Increasing channel capacity and range on urban optical analogAM-VSB CATV systems

It is often desirable to increase the capacity and the covered distance in lightwave TV systems. For doing so, the conventional CATV channel set-usually placed within the 50 to 550 MHz frequency range-may be up-shifted, by means of a subcarrier, to a low microwave frequency range, typically located at 2 GHz. Next, this shifted spectrum directly modulates a laser diode, in the analog AM mode. It is shown that this up-shift procedure may dislodge a number of nonlinear distortion components from the useful TV band. Consequently, the system effective optical modulation index may be increased, allowing for an expansion in the channel capacity or covered distance. This enlarged capacity or distance may compensate for the modest price increase concerning the up-shift equipment. All the performance evaluations presented here were carried out with a rigorous numerical model, and assuming the lightwave systems used the economical AM-VSB format     

Digital dancing

The author considers how a dance community has evolved in cyberspace. The emergence of the World Wide Web has led to an upsurge of creative exploration by dance artists as they discover, in ever-increasing numbers, this new technology's potential. The pervasiveness of information and communications technologies has produced new levels of thought, new concepts, and new types of human interaction. The author discusses the Cassandra Project performance which uses a videoconferencing system over the Internet. Computer networks connecting performers in real time with other performers and audiences at remote sites allow for text, dance and music to serve as improvisational material during the performance     

Effect of preparation method on the dispersion and activity of V2O5–Al2O3 catalysts

Al2O3-supported 12 wt% V2O5 catalysts were prepared by physically grinding both the oxides (solid–solid wetting) and by wet impregnation techniques. The physical mixtures (PM) were treated under two different conditions – calcination in the presence of dry oxygen and wet oxygen. The catalysts were characterized by x-ray diffraction, scanning electron microscopy, electron spin resonance and oxygen and carbon dioxide chemisorptions. Vanadia dispersion of the physical mixture calcined in the presence of wet oxygen was found to be very similar to that of the V2O5/Al2O3 catalyst prepared by the standard impregnation method. Methanol partial oxidation activities of these catalysts were also comparable. This revised version was published online in November 2006 with corrections to the Cover Date.     

Efficient performance analysis of asynchronous cellular CDMA overRayleigh-fading channels

The bit error rate (BER) analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system over a Rayleigh-fading channel often results in complicated expressions even though the Gaussian approximation is applied. A combined probability density function (pdf) approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity. The simplified BER expressions are derived and yield accurate results     

Buffering packetised data: an examination of the crossover effect

Buffer analysis has traditionally relied heavily on the use of traffic models with short range (exponentially decaying) autocorrelation, e.g. Poisson and Markov modulated Poisson processes. Recent literature has suggested the presence of traffic with slowly (hyperbolically) decaying autocorrelation functions; these sources collectively and individually seem to be exhibiting the phenomenon of long range dependence (LRD). Furthermore, it has been claimed that this sort of traffic may exhibit behaviour, when buffered, that is advantageous in that a smaller buffer may be required than would be the case with non-LRD traffic. This phenomenon has been named the crossover effect, and the authors quantify its relevance to ATM networking, using simulation studies of a homogenous mix of chaotic sources. These show that there is a crossover effect, but the key finding is that this effect is much nearer to a buffer length of zero than was predicted by previous theoretical studies, actually occurring at a value so low that it has no practical significance     

On Deciding Readiness and Failure Equivalences for Processes

In this paper, we study the complexity of deciding readiness and failure equivalences for finite state processes and recursively defined processes specified by normed context-free grammars (CFGs) in Greibach normal form (GNF). The results are as follows: (1) Readiness and failure equivalences for processes specified by normed GNF CFGs are both undecidable. For this class of processes, the regularity problem with respect to failure or readiness equivalence is also undecidable. Moreover, all these undecidability results hold even for locally unary processes. In the unary case, these problems become decidable. In fact, they are Π^p₂-complete, We also show that with respect to bisimulation equivalence, the regularity for processes specified by normed GNF CFGs is NL-complete. (2) Readiness and failure equivalences for finite state processes are PSPACE-complete. This holds even for locally unary finite state processes. These two equivalences are co-NP-complete for unary finite state processes. Further, for acyclic finite state processes, readiness and failure equivalences are co-NP-complete and they are NL-complete in the unary case. (3) For finite tree processes, we show that finite trace, readiness, and failure equivalences are all L-complete. Further, the results remain true for the unary case. Our results provide a complete characterization of the computational complexity of deciding readiness and failure equivalences for several important classes of processes.     

Modeling of current-voltage characteristics for strained andlattice matched HEMT's on InP substrate using a variational chargecontrol model

A model for the calculation of the current-voltage characteristics of strained In_0.52Al_0.48As/In_xGa_1-xAs on InP substrate High Electron Mobility Transistors (HEMT's), based on a variational charge control model, is presented. A polynomial fit of the two-dimensional electron gas (2DEG) density is used for the calculation of the current-voltage characteristics. The effect of strain is introduced into the 2DEG density versus gate voltage relation. Very good agreement between the calculated and measured I-V characteristics was obtained. In addition, our results show that, for an indium mole fraction of the In_xGa_1-xAs channel in the range 0.53-0.60, increasing the indium mole fraction lowers the threshold voltage and hence increases the drain current at the same gate bias     

Diagnostic results and their clinical interpretation--or: what you never wanted to know about diagnosis

OBJECTIVE: To analyze HLA-DR4 alleles in New Zealand Polynesians with rheumatoid arthritis (RA). METHODS: Thirty Polynesians and 30 Caucasians with RA, as well as 65 Polynesian and 60 Caucasian healthy blood donors, were DR4 subtyped using the polymerase chain reaction and sequence-specific oligonucleotide probes. RESULTS: The frequency of DR4 (DRB1*04) was increased in both Polynesian (P < 0.001) and Caucasian (P < 0.005) RA patients compared with race-matched controls. Dw4 (DRB1*0401) was detected in 15 of 30 Caucasian patients but only 2 of 30 Polynesian patients (P < 0.001). In Polynesians, RA was associated with Dw15 (DRB1*0405), which was present in 11 of 30 patients and 3 of 65 controls (P < 0.001). Dw13 (DRB1*0403) was the most frequent DR4 allele in healthy Polynesians, but was not significantly associated with RA. CONCLUSION: The predominance of the Dw13 subtype in Polynesians may explain in part the low prevalence of RA in this population. The association of Dw15 with RA in Polynesians supports the hypothesis that the third hypervariable region of DR beta determines susceptibility to RA.