Reducing truck emissions at container terminals in a low carbon economy: Proposal of a queueing-based bi-objective model for optimizing truck arrival pattern

This study proposes a methodology to optimize truck arrival patterns to reduce emissions from idling truck engines at marine container terminals. A bi-objective model is developed minimizing both truck waiting times and truck arrival pattern change. The truck waiting time is estimated via a queueing network. Based on the waiting time, truck idling emissions are estimated. The proposed methodology is evaluated with a case study, where truck arrival rates vary over time. We propose a Genetic Algorithm based heuristic to solve the resulting problem. Result shows that, a small shift of truck arrivals can significantly reduce truck emissions, especially at the gate.     

Order release planning with clearing functions: A queueing-theoretical analysis of the clearing function concept

We consider the problem of planning future order releases in hierarchical production planning and control systems. An established research direction is the clearing function concept: the planned material flow through a production unit is modelled by inventory balance equations for WIP and final products, and the consequences of the stochastic properties of the material flow are modelled by clearing functions, which is the functional relationship between the level of WIP and the maximum output of a work centre in a period.Using a transient M/M/1 model, our paper shows that the usual definition of a nonlinear clearing function suffers from substantial shortcomings concerning both the definition of the function and empirical estimation of its parameters. We propose an alternative transient clearing function and derive a procedure for its parameterization.     

Might randomization in queue discipline be useful when waiting cost is a concave function of waiting time?

This paper suggests that introducing randomization in queue discipline might be welfare enhancing in certain queues for which the cost of waiting is a concave function of waiting time. Concavity can make increased variability in waiting times good not bad for aggregate customer welfare. Such concavity may occur if the costs of waiting asymptotically approach some maximum or if the customer incurs a fixed cost if there is any wait at all. As examples, cost might asymptotically approach a maximum for patients seeking organ transplants who will not live beyond a certain threshold time, and fixed costs could pertain for knowledge workers seeking a piece of information that is required to proceed with their current task, so any delay creates a “set up charge” associated with switching tasks.     

银行排队系统服务效率问题研究

银行排长队现象是困扰银行和客户的难题,其实质是排队系统的效率问题。叫号机变多队一多服务台系统为单队一多服务台系统,改变了排队系统模型。本文运用蒙特卡罗仿真方法对两种排队系统模型进行比较,发现叫号机确实可以有效提升银行服务系统的效率。     

The potty parity problem: Towards gender equality at restrooms in business facilities

In business facilities such as theaters, restaurants, stadiums, and etc., anecdotal evidences suggest that waiting lines for women's restrooms are longer than those for men's. Respectively, there have been growing concerns on ensuring restrooms in business facilities to be equally convenient for both women and men. This issue not only relates to gender equality, but also relates to business performance, since restroom experience directly affects performance efficiency (e.g., revenues, repeat sales, asset turnover, service times, and etc.). Nonetheless, current codes and legislations for designing restrooms in business facilities are not based on objective analyses but on the survey of experts that may be male biased. In this study, we develop a quantitative model using queueing theory and simulations to evaluate the waiting time for restrooms. Using our model, we compare the waiting times between women and men to examine if the current codes and legislations provide equal access. Our analysis reveals that the current standard specified by the Uniform Plumbing Code (UPC) still fails to achieve equal access. The methods demonstrated in this study may serve as a basis for design of restrooms in business facilities and improve both gender equality and performance efficiency in business facilities.     

Throughput time distribution analysis for a one-block warehouse

We develop discrete time models for the throughput time distribution of orders arriving to a one-block warehouse. The models accommodate single- or multi-line orders, and we show how to use them to determine the optimal batch size, given a desired probability of on-time order fulfillment. Experiments suggest that the optimal batch size is slightly higher than one would choose if minimizing average throughput time.     

No-envy in queueing problems

We explore the implications of no-envy(Foley 1967) in the context of queueing problems. We identify an easy way of checking whether a rule satisfies efficiencyand no-envy. The existence of such a rule can easily be established. Next, we ask whether there is a rule satisfying efficiency and no-envytogether with an additional solidarity requirement how agents should be affected as a consequence of changes in the waiting costs. However, there is no rule satisfying efficiency, noenvy, and either one of two cost monotonicity axioms. To remedy the situation, we propose modifications of no-envy, adjusted no-envyand backward/forward no-envy. Finally, we discuss whether three fairness requirements, no-envy, the identical preferences lower bound, and egalitarian equivalence, are compatible in this context.     

Assessing hospital system resilience to disaster events involving physical damage and Demand Surge

This paper investigates the effectiveness of formalized collaboration strategies through which patients can be transferred and resources, including staff, equipment and supplies, can be shared across hospitals in response to a disaster incident involving mass casualties and area-wide damage. Inflicted damage can affect hospital infrastructure and its supporting lifelines, thus impacting capacity and capability or, ultimately, services that are provided. Using a discrete event simulation framework and underlying open queuing network conceptualization involving patient flows through 9 critical units of each hospital, impacts on critical resources, physical spaces and demand are modeled and the hospital system's resilience to these hazard events is evaluated. Findings from numerical experiments on a case study involving multiple hospitals spaced over a large metropolitan region replicating a system similar to the Johns Hopkins Hospital System show the potential of strategies involving not only transfers and resource sharing, but also joint capacity enhancement alternatives to improve post-disaster emergency health care service delivery through joint action.