Extended-window interpolation applied to digital filter design

This paper develops a procedure for the design of frequency-selective interpolation operators that can be computed and saved once and for all. These operators are used to design real-time digital operators: interpolators, FIR differentiators, IIR filters, and composed interpolation and filtering operators. Each real-time operator is a matrix relating sets of data points to sets of interpolated values. Since these matrices are characterized by low norms, they permit reduced-word implementations, and are suitable for real-time processing with array processors and massively parallel machines. The design of the interpolation operators uses windows that, unlike traditional approaches, extend beyond the data interval up to the length permitted by the dimensionality theorem. A new form of the dimensionality theorem is used to minimize the minimax interpolation error within a predetermined frequency range, which may be either the passband of the antialiasing filter or the passband of an analog prototype filter. The main application presented in the paper is the design of combined digital filters and interpolators, which will be referred to as interpolating filters. The frequency responses of such filters, as well as the interpolated time responses, almost coincide with those of the corresponding analog prototypes     

Effects of arginine- and lysine-vasopressin on phospholipase C activity, intracellular calcium concentration and prostaglandin F2alpha secretion in pig endometrial cells

Oxytocin and vasopressin are related peptides that have receptors in the uterus. Species from families other than Suidae produce only arginine-vasopressin; in contrast, pigs apparently express both arginine- and lysine-vasopressin. The aim of this study was to determine whether arginine- or lysine-vasopressin would activate phospholipase C, increase intracellular calcium concentration [Ca(2+)](i) and stimulate PGF(2alpha) production in enriched cultures of stromal, glandular epithelial and luminal epithelial cells from pig endometrium. Cells were obtained from gilts on day 16 after oestrus by differential enzymatic digestion and sieve separation. After 96 h in culture, the cells were treated with 0 or 100 nmol arginine- or lysine-vasopressin l(-1). The responses to 100 nmol oxytocin l(-1) and 100 nmol GnRH l(-1) were used as positive and negative controls, respectively. Consistent with previous results, oxytocin stimulated phospholipase C activity (P < 0.05), increased [Ca(2+)](i) (P < 0.05) and promoted PGF(2alpha) secretion (P < 0.05) from stromal and glandular epithelial cells. Activity of phospholipase C, [Ca(2+)](i) and PGF(2alpha) release were also increased (P < 0.05) by arginine-vasopressin in stromal cells, but the responses were less (P < 0.01) than those induced by oxytocin. An oxytocin antagonist attenuated the [Ca(2+)](i) response of stromal cells to both oxytocin and arginine-vasopressin. Sequential treatment of cells with oxytocin and arginine-vasopressin indicated that oxytocin desensitized the response to oxytocin, but arginine-vasopressin did not similarly desensitize the response to oxytocin. In glandular and luminal epithelial cells, arginine-vasopressin did not stimulate phospholipase C activity, [Ca(2+)](i) or PGF(2alpha) secretion. Neither GnRH nor lysine-vasopressin induced phospholipase C activity, increased [Ca(2+)](i) or stimulated PGF(2alpha) production in any endometrial cell type. These results indicate that oxytocin receptors can bind arginine-vasopressin more readily than they bind lysine-vasopressin. Type 1 vasopressin receptors may also exist in endometrium predominantly on cells other than stromal, glandular epithelial and luminal epithelial cells, as in previous studies both arginine-vasopressin and lysine-vasopressin stimulated phospholipase C activity in endometrial explants to a similar extent as oxytocin.     

Digital filters with implicit interpolated output

The composition of filtering and interpolation operators is applied to the design of digital filters that, optionally, may perform real-time incommensurate sampling rate conversion. This problem arises in applications where the interpolation times may not be known a priori and are calculated in real time. The proposed interpolating filter operators allow the designer to control the interpolation error through a trade-off between computing time and accuracy. The flexibility of the design is exemplified on a few digital communication applications: square root raised cosine filters for controlling the intersymbol interference through pulse shaping, a bandpass filter, and a differentiator     

Sampled signal reconstruction and Nyquist frequency

The discussion focuses only on those remarks of J. Lynn Smith (see ibid., p.14, May 1996) that were directly related to earlier comments (see ibid., p.41, July 1995). It complements Marple's (see ibid., p.24, January 1996) filter-bank analysis and tries to remove some clutter due to the improper test signals used. The frame of this discussion consist of the following three statements: the “successful” use of a sampling rate lower than the Nyquist rate is an illusion; the proposed method is nothing else than an analog form of the well-known filter banks, whose theory is consistent with the (correct) definition of the Nyquist frequency; and in general, the method can not be used with the zero-order hold operation, unless the filters are designed with frequency-dependent magnitude to compensate for the spectrum alteration produced by the sample-and-hold operation     

Matrix operators for numerically stable representation of stifflinear dynamic systems

A new transformation having features similar to the Laplace transform (but numerically oriented) is developed from the Chebyshev polynomials theory. Signals are represented as vectors of Chebyshev coefficients, and linear subsystems as precomputed matrices. The original problem is preprocessed only once to yield matrix invariants for fast recurrent computations. Theoretical implications of the exact digitizing of a tenth-order transfer function and the reduced-order modeling of a stiff system are discussed     

Method for Estimating Sediment Transport in Ice-Covered Channels

A method is proposed for estimating rates of sediment transport in ice-covered alluvial channels. The method extends existing, open-water procedures for estimating rates of sediment transport to conditions of ice-covered flow. A key aspect of the method is the assessment of flow resistance attributable to bed-surface drag. That assessment is used to estimate rates of bed load and suspended load, and thereby total bed-sediment transport rate. Estimation of ice-covered suspended load additionally entails an approximation whereby open-water suspended load is scaled in proportion to the ratio of a reference sediment concentration for ice-covered flow relative to that for open-water flow. The reference concentration is calculated in terms of bed-load rate and shear velocity attributed to bed-surface drag. Flume data are used to develop the method and tentatively verify it. Field verification of the method presently is hampered by the absence of field data on bed sediment transport in ice-covered channels.     

Comments on “Further improvements in digitizingcontinuous-time filters”

This correspondence points out that an algorithm proposed by C. Wan and A.M. Schneider (see ibid., vol.45, no.3, p.533-42, March 1997) as a new digitizing method is, in fact, an extension of the linear interpolation design. Unlike previously published extensions, which incorporate the interpolation step into the s- to z-domain mapping step, this algorithm cascades the interpolator and the analog filter. Original design formulas derived for a rigorous comparison support the assertion that the above algorithm yields less accurate results than the other interpolation designs