10,000 publications from this institution
A novel approach based on the reaction of multifunctional star polymers with chromophore-labelled linear polymers is presented for evaluating the extent of termination by chain–chain coupling during living free-radical polymerizations. A mixed initiating system consisting of an unlabelled, multifunctional initiator and an excess of a monofunctional alkoxyamine initiator containing a chromophore, such as pyrene, is used to initiate the living polymerization of vinyl monomers leading to a mixture of star and linear polymers. The occurrence of chain–chain coupling is readily identified and quantified by isolating the star polymer that is obtained and elucidating the level of incorporation of pyrene units by UV/vis spectroscopy. This allows the level of chain–chain coupling to be determined since the inclusion of pyrene into the star structure is a direct result of termination by radical coupling.
The evolution of the shape of surface cracks in sensitized Type 304 SS in Boiling Water Reactor primary coolant at 288 o C was explored as a function of the corrosion potential and stress intensity using the Coupled Environment Fracture Model (CEFM). The revised CEFM that incorporates Shoji’s model for calculating the crack tip strain rate and more advanced expressions for estimating the stress intensity factor for semi-elliptical surface cracks provides more accurate prediction of the dependence of the crack growth rate on stress intensity factor and offers an alternative explanation for the development of semi-elliptical cracks than that provided by fracture mechanics. The evolution of the shape of surface cracks depends strongly upon environmental variables, such as the corrosion potential, predicting that the minor axis of the ellipse should be oriented perpendicular to the surface due to the dependence of the crack growth rate on the electrochemical crack length.
Abstract An analogue VLSI circuit architecture for the CMOS implementation of cellular neural networks (CNNs) is presented. It is based exclusively on the use of small capacitors and operational transconductance amplifiers operating in continuous time. Integrated circuit implementations of this architecture are very well suited for processing applications requiring large array size and high speed. We describe a systematic design approach for those circuits and present the design, fabrication and testing of two chips. These chips are used for connected component detection applications and are the first working integrated circuit implementation of a CNN. They contain 2000 transistors and have been fabricated using 2 μm CMOS technology. the density is 32 cells per square millimetre of silicon and the time constant of the processing is of the order of 10 −7 s. Experimental results of static and dynamic tests are given, including a complete image‐processing example.
Various equations which have been proposed to provide the 'best' functional form for the dependence of rate upon pressure for reactions in solution have been tested for the extraction of ΔV ≠ and dΔV ≠ /dp for the hydrolysis of benzyl chloride at 30 °C and at pressures over the range 1 to 6895 bar. One hundred individual rate constants were determined for this reaction at pressure increments of 345 bar and provide a sufficiently large body of data to permit application of statistical methods for testing the various rate–pressure functions with little risk of bias.
In this paper, we demonstrate that some hyperchaotic circuits can be synchronized by using only one state variable. We applied three kinds of synchronization schemes, a continuous synchronization, an impulsive synchronization, and a selective synchronization to these hyperchaotic circuits. Their performance is examined from the viewpoint of synchronization stability and convergence time.
The disclosure provides for novel metal-triazolate frameworks, methods of use thereof, and devices comprising the frameworks thereof.
The preparation of large cylindrical macroporous polymer monoliths with internal diameters of up to 50 mm has been studied for the first time for both styrenic and methacrylic monomer systems. The temperature profiles at different locations within the mold have been recorded during these polymerizations, and the occurrence of exotherms and temperature gradients was related to the creation of inhomogeneities in the pore structure. Several techniques, such as decreasing the rate of polymerization and a slow gradual addition of the polymerization mixture to the reaction vessel, were investigated in order to minimize the extent of the reaction exotherm. The latter approach proved especially powerful, as the absence of exotherm allowed the preparation of monoliths with homogeneous pore structures inaccessible by other methods for both monomer systems.
Cellular Nonlinear/Neural Network (CNN) technology is both a revolutionary concept and an experimentally proven new computing paradigm. Analogic cellular computers based on CNNs are set to change the way analog signals are processed and are paving the way to an entire new analog computing industry. This unique undergraduate-level textbook includes many examples and exercises, including CNN simulator and development software accessible via the Internet. It is an ideal introduction to CNNs and analogic cellular computing for students, researchers and engineers from a wide range of disciplines. Leon Chua, co-inventor of the CNN, and Tams Roska are both highly respected pioneers in the field.
This work quantifies the performance of gas-diffusion electrodes using multiphysics modeling and provides design guidance.
In this tutorial we continue our program of clarifying chaos by examining the relationship between chaotic and stochastic processes. To do this, we construct chaotic analogs of stochastic processes, stochastic differential equations, and discuss estimation and prediction models. The conclusion of this section is that from the composition of simple nonlinear periodic dynamical systems arise chaotic dynamical systems, and from the time-series of chaotic solutions of finite-difference and differential equations are formed chaotic processes, the analogs of stochastic processes. Chaotic processes are formed from chaotic dynamical systems in at least two ways. One is by the superposition of a large class of chaotic time-series. The second is through the compression of the time-scale of a chaotic time-series. As stochastic processes that arise from uniform random variables are not constructable, and chaotic processes are constructable, we conclude that chaotic processes are primary and that stochastic processes are idealizations of chaotic processes. Also, we begin to explore the relationship between the prime numbers and the possible role they may play in the formation of chaos.
Abstract : The recent development of metallic alloy systems which can be processed with an amorphous structure over large dimensions, specifically to form metallic glasses at low cooling rates (tilde 10 K/s), has permitted novel measurements of important mechanical properties. These include, fatigue crack growth and fracture toughness behavior, representing the conditions governing the subcritical and critical propagation of cracks. In the present study, bulk plates of a Zr41.2 Ti13.8 Cu12.5 Ni10 Be22.5 alloy, machined into 7 mm thick, 33 mm wide compact tension specimens and fatigue precracked following standard procedures, revealed fracture toughness in the fully amorphous structure of KIc tilde 55 MPa(square root m), i.e., comparable with that of a high strength steel or aluminum alloy. However, annealing to induce partial and full crystallization was found to result in a drastic reduction in fracture toughness to 1 MPa(square root m), i.e., comparable with silica glass. Under cyclic loading, whereas crack propagation behavior of the bulk amorphous metal was similar to that observed in traditional steel and aluminum alloys, the stress-life (S-N) properties of were markedly different. As in more traditional crystalline metallic alloys, the crack propagation mechanism in the metallic glass was associated with alternating blunting and resharpening of the crack tip as evidenced by striations on fatigue fracture surfaces. Alternatively, during S-N tests flaws apparently initiated quite easily due to the lack of microstructural barriers which would normally provide local crack arrest points, thereby giving rise to poor S-N properties.
We used variation in algal d 13 C between river habitats to study the spatial scale of energy flow through river food webs. We found a strong negative relationship between herbivore d 13 C (which reflects algal d 13 C) and water velocity in three productive Northern California rivers but not in unproductive streams. The contrast among habitats suggests that water velocity affects algal d 13 C most strongly when CO2 availability is low relative to photosynthetic rates. Our results help explain the wide variation in published river biota d 13 C and show that past studies using carbon isotope analyses may have significantly underestimated the importance of algal‐derived carbon to river food webs. While flow‐related variation in d 13 C complicates this common application of carbon isotope analysis, we show that it provides a natural tracer of the flux of algal production derived from different habitats within rivers to higher trophic levels. Measurements of consumer d 13 C showed that most invertebrate and vertebrate consumers relied on local production, except for filter‐feeding insects and steelhead trout, which relied on production derived from multiple sources. Stable carbon isotopes may thus be used to spatially delineate the habitats that support river food webs, providing previously unavailable information for understanding and managing river ecosystems.
