Annealing time dependence at very high temperature of electricarc-induced long-period fibre gratings

Long-period fibre gratings fabricated with an electric arc have been annealed at high temperatures. The time dependence of transmitted spectra are reported and related to the evolution of internal stresses in the fibre     

Structured extension of COBOL for handling data bases

The most important aspects of a modest data base management system are described on the basis of our experiences in implementing it. Data structuring facilities of the system include two basic data structures: lists and binary search trees; and a simple rule of their top-down composition. The class of structures that may be obtained this way is rather restricted in comparison with the CODASYL proposal, but still fairly powerfull and permits definition and easy implementation of an elegant data manipulation language (DML). Operations of the DML have simple syntax and semantics and allow implementation in which the structure of the data base is protected against illegal actions on the part of the programmer. Since implementation of the system requires some modest effort, we offer it as an experiment which shows how existing software facilities can be extended in simple and still essential ways, for applications where all the generality of general data base management systems is not really necessary. Design of the system was motivated by the work of Schneidermann and Scheuerman on structured data structures and it contains several important clarifications and improvements of their suggestions, together with implementation aspects.     

Pitting transients analysis of stainless steels at the open circuit potential

Metastable pitting of stainless steels in chloride containing oxidising electrolytes is investigated at rest potential using a new experimental technique allowing to record simultaneously the potential and corrosion current variations. Different industrial surface conditions (BA and 2B) are tested for both ferritic (FeCr type) and austenitic (FeCrNi type) stainless steels. It was shown that the number of pitting events decreases with the exposure time and that BA condition provides better resistance to pitting than 2B. As far as pitting mechanisms are concerned, the potential recovery after pitting does not reflect the pit repassivation but rather refers to the discharge of the surface capacity. Analysing the pitting transients provides quantitative information on the cathodic reaction through the passive film (transfer resistance and surface capacitance). Differences in pitting transient shapes are discussed as well.     

Data Services with uncertain and correlated semantics

Currently, a good portion of datasets on Internet are accessed through data services, where user’s queries are answered as a composition of multiple data services. Defining the semantics of data services is the first step towards automating their composition. An interesting approach to define the semantics of data services is by describing them as semantic views over a domain ontology. However, defining such semantic views cannot always be done with certainty, especially when the service’s returned data are too complex. In such case, a data service is associated with several possible semantic views. In addition, complex correlations may be present among these possible semantic views, mainly when data services encapsulate the same data sources. In this paper, we propose a probabilistic approach to model the semantic uncertainty of data services. Services along with their possible semantic views are represented in probabilistic service registry. The correlations among service semantics are modeled through a directed probabilistic graphical model (Bayesian network). Based on our modeling, we study the problem of compositing correlated data services to answer a user query, and propose an efficient method to compute the different possible compositions and their probabilities.     

Functional modelling of volatility in the Swedish limit order book

The publicly available electronic limit order book at the Stockholm Stock Exchange consists of five levels of prices and quantities of a given stock with a bid and ask side. All changes in the book during one day can be recorded with a time quote. Studying the variation of the quoted price returns as a function of quantity is discussed. In particular, discovering and modelling dynamic behaviours in the volatility of prices and liquidity measures are considered. Applying a functional approach, estimation of the volatility dynamics of the spreads, created as differences between the ask and bid prices, is presented through a case study. For that purpose two-step estimation of functional linear models is used, extending this method to a time series context.     

Genericity in Java: persistent and database systems implications

Lack of parametric polymorphism has been a major obstacle for making Java a viable database programming language. Regrettably, a recently accepted solution for genericity in Java 5.0 has far-reaching negative implications for persistent and database systems because of static and dynamic type violations. Severe implications occur in typical database transactions when processing a variety of database collections. Well-known approaches to persistence in Java, including Java’s own persistence mechanism, do not perform correctly due to incorrect dynamic type information that gets promoted to persistence along with objects. Dynamic checking of types of objects fetched from the persistent store may now lead to unexpected type violations. Further problems occur in reflective transactions as Java Core Reflection now allows dynamic type violations without detecting them or throwing standard exceptions. All of this shows that extending Java with parametric polymorphism has not made Java a more viable database programming language. Both legacy systems, such as those based on the Java binding of the ODMG or JDO, and future Java-related persistent and database technologies will be affected. The source of these problems is in an implementation idiom called type erasure. This paper provides formal proofs of the above implications of type erasure along with specific samples of code in Java 5.0 illustrating these violations. The limitations of the virtual platform and extensions required for persistent systems to solve this problem are also elaborated.     

Impact and vibration detection in composite materials by using intermodal interference in multimode optical fibers

An optical fiber sensor based on the intermodal interference principle is integrated in a composite material to detect impacts and vibrations. Six fibers are integrated at the top of a carbon/epoxy composite panel so as to form a grid into the structure. Spectral and temporal responses to impacts and acoustic vibrations of the sensor are compared with a piezoelectric accelerometer. The tests proved the facility of integration and the high sensitivity of the device. The location of impacts is performed with this arrangement by measuring the arrival times of the front waves to the fibers.     

Evolution of Ti-Based Nonmetallic Inclusions During Solution Treatment of Maraging 250 Steel: Thermodynamic Calculations and Experimental Verification

The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C_xN_1–x) and Ti₄C₂S₂, was investigated experimentally. Their stability in austenite also was analyzed by a thermodynamic analysis of the Fe-Ni-Ti-C-N-S system. It was established that the total concentration of the inclusions decreases from 0.024 pct to 0.008 pct after treatment at 1453 K (1180 °C) for 3 hours. The Ti₄C₂S₂ inclusions completely dissolve in austenite at 1523 K (1250 °C) during 1 hour of treatment. The composition of the carbonitride inclusions is shifted toward higher TiN contents when they dissolve in austenite. Nitrogen-enriched titanium carbonitride inclusions are stable in austenite and their fraction may be reduced only by controlling nitrogen content in the steel. The experimental observations are in good agreement with the results of the thermodynamic analysis.     

Electrochemical aspects of exfoliation corrosion of aluminium alloys: The effects of heat treatment

Electrochemical approaches are used to investigate the exfoliation corrosion (EFC) of a 7XXX series aluminium alloy that has undergone different tempering treatments. EFC was produced under an artificial crevice at open circuit potential in neutral chloride solutions, and is found to be associated to current and potential transients. EFC was also produced under galvanostatic control conditions. Observations made through Scanning Electron Microscopy (SEM) suggest that these transients result from the progression of inter-granular cracks. Last, over-ageing heat treatments that are known to decrease both metal hardness and EFC sensitivity were found to decrease the number of transients.