Operating Systems

The article first describes characteristics of major infrastructure projects. Second, it documents a much neglected topic in economics: that ex ante estimates of costs and benefits are often very different from actual ex post costs and benefits. For large infrastructure projects the consequences are cost overruns, benefit shortfalls, and the systematic underestimation of risks. Third, implications for cost–benefit analysis are described, including that such analysis is not to be trusted for major infrastructure projects. Fourth, the article uncovers the causes of this state of affairs in terms of perverse incentives that encourage promoters to underestimate costs and overestimate benefits in the business cases for their projects. But the projects that are made to look best on paper are the projects that amass the highest cost overruns and benefit shortfalls in reality. The article depicts this situation as ‘survival of the unfittest’. Fifth, the article sets out to explain how the problem may be solved, with a view to arriving at more efficient and more democratic projects, and avoiding the scandals that often accompany major infrastructure investments. Finally, the article identifies current trends in major infrastructure development. It is argued that a rapid increase in stimulus spending, combined with more investments in emerging economies, combined with more spending on information technology is catapulting infrastructure investment from the frying pan into the fire.

A web operating system is an operating system that users can access from any hardware at any location. A peer-to-peer (P2P) grid uses P2P communication for resource management and communication between nodes in a grid and manages resources locally in each cluster, and this provides a proper architecture for a web operating system. Use of semantic technology in web operating systems is an emerging field that improves the management and discovery of resources and services. In this paper, we propose PGSW-OS (P2P grid semantic Web OS), a model based on a P2P grid architecture and semantic technology to improve resource management in a web operating system through resource discovery with the aid of semantic features. Our approach integrates distributed hash tables (DHTs) and semantic overlay networks to enable semantic-based resource management by advertising resources in the DHT based upon their annotations to enable semantic-based resource matchmaking. Our model includes ontologies and virtual organizations. Our technique decreases the computational complexity of searching in a web operating system environment. We perform a simulation study using the Gridsim simulator, and our experiments show that our model provides enhanced utilization of resources, better search expressiveness, scalability, and precision.

"Wireless communication technologies continue to undergo rapid advancement. In recent years, there has been a steep growth in research in the area of wireless sensor networks (WSNs).

In WSNs, communication takes place with the help of spatially distributed, autonomous sensor nodes equipped to sense specific information. WSNs can be found in a variety of both military and civilian applications worldwide. Examples include detecting enemy intrusion on the battlefield, object tracking, habitat monitoring, patient monitoring and fire detection. Sensor networks are emerging as an attractive technology with great promise for the future. However, challenges remain to be addressed in issues relating to coverage and deployment, scalability, quality-of-service, size, computational power, energy efficiency and security.

This highly useful Guide to Wireless Sensor Networks presents a comprehensive account of the fundamental concepts, new ideas and results in the field of WSNs. Offering a wide coverage of subjects, from core issues to specialized topics, this reader-friendly book provides a valuable reference for academics and practitioners alike. With its helpful teaching tools, it is also an ideal textbook for graduate students wishing to learn more about the topic."

This research focuses on using various higher order neural networks (HONNs) to predict the upcoming trends of financial signals. Two HONNs models: the Pi-Sigma neural network and the ridge polynomial neural network were used. Furthermore, a novel HONN architecture which combines the properties of both higher order and recurrent neural network was constructed, and is called dynamic ridge polynomial neural network (DRPNN). Extensive simulations for the prediction of one and five steps ahead of financial signals were performed. Simulation results indicate that DRPNN in most cases demonstrated advantages in capturing chaotic movement in the signals with an improvement in the profit return and rapid convergence over other network models.

The most comprehensive, useful, and sophisticated reference on Solaris 2.x ever published, this book gives you polished, professional tools for tweaking peak performance from both software and hardware and staying on top of capacity needs. And, it's current, featuring information specific to Solaris 2.5.1 and 2.6. Useful to both Solaris newcomers and seasoned pros, this guide features important background theory on queuing models and performance metrics, essential to assessment. It's packed with command output and code samples, plus technical and strategic information on everything from kernel architecture to network configuration and memory management - all with the benefit of tried-and-tested Solaris 2.x experience.

The emergence of the technology of Wireless Sensor Networks has lead to many changes in current and traditional computational techniques. Traditional operating systems do not take into consideration the limitations in space and energy of wireless sensor networks. New system architectures have emerged to overcome these limitations. Each follows one of two design concepts, event driven or thread-driven. Experiments have shown that event-driven systems tend to save more energy and space, while thread-driven systems provide more concurrency and predictability, hence creating a tradeoff. This paper studies the differences between the aforementioned system designs, pointing out the causes of the tradeoff. The paper then introduces a thread-driven scheduling algorithm focusing on the value of preemption to overcome the energy tradeoff brought by event-driven systems. Our proposed algorithm reduces the average amount of energy spent under high system load which was a significant scenario where event driven systems showed better energy savings.

"Nesta terceira edição de Sistemas operacionais modernos, Andrew S. Tanenbaum traz os mais recentes avanços tecnológicos da área e apresenta vasto conteúdo que trata, por exemplo, do Linux, do Windows Vista, de malwares e de sistemas operacionais embarcados (como o Symbian, muito
usado em smartphones)."

""With the advent of large and fast storage devices (eg. SSDs, Flash Disks) file system sizes have grown beyond bounds. Large volume of dynamically changing data makes it difficult to store data on the fly. Consistent backup ensuring integrity and correctness of data is of utmost important. Offline backup schemes result in heavy losses due to large down time. Online backup schemes offer weak consistency guarantees. Transactional file systems offer strong guarantees; however, they hinder the normal functioning of user applications. This results in transaction aborts and sub-optimal performance. This work proposes an online
backup approach that circumvents user transaction aborts due to the backup process in a transactional file system. Conventional serialization approaches ensure consistency with transaction aborts. This work defines a concept “Conflict Dependence” that helps identify conflicts within backup and user transactions.
An efficient implementation within a log-structured file system (LFS) is proposed. It does not require aborts because of the backup process. The backup scheme extends naturally to a versioning in a LFS. ""