Classification and assessment of power system static security using decision tree and random forest classifiers

The power system static security classification and assessment is essential in order to identify the post‐contingency problems and take corrective measures and to protect the system from blackout. In this paper, application of two data mining classifiers have been proposed for the security classification and assessment of a multiclass security problem. To design the security problem, contingency analysis is carried out under N‐1 line outage, and static severity index (SSI) is computed, which is a function of the line overload and the voltage deviation using Newton–Raphson load flow method, considering the variable load and generating conditions. Corresponding to the computed values of SSI, the voltage, phase angle, Mega Volt Ampere line flow and so on, a 1 × 7 pattern vector is generated. The generated pattern vectors are used to design a multiclass security problem. The designed security pattern vectors are given as inputs to the decision tree (DT) and random forest (RF) model in order to classify the security status of the power system. The proposed classifiers are investigated on an IEEE 30‐bus test system. The classification accuracy of the DT and the RF are compared with state‐of‐the‐art classifier models, namely, multilayer perceptron (MLP), radial basis function (RBF), and support vector machine (SVM).The simulation results clearly indicate that the proposed DT and RF classifiers are more efficient, reliable, and out performs MLP, RBF, and SVM classifiers for the assessment of the security status of the power system. Hence, DT and RF classifiers are found to be suitable for online implementation. Copyright © 2015 John Wiley & Sons, Ltd.     

Generation of Arylated Quinones by Iron‐Catalyzed Oxidative Arylation of Phenols: Formal Synthesis of Phellodonin,Sarcodonin ε, Leucomelone and Betulinan A

Biologically and pharmaceutically relevant arylated quinones (Quin‐Ar) have been synthesized via direct C H arylation of a variety of phenols using arylboronic acids. An inexpensive, environmentally friendly iron catalyst, ferric sulphate, Fe₂(SO₄)₃, was employed in this operationally simple and efficient method.

     

Investigation of Inclined Turbulators for Heat Transfer Enhancement in a Solar Air Heater

ABSTRACT

In the present study, the effect of forward inclined turbulators on the heat transfer enhancement in a duct is investigated, for forced convection. Turbulator configurations with three different pitch ratios and three different inclination angles are investigated for seven Reynolds numbers within the range 500–50,000. Investigations are performed experimentally as well as computationally, within a computational fluid dynamics framework. A distinguishing feature of the latter has been the employment of a turbulence model, the transitional shear stress transport model that is applicable throughout the presently considered range of Reynolds numbers containing laminar, transitional, and turbulent regions. At the beginning of the study, measurements and predictions are validated against analytical and empirical expressions known for a plain duct. The results obtained for turbulators configurations indicate that Nusselt number increases with the inclination angle but decreases with the pitch ratio. The influence of the inclination angle on the Nusselt number and thermal enhancement factor is found to be stronger than that of the pitch ratio. For all Reynolds numbers and for all configurations, the thermohydraulic performance is observed to increase, leading to thermal enhancement factors within the range 2–5. In all cases, a quite good agreement of the predictions and experiments is observed, which increases the confidence in the accuracy of both approaches.     

Ultra-thin graphene edges at the nanowire tips: a cascade cold cathode with two-stage field amplification

A multistage field emitter based on graphene-linked ZnO nanowire array is realized by means of spin-coating a graphene dispersion (reduced graphene oxide) over a nanostructured platform followed by plasma modification. Spin-coating leads to interlinking of graphene sheets between the neighboring nanowires whereas plasma etching in the subsequent step generates numerous ultra-sharp graphene edges at the nanowire tips. The inherent tendency of graphene to lay flat over a plane substrate can easily be bypassed through the currently presented nanostructure platform based technique. The turn-on and threshold field significantly downshifted compared to the individual components in the cascade emitter. Through the facile electron transfer from nanowires to graphene due to band bending at the ZnO-graphene interface together with multistage geometrical field enhancement at both the nanowire and graphene edges remain behind this enriched field emission from the composite cold cathode. This strategy will open up a new direction to integrate the functionalities of both the graphene array and several other inorganic nanostructure array for practical electronic devices.     

Extraction chromatographic methods in the sample preparation sequence for thermal ionization mass spectrometric analysis of plutonium isotopes

A sample preparation sequence for actinide isotopic analysis by thermal ionization mass spectrometry (TIMS) is described that includes column-based extraction chromatography as the first separation step, followed by anion-exchange column separations. The sequence is designed to include a wet ashing step after the extraction chromatography to prevent any leached extractant or oxalic acid eluent reagents from interfering with subsequent separations, source preparation, or TIMS ionization. TEVA resin and DGA resin materials, containing extractants that consist only of C, N, O, and H atoms, were investigated for isolation of plutonium. Radiotracer level studies confirmed expected high yields from column-based separation procedures. Femtogram-level studies were carried out with TIMS detection, using multiple monoisotopic spikes applied sequentially throughout the separation sequence. Pu recoveries were 87% and 86% for TEVA and DGA resin separations, respectively. The Pu recoveries from 400 μL anion-exchange column separation sequences were 89% and 93% for trial sequences incorporating TEVA and DGA resin. Thus, a prior extraction chromatography step in the sequence did not interfere with the subsequent anion-exchange separation when a simple wet ash step was carried out in between these column separations. The average measurement efficiency for Pu, encompassing the chemical separation recoveries and the TIMS ionization efficiency, was 2.73% ± 0.77% (2σ) for the DGA resin trials and 2.67% ± 0.54% for the TEVA resin trials, compared to 3.41% and 2.37% (average 2.89%) for two control trials. These compare with an average measurement efficiency of 2.78% ± 1.70%, n = 33 from process benchmark analyses using Pu spikes processed through a sequence of oxalate precipitation, wet ash, iron hydroxide precipitation, and anion-exchange column separations. We conclude that extraction chromatography can be a viable separation procedure as part of a multistep sequence for TIMS sample preparation.     

Modelling of mode-I stable crack growth under hydrogen assisted stress corrosion cracking

The paper presents a new strategy based on combined analytical and finite element (FE) solution to hydrogen assisted stress corrosion crack growth. The diffusion process is solved analytically through both one-and two-dimensional modelling. These solutions are adopted with two-dimensional FE based cohesive zone model of crack extension study. The results fit well with published experimental data and show improvement over the predictions by full FE approach. The new solution approach helps to reduce time required for simulation/computation. The study has produced a relationship between concentration dependent reduction in cohesive strength and plastic strain rate.     

Optical properties of Dy<Superscript>3+</Superscript>-doped sodium–aluminum–phosphate glasses

Trivalent dysprosium (Dy³⁺)-doped sodium–aluminum–phosphate (NAP) glasses were prepared and characterized by their optical absorption, excitation, emission spectra, and decay time measurements. Judd–Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative lifetime and stimulated emission cross section of the ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_15/2 transitions. The luminescence intensity ratio of ⁴F_9/2 → ⁶H_13/2 to ⁴F_9/2 → ⁶H_15/2 transitions of Dy³⁺ in NAP glasses gives the feasibility of extracting white light. The lifetime and quantum efficiency of ⁴F_9/2 level is found to be higher than other reported glasses. With increase in Dy³⁺ ion concentration, the decay from ⁴F_9/2 level is found to be faster with decrease in lifetime due to cross relaxation between Dy³⁺ ions.     

Si1 − xGex metal-oxide-semiconductor capacitors with HfTaOx gate dielectrics

Interfacial reactions and electrical properties of RF sputter deposited HfTaO_x high-k gate dielectric films on Si_1 − xGe_x (x = 19%) are investigated. X-ray photoelectron spectroscopic analyses indicate an interfacial layer containing GeO_x, Hf silicate, SiO_x (layer of Hf-Si-Ge-O) formation during deposition of HfTaO_x. No evidence of Ta-silicate or Ta incorporation was found at the interface. The crystallization temperature of HfTaO_x film is found to increase significantly after annealing beyond 500 °C (for 5 min) along with the incorporation of Ta. HfTaO_x films (with 18% Ta) remain amorphous up to about 500 °C anneal. Electrical characterization of post deposition annealed (in oxygen at 600 °C) samples showed; capacitance equivalent thickness of ~ 4.3-5.7 nm, hysteresis of 0.5-0.8 V, and interface state density = 1.2-3.8 × 10¹² cm^− 2 eV^− 1. The valence and conduction band offsets were determined from X-ray photoelectron spectroscopy spectra after careful analyses of the experimental data and removal of binding energy shift induced by differential charging phenomena occurring during X-ray photoelectron spectroscopic measurements. The valence and conduction band offsets were found to be 2.45 ± 0.05 and 2.31 ± 0.05 eV, respectively, and a band gap of 5.8 ± 05 eV was found for annealed samples.     

Determination of interface state density of PtSi/strained-Si1-xGex/Si Schottky diodes

PtSi/p-strained-Si_1-xGe_x (x=0.19 and x=0.29) Schottky barrier diodes have been fabricated and characterized for the determination of barrier height, ideality factor and the interface state density distribution with energy. Diodes having an epitaxial layer thickness of 20 and 52 nm were modeled with emphasis on comparison with experiment. To achieve better agreement with experimental data, an interfacial layer and associated series resistance were included in the model. The capacitance–voltage (C–V) technique has been used for the determination of the energy distribution of interface state density. The interface state density distribution for the Si_0.81Ge_0.19 and Si_0.71Ge_0.29 diodes is found to decrease with increasing energy from the valence band edge.