Adsorption and Interfacial Properties of Fluids from Molecular Simulation

The objective of this research is to provide molecular-level insight on the adsorption andinterfacial properties of fluids. Molecular simulation is the tool used to perform this work. The adsorption of polar and nonpolar molecules on carbonaceous adsorbents and metal surface is studied by using existing simulation techniques and new techniques developed by ourselves.The interfacial properties of quantum liquid mixtures are investigated using path integral simulations. The physical behavior of a DNA segment interacting with a novel adsorbent, single-walled carbon nanotubes (SWNTs), in aqueous environment is studied by molecular dynamics simulations.We have simulated the adsorption of propane on graphite surface. We obtain good agreement between simulations and experiments on both the isotherms and isosteric heat of adsorption. We haveinvestigated five different propane potential models. We found that the fluid-fluid potential plays a significant role in determining the location of the 1-2 layering transition.We identified an orientational ordering transition for propane in the monolayer. In order to studythe polar molecules adsorbed on graphite, we have developedpotential models including the graphite quadrupole and induction interaction between a polar molecule and the graphite surface. Wehave performed simulations of acetone adsorption on graphite to investigate the layering transitions, geometry, and coverageof acetone in the first, second and third layers. The simulation results agree well with the experimental observations. We have studied the structure of second layer physisorbed carbon monoxide on the Ag(110) metal surface. Both simulation and experiment found that the second layer CO molecules form orientationally ordered structures, with CO bond angles tilting at 45 degrees to the surface normal and azimuthal angles tilting in multiples of 45 degrees to the principal azimuth axis. From the simulation, we conclude that redistribution of charges within the first layer of CO on silver accommodate the formation of ordered second layer CO structures.We have performed parallel hybrid path integral Monte Carlo to study the interfacial properties of pure and mixture quantum liquids. We calculated the surface tension of pure liquid H2,pure liquid D2, and H2/D2 mixtures. The surface tension of pure fluids we calculated from simulations agree well with the experimentaldata. We observed interfacial segregation in the H2/D2 mixtures with H2 migrating to the surface. The H2/D2 mixture therefore exhibits negativedeviations from ideal solution behavior. We studied the adsorption of a DNA segment with12 base pairs on a (8,8) single walled carbon nanotube using the AMBER MD simulation software package. We found that the DNA adsorbs onto the wall of a regular SWNT or a positively charged SWNT, with a time scale of 100 pico-seconds. When the DNA is uncharged the end of the DNA molecule binds to the SWNT surface. DNA binds with its axis nearly parallel to a positively charged SWNT. The angle between the DNA and SWNT axes isabout 20-30 degrees. In contrast, DNA does not bind to negatively charged SWNTs, because of the net negative charge on DNA. We found that the adsorption process does not affect greatly thestructures of the DNA. However, the adsorption on a regular SWNT delays the A-form to B-form conversion for an A-DNA

What parents think about giving nonnutritive sweeteners to their children: A pilot study

Objective. To evaluate parental attitudes toward providing foods and beverages with nonnutritive sweeteners (NNS) to their children and to explore parental ability to recognize NNS in packaged foods and beverages. Methods. 120 parents of children ≥ 1 and ≤18 years of age completed brief questionnaires upon entering or exiting a grocery store. Parental attitudes toward NNS were assessed using an interviewer-assisted survey. Parental selection of packaged food and beverages (with and without NNS) was evaluated during a shopping simulation activity. Parental ability to identify products with NNS was tested with a NNS recognition test. Results. Most parents (72%) disagreed with the statement “NNS are safe for my child to consume.” This was not reflected during the shopping simulation activity because about one-quarter of items selected by parents contained NNS. Parents correctly identified only 23% of NNS-containing items presented as foods or beverages which were sweetened with NNS. Conclusions. The negative parental attitudes toward providing NNS to their children raise the question whether parents are willing to replace added sugars with NNS in an effort to reduce their child’s calorie intake. Our findings also suggest that food labeling should be revised in order for consumers to more easily identify NNS in foods and beverages

Magnetic Resonance Elastography Shear Wave Velocity Correlates with Liver Fibrosis and Hepatic Venous Pressure Gradient in Adults with Advanced Liver Disease

Background. Portal hypertension, an elevation in the hepatic venous pressure gradient (HVPG), can be used to monitor disease progression and response to therapy in cirrhosis. Since obtaining HVPG measurements is invasive, reliable noninvasive methods of assessing portal hypertension are needed. Methods. Noninvasive markers of fibrosis, including magnetic resonance elastography (MRE) shear wave velocity, were correlated with histologic fibrosis and HVPG measurements in hepatitis C (HCV) and/or HIVinfected patients with advanced liver disease enrolled in a clinical trial of treatment with simtuzumab, an anti-LOXL2 antibody. Results. This exploratory analysis includes 23 subjects: 9 with HCV monoinfection, 9 with HIV and HCV, and 5 with HIV and nonalcoholic steatohepatitis. Median Ishak fibrosis score was 4 (range 1-6); 11 subjects (48%) had cirrhosis. Median HVPG was 6 mmHg (range 3-16). Liver stiffness measured by MRE correlated with HVPG ( = 0.64, = 0.01), histologic fibrosis score ( = 0.71, = 0.004), noninvasive fibrosis indices, including APRI ( = 0.81, < 0.001), and soluble LOXL2 ( = 0.82, = 0.001). On stepwise multivariate regression analysis, MRE was the only variable independently associated with HVPG ( 2 = 0.377, = 0.02). Conclusions. MRE of the liver correlated independently with HVPG. MRE is a valid noninvasive measure of liver disease severity and may prove to be a useful tool for noninvasive portal hypertension assessment. Trial Registration Number. This trial is registered with NCT01707472