High-temperature hydrogen sulfide corrosion on the heat-affected zone of the AISI 444 stainless steel caused by Venezuelan heavy petroleum

The aim of this study was to evaluate the effect of welding on the corrosion resistance of the heat-affected zone (HAZ) of the AISI 444 ferritic stainless steel in medium containing Venezuelan heavy oil. AISI 444 steel plates were welded through the use of three levels of welding heat input (4, 6 and 8 kJ/cm). Samples were extracted from the welded plates and thermally treated in three different temperatures (200, 300 e 400 °C), while immerged in petroleum for a period of 4 h. Optical microscopy (OM), scanning electronic microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques were used for the analysis of the surface and transversal section of the joint. Electrochemical trials of cyclic potentiokinetic reactivation of double loop (EPR-DL) were also carried out. It has been concluded that the temperature of treatment has direct influence on the level of material corrosion and that the increase in the welding heat input contributes to a higher level of corrosion.     

Primal-dual approximation algorithms for the Prize-Collecting Steiner Tree Problem

The primal-dual scheme has been used to provide approximation algorithms for many problems. Goemans and Williamson gave a (2−1/(n−1))-approximation for the Prize-Collecting Steiner Tree Problem that runs in O(n³logn) time—it applies the primal-dual scheme once for each of the n vertices of the graph. We present a primal-dual algorithm that runs in O(n²logn), as it applies this scheme only once, and achieves the slightly better ratio of (2−2/n). We also show a tight example for the analysis of the algorithm and discuss briefly a couple of other algorithms described in the literature.     

Exhaust emissions and electric energy generation in a stationary engine using blends of diesel and soybean biodiesel

The present work describes an experimental investigation concerning the electric energy generation using blends of diesel and soybean biodiesel. The soybean biodiesel was produced by a transesterification process of the soybean oil using methanol in the presence of a catalyst (KOH). The properties (density, flash point, viscosity, pour point, cetane index, copper strip corrosion, conradson carbon residue and ash content) of the diesel and soybean biodiesel were determined. The exhaust emissions of gases (CO, CO₂,C_xH_y,O₂, NO, NO_x and SO₂) were also measured. The results show that for all the mixtures tested, the electric energy generation was assured without problems. It has also been observed that the emissions of CO, C_xH_y and SO₂ decrease in the case of diesel–soybean biodiesel blends. The temperatures of the exhaust gases and the emissions of NO and NO_x are similar to or less than those of diesel.     

An interactive method for multiple objective linear fractional programming problems

Multiple objective linear fractional programming (MOLFP) is an important field of research. Using some branch and bound techniques, we have developed a new interactive method for MOLFP that drastically reduces the computational effort needed, while providing guidance for the decision maker in the choice of his/her preferred solutions. The basic idea of the computation phase of the algorithm is to optimize one of the fractional objective functions while constraining the others. Several linear programming problems, organized in a tree structure, are generated as the search evolves. The whole idea is simple and it results in a fast and very intuitive approach to exploring the non-dominated set of solutions in MOLFP, and eventually to finding the preferred solution.This work was supported by the Fundação para a Ciência e Tecnologia and FEDER, project POCTI/32405/GES/2000.     

Ordering and timeliness requirements of dependable real-time programs

It is significantly difficult to program dependable decentralised computer control systems, since they need to integrate fault-tolerance and real-time with distribution. In consequence, architects and programmers turn to new distributed system tools and paradigms, such as: synchronised clocks, causal order, groups, membership, replication, and so forth, to assist them in that task. Their inappropriate use, however, may lead to unexpected inefficiency or failure of programs. There is a common link between all these tools in real-time uses, and that is the rôle of time and order in the behaviour of the system. The purpose of this paper is to establish the limits to their use, in order that the models programmers rely on are not used beyond their validity boundaries. This paper equates the time and order problems of real-time programs in a unified manner. It recalls known fundamental limits of time and order in distributed systems, and then it shows that these limits can be drastically relaxed, if the system support (clock granularity, order discrimination) can be matched to the ordering and timeliness requirements of programs. It finalises by giving concrete guidelines about the use of clocks and about what a programmer can expect from an ordering by distributed timestamps.     

Multiscale Fitting Procedure Using Markov Modulated Poisson Processes

This paper proposes a parameter fitting procedure using Markov Modulated Poisson Processes (MMPPs) that leads to accurate estimates of queuing behavior for network traffic exhibiting long-range dependence behavior. The procedure matches both the autocovariance and marginal distribution of the counting process. A major feature is that the number of states is not fixed a priori, and can be adapted to the particular trace being modeled. The MMPP is constructed as a superposition of L 2-MMPPs and one M-MMPP. The 2-MMPPs are designed to match the autocovariance and the M-MMPP to match the marginal distribution. Each 2-MMPP models a specific time-scale of the data. The procedure starts by approximating the autocovariance by a weighted sum of exponential functions that model the autocovariance of the 2-MMPPs. The autocovariance tail can be adjusted to capture the long-range dependence characteristics of the traffic, up to the time-scales of interest to the system under study. The procedure then fits the M-MMPP parameters in order to match the marginal distribution, within the constraints imposed by the autocovariance matching. The number of states is also determined as part of this step. The final MMPP with M2 ^L states is obtained by superposing the L 2-MMPPs and the M-MMPP. We apply the inference procedure to traffic traces exhibiting long-range dependence and evaluate its queuing behavior through simulation. Very good results are obtained, both in terms of queuing behavior and number of states, for the traces used, which include the well-known Bellcore traces.     

Some remarks on multiple-entry finite automata

Some remarks on multiple-entry finite automata are presented. They deal with the effects of nondeterminism and of other logics on the family of languages accepted, comparison with finite automata (both deterministic and nondeterministic) in terms of number of states and a bound on a decision procedure.     

Multielectrode microprobes for deep-brain stimulation fabricated with a customizable 3-D electroplating process

Although deep-brain stimulation (DBS) can be used to improve some of the severe symptoms of Parkinson's disease (e.g., Bradykinesia, rigidity, and tremors), the mechanisms by which the symptoms are eliminated are not well understood. Moreover, DBS does not prevent neurodegeneration that leads to dementia or death. In order to fully investigate DBS and to optimize its use, a comprehensive long-term stimulation study in an animal model is needed. However, since the brain region that must be stimulated, known as the subthalamic nucleus (STN), is extremely small (500 microm x 500 microm x 1 mm) and deep within the rat brain (10 mm), the stimulating probe must have geometric and mechanical properties that allow accurate positioning in the brain, while minimizing tissue damage. We have designed, fabricated, and tested a novel micromachined probe that is able to accurately stimulate the STN. The probe is designed to minimize damage to the surrounding tissue. The probe shank is coated with gold and the electrode interconnects are insulated with silicon nitride for biocompatibility. The probe has four platinum electrodes to provide a variety of spatially distributed stimuli, and is formed in a novel 3-D plating process that results in a microwire like geometry (i.e., smoothly tapering diameter) with a corresponding mechanically stable shank.