In this letter, we study the use of adaptive controllers to maintain the synchronization of two Chua's oscillators when the channel and circuit parameters are time-varying. We present both computer simulation results and physical experimental results to verify the operation of the designs.
ABSTRACT Fluxes and concentrations of carbon dioxide and 13 CO 2 provide information about ecosystem physiological processes and their response to environmental variation. The biophysical model, CANOAK, was adapted to compute concentration profiles and fluxes of 13 CO 2 within and above a temperate deciduous forest (Walker Branch Watershed, Tennessee, USA). Modifications to the model are described and the ability of the new model ( CANISOTOPE ) to simulate concentration profiles of 13 CO 2 , its flux density across the canopy–atmosphere interface and leaf‐level photosynthetic discrimination against 13 CO 2 is demonstrated by comparison with field measurements. The model was used to investigate several aspects of carbon isotope exchange between a forest ecosystem and the atmosphere. During the 1998 growing season, the mean photosynthetic discrimination against 13 CO 2 , by the deciduous forest canopy (Δ canopy ), was computed to be 22·4‰, but it varied between 18 and 27‰. On a diurnal basis, the greatest discrimination occurred during the early morning and late afternoon. On a seasonal time scale, the greatest diurnal range in Δ canopy occurred early and late in the growing season. Diurnal and seasonal variations in Δ canopy resulted from a strong dependence of Δ canopy on photosynthetically active radiation and vapour pressure deficit of air. Model calculations also revealed that the relationship between canopy‐scale water use efficiency (CO 2 assimilation/transpiration) and Δ canopy was positive due to complex feedbacks among fluxes, leaf temperature and vapour pressure deficit, a finding that is counter to what is predicted for leaves exposed to well‐mixed environments.
Major theories of preattentive human texture perception due to Julesz [5,9] and to Beck [1,2] attribute preattentive texture discrimination to differences in first-order statistics of stimulus features such as orientation, size and brightness of constituent elements. These theories have typically been constructed for black and white dot or line patterns and are not directly applicable to grey scale images. An alternative approach [6,15, 4] has been to exploit the linear mechanisms (psychophysically observed spatial frequency channels and neurophysiologically observed blob, bar- and edge- sensitive neurons) which have been used to explain a range of phenomena in early spatial vision. Some experiments [4,3] suggest that this approach may explain texture perception better than the more symbolic, feature based approach of Beck and Julesz. However no scheme in this framework has been fully specified, implemented and successfully tested. The crucial experimental tests are the following: Does the model correctly predict the texture boundaries found preattentively by human observers, both in images of natural scenes and the synthetic stimuli from psychophysics literature? Even better, does it correctly predict the degree of discriminability for different texture pairs as measured by psychophysical experiments?
The intermolecular addition of the alpha-C-H bonds of unactivated dialkylamines to unactivated olefins in the presence of the chloro amido complex [TaCl3(NEt2)2]2 (2) is described. This process forms the branched insertion products in high yields (up to 96%) and selectivities, and represents a rare example of an intermolecular amine-olefin coupling reaction that does not require preactivation of either substrate. The reaction is shown to encompass the addition of the primary C-H bonds in linear- and branched-methylamines, as well as secondary C-H bonds in higher dialkylamines. The related chloroanilido complex [TaCl3(NMePh)2]2 (4) is also shown to catalyze the addition of N-alkyl-arylamines to olefins at temperatures as low as 90 degreesC. 1H NMR spectroscopy, identification of the catalyst structure, and deuterium-labeling experiments all suggest that reactions catalyzed by 2 and 4 occur by turnover-limiting generation of an eta2-imine complex. These labeling studies also imply that more favorable partitioning of the eta2-imine complex toward reaction with alkene versus regeneration of the starting bis-amido complex accounts for the higher reactivity of the mixed halide amido catalyst versus a homoleptic amido complex.
A unified black box approach is presented for synthesizing nonlinear dc circuit models of 3-terminal devices characterized by two families of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\upsilon-i</tex> curves in piecewise-linear form. In order to model arbitrary curves with nonuniform spacings and slopes, three simple but versatile building blocks-a controlled linear resistance, a controlled concave resistor, and a controlled convex resistor-are introduced and shown to be essential ingredients. The circuit parameters and functions characterizing each element in the black box model can be determined easily from the slopes and breakpoints associated with the segments of the prescribed characteristic curves. The paper concludes with the presentation of several nonlinear dc circuit models for four widely used devices; namely, bipolar transistors, field-effect transistors (FET's), unijunction transistors, and triacs.
The 11th part of our tour through one-dimensional binary Cellular Automata concerns period-2 rules, which form the second group in our classification of the 88 globally-independent CA rules according to the properties of their periodic orbits. In this article, we display the basin tree diagrams of all period-2 rules along with their time-2 characteristic functions, and then we prove that all rules belonging to group 2 have robust period-2 ω-limit orbits for any finite, and infinite, bit string length. This rigorous result, which pairs with the one about period-1 rules given in the tenth installment of our chronicle, confirms what we stated about period-2 rules on the basis of empirical evidence. In the second part of this tutorial, we introduce the notion of quasi global-equivalence and prove that there are only 82 quasi globally-independent CA rules. For the first time, we show that the space-time patterns of globally-independent local rules can depend on each other, and we present an example of quasi-global transformation. We also define the super string 𝄞, and its unique decimal representation x 𝄞 , dubbed the super decimal, which provides a completely transparent yet rigorous proof that rule [Formula: see text] is chaotic when L → ∞. Moreover, we present the basin tree generation formulas, which uncover the analytical relationships between basin trees of globally-equivalent rules. Last but not least, for pedagogical and epistemological reasons, we conclude this paper with the selection of rule[Formula: see text], instead of rule [Formula: see text], as the prototypic universal Turing machine for our future discourse.
We discuss a series of spectra of the Type Ic (helium-poor Ib) supernova (SN) 1987M in the Sc galaxy NGC 2715, obtained over a 6 month interval following its discovery. Two spectra of SNe Ia, SN 1987L in NGC 2336 and SN 1987N in NGC 7606, are also illustrated for comparison. Near maximum brightness, SN 1987M showed all the spectroscopic characteristics of the "helium-poor" variety of SNe Ib identified in 1987 by Wheeler and collaborators, but it may have been subluminous by only 0.6 mag (B) instead of the average value of 1.5 mag. The possible presence of very weak H<SUB>alpha</SUB> must be verified through spectral synthesis. Strong P Cygni profiles of O I λ 7774 and Ca II are visible at early times in the near-infrared spectrum, as previously predicted. The Type IIb SN 1987K, by contrast, exhibits prominent H<SUB>alpha</SUB>_ but no O I λ 7774, although the two objects appear quite similar at blue and visual wavelengths. Strong Co II and Fe II absorption may be present at near-ultraviolet wavelengths in SN 1987M, as in SNe Ia. The data clearly reveal, for the first time, the remarkable transition to the "supernebular phase" of SNe Ib and Ic. Unambiguous [O I] and [Ca II] lines begin to appear less than two months past maximum. The ejected mass is estimated to be small, M<~1 M_sun_, although this number is highly uncertain. Multicolor light curves of SN 1987M, derived from CCD images and spectra, show a rapid decline from maximum brightness, perhaps even steeper than that of typical SNe I. This also suggests a relatively low ejected mass. Furthermore, unlike many SNe Ib, SN 1987M was not superposed on a luminous H II region. It is possible that SNe Ic, such as SN 1987M, have different progenitors or explosion mechanisms than SNe Ib. Specifically, we postulate that SNe Ic result from explosions of white dwarfs, while core collapse in massive, hydrogen- deficient stars produces SNe Ib.
We introduce the concept of a photovoltaic band gap Epvg for amorphous solar cells. This is the minimum photon energy thermodynamically required for the generation, of two free carriers in an operating solar cell. For hydrogenated amorphous silicon the photovoltaic band gap is 1.57 eV at 1-sun illumination.
