Surface-enhanced Raman scattering from individual au nanoparticles and nanoparticle dimer substrates

Surface-enhanced Raman scattering (SERS) intensities for individual Au nanospheres, nanoshells, and nanosphere and nanoshell dimers coated with nonresonant molecules are measured, where the precise nanoscale geometry of each monomer and dimer is identified through in situ atomic force microscopy. The observed intensities correlate with the integrated quartic local electromagnetic field calculated for each specific nanostructure geometry. In this study, we find that suitably fabricated nanoshells can provide SERS enhancements comparable to nanosphere dimers.     

Effect of particle morphology on flow characteristics of a composite plasma spray powder

The effects of BaF₂-CaF₂ particle morphology on National Aeronautics and Space Administration (NASA) PS304 feedstock powder flowability were investigated, BaF₂-CaF₂ eutectic powders were fabricated by comminution (producing an angular morphology) and by gas atomization (producing a spherical morphology). The fluoride powders were added incrementally to the other powder constituents of the NASA PS304 feedstock, (Ni-Cr, Cr₂O₃, and Ag powders). A linear relationship between flow time and concentration of the BaF₂-CaF₂ powder was found. The flow of the powder blend with spherical BaF₂-CaF₂ was better than that with angular BaF₂-CaF₂. The flowability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. However, the flow of the powder blend with spherical fluorides was independent of fluoride concentration. The results suggest that for this material blend, particle morphology plays a significant role in flow behavior, offering potential methods to improve powder flowability and enhance the commercial potential. These findings may be applicable to other difficult-to-flow powders such as cohesive ceramics.     

Behavior of Cyclic Fatigue Cracks in Monolithic Silicon Nitride

Cyclic fatigue-crack propagation behavior in monolithic silicon nitride is characterized in light of current fatiguecrack growth models for ceramics toughened by grainbridging mechanisms, with specific emphasis on the role of load ratio. Such models are based on diminished cracktip shielding in the crack wake under cyclic loads due to frictional-wear degradation of the grain-bridging zone. The notion of cyclic crack growth promoted by diminished shielding is seen to be consistent with measured (long-crack) growth rates, fractography, in situ crack-profile analyses, and measurements of back-face strain compliance. Growth rates are found to display a much larger dependence on the maximum applied stress intensity, K _max than on the applied stress-intensity range, Δ K , with behavior described by the relationship da/dN ∞ K²⁹_maxΔK^1.3. Fatigue thresholds similarly exhibit a marked dependence on the load ratio, R = K _min/ K _max; such effects are shown to be inconsistent with traditional models of fatigue-crack closure. In particular, when characterized in terms of K _max growth rates below ∼10⁻⁹ m/cycle exhibit an inverse dependence on load ratio, an observation which is consistent with the grain-bridging phenomenon; specifically, with increasing R, the sliding disance between the grain bridges is decreased, leading to less frictional wear, and hence less degradation in shielding, per loading cycle. The microstructural origins of such behavior are discussed.     

Nanogoldpharmaceutics (i) The use of colloidal gold to treat experimentally-induced arthritis in rat models; (ii) Characterization of the gold in Swarna bhasma, a microparticulate used in traditional Indian medicine

Nanosized gold particles (27 +/− 3 nm) have been proven to be effective in ameliorating the symptoms of mycobacterial-, collagen- and pristane-induced arthritis in rat models. This contrasts with the drug sodium aurothiomalate that was only effective against mycobacterial-induced arthritis but not to the same extent as Au⁰. Gold in the traditional Indian Ayurvedic medicine,Swarna bhasma (gold ash), has been characterized as globular particles of gold with an average size of 56–57 nm.     

Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: Ti‐6Al‐4V

Hexagonal boron nitride (h‐BN) coatings on Ti‐6Al‐4V substrates undergo complete decomposition in air at 900 °C. This fate is similar to that of this ceramic material on chromia‐former alloys, and unlike that of a mass of powder treated in isolation. As the ceramic and alloy oxidize concurrently, outwardly diffusing aluminum (III) ions but not the predominant titanium (IV) ions react with the boron trioxide that forms around the h‐BN basal plane peripheries. Resultant aluminum borate is incorporated into the growing scale and the boron trioxide diffusion barrier is depleted. By this mechanism, the oxidation of h‐BN is maintained at an enhanced rate, until both this material and its oxide completely decompose. Liberated nitrogen from the oxidation of h‐BN can enter the underlying scale as a randomly distributed solute in rutile solid solution. The post‐coating oxide‐atmosphere interface comprises elongated aluminum borate crystallites protruding through at the boundaries between 3–5 at% nitrogen‐doped rutile grains. It differs significantly from that of oxidized, uncoated Ti‐6Al‐4V, which is occupied by a thin α‐alumina layer atop rutile. This interface does not change with an additional 72 h of heat‐treatment.     

Settling characteristics of microparticles modified by hydrophilic semi-interpenetrating polymer networks

Microparticles of 2-hydroxyethyl methacrylate cross-linked with ethylene glycol dimethacrylate were produced by suspension polymerization. Semi-interpenetrating polymer networks were prepared by diffusion of poly(ethylene oxide) (PEO) solution into the particles. The PEO was allowed to diffuse into the dried particles and the resulting swollen particles were treated with an excess of acetone to collapse them. The ensuing networks consisted of the collapsed particles and the trapped PEO. The modified particles were allowed to settle in water, and characteristic settling times were measured as a function of swelling time. The settling times were compared to those of the unmodified particles. It was found that the settling time changes with volume fraction, particle size, degree of functionality, and amount of swelling. An increased volume fraction in both unmodified and modified particles causes a slower settling rate. The smaller particle sizes fall more slowly, and size difference plays a more significant role in hindering the settling for lower amounts of trapped PEO. As the amount of PEO increases, the settling rate decreases dramatically. Swelling also slows the settling rate, until the particles reach equilibrium. Equilibrium swelling occurs near 10 min for both unmodified and modified particles. Optical photo-microscopy verified the amount of swelling and demonstrated the process of PEO penetration. © 1995 John Wiley & Sons, Inc.     

Stress-controlled direct shear testing of geosynthetic clay liners II: Assessment of shear behavior

This paper is the second of a two-paper set on stress-controlled direct shear testing of geosynthetic clay liners (GCLs). Design of the apparatus, preliminary experiments, and shear deformation mechanisms in heat-treated and non-heat treated needle-punched (NP) GCLs were discussed in Part I. The objective of Part II (this paper) was to evaluate the effects of physical factors (i.e., peel strength and initial normal stress, σ_ni), environmental factors (i.e., temperature and hydration solution), and creep on the internal shear behavior of NP GCLs. In addition, failure conditions of GCLs in the stress-controlled direct shear tests were compared to displacement-controlled direct shear tests to verify results. An increase in internal shear strength developed from increased GCL peel strength or increased normal stress. Elevated temperatures were observed to decrease internal shear strength for both non-heat treated and heat-treated NP GCLs. Specimens hydrated with a calcium-rich synthetic mining solution experienced increased internal shear strength due to cation exchange in the bentonite, whereas specimens hydrated with a highly alkaline synthetic mining solution experienced decreased internal shear strength. Creep tests revealed an increase in time-to-failure with decrease in applied shear stress. Finally, stress states at failure from stress-controlled and displacement-controlled shear tests corresponded to a unique failure envelope, which validates the efficacy of using stress-controlled direct shear tests to assess internal shear behavior and shear strength of NP GCLs.     

The built environment,transportation policy,and population health: a comparison of two cities

This preliminary study assesses the relationship between active transportation, the built environment, and population perceived health in two comparable cities in the Southeastern United States at different stages of improving infrastructure for active commuting. Behavioral Risk Factor Surveillance Survey data from 2006 to 2012 were analyzed for Charlotte, NC, and Jacksonville, FL. The annual difference between the percentage of Charlotte respondents rating physical health as good compared to Jacksonville’s increased at a rate of 13% based on an exponential growth regression model (p = 0.02). Supportive urban and transportation policies aimed at facilitating healthy behaviors are associated with healthier communities.     

Predicting Mechanical Strength of In-Use Firefighter Protective Clothing Using Near-Infrared Spectroscopy

The exact lifespan of in-use firefighter protective clothing is difficult to predict due to the large variations in use between individual garments. Furthermore, testing methods used to evaluate new protective clothing are destructive in nature and could not be applied to in-use garments. Various non-destructive techniques have been proposed for the evaluation of in-use clothing, each possessing its own advantages and disadvantages. The ability of near-infrared spectroscopy to predict the tensile strength of thermally aged fabrics used in protective clothing for wildland firefighters and other workers is investigated here. Fabrics were exposed to heat fluxes from 10 kW/m² to 40 kW/m² for various durations using the cone calorimeter, after which the tensile strength of the fabrics was measured. Temperatures measured during the exposures and results of thermal gravimetric analysis tests were used to interpret changes in tensile strength. Multivariate linear regression was used to develop correlations between the tensile strength and the reflectance values measured between 1500 nm and 2500 nm for new and thermally aged fabrics. It was found that models based on reflectance measurements made at as few as three wavelengths could be used to estimate the tensile strength of the thermally aged specimens.