Application of shadow price in capacity expansion of state dependent routing

We develop a capacity expansion method for state dependent routing which utilizes the concept of shadow price. To cope with the computational complexity which is inherent with the capacity expansion process, special forms of fixed point iteration are developed for network blocking evaluation. The proposed capacity expansion method is illustrated through the example of a well known state dependent routing, namely Least Busy Alternate Routing. We verify the method in simulated networks and the resulting network cost is seen to be quite close to the ones derived from the methods with much higher computational complexity. The proposed method also results in a network design that satisfies the prescribed network blocking probability very accurately.     

Comparative study of the geotechnical properties of the coastal Sabkhas of Saudi Arabia and their hazardous effects

Sabkha is composed of sand deposits mixed with silt and clay intercalated with evaporites. Two types of sabkha are present in Saudi Arabia: the inland sabka, which is found in the northern part of the country and coastal sabkha, which is located along the Red Sea and Arabian Gulf. The main geotechnical hazards include settlement, corrosive action, heave due to salt crystallization/recrystallization and flooding due to the low infiltration rates. This comparative study indicates the engineering properties of the coastal sabkha along the Red Sea differ from those of the sabkha along the Arabian Gulf, which is likely to be more costly to develop.     

Performability of integrated software-hardware components ofreal-time parallel and distributed systems

A method for analyzing performability of the integrated software-hardware components of parallel and distributed systems is presented. The technique uses generalized stochastic Petri nets at the system level (analysis of integrated software-hardware systems). The intractable problem of evaluating a parallel software environment consisting of interacting fault-tolerant parallel tasks is addressed. This is accomplished using a decomposition technique at the task-graph level, where the task graph is decomposed into segments. Recovery blocks are effectively modeled in the interacting parallel modules as well as their supporting hardware. This method greatly facilitates the analysis of performability at the system level. However, the integrated performability model increases the size of the Markov generator matrix. This issue is addressed, and a performability decomposition technique at the task-graph level presented is illustrated by a simple example of a radar command center     

Optimizing vote and quorum assignments for reading and writingreplicated data

In the weighted voting protocol which is used to maintain the consistency of replicated data, the availability of the data to ready and write operations not only depends on the availability of the nodes storing the data but also on the vote and quorum assignments used. The authors consider the problem of determining the vote and quorum assignments that yield the best performance in a distributed system where node availabilities can be different and the mix of the read and write operations is arbitrary. The optimal vote and quorum assignments depend not only on the system parameters, such as node availability and operation mix, but also on the performance measure. The authors present an enumeration algorithm that can be used to find the vote and quorum assignments that need to be considered for achieving optimal performance. When the performance measure is data availability, an analytical method is derived to evaluate it for any vote and quorum assignment. This method and the enumeration algorithm are used to find the optimal vote and quorum assignment for several systems. The enumeration algorithm can also be used to obtain the optimal performance when other measures are considered     

Resource finding in store-and-forward networks

We present a model of searching for a resource in a distributed system whose nodes are connected through a store-and-forward network. Based on this model, we show a lower bound on the number of messages needed to find a resource when nothing is known about the nodes that have the current location of the resource. The model also helps us to establish results about the time complexity of determining a message optimal resource finding algorithm when the probability distribution for the location of the resource in the network is known. We show that the optimization problem is NP-hard for general networks. Finally we show that optimal resource finding algorithms can be determined in polynomial time for a class of tree networks and bidirectional rings. The polynomial algorithms can be used as a basis of heuristic algorithms for general networks.This work was supported in part by NSF grants CCR-8806358 and NCR-8604850     

Time scale decomposition of a class of generalized stochastic Petrinet models

A time-scale decomposition (TSD) algorithm of a class of generalized stochastic Petri net (GSPN) models of systems comprising activities whose duration differ by orders of magnitude is presented. The GSPN model of a system can be decomposed into a hierarchical sequence of aggregated subnets, each of which is valid at a certain time scale. These smaller subnets are solved in isolation and their solutions are combined to get the solution of the whole system. A degradable multiprocessor system which would be intractable using conventional techniques, is analyzed using TSD. The complexity of the TSD algorithm can be orders of magnitude smaller without any significant loss in the accuracy of the result. In general, the error due to aggregation is proportional to the maximum degree of coupling between aggregates. An expression of the error due to aggregation is also given in terms of the ratio of fast and slow transitions in the GSPN model. The algorithm is easy to use and can be easily automated     

On the determination of Oxide Formation Rate for tantalum in chromate bath from cell voltage

Anodic oxide growth has been followed on Ta in chromate solutions by measuring the cell voltage/time relations at current densities between 200 and 700 m?A/cm². It is demonstrated here that the reference electrode can be dispensed with for technical studies, and estimates for the parameters of oxide growth can be calculated from cell voltage/time relations. Results are given for the formation rate, electric field strength, reciprocal capacity and increase of oxide thickness. The formation rate has been found to depend on current density following the empirical relation previously established for valve metals from the results of anodic charging curves. The empirical constants calculated here agree with the values in the literature, thus showing that cell voltage measurements can be used successfully to estimate growth parameters.     

Glomangioma of the popliteal fossa. Apropos of a case

Glomus tumours are relatively uncommon lesions most frequently found in the extremitis, usually in the digits. They are most often solitary lesions but multiple tumours have been reported. If the triad of pain, tenderness and cold intolerance should raise the clinical suspicion of a digital glomus. The histological exam is necessary in the extra digital glomus. We reported a case of fossa poplitea glomangioma with tibialis nerve compression. The treatment of choice was a surgical exision. But the tumour have been redivided a year later without malign transformation.