International survey on PSA figures of merit

Probabilistic safety assessment (PSA) figures of merit represent one of the most interesting topics in the use of PSA for safety-related applications. This is all the more interesting as the viewpoints and opinions of different experts on the use of importance factors could diverge. Even when the experts agree, the use of these measures is likely to involve a number of difficulties or pitfalls, especially if they are used too “mechanically”, without proper care. EDF considered the topic to be sufficiently important and controversial to justify exploratory studies as part of the scientific and technical monitoring program and to get advice, comments, and critical viewpoints from a number of international PSA experts and practitioners. This report presents a synthesis of the results of this international survey.     

New figures of merit for comprehensive functional genomics data: the metabolomics case

In the field of metabolomics, hundreds of metabolites are measured simultaneously by analytical platforms such as gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS) and NMR to obtain their concentration levels in a reliable way. Analytical repeatability (intrabatch precision) is a common figure of merit for the measurement error of metabolites repeatedly measured in one batch on one platform. This measurement error, however, is not constant as its value may depend on the concentration level of the metabolite. Moreover, measurement errors may be correlated between metabolites. In this work, we introduce new figures of merit for comprehensive measurements that can detect these nonconstant correlated errors. Furthermore, for the metabolomics case we identified that these nonconstant correlated errors can result from sample instability between repeated analyses, instrumental noise generated by the analytical platform, or bias that results from data pretreatment.     

Fisher information and surrogate figures of merit for the task-based assessment of image quality

Fisher information can be used as a surrogate for task-based measures of image quality based on ideal observer performance. A new and improved derivation of the Fisher information approximation for ideal-observer detectability is provided. This approximation depends only on the presence of a weak signal and does not depend on Gaussian statistical assumptions. This is also not an asymptotic result and therefore applies to imaging, where there is typically only one dataset, albeit a large one. Applications to statistical mixture models for image data are presented. For Gaussian and Poisson mixture models the results are used to connect reconstruction error with ideal-observer detection performance. When the task is the estimation of signal parameters of a weak signal, the ensemble mean squared error of the posterior mean estimator can also be expanded in powers of the signal amplitude. There is no linear term in this expansion, and it is shown that the quadratic term involves a Fisher information kernel that generalizes the standard Fisher information. Applications to imaging mixture models reveal a close connection between ideal performance on these estimation tasks and detection tasks for the same signals. Finally, for tasks that combine detection and estimation, we may also define a detectability that measures performance on this combined task and an ideal observer that maximizes this detectability. This detectability may also be expanded in powers of the signal amplitude, and the quadratic term again involves the Fisher information kernel. Applications of this approximation to imaging mixture models show a relation with the pure detection and pure estimation tasks for the same signals.     

Two-dimensional indexing polynomial-based pre-distorter for power amplifiers with memory effects

An improved segmented polynomial-based pre-distortion method and a novel memory polynomialbased pre-distortion method with two-dimensional indexing are proposed in digital baseband power amplifier pre-distortion systems. Through computer simulations and corresponding analysis, the feasibility and reliability of the proposed methods are verified with three different polynomial formats in the evaluation of relative mean square error, the convergence speed, the random access memory storage units and the power spectral density.     

Estimation of quartz resonator Q and other figures of merit by an energy sink method

An important determinant of the quality factor Q of a quartz resonator is the loss of energy from the electrode area to the base via the mountings. The acoustical characteristics of the plate resonator are changed when the plate is mounted onto a base substrate. The base substrate affects the frequency spectra of the plate resonator. A resonator with a high Q may not have a similarly high Q when mounted on a base. Hence, the base is an energy sink and the Q will be affected by the shape and size of this base. A lower bound Q will be obtained if the base is a semi-infinite base since it will absorb all acoustical energies radiated from the resonator. A scaled boundary finite element method is employed to model a semi-infinite base. The frequency spectra of the quartz resonator with and without the base are presented. In addition to the loss of energy via the base, there are other factors which affect the resonator Q, such as, for example, material dissipation, and damping at the interfaces of quartz and electrodes. The energy dissipation due to material damping increases with the resonant frequency and the reduction of resonator size; hence material damping becomes important in the current and future miniaturized resonators operating at very high frequencies. An energy sink model along with material dissipation would provide realistic Q, motional capacitance, motional resistance, and other figures of merit useful for designing resonators. The model could be used for evaluating resonator and mountings designs of microelectromechanical systems and miniaturized devices. The effect of the mountings, and plate and electrode geometries on the resonator Q and other electrical parameters are presented for AT-cut quartz resonators. Model results from the energy sink method were compared with experimental results and were found to be good.     

Analysis and evaluation of harmonic suppression of lumped-element networks suitable for high-frequency class-E operation condition approximation

The harmonic output of microwave lumped-element class-E load-coupling topologies is assessed. Measurement results on fabricated C-band class-E power amplifiers with either a modified lowpass and an optimised second-harmonic impedance network show that the latter provides better performance not only in terms of output power, gain and efficiency, but also in regard to harmonic suppression. Compared with the common modified lowpass network, harmonic content in the load of the optimised second-harmonic impedance topology at the second-, third- and fourth-harmonic frequencies are lower by more than 5.8, 10 and 5.8 dB, respectively.     

Wavelength dependence and figures of merit of ultrafast third-order optical nonlinearity of a conjugated 3,3'-bipyridine derivative

The wavelength dependence and figures of merit of the third-order optical nonlinearity of a conjugated 3,3'-bipyridine derivative, a designed nondipolar structure of the donor-acceptor-acceptor-donor type, are reported. Z scans reveal positive nonlinear refractive-index changes for wavelengths longer than the one-photon absorption wavelength. Although the value of nonlinear Kerr coefficient n2 decreases from 6.0(+/- 0.2) x 10(-6) cm2/GW at 750 nm to 4.6(+/- 0.7) x 10(-6) cm2/GW at 1550 nm, the value of nonlinear absorption beta decreases from 0.084 cm/GW at 750 nm to a negligible value at 1550 nm, giving rise to excellent nonlinearity-to-loss figures of merit at telecommunications wavelengths.     

Microwave power amplifiers based on AlGaN/GaN transistors with a two-dimensional electron gas

A technique for synthesis of microwave power amplifiers based on transistors with a AlGaN/GaN heterojunction is discussed. Special focus is on the development of a technique for synthesis of transformation circuits of the power amplifier to increase efficiency with a retained high output power. The use of independent matching at the harmonic frequencies and fundamental frequency makes it possible to control the attainable efficiency in a wide frequency band along with the total suppression of harmonics beyond the operational band. Microwave power amplifiers for operation at 4 and 9 GHz have been developed and experimentally investigated.     

Numerical characterization of a piezoelectric composite with hollow metal fillers including new figures of merit,pore shape effects,and distinct piezoceramic types

International Journal of Mechanics and Materials in Design - This paper focuses on the numerical analysis of the properties of porous piezoelectric composites with metal-doped pore surfaces and...     

Safety measures associated with the operation of engines on various alternative fuels

This paper reviews the safety of the operation of conventional engines on various alternative fuels. It is shown that methane in the form of compressed natural gas (CNG) is a safer engine fuel than common gasoline or other alternative fuels such as propane or hydrogen. The paper also describes the safety procedures adopted in the design and operation of a conventional laboratory engine on rich mixtures of methane and oxygen enriched air for hydrogen and synthesis gas (i.e. CO + H₂) production.     

Distortion cancellation performance of miniature delay filters for feed-forward linear power amplifiers

The technique of feed-forward amplitude control has been widely used in the linearization of power amplifiers for wireless communication systems. In this technique, an error signal due to third order intermodulation distortion (IMD) is extracted, amplified, and used to correct the delayed main line distorted signal. For example, a miniature prototype base station for the Global System for Mobile Communications/Code Division Multiple Access (GSM/CDMA) cellular system uses feed-forward amplifiers with bulky and expensive coaxial cables, about 20 feet in length, to provide about 25 ns of delay. This paper shows alternate space-saving approaches of achieving these delays using three different types of delay filters: electromagnetic interdigital/lumped (<2.5"), ceramic (<1.8"), and ladder-type surface acoustic wave (SAW) (0.15"). The delay lines introduce phase and amplitude imbalance and delay mismatch in the linearization loop due to fabrication tolerances. These adversely affect the IMD cancellation. Using an RF system simulation tool, this paper critically compares the IMD cancellation performance achieved using the three technologies. Simulation results show that the optimization of delay mismatch can achieve the desired cancellation more easily than other parameters. It is shown that, if the critical system parameter (phase deviation from linearity), is maintained at <2.5/spl deg/ peak-to-peak over a 20 MHz bandwidth in the frequency range 855 MHz to 875 MHz, one can achieve 25 dB of IMD cancellation performance. This paper concludes with the suggestion of a set of realistic specifications for a miniature delay filter for the low power loop of the feed-forward amplifier.     

Issues associated with two-shift operation of combined cycle generating plant

Abstract

Diverse experiences associated with two-shifting of conventional generating units are largely relevant to the ‘balance of plant’ in combined cycle generating units (CCGTs). Although two-shifting has adversely impacted upon reliability and availability, and incurred substantial additional maintenance costs on many conventional units, this has not been the case for all installations. Reference 1, for example, reports that four large coal-fired units, which have been extensively two-shifted for more than 15 years, have experienced no major and just a few minor problems attributable to many shutdown-startup cycles. These units are capable of more than 200,000 hours running with more than 6,000 starts; only a small additional maintenance cost is attributable to two-shifting.

Startups and shutdowns impose more onerous conditions on critical parts of many components of most fossil-fired generating plant than experienced when operating continuously at maximum rating (the steady-state condition at which unit and component design verification analysis is generally performed). The generic root cause of many of the major and the miscellany of lesser problems attributable to two-shifting has been a general omission by equipment designers, architect-engineers and purchasers to determine, during the design phase, (i) realistic transient conditions imposed on various components during unit startups and shutdowns. and (ii) the consequential life expenditure from cyclic thermal-mechanical cyclic loadings and other mechanisms of material degradation caused by mechanical load cycles.

It is feasible to design CCGTs capable of very extensive two-shifting without thermally induced failures in the balance of plant [2–4]. However, CCGTs do have additional difficulties to understand and manage by appropriate design and operation. For example, CCGTs:

have to consider the additional operational and cost implications associated with two-shifting the gas turbine (GT);

have more complex cycles, which are additional complications to operation during shutdowns and startups;

impose more severe conditions on the superheater and economizer of the HRSG during both the shutdown and startup process than is experienced in conventional boilers.

Therefore CCGTs require even more design attention than conventional units to enable them to twoshift without adversely impacting reliability and availability and without incurring excessive additional maintenance costs for the balance of plant.

For either a CCGT or conventional coal-fired generating plant, one of the requirements for troublefree two-shift operation is that all parts subjected to significant heating and/or cooling during CCGT startups and shutdowns require good thermal flexibility. Thermal flexibility in the critical parts of the plant is achieved by a combination of:

appropriate conceptual and detailed design of the key equipment; i.e., the GT, steam turbine (ST), and HRSG

appropriate design of key auxiliary systems which influence the conditions imposed on HRSG and ST;

unit operating procedures for CCGT shutdowns and startups that minimize thermal stresses in all critical parts of GT, ST and HRSG.

The importance of having good thermal flexibility to minimize distress from thermally-induced low cycle fatigue (LCF) caused by unit shutdowns and startups has been well-publicised. There have been many failures of tubes at attachments to superheater and economizer headers most of which are attributable to transient high stresses developed during startups (in some cases in less than 200 startups). Despite this, CCGTs continue to be installed with design weaknesses that would not be difficult nor costly to correct on a new installation, and operating procedures unnecessarily harmful to the HRSG continue to be widely used.

Good thermal flexibility is only one of the crucially important objectives for CCGTs intended for twoshifting. This paper discusses several other technical challenges to be overcome for a CCGT to provide high startup reliability without adverse impact on CCGT reliability and availability. It also addresses the minimum additional maintenance cost for the ‘balance of plant’ that is attributable to two-shifting.     

Visual signal detection in structured backgrounds. III. Calculation of figures of merit for model observers in statistically nonstationary backgrounds

Models of human visual detection have been successfully used in computer-generated noise. For these backgrounds, which are generally statistically stationary, model performance can be readily calculated by computing the index of detectability d' from the noise power spectrum, the signal profile, and the model template. However, model observers are ultimately needed in more real backgrounds, which may be statistically non-stationary. We investigated different methods to calculate figures of merit for model observers in real backgrounds based on different assumptions about image stationarity. We computed performance of the nonpre-whitening matched-filter observer with an eye filter on mammography and coronary angiography for an additive or a multiplicative signal. Performance was measured either by applying the model template to the images or by computing closed-form expressions with various assumptions about image stationarity. Results show first that the structured backgrounds investigated cannot be considered stationary. Second, traditional closed-form expressions of detectability calculated from the noise power spectra with the assumption of background stationarity lead to erroneous estimates of model performance. Third, the most accurate way of measuring model performances is by directly applying the model template on the images or by computing a closed-form expression that does not assume image stationarity.     

High power factor operation of resonant converters on the utility line

Operation and characteristics of resonant converters on the utility line are presented. Series-parallel (LCC-type) resonant converter operating with discontinuous current mode and continuous current mode (variable frequency control as well as fixed-frequency) are considered. Design examples are presented. SPICE simulation and experimental results obtained for the designed converters (rated at 150 W) are presented to verify the theory. It is shown that high line power factor (>0.95) and line current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter for a wide load range (from full load to 10% rated load) without any active control, and the switch peak current decreases with the load current. With active line current control, low distortion and zero voltage switching for the entire cycle are realized.     

Calculation of the frequency characteristics of DC amplifiers with modulation-demodulation

The frequency characteristics of dc amplifiers with modulation-demodulation are calculated with allowance for the limitation on the frequency characteristic of the carrier amplifier in the low-frequency region. Examples are used to show that the carrier frequency in these amplifiers can exceed the maximum frequency in the spectrum of the amplified signal only by a factor of 1.1–1.2. Translated from Izmeritel’naya Tekhnika, No. 8, pp. 51–53, August, 1996.     

Enhanced architecture for microwave currentmode class-D amplifiers applied to the design of an S-band GaN-based power amplifier

An enhanced architecture for the design of current-mode class-D (CMCD) power amplifiers (PAs) at microwave frequencies is presented. In the proposed structure, the harmonic impedance loading conditions of CMCD amplifiers are realised by using multiharmonic output impedance transformation networks instead of a combination of balun and lumped element tanks, typically used in CMCD PA designs. The advantage of the proposed approach is to remove design complexity from the balun and lumped element tank. A 39 dBm GaNbased CMCD PA was designed at 2.35 GHz ? to the best knowledge of the authors the highest frequency for a CMCD PA reported in open literature ? to validate and to demonstrate the capabilities of this architecture. The fabricated PA achieves 68% DC-to-RF efficiency (η) and 65% power added efficiency. A comparison between this S-band amplifier and a conventional wideband-balun-resonant-tank CMCD PA at 1 GHz using a similar commercial active device demonstrates the frequency coverage and performance improvement of the proposed topology.     

High-performance bismuth-telluride compounds with highly stable thermoelectric figure of merit

The p-type (Bi_0.25Sb_0.75)₂Te₃ ingot doped with 8 wt% excess Te alone and the n-type Bi₂ (Te_0.94Se_0.06)₃ ingot codoped with 0.068 wt% I and 0.017 wt% Te were grown by the Bridgman method and annealed at 673 K for 5 h in a hydrogen stream. The electrical resistivity ρ, Seebeck coefficient α and thermal conductivity κ before and after annealing were measured at 298 K, so that the annealing degraded significantly ZT of the p-type specimen but enhanced remarkably that of the n-type one. The temperature dependences of ρ, α and κ of the as-grown p-type and annealed n-type specimens with higher ZT were investigated in the temperature range from 200 to 360 K. As a result, ZT values of the as-grown p-type and annealed n-type specimens have a broad peak and reached great values of 1.19 and 1.13 at approximately 320 K, respectively. The present materials were thus found to be far superior to any other bismuth-telluride compound in the thermal stability of energy conversion efficiency in addition to the high performance.