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The modern power system has undergone a paradigm shift in terms of geographical sprawl through extensive interconnection as well as technological innovations. As a consequence, the wide-area measurement system has evolved to cope with the requirements of efficient operation, monitoring, and control of such a complex system. The phasor measurement unit is the edifice of such a system; therefore, its reliable operation has assumed utmost importance. This has led to recent research focusing on the reliability assessment of phasor measurement units. In order to overcome the difficulties associated with decision making using a single reliability index, as is done in most traditional reliability assessment techniques, the well-being analysis framework has been employed in this article for phasor measurement units. This article presents a methodology using a Markov model in conjunction with event tree analysis to embark upon a set of health indices for phasor measurement units. The most significant contribution of this article is to arrive at three well-being indices for healthy, marginal, and risky states. In addition, the effect of failure rate and repair rate of sensitive components of phasor measurement unit on the well-being indices has been investigated for reliability planning. [ABSTRACT FROM AUTHOR]

We report on the substantial persistent photoconductivity (PPC) response exhibited by the zinc oxide (ZnO) nanorod-based ultraviolet (UV) photodetection system. An increase in photocurrent and, hence, rise in PPC was observed for larger UV exposure times at regular intervals. Triggered by quantum efficiency, the increment in sustained conduction band electrons is proposed as the main reason behind the increased photocurrent response. In contrast, the trap centers located below the conduction band are expected to slow down the recombination rate, which accounts for the rise in PPC. The lowering of PPC upon annealing suggests the surface dependent nature of the PPC. The growth and decay mechanism of PPC has a direct relevance while assessing figure of merit of prototype nanostructure-based optical sensor and UV photodetectors. [ABSTRACT FROM AUTHOR]

We report on the effect of 80 keV Ar+ ion irradiation on the luminescence response of zinc oxide (ZnO) nanosticks synthesized using a simple microemulsion route. The formation of nanoscale rods was confirmed from the transmission electron microscopy, whereas the hexagonal wurtzite phase of the nanorods was detected in an X-ray diffraction pattern. The photoluminescence pattern of the nanorods was dominated by various native defect states of ZnO, which are responsible for the quenching of the typical band edge emission of ZnO. Under Ar+ ion irradiation at a fluence of 1×1013 ions/cm2, the band edge emission was recovered owing to the suppression of oxygen vacancy defects. In addition, the formation of new zinc vacancy and ionized zinc interstitial defects were also evident. Conversely, the band edge emission was found to be quenched as a result of the creation of more oxygen vacancy (VO) defects due to ion irradiation (fluence: 1×1015 ions/cm2). The nuclear energy loss of the Ar+ ions in ZnO is responsible for the formation of point (vacancy-related) defects, while relatively small amount of electronic energy loss of the Ar+ ion results in the ionization of the neutral zinc interstitial (Zni) defects. The energy deposition scheme of the energetic ions has been elaborated with the help of theoretical modeling that explains the observed features quite satisfactorily. [ABSTRACT FROM AUTHOR]

The optimum Mn-incorporation and interrelated luminescence characteristics of solid-state derived, PbO-free, nanoscale PbTiO3 systems are reported. X-ray diffraction analysis of the nanosystems predicts a maximum value of tetragonality (∼1.06), for a given stoichiometry, namely Mn:Ti = 0.11. Photoluminescence (PL) studies reveal an intense emission peak (λem ∼ 604 nm), which is ascribed to the disordered inorganic phase of lead titanate containing non-bridging oxygen defects. The incorporation of Mn into the lead titanate system has resulted in a more symmetric PL peak owing to its association with Mn2+-related orange emission. Excessive Mn-doping was found to hinder the radiative process significantly owing to the presence of untreated MnO2 phase or the development of a thin MnO2 overlayer on the nanostructure surface. [ABSTRACT FROM AUTHOR]

Assessment of software reliability has emerged as an area of utmost importance in recent times with the proliferation of software-based systems. Conventional software reliability assessment is done by applying software models that incorporate the unfortunate drawback of requiring previous failure data to formulate the model based on statistical methodologies. But highly dependable software systems used for safety-critical applications, such as computer relays for power system transmission line protection, produce little failure data. This article presents a methodology using statistics of extremes to embark upon software success estimation. The estimate so obtained is an indicator analogous to the conventional reliability index. This estimated reliability is further employed for assessing software's health more effectively by means of well-being analysis. The most significant contribution of this article is to compute the software well-being indices for healthy, marginal, and risky states. A case study for software used in computer relaying of power system transmission line protection validates the efficacy of the proposed methodology, especially for safety-critical applications. [ABSTRACT FROM AUTHOR]

A digital relay can be conceived as a digital signal processor in which the values of line currents and voltages are continuously monitored and processed. Hence, the heart of the digital relay is the software used for implementing the relaying algorithms in an efficient way. Assessment of software reliability is an area of utmost importance for such software-based systems for safety-critical applications such as digital relaying of power transmission lines. But software testing of safety-critical systems is particularly challenging because of the availability of meager failure data. Therefore, this article presents a methodology for estimating software reliability of digital relaying using statistics of extremes. The unique advantages of using such a methodology are the independence of the evaluation of the test sampling order, the amount of available data, and a priori knowledge about the underlying distribution of any parameter. The case studies demonstrate the efficacy of proposed methodology for evaluating the software reliability for digital relaying of transmission lines. [ABSTRACT FROM AUTHOR]

We report processing and luminescence decay characteristics of Cd1-xZnxS composite nanocrystals (NCs) conjugated with bovine serum albumin (BSA) proteins. Time-resolved study on unconjugate NCs (with dimensions less than the bulk exciton Bohr radius) suggests that in the radiative emission, the fast (τ1) and the slow (τ2) carrier components are equally competitive for a given stoichiometry. Conversely, bioconjugate NCs advocate that the decay component due to the free exciton recombination is ∼9 times faster than the component due to the surface recombination emission. The observation of two distinct decay parameters is due to the fact that the NCs have experienced photostability by way of binding and protecting NC surface with biomolecules (BSA) as binding agents. The occurrence of two decay constants would help in extracting information with regard to the nature of surface recombination, free-exciton relaxation along with the strength of emission. Furthermore, with the increase in % Zn, slow carrier component gets slower owing to the incorporation of extra surface traps due to Zn/Cd incompatibility while making perfect lattice sites in the NCs. As a result, surface emission intensity gets improved compared to the radiative intensity due to core-state direct transitions. Understanding photoluminescence decay of bioconjugated NCs, on a comparative basis, would find scope for biomolecular labelling, sensing and electrophysiology applications. [ABSTRACT FROM AUTHOR]