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A crossing between phases: Polarity makes a difference in distinguishing substrates of otherwise nearly identical chemical reactivities. A one-pot cascade reaction involving nitromethane and two aliphatic aldehydes with similar reactivities has been developed (see scheme). The use of a biphasic reaction medium with two different organic catalysts results in the controlled incorporation of both aldehyde substrates into a single major cross-product.
Abstract : The algorithm for quadratic global optimization performed by a cellular neural network (CNN) with a slowly varying slope of the output characteristic is analyzed. It is shown that the only CNN which finds the global minimum of a quadratic function for any values of the input parameters is the network composed by only two cells. If the dimension is higher than two, even the CNN described by the simplest one-dimensional space-invariant template A=A(exp 1), A (exp 0), A (exp 1), fails to find the global minimum in a subset of the parameter space. Extensive simulations show that the CNN described by the above three-element template works correctly within several parameter ranges; however, if the parameters are chosen according to a random algorithm, the error rate increases with the number of cells.
Fatigue crack propagation behavior has been examined in a commercial 12.7 mm thick plate of Al-Cu-Li-Zr alloy, 2090, with specific emphasis on the effect of single compression overload cycles. Based on low load ratio experiments on cracks arrested at the fatigue threshold (ΔKTH), it is found that crack growth at ΔKTH can be promoted through the application of periodic compression cycles, of magnitude two times the peak tensile load. Similar to 2124 and 7150 aluminum alloys, such compression-induced crack growth at the threshold decelerates progressively until the crack re-arrests, consistent with the reduction and subsequent re-generation of crack closure. The compressive loads required to cause such behavior, however, are far smaller in the 2090 alloy. Such diminished resistance of aluminum-lithium alloys to compression cycles is discussed in terms their enhanced “extrinsic” crack growth resistance from crack path deflection and resultant crack closure, and the reduction in the closure from the compaction of fracture surface asperities by moderate compressive stresses.
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The present consumption of energy in the United States is mostly from fossil fuels, and that pattern is not likely to change, as carbon based fuels will likely remain plentiful and low in cost. This paper, even considering the above supply predictions, examines some drivers for changing the U.S. primary fuel sources. Identified are: a desire to reduce the nation's dependence on imported petroleum; the need for clean burning fuels; and the increasing concern about man-made carbon dioxide emissions being released into the atmosphere. The paper identifies the following four areas for research opportunities for the chemical sciences: technologies that are carbon efficient; technologies that enable carbon dioxide sequestration; technologies that enable the use of natural gas to produce liquid fuels; and, technologies that enable the use of biomass, solar energy, and renewable sources of energy in general.
Research Article| April 01, 1993 Thermochronologic record of pluton emplacement, deformation, and exhumation at Courtright shear zone, central Sierra Nevada, California Paul R. Renne; Paul R. Renne 1Institute of Human Origins Geochronology Center, 2453 Ridge Road, Berkeley, California 94709 Search for other works by this author on: GSW Google Scholar Othmar T. Tobisch; Othmar T. Tobisch 2Department of Earth Sciences, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Jason B. Saleeby Jason B. Saleeby 3Department of Earth and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 Search for other works by this author on: GSW Google Scholar Author and Article Information Paul R. Renne 1Institute of Human Origins Geochronology Center, 2453 Ridge Road, Berkeley, California 94709 Othmar T. Tobisch 2Department of Earth Sciences, University of California, Santa Cruz, California 95064 Jason B. Saleeby 3Department of Earth and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1993) 21 (4): 331–334. https://doi.org/10.1130/0091-7613(1993)021<0331:TROPED>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul R. Renne, Othmar T. Tobisch, Jason B. Saleeby; Thermochronologic record of pluton emplacement, deformation, and exhumation at Courtright shear zone, central Sierra Nevada, California. Geology 1993;; 21 (4): 331–334. doi: https://doi.org/10.1130/0091-7613(1993)021<0331:TROPED>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Thermochronology and thermobarometry of two plutons and a ductile shear zone at their contact in the central Sierra Nevada, California, as defined over the range 700 to 300 °C by 40Ar/39Ar dating of hornblende and biotite and U-Pb dating of zircon, indicate that ductile shear coincided closely with dramatically increased cooling and possible decompression of both plutons. Deformation occurred as the younger (∼90 Ma) Mount Givens pluton was emplaced against the older (∼102 Ma) Dinkey Creek pluton, which was softened by conductive heating, during extension. These events coincided with significant regional exhumation, possibly a result of crustal inflation, recorded by a major pulse of rapid sediment accumulation in contemporaneous fore-arc strata of the Great Valley sequence. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The differentiation of vaccine from non-vaccine isolates is important for disease control. Based on single nucleotide polymorphisms identified by comparison of the genomes of the Koganei 65-0.15 vaccine strain and a reference strain of Erysipelothrix rhusiopathiae, we developed a PCR assay that can differentiate the vaccine strain from field isolates.
Two basic approaches to device modeling are presented. The physical approach consists of 4 basic steps: 1) device physics analysis and partitioning, 2) physical equation formulation, 3) equation simplification and solution, and 4) nonlinear network synthesis. The black-box approach consists also of 4 basic steps: 1) experimental observations, 2) mathematical modeling, 3) model validation, and 4) nonlinear network synthesis. Each approach is ilustrated with 2 examples: Gunn Diode and SCR for the physical approach and Hysteretic Inductor and Memristive Device for the black-box approach. While the techniques for carrying out the first 3 steps in each approach presently involve more art than science, a unified theory for carrying out the last step (nonlinear network synthesis) is beginning to emerge. In particular, the universe of all lumped nonlinear circuit elements can now be classified into algebraic and dynamic elements via a completely logical axiomatic approach. Contrary to what is the case in linear circuit theory, it is shown that an infinite variety of basic algebraic and dynamic elements will be needed in the eventual formulation of a unified theory on device modeling. Consequently, these elements are given a complete and in-depth treatment in this paper. This material can also be regarded as a self-contained survey of the state-of-the-art on nonlinear network synthesis.
The role of crack tip shielding in retarding fatigue crack growth has been examined in duplex microstructures, with the objective of achieving maximum resistance to fatigue. Specifically, ferritic-martensitic structures have been developed in AISI 1008 steel, where shielding is generated from crack deflection and resultant crack closure. Such techniques yield fatigue thresholds which are 100% higher than in normalized structures, i.e., over 20 MPam, representing the highest thresholds reported for a metallic alloy to date. Effects of the dual-phase microstructures on crack initiation and small crack (10 to 1000 μm) growth are quite different. Structures which show the highest resistance to long crack growth show the lowest resistance to crack initiation and small crack growth, characteristic of behavior influenced by the mutual competition of intrinsic and extrinsic (shielding) “toughening” mechanisms.
