A new empirical distribution for the uncertainty analysis of the top event of a fault tree

A new empirical statistical distribution is reported, which describes the probability distribution of the unavailability Q_TOP for the top event of a fault tree. The distribution can be fitted using linear regression analysis. Investigations into the fit of the new distribution are reported, and as specific examples, two fault trees described in Reactor Safety Study are studied. The proposed distribution fits very well in both the cases, as shown by the χ² test. For comparison, Johnson's S_L and S_B distributions, the log-normal distribution and the hybrid log-normal distribution are fitted to the same fault trees using the exact regression analysis method. Johnson's S_B distribution cannot be fitted in the case of one of the fault trees as the necessary iterative process does not converge. For the other fault tree, the S_B distribution fits very well. Johnson's S_L distribution, the log-normal distribution and the hybrid log-normal distribution do not fit as well as the distribution proposed here and the χ² test failed. Also, Johnson's distributions require the use of either an approximate method, involving a number of trials and errors, or non-linear regression analysis for fitting. The proposed distribution can, on the other hand, be fitted exactly using linear regression analysis and is, therefore, no more difficult to fit than the log-normal distribution. It is therefore concluded that the proposed distribution is most suited to describe the probability distribution of the unavailability for the top event of fault tree. Its suitability as a substitute for Johnson's distributions is also investigated. As specific examples, two statistical distributions in a text-book, for which fitting of Johnson's distributions has been suggested, are studied. The proposed distribution fits very well, as shown by the χ² test. The proposed distribution is thus a good substitute for Johnson's S_B distribution.     

Crystallization of cystine

Cystine is an amino acid, which is a constituent of the urinary stones. It also is deposited in eyes, thyroid glands, bone marrow and white blood corpuscles. Crystals of cystine have been grown by both solution and gel methods. Small bunched hexagonal crystals, along with many other morphological crystals of size 0.3 mm across, were obtained. The crystals were analysed by X-ray diffraction and IR analyses.     

Growth,structural, thermal,optical, and electrical properties of potassium succinate–succinic acid crystal

Potassium succinate–succinic acid (KSSA), semi-organic single crystals were grown by slow evaporation growth technique using water solvent. Single crystal X-ray diffraction study revealed that the KSSA crystal belongs to monoclinic system. FT-IR and FT-Raman spectral studies were performed to identify the vibrations of functional groups. TGA/DTA analyses were carried out to characterize the melting behavior and stability of the title compound. The UV–Vis–NIR spectrum showed that the grown crystal is transparent in the entire visible region. Fluorescence studies were carried out in the range of 200–700 nm. The optical nonlinearity of KSSA was investigated at 532 nm using 7 ns laser pulses, employing the open aperture Z-scan technique. The photoconductivity study was carried out to know the conducting nature of the crystal. The laser damage threshold was measured using Q-switched Nd:YAG laser (1064 nm). Electrical properties of the crystal are studied using Hall Effect measurement.     

Portable,parallel grid dye-sensitized solar cell module prepared by screen printing

Screen-printing technology is used to fabricate large dye-sensitized solar cells (DSSCs). The high series-resistance associated with transparent conductive oxide glass substrates causes poor performance in large DSSCs especially at an exposure of 1 sun. The DSSC design has an embedded silver grid; a fluorine-doped tin oxide (FTO) glass substrate and stripe type titanium dioxide (TiO₂) active layers introduced by screen-printing. The counter electrode is prepared from a screen printable paste based on hexachloro platinic acid. A DSSC module, which consists of five stripe-type working electrodes on a 5 cm × 5 cm, embedded silver grid FTO glass substrate, shows stable performance with an energy conversion efficiency of 5.45% under standard test conditions.     

Heat exchanger fouling model and preventive maintenance scheduling tool

The crude preheat train (CPT) in a petroleum refinery consists of a set of large heat exchangers which recovers the waste heat from product streams to preheat the crude oil. In these exchangers the overall heat transfer coefficient reduces significantly during operation due to fouling. The rate of fouling is highly dependent on the properties of the crude blends being processed as well as the operating temperature and flow conditions. The objective of this paper is to develop a predictive model using statistical methods which can a priori predict the rate of the fouling and the decrease in heat transfer efficiency in a heat exchanger. A neural network based fouling model has been developed using historical plant operating data. Root mean square error (RMSE) of the predictions in tube- and shell-side outlet temperatures of 1.83% and 0.93%, respectively, with a correlation coefficient, R², of 0.98 and correct directional change (CDC) values of more than 92% show that the model is adequately accurate. A case study illustrates the methodology by which the predictive model can be used to develop a preventive maintenance scheduling tool.     

A multi coding technique to reduce transition activity in VLSI circuits

Advances in VLSI technology have enabled the implementation of complex digital circuits in a single chip, reducing system size and power consumption. In deep submicron low power CMOS VLSI design, the main cause of energy dissipation is charging and discharging of internal node capacitances due to transition activity. Transition activity is one of the major factors that also affect the dynamic power dissipation. This paper proposes power reduction analyzed through algorithm and logic circuit levels. In algorithm level the key aspect of reducing power dissipation is by minimizing transition activity and is achieved by introducing a data coding technique. So a novel multi coding technique is introduced to improve the efficiency of transition activity up to 52.3% on the bus lines, which will automatically reduce the dynamic power dissipation. In addition, 1 bit full adders are introduced in the Hamming distance estimator block, which reduces the device count. This coding method is implemented using Verilog HDL. The overall performance is analyzed by using Modelsim and Xilinx Tools. In total 38.2% power saving capability is achieved compared to other existing methods.