Digital signal processing. 1. Digital filters and the DFT

The wide availability of inexpensive and relatively fast digital signal processing chips has given rise to a great expansion in the application of these devices in many areas, particularly consumer electronics. The ease with which digital processing operations can now be performed has allowed the realisation of highly sophisticated signal processing algorithms. The paper introduces the first of two main areas of digital signal processing, namely digital filtering and Fourier transformation. An overview is presented of both finite impulse response and infinite impulse response digital filter types. These designs are later extended to cover the concept of an adaptive filter, which automatically trains or adapts its characteristics or frequency response to compensate for signal distortions or interference. Finally, the discrete Fourier transform is introduced for measuring the frequency spectrum of a signal     

Deformation measurement of RF MEMS switches by optical interference

The RF switches were fabricated based on microelectromechanical techniques. For good RF performances, the precise control is needed over the contact separation when switch is open and over the contact force when the switch is closed. In this paper, the optical interference technique has been applied to make the accurate measurement of the contact position and the height distribution of the actuators. The shape changes of switches can be observed in original shape and in actuated state. The results were compared with the scan electronic microscope (SEM) measurement.     

Nucleation, Growth, and Scaling in Slow Combustion

We study the nucleation and growth of flame fronts in slow combustion. This is modeled by a set of reaction-diffusion equations for the temperature field, coupled to a background of reactants and augmented by a term describing random temperature fluctuations for ignition. We establish connections between this model and the classical theories of nucleation and growth of droplets from a metastable phase. Our results are in good agreement with theoretical predictions.     

Tunable liquid crystal reflectarray patch element

Numerical and measured results are employed at X-band to demonstrate that the electrical properties of nematic state liquid crystal can be exploited to produce phase shifters for beam scanning printed reflectarray antennas with a tunable range greater than 180/spl deg/.     

Computation of total capacity for discrete memoryless multiple-access channels

The Arimoto-Blahut (1972) algorithm is generalized for computation of the total capacity of discrete memoryless multiple-access channels (MAC). In addition, a class of MAC is defined with the property that the uniform distribution achieves the total capacity. These results are based on the specialization of the Kuhn-Tucker condition for the total capacity of the MAC, and an extension of a known symmetry property for single-user channels.     

Enumeration of totally positive Grassmann cells

Postnikov (Webs in totally positive Grassmann cells, in preparation) has given a combinatorially explicit cell decomposition of the totally nonnegative part of a Grassmannian, denoted Gr_k,n⁺, and showed that this set of cells is isomorphic as a graded poset to many other interesting graded posets. The main result of our work is an explicit generating function which enumerates the cells in Gr_k,n⁺ according to their dimension. As a corollary, we give a new proof that the Euler characteristic of Gr_k,n⁺ is 1. Additionally, we use our result to produce a new q-analog of the Eulerian numbers, which interpolates between the Eulerian numbers, the Narayana numbers, and the binomial coefficients.     

The determination of low d5-phenylalanine enrichment (0.002-0.09 atom percent excess), after conversion to phenylethylamine, in relation to protein turnover studies by gas chromatography/electron ionization mass spectrometry.

A gas chromatography/mass spectrometry (GC/MS) method for measuring very low levels of enrichment of d5-phenylalanine (0.002-0.09 atom percent excess) is described. This method makes it possible to determine the enrichment of amino acid incorporated into tissue protein during studies of protein synthesis in man. Phenylalanine is enzymatically converted to phenylethylamine and the d5-enrichment is measured in the heptafluorobutyryl derivative by selective-ion recording under electron ionization conditions. The coefficients of variation for muscle-protein hydrolysate samples enriched with d5-phenylalanine at the 0.005 and 0.05 atom percent excess levels were 6.0 and 1.2%, respectively. This precision at low enrichment and the small amount of protein needed (about 1 mg) provide real advantages for clinical studies of tissue protein synthesis. Moreover, in contrast to the conventional approach which uses GC/MS for plasma amino acids (typically 2-20 atom percent excess) but gas isotope-ratio mass spectrometry for protein-bound amino acids, the enrichment of both plasma-free and protein-bound d5-phenylalanine can be measured with a single instrument.     

Performance of a CDMA System with an Adaptive Receiver and a New Family of Complex Valued Spreading Sequences

This paper presents the results of a capacity evaluation for a direct-sequence (DS), code-division, multiple access (CDMA) system over both an additive white Gaussian noise (AWGN) channel and a Rayleigh fading channel. The system considered uses an adaptive receiver. The performance of sets of sequences from various binary and complex valued families is examined. The performance of the system is measured in terms of the total efficiency, and it is shown that the new sequence sets offer higher system capacity and lower signal-to-noise power spectral density ratios.