Inventory management in railway sleepers: A simulation model for replacement strategies

This paper describes the development of a simulation model to assess the inventory requirements of alternative rail sleeper replacement strategies. The main aim of the model is to determine the optimal replacement strategy, given replacement costs and resultant train operating cost benefits. We consider the replacement problem under the following assumptions: The time to failure under constant stress follows a Weibull distribution and the scale parameter is a function of stress level and the three stress levels under normal (all adjacent units are good), medium-stress (one adjacent unit has failed) and high-stress conditions (two adjacent units are failed) are considered. The cumulative exposure model is used to model the failure distributions. The operational cost per unit time depends on the maximum number of consecutive failed units. The replacement cost consists of the fixed cost and variable cost proportional to the number of units replaced. A finite horizon is considered and total expected cost is a criterion for comparing the proposed policies. The model has been tested using rail system data and the results are presented in this paper

Maintenance optimization of a production system with buffercapacity

Marketing;Optimization;produktieleer/ produktieplanning

Optimal Unemployment Insurance and Voting

The framework of a general equilibrium heterogeneous agent model is used to study the optimal design of an unemployment insurance (UI) scheme and the voting behaviour on unemployment policy reforms. In a first step, the optimal defined benefit and defined replacement ratio UI systems are obtained in simulations. Then, the question whether switching to such an optimal system from the status quo would be approved by a majority of the voters is explored. Finally, the transitional dynamics following a policy change are analysed. Accounting for this transition has an important influence on the voting outcome.insurance, heterogeneous agents, job search, voting, human capital

Optimal Unemployment Insurance in a Search Model with Variable Human Capital

The framework of a general equilibrium heterogeneous agents model is used to study the optimal design of an unemployment insurance scheme and the voting behaviour on unemployment policy reforms. Agents, who have a limited lifetime and participate in the labour market until they reach the retirement age, can either be employed or unemployed in each period of their working life. Unemployed agents receive job offers of different (match) qualities. Moreover, unemployed agents suffer a decline of their individual productivity during unemployment, whereas the productivity of employed agents increases over time. Any form of unemployment insurance must take into account an important trade-off. On the one hand, generous benefits are desirable as they provide good insurance of the risk-averse agents against unforeseen income fluctuations (caused by layoffs and the randomness of individual job offers). On the other hand, high benefits induce a moral-hazard problem, as certain groups of agents choose to decline job offers that, while not being as attractive as the unemployment benefit from an individual point of view, a central planner would make them accept. An optimal unemployment insurance scheme is one that maximizes the expected lifetime utility of a newly born agent. Two types of unemployment insurance are considered, one with defined benefits and one with defined replacement ratios. A numerical version of the model is calibrated to the West German economy and simulated at ½-monthly frequency, resulting in an agent’s life-span of 1440 periods. The welfare maximising unemployment insurance scheme is determined in simulations. Under this optimal system, no payments are made to short-term unemployed agents. Long-term unemployed receive rather low (social assistance level) benefits, the optimal level of which depends on the assumed degree of risk aversion. Defined benefit systems provide a higher welfare than defined replacement ratios. I then address the question whether the majority of population would support the optimal system given the status quo. It turns out that older or unemployed agents tend vote in favour of the status quo, whereas young employed agents would approve the reform. If voters can choose between keeping their current unemployment system and jumping to the equilibrium associated with the optimal policy, there is a slight majority of just above 50% for the optimal policy. Finally, a more realistic case is considered, in which voters do not choose between the long-rung equilibria associated with policy changes, but take into account the transition process to the new equilibrium. The adjustment process of the macro environment after the policy reform is computed for a time span of sixty years. As some of the relevant variables adjust very slowly to their new long-run equilibrium values, the effect of the transition process on voting behaviour cannot be neglected

Analysis and computation of (n,N): Strategies for maintenance of a two-component system

Computer Science;produktieleer/ produktieplanning

A Periodicity Metric for Assessing Maintenance Strategies

Organised by: Cranfield UniversityThe maintenance policy in manufacturing systems is devised to reset the machines functionality in an economical fashion in order to keep the products quality within acceptable levels. Therefore, there is a need for a metric to evaluate and quantify function resetting due to the adopted maintenance policy. A novel metric for measuring the functional periodicity has been developed using the complexity theory. It is based on the rate and extent of function resetting. It can be used as an important criterion for comparing the different maintenance policy alternatives. An industrial example is used to illustrate the application of the new metric.Mori Seiki – The Machine Tool Company; BAE Systems; S4T – Support Service Solutions: Strategy and Transitio

On the optimal progressivity of the income tax code

This paper computes the optimal progressivity of the income tax code in a dynamic general equilibrium model with household heterogeneity in which uninsurable labor productivity risk gives rise to a nontrivial income and wealth distribution. A progressive tax system serves as a partial substitute for missing insurance markets and enhances an equal distribution of economic welfare. These beneficial effects of a progressive tax system have to be traded off against the efficiency loss arising from distorting endogenous labor supply and capital accumulation decisions. Using a utilitarian steady state social welfare criterion we find that the optimal US income tax is well approximated by a flat tax rate of 17:2% and a fixed deduction of about $9,400. The steady state welfare gains from a fundamental tax reform towards this tax system are equivalent to 1:7% higher consumption in each state of the world. An explicit computation of the transition path induced by a reform of the current towards the optimal tax system indicates that a majority of the population currently alive (roughly 62%) would experience welfare gains, suggesting that such fundamental income tax reform is not only desirable, but may also be politically feasible. JEL Klassifikation: E62, H21, H24