Java based replicated server objects and their remote method invocations in a distributed environment

A distributed system is said to be fault‐tolerant if it is able to provide important services despite partial failures of the computers or software objects in the system. These systems are needed to support applications such as remote access and control, virtual mobile offices and wide area collaborative systems where there are chances of failures in the network and software objects. Fault‐tolerance is usually achieved by replicating the objects in the system. Traditional distributed applications constructed using Java RMI (remote method invocation) are not fault‐tolerant because of the lack of support of object replication. The objective of the present work is to design a remote method invocation that supports server object replication. To provide a fault‐tolerant service to the remote client objects, server objects are actively replicated. The problems associated with the method invocation in the context of active server object replication are presented and solutions are discussed and implemented. Copyright © 2001 John Wiley & Sons, Ltd.     

Simulating perfect channels with probabilistic lossy channels

We consider the problem of deciding whether an infinite-state system (expressed as a Markov chain) satisfies a correctness property with probability 1. This problem is, of course, undecidable for general infinite-state systems. We focus our attention on the model of probabilistic lossy channel systems consisting of finite-state processes that communicate over unbounded lossy FIFO channels. Abdulla and Jonsson have shown that safety properties are decidable while progress properties are undecidable for non-probabilistic lossy channel systems. Under assumptions of “sufficiently high” probability of loss, Baier and Engelen have shown how to check whether a property holds of probabilistic lossy channel system with probability 1. In this paper, we consider a model of probabilistic lossy channel systems, where messages can be lost only during send transitions. In contrast to the model of Baier and Engelen, once a message is successfully sent to channel, it can only be removed through a transition which receives the message. We show that checking whether safety properties hold with probability 1 is undecidable for this model. Our proof depends upon simulating a perfect channel, with a high degree of confidence, using lossy channels.     

Melt fracture and wall slip of thermoplastic vulcanizates

Thermoplastic vulcanizates (TPVs) are blends of polypropylene (PP) (thermoplastic phase) and ethylene propylene diene monomer (EPDM) rubber (rubber phase) in which a high content of rubber EPDM is cross-linked and dispersed in a thermoplastic matrix (PP) in the presence of oil (lubricant) and filler. Depending on the molecular characteristics of the constituent polymers, the level of curing and the amount of cross-linked rubber, their processing (extrusion) exhibits various difficulties such as melt fracture (extrudate distortions). In this study, a number of different TPVs with various characteristics, including the degree of curing and amount of cross-linked rubber are examined in capillary extrusion at two different temperatures (190°C and 205°C) relevant to real processing. First, the effect of the temperature on the yield stress is investigated using rheological measurements. Consequently, the flow behavior of the TPVs in capillary flow is studied concluding that TPVs slip massively (nearly plug flow) due to the presence of lubricant and the vulcanized rubber phase. Although there is little slip observed in PP samples, EPDMs themselves exhibit severe slip and melt fracture. As a consequence, the TPV samples essentially follow the slip behavior of EPDMs. Finally, the melt fracture analysis of several TPVs has shown that with increase of temperature and amount of cross-linked rubber, the severity of TPVs' surface defects increases accordingly.     

Experimental study of a liquid film flowing over a perforation

Perforations are one of the recognized geometrical features that contribute to liquid redistribution in corrugated sheet packings. Our experimental study focuses on a simplified but relevant configuration: a thin liquid film flowing on either side of a vertical plate with a circular perforation. We focus on the curtain mode when the liquid fills the perforation. Confocal chromatic imaging reveals a capillary ridge upstream of the perforation, an inertial ridge downstream, and a varicose capillary wave standing on the liquid curtain. We show that the wavelength is selected such that the velocity of the wave both satisfies Taylor's dispersion relation and matches the curtain local speed. We examine the effect of perforation size, supply conditions, and liquid properties on the curtain transition. Lastly, we propose a simple model based on a momentum balance that describes the effect of these parameters on the Reynolds number at which curtain forms.     

Influence of device structure and growth conditions on the tunneling characteristics of Si/Si1−xGex double barrier structures

We have investigated different Si/Si_1−xGe_x hole resonant tunneling structures. We demonstrate the advantages of grading the Ge concentration in the spacer layers, which allows for a smoother potential profile in the spacer layers and a higher Ge concentration in the well, and hence higher bandoffsets. This leads to an improvement of the resonances seen in the I–V characteristics of these devices. Structures grown at different temperatures emphasize the importance of obtaining abrupt Si/Si_1−xGe_x double barrier heterointerfaces in order to obtain good I–V characteristics. Short-term post annealing at ⋟500°C, well below temperatures where strain relaxation or dopant diffusion into the barrier layers occur, is shown to destroy the resonances. We believe this is due to monolayer interdiffusion at the barriers, destroying the abruptness of the interfaces.     

Carbon monoxide methanation over FeTi1-x Sn x intermetallics: Role of second phase

Partial substitution of Sn in place of Ti in FeTi leads to enhanced hydrogen chemisorption and to increase in its catalytic activity for CO dissociation and methanation. Sn substitution gives rise to a dispersed second phase of Fe₂Ti in the bulk and to iron cluster formation at catalyst surface. The role of secondary phase in the enhancement of catalytic activity is discussed.     

Synthesis of layered MgHPO4. 1.2H2O under ambient conditions

Layered Magnesium Phosphate MgHPO_4. 1.2H₂O is synthesized by the direct ambient pressure and temperature reaction between MgCl₆. 6H₂O and phosphoric acid at pH 6.0. A detailed study has been performed on the temperature dependance of the reversible dehydration-rehydration process that takes place in this material.     

Under-approximation Heuristics for Grid-based Bounded Model Checking

In this paper, we consider the effect of BDD-based under-approximation on a hybrid approach using BDDs and SAT-BMC for error detection on a computing grid. We experimentally study effect of under-approximation approaches on a non-traditional parallelization of BMC based on state space partitioning. This parallelization is accomplished by executing multiple instances of BMC independently from different seed states, that are selected from the reachable states in different partitions. Such states are spread out across the state space and can potentially be deep. Since all processors work independently of each other, this scheme is suitable for bug hunting using a grid-like network. Our experimental results demonstrate improvement over existing approaches, and we show that the method can effectively utilize a large grid network.