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The cross-coupling reaction of aryl bromides and iodides with aliphatic and aromatic thiols catalyzed by palladium complexes of the bisphosphine ligand CyPF-tBu (1) is reported. Reactions occur in excellent yields, broad scope, high tolerance of functional groups, and with turnover numbers that exceed those of previous catalysts by 2 or 3 orders of magnitude. These couplings of bromo- and iodoarenes are more efficient than the corresponding reactions of chloroarenes and could be conducted with less catalyst loading and/or milder reaction conditions. Consequently, limitations regarding scope and functional group tolerance previously reported in the coupling of aryl chlorides are now overcome.
We analyze the characteristics of overlay routing networks generated by selfish nodes playing competitive network construction games. We explore several networking scenarios - some simplistic, others more realistic - and analyze the resulting Nash equilibrium graphs with respect to topology, performance, and resilience. We find a fundamental tradeoff between performance and resilience, and show that limiting the degree of nodes is of great importance in controlling this balance. Further, by varying the cost function, the game produces widely different topologies; one parameter in particular - the relative cost between maintaining an overlay link and increasing the path length to other nodes - can generate topologies with node-degree distributions whose tails vary from exponential to power-law. We conclude that competitive games can create overlay routing networks satisfying very diverse goals.
The authors have been investigating a new route to stable yttrium and lanthanide silyl derivatives, Cp*{sub 2}LnSiH(SiMe{sub 3}){sub 2} (Ln = Y, Nd, Sm), by the reaction of Cp*{sub 2}LnCH(SiMe{sub 3}){sub 2} with H{sub 2}Si(SiMe{sub 3}){sub 2}. The mechanism of this reaction, which does not go through a simple sigma bond metathesis, and the generality of this route to the synthesis of other lanthanide silyls will be discussed. In addition, this paper will report reactivity studies of these complexes with various substrates (e.g., Ph{sub 2}SiH{sub 2}, Ph{sub 3}SiSiH{sub 3}, MeSiH{sub 3}) which indicate that Ln-Si bonds are quite reactive.
A simple physically-based model for the abrasive wear of composite materials is presented based on the mechanics and mechanisms associated with sliding wear in soft (ductile)- matrix composites containing hard (brittle) reinforcement particles. The model is based on the assumption that any portion of the reinforcement that is removed as wear debris cannot contribute to the wear resistance of the matrix material. The size of this non-contributing portion (NCP) of reinforcement is estimated by modeling three primary wear mechanisms, specifically, plowing, cracking at the matrix/reinforcement interface or in the reinforcement, and particle removal. Critical variables describing the role of the reinforcement, such as relative size, fracture toughness and the nature of the matrix/reinforcement interface, are characterized by a single contribution coefficient, C. Predictions are compared with the results of experimental two-body (pin-on-drum) abrasive wear tests performed on a model aluminum particulate-reinforced epoxy-matrix composite material.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron Paramagnetic Resonance Studies of Copper Ion-Exchanged ZSM-5Sarah C. Larsen, Adam Aylor, Alexis T. Bell, and Jeffrey A. ReimerCite this: J. Phys. Chem. 1994, 98, 44, 11533–11540Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://pubs.acs.org/doi/10.1021/j100095a039https://doi.org/10.1021/j100095a039research-articleACS PublicationsRequest reuse permissionsArticle Views1426Altmetric-Citations267LEARN 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
Abstract : The goal of designing and building a high performance CNN Universal Machine integrated circuit with demonstrable image processing capabilities was achieved during the contract funding period. The design of the CNN Universal Chip architecture was conducted under the guidance of theoretical results explicating the robust elemental processing capabilities of such cellular analog hardwares, which were developed under this contract. Furthermore, the analogic algorithms needed for implementing the specific image processing techniques required in several target application areas were designed.
Abstract The purpose of this paper is to study the CMOS latchup phenomenon from a non‐linear circuit theoretic standpoint by using some recently developed results on negative‐resistance devices. We introduce a simple mechanism to describe the latchup phenomenon based on a special circuit topology called feedback structure , which is shown to be responsible for the occurrence of latchup. Several guidelines are proposed to prevent latchup by destroying the feedback structure. In addition to the characterization of the steady‐state behaviour, we use a first‐order circuit model to analyze the latchup dynamics during the turn‐on process and give a stability analysis of the circuit dynamics. All existing techniques to prevent latchup are shown to follow naturally from our guidelines , which are derived using nonlinear circuit theory.
In photonic crystals, electromagnetic waves can be confined in all three dimensions – leading to very small mode volumes. A computational search has been made for the smallest electromagnetic mode volume which occurs in two-dimensional, dielectric photonic crystals slabs. The smallest mode volume found was V ≈ 2(λ/2n)3, where n is the refractive index. This small mode volume can lead to significant enhancement of spontaneous emission rates in semiconductor nano-cavities due to the Purcell effect.
The direct, Ir-catalyzed, regio- and enantioselective amination of allylic alcohols with Lewis acid activators to form branched allylic amine products is reported. The reactions of arylamines, benzylic amines, and secondary aliphatic amines in the presence of Nb(OEt)5 as activator occurred with high regioselectivities and high enantioselectivities. These results led to the development of Ir-catalyzed reactions of allylic alcohol with arylamines and BPh3 as activator in catalytic amounts. These reactions are rare examples of enantioselective substitutions of allylic alcohols. They are particularly unusual examples of the substitution of allylic alcohols to generate branched substitution products from monosubstituted allylic alcohols and of enantioselective substitutions of allylic alcohols with amine nucleophiles.
