Abstract A simplified method is proposed for modeling the chemistry and potential distribution in a stress corrosion crack in sensitized stainless steel in boiling water reactor (BWR) coolant environments. The model is based on an assumption that only those species that are present at the largest concentrations in the crevice determine the potential distribution down the crack. The advantage of this method is that it permits simplification of the mathematics and allows predictions to be made of the potential and concentration distributions without knowing various parameters, such as the equilibrium constants for homogeneous chemical reactions in the cavity and diffusion coefficients of species that are present at relatively low concentrations near the crack tip. In some important cases, analytical expressions can be obtained for the pH, potential near the crack tip, and crack propagation rate. The conditions for which the potential on the crack flanks and in the vicinity of the crack tip coincides with the free corrosion potential in the local environment, and hence for which there exists a balance between rates of the local anodic and cathodic partial processes, are determined. The impact of the potential drop in the external environment on the potential and concentration distributions down the crack and on the crack propagation rate is also investigated. Excellent agreement is obtained between calculated and measured crack growth rates.
Technical Objectives: Research the application of liftoff transfer of epitaxial material to foreign substrates including: surface chemistry, electrical, mechanical, thermal and optical properties of Van der Waals bonded materials; III-V devices bonded to silicon circuitry and to other substrates with enhanced optical, electrical or thermal properties; integrated optical devices incorporating lifted-off material and/or devices with LiNbO$ sub 3$, glass or other substrates. Approach: This effort addresses the need for new technologies which can fully utilize the performance advantages of III-V (GaAs, InGaAs, InGaAsP, and InP) materials for electronic and opto-electronic applications. Specifically, the program is directed at demonstrating the potential of epitaxial liftoff as a technology to enable the realization of 'monolithic' optoelectronic devices with the characteristics of epitaxial material. That is, by transfer of epitaxial material to foreign substrates in a form that permits material processing and device fabrication to proceed as though the epitaxial material were grown directly on the substrate.
Abstract. The net ecosystem exchange of CO2 (NEE) varies at time scales from seconds to years and longer via the response of its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), to physical and biological drivers. Quantifying the relationship between flux and climate at multiple time scales is necessary for a comprehensive understanding of the role of climate in the terrestrial carbon cycle. Orthonormal wavelet transformation (OWT) can quantify the strength of the interactions between gappy eddy covariance flux and micrometeorological measurements at multiple frequencies while expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the response of terrestrial carbon flux to climatic variability. The variability of NEE, GEP and RE, and their co-variability with dominant climatic drivers, are explored with nearly one thousand site-years of data from the FLUXNET global dataset consisting of 253 eddy covariance research sites. The NEE and GEP wavelet spectra were similar among plant functional types (PFT) at weekly and shorter time scales, but significant divergence appeared among PFT at the biweekly and longer time scales, at which NEE and GEP were relatively less variable than climate. The RE spectra rarely differed among PFT across time scales as expected. On average, RE spectra had greater low frequency (monthly to interannual) variability than NEE, GEP and climate. CANOAK ecosystem model simulations demonstrate that "multi-annual" spectral peaks in flux may emerge at low (4+ years) time scales. Biological responses to climate and other internal system dynamics, rather than direct ecosystem response to climate, provide the likely explanation for observed multi-annual variability, but data records must be lengthened and measurements of ecosystem state must be made, and made available, to disentangle the mechanisms responsible for low frequency patterns in ecosystem CO2 exchange.
No abstract is provided for this article.
The mechanism whereby foundation loading is transmitted through the column has received little attention from researchers. This paper reports on some interesting findings obtained from a laboratory-based model study in respect of this issue. The model tests were carried out on samples of soft clay, 300 mm in diameter and 400 mm high. The samples were reinforced with fully penetrating stone columns, of three different diameters, made of crushed basalt. Four pressure cells were located along each stone column. The 60 mm diameter footing used in the model was supported on a clay bed reinforced with a stone column and subjected to foundation loading under drained conditions. The results show that the dissipation of excess pore water pressure developed during the initial application of total stresses, when the foundation was subjected to no loading, generated considerable stresses within the column, and that this was directly attributable to the development of negative skin friction. The pressure distributions in the column during foundation loading showed some complex behaviour.
Abstract not Available.
In the field of satellite imagery, good image acquisition chains are constructed such that the produced image being transmitted from the satellite to the ground is well sampled (in order to achieve a posteriori good restoration results for example). This means that the Nyquist-Shannon sampling theorem is satisfied [1]. However this theorem does not take into account the properties of the signal to be transmitted. Some recent works have used prior knowledge of the signal properties such as its sparsity. This new theory has recently been extensively used in the literature since it offers nice mathematical results for acquiring and reconstructing a sparse or compressible signal. This method has already been used in remote sensing, especially in the Herschel mission, which is a satellite dedicated to observation of the universe. In this work, we propose to analyse the applicability of compressed sensing in the framework of earth observation with high resolution satellite imagery, considering simultaneously the impact on the image quality performances, the on-board capacities and the adaptability to on-board hard physical constraints.
Spectroscopic techniques (X-ray absorption, Raman, and UV−visible) were utilized to monitor the effect of adsorbed water, calcination temperature, and reduction in H2 on the structure of dispersed VOx for vanadia supported on SiO2, Al2O3, TiO2, ZrO2, and HfO2 prepared with VOx surface densities ranging from 0.46 VOx/nm2 to 11.1 VOx/nm2. Supported vanadia was found to exist as monovanadate, polyvanadate, or V2O5 species, the distribution among these species depending on the support for a given VOx surface density. Dehydration resulted in the appearance of monovanadate species on all supports, with the extent of these species decreasing in the order HfO2 > Al2O3 > ZrO2 > TiO2 > SiO2. Hydration of the samples caused a decrease in the monovanadate species and a slight increase in polyvanadate species. Oxidation at elevated temperature resulted in an increase in the crystallinity of V2O5 present on SiO2, a conversion of V2O5 into polyvanadate species on Al2O3, and the appearance of mixed-metal oxide phases on TiO2, ZrO2 (ZrV2O7), and HfO2 (HfV2O7). The appearance of an interaction between vanadia and titania coincides with the transformation from anatase to rutile TiO2. ZrV2O7 and HfV2O7 are postulated to form via the interaction of surface VOx species with the support as the support begins to undergo a phase transition from tetragonal to monoclinic. H2 reduction produced limited changes in the structure of dispersed vanadia except on Al2O3, where V2O5 was transformed into polyvanadate species.
Investigated are the steady-forced and earthquake responses of single-degree-of-freedom (SDF) systems with a nonlinear viscoelastic damper (VED), which consists of a nonlinear fluid viscous damper (FVD) connected in series to a linear elastic bracing element (chevron or inverted V-shaped braces). For a wide range of bracing stiffness, nonlinear dampers are advantageous because they achieve essentially the same reduction in system responses but with a significantly reduced force. Damper nonlinearity has little influence on the structural response in the velocity-sensitive region of the spectrum even if the bracing is fairly flexible, but differences up to 16% were observed in other spectral regions. As expected, supplemental damping reduces structural response and the response reduction depends on the bracing stiffness, with this dependence varying with the spectral regions. For practical applications, a procedure is presented to estimate the design values of structural deformation, structural force, foundation shear, and damper force directly from the earthquake design (or response) spectrum. Finally, a procedure is presented to determine the damper and bracing properties necessary to limit the structural deformation to some design value or to the structural capacity.
