Characterization of groundrolls in the North-West of Niger Delta Nigeria,West Africa

A study of the character and dispersion patterns of groundrolls during seismic survey in the North – West of Niger Delta was undertaken in order to provide information and data for its suppression. Eighty – three raw monitor records were analysed for their frequency, velocity and wavelength characteristics. The results showed that the predominant phase velocities ranged from 278 to 726 m/s with a mean of 376 m/s, the frequency values were 5.3 to 14.1 Hz with a mean of 6.5 Hz. The results showed that the groundrolls in this area were dispersive and this is consistent with the theory of groundrolls in nature and velocity layering and non – homogenous nature of the Niger Delta. Vistal – 12 processing software was also used to carry out F–K analysis on the raw monitor records with groundrolls and the output showed clear monitor record without groundroll. The groundrolls could be suppressed by keeping the geophones arrays and source patterns at distances of not less than 10 m and 70 m respectively instead of 5 m and 50 m used in the survey.     

Integrating the grouping and layout problems in cellular manufacturing systems

In this paper, the simultaneous solution of the machine grouping and layout problems in cellular manufacturing systems is explored. A model for the combined problem is presented. Since the model is complex to solve using traditional optimization techniques, a suboptimal procedure involving the use of a simulated annealing based algorithm is suggested. Results with a numerical example are presented. An alternative formulation based on quandratic assignment problem is also presented.     

Approximating queue lengths inM(t)/G/1 queue using the maximum entropy principle

Using the discrete time approach a model is developed for obtaining the expected queue length of theM(t)/G/1 queue. This type of queue occurs in different forms in transportation and traffic systems and in communications and manufacturing systems. In order to cut down the very high computational efforts required to evaluate the performance measures in such queues by exact methods, the Maximum Entropy Principle is used to approximate the expected queue length which is one of the most commonly used performance measures. A procedure is then developed for reducing the error encountered when this approximation is adopted. The results from this paper will encourage the practitioners to use the appropriate time-varying queueing models when the need arises instead of resorting to very poor approximations.     

An approximation method for queues in series with blocking

An approximation method for the analysis of queues in series with exponential servers, Poisson arrivals and blocking, is presented. The analysis considers cells consisting of three nodes with revised arrival and service processes. A recursive scheme is developed for the calculation of the steady state probability distributions of the number of items/customers at each node, and also the joint steady state probability distributions of the number of items for triplets of nodes are provided. This approximation method seems to yield encouraging results when compared with those obtained by the other methods and simulation.