Publications

In this paper, the structure, principle and framework of chaotic digital code-division multiple access ((CD) 2 MA) communication systems are presented. Unlike the existing CDMA systems, (CD) 2 MA systems use continuous pseudo-random time series to spread the spectrum of message signal and the spread signal is then directly sent through a channel to the receiver. In this sense, the carrier used in (CD) 2 MA is a continuous pseudo-random signal instead of a single tone as used in CDMA. We give the statistical properties of the noise-like carriers. In a (CD) 2 MA system, every mobile station has the same structure and parameters, only different initial conditions are assigned to different mobile stations. Instead of synchronizing two binary pseudo-random sequences as in CDMA systems, we use an impulsive control scheme to synchronize two chaotic systems in (CD) 2 MA. The simulation results show that the channel capacity of (CD) 2 MA is twice as large than that of CDMA.

Abstract The effects of applied hydrostatic pressure on the optical transitions in semiconducting single‐walled carbon nanotubes with different diameters and chiralities have been studied using optical absorption and photoluminescence spectroscopy. The excitonic transitions associated with the band‐gap (the first van Hove transition) energies in the carbon nanotubes are found to shift to lower energy at a rate depending on nanotube structure. The excitonic transitions between the first excited confinement states (the second van Hove transitions) are found to be much less sensitive to the applied hydrostatic pressure. All nanotubes show a dependence on their chirality in terms of pressure coefficient of the band‐gap energy, with the larger‐diameter nanotubes exhibiting a higher sensitivity of the band‐gap energy to hydrostatic pressure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Abstract The scope and limitations of the regioselective directed silylation of benzylic amines and subsequent reductive cyclization to azasilolanes (III) and (V) using norbornene as hydrogen acceptor is developed.

<title>Abstract</title> Engineering the heterologous expression of polyketide synthases (PKSs) in <italic>Escherichia coli</italic> has led to the production of various valuable natural and unnatural products. However, the limited availability of malonyl-CoA (M-CoA) in <italic>E. coli</italic> remains a significant impediment to efficient polyketide overproduction. In this study, engineered <italic>E. coli</italic> strains were developed to augment M-CoA levels for enhanced polyketide production by introducing a malonate transport and CoA ligation pathway. Additionally, control over the M-CoA pool was achieved by disrupting the endogenous M-CoA pathway and reconstituting it through malonate supplementation. The engineered strains exhibited increased M-CoA, fatty acid and polyketide titers, improved substrate selectivity of PKSs, and successful production of &gt; 99% uniformly labeled ¹³C polyketides. Adaptive laboratory evolution of these strains provided valuable insights into pathways governing the M-CoA pools and the accumulation of mutations that resulted in significantly increased M-CoA and polyketide levels. This approach not only enhances the utility of <italic>E. coli</italic> as a heterologous host for polyketides but also illuminates the intricate dynamics of M-CoA modulation in these systems.

Using the Kuhn-Tucker conditions from mathematical programming theory, a canonical nonlinear programming circuit for simulating general nonlinear programming problems has been developed. This circuit is canonical in the sense that its topology remains unchanged and that it requires only a minimum number of 2-terminal nonlinear circuit elements. Rather than solving the problem by iteration using a digital computer, we obtain the answer by setting up the associated nonlinear programming circuit and measuring the node voltages. In other words, the nonlinear programming circuit is simply a special purpose analog computer containing a repertoire of nonlinear function building blocks. To demonstrate the feasibility and advantage of this approach, several circuits have been built and measured. In all cases, the answers are obtained almost instantaneously in real time and are accurate to within 3 percent of the exact answers.

We demonstrate that a configuration of a dead-loaded cable network minimizes the potential energy absolutely if and only if the network is in equilibrium, the cable forces are non-negative and the cable stretches belong to domains of convexity of the cable strain energy functions. For convex strain energies, we construct a relaxed energy density that automatically accounts for slackening of the cables.

Numerical results are presented for complex-valued dynamic (frequency-dependent) stiffness influence coefficients for a homogeneous isotropic linearly viscoelastic half-space in plane strain or generalized plane stress. These influence coefficients, defined for uniformly spaced nodal points at the surface, are obtained from solutions of two boundary value problems, associated with unit harmonic displacements prescribed separately in each of the two-degrees-of-freedom of one nodal point with all other nodal points kept fixed. Results for two viscoelastic models, Voigt solid and constant hysteretic solid, are included. Utilizing the results of this work, the earthquake response of a structure, idealized as a two-dimensional finite element system, on the surface of a viscoelastic half-space in plane strain or generalized plane stress can be analyzed by the substructure method. Because the boundary value problems were solved for unit displacements at individual nodal points on the surface of the foundation, it would not be necessary to limit the base of the structure to a rigid plate.

The electrochemical reduction of carbon dioxide is sensitive to electrolyte polarization, which causes gradients in pH and the concentration of carbon dioxide to form near the cathode surface. It is desirable to measure the concentration of reaction-relevant species in the immediate vicinity of the cathode because the intrinsic kinetics of carbon dioxide reduction depend on the composition of the local reaction environment. Meeting this objective has proven difficult because conventional analytical methods only sample products from the bulk electrolyte. In this study, we describe the use of differential electrochemical mass spectrometry to measure the concentration of carbon dioxide and reaction products in the immediate vicinity of the cathode surface. This capability is achieved by coating the electrocatalyst directly onto the pervaporation membrane used to transfer volatile species into the mass spectrometer, thereby enabling species to be sampled directly from the electrode-electrolyte interface. This approach has been used to investigate hydrogen evolution and carbon dioxide reduction over Ag and Cu. We find that the measured CO₂ reduction activity of Ag agrees well with what is measured by gas chromatography of the effluent from an H-cell operated with the same catalyst and electrolyte. A distinct advantage of our approach is that it enables observation of the depletion of carbon dioxide near the cathode surface due to reaction with hydroxyl anions evolved at the cathode surface, something that cannot be done using conventional analytical techniques. We also demonstrate that the influence of this relatively slow chemical reaction can be minimized by evaluating electrocatalytic activity during a rapid potential sweep, thereby enabling measurement of the intrinsic kinetics. For CO₂ reduction over Cu, nine products can be observed simultaneously in real time. A notable finding is that the abundance of aldehydes relative to alcohols near the cathode surface is much higher than that observed in the bulk electrolyte. It is also observed that for increasingly cathodic potentials the relative abundance of ethanol increases at the expense of propionaldehyde. These findings suggest that acetaldehyde is a precursor to ethanol and propionaldehyde and that propionaldehyde is a precursor to n-propanol.

Außergewöhnlich schnelle oxidative Addition eines Arylchlorids (oder eines desaktivierten Arylbromids) an ein aktives Pd0-Zentrum, das durch sterisch anspruchsvolle Phosphane koordiniert wird, erfolgt bei Kupplungsreaktionen, die durch luftstabile PdI-Dimere, wie im Schema gezeigt, katalysiert werden. Infolgedessen sind die Reaktionen von Arylchloriden oder -bromiden mit Aminen und Boronsäuren bei Raumtemperatur innerhalb weniger Minuten abgeschlossen (1-Ad=1-Adamantyl). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2002/z50085_s.pdf or from the author. 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.