The Direct Solution of Nonconvex Nonlinear FIR Filter Design Problems by a SIP Method

FIR filter design problems in the frequency domain are nonlinear (semi-infinite) optimization problems. In practice, however, these almost always have not been approached directly, but been solved in a simplified form and/or only under restricting assumptions. In this paper, quite general mathematical formulations of the four main design approximation problems in the frequency domain are presented, which enable the derivation of theoretical results (collected here from R. Reemtsen, 2000b, 2000c) and the application of general-purpose optimization procedures to their direct solution. For the actual solution, a nonlinear semi-infinite programming method from the thesis (S. Görner, Ph.D. Thesis, Technische Universität Berlin, Berlin, 1997) of the first author is discussed and applied to several specific design problems. In some cases, the computed solution of the nonlinear problem is compared with that of a convex approximation of the problem.     

THE SIMULTANEOUS APPROXIMATION OF MAGNITUDE AND PHASE BY FIR DIGITAL FILTERS. I: A NEW APPROACH

The non-linear problem of simultaneous approximation of the magnitude and phase by an FIR digital filter is studied. Usually this problem is solved indirectly by solution of the complex Chebyshev approximation problem of the frequency response of the filter, which can be described as a linear or non-linear convex semi-infinite programming problem. In the present first part of the paper the relationship between the magnitude/phase problem and the Chebyshev problem is investigated and an alternative approximate representation in the form of a convex semi-infinite programming problem is derived. The latter problem can be solved by the same methods for such problems which were used previously by the authors for the solution of (constrained) complex Chebyshev approximation problems. In part II of the paper some earlier approaches to FIR filter design are reconsidered and discussed with regard to the magnitude/phase problem. It is further demonstrated there by several examples of filter designs that the new approach of this paper leads to very good results. © 1997 by John Wiley & Sons, Ltd.     

Peripheral tolerance to class I mismatched renal allografts in miniature swine: donor antigen-activated peripheral blood lymphocytes from tolerant swine inhibit antidonor CTL reactivity

Studies utilizing partially inbred miniature swine have demonstrated that a short course of cyclosporin A leads to indefinite survival of two haplotype class I mismatched renal allografts. In the present study, we have examined peripheral regulatory mechanisms that may be involved in maintenance of tolerance by coculturing PBL from long-term tolerant animals with naive recipient-matched PBL in cell-mediated lympholysis assays. We show that PBL from tolerant animals, primed in vitro with donor Ag, suppress antidonor CTL reactivity by naive recipient-matched PBL. Suppression was not observed when PBL from naive animals, primed with donor-matched PBL, were cocultured with PBL from a second naive animal, nor did PBL from either tolerant or naive recipient-matched control animals, primed with third-party Ag, suppress the generation of anti-third-party CTL by a second naive animal. The suppression was cell dose-dependent, radiation-sensitive, required cell-to-cell contact not reversed by the provision of exogenous IL-2, and associated with lower levels of IL-2R expression on the suppressive effector group (particularly the CD8 single positive cells) when compared with the control effector group. These data indicate an association between the presence of peripheral regulatory cells demonstrable in vitro and the maintenance of tolerance to renal allografts.     

Bicriterial Design of Digital Filters

A problem of technical interest is the solution of approximation problems which make a tradeoff between the L ₂ norm and the L norm error criteria. This problem is investigated in the framework of filter design with respect to two conflicting optimality goals. The particular interest in L ₂-L norm compromise filters has been raised by a paper of Adams (IEEE Trans. on Circuits and Systems vol. 39, pp. 376–388, 1991), who suggested to compute such FIR filters by solution of certain constrained L ₂ approximation problems which require a proper choice of weights. It is shown in this paper that bicriterial filter design problems can be approached by classical methods from multicriteria optimization and that especially reference point approximation with the ideal point as reference point is a suitable tool to deal with Adams' problem. Solutions from this latter approach do especially not depend on the choice of weights and yield the best possible compromise filters with respect to a prescribed measure. The resulting optimization problems can be solved with (semi-infinite) programming methods having proven convergence under standard assumptions. Examples of L ₂-L norm compromise designs of a linear-phase FIR and an IIR filter are presented.     

Coating of intravascular balloon with paclitaxel prevents constrictive remodeling of the dilated porcine femoral artery due to inhibition of intimal and media fibrosis

Here we investigated how a coating of intravascular balloon with paclitaxel (drug-coated balloon; DCB, Freeway?) impacted porcine peripheral artery vascular function and remodeling. Domestic swine (n = 54) underwent percutaneous overstretch balloon dilation of femoral and iliac arteries, controlled by angiography and optical coherence tomography (OCT). Paclitaxel tissue uptake was measured at 1 h and 1, 3, and 9 days post-dilation. At these time-points and at 32 ± 2 days, vascular function of the dilated arteries was assessed using the organ chamber model. Neointimal growth and remodeling indices were determined using OCT and histology at 32 ± 2 days. Intima and media fibrosis were quantified by picrosirius red staining. Post-inflation femoral artery tissue drug levels were 460 ± 214, 136 ± 123, 14 ± 6, and 0.1 ± 0.1 ng/mg at 1 h and 1, 3, and 9 days, respectively. Compared to plain balloon, Freeway? resulted in a significantly smaller neointimal area (P < 0.05), less tunica intima (8.0 ± 5.4 vs 14.2 ± 4.7 %) and media fibrosis (15.6 ± 7.7 vs 24.5 ± 5.4 %), and less femoral artery constrictive remodeling (remodeling index: 1.08 ± 0.08 vs 0.94 ± 0.08). The DCB was associated with significantly increased vasoconstrictor tone and endothelium-dependent vasodilation impairment shortly after post-overstretch injury. Overall, DCB dilation of peripheral arteries resulted in high drug uptake into arterial tissue. Compared with the plain balloon, the DCB was associated with decreased vessel wall fibrosis after balloon overstretch injury, and reduced degrees of constrictive remodeling and neointimal hyperplasia.     

In Operando Optical Tracking of Oxygen Vacancy Migration and Phase Change in few Nanometers Ferroelectric HZO Memories

Ferroelectric materials offer a low-energy, high-speed alternative to conventional logic and memory circuitry. Hafnia-based films have achieved single-digit nm ferroelectricity, enabling further device miniaturization. However, they can exhibit nonideal behavior, specifically wake-up and fatigue effects, leading to unpredictable performance variation over consecutive electronic switching cycles, preventing large-scale commercialization. The origins are still under debate. Using plasmon-enhanced spectroscopy, a non-destructive technique sensitive to <1% oxygen vacancy variation, phase changes, and single switching cycle resolution, the first real-time in operando nanoscale direct tracking of oxygen vacancy migration in 5 nm hafnium zirconium oxide during a pre-wake-up stage is provided. It is shown that the pre-wake-up leads to a structural phase change from monoclinic to orthorhombic phase, which further determines the device wake-up. Further migration of oxygen ions in the phase changed material is then observed, producing device fatigue. These results provide a comprehensive explanation for the wake-up and fatigue with Raman, photoluminescence and darkfield spectroscopy, combined with density functional theory and finite-difference time-domain simulations.