Controlling lead times and minor ordering costs in the joint replenishment problem with stochastic demands under the class of cyclic policies

In this paper, we consider the periodic review joint replenishment problem under the class of cyclic policies. For each item, the demand in the protection interval is assumed stochastic. Moreover, a fraction of shortage is lost, while the other quota is backordered. We suppose that lead times and minor ordering costs are controllable. The problem concerns determining the cyclic replenishment policy, the lead times, and the minor ordering costs in order to minimize the long‐run expected total cost per time unit. We established several properties of the cost function, which permit us to derive a heuristic algorithm. A lower bound on the minimum cost is obtained, which helps us to evaluate the effectiveness of the proposed heuristic. The heuristic is also compared with a hybrid genetic algorithm that is specifically developed for benchmarking purposes. Numerical experiments have been carried out to investigate the performance of the heuristic

Comparative Simulation Study and Economic Analysis of Thermal Recovery Processes in Athabasca Reservoirs

Simulation studies of three thermal recovery processes used in Athabasca reservoirs have been carried out for a 10-year production period. The recovery processes studied are Steam-Assisted Gravity Drainage (SAGD), Fast-SAGD, and Expanding Solvent-SAGD (ES-SAGD). Normal pentane (n-C5) was the solvent of choice used in ES-SAGD simulations with its molar concentration varied from 2% to 5.9%. The main objective of this study is to conduct an economic analysis of the three recovery processes with the goal of determining the most economically viable process. The economic indicator that will be assessed to ascertain the most viable recovery process is their Net Present Value (NPV.) 2D simulation studies based on homogeneous Athabasca reservoirs have been performed. Results obtained show that of the three recovery processes, Fast-SAGD had the lowest cumulative oil produced, followed by SAGD and ES-SAGD, the highest. The cumulative oil produced also increased with increasing molar concentration of n-C5. Furthermore, it was shown that as expected, the CSOR of ES-SAGD was the lowest of them while that of Fast-SAGD was the highest. The CSOR of the ES-SAGD processes reduced as the concentration of the n-C5 increased. The economic analysis showed that of the three recovery processes, ES-SAGD is the most economically viable process. Furthermore, the effect of solvent on the viability of ES-SAGD over the other recovery processes is dependent on the price regime of pentane. In this analysis, two extreme price regimes were chosen and the result showed that for a low price regime, varying the molar ratios of n-C5 had a significant effect on the NPV up to a point before its effect diminishes. In fact, increasing the molar concentration of n-C5 from 2% to 3.76% significantly increased the NPV while further increasing it from 3.76% to 4% and thereafter to 5.9% had no noticeable effect. However, it seems that increasing it from 3.76% to 5.9% had a diminishing effect especially after the 3-year period. Nevertheless, the significant NPV improvement ES-SAGD has over SAGD and Fast-SAGD diminishes once the price regime of pentane is more than 3 times that of oil. In fact, this high price regime showed that 5.9% molar concentration of n-C5 is no longer more viable than the SAGD counterpart. There is still some benefit up till about 4% molar concentration of n-C5 but this benefit is greatly diminished. In conclusion, ES-SAGD has been shown to be the best recovery process for Athabasca reservoirs based on economics but further research is needed to evaluate the molar concentration that will provide the most economic benefit for a real Athabasca reservoir

Lower bounds for production/inventory problems by cost allocation

This thesis presents a cost allocation method for deriving lower bounds on costs of feasible policies for a class of production/inventory problems. Consider the joint replenishment problem where a group of items is replenished together or individually. A sequence of reorders for any particular item will incur holding, backorder and set-up costs specific to the item, in addition whenever any item is replenished a joint cost is incurred. What is required of the total problem is the minimization of a cost function of the replenishment sequence or policy. The cost allocation method consists of decomposing the total problem into sub-problems, one for each item, by allocating the joint cost amongst the items in such a way that every item in the group receives a positive allocation or none. The result is that, for an arbitrary feasible cost allocation, the sum of the minimum costs for the subproblems is a lower bound on the cost of any feasible policy to the total problem. The results for the joint replenishment problem follows: For the constant and continuous demand case we reproduce the lower bound of Jackson, Maxwell and Muckstadt more easily than they did. For the multi-item dynamic lot-size problem, we generalize Silver-Meal and part-period balancing heuristics, and derive a cost allocation bound with little extra work. For the 'can-order' system, we use periodic policies derived from the cost allocation method and show that they are superior to the more complex (s,c,S) policies. The cost allocation method is easily generalized to pure distribution problems where joint replenishment decisions are taken at several facilities. For example, for the one-warehouse multi-retailer problem, we reproduce Roundy's bound more easily than he did. For the multi-facility joint replenishment problem (a pure distribution system with an arbitrary number of warehouses), we give a lower bound algorithm whose complexity is dr log r where d is the maximum number of facilities which replenish a particular item and r is the number of items.Business, Sauder School ofGraduat

Opportunities for third world industrialization : dependency theory and the newly industrializing countries

This study is an exploration of dependency theory and the Newly Industrializing Countries (NICs). The issues which are addressed are threefold: 1. An exploration of dependency theory, especially the variant of it that is advocated by Frank, Amin and Wallerstein. These authors have constantly maintained that growth is not possible in the Third World as long as the region is integrated into the world capitalist economy. The NICs, particularly Taiwan and South Korea are testimonies that that assumption is not entirely valid because they are incorporated and have also witnessed impressive economic growth. 2. An examination of the debate over the character of the NICs. An analysis of Taiwan and South Korea shows that they have experienced considerable economic growth. However, there is limited transformation in the standard of life of the citizens. 3. The factors that are responsible for the economic growth of Taiwan and South Korea are hypothesized. These factors are both external and internal to these countries. They are (a) a strongly polarized international ideological atmosphere which made these countries client states of the United States of America, (b) an inflow of massive aid from the U.S to these states and (c) the presence of a strong state apparatus in these countries. The state institutions combined internal creativity with the opportunities provided by the international scene to initiate and implement good strategies for their industrial transformation. The lessons other Third World countries can learn from Taiwan and South Korea is that East and West rivalry can create opportunities for strategic countries in the region of conflict. But the internal dynamics of the countries have to be responsible for seizing the chance and for utilizing it well.Arts, Faculty ofAnthropology, Department ofGraduat

A Lower Bound and an Efficient Heuristic for Multistage Multiproduct Distribution Systems

This paper concerns lot-sizing in a multistage and multifacility pure distribution network. A facility at the end of the distribution network experiences a deterministic and continuous demand. Each facility has an echelon holding cost rate for each item it distributes, and a facility-dependent set up cost. In this paper an algorithm is presented of complexity 0(rd log r) where r is the number of end facilities and d is the maximum depth of the distribution system. The algorithm exploits a lower bound obtained by decomposing the distribution network into facilities-in-series problems. Using a set up cost allocation procedure, the maximum of the continuous solution of the decomposed problem is obtained. This maximizing solution provides the lower bound which is used for solving the distribution problem. This gives a power-of-two heuristic with a worst case performance no more than 2% above optimal.inventory, multi-stage, distribution, lower bound, heuristic

Comparative sonographic evaluation of intra-renal resistive index among adult patients with essential hypertension and normotensives in a Nigerian tertiary institution

The intra-renal resistive index is a Doppler parameter that is useful in predicting adult hypertensive patients who are likely to develop nephrosclerosis and to follow up hypertensive patients on reno-protective drugs to determine effects of drugs on renal function. This was a prospective cross-sectional comparative descriptive study conducted at the University of Benin Teaching Hospital (UBTH). It involved the use of Doppler ultrasound assessment of intra-renal resistive index in 50 hypertensive individuals and 50 “age-and-sex” matched normotensive controls. The data was analyzed using statistical package for social sciences(SPSS) version 20.0. Correlation tests were considered significant at p-value less than or equal to 0.05 at 95% confidence interval.The mean intra-renal resistive index in this study was 0.60 ± 0.05 with a range of 0.49 - 0.70 in the hypertensives and 0.57 ± 0.05 with a range of 0.47 - 0.70 for the normotensives. Among the hypertensive subjects a significant positive correlation was found between the intrarenal resistive index and the pulse pressure (r= 0.327, p= 0.018). The pulse pressure is also the only independent predictor of the intra-renal resistive index among hypertensive subjects. There was significantly higher intra-renal RI value among the hypertensive subjects compared to the normotensives. The intra-renal RI showed a positive correlation with the pulse pressure and it was only independent predictor of the resistive index.Keywords: Resistivity index, resistive index, RI, intra-renal RI, hypertensio

An Audit of the Histopathological Pattern of Ameloblastoma in Kano, Nigeria

Objective: To describe the spectrum, frequency, age and sex distribution of ameloblastomas seen in Kano, as well as compare the findings with  previous studies done in Nigeria, Africa and other parts of the world. Materials and Methods: This was a 5 year retrospective study from 2nd January, 2010 to 31st December, 2014 of all ameloblastomas diagnosed at the pathology department of Aminu Kano Teaching Hospital, Kano, Nigeria. Results: Sixty four cases of ameloblastomas were diagnosed during the five year study period with a male to female ratio of 2:1. The ages ranged from 16 to 75 years (mean age of 33.4) and relative peak age of incidence occurred in the 40 - 49 years group. Solid/Multicystic type accounted for majority (57 cases, 89.1%) of ameloblastomas followed by unicystic variant (5 cases,7.8%), while the desmoplastic and peripheral variants  comprising the remaining 2 cases (3.1%). The mandible was the commonest site of involvement accounting for 57cases(89.1%), while maxilla and alveolar mucosa accounted for 6 cases (9.4%) and 1case (1.6%) respectively. Conclusion: This study showed that ameloblastoma has significant male predilection and affecting predominantly patients in the third to fifth  decades. It revealed a higher incidence of solid/multicystic ameloblastomas over unicystic variants. The demographic and histological features are similar to reports from other parts of Nigeria and elsewhere. Key words: Ameloblastomas, solid/mulicystic, unicystic, desmoplastic and peripheral variants