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251.
252.
This paper presents an improved, significantly more efficient formulation of an existing model for bulk cargo or semi-bulk cargo ship scheduling problems with a single loading port. The original model, published by Ronen in 1986, was formulated as a non-linear, mixed integer program. In this work, the authors were able to re-formulate it into a linear one, by eliminating all the non-linearities of the original model. In addition, this model has far fewer integer variables than the original one. A numerical example has been given to illustrate the elimination of non-linearities and how 40 integer variables, in the original model, are reduced to just eight. This example also shows that this model is better at finding exact optimal solutions than the original one. It is also worth observing that the resulting model is a generalization of the ‘capacitated facility location problem’. 相似文献
253.
Alan H. Robinson 《Coastal management》2013,41(1-2):5-34
This article reviews the historical development of the category of national park known as “national seashore,”; and traces the evolution of basic planning and management policies that are applied to such areas. Also reviewed is the current sequential approach applied by the National Park Service in all its planning efforts, including a discussion of the impact of the National Environmental Policy Act on park planning. Several examples are provided to illustrate a variety of planning problems common to the sashore environment. Finally, comments are provided on the future promise of seashore and barrier island conservation and development, as well as the future role of other agencies and private organizations. 相似文献
254.
Abstract The National Park Service is required by law to conserve nationally significant resources for public benefit. Susceptibility to local short‐term economic pressures and a lack of understanding of resource dynamics can jeopardize mandate compliance. Assateague National Seashore is an example of a dynamic barrier island where early understanding of ecologic factors should have preceded its establishment and must precede its management and development. Research conducted on a similar system has demonstrated the dramatic environmental impacts and high maintenance costs associated with an inappropriate recreation management scheme. Alternatives are available which minimize resource degradation and maintenance costs without restricting visitation. To better ensure incorporation of long‐run ecologic and economic criteria into the decision‐making process, a proposal is put forward which recognizes the need for an expanded research effort and close adherence to early planning steps. 相似文献
255.
ABSTRACTA dynamic model for marginal cost pricing of port infrastructures links costs to system performance by combining a power-law function with time-dependent queueing analysis. Additionally, the model incorporates the marginal cost of capacity, including the effects of economies of scale. This allows the calculation of the marginal cost price under a dynamic framework. The model accounts for nonlinear behaviour of port demand, which is sensitive to price and service levels. The effects over time of cost and service levels on the port’s operational performance are quantified. The proposed model allows determining the optimal timing for capacity investment. The model is a starting point for the application of marginal cost pricing to ports. However, for practical application of such pricing method it is necessary to apply a system’s approach, as productivity and costs must be assessed at the terminal’s component level. This should allow the derivation of a marginal cost function at the terminal’s component level. 相似文献
256.
Anthony C. Homan 《Maritime Policy and Management》2013,40(2):105-107
Little has been written about the ship demolition market, an essential element in the supply/demand balance for shipping. Either technical or economic obsolescence may be the cause for scrapping a ship, where the latter is strongly influenced not only by anticipated freight market levels, but the rate at which more efficient ships are being introduced. The scrap value of a ship is a function both of the realizable value of the materials within the ship and cost of demolition. Both are strongly influenced by the cost structures prevailing in the likely country of demolition. The paper explores not only the fundamentals of the ship demolition market, but the trends from the 1960s to the present. The shipbreaking market has moved in that time from being West European-centred to Asian-centred, concentrating for some years in Taiwan, but now shifting to the Indian subcontinent. 相似文献
257.
A cost-benefit analysis is conducted on the double-hull requirements for oil tankers in United States' waters contained in the U.S. Oil Pollution Act of 1990. The benefits of reduced spillage are compared with the increased construction and operations costs of double-hulled vessels. In the most probable scanario, the expected benefits are only 20% of the expected costs. Double-hulls do not even show a positive net present value with the most favorable assumptions. Even if double-hulls prevent all of the spillage that occurs due to collisions and groundings, and that the damage per gallon spilled is as extensive as in the ‘Exxon Valdez’ incident, the benefits are under half of the costs. 相似文献
258.
259.
Y.H. Venus Lun Michael BrowneKee-hung Lai Christina W.Y. WongT.C.E. Cheng 《Research in Transportation Economics》2011,32(1):64-70
Container shipping and its related service sectors help accelerate globalization of the world economy. This industry has been experiencing rapid growth, prompting container terminal operators to increase their handling capacity in response. Providing container terminal services requires substantial capital investment in physical assets such as cargo handling facilities and information systems. On the other hand, operating container terminals is a long-term investment that typically spans several business cycles. Hence prudent asset management using appropriate tools is critical for container terminal operators to sustain their businesses. Generally, due to risk-adverseness, investors are unwilling to take more risk in their investment unless they can reap a higher return. Contrary to this argument, this study finds no direct influence of better firm performance as a proxy of higher return on business risk-taking by container terminal operators. Instead, scale of operations is positively associated with business risk-taking, suggesting that container terminal operators with a larger scale of operations are willing to take more business risk. 相似文献
260.