Predictability of software-reliability models

A two-component predictability measure that characterizes the long-term predictive capability of a model is presented. One component, average error, measures how well a model predicts throughout the testing phase. The other component, average bias, measures the general tendency to overestimate or underestimate the number of faults. Data sets for both large and small projects from diverse sources with various initial fault density ranges have been analyzed. The results show that: (i) the logarithmic model seems to predict well in most data sets, (ii) the inverse polynomial model can be used as the next alternative, and (iii) the delayed S-shaped model, which in some data sets fit well generally performed poorly. The statistical analysis shows that these models have appreciably different predictive capabilities     

CNTs in Optoelectronic Devices: New Structural and Photophysical Insights on Porphyrin‐DWCNTs Hybrid Materials

The preparation and physical characterization of diverse porphyrin‐derived double‐walled carbon nanotubes (DWCNTs) conjugates are described. A porphyrin molecule is covalently linked and physically adsorbed to COOH‐derived DWCNTs. The photophysical properties of all porphyrin‐CNTs derivatives are studied in solution and in polymeric matrices. Definitive experimental evidence for photoinduced electron and/or energy transfer processes involving the porphyrin chromophores and the CNT wall is not obtained, but solid‐state UV‐vis absorption profiles display electronic transitions fingerprinting J‐ and H‐ type aggregates, where porphyrin molecules intermolecularly interact “head‐to‐tail” and “face‐to‐face”, respectively. In parallel, molecular modeling based on force‐field simulations is performed to understand the structure of the porphyrin‐CNTs interface and the nature of the interactions between the porphyrins and the DWCNTs. Finally, multilayered ‐ type devices are fabricated with the aim of investigating the interaction of the porphyrin‐derived DWCNTs with poly(3‐hexylthiophene)‐pyrene matrices containing small amounts of 1‐[3‐(methoxycarbonyl)propyl]‐1‐phenyl‐[6.6]C₆₁.     

Behaviour of power MOSFETs at cryogenic temperatures

In this paper an investigation is reported on Siemens-power-metal-oxide-semiconductor (SIPMOS) transistors of both p and n channel types, for their suitability for cryogenic applications. The drain characteristics, temperature dependence of R_ds(on) and switching behaviour have been studied in the temperature range 4.2 – 300 K in BSS91 and BSS92 MOSFETs. The experiments reveal that these types of power transistors are well suited for operations down to ≈ 30 K. However, below 30 K the operating characteristics make them unsuitable for application. This arises because of carrier freeze-out in the n⁻ region on the substrate, which forms a drain.     

Experimental measurements of fluence distribution in a UV reactor using fluorescent microspheres

One concern with current techniques of UV reactor validation is that they provide only a measure of the mean UV fluence. In this research, the actual fluence distribution of a UV reactor is measured through the use of photochemically active fluorescent microspheres. Experimental tests were performed in a pilot-scale monochromatic UV 254 nm reactor operated at two flow rates. Analysis of the fluorescence intensity decay was performed using collimated beam experiments for determination of decay rate kinetics. A stochastic hierarchal process involving Bayesian statistics, and the Markov chain Monte Carlo integration technique was used to correlate the microsphere fluorescence intensity distribution to the UV fluence distribution. The experimental UV fluence distribution was compared with the fluence distribution predicted using a computational fluid dynamics model. The results showed that the fluorescent microspheres measured a wider distribution of UV fluences with a flow rate of 3 gpm than with 7.5 gpm. The principal differences between the modeled and the measured distribution were in the low UV fluences where the microspheres predicted lower fluence levels than the model. The use of microspheres is demonstrated as a novel technique for measurement of the fluence distribution in UV reactors. This technique has both fundamental and practical implications for reactor evaluation and testing and could improve confidence in the future use of mathematical models for UV reactor characterization. It also serves as a complement to biodosimetry testing by providing greater insights regarding reactor behavior and validation.