Realization of perfect reconstruction non-uniform filter banks via a tree structure

Obviously, a tree structure filter bank can be realized via a non-uniform filter bank, and perfect reconstruction is achieved if and only if each branch of the tree structure can provide perfect reconstruction. In this paper, the converse of this problem is studied. We show that a perfect reconstruction non-uniform filter bank with decimation ratio {2,4,4} can be realized via a tree structure and each branch of the tree structure achieves perfect reconstruction

Helicopter rotor loads using matched asymptotic expansions: User's manual

Computer programs were developed to implement the computational scheme arising from Van Holten's asymptotic method for calculating airloads on a helicopter rotor blade in forward flight, and a similar technique which is based on a discretized version of the method. The basic outlines of the two programs are presented, followed by separate descriptions of the input requirements and output format. Two examples illustrating job entry with appropriate input data and corresponding output are included. Appendices contain a sample table of lift coefficient data for the NACA 0012 air foil and listings of the two programs

Helicopter rotor loads using discretized matched asymptotic expansions

The numerical practicality of a matched asymptotic expansion approach for the computation of unsteady three dimensional airloads on a helicopter rotor was improved. This effort utilizes a discretized repesentation of the doublet strength distribution and helical streamlines to decrease the computational requirements of the original analysis. The continuous variation of the doublet strength was approximated by piecewise constant or piecewise quadratic distributions, and the helical trajectory of a fluid particle was approximated by connected straight line segments. As a direct result of these simplified representations the computational time required for the execution of a typical flight condition was reduced by an order of magnitude with respect to the requirements of the original analysis. Airloads which were computed using the discretized method for a two bladed model rotor and a full scale four bladed rotor are in close agreement with measured results and airloads from the original asymptotic analysis. For conditions characterized by significant rotor/wake interaction the piecewise constant representation requires a reduced azimuth spacing to maintain acceptable accuracy

On the minimum phase property of prediction-error polynomials

We provide a simple proof of the minimum phase property of the optimum linear prediction polynomial. The proof follows directly from the fact that the minimized prediction error has to satisfy the orthogonality principle. Additional insights provided by this proof are also discussed

Center-commissioned external review of International Water Management Institute: Consolidated report, 19-29 May 2003

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Properties of a New Dental Porcelain

A high strength dental porcelain OPTEC, HSP™ has recently been introduced for use in the fabrication of crowns, three-unit anterior bridges with a single pontic, inlays, on lays, veneers, etc., without a metal substrate. This investigation reports the results of our research involving the characterization of the structure properties and thermally induced transformations of this porcelain. It has been found that the material possesses superior strength and other properties relative to conventional porcelains. The improved properties appear to result from the presence of a very fine and relatively dense distribution of leucite crystals. Scanning electron microscopy indicates, however, that the new product needs additional optimization to improve uniformity of crystallite distribution. Scanning electron microscopy and X-ray diffraction studies also reveal well defined structural and crystallographic transformations during thermal treatment at selected temperature ranges. The primary transformation appears to be crystallization of metastable sanidine from the glass matrix. The crystallization of sanidine leads to a translucent to opaque transition. The transformations appear to follow the phase transitions expected from the phase diagrams

Design of doubly-complementary IIR digital filters using a single complex allpass filter, with multirate applications

It is shown that a large class of real-coefficient doubly-complementary IIR transfer function pairs can be implemented by means of a single complex allpass filter. For a real input sequence, the real part of the output sequence corresponds to the output of one of the transfer functions G(z) (for example, lowpass), whereas the imaginary part of the output sequence corresponds to its "complementary" filter H(z)(for example, highpass). The resulting implementation is structurally lossless, and hence the implementations of G(z) and H(z) have very low passband sensitivity. Numerical design examples are included, and a typical numerical example shows that the new implementation with 4 bits per multiplier is considerably better than a direct form implementation with 9 bits per multiplier. Multirate filter bank applications (quadrature mirror filtering) are outlined