Although sub-100 nm nanoclusters of metal nanoparticles are of interest in many fields including biomedical imaging, sensors, and catalysis, it has been challenging to control their morphologies and chemical properties. Herein, a new concept is presented to assemble equilibrium Au nanoclusters of controlled size by tuning the colloidal interactions with a polymeric stabilizer, PLA(1k)-b-PEG(10k)-b-PLA(1k). The nanoclusters form upon mixing a dispersion of similar to 5 nm Au nanospheres with a polymer solution followed by partial solvent evaporation. A weakly adsorbed polymer quenches the equilibrium nanocluster size and provides steric stabilization. Nanocluster size is tuned from similar to 20 to similar to 40 nm by experimentally varying the final Au nanoparticle concentration and the polymer/Au ratio, along with the charge on the initial Au nanoparticle surface. Upon biodegradation of the quencher, the nanoclusters reversibly and fully dissociate to individual similar to 5 nm primary particles. Equilibrium cluster size is predicted semiquantitatively with a free energy model that balances short-ranged depletion and van der Waals attractions with longer-ranged electrostatic repulsion, as a function of the Au and polymer concentrations. The close spacings of the Au nanoparticles In the clusters produce strong NIR extinction over a broad range of wavelengths from 650 to 900 nm, which is of practical interest in biomedical imaging.
This paper uses a genetic algorithm to systematically examine the underlying characteristics of the optimal bus transit route network design problem BTRNDP with variable transit demand. A multiobjective nonlinear mixed integer model is formulated for the BTRNDP. The proposed solution framework consists of three main components: an initial candidate route set generation procedure ICRSGP that generates all feasible routes incorporating practical bus transit industry guidelines; and a network analysis procedure NAP that decides transit demand matrix, assigns transit trips, determines service frequencies, and computes performance measures; and a genetic algorithm procedure GAP that combines these two parts, guides the candidate solution generation process, and selects an optimal set of routes from the huge solution space. A C++ program code is developed to implement the proposed solution methodology for the BTRNDP with variable transit demand. An example network is successfully tested as a pilot study. Sensitivity analyses are performed. Comprehensive characteristics underlying the BTRNDP, including the effect of route set size, the effect of demand aggregation, and the redesign of the existing transit network issue, are also presented.
This study presents an evaluation of the potential impacts on TxDOT revenues of substituting liquefied natural gas (LNG), compressed natural gas (CNG), and liquefied petroleum gas (LPG) for traditional diesel or gasoline vehicle fuels in Texas. Time series analyses are conducted for LNG, CNG, and LPG to estimate a model to forecast diesel and gasoline consumption for years 2012 to 2025. Taking into account the federal and state fuel taxes, the revenue generated from traditional fuel consumption is compared to three alternative fuel substitution scenarios. Overall, if the Federal and State excise tax rates remain at current levels the analysis suggests that substitution of LNG and LPG for traditional fuels will generate more revenue for the forecast years. However, substitution of CNG for gasoline consumption will reduce revenue if the Federal and State excise tax rates remain the same for the forecast years.
Predicting the longevity of non-aqueous phase liquid (NAPL) source zones has proven to be a difficult modeling problem that has yet to be resolved. Research efforts towards understanding NAPL depletion have focused on developing empirical models that relate lumped mass transfer rates to velocities and organic saturations. These empirical models are often unable to predict NAPL dissolution for systems different from those used to calibrate them, indicating that system-specific factors important for dissolution are not considered. This introduces the need for a calibration step before these models can be reliably used to predict NAPL dissolution for systems of arbitrary characteristics.
In this paper, five published Sherwood–Gilland models are evaluated using experimental observations from the dissolution of two laboratory-scale complex three-dimensional NAPL source zones. It is shown that the relative behavior of the five models depends on the system and source zone characteristics. Through a theoretical analysis, comparing Sherwood–Gilland type models to a process-based, thermodynamic dissolution model, it is shown that the coefficients of the Sherwood–Gilland models can be related to measurable soil properties. The derived dissolution model with soil-dependent coefficients predicts concentrations identical to those predicted by the thermodynamic dissolution model for cases with negligible hysteresis. This correspondence breaks down when hysteresis has a significant impact on interfacial areas. In such cases, the derived dissolution model will slightly underestimate dissolved concentrations at later times, but is more likely to capture system-specific dissolution rates than Sherwood–Gilland models.
Though gold nanoparticles have been considered bio-inert, recent studies have questioned their safety. To reduce the potential for toxicity, we developed a nanoclustering of gold and iron oxide as a nanoparticle (nanorose) which biodegrades into subunits to facilitate rapid excretion. In this present study, we demonstrate acid and macrophage lysosomal degradation of nanorose via loss of the near-infrared optical shift, and clearance of the nanorose in vivo following i.v. administration in C57BL/6 mice by showing gold concentration is significantly reduced in 11 murine tissues in as little as 31 days (P < 0.01). Hematology and chemistry show no toxicity of nanorose injected mice up to 14 days after administration. We conclude that the clustering design of nanorose does enhance the excretion of these nanoparticles, and that this could be a viable strategy to limit the potential toxicity of gold nanoparticles for clinical applications. From the Clinical Editor: The potential toxicity of nanomaterials is a critically important limiting factor in their more widespread clinical application. Gold nanoparticles have been classically considered bio-inert, but recent studies have questioned their safety. The authors of this study have developed a clustering gold and iron oxide nanoparticle (nanorose), which biodegrades into subunits to facilitate rapid excretion, resulting in reduced toxicity. Published by Elsevier Inc.
This paper presents the results of a detailed experimental study into the mechanical properties of ASTM A992 structural steel at elevated temperatures. Critical testing issues, including temperature measurement, temperature control, and extensometer use, along with the testing equipment and procedures are briefly explained. Tensile steady-state temperature tests are conducted on samples of ASTM A992 steel at temperatures up to 1000 °C. Full stress-strain curves, representing steel coupons tested to fracture at elevated temperatures, are generated. Important mechanical properties such as yield stress, tensile strength, proportional limit, elastic modulus and elongation are obtained from the stress-strain curves. Results are compared with elevated-temperature properties specified by Eurocode 3 and by the AISC Specification. When defined as the stress at 2% total strain, the measured yield stress values agree reasonably well with the corresponding values from Eurocode 3 and the AISC Specification. However, for more conventional definitions of yield stress, such as the 0.2% offset yield stress, the agreement is poor. It is observed that the yield stress of steel at elevated temperatures up to about 600 °C is highly dependent on the manner in which yield stress is defined. The effects of displacement loading rates on steel strength and static yielding behavior are also investigated. It is shown that the displacement rate has a large impact on the steel strength at elevated temperatures, especially at temperatures higher than 600 °C. Further work is needed to fully characterize the time-dependent effects on the elevated-temperature stress-strain response of structural steel. Additionally, this paper presents results of Charpy V-Notch (CVN) tests on ASTM A992 steel at elevated temperatures.