Parallel query processing with zigzag trees

In this article, we describe our approach to the compile-time optimization and parallelization of queries for execution in DBS3 or EDS. DBS3 is a shared-memory parallel database system, while the EDS system has a distributed-memory architecture. Because DBS3 implements a parallel dataflow execution model, this approach applies to both architectures. Using randomized search strategies enables the exploration of a search space large enough to include zigzag trees, which are intermediate between left-deep and right-deep trees. Zigzag trees are shown to provide better response time than right-deep trees in case of limited memory. Performance measurements obtained using the DBS3 prototype show the advantages of zigzag trees under various conditions.     

Adsorption and desorption dynamics of associative polymers onto particulates of titanium dioxide,alumina and quartz

The authors have been investigating the adsorption and desorption dynamics of nonionic water soluble polymers on inorganic particles. The influence of the nature of polymers with and without associating hydrophobic end groups, the nature of adsorbents [TiO₂, Al₂O₃ (neutral, acid and basic), and SiO₂], polymer concentrations, linear velocity of fluids, and mutual diffusion of polymer molecules on the patterns of adsorption and desorption distribution of polymer concentrations are shown. The model polymer is a nonionic polyurethane polymer based on ethylene oxide. The polymer's structure is R-O-(DI-PEO)₆-DI-O-R (R is C₁₆H₃₃, DI is isophorone diisocyanate, and PEO is CARBOWAX^TM with a molecular weight of 8200). The phenomenological models of association and dissociation kinetics of associative polymers are suggested. The half-lives of clusters into adsorption and desorption layers are estimated. It is shown that heats of desorption of associative polymers are dependent essentially on heats of dissociation of clusters.     

Crosslinking of elastomers upon ageing: a kinetic approach based on crystallinity changes followed by DSC

It was observed that crosslinking reactions resulting both from peroxide decomposition or photoageing at wavelengths longer than 300 nm involve a drastic decrease of the crystallinity of some dienic elastomers, such as polybutadienes (rich in cis 1,4 and 1,2 microstructures) and polycyclo‐octene. By comparing precisely the rate of decomposition of dicumyl peroxide and that of the crystallinity decrease, it was possible to show that the kinetics of crystallinity loss observed upon ageing can be identified with that of the crosslinking of elastomers. The results indicate that the crosslinking process can be followed directly by DSC measurement of the crystallization/melting cycle. © 2003 Society of Chemical Industry     

Distributed Graph Traversals by Relabelling Systems with Applications

Graph traversals are in the basis of many distributed algorithms. In this paper, we use graph relabelling systems to encode two basic graph traversals which are the broadcast and the convergecast. This encoding allows us to derive formal, modular and simple encoding for many distributed graph algorithms. We illustrate this method by investigating the distributed computation of a breadth-first spanning tree and the distributed computation of a minimum spanning tree. Our formalism allows to focus on the correctness of a distributed algorithm rather than on the implementation and the communication details.     

Delay Mitigation in the Malaysian Construction Industry

This paper describes the importance of applying proper management in dealing with delays in construction for a growing economy. The main objective of this paper is to identify the management tools that are practiced in the local construction industry in mitigating delay. It also aims to identify the main factors that lead to project delays and to suggest recommendations on how to overcome or mitigate effects of the problem. Data is gathered from responses from questionnaire survey and interviews with those involved in construction project. The surveys and research findings indicate that delay incidents occur mainly during the construction phase of a project and one or more parties usually contribute to delay. This paper highlights the importance of having more experienced and capable construction managers as well as skilled laborers to enable the industry to develop at a faster rate either nationally or internationally.     

Sternomental distance as the sole predictor of difficult laryngoscopy in obstetric anaesthesia

BACKGROUND AND AIMS OF THE STUDY: The first generation of pericardial valves was withdrawn from the market because of an excessive rate of premature failure. With an original design, the Carpentier-Edwards pericardial valve promised improved results. MATERIALS AND METHODS: From July 1984 to December 1993, 71 patients underwent double mitral and aortic valve replacement with the Carpentier-Edwards pericardial valve. Mean age was 63.4 years. 58% were male, mean clinical status was 2.9 with 71% of patients in NYHA class III or IV, 55% were in atrial fibrillation. All patients were followed for an average of 4.17 years after their operation, and total follow up was 296 patients years. RESULTS: Operative mortality was 7% (5/71). At this point of the study, 70% of patients are in clinical NYHA class I or II, 42% of patients are in atrial fibrillation and 66% receive anticoagulation treatment. We observed 19 late deaths with an actuarial survival of 58% +/- 14% at ten years. Valve-related complications include four endocarditis, four reoperations, seven anticoagulant-related hemorrhages, two structural failures, one thromboembolic episode, and one sudden death. Two patients died of valve-related causes. After 10 years, freedom from valve related death is 97% +/- 3%, from endocarditis 90% +/- 8%, from reoperation 87% +/- 10%, from thromboembolic complications 98% +/- 2%, from valve failure 93% +/- 7%, and freedom from all complications is 58% +/- 18%. No failure in patients older than 60 years was noted and no leaflet tear was observed. CONCLUSIONS: The 10-year results of this pericardial bioprosthesis make this valve an outstanding choice when a bioprosthesis is required and in patients over 60 years old.     

Adaptive Self-Tuning Speed Control for Permanent-Magnet Synchronous Motor Drive With Dead Time

In this paper, an adaptive self-tuning speed control for a permanent-magnet synchronous motor (PMSM) drive with dead time is proposed. Firstly, to equivalently place the dead time element outside the closed-loop speed control, a dead time compensator (DTC), based on the Smith predictor and a self-tuning proportional-integral model-following controller (ST-PI-MFC) is proposed. The model-following error is used to adaptively update the gains of the ST-PI-MFC via the affine projection algorithm (APA). Secondly, a disturbance observer, based on the time delay control (TDC) approach is used for torque feed forward control. The system's model is greatly simplified when the disturbance observer is combined with the motor. Relying on the simplified model, a natural adaptive observer is used to estimate the motor speed. Unknown motor parameters are estimated by minimizing the state estimation error using an iterative gradient algorithm offered by the affine projection. The estimated parameters are used to update the gains of the integral-proportional (IP) servo loop controller, the disturbance observer and the Smith model. The validity and usefulness of the proposed control scheme are verified through simulation and experimental results     

Thin steel plate shear walls behavior and analysis

Steel plate shear walls have been used in buildings in North America and Japan. Until recently, the design practice has been to limit the strength of the wall to the buckling strength of the plate. The post-buckling strength of thin plates subjected to shear has been recognized for more than 60 years, since it was outlined by Wagner in the early 1930s. Tests of a quarter and one third scale specimens of thin steel plate shear walls under cyclic loading were performed; the tests are described and the results are summarized. An analytical model to determine the behavior of thin steel plate shear walls was developed and is given. The model is capable of depicting the behavior of walls with plates welded or bolted to the surrounding beams and columns of the building frame. Comparisons between the analytical and experimental results are made.