Spatial and Temporal Variabilities of Sediment Delivery Ratio

Sediment contribution of specific areas of a watershed is an important consideration, but one that is often overlooked, when developing watershed management plans. Understanding sediment delivery to the watershed outlet is one method for identifying high contribution areas. In this study, a new methodology for calculating individual subbasin sediment delivery ratio (SDR) was developed within the Soil and Water Assessment Tool (SWAT) for two Michigan watersheds. Subbasins with the greatest SDR had two defining characteristics: high erosion rates and close proximity to the watershed outlet. The impact of best management practice (BMP) implementation (no-tillage and Conservation Reserve Program) on sediment yield reduction at the watershed outlet was compared for two targeting methods (SDR and erosion rate). Identifying SDR of individual subbasins for implementation of BMPs is more effective method for addressing water quality concerns at the watershed outlet than the widely used targeting high risk erosion areas. Watershed SDR was found to be highly variable on a monthly basis, due to changes in sediment yield, which is in turn affected by factors such as precipitation and surface runoff. Finally, watershed SDR calculated using the physically-based SWAT model was compared to four empirically-based areal relationships with SDR. While some area methods reproduced the SWAT-SDR, the variations between areal methods indicate that more detailed physical characteristics should be considered in watershed SDR calculation.     

Base resistance of drilled shafts in soft rock using in situ load tests: A limit state approach

This paper presents a probabilistic limit state framework for the evaluation of the base resistance of drilled shafts in soft rock. In situ load tests and the Griffith fracture theory are used to evaluate the mode of failure for the rock mass under the drilled shaft base. The base resistance or the limit state in the context of this paper is defined by the contact pressure at which load induced vertical to subvertical cracks form and the contact pressure-displacement relationship passes into a steep and fairly straight tangent. The parameters affecting the base resistance are evaluated using an in situ load test database. A statistical approach using the maximum likelihood method is utilized for the development of the design model for the base resistance. Reliability analysis is used to calibrate the corresponding resistance factors. The in situ load tests and the Griffith fracture theory suggest that the soft rock mass underlying the drilled shaft base primarily fails by the formation of vertical to subvertical cracks. Field observations indicate that the displacements in the underlying rock mass are largely in the vertical direction and that the base displacements required to mobilize the proposed base resistance are generally less than 30 mm. Load test data show that the base resistance is chiefly related to the unconfined compressive strength of soft rock. The calculated resistance factors are found to slightly decrease with increase in the span length of the structure and increase with the increase in the foundation redundancy.     

Onset coarsening-coalescence kinetics of γ-type related Al2O3 nanoparticles: Implications to their assembly in a laser ablation process

An onset coarsening-coalescence event based on the incubation time of cylindrical mesopore formation and a significant decrease of specific surface area by 50% and 70% relative to the dry pressed samples was determined by N₂ adsorption–desorption hysteresis isotherm for two Al₂O₃ powders having 50 and 10 nm in diameter respectively on an average and with γ-type related structures, i.e. γ- and its distortion derivatives δ- and/or θ-types with {1 0 0}/{1 1 1} facets and twinning according to transmission electron microscopy. In the temperature range of 1100–1400 °C, both powders underwent onset coarsening-coalescence before reconstructive transformation to form the stable α-type. The apparent activation energy for such a rapid coarsening-coalescence event was estimated as 241 ± 18 and 119 ± 19 kJ/mol, for 50 and 10 nm-sized particles, respectively indicating easier surface diffusion and particle movement for the latter. The size dependence of surface relaxation and onset coarsening-coalescence of the γ-type related Al₂O₃ nanoparticles agrees with their recrystallization–repacking upon electron irradiation and accounts for their assembly into nano chain aggregates or a close packed manner under the radiant heating effect in a dynamic laser ablation process.     

Eutectic Combinations as a Pathway to the Formation of Substrate‐Based Au‐Ge Heterodimers and Hollowed Au Nanocrescents with Tunable Optical Properties

Pairs of immiscible elements with deep eutectics are used to synthesize periodic arrays of heterodimers and hollowed metal nanocrescents. In the devised route, substrate‐immobilized Au or Ag nanostructures act as heterogeneous nucleation sites for Ge adatoms. At elevated temperatures the adatoms collect in sufficient quantities to transform each site into a AuGe liquid alloy which, upon cooling, phase separates into elemental components sharing a common interface. The so‐formed Au‐Ge and Ag‐Ge heterodimers exhibit a complex morphology characterized by a noble metal nanocrescent which partially encapsulates one end of the Ge domain. Through the use of a selective etch the Ge component is removed, leaving behind a periodic array of hollow noble metal nanocrescents on the surface of the substrate. Optical characterization of both the heterodimers and nanocrescents indicates that the presence of Ge gives rise to a relative blue‐shift in the localized surface plasmon peak, a result that is in stark contrast to the red‐shifts typically observed when plasmonic nanostructures are in contact with a dielectric medium. Simulations are used to both rationalize the observed shift and show the potential for deriving unexpected behaviors when semishell‐like noble metal structures are in contact with high permittivity dielectric mediums.     

Thermally activated rotation of Co1−xO particles within zirconia grains

Yttria partially stabilized zirconia (Y-PSZ) and Co_1−xO powders in 4:1 molar ratio were sintered and then annealed at 1300 and 1600°C to investigate the orientation change of Co_1−xO particles within Y-PSZ grains. Transmission electron microscopic observations indicated the Co_1−xO particles remained nonepitaxy in Y-PSZ grains after annealing at 1300°C for 300 h. When fired at 1600°C for 1–100 h, submicro-sized Co_1−xO particles (denoted as C) reached parallel epitaxy relationship, i.e. [100]_C//[100]_Z, [010]_C//[010]_Z and another relationship, i.e. [111]_C//[100]_Z, //[011]_Z with respect to the host zirconia grain (denoted as Z) nearly free of tetragonal precipitates. On the other hand, larger intragranular Co_1−xO particles (>1 μm in diameter) failed to reach epitaxial orientations even subject to prolonged annealing (100 h) at 1600°C. The temperature and size dependence of orientation change of the intragranular particle is in accordance with theoretical consideration of Brownian type rotation of the particle above a critical temperature for anchorage release at interface.     

Separable identification of nonlinear aggregate power system loads

An identification algorithm for a power system load model is proposed in this paper. The overall non-convex identification problem is separated into convex and non-convex subproblems, allowing for a global optimum to be found.     

Onset coarsening-coalescence kinetics of ZrO2 and less refractory TiO2 nanoparticles: Effect of homologous temperature and phase transformation

Specific surface area change of ZrO₂ (predominant tetragonal - (t) symmetry, 30-50 nm) and less refractory TiO₂ anatase nanoparticles (20-50 nm) upon isothermal firing at 700-1000 °C in air was determined by N₂ adsorption-desorption hysteresis isotherm. The nanoparticles underwent onset coarsening-coalescence within minutes without appreciable phase transformation for TiO₂, but with extensive transformation into monoclinic (m-) symmetry for ZrO₂. The apparent activation energy of such a process being not much higher for ZrO₂ (77 ± 23 kJ/mol) than TiO₂ (56 ± 3 kJ/mol) nanoparticles can be attributed to transformation plasticity. The minimum temperature for coarsening/coalescence of the present ZrO₂ and TiO₂ nanoparticles was estimated as 710 and 641 °C, respectively.