A lattice realization for 2-D separable-denominator digital filters

New properties useful in connection with 1-D and 2-D lattice realizations are developed. These properties enable one to represent given, complicated 2-D separable-denominator digital filters in terms of simpler, more elemental building blocks which consist of two 1-D lattice realizations having dynamics in different directions and connected in a cascade form. The matrix-relationship between a 2-D discrete Schwarz form and a controller-observer canonical form is also derived. A notable property of the proposed 2-D lattice realization is that the impulse response energy of a 2-D separable-denominator digital filter can be readily obtained from the reflection coefficients and input/output tapped coefficients of the realization.This work was supported by the National Science Council of the Republic of China under Grant NSC79-0402-E0006-02, the US Army Research Office under Grant DAAL-03-91-G0106, and the NASA-Johnson Space Center under Grant NAG-9-380.     

Some general principles of dynamic instability of solid bodies

Résumé Ce travail représente une étude de l'équilibre des corps solides, avec un intérêt special accordé aux corps élastiques et à ceux de Voigt-Kelvin. Les efforts appliqués peuvent avoir des composants non conservatifs et gyroscopiques, quoique la dépendance explicite du temps soit exclue. Il est bien connu que, pour une catégorie de problèmes tellement large, l'établissement des conditions de la stabilité par les méthodes classiques de statique ou d'énergie n'est pas toujours applicable.Le traitement du problème essaie d'être assez compréhensif. En utilisant la méthode des vibrations modales on établie des critères généraux de stabilité sur la base d'une «énergie équivalente». Ces critères sont d'une telle généralité qu'ils contiennent, comme cas spéciaux, les critères publiés auparavant. En plus, de nouveaux principes ont été développés et démontrés à l'aide d'un exemple numérique.

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This work was supported by the National Science Foundation through Grant GK-368 to the University of Illinois at Chicago Circle.     

A polarization-independent and contrast-ratio-enhancing module for all-optical wavelength shifting using SOA's

We demonstrate a polarization-independent and contrast-ratio-enhancing all-optical wavelength shifting module using polarization-dependent SOA's. When comparing our robust module to a single polarization-dependent SOA wavelength shifter, we reduce the polarization dependence from 3.5-0.5 dB and the contrast-ratio-induced power penalty from 5-1.5 dB when upshifting over 19 nm at 1 Gb/s.     

An improved inverted δ-doped GaAs/InGaAs pseudomorphicheterostructure grown by MOCVD

This letter demonstrates a novel GaAs/In_0.25Ga_0.75 As/GaAs pseudomorphic heterostructure with δ-doping on the buffer prepared by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The proposed device with a 1.5×80 μm² gate reveals an extrinsic transconductance as high as 250 (305) mS/mm and a saturation current density as high as 790 (890) mA/mm at 300 (77) K. Significantly improvements on forward gate voltage swing (up to 3 V) and on reverse leakage current (smaller than 10 μA/mm at -6.5 V) are demonstrated due to inverted parallel conduction (IPC) effect. We also carried out secondary-ion mass spectrometry (SIMS) profiles to confirm the quality of the proposed device     

A scalable synthesis of an azabicyclooctanyl derivative, a novel DPP-4 inhibitor

A practical synthetic strategy to a chiral azabicycclooctanyl derivative (1), a potent DPP-4 inhibitor, starting from a commercially available nortropine is described. The stereogenic center of 1 was established employing a modified protocol of Ellman's diastereoselective addition of a benzylic nucleophile to tert-butanesulfinimine. Other key steps include Corey-Chaykovsky reaction, Meinwald rearrangement, and CDMT-promoted amide bond formation involving a sterically hindered amine 2.     

IMPLEMENTATION OF VORTEX FILAMENT METHODS ON PARALLEL MACHINES WITH DISTRIBUTED ADAPTIVE DATA STRUCTURE

This paper addressed the implementation of vortex filament methods on parallel machines with distributed memory to simulate a three-dimensionally evolving jet. Vortical structure developments due to Kelvin–Helmholtz instability of the axially perturbed jet are also examined. The implementation is conducted in a single-programme multiple-data (SPMD) environment and the parallelism is focused on issues of data distribution, efficient support of parallel I/O and overlapping of communications with computations. In addition, since the number of segment markers in a filament is dynamically growing according to the requirement of numerical accuracy, a novel packet-oriented data structure is proposed not only to partition filament segment markers among distributed processors but also to support dynamical load balancing at run time. This work is the first to apply packet-oriented structures to implement a parallel vortex filament method. Experimental results indicate performance improvement from 1·5 to 2·6 times over static schemes on nCUBE2, DEC Alpha and IBM SP2 by incorporating the proposed scheme with packet-oriented structures. © 1997 by John Wiley & Sons, Ltd. Int. j. numer. methods fluids 24: 939–951, 1997.     

Halogenated ketenes. 39. A new synthesis for substituted coumarins

A new general synthesis of substituted coumarins is described. The in situ cycloaddition of chloroketenes with α-methoxymethylenecyclohexanones yields (4 + 2) cycloaddition products, 3,4-dihydro-2-pyranones. The chlorine atom is reductively removed and methanol is spontaneously eliminated to yield the 5,6,7,8-tetra-hydrocoumarins. Dehydrogenation of these compounds results in good yields of the substituted coumarins.     

DiffServ-aware multicasting in a mobile IPv6 network

In this paper we propose an algorithm to establish a DiffServ-Aware Multicast Tree (DAMT) in a mobile IPv6 network. We first use the modified Prim’s algorithm to construct the Maximum Available Bandwidth Map (MABM) in a mobile IPv6 network. Then, both the extended multicast routing table stored in each Edge Router (ER) and the Interface QoS Table (IQT) stored in each Core Router (CR) are created and used to construct a DAMT. Finally, the constructed MABM can be rearranged (R-MABM) in order to keep the same QoS as a Mobile Node (MN) had in the home network when the MN has moved to a new ER. The proposed algorithm solves the architectural conflicts for the integration of multicasting support in the Diffserv network as well as the problems of the Neglected Reservation Sub-tree (NRS) and receiver heterogeneity. It also solves a MN’s QoS requirement when the MN moves from one network to another. Simulation results indicate that the proposed algorithm offers better performance than existing approaches in average delay, average packet loss rate, average throughput, the number of control overhead, the usage of bandwidth, the amount of saved link bandwidth, and the accumulated time to find a feasible path, especially in the case where the number of new join MN is large and traffic loads are heavy.     

Digital modeling and control of multiple time-delayed distributed power grid

Distributed power grid (DPG) control systems are so highly interconnected that the effects of local disturbances as well as transmission time delays can be amplified as they propagate through a complex network of transmission lines. These effects deteriorate control performance and could possibly destabilize the overall system. In this paper, a new approximated discretization method and digital design for DPG control systems with multiple state, input and output delays as well as a generalized bilinear transformation method are presented. Based on a procedure for the generation of impulse response data, the multiple fractional/integer time-delayed continuous-time system is transformed to a discrete-time model with multiple integer time delays. To implement the digital modeling, the singular value decomposition (SVD) of a Hankel matrix together with an energy loss level is employed to obtain an extended discrete-time state space model. Then, the extended discrete-time state space model of the DPG control system is reformulated as an integer time-delayed discrete-time system by computing its observable canonical form. The proposed method can closely approximate the step response of the original continuous time-delayed DPG control system by choosing various energy loss levels. For completeness, an optimal digital controller design for the DPG control system and a generalized bilinear transformation method with a tunable parameter are also provided, which can re-transform the integer time-delayed discrete-time model to its continuous-time model. Illustrative examples are given to demonstrate the effectiveness of the developed method.