OTDM transmitter using WDM-TDM conversion with an electroabsorptionwavelength converter

An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal     

A systematic techno-economic assessment of a WEC system installation for low-cost electrification of a habitable dwelling

This paper deals with the technical feasibility and economic viability of a grid connected wind-energy conversion system (WECS) used to cover the energy demand of an average habitable dwelling. The various parts of the wind-energy system are described and the useful electrical energy production is determined using a simulation program based on the Monte Carlo method. An economic analysis of the WEC system is performed using a computerized assessment tool. Important financial indices are calculated and financial scenarios investigated.     

Advanced Method for Single Crystal Casting of Turbine Blades for Gas Turbine Engines and Plants

A method for fabricating single crystal blades that combines the techniques of seed crystals and selection is suggested. The method realizes the advantages of both techniques, i.e., the high structural perfection and the possibility of fabricating single crystals with specified spatial orientation. Metallographic and x-ray diffraction analyses are used to study the processes of nucleation of the single crystal structure of blade castings fabricated from high-temperature nickel alloys by the method of selection and seed crystals. A commercial process for fabricating cast single crystal turbine blades by the new method is suggested.     

The effects of pressure on the isothermal fluid behavior of bituminous coals

An investigation into the effects of pressure (helium gas) on the isothermal fluid behavior includes: (1) the effect of pressure on the rate of melting and coking as evidenced by the rate constants k(melt) and k(coke); (2) the effect of pressure on the energies of activation of melting and coking; (3) the effects of pressure on the characteristic times; (4) the effects of pressure on the maximum isothermal fluidity. Results from the effects of pressure on k(melt) revealed that it was generally the high total sulfur, low nitrogen, low reactives/mineral matter ratio, medium rank coals which show the greatest increase in k(melt), whereas the highest rank coals show the least decrease in k(coke). The energies of activation of melting and coking were not significantly affected by pressure. The investigation also reveals increases or decreases in the respective times of softening, maximum fluidity, resolidification and total time of fluid behavior under isothermal pressurized conditions. There appears the possibility that these shifts may be rank dependent. Additionally, the lower rank coals show the largest relative increase in their fluidities when subjected to pressure. Empirical relationships were derived in order to quantitatively predict the maximum isothermal fluidity for most (fluid) coals at a given pressure.     

Fast algorithms for estimating the correlation functions of large signals

A fast algorithm is proposed for estimating the auto- and cross-correlation functions of a large signal. The algorithm is based on the sectioning method by the fast Fourier transform. We determine the optimal length of the portion of data read from external memory into RAM which achieves T_min—a minimum processing time. An estimate of T_min is obtained.Translated from Kibernetika, No. 3, pp. 78–81, May–June, 1991.     

An expert diagnostic system for the MACRO experiment at the GranSasso Laboratory

The maintenance of the MACRO (a Monopoles, Astrophysics and Cosmic Ray Observatory), a large-area detector that will be used to search for rare constituents or phenomena in cosmic radiation penetrating deep underground, is addressed. A real-time expert system for diagnosing detector and data acquisition system anomalies, which is based on the NEXPERT commercial tool, is described. It performs online diagnosis and, if an abnormal condition is identified, takes the appropriate action to reduce the unavailability of the apparatus. The data acquisition system is CAMAC-based, and the sensor modules, which gather the significant values for diagnosis, are implemented in the VME crate     

Systematic characterization of Cl2 reactive ion etchingfor improved ohmics in AlGaN/GaN HEMTs

Pre-metal-deposition reactive ion etching (RIE) was performed on an Al_0.3Ga_0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs     

Reduced and differential parallel interference cancellation forCDMA systems

Since code division multiple access systems in multipath environments suffer from multiple access interference (MAI), multiuser detection schemes should be used in the receivers. Parallel interference cancellation (PIC) is a promising method to combat MAI due to its relatively low computational complexity and good performance. It is shown that the complexity of PIC is still high for realistic scenarios in terms of the symbol rate, the number of users, spreading gain, and multipath components. However, two novel methods are introduced to reduce significantly the complexity without sacrificing performance. The first approach, called reduced PIC, takes advantage of the composition of the interference to concentrate interference cancellation only on significant terms. The second approach, called differential PIC, exploits the multistage character of PIC to avoid unnecessary double calculations of certain terms in consecutive stages. It is shown that a combination of both approaches leads to a performance very close to the single-user bound whereas the complexity can be kept on the order of the conventional RAKE receiver     

Sequential tripping strategy for a transmission network back-upprotection expert system

This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System