In einem anderen Stern: Sternpolymere können sonst nicht kompatible Säure- und Base-Katalysatoren wie para-Toluolsulfonsäure- oder 4-(Dialkylamino)pyridin-Einheiten in ihrem sterisch abgeschirmten Inneren tragen (siehe Schema). Die Sternpolymere vermitteln homogen katalysierte Reaktionskaskaden in Eintopfverfahren, beispielsweise eine Sequenz aus säurekatalysierter Entschützung und durch ein nucleophiles Amin katalysierter Baylis-Hillman-Reaktion.

An electronic instrument for displaying any perspective of a three-dimensional surface S generated by three time-varying (not necessarily periodic) signals is described. The surface S is a three-dimensional Lissajous figure which need not be a closed curve as is typical of all strange attractors. This analog (not digital) instrument is designed to rotate S along any axis (not just the X-, Y-, Z-axis) through any prescribed solid angles (0°-360°) in the three-dimensional coordinate system in real time. The instrument works as a preprocessor for a standard oscilloscope and is built with components capable of displaying time-varying signals with a frequency spectrum from 0 to 20 kHz. To illustrate some immediate applications of this instrument, strange attractors associated with both autononmus and nonautonomous circuits are presented in many different perspectives and cross sections. In particular, numerous cross sections of these strange attractors which have never been seen before can be easily displayed in any desired perspective in real time. Such cross sections have proved to be most revealing and invaluable in dissecting and uncovering the fine structures of strange attractors.

Die Polarität ist es, die den Unterschied zwischen Substraten mit sonst fast identischer chemischer Reaktivität macht. Eine Eintopf-Kaskadenreaktion von Nitromethan und zwei aliphatischen Aldehyden ähnlicher Reaktivitäten wurde entwickelt (siehe Schema). Die Verwendung eines zweiphasigen Reaktionsmediums mit zwei verschiedenen organischen Katalysatoren führte zur hochselektiven Bildung eines einzigen von vier möglichen Produkten. 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.

We have used single-molecule-resolved scanning tunneling microscopy to measure the photomechanical switching rates of azobenzene-derived molecules at a gold surface during exposure to UV and visible light. This enables the direct determination of both the forward and reverse photoswitching cross sections for surface-mounted molecules at different wavelengths. In a dramatic departure from molecular behavior in solution-based environments, visible light does not efficiently reverse the reaction for azobenzene-derived molecules at a gold surface.

The preparation of nanoporous size-selective hypercrosslinked polymer networks containing 37−92% of pores small enough for hydrogen adsorption but too small to allow penetration of nitrogen has been studied. Polyaniline and diaminobenzene were coupled with diiodobenzene and tribromobenzene using Ullman and Buchwald synthetic routes. The resulting porous polymer networks consist of aromatic rings linked through a trivalent nitrogen atom. The Buchwald reaction appears to be more effective than the Ullman synthesis for the production of such materials. The use of solvents with higher Hildebrand solubility coefficients during synthesis affords polymers with higher surface areas. The nanoporous polymers possess unusually high initial enthalpies of adsorption of hydrogen reaching values of up to −18 kJ/mol.

An extremely efficient breakpoint-hopping algorithm is presented for tracing the driving-point and transfer characteristics of any nonlinear circuit made of linear (possibly multi-terminal) resistors, dc independent sources, linear controlled sources (all 4 types) and 2-terminal nonlinear resistors described by piecewise-linear <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\upsilon - i</tex> characteristics. Most resistive nonlinear electronic circuits can be realistically modeled by such circuits. The algorithm can trace not only violently nonlinear (with sharp turning points) and multivalued characteristics, but also characteristics composed of several disconnected branches, provided one point in each branch is given. The remarkable computational efficiency of the breakpoint-hopping algorithm is due to two key properties built into the algorithm: 1) the circuit equation is formulated into a special form; namely, a canonical piecewise-linear equation with a lattice structure. 2) the algorithm finds only the breakpoints and possibly one point on each end (unbounded) segment via explicit formulas (hence no convergence problem). These data points represent the minimal amount of information needed to specify a piecewise-linear characteristic uniquely.

Abstract Techniques formerly developed in the theory of Poincaré half‐maps are modified and applied to the three‐region piecewise‐linear continuous dynamical system associated with Chua's circuit. Both transfer and return maps, induced by the trajectories inside the intermediate region in state space, are formulated as implicit equations. the boundaries of the domains of these maps are determined explicitly, using the method for calculating the initial points of touching trajectories subject to appropriate switching dynamics. A charting of the canonical parameter space of the dynamics that acts on the intermediate region is indicated. Among other things, this chart reveals the existence of new types of chaotic attractors different from the double scroll and Rössler attractors previously discovered from Chua's circuit.

An extremely simple cloning template for a cellular neural network (CNN) is presented that is capable of detecting the number of connected components of a vector in (+1, -1)/sup N/. By exploiting this capability, an architecture for a handwritten character recognition system was obtained. A preliminary test result (100 handwritten numbers, 0-9) shows 94-100% correct recognition rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Abstract This paper describes the dynamics of the simplest physical system known to date whose chaotic dynamics and rich bifurcation phenomena have been observed not only in the laboratory, but also reconfirmed by extensive computer simulation of its associated mathematical model: a 3rd‐order autonomous ordinary differential equation. The physical system is a 5‐element electrical circuit whose only non‐linearity is a non‐linear resistor characterized by a 3‐segment piecewise‐linear voltage‐current characteristic. Despite the simplicity of the circuit, however, it is imbued with an extremely rich variety of bifurcation phenomena. By changing the capacitance values, many phenomena, including Hopf bifurcation, period‐doubling cascades, Rössler's spiral‐type and screw‐type attractors, 4 periodic windows, ‘double‐scroll’ attractor, 1 boundary crisis, 5 Shilnikov‐type phenomenon, 6 etc. have been observed experimentally and confirmed by computer simulation. Other attractors and periodic windows have also been observed by varying the conductance values. In addition, Rössler's spiral‐type and screw‐type attractors have been observed from the same circuit, where the non‐linear resistor has only one break point, i.e. it is described by a 2‐ segment piecewise‐linear v ‐ i characteristic. This means that extremely complicated non‐periodic (chaotic) waveforms can arise in the simplest third‐order uncoupled electrical circuit in which all elements except one (a resistor ) are linear and passive, and in which the constitutive relation of the non‐linear resistor is made of the simplest conceivable non‐linearity, namely 2 straight‐line segments.

Abstract Necessary and sufficient conditions are given for resistive circuits containing both monotone‐increasing non‐linear resistors and monotone‐decreasing non‐linear resistors (called negative non‐linear resistors), in addition to controlled sources and op‐amps, to have a unique solution for all circuit parameters. Several theorems are given for various classes of circuits containing different combinations of active circuit elements. the theorems are couched mostly in topological terms and can therefore be checked by inspection.

In a beautiful recent experiment Sakagami et al. have recorded, on magnetic tape, the spatial field distribution produced in laser-plasma interaction. The standard infinite-plane theory of magnetic field produced by resonance absorption is unable to explain their experimental observations. This Letter proposes that finite geometry effects in resonance absorption produce a new magnetic field contribution which is responsible for their results.

We illustrate how to form the Taylor polynomial for a stable or unstable manifold when considered as a curve in the plane. Our method does not use power series or assume that the manifold is analytic as is done in the method of Poincaré. Instead we use simple calculus to obtain closed form expressions for the Taylor coefficients.