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This paper presents an application of the weighted least squares (WLS) method to the design of sharp linear phase finite-impulse response (FIR) digital filters synthesized using a modified frequency-response masking (FRM) structure. In our approach, the original minimax design problem is converted into a WLS problem. The WLS problem is highly nonlinear with respect to the coefficients of the filter. However, it can be decomposed into four linear least squares (LS) problems, each of which can be solved analytically. The design problem is then solved iteratively by using an alternating variable approach. The effectiveness of the method is demonstrated through solving a low-pass linear phase sharp FIR digital filter example. Index Terms--Frequency-response masking (FRM), minimax error, weighted least squares (WLS), alternating variable approach.

In this paper, we formulate a general design of transversal filter structures with maximum relative passband-to-stopband energy ratio subject to complex frequency response constraints in the passband and the stopband as well as additional constraints such as null constraints. These null constraints are important for applications where the suppression of noise at certain frequencies are important. Additional constraints are introduced allowing approximately linear phase and constant group delay in the passband. For a given set of basis functions, the design problem can be formulated as a semi-infinite quadratic optimization problem in the filter coefficients, which are the decision variables to be optimized. In this paper, we focus on the design of digital Laguerre filter and digital finite impulse response (FIR) filter structures. A modified bridging algorithm is developed for searching for the optimum pole of the Laguerre filters. Design examples are given to demonstrate the effectiveness of the proposed algorithm. Index Terms--Bridging method, digital Laguerre filter, group delay constraints, maximum passband-to-stopband energy ratio.

Algorithms for solving the envelope-constrained filtering problem have been presented. Unconstrained minimization problems are constructed to approximate the original problem. The findings indicate that the parameters of the unconstrained problem can be chosen to yield a filter whereby the noise gain deviation from that of the optimal EC filter is less than any prescribed tolerance. The efficiency of these algorithms is confirmed by numerical results.

In this paper, singular control systems are studied from the frequency domain point of view. The proper stable factorization of a singular system is derived. The stability of the closed-loop system consisting of a singular system and controller is addressed. Most significantly, all proper stabilizing controllers are parameterized for a given singular system. Index Terms - Factorization of system plant, singular systems, stabilizing controller, Youla parameterization.

In a recent paper, a set of necessary and sufficient conditions for the existence of solutions to the combined sensitivity and complementary sensitivity (CSCS) problem in control systems was given. However, a practical method for constructing solutions to this problem was not presented. The computation procedure that was proposed involves constructing a sequence of rational functions to approximate an irrational function and may result in complicated high-order controllers. In this paper, we consider the synthesis aspect of the CSCS problem and derive an algorithm for constructing controllers that solve our CSCS problem in a simple manner. Moreover, an error in the closed-form solution of the Nevanlinna-Pick interpolation problem is revealed.

This paper is concerned with instantaneous jumps in the state trajectory of a singular system. It is shown that such jumps generically exist at the initial time due to inconsistent initial states. The formula for the jumps is derived, which indicates that the jumps linearly depend on the initial state. Moreover, the set of all initial states which do not cause any state jumps for any output feedback is characterized and is revealed to be a linear subspace. In the meantime, the necessary and sufficient conditions are given for the existence of an output feedback to suppress completely the jumps for a given initial state. Finally, we formulate the problem of designing an output feedback not only to stabilize the plant but also to achieve minimum initial jumps as a minimization problem.

A novel method for optimizing envelope-constrained filters with uncertain input (ECUI) uses a standard quadratic programing problem to yield an efficient solution. The process enables a given signal to occur within a designated envelope or mask. The algorithm proposed has superior convergence characteristics compared to previous ECUI proposals.

In this paper, we present a new method for solving a class of optimization problems with nonsmooth constraints. In particular, we apply the method to the design of narrow-band minimum-power antenna array processors which are robust in the presence of errors such as array element placement, look direction misalignment and frequency offset. We first show that the constrained minimum power problem has a unique global minimum provided that the constraint set is nonempty. We then show how the design problem derived directly from considerations of the sensitivity of the antenna array processor to errors can be transformed into a quadratic programming problem with linear inequality constraints which can be solved efficiently by the standard active set strategy. We also present numerical results for two types of nonsmooth constraints developed to provided robustness. These results confirm the effectiveness of the method described in this paper.

We report the synthesis of zinc-blende CrTe (zb-CrTe) as highly oriented crystalline grains in films of 100-nm thickness. The structural properties of the film were characterized using high-resolution transmission electron microscopy (HRTEM) and selective-area electron diffraction (SAED). Temperature-dependent magnetization measurements show that the Curie temperature of the film is ~327 K. Angular M-H measurements indicate that the CrTe films have an in-plane easy axis of magnetization along the [0[bar.1]1] direction of GaAs. Index Terms--CrTe, ferromagnetic, molecular-beam epitaxy, zinc-blende.

We investigated the effect of magnetic-electric barriers on electron transport in the two-dimensional electron gas (2DEG) of a Al-GaAs-GaAs heterostructure. It is found that electric potential can be controlled to achieve both spin and charge conductance modulation in this material system, with the requisite condition being the presence of magnetic barriers to break the time reversal symmetry of the system. The use of electrical potential rather than applied magnetic fields as an external control parameter to achieve spin/charge conductance modulation promises a simpler device design for practical realization. Index Terms--Ballistic, device, resonant tunneling, spin-polarized current.

In this paper, we propose an alternative method to improve magnetoresistance by inserting a thin ferromagnetic (FM) layer into the nonmagnetic (NM) spacer of a basic spin-valve (SV) trilayer (FM1-NM-FM1), thus creating a penta-layer SV structure (FM1-NMFM2-NM-FM1). We investigated the effect of increasing the resistivity ([[rho].sub.F2]) of the FM2 on overall magnetoresistance (MR). We performed both analytical and numerical studies on the MR of the current perpendicular-to-plane (CPP) structure using the phenomenological spin drift-diffusion models. For finite [[rho].sub.F2], the MR profile is dependent on the intrinsic conductance polarization ([[alpha].sub.F2]) of FM2. We found that inserting FM2 enhances MR when [[alpha].sub.F2] exceeds a critical value of [[alpha].sub.2C]. It is found that MR can be doubled by inserting a FM layer with high [[alpha].sub.F2], such as the half-metallic [Cr.sub.2]O. We have numerically calculated [MR.sub.max]. and the corresponding [[rho].sub.F20] values for different [[alpha].sub.F2] values. Finally, we studied the effect of spin relaxation on the MR of the CPP SV. Index Terms--Current perpendicular-to-plane (CPP)-GMR, ferromagnetic, magnetoresistance (MR), spin valve (SV).

The use of microphone arrays for video conferences, hands-free mobile telephony and computer applications has created the demand for near-field broadband beamformer design methods. Here, a general broadband beamformer design problem is formulated as a weighted Chebyshev optimization problem, and a method to solve the resulting functionally-constrained problem is presented. The formulation can also be applied to the design of multidimensional digital finite-impulse response (FIR) filters with an arbitrarily specified amplitude and phase. Numerical results that demonstrate the minimax near-field behavior of the designed beamformers are given. Index Terms - Beamforming, Chebyshev optimization, near field.