Time-Frequency Coherent Modulation Filtering of Nonstationary Signals

Modulation filtering is a class of techniques for filtering slowly-varying modulation envelopes of frequency subbands of a signal, ideally without affecting the subband signal's temporal fine-structure. Coherent modulation filtering is a potentially more effective type of such techniques where, via an explicit product model, subband envelopes are determined from demodulation of the subband signal with a coherently detected subband carrier. In this paper we propose a coherent modulation filtering technique based on detecting the instantaneous frequency of a subband from its time-frequency representation. We devise theory to show that coherent modulation filtering imposes a new bandlimiting constraint on the product of the modulator and carrier as well as the ability to recover arbitrarily chosen envelopes and carriers from their modulation product. We then formally show that a carrier estimate based on the time-varying spectral center-of-gravity satisfies the bandlimiting condition. This bandwidth constraint leads to effective and artifact-free modulation filters, offering new approaches for potential signal modification. However, the spectral center-of-gravity does not, in general, satisfy the condition of arbitrary carrier recovery. Finally, the results from modulation-filtering a speech signal are then used to validate the theory.     

Catalysis in Polymerization

Hardly a single polymerization process exists in which certain accelerating, regulating, and modifying ingredients are not used with great advantage even though they might be present only in very small quantities. In the early years of the art, when there did not yet exist a well-founded understanding of the mechanism of polymerization processes, the action of these ingredients and additives so much resembled the phenomenon of normal catalysis that the name catalysts was used for them. Today, in the clarifying hindsight of a rather well-developed theory of polymerization reactions, it is evident that in most cases the role of these substances during the formation of macromolecules does not fall in the domain of the classical definitions of the words catalysis and catalyst.     

Chemometric Approach to Characterization of Flour Mill Streams: Chemical and Rheological Properties

The aim of the present study was to utilize chemometric methods (the principal component analysis and hierarchical cluster analysis) for monitoring the certain aspects of flour mill streams quality and their interrelation to selected rheological properties. Thirty-seven flour mill streams were separated from industrial mill of 300 t/day capacity. All flour streams were analyzed for ash, protein, wet gluten, and damaged starch content and rheological properties as determined by Brabender Farinograph, Extensograph, and Amylograph. The obtained results indicated that break, sizing, and reduction flour streams exhibited different rheological behavior in relation to a change in protein, wet gluten, ash, and mechanically damaged starch content within the milling passages. Rheological properties of dough during mixing and kneading as well as during extension were different with regard to the technological phase of milling from which they were extracted. The obtained results could be utilized for selection of certain flour streams in production of special-purpose flours.     

Optical phase-locked PSK heterodyne experiment at 4 Gb/s

A 4 Gb/s phase-locked optical PSK (phase shift keying) heterodyne communication system is demonstrated. The receiver was implemented with a single 100-Ω loaded p-i-n photodiode and a 1320-nm diode-pumped miniature Nd:YAG laser as a local oscillator. For a 2⁷-1 PRBS (pseudorandom bit sequence), the receiver sensitivity was -34.2 dBm or 631 photons/bit. The corresponding power on the surface of the detector was -37.3 dBm or 309 photons/bit. With a 2¹⁵-1 PRBS, a 2.6 dB additional sensitivity degradation was observed due to the nonideal frequency response of the phase modulator and the receiver amplifiers     

Fast spin-echo imaging of the brain and spine

The recent advent and implementation of rapid spin-echo techniques has allowed increased imaging speed while maintaining spin-echo-like contrast. This review explains the basis of fast spin-echo imaging and attempts to elucidate the etiology of the differences between it and spin-echo imaging. Clinical applications and limitations of fast spin-echo imaging in the brain and spine will also be addressed.     

A method for measuring precipitation parameters using radar reflectivity and optical extinction

A method is described by which radar reflectivity and optical extinction are used to determine precipitation parameters, such as liquid water content and rainfall rate, and an exponential approximation to the raindrop size spectrum. The improvement in the accuracy of the results over that which is possible using empirical relations is demonstrated by applying the method to a set of experimentally observed raindrop size spectra. It is also shown that the assumption of an exponential spectrum is not a necessary feature of the method and that any two parameter drop size distribution can be employed.     

560 Mb/s optical PSK synchronous heterodyne experiment

A phase-locked optical heterodyne receiver constructed using a 1320-nm diode-pumped miniature Nd:YAG ring laser is discussed. Using this receiver and a transmitter based on another Nd:YAG laser, a 560-Mb/s phase-shift keying (PSK) synchronous heterodyne transmission was demonstrated over 78 km of single-mode fiber. With an optical phase-locked loop (PLL) natural frequency of 32 kHz and a damping factor of 1.46, the receiver sensitivity, measured at the output of the transmission link, was -48.7 dBm, or 159 photons/b. The corresponding detected sensitivity, measured on the surface of the p-i-n diode, was -51.8 dBm or 78 photons/b. This result suggests that the receiver sensitivity would have been about 82 photons/b if a balanced receiver with 0.2-dB excess coupler loss had been used. The impact of the finite intermediate frequency (IF) on heterodyne system performance was investigated; it was found that an IF of at least twice the bit rate is needed for a negligibly small penalty     

Intensity noise in ASK coherent lightwave receivers

The effect of local oscillator intensity noise on the performance of two and three-branch ASK homodyne receivers and single-branch ASK heterodyne receivers is investigated and an optimum local oscillator power is found. At optimum local oscillator power, both the three-branch and heterodyne receivers are found to have a somewhat better sensitivity than the two-branch receiver. If the local oscillator power is high than the optimum value, the three-branch receiver is significantly less sensitive to intensity noise than the other two receivers