Several representative examples of nonlinear electronic circuits modeled by discontinuous 1-dimensional maps, including the 1-D maps derived from Chua's circuit, are reviewed. Although very little general results are presently available for studying the chaotic dynamics of such 1-D maps, an important subclass C where useful properties are known is identified and reviewed. This subclass is characterized by monotonic expansive maps within each continuous subinterval, and where the map assumes at each discontinuity point a left and a right limit equal in value to the boundary (end points) of the defining interval I. The main property characterizing discontinuous maps belonging to class C is that they possess a "good" invariant measure, which can be translated roughly by saying the associated chaotic attractor can be proved rigorously to be ergodic.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Despite substantial clinical interest in the fracture resistance of human dentin, there is little mechanistic information in archival literature that can be usefully used to model such fracture. In fact, although the fracture event indent in, akin to other mineralized tissues like bone, is widely believed to be locally strain-controlled, there has never been any scientific proof to support this belief. The present study seeks to address this issue through the use of a novel set of in vitro experiments in Hanks' balanced salt solution involving a double-notched bend test geometry, which is designed to discern whether the critical failure events involved in the onset of fracture are locally stress- or strain-controlled. Such experiments are further used to characterize the notion of ''plasticity'' in dentin and the interaction of cracks with the salient microstructural features. It is observed that fracture in dentin is indeed locally strain-controlled and that the presence of dentinal tubules does not substantially affect this process of crack initiation and growth. The results presented are believed to be critical steps in the development of a micromechanical model for the fracture of human dentin that takes into consideration the influence of both the microstructure and the local failure mode.
An extraordinary downfield-shifted 29Si{1H} NMR signal is seen at δ=338.5 for the platinum silylene complex [(dippe)(H)Pt=SiMes2][MeB(C6F5)3] (2). This remarkably stable metal silylene complex was obtained from 1 in the first intramolecular 1,2-hydride migration from silicon to a transition metal. dippe=iPr2PCH2CH2PiPr2, Mes=2,4,6-Me3C6H2.
Abstract The title compound is formed upon addition of (II) to the reactive η2‐silaacyl derivative (I) and prepared more conveniently starting with (IV).
The primary objectives of the proposed research was the development of deterministic, physico-electrochemical models for predicting the accumulation of localized corrosion damage (pitting corrosion, stress corrosion cracking and corrosion fatigue) in the primary coolant circuits of the currently operating fleet of Light Water Reactors (LWRs) and the embedment of the models into the Grizzly code currently currently being developed at the Idaho National Laboratory as part of their program on nuclear power plant component aging. Localized corrosion in LWR (BWR and PWR) primary coolant circuits (PCC) is primarily an electrochemical phenomenon, augmented by mechanics and microstructure, the rate of which is determined by certain electrochemical properties, such as the electrochemical corrosion potential (ECP), solution conductivity, temperature, pH, flow rate, and the kinetics of the reduction of redox depolarizers (e.g. O<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, and H<sub>2</sub>) on the surfaces external to the crack, in addition to mechanical loading (stress intensity factor on the crack) and micro-structural/micro-chemical factors (grain size, precipitates, etc). Because the efficient control of environmentally-assisted cracking (EAC) damage accumulation requires the accurate control of these parameters, it is necessary to develop codes that can accurately predict ECP and crack growth rate (CGR) at any point in the primary coolant circuit (PCC) over wide ranges of temperature (25 °C to 320 °C), pH (6 – 8), ECP (-0.9 V<sub>she</sub> to 0.2 V<sub>she</sub>), solution conductivity, flow rate (1 – 6 m/s), and stress intensity factor (5 MPa.m<sup>1/2</sup> – 50 MPa.m<sup>1/2</sup>). Knowledge of these parameters, along with suitable damage prediction codes, would allow an operator to predict the accumulated damage in PCC as a function of the future operating history of the reactor (the “corrosion evolutionary path,” CEP). In performing this study, we have further developed our previous prediction codes in the form of BWR_MASTER and PWR_MASTER by upgrading all sub-models for calculating radiolytic species concentration, ECP, and crack growth rate (CGR) as a function of reactor operating variables (power, radiation density, temperature, location in the PCC, flow velocity, coolant pH and conductivity, and operating history). The codes have been used to predict the accumulation of IGSCC damage in Type 304 SS in the core shroud of a BWR over a fuel cycle and to estimate the damage at the same location during start-up, considering transients in reactor power, temperature, and conductivity (due to hide-out/hide-out return). The predicted damage is in good agreement with plant observation. Regarding PWRs, we have developed two new models for calculating CGR in mill-annealed, Alloy 600, by considerably upgrading the MPM (mixed potential model for estimating the ECP), the Coupled Environment Fracture Model (CEFM) that were originally developed to predict ECP and CGR in sensitized stainless steels, to predict CGR in nickel-base alloys, as well as developing a micro-void pressurization model for also estimating CGR in MA Alloy 600. Both CGR models yield CGRs that are in excellent agreement with the experiment. We have also successfully developed crack initiation models for both stainless steels and mill-annealed, Alloy 600. That for stainless steels is based on a pit being the initiation site, whereas in that for mill-annealed, Alloy 600 postulates that initiation occurs at emergent grain boundaries that have been wedged open by internal oxidation. Experiments show that the crack initiation time (CIT) is highly distributed and is a seemingly, random quantity that exhibits trends with various system properties, such as surface stress, hardness, yield strength, etc. Although not identified in the SoW, we have developed a theoretical framework for describing the distributions in the CIT by assuming a normal distribution in the number of initiation sites with respect to surface stress. It is well-known from experiment that CGRs are highly distributed quantities also, with almost all systems exhibiting log-normal distributions. In work outside of that proposed, we used the ANN and CEFM to confirm that a log-normal distribution in CGR is expected theoretically if the independent variables are normally distributed. This work essentially defines the accuracy that one might expect in the calculated CGR due to randomness in the independent variables. To provide fundamental, input data for the various models, we have made extensive measurement of the kinetic parameters (exchange current density and Tafel constants) for the oxygen electrode reaction (OER) and the hydrogen electrode reaction (OER) on stainless steels (Types 304 and 316) and nickel-base alloys (Alloys 600 and 690) in reactor coolant at temperatures to 300 °C and as a function of pH, [O<sub>2</sub>], and [H<sub>2</sub>]. We have also optimized the Point Defect Model for passivity and passivity breakdown on measured electrochemical impedance spectroscopic (EIS) data for all alloys studied in this work to extract PDM parameter values that are then used to calculate the passive current density (general corrosion rate) and barrier layer thickness as a function of voltage, temperature, and pH. Thus, we have, at last, a reasonably comprehensive database for model parameters. Also outside of the SoW, we have developed a new, innovative method for monitoring, in situ, the hydriding of zirconium alloy fuel cladding under reactor operating conditions by optimizing a modified PDM for hydride/oxide formation on experimental EIS data. We have demonstrated the technique on pure zirconium in PWR coolant at 250 °C. Finally, also in addition to the SoW, we developed Fracture Impedance Spectroscopy, which draws an analogy with current flow in a passive electrical circuit in analyzing crack growth under fatigue loading conditions.
Abstract not Available.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUse of polymeric catalysts in the pore-size-specific functionalization of porous polymersVladimir Smigol, Frantisek Svec, and Jean M. J. FrechetCite this: Macromolecules 1993, 26, 21, 5615–5620Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://pubs.acs.org/doi/10.1021/ma00073a013https://doi.org/10.1021/ma00073a013research-articleACS PublicationsRequest reuse permissionsArticle Views353Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Smarter Katalysator: Eine Methode für die Palladium-katalysierte γ-Arylierung von α,β-ungesättigten Estern wurde entwickelt, die über Silylketenacetale verläuft und ohne Fluorid-Aktivatoren auskommt. Die Kupplung gelingt mit elektronenreichen und elektronenarmen Aryl- und Vinylbromiden in hohen Ausbeuten, und andere funktionelle Gruppen werden gut toleriert. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Abstract. The effect of photoinhibition on the activity of photosystem II (PSII) in spinach chloroplasts was investigated. Direct light‐induced absorbance change measurements at 320 nm (Δ A 320 ) provided a measure of the PSII charge separation reaction and revealed that photoinhibition prevented the stable photoreduction of the primary quinone acceptor Q A . Sensitivity to photoinhibition was substantially enhanced by treatment of thylakoids with NH 2 OH which extracts manganese from the H 2 O‐splitting enzyme and prevents electron donation to the reaction centre. Incubation with 3‐(3,4,‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) during light exposure did not affect the extent of photoinhibitory damage. The chlorophyll (Chl) b ‐less chlorina (2 mutant of barley displayed a significantly smaller light‐harvesting antenna size of PSII (about 20% of that in wild type chloroplasts) and, simultaneously, a lower sensitivity to photoinhibition. These observations suggest that photoinhibition depends on the amount of light absorbed by PSII and that the process of photoinhibition is accelerated when electron donation to the reaction centre is prevented. It is postulated that the probability of photoinhibition is greater when excitation energy is trapped by P680 + , the oxidized form of the PSII reaction centre. The results are discussed in terms of the D1/D2 heterodimer which contains the functional PSII components P680, pheophytin, Q A and Q B .
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnalysis of the design of bubble-column reactors for Fischer-Tropsch synthesisDavid Stern, Alexis T. Bell, and Heinz HeinemannCite this: Ind. Eng. Chem. Process Des. Dev. 1985, 24, 4, 1213–1219Publication Date (Print):October 1, 1985Publication History Published online1 May 2002Published inissue 1 October 1985https://pubs.acs.org/doi/10.1021/i200031a053https://doi.org/10.1021/i200031a053research-articleACS PublicationsRequest reuse permissionsArticle Views227Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
