A Spectral Factorization Approach to Pseudo-QMF Design

A new approach to the design of M-channel pseudoquadrature-mirror-filter (QMF) banks is presented. In this approach, the prototype filter is obtained as a spectral factor of a 2Mth band filter. This completely eliminates the need for optimization whereas in conventional pseudo-QMF designs, the main computational effort is in optimization of the prototype. As in the conventional approach, the aliasing cancellation (AC) constraint ensures that all the significant aliasing terms are canceled. The overall transfer function T(z) of the analysis/synthesis system has a linear phase and an approximately “flat” magnitude response in the frequency region ε ≤ ω ≤ (π - ε), where ε depends on the transition bandwidth of the prototype and 0 < ε < (π/2M). Three design examples are included

Breakthroughs in Shared Measurement and Social Impact

A surprising new breakthrough is emerging in the social sector: A handful of innovative organizations have developed web-based systems for reporting the performance, measuring the outcomes, and coordinating the efforts of hundreds or even thousands of social enterprises within a field. These nascent efforts carry implications well beyond performance measurement, foreshadowing the possibility of profound changes in the vision and effectiveness of the entire nonprofit sector. This paper, based on six months of interviews and research by FSG Social Impact Advisors, examines twenty efforts to develop shared approaches to performance, outcome, or impact measurement across multiple organizations. The accompanying appendices include a short description of each system and four more in-depth case studies

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

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

Structure/permeability relationships of silicon-containing polyimides

The permeability to H2, O2, N2, CO2 and CH4 of three silicone-polyimide random copolymers and two polyimides containing silicon atoms in their backbone chains, was determined at 35.0 C and at pressures up to about 120 psig (approximately 8.2 atm). The copolymers contained different amounts of BPADA-m-PDA and amine-terminated poly (dimethyl siloxane) and also had different numbers of siloxane linkages in their silicone component. The polyimides containing silicon atoms (silicon-modified polyimides) were SiDA-4,4'-ODA and SiDA-p-PDA. The gas permeability and selectivity of the copolymers are more similar to those of their silicone component than of the polyimide component. By contrast, the permeability and selectivity of the silicon-modified polyimides are more similar to those of their parent polyimides, PMDA-4,4'-ODA and SiDA-p-PDA. The substitution of SiDA for the PMDA moiety in a polyimide appears to result in a significant increase in gas permeability, without a correspondingly large decrease in selectivity. The potential usefulness of the above polymers and copolymers as gas separation membranes is discussed

On arbitrary-level IIR and FIR filters

A recently published method for designing IIR (infinite-impulse-response) digital filters with multilevel magnitude responses is reinterpreted from a different viewpoint. On the basis of this interpretation, techniques for extending these results to the case of finite-impulse-response (FIR) filters are developed. An advantage of the authors' method is that, when the arbitrary-level filter is implemented, its power-complementary filter, which may be required in specific applications, is obtained simultaneously. Also, by means of a tuning factor (a parameter of the scaling matrix), it is possible to generate a whole family of arbitrary-level filters

Application of Design of Experiments to Extrusion Freeform Fabrication (EFF) of Functional Ceramic Prototypes

Extrusion Freeform Fabrication (EFF) is an adaptation of the Stratasys Fused Deposition Modeling (FDM) process for the Solid Freeform Fabrication (SFF) of functional ceramic prototypes. It is a complex process involving many process variables, including parameters that are operation, machine, materials, and geometry specific. A Taguchi factorial Design of Experiments (DOE) technique was utilized to study the effects of machine specific process parameters as well as their interactions based on the mechanical and physical properties of sintered ceramics specimens. Post-processing software was developed to control and modify these parameters. This software interface wasdesigned to mimic the Quickslice™ interface for setting motion parameters based upon the material and the operation. The results of this investigation provided useful information for the experimental analysis of the machine specific process parameters. Suitable parameters were selected for the EFF process for fabricating representative ceramic prototypes. With the optimized parameters, complicated parts were successfully fabricated using both Kyocera SN282 and Starck M-11 silicon nitride powders.Mechanical Engineerin

Optimal Power Flow with Hybrid Distributed Generators and Unified Controller

Optimal power flow (OPF) study is conducted on a power system to achieve one of the following objectives: cost/loss minimization or available transfer capability (ATC) calculation in a deregulated environment. Distributed generation (DG) is a small source of electric power conversion from non-conventional energy sources and Hybrid DGs which often the most cost-effective and reliable way to produce power. The optimality of control variables and minimum value of objective functions in OPF study would definitely change when DGs are interconnected to the grid. The change would be respect to the location, quantity and combination of power injection by DGs. On the other hand, FACTS controllers are effective in utilizing the existing of transmission network which is very important especially in a deregulated system. Unified power flow controller (UPFC), a second generation FACTS controller, is well known for minimizing the cost of generation/losses with a good voltage profile as well as for ATC improvement. This paper conducts a detailed OPF study on a 9 bus system for the above mentioned three objectives to analyze the effect of DGs with and without UPFC. From the results, it is found that hybrid DGs along with UPFC yields better performance in many aspects

Cosine-modulated FIR filter banks satisfying perfect reconstruction

The authors obtain a necessary and sufficient condition on the 2M (M = number of channels) polyphase components of a linear-phase prototype filter of length N = 2mM (where m = an arbitrary positive integer), such that the polyphase component matrix of the modulated filter is lossless. The losslessness of the polyphase component matrix, in turn, is sufficient to ensure that the analysis/synthesis system satisfies perfect reconstruction (PR). Using this result, a novel design procedure is presented based on the two-channel lossless lattice. This enables the design of a large class of FIR (finite impulse response)-PR filter banks, and includes the N = 2M case. It is shown that this approach requires fewer parameters to be optimized than in the pseudo-QMF (quadrature mirror filter) designs and in the lossless lattice based PR-QMF designs (for equal length filters in the three designs). This advantage becomes significant when designing long filters for large M. The design procedure and its other advantages are described in detail. Design examples and comparisons are included