10,000 publications from this institution
Developing new approaches for improving the critical current density ( J c) in bulk high-temperature superconductors is important to the commercialization of these materials in power transmission cables and other applications ([1][1]). I. Chong et al . (Reports,[2 May, p. 770][2]) ([2][3]) describe
This special issue aims to explore critical elements of the overall design, user experience, and resulting solutions related to using pervasive computing technologies to inform our understanding of the dynamics of ourselves and our ecosystem, community, and urban landscapes. This issue not only explores pervasive technologies but also reviews practical solutions for improving citizens' health, wellbeing, and everyday lives. Careful attention is also paid to the interplay of social media within this landscape of pervasive analytics and citizen science.
Abstract This paper develops a modal pushover analysis‐ (MPA) based approximate procedure to quantify the collapse potential of structural systems. The computationally demanding incremental dynamic analysis (IDA) of the structural system is avoided by MPA of the structure in conjunction with empirical equations for the collapse strength ratio for the first‐mode single‐degree‐of‐freedom (SDF) system; higher modes of vibration play essentially no role in estimating the ground motion intensity required to cause collapse of the structure. Presented are collapse fragility curves for 6‐, 9‐, and 20‐story regular special moment‐resisting teel frames computed by the exact and approximate procedures, demonstrating that the MPA‐based approximate procedure requires only a small fraction (1% in one example) of the computational effort inherent in exact IDA and still achieves highly accurate results. Copyright © 2010 John Wiley & Sons, Ltd.
Rh(111). Ethanol and acetaldehyde are formed from CO + H{sub 2} by parallel routes on Rh catalysts which do not contain interacting supports or oxide promoters; i.e., the two compounds result from CO insertion into different metal-hydrocarbon bonds. Aldehydes decarbonylate via {alpha}-CH scission to form acyl, followed by C-C scission to release an alkyl ligand; this ligand undergoes hydrogenation and dehydrogenation steps. Alcohols form surface alkoxides, but these do not dehydrogenate further to the aldehydes, they release CO + H{sub 2} but no volatile hydrocarbon. These results indicate that {beta}-CH scissors to form a surface oxametallacycle intermediate; supporting evidence is spresented for this intermediate. Chemistry of alcohols blocked to different extends at the {beta}-position was also studied; complete blocking (CF{sub 3}CH{sub 2}OH) forces the reaction to follow the aldehyde-acyl path, while partial substitution at the {beta} position (branched alcohols) favors the oxametallacycle pathway. (DLC)
NGC 4395 is one of the least luminous and nearest known type 1 Seyfert\ngalaxies, and it also lacks a bulge. We present an HST I-band image of its\nnuclear region and Keck high-resolution (8 km/s) echelle spectra containing the\nCa II near-infrared triplet. In addition to the unresolved point source, there\nis a nuclear star cluster of size r ~ 3.9 pc; the upper limit on its velocity\ndispersion is only 30 km/s. We thus derive an upper limit of 6.2x10^6 solar\nmasses for the mass of the compact nucleus. Based on the amount of spatially\nresolved light in the HST image, a sizable fraction of this is likely to reside\nin stars. Hence, this estimate sets a stringent upper limit on the mass of the\ncentral black hole. We argue, from other lines of evidence, that the true mass\nof the black hole is likely to be 10^4-10^5 solar masses. Although the black\nhole is much less massive than those thought to exist in classical active\ngalactic nuclei, its accretion rate of L_bol/L_Edd ~ 2x10^-2 to 2x10^-3 is\nconsistent with the mass-luminosity relation obeyed by classical AGNs. This may\nexplain why NGC 4395 has a high-excitation (Seyfert) emission-line spectrum;\nactive galaxies having low-ionization spectra seem to accrete at significantly\nlower rates. NGC 4395, a pure disk galaxy, demonstrates that supermassive black\nholes are not associated exclusively with bulges.\n
Silicon-based microelectromechanical systems (MEMS) have been a prominent material platform since micromachining technologies were adapted from the microelectronics industry. Fatigue-induced drift and other degradation of MEMS are critical considerations for a wide range of circuit, sensor, and display technologies. The first objective of this chapter is to provide a review of what is currently known about the fracture and high cycle fatigue behavior of silicon structural films. The second objective is to review the fracture mechanics-based design methodologies that ensure reliable MEMS in safety-critical applications.
Hydrogen Peroxide (H 2 O 2 ) is one of many reactive oxygen species (ROS) that plays vital roles in intracellular signaling and stress processes, but its transient nature has made deciphering its roles in transcellular signaling a significant challenge. We have designed boronate caged small‐molecule probes bearing a fluoromethylene pendant group that serves as a latent quinone methide source that can undergo a tandem activity‐based sensing and biomolecule labeling reaction cascade to produce a spatially localized fluorescence signal upon exposure to H 2 O 2 . This strategy enables us to capture and record spatial information on ROS fluxes and has enabled us to move beyond studying intracellular H 2 O 2 signaling to identifying and mapping cell‐to‐cell H 2 O 2 communication in a microglia‐neuron co‐culture cell model, where selective activation of microglia for ROS production increases H 2 O 2 in nearby neurons.
The electrochemistry of pure aluminum and six alloys containing elements such as Ga, In, Tl, Mg, and Mn in at temperatures of 25°, 50°, and 80°C is reported. Alloy electrodissolution and hydrogen evolution were explored separately by delineating the current/voltage curves for the anodic and cathodic partial reactions using the technique described in Part II of this series (1). Aluminum is shown to be a passive metal in concentrated potassium hydroxide solution, at least at 25° and 50°C, with the active‐to‐passive transition being evident at the lowest temperature. At potentials more positive than the open‐circuit value, aluminum dissolves in the transpassive mode yielding a nearly linear current/voltage curve. The minor alloying elements (particularly Ga, In, Tl, Mn, and Mg) passivate aluminum by forming a protective layer on the base aluminum. Activation of the alloy occurs by the oxidation of this layer to form soluble products; in those alloys containing gallium the oxidation of Ga to appears to determine the critical activation potential . The alloying elements also inhibit hydrogen evolution, partly by decreasing the exchange current density but also by modifying the Tafel constant. The kinetic data for hydrogen evolution have been used to estimate surface coverages of the alloying elements as a function of potential and temperature.
A highly efficient sp² C-H amination using oxime esters is presented. The reaction is proposed to proceed via oxidative addition of the Pd(0) species into the N-O bond. Strong evidence is provided by an isolated Pd(II) complex generated from oxidative addition of Pd(0) into the N-O bond.
