Advanced Call Scheduling for Testing a Telecommunications Network

This paper describes an advanced scheduling system and method for generating large volumes of calls to be used for testing a telecommunications network. The system is capable of preparing large-scale and complex network tests by viewing the task as a scheduling problem. The various requirements of the scheduling problem are analysed and represented as constraints or optimisation criteria. A fast heuristic method is proposed for solving the problem. The approach is based on a greedy algorithm for constructing solutions and it incorporates limited backtracking and dynamic value-ordering heuristics. The algorithm and system are currently being used for call charge verification in BT's PSTN and CSP networks.     

116-fs soliton source based on an Er-Yb codoped waveguide amplifier

A passively mode-locked soliton ring fiber laser is investigated that utilizes a 4.5-cm erbium-ytterbium (Er-Yb) codoped waveguide amplifier as the gain element. The resulting short cavity (1.3 m of fiber) eliminates multipulsing behaviour and reduces the effects of resonant sidebands, enabling generation of 116-fs solitons with a pulse energy of 160 pJ at a fundamental repetition rate of 130 MHz     

A comparison of the trap properties and locations within GaAs fieldeffect transistors measured under different bias conditions

The activation energy and capture cross section of traps found in GaAs field effect transistors (GaAs FETs) have been measured with both ohmic channel and current saturation bias using a variety of transient, frequency dispersion, and noise spectroscopy techniques. With current saturation bias these effects have been seen in both the transconductance and the output conductance. The results for all methods and bias conditions are compared with those found by others. The relative sensitivity of the techniques and the location of the traps are discussed     

An oil import fee and drilling activity in the USA : A comment

Edward F. Renshaw's [5] recent analysis of the impact of a $5/bbl oil import fee on drilling activity in the USA is re-examined. Specifically, this comment shows: (i) the initial stimulus to the US rotary rig count of 420 new rigs would not completely disappear over the next five years, but last much longer; (ii) the initial employment impact would be more than twice as large as Renshaw suggested (39 060 rather than 18 480); and (iii) the relevant social cost per new job (excluding transfers) could be as small as $19 200, more than 80 times smaller than Renshaw's estimate of $1.6 million.     

Dielectric characterization of low-loss materials a comparison oftechniques

Measurements on low-loss materials using closed and open cavity resonators, and dielectric resonator methods are presented. Results indicate that consistent measurement results can be obtained with a number of well-characterized fixtures. Uncertainties associated with each method are addressed. Measurements also were performed on materials used in previous intercomparisons     

Performance of uprated substations in contaminated environments

Uprated substations have proven to be a viable economic alternative to rebuilding in order to increase power system capacity. The key economic factor in uprated designs is the use of lower than traditional insulation margins in high voltage substations. The experience of these uprated substations has been good and insulation design procedures for uprated substations have been developed to show other engineers how to take advantage of this design alternative. While these design procedures and other publications including the results of actual tests have given ample evidence of the success of the uprated designs, it has been noted that several areas need more study and testing. Among those areas which need further study are the effects of the dynamic forces caused by higher fault currents in the uprated substations and the ability of the reduced creepage distances of the uprated design to withstand pollution severity. This study covers the pollution severity issue by examining the results of flashover tests on the uprated substation insulators under various contamination conditions. The tests, which were done at the EPRI Power Deliver Center at Lenox, USA, are believed to be the only flashover tests ever conducted with uprated insulators. As might be expected, the uprated design is shown to be very sensitive to pollution severity. Sites chosen for uprating should include a pollution severity assessment as part of the design review     

MQW wavelength-tunable DBR lasers with monolithically integrated external cavity electroabsorption modulators with low-driving voltages fabricated by selective-area MOCVD

The design and operation of multiple-quantum-well (MQW) wavelength-tunable distributed Bragg reflector (DBR) InGaAs QW lasers with nonabsorbing gratings and monolithically integrated external cavity electroabsorption modulators fabricated by selective-area MOCVD are presented. Uncoated devices exhibit CW threshold currents as low as 10.5 mA with slope efficiencies of 0.21 W/A from the laser facet. Wavelength tuning of 7 nm is obtained by injection current heating of the DBR section. These devices also exhibit extinction ratios of 18 dB from the modulator facet at a low modulator bias of 1 V, when measured with a broad-area detector. When coupled to a singlemode fiber, these devices exhibited high extinction ratios of 40 dB at a modulator bias of 1.25 V.     

Equivalence of generalized joint signal representations ofarbitrary variables

Joint signal representations (JSRs) of arbitrary variables generalize time-frequency representations (TFRs) to a much broader class of nonstationary signal characteristics. Two main distributional approaches to JSRs of arbitrary variables have been proposed by Cohen (see Time-Frequency Analysis, Englewood Cliffs, NJ, Prentice Hall, 1995 and Proc. SPIE 1566, San Diego, 1991) and Baraniuk (see Proc. IEEE Int. Conf. Acoust., Speech Signal Processing, ICASSP'94, vol.3, p.357-60, 1994). Cohen's method is a direct extension of his original formulation of TFRs, and Baraniuk's approach is based on a group theoretic formulation; both use the powerful concept of associating variables with operators. One of the main results of the paper is that despite their apparent differences, the two approaches to generalized JSRs are completely equivalent. Remarkably, the JSRs of the two methods are simply related via axis warping transformations, with the broad implication that JSRs with radically different covariance properties can be generated efficiently from JSRs of Cohen's method via simple pre- and post-processing. The development in this paper, which is illustrated with examples, also illuminates other related issues in the theory of generalized JSRs. In particular, we derive an explicit relationship between the Hermitian operators in Cohen's method and the unitary operators in Baraniuk's approach, thereby establishing the relationship between the two types of operator correspondences     

Growth and optical characterization of strained CdZnTe/ CdTe quantum wells

We have grown strained Cd_1-xZn_xTe(x ≈ 0.2)/CdTe single and multiple quantum wells by molecular beam epitaxy. GaAs was used as a substrate. The well widths were systematically increased until the critical thickness was exceeded. Low-temperature (liquid helium) photoluminescence (PL) spectroscopy was used to characterize the films. Two prominent PL peaks were observed: one arising from the quantum well and the other from the barrier material. The energy of the quantum well luminescence is consistent with theory when strain is included. The critical layer thickness for the CdTe quantum wells was found to be between 150 and 175 å, in agreement with the model of Matthews and Blakeslee.