micropollutant adsorption by VaCNT membranes is quantified and explained via the interplay of the hydrodynamic drag and friction forces acting on the hormone, and the adhesive and repulsive forces between the hormone and the inner carbon nanotube wall. It is concluded that a drag force above 2.2 × 10$^{−3}$ pN overcomes the friction force resulting in insignificant adsorption, whereas lowering the drag force from 2.2 × 10$^{−3}$ to 4.3 × 10$^{−4}$ pN increases the adsorbed mass of hormones from zero to 0.4 ng cm$^{−2}$. At a low drag force of 1.6 × 10$^{−3}$ pN, the adsorbed mass of four hormones is correlated with the hormone−wall adhesive (van der Waals) force. These findings explain micropollutant adsorption in nanopores via the forces acting on the micropollutant along and perpendicular to the flow, which can be exploited for selectivity

Self-assembly of Ni–Fe layered double hydroxide at room temperature for oxygen evolution reaction

Active and stable electrocatalysts are the key to water electrolysis for hydrogen production. This paper reports a facile direct growth method to synthesize NiFe-layered double hydroxides (LDHs) on nickel foil as an electrocatalyst for the oxygen evolution reaction. The NiFe-LDH is synthesized by a galvanic process at room temperature without any additional energy for synthesis. The synthesized NiFe-LDH is a karst landform with abundant active sites and efficient mass diffusion. The NiFe-LDH with an oxygen defect show excellent electrocatalytic performance for the OER, with a low overpotential (272 mV at 10 mA/cm2), a small Tafel slope (43 mV/dec), and superior durability. Direct growth synthesis provide excellent electrical conductivity as well as strong bonding between the catalyst layer and the substrate. In addition, this synthesis process is simple to apply in the fabrication of a large size electrode and is believed to be applicable to commercialized alkaline water electrolysis

Association between Workplace Risk Factor Exposure and Sleep Disturbance: Analysis of the 2nd Korean Working Conditions Survey

OBJECTIVES: Sleep is essential for human beings to live and work properly. This study was conducted to investigate the relationship between occupational exposures to workplace risk factors and sleep disturbance in Korean workers. METHODS: The data were drawn from the second Korean Working Conditions Survey (KWCS); a total of 7,112 paid workers were analyzed. The independent variables were occupational exposures such as physical, chemical, biological, and psychosocial risk factor in the workplace, and psychosocial risk factor was divided into five categories (job demand, job control, social support, job insecurity, lack of reward). We estimated the relationship between various occupational exposures and sleep disturbance using multivariate logistic regression analysis. RESULTS: The results showed that people who exposed to physical, chemical, biological, and psychosocial (high job demand, inadequate social support, lack of reward) risk factors were more likely to increase the risk of sleep disturbance. Furthermore, after adjusting for general and occupational characteristics, we found significant positive associations between exposures to physical (odds ratios [OR] 1.47, 95% confidence interval [CI] 1.05-2.07) and psychosocial (high job demand (OR 2.93, 95% CI 2.16-3.98), inadequate social support (OR 1.57, 95% CI 1.14-2.15), lack of reward (OR 1.45, 95% CI 1.08-1.96)) risk factors and sleep disturbance. CONCLUSION: These results suggest that occupational exposures to physical and psychosocial workplace risk factors are significantly related to sleep disturbance

Combined aberrant expression of E-cadherin and S100A4, but not β-catenin is associated with disease-free survival and overall survival in colorectal cancer patients

BACKGROUND/AIMS: Epithelial-to-mesenchymal transition (EMT) in cancers is related to metastasis, recurrence, and poor prognosis. We evaluated whether EMT-related proteins can act as prognostic biomarkers in colorectal cancer (CRC) patients. METHODS: We evaluated the expression of E-cadherin, β-catenin, and S100A4 by immunohistochemistry (IHC) in 333 CRC tissues from the tumor center and invasive margin. Tumor budding, cell grade, tumor stage, type of tumor growth, peritumoral lymphocyte infiltration (TLI), and perineural- or lymphovascular invasion were evaluated as pathological parameters. mRNA levels of E-cadherin, N-cadherin, β-catenin, and S100A4 from 68 specimens from the same set were analyzed by real time quantitative RT-PCR. RESULTS: Loss of E-cadherin, nuclear β-catenin, and gain of S100A4 were higher in the invasive margin than in the tumor center. Loss of E-cadherin was associated with cell grade, macroscopic type, perineural invasion, and tumor budding, β-catenin with microsatellite instability and tumor site, and S100A4 with growth type, macroscopic type, AJCC stage, lymphovascular invasion, and perineural invasion. The aberrant expression of E-cadherin and S100A4 not β-catenin in the invasive margin was a significant and independent risk factor for disease-free and overall-survival by multivariate analysis, along with AJCC stage and perineural invasion. mRNA levels of β-catenin and S100A4 were correlated with the IHC findings at the tumor invasive margin. E-cadherin and N-cadherin showed a weak inverse correlation. CONCLUSIONS: The combination of loss of E-cadherin and gain of S100A4 in the tumor invasive margin can be used to stratify patients with the same AJCC stage into different survival groups. VIRTUAL SLIDES: The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/939828962924467

Melatonin receptor 1 B polymorphisms associated with the risk of gestational diabetes mellitus

<p>Abstract</p> <p>Backgrounds</p> <p>Two SNPs in <it>melatonin receptor 1B </it>gene, <it>rs10830963 </it>and <it>rs1387153 </it>showed significant associations with fasting plasma glucose levels and the risk of Type 2 Diabetes Mellitus (T2DM) in previous studies. Since T2DM and gestational diabetes mellitus (GDM) share similar characteristics, we suspected that the two genetic polymorphisms in <it>MTNR1B </it>may be associated with GDM, and conducted association studies between the polymorphisms and the disease. Furthermore, we also examined genetic effects of the two polymorphisms with various diabetes-related phenotypes.</p> <p>Methods</p> <p>A total of 1,918 subjects (928 GDM patients and 990 controls) were used for the study. Two <it>MTNR1B </it>polymorphisms were genotyped using TaqMan assay. The allele distributions of SNPs were evaluated by <it>x</it>²models calculating odds ratios (ORs), 95% confidence intervals (CIs), and corresponding <it>P </it>values. Multiple regressions were used for association analyses of GDM-related traits. Finally, conditional analyses were also performed.</p> <p>Results</p> <p>We found significant associations between the two genetic variants and GDM, <it>rs10830963</it>, with a corrected <it>P </it>value of 0.0001, and <it>rs1387153</it>, with the corrected <it>P </it>value of 0.0008. In addition, we also found that the two SNPs were associated with various phenotypes such as homeostasis model assessment of beta-cell function and fasting glucose levels. Further conditional analyses results suggested that <it>rs10830963 </it>might be more likely functional in case/control analysis, although not clear in GDM-related phenotype analyses.</p> <p>Conclusion</p> <p>There have been studies that found associations between genetic variants of other genes and GDM, this is the first study that found significant associations between SNPs of <it>MTNR1B </it>and GDM. The genetic effects of two SNPs identified in this study would be helpful in understanding the insight of GDM and other diabetes-related disorders.</p