Evaluation of high Ni-Cr-Mo alloys for the construction of sulfur dioxide scrubber plants

Corrosion in wet lime/limestone systems used for flue gas desulfurization in thermal power plants is of great concern. The frequent variations in acidity and in chloride and fluoride ion concentrations experienced by such systems pose a serious threat to the materials of construction. Currently used materials mostly type 316L stainless steel often fail to meet their life expectancy. The present study evaluates the performance of advanced Ni- Cr- Mo alloys 59 and C- 276 in a simulated sulfur dioxide scrubber environment. Accelerated tests showed that high Ni- Cr- Mo alloys have little tendency to leach metal ions such as chromium, nickel, and molybdenum at different impressed potentials. Scanning electron microscopy was used to examine the morphology of pitting attack.     

Corrosion induced failure of a stainless steel orthopaedic implant device

Failure investigation was carried out for the fractured orthopaedic implant device (Sherman bone plate) which fractured in the ulna of the right hand of a patient. Marked macroscopic beach marks were radiating from the pit present in the inner side of the countersunk hole. Fatigue striations, microcracks and pitting attack were noticed in the fractured site of the implant. Electrochemical potentiokinetic reactivation test on failed implant showed a significant reactivation peak indicating the presence of chromium-depleted regions. The failure of the Sherman bone plate was the consequence of corrosion fatigue due to the propagation of cracks radiating from the pit present in the crevice. The crack propagation was aggravated by the biomechanical force exerted on the implant.     

Screening and Evaluation of Polyhydroxybutyrate-Producing Strains from Indigenous Isolate Cupriavidus taiwanensis Strains

Polyhydroxyalkanoate (PHA) is a biodegradable material with many potential biomedical applications, including medical implants and drug delivery. This study developed a system for screening production strains in order to optimize PHA production in Cupriavidus taiwanensis 184, 185, 186, 187, 204, 208, 209 and Pseudomona oleovorans ATCC 29347. In this study, Sudan black B staining, Infrared (IR) and Gas Chromatography (GC) analysis indicated that the best strain for PHA synthesis is C. taiwanensis 184, which obtains polyhydroxybutyrate (PHB). Cultivation of C. taiwanensis 184 under a pH of 7.0, at 30 °C, and at an agitation rate of 200 rpm, obtained a PHB content of 10% and PHB production of 0.14 g/L. The carbon and nitrogen types selected for analysis of PHB production by C. taiwanensis 184 were gluconic acid and NH(4)Cl, respectively. Optimal carbon/nitrogen ratio for PHB production was also determined. This study demonstrated a PHB content of 58.81% and a PHB production of 2.44 g/L when the carbon/nitrogen ratio of 8/1 was selected for C. taiwanensis 184. A two-stage fermentation strategy significantly enhanced PHB content and PHB production. Under a two-stage fermentation strategy with nutrient-limited conditions, C. taiwanensis 184 obtained a PHB content of 72% and a PHB concentration of 7 g/L. Finally, experimental results confirmed that optimizing the growth medium and fermentation conditions for cultivating the indigenous C. taiwanensis 184 strain substantially elevated PHB content from 10% to 72% and PHB production from 0.14 g/L to 7 g/L, respectively.     

Synthesis of substituted poly (arylene vinylene) films by vapor deposition polymerization

Summary An efficient method for the synthesis of PPV based polymers, poly ( 2,5-dimethyl-1,4-phenylene vinylene) (DMe-PPV) and poly (2,5-dimethoxy-1,4-phenylene vinylene) (DOMe-PPV) were developed using 2,5-dimethyl-1,4-bis ( chloromethyl ) benzene and 2,5-dimethoxy 1,4-bis ( chloromethyl ) benzene via vapor phase pyrolysis and followed by vapor deposition polymerization. The structure of polymer films were confirmed by FT-IR, solid state NMR and elemental analysis. Thermal gravimetry analysis reveals that the precursor polymer films form a conjugated polymer after thermal conversion at 250°C. The optical and electrical properties of the polymer films were investigated by UV-Vis absorption and photoluminescence spectroscopies. Electroluminescent devices were fabricated using these polymers. Received: 18 May 2000/Revised version: 21 July 2000/Accepted: 28 July 2000     

Electrochemical,SEM and XPS investigations on phosphoric acid treated surgical grade type 316L SS for biomedical applications

A simple surface pre-treatment method was attempted to establish a stable passive layer on the surface of surgical grade stainless steel (SS) of type 316L for biomedical applications. Surgical grade type 316L SS specimens were subjected to H₃PO₄ treatment for 1 h by completely immersing them in the acid solutions to develop a passive barrier film. The effect of various concentrations of phosphoric acid on the localized corrosion resistance behavior of type 316L SS was investigated through electrochemical techniques using cyclic polarization studies and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS) was used to evaluate the nature and composition of the passive films. The surface morphology and relative elemental composition of the untreated and acid treated surfaces subjected to anodic polarization was studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) techniques, respectively. Compared with untreated (pristine) 316L SS, the 40% acid treated surface formed a stable passive layer that had superior corrosion resistance.     

A survey of the state of the art in learning the kernels

In recent years, the machine learning community has witnessed a tremendous growth in the development of kernel-based learning algorithms. However, the performance of this class of algorithms greatly depends on the choice of the kernel function. Kernel function implicitly represents the inner product between a pair of points of a dataset in a higher dimensional space. This inner product amounts to the similarity between points and provides a solid foundation for nonlinear analysis in kernel-based learning algorithms. The most important challenge in kernel-based learning is the selection of an appropriate kernel for a given dataset. To remedy this problem, algorithms to learn the kernel have recently been proposed. These methods formulate a learning algorithm that finds an optimal kernel for a given dataset. In this paper, we present an overview of these algorithms and provide a comparison of various approaches to find an optimal kernel. Furthermore, a list of pivotal issues that lead to efficient design of such algorithms will be presented.     

Formalizing real-time scheduling using priority-based supervisory control of discrete-event systems

In this note, we formalize real-time task scheduling by applying an extension of supervisory control theory (SCT) of discrete-event systems to real-time models. The set of all possible timed traces of the system is specified by a discrete timed automaton where each transition is associated with an event occurrence or the passage of one unit of time. We introduce priorities to SCT, and apply them to the setting of discrete timed automata in order to develop a formal and unified framework for task scheduling on a single CPU.     

English to Tamil machine translation system using universal networking language

This paper proposes English to Tamil machine translation system, using the universal networking language (UNL) as the intermediate representation. The UNL approach is a hybrid approach of the rule and knowledge-based approaches to machine translation. UNL is a declarative formal language, specifically designed to represent semantic data extracted from a natural language text. The input English sentence is converted to UNL (enconversion), which is then converted to a Tamil sentence (deconversion) by ensuring that the meaning of the input sentence is preserved. The representation of UNL was modified to suit the translation process. A new sentence formation algorithm was also proposed to rearrange the translated Tamil words to sentences. The translation system was evaluated using bilingual evaluation understudy (BLEU) score. A BLEU score of 0.581 was achieved, which is an indication that most of the information in the input sentence is retained in the translated sentence. The scores obtained using the UNL based approach were compared with existing approaches to translation, and it can be concluded that the UNL is a more suited approach to machine translation.