Effects of Multirate Systems on the Statistical Properties of Random Signals

In multirate digital signal processing, we often encounter time-varying linear systems such as decimators, interpolators, and modulators. In many applications, these building blocks are interconnected with linear filters to form more complicated systems. It is often necessary to understand the way in which the statistical behavior of a signal changes as it passes through such systems. While some issues in this context have an obvious answer, the analysis becomes more involved with complicated interconnections. For example, consider this question: if we pass a cyclostationary signal with period K through a fractional sampling rate-changing device (implemented with an interpolator, a nonideal low-pass filter and a decimator), what can we say about the statistical properties of the output? How does the behavior change if the filter is replaced by an ideal low-pass filter? In this paper, we answer questions of this nature. As an application, we consider a new adaptive filtering structure, which is well suited for the identification of band-limited channels. This structure exploits the band-limited nature of the channel, and embeds the adaptive filter into a multirate system. The advantages are that the adaptive filter has a smaller length, and the adaptation as well as the filtering are performed at a lower rate. Using the theory developed in this paper, we show that a matrix adaptive filter (dimension determined by the decimator and interpolator) gives better performance in terms of lower error energy at convergence than a traditional adaptive filter. Even though matrix adaptive filters are, in general, computationally more expensive, they offer a performance bound that can be used as a yardstick to judge more practical "scalar multirate adaptation" schemes

Effect of lithium on acetylcholine esterase activity, and isozyme pattern in developing chick brain

Acetylcholine Esterase is an enzyme, which hydrolyses acetylcholine and is used as a marker for cholinergic neural function. It is known to be involved in synaptogenesis. While on one hand it is known to be a marker for the developing chick brain it is also implicated in neurodegenerative diseases. In vertebrates the protein is synthesized by a single gene and undergoes alternative splicing to give 6-8 isoforms. Isozyme patterns of acetylcholine esterase have been suggested to be useful prognostic markers of neuronal degeneration. Lithium a well-known teratogen is known to induce apoptosis in the developing chick brain. Understanding the dynamics of acetylcholine esterase isoform pattern in lithium induced neural tissue damage would help elucidating the role of these isoforms in frank neurodegenerative diseases. We have therefore studied activity and isozyme pattern of acetylcholine esterase in lithium treated and control 7 day old developing chick brain and report the same

A review of turbulence measurements using ground-based wind lidars

A review of turbulence measurements using ground-based wind lidars is carried out. Works performed in the last 30 yr, i.e., from 1972–2012 are analyzed. More than 80% of the work has been carried out in the last 15 yr, i.e., from 1997–2012. New algorithms to process the raw lidar data were pioneered in the first 15 yr, i.e., from 1972–1997, when standard techniques could not be used to measure turbulence. Obtaining unfiltered turbulence statistics from the large probe volume of the lidars has been and still remains the most challenging aspect. Until now, most of the processing algorithms that have been developed have shown that by combining an isotropic turbulence model with raw lidar measurements, we can obtain unfiltered statistics. We believe that an anisotropic turbulence model will provide a more realistic measure of turbulence statistics. Future development in algorithms will depend on whether the unfiltered statistics can be obtained without the aid of any turbulence model. With the tremendous growth of the wind energy sector, we expect that lidars will be used for turbulence measurements much more than ever before