Average Case Analyses of List Update Algorithms, with Applications to Data Compression

We study the performance of the Timestamp (0) (TS(0)) algorithm for self-organizing sequential search on discrete memoryless sources. We demonstrate that TS(0) is better than Move-to-front on such sources, and determine performance ratios for TS(0) against the optimal off-line and static adversaries in this situation. Previous work on such sources compared on-line algorithms only with static adversaries. One practical motivation for our work is the use of the Move-to-front heuristic in various compression algorithms. Our theoretical results suggest that in many cases using TS(0) in place of Move-to-front in schemes that use the latter should improve compression. Tests using implementations on a standard corpus of test documents demonstrate that TS(0) leads to improved compression. Received December 3, 1995; revised April 5, 1997.     

我国合成树脂工业进展及面临的挑战

本文回顾了过去十年来我国合成树脂工业的发展,预测了到本世纪末以及2010年的前景,讨论了目前存在的问题及面临的挑战,提出了重要的问题是提高市场竞争力。     

Unit Maintenance Scheduling: A robust model,based on fuzzy cost factors and peak loads

As a mid-term planning scheduling, Unit Maintenance Scheduling (UMS) has a significant effect on Generation companies (Gencos) profit. System Operator (SO) is a central entity that provides the Gencos with related maintenance schedule. This schedule would be finalized through repetitive iterations between the SO and different Gencos in the market, to come up with a generally accepted schedule. Bidding strategy, on the other side, does affect the Gencos profit. Being considered as a short-term planning, bidding process is done on the hourly basis to determine the allocated demand to each Genco for each hour of the day. These short-term and mid-term schedules planning received enough attention in the literature, but to consider both simultaneously has not been well studied. In addition, one may not have all the information for the future periods. For production cost factors and load, an estimation can be obtained from the historical data, but that would not be the exact value and there remains an uncertainty on the value of these parameters. This would highlight the importance of developing a robust model that protect the schedule against changes in the values of these parameters, and ensure an acceptable, near optimal solution as well. In this paper, we would model the uncertainties in load and production cost factors, based on a fuzzy framework. The UMS problem is modeled and solved as a dynamic non-cooperative fuzzy game. The results show the effectiveness of the proposed approach.     

Global managemenT : A new challenge for oil companies

The oil industry went global well before the word became fashionable. Decades ago, the majors succeeded in integrating their activities so that they achieved almost total mastery over their environment. The changes of the past 20 years, in particular, the nationalizations of the early 1970s imposed new challenges on large oil companies. They now face the complexity of a more competitive environment that they no longer control. The response of many companies has been to redesign their organizations so as to reduce the layers of command. This paper goes further, suggesting a model of organization which favours lateral relations and increases the input of country affiliates in the strategic planning process.     

食糖市场营销战略分析

2005/06年制糖期全国食糖产量881.5万t,消费量估计达到1070万t,主产区白糖平均售价达到4500元/t,制糖企业取得很好效益.新形势下制糖行业将发生转变,一是食糖流通企业经过整合力量不断壮大,二是市场化、国际化程度逐步提高,三是食糖价格将总体走高,四是甜菜糖和淀粉糖将加速发展.在新形势下制糖企业必须努力提高市场竞争力,制定市场营销战略,重视销售网络渠道建设,不断扩大市场份额.     

The market and consumer welfare effects of mid-level ethanol blends in the US fuel market

This study examines the prospect that a consumer-driven market could eventually replace the myriad regulations and demand quotas in the US ethanol and gasoline fuel market. Given efficient households that minimize the cost of operating automobiles, recent vehicle technology that improves blended fuel substitution, and typical market conditions of the last five years, blended fuels with 20% ethanol concentration could occupy a volume of 82.2 billion gallons in a 138.3 billion gallon gasoline market. The consumer welfare gain associated with blended fuel is $15.9 billion annually for US consumers, or about $1000 over the life of a vehicle.The ethanol demand associated with a voluntary blended fuel market is 16.4 BGY, slightly more than the conventional component of the Renewable Fuels Standard. It is time to replace the corn RFS with a free market. But an active competition policy in the fuel marketing system may also be required. Intervention for the impending Biomass Ethanol Industry, such as a subsidy or an exemption a carbon tax, may also be in order.     

OPEC's production under fluctuating oil prices: further test of the target revenue theory

Oil production cutbacks in recent years by OPEC members to stabilize price and to increase revenues warrant further empirical verification of the target revenue theory (TRT). We estimate a modified version of Griffin (1985) target revenue model using data from 1973 to 2000. The sample period, unlike previous investigations, includes phases of both price increase (1970s) and price decrease (1980s–1990s), thus providing a better framework for examining production behavior. The results, like the earlier study, are not supportive of the strict version of the TRT, however, evidence (negative and significant elasticity of supply) of the partial version are substantiated. Further empirical estimates do not support the competitive pricing model, hypothesizing a positive elasticity of supply. OPEC's loss of market share and the drop in the share of oil-based energy should signal an adjustment in pricing and production strategies.     

Influence of water vapor on hydrogen permeation through 2.5 μm Pd-Ag membranes

Hydrogen permeation experiments were performed to evaluate the influence of water vapor on hydrogen permeability in 80-20% by weight Pd-Ag membranes of 2.5 μm thickness. In particular, hydrogen flux was measured in pure hydrogen permeation tests as well as in experiments with binary mixtures containing also nitrogen or water vapor, that were performed at temperatures ranging from 473 to 723 K and at a transmembrane pressure differences up to about 3 bar. The membranes, supplied by NGK Insulator Ltd., Japan, showed a very high hydrogen permeance and lifetime, as well as virtually infinite selectivity (exceeding 10000 for H₂-N₂ mixtures). The experiments in hydrogen-nitrogen mixtures were carried out at different temperatures, hydrogen concentrations and feed flow rates and confirmed the existence of a non-negligible concentration polarization phenomenon in the experimental module. The gas phase mass transport and the module fluid dynamics were thus analyzed and the dimensionless numbers characterizing these processes were evaluated at the different operative conditions; a linear correlation was found to hold between Sherwood and Péclet numbers. Interestingly, the hydrogen permeate fluxes measured with feeds containing H₂-H₂O mixtures resulted always lower than those obtained for the nitrogen-hydrogen mixtures performed at the same hydrogen mole fraction and operative conditions: in particular, the hydrogen flux depletion increased with decreasing temperature and/or increasing the concentration of water vapor. All the experimental evidences suggest a clear interaction between water vapor and metallic layer, causing a lower hydrogen adsorption capacity of the membrane surface. That phenomenon is reversible, since the original permeance of the membrane was restored once the water vapor was removed from the feed, and is apparently due to a competitive H₂-H₂O adsorption on the Pd-Ag surface. The hydrogen flux depletion was then modeled by considering the simultaneous effects of gas phase resistance and competitive adsorption on the surface, obtaining a rather good agreement between experimental data and calculated results.     

Small-scale CDM projects in a competitive electricity industry: How good is a simplified baseline methodology?

Setting baseline emissions is one of the principal tasks involved in awarding credits for greenhouse gas emission (GHG) mitigation projects under the Clean Development Mechanism (CDM). An emission baseline has to be project-specific in order to be accurate. However, project-specific baseline calculations are subject to high transaction costs, which disadvantage small-scale projects. For this reason, the CDM-Executive Board (CDM-EB) has approved simplified baseline methodologies for selected small-scale CDM project categories. While the simplified methods help reduce the transaction cost, they may also result in inaccuracies in the estimation of emission reductions from CDM projects. The purpose of this paper is to present a rigorous economic scheduling method for calculating the GHG emission reduction in a hypothetical competitive electricity industry due to the operation of a renewable energy-based power plant under CDM and compare the GHG emission reduction derived from the rigorous method with that obtained from the use of a simplified (i.e., standardized) method approved by the CDM-EB. A key finding of the paper is that depending upon the level of power demand, prices of electricity and input fuels, the simplified method can lead to either significant overestimation or substantial underestimation of emission reduction due to the operation of renewable energy-based power projects in a competitive electricity industry.