Flow in a channel rotated impulsively

Summary A study is made on the unsteady flow of a viscous and incompressible fluid in a channel bounded by two parallel plates for the two cases, (1) when it is rotated impulsively with the constant angular velocity and (2) when the rotating channel is stopped abruptly. In both cases exact solutions of the equations of motion are obtained. It is found that in the first case the steady state conditions are reached in an oscillatory manner, while this phenomenon is not found in the latter case.With 4 Figures     

RemusDB: transparent high availability for database systems

In this paper, we present a technique for building a high-availability (HA) database management system (DBMS). The proposed technique can be applied to any DBMS with little or no customization, and with reasonable performance overhead. Our approach is based on Remus, a commodity HA solution implemented in the virtualization layer, that uses asynchronous virtual machine state replication to provide transparent HA and failover capabilities. We show that while Remus and similar systems can protect a DBMS, database workloads incur a performance overhead of up to 32 % as compared to an unprotected DBMS. We identify the sources of this overhead and develop optimizations that mitigate the problems. We present an experimental evaluation using two popular database systems and industry standard benchmarks showing that for certain workloads, our optimized approach provides fast failover ( $\le $ 3 s of downtime) with low performance overhead when compared to an unprotected DBMS. Our approach provides a practical means for existing, deployed database systems to be made more reliable with a minimum of risk, cost, and effort. Furthermore, this paper invites new discussion about whether the complexity of HA is best implemented within the DBMS, or as a service by the infrastructure below it.     

A Distributed Mechanism for Handling of Adaptive/Intelligent Selfish Misbehaviour at MAC Layer in Mobile Ad Hoc Networks

Medium access control(MAC) protocols such as IEEE 802.11 are used in wireless networks for sharing of the wireless medium.The random nature of the protocol operation together with the inherent difficulty of monitoring in the open poses significant challenges.All nodes are expected to comply with the protocol rules.But,some nodes in order to gain greater benefits misbehave by not complying with the rules.One such selfish misbehavior is waiting for smaller back-off intervals when compared to the other node...     

Agent-based supply chain management—1: framework

In the face of highly competitive markets and constant pressure to reduce lead times, enterprises today consider supply chain management to be the key area where improvements can significantly impact the bottom line. More enterprises now consider the entire supply chain structure while taking business decisions. They try to identify and manage all critical relationships both upstream and downstream in their supply chains. Some impediments to this are that the necessary information usually resides across a multitude of resources, is ever changing, and is present in multiple formats. Most supply chain decision support systems (DSSs) are specific to an enterprise and its supply chain, and cannot be easily modified to assist other similar enterprises and industries. In this two-part paper, we propose a unified framework for modeling, monitoring and management of supply chains. The first part of the paper describes the framework while the second part illustrates its application to a refinery supply chain. The framework integrates the various elements of the supply chain such as enterprises, their production processes, the associated business data and knowledge and represents them in a unified, intelligent and object-oriented fashion. Supply chain elements are classified as entities, flows and relationships. Software agents are used to emulate the entities i.e. various enterprises and their internal departments. Flows—material and information—are modeled as objects. The framework helps to analyze the business policies with respect to different situations arising in the supply chain. We illustrate the framework by means of two case studies. A DSS for petrochemical cluster management is described together with a prototype DSS for crude procurement in a refinery.     

Agent-based supply chain management—2: a refinery application

The refinery business involves tasks that span several departments and process large amount of data. Among others, these include crude procurement, logistics and scheduling (storage, distillation units, etc.). Current refinery decision support systems (DSSs) fail to integrate all the decision-making processes of a refinery, to interface with other systems in place, to incorporate dynamic data from various sources and to assist different departments concurrently. In part 1 of this two-part paper, we proposed an agent-based framework for supply chain DSSs. Here, we demonstrate its application through a prototype DSS, called petroleum refinery integrated supply chain modeler and simulator or PRISMS, for crude procurement. PRISMS serves as a central DSS through which all processes of a refinery can be studied and enables integrated decisions with respect to the overall refinery business. In particular, PRISMS can be used to study the effects of internal policies of the refinery and its various departments. We illustrate this through three detailed ‘what-if’ studies that provide an insight into how the business responds to changes in policies, exogenous events and plant modifications.     

Online fault diagnosis and state identification during process transitions using dynamic locus analysis

Chemical plants operate in a variety of states; some of these are steady states while others including grade changes, startup, shutdown, and maintenance operations are transitions. Transition operations are usually challenging and more prone to abnormalities. Therefore, automated process monitoring during transitions is important. In this paper, we propose a new signal comparison-based approach, called dynamic locus analysis, for online state identification and fault diagnosis during process transitions. Dynamic locus analysis is an extension of Smith and Waterman's [1981. Identification of common molecular subsequence. Journal of Molecular Biology 147, 195-197] discrete sequence comparison algorithm to continuous signals. It uses dynamic programming to efficiently identify the portion of a long reference signal that best matches another signal. During online application, signals from real-time sensors are compared with those from prior process runs to identify the current process state as well as estimate its progress. Run-to-run variations between the reference and online signals are accounted for by using dynamic time warping (DTW) for signal comparison. Dynamic locus analysis can be directly used for multivariate temporal signals and has the computational efficiency needed for real-time application. Extensive testing on three case studies—the Tennessee Eastman challenge problem, a lab-scale distillation column, and a simulated fluidized catalytic cracking unit—reveal that the proposed method can quickly identify normal as well as abnormal process states.     

Studies on the wet dehulling of sesame seed to obtain superior grade protein concentrates

Easy removal of the fibrous colored skin of sesame seed was accomplished by contacting the seed with lye solution under optimal conditions. The decuticled seed was dried mechanically and a yield of 85% on the raw material was obtained. Screw pressed or pre-press solvent extracted flour derived from the dehulled seed had an attractive white appearance, was free from bitterness and had a lower crude fibre and oxalic acid content. Both in the content of protein and its nutritional quality, the meal was found to be superior to commercial sesame cake. Heat treatment inherent to expeller operation was found to have beneficial effect on sesame protein.     

Application of porous media models to the study of deep bed filtration

Two porous media models — capillaric and Brinkman — were used for the study of deep bed filtration and to calculate the filter coefficient and the pressure drop increase during the course of filtration. The filter coefficient was estimated with trajectory calculations which determine the path of particulate matters as they pass through the filter. A number of relevant forces were included and their effects determined. The Brinkman model was found to give good agreement with experimental results and the filter coefficients based on capillaric model were approximately one to two orders of magnitude lower than experimental data. Both models fail to give reasonable estimates on the pressure drop increase and the discrepancies between the model and the experimental values were two to three orders of magnitude. This is largely due to the failure of the models to distinguish the different roles played by the filter grains and by the particulate matters retained. The filter grains constitute a matrix of passages as conduits for the liquid flow, and the deposited particulate matters act primarily to modify these flow passages (i.e. to restrict the flow). Such a distinction is however not possible with the use of these models.