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Properties of the carbon nanotube structure have been extensively examined in several analytical and numerical studies. The present paper, describes a cellular automata based numerical model to study the behavior of a single-walled carbon nanotube and to compute intrinsic properties such as an equivalent Young’s modulus. The cellular automata model derives from local rules of interaction among neighboring sites that evolve the state of each site locally. In the present approach, each site was occupied by a carbon atom, with its position representing the state variable for the site. The interaction rules were based on a minimization of the bonding energy between an atom and its three neighboring atoms, and from which a new position can be derived. The bonding energy was calculated using the empirical formulation suggested by Tersoff; a quasi-second order numerical approach was used to find a solution to the energy minimization problem. The Young’s modulus obtained from the proposed approach compares well against published results and those obtained from a molecular dynamics simulation. The computational cost of the cellular automata was also shown to be significantly lower than molecular dynamics. The proposed approach promises to be effective in computing other properties of such nanostructures, and can be extended to multi-wall configurations. [Copyright &y& Elsevier]

Hyaluronic acid (HA) is highly biocompatible and is therefore utilized in various medical fields. Recent efforts have achieved a wide variety of HA-based hydrogel fabrications and their potent applications in tissue engineering. Nevertheless, HA hydrogels have limitations in physical property control due to the nature of HA. In this study, a hybrid hydrogel was formed with hyaluronic acid-methacrylate (HAMA) and silk fibroin-methacrylate (SFMA) via photopolymerization, followed by physical cross-linking of silk fibroin (SF) chains. The photopolymerization was completed within 5 min under UV irradiation, although the gel point increased with an increase in SFMA content. By ethanol treatment, the SF domain formed β-sheet structures, resulting in double network in HA/SF hybrid hydrogel. As a result, the shear modulus of the HA/SF hybrid hydrogel significantly increased with an increase of SFMA content, while the swelling ratio decreased. In addition, the HA/SF hybrid hydrogel exhibited gel-sol transition under shear stress, suggesting potential application as an injectable material. Image 1 • Dual cross-linking of hyaluronic acid/silk fibroin network. • Tunable hydrogel property based on photopolymerization and ethanol treatment. • Reversible gel-sol transition under shear stress. [ABSTRACT FROM AUTHOR]

The climate, topography, high population and associated emissions of California pose unique challenges in attaining the ozone (O 3) National Ambient Air Quality Standard. California's Sierra Nevada Mountains are situated east, and downwind of, the San Joaquin Valley (SJV), which has some of the worst air quality in the US. This work reports surface and vertical O 3 observations over the Sierra Nevada Mountains and the SJV from 1998 to 2018. Over this period, the O 3 concentrations observed on highly polluted days (95th percentile) decreased, primarily because of summertime emission reductions. Analysis of surface site diurnal data highlights the impacts that the SJV has on the Sierra Nevada Mountains, particularly at lower elevations. O 3 typically remains higher overnight at mountain sites, compared to SJV sites, and as a result mountain sites can have high cumulative exposure to O 3. Evidence of local and transport effects on O 3 trends across the Sierra Nevada Mountains is presented through examining of the timing of O 3 exceedances and correlations with different surface sites and with O 3 aloft. The data indicate a strong regional influence of emissions from the SJV over the Sierra Nevada Mountains and aloft up to 3 km. • Long-term compression of the O 3 range in Sierra Nevada Mountains, with decreases in the 95th percentile and increases in the 5th percentile. • The O 3 diurnal cycles are driven by transport of pollution, O 3 remains elevated over night at elevated sites increasing cumulative exposure. • Sierra Nevada Mountain O 3 show increased correlations with O 3 aloft during spring, highlighting the increased influence the free-troposphere. [ABSTRACT FROM AUTHOR]